Tyrosine kinase-mediated activation of NAD(P)H oxidase enhances proliferative capacity of diabetic vascular smooth muscle cells

To investigate a potential molecular basis for a link between diabetes and atherosclerosis, experiments were performed to determine the role of NAD(P)H oxidase in the enhanced proliferative capacity of vascular smooth muscle cells (VSMC) from OLETF rat, an animal model of type 2 diabetes. An enhanced proliferative response to 10% fetal bovine serum with an increased cell cycle progression from G1 to S phase as well as an augmented superoxide generation with an increased NAD(P)H oxidase activity were observed in diabetic versus control VSMC. Both the enhanced proliferation and superoxide generation in diabetic VSMC were significantly attenuated not only by diphenyleneiodonium (10 μM) and apocynin (100 μM), NAD(P)H oxidase inhibitors but also by protein tyrosine kinase inhibitors such as genistein (100 μM) and AG 112 (100 μM). Furthermore, the enhanced NAD(P)H oxidase activity in diabetic VSMC was significantly attenuated by genistein and AG112, but not by daidzein (100 μM), a genistein analogue devoid of protein tyrosine kinase inhibitory properties. Based on these results, it is suggested that the enhanced proliferative capacity of diabetic VSMC is closely related to the activation of NAD(P)H oxidase that is induced through activation of protein tyrosine kinase.