Lovastatin Inhibits Thrombospondin-1-Induced Smooth Muscle Cell Chemotaxis

Abstract

Thrombospondin-1 (TSP-1) induces vascular smooth muscle cell (VSMC) migration and is important in the development of intimal hyperplasia. HMG-CoA reductase inhibitors, such as lovastatin, reduce the incidence of vascular restenosis after angioplasty by both cholesterol lowering and pleiotropic effects. Inhibition of the mevalonate pathway is largely responsible for these pleiotropic properties. This inhibition prevents isoprenylation of the small G proteins, Rho and Ras, by geranylgeranyl and farnesyl pyrophosphate, respectively. Isoprenylation is required for Ras and Rho activation, which is relevant for cell migration. Lovastatin inhibits TSP-1-induced VSMC chemotaxis by inhibiting small G proteins via the mevalonate pathway. Chemotaxis was assessed using a modified Boyden chamber. Quiescent VSMCs were pretreated with serum free media (SFM), lovastatin with or without mevalonate farnesyl (FTI), geranylgeranyl transferase inhibitors (GGTI), farnesyl transferase inhibitor (FPT), or the Rho kinase inhibitor (Y-27632). Chemoattractants were SFM or TSP-1. Comparisons were made by ANOVA followed by post-hoc testing (P<0.05). The effect of lovastatin on Ras activation was evaluated using cells pretreated with SFM or lovastatin, with or without mevalonate prior to TSP-1 exposure. Western blot for Ras activation was performed. Lovastatin dose-dependently inhibited TSP-1-induced chemotaxis, which was reversed by mevalonate. Mevalonate did not induce chemotaxis independently. FTI and FPT, but not GGTI or Y-27632, inhibited TSP-1-induced Ras activation and TSP-1-induced chemotaxis. Lovastatin inhibition of Ras activation was reversed with mevalonate. Ras, not Rho, is relevant for TSP-1-induced VSMC chemotaxis. These data suggest that lovastatin suppresses TSP-1-induced chemotaxis by inhibition of Ras.