Abstract
Pregnane X receptor (PXR) is a member of nuclear receptor superfamily and responsible for the detoxification of xenobiotics. Recent studies demonstrated that PXR was also expressed in the vasculature and protected the vessels from endogenous and exogenous insults, thus representing a novel gatekeeper in vascular defense. In this study, we examined the potential function of PXR in the neointimal formation following vascular injury. In the rat carotid artery after balloon injury, overexpression of a constitutively active PXR increased the intima-to-media ratio in the injured region. PXR increased cell proliferation and migration in cultured rat aortic smooth muscle cells (SMCs) by inducing the expressions of cyclins (cyclin A, D1, and E) and cyclin-dependent kinase 2. In addition, PXR increased the phosphorylation and activation of extracellular-signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). Inactivation of ERK1/2 and p38 MAPK pathways using selective inhibitors (U0126 and SB203580) abrogated PXR-induced SMC proliferation and migration. Furthermore, cigarette smoke particles (CSP) activated PXR in SMCs. Knockdown of PXR by small interfering RNA suppressed the cell proliferation, migration, and activation of the MAPK pathways by CSP. These findings suggested a novel role for PXR in promoting SMC proliferation and migration, and neointimal hyperplasia. Therefore, PXR may be a potential therapeutic target for vascular disease related to xenobiotics such as cigarette smoking and other environmental pollutants.