Altered arterial smooth muscle in cerebrovascular dysfunction during aging: remodeling of adhesion molecules - Cerebral small vessel disease (CSVD) could be caused by resistance artery narrowing, small cerebral artery embolism, capillary rarefaction and other etiologies. The prevalence of CSVD increases significantly with aging, and accounts for 25% of ischemic stroke and 45% of dementia, with hypertension being the preeminent risk factor. Mechanistically, an exaggerated myogenic response (vasoconstriction to increased pressure) and endothelial dysfunction are major causes of excessive resistance artery narrowing. Our preliminary data on rat supracerebellar artery (SCA) suggested that under steady-state myogenic vessel tone, the phosphorylated myosin light chain (pMLC) polarized to the outer layer smooth muscle cells (VSMC). This novel observation suggested a previously unknown signaling mechanism that drives MLC phosphorylation predominantly in the outer VSMC layers of the vessel wall, which subsequently maintains the SCA myogenic tone. Cell adhesion molecules, both integrin α5β1 and N-cadherin, are capable of mediating mechanical force-induced VSMC contraction. Preliminary data has suggested that, similar to pMLC, the clustering of N-cadherin peaked in the outer layer VSMC of SCA, and its expression increases in SCAs of spontaneous hypertensive rats, while increased integrin α5β1 expression was also reported in experimental hypertension. These results lead us to hypothesize that the transmural MLC phosphorylation gradient is at least in-part regulated by vessel wall tension through integrin α5β1− and N-cadherin-mediated mechanotransduction, and augmentation of these molecules inappropriately increases cerebral artery myogenic tone during aging combined with experimental hypertension. As a corollary, alterations in cellular adhesion and remodeling may contribute to cerebrovascular dysfunction and ultimately sequelae such as a decline in cognitive function. We will compare between young and aged groups of a genetic hypertensive rat model (SHR vs. WKY). A multi-level experimental approach will be employed, using pressurized blood vessels and isolated VSMCs along with confocal/super-resolution microscopy, immunofluorescence, and atomic force microscopy (AFM), to test these specific aims: Aim1: Demonstrate that comorbid aging and hypertension increases the recruitment of integrin α5β1 and N-cadherin to the outer VSMC layers in cerebral arteries; Aim2: Demonstrate that VSMCs isolated from aged and hypertensive animal show increased mechanically-activated contractile signaling mediated through integrin α5β1 and N-cadherin; and Aim3: Determine the effects of inhibiting integrin α5β1 and N-cadherin on the cognitive function of aged and hypertensive animals. These studies will establish the basic biology of cellular remodeling involved in the maintenance of myogenic tone in cerebral small arteries in association with aging and hypertension, and will potentially provide targets for the development of novel therapeutic approaches directed at reducing excessive cerebral vessel myogenic responsiveness.
