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(Circulation Research. 2004;94:1383.)
© 2004 American Heart Association, Inc.

Integrative Physiology

RhoA Activation by Hypoxia in Pulmonary Arterial Smooth Muscle Cells Is Age and Site Specific

Karine Bailly, Anne J. Ridley, Susan M. Hall, Sheila G. Haworth

From the Vascular Biology and Pharmacology Unit (K.B., S.M.H., S.G.H.), Institute of Child Health, University College London, UK; Ludwig Institute for Cancer Research (A.J.R.), Royal Free and University College Medical School Branch, London, UK; and the Department of Biochemistry and Molecular Biology (A.J.R.), University College London, UK.

Correspondence to Professor S.G. Haworth, Developmental Vascular Biology and Pharmacology Unit, Institute of Child Health, University College London, 30 Guilford St, London WC1N 1EH, UK. E-mail S.Haworth{at}ich.ucl.ac.uk

Hypoxia induces vasoconstriction of pulmonary arteries through contraction of smooth muscle cells (SMCs). The GTPase RhoA regulates smooth muscle contractility and actin cytoskeletal remodeling through the Rho-associated kinase (ROCK). We previously found that the postnatal fall in pulmonary vascular resistance was associated with actin cytoskeletal remodeling in porcine pulmonary arterial SMCs (PASMCs) in vivo. Here, we investigated the effects of acute and chronic hypoxia on the morphology and RhoA activity of PASMCs from fetal and neonatal piglets. Acute hypoxia enhanced actin stress fiber formation and RhoA activity in both inner and outer medial PASMCs from the fetus but only in the inner medial PASMCs from normal 3-day-old piglets. The increased stress fiber formation was dependent on Rho and ROCK. In outer medial PASMCs from 14-day-old animals, acute hypoxia decreased RhoA activity. Interestingly, outer medial PASMCs from animals exposed to chronic hypoxia had fewer stress fibers associated with a lower basal RhoA activity. Treatment of PASMCs from normal 3-day-old piglets with Rho or ROCK inhibitors for 24 hours induced a similar morphology. Rac activity was not altered by either acute or chronic hypoxia. These data show that acute hypoxia induces RhoA activation only in PASMCs from young animals, whereas chronic hypoxia selectively downregulates RhoA activity in outer medial PASMCs leading to an altered phenotype.

Key Words: pulmonary • smooth muscle cell • hypoxia • Rho • Rac

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