HNF4α and the Ca-channel TRPC1 are novel disease candidate genes in diabetic nephropathy

Abstract

OBJECTIVE-The nuclear receptor hepatic nuclear factor 4α (HNF4α) is a master regulatory protein and an essential player in the control of a wide range of metabolic processes. Dysfunction of HNF4α is associated with metabolic disorders including diabetes. We were particularly interested in investigating molecular causes associated with diabetic nephropathy. RESEARCH DESIGN AND METHODS-Novel disease candidate genes were identified by the chromatin immunoprecipita-tion-cloning assay and by sequencing of immunoprecipitated DNA. Expression of candidate genes was analyzed in kidney and liver of Zucker diabetic fatty (ZDF) and of streptozotocin (STZ)-administered rats and after siRNA-mediated silencing of HNF4α. RESULTS-We identified the calcium-permeable nonselective transient receptor potential cation channel, subfamily C, member 1(TRPC1) as a novel HNF4α gene target. Strikingly, TRPC1 is localized on human chromosome 3q22-24, i.e., a region considered to be a hotspot for diabetic nephropathy. We observed a significant reduction of TRPC1 gene expression in kidney and liver of diabetic ZDF and of STZ-administered rats as a result of HNF4α dysfunction. We found HNF4α and TRPC1 protein expression to be repressed in kidneys of diabetic patients diagnosed with nodular glomerulosceloris as evidenced by immunohistochemistry. Finally, siRNA-mediated functional knock down of HNF4α repressed TRPC1 gene expression in cell culture experiments. CONCLUSIONS-Taken collectively, results obtained from animal studies could be translated to human diabetic nephropathy; there is evidence for a common regulation of HNF4α and TRPC1 in human and rat kidney pathologies. We propose dysregulation of HNF4α and TRPC1 as a possible molecular rationale in diabetic nephropathy. © 2008 by the American Diabetes Association.