Mechanisms and Consequences of Calcification in Aortic Valvular Stenosis

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Studies during the current period of funding have focused on cardiovascular effects of oxidative stress. The investigators observed oxidative stress in the aortic valve of "Reversa" (ldl"'7apoB^��'^��/Mttp'""/Mx1- Cre**) mice, and found that 1/3 ofthe mice develop moderately severe calcific aortic valvular stenosis (CAVS). The investigators now propose to test the hypotheses that 1) local and humoral mechanisms associated with oxidative stress and infiammation contribute to development of CAVS, and 2) mechanisms that reduce oxidative stress and infiammation inhibit development and progression of CAVS. A medical intervention to slow the progression of CAVS would be of great value. The invesfigators have demonstrated, with published and preliminary data, that two approaches can suppress signaling in the osteogenic pathway and reduce calcification of the aortic valve. Pharmacological interventions and complementary genetically altered mice will be used to examine mechanisms that may contribute to CAVS. The investigators will measure gene expression in aortic valves of mice, and function of the valve. One goal is to detennine whether osteoprotegerin (OPG), an endogenous decoy receptor of receptor- activator of NFKB ligand (RANKL), decreases expression of osteogenic genes, reduces calcification of the valve, and slows progression of aortic stenosis in mice with moderate aortic stenosis. Studies also are proposed to test the hypothesis that OPG deficiency (OPG"'' mice) accelerates CAVS. The second goal is to determine whether two interacting endogenous systems, renin-angiotensin and PPARy, modulate development of CAVS. One hypothesis is that ATI receptors contribute to development of CAVS. Studies are planned to determine whether an antagonist of ATI receptors (but not an angiotensin- converting enzyme inhibitor) decreases expression of osteogenic genes and inhibits development of CAVS in Reversa mice. Studies also are planned to test the hypothesis that susceptibility to CAVS is reduced in ATlr"'' mice. Finally, studies are planned to test the hypotheses that pioglitazone (a PPARy ligand) protects against development of CAVS in Reversa mice and, in endothelium-targeted dominant negative PPARy mice (E-V290M), susceptibility to CAVS is increased. The goal of this project is to use an experimental model of CAVS with hemodynamically significant stenosis to clarify molecular mechanisms of CAVS, functional consequences of calcification, and to explore possible therapeutic approaches. RELEVANCE (See instructions): Calcific aortic valve stenosis (CAVS) is a common clinical problem, and is the second most common indication for cardiac surgery. These studies will determine whether three novel therapeutic interventions may slow, or reverse, the progression of CAVS. If any one of these approaches proves to be effective in slowing progression of CAVS, it could lead to clinical studies that fundamentally alter clinical treatment of CAVS.