NADPH oxidase signaling, blood pressure sensing and the development of myogenic tone

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Under dynamic conditions, arterial tone is regulated by multiple stimuli including neuronal activity, tissue metabolism and intravascular pressure. A century ago, Bayliss first observed that arteries could respond to changes in blood pressure. The “myogenic response” has been documented in various vascular beds and is dependent upon a rise in smooth muscle [Ca2+]. Elevated pressure augments smooth muscle [Ca2+] by activating signal transduction pathways that: 1) depolarize smooth muscle and elevate Ca2+ channel activity; and 2) mobilize internal Ca2+ stores. While some of the ion channels driving myogenic tone development have have been identified, the signaling cascades which enable pressure modulation have not. Present day work typically focuses on standard G-protein coupled mechanisms and few venture “outside this signaling box” to consider novel molecules. This includes reactive oxygen species whose production could be facilitated by NADPH oxidases (NOX), enzymes known to associate with mechanosensitive proteins.***Consistent with our long term interests in the myogenic response, this NSERC proposal will explore the linkage between intravascular pressure, NOX signaling and myogenic tone in the cerebral circulation. The three aims will:***1) Determine whether NOX facilitates myogenic tone. ***2) Determine whether NOX facilitates myogenic tone via electromechanical coupling.***3) Determine whether NOX modulates ion channels sensitive to mechanical stimuli.***Our overarching hypothesis states that NOX (in particular NOX1) augments TRPC6 and/or TRPM4 activity in vascular smooth muscle by generating H2O2 and activating PKC. This increase in depolarizing current will facilitate pressure-induced depolarization, an event that will elevate cytosolic [Ca2+] and myogenic tone. Our experimental approach will synergistically employ: 1) vessel myography to assess tone, membrane potential, and cytosolic [Ca2+], 2) Q-PCR and immunohistochemistry to determine NOX expression and localization; and 3) electrophysiology to ascertain ion channel activity. Experiments will be performed in cerebral arteries isolated from rat, NOX1-/- mice and humans. Our focus on pressure-sensing and NOX signaling will foster a deeper mechanistic appreciation of the myogenic response and its biological significance to blood pressure and blood flow regulation.