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Li SS, Liu QJ, Bao JX, Lu MT, Deng BQ, Li WW, Cao CC. Counteracting TGM2 by a Fibroin peptide ameliorated Adriamycin-induced nephropathy via regulation of lipid metabolism through PANX1-PPAR α/PANK1 pathway. Transl Res 2024; 271:26-39. [PMID: 38734063 DOI: 10.1016/j.trsl.2024.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 04/28/2024] [Accepted: 05/08/2024] [Indexed: 05/13/2024]
Abstract
Peptide drug discovery for the treatment of chronic kidney disease (CKD) has attracted much attention in recent years due to the urge to find novel drugs and mechanisms to delay the progression of the disease. In this study, we identified a novel short peptide (named YR-7, primary sequence 'YEVEDYR') from the natural Fibroin protein, and demonstrated that it significantly alleviated pathological renal changes in ADR-induced nephropathy. PANX1 was identified as the most notably upregulated component by RNA-sequencing. Further analysis showed that YR-7 alleviated the accumulation of lipid droplets via regulation of the lipid metabolism-related proteins PPAR α and PANK1. Using chemical proteomics, fluorescence polarization, microscale thermophoresis, surface plasmon resonance, and molecular docking, YR-7 was proven to directly bind to β-barrel domains of TGM2 protein to inhibit lipid accumulation. TGM2 knockdown in vivo increased the protein levels of PPAR α and PANK1 while decreased the levels of fibrotic-related proteins to alleviate nephropathy. In vitro, overexpression TGM2 reversed the protective effects of YR-7. Co-immunoprecipitation indicated that TGM2 interacted with PANX1 to promote lipid deposition, and pharmacological inhibition or knockdown of PANX1 decreased the levels of PPAR α and PANK1 induced by ADR. Taken together, our findings revealed that TGM2-PANX1 interaction in promoting lipid deposition may be a new signaling in promoting ADR-induced nephropathy. And a novel natural peptide could ameliorate renal fibrosis through TGM2-PANX1-PPAR α/PANK1 pathway, which highlight the potential of it in the treatment of CKD.
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Affiliation(s)
- Shan-Shan Li
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China
| | - Qiao-Juan Liu
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China
| | - Jia-Xin Bao
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China
| | - Meng-Ting Lu
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China
| | - Bing-Quan Deng
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China
| | - Wen-Wen Li
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China
| | - Chang-Chun Cao
- Department of Nephrology, Sir Run Run hospital, Nanjing Medical University, Nanjing, China.
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Guerra-Cantera S, Frago LM, Espinoza-Chavarria Y, Collado-Pérez R, Jiménez-Hernaiz M, Torrecilla-Parra M, Barrios V, Belsham DD, Laursen LS, Oxvig C, Argente J, Chowen JA. Palmitic Acid Modulation of the Insulin-Like Growth Factor System in Hypothalamic Astrocytes and Neurons. Neuroendocrinology 2024:1-17. [PMID: 39043147 DOI: 10.1159/000540442] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/24/2023] [Accepted: 07/17/2024] [Indexed: 07/25/2024]
Abstract
INTRODUCTION Insulin-like growth factor (IGF)1 and IGF2 have neuroprotective effects, but less is known regarding how other members of the IGF system, including IGF binding proteins (IGFBPs) and the regulatory proteinase pappalysin-1 (PAPP-A) and its endogenous inhibitor stanniocalcin-2 (STC2) participate in this process. Here, we analyzed whether these members of the IGF system are modified in neurons and astrocytes in response to palmitic acid (PA), a fatty acid that induces cell stress when increased centrally. METHODS Primary hypothalamic astrocyte cultures from male and female PND2 rats and the pro-opiomelanocortin (POMC) neuronal cell line, mHypoA-POMC/GFP-2, were treated with PA, IGF1 or both. To analyze the role of STC2 in astrocytes, siRNA assays were employed. RESULTS In astrocytes of both sexes, PA rapidly increased cell stress factors followed by increased Pappa and Stc2 mRNA levels and then a decrease in Igf1, Igf2, and Igfbp2 expression and cell number. Exogenous IGF1 did not revert these effects. In mHypoA-POMC/GFP-2 neurons, PA reduced cell number and Pomc and Igf1 mRNA levels, and increased Igfbp2 and Stc2, again with no effect of exogenous IGF1. PA increased STC2 expression, but no effects of decreasing its levels by interference assays or exogenous STC2 treatment in astrocytes were found. CONCLUSIONS The response of the IGF system to PA was cell and sex specific, but no protective effects of the IGFs were found. However, the modifications in hypothalamic PAPP-A and STC2 indicate that further studies are required to determine their role in the response to fatty acids and possibly in metabolic control.
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Affiliation(s)
- Santiago Guerra-Cantera
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Department of Pediatrics, Universidad Autónoma de Madrid, Madrid, Spain
- Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain
| | - Laura M Frago
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Department of Pediatrics, Universidad Autónoma de Madrid, Madrid, Spain
- Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain
| | - Yesenia Espinoza-Chavarria
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
| | - Roberto Collado-Pérez
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Department of Pediatrics, Universidad Autónoma de Madrid, Madrid, Spain
| | - María Jiménez-Hernaiz
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain
| | - Marta Torrecilla-Parra
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
| | - Vicente Barrios
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain
| | - Denise D Belsham
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Lisbeth S Laursen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Claus Oxvig
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Jesús Argente
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Department of Pediatrics, Universidad Autónoma de Madrid, Madrid, Spain
- Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain
- IMDEA Food Institute, CEI UAM + CSIC, Madrid, Spain
| | - Julie A Chowen
- Department of Endocrinology, Hospital Infantil Universitario Niño Jesús, Instituto de Investigación La Princesa, Madrid, Spain
- Centro de Investigación Biomédica en Red de Fisiopatología de la Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain
- IMDEA Food Institute, CEI UAM + CSIC, Madrid, Spain
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3
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Conover CA, Oxvig C. The Pregnancy-Associated Plasma Protein-A (PAPP-A) Story. Endocr Rev 2023; 44:1012-1028. [PMID: 37267421 DOI: 10.1210/endrev/bnad017] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 05/01/2023] [Accepted: 05/31/2023] [Indexed: 06/04/2023]
Abstract
Pregnancy-associated plasma protein-A (PAPP-A) was first identified in the early 1970s as a placental protein of unknown function, present at high concentrations in the circulation of pregnant women. In the mid-to-late 1990s, PAPP-A was discovered to be a metzincin metalloproteinase, expressed by many nonplacental cells, that regulates local insulin-like growth factor (IGF) activity through cleavage of high-affinity IGF binding proteins (IGFBPs), in particular IGFBP-4. With PAPP-A as a cell surface-associated enzyme, the reduced affinity of the cleavage fragments results in increased IGF available to bind and activate IGF receptors in the pericellular environment. This proteolytic regulation of IGF activity is important, since the IGFs promote proliferation, differentiation, migration, and survival in various normal and cancer cells. Thus, there has been a steady growth in investigation of PAPP-A structure and function outside of pregnancy. This review provides historical perspective on the discovery of PAPP-A and its structure and cellular function, highlights key studies of the first 50 years in PAPP-A research, and introduces new findings from recent years.
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Affiliation(s)
- Cheryl A Conover
- Division of Endocrinology, Mayo Clinic, Rochester, MN 55905, USA
| | - Claus Oxvig
- Department of Molecular Biology and Genetics, Aarhus University, 8000 Aarhus, Denmark
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4
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Oxvig C, Conover CA. The Stanniocalcin-PAPP-A-IGFBP-IGF Axis. J Clin Endocrinol Metab 2023; 108:1624-1633. [PMID: 36718521 DOI: 10.1210/clinem/dgad053] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2022] [Revised: 01/20/2023] [Accepted: 01/25/2023] [Indexed: 02/01/2023]
Abstract
The pappalysin metalloproteinases, PAPP-A and PAPP-A2, have emerged as highly specific proteolytic enzymes involved in the regulation of insulin-like growth factor (IGF) signaling. The only known pappalysin substrates are a subset of the IGF binding proteins (IGFBPs), which bind IGF-I or IGF-II with high affinity to antagonize receptor binding. Thus, by cleaving IGFBPs, the pappalysins have the potential to increase IGF bioactivity and hence promote IGF signaling. This is relevant both in systemic and local IGF regulation, in normal and several pathophysiological conditions. Stanniocalcin-1 and -2 were recently found to be potent pappalysin inhibitors, thus comprising the missing components of a complete proteolytic system, the stanniocalcin-PAPP-A-IGFBP-IGF axis. Here, we provide the biological context necessary for understanding the properties of this molecular network, and we review biochemical data, animal experiments, clinical data, and genetic data supporting the physiological operation of this branch as an important part of the IGF system. However, although in vivo data clearly illustrate its power, it is a challenge to understand its subtle operation, for example, multiple equilibria and inhibitory kinetics may determine how, where, and when the IGF receptor is stimulated. In addition, literally all of the regulatory proteins have suspected or known activities that are not directly related to IGF signaling. How such activities may integrate with IGF signaling is also important to address in the future.
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Affiliation(s)
- Claus Oxvig
- Department of Molecular Biology and Genetics, Aarhus University, DK-8000 C, Aarhus, Denmark
| | - Cheryl A Conover
- Division of Endocrinology, Mayo Clinic, Rochester, MN 55905, USA
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5
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Zhong Q, Chu H, Wang G, Zhang C, Li R, Guo F, Meng X, Lei X, Zhou Y, Ren R, Tao L, Li N, Gao N, Wei Y, Qiao J, Hang J. Structural insights into the covalent regulation of PAPP-A activity by proMBP and STC2. Cell Discov 2022; 8:137. [PMID: 36550107 PMCID: PMC9780223 DOI: 10.1038/s41421-022-00502-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2022] [Accepted: 11/25/2022] [Indexed: 12/24/2022] Open
Abstract
Originally discovered in the circulation of pregnant women as a protein secreted by placental trophoblasts, the metalloprotease pregnancy-associated plasma protein A (PAPP-A) is also widely expressed by many other tissues. It cleaves insulin-like growth factor-binding proteins (IGFBPs) to increase the bioavailability of IGFs and plays essential roles in multiple growth-promoting processes. While the vast majority of the circulatory PAPP-A in pregnancy is proteolytically inactive due to covalent inhibition by proform of eosinophil major basic protein (proMBP), the activity of PAPP-A can also be covalently inhibited by another less characterized modulator, stanniocalcin-2 (STC2). However, the structural basis of PAPP-A proteolysis and the mechanistic differences between these two modulators are poorly understood. Here we present two cryo-EM structures of endogenous purified PAPP-A in complex with either proMBP or STC2. Both modulators form 2:2 heterotetramer with PAPP-A and establish extensive interactions with multiple domains of PAPP-A that are distal to the catalytic cleft. This exosite-binding property results in a steric hindrance to prevent the binding and cleavage of IGFBPs, while the IGFBP linker region-derived peptides harboring the cleavage sites are no longer sensitive to the modulator treatment. Functional investigation into proMBP-mediated PAPP-A regulation in selective intrauterine growth restriction (sIUGR) pregnancy elucidates that PAPP-A and proMBP collaboratively regulate extravillous trophoblast invasion and the consequent fetal growth. Collectively, our work reveals a novel covalent exosite-competitive inhibition mechanism of PAPP-A and its regulatory effect on placental function.
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Affiliation(s)
- Qihang Zhong
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China ,grid.419897.a0000 0004 0369 313XKey Laboratory of Assisted Reproduction, Ministry of Education, Beijing, China ,Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproduction, Beijing, China ,grid.411642.40000 0004 0605 3760National Clinical Research Center for Obstetrics and Gynecology, Beijing, China
| | - Honglei Chu
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China ,grid.419897.a0000 0004 0369 313XKey Laboratory of Assisted Reproduction, Ministry of Education, Beijing, China ,Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproduction, Beijing, China ,grid.411642.40000 0004 0605 3760National Clinical Research Center for Obstetrics and Gynecology, Beijing, China
| | - Guopeng Wang
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Cheng Zhang
- grid.412474.00000 0001 0027 0586Department of Gastrointestinal Oncology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Peking University Cancer Hospital & Institute, Beijing, China
| | - Rong Li
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China ,grid.419897.a0000 0004 0369 313XKey Laboratory of Assisted Reproduction, Ministry of Education, Beijing, China ,Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproduction, Beijing, China ,grid.411642.40000 0004 0605 3760National Clinical Research Center for Obstetrics and Gynecology, Beijing, China
| | - Fusheng Guo
- grid.11135.370000 0001 2256 9319Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Natural and Biomimetic Drugs, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Department of Chemical Biology, College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Xinlu Meng
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China
| | - Xiaoguang Lei
- grid.11135.370000 0001 2256 9319Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Natural and Biomimetic Drugs, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Department of Chemical Biology, College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China ,grid.510951.90000 0004 7775 6738Institute for Cancer Research, Shenzhen Bay Laboratory, Shenzhen, Guangdong China
| | - Youli Zhou
- grid.10784.3a0000 0004 1937 0482School of Life and Health Sciences, The Chinese University of Hong Kong, Shenzhen, Guangdong China
| | - Ruobing Ren
- grid.10784.3a0000 0004 1937 0482School of Life and Health Sciences, The Chinese University of Hong Kong, Shenzhen, Guangdong China ,grid.8547.e0000 0001 0125 2443Shanghai Key Laboratory of Metabolic Remodeling and Health, Institute of Metabolism and Integrative Biology, Fudan University, Shanghai, China
| | - Lin Tao
- grid.412636.40000 0004 1757 9485Department of Orthopedics, First Hospital of China Medical University, Shenyang, Liaoning China
| | - Ningning Li
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Ning Gao
- grid.11135.370000 0001 2256 9319State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Yuan Wei
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China ,grid.419897.a0000 0004 0369 313XKey Laboratory of Assisted Reproduction, Ministry of Education, Beijing, China ,Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproduction, Beijing, China ,grid.411642.40000 0004 0605 3760National Clinical Research Center for Obstetrics and Gynecology, Beijing, China
| | - Jie Qiao
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China ,grid.419897.a0000 0004 0369 313XKey Laboratory of Assisted Reproduction, Ministry of Education, Beijing, China ,Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproduction, Beijing, China ,grid.411642.40000 0004 0605 3760National Clinical Research Center for Obstetrics and Gynecology, Beijing, China ,grid.11135.370000 0001 2256 9319Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Jing Hang
- grid.411642.40000 0004 0605 3760Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China ,grid.419897.a0000 0004 0369 313XKey Laboratory of Assisted Reproduction, Ministry of Education, Beijing, China ,Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproduction, Beijing, China ,grid.411642.40000 0004 0605 3760National Clinical Research Center for Obstetrics and Gynecology, Beijing, China
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Xiaotangzhike Pill Attenuates the Progression of Diabetes In Vivo through the Mediation of the Akt/GSK-3 β Axis. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2022; 2022:6709506. [PMID: 36588590 PMCID: PMC9797293 DOI: 10.1155/2022/6709506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/25/2022] [Revised: 11/24/2022] [Accepted: 12/12/2022] [Indexed: 12/24/2022]
Abstract
Background Diabetes seriously threatens the health of people. Traditional Chinese medicine has been proven to inhibit the progression of diabetes. Meanwhile, the Xiaotangzhike pill (XTZK) was known to alleviate the symptom of diabetes. Thus, this research decided to investigate the mechanism underlying the impact of XTZK in diabetes remains unexplored. Methods To assess the impact of XTZK in diabetes, in vivo model of diabetes was constructed. The contents of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) in the rats were tested by the commercial kits. In addition, Masson and hematoxylin and eosin (H&E) staining were applied for assessing the histological changes and fibrosis in the rats, respectively. Furthermore, a western blot was applied to assess the protein levels. Results Streptozotocin (STZ) significantly increased the levels of area under the curve (AUC), TG, TC, LDL-C, and decreased the contents of HDL-C in rats, while these phenomena were partially reversed by XTZK. In addition, STZ notably induced inflammatory infiltration and fibrosis in the liver tissues of rats, which was greatly restored by XTZK. The levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and malondialdehyde (MDA) in the serum of rats were notably upregulated by STZ, while the effect of STZ was markedly abolished by XTZK. Meanwhile, STZ-caused the upregulation of p-Smad2 and α-SMA in rats was restored by XTZK. Furthermore, XTZK notably inhibited the progression of Qi and Yin deficiency syndrome in diabetes through the mediation of the Akt/GSK-3β axis. Conclusion The Xiaotangzhike pill attenuates the progression of diabetes through the mediation of the Akt/GSK-3β axis. Hence, our study might supply a novel insight into discovering new strategies against diabetes.
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Structure of the proteolytic enzyme PAPP-A with the endogenous inhibitor stanniocalcin-2 reveals its inhibitory mechanism. Nat Commun 2022; 13:6084. [PMID: 36257932 PMCID: PMC9579167 DOI: 10.1038/s41467-022-33698-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 09/27/2022] [Indexed: 12/24/2022] Open
Abstract
The metzincin metalloproteinase PAPP-A plays a key role in the regulation of insulin-like growth factor (IGF) signaling by specific cleavage of inhibitory IGF binding proteins (IGFBPs). Using single-particle cryo-electron microscopy (cryo-EM), we here report the structure of PAPP-A in complex with its endogenous inhibitor, stanniocalcin-2 (STC2), neither of which have been reported before. The highest resolution (3.1 Å) was obtained for the STC2 subunit and the N-terminal approximately 1000 residues of the PAPP-A subunit. The 500 kDa 2:2 PAPP-A·STC2 complex is a flexible multidomain ensemble with numerous interdomain contacts. In particular, a specific disulfide bond between the subunits of STC2 and PAPP-A prevents dissociation, and interactions between STC2 and a module located in the very C-terminal end of the PAPP-A subunit prevent binding of its main substrate, IGFBP-4. While devoid of activity towards IGFBP-4, the active site cleft of the catalytic domain is accessible in the inhibited PAPP-A·STC2 complex, as shown by its ability to hydrolyze a synthetic peptide derived from IGFBP-4. Relevant to multiple human pathologies, this unusual mechanism of proteolytic inhibition may support the development of specific pharmaceutical agents, by which IGF signaling can be indirectly modulated.
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