Regulatory Effects of Interleukin‐1β and Prostaglandin E2 on Expression of Receptor Activator of Nuclear Factor‐κB Ligand in Human Periodontal Ligament Cells

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Abstract
Background: Receptor activator of nuclear factor‐κB ligand (RANKL), which is expressed on the cell membrane of osteoblasts/ stromal cells, stimulates osteoclastogenesis. We investigated the regulatory effects of interleukin‐1β (IL‐1β) and prostaglandin E2 (PGE2) on expression of RANKL in human periodontal ligament (HPDL) cells and the mechanisms involved in the PGE2 effect.Methods: The HPDL cells were treated with IL‐1β, alone or in combination with indomethacin (INDO) or NS398, a cyclooxygenase‐ 2 (COX‐2) inhibitor. The HPDL cells were also pretreated with H89, a protein kinase A (PKA) inhibitor or GF109203X, a protein kinase C (PKC) inhibitor and subsequently treated with PGE2, PGE receptor (EP)2 agonist, EP4 agonist, forskolin, dibutyryl cAMP (db‐cAMP), or 3‐(isobutyl)‐1‐methylxantine (IBMX). After each treatment, expression of EP2, EP4, or RANKL mRNA was analyzed by reverse transcription‐polymerase chain reaction and Southern hybridization. Expression of RANKL protein was detected by Western blotting, and cAMP accumulation was determined using a cAMP enzyme immunoassay kit.Results: IL‐1β stimulated the expression of RANKL at messenger RNA (mRNA) and protein levels in HPDL cells. Endogenous PGE2 partially mediated the IL‐1β–induced RANKL mRNA expression. Exogenously added PGE2 also stimulated RANKL expression at mRNA and protein levels in the cells. The PGE2‐ stimulated RANKL expression was mediated by EP2/4 and cAMP‐dependent PKA, while PKC was possibly involved in the PGE2 action.Conclusion: Human periodontal ligament cells activated with inflammatory factors such as IL‐1β and PGE2 may directly stimulate osteoclastogenesis through RANKL, which is stimulated to express by these factors. J Periodontol 2004;75:249‐259.

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