Rho Kinases and Cardiac Remodeling

Abstract

Hypertensive cardiac remodeling is characterized by left ventricular hypertrophy and interstitial fibrosis, which can lead to heart failure with preserved ejection fraction. The Rho-associated coiled-coil containing kinases (ROCKs) are members of the serine/threonine protein kinase family, which mediates the downstream effects of the small GTP-binding protein RhoA. There are 2 isoforms: ROCK1 and ROCK2. They have different functions in different types of cells and tissues. There is growing evidence that ROCKs contribute to the development of cardiovascular diseases, including cardiac fibrosis, hypertrophy, and subsequent heart failure. Recent experimental studies using ROCK inhibitors, such as fasudil, have shown the benefits of ROCK inhibition in cardiac remodeling. Mice lacking each ROCK isoform also exhibit reduced myocardial fibrosis in a variety of pathological models of cardiac remodeling. Indeed, clinical studies with fasudil have suggested that ROCKs could be potential novel therapeutic targets for cardiovascular diseases. In this review, we summarize the current understanding of the roles of ROCKs in the development of cardiac fibrosis and hypertrophy and discuss their therapeutic potential for deleterious cardiac remodeling. (Circ J 2016; 80: 1491-1498).

Figure 1

Structure of Rho-associated coiled-coil containing kinases (ROCKs). ROCK1 and ROCK2 have 1,354 and 1,388 amino acids, respectively. Both consist of an N-terminal kinase domain, followed by a coiled-coil-forming region containing a Rho-binding domain (RBD) and a C-terminal cysteine-rich domain (CRD) located within the pleckstrin homology (PH) motif. The isoforms share an overall 65% homology in amino acid sequence and 92% homology in their kinase domains.

Figure 2

Closed-to-open conformation of Rho-associated coiled-coil containing kinase (ROCK) activation. In the inactive form, the pleckstrin homology and Rho-binding domain (RBD) domain bind to the N-terminus of the enzyme, forming an autoinhibitory loop. Binding of GTP-RhoA to the RBD opens the configuration, leading to the active kinase form of ROCK. ROCKs are also activated after the cleavage of the C-terminus of ROCK1 and ROCK2 by caspase-3 and granzyme B, respectively. CRD, C-terminal cysteine-rich domain.

Figure 3

Role of Rho-associated coiled-coil containing kinases (ROCKs) in cardiac remodeling. Pharmacological studies using ROCK inhibitors have shown activation of RhoA/ROCKs signaling in response to hypertrophic stimuli. Both ROCK1 and ROCK2 contribute to cardiomyocyte apoptosis and cardiac fibrosis through upregulation of caspase-3 and connective tissue growth factor (CTGF), respectively. Caspase-3 activates ROCK1 in a positive feedback loop. In addition, ROCK2 mediates cardiomyocyte hypertrophy and fetal gene expression by activation of serum response factor (SRF) and extracellular signal-regulated kinase (ERK) through inhibition of four-and-a-half LIM-only protein 2 (FHL2).

Figure 4

Involvement of Rho-associated coiled-coil containing kinases (ROCKs) in pathological fibrosis in multiple organs.

Figure 5

Regulation of the ROCK/MRTF/SRF pathway in fibroblasts. ROCKs activate myocardin-related transcription factor (MRTF) and serum response factor (SRF). which leads to profibrotic gene expression in myofibroblasts. RhoA/ROCKs activation by extracellular stimuli promotes the assembly of F-actin, which enables MRTF to dissociate from G-actin, leading to its nuclear translocation and subsequent binding to SRF. SRF/MRTF initiates transcription of several profibrotic genes. ROCKs, Rho-associated coiled-coil containing kinases; TGF, transforming growth factor.

Figure 6

ROCK-mediated fibroblast-myofibroblast differentiation. Activation of ROCK/MRTF/SRF target genes promotes fibroblast to myofibroblast differentiation as exhibited by the expression of α-smooth muscle actin (SMA), a marker of myofibroblasts. The increased production of collagen by myofibroblasts is critical for fibrotic diseases. MRTF, myocardin-related transcription factor; ROCK, Rho-associated coiled-coil containing kinase; SRF, serum response factor.