NO Attenuates Insulin Signaling and Motility in Aortic Smooth Muscle Cells via Protein Tyrosine Phosphatase 1B–Mediated Mechanism

Abstract

Objective-Hyperinsulinemia is a significant risk factor for the pathogenesis of vascular disease. Protein tyrosine phosphatase 1B (PTP1B) has been recognized as a modulator of insulin signaling in nonvascular cells, and we have recently reported that NO increases the activity of PTP1B in rat vascular smooth muscle cells. In the present study, we tested the hypothesis that NO attenuates insulin-stimulated cell motility via a PTP1B-mediated mechanism involving downregulation of insulin signal transduction. Methods and Results-Treatment of primary aortic smooth muscle cells from newborn rats with the NO donor S-nitroso-N-acetylpenicillamine reduced cell motility, tyrosine phosphorylation levels of insulin receptor ␤ subunit and insulin receptor substrate-1, and extracellular signal-regulated kinase activity. Overexpression of wild-type PTP1B via an adenoviral vector blocked the capacity of insulin to stimulate cell motility and insulin receptor phosphorylation, whereas expression of a dominant-negative mutant of PTP1B attenuated the capacity of NO to decrease cell motility. Conclusions-Our findings indicate that activation of PTP1B is necessary and sufficient to account for the capacity of NO to decrease insulin-stimulated signal transduction and cell motility in cultured aortic smooth muscle cells. The results could explain the capacity of NO to oppose neointima formation in states of hyperinsulinemia. Key Words: cell signaling Ⅲ signal transduction Ⅲ atherosclerosis Ⅲ growth factors Ⅲ type 2 diabetes T ype II diabetes is a major risk factor for the pathogenesis of vascular disease, including that associated with hypertension and atherosclerosis. That diabetes increases the frequency of coronary vessel restenosis occurring after angioplasty is also well established. 1 Most forms of vascular disease in conduit arteries manifest neointimal enlargement, and although type II diabetes is associated with hyperglycemia as well as hyperinsulinemia, recent studies have suggested that elevated insulin levels may be the more important factor in the pathogenesis of neointimal enlargement. 2,3 The proliferation and motility of vascular smooth muscle cells is regulated in reciprocal fashion by stimulators (eg, fibroblast growth factor, platelet-derived growth factor, and heparin-binding epidermal growth factor) and inhibitors of mitogenesis or motility (eg, prostanoids, heparin, atrial natriuretic factor, and transforming growth factor-␤). 4 -7 Similar to many other growth factors, insulin has the capacity to stimulate cell motility in vitro, which could explain the pathogenesis of diabetic neointimal growth. 3,8 Early studies from several laboratories, including ours, have reported that NO decreases vascular smooth muscle cell proliferation in subcultured cells from adult rats or in primary cultures from newborn rats. 9,10 More recent studies have reported that NO also inhibits aortic smooth muscle cell motility. 11,12 Furthermore, several studies in vivo have reported that NO, or its precursor arginine, attenuates neointima ...

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“…Western blotting analysis was performed as previously described [29]. Cells were lysed in RIPA buffer containing 1 mM sodium vanadate, 1 mM sodium fluoride, and phosphatase inhibitor cocktail (Sigma, St. Louis, MO).…”