At the early stage of diabetes, the GFR becomes supernormal. This early hemodynamic phenotype provokes the subsequent demise of a diabetic kidney. The diabetic hyperfiltration is derived from a combined decreased responsiveness of both the renal afferent arterioles and the MCs to vasoconstrictors. Reduced Ca2+ influx is a critical contributing factor to the hypocontractility of MCs in diabetes. However, the underlying mechanism(s) are still poorly understood. Furthermore, emerging evidence implicates NADPH oxidases-, particularly Nox4-derived ROS in the development of diabetic nephropathy. However, the underlying mechanism and downstream signaling pathway are at a large extent unknown. This proposal seeks to test the hypothesis that TRPC6 protein, a newly found Ca2+ permeable channel protein, contributes to the contractile function of MCs and downregulation of the protein in MCs by NADPH oxidases-mediated ROS results in diabetic hyperfiltration.
Three specific aims will be tested. (1) Determine whether TRPC6 regulates contractile function and Ca2+ signaling of glomerular MCs in in vitro, ex vivo, and in vivo systems. (2) Explore the postulate that ROS mediate downregulation of TRPC6 protein expression in glomerular MCs by diabetes in an in vitro (cultured MCs) and in vivo animal model. (3) Determine the source of ROS, focusing on NADPH oxidases, and the molecules downstream ROS, focusing on NF-?B, in the signaling pathway of TRPC6 downregulation by diabetes. The information obtained from this novel study will advance our current understanding of the molecular mechanism for the development of diabetic nephropathy, and therefore provides a rationale for drug design and clinical treatment of diabetes by intervening in the proposed pathway. In addition, TRPC6 has been found to play an important role in a variety of cell types. However, regulation of TRPC6 channel, particularly at gene transcriptional level, is unknown currently. The proposed studies will tackle this important issue by investigating if ROS repress TRPC6 gene transcription through the NF-?B mechanism. Thus, this project is of interest to both ROS and TRPC6 fields.
The proposed study is to test the hypothesis that a decrease in expression level of TRPC6 channel protein leads to the diabetic hyperfiltration at early stage of Diabetes. We further propose that a reactive oxygen species-involved signaling pathway mediates the decrease in TRPC6 protein in diabetes.
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