New insights into RhoA/Rho-kinase signaling: a key regulator of vascular contraction

Abstract

While Rho-signalling controlling vascular contraction is a canonical mechanism, with the modern approaches used in research, we are advancing our understanding and details into this pathway are often uncovered. RhoA-mediated Rho-kinase is the major regulator of vascular smooth muscle cells and a key player manoeuvring other functions in these cells. The discovery of new interactions, such as oxidative stress and hydrogen sulphide with Rho signalling are emerging addition not only in the physiology of the smooth muscle, but especially in the pathophysiology of vascular diseases. Likewise, the interplay between ageing and Rho-kinase in the vasculature has been recently considered. Importantly, in smooth muscle contraction, this pathway may also be affected by sex hormones, and consequently, sex-differences. This review provides an overview of Rho signalling mediating vascular contraction and focuses on recent topics discussed in the literature affecting this pathway such as ageing, sex differences and oxidative stress.

Keywords: RhoA/Rho-kinase; ageing; oxidative stress; sex-difference; vascular contraction.

Figure 1.

Canonical pathways in smooth muscle contraction. GPCR is known to be involved in smooth muscle contraction through two main mechanisms. Once activated, the α subunit associated with the receptor dissociates and activates phospholipase C (PLC), which functions to convert phosphatidylinositol 4,5-bisphosphate (PIP₂) to inositol trisphosphate (IP₃). IP₃ further induces the release of Ca²⁺ from the sarcoplasmic reticulum and thus results in an increase in intracellular Ca²⁺ levels. Ca²⁺ binds to calmodulin (CaM) which activates myosin light chain kinase (MLCK), responsible for phosphorylating myosin light chain (MLC), therefore inducing contraction. Moreover, contraction could also be promoted through Ca²⁺ induced activation of PKC. This stimulates activation of CPI, an inhibitor of myosin light chain phosphatase (MLCP), consequently preventing the removal of the phosphate group and terminating contraction. The second mechanism entails GPCR activation of a GEF that works to activate Rho through its conversion from Rho-GDP to Rho-GTP. Rho further activates its associated kinases, ROCK1 and ROCK2, which have shown capabilities of inhibiting eNOS, consequently decreasing NO production and relaxation. ROCK1/2 can also promote CPI and directly inhibit MLCP, inducing contraction. Various studies have shown the regulatory mechanisms of RhoE, GEM, and arachidonic acid on RhoA and RhoA-kinase. Other possible regulators are currently still under investigation. Created with BioRender.com

Figure 2.

Current details into the mechanism by which Rho signalling regulates smooth muscle contraction. Not only the well-described gas NO might inhibit Rho-kinase, but also H₂S, which the physiological functions and targets are currently under extensive investigation (first box). Gender differences and ageing also are highlighted in the literature as they drive differences in smooth muscle contraction by affecting Rho-kinase. Oestrogen inhibits Rho-kinase via specific G-protein coupling receptor (GPCER1) in young females (second box), and crosstalk between Rho-kinase and ROS is observed during ageing followed by decreasing NO availability (third box). Created with BioRender.com