Pannexin 1 and sympathetic vasoconstriction

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PROJECT 2 PROJECT SUMMARY The fastest growing type of hypertension is sympathetically driven due to its close association with obesity, itself reaching epidemic proportions. In this form of hypertension, the effect of sympathetic nerve (SN) activity – i.e., release of norepinephrine (NE) to bind α-adrenergic receptors (α-AR) on smooth muscle cells (SMC) on SMC – is enhanced. NE is a potent vasoconstrictor and can strongly increase blood pressure. Thus, the smooth muscle cells of resistance arteries is a major site for SN-driven hypertension. Our PPG has recently made important discoveries in understanding the α−AR-mediated vasoconstriction pathway, which have forced us to re-think the classical mechanism whereby sympathetic nerve induces SMC constriction. In resistance arteries, we found that α-AR activation (and not other vasoconstriction receptor pathways) induced Pannexin 1 (Panx1) channel opening on SMC to release ATP. This work identifies a key functional role for Panx1-derived ATP, and raises new questions on the interaction between sympathetic nerve and SMCs. Furthermore, our PPG recently discovered that the potent anti-hypertensive drug spironolactone acts directly on Panx1 channels to lower blood pressure, independent of mineralocorticoid receptors. This work may have “unmasked” Panx1 as an important additional component to the anti-hypertensive effects of spironolactone. Together, our published and preliminary data provide the premise for the hypothesis tested in this proposal: Pannexin 1 links the sympathetic nervous system to arterial function. We propose two aims to test this hypothesis. In Specific Aim 1, we hypothesize that Pannexin 1 channels regulate sympathetic nerve control of peripheral resistance in hypertension. This aim will incorporate models of sympathetic hypertension with Panx1 genetic knockout to determine if Panx1 intervention can reverse high blood pressure. Additional Panx1 over-expression models and new Panx1 pharmacological activators will help determine whether Panx1 can modulate blood pressure. In Specific Aim 2, we ask further on the communication between sympathetic nerves and smooth muscle cells. We will examine the purinergic signaling domain directly, by visualizing ATP release and stimulating sympathetic nerves directly. A translational component will compare our findings to humans with and without hypertension. The feasibility of accomplishing these aims is underscored by all proposed knockout mice being in hand, an IRB in place for human samples, and the strong preliminary data. The integration of Project 2 with other Projects on this P01 provides us with an opportunity to explore a novel pharmacological target for sympathetic nerve-driven hypertension that could not have been achieved alone.