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Myogenic Vasoconstriction Requires Canonical Gq/11 Signaling of the Angiotensin II Type 1 Receptor
(2022)
Background
Blood pressure and tissue perfusion are controlled in part by the level of intrinsic (myogenic) arterial tone. However, many of the molecular determinants of this response are unknown. We previously found that mice with targeted disruption of the gene encoding the angiotensin II type 1a receptor (AT1AR) (Agtr1a), the major murine angiotensin II type 1 receptor (AT1R) isoform, showed reduced myogenic tone; however, uncontrolled genetic events (in this case, gene ablation) can lead to phenotypes that are difficult or impossible to interpret.
Methods and Results
We tested the mechanosensitive function of AT1R using tamoxifen‐inducible smooth muscle‐specific AT1aR knockout (smooth muscle‐Agtr1a−/−) mice and studied downstream signaling cascades mediated by Gq/11 and/or β‐arrestins. FR900359, Sar1Ile4Ile8‐angiotensin II (SII), TRV120027 and TRV120055 were used as selective Gq/11 inhibitor and biased agonists to activate noncanonical β‐arrestin and canonical Gq/11 signaling of the AT1R, respectively. Myogenic and Ang II‐induced constrictions were diminished in the perfused renal vasculature, mesenteric and cerebral arteries of smooth muscle‐Agtr1a−/− mice. Similar effects were observed in arteries of global mutant Agtr1a−/− but not Agtr1b−/− mice. FR900359 decreased myogenic tone and angiotensin II‐induced constrictions whereas selective biased targeting of AT1R‐β‐arrestin signaling pathways had no effects.
Conclusions
This study demonstrates that myogenic arterial constriction requires Gq/11‐dependent signaling pathways of mechanoactivated AT1R but not G protein‐independent, noncanonical pathways in smooth muscle cells.
Abstract
Caveolae position CaV3.2 (T‐type Ca2+ channel encoded by the α‐3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca2+ influx to trigger Ca2+ sparks and large‐conductance Ca2+‐activated K+ channel feedback in vascular smooth muscle. We hypothesize that this mechanism of Ca2+ spark generation is affected by age. Using smooth muscle cells (VSMCs) from mouse mesenteric arteries, we found that both Cav3.2 channel inhibition by Ni2+ (50 µM) and caveolae disruption by methyl‐ß‐cyclodextrin or genetic abolition of Eps15 homology domain‐containing protein (EHD2) inhibited Ca2+ sparks in cells from young (4 months) but not old (12 months) mice. In accordance, expression of Cav3.2 channel was higher in mesenteric arteries from young than old mice. Similar effects were observed for caveolae density. Using SMAKO Cav1.2−/− mice, caffeine (RyR activator) and thapsigargin (Ca2+ transport ATPase inhibitor), we found that sufficient SR Ca2+ load is a prerequisite for the CaV3.2‐RyR axis to generate Ca2+ sparks. We identified a fraction of Ca2+ sparks in aged VSMCs, which is sensitive to the TRP channel blocker Gd3+ (100 µM), but insensitive to CaV1.2 and CaV3.2 channel blockade. Our data demonstrate that the VSMC CaV3.2‐RyR axis is down‐regulated by aging. This defective CaV3.2‐RyR coupling is counterbalanced by a Gd3+ sensitive Ca2+ pathway providing compensatory Ca2+ influx for triggering Ca2+ sparks in aged VSMCs.