Inhibition of the AMP-Activated Protein Kinase-α2 Accentuates Agonist-Induced Vascular Smooth Muscle Contraction and High Blood Pressure in Mice

Abstract

The aim of the present study was to determine the effects and molecular mechanisms by which AMP-activated protein kinase (AMPK) regulates smooth muscle contraction and blood pressure in mice. In cultured human vascular smooth muscle cells (HMSC), we observed that activation of AMPK by AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside) inhibited agonists-induced phosphorylation of myosin light chain (MLC) and myosin phosphatase targeting subunit 1 (MYPT1). Conversely, AMPK inhibition with pharmacologic or genetic means potentiated agonists-induced the phosphorylation of MLC and MYPT1 while inhibited both Ras homolog gene family, member A (RhoA) and Rho-associated kinase (ROCK) activity. Further, AMPK activation or ROCK inhibition with Y27632 abolished agonists-induced phosphorylation of MLC and MYPT1. Gene silencing of p190-guanosine triphosphatase-activating protein (p190-GAP) abolished the effects of AMPK activation on MLC, MYPT1, and RhoA in HSMC. Ex vivo analyses revealed that agonist-induced contractions of the mesenteric artery and aortas were stronger in both AMPKα1−/− and AMPKα2−/− knockout mice than in wild-type mice. Inhibition of ROCK with Y27632 normalized agonist-induced contractions of AMPKα1−/− and AMPKα2−/− vessels. AMPKα2−/− mice had higher blood pressure along with decreased serine phosphorylation of p190-guanosine triphosphatase-activating protein (p190-GAP). Finally, inhibition of the RhoA/ROCK pathway with Y27632, which suppressed MYPT1 and MLC phosphorylation, lowered blood pressure in AMPKα2−/− mice. In conclusion, AMPK decreases vascular smooth muscle cell contractility by inhibiting p190-GAP-dependent RhoA activation, indicating AMPK may be a new therapeutic target in lowering high blood pressure.

The AMP-Related Kinase (AMPK) Induces Ca 2+ -Independent Dilation of Resistance Arteries by Interfering With Actin Filament Formation

“…Unexpectedly, this seemed not to be because of an activation of MLCP as reported earlier 18,32 but was associated with an increase in G-actin, as well as thinning and rarefaction of VSM-actin filaments. Our data are consistent with the view that this AMPK effect involves cofilin activation.…”

“…AMPK can induce smooth muscle relaxation directly by a decrease of [Ca 2+ ] i or of Ca 2+ sensitivity. [16][17][18][19][20][21] In a recent study, we identified AMPK as a new potential upstream kinase of the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) regulator phospholamban and a regulator of the BK Ca (large conductance calcium-activated potassium) channel in microvascular smooth muscle. Nonetheless, there was still an additional, slowly developing vasodilation, which was probably Ca 2+ -independent because it was still observed after inhibition of SERCA BK Ca .…”

“…However, AMPK has also been reported to interfere with upstream regulators of the myosin phosphatase and to phosphorylate MLCK, thereby inhibiting its activity. 18,28 Both mechanisms would also result in Ca 2+ -independent relaxation of blood vessels. In view of the decisive role of microvessels in remodeling processes and the fact that microvascular regulatory pathways often differ from those in larger vessels, we studied whether and how AMPK could affect actin remodeling processes in microvascular smooth muscle and whether this could reduce microvascular tone in a Ca 2+ -independent manner.…”

AMPK Dilates Resistance Arteries via Activation of SERCA and BK Ca Channels in Smooth Muscle

“…31 Although ongoing studies in our laboratory indicate (slowly incipient) effects of AMPK on calcium sensitivity in resistance arteries as well, we focused in the present study on the mechanisms of calcium decrease. We identified 2 underlying mechanisms: increased SERCA activity as a result of enhanced phospholamban phosphorylation and, although to our surprise functionally less effective, smooth muscle hyperpolarization induced by stimulation of BK Ca channels.…”

Inhibitor κB Kinase

“…9,10 Although MLCK is generally accepted as a key regulator of smooth muscle contraction, 11 numerous studies during the past 3 decades have pointed to other systems for regulation of the degree of tension developed and borne by smooth muscle. Notably, the activity of myosin phosphatase is highly regulated by both calcium-dependent and calcium-independent mechanisms, [12][13][14][15] and numerous hypotheses champion thin filament-based regulation, 16 including alterations in cytoskeletal structures. 17 Smooth muscle actomyosin cross-bridges not only rapidly generate tension but also hold tension.…”