Aging is associated with progressive increases in cardiovascular calcification1. Hemodynamically significant aortic valve stenosis affects 3% of the population over age 65. Patients with even moderate aortic valve stenosis (peak velocity of 3-4 m/sec) have a 5 year event-free survival of less than 40%, with the only approved treatment being valve replacement surgery. Recent work, however, described the presence of osteoblast-like cells, osteoclast-like cells, and bone matrix in calcified aortic valves, which suggests that valve calcification is an active, potentially modifiable process. Preliminary data from our group suggest that there are substantial epigenetic modifications present in cells from calcified aortic valves. Specifically, expression of sirtuin 6 is markedly reduced in stenotic valves and strongly associated with increases in protein and histone acetylation. Experimentally, global deletion of SIRT6 in mice results in a dramatic progeroid phenotype, and patients with progeroid syndromes have a much greater propensity for development of cardiovascular calcification. As many risk factors for valve calcification are associated with increases in oxidative stress, we also sought to determine whether there is a link between increases in oxidative stress and histone acetylation/sirtuin activity. Thus, the aims of the current application is to experimentall determine whether: 1) increases in oxidative stress increase histone acetylation and accelerate progression of aortic valve calcification and stenosis, 2) altering SIRT6 levels accelerates or slows progression of aortic valve stenosis in hypercholesterolemic mice, and 3) deletion of SIRT6 in vascular endothelium or neural crest-derived cells (i.e., cells that form the aortic valve and outflow tract) accelerate progression of CAVS. We will use a combination of novel in vivo animal models and in vitro methods to identify mechanisms whereby oxidative stress and SIRT6 impact osteoblast/osteoblast-like cell differentiation and activity in aortic valves. By using thes approaches to identify mechanisms that slow the progression of calcific aortic valve disease, we hope to identify therapies that will improve both the lifespan and health span of humans.
Calcium deposition in stenotic aortic valves is associated with increases in oxidative stress. We recently found that increased oxidative stress was associated with reduced sirtuin deacetylase expression and increased histone acetylation. Interestingly, mice deficient in SIRT6 have a profound progeroid phenotype. Whether increases in oxidative stress or reductions in SIRT6 accelerate development of aortic valve calcification and stenosis, however, is unknown. This proposal uses novel mouse models to examine the effects of: 1) global catalase deficiency or overexpression on histone acetylation, gene expression, and aortic valve function in hypercholesterolemic mice in vivo, 2) global SIRT6 deficiency or overexpression on histone acetylation, gene expression, and aortic valve function in hypercholesterolemic mice in vivo, and 3) tissue specific deletion of SIRT6 in endothelium (Tie2-Cre) or interstitial cells (Pax3-Cre;targets neural crest cells during development) histone acetylation, gene expression, and aortic valve function in vivo. Collectively, we anticipate the information gleaned from these studies will not only identify SIRT6 as a novel regulator of aortic valve function in mice, but will also contribute to development of innovative therapies that will attenuated age-related aortic valve dysfunction and associated cardiovascular morbidity and mortality in humans.
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