Limits...
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.

Show MeSH

Related in: MedlinePlus

Total cofilin and phospho-cofilin (p-cofilin), the active and inactive states respectively, in isolated glomeruli from podoRac1−/−, podoCdc42−/−, and floxed control mice by Western and densitometry analysis. (A and C) Compared to all floxed controls, protein expression of p-cofilin/total cofilin in glomeruli from podoRac1−/− appear similar. In stark contrast, (B and D) podoCdc42−/− glomeruli display no appreciable p-cofilin, highlighting a significant imbalance in cofilin phosphorylation.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3815690&req=5

Figure 5: Total cofilin and phospho-cofilin (p-cofilin), the active and inactive states respectively, in isolated glomeruli from podoRac1−/−, podoCdc42−/−, and floxed control mice by Western and densitometry analysis. (A and C) Compared to all floxed controls, protein expression of p-cofilin/total cofilin in glomeruli from podoRac1−/− appear similar. In stark contrast, (B and D) podoCdc42−/− glomeruli display no appreciable p-cofilin, highlighting a significant imbalance in cofilin phosphorylation.

Mentions: Cofilin is a tightly regulated effector molecule for both Cdc42 and Rac1 that severs actin filaments and promotes disassembly which are essential for actin remodeling and productive membrane protrusions.8, 9 Cofilin inactivation occurs through phosphorylation by LIM kinases, which are activated by the PAK family of Rac/Cdc42-dependent kinases. Western blot analysis of phospho-cofilin to cofilin ratio from isolated glomeruli revealed a near total loss of phospho-cofilin in podoCdc42−/− mice compared to all floxed controls (0.005±0.005 versus 0.62±0.14, P<0.05), but no significant change in the phosphorylation status in podoRac1−/− mice (0.56±0.16 versus 0.62±0.14, P=0.78) (Figure 5). Thus loss of Cdc42 in podocytes results in a significant imbalance in cofilin activation.


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)

Total cofilin and phospho-cofilin (p-cofilin), the active and inactive states respectively, in isolated glomeruli from podoRac1−/−, podoCdc42−/−, and floxed control mice by Western and densitometry analysis. (A and C) Compared to all floxed controls, protein expression of p-cofilin/total cofilin in glomeruli from podoRac1−/− appear similar. In stark contrast, (B and D) podoCdc42−/− glomeruli display no appreciable p-cofilin, highlighting a significant imbalance in cofilin phosphorylation.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Total cofilin and phospho-cofilin (p-cofilin), the active and inactive states respectively, in isolated glomeruli from podoRac1−/−, podoCdc42−/−, and floxed control mice by Western and densitometry analysis. (A and C) Compared to all floxed controls, protein expression of p-cofilin/total cofilin in glomeruli from podoRac1−/− appear similar. In stark contrast, (B and D) podoCdc42−/− glomeruli display no appreciable p-cofilin, highlighting a significant imbalance in cofilin phosphorylation.
Mentions: Cofilin is a tightly regulated effector molecule for both Cdc42 and Rac1 that severs actin filaments and promotes disassembly which are essential for actin remodeling and productive membrane protrusions.8, 9 Cofilin inactivation occurs through phosphorylation by LIM kinases, which are activated by the PAK family of Rac/Cdc42-dependent kinases. Western blot analysis of phospho-cofilin to cofilin ratio from isolated glomeruli revealed a near total loss of phospho-cofilin in podoCdc42−/− mice compared to all floxed controls (0.005±0.005 versus 0.62±0.14, P<0.05), but no significant change in the phosphorylation status in podoRac1−/− mice (0.56±0.16 versus 0.62±0.14, P=0.78) (Figure 5). Thus loss of Cdc42 in podocytes results in a significant imbalance in cofilin activation.

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