PKA AND IP3R BY TGFB IN DIABETIC KIDNEY DISEASE

Thomas Jefferson University, Philadelphia PA

Investigators

Linked publications & trials

Abstract

DESCRIPTION (Adapted from Investigator's Abstract): Transforming growth factor-beta (TGF-beta) has been recently recognized to be a pivotal factor in mediating excessive matrix deposition in many disease states, including diabetic nephropathy. Studies from this group have demonstrated that TGF-beta activity attenuates high glucose-induced matrix stimulation in mesangial cells in vitro, attenuates diabetes-induced matrix accumulation and glomerular hypertrophy in vivo, and in recent data attenuates progression of renal failure. Diabetic glomerular disease has been associated with mesangial matrix accumulation, altered intracellular calcium mobilization, and abnormal vascular regulation. As TGF-beta promotes matrix synthesis and regulates intracellular calcium in mesangial cells, this group postulates that TGF-beta plays an important role in both diabetes-induced matrix accumulation and altered glomerular vasoregulation. The intracellular signaling pathways employed by TGF-beta in mesangial cells which underlie these effects are the focus of the current application. Several candidate pathways have been found to be stimulated by TGF-beta, the best characterized being the Smad pathway; however the relationship of the Smad pathway to matrix stimulation has not been established. Recent studies by this group have demonstrated that TGF-beta stimulates protein kinase A (PKA) activity in mesangial cells without raising intracellular cyclic AMP levels. The precise mechanisms of TGF-beta induced stimulation of PKA will be established. Dr. Sharma will also examine whether TGF-beta induced PKA activation and Smad activation are of importance in stimulating extracellular matrix molecules. One consequence of TGF- beta-induced PKA activation appears to be phosphorylation and down-regulation of the type I inositol 1.4.5-trisphosphate receptor (IP3R), the IP3, gated intracellular calcium channel. Additional studies have demonstrated that TGF-beta reduces protein expression of both types I and III IP3R isoforms. The mechanisms underlying TGF-beta induced regulation of the IP3Rs will be explored. The functional consequences of reduced IP3R expression in mesangial cells will be evaluated by measuring IP3 sensitivity and intracellular calcium mobilization in both intact and permeabilized cells. As TGF-beta is over-expressed by mesangial cells cultured in high glucose and in the glomeruli of diabetic rats, Dr. Sharma proposes to evaluate whether TGF-beta induced PKA activation and TGF-beta-induced IP3R regulation play important roles in diabetes-induced glomerular matrix production and altered reactivity of glomerular mesangial cells to vasoconstrictors in both in vitro and in vivo models. Understanding these pathways will lead to rational designs for interventional strategies to block specific TGF-beta-induced effects that contribute to the pathogenesis of diabetic nephropathy.