Podocyte Cell Cycle Regulation after DNA Damage

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Project Summary/Abstract The comprehensive term “podocytopathy” represents a poorly defined diagnostic entity, which includes a wide spectrum of histologic patterns of glomerular disease, all characterized by structural changes to the glomerular filter and proteinuria. Current pathomechanistic insights into this diverse group of diseases are limited, and, with the exception of few promising studies, have not provided substantial therapeutic guidance. Pathologically, podocyte loss remains the single unifying observation and closely correlates with disease progression. Podocyte death has recently gained acceptance as a key pathway to podocyte loss, although the molecular mechanisms remain elusive. Hic-5, a member of the LIM domain family of proteins, is increased in podocytes along the glomerular filtration barrier in human podocytopathies. Distinct from a pure function as a focal adhesion protein, our novel preliminary data suggest a pro-survival role for hic-5 in podocytes following injurious events. Specifically, our findings indicate that hic-5 protects podocytes from cell death by mediating cell cycle control through stabilization of p21 after genotoxic stress in vitro and in vivo, thereby maintaining the structural integrity of the glomerular filtration barrier, ameliorating proteinuria and preventing glomerular scarring. The overarching goal of this proposal is to elucidate the pro-survival role of hic-5 following podocyte injury by studying its effect on cell cycle checkpoint control. Specifically, we aim to: 1) Define on a molecular level how hic-5 mediates changes in the podocyte cell cycle after DNA damage by using a podocyte cell line in vitro and murine Adriamycin nephropathy as a model of genotoxic glomerular injury in vivo; and 2) Examine whether the presence of hic-5 in podocyte foot processes results in the activation of a pro-survival signature in podocytopathies in vivo by use of an innovative super-resolution immunofluorescence microscopy technique to validate our findings in human disease. Understanding the role of hic-5 in preventing podocyte loss by regulating the podocyte cell cycle may guide our efforts to discover pathways to nephron loss, identify prognostic biomarkers and develop targeted podocyte-specific therapies for proteinuric kidney diseases.