Cyclic Mechanical Strain Induces Interleukin-6 Expression via Prostaglandin E-2 Production by Cyclooxygenase-2 in MC3T3-E1 Osteoblast-like Cells

Interleukin(IL)-6, produced by osteoblasts, is one of the key cytokines that promote bone resorption. This study examined the effect of cyclic mechanical strain on the expression of IL-6 mRNA and protein, and the induction mechanism of IL-6 in MC3T3-E1 osteoblast-like cells using RT-PCR and ELISA. MC3T3-E1 cells were cultured in a-MEM with 10% FBS on flexible, collagen.-coated membranes and subjected to cyclic mechanical strain at 6 cycles/min. The production of IL-6 protein was increased at 3 h, reached a peak at 6 h, and was maintained up to 24 h by the cyclic mechanical strain. The strain increased the production of IL-6 protein in a force-dependent manner. The expression of IL-6 mRNA was increased by the cyclic mechanical strain. Prostaglandin(PG) E2 production was induced at 1 h, dramatically increased to 3 h, and was gradually increased from 3 to 24 h by the cyclic mechanical strain. The strain increased PGE(2) production in a force-dependent manner. Treatment with PGE(2) increased the production of IL-6 protein from MC3T3-E1 cells. The cyclic mechanical strain promoted cyclooxygenase (COX)-2 but not COX-1 mRNA expression. Pretreatment with indomethacin and NS-398 prevented PGE(2) production and partly inhibited the production of IL-6 protein induced by the cyclic mechanical strain. These findings suggest that cyclic mechanical strain increases IL-6 expression in osteoblasts, the induction of which is in part mediated via PGE(2) production by COX-2.