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Abnormal growth of the intimal layer of blood vessels (neointima formation) contributes to the progression of atherosclerosis and in-stent restenosis.Recent evidence shows that the 18-kDa translocator protein (TSPO),a mitochondrial membrane protein,is involved in diverse cardiovascular diseases.In this study we investigated the role of endogenous TSPO in neointima formation after angioplasty in vitro and in vivo.We established a vascular injury model in vitro by using platelet-derived growth factor-BB (PDGF-BB) to stimulate rat thoracic aortic smooth muscle cells (A10 cells).We found that treatment with PDGF-BB (1-20 ng/mL) dosedependently increased TSPO expression in A10 cells,which was blocked in the presence of PKC inhibitor or MAPK inhibitor.Overexpression of TSPO significantly promoted the proliferation and migration in A10 cells,whereas downregulation of TSPO expression by siRNA or treatment with TSPO ligands PK1 1195 or Ro5-4864 (1 04 nM) produced the opposite effects.Furthermore,we found that PK1 1195 (10-104 nM) dose-dependently activated AMPK in A10 cells.PK1 1195-induced inhibition on the proliferation and migration of PDGF-BB-treated A10 cells were abolished by compound C (an AMPK-specific inhibitor,103 nM).In rats with balloon-injured carotid arteries,TSPO expression was markedly upregulated in the carotid arteries.Administration of PK1 1195 (3 mg/kg every 3 days,ip),starting from the initial balloon injury and lasting for 2 weeks,greatly attenuated carotid neointima formation by suppressing balloon injury-induced phenotype switching of VSMCs (increased cα-SMA expression).These results suggest that TSPO is a vascular injury-response molecule that promotes VSMC proliferation and migration and is responsible for the neointima formation after vascular injury,which provides a novel therapeutic target for various cardiovascular diseases including atherosclerosis and restenosis.