Shear stress stimulated endothelial cell derived PDGF and IL-1 alpha both stimulate SMC chemotaxis via the MAPK pathway

Abstract

Hemodynamic forces such as shear stress (SS) are implicated in the pathogenesis of atherosclerosis and neointimal hyperplasia. SS stimulates endothelial cells (EC) to secrete factors such as platelet-derived growth factor-BB (PDGF) and interleukin-1 alpha (IL-1) that attract smooth muscle cell (SMC) migration. The purpose of this study was to determine whether SS stimulated EC secretion of PDGF and IL-1 both induce SMC migration via the SMC mitogen activated protein kinase (MAPK) signaling pathway. Bovine aortic EC were exposed to arterial levels of oscillatory SS (14 dyne/cm2) for 16 hours (control EC, static conditions). The resulting conditioned medium (CM) was used as a chemoattractant in a modified Boyden chamber to assess SMC migration for 4 hours. Excess amount of neutralizing antibodies against IL-1 or PDGF were included in the CM, or the MAPK inhibitor PD98059 preincubated with SMC, for some experiments. Phosphorylated and total MAPK (ERK1/2) were assessed by Western blot. Results were analyzed with ANOVA. CM from EC exposed to SS stimulated SMC chemotaxis 3-fold compared with CM from EC grown under static conditions (p < 0.01). IL-1 (0.1 pg/ml) stimulated SMC chemotaxis by 87% compared to medium alone, a similar degree as PDGF. Antibodies against IL-1 decreased SMC migration stimulated by CM by 42%, a similar degree inhibited by antibodies against PDGF. Both PDGF and IL-1 stimulated SMC MAPK activity that was inhibited by antibodies to PDGF or IL-1; SMC chemotaxis was similarly inhibited by the MAPK inhibitor PD98059. SS stimulation of SMC migration may depend in part upon EC production of soluble factors such as IL-1 and PDGF, both of which activate the SMC MAPK signal transduction pathway. These results suggest that the effects of hemodynamic forces on the blood vessel may involve complex paracrine mechanisms and that the MAPK pathway may be a converging site of control.