Research ArticleVASCULAR BIOLOGY

RSK2 contributes to myogenic vasoconstriction of resistance arteries by activating smooth muscle myosin and the Na+/H+ exchanger

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Sci. Signal.  30 Oct 2018:
Vol. 11, Issue 554, eaar3924
DOI: 10.1126/scisignal.aar3924

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RSK2 restricts blood vessel diameter

Phosphorylation of myosin enables smooth muscle cells to contract and cause vasoconstriction. This phosphorylation event has generally been attributed to myosin light chain kinase (MLCK). However, Artamonov et al. discovered that the kinase RSK2 was activated by intraluminal pressure or stimuli that promote vasoconstriction in resistance arteries and that it phosphorylated smooth muscle myosin. In addition, RSK2 phosphorylated the Na+/H+ exchanger, a transporter that increases intracellular pH when activated, leading to Ca2+ transients that would be expected to activate MLCK and thereby also contribute to vasoconstriction. Accordingly, mice deficient in RSK2 had dilated arteries and lower blood pressure than their wild-type littermates. These results identify RSK2 as a potential drug target for manipulating blood pressure.

Abstract

Smooth muscle contraction is triggered when Ca2+/calmodulin-dependent myosin light chain kinase (MLCK) phosphorylates the regulatory light chain of myosin (RLC20). However, blood vessels from Mlck-deficient mouse embryos retain the ability to contract, suggesting the existence of additional regulatory mechanisms. We showed that the p90 ribosomal S6 kinase 2 (RSK2) also phosphorylated RLC20 to promote smooth muscle contractility. Active, phosphorylated RSK2 was present in mouse resistance arteries under normal basal tone, and phosphorylation of RSK2 increased with myogenic vasoconstriction or agonist stimulation. Resistance arteries from Rsk2-deficient mice were dilated and showed reduced myogenic tone and RLC20 phosphorylation. RSK2 phosphorylated Ser19 in RLC in vitro. In addition, RSK2 phosphorylated an activating site in the Na+/H+ exchanger (NHE-1), resulting in cytosolic alkalinization and an increase in intracellular Ca2+ that promotes vasoconstriction. NHE-1 activity increased upon myogenic constriction, and the increase in intracellular pH was suppressed in Rsk2-deficient mice. In pressured arteries, RSK2-dependent activation of NHE-1 was associated with increased intracellular Ca2+ transients, which would be expected to increase MLCK activity, thereby contributing to basal tone and myogenic responses. Accordingly, Rsk2-deficient mice had lower blood pressure than normal littermates. Thus, RSK2 mediates a procontractile signaling pathway that contributes to the regulation of basal vascular tone, myogenic vasoconstriction, and blood pressure and may be a potential therapeutic target in smooth muscle contractility disorders.

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