Rac1 Activation in Podocytes Induces Rapid Foot Process Effacement and Proteinuria

Abstract

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 complex podocyte forms the final cellular barrier to filtration. Injury to the podocyte results in a morphological change called foot process effacement, which is a ubiquitous feature of proteinuric diseases. The exact mechanism underlying foot process effacement is not known, but recently it has been proposed that this change might reflect activation of the Rac1 GTPase. To test this hypothesis, we generated a podocyte-specific, inducible transgenic mouse line that expressed constitutively active Rac1. When the Rac1 transgene was induced, we observed a rapid onset of proteinuria with focal foot process effacement. Using superresolution imaging, we verified that the induced transgene was expressed in damaged podocytes with altered foot process morphology. This work sheds new light on the complex balance of Rho GTPase signaling that is required for proper regulation of the podocyte cytoskeleton.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00730-13.

ACKNOWLEDGMENTS

We are grateful for the help of Jacqueline Mudd from the Murine Embryonic Stem Cell Core of the Siteman Cancer Center in generating the recombinant embryonic stem cells. We thank Michael White from the Transgenic Knockout Microinjection Core of the Department of Pathology and Immunology for technical assistance in generating the chimeric mice and Jaclynn Lett for EM sample preparation and assistance with imaging (Microscopy and Digital Imaging Core in the Research Center for Auditory and Visual Studies, Department of Otolaryngology, Washington University School of Medicine; funded by NIH grant P30DC004665). We appreciate Rudolf Jaenisch for sharing the KH2 ES cell line and Takako Sasaki for providing the laminin β2 antiserum. We also thank Jiancheng Hu for reagents and helpful discussions.

This research was supported by the Howard Hughes Medical Institute and NIH grant R01DK058366 to A. S. Shaw and by NIH grant R21DK095419 to J. H. Miner.

We declare no conflict of interest.