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HNF4 and the Ca-Channel TRPC1 Are Novel Disease Candidate Genes in Diabetic Nephropathy

¹ Fraunhofer Institute of Toxicology and Experimental Medicine, Center of Molecular Medicine and Medical Biotechnology, Hannover, Germany
² Center of Pharmacology and Toxicology, Medical School of Hannover, Hannover, Germany

Address correspondence and reprint requests to Prof. Dr. Jürgen Borlak, Fraunhofer Institute of Toxicology and Experimental Medicine, Center of Molecular Medicine and Medical Biotechnology, Nikolai-Fuchs-Str. 1, 30625 Hannover, Germany. E-mail: borlak{at}item.fraunhofer.de

Abbreviations: ChIP, chromatin immunoprecipitation; DAG, diacylglycerol; EMSA, electrophoretic mobility shift assay; HNF4, hepatic nuclear factor 4; HNF1pro, HNF1-promoter; IP₃, inositol-triphosphate; PKC, proteinkinase C; PLC, phospholipase C; PLCB1, β1 isoform of PLC; SOC, store operated channel; STZ, streptozotocin; TRPC1, transient receptor potential cation channel, subfamily C, member 1

OBJECTIVE—The nuclear receptor hepatic nuclear factor 4 (HNF4) is a master regulatory protein and an essential player in the control of a wide range of metabolic processes. Dysfunction of HNF4 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 immunoprecipitation–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 HNF4.

RESULTS—We identified the calcium-permeable nonselective transient receptor potential cation channel, subfamily C, member 1 (TRPC1) as a novel HNF4 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 HNF4 dysfunction. We found HNF4 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 HNF4 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 HNF4 and TRPC1 in human and rat kidney pathologies. We propose dysregulation of HNF4 and TRPC1 as a possible molecular rationale in diabetic nephropathy.

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