Abnormalities in renal cell proliferation and extracellular matrix accumulation are causal factors of diabetic nephropathy. The long-term objective of our research is to elucidate the molecular signaling mechanisms that regulate renal cell proliferation and extracellular matrix deposition. Fibronectin (Fn) is an important component of renal extracellular matrices. Fibronectin matrix deposition is initiated by specific Fn binding integrins, and the matrix deposition process can be regulated by signaling pathways that control the integrin activities. Integrin-linked kinase, a serine/threonine kinase implicated in integrin signaling, is involved in the regulation of Fn matrix deposition and cell proliferation. Overexpression of ILK in a model cell system stimulated Fn matrix deposition. Moreover, ILK expression in mesangial cells was increased in response to angiotensin II and high glucose. Integrin-linked kinase is potentially linked to the IRS-1 signaling pathways via interactions mediated by the LIM protein PINCH and a novel SH2/SH3 containing protein that is homologous to Nck (designated as Nck-2). This research project is designed to critically evaluate the role of ILK signaling in regulating renal cell proliferation and Fn matrix deposition. First, ILK will be over-expressed in mesangial cells by DNA transfer methods and its effect on integrin activation and Fn matrix deposition will be determined. Second, the interactions between ILK, PINCH, Nck-2 and IRS-1 will be analyzed in vitro and in cells, and reagents that inhibit the specific interactions will be generated. Finally, the functional significance of the specific protein-protein interactions in renal Fn matrix deposition and cell proliferation will be determined by introducing the inhibitory reagents into renal mesangial and interstitial fibroblastic cells. The proposed studies will elucidate the role of the ILK signaling pathway in regulation of renal cell proliferation and Fn matrix deposition, and may potentially translate into novel therapeutic approaches to control matrix deposition and cell proliferation and, consequently, the outcome of diabetic nephropathy.
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