Antioxidants Relieve Phosphatase Inhibition and Reduce PDGF Signaling in Cultured VSMCs and in Restenosis

Abstract

Objective— Growth factor– and reactive oxygen species (ROS)-induced activation of VSMCs is involved in vascular disease. This study investigates whether inhibitory oxidation of protein tyrosine phosphatases (PTPs) contributes to signaling in VSMCs in vitro and in vivo, and analyzes whether ROS- and growth factor–dependent vascular smooth muscle cell (VSMC) signaling is blunted by antioxidants that are able to activate oxidized PTPs. Methods and Results— Signaling induced by H 2 O 2 and platelet-derived growth factor (PDGF) was analyzed in VSMCs with or without the antioxidants N-acetyl-cysteine (NAC) and tempol. Effects of antioxidants on PDGF-stimulated chemotaxis and proliferation were determined. In vivo effects of antioxidants were analyzed in the rat carotid balloon-injury model, by analyzing neointima formation, cell proliferation, PDGF β-receptor status, and PTP expression and activity. NAC treatment prevented H 2 O 2 -induced PTP inhibition, and reduced H 2 O 2 - and ligand-induced PDGF β-receptor phosphorylation, PDGF-induced proliferation, and chemotaxis of VSMCs. Antioxidants inhibited neointima formation and reduced PDGF receptor phosphorylation in the neointima and also increased PTP activity. Conclusion— PTP-inhibition was identified as an intrinsic component of H 2 O 2 - and PDGF-induced signaling in cultured VSMCs. The reduction in PDGF β-receptor phosphorylation in vivo, and the increase in PTP activity, by antioxidants indicate activation of oxidized PTPs as a previously unrecognized mechanism for the antirestenotic effects of antioxidants. The findings thus suggest, in general terms, reactivation of oxidized PTPs as a novel antirestenotic strategy.