Prostaglandin mediated modulation of transforming growth factor-β metabolism in primary mouse osteoblastic cells in vitro

Prostaglandins and transforming growth factor-β (TGF-β) are both important local regulators of bone metabolism, but their actions on bone are complex. Prostaglandins mediate bone loss due to immobilization, but prostaglandin E₂ (PGE₂) treatment stimulates bone formation in vivo. TGF-β may have both anabolic and catabolic effects on bone in vitro. In this study, we tested the effects of PGE₂ on TGF-β release and on TGF-β messenger RNA (mRNA) levels in neonatal mouse calvarial cell cultures. We also examined the relationship between endogenous prostaglandin production as a result of mechanical stress and the release of TGF-β. Addition of PGE₂ (10⁻⁸ − 10⁻⁶ M) to the culture medium stimulated the release of TGF-β peptide (active plus latent) after 24 and 48 h in a dose-related manner. This upregulation was paralleled by an increased expression of TGF-β mRNA levels. Mechanical stimulation by 1 h treatment with pulsating fluid flow (producing a shear stress of 0.5 ± 0.02 Pa at 5 Hz) resulted 1 h posttreatment in increased production of PGE₂, prostaglandin I₂ (PGI₂), and prostaglandin F_2a. In addition, the release of TGF-β activity but not TGF-β peptide was decreased 24 h after PFF treatment. Addition of indomethacin, which blocks endogenous prostaglandin production, neutralized the effect of PFF treatment on TGF-β activity, indicating that the effect of stress was mediated by endogenous prostaglandins. These results suggest that PGE₂ and other prostaglandins (probably PGI₂ and/or PGF_2a) have opposite effects on TGF-β metabolism in bone cells, as PGE₂ upregulates TGF-β expression and synthesis while other prostaglandins downregulate TGF-β activation. © 1996 Wiley-Liss, Inc.