Angiotensin-hypertension is a dominant risk factor for cerebral vascular degeneration and stroke, but underlying molecular mechanisms are incompletely understood. In the cerebral circulation, degenerative changes associated with a fibrogenic response are important for development of lipohyalinosis, which is found almost exclusively in cerebral vessels. Transforming growth factor beta1 (TGFbeta1), a key element in the fibrogenic response, is elevated in humans with hypertension, especially in African-Americans. In our preliminary studies, we have found that: (i) TGFbeta levels are increased in serum and in the walls of cerebral vessels in angiotensin II (Ang)-hypertensive rats (AHR); (ii) AHR is associated with oxidative endothelial injury (OEI), and OEI itself can lead to a fibrogenic response in VSMC in vivo; (iii) acute exposure to TGFbeta and chronic exposure to Ang cause """"""""nitrate tolerance"""""""", i.e., abrogates NO/cGMP-dependent protein kinase I (cGKI)-dependent effects on L-type calcium channels and on calcium-activated potassium (maxi-K) channels involved in vasorelaxation. In addition, we developed a powerful new technique to study signaling pathways in cerebral vascular smooth muscle cells (VSMC) in vivo, which makes use of chronic infusion of (unpackaged) antisense-oligodeoxynucleotides into cisterna magna for selective, targeted downregulation of key signaling molecules in VSMC of basilar artery. In this grant, we will use patch clamp and molecular techniques to pursue 3 specific aims: SA1: We will measure the fibrogenic response (TGFbeta cytokines, receptors and their functional activity) in cerebral blood vessels following Ang infusion. SA2: We will determine the signaling pathway that gives rise to the fibrogenic response in cerebral blood vessels following Ang infusion, with the goal of evaluating the role OEI, endothelin and downstream VSMC signaling, including CaMKII and AP-I. SA3: We will study the mechanism of TGFbeta-induced and Ang-induced nitrate tolerance. The proposed studies, which are based on several entirely original observations, will provide novel mechanistic insights relevant to understanding changes in the walls of cerebral vessels in hypertension that predispose to stroke.
Showing the most recent 10 out of 24 publications
