1
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Cao N, Wang H. Insulin augments angiotensin II-induced myocardial fibrosis via the MEK/STAT3 pathway. Heliyon 2023; 9:e22860. [PMID: 38125490 PMCID: PMC10731081 DOI: 10.1016/j.heliyon.2023.e22860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 11/20/2023] [Accepted: 11/21/2023] [Indexed: 12/23/2023] Open
Abstract
Regular insulin therapy is significantly related to worse cardiovascular outcomes in patients with type 2 diabetes and heart failure. However, the mechanisms of the causal relationship remain unclear. In this study, we observed the effect of insulin on cardiac structure and function and found that insulin dramatically augmented angiotensin II (Ang II)-induced cardiac dysfunction, as well as the proliferation and collagen production of primary cardiac fibroblasts. Total STAT3 expression, but not activation was stimulated by insulin; the effect of insulin on Ang II-induced fibrosis disappeared when STAT3 was blocked and could be entirely suppressed by the MEK inhibitor PD0325901. Our findings suggest a noninsulin-dependent glucose-lowering regimen for patients with type 2 diabetes (T2DM) and heart failure (HF).
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Affiliation(s)
- Nanyu Cao
- Department of Cardiology, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, China
| | - Heyang Wang
- Department of Cardiology, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, China
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2
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Sakr HF, Sirasanagandla SR, Das S, Bima AI, Elsamanoudy AZ. Insulin Resistance and Hypertension: Mechanisms Involved and Modifying Factors for Effective Glucose Control. Biomedicines 2023; 11:2271. [PMID: 37626767 PMCID: PMC10452601 DOI: 10.3390/biomedicines11082271] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2023] [Revised: 07/18/2023] [Accepted: 08/01/2023] [Indexed: 08/27/2023] Open
Abstract
Factors such as aging, an unhealthy lifestyle with decreased physical activity, snacking, a standard Western diet, and smoking contribute to raising blood pressure to a dangerous level, increasing the risk of coronary artery disease and heart failure. Atherosclerosis, or aging of the blood vessels, is a physiological process that has accelerated in the last decades by the overconsumption of carbohydrates as the primary sources of caloric intake, resulting in increased triglycerides and VLDL-cholesterol and insulin spikes. Classically, medications ranging from beta blockers to angiotensin II blockers and even calcium channel blockers were used alone or in combination with lifestyle modifications as management tools in modern medicine to control arterial blood pressure. However, it is not easy to control blood pressure or the associated complications. A low-carbohydrate, high-fat (LCHF) diet can reduce glucose and insulin spikes, improve insulin sensitivity, and lessen atherosclerosis risk factors. We reviewed articles describing the etiology of insulin resistance (IR) and its impact on arterial blood pressure from databases including PubMed, PubMed Central, and Google Scholar. We discuss how the LCHF diet is beneficial to maintaining arterial blood pressure at normal levels, slowing down the progression of atherosclerosis, and reducing the use of antihypertensive medications. The mechanisms involved in IR associated with hypertension are also highlighted.
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Affiliation(s)
- Hussein F. Sakr
- Department of Physiology, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat 123, Oman
| | - Srinivasa Rao Sirasanagandla
- Department of Human and Clinical Anatomy, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat 123, Oman; (S.R.S.); (S.D.)
| | - Srijit Das
- Department of Human and Clinical Anatomy, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat 123, Oman; (S.R.S.); (S.D.)
| | - Abdulhadi I. Bima
- Department of Clinical Biochemistry, Faculty of Medicine, King Abdulaziz University, Jeddah 21465, Saudi Arabia; (A.I.B.); (A.Z.E.)
| | - Ayman Z. Elsamanoudy
- Department of Clinical Biochemistry, Faculty of Medicine, King Abdulaziz University, Jeddah 21465, Saudi Arabia; (A.I.B.); (A.Z.E.)
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3
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Palmer BF, Clegg DJ. Starvation Ketosis and the Kidney. Am J Nephrol 2021; 52:467-478. [PMID: 34350876 DOI: 10.1159/000517305] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 05/14/2021] [Indexed: 02/03/2023]
Abstract
BACKGROUND The remarkable ability of the body to adapt to long-term starvation has been critical for survival of primitive man. An appreciation of these processes can provide the clinician better insight into many clinical conditions characterized by ketoacidosis. SUMMARY The body adapts to long-term fasting by conserving nitrogen, as the brain increasingly utilizes keto acids, sparing the need for glucose. This shift in fuel utilization decreases the need for mobilization of amino acids from the muscle for purposes of gluconeogenesis. Loss of urinary nitrogen is initially in the form of urea when hepatic gluconeogenesis is dominant and later as ammonia reflecting increased glutamine uptake by the kidney. The carbon skeleton of glutamine is utilized for glucose production and regeneration of consumed HCO3-. The replacement of urea with NH4+ provides the osmoles needed for urine flow and waste product excretion. Over time, the urinary loss of nitrogen is minimized as kidney uptake of filtered ketone bodies becomes more complete. Adjustments in urine Na+ serve to minimize kidney K+ wasting and, along with changes in urine pH, minimize the likelihood of uric acid precipitation. There is a sexual dimorphism in response to starvation. Key Message: Ketoacidosis is a major feature of common clinical conditions to include diabetic ketoacidosis, alcoholic ketoacidosis, salicylate intoxication, SGLT2 inhibitor therapy, and calorie sufficient but carbohydrate-restricted diets. Familiarity with the pathophysiology and metabolic consequences of ketogenesis is critical, given the potential for the clinician to encounter one of these conditions.
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Affiliation(s)
- Biff F Palmer
- Division of Nephrology, Department of Medicine, University of Texas Southwestern Medical Center, El Paso, Texas, USA
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4
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Li Y, Zhou X, Sun SX. Hydrogen, Bicarbonate, and Their Associated Exchangers in Cell Volume Regulation. Front Cell Dev Biol 2021; 9:683686. [PMID: 34249935 PMCID: PMC8264760 DOI: 10.3389/fcell.2021.683686] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2021] [Accepted: 05/31/2021] [Indexed: 11/25/2022] Open
Abstract
Cells lacking a stiff cell wall, e.g., mammalian cells, must actively regulate their volume to maintain proper cell function. On the time scale that protein production is negligible, water flow in and out of the cell determines the cell volume variation. Water flux follows hydraulic and osmotic gradients; the latter is generated by various ion channels, transporters, and pumps in the cell membrane. Compared to the widely studied roles of sodium, potassium, and chloride in cell volume regulation, the effects of proton and bicarbonate are less understood. In this work, we use mathematical models to analyze how proton and bicarbonate, combined with sodium, potassium, chloride, and buffer species, regulate cell volume upon inhibition of ion channels, transporters, and pumps. The model includes several common, widely expressed ion transporters and focuses on obtaining generic outcomes. Results show that the intracellular osmolarity remains almost constant before and after cell volume change. The steady-state cell volume does not depend on water permeability. In addition, to ensure the stability of cell volume and ion concentrations, cells need to develop redundant mechanisms to maintain homeostasis, i.e., multiple ion channels or transporters are involved in the flux of the same ion species. These results provide insights for molecular mechanisms of cell volume regulation with additional implications for water-driven cell migration.
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Affiliation(s)
- Yizeng Li
- Department of Mechanical Engineering, Kennesaw State University, Marietta, GA, United States
| | - Xiaohan Zhou
- Department of Physics, University of Toronto, Toronto, ON, Canada
| | - Sean X. Sun
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, United States
- Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, MD, United States
- Center for Cell Dynamics, Johns Hopkins School of Medicine, Baltimore, MD, United States
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5
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Pina AF, Borges DO, Meneses MJ, Branco P, Birne R, Vilasi A, Macedo MP. Insulin: Trigger and Target of Renal Functions. Front Cell Dev Biol 2020; 8:519. [PMID: 32850773 PMCID: PMC7403206 DOI: 10.3389/fcell.2020.00519] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 06/02/2020] [Indexed: 12/16/2022] Open
Abstract
Kidney function in metabolism is often underestimated. Although the word “clearance” is associated to “degradation”, at nephron level, proper balance between what is truly degraded and what is redirected to de novo utilization is crucial for the maintenance of electrolytic and acid–basic balance and energy conservation. Insulin is probably one of the best examples of how diverse and heterogeneous kidney response can be. Kidney has a primary role in the degradation of insulin released in the bloodstream, but it is also incredibly susceptible to insulin action throughout the nephron. Fluctuations in insulin levels during fast and fed state add another layer of complexity in the understanding of kidney fine-tuning. This review aims at revisiting renal insulin actions and clearance and to address the association of kidney dysmetabolism with hyperinsulinemia and insulin resistance, both highly prevalent phenomena in modern society.
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Affiliation(s)
- Ana F Pina
- Centro de Estudos de Doenças Crónicas, NOVA Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal.,ProRegeM Ph.D. Programme, NOVA Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal.,Department of Medical Sciences, University of Aveiro, Aveiro, Portugal
| | - Diego O Borges
- Centro de Estudos de Doenças Crónicas, NOVA Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal.,Molecular Biosciences Ph.D. Programme, Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Maria João Meneses
- Centro de Estudos de Doenças Crónicas, NOVA Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal.,ProRegeM Ph.D. Programme, NOVA Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal
| | - Patrícia Branco
- Department of Nephrology, Centro Hospitalar Lisboa Ocidental, Lisbon, Portugal.,Portuguese Diabetes Association - Education and Research Center (APDP-ERC), Lisbon, Portugal
| | - Rita Birne
- Department of Nephrology, Centro Hospitalar Lisboa Ocidental, Lisbon, Portugal.,Portuguese Diabetes Association - Education and Research Center (APDP-ERC), Lisbon, Portugal
| | - Antonio Vilasi
- Institute of Clinical Physiology - National Research Council, Reggio Calabria Unit1, Reggio Calabria, Italy
| | - Maria Paula Macedo
- Centro de Estudos de Doenças Crónicas, NOVA Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal.,Department of Medical Sciences, University of Aveiro, Aveiro, Portugal.,Portuguese Diabetes Association - Education and Research Center (APDP-ERC), Lisbon, Portugal
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6
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Soltani S, Kolahdouz Mohammadi R, Shab-Bidar S, Vafa M, Salehi-Abargouei A. Sodium status and the metabolic syndrome: A systematic review and meta-analysis of observational studies. Crit Rev Food Sci Nutr 2017; 59:196-206. [DOI: 10.1080/10408398.2017.1363710] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Sepideh Soltani
- Department of Nutrition, School of Public Health, Iran University of Medical Sciences, Hemaat Highway, Tehran, Iran
| | - Roya Kolahdouz Mohammadi
- Department of Nutrition, School of Public Health, Iran University of Medical Sciences, Hemaat Highway, Tehran, Iran
| | - Sakineh Shab-Bidar
- Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran
| | - Mohammadreza Vafa
- Department of Nutrition, School of Public Health, Iran University of Medical Sciences, Hemaat Highway, Tehran, Iran
| | - Amin Salehi-Abargouei
- Nutrition and Food Security Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
- Department of Nutrition, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
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7
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Horita S, Nakamura M, Suzuki M, Satoh N, Suzuki A, Homma Y, Nangaku M. The role of renal proximal tubule transport in the regulation of blood pressure. Kidney Res Clin Pract 2017; 36:12-21. [PMID: 28428931 PMCID: PMC5331971 DOI: 10.23876/j.krcp.2017.36.1.12] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 10/18/2016] [Accepted: 12/05/2016] [Indexed: 12/15/2022] Open
Abstract
The electrogenic sodium/bicarbonate cotransporter 1 (NBCe1) on the basolateral side of the renal proximal tubule plays a pivotal role in systemic acid-base homeostasis. Mutations in the gene encoding NBCe1 cause severe proximal renal tubular acidosis accompanied by other extrarenal symptoms. The proximal tubule reabsorbs most of the sodium filtered in the glomerulus, contributing to the regulation of plasma volume and blood pressure. NBCe1 and other sodium transporters in the proximal tubule are regulated by hormones, such as angiotensin II and insulin. Angiotensin II is probably the most important stimulator of sodium reabsorption. Proximal tubule AT1A receptor is crucial for the systemic pressor effect of angiotensin II. In rodents and rabbits, the effect on proximal tubule NBCe1 is biphasic; at low concentration, angiotensin II stimulates NBCe1 via PKC/cAMP/ERK, whereas at high concentration, it inhibits NBCe1 via NO/cGMP/cGKII. In contrast, in human proximal tubule, angiotensin II has a dose-dependent monophasic stimulatory effect via NO/cGMP/ERK. Insulin stimulates the proximal tubule sodium transport, which is IRS2-dependent. We found that in insulin resistance and overt diabetic nephropathy, stimulatory effect of insulin on proximal tubule transport was preserved. Our results suggest that the preserved stimulation of the proximal tubule enhances sodium reabsorption, contributing to the pathogenesis of hypertension with metabolic syndrome. We describe recent findings regarding the role of proximal tubule transport in the regulation of blood pressure, focusing on the effects of angiotensin II and insulin.
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Affiliation(s)
- Shoko Horita
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Motonobu Nakamura
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Masashi Suzuki
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Nobuhiko Satoh
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Atsushi Suzuki
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Yukio Homma
- Department of Urology, The University of Tokyo Hospital, Tokyo, Japan
| | - Masaomi Nangaku
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
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8
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Selective Insulin Resistance in the Kidney. BIOMED RESEARCH INTERNATIONAL 2016; 2016:5825170. [PMID: 27247938 PMCID: PMC4876201 DOI: 10.1155/2016/5825170] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 04/04/2016] [Accepted: 04/07/2016] [Indexed: 12/12/2022]
Abstract
Insulin resistance has been characterized as attenuation of insulin sensitivity at target organs and tissues, such as muscle and fat tissues and the liver. The insulin signaling cascade is divided into major pathways such as the PI3K/Akt pathway and the MAPK/MEK pathway. In insulin resistance, however, these pathways are not equally impaired. For example, in the liver, inhibition of gluconeogenesis by the insulin receptor substrate (IRS) 2 pathway is impaired, while lipogenesis by the IRS1 pathway is preserved, thus causing hyperglycemia and hyperlipidemia. It has been recently suggested that selective impairment of insulin signaling cascades in insulin resistance also occurs in the kidney. In the renal proximal tubule, insulin signaling via IRS1 is inhibited, while insulin signaling via IRS2 is preserved. Insulin signaling via IRS2 continues to stimulate sodium reabsorption in the proximal tubule and causes sodium retention, edema, and hypertension. IRS1 signaling deficiency in the proximal tubule may impair IRS1-mediated inhibition of gluconeogenesis, which could induce hyperglycemia by preserving glucose production. In the glomerulus, the impairment of IRS1 signaling deteriorates the structure and function of podocyte and endothelial cells, possibly causing diabetic nephropathy. This paper mainly describes selective insulin resistance in the kidney, focusing on the proximal tubule.
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9
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Abstract
Individuals with diabetes are not only at high risk of developing heart failure but are also at increased risk of dying from it. Fortunately, antiheart failure therapies such as angiotensin-converting-enzyme inhibitors, β blockers and mineralocorticoid-receptor antagonists work similarly well in individuals with diabetes as in individuals without the disease. Response to intensive glycaemic control and the various classes of antihyperglycaemic agent therapy is substantially less well understood. Insulin, for example, induces sodium retention and thiazolidinediones increase the risk of heart failure. The need for new glucose-lowering drugs to show cardiovascular safety has led to the unexpected finding of an increase in the risk of admission to hospital for heart failure in patients treated with the dipeptidylpeptidase-4 (DPP4) inhibitor, saxagliptin, compared with placebo. Here we review the relation between glycaemic control and heart failure risk, focusing on the state of knowledge for the various types of antihyperglycaemic drugs that are used at present.
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Affiliation(s)
- Richard E Gilbert
- Division of Endocrinology, St Michael's Hospital, University of Toronto, On, Canada.
| | - Henry Krum
- Centre of Cardiovascular Research and Education in Therapeutics, Monash University, Melbourne, VIC, Australia
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10
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Seki G, Nakamura M, Suzuki M, Satoh N, Horita S. Species differences in regulation of renal proximal tubule transport by certain molecules. World J Nephrol 2015; 4:307-312. [PMID: 25949945 PMCID: PMC4419141 DOI: 10.5527/wjn.v4.i2.307] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 12/24/2014] [Accepted: 01/20/2015] [Indexed: 02/06/2023] Open
Abstract
Renal proximal tubules (PTs) play important roles in the regulation of acid/base, plasma volume and blood pressure. Recent studies suggest that there are substantial species differences in the regulation of PT transport. For example, thiazolidinediones (TZDs) are widely used for the treatment of type 2 diabetes mellitus, but the use of TZDs is associated with fluid overload. In addition to the transcriptional enhancement of sodium transport in distal nephrons, TZDs rapidly stimulate PT sodium transport via a non-genomic mechanism depending on peroxisome proliferator activated receptor γ/Src/epidermal growth factor receptor (EGFR)/MEK/ERK. In mouse PTs, however, TZDs fail to stimulate PT transport probably due to constitutive activation of Src/EGFR/ERK pathway. This unique activation of Src/ERK may also affect the effect of high concentrations of insulin on mouse PT transport. On the other hand, the effect of angiotensin II (Ang II) on PT transport is known to be biphasic in rabbits, rats, and mice. However, Ang II induces a concentration-dependent, monophasic transport stimulation in human PTs. The contrasting responses to nitric oxide/guanosine 3’,5’-cyclic monophosphate pathway may largely explain these different effects of Ang II on PT transport. In this review, we focus on the recent findings on the species differences in the regulation of PT transport, which may help understand the species-specific mechanisms underlying edema formation and/or hypertension occurrence.
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11
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Schrödl-Häußel M, Theparambil SM, Deitmer JW, Roussa E. Regulation of functional expression of the electrogenic sodium bicarbonate cotransporter 1, NBCe1 (SLC4A4), in mouse astrocytes. Glia 2015; 63:1226-39. [DOI: 10.1002/glia.22814] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Revised: 02/17/2015] [Accepted: 02/18/2015] [Indexed: 12/25/2022]
Affiliation(s)
- Magdalena Schrödl-Häußel
- Department of Molecular Embryology; Institute for Anatomy and Cell Biology, University of Freiburg; Freiburg Germany
| | - Shefeeq M. Theparambil
- Department of General Zoology; FB Biology, University of Kaiserslautern; Kaiserslautern Germany
| | - Joachim W. Deitmer
- Department of General Zoology; FB Biology, University of Kaiserslautern; Kaiserslautern Germany
| | - Eleni Roussa
- Department of Molecular Embryology; Institute for Anatomy and Cell Biology, University of Freiburg; Freiburg Germany
- Department of Neuroanatomy; University of Freiburg; Freiburg Germany
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12
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Preserved Na/HCO3 cotransporter sensitivity to insulin may promote hypertension in metabolic syndrome. Kidney Int 2014; 87:535-42. [PMID: 25354240 DOI: 10.1038/ki.2014.351] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 08/29/2014] [Accepted: 09/04/2014] [Indexed: 01/01/2023]
Abstract
Hyperinsulinemia can contribute to hypertension through effects on sodium transport. To test whether the stimulatory effect of insulin on renal proximal tubule sodium transport is preserved in insulin resistance, we compared the effects of insulin on abdominal adipocytes and proximal tubules in rats and humans. Insulin markedly stimulated the sodium-bicarbonate cotransporter (NBCe1) activity in isolated proximal tubules through the phosphoinositide 3-kinase (PI3-K) pathway. Gene silencing in rats showed that while insulin receptor substrate (IRS)1 mediates the insulin effect on glucose uptake into adipocytes, IRS2 mediates the insulin effect on proximal tubule transport. The stimulatory effect of insulin on glucose uptake into adipocytes was severely reduced, but its stimulatory effect on NBCe1 activity was completely preserved in insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rats and patients with insulin resistance. Despite widespread reduction of IRS1 and IRS2 expression in insulin-sensitive tissues, IRS2 expression in the kidney cortex was exceptionally preserved in both OLETF rats and patients with insulin resistance. Unlike liver, acute insulin injection failed to change the expression levels of IRS2 and sterol regulatory element-binding protein 1 in rat kidney cortex, indicating that regulatory mechanisms of IRS2 expression are distinct in liver and kidney. Thus, preserved stimulation of proximal tubule transport through the insulin/IRS2/PI3-K pathway may play an important role in the pathogenesis of hypertension associated with metabolic syndrome.
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13
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Roles of renal proximal tubule transport in acid/base balance and blood pressure regulation. BIOMED RESEARCH INTERNATIONAL 2014; 2014:504808. [PMID: 24982885 PMCID: PMC4058521 DOI: 10.1155/2014/504808] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 05/16/2014] [Indexed: 02/06/2023]
Abstract
Sodium-coupled bicarbonate absorption from renal proximal tubules (PTs) plays a pivotal role in the maintenance of systemic acid/base balance. Indeed, mutations in the Na+-HCO3− cotransporter NBCe1, which mediates a majority of bicarbonate exit from PTs, cause severe proximal renal tubular acidosis associated with ocular and other extrarenal abnormalities. Sodium transport in PTs also plays an important role in the regulation of blood pressure. For example, PT transport stimulation by insulin may be involved in the pathogenesis of hypertension associated with insulin resistance. Type 1 angiotensin (Ang) II receptors in PT are critical for blood pressure homeostasis. Paradoxically, the effects of Ang II on PT transport are known to be biphasic. Unlike in other species, however, Ang II is recently shown to dose-dependently stimulate human PT transport via nitric oxide/cGMP/ERK pathway, which may represent a novel therapeutic target in human hypertension. In this paper, we will review the physiological and pathophysiological roles of PT transport.
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14
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Maeda S, Kuwahara-Otani S, Tanaka K, Hayakawa T, Seki M. Origin of efferent fibers of the renal plexus in the rat autonomic nervous system. J Vet Med Sci 2014; 76:763-5. [PMID: 24430660 PMCID: PMC4073349 DOI: 10.1292/jvms.13-0617] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To clarify the origin of efferent nerves containing renal plexus, the
retrograde neuronal tracing was utilized with a new exact closed injection system with
microcapsules. The microcapsule was positioned in the rat left renal plexus, and the
capsule was filled with fluoro-gold. Retrograde labeled cells were observed in the
ipsilateral sympathetic trunk, especially T12 and T13, and the ipsilateral suprarenal
ganglia (SrG). There were no labeled cells in the parasympathetic nuclei in medulla
oblongata and sacral cords. These results indicated that the origins of efferent nerves in
the rat renal plexus are almost all sympathetic ganglia, such as sympathetic trunk and
SrG, and cells in other ganglia may be secondary or accessory innervations.
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Affiliation(s)
- Seishi Maeda
- Department of Anatomy and Cell Biology, Hyogo College of Medicine, 1-1 Mukogawa, Nishinomiya, Hyogo 663-8501, Japan
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15
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Lanzafame AA, Christopoulos A, Mitchelson F. Cellular Signaling Mechanisms for Muscarinic Acetylcholine Receptors. ACTA ACUST UNITED AC 2011. [DOI: 10.3109/10606820308263] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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16
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Horita S, Seki G, Yamada H, Suzuki M, Koike K, Fujita T. Insulin resistance, obesity, hypertension, and renal sodium transport. Int J Hypertens 2011; 2011:391762. [PMID: 21629870 PMCID: PMC3095959 DOI: 10.4061/2011/391762] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 02/16/2011] [Indexed: 12/12/2022] Open
Abstract
Sodium transport through various nephron segments is quite important in regulating sodium reabsorption and blood pressure. Among several regulators of this process, insulin acts on almost all the nephron segments and is a strong enhancer of sodium reabsorption. Sodium-proton exchanger type 3 (NHE3) is a main regulator of sodium reabsorption in the luminal side of proximal tubule. In the basolateral side of the proximal tubule, sodium-bicarbonate cotransporter (NBCe1) mediates sodium and bicarbonate exit from tubular cells. In the distal nephron and the connecting tubule, epithelial sodium channel (ENaC) is of great importance to sodium reabsorption. NHE3, NBCe1, and ENaC are all regulated by insulin. Recently with-no-lysine (WNK) kinases, responsible for familial hypertension, stimulating sodium reabsorption in the distal nephron, have been found to be also regulated by insulin. We will discuss the regulation of renal sodium transport by insulin and its roles in the pathogenesis of hypertension in insulin resistance.
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Affiliation(s)
- Shoko Horita
- Department of Internal Medicine, Faculty of Medicine, The University of Tokyo 7-3-1 Hongo, Bunkyo, Tokyo 113-8655, Japan
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17
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Carew RM, Sadagurski M, Goldschmeding R, Martin F, White MF, Brazil DP. Deletion of Irs2 causes reduced kidney size in mice: role for inhibition of GSK3beta? BMC DEVELOPMENTAL BIOLOGY 2010; 10:73. [PMID: 20604929 PMCID: PMC2910663 DOI: 10.1186/1471-213x-10-73] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Accepted: 07/06/2010] [Indexed: 11/10/2022]
Abstract
BACKGROUND Male Irs2-/- mice develop fatal type 2 diabetes at 13-14 weeks. Defects in neuronal proliferation, pituitary development and photoreceptor cell survival manifest in Irs2-/- mice. We identify retarded renal growth in male and female Irs2-/- mice, independent of diabetes. RESULTS Kidney size and kidney:body weight ratio were reduced by approximately 20% in Irs2-/- mice at postnatal day 5 and was maintained in maturity. Reduced glomerular number but similar glomerular density was detected in Irs2-/- kidney compared to wild-type, suggesting intact global kidney structure. Analysis of insulin signalling revealed renal-specific upregulation of PKBbeta/Akt2, hyperphosphorylation of GSK3beta and concomitant accumulation of beta-catenin in Irs2-/- kidney. Despite this, no significant upregulation of beta-catenin targets was detected. Kidney-specific increases in Yes-associated protein (YAP), a key driver of organ size were also detected in the absence of Irs2. YAP phosphorylation on its inhibitory site Ser127 was also increased, with no change in the levels of YAP-regulated genes, suggesting that overall YAP activity was not increased in Irs2-/- kidney. CONCLUSIONS In summary, deletion of Irs2 causes reduced kidney size early in mouse development. Compensatory mechanisms such as increased beta-catenin and YAP levels failed to overcome this developmental defect. These data point to Irs2 as an important novel mediator of kidney size.
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Affiliation(s)
- Rosemarie M Carew
- UCD Diabetes Research Centre, UCD Conway Institute, School of Medicine and Medical Science, University College Dublin, Belfield Dublin 4, Ireland
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18
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Bernardo AA, Bernardo CM, Espiritu DJ, Arruda JAL. The sodium bicarbonate cotransporter: structure, function, and regulation. Semin Nephrol 2007; 26:352-60. [PMID: 17071329 DOI: 10.1016/j.semnephrol.2006.07.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The role of the Na(+)-coupled HCO(3)(-) transporter (NBC) family is indispensable in acid-base homeostasis. Almost all tissues express a member of the NBC family. NBC has been studied extensively in the kidney and plays a role in proximal tubule HCO(3)(-) reabsorption. Although the exact function of this transporter family on other tissues is not very clear, the ubiquitous expression of NBC family suggests a role in cell pH regulation. Altered NBC activity caused by mutations of the gene responsible for NBC protein expression results in pathophysiologic conditions. Mutations of NBC resulting in important clinical disorders have been reported extensively on one member of the NBC family, the kidney NBC (NBC1). These mutations have led to several structural studies to understand the mechanism of the abnormal NBC1 activity.
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Affiliation(s)
- Angelito A Bernardo
- Department of Medicine, Section of Nephrology, University of Illinois at Chicago, 820 S. Wood Street, Chicago, IL 60612, USA
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19
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Soodvilai S, Wright SH, Dantzler WH, Chatsudthipong V. Involvement of tyrosine kinase and PI3K in the regulation of OAT3-mediated estrone sulfate transport in isolated rabbit renal proximal tubules. Am J Physiol Renal Physiol 2005; 289:F1057-64. [PMID: 15956776 DOI: 10.1152/ajprenal.00185.2005] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
It was shown previously that OAT3 activity was differentially regulated by protein kinases including MAPK, PKA, and PKC. The present study investigated the short-term effect of tyrosine kinase and phosphatidylinositol 3-kinase (PI3K) on OAT3-mediated organic anion transport in S2 segments of renal proximal tubules. Genistein, a tyrosine kinase inhibitor, and wortmannin, a PI3K inhibitor, inhibited transport of estrone sulfate, a prototypic substrate for OAT3, in a dose-dependent manner. Previously, we showed that epidermal growth factor (EGF) stimulated OAT3 activity via the MAPK pathway. In the present study, we investigated whether EGF-stimulated OAT3 activity was dependent on tyrosine kinase and PI3K. We showed that EGF stimulation of OAT3 was reduced by inhibition of tyrosine kinase or PI3K, suggesting that they play a role in the stimulatory process. Inhibitory effects also indicated that tyrosine kinase and PI3K are involved in the MAPK pathway for EGF stimulation of OAT3 in intact renal proximal tubules, with PI3K acting upstream and tyrosine kinase acting downstream of mitogen-activated/extracellular signal-regulated kinase kinase activation.
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Affiliation(s)
- S Soodvilai
- Dept. of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand 10400
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20
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Zheng Y, Yamada H, Sakamoto K, Horita S, Kunimi M, Endo Y, Li Y, Tobe K, Terauchi Y, Kadowaki T, Seki G, Fujita T. Roles of insulin receptor substrates in insulin-induced stimulation of renal proximal bicarbonate absorption. J Am Soc Nephrol 2005; 16:2288-95. [PMID: 15975995 DOI: 10.1681/asn.2005020193] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Insulin resistance is frequently associated with hypertension, but the mechanism underlying this association remains speculative. Although insulin is known to modify renal tubular functions, little is known about roles of insulin receptor substrates (IRS) in the renal insulin actions. For clarifying these issues, the effects of insulin on the rate of bicarbonate absorption (JHCO3-) were compared in isolated renal proximal tubules from wild-type, IRS1-deficient (IRS1-/-), and IRS2-deficient (IRS2-/-) mice. In wild-type mice, physiologic concentrations of insulin significantly increased JHCO3-. This stimulation was completely inhibited by wortmannin and LY-294002, indicating that the phosphatidylinositol 3-kinase pathway mediates the insulin action. The stimulatory effect of insulin on JHCO3- was completely preserved in IRS1-/- mice but was significantly attenuated in IRS2-/- mice. Similarly, insulin-induced Akt phosphorylation was preserved in IRS1-/- mice but was markedly attenuated in IRS2-/- mice. Furthermore, insulin-induced tyrosine phosphorylation of IRS2 was more prominent than that of IRS1. These results indicate that IRS2 plays a major role in the stimulation of renal proximal absorption by insulin. Because defects at the level of IRS1 may underlie at least some forms of insulin resistance, sodium retention, facilitated by hyperinsulinemia through the IRS1-independent pathway, could be an important factor in pathogenesis of hypertension in insulin resistance.
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Affiliation(s)
- Yanan Zheng
- Department of Internal Medicine, Faculty of Medicine, Tokyo University, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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21
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Espiritu DJD, Yang VL, Bernardo AA, Arruda JAL. Regulation of renal Na+/HCO3- cotransporter stimulation by CO2: role of phosphorylation, exocytosis and protein synthesis. J Membr Biol 2005; 199:39-49. [PMID: 15366422 DOI: 10.1007/s00232-004-0675-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The sodium bicarbonate cotransporter (NBC1) mediates bicarbonate reabsorption in the renal proximal tubule. NBC1 activity is stimulated by 10% CO2, however, the mechanism is poorly understood. Here, we examined the mechanism of NBC1 regulation by 10% CO2 using an immortalized human proximal tubule cell line (HK2). In cells exposed to 10% CO2, the cotransporter activity (measured as deltapH/min) increased within minutes and this increase was maintained for 6 to 24 h. Early NBC1 stimulation was accompanied by increased NBC1 phosphorylation. Basolateral membrane NBC1 protein increased by 30 min and reached a maximum at 6 h. Increased NBC activity at 6 h was accounted for by increased NBC exocytosis to the basolateral membrane and not by decreased endocytosis. Latruncullin B (an actin cytoskeleton inhibitor) did not prevent CO2-induced stimulation, while nocodazole (a microtubule-disrupting agent) abrogated the stimulatory effect of 10% CO2. A significant increase in NBC1 mRNA expression level was observed at 6 h and maintained for 24 h. Total NBC1 protein increased at 12 to 24 h with 10% CO2 incubation and this effect was blocked by cycloheximide. In summary, the present study demonstrates that early activation of NBC1 activity by 10% CO2 was mediated by NBC1 phosphorylation. The stimulation of cotransporter activity observed at 6 h was due to exocytosis, while the late effect starting from 12 h was accounted for by increased protein synthesis.
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Affiliation(s)
- D J D Espiritu
- Section of Nephrology, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612-7315, USA
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22
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Boehmer C, Embark HM, Bauer A, Palmada M, Yun CH, Weinman EJ, Endou H, Cohen P, Lahme S, Bichler KH, Lang F. Stimulation of renal Na+ dicarboxylate cotransporter 1 by Na+/H+ exchanger regulating factor 2, serum and glucocorticoid inducible kinase isoforms, and protein kinase B. Biochem Biophys Res Commun 2004; 313:998-1003. [PMID: 14706641 DOI: 10.1016/j.bbrc.2003.12.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Renal tubular citrate transport is accomplished by electrogenic Na(+) coupled dicarboxylate transporter NaDC-1, a carrier subjected to regulation by acidosis. Trafficking of the Na(+)/H(+) exchanger NHE3 is controlled by NHE regulating factors NHERF-1 and NHERF-2 and the serum and glucocorticoid inducible kinase SGK1. To test for a possible involvement in NaDC-1 regulation, mRNA encoding NaDC-1 was injected into Xenopus oocytes with or without cRNA encoding NHERF-1, NHERF-2, SGK1, SGK2, SGK3, and/or the constitutively active form of the related protein kinase B ((T308,S473D)PKB). Succinate induced inward currents (I(succ)) were taken as a measure of transport rate. Coexpression of neither NHERF-1 nor NHERF-2 in NaDC-1 expressing oocytes significantly altered I(succ). On the other hand, coexpression of SGK1, SGK3, and (T308,S473D)PKB stimulated I(succ), an effect further stimulated by additional coexpression of NHERF-2 but not of NHERF-1. The action of the kinases and NHERF-2 may link urinary citrate excretion to proximal tubular H(+) secretion.
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Affiliation(s)
- Christoph Boehmer
- Department of Physiology I, University of Tübingen, Tübingen D-72076, Germany
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23
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Jae Han H, Yeong Park J, Jung Lee Y, Taub M. Epidermal growth factor inhibits14C-?-methyl-d-glucopyranoside uptake in renal proximal tubule cells: Involvement of PLC/PKC, p44/42 MAPK, and cPLA2. J Cell Physiol 2004; 199:206-16. [PMID: 15040003 DOI: 10.1002/jcp.10438] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The effect of EGF on (14)C-alpha-methyl-D-glucopyranoside (alpha-MG) uptake and its related signaling pathways were examined in primary cultured rabbit renal proximal tubule cells (PTCs). Epidermal growth factor (EGF) (50 ng/ml) was found to inhibit alpha-MG uptake, a distinctive proximal tubule marker. The EGF effect was blocked by AG1478 (an EGF receptor antagonist) or genistein and herbimycin (tyrosine kinase inhibitors), respectively. In addition, the EGF-induced inhibition of alpha-MG uptake was blocked by neomycin and U73122 (phospholipase C inhibitors) as well as staurosporine, H-7, and bisindolylmaleimide I (protein kinase C inhibitors). EGF was also observed to increase inositol phosphate formation. Furthermore, both the EGF-induced inhibition of alpha-MG uptake and increase of arachidonic acid (AA) release were blocked by AACOCF(3) (a cytosolic phospholipase A(2) inhibitor), indomethacin (a cyclooxygenase inhibitor), and econazole (a cytochrome P-450 epoxygenase inhibitor). We examined the involvement of mitogen-activated protein kinases (MAPKs) in mediating the effect of EGF on alpha-MG uptake. Indeed, EGF increased phosphorylation of p44/p42 MAPK and the EGF-induced inhibition of alpha-MG uptake as well as the stimulatory effect of EGF on AA release was blocked by PD 98059 (a p44/42 MAPK inhibitor), suggesting a causal relationship. However, inhibitors of PKC also prevented the EGF-induced increase of AA release. In conclusion, EGF partially inhibited alpha-MG uptake via PLC/PKC, p44/42 MAPK, and PLA(2) signaling pathways.
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Affiliation(s)
- Ho Jae Han
- Department of Veterinary Physiology, College of Veterinary Medicine, Hormone Research Center, Chonnam National University, Gwangju, Korea.
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24
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Espiritu DJD, Bernardo AA, Robey RB, Arruda JAL. A central role for Pyk2-Src interaction in coupling diverse stimuli to increased epithelial NBC activity. Am J Physiol Renal Physiol 2002; 283:F663-70. [PMID: 12217857 DOI: 10.1152/ajprenal.00338.2001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Regulation of renal Na-HCO cotransporter (NBC1) activity by cholinergic agonists, ANG II, and acute acidosis (CO(2)) requires both Src family kinase (SFK) and classic MAPK pathway activation. The nonreceptor tyrosine kinase proline-rich tyrosine kinase 2 (Pyk2) couples discrete G protein-coupled receptor and growth factor receptor signaling to SFK activation. We examined the role of Pyk2-SFK interaction in coupling these stimuli to increased NBC1 activity in opossum kidney cells. Carbachol increased tyrosine autophosphorylation of endogenous Pyk2 and ectopically expressed wild-type Pyk2 and were abrogated by kinase-dead mutant (Pyk2-KD) overexpression. Pyk2 phosphorylation was calcium/calmodulin dependent, and Pyk2 associated with Src by means of SH2 domain interaction. Pyk2 phosphorylation and Pyk2-Src interaction by carbachol were mimicked by both ANG II and CO(2). To correlate Pyk2 autophosphorylation and Pyk2-Src interaction with NBC activity, cotransporter activity was measured in untransfected cells and in cells overexpressing Pyk2-KD in the presence or absence of carbachol, ANG II, or CO(2). In Pyk2-KD-overexpressing cells, the effect of carbachol, ANG II, and CO(2) was abolished. We conclude that Pyk2 plays a central role in coupling carbachol, ANG II, and CO(2) to increased NBC activity. This coupling is mediated by Pyk2 autophosphorylation and Pyk2-Src interaction.
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Affiliation(s)
- Doris Joy D Espiritu
- Section of Nephrology, Department of Medicine, University of Illinois at Chicago, 60612, USA
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25
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Robey RB, Ruiz OS, Baniqued J, Mahmud D, Espiritu DJ, Bernardo AA, Arruda JA. SFKs, Ras, and the classic MAPK pathway couple muscarinic receptor activation to increased Na-HCO(3) cotransport activity in renal epithelial cells. Am J Physiol Renal Physiol 2001; 280:F844-50. [PMID: 11292627 DOI: 10.1152/ajprenal.2001.280.5.f844] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cholinergic agents are known to affect the epithelial transport of H2O and electrolytes in the kidney. In proximal tubule cells, cholinergic agonists increase basolateral Na-HCO(3) cotransport activity via M(1) muscarinic receptor activation. The signaling intermediates that couple these G protein-coupled receptors to cotransporter activation, however, are not well defined. We therefore sought to identify distal effectors of muscarinic receptor activation that contribute to increased NBC activity in cultured proximal tubule cells. As demonstrated previously for acute CO2-regulated cotransport activity, we found that inhibitors of Src family kinases (SFKs) or the classic mitogen-activated protein kinase (MAPK) pathway prevented the stimulation of NBC activity by carbachol. The ability of carbachol to activate Src, as well as the proximal (Raf) and distal [extracellular signal-regulated kinases 1 and 2 (ERK1/2)] elements of the classic MAPK module, was compatible with these findings. Cholinergic stimulation of ERK1/2 activity was also completely prevented by overexpression of a dominant negative mutant of Ras (N17-Ras). Taken together, these findings suggest a requirement for the sequential activation of SFKs, Ras, and the classic MAPK pathway [Raf-->MAPK/ERK kinase (MEK)-->ERK]. These findings provide important insights into the molecular mechanisms underlying cholinergic regulation of NBC activity in renal epithelial cells. They also suggest a specific mechanism whereby cholinergic stimulation of the kidney can contribute to pH homeostasis.
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Affiliation(s)
- R B Robey
- Section of Nephrology, Department of Medicine, University of Illinois at Chicago College of Medicine, Chicago, IL 60612, USA
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26
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Ruiz OS, Robey RB, Qiu YY, Wang LJ, Li CJ, Ma J, Arruda JA. Regulation of the renal Na-HCO(3) cotransporter. XI. Signal transduction underlying CO(2) stimulation. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:F580-6. [PMID: 10516283 DOI: 10.1152/ajprenal.1999.277.4.f580] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have previously shown that CO(2) stimulation of the renal Na-HCO(3) cotransporter (NBC) activity is abrogated by general inhibitors of protein tyrosine kinases. The more selective inhibitor herbimycin also blocked this effect at concentrations known to preferentially inhibit Src family kinases (SFKs). We therefore examined a role for SFKs in CO(2)-stimulated NBC activity. To this end, we engineered OK cells to express the COOH-terminal Src kinase (Csk), a negative regulator of SFKs. CO(2) stimulated NBC activity normally in beta-galactosidase-expressing and untransfected control cells. In contrast, Csk-expressing cells had normal baseline NBC activity that was not stimulated by CO(2). CO(2) stimulation increased both total SFK activity and specific tyrosine phosphorylation of Src. The specific MEK1/2 inhibitor PD-98059 completely inhibited the CO(2) stimulation of NBC activity as well as the accompanying phosphorylation and activation of ERK1/2. Our data suggest the involvement of both SFKs, probably Src, and the "classic" MAPK pathway in mediating CO(2)-stimulated NBC activity in renal epithelial cells.
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Affiliation(s)
- O S Ruiz
- University of Illinois at Chicago, West Side Division, Chicago, Illinois 60612-7315, USA.
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