Reactive oxygen species (ROS) mediates the aberrant contractility in
hypertension. Abnormal contractility occurs in atherosclerotic vessels but changes in
proteins that regulate contractility remain poorly understood.
Myosin phosphatase (MP) activity, which regulates smooth muscle relaxation, is regulated by the phosphorylation of its regulatory subunit, MP targeting subunit 1 (MYPT1). In the present study, we examined the roles of ROS in MP subunit expression both in cultured human aortic smooth muscle cells (HASMCs) and during
atherosclerosis progression in
apolipoprotein E-knockout (
apoE-KO) mice. Furthermore, the effect of decreased MYPT1 on actin cytoskeleton and cell migration activity was assessed in HASMCs.
Short hairpin RNA-mediated knockdown of MYPT1 increased stress fibers and attenuated
platelet-derived growth factor-induced cell migration in HASMCs.
Superoxide anion-inducing agent
LY83583 downregulated MYPT1
mRNA and
protein levels, but did not affect the phosphorylation of MYPT1 and catalytic subunit of MP, PP1δ. The LY83583-induced decrease in MYPT1 was abolished by co-treating with
superoxide dismutase or by inhibiting
NADPH oxidase with
diphenyleneiodonium. Treatment of
peroxynitrite, but not
hydrogen peroxide (H2O2), downregulated MYPT1
protein expression and induced MYPT1 phosphorylation without affecting
mRNA levels. Co-treatment with a
proteasome inhibitor,
MG-132, eliminated
peroxynitrite-induced MYPT1 downregulation. In
apoE-KO mice, MYPT1
protein, but not
mRNA, levels were markedly decreased in 16-week- and 24-week-old mice. Oral
estrogen treatment, which was previously shown to decrease aortic ROS levels, upregulated aortic MYPT1 expression. Moreover, reduction in MYPT1 expression correlated with increased aortic sensitivity toward
vasoconstrictors. These results suggested that during
atherosclerosis progression oxidative stress mediates the downregulation of MYPT1, which may inhibit smooth muscle cell migration and contribute to the aberrant contractility.