Abstract 980: Nicotine Activates p44/42 MAPK Signaling in Vascular Smooth Cells and Exacerbates Vascular Inflammation and Neointimal Formation after Vascular Injury
Objectives: Cigarette smoking is implicated in the formation of occlusive vascular diseases. However, the effect of nicotine on development of neointima has not been well studied. We hypothesized that nicotine increases intimal hyperplasia after vascular injury by activating p44/42 mitogen-activated protein kinases (MAPK) in vascular smooth muscle cells (VSMCs).
Methods and Results: The presence of nicotine receptors (nAchR) on VSMCs were demonstrated by Western blot and immunohistochemistry. Although VSMCs expressed several nAChR subunits, the α7 was the most abundant both in vitro and in vivo. This finding was confirmed by the binding of α-bungarotoxin to the surface of VSMCs. Activation of the nAChR by nicotine induced rapid activation of p44/42 MAPK in VSMCs. The p44/42 MAPK activation by nicotine was dose-dependent, reached the maximum within 5 minutes, and returned to basal levels 20 minutes later. Simultaneously to the p44/42 MAPK activation, nicotine induced the p38 MAPK phosphorilation. Nicotine had no effect on the activation of other MAPKs such as SAP/JNK and ERK5. To demonstrate that nicotine had mitogenic effects on VSMCs in vivo, control rats (n=9) and rats chronically exposed to nicotine (100 mg/L in drinking water, n=10) were submitted to vascular injury in the left femoral artery. The cotinine levels in the nicotine treated rats were higher than in control animals, and similar to the ones observed in active smokers (578.27 ± 149.94 vs. 13.30 ± 10.08 ng/mL). Rats that received nicotine developed more neointima after vascular injury than controls (intima/media ratio was 0.42 ± 0.23 and 0.14 ± 0.07, respectively, p=0.02). The neointimas of nicotine treated animals had 1.4 folds higher Ki67+ VSMCs (p=0.04) than those of controls. The injured arteries of nicotine treated animals demonstrated increased macrophage infiltration than those of controls (850 ± 230 vs. 396 ± 87 macrophages per mm2, p=0.006).
Conclusions: Nicotine enhanced proliferation of VSMCs in vivo and exacerbated neointimal formation after vascular injury. The mitogenic effect of nicotine on VSMCs is mediated by the activation of p44/42 MAPK through the non-neuronal nAChR. These findings may, in part, explain the association between tobacco smoking and vascular diseases.