TNF-alpha-induced migration of vascular smooth muscle cells is MAPK dependent

Migration of vascular smooth muscle cells (VSMC) is a key event in neointim al formation and atherosclerosis that may be linked to the accumulation of inflammatory cells and release of chemotactic cytokines, Tumor necrosis fac tor-alpha (TNF-alpha) induces chemotaxis of inflammatory cells and fibrobla sts, but little is known about chemotactic signaling by TNF-alpha in VSMC, The aim of this study was to investigate the role of TNF-alpha in VSMC migr ation and to elucidate the chemotactic signaling pathways mediating this ac tion. TNF-alpha (50 to 400 U/mL) induced migration of cultured rat aortic V SMC in a dose-dependent manner. Because activation of the extracellular sig nal-regulated kinase 1/2 mitogen-activated protein kinase (MAPK) is known t o be required in platelet-derived growth factor-directed and angiotensin II -directed migration of these cells, we used the MAPK-inhibitor PD98059 to d etermine if chemotactic signaling by TNF-alpha involves the MAPK pathway as well. We found that TNF-alpha-directed migration was substantially inhibit ed by PD98059, TNF-alpha (100 U/mL) transiently activated MAPK with a maxim al induction 10 minutes after stimulation that returned to baseline levels by 2 hours after treatment. Only a single peak of increased MAPK activity w as seen. PD98059 also blocked TNF-alpha-stimulated MAPK activation in a con centration-dependent manner, which is consistent with its inhibition of TNF -alpha-directed migration. To identify which TNF-cr receptor is involved in TNF-alpha-induced MAPK activation, antibodies against the p55 TNF-alpha re ceptor-1 (TNF-R1) and the p75 TNF-alpha receptor-2 (TNF-R2) were used. VSMC express both receptors, but TNF-cr-induced MAPK activation was inhibited o nly by the TNF-R1 antibody. The TNF-R2 antibody had no effect. Thiazolidine diones are known to inhibit TNF-alpha signaling in adipose tissue and atten uate platelet-derived growth factor-directed and angiotensin II-directed mi gration in VSMC, We therefore investigated the effects of the thiazolidined iones troglitazone (TRO) and rosiglitazone (RSG) on TNF-alpha-induced migra tion. Both TRO and RSG inhibited migration, but neither attenuated TNF-alph a-induced MAPK activation, indicating that their antimigration activity was exerted downstream of MAPK, These experiments provide the first evidence t hat early activation of MAPK is a crucial event in TNF-cu-mediated signal t ransduction leading to VSMC migration. Moreover, inhibition of TNF-alpha-di rected migration by the insulin sensitizers TRO and RSG underscores their p otential as vasculoprotective agents.