Diabetic nephropathy is a common complication of diabetes mellitus types 1 and 2. Prevention of chronic renal failure is one of the most important challenges in medicine for nephrologists and nephrology researchers, Diabetic nephropathy is characterized by changes in the structure of glomerular basement membranes, and progressive expansion of the mesangial matrix. Glomerular mesangial cells are considered to be modified pericyte-like cells (perivascular cells) that envelope most small and large blood vessels. NG2, a cell surface chondroitin sulfate proteoglycan is a specific marker for pericytes and specifically expresses in mesangial cells of the human and mouse kidneys when compared to other cell types of the glomeruli, Our preliminary studies suggest that NG2 expression increases in the mouse models of diabetic nephropathy. Such increase in NG2 expression directly correlates with an increased proliferation of mesangial cells and production of extracellular matrix in the glomeruli of mice with hyperglycemia induced by streptozotocin (STZ). Utilizing novel NG2 specific mouse transgenic reagents, our aim one in this grant application proposes to study the contribution of NG2 positive mesangial cells in the initiation and progression of diabetic nephropathy.
Our second aim i s to gain mechanistic insights into the progression of this disease by deleting TGF-? regulated signaling molecules in NG2 positive mesangial cells. To achieve aim one, we will induce diabetic nephropathy by multiple low dose injection of STZ in transgenic mice in which mesangial cells are transgenically tagged with yellow fluorescent protein or viral thymidine kinase (to ablate proliferating mesangial cells at specific time points using ganciclovir) and evaluate the functional contribution of NG2 to early phases of diabetic nephropathy. Additionally, NG2 positive mesangial cells from both diabetic and control mice will be isolated by FACS sorting and their proliferation, migration, and ECM deposition properties will be investigated in the culture system, TGF-? is a key modulator of hyperglycemia induced mesangial cells acivity in diabetic nephropathy and thus to further gain mechanistic insight into this signaling axis, in our second aim we will specifically delete TGF-? receptor II and its downstream intracellular signaling modulator Smad4 in NG2 positive mesangial cells. We plan to achieve this by mating NG2-Cre mice with TGF-? Rll floxed and Smad4 floxed mice. STZ induced diabetes in these mice will determine the contribution of TGF-? signaling pathway in these novel mouse models. Collectively these studies will elucidate novel mechanisms associated with early diabetic nephropathy and open new avenues to explore therapies.
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