Smith, Leslie A

Sirtuin-6 (SIRT6) is a protein deacetylase that functions in several pathways related to aging, as complete loss of SIRT6 in mice elicits multiple age-associated phenotypes and premature death. While increasing age is a major risk factor for development of calcific aortic valve disease (CAVD), it is unclear whether loss of SIRT6 accelerates aortic valve calcification. Here, we report the role of SIRT6 in a subset of aortic valve interstitial cell progenitors (neural crest-derived VICs) by crossing mice carrying Cre recombinase under the control of a PAX3 promoter with mice harboring a SIRT6 gene that can be conditionally inactivated (SIRT6 FL/+ ). We hypothesized that tissue-specific reductions of SIRT6 would increase calcification, increase pro-osteogenic signaling, and impair aortic valve function. We examined mice of the genotypes Cre-/SIRT6 FL/+ or Cre+/ SIRT6 FL/+ at two different time points: young (3 months) and old (14-24 months). First, we used qRT-PCR to demonstrate that SIRT6 was effectively reduced in the aortic valve from PAX3-cre/SIRT6 FL/FL mice. Although reductions in SIRT6 did not change aortic valve calcium (Alizarin Red) in young mice, reducing SIRT6 increased valvular calcium levels in old mice compared to their WT littermates. Interestingly, protein levels of osterix were substantially increased in young, SIRT6-deficient mice compared to WT littermates but were paradoxically decreased in old SIRT6-deficient mice. Regardless of age, histopathological, or molecular changes, we did not observe detectable changes in cusp separation distance at any time point. Collectively, these data suggest that, contrary to our hypothesis, depletion of SIRT6 in neural crest cells—which are key progenitors of valve interstitial cells—is not sufficient to impair aortic valve function. Importantly, this finding suggests that age-associated reductions in SIRT6 may be a permissive context for development of CAVD but relies heavily on the presence of additional risk factors.