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Published on: September 1, 2015
Podocyte-specific loss of Cdc42 leads to congenital nephropathy
Rizaldy P Scott1, Steve P Hawley, Julie Ruston
1Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
Abstract:
Rho family GTPases are molecular switches best known for their pivotal role in dynamic regulation of the actin cytoskeleton. The prototypic members of this family are Cdc42, Rac1, and RhoA; these GTPases contribute to the breakdown of glomerular filtration and the resultant proteinuria, but their functions in normal podocyte physiology remain poorly understood. Here, mice lacking Cdc42 in podocytes developed congenital nephropathy and died as a result of renal failure within 2 weeks after birth. In contrast, mice lacking Rac1 or RhoA in podocytes were overtly normal and lived to adulthood. Kidneys from Cdc42-mutant mice exhibited protein-filled microcysts with hallmarks of collapsing glomerulopathy, as well as extensive effacement of podocyte foot processes with abnormal junctional complexes. Furthermore, we observed aberrant expression of several podocyte markers and cell polarity proteins in the absence of Cdc42, indicating a disruption of the slit diaphragm. Kidneys from Rac1- and RhoA-mutant mice, however, had normal glomerular morphology and intact foot processes. A nephrin clustering assay suggested that Cdc42 deficiency, but not Rac1 or RhoA deficiency, impairs the polymerization of actin at sites of nephrin aggregates. Taken together, these data highlight the physiological importance of Cdc42, but not Rac1 or RhoA, in establishing podocyte architecture and glomerular function.
Insights
Cellular Cdc42 (cell division cycle 42) is crucial for kidney podocyte function and glomerular filtration. Its absence causes severe congenital nephropathy, unlike Rac1 or RhoA, highlighting Cdc42
Area of Science:
- Nephrology
- Cell Biology
- Molecular Biology
Background:
- Rho family GTPases, including Cdc42, Rac1, and RhoA, regulate the actin cytoskeleton.
- Their roles in normal podocyte physiology and glomerular filtration are not fully understood.
- These GTPases are implicated in glomerular filtration breakdown and proteinuria.
Purpose of the Study:
- To investigate the specific functions of Cdc42, Rac1, and RhoA in podocyte physiology.
- To determine the impact of these GTPases on podocyte structure and glomerular function.
- To elucidate the role of Cdc42 in maintaining the slit diaphragm and podocyte architecture.
Main Methods:
- Generation of podocyte-specific knockout mice for Cdc42, Rac1, and RhoA.
- Histological examination of kidney tissues to assess glomerular morphology and podocyte structure.
- Analysis of podocyte marker and cell polarity protein expression.
- Nephrin clustering assay to evaluate actin polymerization dynamics.
Main Results:
- Mice lacking Cdc42 in podocytes developed congenital nephropathy and died within two weeks.
- Cdc42-deficient kidneys showed collapsing glomerulopathy, effaced foot processes, and disrupted slit diaphragms.
- Mice lacking Rac1 or RhoA in podocytes were phenotypically normal with intact glomerular structure.
- Cdc42 deficiency impaired actin polymerization at nephrin aggregates, unlike Rac1 or RhoA deficiency.
Conclusions:
- Cdc42 is essential for podocyte architecture and glomerular function.
- Rac1 and RhoA are not critical for normal podocyte physiology.
- Cdc42 plays a vital role in maintaining the integrity of the slit diaphragm and podocyte filtration barrier.
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