Damage-Associated Molecular Patterns in Hypertension

PROGRAM SUMMARY PROGRAM DIRECTOR, WEBB The integrating theme and unifying hypothesis of this program project centers on the role played by damage- associated-molecular patterns (DAMPs) in hypertension. DAMPs are alarm signals generated from injured host cells, damaged tissues or metabolic stress and are recognized by the innate immune system. We hypothesize that sustained activation of the innate immune system in hypertension is maladaptive, leading to activation of circulating neutrophils and monocytes in the peripheral circulation, which home to the vasculature, and cause increased tissue destruction and low-grade inflammation. These inflammatory events contribute to increased vasoconstriction, vascular remodeling, and renal injury that occur under the action of initiating factors to increase blood pressure. Project 1 will test the hypothesis that in hypertension, exaggerated apoptosis and necrosis in the vascular wall give rise to mitochondrial DNA (mtDNA), a DAMP that activates Toll-like receptor 9 (TLR9) causing vascular inflammation, vasoconstriction and endothelial dysfunction. In Project 2, it is hypothesized that cell death induces high mobility group box 1 (HMGB1) release and TLR4 activation resulting in dentritic cell (DC) and T cell activation and increases in blood pressure in both sexes. However, due to a sex difference in the type of cell death, the molecular pathway driving immune-based hypertension in females favors greater T regulatory cell (Treg) formation. This hypothesis predicts that necrosis results in greater HMGB1 release and TLR4 activation in males leading to myeloid DC activation of Th17 cells and increases in blood pressure and end-organ damage relative to females, while greater apoptosis in females limits HMGB1 release and activates plasmacytoid DC to increase Treg formation limiting increases in blood pressure and injury relative to males. Project 3 tests the hypothesis that high circulating DAMPs stimulate inappropriate nitric oxide (NO) production by vasa recta (VR) endothelial cells in low sheer states. This NO production is detrimental as it inhibits spontaneous rhythmic contractions of VR pericytes that normally act to prevent red blood cell aggregations under these conditions. RBC occlusion of the VR then leads to rarefaction of the surrounding medullary vasculature, impaired pressure-natriuresis and hypertension. These conceptually unique approaches, combined with novel technological tools will advance our understanding of the molecular and physiological mechanisms underlying the initiation of vascular injury and end organ damage of hypertension. All projects will use the spontaneously hypertensive rat as an animal model. This highly integrative and collaborative approach of the three component projects is supported by an Administrative Core (Core A), the Animal Use and Instrumentation Core (Core B) and the Bioinflammation Core (Core C).