Functional analysis of the novel podocyte-specific gene R3hdml for renal aging and progressive renal disease
Final Report Abstract
Despite current medical advances, the development and progression of kidney diseases cannot be stopped and represents a socio-economic health problem worldwide. Our laboratory is interested in the function of podocytes, which are part of the glomerular filtration barrier and whose defect can be associated with numerous kidney diseases. They are only capable of regeneration to a limited extent and are sensitive to aging processes, reactive oxygen species and metabolites. As part of our investigations into the influences on the progression of kidney diseases, we were able to identify the serine protease inhibitor R3hdml in an RNA screen from mouse podocytes, which was expressed significantly less strongly than in young controls. Serine proteases and their inhibitors represent the most common and largest group of proteolytic enzymes and inhibitors involved in many biological processes. They influence the course of chronic kidney disease both positively and negatively. In in situ hybridizations on mouse embryos, we were able to detect R3hdml exclusively on the podocytes during early murine kidney development with the beginning of podocyte formation (E14.5) and not in any other organ at this point in time. We investigated different influences of cellular stressors in the mouse model of diabetic nephropathy and kidney aging and were able to detect significant changes in the expression and protein amount of R3hdml. In in vitro analyzes of immortalized podocytes, we were able to show that overexpression of R3hdml inhibits TGFβ-induced phosphorylation of p38 MAPK. In a mass spectroscopic analysis, we were able to identify potential interaction partners of R3hdml. Analogously, in vivo analyzes of our generated constitutive R3hdml-deficient mouse line confirmed that young R3hdml-deficient mice show a significantly increased amount of p38 MAPK phosphorylation in the renal cortex. R3hdml ablation leads to greater glomerulosclerosis in aging and greater tubular damage in mice associated with chronic kidney disease such as STZ-induced type I diabetes. Here we were able to observe noticeable significant inflammatory reactions, increased fibrosis and significantly retarded regeneration. In summary, the function of R3hdml as a serine protease inhibitor is reflected in a reduction in p38 MAPK phosphorylation. R3hdml thus seems to play a crucial role in the development of podocytes, in the maintenance of kidney function and in the regulation of progressive kidney diseases.
