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Özdemir ÖÜ, Yurt K, Pektaş AN, Berk Ş. Evaluation and normalization of a set of reliable reference genes for quantitative sgk-1 gene expression analysis in Caenorhabditis elegans-focused cancer research. Nucleosides Nucleotides Nucleic Acids 2024:1-20. [PMID: 38359339 DOI: 10.1080/15257770.2024.2317413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Accepted: 02/06/2024] [Indexed: 02/17/2024]
Abstract
Multiple signaling pathways have been discovered to play a role in aging and longevity, including the insulin/IGF-1 signaling system, AMPK pathway, TOR signaling, JNK pathway, and germline signaling. Mammalian serum and glucocorticoid-inducible kinase 1 (sgk-1), which has been associated with various disorders including hypertension, obesity, and tumor growth, limits survival in C. elegans by reducing DAF-16/FoxO activity while suppressing FoxO3 activity in human cell culture. C. elegans provides significant protection for a number of genes associated with human cancer. The best known of these are the lin-35/pRb (mammalian ortholog pRb) and CEP-1 (mammalian ortholog p53) genes. Therefore, in this study, we aimed to investigate the expression analyzes of sgk-1, which is overexpressed in many types of mammalian cancer, in mutant lin-35 and to demonstrate the validation of reference genes in wild-type N2 and mutant lin-35 for C. elegans-focused cancer research. To develop functional genomic studies in C. elegans, we evaluated the expression stability of five candidate reference genes (act-1, ama-1, cdc-42, pmp-3, iscu-1) by quantitative real-time PCR using five algorithms (geNorm, NormFinder, Delta Ct method, BestKeeper, RefFinder) in N2 and lin-35 worms. According to our findings, act-1 and cdc-42 were effective in accurately normalizing the levels of gene expression in N2 and lin-35. act-1 and cdc-42 also displayed the most consistent expression patterns, therefore they were utilized to standardize expression level of sgk-1. Furthermore, our results clearly showed that sgk-1 was upregulated in lin-35 worms compared to N2 worms. Our results highlight the importance of definitive validation using mostly expressed reference genes.
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Affiliation(s)
- Özgür Ülkü Özdemir
- Department of Molecular Biology and Genetics, Faculty of Science, Sivas Cumhuriyet University, Sivas, Turkey
| | - Kübra Yurt
- Department of Molecular Biology and Genetics, Faculty of Science, Sivas Cumhuriyet University, Sivas, Turkey
| | - Ayşe Nur Pektaş
- Advanced Technology Research and Application Center (CUTAM), Sivas Cumhuriyet University, Sivas, Turkey
| | - Şeyda Berk
- Department of Molecular Biology and Genetics, Faculty of Science, Sivas Cumhuriyet University, Sivas, Turkey
- Advanced Technology Research and Application Center (CUTAM), Sivas Cumhuriyet University, Sivas, Turkey
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Maestro I, Madruga E, Boya P, Martínez A. Identification of a new structural family of SGK1 inhibitors as potential neuroprotective agents. J Enzyme Inhib Med Chem 2023; 38:2153841. [PMID: 36637025 PMCID: PMC9848319 DOI: 10.1080/14756366.2022.2153841] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
SGK1 is a serine/threonine kinase involved in several neurodegenerative-related pathways such as apoptosis, neuroinflammation, ionic channel regulation, and autophagy, among others. Despite its potential role as a pharmacological target against this kind of diseases, there are no reported inhibitors able to cross the BBB so far, being a field yet to be explored. In this context, a structure-based virtual screening against this kinase was performed, pointing out the deazapurine moiety as an interesting and easy-to-derivatize scaffold. Moreover, these inhibitors are able to i) exert neuroprotection in an in vitro model of AD and ii) block mitophagy in a PRKN-independent manner, reinforcing the hypothesis of SGK1 inhibitors as neuroprotective chemical tools.
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Affiliation(s)
- Ines Maestro
- Centro de Investigaciones, Biológicas Margarita Salas-CSIC, Madrid, Spain,Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos III, Madrid, Spain
| | - Enrique Madruga
- Centro de Investigaciones, Biológicas Margarita Salas-CSIC, Madrid, Spain
| | - Patricia Boya
- Centro de Investigaciones, Biológicas Margarita Salas-CSIC, Madrid, Spain
| | - Ana Martínez
- Centro de Investigaciones, Biológicas Margarita Salas-CSIC, Madrid, Spain,Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos III, Madrid, Spain,CONTACT Ana Martínez CIB-CSIC, Ramiro Maeztu 9, Madrid, 28040, Spain
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3
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Usenko T, Bezrukova A, Rudenok MM, Basharova K, Shadrina MI, Slominsky PA, Zakharova E, Pchelina S. Whole Transcriptome Analysis of Substantia Nigra in Mice with MPTP-Induced Parkinsonism Bearing Defective Glucocerebrosidase Activity. Int J Mol Sci 2023; 24:12164. [PMID: 37569538 PMCID: PMC10418497 DOI: 10.3390/ijms241512164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 07/21/2023] [Accepted: 07/26/2023] [Indexed: 08/13/2023] Open
Abstract
Mutations in the GBA1 gene represent the major genetic risk factor for Parkinson's disease (PD). The lysosomal enzyme beta-glucocerebrosidase (GCase) encoded by the GBA1 gene participates in both the endolysosomal pathway and the immune response. Disruption of these mechanisms is involved in PD pathogenesis. However, molecular mechanisms of PD associated with GBA1 mutations (GBA-PD) are unknown today in particular due to the partial penetrance of GBA1 variants in PD. The modifiers of GBA1 penetrance have not been elucidated. We characterized the transcriptomic profiles of cells from the substantia nigra (SN) of mice with co-injection with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and selective inhibitor of GCase activity (conduritol-β-epoxide, (CBE)) to mimic PD bearing GCase dysfunction (MPTP+CBE), mice treated with MPTP, mice treated with CBE and control mice treated with injection of sodium chloride (NaCl) (vehicle). Differential expression analysis, pathway enrichment analysis, and outlier detection were performed. Functional clustering of differentially represented transcripts revealed more processes associated with the functioning of neurogenesis, inflammation, apoptosis and autophagy in MPTP+CBE and MPTP mice than in vehicle mice, with a more pronounced alteration of autophagy processes in MPTP+CBE mice than in MPTP mice. The PI3K-Akt-mTOR signaling pathway may be considered a potential target for therapy in PD with GCase dysfunction.
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Affiliation(s)
- Tatiana Usenko
- Petersburg Nuclear Physics Institute Named by B.P. Konstantinov of National Research Centre «Kurchatov Institute», 188300 Gatchina, Russia; (T.U.); (A.B.); (K.B.); (S.P.)
- Department of Molecular Genetic and Nanobiological Technologies, Pavlov First Saint-Petersburg State Medical University, 197022 Saint-Petersburg, Russia
| | - Anastasia Bezrukova
- Petersburg Nuclear Physics Institute Named by B.P. Konstantinov of National Research Centre «Kurchatov Institute», 188300 Gatchina, Russia; (T.U.); (A.B.); (K.B.); (S.P.)
- Department of Molecular Genetic and Nanobiological Technologies, Pavlov First Saint-Petersburg State Medical University, 197022 Saint-Petersburg, Russia
| | - Margarita M. Rudenok
- Institute of Molecular Genetics, Russian Academy of Sciences, 123182 Moscow, Russia; (M.M.R.); (M.I.S.); (P.A.S.)
| | - Katerina Basharova
- Petersburg Nuclear Physics Institute Named by B.P. Konstantinov of National Research Centre «Kurchatov Institute», 188300 Gatchina, Russia; (T.U.); (A.B.); (K.B.); (S.P.)
| | - Maria I. Shadrina
- Institute of Molecular Genetics, Russian Academy of Sciences, 123182 Moscow, Russia; (M.M.R.); (M.I.S.); (P.A.S.)
| | - Petr A. Slominsky
- Institute of Molecular Genetics, Russian Academy of Sciences, 123182 Moscow, Russia; (M.M.R.); (M.I.S.); (P.A.S.)
| | - Ekaterina Zakharova
- Research Center for Medical Genetics, Laboratory of Hereditary Metabolic Diseases, 115522 Moscow, Russia
| | - Sofya Pchelina
- Petersburg Nuclear Physics Institute Named by B.P. Konstantinov of National Research Centre «Kurchatov Institute», 188300 Gatchina, Russia; (T.U.); (A.B.); (K.B.); (S.P.)
- Department of Molecular Genetic and Nanobiological Technologies, Pavlov First Saint-Petersburg State Medical University, 197022 Saint-Petersburg, Russia
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Saha B, Shabbir W, Takagi E, Duan XP, Leite Dellova DCA, Demko J, Manis A, Loffing-Cueni D, Loffing J, Sørensen MV, Wang WH, Pearce D. Potassium Activates mTORC2-dependent SGK1 Phosphorylation to Stimulate Epithelial Sodium Channel: Role in Rapid Renal Responses to Dietary Potassium. J Am Soc Nephrol 2023; 34:1019-1038. [PMID: 36890646 PMCID: PMC10278851 DOI: 10.1681/asn.0000000000000109] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 02/06/2023] [Indexed: 03/10/2023] Open
Abstract
SIGNIFICANCE STATEMENT Rapid renal responses to ingested potassium are essential to prevent hyperkalemia and also play a central role in blood pressure regulation. Although local extracellular K + concentration in kidney tissue is increasingly recognized as an important regulator of K + secretion, the underlying mechanisms that are relevant in vivo remain controversial. To assess the role of the signaling kinase mTOR complex-2 (mTORC2), the authors compared the effects of K + administered by gavage in wild-type mice and knockout mice with kidney tubule-specific inactivation of mTORC2. They found that mTORC2 is rapidly activated to trigger K + secretion and maintain electrolyte homeostasis. Downstream targets of mTORC2 implicated in epithelial sodium channel regulation (SGK1 and Nedd4-2) were concomitantly phosphorylated in wild-type, but not knockout, mice. These findings offer insight into electrolyte physiologic and regulatory mechanisms. BACKGROUND Increasing evidence implicates the signaling kinase mTOR complex-2 (mTORC2) in rapid renal responses to changes in plasma potassium concentration [K + ]. However, the underlying cellular and molecular mechanisms that are relevant in vivo for these responses remain controversial. METHODS We used Cre-Lox-mediated knockout of rapamycin-insensitive companion of TOR (Rictor) to inactivate mTORC2 in kidney tubule cells of mice. In a series of time-course experiments in wild-type and knockout mice, we assessed urinary and blood parameters and renal expression and activity of signaling molecules and transport proteins after a K + load by gavage. RESULTS A K + load rapidly stimulated epithelial sodium channel (ENaC) processing, plasma membrane localization, and activity in wild-type, but not in knockout, mice. Downstream targets of mTORC2 implicated in ENaC regulation (SGK1 and Nedd4-2) were concomitantly phosphorylated in wild-type, but not knockout, mice. We observed differences in urine electrolytes within 60 minutes, and plasma [K + ] was greater in knockout mice within 3 hours of gavage. Renal outer medullary potassium (ROMK) channels were not acutely stimulated in wild-type or knockout mice, nor were phosphorylation of other mTORC2 substrates (PKC and Akt). CONCLUSIONS The mTORC2-SGK1-Nedd4-2-ENaC signaling axis is a key mediator of rapid tubule cell responses to increased plasma [K + ] in vivo . The effects of K + on this signaling module are specific, in that other downstream mTORC2 targets, such as PKC and Akt, are not acutely affected, and ROMK and Large-conductance K + (BK) channels are not activated. These findings provide new insight into the signaling network and ion transport systems that underlie renal responses to K +in vivo .
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Affiliation(s)
- Bidisha Saha
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
| | - Waheed Shabbir
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
| | - Enzo Takagi
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
| | - Xin-Peng Duan
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - Deise Carla Almeida Leite Dellova
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
- Current address: Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, Sao Paulo, Brazil
| | - John Demko
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
| | - Anna Manis
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
| | | | | | - Mads Vaarby Sørensen
- Department of Biomedicine, Unit of Physiology, Aarhus University, Aarhus, Denmark
| | - Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, New York
| | - David Pearce
- Department of Medicine, Division of Nephrology, Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, California
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Abstract
Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.
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Affiliation(s)
- Jermaine G Johnston
- Division of Nephrology, Hypertension and Renal Transplantation, Department of Medicine, University of Florida, Gainesville, Florida, USA
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida, USA
- Nephrology Section, Veteran Administration Medical Center, North Florida/South Georgia Malcom Randall Department of Veterans Affairs Medical Center, Gainesville, Florida, USA
| | - Amanda K Welch
- Division of Nephrology, Hypertension and Renal Transplantation, Department of Medicine, University of Florida, Gainesville, Florida, USA
- Nephrology Section, Veteran Administration Medical Center, North Florida/South Georgia Malcom Randall Department of Veterans Affairs Medical Center, Gainesville, Florida, USA
| | - Brian D Cain
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida, USA
| | - Peter P Sayeski
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida, USA
| | - Michelle L Gumz
- Division of Nephrology, Hypertension and Renal Transplantation, Department of Medicine, University of Florida, Gainesville, Florida, USA
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida, USA
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida, USA
- Nephrology Section, Veteran Administration Medical Center, North Florida/South Georgia Malcom Randall Department of Veterans Affairs Medical Center, Gainesville, Florida, USA
| | - Charles S Wingo
- Division of Nephrology, Hypertension and Renal Transplantation, Department of Medicine, University of Florida, Gainesville, Florida, USA
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida, USA
- Nephrology Section, Veteran Administration Medical Center, North Florida/South Georgia Malcom Randall Department of Veterans Affairs Medical Center, Gainesville, Florida, USA
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Verma AK, Ahmed SF, Hossain MS, Bhojiya AA, Upadhyay SK, Srivastava AK, Singh N, Harina H, Rahaman MM, Bahadur NM. Unlocking SGK1 inhibitor potential of bis-[1-N,7-N, pyrazolo tetraethoxyphthalimido{-4-(3,5-Dimethyl-4-(spiro-3-methylpyazolo)-1,7-dihydro-1H-dipyrazolo[3,4-b;4',3'-e]pyridin-8-yl)}]p-disubstituted phenyl compounds: a computational study. J Biomol Struct Dyn 2022; 40:13412-13431. [PMID: 34696688 DOI: 10.1080/07391102.2021.1988711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
SGK1 (Serum and Glucocorticoid Regulated Kinase 1), a serine/threonine kinase that is activated by various stimuli, including serum and glucocorticoids. It controls inflammation, apoptosis, hormone release, neuro-excitability and cell proliferation, all of which play an important role in cancer progression and metastasis. SGK1 was recently proposed as a potential drug target for cancer, diabetes, and neurodegenerative diseases. In this study, molecular docking, physiochemical, toxicological properties and molecular dynamic simulation of the Bis-[1-N,7-N, Pyrazolo tetraethoxyphthalimido{-4-(3,5-Dimethyl-4-(spiro-3-methylpyazolo)-1,7-dihydro-1H-dipyrazolo[3,4-b;4',3'-e]pyridin-8-yl)}]p-disubstituted phenyl compoundsand reference EMD638683 against new SGK1 target protein. Compared to the reference inhibitor EMD638683, we choose the best compounds (series 2-6) based on the binding energy (in the range from -11.0 to -10.6 kcal/mol). With the exception of compounds 2 and 6, none of the compounds posed a risk for AMES toxicity or carcinogenicity due to their toxicological properties. 100 ns MD simulation accompanied by MM/PBSA energy calculations and PCA. According to MD simulation results, the binding of compounds 3, 4 and 5 stabilizes the SGK1 structure and causes febrile conformational changes compared to EMD638683. As a result of this research, the final selected compounds 3, 4 and 5 can be used as scaffolds to develop promising SGK1 inhibitors for the treatment of related diseases such as cancer.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Abhishek Kumar Verma
- Department of Life Sciences, Faculty of Science and Technology, Mewar University, Gangrar, Chittorgarh, Rajasthan, India
| | - Sk Faisal Ahmed
- Department of Biotechnology and Genetic Engineering, Noakhali Science and Technology University, Sonapur, Noakhali, Bangladesh
| | - Md Shahadat Hossain
- Department of Biotechnology and Genetic Engineering, Noakhali Science and Technology University, Sonapur, Noakhali, Bangladesh
| | - Ali Asger Bhojiya
- Faculty of Agriculture and Veterinary Sciences, Mewar University, Gangrar, Chittorgarh, Rajasthan, India
| | - Sudhir K Upadhyay
- Department of Environmental Science, V.B.S. Purvanchal University, Jaunpur, Uttar Pradesh, India
| | | | - Nripendra Singh
- Department of Pharmacy, V.B.S, Purvanchal University, Jaunpur, Uttar Pradesh, India
| | - Harina Harina
- Department of Life Sciences, Faculty of Science and Technology, Mewar University, Gangrar, Chittorgarh, Rajasthan, India
| | | | - Newaz Mohammed Bahadur
- Department of Applied Chemistry and Chemical Engineering, Noakhali Science and Technology University, Sonapur, Noakhali, Bangladesh
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Castañeda-Bueno M, Ellison DH. Blood pressure effects of sodium transport along the distal nephron. Kidney Int 2022; 102:1247-1258. [PMID: 36228680 PMCID: PMC9754644 DOI: 10.1016/j.kint.2022.09.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 08/22/2022] [Accepted: 09/01/2022] [Indexed: 11/06/2022]
Abstract
The mammalian distal nephron is a target of highly effective antihypertensive drugs. Genetic variants that alter its transport activity are also inherited causes of high or low blood pressure, clearly establishing its central role in human blood pressure regulation. Much has been learned during the past 25 years about salt transport along this nephron segment, spurred by the cloning of major transport proteins and the discovery of disease-causing genetic variants. Recognition is increasing that substantial cellular and segmental heterogeneity is present along this segment, with electroneutral sodium transport dominating more proximal segments and electrogenic sodium transport dominating more distal segments. Coupled with recent insights into factors that modulate transport along these segments, we now understand one important mechanism by which dietary potassium intake influences sodium excretion and blood pressure. This finding has solved the aldosterone paradox, by demonstrating how aldosterone can be both kaliuretic, when plasma potassium is elevated, and anti-natriuretic, when extracellular fluid volume is low. However, what also has become clear is that aldosterone itself only stimulates a portion of the mineralocorticoid receptors along this segment, with the others being activated by glucocorticoid hormones instead. These recent insights provide an increasingly clear picture of how this short nephron segment contributes to blood pressure homeostasis and have important implications for hypertension prevention and treatment.
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Affiliation(s)
- María Castañeda-Bueno
- Department of Nephrology and Mineral Metabolism, National Institute of Medical Sciences and Nutrition, Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - David H Ellison
- Division of Nephrology and Hypertension, Department of Medicine, Oregon Health and Science University, Portland, Oregon, USA; Oregon Clinical & Translational Research Institute, Oregon Health & Science University, Portland, Oregon, USA; LeDucq Transatlantic Network of Excellence, Portland, Oregon, USA; Renal Section, VA Portland Healthcare System, Portland, Oregon, USA.
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8
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Saha B, Leite-Dellova DCA, Demko J, Sørensen MV, Takagi E, Gleason CE, Shabbir W, Pearce D. WNK1 is a chloride-stimulated scaffold that regulates mTORC2 activity and ion transport. J Cell Sci 2022; 135:jcs260313. [PMID: 36373794 PMCID: PMC9789407 DOI: 10.1242/jcs.260313] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 10/26/2022] [Indexed: 11/16/2022] Open
Abstract
Mammalian (or mechanistic) target of rapamycin complex 2 (mTORC2) is a kinase complex that targets predominantly Akt family proteins, SGK1 and protein kinase C (PKC), and has well-characterized roles in mediating hormone and growth factor effects on a wide array of cellular processes. Recent evidence suggests that mTORC2 is also directly stimulated in renal tubule cells by increased extracellular K+ concentration, leading to activation of the Na+ channel, ENaC, and increasing the electrical driving force for K+ secretion. We identify here a signaling mechanism for this local effect of K+. We show that an increase in extracellular [K+] leads to a rise in intracellular chloride (Cl-), which stimulates a previously unknown scaffolding activity of the protein 'with no lysine-1' (WNK1) kinase. WNK1 interacts selectively with SGK1 and recruits it to mTORC2, resulting in enhanced SGK1 phosphorylation and SGK1-dependent activation of ENaC. This scaffolding effect of WNK1 is independent of its own kinase activity and does not cause a generalized stimulation of mTORC2 kinase activity. These findings establish a novel WNK1-dependent regulatory mechanism that harnesses mTORC2 kinase activity selectively toward SGK1 to control epithelial ion transport and electrolyte homeostasis.
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Affiliation(s)
- Bidisha Saha
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Deise C. A. Leite-Dellova
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, Sao Paulo 13635-900, Brazil
| | - John Demko
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Mads Vaarby Sørensen
- Departments of Biomedicine and Physiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Enzo Takagi
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Catherine E. Gleason
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - Waheed Shabbir
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
| | - David Pearce
- Division of Nephrology, Departments of Medicine and Cellular & Molecular Pharmacology,University of California at San Francisco, San Francisco, CA 94158, USA
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9
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Guidone D, Buccirossi M, Scudieri P, Genovese M, Sarnataro S, De Cegli R, Cresta F, Terlizzi V, Planelles G, Crambert G, Sermet I, Galietta LJ. Airway surface hyperviscosity and defective mucociliary transport by IL-17/TNF-α are corrected by β-adrenergic stimulus. JCI Insight 2022; 7:164944. [PMID: 36219481 DOI: 10.1172/jci.insight.164944] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 10/05/2022] [Indexed: 12/15/2022] Open
Abstract
The fluid covering the surface of airway epithelia represents a first barrier against pathogens. The chemical and physical properties of the airway surface fluid are controlled by the activity of ion channels and transporters. In cystic fibrosis (CF), loss of CFTR chloride channel function causes airway surface dehydration, bacterial infection, and inflammation. We investigated the effects of IL-17A plus TNF-α, 2 cytokines with relevant roles in CF and other chronic lung diseases. Transcriptome analysis revealed a profound change with upregulation of several genes involved in ion transport, antibacterial defense, and neutrophil recruitment. At the functional level, bronchial epithelia treated in vitro with the cytokine combination showed upregulation of ENaC channel, ATP12A proton pump, ADRB2 β-adrenergic receptor, and SLC26A4 anion exchanger. The overall result of IL-17A/TNF-α treatment was hyperviscosity of the airway surface, as demonstrated by fluorescence recovery after photobleaching (FRAP) experiments. Importantly, stimulation with a β-adrenergic agonist switched airway surface to a low-viscosity state in non-CF but not in CF epithelia. Our study suggests that CF lung disease is sustained by a vicious cycle in which epithelia cannot exit from the hyperviscous state, thus perpetuating the proinflammatory airway surface condition.
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Affiliation(s)
- Daniela Guidone
- Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli, Italy
| | | | - Paolo Scudieri
- U.O.C. Genetica Medica, IRCCS Istituto Giannina Gaslini, Genova, Italy.,Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genova, Genova, Italy
| | - Michele Genovese
- Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli, Italy
| | - Sergio Sarnataro
- Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli, Italy
| | - Rossella De Cegli
- Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli, Italy
| | - Federico Cresta
- Centro Fibrosi Cistica, IRCCS Istituto Giannina Gaslini, Genova, Italy
| | - Vito Terlizzi
- Meyer Children's Hospital, Cystic Fibrosis Regional Reference Center, Department of Paediatric Medicine, Firenze, Italy
| | - Gabrielle Planelles
- Centre de Recherche des Cordeliers, INSERM UMRS 1138, Sorbonne Université, Université Paris Cité, Paris, France.,CNRS EMR 8228, Paris, France
| | - Gilles Crambert
- Centre de Recherche des Cordeliers, INSERM UMRS 1138, Sorbonne Université, Université Paris Cité, Paris, France.,CNRS EMR 8228, Paris, France
| | | | - Luis Jv Galietta
- Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli, Italy.,Department of Translational Medical Sciences (DISMET), University of Napoli "Federico II", Napoli, Italy
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10
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Jang H, Park Y, Jang J. Serum and glucocorticoid-regulated kinase 1: Structure, biological functions, and its inhibitors. Front Pharmacol 2022; 13:1036844. [PMID: 36457711 PMCID: PMC9706101 DOI: 10.3389/fphar.2022.1036844] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Accepted: 10/20/2022] [Indexed: 08/11/2023] Open
Abstract
Serum and glucocorticoid-regulated kinase 1 (SGK1) is a serine/threonine kinase belonging to the protein kinase A, G, and C (AGC) family. Upon initiation of the phosphoinositide 3-kinase (PI3K) signaling pathway, mammalian target of rapamycin complex 2 (mTORC2) and phosphoinositide-dependent protein kinase 1 (PDK1) phosphorylate the hydrophobic motif and kinase domain of SGK1, respectively, inducing SGK1 activation. SGK1 modulates essential cellular processes such as proliferation, survival, and apoptosis. Hence, dysregulated SGK1 expression can result in multiple diseases, including hypertension, cancer, autoimmunity, and neurodegenerative disorders. This review provides a current understanding of SGK1, particularly in sodium transport, cancer progression, and autoimmunity. In addition, we summarize the developmental status of SGK1 inhibitors, their structures, and respective potencies evaluated in pre-clinical experimental settings. Collectively, this review highlights the significance of SGK1 and proposes SGK1 inhibitors as potential drugs for treatment of clinically relevant diseases.
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Affiliation(s)
- Hyunsoo Jang
- College of Pharmacy, Korea University, Sejong, South Korea
| | - Youngjun Park
- Laboratory of Immune and Inflammatory Disease, College of Pharmacy, Jeju Research Institute of Pharmaceutical Sciences, Jeju National University, Jeju, South Korea
- Interdisciplinary Graduate Program in Advanced Convergence Technology and Science, Jeju National University, Jeju, South Korea
| | - Jaebong Jang
- College of Pharmacy, Korea University, Sejong, South Korea
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11
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Abstract
PURPOSE OF REVIEW This review provides an up-to-date understanding about the regulation of epithelial sodium channel (ENaC) expression and function. In particular, we will focus on its implication in renal Na+ and K+ handling and control of blood pressure using transgenic animal models. RECENT FINDINGS In kidney, the highly amiloride-sensitive ENaC maintains whole body Na+ homeostasis by modulating Na+ transport via epithelia. This classical role is mostly confirmed using genetically engineered animal models. Recently identified key signaling pathways that regulate ENaC expression and function unveiled some nonclassical and unexpected channel regulatory processes. If aberrant, these dysregulated mechanisms may also result in the development of salt-dependent hypertension.The purpose of this review is to highlight the most recent findings in renal ENaC regulation and function, in considering data obtained from animal models. SUMMARY Increased ENaC-mediated Na+ transport is a prerequisite for salt-dependent forms of hypertension. To treat salt-sensitive hypertension it is crucial to fully understand the function and regulation of ENaC.
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Affiliation(s)
- Elodie Ehret
- Department of Biomedical Sciences, Faculty of Biology and Medicine, University of Lausanne, Lausanne
| | - Edith Hummler
- Department of Biomedical Sciences, Faculty of Biology and Medicine, University of Lausanne, Lausanne
- National Center of Competence in Research, Kidney.CH, Zurich, Switzerland
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12
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Yu Z, Chen J, Takagi E, Wang F, Saha B, Liu X, Joubert LM, Gleason CE, Jin M, Li C, Nowotny C, Agard D, Cheng Y, Pearce D. Interactions between mTORC2 core subunits Rictor and mSin1 dictate selective and context-dependent phosphorylation of substrate kinases SGK1 and Akt. J Biol Chem 2022; 298:102288. [PMID: 35926713 PMCID: PMC9440446 DOI: 10.1016/j.jbc.2022.102288] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 07/04/2022] [Accepted: 07/05/2022] [Indexed: 12/02/2022] Open
Abstract
Mechanistic target of rapamycin complex 2 (mTORC2) is a multi-subunit kinase complex, central to multiple essential signaling pathways. Two core subunits, Rictor and mSin1, distinguish it from the related mTORC1 and support context-dependent phosphorylation of its substrates. mTORC2 structures have been determined previously; however, important questions remain, particularly regarding the structural determinants mediating substrate specificity and context-dependent activity. Here, we used cryo-EM to obtain high-resolution structures of the human mTORC2 apo-complex in the presence of substrates Akt and SGK1. Using functional assays, we then tested predictions suggested by substrate-induced structural changes in mTORC2. For the first time, we visualized in the apo-state the side chain interactions between Rictor and mTOR that sterically occlude recruitment of mTORC1 substrates and confer resistance to the mTORC1 inhibitor rapamycin. Also in the apo-state, we observed that mSin1 formed extensive contacts with Rictor via a pair of short α-helices nestled between two Rictor helical repeat clusters, as well as by an extended strand that makes multiple weak contacts with Rictor helical cluster 1. In co-complex structures, we found that SGK1, but not Akt, markedly altered the conformation of the mSin1 N-terminal extended strand, disrupting multiple weak interactions while inducing a large rotation of mSin1 residue Arg-83, which then interacts with a patch of negatively charged residues within Rictor. Finally, we demonstrate mutation of Arg-83 to Ala selectively disrupts mTORC2-dependent phosphorylation of SGK1, but not of Akt, supporting context-dependent substrate selection. These findings provide new structural and functional insights into mTORC2 specificity and context-dependent activity.
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Affiliation(s)
- Zanlin Yu
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Junliang Chen
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Enzo Takagi
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Feng Wang
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Bidisha Saha
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Xi Liu
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, USA
| | - Lydia-Marie Joubert
- Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California, USA
| | - Catherine E Gleason
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Mingliang Jin
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Chengmin Li
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Carlos Nowotny
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - David Agard
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA
| | - Yifan Cheng
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA; Howard Hughes Medical Institute, University of California San Francisco, San Francisco, California, USA
| | - David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA.
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13
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Aromolaran KA, Do J, Bernardi J, Aromolaran AS. mTOR Modulation of IKr through hERG1b-Dependent Mechanisms in Lipotoxic Heart. Int J Mol Sci 2022; 23:8061. [PMID: 35897638 PMCID: PMC9329916 DOI: 10.3390/ijms23158061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 07/17/2022] [Accepted: 07/20/2022] [Indexed: 12/04/2022] Open
Abstract
In the atria, the rapid delayed rectifier channel (IKr) is a critical contributor to repolarization. In lipotoxic atria, increased activity of the serine/threonine mammalian target of rapamycin (mTOR) may remodel IKr and predispose patients to arrhythmias. To investigate whether mTOR produced defects in IKr channel function (protein expression and gating mechanisms), electrophysiology and biochemical assays in HEK293 cells stably expressing hERG1a/1b, and adult guinea pig atrial myocytes were used. Feeding with the saturated fatty acid palmitic acid high-fat diet (HFD) was used to induce lipotoxicity. Lipotoxicity-challenged HEK293 cells displayed an increased density of hERG1a/1b currents due to a targeted and significant increase in hERG1b protein expression. Furthermore, lipotoxicity significantly slowed the hERG1a/1b inactivation kinetics, while the activation and deactivation remained essentially unchanged. mTOR complex 1 (mTORC1) inhibition with rapamycin (RAP) reversed the increase in hERG1a/1b density and inactivation. Compared to lipotoxic myocytes, RAP-treated cells displayed action potential durations (APDs) and IKr densities similar to those of controls. HFD feeding triggered arrhythmogenic changes (increased the IKr density and shortened the APD) in the atria, but this was not observed in low-fat-fed controls. The data are the first to show the modulation of IKr by mTORC1, possibly through the remodeling of hERG1b, in lipotoxic atrial myocytes. These results offer mechanistic insights with implications for targeted therapeutic options for the therapy of acquired supraventricular arrhythmias in obesity and associated pathologies.
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14
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Zhang L, Yang Y, Aroor AR, Jia G, Sun Z, Parrish A, Litherland G, Bonnard B, Jaisser F, Sowers JR, Hill MA. Endothelial sodium channel activation mediates DOCA-salt-induced endothelial cell and arterial stiffening. Metabolism 2022; 130:155165. [PMID: 35183546 PMCID: PMC8977070 DOI: 10.1016/j.metabol.2022.155165] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 02/09/2022] [Accepted: 02/14/2022] [Indexed: 11/24/2022]
Abstract
INTRODUCTION High salt intake and aldosterone are both associated with vascular stiffening in humans. However, our preliminary work showed that high dietary salt alone did not increase endothelial cell (EC) or vascular stiffness or endothelial sodium channel (EnNaC) activation in mice, presumably because aldosterone production was significantly suppressed as a result of the high salt diet. We thus hypothesized that high salt consumption along with an exogenous mineralocorticoid would substantially increase EC and vascular stiffness via activation of the EnNaC. METHODS AND RESULTS Mice were implanted with slow-release DOCA pellets and given salt in their drinking water for 21 days. Mice with either specific deletion of the alpha subunit of EnNaC or treated with a pharmacological inhibitor of mTOR, a downstream signaling molecule involved in mineralocorticoid receptor activation of EnNaC, were studied. DOCA-salt treated control mice had increased blood pressure, EC Na+ transport activity, EC and arterial stiffness, which were attenuated in both the αEnNaC-/- and mTOR inhibitor treated groups. Further, depletion of αEnNaC prevented DOCA-salt-induced impairment in EC-dependent vascular relaxation. CONCLUSION While high salt consumption alone does not cause EC or vascular stiffening, the combination of EC MR activation and high salt causes activation of EnNaC which increases EC and arterial stiffness and impairs vascular relaxation. Underlying mechanisms appear to include mTOR signaling.
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Affiliation(s)
- Liping Zhang
- Dalton Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA; Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Yan Yang
- Dalton Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Annayya R Aroor
- Diabetes and Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Guanghong Jia
- Diabetes and Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Zhe Sun
- Dalton Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Alan Parrish
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Garrett Litherland
- Dalton Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA; Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Benjamin Bonnard
- INSERM, UMRS 1138, Cordeliers Research Center, Sorbonne Université, Université de Paris, F-75006 Paris, France
| | - Frederic Jaisser
- INSERM, UMRS 1138, Cordeliers Research Center, Sorbonne Université, Université de Paris, F-75006 Paris, France
| | - James R Sowers
- Dalton Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA; Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO 65211, USA; Diabetes and Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA
| | - Michael A Hill
- Dalton Cardiovascular Research Center, School of Medicine, University of Missouri, Columbia, MO 65211, USA; Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri, Columbia, MO 65211, USA.
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15
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Abstract
The kidney maintains electrolyte, water, and acid-base balance, eliminates foreign and waste compounds, regulates blood pressure, and secretes hormones. There are at least 16 different highly specialized epithelial cell types in the mammalian kidney. The number of specialized endothelial cells, immune cells, and interstitial cell types might even be larger. The concerted interplay between different cell types is critical for kidney function. Traditionally, cells were defined by their function or microscopical morphological appearance. With the advent of new single-cell modalities such as transcriptomics, epigenetics, metabolomics, and proteomics we are entering into a new era of cell type definition. This new technological revolution provides new opportunities to classify cells in the kidney and understand their functions.
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Affiliation(s)
- Michael S Balzer
- Department of Medicine, Renal Electrolyte and Hypertension Division, University of Pennsylvania, Philadelphia, Pennsylvania, USA;
- Institute of Diabetes Obesity and Metabolism, University of Pennsylvania, Philadelphia, Philadelphia, USA
| | - Tibor Rohacs
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey, USA
| | - Katalin Susztak
- Department of Medicine, Renal Electrolyte and Hypertension Division, University of Pennsylvania, Philadelphia, Pennsylvania, USA;
- Institute of Diabetes Obesity and Metabolism, University of Pennsylvania, Philadelphia, Philadelphia, USA
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16
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Chen B, Fluitt MB, Brown AL, Scott S, Gadicherla A, Ecelbarger CM. Selective Deletion of the Mechanistic Target of Rapamycin From the Renal Collecting Duct Principal Cell in Mice Down-Regulates the Epithelial Sodium Channel. Front Physiol 2022; 12:787521. [PMID: 35058797 PMCID: PMC8764147 DOI: 10.3389/fphys.2021.787521] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 11/15/2021] [Indexed: 12/17/2022] Open
Abstract
The mechanistic target of rapamycin (mTOR), a serine-threonine-specific kinase, is a cellular energy sensor, integrating growth factor and nutrient signaling. In the collecting duct (CD) of the kidney, the epithelial sodium channel (ENaC) essential in the determination of final urine Na+ losses, has been demonstrated to be upregulated by mTOR, using cell culture and mTOR inhibition in ex vivo preparations. We tested whether CD-principal cell (PC) targeted deletion of mTOR using Cre-lox recombination would affect whole-body sodium homeostasis, blood pressure, and ENaC regulation in mice. Male and female CD-PC mTOR knockout (KO) mice and wild-type (WT) littermates (Cre-negative) were generated using aquaporin-2 (AQP2) promoter to drive Cre-recombinase. Under basal conditions, KO mice showed a reduced (∼30%) natriuretic response to benzamil (ENaC) antagonist, suggesting reduced in vivo ENaC activity. WT and KO mice were fed normal sodium (NS, 0.45% Na+) or a very low Na+ (LS, <0.02%) diet for 7-days. Switching from NS to LS resulted in significantly higher urine sodium losses (relative to WT) in the KO with adaptation occurring by day 2. Blood pressures were modestly (∼5-10 mm Hg) but significantly lower in KO mice under both diets. Western blotting showed KO mice had 20-40% reduced protein levels of all three subunits of ENaC under LS or NS diet. Immunohistochemistry (IHC) of kidney showed enhanced apical-vs.-cellular localization of all three subunits with LS, but a reduction in this ratio for γ-ENaC in the KO. Furthermore, the KO kidneys showed increased ubiquitination of α-ENaC and reduced phosphorylation of the serum and glucocorticoid regulated kinase, type 1 [serum glucocorticoid regulated kinase (SGK1)] on serine 422 (mTOR phosphorylation site). Taken together this suggests enhanced degradation as a consequence of reduced mTOR kinase activity and downstream upregulation of ubiquitination may have accounted for the reduction at least in α-ENaC. Overall, our data support a role for mTOR in ENaC activity likely via regulation of SGK1, ubiquitination, ENaC channel turnover and apical membrane residency. These data support a role for mTOR in the collecting duct in the maintenance of body sodium homeostasis.
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Affiliation(s)
- Bruce Chen
- Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC, United States
| | - Maurice B. Fluitt
- Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC, United States
- Department of Medicine, Howard University, Washington, DC, United States
| | - Aaron L. Brown
- Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC, United States
| | - Samantha Scott
- Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC, United States
| | - Anirudh Gadicherla
- Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC, United States
| | - Carolyn M. Ecelbarger
- Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC, United States
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17
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Pearce D, Manis AD, Nesterov V, Korbmacher C. Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology. Pflugers Arch 2022; 474:869-884. [PMID: 35895103 PMCID: PMC9338908 DOI: 10.1007/s00424-022-02732-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 07/09/2022] [Accepted: 07/11/2022] [Indexed: 02/03/2023]
Abstract
Regulated Na+ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na+ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na+ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K+, Ca++, Mg++, Cl-, and HCO3-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na+ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na+ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na+ and K+ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K+ concentrations are involved in the reciprocal regulation of Na+-Cl- cotransporter (NCC) and ENaC activity to adjust renal K+ secretion to dietary intake.
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Affiliation(s)
- David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Anna D. Manis
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA USA
| | - Viatcheslav Nesterov
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
| | - Christoph Korbmacher
- Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany, Erlangen, Germany
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18
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Abstract
Aldosterone is a major mineralocorticoid steroid hormone secreted by glomerulosa cells in the adrenal cortex. It regulates a variety of physiological responses including those to oxidative stress, inflammation, fluid disruption, and abnormal blood pressure through its actions on various tissues including the kidney, heart, and the central nervous system. Aldosterone synthesis is primarily regulated by angiotensin II, K+ concentration, and adrenocorticotrophic hormone. Elevated serum aldosterone levels increase blood pressure largely by increasing Na+ re-absorption in the kidney through regulating transcription and activity of the epithelial sodium channel (ENaC). This review focuses on the signaling pathways involved in aldosterone synthesis and its effects on Na+ reabsorption through ENaC.
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Affiliation(s)
- Akaki Tsilosani
- Department of Regenerative & Cancer Cell Biology, Albany Medical College, Albany, NY, United States
| | - Chao Gao
- Department of Regenerative & Cancer Cell Biology, Albany Medical College, Albany, NY, United States
| | - Wenzheng Zhang
- Department of Regenerative & Cancer Cell Biology, Albany Medical College, Albany, NY, United States
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19
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Abstract
The mechanistic target of rapamycin (mTOR) forms two distinct intracellular multiprotein complexes that control a multitude of intracellular processes linked to metabolism, proliferation, actin cytoskeleton, and survival. Recent studies have identified the importance of these complexes for transport regulation of ions and nutrients along the entire nephron. First reports could link altered activity of these complexes to certain disease entities, i.e. diabetic nephropathy, acute kidney injury or hyperkalemia.
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Affiliation(s)
- Florian Grahammer
- Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Tobias B Huber
- Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Ferruh Artunc
- Department of Internal Medicine, Division of Endocrinology, Diabetology, and Nephrology, University Hospital Tübingen, Tübingen, Germany.,Institute of Diabetes Research and Metabolic Diseases, Helmholtz Center Munich, University Tübingen, Tübingen, Germany.,German Center for Diabetes Research, University Tübingen, Tübingen, Germany
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20
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Schlingmann KP, Jouret F, Shen K, Nigam A, Arjona FJ, Dafinger C, Houillier P, Jones DP, Kleinerüschkamp F, Oh J, Godefroid N, Eltan M, Güran T, Burtey S, Parotte MC, König J, Braun A, Bos C, Ibars Serra M, Rehmann H, Zwartkruis FJ, Renkema KY, Klingel K, Schulze-Bahr E, Schermer B, Bergmann C, Altmüller J, Thiele H, Beck BB, Dahan K, Sabatini D, Liebau MC, Vargas-Poussou R, Knoers NV, Konrad M, de Baaij JH. mTOR-Activating Mutations in RRAGD Are Causative for Kidney Tubulopathy and Cardiomyopathy. J Am Soc Nephrol 2021; 32:2885-2899. [PMID: 34607910 PMCID: PMC8806087 DOI: 10.1681/asn.2021030333] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 07/07/2021] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Over the last decade, advances in genetic techniques have resulted in the identification of rare hereditary disorders of renal magnesium and salt handling. Nevertheless, approximately 20% of all patients with tubulopathy lack a genetic diagnosis. METHODS We performed whole-exome and -genome sequencing of a patient cohort with a novel, inherited, salt-losing tubulopathy; hypomagnesemia; and dilated cardiomyopathy. We also conducted subsequent in vitro functional analyses of identified variants of RRAGD, a gene that encodes a small Rag guanosine triphosphatase (GTPase). RESULTS In eight children from unrelated families with a tubulopathy characterized by hypomagnesemia, hypokalemia, salt wasting, and nephrocalcinosis, we identified heterozygous missense variants in RRAGD that mostly occurred de novo. Six of these patients also had dilated cardiomyopathy and three underwent heart transplantation. We identified a heterozygous variant in RRAGD that segregated with the phenotype in eight members of a large family with similar kidney manifestations. The GTPase RagD, encoded by RRAGD, plays a role in mediating amino acid signaling to the mechanistic target of rapamycin complex 1 (mTORC1). RagD expression along the mammalian nephron included the thick ascending limb and the distal convoluted tubule. The identified RRAGD variants were shown to induce a constitutive activation of mTOR signaling in vitro. CONCLUSIONS Our findings establish a novel disease, which we call autosomal dominant kidney hypomagnesemia (ADKH-RRAGD), that combines an electrolyte-losing tubulopathy and dilated cardiomyopathy. The condition is caused by variants in the RRAGD gene, which encodes Rag GTPase D; these variants lead to an activation of mTOR signaling, suggesting a critical role of Rag GTPase D for renal electrolyte handling and cardiac function.
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Affiliation(s)
- Karl P. Schlingmann
- Department of General Pediatrics, University Children’s Hospital, Münster, Germany
| | - François Jouret
- Division of Nephrology, Department of Internal Medicine, University of Liège Hospital, Liège, Belgium,Interdisciplinary Group of Applied Genoproteomics, Cardiovascular Sciences, University of Liège, Liège, Belgium
| | - Kuang Shen
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts,Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts,Koch Institute for Integrative Cancer Research, Cambridge, Massachusetts,Broad Institute of Harvard and Massachusetts Institute of Technology, Cambridge, Massachusetts,Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts
| | - Anukrati Nigam
- Department of Genetics, Center for Molecular Medicine, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Francisco J. Arjona
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Claudia Dafinger
- Department of Pediatrics and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany,Department II of Internal Medicine and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany
| | - Pascal Houillier
- Cordeliers Research Center, Centre National de la Recherche Scientifique (CNRS), ERL8228, Institut National de la Santé et de la Recherche Médicale (INSERM), Sorbonne University, University of Paris, Paris, France,Department of Physiology, Assistance Publique-Hôpitaux de Paris (AP-HP), European Hospital Georges Pompidou, Paris, France,Reference Center for Hereditary Renal Diseases in Children and Adults (MARHEA), Paris, France
| | - Deborah P. Jones
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Felix Kleinerüschkamp
- Department of Pediatric Cardiology, University Children’s Hospital, Münster, Germany
| | - Jun Oh
- Department of Pediatrics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Nathalie Godefroid
- Division of Pediatric Nephrology, Saint-Luc University Clinics, Catholic University of Louvain, Brussels, Belgium
| | - Mehmet Eltan
- Department of Pediatric Endocrinology and Diabetes, School of Medicine, Marmara University, Istanbul, Turkey
| | - Tülay Güran
- Department of Pediatric Endocrinology and Diabetes, School of Medicine, Marmara University, Istanbul, Turkey
| | - Stéphane Burtey
- Center for Nephrology and Renal Transplantation, Assistance Publique-Hôpitaux de Marseille, Aix-Marseille University, Marseille, France
| | - Marie-Christine Parotte
- Division of Nephrology-Dialysis, Department of Internal Medicine, CHR Verviers East Belgium, Verviers, Belgium
| | - Jens König
- Department of General Pediatrics, University Children’s Hospital, Münster, Germany
| | - Alina Braun
- Department of Pediatrics and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany,Department II of Internal Medicine and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany
| | - Caro Bos
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Maria Ibars Serra
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Holger Rehmann
- Department of Molecular Cancer Research, Center for Molecular Medicine, Oncode Institute, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Fried J.T. Zwartkruis
- Department of Molecular Cancer Research, Center for Molecular Medicine, Oncode Institute, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Kirsten Y. Renkema
- Department of Genetics, Center for Molecular Medicine, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Karin Klingel
- Cardiopathology, Institute for Pathology and Neuropathology, University Hospital Tübingen, Tübingen, Germany
| | - Eric Schulze-Bahr
- Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital Münster, Münster, Germany
| | - Bernhard Schermer
- Department II of Internal Medicine and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany,CECAD, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany
| | - Carsten Bergmann
- Limbach Genetics, Medizinische Genetik Mainz, Mainz, Germany,Division of Nephrology, Department of Medicine, University Hospital Freiburg, Breisgau, Germany
| | - Janine Altmüller
- Cologne Center for Genomics, University of Cologne, Cologne, Germany
| | - Holger Thiele
- Cologne Center for Genomics, University of Cologne, Cologne, Germany
| | - Bodo B. Beck
- Institute of Human Genetics, University Hospital Cologne and University of Cologne, Faculty of Medicine, Cologne, Germany,Center for Molecular Medicine Cologne, University of Cologne, Faculty of Medicine, University Hospital Cologne, Cologne, Germany,Center for Rare Diseases, Medical Faculty, University of Cologne and University Hospital Cologne, Cologne, Germany
| | - Karin Dahan
- Center of Human Genetics, Gosselies, Belgium,Division of Nephrology, Saint-Luc University Clinics, Catholic University of Louvain, Brussels, Belgium
| | - David Sabatini
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts,Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts,Koch Institute for Integrative Cancer Research, Cambridge, Massachusetts,Broad Institute of Harvard and Massachusetts Institute of Technology, Cambridge, Massachusetts
| | - Max C. Liebau
- Department of Pediatrics and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany,Department II of Internal Medicine and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne and University Hospital Cologne, Cologne, Germany,Center for Rare Diseases, Medical Faculty, University of Cologne and University Hospital Cologne, Cologne, Germany
| | - Rosa Vargas-Poussou
- Department of Genetics, AP-HP, European Hospital Georges Pompidou, Paris, France
| | - Nine V.A.M. Knoers
- Department of Genetics, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Martin Konrad
- Department of General Pediatrics, University Children’s Hospital, Münster, Germany
| | - Jeroen H.F. de Baaij
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
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21
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Campbell GR, Spector SA. Induction of Autophagy to Achieve a Human Immunodeficiency Virus Type 1 Cure. Cells 2021; 10:cells10071798. [PMID: 34359967 PMCID: PMC8307643 DOI: 10.3390/cells10071798] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Revised: 07/13/2021] [Accepted: 07/13/2021] [Indexed: 02/06/2023] Open
Abstract
Effective antiretroviral therapy has led to significant human immunodeficiency virus type 1 (HIV-1) suppression and improvement in immune function. However, the persistence of integrated proviral DNA in latently infected reservoir cells, which drive viral rebound post-interruption of antiretroviral therapy, remains the major roadblock to a cure. Therefore, the targeted elimination or permanent silencing of this latently infected reservoir is a major focus of HIV-1 research. The most studied approach in the development of a cure is the activation of HIV-1 expression to expose latently infected cells for immune clearance while inducing HIV-1 cytotoxicity—the “kick and kill” approach. However, the complex and highly heterogeneous nature of the latent reservoir, combined with the failure of clinical trials to reduce the reservoir size casts doubt on the feasibility of this approach. This concern that total elimination of HIV-1 from the body may not be possible has led to increased emphasis on a “functional cure” where the virus remains but is unable to reactivate which presents the challenge of permanently silencing transcription of HIV-1 for prolonged drug-free remission—a “block and lock” approach. In this review, we discuss the interaction of HIV-1 and autophagy, and the exploitation of autophagy to kill selectively HIV-1 latently infected cells as part of a cure strategy. The cure strategy proposed has the advantage of significantly decreasing the size of the HIV-1 reservoir that can contribute to a functional cure and when optimised has the potential to eradicate completely HIV-1.
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Affiliation(s)
- Grant R. Campbell
- Division of Infectious Diseases, Department of Pediatrics, University of California San Diego, La Jolla, CA 92093, USA;
- Correspondence: ; Tel.: +1-858-534-7477
| | - Stephen A. Spector
- Division of Infectious Diseases, Department of Pediatrics, University of California San Diego, La Jolla, CA 92093, USA;
- Rady Children’s Hospital, San Diego, CA 92123, USA
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22
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Abstract
The Epithelial Na+ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na+ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.
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Affiliation(s)
- Daniela Rotin
- The Hospital for Sick Children, and The University of Toronto, Toronto, Canada
| | - Olivier Staub
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
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23
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Zheleznova NN, Kumar V, Kurth T, Cowley AW. Hydrogen peroxide (H 2O 2) mediated activation of mTORC2 increases intracellular Na + concentration in the renal medullary thick ascending limb of Henle. Sci Rep 2021; 11:7300. [PMID: 33790341 PMCID: PMC8012714 DOI: 10.1038/s41598-021-86678-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 03/05/2021] [Indexed: 11/22/2022] Open
Abstract
Hydrogen peroxide (H2O2) production in the renal outer medulla is an important determinant of renal medullary blood flow and blood pressure (BP) salt-sensitivity in Dahl salt-sensitive (SS) rats. The mechanisms and pathways responsible for these actions are poorly understood. Recently, we have discovered that the mTOR complex 2 (mTORC2) plays a critical role in BP salt-sensitivity of SS rats by regulating Na+ homeostasis. PP242, an inhibitor of mTORC1/2 pathways exhibits potent natriuretic actions and completely prevented salt-induced hypertension in SS rats. In the present study, we have found that chronic infusion of H2O2 into the single remaining kidney of Sprague Dawley (SD) rats (3 days) stimulated the functional marker (pAKTSer473/AKT) of mTORC2 activity measured by Western Blot analysis. No changes in mTORC1 activity in OM were observed as determined by pS6Ser235/236/S6. Using fluorescent microscopy and the Na+ sensitive dye Sodium Green, we have shown that H2O2 (100 µM added in the bath) increased intracellular sodium concentration ([Na+]i) in renal medullary thick ascending limbs (mTALs) isolated from SD rats. These responses were almost completely abolished by pretreatment of mTAL with 10 µM PP242, indicating that mTORC1/2 pathways were involved in the H2O2 induced increase of [Na+]i. mTAL cell volume remained unchanged (± 1%) by H2O2 as determined by 3D reconstruction confocal laser scanning microscopy techniques. Consistent with the microscopy data, Western Blot analysis of proteins obtained from freshly isolated mTAL treated with 100 µM H2O2 exhibited increased activity/phosphorylation of AKT (pAKTSer473/AKT) that was inhibited by PP242. This was associated with increased protein activity of the apical membrane cotransporter Na+-K+-2Cl- (NKCC2) and the Na/H exchanger (NHE-3). Na+-K+-ATPase activity was increased as reflected an increase in the ratio of pNa+-K+-ATPaseSer16 to total Na+-K+-ATPase. Overall, the results indicate that H2O2 mediated activation of mTORC2 plays a key role in transducing the observed increases of cytosolic [Na+]i despite associated increases of basolateral pump activity.
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Affiliation(s)
- Nadezhda N Zheleznova
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI, 53226, USA.
| | - Vikash Kumar
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI, 53226, USA
| | - Theresa Kurth
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI, 53226, USA
| | - Allen W Cowley
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI, 53226, USA.
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24
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Lee HJ, Mariappan MM, Norton L, Bakewell T, Feliers D, Oh SB, Donati A, Rubannelsonkumar CS, Venkatachalam MA, Harris SE, Rubera I, Tauc M, Ghosh Choudhury G, Kahn CR, Sharma K, DeFronzo RA, Kasinath BS. Proximal tubular epithelial insulin receptor mediates high-fat diet-induced kidney injury. JCI Insight 2021; 6:143619. [PMID: 33400689 PMCID: PMC7934847 DOI: 10.1172/jci.insight.143619] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 12/29/2020] [Indexed: 01/04/2023] Open
Abstract
The role of insulin receptor (IR) activated by hyperinsulinemia in obesity-induced kidney injury is not well understood. We hypothesized that activation of kidney proximal tubule epithelial IR contributes to obesity-induced kidney injury. We administered normal-fat diet (NFD) or high-fat diet (HFD) to control and kidney proximal tubule IR–knockout (KPTIRKO) mice for 4 months. Renal cortical IR expression was decreased by 60% in male and female KPTIRKO mice. Baseline serum glucose, serum creatinine, and the ratio of urinary albumin to creatinine (ACR) were similar in KPTIRKO mice compared to those of controls. On HFD, weight gain and increase in serum cholesterol were similar in control and KPTIRKO mice; blood glucose did not change. HFD increased the following parameters in the male control mice: renal cortical contents of phosphorylated IR and Akt, matrix proteins, urinary ACR, urinary kidney injury molecule-1–to-creatinine ratio, and systolic blood pressure. Renal cortical generation of hydrogen sulfide was reduced in HFD-fed male control mice. All of these parameters were ameliorated in male KPTIRKO mice. Interestingly, female mice were resistant to HFD-induced kidney injury in both genotypes. We conclude that HFD-induced kidney injury requires renal proximal tubule IR activation in male mice.
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Affiliation(s)
- Hak Joo Lee
- Center for Renal Medicine, Division of Nephrology
| | | | - Luke Norton
- Division of Diabetes, Department of Medicine
| | | | | | - Sae Byeol Oh
- Center for Renal Medicine, Division of Nephrology
| | | | | | | | - Stephen E Harris
- Department of Periodontics, University of Texas Health, San Antonio, Texas, USA
| | - Isabelle Rubera
- Universite Cote d'Azur, CNRS - UMR-7370, Laboratoire de Physiomédecine Moléculaire, Nice, France
| | - Michel Tauc
- Universite Cote d'Azur, CNRS - UMR-7370, Laboratoire de Physiomédecine Moléculaire, Nice, France
| | - Goutam Ghosh Choudhury
- Center for Renal Medicine, Division of Nephrology.,VA Research and.,Geriatric Research, Education and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas, USA
| | - C Ronald Kahn
- Joslin Diabetes Center and Harvard Medical School, Boston, Massachusetts, USA
| | - Kumar Sharma
- Center for Renal Medicine, Division of Nephrology.,VA Research and
| | | | - Balakuntalam S Kasinath
- Center for Renal Medicine, Division of Nephrology.,VA Research and.,Geriatric Research, Education and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas, USA
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25
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Heberle AM, Rehbein U, Rodríguez Peiris M, Thedieck K. Finding new edges: systems approaches to MTOR signaling. Biochem Soc Trans 2021; 49:41-54. [PMID: 33544134 DOI: 10.1042/BST20190730] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 12/23/2020] [Accepted: 01/05/2021] [Indexed: 11/17/2022]
Abstract
Cells have evolved highly intertwined kinase networks to finely tune cellular homeostasis to the environment. The network converging on the mechanistic target of rapamycin (MTOR) kinase constitutes a central hub that integrates metabolic signals and adapts cellular metabolism and functions to nutritional changes and stress. Feedforward and feedback loops, crosstalks and a plethora of modulators finely balance MTOR-driven anabolic and catabolic processes. This complexity renders it difficult — if not impossible — to intuitively decipher signaling dynamics and network topology. Over the last two decades, systems approaches have emerged as powerful tools to simulate signaling network dynamics and responses. In this review, we discuss the contribution of systems studies to the discovery of novel edges and modulators in the MTOR network in healthy cells and in disease.
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26
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Abstract
Potassium often has a negative connotation in Nephrology as patients with chronic kidney disease (CKD) are prone to develop hyperkalaemia. Approaches to the management of chronic hyperkalaemia include a low potassium diet or potassium binders. Yet, emerging data indicate that dietary potassium may be beneficial for patients with CKD. Epidemiological studies have shown that a higher urinary potassium excretion (as proxy for higher dietary potassium intake) is associated with lower blood pressure (BP) and lower cardiovascular risk, as well as better kidney outcomes. Considering that the composition of our current diet is characterized by a high sodium and low potassium content, increasing dietary potassium may be equally important as reducing sodium. Recent studies have revealed that dietary potassium modulates the activity of the thiazide-sensitive sodium-chloride cotransporter in the distal convoluted tubule (DCT). The DCT acts as a potassium sensor to control the delivery of sodium to the collecting duct, the potassium-secreting portion of the kidney. Physiologically, this allows immediate kaliuresis after a potassium load, and conservation of potassium during potassium deficiency. Clinically, it provides a novel explanation for the inverse relationship between dietary potassium and BP. Moreover, increasing dietary potassium intake can exert BP-independent effects on the kidney by relieving the deleterious effects of a low potassium diet (inflammation, oxidative stress and fibrosis). The aim of this comprehensive review is to link physiology with clinical medicine by proposing that the same mechanisms that allow us to excrete an acute potassium load also protect us from hypertension, cardiovascular disease and CKD.
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Affiliation(s)
- Kuang-Yu Wei
- Department of Internal Medicine, Division of Nephrology and Transplantation, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands.,Department of Internal Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Martin Gritter
- Department of Internal Medicine, Division of Nephrology and Transplantation, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Liffert Vogt
- Department of Internal Medicine, Division of Nephrology, Amsterdam University Medical Center, Amsterdam, The Netherlands
| | - Martin H de Borst
- Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Joris I Rotmans
- Department of Internal Medicine, Division of Nephrology, Leiden University Medical Center, Leiden, The Netherlands
| | - Ewout J Hoorn
- Department of Internal Medicine, Division of Nephrology and Transplantation, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
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27
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Maestro I, Boya P, Martinez A. Serum- and glucocorticoid-induced kinase 1, a new therapeutic target for autophagy modulation in chronic diseases. Expert Opin Ther Targets 2020; 24:231-243. [PMID: 32067528 DOI: 10.1080/14728222.2020.1730328] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Introduction: Autophagy, a basic cellular degradation pathway essential for survival, is altered both in aging and in many chronic human diseases, including infections, cancer, heart disease, and neurodegeneration. Identifying new therapeutic targets for the control and modulation of autophagy events is therefore of utmost importance in drug discovery. Serum and glucocorticoid activated kinase 1 (SGK1), known for decades for its role in ion channel modulation, is now known to act as a switch for autophagy homeostasis, and has emerged as a novel and important therapeutic target likely to attract considerable research attention in the coming years.Areas covered: In this general review of SGK1 we describe the kinase's structure and its roles in physiological and pathological contexts. We also discuss small-molecule modulators of SGK1 activity. These modulators are of particular interest to medicinal chemists and pharmacists seeking to develop more potent and selective drug candidates for SGK1, which, despite its key role in autophagy, remains relatively understudied.Expert opinion: The main future challenges in this area are (i) deciphering the role of SGK1 in selective autophagy processes (e.g. mitophagy, lipophagy, and aggrephagy); (ii) identifying selective allosteric modulators of SGK1 with specific biological functions; and (iii) conducting first-in-man clinical studies.
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Affiliation(s)
- Inés Maestro
- Centro de Investigaciones Biológicas Margarita Salas-CSIC, Madrid, Spain
| | - Patricia Boya
- Centro de Investigaciones Biológicas Margarita Salas-CSIC, Madrid, Spain
| | - Ana Martinez
- Centro de Investigaciones Biológicas Margarita Salas-CSIC, Madrid, Spain.,Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos III, Madrid, Spain
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28
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Chang FS, Wang Y, Dmitriev P, Gross J, Galione A, Pears C. A two-pore channel protein required for regulating mTORC1 activity on starvation. BMC Biol 2020; 18:8. [PMID: 31969153 PMCID: PMC6977259 DOI: 10.1186/s12915-019-0735-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 12/20/2019] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Two-pore channels (TPCs) release Ca2+ from acidic intracellular stores and are implicated in a number of diseases, but their role in development is unclear. The social amoeba Dictyostelium discoideum proliferates as single cells that aggregate to form a multicellular organism on starvation. Starvation is sensed by the mTORC1 complex which, like TPC proteins, is found on acidic vesicles. Here, we address the role of TPCs in development and under starvation. RESULTS We report that disruption of the gene encoding the single Dictyostelium TPC protein, TPC2, leads to a delay in early development and prolonged growth in culture with delayed expression of early developmental genes, although a rapid starvation-induced increase in autophagy is still apparent. Ca2+ signals induced by extracellular cAMP are delayed in developing tpc2- cells, and aggregation shows increased sensitivity to weak bases, consistent with reduced acidity of the vesicles. In mammalian cells, the mTORC1 protein kinase has been proposed to suppress TPC channel opening. Here, we show a reciprocal effect as tpc2- cells show an increased level of phosphorylation of an mTORC1 substrate, 4E-BP1. mTORC1 inhibition reverses the prolonged growth and increases the efficiency of aggregation of tpc2- cells. CONCLUSION TPC2 is required for efficient growth development transition in Dictyostelium and acts through modulation of mTORC1 activity revealing a novel mode of regulation.
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Affiliation(s)
- Fu-Sheng Chang
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Yuntao Wang
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Phillip Dmitriev
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Julian Gross
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK
| | - Antony Galione
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK
| | - Catherine Pears
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
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29
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Schaub T, Gürgen D, Maus D, Lange C, Tarabykin V, Dragun D, Hegner B. mTORC1 and mTORC2 Differentially Regulate Cell Fate Programs to Coordinate Osteoblastic Differentiation in Mesenchymal Stromal Cells. Sci Rep 2019; 9:20071. [PMID: 31882658 PMCID: PMC6934532 DOI: 10.1038/s41598-019-56237-w] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 12/04/2019] [Indexed: 01/02/2023] Open
Abstract
Vascular regeneration depends on intact function of progenitors of vascular smooth muscle cells such as pericytes and their circulating counterparts, mesenchymal stromal cells (MSC). Deregulated MSC differentiation and maladaptive cell fate programs associated with age and metabolic diseases may exacerbate arteriosclerosis due to excessive transformation to osteoblast-like calcifying cells. Targeting mTOR, a central controller of differentiation and cell fates, could offer novel therapeutic perspectives. In a cell culture model for osteoblastic differentiation of pluripotent human MSC we found distinct roles for mTORC1 and mTORC2 in the regulation of differentiation towards calcifying osteoblasts via cell fate programs in a temporally-controlled sequence. Activation of mTORC1 with induction of cellular senescence and apoptosis were hallmarks of transition to a calcifying phenotype. Inhibition of mTORC1 with Rapamycin elicited reciprocal activation of mTORC2, enhanced autophagy and recruited anti-apoptotic signals, conferring protection from calcification. Pharmacologic and genetic negative interference with mTORC2 function or autophagy both abolished regenerative programs but induced cellular senescence, apoptosis, and calcification. Overexpression of the mTORC2 constituent rictor revealed that enhanced mTORC2 signaling without altered mTORC1 function was sufficient to inhibit calcification. Studies in mice reproduced the in vitro effects of mTOR modulation with Rapamycin on cell fates in vascular cells in vivo. Amplification of mTORC2 signaling promotes protective cell fates including autophagy to counteract osteoblast differentiation and calcification of MSC, representing a novel mTORC2 function. Regenerative approaches aimed at modulating mTOR network activation patterns hold promise for delaying age-related vascular diseases and treatment of accelerated arteriosclerosis in chronic metabolic conditions.
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Affiliation(s)
- Theres Schaub
- Clinic for Nephrology and Intensive Care Medicine, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany
- Institute of Cell Biology and Neurobiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Dennis Gürgen
- Clinic for Nephrology and Intensive Care Medicine, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Center for Cardiovascular Research (CCR), Charité University Hospital, Berlin, Germany
- Experimental Pharmacology & Oncology Berlin-Buch GmbH, Berlin, Germany
| | - Deborah Maus
- Clinic for Nephrology and Intensive Care Medicine, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Junior Research Group 2: Metabolism of Microbial Pathogens, Robert Koch Institute, Berlin, Germany
| | - Claudia Lange
- Clinic for Stem Cell Transplantation, Department of Cell and Gene Therapy, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Victor Tarabykin
- Institute of Cell Biology and Neurobiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Duska Dragun
- Clinic for Nephrology and Intensive Care Medicine, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany.
- Center for Cardiovascular Research (CCR), Charité University Hospital, Berlin, Germany.
- Berlin-Brandenburg School for Regenerative Therapies (BSRT), Berlin, Germany.
| | - Björn Hegner
- Clinic for Nephrology and Intensive Care Medicine, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
- Center for Cardiovascular Research (CCR), Charité University Hospital, Berlin, Germany
- Berlin-Brandenburg School for Regenerative Therapies (BSRT), Berlin, Germany
- Vivantes Ida Wolff Hospital for Geriatric Medicine, Berlin, Germany
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30
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Kumar V, Evans LC, Kurth T, Yang C, Wollner C, Nasci V, Zheleznova NN, Bukowy J, Dayton A, Cowley AW. Therapeutic Suppression of mTOR (Mammalian Target of Rapamycin) Signaling Prevents and Reverses Salt-Induced Hypertension and Kidney Injury in Dahl Salt-Sensitive Rats. Hypertension 2019; 73:630-639. [PMID: 30595123 DOI: 10.1161/hypertensionaha.118.12378] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
mTOR (mammalian target of rapamycin) signaling has emerged as a key regulator in a wide range of cellular processes ranging from cell proliferation, immune responses, and electrolyte homeostasis. mTOR consists of 2 distinct protein complexes, mTORC1 (mTOR complex 1) and mTORC2 (mTOR complex 2) with distinct downstream signaling events. mTORC1 has been implicated in pathological conditions, such as cancer and type 2 diabetes mellitus in humans, and inhibition of this pathway with rapamycin has been shown to attenuate salt-induced hypertension in Dahl salt-sensitive rats. Several studies have found that the mTORC2 pathway is involved in the regulation of renal tubular sodium and potassium transport, but its role in hypertension has remained largely unexplored. In the present study, we, therefore, determined the effect of mTORC2 inhibition with compound PP242 on salt-induced hypertension and renal injury in salt-sensitive rats. We found that PP242 not only completely prevented but also reversed salt-induced hypertension and kidney injury in salt-sensitive rats. PP242 exhibited potent natriuretic actions, and chronic administration tended to produce a negative Na+ balance even during high-salt feeding. The results indicate that mTORC2 and the related downstream associated pathways play an important role in regulation of sodium balance and arterial pressure regulation in salt-sensitive rats. Therapeutic suppression of the mTORC2 pathway represents a novel pathway for the potential treatment of hypertension.
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Affiliation(s)
- Vikash Kumar
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Louise C Evans
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Theresa Kurth
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Chun Yang
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Clayton Wollner
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Victoria Nasci
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | | | - John Bukowy
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Alex Dayton
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
| | - Allen W Cowley
- From the Department of Physiology, Medical College of Wisconsin, Milwaukee
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31
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Akhoon BA, Gandhi NS, Pandey R. Computational insights into the active structure of SGK1 and its implication for ligand design. Biochimie 2019; 165:57-66. [DOI: 10.1016/j.biochi.2019.07.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Accepted: 07/08/2019] [Indexed: 11/27/2022]
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32
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Hosoda E, Hiraoka D, Hirohashi N, Omi S, Kishimoto T, Chiba K. SGK regulates pH increase and cyclin B-Cdk1 activation to resume meiosis in starfish ovarian oocytes. J Cell Biol 2019; 218:3612-3629. [PMID: 31537709 PMCID: PMC6829648 DOI: 10.1083/jcb.201812133] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 07/19/2019] [Accepted: 08/15/2019] [Indexed: 12/31/2022] Open
Abstract
Tight regulation of intracellular pH (pHi) is essential for biological processes. Fully grown oocytes, having a large nucleus called the germinal vesicle, arrest at meiotic prophase I. Upon hormonal stimulus, oocytes resume meiosis to become fertilizable. At this time, the pHi increases via Na+/H+ exchanger activity, although the regulation and function of this change remain obscure. Here, we show that in starfish oocytes, serum- and glucocorticoid-regulated kinase (SGK) is activated via PI3K/TORC2/PDK1 signaling after hormonal stimulus and that SGK is required for this pHi increase and cyclin B-Cdk1 activation. When we clamped the pHi at 6.7, corresponding to the pHi of unstimulated ovarian oocytes, hormonal stimulation induced cyclin B-Cdk1 activation; thereafter, oocytes failed in actin-dependent chromosome transport and spindle assembly after germinal vesicle breakdown. Thus, this SGK-dependent pHi increase is likely a prerequisite for these events in ovarian oocytes. We propose a model that SGK drives meiotic resumption via concomitant regulation of the pHi and cell cycle machinery.
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Affiliation(s)
- Enako Hosoda
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Daisaku Hiraoka
- Science and Education Center, Ochanomizu University, Tokyo, Japan
| | | | - Saki Omi
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Takeo Kishimoto
- Science and Education Center, Ochanomizu University, Tokyo, Japan
| | - Kazuyoshi Chiba
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
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33
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Nakamura M, Tsukada H, Seki G, Satoh N, Mizuno T, Fujii W, Horita S, Moriya K, Sato Y, Kume H, Nangaku M, Suzuki M. Insulin promotes sodium transport but suppresses gluconeogenesis via distinct cellular pathways in human and rat renal proximal tubules. Kidney Int 2019; 97:316-326. [PMID: 31735358 DOI: 10.1016/j.kint.2019.08.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2018] [Revised: 08/02/2019] [Accepted: 08/08/2019] [Indexed: 01/11/2023]
Abstract
Insulin is known to promote sodium transport and regulate gluconeogenesis in renal proximal tubules. Although protein kinase B (also known as Akt) and mammalian target of rapamycin complexes (mTORC) have been established as key regulators in the insulin signaling pathway, their roles in proximal tubules are poorly understood. To help define this, we examined the components of insulin signaling in sodium transport and gluconeogenesis in isolated human and rat proximal tubules, and also investigated the role of insulin in sodium handling and mTORC1 in insulin signaling in vivo. In isolated human and rat proximal tubules, Akt and mTORC1/2 inhibition suppressed insulin-stimulated sodium-bicarbonate co-transporter 1 (NBCe1) activity, whereas mTORC1 inhibition had no effect. Akt2 and mTORC2 gene silencing largely inhibited insulin-stimulated NBCe1 activity, whereas silencing of Akt1 and mTORC1 had no effect. Furthermore, insulin decreased sodium excretion, and this effect depended on phosphoinositide 3 kinase in vivo. Moreover, insulin reduced glucose production in rat proximal tubules and the expression of gluconeogenic genes in human and rat proximal tubules. Akt and mTORC1 inhibition largely abolished the observed insulin-mediated inhibitory effects. Gene silencing of insulin receptor substrate 1 (IRS1), Akt2, mTORC1, and mTORC2 also abolished insulin-mediated inhibition of gluconeogenesis. Additionally, in vivo, mTORC1 inhibition abolished insulin-mediated inhibitory effects in rat proximal tubules, although not in liver. These results indicate that insulin-stimulated proximal tubule sodium transport is mediated via the Akt2/mTORC2 pathway, whereas insulin-suppressed proximal tubule gluconeogenesis is mediated via the IRS1/Akt2/mTORC1/2 pathway. Thus, distinct pathways may play important roles in hypertension and hyperglycemia in metabolic syndrome and diabetes.
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Affiliation(s)
- Motonobu Nakamura
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
| | - Hiroyuki Tsukada
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
| | - George Seki
- Department of Nephrology, Yaizu City Hospital, Shizuoka, Japan
| | - Nobuhiko Satoh
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan; Department of Infection Control and Prevention, The University of Tokyo, Tokyo, Japan
| | - Tomohito Mizuno
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
| | - Wataru Fujii
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
| | - Shoko Horita
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
| | - Kyoji Moriya
- Department of Infection Control and Prevention, The University of Tokyo, Tokyo, Japan
| | - Yusuke Sato
- Department of Urology, The University of Tokyo, Tokyo, Japan
| | - Haruki Kume
- Department of Urology, The University of Tokyo, Tokyo, Japan
| | - Masaomi Nangaku
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
| | - Masashi Suzuki
- Health Service Center, Tokyo Gakugei University, Tokyo, Japan.
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Wright KD, Miller BS, El-Meanawy S, Tsaih SW, Banerjee A, Geurts AM, Sheinin Y, Sun Y, Kalyanaraman B, Rui H, Flister MJ, Sorokin A. The p52 isoform of SHC1 is a key driver of breast cancer initiation. Breast Cancer Res 2019; 21:74. [PMID: 31202267 PMCID: PMC6570928 DOI: 10.1186/s13058-019-1155-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 05/23/2019] [Indexed: 01/23/2023] Open
Abstract
Background SHC1 proteins (also called SHCA) exist in three functionally distinct isoforms (p46SHC, p52SHC, and p66SHC) that serve as intracellular adaptors for several key signaling pathways in breast cancer. Despite the broad evidence implicating SHC1 gene products as a central mediator of breast cancer, testing the isoform-specific roles of SHC1 proteins have been inaccessible due to the lack of isoform-specific inhibitors or gene knockout models. Methods Here, we addressed this issue by generating the first isoform-specific gene knockout models for p52SHC and p66SHC, using germline gene editing in the salt-sensitive rat strain. Compared with the wild-type (WT) rats, we found that genetic ablation of the p52SHC isoform significantly attenuated mammary tumor formation, whereas the p66SHC knockout had no effect. Rats were dosed with 7,12-dimethylbenz(a)anthracene (DMBA) by oral gavage to induce mammary tumors, and progression of tumor development was followed for 15 weeks. At 15 weeks, tumors were excised and analyzed by RNA-seq to determine differences between tumors lacking p66SHC or p52SHC. Results Compared with the wild-type (WT) rats, we found that genetic ablation of the p52SHC isoform significantly attenuated mammary tumor formation, whereas the p66SHC knockout had no effect. These data, combined with p52SHC being the predominant isoform that is upregulated in human and rat tumors, provide the first evidence that p52SHC is the oncogenic isoform of Shc1 gene products in breast cancer. Compared with WT tumors, 893 differentially expressed (DE; FDR < 0.05) genes were detected in p52SHC KO tumors compared with only 18 DE genes in the p66SHC KO tumors, further highlighting that p52SHC is the relevant SHC1 isoform in breast cancer. Finally, gene network analysis revealed that p52SHC KO disrupted multiple key pathways that have been previously implicated in breast cancer initiation and progression, including ESR1 and mTORC2/RICTOR. Conclusion Collectively, these data demonstrate the p52SHC isoform is the key driver of DMBA-induced breast cancer while the expression of p66SHC and p46SHC are not enough to compensate. Electronic supplementary material The online version of this article (doi:10.1186/s13058-019-1155-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Kevin D Wright
- Cardiovascular Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Department of Medicine, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Bradley S Miller
- Cardiovascular Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Department of Medicine, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Sarah El-Meanawy
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Free Radical Research Center, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Shirng-Wern Tsaih
- Cardiovascular Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Anjishnu Banerjee
- Institute for Health and Equity, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Aron M Geurts
- Cardiovascular Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Yuri Sheinin
- Department of Pathology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Yunguang Sun
- Department of Pathology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Balaraman Kalyanaraman
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Free Radical Research Center, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Hallgeir Rui
- Department of Pathology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Michael J Flister
- Cardiovascular Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.,Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA
| | - Andrey Sorokin
- Cardiovascular Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA. .,Department of Medicine, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI, 53226, USA.
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35
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Sørensen MV, Saha B, Jensen IS, Wu P, Ayasse N, Gleason CE, Svendsen SL, Wang WH, Pearce D. Potassium acts through mTOR to regulate its own secretion. JCI Insight 2019; 5:126910. [PMID: 31013253 DOI: 10.1172/jci.insight.126910] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Potassium (K+) secretion by kidney tubule cells is central to electrolyte homeostasis in mammals. In the K+ secretory "principal" cells of the distal nephron, electrogenic Na+ transport by the epithelial sodium channel (ENaC) generates the electrical driving force for K+ transport across the apical membrane. Regulation of this process is attributable in part to aldosterone, which stimulates the gene transcription of the ENaC-regulatory kinase, SGK1. However, a wide range of evidence supports the conclusion that an unidentified aldosterone-independent pathway exists. We show here that in principal cells, K+ itself acts through the type 2 mTOR complex (mTORC2) to activate SGK1, which stimulates ENaC to enhance K+ excretion. The effect depends on changes in K+ concentration on the blood side of the cells, and requires basolateral membrane K+-channel activity. However, it does not depend on changes in aldosterone, or on enhanced distal delivery of Na+ from upstream nephron segments. These data strongly support the idea that K+ is sensed directly by principal cells to stimulate its own secretion by activating the mTORC2-SGK1 signaling module, and stimulate ENaC. We propose that this local effect acts in concert with aldosterone and increased Na+ delivery from upstream nephron segments to sustain K+ homeostasis.
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Affiliation(s)
- Mads Vaarby Sørensen
- Departments of Biomedicine and Physiology, Aarhus University, Aarhus, Denmark.,Aarhus Institute for Advanced Studies, Aarhus University, Aarhus, Denmark
| | - Bidisha Saha
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | - Iben Skov Jensen
- Departments of Biomedicine and Physiology, Aarhus University, Aarhus, Denmark
| | - Peng Wu
- Department of Pharmacology, New York Medical College, Valhalla, New York, USA
| | - Niklas Ayasse
- Departments of Biomedicine and Physiology, Aarhus University, Aarhus, Denmark
| | - Catherine E Gleason
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
| | | | - Wen-Hui Wang
- Department of Pharmacology, New York Medical College, Valhalla, New York, USA
| | - David Pearce
- Department of Medicine, Division of Nephrology, and Department of Cellular and Molecular Pharmacology, UCSF, San Francisco, California, USA
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36
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Shariati MBH, Niknafs B, Seghinsara AM, Shokrzadeh N, Alivand MR. Administration of dexamethasone disrupts endometrial receptivity by alteration of expression of miRNA 223, 200a, LIF, Muc1, SGK1, and ENaC via the ERK1/2-mTOR pathway. J Cell Physiol 2019; 234:19629-19639. [PMID: 30993706 DOI: 10.1002/jcp.28562] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2018] [Revised: 02/28/2019] [Accepted: 03/06/2019] [Indexed: 12/30/2022]
Abstract
Successful implantation of embryos requires endometrial receptivity. Glucocorticoids are one of the factors influencing the implantation window. In this study, 40 female BALB/c mice were used to study the impacts of dexamethasone administration on endometrial receptivity markers during implantation window. The mice mated and were randomly divided into four groups: control (vehicle), dexamethasone (100 μg/kg, IP), PP242 (30 mg/kg, IP), and dexamethasone + PP242 (Dex + PP242). On the Day 4th and 5th of gestation, mice received their respective treatments and were killed on the 5th day. To assess the expression of Muc1, leukemia inflammatory inhibitor (LIF), serum/glucocorticoid-inducible kinase 1 (SGK1), epithelial Na+ channel (ENaC), miRNA 200a, and miRNA 223-3p in the endometrium real-time polymerase chain reaction was performed. Furthermore, using Western blot analysis protein expressions of extracellular signal-regulated kinase 1/2 (ERK1/2), mammalian target of rapamycin (mTOR), and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) were evaluated. Periodic Acid-Schiff staining was used to examine the histomorphological changes of the uterus. According to the results dexamethasone declined the expression of LIF, whereas upregulated expression of Muc1, SGK1, ENaC mRNA, miRNA 200a, and miRNA 223-3p in the endometrium. In addition, PP242, an mTOR inhibitor, induced mRNA expression of Muc1, miRNA200a, and miRNa223-3p whereas it declined the expression of LIF. Moreover, activity of the ERK1/2-mTOR pathway in the endometrial cells was deterred by dexamethasone and PP242. Nonstop epithelium proliferation and elevated surface glycoproteins layer on epithelium of dexamethasone and/or PP242-received groups were divulged through histochemical analysis. According to the above mentioned results, uterine receptivity during implantation period was declined by dexamethasone, at least in part, through modulation of involved genes in endometrial receptivity and inhibition of the ERK1/2-mTOR pathway.
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Affiliation(s)
| | - Behrooz Niknafs
- Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.,Department of Reproductive Biology, Faculty of Advanced Medical Sciences, Tabriz University of Medical Science, Tabriz, Iran
| | - Abbas Majdi Seghinsara
- Department of Anatomical Sciences, Faculty of Medicine, Tabriz University of Medical Science, Tabriz, Iran
| | - Naser Shokrzadeh
- Infertility and Reproductive Health Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran
| | - Mohammad Reza Alivand
- Department of Genetic, Facualty of Medcine, Tabriz University of Medical Sciences, Tabriz, Iran
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37
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Brooks DL, Garza AE, Katayama IA, Romero JR, Adler GK, Pojoga LH, Williams GH. Aldosterone Modulates the Mechanistic Target of Rapamycin Signaling in Male Mice. Endocrinology 2019; 160:716-728. [PMID: 30726893 PMCID: PMC6397424 DOI: 10.1210/en.2018-00989] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Accepted: 01/31/2019] [Indexed: 12/12/2022]
Abstract
Both mechanistic target of rapamycin (mTOR) pathway and aldosterone are implicated in the development of cardiovascular and renal disease. However, the interaction between aldosterone and the mTOR pathway is unknown. We hypothesized the following: that (i) increased aldosterone will modulate the activity of the mTORC1 and mTORC2 molecular pathways in the heart and kidney; (ii) a physiologic increase in aldosterone will affect these pathways differently than a pathophysiologic one; and (iii) the changes in the mTOR level/activity will differ between the heart and kidney. In both kidney and heart tissues, phosphorylation of mTOR is significantly decreased when aldosterone levels are physiologically increased (by dietary sodium restriction), followed by a decrease in phosphorylated p70S6K1 in cardiac, but not renal, tissue. Sirtuin 1, an epigenetic modulator, is decreased in the heart but increased in the kidney. Conversely, pathophysiologic aldosterone levels (an infusion for 3 weeks) had divergent effects on phosphorylated mTOR and the downstream substrates of mTORC1 and mTORC2 in cardiac and renal tissues. Increased aldosterone levels significantly alter mTOR activity in the heart and kidney. In the kidney, substantial differences were noted if the increase was produced physiologically vs pathophysiologically, suggesting that mTOR activity, in part, may mediate aldosterone-induced renal damage. Thus, modulating mTOR activity may reduce aldosterone-dependent renal damage similar to mineralocorticoid receptor blockade but potentially with less adverse side effects.
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Affiliation(s)
- Danielle L Brooks
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
- Correspondence: Danielle L. Brooks, PhD, Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, 221 Longwood Avenue, Boston, Massachusetts 02115. E-mail:
| | - Amanda E Garza
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
| | - Isis A Katayama
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
| | - Jose R Romero
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
| | - Gail K Adler
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
| | - Luminita H Pojoga
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
| | - Gordon H Williams
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital, Boston, Massachusetts
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38
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Ma X, Zhang L, Song J, Nguyen E, Lee RS, Rodgers SJ, Li F, Huang C, Schittenhelm RB, Chan H, Chheang C, Wu J, Brown KK, Mitchell CA, Simpson KJ, Daly RJ. Characterization of the Src-regulated kinome identifies SGK1 as a key mediator of Src-induced transformation. Nat Commun 2019; 10:296. [PMID: 30655532 PMCID: PMC6336867 DOI: 10.1038/s41467-018-08154-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2017] [Accepted: 12/20/2018] [Indexed: 12/13/2022] Open
Abstract
Despite significant progress, our understanding of how specific oncogenes transform cells is still limited and likely underestimates the complexity of downstream signalling events. To address this gap, we use mass spectrometry-based chemical proteomics to characterize the global impact of an oncogene on the expressed kinome, and then functionally annotate the regulated kinases. As an example, we identify 63 protein kinases exhibiting altered expression and/or phosphorylation in Src-transformed mammary epithelial cells. An integrated siRNA screen identifies nine kinases, including SGK1, as being essential for Src-induced transformation. Accordingly, we find that Src positively regulates SGK1 expression in triple negative breast cancer cells, which exhibit a prominent signalling network governed by Src family kinases. Furthermore, combined inhibition of Src and SGK1 reduces colony formation and xenograft growth more effectively than either treatment alone. Therefore, this approach not only provides mechanistic insights into oncogenic transformation but also aids the design of improved therapeutic strategies. The systemic understanding of oncogenic kinase signalling is still limited. Here, the authors combine chemical proteomics with functional screens to assess the impact of oncogenic Src on the expressed kinome and identify SGK1 as a critical mediator of Src-induced cell transformation.
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Affiliation(s)
- Xiuquan Ma
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Luxi Zhang
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Jiangning Song
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia.,Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Monash Centre for Data Science, Faculty of Information Technology, Monash University, Melbourne, VIC, 3800, Australia
| | - Elizabeth Nguyen
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Rachel S Lee
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Samuel J Rodgers
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Fuyi Li
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia.,Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia
| | - Cheng Huang
- Monash Biomedical Proteomics Facility and Monash Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia
| | - Ralf B Schittenhelm
- Monash Biomedical Proteomics Facility and Monash Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia
| | - Howard Chan
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Chanly Chheang
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Jianmin Wu
- Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Centre for Cancer Bioinformatics, Peking University Cancer Hospital & Institute, Beijing, 100142, China
| | - Kristin K Brown
- Cancer Therapeutics Program and Cancer Metabolism Program, Peter MacCallum Cancer Centre, Melbourne, VIC, 3000, Australia.,Department of Biochemistry and Molecular Biology, The University of Melbourne, Melbourne, VIC, 3010, Australia.,Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, VIC, 3010, Australia
| | - Christina A Mitchell
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia
| | - Kaylene J Simpson
- Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, VIC, 3010, Australia.,Victorian Centre for Functional Genomics, Peter MacCallum Cancer Centre, Melbourne, VIC, 3000, Australia
| | - Roger J Daly
- Cancer Program, Biomedicine Discovery Institute, Monash University, Melbourne, VIC, 3800, Australia. .,Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC, 3800, Australia.
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39
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Kamel KS, Schreiber M, Halperin ML. Renal potassium physiology: integration of the renal response to dietary potassium depletion. Kidney Int 2018; 93:41-53. [PMID: 29102372 DOI: 10.1016/j.kint.2017.08.018] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 07/31/2017] [Accepted: 08/03/2017] [Indexed: 01/30/2023]
Abstract
We summarize the current understanding of the physiology of the renal handling of potassium (K+), and present an integrative view of the renal response to K+ depletion caused by dietary K+ restriction. This renal response involves contributions from different nephron segments, and aims to diminish the rate of excretion of K+ as a result of: decreasing the rate of electrogenic (and increasing the rate of electroneutral) reabsorption of sodium in the aldosterone-sensitive distal nephron (ASDN), decreasing the abundance of renal outer medullary K+ channels in the luminal membrane of principal cells in the ASDN, decreasing the flow rate in the ASDN, and increasing the reabsorption of K+ in the cortical and medullary collecting ducts. The implications of this physiology for the association between K+ depletion and hypertension, and K+ depletion and formation of calcium kidney stones are discussed.
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Affiliation(s)
- Kamel S Kamel
- Renal Division, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada; Keenan Research Center, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada.
| | - Martin Schreiber
- Renal Division, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada
| | - Mitchell L Halperin
- Renal Division, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada; Keenan Research Center, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada
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40
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Ahi EP, Singh P, Lecaudey LA, Gessl W, Sturmbauer C. Maternal mRNA input of growth and stress-response-related genes in cichlids in relation to egg size and trophic specialization. EvoDevo 2018; 9:23. [PMID: 30519389 PMCID: PMC6271631 DOI: 10.1186/s13227-018-0112-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2018] [Accepted: 11/22/2018] [Indexed: 01/21/2023] Open
Abstract
BACKGROUND Egg size represents an important form of maternal effect determined by a complex interplay of long-term adaptation and short-term plasticity balancing egg size with brood size. Haplochromine cichlids are maternal mouthbrooders showing differential parental investment in different species, manifested in great variation in egg size, brood size and duration of maternal care. Little is known about maternally determined molecular characters of eggs in fishes and their relation to egg size and trophic specialization. Here we investigate maternal mRNA inputs of selected growth- and stress-related genes in eggs of mouthbrooding cichlid fishes adapted to different trophic niches from Lake Tanganyika, Lake Malawi, Lake Victoria and compare them to their riverine allies. RESULTS We first identified two reference genes, atf7ip and mid1ip1, to be suitable for cross-species quantification of mRNA abundance via qRT-PCR in the cichlid eggs. Using these reference genes, we found substantial variation in maternal mRNA input for a set of candidate genes related to growth and stress response across species and lakes. We observed negative correlation of mRNA abundance between two of growth hormone receptor paralogs (ghr1 and ghr2) across all haplochromine cichlid species which also differentiate the species in the two younger lakes, Malawi and Lake Victoria, from those in Lake Tanganyika and ancestral riverine species. Furthermore, we found correlations between egg size and maternal mRNA abundance of two growth-related genes igf2 and ghr2 across the haplochromine cichlids as well as distinct clustering of the species based on their trophic specialization using maternal mRNA abundance of five genes (ghr1, ghr2, igf2, gr and sgk1). CONCLUSIONS These findings indicate that variations in egg size in closely related cichlid species can be linked to differences in maternal RNA deposition of key growth-related genes. In addition, the cichlid species with contrasting trophic specialization deposit different levels of maternal mRNAs in their eggs for particular growth-related genes; however, it is unclear whether such differences contribute to differential morphogenesis at later stages of development. Our results provide first insights into this aspect of gene activation, as a basis for future studies targeting their role during ecomorphological specialization and adaptive radiation.
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Affiliation(s)
- Ehsan Pashay Ahi
- Institute of Biology, University of Graz, Universitätsplatz 2, 8010 Graz, Austria
- Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, 75236 Uppsala, Sweden
| | - Pooja Singh
- Institute of Biology, University of Graz, Universitätsplatz 2, 8010 Graz, Austria
| | | | - Wolfgang Gessl
- Institute of Biology, University of Graz, Universitätsplatz 2, 8010 Graz, Austria
| | - Christian Sturmbauer
- Institute of Biology, University of Graz, Universitätsplatz 2, 8010 Graz, Austria
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Samidurai A, Kukreja RC, Das A. Emerging Role of mTOR Signaling-Related miRNAs in Cardiovascular Diseases. Oxid Med Cell Longev 2018; 2018:6141902. [PMID: 30305865 DOI: 10.1155/2018/6141902] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2018] [Accepted: 07/04/2018] [Indexed: 12/21/2022]
Abstract
Mechanistic/mammalian target of rapamycin (mTOR), an atypical serine/threonine kinase of the phosphoinositide 3-kinase- (PI3K-) related kinase family, elicits a vital role in diverse cellular processes, including cellular growth, proliferation, survival, protein synthesis, autophagy, and metabolism. In the cardiovascular system, the mTOR signaling pathway integrates both intracellular and extracellular signals and serves as a central regulator of both physiological and pathological processes. MicroRNAs (miRs), a class of short noncoding RNA, are an emerging intricate posttranscriptional modulator of critical gene expression for the development and maintenance of homeostasis across a wide array of tissues, including the cardiovascular system. Over the last decade, numerous studies have revealed an interplay between miRNAs and the mTOR signaling circuit in the different cardiovascular pathophysiology, like myocardial infarction, hypertrophy, fibrosis, heart failure, arrhythmia, inflammation, and atherosclerosis. In this review, we provide a comprehensive state of the current knowledge regarding the mechanisms of interactions between the mTOR signaling pathway and miRs. We have also highlighted the latest advances on mTOR-targeted therapy in clinical trials and the new perspective therapeutic strategies with mTOR-targeting miRs in cardiovascular diseases.
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Brown AL, Fluitt MB, Ecelbarger CM. Mechanistic target of rapamycin: integrating growth factor and nutrient signaling in the collecting duct. Am J Physiol Renal Physiol 2018; 315:F413-F416. [PMID: 29846113 DOI: 10.1152/ajprenal.00170.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The renal collecting duct and other postmacula densa sites are the primary tubular regions for fine-tuning of electrolyte homeostasis in the body. A role for the mechanistic target of rapamycin (mTOR), a serine-threonine kinase, has recently been appreciated in this regulation. mTOR exists in two distinct multiprotein functional complexes, i.e., mTORC1 and mTORC2. Upregulation of mTORC1, by growth factors and amino acids, is associated with cell cycle regulation and hypertrophic changes. In contrast, mTORC2 has been demonstrated to have a role in regulating Na+ and K+ reabsorptive processes, including those downstream of insulin and serum- and glucocorticoid-regulated kinase (SGK). In addition, mTORC2 can upregulate mTORC1. A number of elegant in vitro and in vivo studies using cell systems and genetically modified mice have revealed mechanisms underlying activation of the epithelial Na+ channel (ENaC) and the renal outer medullary K+ channel (ROMK) by mTORC2. Overall, mTOR in its systematic integration of phosphorylative signaling facilitates the delicate balance of whole body electrolyte homeostasis in the face of changes in metabolic status. Thus, inappropriate regulation of renal mTOR has the potential to result in electrolyte disturbances, such as acidosis/alkalosis, hyponatremia, and hypertension. The goal of this minireview is to highlight the physiological role of mTOR in its complexes in regulating electrolyte homeostasis in the aldosterone-sensitive distal nephron.
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Affiliation(s)
- Aaron L Brown
- Department of Medicine, Georgetown University , Washington, District of Columbia
| | - Maurice B Fluitt
- Department of Medicine, Georgetown University , Washington, District of Columbia
| | - Carolyn M Ecelbarger
- Department of Medicine, Georgetown University , Washington, District of Columbia
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Abstract
Type II nephronophthisis (NPHP2) is an autosomal recessive renal cystic disorder characterized by mutations in the inversin gene. Humans and mice with mutations in inversin have enlarged cystic kidneys that may be due to fluid accumulation resulting from altered ion transport. To address this, transepithelial ion transport was measured in shRNA-mediated inversin-depleted mouse cortical collecting duct (mCCD) cells. Loss of inversin decreased the basal ion flux in mCCD cells compared with controls. Depletion of inversin decreased vasopressin-induced Na+ absorption but did not alter Cl- secretion by mCCD cells. Addition of amiloride, a specific blocker of the epithelial sodium channel (ENaC), abolished basal ion transport in both inversin knockdown and control cells, indicating ENaC involvement. Transcript levels of ENaC β-subunit were reduced in inversin-knockdown cells consistent with decreased ENaC activity. Furthermore, Nedd4l (neural precursor cell expressed, developmentally downregulated 4 like), an upstream negative regulator of ENaC, was evaluated. The relative amount of the phosphorylated, inactive Nedd4l was decreased in inversin-depleted cells consistent with decreased ENaC activity. The protein levels of Sgk1 (serum and glucocorticoid-inducible kinase), which phosphorylates Nedd4l, remained unchanged although the transcript levels were increased in inversin-depleted cells. Interestingly, mRNA and protein levels of Crtc2 (Creb-regulated transcription coactivator) kinase, a positive regulator of Sgk1, were decreased in inversin-depleted cells. Together these results suggest that loss of inversin decreases Na+ transport via ENaC, mediated in part by transcriptional and posttranslational regulation of Crtc2/Sgk1/Nedd4l axis as a contributory mechanism for enlarged kidneys in NPHP2.
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Affiliation(s)
- Nalini H Kulkarni
- Department of Biology, Indiana University-Purdue University at Indianapolis , Indianapolis, Indiana
| | - Rosamund C Smith
- Department of Biology, Indiana University-Purdue University at Indianapolis , Indianapolis, Indiana
| | - Bonnie L Blazer-Yost
- Department of Biology, Indiana University-Purdue University at Indianapolis , Indianapolis, Indiana
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Abstract
Activation of the PI3K pathway is central to a variety of physiological and pathological processes. In these contexts, AKT is classically considered the de facto mediator of PI3K-dependent signaling. However, in recent years, accumulating data point to the existence of additional effectors of PI3K activity, parallel to and independent of AKT, that play critical and unique roles in mediating different developmental, homeostatic, and pathological processes. In this review, I summarize and discuss our current understanding of the function of the serine/threonine kinase SGK1 as a downstream effector of PI3K, and try to separate targets and pathways validated as uniquely SGK1-dependent from those shared with AKT.
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Mansley MK, Watt GB, Francis SL, Walker DJ, Land SC, Bailey MA, Wilson SM. Dexamethasone and insulin activate serum and glucocorticoid-inducible kinase 1 (SGK1) via different molecular mechanisms in cortical collecting duct cells. Physiol Rep 2016; 4:4/10/e12792. [PMID: 27225626 PMCID: PMC4886164 DOI: 10.14814/phy2.12792] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 03/29/2016] [Indexed: 01/12/2023] Open
Abstract
Serum and glucocorticoid-inducible kinase 1 (SGK1) is a protein kinase that contributes to the hormonal control of renal Na(+) retention by regulating the abundance of epithelial Na(+) channels (ENaC) at the apical surface of the principal cells of the cortical collecting duct (CCD). Although glucocorticoids and insulin stimulate Na(+) transport by activating SGK1, the responses follow different time courses suggesting that these hormones act by different mechanisms. We therefore explored the signaling pathways that allow dexamethasone and insulin to stimulate Na(+) transport in mouse CCD cells (mpkCCDcl4). Dexamethasone evoked a progressive augmentation of electrogenic Na(+) transport that became apparent after ~45 min latency and was associated with increases in SGK1 activity and abundance and with increased expression of SGK1 mRNA Although the catalytic activity of SGK1 is maintained by phosphatidylinositol-OH-3-kinase (PI3K), dexamethasone had no effect upon PI3K activity. Insulin also stimulated Na(+) transport but this response occurred with no discernible latency. Moreover, although insulin also activated SGK1, it had no effect upon SGK1 protein or mRNA abundance. Insulin did, however, evoke a clear increase in cellular PI3K activity. Our data are consistent with earlier work, which shows that glucocorticoids regulate Na(+) retention by inducing sgk1 gene expression, and also establish that this occurs independently of increased PI3K activity. Insulin, on the other hand, stimulates Na(+) transport via a mechanism independent of sgk1 gene expression that involves PI3K activation. Although both hormones act via SGK1, our data show that they activate this kinase by distinct physiological mechanisms.
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Affiliation(s)
- Morag K Mansley
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
| | - Gordon B Watt
- Medical Research Institute, College of Medicine, Dentistry and Nursing, Ninewells Hospital and Medical School, University of Dundee, Dundee, UK
| | - Sarah L Francis
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
| | - David J Walker
- Medical Research Institute, College of Medicine, Dentistry and Nursing, Ninewells Hospital and Medical School, University of Dundee, Dundee, UK
| | - Stephen C Land
- Medical Research Institute, College of Medicine, Dentistry and Nursing, Ninewells Hospital and Medical School, University of Dundee, Dundee, UK
| | - Matthew A Bailey
- The British Heart Foundation Centre for Cardiovascular Science, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, UK
| | - Stuart M Wilson
- Division of Pharmacy, School of Medicine, Pharmacy and Health, Durham University Queen's Campus, Stockton-on-Tees, UK
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Abstract
BACKGROUND Recent studies reported increased (Pro)renin receptor (PRR) expression during low-salt intake. We hypothesized that PRR plays a role in regulation of renal epithelial sodium channel (ENaC) through serum and glucocorticoid-inducible kinase isoform 1 (SGK-1)-neural precursor cell expressed, developmentally downregulated 4-2 (Nedd4-2) signaling pathway. METHOD Male Sprague-Dawley rats on normal-sodium diet and mouse renal inner medullary collecting duct cells treated with NaCl at 130 mmol/l (normal salt), or 63 mmol/l (low salt) were studied. PRR and α-ENaC expressions were evaluated 1 week after right uninephrectomy and left renal interstitial administration of 5% dextrose, scramble shRNA, or PRR shRNA (n = 6 each treatment). RESULTS In-vivo PRR shRNA significantly reduced expressions of PRR throughout the kidney and α-ENaC subunits in the renal medulla. In inner medullary collecting duct cells, low salt or angiotensin II (Ang II) augmented the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC (P < 0.05). Low salt or Ang II increased the phosphorylation of Nedd4-2. In cells treated with low salt or Ang II, PRR siRNA significantly downregulated the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC expression (P < 0.05). CONCLUSION We conclude that PRR contributes to the regulation of α-ENaC via SGK-1-Nedd4-2 signaling pathway.
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Lou Y, Zhang F, Luo Y, Wang L, Huang S, Jin F. Serum and Glucocorticoid Regulated Kinase 1 in Sodium Homeostasis. Int J Mol Sci 2016; 17:ijms17081307. [PMID: 27517916 PMCID: PMC5000704 DOI: 10.3390/ijms17081307] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 08/02/2016] [Accepted: 08/03/2016] [Indexed: 12/13/2022] Open
Abstract
The ubiquitously expressed serum and glucocorticoid regulated kinase 1 (SGK1) is tightly regulated by osmotic and hormonal signals, including glucocorticoids and mineralocorticoids. Recently, SGK1 has been implicated as a signal hub for the regulation of sodium transport. SGK1 modulates the activities of multiple ion channels and carriers, such as epithelial sodium channel (ENaC), voltage-gated sodium channel (Nav1.5), sodium hydrogen exchangers 1 and 3 (NHE1 and NHE3), sodium-chloride symporter (NCC), and sodium-potassium-chloride cotransporter 2 (NKCC2); as well as the sodium-potassium adenosine triphosphatase (Na+/K+-ATPase) and type A natriuretic peptide receptor (NPR-A). Accordingly, SGK1 is implicated in the physiology and pathophysiology of Na+ homeostasis. Here, we focus particularly on recent findings of SGK1’s involvement in Na+ transport in renal sodium reabsorption, hormone-stimulated salt appetite and fluid balance and discuss the abnormal SGK1-mediated Na+ reabsorption in hypertension, heart disease, edema with diabetes, and embryo implantation failure.
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Affiliation(s)
- Yiyun Lou
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
- Department of Gynaecology, Hangzhou Hospital of Traditional Chinese Medicine, Hangzhou 310007, Zhejiang, China.
| | - Fan Zhang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Yuqin Luo
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Liya Wang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Shisi Huang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Fan Jin
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
- Key Laboratory of Reproductive Genetics, National Ministry of Education (Zhejiang University), Women's Reproductive Healthy Laboratory of Zhejiang Province, Hangzhou 310058, Zhejiang, China.
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Fantus D, Rogers NM, Grahammer F, Huber TB, Thomson AW. Roles of mTOR complexes in the kidney: implications for renal disease and transplantation. Nat Rev Nephrol 2016; 12:587-609. [PMID: 27477490 DOI: 10.1038/nrneph.2016.108] [Citation(s) in RCA: 134] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.
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Abstract
PURPOSE The aim of this study was to investigate the effect of miRNA-7-5p on human alveolar epithelial sodium channels and clarify the pathway in which miRNA-7-5p regulates the expression of ENaC in ARDS. MATERIALS AND METHODS Dual luciferase target gene validation experiments were used to confirm whether mTOR and SGK-1 are the target genes of miRNA-7-5p. Then, we overexpressed and inhibited miRNA-7-5p in the human alveolar epithelial cell line A549, respectively. LPS at a concentration of 100 ng/mL was used to stimulate the cells. The expressions ofmiRNA-7-5p, mTOR, SGK-1, p-Akt-Ser473, α-, β-, and γ-ENaC were detected by quantitative RT polymerase chain reaction (qRT-PCR) and western blotting. RESULTS In this study, we first confirmed that mTOR and SGK-1 are the target genes of miRNA-7-5p. Then, we found that mRNA expression levels of both mTOR and SGK-1 were downregulated to 0.54- and 0.3-fold, respectively, in the miRNA-7-5p mimic groups than the blank controls (P < 0.01). MiRNA-7-5p overexpression inhibited mTORC2/SGK-1 signaling pathway activity and reduced ENaC expression. The expression of miRNA-7-5p was significantly upregulated in A549 cells stimulated with lipopolysaccharide (LPS) and downregulated mRNA expression levels of both mTOR and SGK-1. After transfection with miRNA-7-5p inhibitors, we found that the mTORC2/SGK-1 pathway activity was restored compared to the group with LPS stimulation only, and the ENaC expression was also obviously increased. CONCLUSION Our results demonstrate that miRNA-7-5p can regulate the expression of human alveolar ENaC by targeting the mTORC2/SGK-1 signaling pathway. The inhibition of miRNA-7-5p can enhance the expression of ENaC, which may provide a new target for the treatment of ARDS.
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Affiliation(s)
- Ke Qin
- a Department of Respiratory Medicine , The Second Affiliated Hospital of Chongqing Medical University , Chongqing , China
| | - Xi Zhong
- a Department of Respiratory Medicine , The Second Affiliated Hospital of Chongqing Medical University , Chongqing , China
| | - Daoxin Wang
- a Department of Respiratory Medicine , The Second Affiliated Hospital of Chongqing Medical University , Chongqing , China
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Grahammer F, Nesterov V, Ahmed A, Steinhardt F, Sandner L, Arnold F, Cordts T, Negrea S, Bertog M, Ruegg MA, Hall MN, Walz G, Korbmacher C, Artunc F, Huber TB. mTORC2 critically regulates renal potassium handling. J Clin Invest 2016; 126:1773-82. [PMID: 27043284 DOI: 10.1172/jci80304] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 02/18/2016] [Indexed: 12/12/2022] Open
Abstract
The mTOR pathway orchestrates cellular homeostasis. The rapamycin-sensitive mTOR complex (mTORC1) in the kidney has been widely studied; however, mTORC2 function in renal tubules is poorly characterized. Here, we generated mice lacking mTORC2 in the distal tubule (Rictorfl/fl Ksp-Cre mice), which were viable and had no obvious phenotype, except for a 2.5-fold increase in plasma aldosterone. Challenged with a low-Na+ diet, these mice adequately reduced Na+ excretion; however, Rictorfl/fl Ksp-Cre mice rapidly developed hyperkalemia on a high-K+ diet, despite a 10-fold increase in serum aldosterone levels, implying that mTORC2 regulates kaliuresis. Phosphorylation of serum- and glucocorticoid-inducible kinase 1 (SGK1) and PKC-α was absent in Rictorfl/fl Ksp-Cre mice, indicating a functional block in K+ secretion activation via ROMK channels. Indeed, patch-clamp experiments on split-open tubular segments from the transition zone of the late connecting tubule and early cortical collecting duct demonstrated that Ba2+-sensitive apical K+ currents were barely detectable in the majority of Rictorfl/fl Ksp-Cre mice. Conversely, epithelial sodium channel (ENaC) activity was largely preserved, suggesting that the reduced ability to maintain K+ homeostasis is the result of impaired apical K+ conductance and not a reduced electrical driving force for K+ secretion. Thus, these data unravel a vital and nonredundant role of mTORC2 for distal tubular K+ handling.
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