Cardiovascular and Cerebrovascular Aging–New Mechanisms and Insights: Resveratrol treatment rescues neurovascular coupling in aged mice: role of improved cerebromicrovascular endothelial function and downregulation of NADPH oxidase

normal brain function is critically dependent on a continuous, tightly controlled supply of oxygen and glucose through cerebral blood flow (CBF). Although energetic demands of neurons are very high, the brain has very little reserve capacity. During periods of intense neuronal activity, there is a requirement for rapid increases in oxygen and glucose delivery. This is ensured by neurovascular coupling, a vital mechanism of regulation of CBF that maintains optimal microenvironment of cerebral tissue by adjusting local blood flow to local neuronal activity (3). Since higher processes in the brain occur almost instantly, moment-to-moment adjustment of CBF via neurovascular coupling is essential for the maintenance of normal neuronal function. There is strong evidence that neurovascular coupling is impaired in the elderly (12, 40, 43, 53), which likely contributes to a significant age-related decline in higher cortical function, including cognition (38) and gait coordination (39). Thus therapeutic interventions that improve neurovascular coupling in elderly patients have the potential to improve a range of age-related neurological deficits. Neurovascular coupling and cerebral functional hyperemia depend on a coordinated interaction of activated neurons, astrocytes, and vascular endothelial and smooth muscle cells. Transduction of signals from neurons and astrocytes initiate regional vasodilation in the cerebral microcirculation, which involve production and release of nitric oxide (NO) by microvascular endothelial cells (14, 41, 55). Previous studies demonstrate that aging is associated with an increased production of NADPH oxidase-derived reactive oxygen species (ROS) in the cerebral microvasculature, which contribute to compromised neurovascular coupling in aged mice (28), likely by decreasing bioavailability of NO and promoting endothelial dysfunction (13, 28, 43, 53). On the basis of the aforementioned findings it is logical to hypothesize that pharmacological treatments that improve endothelial function will have the capacity to improve neurovascular coupling in aged individuals. Recent studies provide strong evidence that treatment of laboratory rodents with resveratrol (3,4′,5-trihydroxystilbene), a plant-derived polyphenolic compound, exerts significant endothelial protective effects in the aorta and vessels from the peripheral circulation both during aging and in pathophysiological conditions that are associated with accelerated vascular aging (31, 46, 50, 51, 57). Importantly, resveratrol was shown to increase bioavailability of endothelium-derived NO and inhibit NADPH oxidases in large vessels (31, 33, 54, 56, 57). Although resveratrol has been shown to exert beneficial effects on the age-dependent decline in cognitive function (26, 58), its potential protective effect on the aged cerebral microvasculature has not been investigated. The present study was designed to test the hypothesis that resveratrol treatment, similar to its documented vasoprotective effects in the aorta, can restore cerebromicrovascular endothelial function and thus improve neurovascular coupling in aged mice. To achieve this goal, aged mice were treated with resveratrol followed by tests for neurovascular coupling and cerebromicrovascular endothelial function. Markers of oxidative stress and expression of NADPH oxidase in the cerebral cortex were also assessed. To substantiate the in vivo findings, the effects of resveratrol on ROS production and expression of NADPH oxidase in activated cultured astrocytes and in cerebromicrovascular endothelial cells derived from aged animals were obtained in vitro.