Augmented prostaglandin E2 generation resulting from increased activities of cytosolic and secretory phospholipase A2 and induction of cyclooxygenase-2 in interleukin-1 beta-stimulated rat calvarial cells during the mineralizing phase.

OBJECTIVE AND DESIGN

To assess prostaglandin (PG) E2 production by osteoblasts during the mineralizing phase after interleukin (IL)-1beta stimulation, using an in vitro system of rat calvarial cells cultured for 21 days.

METHODS

The cells, which reached confluence after 3 days, were designated day 0 cells. Culture was continued for a further 21 days after confluence. The cells on the 21st day of the culture were designated day 21 cells.

RESULTS

The PGE2 concentration in the medium of the day 21 cells was increased 72 h after IL-1beta treatment, and reached a peak level approximately 1,400 times that of the day 0 cells 6 h after IL-1beta treatment. We examined the effects of IL-1beta on PGE2 production and changes in the relevant enzyme activities, and found that the activities of cytosolic phospholipase A2 (cPLA2), type II secretory PLA2 (sPLA2) and cyclooxygenase (COX)-2 in the day 21 cells were increased. Both selective COX-2 inhibitor and cPLA2 inhibitor abolished PGE2 generation, whereas an sPLA2 inhibitor partially inhibited it. Taken together, these results indicate that COX-2 and cPLA2 play pivotal roles and sPLA2 is involved in IL-1beta-stimulated PGE2 production by these cells. Furthermore, we found that IL-Ibeta treatment induced PGE synthase activity and this correlated well with PGE2 production.

CONCLUSION

Augmented PGE2 production by mineralizing osteoblasts after IL-1beta treatment, and the involvement of IL-1beta-induced cPLA2, sPLA2, COX-2 and PGE synthase activities in this phenomenon were demonstrated.