Decreased perivascular fibrosis but not cardiac hypertrophy in ROCK1 ^+/- haploinsufficient mice

Background - Rho GTPase and its downstream target, Rho-associated kinase (ROCK), have been implicated in diverse cardiovascular diseases such as cardiac hypertrophy. However, pharmacological inhibitors of ROCK are not entirely specific, nor can they discriminate between the ROCK isoforms ROCK1 and ROCK2. To determine the specific role of ROCK1 in the development of cardiac hypertrophy, we generated ROCK1^+/- haploinsufficient mice and determined whether cardiac hypertrophy and remodeling are decreased in these mice. Methods and Results - Litters of ROCK1^-/- mice on C57B1/6 background were markedly underrepresented, suggesting lethality in utero or postnatally. ROCK1^+/- mice, however, are viable and fertile with no obvious phenotypic abnormalities. Basal blood pressure, heart rate, and cardiac dimension and function in ROCK1^+/- mice were similar to those in wild-type (WT) littermates. Infusion of angiotensin II (400 ng · kg ^-1 · min^-1 for 28 days) or treatment with N ^G-nitro-L-arginine methyl ester (1 mg/mL in drinking water for 28 days) caused similar increases in systolic blood pressure, left ventricular wall thickness, left ventricular mass, ratio of heart weight to tibial length, and cardiomyocyte size in ROCK1^+/- mice and WT littermates. In contrast, perivascular fibrosis in hearts was increased to a lesser extent in ROCK1 ^+/- mice compared with WT littermates. This was associated with decreased expression of transforming growth factor-β, connective tissue growth factor, and type III collagen. In addition, perivascular fibrosis induced by transaortic constriction or myocardial infarction was decreased in ROCK1^+/- mice compared with WT littermates. Conclusions - These findings indicate ROCK1 is critical for the development of cardiac fibrosis, but not hypertrophy, in response to various pathological conditions and suggest that signaling pathways leading to the hypertrophic and profibrotic response of the heart are distinct.