α1-nAchR-Mediated Signaling Through Lipid Raft Is Required for Nicotine-Induced NLRP3 Inflammasome Activation and Nicotine-Accelerated Atherosclerosis

Background Nicotine exerts direct effects on multiple cell types in the cardiovascular system by associating with its high-affinity nicotinic acetylcholine receptors (nAchRs). Lipid raft is a membrane microdomain that recruits various receptors and signaling molecules for coordinating cellular immune response and many others signaling processes. Here, we aim to identify the essential role of lipid raft in mediating nicotine-triggered inflammatory and nicotine-accelerated atherosclerosis, and to figure out the specific receptor of nicotine-induced Nod-like receptor protein 3 (NLRP3) inflammasome activation in macrophage. Methods and Results ApoE(-/-) mice were fed with a high-fat diet to build atherosclerosis model. Methyl-beta-cyclodextrin was used to interrupt intact lipid raft. We confirmed that nicotine triggered NLRP3 inflammasome activation and induced macrophage migration into atherosclerotic plaque, thus accelerated atherosclerosis in apoE(-/-) mice fed with a high-fat diet. Mechanically, nicotine increased the expression of alpha 1-nAChR and stimulated the accumulation of alpha 1-nAChR in lipid raft, leading to NLRP3 inflammasome activation in macrophage. Conversely, silencing of alpha 1-nAChR in macrophage sufficiently blocked the pro-inflammasome activation effect of nicotine, indicating that alpha 1-nAChR was the specific receptor for nicotine in triggering NLRP3 inflammasome in macrophage. Furthermore, both the destruction of lipid raft by methyl-beta-cyclodextrin and the interference of lipid raft clustering by silencing acid sphingomyelinase reversed nicotine-induced NLRP3 inflammasome activation by reducing the accumulation of alpha 1-nAChR in lipid raft in macrophage, suggesting lipid raft-mediated accumulation of alpha 1-nAChR was the key event in regulating the pro-inflammatory effects of nicotine in macrophage. Importantly, nicotine-induced NLRP3 inflammasome activation and macrophage migration into atherosclerotic plaque were reversed by methyl-beta-cyclodextrin, making a significant improvement for atherosclerosis in apoE(-/-) mice fed with a high-fat diet. Conclusion alpha 1-nAChR-mediated signaling through lipid raft is required for NLRP3 inflammasome activation and pro-atherosclerotic property of nicotine.