Abstract 16516: ROCK2 in Vascular Smooth Muscle Cells Plays a Crucial Role for Hypoxia-Induced Pulmonary Hypertension in Mice
Background: Pulmonary hypertension (PH) still remains a fatal disease characterized by progressive increase in pulmonary artery pressure and pulmonary vascular resistance. We have previously demonstrated that the Rho/Rho-kinase (ROCK) pathway in vascular smooth muscle cells (VSMC) plays an important role in the pathogenesis of cardiovascular diseases including PH by accelerating vasoconstriction, migration and proliferation of VSMC. There are 2 isoforms of Rho-kinase, ROCK1 and ROCK2, and they have different functions with ROCK1 for circulating inflammatory cells and ROCK2 for the vasculature. However, it remains to be examined how ROCK2 in VSMC is involved in the pathogenesis of PH. In this study, we addressed this point by developing VSMC-specific ROCK2-deficient (ROCK2+/−) mice.
Methods and Results: We first confirmed by immunostaining that ROCK2 was highly expressed in the pulmonary arteries from PH patients compared with controls (normal tissue from lung cancer patients). We then developed VSMC-specific ROCK2+/− mice under the control of the SM22α promoter. These mutant mice revealed normal growth and body weight under physiological conditions. The growth rate of VSMC in vitro was slower in ROCK2+/− mice compared with littermates (first-passage days; 35.5 vs. 17.0). VSMC migration was also reduced in ROCK2+/− VSMC compared with control VSMC. After hypoxic exposure (1% O2 for 24 hours), ROCK activity (as evaluated by the extent of phosphorylation of myosin binding subunit, a downstream target of ROCK) was significantly increased in control VSMC in vitro (P<0.05, n=5 each). Chronic hypoxia (10% O2 for 4 weeks) significantly increased ROCK2 expression and ROCK activity in lung tissues from littermates (P<0.05 and P<0.01, respectively, n=4 each) and the development of right ventricular hypertrophy induced by chronic hypoxia in vivo was evident in littermates but was suppressed in ROCK2−/− mice (RV/LV+septum ratio, 0.41±0.02 vs. 0.26±0.03, P<0.01). Finally, the treatment with a specific Rho-kinase inhibitor, fasudil, ameliorated hypoxia-induced PH in mice in vivo.
Conclusions: These results provide the first direct evidence that ROCK2 in VSMC plays a crucial role in the pathogenesis of hypoxia-induced PH in mice.
- © 2010 by American Heart Association, Inc.