Increased RhoA/Rho-Kinase Signaling Mediates Spontaneous Tone in Aorta from Angiotensin II-Induced Hypertensive Rats

Abstract

Spontaneous tone in large arteries may contribute to the pathogenesis of hypertension. Reactive oxygen species and Ca 2ϩ influx have been shown to stimulate the development of spontaneous tone in isolated aortic rings in several models of hypertensive rats. The aim of this study was to investigate the role of the RhoA/Rho-kinase signaling pathway in the development of spontaneous tone in angiotensin II-induced hypertension and to explore the underlying mechanisms of RhoA/Rho-kinase activation. Our results showed that spontaneous tone was greatly enhanced in endothelium-denuded aortic rings from angiotensin II-induced hypertensive rats compared with their normotensive counterparts (73 Ϯ 5 versus 7 Ϯ 3% of phenylephrine-induced maximal contraction, respectively). The Rhokinase inhibitor (R)-(ϩ)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide (Y-27632) (0.1-10 M) concentration dependently inhibited spontaneous tone in aortic rings from angiotensin II-treated rats. NADPH oxidase inhibitors diphenylene iodonium and apocynin also significantly reduced spontaneous tone. Chronic angiotensin II treatment markedly increased RhoA protein expression (57%) but had no effect on Rho guanine nucleotide exchange factor mRNA or Rho-kinase protein expression levels. In endothelium-denuded rings from normotensive rats, angiotensin II (100 nM) increased RhoA membrane translocation and phosphorylation of the myosin light chain phosphatase target subunit, which were both blocked by the NADPH oxidase inhibitor diphenylene iodonium (10 M). In conclusion, these data suggest that chronic treatment with angiotensin II leads to up-regulation of the RhoA/ Rho-kinase pathway, contributing to spontaneous tone development in rat aorta. Increased NADPH oxidase-dependent reactive oxygen species may be one of the mechanisms mediating the RhoA/Rho-kinase activation.Angiotensin II (Ang II) produced by the renin-angiotensin system is an important hormone in the homeostasis of cardiovascular and renal function. Increased circulating Ang II promotes inflammation and cell growth and increases vascular reactivity (Kagiyama et al., 2002;Seshiah et al., 2002). It is well known that activation of Ang II type I receptor (AT 1 ) increases free intracellular Ca 2ϩ concentration and myosin light chain (MLC) kinase activity, leading to MLC phosphorylation and subsequent smooth muscle contraction. Recent studies suggest that the phosphorylation state of MLC is also modulated by RhoA/Rho-kinase, a Ca 2ϩ sensitization signaling pathway through which smooth muscle is able to contract when the intracellular Ca 2ϩ concentration is low (Somlyo and Somlyo, 2003).The activity of RhoA is regulated by Rho guanine nucleotide exchange factors (RhoGEFs) and Rho GDP disassociation inhibitors (Somlyo and Somlyo, 2003). In its inactive state, RhoA binds with GDP and forms a complex with GDP disassociation inhibitors in the cytosol. When RhoGEF is activated by G protein-coupled receptors such as AT 1 or receptor tyrosine kinase, it facilitates the exchange of ...

Angiotensin II regulates the LARG/RhoA/MYPT1 axis in rat vascular smooth muscle in vitro

“…Hypertension increases arterial tone in both small resistance arteries (myogenic tone) and large conduit arteries (spontaneous tone). It has also been established that RhoA signaling mediates the development of spontaneous tone in Ang II-induced hypertensive rats [4] . Our current findings may aid the elucidation of the mechanism involved in controlling spontaneous tone in the vascular wall of large conduit arteries.…”

“…A link between Ang II type 1 receptors (AT 1 ) and the RhoA/ Rho kinase pathway has been reported [4,11] . Three RhoGEFs may link AT 1 to RhoA activation: PSD-95/Disc-large/ZO-1 homology (PDZ)-RhoGEF, leukemia-associated RhoGEF (LARG), and p115-RhoGEF [4,12,13] .…”

“…Three RhoGEFs may link AT 1 to RhoA activation: PSD-95/Disc-large/ZO-1 homology (PDZ)-RhoGEF, leukemia-associated RhoGEF (LARG), and p115-RhoGEF [4,12,13] . It has been reported that Ang II transiently upregulates the expression of LARG mRNA and protein, but not PDZ-RhoGEF or p115-RhoGEF in a rat VSMC model [14] .…”

“…Activation of Ang II receptors, which increases free intracellular Ca 2+ concentrations and increases myosin light chain (MLC) kinase activity, can cause vessel constriction. These events result in MLC phosphorylation and subsequent smooth muscle contraction [1][2][3][4] . However, a portion of the agonist-induced smooth muscle contraction, termed Ca 2+ sensitization, is mediated by the Ca 2+ -independent activation of monomeric G protein RhoA and the downstream target Rho-kinase [4,5] .…”

Effect of an angiotensin II receptor blocker and a calcium channel blocker on hypertension associated penile dysfunction in a rat model

“…Angiotensin II increases NADPH oxidase-dependent ROS production, followed by the stimulating RhoA/Rho kinase-signaling pathway, and decreasing the eNOS activity via the activation of the AT1R. These responses lead to an increase in the cavernosal smooth muscle contraction and the penile erectile tissue damage, resulting in the development of hypertension-associated ED (14)(15)(16). Pre- expression.…”