Abstract 1678: Nicotine Upregulates Early Growth Factor-1 Expression in Vascular Smooth Muscle Cell via ERK 1/2-Elk-1 Signaling and Exacerbates Neointimal Formation after Vascular Injury
Objectives: Cigarette smoking is implicated in the formation of occlusive vascular diseases. However, the effect of nicotine on the post-injury neointimal development is as yet under studied. We hypothesized that nicotine increases intimal hyperplasia after vascular injury by upregulating the atherogenic transcription factor Egr-1 in vascular smooth muscle cells (VSMCs) via the ERK 1/2 -ELK-1 signaling pathway.
Methods and Results: MEK-1/2 and its downstream kinases ERK 1/2 were rapidly activated in rat VSMC by exposure to nicotine (Western blot). Simultaneously to the ERK activation, nicotine induced a modest activation of p38 MAPK. Nicotine had no effect on the activation of other Mitogen Activated Protein Kinases such as SAP/JNK and ERK5. The phosphorylation of ELK-1 and the up-regulation of Egr-1 gene expression were detected after nicotine-mediated ERK activation. This increase in Egr-1 transcription factor was further confirmed by Western blot and EMSA. MEK-1/2 pharmacological blocker PD98059 (10 μM) abolished Egr-1 induction by nicotine and VSMC proliferation. 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 those 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 fold higher Ki67+ VSMCs (p = 0.04) than those of controls.
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 up-regulation of Egr-1 transcription factor via ERK-1/2-ELK-1 signaling pathway. These findings may in part explain the association between tobacco smoking and vascular diseases.
This research has received full or partial funding support from the American Heart Association, AHA Greater Southeast Affiliate (Alabama, Florida, Georgia, Louisiana, Mississippi, Puerto Rico & Tennessee).