The effects of prostaglandin E2 on DNA and collagen synthesis in osteoblasts in vitro

The effects of prostaglandin E2(PGE2) on DNA and collagen synthesis in two separate cell populations were investigated. In view of their morphology, ALPase activity, DNA and collagen synthesis, and response to PGE2, one population was in an undifferentiated state consisting of preosteoblast-like (PL) cells and the other was in a differentiated state consisting predominantly of osteoblast-like (OB) cells. As parameters of bone-forming activity, the incorporation of 3H-thymidine into DNA and the incorporation of 3H-proline into collagenase digestible protein were measured to assess DNA and collagen synthesis. The cells were treated with PGE2 in the presence of indomethacin (IM) to avoid the influence of endogenous prostaglandins. At 24 hours, IM stimulated the DNA synthesis in both cell populations. Furthermore, a greater stimulation was found in the PL cells than in the OB cells. On the other hand, exogenously supplemented PGE2 reversed the IM-induced stimulation of DNA synthesis. In contrast, high concentrations of PGE2 alone increased the DNA synthesis. With respect to collagen synthesis, IM showed an inhibitory effect, especially in the PL cells. This inhibitory effect was also reversed by the addition of PGE2. In addition to the stimulation of collagen synthesis, PGE2 enhanced the proportion of protein synthesized as collagen. In the PL cells, the percentage of collagen synthesis was markedly decreased when cultured with IM for 48 hours. These results suggested that the effects of IM were mediated in part via its ability to reduce biosynthesis of prostaglandins, and that PGE2 is a multifunctional autocrine regulator of bone formation.