Enhanced Escherichia coli invasion of human brain microvascular endothelial cells is associated with alternations in cytoskeleton induced by nicotine

Although epidemiological studies have shown that exposure to tobacco smoking significantly increases the risk of bacterial meningitis, heretofore the pathogenic effects of smoking on this disease have been poorly understood. In order to dissect this issue, we have investigated the effects of nicotine, the major component of tobacco, on E. coli invasion of human brain microvascular endothelial cells (HBMEC). Our studies showed that E. coli invasion of HBMEC was significantly enhanced by nicotine in a dose-dependent manner. The nicotine-mediated enhancement was associated with actin cytoskeleton rearrangement and morphological changes in the eukaryotic host cell that are essential for bacterial entry. The recombinant IbeA protein and alpha-bungarotoxin (a nicotinic acetylcholine receptor antagonist) were able to efficiently block the nicotine-mediated cellular effects, suggesting the involvement of the IbeA and nicotinic receptors. Blocking of phosphatidylinositol 3-kinase (PI3K) by LY294002 abolished the entry of E. coli in HBMECs treated with nicotine in a dose-dependent manner. Inhibition of PI3K was associated with decreased phosphorylation of Akt and actin cytoskeletal rearrangement. In contrast to PI3K, blockage of Rho kinase (ROCK) by Y27632 upregulated both nicotine- and E. coli-mediated cellular responses. Thus, this study provides experimental evidence for the first time that the major component of tobacco, nicotine, enhances meningitic E. coli invasion of HBMEC through modulation of cytoskeleton.