Nitric Oxide–Dependent Feedback Loop Regulates Transient Receptor Potential Vanilloid 4 (TRPV4) Channel Cooperativity and Endothelial Function in Small Pulmonary Arteries

Abstract

BackgroundRecent studies demonstrate that spatially restricted, local Ca2+ signals are key regulators of endothelium‐dependent vasodilation in systemic circulation. There are drastic functional differences between pulmonary arteries (PAs) and systemic arteries, but the local Ca2+ signals that control endothelium‐dependent vasodilation of PAs are not known. Localized, unitary Ca2+ influx events through transient receptor potential vanilloid 4 (TRPV4) channels, termed TRPV4 sparklets, regulate endothelium‐dependent vasodilation in resistance‐sized mesenteric arteries via activation of Ca2+‐dependent K+ channels. The objective of this study was to determine the unique functional roles, signaling targets, and endogenous regulators of TRPV4 sparklets in resistance‐sized PAs.Methods and ResultsUsing confocal imaging, custom image analysis, and pressure myography in fourth‐order PAs in conjunction with knockout mouse models, we report a novel Ca2+ signaling mechanism that regulates endothelium‐dependent vasodilation in resistance‐sized PAs. TRPV4 sparklets exhibit distinct spatial localization in PAs when compared with mesenteric arteries, and preferentially activate endothelial nitric oxide synthase (eNOS). Nitric oxide released by TRPV4‐endothelial nitric oxide synthase signaling not only promotes vasodilation, but also initiates a guanylyl cyclase‐protein kinase G‐dependent negative feedback loop that inhibits cooperative openings of TRPV4 channels, thus limiting sparklet activity. Moreover, we discovered that adenosine triphosphate dilates PAs through a P2 purinergic receptor‐dependent activation of TRPV4 sparklets.ConclusionsOur results reveal a spatially distinct TRPV4‐endothelial nitric oxide synthase signaling mechanism and its novel endogenous regulators in resistance‐sized PAs.

Augmented astrocyte microdomain Ca2+ dynamics and parenchymal arteriole tone in angiotensin II‐infused hypertensive mice

“…Functionally, higher resting astrocyte Ca 2+ levels were associated with augmented levels of PA tone as lowering Ca 2+ within the astrocytic syncytium decreased tone with a greater effect observed in hypertension (Figure 2g). A number of mechanisms could increase astrocyte Ca 2+ during Ang II-induced hypertension including: direct Ang II actions on astrocytes, mechanotransduction via increased stretching of astrocyte processes (as those evoked during adjustments in PA diameter; Kim et al, 2015) and/or via the action of endothelium-mediated signals [e.g., nitric oxide (Kohler et al, 2006;Marziano et al, 2017;Mendoza et al, 2010) and EETs (Dunn et al, 2013;Earley et al, 2009;Vriens et al, 2005)]. Based on poor evidence for AT1R expression in cortical astrocytes and established Ang II-induced endothelial dysfunction (Chrissobolis, Banfi, Sobey, & Faraci, 2012;Chrissobolis, Miller, Drummond, Kemp-Harper, & Sobey, 2011;De Silva et al, 2016;Girouard, Park, Anrather, Zhou, & Iadecola, 2007), we propose hypertension increases the sensitivity of mechanosensitive TRPV4 channels expressed on astrocytes.…”

The Endothelium: The Vascular Information Exchange

“…A recent study has shown that TRPV4-mediated sparklets underlie ATP driven activation of endothelial NOS in mouse small pulmonary arteries. The resulting NO initiates vasodilation and also guanylyl cyclase-protein kinase G signaling in the endothelium that limits TRPV4 channel cooperativity and serves as a negative feedback signal to regulate TRPV4 channel function [17]. This description of ATP-evoked, spatially distinct TRPV4 sparklets and localized TRPV4-NOS signaling support a novel paradigm that NOS can be activated by spatially restricted Ca 2+ signals, and identifies TRPV4 channels as a key regulator of NOS activity in the pulmonary microcirculation.…”

“…This idea is supported by the demonstration that in rat pulmonary arteries, vasodilation to the TRPV4 agonist GSK1016790A was mediated by activation of SK Ca channels [52]. In the same vessels, and in mouse small pulmonary arteries, shear stress-stimulated TRPV4 activity was also linked to NO production [17] suggesting a further link between TRPV4 and NOS.…”

“…However, NOS has now been localized close to MEGJs [117] and in co-cultures stimulation of smooth muscle cells with phenylephrine leads to MEGJ specific NOS phosphorylation within endothelial cells to increase NO [118]. Also, in mouse mesenteric vessels, phenylephrine stimulated endothelial TRPV4 sparklets in an InsP 3 -dependent manner, to engage SK Ca and IK Ca channels as well as, to a lesser extent, NOS [17]. Thus, given the ability of IK Ca channels to modulate endothelial Ca 2+ dynamics [12,113,114], it may be proposed that activation of IK Ca channels at MEGJs following stimulation of smooth muscle cells by GPCR agonists, may amplify dynamic Ca 2+ signals to enhance NO production.…”

“…Exposure of the endothelium to TRPV4 agonists and/or acetylcholine increased the activity of these discrete Ca 2+ signals which were linked to activation of both IK Ca and small conductance (SK Ca )Ca 2+ -activated K + channels, effects which were absent in arteries from mice lacking TRPV4 [14]. In rat cremaster arterioles, clustering of TRPV4-mediated sparklets in endothelial projections was linked exclusively to activation of IK Ca channels [16] and in mouse small pulmonary arteries, shear stress-stimulated TRPV4 activity was linked to NO production [17]. Larger endothelial sparklets mediated by simultaneous opening of two TRPA1 and leading to activation of IK Ca channels were shown to underlie dilation to reactive oxygen species in rat cerebral arteries [18].…”