Involvement of PGE Synthesis in the Effect of Intermittent Pressure and Interleukin-1β on Bone Resorption

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Abstract
Human periodontal ligament (PDL) fibroblasts, cultured from extracted healthy premolars, and a cloned osteogenic cell line (MC3T3-E1) were used in this study to determine the effect of intermittent pressure on bone resorption. Cells (1 x 105) were incubated with BGJb medium in the presence or absence of the following factors: intermittent negative ( - 30 g/cm2) or positive (30 g/cm2) hydrostatic pressure and interleukin-lp (IL-1β, 1 ng/mL), for 24 h. Conditioned media (CM) generated from cultures of either cell types were used for prostaglandin E (PGE) assay, bone resorption assay, and assessment of osteoclast (OC)-like cell formation. Unstimulated PDL fibroblasts or MC3T3-E1 cells produced measurable amounts of PGE and bone-resorbing activity as measured by 45Ca released from mouse calvaria and OC-like cells. IL-1β-treated cells showed significantly elevated levels of PGE, bone resorption, and OC-like cell formation, as compared with unstimulated cells. Intermittent positive pressure (IPP) alone stimulated PGE production, but the resultant CM did not stimulate bone resorption or OC-like cell formation when IPP was applied to either cell type. The application of IPP, together with IL-1β in CM, caused a slight increase in the number of a-like cells, as compared with that of IL-1β-treated CM in both cell types. On the other hand, direct application of IPP on mouse bone-marrow cultures significantly increased the number of OC-like cells. This effect was additive in combination with either CM from unstimulated cells or exogenous addition of PGE2. These results suggest that locally produced autocrines or paracrines can modify the effect of mechanical stress on periodontal and bone cells via PGE synthesis. One of the roles of PGE elaboration in response to mechanical or chemical stimuli is osteoclast recruitment.