Endothelial cells (ECs) lining blood vessels are pivotal regulators of vascular tone. Their function is disrupted in cardiovascular diseases, including hypertension. Although some of the molecular players involved in mediating endothelial-dependent vascular regulation have been identified, key aspects of their signaling linkages remain poorly understood. Importantly, how these molecular circuits are spatially organized to enable efficient signaling is largely unknown. In this proposal, we test the novel hypothesis that EC A-kinase anchoring protein (AKAP150) and transient receptor potential vanilloid 4 (TRPV4) channels form the core of a dynamic integrator of endothelial and smooth muscle cell (SMC) signaling that is localized at myendothelial projections (MEPs)-specialized projections through the internal elastic lamina that connect ECs with adjacent SMCs through gap junctions. In support of this, we provide novel data that AKAP150, which binds protein kinase C (PKC), protein kinase A (PKA) and calcineurin (PP2B), is required for Gq-protein coupled receptor (GqPCR) activation of TRPV4 channels exclusively at MEPs. In contrast, shear stress preferentially stimulates non-MEP TRPV4 channels. Moreover, AKAP150 promotes cooperative gating of TRPV4 channels in a 4- channel metastructure but, surprisingly, is not a determining factor of TRPV4 channel agonist sensitivity, which is dramatically different between cerebral and mesenteric resistance arteries. Importantly, our data demonstrate that this signaling network is disrupted in hypertension through changes in local coupling caused by the loss of MEP AKAP150.
In Aim 1, we investigate the roles of AKAP150-bound PKC, PKA and PP2B as well as caveolin-1 in the regulation of MEP TRPV4 activity and cooperativity using a genetically encoded, EC- specific Ca2+ biosensor (GCaMP2), an optogenetic technique for controlling spatial production of IP3/diacyl glycerol, and genetic mouse models of major network elements. We also explore the basis for the striking difference in TRPV4 agonist sensitivity between cerebral and systemic (mesenteric) arteries.
In Aim 2, we use a variety of approaches, including multi-photolysis of caged IP3 and Ca2+, to define mechanisms of myoendothelial feedback to MEPs and shear stress-induced vasodilation via activation of non-MEP TRPV4 channels.
In Aim 3, we use insights gained from Aims 1 and 2 to unravel the nature of the dysfunction of the MEP signaling network in hypertension using two mouse models. Taken together, these experiments will provide an unparalleled view of the bidirectional signaling network in MEPs and represent the first detailed exploration of the defects in local connections that likely contribute to endothelial dysfunction in hypertension.
The cell layer (endothelium) that lines small blood vessels (arteries) is a critical mediator of vascular function, serving as both a physical barrier to the surrounding tissue and a modulator of blood flow. Disruption of the endothelium is a hallmark of vascular diseases such as hypertension. This project defines the operation of a novel endothelial signaling network responsible for efficient relaxation of arteries and regulation of blood flow.
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