Cigarette Smoke and Nicotine-Induced Remodeling of Actin Cytoskeleton and Extracellular Matrix by Vascular Smooth Muscle Cells

Cigarette smoking is a significant risk factor for atherosclerosis, which involves the invasion of vascular smooth muscle cells (VSMCs) from the media to intima. Many invasive cells remodel the actin cytoskeleton to form podosomes, which regulate metalloproteinase (MMP) release for extracellular matrix (ECM) degradation. We tested the hypothesis that cigarette smoke extract (CSE) modulates the structure and function of podosomes in VSMCs. We found that, in response to PKC activation by phorbol dibutyrate (PDBu), untreated A7r5 VSMCs formed podosomes, whereas CSE, nicotine, and carbachol-treated cells formed actin-rich rings. The nicotinic acetylcholine receptor (nAChR) antagonist α-bungarotoxin abolished the effects of nicotine and carbachol on actin-rich ring formation. Immunofluorescence labeling experiments localized MMP-2 and nAChRs at the actin-rich rings. Nicotine-induced actin-rich ring formation required 6-12 hr exposure, and was sensitive to the protein synthesis inhibitor cycloheximide. Conditioned media collected from cell culture of nicotine-treated cells induced podosome remodeling in untreated cells. When cells were cultured on DQ-gelatin, untreated cells exhibited a fibrillar network of fluorescence from DQ-gelatin degradation, which, upon PDBu stimulation, reorganized into peripheral dots and migrated towards the perinuclear region. In contrast, nicotine-treated cells, upon PDBu stimulation, reorganized the fluorescence into perinuclear fibrils, which dispersed into small dots and disappeared rapidly over time. Results from this study suggest that nicotine, by activating nAChRs and inducing phenotypic modulation, may prime VSMCs to become hyperresponsive to PKC activation with an enhanced ability to remodel the actin cytoskeleton and release MMP for invasion of the ECM. This study was supported by NIH grant HL-52714.