Recruitment of αα7 nicotinic acetylcholine receptor to caveolin-1-enriched lipid rafts is required for nicotine-enhanced Escherichia coli K1 entry into brain endothelial cells

Author： Chi Feng Wang Lin Zheng Xueye Jong Ambrose Huang Sheng-He

Publisher： Future Medicine

ISSN： 1746-0913

Source： Future Microbiology, Vol.6, Iss.8, 2011-08, pp. : 953-966

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Abstract

Aim: We investigate how the αα7 nicotinic acetylcholine receptor (αα7 nAChR), an essential regulator of inflammation, contributes to the αα7 agonist nicotine-enhanced Escherichia coli K1 invasion of human brain microvascular endothelial cells (HBMECs) through lipid rafts/caveolae-mediated signaling. Materials & methods: αα7 nAChR-mediated signaling and bacterial invasion were defined by lipid raft fractionation, immunofluorescence microscopy and siRNA knockdown. Results: Nicotine-enhanced bacterial invasion was dose-dependently inhibited by two raft-disrupting agents, nystatin and filipin. Significant accumulation of the lipid raft marker GM3 was observed in HBMEC induced by E. coli K1 and nicotine. The recruitment of αα7 nAChR and related signaling molecules, including vimentin, and Erk1/2, to caveolin-1 enriched lipid rafts was increased upon treatment with E44 or E44 plus nicotine. Erk1/2 activation (phosphorylation), which is required for αα7 nAChR-mediated signaling and E44 invasion, was associated with lipid rafts and nicotine-enhanced bacterial infection. Furthermore, E44 invasion, E44/nicotine-induced activation of Erk1/2 and clustering of αα7 nAChR and caveolin-1 was specifically blocked by both siRNAs. Conclusion: αα7 nAChR-mediated signaling through lipid rafts/caveolae is required for nicotine-enhanced E. coli K1 invasion of HBMEC.