Progressive chronic renal disease is a major public health problem. The glomerulosclerosis observed in several models of chronic renal failure is attributed in part to increased cellular proliferation, hypertrophy, and extracellular matrix production. Distal components (angiotensin II and aldosterone) of the renin-angiotensin aldosterone system (RAAS) are major contributants to the progression of chronic renal failure. Although angiotensin II and aldosterone can exert effects on systemic and intraglomerular hemodynamics, emerging evidence suggests that each may have direct cellular effects mediated in part through growth factor signaling pathways. Both plasma membrane receptor related signal transduction and traditional nuclear signaling events are possible mechanisms by which growth may be induced. However, specific downstream cellular and subcellular modulators which respond to plasma membrane signals and that result in unabated growth, matrix production, and ultimately glomerulosclerosis remain poorly defined. Hypothesis and Goals: Demonstrate that aldosterone acts as a mesangial cell growth factor (inducing cellular growth and matrix production) by two mechanisms: 1) activation of non-genomic plasma membrane receptor cell signaling pathways and 2) by classical ligand-receptor translocation to the nucleus.
Specific Aim 1 : To determine whether aldosterone mediated effects on growth and matrix production occur through non-genomic cell surface receptor signaling events that increase the generation of the growth factor TGF-beta. Specifically, they will determine: 1) whether aldosterone increases mesangial cell TGF-beta message, protein, and bioactivity; 2) whether TGF-beta message protein and bioactivity can be blocked by chemical inhibitors of growth associated molecules; 3) whether TGF-beta message protein and bioactivity can be blocked by dominant-negative mutants of growth associated molecules; and 4) whether the aldosterone-induced signaling cascade can be mimicked by activated mutants of growth associated signaling molecules.
Specific Aim 2 : Determine the pathways through which aldosterone increases TGF-beta and regulates mesangial cell proliferation and matrix production. Methodologies to be used include cell culture, studies of cell proliferation and matrix production, transcription activities, production of dominant negative mutants, transient transfection and fluorescence activated cell sorting. The studies will define pathways that can be targeted to slow the progression of chronic renal failure.
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