Role of Gαq in smooth muscle cell proliferation

Abstract

Background G protein–linked receptors are involved in the processes that lead to intimal hyperplasia. This study examined the role of Gαq signaling pathways in vascular smooth muscle cell (SMC) proliferation in vitro. Methods Rat pulmonary artery SMCs were cultured in vitro. Standard assays of cellular DNA synthesis, proliferation, phospholipase C-β (PLCβ) activation, and extracellular signal-regulated kinase (ERK1/2) phosphorylation were used to study the response to angiotensin II (a specific Gαq agonist; 0.1-100 μmol/L) in the presence and absence of GP-2A (a competitive Gαq inhibitor; 10 μmol/L) and the PLCβ inhibitor U73122 (10μmol/L). Results Angiotensin II induced SMC DNA synthesis and cell proliferation. DNA synthesis was inhibited by both Gαq inhibitor, GP-2A, and PLCβ inhibitor U73122, in a dose-dependent manner (66% ± 7% of angiotensin II alone at 10 μmol/L for GP-2A [ P < .05] and 63% ± 6% for U73122). GP-2A completely inhibited angiotensin II–induced Gαq-mediated PLCβ phosphorylation. Activation of ERK1/2 by angiotensin II was significantly reduced by GP-2A ( P < .05) and by PLCβ inhibition ( P < .05). Conclusion Inhibition of Gαq decreases PLCβ and ERK1/2 phosphorylation, leading to decreased SMC proliferation in vitro. Understanding specific signal transduction pathways will be an integral component of anti-restenosis therapy. Clinical Relevance The universal response of a blood vessel to injury is chronic wound healing, which includes the development of intimal hyperplasia and subsequent remodeling of the vessel wall. This can lead to luminal narrowing in as many as 30% of patients undergoing angioplasty. Neointimal formation is the principal cause of in-stent recurrent stenosis. Intimal hyperplasia is in part produced by smooth muscle cell (SMC) proliferation. Understanding the keys to the proliferation of SMCs will enable therapies to be developed that may inhibit the initial development of intimal hyperplasia. Whereas in the past many studies focused on the multiple mechanical, humoral, and cellular elements that induce SMC proliferation, molecular therapeutics focuses on key choke points within the cell that can be used to inhibit proliferation. One of these key choke points is signal transduction. Gαq is one of the ubiquitous signal transduction proteins on the membrane of SMCs. Inhibiting G proteins, such as Gαq, would enable interference with a significant amount of the mechanical, humeral, and cellular elements that produce SMC proliferation, and thus decrease the development of intimal hyperplasia. The present study identifies and begins to map out the role of Gαq in SMC proliferation and investigates the possible use of a small peptide in its inhibition. Other data suggest that inhibition of other G proteins will also decrease intimal hyperplasia. This is therefore a fertile area for the development of therapeutics to inhibit intimal hyperplasia. The direct relevance to the clinician is that this study identifies a transduction pathway that may be inhibited, and points in the direction of a possible molecular therapeutic target that would be beneficial as an adjunct to angioplasty or as part of a drug-eluding stent regimen.