K. Peppel, L. Zhang, T. T. T. Huynh, X. Huang, A. Jacobson, L. Brian, S. T. Exum, P.-O. Hagen and N. J. Freedman. Overexpression of G Protein-Coupled Receptor Kinase-2 in Smooth Muscle Cells Reduces Neointimal Hyperplasia. Journal of Molecular Cellular Cardiology (2002) 34, 1399–1409. The activation of vascular smooth muscle cells (SMCs) in neointimal hyperplasia involves signaling through receptor tyrosine kinases as well as G protein-coupled receptors. Overexpression of G protein-coupled receptor kinase-2 (GRK2) in SMCs can attenuate mitogenic signaling and proliferation in response to not only several G protein-coupled receptor agonists, but also platelet-derived growth factor (PDGF). To test whether overexpression of GRK2 could inhibit other SMC responses implicated in neointimal hyperplasia, we assessed SMC chemotaxis and mitogenic signaling evoked by PDGF and G_q-coupled receptor agonists. To test the effects of GRK2 overexpression on neointimal hyperplasia in vivo, we employed a rabbit autologous vein graft model system. GRK2 overexpression reduced PDGF-promoted SMC chemotaxis by 85% (P<0.01), but had no effect on chemotaxis promoted by epidermal growth factor (EGF). Congruently, GRK2 overexpression reduced by ∼50% (P<0.05) the [³H]thymidine incorporation induced by combinations of PDGF and Gq-coupled receptor agonists, but had no effect on that induced by PDGF plus EGF. PDGF-, but not EGF-promoted phosphoinositide 3-kinase activity in SMCs was also inhibited by GRK2 overexpression. In rabbit vein grafts, we achieved GRK2 overexpression in medial SMCs, reduced cell proliferation during the first week after graft implantation, and reduced steady state neointimal thickness by 29% (P<0.01), without affecting medial thickness or potentiating SMC apoptosis. Because of its ability to dampen chemotactic and mitogenic signaling through PDGF and Gq-coupled receptors, GRK2 overexpression in SMCs may be a useful therapeutic approach for neointimal hyperplasia.