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Chronic Nicotine Exposure Enhances Insulin-Induced Mitogenic Signaling via Up-Regulation of 7 Nicotinic Receptors in Isolated Rat Aortic Smooth Muscle Cells

Department of Clinical Pharmacology, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan

Address all correspondence and requests for reprints to: Toshiyasu Sasaoka, M.D., Ph.D., Department of Clinical Pharmacology, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan. E-mail: tsasaoka{at}pha.u-toyama.ac.jp.

Insulin resistance and smoking are significant risk factors for cardiac and cerebral vascular diseases. Because vascular smooth muscle cells play a key role in the development and progression of atherosclerosis, we investigated the effect of nicotine on insulin-induced mitogenic signaling in aortic vascular smooth muscle cells isolated from Sprague Dawley rats. RT-PCR revealed the expression of 2–7, 10, ß1–3, , and subunits of the nicotinic acetylcholine receptor (nAChR) in the cells. Short-term nicotine treatment stimulated phosphorylation of p44/42-MAPK, p38-MAPK, and signal transducer and activator of transcription 3. However, an additive effect of nicotine pretreatment on insulin stimulation was only observed on p44/42-MAPK. The nicotine-induced phosphorylation of p44/42-MAPK and [methyl-³H]thymidine incorporation were effectively suppressed by a 7-nAChR-selective antagonist, methyllycaconitine, and the phosphorylation of p44/42-MAPK was stimulated by a 7-nAChR-specific agonist, GTS21. Furthermore, the phosphorylation was mediated via calmodulin kinase II, Src, and Shc. Interestingly, long-term (48-h) pretreatment with nicotine increased the amount of 7-AChR in the plasma membrane and insulin-induced phosphorylation of p44/42-MAPK. These results provide the first evidence that acute exposure to nicotine enhances insulin-induced mitogenesis predominantly by affecting the phosphorylation of p44/42-MAPK and that chronic exposure further augments the insulin signal via up-regulation of 7-nAChR, which may be crucial for the development and progression of atherosclerosis in large vessels.

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