Effect of Cytosolic Phospholipase A₂ on Proinflammatory Cytokine-induced Bone Resorptive Genes Including Receptor Activator of Nuclear Factor Kappa B Ligand in Human Dental Pulp Cells

Introduction: Although cytokines stimulate prostaglandin E₂ (PGE₂) production and cyclooxygenase-2 (COX-2) gene expression in human dental pulp cells (HDPCs), the involvement of cytosolic phospholipase A₂ (cPLA₂) has not been assessed. The purpose of this study was to examine the role of cPLA₂ on the regulation of proinflammatory cytokine-stimulated genes associated with osteoclast differentiation or bone resorption. Methods: Tumor necrosis factor-α (TNF-α) and interleukin-1α (IL-1α)-induced COX-2 and receptor activator of nuclear factor kappa B ligand (RANKL) mRNA and protein expression in the HDPCs was determined by using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. PGE₂ release and osteoclast-related gene expression were measured by enzyme-linked immunosorbent assay and RT-PCR. Results: Stimulation with TNF-α and IL-1α synergistically increased levels of COX-2 as well as RANKL mRNA and protein expression. Osteoclast markers (macrophage colony-stimulating factor [M-CSF], matrix metalloproteinase-9 [MMP-9], and tartrate-resistant acid phosphatase [TRAP]) and osteolysis regulating cytokines or osteoclastogenic cytokines (IL-6, IL-11, and Il-17) were up-regulated in HDPCs after IL-1α and TNF-α treatment. A cPLA₂ inhibitor attenuated both the cytokine-stimulated PGE₂ release as well as changes in osteoclast differentiation-related genes like RANKL. Conclusions: These results suggest that cPLA₂ is involved in inflammatory cytokine-induced osteoclastogenic gene expression and consequent damage or destruction.