Podocyte-specific RAP1GAP expression contributes to focal segmental glomerulosclerosis–associated glomerular injury
Uma Potla, … , Paul E. Klotman, Lewis Kaufman
Uma Potla, … , Paul E. Klotman, Lewis Kaufman
Published March 18, 2014
Citation Information: J Clin Invest. 2014;124(4):1757-1769. https://doi.org/10.1172/JCI67846.
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Research Article

Podocyte-specific RAP1GAP expression contributes to focal segmental glomerulosclerosis–associated glomerular injury

Abstract

Injury to the specialized epithelial cells of the glomerulus (podocytes) underlies the pathogenesis of all forms of proteinuric kidney disease; however, the specific genetic changes that mediate podocyte dysfunction after injury are not fully understood. Here, we performed a large-scale insertional mutagenic screen of injury-resistant podocytes isolated from mice and found that increased expression of the gene Rap1gap, encoding a RAP1 activation inhibitor, ameliorated podocyte injury resistance. Furthermore, injured podocytes in murine models of disease and kidney biopsies from glomerulosclerosis patients exhibited increased RAP1GAP, resulting in diminished glomerular RAP1 activation. In mouse models, podocyte-specific inactivation of Rap1a and Rap1b induced massive glomerulosclerosis and premature death. Podocyte-specific Rap1a and Rap1b haploinsufficiency also resulted in severe podocyte damage, including features of podocyte detachment. Over-expression of RAP1GAP in cultured podocytes induced loss of activated β1 integrin, which was similarly observed in kidney biopsies from patients. Furthermore, preventing elevation of RAP1GAP levels in injured podocytes maintained β1 integrin–mediated adhesion and prevented cellular detachment. Taken together, our findings suggest that increased podocyte expression of RAP1GAP contributes directly to podocyte dysfunction by a mechanism that involves loss of RAP1-mediated activation of β1 integrin.

Authors

Uma Potla, Jie Ni, Justin Vadaparampil, Guozhe Yang, Jeremy S. Leventhal, Kirk N. Campbell, Peter Y. Chuang, Alexei Morozov, John C. He, Vivette D. D’Agati, Paul E. Klotman, Lewis Kaufman

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Figure 4

Podocyte-specific inactivation of both Rap1a and Rap1b induces massive glomerulosclerosis and death.

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Podocyte-specific inactivation of both Rap1a and Rap1b induces massive g...
(A) The majority of DKO mice died by 8 weeks of age. (B) Calculated urine protein/creatinine ratios confirmed massive proteinuria in DKO versus control mice. (C) Kidney histology from mice aged 3 weeks. Control mice demonstrated patent glomerular capillaries with a normal-appearing mesangium (top left). DKO mice (top right and bottom row) showed severe mesangial expansion affecting all glomeruli. Some glomeruli demonstrated early lesions of segmental sclerosis with overlying epithelial hyperplasia (bottom left). (D) By 6 weeks of age, DKO renal pathology drastically worsened. There was diffuse and severe glomerulosclerosis affecting all glomeruli, giving the kidney an end-stage appearance (top left). The interstitium showed widespread tubular microcysts with diffuse proteinaceous casts (top right). A prominent feature was collapsing glomerulosclerosis with overlying epithelial cell hypertrophy and hyperplasia (bottom row). (E) Glomerular collapse was often severe, with prominent pseudocrescent formation. Immunostaining of a serial section confirmed strong glomerular Ki-67 expression. Original magnification, ×400 (C, top); ×200 (D, top); ×600 (C and D, bottom, and E).