Background: Endothelial cells (ECs) are constantly subjected to blood flow-generated mechanical forces including shear stress and cyclic strain. Shear stress modulates vascular structure and function by regulating the expression of many genes. We have previously demonstrated that low shear stress induces the IL-8 gene expression in ECs. The present study was undertaken to investigate the roles of MAPKs in the regulation of the shear stress-induced IL-8 gene expression in human umbilical vein endothelial cells (HUVECs).
Methods: Cultured HUVECs were exposed to low shear stress (4.2 dyne/cm(2)). The phosphorylation of MAPKs including ERK1/2, JNK and p38, was detected by Western blot. Immunocytochemistry was employed to measure the distribution and intensity of MAPKs. Inhibitors, a dominant negative-p38 and RNAi for JNK, were used to block the MAPK pathways, after which the LightCycler system was employed to assay the IL-8 gene expression.
Findings: The activation of ERK1/2, p38 MAPK and JNK1/2 was observed in ECs exposed to low shear stress. Furthermore, phospho-ERK1/2, JNK1/2 and p38 MAPK translocated from the cytoplasm into the nucleus. Inhibition of ERK1/2, JNK1/2 and p38 MAPK with PD98059, SP600125 and SB203580, respectively, led to the suppression of the shear stress-induced IL-8 gene expression (P<0.01), which was also blocked by JNK1/2 siRNA (small interfering RNA) (P<0.01). DN-p38, a dominant negative mutant of p38 MAPK, attenuated the shear stress-induced IL-8 promoter-mediated green fluorescent protein expression (P<0.05).
Interpretation: These results suggest that ERK1/2, JNK1/2 and p38 MAPK are all involved in the low shear stress-induced IL-8 gene expression. Understanding the mechanism by which low shear stress regulates IL-8 gene expression may provide insight into the initiation of atherosclerosis.