BackgroundIn blood vessels, the endothelium is a crucial signal transduction interface in control of vascular tone and blood pressure to ensure energy and oxygen supply according to the organs' needs. In response to vasoactive factors and to shear stress elicited by blood flow, the endothelium secretes vasodilating or vasocontracting autacoids, which adjust the contractile state of the smooth muscle. In endothelial sensing of shear stress, the osmo- and mechanosensitive Ca2+-permeable TRPV4 channel has been proposed to be candidate mechanosensor. Using TRPV4−/− mice, we now investigated whether the absence of endothelial TRPV4 alters shear-stress-induced arterial vasodilation.Methodology/Principal FindingsIn TRPV4−/− mice, loss of the TRPV4 protein was confirmed by Western blot, immunohistochemistry and by in situ-patch–clamp techniques in carotid artery endothelial cells (CAEC). Endothelium-dependent vasodilation was determined by pressure myography in carotid arteries (CA) from TRPV4−/− mice and wild-type littermates (WT). In WT CAEC, TRPV4 currents could be elicited by TRPV4 activators 4α-phorbol-12,13-didecanoate (4αPDD), arachidonic acid (AA), and by hypotonic cell swelling (HTS). In striking contrast, in TRPV4−/− mice, 4αPDD did not produce currents and currents elicited by AA and HTS were significantly reduced. 4αPDD caused a robust and endothelium-dependent vasodilation in WT mice, again conspicuously absent in TRPV4−/− mice. Shear stress-induced vasodilation could readily be evoked in WT, but was completely eliminated in TRPV4−/− mice. In addition, flow/reperfusion-induced vasodilation was significantly reduced in TRPV4−/− vs. WT mice. Vasodilation in response to acetylcholine, vasoconstriction in response to phenylephrine, and passive mechanical compliance did not differ between genotypes, greatly underscoring the specificity of the above trpv4-dependent phenotype for physiologically relevant shear stress.Conclusions/SignificanceGenetically encoded loss-of-function of trpv4 results in a loss of shear stress-induced vasodilation, a response pattern critically dependent on endothelial TRPV4 expression. Thus, Ca2+-influx through endothelial TRPV4 channels is a molecular mechanism contributing significantly to endothelial mechanotransduction.
In endothelial sensing of shear stress, the Ca2+‐permeable TRPV4 channel was proposed a candidate mechanosensor. Using TRPV4−/− mice, we investigated whether the absence of endothelial TRPV4 alters shear‐stress‐induced vasodilation. Loss of the TRPV4 protein and function was confirmed by IHC and electrophysiology in endothelium of TRPV4−/− mice. Agonist‐ and shear stress‐induced vasodilation was determined by pressure myography in carotid artery (CA) of TRPV4−/− and TRPV4+/+ mice (WT). In WT CAEC, TRPV4 was activated by the pharmacological TRPV4‐opener 4alphaPDD, arachidonic acid (AA), and by hypotonic cell swelling (HTS). In CAEC of TRPV4−/−, 4alphaPDD did not produce currents and currents in response to AA and HTS were greatly reduced. 4alphaPDD elicited a robust and strictly endothelium‐dependent vasodilation in WT mice, again strikingly absent in TRPV4−/− mice. Shear stress‐induced vasodilation was present in WT, but was eliminated in TRPV4−/− mice. Flow‐induced vasodilation was significantly reduced in TRPV4−/− vs. WT mice. In conclusion, loss of TRPV4 abolishes shear stress‐induced vasodilation. Thus, Ca2+‐influx through endothelial TRPV4 channels is a critical mechanism contributing to endothelial mechanotransduction.
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