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Lionaki S, Liapis G, Boletis JN. Pathogenesis and Management of Acute Kidney Injury in Patients with Nephrotic Syndrome Due to Primary Glomerulopathies. ACTA ACUST UNITED AC 2019; 55:medicina55070365. [PMID: 31336742 PMCID: PMC6681356 DOI: 10.3390/medicina55070365] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2019] [Revised: 07/03/2019] [Accepted: 07/08/2019] [Indexed: 01/10/2023]
Abstract
Acute kidney injury in the context of nephrotic syndrome is a serious and alarming clinical problem. Largely, acute kidney injury is a relatively frequent complication among patients with comorbidities while it has been independently associated with an increased risk of adverse outcomes, including death and chronic kidney disease. Nephrotic syndrome, without hematuria or with minimal hematuria, includes a list of certain glomerulopathies; minimal change disease, focal segmental glomerulosclerosis and membranous nephropathy. In the light of primary nephrotic syndrome, pathophysiology of acute kidney injury is differentiated by the nature of the primary disease and the severity of the nephrotic state. This review aims to explore the clinical circumstances and pathogenetic mechanisms of acute kidney injury in patients with nephrotic syndrome due to primary glomerulopathies, focusing on newer perceptions regarding the pathogenesis and management of this complicated condition, for the prompt recognition and timely initiation of appropriate treatment in order to restore renal function to its baseline level. Prompt recognition of the precise cause of acute kidney injury is crucial for renal recovery. Clinical characteristics, laboratory and serological findings along with histopathological findings, if required, will reveal the implicated pathway leading to individualized approach and management.
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Affiliation(s)
- Sophia Lionaki
- Nephrology Department & Transplantation Unit, Laiko Hospital, Faculty of Medicine, National & Kapodistrian University of Athens, 11527 Athens, Greece.
| | - George Liapis
- Department of Pathology, Laiko Hospital, Faculty of Medicine, National & Kapodistrian University of Athens, 11527 Athens, Greece
| | - John N Boletis
- Nephrology Department & Transplantation Unit, Laiko Hospital, Faculty of Medicine, National & Kapodistrian University of Athens, 11527 Athens, Greece
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2
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Gupta S, Pepper RJ, Ashman N, Walsh SB. Nephrotic Syndrome: Oedema Formation and Its Treatment With Diuretics. Front Physiol 2019; 9:1868. [PMID: 30697163 PMCID: PMC6341062 DOI: 10.3389/fphys.2018.01868] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 12/11/2018] [Indexed: 01/01/2023] Open
Abstract
Oedema is a defining element of the nephrotic syndrome. Its' management varies considerably between clinicians, with no national or international clinical guidelines, and hence variable outcomes. Oedema may have serious sequelae such as immobility, skin breakdown and local or systemic infection. Treatment of nephrotic oedema is often of limited efficacy, with frequent side-effects and interactions with other pharmacotherapy. Here, we describe the current paradigms of oedema in nephrosis, including insights into emerging mechanisms such as the role of the abnormal activation of the epithelial sodium channel in the collecting duct. We then discuss the physiological basis for traditional and novel therapies for the treatment of nephrotic oedema. Despite being the cardinal symptom of nephrosis, few clinical studies guide clinicians to the rational use of therapy. This is reflected in the scarcity of publications in this field; it is time to undertake new clinical trials to direct clinical practice.
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Affiliation(s)
- Sanjana Gupta
- UCL Centre for Nephrology, University College London, London, United Kingdom.,Renal Unit, The Royal London Hospital, Bart's Health NHS Trust, London, United Kingdom
| | - Ruth J Pepper
- UCL Centre for Nephrology, University College London, London, United Kingdom
| | - Neil Ashman
- Renal Unit, The Royal London Hospital, Bart's Health NHS Trust, London, United Kingdom
| | - Stephen B Walsh
- UCL Centre for Nephrology, University College London, London, United Kingdom
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3
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Hu MC, Bobulescu IA, Quiñones H, Gisler SM, Moe OW. Dopamine reduces cell surface Na +/H + exchanger-3 protein by decreasing NHE3 exocytosis and cell membrane recycling. Am J Physiol Renal Physiol 2017; 313:F1018-F1025. [PMID: 28768665 DOI: 10.1152/ajprenal.00251.2017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 07/14/2017] [Accepted: 07/24/2017] [Indexed: 01/06/2023] Open
Abstract
The intrarenal autocrine-paracrine dopamine (DA) system mediates a significant fraction of the natriuresis in response to a salt load. DA inhibits a number of Na+ transporters to effect sodium excretion, including the proximal tubule Na+/H+ exchanger-3 (NHE3). DA represent a single hormone that regulates NHE3 at multiple levels, including translation, degradation, endocytosis, and protein phosphorylation. Because cell surface NHE3 protein is determined by the balance between exocytotic insertion and endocytotic retrieval, we examined whether DA acutely affects the rate of NHE3 exocytosis in a cell culture model. DA inhibited NHE3 exocytosis at a dose-dependent manner with a half maximal around 10-6 M. The DA effect on NHE3 exocytosis was blocked by inhibition of protein kinase A and by brefeldin A, which inhibits endoplasmic reticulum-to-Golgi transport. NHE3 directly interacts with the ε-subunit of coatomer protein based on yeast-two-hybrid and coimmunoprecipitation. Because NHE3 has been shown to be recycled back to the cell membrane after endocytosis, we measured NHE3 recycling using a biochemical reinsertion assay and showed that reinsertion of NHE3 back to the membrane is also inhibited by DA. In conclusion, among the many mechanisms by which DA reduces apical membrane NHE3 and induces proximal tubule natriuresis, one additional mechanism is inhibition of exocytotic insertion and reinsertion of NHE3 in the apical cell surface.
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Affiliation(s)
- Ming Chang Hu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; .,Charles and Jane Pak Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - I Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Charles and Jane Pak Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Henry Quiñones
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Serge M Gisler
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Orson W Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas; and.,Charles and Jane Pak Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
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4
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Abstract
Edema is a common complication of numerous renal disease. In the recent past several aspects of the pathophysiology of this condition have been elucidated. We herein present a case of nephrotic syndrome in a 30 year-old men. The discussion revolves around the following key questions on fluid accumulation in renal disease: 1. What is edema? What diseases can cause edema? 2. What are the mechanisms of edema in nephrotic syndrome? 2a. The “underfill” theory 2b. The “overfill” theory 2c. Tubulointerstitial inflammation 2d. Vascular permeability 3. What are the mechanisms of edema in nephritic syndrome? 4. How can the volume status be assessed in patients with nephrotic syndrome? 5. What are therapeutic strategies for edema management? 6. What are the factors affecting response to diuretics? 7. How can we overcome the diuretics resistance? 7a. Effective doses of loop diuretics 7b. Combined diuretic therapy 7c. Intravenous administration of diuretics 7d. Albumin infusions 7e. Alternative methods of edema management 8. Conclusion.
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5
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Jia Z, Zhuang Y, Hu C, Zhang X, Ding G, Zhang Y, Rohatgi R, Hua H, Huang S, He JCJ, Zhang A. Albuminuria enhances NHE3 and NCC via stimulation of mitochondrial oxidative stress/angiotensin II axis. Oncotarget 2016; 7:47134-47144. [PMID: 27323402 PMCID: PMC5216930 DOI: 10.18632/oncotarget.9972] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Accepted: 05/20/2016] [Indexed: 12/31/2022] Open
Abstract
Imbalance of salt and water is a frequent and challenging complication of kidney disease, whose pathogenic mechanisms remain elusive. Employing an albumin overload mouse model, we discovered that albuminuria enhanced the expression of NHE3 and NCC but not other transporters in murine kidney in line with the stimulation of angiotensinogen (AGT)/angiotensin converting enzyme (ACE)/angiotensin (Ang) II cascade. In primary cultures of renal tubular cells, albumin directly stimulated AGT/ACE/Ang II and upregulated NHE3 and NCC expression. Blocking Ang II production with an ACE inhibitor normalized the upregulation of NHE3 and NCC in cells. Interestingly, albumin overload significantly reduced mitochondrial superoxide dismutase (SOD2), and administration of a SOD2 mimic (MnTBAP) normalized the expression of NHE3, NCC, and the components of AGT/ACE pathway affected by albuminuria, indicating a key role of mitochondria-derived oxidative stress in modulating renin-angiotensin system (RAS) and renal sodium transporters. In addition, the functional data showing the reduced urinary excretion of Na and Cl and enhanced response to specific NCC inhibitor further supported the regulatory results of sodium transporters following albumin overload. More importantly, the upregulation of NHE3 and NCC and activation of ACE/Ang II signaling pathway were also observed in albuminuric patient kidneys, suggesting that our animal model accurately replicates the human condition. Taken together, these novel findings demonstrated that albuminuria is of importance in resetting renal salt handling via mitochondrial oxidative stress-initiated stimulation of ACE/Ang II cascade. This may also offer novel, effective therapeutic targets for dealing with salt and water imbalance in proteinuric renal diseases.
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Affiliation(s)
- Zhanjun Jia
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - Yibo Zhuang
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - Caiyu Hu
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - Xintong Zhang
- The First Clinical Medical College of Nanjing Medical University, Nanjing, China
| | - Guixia Ding
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - Yue Zhang
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - Rajeev Rohatgi
- Department of Medicine, Mount Sinai School of Medicine, New York, New York, USA
| | - Hu Hua
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - Songming Huang
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
| | - John Ci-jiang He
- Division of Nephrology, Department of Medicine, Mount Sinai School of Medicine, New York, New York, USA
| | - Aihua Zhang
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Jiangsu Key Laboratory of Pediatrics, Nanjing Medical University, Nanjing, China
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Golden MH. Nutritional and other types of oedema, albumin, complex carbohydrates and the interstitium - a response to Malcolm Coulthard's hypothesis: Oedema in kwashiorkor is caused by hypo-albuminaemia. Paediatr Int Child Health 2015; 35:90-109. [PMID: 25844980 DOI: 10.1179/2046905515y.0000000010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The various types of oedema in man are considered in relation to Starling's hypothesis of fluid movement from capillaries, with the main emphasis on nutritional oedema and the nephrotic syndrome in children. It is concluded that each condition has sufficient anomalous findings to render Starling's hypothesis untenable. The finding that the endothelial glycocalyx is key to control of fluid movement from and into the capillaries calls for complete revision of our understanding of oedema formation. The factors so far known to affect the function of the glycocalyx are reviewed. As these depend upon sulphated proteoglycans and other glycosaminoglycans, the argument is advanced that the same abnormalities will extend to the interstitial space and that kwashiorkor is fundamentally related to a defect in sulphur metabolism which can explain all the clinical features of the condition, including the formation of oedema.
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Key Words
- Albumin,
- Aldosterone,
- Angiotensin,
- Beriberi,
- Edema,
- Epidemic dropsy,
- Famine oedema,
- Glycocalyx,
- Glycosaminoglycans,
- Heart failure,
- Hunger oedema,
- Kwashiorkor,
- Malnutrition,
- Nephrotic syndrome,
- Oedema,
- Potassium deficiency,
- Pre-eclampsia,
- Protein-energy malnutrition,
- Proteoglycans,
- Renin,
- Salt,
- Severe acute malnutrition
- Vitamin E deficiency,
- War oedema,
- Water,
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7
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Ellis D. Pathophysiology, Evaluation, and Management of Edema in Childhood Nephrotic Syndrome. Front Pediatr 2015; 3:111. [PMID: 26793696 PMCID: PMC4707228 DOI: 10.3389/fped.2015.00111] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 12/07/2015] [Indexed: 01/22/2023] Open
Abstract
Generalized edema is a major presenting clinical feature of children with nephrotic syndrome (NS) exemplified by such primary conditions as minimal change disease (MCD). In these children with classical NS and marked proteinuria and hypoalbuminemia, the ensuing tendency to hypovolemia triggers compensatory physiological mechanisms, which enhance renal sodium (Na(+)) and water retention; this is known as the "underfill hypothesis." Edema can also occur in secondary forms of NS and several other glomerulonephritides, in which the degree of proteinuria and hypoalbuminemia, are variable. In contrast to MCD, in these latter conditions, the predominant mechanism of edema formation is "primary" or "pathophysiological," Na(+) and water retention; this is known as the "overfill hypothesis." A major clinical challenge in children with these disorders is to distinguish the predominant mechanism of edema formation, identify other potential contributing factors, and prevent the deleterious effects of diuretic regimens in those with unsuspected reduced effective circulatory volume (i.e., underfill). This article reviews the Starling forces that become altered in NS so as to tip the balance of fluid movement in favor of edema formation. An understanding of these pathomechanisms then serves to formulate a more rational approach to prevention, evaluation, and management of such edema.
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Affiliation(s)
- Demetrius Ellis
- Division of Pediatric Nephrology, Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine , Pittsburgh, PA , USA
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8
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Hu MC, Di Sole F, Zhang J, McLeroy P, Moe OW. Chronic regulation of the renal Na(+)/H(+) exchanger NHE3 by dopamine: translational and posttranslational mechanisms. Am J Physiol Renal Physiol 2013; 304:F1169-80. [PMID: 23427139 DOI: 10.1152/ajprenal.00630.2012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The intrarenal autocrine/paracrine dopamine (DA) system contributes to natriuresis in response to both acute and chronic Na(+) loads. While the acute DA effect is well described, how DA induces natriuresis chronically is not known. We used an animal and a cell culture model to study the chronic effect of DA on a principal renal Na(+) transporter, Na(+)/H(+) exchanger-3 (NHE3). Intraperitoneal injection of Gludopa in rats for 2 days elevated DA excretion and decreased total renal cortical and apical brush-border NHE3 antigen. Chronic treatment of an opossum renal proximal cell line with DA decreased NHE3 activity, cell surface and total cellular NHE3 antigen, but not NHE3 transcript. The decrease in NHE3 antigen was dose and time dependent with maximal inhibition at 16-24 h and half maximal effect at 3 × 10(-7) M. This is in contradistinction to the acute effect of DA on NHE3 (half maximal at 2 × 10(-6) M), which was not associated with changes in total cellular NHE3 protein. The DA-induced decrease in total NHE3 protein was associated with decrease in NHE3 translation and mediated by cis-sequences in the NHE3 5'-untranslated region. DA also decreased cell surface and total cellular NHE3 protein half-life. The DA-induced decrease in total cellular NHE3 was partially blocked by proteasome inhibition but not by lysosome inhibition, and DA increased ubiquitylation of total and surface NHE3. In summary, chronic DA inhibits NHE3 with mechanisms distinct from its acute action and involves decreased NHE3 translation and increased NHE3 degradation, which are novel mechanisms for NHE3 regulation.
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Affiliation(s)
- Ming Chang Hu
- Dept. of Internal Medicine, Univ. of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8885, USA
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9
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Girardi ACC, Di Sole F. Deciphering the mechanisms of the Na+/H+ exchanger-3 regulation in organ dysfunction. Am J Physiol Cell Physiol 2012; 302:C1569-87. [DOI: 10.1152/ajpcell.00017.2012] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The Na+/H+ exchanger-3 (NHE3) belongs to the mammalian NHE protein family and catalyzes the electro-neutral exchange of extracellular sodium for intracellular proton across cellular membranes. Its transport function is of essential importance for the maintenance of the body's salt and water homeostasis as well as acid-base balance. Indeed, NHE3 activity is finely regulated by a variety of stimuli, both acutely and chronically, and its transport function is fundamental for a multiplicity of severe and world-wide infection-pathological conditions. This review aims to provide a concise overview of NHE3 physiology and discusses the role of NHE3 in clinical conditions of prominent importance, specifically in hypertension, diabetic nephropathy, heart failure, acute kidney injury, and diarrhea. Study of NHE3 function in models of these diseases has contributed to the deciphering of mechanisms that control the delicate ion balance disrupted in these disorders. The majority of the findings indicate that NHE3 transport function is activated before the onset of hypertension and inhibited thereafter; NHE3 transport function is also upregulated in diabetic nephropathy and heart failure, while it is reported to be downregulated in acute kidney injury and in diarrhea. The molecular mechanisms activated during these pathological conditions to regulate NHE3 transport function are examined with the aim of linking NHE3 dysfunction to the analyzed clinical disorders.
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Affiliation(s)
| | - Francesca Di Sole
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; and
- Center of Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
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10
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Yan Y, Haller S, Shapiro A, Malhotra N, Tian J, Xie Z, Malhotra D, Shapiro JI, Liu J. Ouabain-stimulated trafficking regulation of the Na/K-ATPase and NHE3 in renal proximal tubule cells. Mol Cell Biochem 2012; 367:175-83. [PMID: 22618525 DOI: 10.1007/s11010-012-1331-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Accepted: 05/03/2012] [Indexed: 01/11/2023]
Abstract
We have demonstrated that ouabain regulates protein trafficking of the Na/K-ATPase α1 subunit and NHE3 (Na/H exchanger, isoform 3) via ouabain-activated Na/K-ATPase signaling in porcine LLC-PK1 cells. To investigate whether this mechanism is species-specific, ouabain-induced regulation of the α1 subunit and NHE3 as well as transcellular (22)Na(+) transport were compared in three renal proximal tubular cell lines (human HK-2, porcine LLC-PK1, and AAC-19 originated from LLC-PK1 in which the pig α1 was replaced by ouabain-resistant rat α1). Ouabain-induced inhibition of transcellular (22)Na(+) transport is due to an ouabain-induced redistribution of the α1 subunit and NHE3. In LLC-PK1 cells, ouabain also inhibited the endocytic recycling of internalized NHE3, but has no significant effect on recycling of endocytosed α1 subunit. These data indicated that the ouabain-induced redistribution of the α1 subunit and NHE3 is not a species-specific phenomenon, and ouabain-activated Na/K-ATPase signaling influences NHE3 regulation.
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Affiliation(s)
- Yanling Yan
- Department of Medicine, University of Toledo College of Medicine, Toledo, OH 43614-2598, USA
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11
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Affiliation(s)
- M Sahay
- Department of Nephrology, Osmania General Hospital, Osmania Medical College, Hyderabad, Andhra Pradesh, India
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12
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Pao AC, Bhargava A, Di Sole F, Quigley R, Shao X, Wang J, Thomas S, Zhang J, Shi M, Funder JW, Moe OW, Pearce D. Expression and role of serum and glucocorticoid-regulated kinase 2 in the regulation of Na+/H+ exchanger 3 in the mammalian kidney. Am J Physiol Renal Physiol 2010; 299:F1496-506. [PMID: 20926631 PMCID: PMC3006302 DOI: 10.1152/ajprenal.00075.2010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Accepted: 09/14/2010] [Indexed: 01/30/2023] Open
Abstract
Serum and glucocorticoid-regulated kinase 2 (sgk2) is 80% identical to the kinase domain of sgk1, an important mediator of mineralocorticoid-regulated sodium (Na(+)) transport in the distal nephron of the kidney. The expression pattern and role in renal function of sgk2 are virtually uncharacterized. In situ hybridization and immunohistochemistry of rodent kidney coupled with real-time RT-PCR of microdissected rat kidney tubules showed robust sgk2 expression in the proximal straight tubule and thick ascending limb of the loop of Henle. Sgk2 expression was minimal in distal tubule cells with aquaporin-2 immunostaining but significant in proximal tubule cells with Na(+)/H(+) exchanger 3 (NHE3) immunostaining. To ascertain whether mineralocorticoids regulate expression of sgk2 in a manner similar to sgk1, we examined sgk2 mRNA expression in the kidneys of adrenalectomized rats treated with physiological doses of aldosterone together with the glucocorticoid receptor antagonist RU486. Northern blot analysis and in situ hybridization showed that, unlike sgk1, sgk2 expression in the kidney was not altered by aldosterone treatment. Based on the observation that sgk2 is expressed in proximal tubule cells that also express NHE3, we asked whether sgk2 regulates NHE3 activity. We heterologously expressed sgk2 in opossum kidney (OKP) cells and measured Na(+)/H(+) exchange activity by Na(+)-dependent cell pH recovery. Constitutively active sgk2, but not sgk1, stimulated Na(+)/H(+) exchange activity by >30%. Moreover, the sgk2-mediated increase in Na(+)/H(+) exchange activity correlated with an increase in cell surface expression of NHE3. Together, these results suggest that the pattern of expression, regulation, and role of sgk2 within the mammalian kidney are distinct from sgk1 and that sgk2 may play a previously unrecognized role in the control of transtubular Na(+) transport through NHE3 in the proximal tubule.
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Affiliation(s)
- Alan C Pao
- Div. of Nephrology, Dept. of Medicine, Stanford Univ., 780 Welch Rd., Suite 106, Palo Alto, CA 94304, USA.
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13
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Pierre SV, Belliard A, Sottejeau Y. Modulation of Na(+)-K(+)-ATPase cell surface abundance through structural determinants on the α1-subunit. Am J Physiol Cell Physiol 2010; 300:C42-8. [PMID: 21048163 DOI: 10.1152/ajpcell.00386.2010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Through their ion-pumping and non-ion-pumping functions, Na(+)-K(+)-ATPase protein complexes at the plasma membrane are critical to intracellular homeostasis and to the physiological and pharmacological actions of cardiotonic steroids. Alteration of the abundance of Na(+)-K(+)-ATPase units at the cell surface is one of the mechanisms for Na(+)-K(+)-ATPase regulation in health and diseases that has been closely examined over the past few decades. We here summarize these findings, with emphasis on studies that explicitly tested the involvement of defined regions or residues on the Na(+)-K(+)-ATPase α1 polypeptide. We also report new findings on the effect of manipulating Na(+)-K(+)-ATPase membrane abundance by targeting one of these defined regions: a dileucine motif of the form [D/E]XXXL[L/I]. In this study, opossum kidney cells stably expressing rat α1 Na(+)-K(+)-ATPase or a mutant where the motif was disrupted (α1-L499V) were exposed to 30 min of substrate/coverslip-induced-ischemia followed by reperfusion (I-R). Biotinylation studies suggested that I-R itself acted as an inducer of Na(+)-K(+)-ATPase internalization and that surface expression of the mutant was higher than the native Na(+)-K(+)-ATPase before and after ischemia. Annexin V/propidium iodide staining and lactate dehydrogenase release suggested that I-R injury was reduced in α1-L499V-expressing cells compared with α1-expressing cells. Hence, modulation of Na(+)-K(+)-ATPase cell surface abundance through structural determinants on the α-subunit is an important mechanism of regulation of cellular Na(+)-K(+)-ATPase in various physiological and pathophysiological conditions, with a significant impact on cell survival in face of an ischemic stress.
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Affiliation(s)
- Sandrine V Pierre
- Department of Physiology and Pharmacology, University of Toledo College of Medicine, Ohio 43614-2598, USA.
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14
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Sottejeau Y, Belliard A, Duran MJ, Pressley TA, Pierre SV. Critical role of the isoform-specific region in alpha1-Na,K-ATPase trafficking and protein Kinase C-dependent regulation. Biochemistry 2010; 49:3602-10. [PMID: 20302352 DOI: 10.1021/bi9021999] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The isoform-specific region (ISR) is a region of structural heterogeneity among the four isoforms of the catalytic alpha-subunit of the Na,K-ATPase and an important structural determinant for isoform-specific functions. In the present study, we examined the role of a potential dileucine clathrin adaptor recognition motif [DE]XXXL[LI] embedded within the alpha1-ISR. To this end, a rat alpha1 construct where leucine 499 was replaced by a valine (as found in the alpha2 isoform sequence) was compared to wild-type rat alpha1 after stable expression in opossum kidney cells. Total Na,K-ATPase expression, activity, or in situ (86)Rb(+) transport was not affected by the L499V mutation. However, surface Na,K-ATPase expression was nearly doubled. This increase was associated with a reduced rate of internalization from the cell surface of about 50% after a 4 h chase and became undetectable if clathrin-coated pit-mediated trafficking was blocked with chlorpromazine. Further, PKC-induced stimulation of Na,K-ATPase-mediated (86)Rb(+) uptake was doubled in mutant-expressing cells, comparable to the chimera containing the intact alpha2-ISR. Similar results were observed when the potential motif was disrupted by means of an E495S mutation. These findings suggest that a dileucine motif embedded within the Na,K-ATPase alpha1-ISR plays a critical role in the surface expression of Na,K-ATPase alpha1 polypeptides at steady state and in the response to PKC activation.
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Affiliation(s)
- Yoann Sottejeau
- Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, Ohio 43614, USA
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15
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Alexander RT, Grinstein S. Tethering, recycling and activation of the epithelial sodium–proton exchanger, NHE3. J Exp Biol 2009; 212:1630-7. [DOI: 10.1242/jeb.027375] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
NHE3 is a sodium–proton exchanger expressed predominantly in the apical membrane of renal and intestinal epithelia, where it plays a key role in salt and fluid absorption and pH homeostasis. It performs these functions through the exchange of luminal sodium for cytosolic protons. Acute regulation of NHE3 function is mediated by altering the total number of exchangers in the plasma membrane as well as their individual activity. Traffic between endomembrane and plasmalemmal pools of NHE3 dictates the density of exchangers available at the cell surface. The activity of the plasmalemmal pool, however,is not fixed and can be altered by the association with modifier proteins, by post-translational alterations (such as cAMP-mediated phosphorylation) and possibly also via interaction with specific plasmalemmal phospholipids. Interestingly, association with cytoskeletal components affects both levels of regulation, tethering NHE3 molecules at the surface and altering their intrinsic activity. This paper reviews the role of proteins and lipids in the modulation of NHE3 function.
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Affiliation(s)
- R. Todd Alexander
- Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada,T6G 2R7
| | - Sergio Grinstein
- Program in Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada,M5G 1X8
- Department of Biochemistry, University of Toronto, Ontario, Canada
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Bobulescu IA, Moe OW. Luminal Na(+)/H (+) exchange in the proximal tubule. Pflugers Arch 2009; 458:5-21. [PMID: 18853182 PMCID: PMC2878283 DOI: 10.1007/s00424-008-0595-1] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 09/26/2008] [Indexed: 12/11/2022]
Abstract
The proximal tubule is critical for whole-organism volume and acid-base homeostasis by reabsorbing filtered water, NaCl, bicarbonate, and citrate, as well as by excreting acid in the form of hydrogen and ammonium ions and producing new bicarbonate in the process. Filtered organic solutes such as amino acids, oligopeptides, and proteins are also retrieved by the proximal tubule. Luminal membrane Na(+)/H(+) exchangers either directly mediate or indirectly contribute to each of these processes. Na(+)/H(+) exchangers are a family of secondary active transporters with diverse tissue and subcellular distributions. Two isoforms, NHE3 and NHE8, are expressed at the luminal membrane of the proximal tubule. NHE3 is the prevalent isoform in adults, is the most extensively studied, and is tightly regulated by a large number of agonists and physiological conditions acting via partially defined molecular mechanisms. Comparatively little is known about NHE8, which is highly expressed at the lumen of the neonatal proximal tubule and is mostly intracellular in adults. This article discusses the physiology of proximal Na(+)/H(+) exchange, the multiple mechanisms of NHE3 regulation, and the reciprocal relationship between NHE3 and NHE8 at the lumen of the proximal tubule.
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Affiliation(s)
- I. Alexandru Bobulescu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
| | - Orson W. Moe
- Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA,
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8856, USA
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Kastner C, Pohl M, Sendeski M, Stange G, Wagner CA, Jensen B, Patzak A, Bachmann S, Theilig F. Effects of receptor-mediated endocytosis and tubular protein composition on volume retention in experimental glomerulonephritis. Am J Physiol Renal Physiol 2009; 296:F902-11. [PMID: 19193726 DOI: 10.1152/ajprenal.90451.2008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Human glomerulonephritis (GN) is characterized by sustained proteinuria, sodium retention, hypertension, and edema formation. Increasing quantities of filtered protein enter the renal tubule, where they may alter epithelial transport functions. Exaggerated endocytosis and consequent protein overload may affect proximal tubules, but intrinsic malfunction of distal epithelia has also been reported. A straightforward assignment to a particular tubule segment causing salt retention in GN is still controversial. We hypothesized that 1) trafficking and surface expression of major transporters and channels involved in volume regulation were altered in GN, and 2) proximal tubular endocytosis may influence locally as well as downstream expressed tubular transporters and channels. Effects of anti-glomerular basement membrane GN were studied in controls and megalin-deficient mice with blunted proximal endocytosis. Mice displayed salt retention and elevated systolic blood pressure when proteinuria had reached 10-15 mg/24 h. Surface expression of proximal Na(+)-coupled transporters and water channels was in part [Na(+)-P(i) cotransporter IIa (NaPi-IIa) and aquaporin-1 (AQP1)] increased by megalin deficiency alone, but unchanged (Na(+)/H(+) exchanger 3) or reduced (NaPi-IIa and AQP1) in GN irrespective of the endocytosis defect. In distal epithelia, significant increases in proteolytic cleavage products of alpha-epithelial Na(+) channel (ENaC) and gamma-ENaC were observed, suggesting enhanced tubular sodium reabsorption. The effects of glomerular proteinuria dominated over those of blunted proximal endocytosis in contributing to ENaC cleavage. Our data indicate that ENaC-mediated sodium entry may be the rate-limiting step in proteinuric sodium retention. Enhanced proteolytic cleavage of ENaC points to a novel mechanism of channel activation which may involve the action of filtered plasma proteases.
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Affiliation(s)
- Christian Kastner
- Charité-Universitätsmedizin Berlin, Institut für Vegetative Anatomie, Philippstr. 12, 10115 Berlin, Germany
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Yang X, Huang HC, Yin H, Alpern RJ, Preisig PA. RhoA required for acid-induced stress fiber formation and trafficking and activation of NHE3. Am J Physiol Renal Physiol 2007; 293:F1054-64. [PMID: 17686951 DOI: 10.1152/ajprenal.00295.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Exposure to an acid load increases apical membrane Na+/H+ antiporter (NHE3) activity, a process that involves exocytic trafficking of the transporter to the apical membrane. We have previously shown that an intact microfilament structure is required for this exocytic process (Yang X, Amemiya M, Peng Y, Moe OW, Preisig PA, Alpern RJ. Am J Physiol Cell Physiol 279: C410–C419, 2000). The present studies demonstrate that acid-induced stress fiber formation is required for stimulation of NHE3 activity. Formation of stress fibers is associated with acid-induced tyrosine phosphorylation and increases in protein abundance of two focal adhesion proteins, p125FAK and paxillin. The Rho kinase inhibitor Y27632 completely blocks acid-induced stress fiber formation and the increases in apical membrane NHE3 abundance and activity, but it has no effect on acid-induced tyrosine phosphorylation of p125FAK or paxillin. Herbimycin A completely blocks acid-induced tyrosine phosphorylation of p125FAK and paxillin but only partially blocks stress fiber formation and NHE3 activation. These studies demonstrate that Rho kinase mediates acid-induced stress fiber formation, which is required for NHE3 exocytosis, and increases in NHE3 activity. Acid-induced tyrosine phosphorylation of the focal adhesion proteins p125FAK and paxillin is not Rho kinase dependent. Thus these two acid-mediated effects are associated, yet independent processes.
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Affiliation(s)
- Xiaojing Yang
- Department of Internal Medicine, University of Texas Southwestern Medical School, Dallas, Texas, USA
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Abstract
NHE3 is the brush-border (BB) Na+/H+exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na+absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.
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Affiliation(s)
- Mark Donowitz
- Department of Medicine, GI Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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Abstract
The possibility that proteinuria may accelerate kidney disease progression to end-stage renal failure has received support from the results of increasing numbers of experimental and clinical studies. Evidence indicating that this process occurs through multiple pathways, including induction of tubular chemokine expression and complement activation that lead to inflammatory cell infiltration in the interstitium and sustained fibrogenesis, is reviewed. Macrophages are prominent in the interstitial inflammatory infiltrate. This cell type mediates progression of renal injury to the extent that macrophage numbers in renal biopsy predict renal survival in patients with chronic renal disease. Chemoattractants and adhesive molecules for inflammatory cells are upregulated by excess ultrafiltered protein load of proximal tubular cells via activation of NF-kappaB-dependent and NF-kappaB-independent pathways. This mechanism is a potential target for therapeutic approaches, as shown by beneficial effects of manipulations with inhibitory molecules of NF-kappaB activation or of chemokine receptors in experimental studies. Targeting complement synthesis or activation in proximal tubule might offer novel therapeutic opportunities. Finally, proximal tubular cell receptors for uptake of plasma proteins that are under investigation may provide activation signals on excess tubular protein handling.
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Affiliation(s)
- Mauro Abbate
- Mario Negri Institute for Pharmacological Research, Bergamo, Italy
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Abstract
The kidney plays key roles in extracellular fluid pH homeostasis by reclaiming bicarbonate (HCO(3)(-)) filtered at the glomerulus and generating the consumed HCO(3)(-) by secreting protons (H(+)) into the urine (renal acidification). Sodium-proton exchangers (NHEs) are ubiquitous transmembrane proteins mediating the countertransport of Na(+) and H(+) across lipid bilayers. In mammals, NHEs participate in the regulation of cell pH, volume, and intracellular sodium concentration, as well as in transepithelial ion transport. Five of the 10 isoforms (NHE1-4 and NHE8) are expressed at the plasma membrane of renal epithelial cells. The best-studied isoform for acid-base homeostasis is NHE3, which mediates both HCO(3)(-) absorption and H(+) excretion in the renal tubule. This article reviews some important aspects of NHEs in the kidney, with special emphasis on the role of renal NHE3 in the maintenance of acid-base balance.
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Affiliation(s)
- I Alexandru Bobulescu
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
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Biemesderfer D. Regulated intramembrane proteolysis of megalin: Linking urinary protein and gene regulation in proximal tubule? Kidney Int 2006; 69:1717-21. [PMID: 16557231 DOI: 10.1038/sj.ki.5000298] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Regulated intramembrane proteolysis (RIP) represents an evolutionarily conserved process linking receptor function with transcriptional regulation. Best characterized by the Notch signaling pathway, RIP involves regulated ectodomain shedding followed by gamma-secretase-mediated release of the C-terminal, cytosolic domain. The C-terminus in turn translocates to the nucleus where it interacts with other proteins to regulate expression of specific genes. Recent studies in our laboratory have shown that megalin, a scavenger receptor in proximal tubule, is subjected to RIP in a manner very similar to that of Notch. We showed that megalin in subjected to protein kinase C-regulated, metalloprotease-mediated ectodomain shedding producing a membrane-associated C-terminal fragment (MCTF). The MCTF in turn forms the substrate for gamma-secretase. These data implicate megalin as a central element of a Notch-like signaling pathway linking protein reabsorption and gene regulation in proximal tubule. The likelihood that megalin processing plays an important role in the progression of proteinuric kidney disease is discussed.
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Affiliation(s)
- D Biemesderfer
- Section of Nephrology, Department of Internal Medicine, School of Medicine, Yale University, New Haven, Connecticut 06520, USA.
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Klisic J, Nief V, Reyes L, Ambuhl PM. Acute and Chronic Regulation of the Renal Na +/H + Exchanger NHE3 in Rats with STZ-Induced Diabetes mellitus. ACTA ACUST UNITED AC 2006; 102:p27-35. [PMID: 16244498 DOI: 10.1159/000089091] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2004] [Accepted: 07/12/2005] [Indexed: 01/24/2023]
Abstract
BACKGROUND Early stages of diabetic nephropathy are characterized by alterations of glomerular filtration, increased tubular sodium and water reabsorption, and systemic volume expansion, which may be a major cause for the development of hypertension. As a significant fraction of renal salt and water transport is mediated by the proximal tubular Na+/H+ exchanger NHE3, we investigated its regulation in rats with STZ-induced diabetes mellitus. METHODS Male Sprague-Dawley rats were injected +/- streptozotocin (STZ, 60 mg/kg), and sacrificed after 2, 7 or 14 days. Renal cortical BBM vesicles were prepared to measure Na+/H+ exchange (NHE) activity and NHE3 protein abundance. Cortical NHE3 mRNA was extracted to perform Northern blot analysis. Pharmacological inhibitors were used in vivo and in vitro in order to identify isoform specificity conferring changes in NHE activity mediated by the diabetic milieu. RESULTS Compared to control rats, STZ rats were clearly hyperglycemic at all time points studied. NHE activity was significantly increased by 40 and 37% in diabetic rats after 7 and 14 days, respectively, but not after 2 days. The increase in Na+/H+ exchange activity was not inhibited by HOE-642 (3 microM). Administration of exogenous insulin to diabetic rats resulted in lower blood sugars, but not NHE activity. Moreover, serum glucose concentration did not correlate with NHE activity in any subgroup nor in all animals analyzed together. However, in STZ rats supplemented with exogenous insulin NHE activity was positively correlated with serum insulin concentrations (r = 0.86, p < 0.01). In vivo, the increase in NHE activity induced by STZ could be completely inhibited when rats were fed 6 ppm of HOE-642 with the diet over 14 days. The changes in Na+/H+ exchange activity were not paralleled by changes in NHE3 protein or mRNA abundance in diabetic rats at any of the time points investigated. CONCLUSIONS These results suggest that proximal tubular Na/H exchange activity is modified in the early stage of diabetes mellitus.
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Affiliation(s)
- Jelena Klisic
- Department of Physiology, University of Zurich-Irchel, Zurich, Switzerland
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Abstract
Hypertension is an important and widely prevalent risk factor for the development of chronic kidney disease (CKD), which unfortunately may progress to end-stage renal disease. CKD is a progressive condition that causes significant morbidity and mortality. Diabetes is the leading cause of end-stage renal disease in the Western world. Both hypertension and diabetes are the causative factors for the occurrence of CKD and its consequences. Aggressive control of hypertension and diabetes is indicated to reduce the risk for kidney disease in the community. Certainly, effective control of hypertension is a proven modality to prevent renal disease. The concept of decreasing the systemic blood pressure as well as the intraglomerular pressure has led to the application of rational therapeutic options in patients with renal insufficiency. Although treatment of hypertension alone is critical, drugs that block the renin-angiotensin system have been shown to have special renal (and cardiovascular) benefits. Early detection and treatment of microalbuminuria is an integral part of disease management. This article reviews the pathophysiologic and therapeutic implications of the link between hypertension and the kidney.
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Camici M. Molecular pathogenetic mechanisms of nephrotic edema: progress in understanding. Biomed Pharmacother 2005; 59:215-23. [PMID: 15893443 DOI: 10.1016/j.biopha.2004.11.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2004] [Accepted: 11/26/2004] [Indexed: 10/25/2022] Open
Abstract
Molecular and pathogenetic mechanisms in sodium retention and water reabsorption of nephrotic edema are discussed. Are reported and analyzed molecular mechanisms about sodium retention in collecting duct cells regarding activation and surface expression of epithelial sodium channels (ENaC) and sodium-potassium-ATPase (Na,K-ATPase) by aldosterone, vasopressin, natriuretic peptide system (underfill theory): is necessary a better understanding about the dysregulation of ENaC and Na,K-ATPase surface expression and the resistance to natriuretic peptide system. Are also reported and analyzed molecular mechanisms of sodium retention in proximal tubule cells regarding intrinsic albumin toxicity upon type 3 sodium-hydrogen exchanger ionic pump and the activity of sodium-hydrogen exchanger regulatory factor protein (overfill theory): a better knowledge about the link between albumin, sodium-hydrogen exchanger type 3 (NHE3) ionic pump, sodium-hydrogen exchanger regulatory factor protein is necessary. Then molecular mechanisms of vasopressin free water retention through acquaporin water channels in collecting duct cells are discussed: further studies are necessary to understand vasopressin release pathway (osmotic/nonosmotic) and V2 receptor activation with cell surface expression of renal acquaporins water channel.
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Affiliation(s)
- Marcello Camici
- Department of Internal Medicine, Pisa University, Via Roma 67, 56126 Pisa, Italy.
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Ashman N, Harwood SM, Kieswich J, Allen DA, Roberts NB, Mendes-Ribeiro AC, Yaqoob MM. Albumin stimulates cell growth, L-arginine transport, and metabolism to polyamines in human proximal tubular cells. Kidney Int 2005; 67:1878-89. [PMID: 15840035 DOI: 10.1111/j.1523-1755.2005.00286.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Pure albumin stimulates proximal tubular epithelial cell (PTEC) proliferation, and may have a role in homeostasis in health, as well as in disrupted PTEC turnover in proteinuric nephropathies. We investigated a role for arginine and its metabolites, the polyamines, in this process, given the ability of polyamines to trigger proliferation in other mammalian cells. METHODS [(3)H]-L-arginine uptake was examined after incubation with 20 mg/mL recombinant human serum albumin (rHSA) in HK-2 PTEC monolayers. Nitric oxide synthase (NOS) and arginase activity was measured; NOS, arginase, and ornithine decarboxylase (ODC) expression was identified by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Polyamine synthesis and intracellular amino acid concentrations were compared using high-performance liquid chromatography, and cell growth measured by [(3)H]-thymidine incorporation. RESULTS In HK-2 PTEC exposed to 20 mg/mL rHSA for 24 hours, cell proliferation as determined by [(3)H]-thymidine incorporation was increased. In parallel, L-arginine transport capacity was increased in a dose- and time-dependent manner. This effect was specific to rHSA, and was not seen with transferrin or immunoglobulin G. The intracellular concentration of L-arginine remained unchanged, although L-ornithine was increased with rHSA incubation. rHSA up-regulated type II arginase mRNA, and increased arginase activity, although no difference in nitric oxide synthase expression or activity was seen. ODC mRNA was increased, as were intracellular polyamine concentrations. alpha-Difluoromethylornithine (DFMO), an ODC inhibitor, reduced intracellular polyamine concentrations and rHSA-induced cell proliferation to control levels. CONCLUSION The arginine-ornithine-polyamine pathway appears enhanced in PTEC incubated with rHSA and is involved in cellular proliferation; this may offer novel approaches to understanding progressive proteinuric nephropathies.
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Affiliation(s)
- Neil Ashman
- Department of Clinical Chemistry, University of Liverpool, Liverpool, United Kingdom.
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Abstract
Albumin is the most abundant protein in serum and contributes to the maintenance of oncotic pressure as well as to transport of hydrophobic molecules. Although albumin is a large anionic protein, it is not completely retained by the glomerular filtration barrier. In order to prevent proteinuria, albumin is reabsorbed along the proximal tubules by receptor-mediated endocytosis, which involves the binding proteins megalin and cubilin. Endocytosis depends on proper vesicle acidification. Disturbance of endosomal acidification or loss of the binding proteins leads to tubular proteinuria. Furthermore, endocytosis is subject to modulation by different signaling systems, such as protein kinase A (PKA), protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3-K) and transforming growth factor beta (TGF-beta). In addition to being reabsorbed in the proximal tubule, albumin can also act as a profibrotic and proinflammatory stimulus, thereby initiating or promoting tubulo-interstitial diseases.
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Affiliation(s)
- Michael Gekle
- Physiologisches Institut, University of Würzburg, 97070 Würzburg, Germany.
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Hryciw DH, Ekberg J, Lee A, Lensink IL, Kumar S, Guggino WB, Cook DI, Pollock CA, Poronnik P. Nedd4-2 Functionally Interacts with ClC-5. J Biol Chem 2004; 279:54996-5007. [PMID: 15489223 DOI: 10.1074/jbc.m411491200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Constitutive albumin uptake by the proximal tubule is achieved by a receptor-mediated process in which the Cl(-) channel, ClC-5, plays an obligate role. Here we investigated the functional interaction between ClC-5 and ubiquitin ligases Nedd4 and Nedd4-2 and their role in albumin uptake in opossum kidney proximal tubule (OK) cells. In vivo immunoprecipitation using an anti-HECT antibody demonstrated that ClC-5 bound to ubiquitin ligases, whereas glutathione S-transferase pull-downs confirmed that the C terminus of ClC-5 bound both Nedd4 and Nedd4-2. Nedd4-2 alone was able to alter ClC-5 currents in Xenopus oocytes by decreasing cell surface expression of ClC-5. In OK cells, a physiological concentration of albumin (10 mug/ml) rapidly increased cell surface expression of ClC-5, which was also accompanied by the ubiquitination of ClC-5. Albumin uptake was reduced by inhibiting either the lysosome or proteasome. Total levels of Nedd4-2 and proteasome activity also increased rapidly in response to albumin. Overexpression of ligase defective Nedd4-2 or knockdown of endogenous Nedd4-2 with small interfering RNA resulted in significant decreases in albumin uptake. In contrast, pathophysiological concentrations of albumin (100 and 1000 mug/ml) reduced the levels of ClC-5 and Nedd4-2 and the activity of the proteasome to the levels seen in the absence of albumin. These data demonstrate that normal constitutive uptake of albumin by the proximal tubule requires Nedd4-2, which may act via ubiquitination to shunt ClC-5 into the endocytic pathway.
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Affiliation(s)
- Deanne H Hryciw
- School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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Hryciw DH, Lee EM, Pollock CA, Poronnik P. MOLECULAR CHANGES IN PROXIMAL TUBULE FUNCTION IN DIABETES MELLITUS. Clin Exp Pharmacol Physiol 2004; 31:372-9. [PMID: 15191416 DOI: 10.1111/j.1440-1681.2004.04001.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Diabetic kidney disease is initially associated with hypertension and increased urinary albumin excretion. The hypertension is mediated by enhanced volume expansion due to enhanced salt and water retention by the kidney. The increased urinary albumin is not only due to increased glomerular leak, but also to a decrease in albumin reabsorption by the proximal tubule. The precise molecular mechanisms underlying these two phenomena and whether there is any link between the increase in Na(+) retention and proteinuria remain unresolved. There is significant evidence to suggest that increased Na(+) retention by the proximal tubule Na(+)/H(+) exchanger isoform 3 (NHE3) can play a role in some forms of hypertension. Increased NHE3 activity in models of diabetes mellitus may explain, in part, the enhanced salt retention observed in patients with diabetic kidney disease. The NHE3 also plays a role in receptor-mediated albumin uptake in the proximal tubule. The uptake of albumin requires the assembly of a macromolecular complex that is thought to include the megalin/cubulin receptor, NHE3, the vacuolar type H(+)-ATPase (v-H(+)-ATPase), the Cl(-) channel ClC-5 and interactions with the actin cytoskeleton. The NHE3 seems to exist in two functionally distinct membrane domains, one involved with Na(+) reabsorption and the other involved in albumin uptake. The present review focuses on the evidence derived from in vivo studies, as well as complementary studies in cell culture models, for a dual role of NHE3 in both Na(+) retention and albumin uptake. We suggest a possible mechanism by which disruption of the proximal tubule albumin uptake mechanism in diabetes mellitus may lead to both increased Na(+) retention and proteinuria.
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Affiliation(s)
- Deanne H Hryciw
- School of Biomedical Sciences, University of Queensland, St Lucia, Queensland, Australia
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