In diabetic nephropathy, renal failure is correlated with tubulointerstitial fibrosis as well as with glomerular mesangial expansion. The mechanisms mediating kidney damage undoubtedly stem from chronic hyperglycemia, but the intermediary steps are not completely understood. Studies of the effects of high glucose concentration in culture have demonstrated stimulation of extracellular matrix (ECM) biosynthesis and development of tubuloepithelial hypertrophy. High glucose levels increase TGF-beta1 mRNA and bioactivity in renal cells; moreover, neutralizing anti-TGF-beta and ECM production. Additionally, in vivo studies in streptozotocin-diabetic mice have linked the development of renal hypertrophy to increased expression of TGF-beta1 and the hype II TGF-beta antibodies attenuate kidney hypertrophy and the overexpression of mRNAs encoding collagen IV and fibronectin. This body of information underlies the rationale for embarking on the studies in this proposal which will test the hypothesis that the stimulatory effects of high ambient glucose on renal hypertrophy and ECM production are mediated by activation of particular PKC isoforms and are accompanied by up-regulation of the TGF-beta system in the kidney.
Specific Aim #1 will systematically examine the mechanisms whereby high glucose levels induce transcriptional activation of TGF-beta1 in proximal tubular cells and resident renal fibroblasts, including the identification of unique glucose-responsive cis-acting elements in the TGF-beta1 promoter.
Specific Aim #2 will explore the role of specific PKC isoforms which mediate the effects of high glucose and examine the link between increased high glucose concentration and the stimulation of TGF-beta1 expression, perhaps through transcriptional activation of AP1-like sites in the TGF-beta1 promoter.
In Specific Aim #3, corroborative in vivo studies will be performed to intercept the activity of renal TGF-beta by the long-term administration of neutralizing anti-TGF-beta antibodies to diabetic mice. These studies should provide a detailed mechanistic understanding of the untoward effects of hyperglycemia in diabetic nephropathy that may lead to novel therapeutic interventions even in the face of suboptimal glycemic control.
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