Nicotine-mediated autophagy of vascular smooth muscle cell accelerates atherosclerosis via nAChRs/ROS/NF-κB signaling pathway

Background and aims: Cigarette smoking is an established risk factor for atherosclerosis. Nicotine, the major constituent of cigarettes, mediates the phenotype switching of vascular smooth muscle cells (VSMCs) and contributes to atherogenesis. Recent studies show that Autophagy regulates atherogenesis via several pathways. The aim of this study is to determine whether nicotine regulates Autophagy and subsequently mediates the phenotypic transition of VSMCs.

Methods and results: Oil Red O and HE staining of aortic sections of ApoE^-/- mice showed that nicotine promoted atherosclerosis, and in situ expression of α-SMA indicated the involvement of VSMCs. Western blotting documented that nicotine induced the aorta Autophagy. Cultured VSMCs treated with nicotine resulted in the increase of LC3 II-to-LC3 I ratio and the decrease of p62, along with GFP-LC3 puncta assay and transmission electron microscopy, further reflecting nicotine-induced Autophagy. In addition, Western blotting and quantitative Real-Time PCR showed that VSMCs exposed to nicotine underwent changes in the expression of differentiation markers (α-SMA, SM22α and osteopontin), confirming the role of nicotine in VSMC differentiation. Transwell migration and scratch assays demonstrated that nicotine increased the migratory capacity of VSMCs. Finally, nicotine also increased the levels of Reactive Oxygen Species (ROS), as measured by DCFH-DA staining. After respectively inhibiting Autophagy (3-MA), oxidative stress (NAC), NF-κB activity (BAY 11-7082, si-p65) and nicotinic acetylcholine receptors (nAChRs, hexamethonium), nicotine-induced Autophagy and VSMC phenotype switching were reversed.

Conclusions: Nicotine-induced Autophagy promotes the phenotype switching of VSMCs and accelerates atherosclerosis, which is partly mediated by the nAChRs/ROS/NF-κB signaling pathway.