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

Abstract

Migration of vascular smooth muscle cells (VSMC) is a key event in neointimal formation and atherosclerosis that may be linked to the accumulation of inflammatory cells and release of chemotactic cytokines. Tumor necrosis factor-α (TNF-α) induces chemotaxis of inflammatory cells and fibroblasts, but little is known about chemotactic signaling by TNF-α in VSMC. The aim of this study was to investigate the role of TNF-α in VSMC migration and to elucidate the chemotactic signaling pathways mediating this action. TNF-α (50 to 400 U/mL) induced migration of cultured rat aortic VSMC in a dose-dependent manner. Because activation of the extracellular signal- regulated kinase 1/2 mitogen-activated protein kinase (MAPK) is known to be required in platelet-derived growth factor-directed and angiotensin II- directed migration of these cells, we used the MAPK-inhibitor PD98059 to determine if chemotactic signaling by TNF-α involves the MAPK pathway as well. We found that TNF-α-directed migration was substantially inhibited by PD98059. TNF-α (100 U/mL) transiently activated MAPK with a maximal induction 10 minutes after stimulation that returned to baseline levels by 2 hours after treatment. Only a single peak of increased MAPK activity was seen. PD98059 also blocked TNF-α-stimulated MAPK activation in a concentration-dependent manner, which is consistent with its inhibition of TNF-α-directed migration. To identify which TNF-α receptor is involved in TNF-α-induced MAPK activation, antibodies against the p55 TNF-α receptor-1 (TNF-R1) and the p75 TNF-α receptor-2 (TNF-R2) were used. VSMC express both receptors, but TNF-α-induced MAPK activation was inhibited only by the TNF- R1 antibody. The TNF-R2 antibody had no effect. Thiazolidinediones are known to inhibit TNF-α signaling in adipose tissue and attenuate platelet-derived growth factor-directed and angiotensin II-directed migration in VSMC. We therefore investigated the effects of the thiazolidinediones troglitazone (TRO) and rosiglitazone (RSG) on TNF-α-induced migration. Both TRO and RSG inhibited migration, but neither attenuated TNF-α-induced MAPK activation, indicating that their antimigration activity was exerted downstream of MAPK. These experiments provide the first evidence that early activation of MAPK is a crucial event in TNF-α-mediated signal transduction leading to VSMC migration. Moreover, inhibition of TNF-α-directed migration by the insulin sensitizers TRO and RSG underscores their potential as vasculoprotective agents.