Vascular and Endothelial Biology of Aging

Although aging is one of the greatest risk factors for vascular disease, very little is known regarding mechanisms that control the progression of vascular aging at the level of the endothelial cell. Endothelial dysfunction - a critical element of carotid artery and cerebrovascular disease - progresses with age, contributing to hypoperfusion, increased risk for ischemic stroke, and cognitive decline. Studies from several laboratories support the concept that age-induced endothelial dysfunction may occur earlier and be larger in magnitude in the cerebral circulation than in blood vessels outside of the brain. Thus, the circulation of the brain may be particularly sensitive to age-induced endothelial dysfunction. In relation to underlying mechanisms, angiotensin II type 1 receptors, NADPH oxidase, and oxidative stress appear to play a key role in age-related vascular dysfunction. The nuclear receptor peroxisome proliferator-activated receptor-g (PPARg) exerts protective effects in the vasculature when pharmacologically activated. We recently examined the hypothesis that endothelial PPARg protects against vascular aging. We studied carotid arteries from adult and old transgenic mice with endothelial specific expression of a human dominant negative mutation in PPARg driven by the vascular cadherin promoter (designated E-V290M), along with non-transgenic littermates. Endothelial function was similar in arteries from adult non-transgenic and E-V290M mice as well as old non-transgenic mice. In contrast, there was a marked reduction in endothelial function in old E-V290M mice. This augmented endothelial dysfunction was not altered by inhibition of cyclooxygenase, but was restored to normal by a superoxide scavenger, an inhibitor of NADPH oxidase, or inhibition of Rho kinase. Oxidant and inflammatory related mechanisms often interact. Vascular expression of interleukin-6, another mediator of vascular disease, was increased 1.6-fold in old non-transgenic mice, but almost 9-fold in old E-V290M mice. Expression of CDKN2A, a molecular marker of senescence, was ~two-fold greater in old E-V290M mice compared to controls. These findings provide the first evidence that senescence and age-related vascular dysfunction is accelerated following cell-specific interference with endothelial PPARg through mechanisms that involve oxidative stress, inflammation, and Rho kinase. This critical role for endothelial PPARg has implications for vascular pathophysiology as well as therapeutic approaches for age-induced large and small vessel disease.