ROCK (RhoA/Rho Kinase) in Cardiovascular-Renal Pathophysiology: A Review of New Advancements

Abstract

Rho-associated, coiled-coil containing kinases (ROCK) were originally identified as effectors of the RhoA small GTPase and found to belong to the AGC family of serine/threonine kinases. They were shown to be downstream effectors of RhoA and RhoC activation. They signal via phosphorylation of proteins such as MYPT-1, thereby regulating many key cellular functions including proliferation, motility and viability and the RhoA/ROCK signaling has been shown to be deeply involved in arterial hypertension, cardiovascular-renal remodeling, hypertensive nephropathy and posttransplant hypertension. Given the deep involvement of ROCK in cardiovascular-renal pathophysiology and the interaction of ROCK signaling with other signaling pathways, the reports of trials on the clinical beneficial effects of ROCK's pharmacologic targeting are growing. In this current review, we provide a brief survey of the current understanding of ROCK-signaling pathways, also integrating with the more novel data that overall support a relevant role of ROCK for the cardiovascular-renal physiology and pathophysiology.

Keywords: Bartter’s syndrome; Gitelman’s syndrome; ROCK; Rho; Rho kinase; cardiovascular remodeling; hypertension; hypertensive nephropathy; kidney remodeling; posttransplant hypertension.

Figure 1

(A) Structure of Rho-associated coiled-coil containing kinase (ROCK) 1 and ROCK2. Both isoforms consist of a N-terminal kinase domain, a coiled-coil domain containing a Rho binding domain (RBD), a pleckstrin homology (PH) motif and a C-terminal cysteine-rich domain. ROCK1 and ROCK2 share 65% overall homology in amino acid sequence. (B) Inactivation/activation of ROCK. When the N-terminus is next to C-terminus, i.e., showing a closed configuration, the ROCK is inactive because of the auto-inhibitory loop. The opening of the loop can be caused 1) by caspase-3, or caspase-2 and granzyme B, that cleave the C-terminus of ROCK1 and ROCK2, respectively, or 2) by a Rho-dependent pathway, via binding of GTP-RhoA to the RBD, driven by angiotensin II, endothelin (ET) 1, fibroblast growth factor (FGF) and TGFβ, interleukin (IL)-1 or interferon γ. Modified from Hartmann, S., et al. [2] and Shimizu, T., et al. [3].

Figure 2

Upstream and downstream regulation of ROCK. Activation of G protein-coupled receptors, e.g., AT1 or ET-1, or receptors for cytokines or other growth factors, activate RhoGEF that, in turn phosphorylates RhoA/ROCK. The major ROCK downstream pathways are (1) myosin light chain phosphatase (MLCP)/MLC, (2) ezrin, radixin and moesin (ERM), (3) myocardin and serum response factor (SRF), (4) LIM (Lin-11, Isl-1,Mec-3))/cofilin, (5) assembly of F-actin with release of myocardin-related transcription factor (MRTF). The assembly of F-actin enables MRTF to dissociate from G-actin, leading to MRTF nuclear translocation and binding to SRF, which triggers transcription of genes involved in cardiovascular remodeling. However, all pathways concur to the development of smooth muscle cell proliferation, transition of myocytes into myofibroblasts and fibrosis, or stress fibers formation.

Figure 3

Schematic representation of Angiotensin II-mediated pathways involving RhoA/ROCK in arterial hypertension (A) and Bartter’s and Gitelman’s syndromes (B). Angiotensin II, via angiotensin II type 1 receptor (AT1R), activates the cascade RhoGEF/RhoA/ROCK, which leads to vascular remodeling, cardiac and renal fibrosis, and atherogenesis in hypertension (Panel A). The sketch reports the NF-κB/PAI-1 and NADPH oxidase/ superoxide anion (O₂⁻) as representative ROCK downstream pathways, but other pathways can be involved (see Figure 2). AT1-mediated pathways also involve mitogen-activated protein kinases (MAPK and ERK 1/2), diacylglycerol (DAG)/protein kinase C (PKC) and inositol triphosphate (IP3), which leads to increased Ca²⁺ release in the cytosol with vasoconstriction. In Bartter’s and Gitelman’s syndromes (Panel B), despite increased levels of Angiotensin II, the pathways leading to vasodilatation prevail on those leading to vasoconstriction due to post receptor abnormalities including blunted Gαq protein signaling and activation of the regulatory G protein signaling 2 (RGS2). RGS2 causes activation of endothelial nitric oxide synthase (eNOS) with increased Nitric Oxide (NO) release and blunted ROCK activity and signaling, with reduced intracellular Ca²⁺ sensitivity finally leading to vasodilation. Modified from Calò, L.A. et al. [1,25].