Cholesterol Dependence of Vascular ERK1/2 Activation and Growth in Response to Stretch

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Abstract
Objective— Stretch-induced growth of the vascular wall plays a role in hypertension and neointima formation. Its signal pathways involve integrins, cytoskeleton, membrane receptors, and ion channels, some of which are organized in cholesterol-rich, membrane domains such as lipid rafts or caveolae. This study tested the role of rafts/caveolae in stretch-induced vascular growth by manipulation of membrane cholesterol contents. Methods and Results— Growth and protein synthesis were induced by mechanical stretch of rat portal veins in vitro. Sucrose gradient centrifugation showed stretch-induced tyrosine phosphorylation primarily in fractions containing caveolin-1. Disruption of membrane caveolae with use of methyl-β-cyclodextrin (mβcd) reduced weight gain, protein synthesis, and DNA synthesis to levels in unstretched, control veins. These effects were partially reversed by restoration of cellular cholesterol contents. Inhibited growth was associated with abolished activation of extracellular signal–regulated kinase (ERK) 1/2 in response to stretch and endothelin-1 (ET-1) but not to angiotensin II. Inhibition of ET-1 type A (ET A ) receptors by RF139317 or endothelin-converting enzyme by phosphoramidone abolished stretch-induced ERK1/2 activation, which was, however, unaffected by removal of the endothelium. Conclusions— Stretch-induced growth signaling in vascular smooth muscle depends on cholesterol-rich, membrane microdomains by a mechanism involving ET A receptors that respond to endogenous ET-1 production.