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Divergent functions of the Rho GTPases Rac1 and Cdc42 in podocyte injury.

Blattner SM, Hodgin JB, Nishio M, Wylie SA, Saha J, Soofi AA, Vining C, Randolph A, Herbach N, Wanke R, Atkins KB, Gyung Kang H, Henger A, Brakebusch C, Holzman LB, Kretzler M - Kidney Int. (2013)

Bottom Line: Here, we employed podocyte-specific Cre-lox technology and found that mice with deletion of Rac1 display normal podocyte morphology without glomerular dysfunction well into adulthood.Cdc42 is necessary for the maintenance of podocyte structure and function, but Rac1 is entirely dispensable in physiological steady state.However, Rac1 has either beneficial or deleterious effects depending on the context of podocyte impairment.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Division of Nephrology, University of Michigan, Ann Arbor, Michigan, USA.

ABSTRACT
Podocytes are highly specialized epithelial cells with complex actin cytoskeletal architecture crucial for maintenance of the glomerular filtration barrier. The mammalian Rho GTPases Rac1 and Cdc42 are molecular switches that control many cellular processes, but are best known for their roles in the regulation of actin cytoskeleton dynamics. Here, we employed podocyte-specific Cre-lox technology and found that mice with deletion of Rac1 display normal podocyte morphology without glomerular dysfunction well into adulthood. Using the protamine sulfate model of acute podocyte injury, podocyte-specific deletion of Rac1 prevented foot process effacement. In a long-term model of chronic hypertensive glomerular damage, however, loss of Rac1 led to an exacerbation of albuminuria and glomerulosclerosis. In contrast, mice with podocyte-specific deletion of Cdc42 had severe proteinuria, podocyte foot process effacement, and glomerulosclerosis beginning as early as 10 days of age. In addition, slit diaphragm proteins nephrin and podocin were redistributed, and cofilin was dephosphorylated. Cdc42 is necessary for the maintenance of podocyte structure and function, but Rac1 is entirely dispensable in physiological steady state. However, Rac1 has either beneficial or deleterious effects depending on the context of podocyte impairment. Thus, our study highlights the divergent roles of Rac1 and Cdc42 function in podocyte maintenance and injury.

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Albuminuria and percent glomerulosclerosis in UNX/DOCA-salt mice. (A) Albumin-to-creatinine ratio at 1 week before, and 2 and 4 weeks after uninephrectomy and DOCA treatment demonstrate significantly more albuminuria in podoRac1−/− mice than Rac1 fl/fl control mice. (B) UNX/DOCA-salt treated podoRac1−/− demonstrates twice the glomerulosclerosis than Rac1 fl/fl control mice. Sham treated mice of both genotypes showed no glomerulosclerosis (data not shown). (C and D) Representative PAS stained glomerulus at 20× and 40× magnification from UNX/DOCA-salt treated podoRac1−/− mouse demonstrating segmental sclerosis. *P<0.05, #P=0.19
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Figure 9: Albuminuria and percent glomerulosclerosis in UNX/DOCA-salt mice. (A) Albumin-to-creatinine ratio at 1 week before, and 2 and 4 weeks after uninephrectomy and DOCA treatment demonstrate significantly more albuminuria in podoRac1−/− mice than Rac1 fl/fl control mice. (B) UNX/DOCA-salt treated podoRac1−/− demonstrates twice the glomerulosclerosis than Rac1 fl/fl control mice. Sham treated mice of both genotypes showed no glomerulosclerosis (data not shown). (C and D) Representative PAS stained glomerulus at 20× and 40× magnification from UNX/DOCA-salt treated podoRac1−/− mouse demonstrating segmental sclerosis. *P<0.05, #P=0.19

Mentions: UNX/DOCA-salt treated mice of either group displayed elevated albuminuria at 2 and 4 weeks, however, urine albumin in UNX/DOCA-salt treated podoRac1−/− mice was nearly twice that of Rac1-fl/fl at 2 weeks (P<0.05) and 4 weeks (Figure 9A), although the difference was not significant at the latter time point (P=0.19). The percentage of glomeruli with segmental and global sclerosis was likewise doubled in treated podoRac1−/− mice at 4 weeks versus treated controls, (Figure 9, B-D) indicating an exacerbation of podocyte injury, rather than protection, in podoRac1−/− mice. Though increased in frequency, the morphologic appearance of segmental sclerosis in UNX/DOCA-salt treated podoRac1−/− mice was indistinguishable from Rac1-fl/fl controls. A qualitative ultrastructural examination by TEM revealed focal and segmental podocyte foot process effacement in both UNX/DOCA-salt treated podoRac1−/− and Rac1-fl/fl mice (Figure 10, A and B, and Supplementary Figure 1), which is consistent with the focal nature of effacement in glomerular hyperfiltration injury akin to secondary focal segmental glomerulosclerosis (FSGS), such as seen in hypertensive or obese humans.12 Interestingly, we observed focal foot process effacement in UNX/DOCA-salt treated podoRac1−/−mice, indicating that Rac1-independent mechanisms of effacement exist.


Divergent functions of the Rho GTPases Rac1 and Cdc42 in podocyte injury.

Blattner SM, Hodgin JB, Nishio M, Wylie SA, Saha J, Soofi AA, Vining C, Randolph A, Herbach N, Wanke R, Atkins KB, Gyung Kang H, Henger A, Brakebusch C, Holzman LB, Kretzler M - Kidney Int. (2013)

Albuminuria and percent glomerulosclerosis in UNX/DOCA-salt mice. (A) Albumin-to-creatinine ratio at 1 week before, and 2 and 4 weeks after uninephrectomy and DOCA treatment demonstrate significantly more albuminuria in podoRac1−/− mice than Rac1 fl/fl control mice. (B) UNX/DOCA-salt treated podoRac1−/− demonstrates twice the glomerulosclerosis than Rac1 fl/fl control mice. Sham treated mice of both genotypes showed no glomerulosclerosis (data not shown). (C and D) Representative PAS stained glomerulus at 20× and 40× magnification from UNX/DOCA-salt treated podoRac1−/− mouse demonstrating segmental sclerosis. *P<0.05, #P=0.19
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3815690&req=5

Figure 9: Albuminuria and percent glomerulosclerosis in UNX/DOCA-salt mice. (A) Albumin-to-creatinine ratio at 1 week before, and 2 and 4 weeks after uninephrectomy and DOCA treatment demonstrate significantly more albuminuria in podoRac1−/− mice than Rac1 fl/fl control mice. (B) UNX/DOCA-salt treated podoRac1−/− demonstrates twice the glomerulosclerosis than Rac1 fl/fl control mice. Sham treated mice of both genotypes showed no glomerulosclerosis (data not shown). (C and D) Representative PAS stained glomerulus at 20× and 40× magnification from UNX/DOCA-salt treated podoRac1−/− mouse demonstrating segmental sclerosis. *P<0.05, #P=0.19
Mentions: UNX/DOCA-salt treated mice of either group displayed elevated albuminuria at 2 and 4 weeks, however, urine albumin in UNX/DOCA-salt treated podoRac1−/− mice was nearly twice that of Rac1-fl/fl at 2 weeks (P<0.05) and 4 weeks (Figure 9A), although the difference was not significant at the latter time point (P=0.19). The percentage of glomeruli with segmental and global sclerosis was likewise doubled in treated podoRac1−/− mice at 4 weeks versus treated controls, (Figure 9, B-D) indicating an exacerbation of podocyte injury, rather than protection, in podoRac1−/− mice. Though increased in frequency, the morphologic appearance of segmental sclerosis in UNX/DOCA-salt treated podoRac1−/− mice was indistinguishable from Rac1-fl/fl controls. A qualitative ultrastructural examination by TEM revealed focal and segmental podocyte foot process effacement in both UNX/DOCA-salt treated podoRac1−/− and Rac1-fl/fl mice (Figure 10, A and B, and Supplementary Figure 1), which is consistent with the focal nature of effacement in glomerular hyperfiltration injury akin to secondary focal segmental glomerulosclerosis (FSGS), such as seen in hypertensive or obese humans.12 Interestingly, we observed focal foot process effacement in UNX/DOCA-salt treated podoRac1−/−mice, indicating that Rac1-independent mechanisms of effacement exist.

Bottom Line: Here, we employed podocyte-specific Cre-lox technology and found that mice with deletion of Rac1 display normal podocyte morphology without glomerular dysfunction well into adulthood.Cdc42 is necessary for the maintenance of podocyte structure and function, but Rac1 is entirely dispensable in physiological steady state.However, Rac1 has either beneficial or deleterious effects depending on the context of podocyte impairment.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Division of Nephrology, University of Michigan, Ann Arbor, Michigan, USA.

ABSTRACT
Podocytes are highly specialized epithelial cells with complex actin cytoskeletal architecture crucial for maintenance of the glomerular filtration barrier. The mammalian Rho GTPases Rac1 and Cdc42 are molecular switches that control many cellular processes, but are best known for their roles in the regulation of actin cytoskeleton dynamics. Here, we employed podocyte-specific Cre-lox technology and found that mice with deletion of Rac1 display normal podocyte morphology without glomerular dysfunction well into adulthood. Using the protamine sulfate model of acute podocyte injury, podocyte-specific deletion of Rac1 prevented foot process effacement. In a long-term model of chronic hypertensive glomerular damage, however, loss of Rac1 led to an exacerbation of albuminuria and glomerulosclerosis. In contrast, mice with podocyte-specific deletion of Cdc42 had severe proteinuria, podocyte foot process effacement, and glomerulosclerosis beginning as early as 10 days of age. In addition, slit diaphragm proteins nephrin and podocin were redistributed, and cofilin was dephosphorylated. Cdc42 is necessary for the maintenance of podocyte structure and function, but Rac1 is entirely dispensable in physiological steady state. However, Rac1 has either beneficial or deleterious effects depending on the context of podocyte impairment. Thus, our study highlights the divergent roles of Rac1 and Cdc42 function in podocyte maintenance and injury.

Show MeSH
Related in: MedlinePlus