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

IntroductionAlthough 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.MethodsTumor 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.ResultsStimulation 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.ConclusionsThese results suggest that cPLA2 is involved in inflammatory cytokine-induced osteoclastogenic gene expression and consequent damage or destruction.