Rescue Treatment with a Rho-Kinase Inhibitor Normalizes

22 23 Chronic pulmonary hypertension in infancy and childhood is characterized by a fixed and 24 progressive increase in pulmonary arterial pressure and resistance, pulmonary arterial remodeling 25 and right-ventricular hypertrophy and systolic dysfunction. These abnormalities are replicated in 26 neonatal rats chronically exposed to hypoxia from birth in which increased activity of Rho-kinase 27 (ROCK) is critical to injury, as evidenced by preventive effects of ROCK inhibitors. Our 28 objective in the present study was to examine the reversing effects of a “late” or “rescue” 29 approach to treatment with a ROCK inhibitor on the pulmonary and cardiac manifestations of 30 established chronic hypoxic pulmonary hypertension. Rat pups were exposed to air or hypoxia 31 (13% O2) from postnatal day 1 and were treated with Y-27632 (15 mg/kg) or saline vehicle by 32 twice daily subcutaneous injection commencing on day 14, for up to 7 days. Treatment with Y33 27632 significantly attenuated right-ventricular hypertrophy, reversed arterial wall remodeling 34 and completely normalized right-ventricular systolic function in hypoxia-exposed animals. 35 Reversal of arterial wall remodeling was accompanied by increased apoptosis and attenuated 36 content of endothelin (ET)-1 and ET A-receptors. Treatment of primary cultured juvenile rat 37 pulmonary artery smooth muscle cells with Y-27632 attenuated serum-stimulated ROCK activity 38 and proliferation, and increased apoptosis. Smooth muscle apoptosis was also induced by short 39 interfering RNA-mediated knockdown of ROCK-II, but not of ROCK-I. We conclude that 40 sustained rescue treatment with a ROCK inhibitor reversed both the hemodynamic and structural 41 abnormalities of chronic hypoxic pulmonary hypertension in juvenile rats and normalized right42 ventricular systolic function. Attenuated expression and activity of ET-1 and its A-type receptor 43 Y-27632 Reverses Chronic Neonatal Pulmonary Hypertension Manuscript H-00595-2010.R2 3 on pulmonary arterial smooth muscle was a likely contributor to the stimulatory effects of ROCK 44 inhibition on apoptosis. In addition, our data suggest that ROCK-II may be dominant in 45 enhancing survival of pulmonary arterial smooth muscle. 46 47