Role of Autophagy in Age-Related Vascular Dysfunction

Advancing age is the major risk factor for cardiovascular diseases (CVD), primarily because aging results in the development of vascular endothelial dysfunction and stiffening of large elastic arteries. Both vascular endothelial dysfunction and arterial stiffening are associated with increased oxidative stress and inflammation, but the underlying mechanisms are incompletely understood. Autophagy(definition), the cellular process of degrading damaged macromolecules/organelles, inhibits oxidative stress and inflammation. Thus, the goal of this dissertation was to determine the role of autophagy in age-related vascular endothelial dysfunction and arterial stiffening, and to establish the efficacy of autophagy-enhancing interventions for restoring/improving function. In arteries of older humans and mice, expression of autophagy markers was impaired by ~40% and was associated with vascular endothelial dysfunction, indicated by an ~25% reduction in endothelium-dependent dilation (EDD). Impaired EDD was mediated by reduced nitric oxide (NO) bioavailability, and was associated with increased oxidative stress and inflammation. In old mice, treatment with the autophagy-enhancing agent trehalose restored expression of autophagy markers and rescued NO-mediated EDD by reducing oxidative stress and inflammation. In cultured endothelial cells, autophagy inhibition increased oxidative stress and reduced NO, whereas trehalose enhanced NO via an autophagy- dependent mechanism. In mice, aging was also associated with impaired expression of mitochondrial autophagy (mitophagy) mediators, greater activation of the mitochondrial redox/dysfunction sensor p66shc and increased arterial stiffness, indicated by ~25% higher aortic pulse wave velocity (aPWV). Trehalose restored mitophagy mediators, reduced p66shc activation and normalized aPWV in old mice. In aortic rings studied in vitro, mitochondrial dysfunction(definition) increased p66shc activation and mechanical stiffness; co-incubation with trehalose prevented these effects. The autophagy-enhancer spermidine had similar effects on aPWV and EDD with aging. In old mice, spermidine supplementation normalized aPWV, restored NO- mediated EDD and reduced indices of arterial oxidative stress, including superoxide production and nitrotyrosine levels. These effects of spermidine were associated with enhanced arterial expression of autophagy markers. Collectively, these results indicate that autophagy is impaired with aging in vascular tissues. These findings also suggest that autophagy/mitophagy preserves vascular endothelial function and prevents arterial stiffening with age. Autophagy- enhancing strategies may therefore have therapeutic efficacy for ameliorating age- associated arterial dysfunction and preventing CVD.