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Abstract
Rho family GTPases are molecular switches best known for their pivotal role in dynamic regulation of the actin cytoskeleton, but also of cellular morphology, motility, adhesion and proliferation. The prototypic members of this family (RhoA, Rac1 and Cdc42) also contribute to the normal kidney function and play important roles in the structure and function of various kidney cells including tubular epithelial cells, mesangial cells and podocytes. The kidney's vital filtration function depends on the structural integrity of the glomerulus, the proximal portion of the nephron. Within the glomerulus, the architecturally actin-based cytoskeleton podocyte forms the final cellular barrier to filtration. The glomerulus appears as a highly dynamic signalling hub that is capable of integrating intracellular cues from its individual structural components. Dynamic regulation of the podocyte cytoskeleton is required for efficient barrier function of the kidney. As master regulators of actin cytoskeletal dynamics, Rho GTPases are therefore of critical importance for sustained kidney barrier function. Dysregulated activities of the Rho GTPases and of their effectors are implicated in the pathogenesis of both hereditary and idiopathic forms of kidney diseases. Diabetic nephropathy is a progressive kidney disease that is caused by injury to kidney glomeruli. High glucose activates RhoA/Rho-kinase in mesangial cells, leading to excessive extracellular matrix production (glomerulosclerosis). This RhoA/Rho-kinase pathway also seems involved in the post-transplant hypertension frequently observed during treatment with calcineurin inhibitors, whereas Rac1 activation was observed in post-transplant ischaemic acute kidney injury.
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Affiliation(s)
- Clara Steichen
- Inserm UMR-1082 Irtomit, Poitiers, France,Faculté De Médecine Et De Pharmacie, Université De Poitiers, Poitiers, France
| | - Claude Hervé
- Inserm UMR-1082 Irtomit, Poitiers, France,CONTACT Claude HervéInserm UMR-1082 Irtomit, Poitiers, France
| | - Thierry Hauet
- Inserm UMR-1082 Irtomit, Poitiers, France,Faculté De Médecine Et De Pharmacie, Université De Poitiers, Poitiers, France,Department of Medical Biology, Service De Biochimie, CHU De Poitiers, Poitiers, France
| | - Nicolas Bourmeyster
- Faculté De Médecine Et De Pharmacie, Université De Poitiers, Poitiers, France,Department of Medical Biology, Service De Biochimie, CHU De Poitiers, Poitiers, France,Laboratoire STIM CNRS ERL 7003, Université de Poitiers, Poitiers Cédex, France
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Blaine J, Dylewski J. Regulation of the Actin Cytoskeleton in Podocytes. Cells 2020; 9:cells9071700. [PMID: 32708597 PMCID: PMC7408282 DOI: 10.3390/cells9071700] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 06/30/2020] [Accepted: 07/07/2020] [Indexed: 12/13/2022] Open
Abstract
Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation.
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Affiliation(s)
- Judith Blaine
- Renal Division, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA;
| | - James Dylewski
- Renal Division, University of Colorado Anschutz Medical Campus and Denver Health Medical Center, Aurora, CO 80045, USA
- Correspondence: ; Tel.: +303-724-4841
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Nihalani D, Solanki AK, Arif E, Srivastava P, Rahman B, Zuo X, Dang Y, Fogelgren B, Fermin D, Gillies CE, Sampson MG, Lipschutz JH. Disruption of the exocyst induces podocyte loss and dysfunction. J Biol Chem 2019; 294:10104-10119. [PMID: 31073028 PMCID: PMC6664173 DOI: 10.1074/jbc.ra119.008362] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 05/06/2019] [Indexed: 11/06/2022] Open
Abstract
Although the slit diaphragm proteins in podocytes are uniquely organized to maintain glomerular filtration assembly and function, little is known about the underlying mechanisms that participate in trafficking these proteins to the correct location for development and homeostasis. Identifying these mechanisms will likely provide novel targets for therapeutic intervention to preserve podocyte function following glomerular injury. Analysis of structural variation in cases of human nephrotic syndrome identified rare heterozygous deletions of EXOC4 in two patients. This suggested that disruption of the highly-conserved eight-protein exocyst trafficking complex could have a role in podocyte dysfunction. Indeed, mRNA profiling of injured podocytes identified significant exocyst down-regulation. To test the hypothesis that the exocyst is centrally involved in podocyte development/function, we generated homozygous podocyte-specific Exoc5 (a central exocyst component that interacts with Exoc4) knockout mice that showed massive proteinuria and died within 4 weeks of birth. Histological and ultrastructural analysis of these mice showed severe glomerular defects with increased fibrosis, proteinaceous casts, effaced podocytes, and loss of the slit diaphragm. Immunofluorescence analysis revealed that Neph1 and Nephrin, major slit diaphragm constituents, were mislocalized and/or lost. mRNA profiling of Exoc5 knockdown podocytes showed that vesicular trafficking was the most affected cellular event. Mapping of signaling pathways and Western blot analysis revealed significant up-regulation of the mitogen-activated protein kinase and transforming growth factor-β pathways in Exoc5 knockdown podocytes and in the glomeruli of podocyte-specific Exoc5 KO mice. Based on these data, we propose that exocyst-based mechanisms regulate Neph1 and Nephrin signaling and trafficking, and thus podocyte development and function.
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Affiliation(s)
- Deepak Nihalani
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425,
| | - Ashish K Solanki
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Ehtesham Arif
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Pankaj Srivastava
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Bushra Rahman
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Xiaofeng Zuo
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Yujing Dang
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425
| | - Ben Fogelgren
- the Department of Anatomy, Biochemistry, and Physiology, University of Hawaii at Manoa, Honolulu, Hawaii 96813
| | | | | | - Matthew G Sampson
- the Department of Pediatrics-Nephrology and.,Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, Michigan 48109, and
| | - Joshua H Lipschutz
- From the Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425.,the Department of Medicine, Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina 29401
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Lv Z, Hu M, Fan M, Li X, Lin J, Zhen J, Wang Z, Jin H, Wang R. Podocyte-specific Rac1 deficiency ameliorates podocyte damage and proteinuria in STZ-induced diabetic nephropathy in mice. Cell Death Dis 2018; 9:342. [PMID: 29497040 PMCID: PMC5832796 DOI: 10.1038/s41419-018-0353-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2017] [Revised: 01/22/2018] [Accepted: 01/23/2018] [Indexed: 12/12/2022]
Abstract
Activation of Ras-related C3 botulinum toxin substrate 1 (Rac1) has been implicated in diverse kidney diseases, yet its in vivo significance in diabetic nephropathy (DN) is largely unknown. In the present study, we demonstrated a podocyte-specific Rac1-deficient mouse strain and showed that specific inhibition of Rac1 was able to attenuate diabetic podocyte injury and proteinuria by the blockade of Rac1/PAK1/p38/β-catenin signaling cascade, which reinstated the integrity of podocyte slit diaphragms (SD), rectified the effacement of foot processes (FPs), and prevented the dedifferentiation of podocytes. In vitro, we showed Rac1/PAK1 physically bound to β-catenin and had a direct phosphorylation modification on its C-terminal Ser675, leading to less ubiquitylated β-catenin, namely more stabilized β-catenin, and its nuclear migration under high-glucose conditions; further, p38 activation might be responsible for β-catenin nuclear accumulation via potentiating myocyte-specific enhancer factor 2C (MEF2c) phosphorylation. These findings provided evidence for a potential renoprotective and therapeutic strategy of cell-specific Rac1 deficiency for DN and other proteinuric diseases.
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Affiliation(s)
- Zhimei Lv
- Department of Nephrology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, China
| | - Mengsi Hu
- Department of Nephrology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, China
| | - Minghua Fan
- Department of Obstetrics and Gynecology, The Second Hospital of Shandong University, Jinan, China
| | - Xiaobing Li
- Institute of Basic Medicine, Shandong Academy of Medical Sciences, Jinan, China
| | - Jiangong Lin
- Department of Nephrology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, China
| | - Junhui Zhen
- Department of Pathology, School of Medicine, Shandong University, Jinan, China
| | - Ziyang Wang
- Department of Nephrology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, China
| | - Haijun Jin
- Department of Internal Medicine Clinic, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, China
| | - Rong Wang
- Department of Nephrology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, China.
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Maier M, Baldwin C, Aoudjit L, Takano T. The Role of Trio, a Rho Guanine Nucleotide Exchange Factor, in Glomerular Podocytes. Int J Mol Sci 2018; 19:ijms19020479. [PMID: 29415466 PMCID: PMC5855701 DOI: 10.3390/ijms19020479] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/03/2018] [Accepted: 02/03/2018] [Indexed: 12/16/2022] Open
Abstract
Nephrotic syndrome is a kidney disease featured by heavy proteinuria. It is caused by injury to the specialized epithelial cells called “podocytes” within the filtration unit of the kidney, glomerulus. Previous studies showed that hyperactivation of the RhoGTPase, Rac1, in podocytes causes podocyte injury and glomerulosclerosis (accumulation of extracellular matrix in the glomerulus). However, the mechanism by which Rac1 is activated during podocyte injury is unknown. Trio is a guanine nucleotide exchange factor (GEF) known to activate Rac1. By RNA-sequencing, we found that Trio mRNA is abundantly expressed in cultured human podocytes. Trio mRNA was also significantly upregulated in humans with minimal change disease and focal segmental glomerulosclerosis, two representative causes of nephrotic syndrome. Reduced expression of Trio in cultured human podocytes decreased basal Rac1 activity, cell size, attachment to laminin, and motility. Furthermore, while the pro-fibrotic cytokine, transforming growth factor β1 increased Rac1 activity in control cells, it decreases Rac1 activity in cells with reduced Trio expression. This was likely due to simultaneous activation of the Rac1-GTPase activation protein, CdGAP. Thus, Trio is important in the basal functions of podocytes and may also contribute to glomerular pathology, such as sclerosis, via Rac1 activation.
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Affiliation(s)
- Mirela Maier
- Division of Experimental Medicine, McGill University, Montreal, QC H3A 0G4, Canada.
| | - Cindy Baldwin
- Division of Nephrology, McGill University Health Centre, Montreal, QC H4A 3J1, Canada.
| | - Lamine Aoudjit
- Division of Nephrology, McGill University Health Centre, Montreal, QC H4A 3J1, Canada.
| | - Tomoko Takano
- Division of Experimental Medicine, McGill University, Montreal, QC H3A 0G4, Canada.
- Division of Nephrology, McGill University Health Centre, Montreal, QC H4A 3J1, Canada.
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Robins R, Baldwin C, Aoudjit L, Côté JF, Gupta IR, Takano T. Rac1 activation in podocytes induces the spectrum of nephrotic syndrome. Kidney Int 2017; 92:349-364. [PMID: 28483380 DOI: 10.1016/j.kint.2017.03.010] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 02/09/2017] [Accepted: 03/02/2017] [Indexed: 11/19/2022]
Abstract
Hyper-activation of Rac1, a small GTPase, in glomerular podocytes has been implicated in the pathogenesis of familial proteinuric kidney diseases. However, the role of Rac1 in acquired nephrotic syndrome is unknown. To gain direct insights into this, we generated a transgenic mouse model expressing a doxycycline-inducible constitutively active form of Rac1 (CA-Rac1) in podocytes. Regardless of the copy number, proteinuria occurred rapidly within five days, and the histology resembled minimal change disease. The degree and severity of proteinuria were dependent on the transgene copy number. Upon doxycycline withdrawal, proteinuria resolved completely (one copy) or nearly completely (two copy). After one month of doxycycline treatment, two-copy mice developed glomerulosclerosis that resembled focal segmental glomerulosclerosis (FSGS) with urinary shedding of transgene-expressing podocytes. p38 MAPK was activated in podocytes upon CA-Rac1 induction while a p38 inhibitor attenuated proteinuria, podocyte loss, and glomerulosclerosis. Mechanistically, activation of Rac1 in cultured mouse podocytes reduced adhesiveness to laminin and induced redistribution of β1 integrin, and both were partially reversed by the p38 inhibitor. Activation of Rac1 in podocytes was also seen in kidney biopsies from patients with minimal change disease and idiopathic FSGS by immunofluorescence while sera from the same patients activated Rac1 in cultured human podocytes. Thus, activation of Rac1 in podocytes causes a spectrum of disease ranging from minimal change disease to FSGS, due to podocyte detachment from the glomerular basement membrane that is partially dependent on p38 MAPK.
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Affiliation(s)
- Richard Robins
- Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada
| | - Cindy Baldwin
- Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada
| | - Lamine Aoudjit
- Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada
| | - Jean-François Côté
- Institut de Recherches Cliniques de Montréal (IRCM), Department of Medicine (Program of Molecular Biology), Université de Montréal, Montreal, Quebec, Canada; Department of Biochemistry, Université de Montréal, Montreal, Quebec, Canada; Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
| | - Indra R Gupta
- Department of Pediatrics, McGill University Health Centre, Montreal, Quebec, Canada
| | - Tomoko Takano
- Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada.
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