Increased pulse pressure due to age-related vascular stiffening is a dominant risk factor for cardiovascular morbidity and mortality. However, pulsatility also occurs with exercise at all ages, reduces vascular tone and can benefit organ perfusion. This proposal advances the novel hypothesis that reduced wall compliance can itself markedly alter endothelial mechano- signaling to pulse perfusion; switching off cascades more favorable to the vasculature while turning on signaling that contributes to cardiovascular risk. To support this is preliminary data showing Akt, a kinase associated with beneficial endothelial responses, is markedly activated when endothelial cells are exposed to pulse flow and stretch, but that this is prevented if tube compliance is low, suggesting that a decrease in vessel compliance may be responsible for the vascular risk associated with increased pulse pressure in the elderly. Using a unique computer-servo-apparatus in which endothelial cells cultured within distensible or stiff tubes are exposed to pulse perfusion, signaling mechanisms by which conduit distensibility influences endothelial physiology will be elucidated. The effect of conduit compliance on changes in FAK, c-Src, ERKs, JNKs, NF-KB, PI-3K, Akt, and rac1 will be studied. The role of these changes in mediating normal and abnormal endothelial function will be determined by measuring physiologic endpoints including endothelial cell migration, proliferation and apoptosis, and endothelial-leukocyte adhesion. By also examining these physiologic endpoints in senescent endothelial cells, this proposal will also determine if compliance can act as a mitigating factor for endothelial dysfunction seen in aged vessels. Finally, possible interactions and feedback that occur between beneficial (Akt-induced NO synthesis) and harmful (rac1- induced oxidative stress) signaling, that may account for differences in endothelial physiology seen in compliant and non- compliant tubes will be explored. The novel hypotheses presented in this proposal, and the unique tools to test them, promise to significantly advance current understanding of how structural properties of a vessel can influence endothelial cell responses to hemodynamic forces. Elucidation of these mechanisms should clarify the dichotomous effects of pulse perfusion and pulse pressure on vascular tone and risk, and help guide towards new therapies to offset the effects of vascular stiffening in the elderly.