Mechanical stress-induced interleukin-1beta expression through adenosine triphosphate/P2X7 receptor activation in human periodontal ligament cells

Background and Objective Mechanical stress is an important factor in maintaining homeostasis of the periodontium. Interleukin-1beta (IL-1) and adenosine triphosphate (ATP) are considered potent inflammatory mediators. In macrophages, ATP-activated P2X7 receptor is involved in IL-1 processing and release. Our previous works demonstrated mechanical stress-induced expression of osteopontin and RANKL through the ATP/P2Y1 receptor in human periodontal ligament (HPDL) cells. This study was designed to examine the effect of mechanical stress on IL-1 expression in HPDL cells, as well as the mechanism and involvement of ATP and the P2 purinergic receptor. Material and Methods Cultured HPDL cells were treated with continuous compressive loading. IL-1 expression was analyzed at both mRNA and protein levels, using RT-PCR and ELISA, respectively. Cell viability was examined using the MTT assay. ATP was also used to stimulate HPDL cells. Inhibitors, antagonists and the small interfering RNA (siRNA) technique were used to investigate the role of ATP and the specific P2 subtypes responsible for IL-1 induction along with the intracellular mechanism. Results Mechanical stress could up-regulate IL-1 expression through the release of ATP in HPDL cells. ATP alone was also capable of increasing IL-1 expression. The induction of IL-1 was markedly inhibited by inhibitors and by siRNA targeting the P2X7 receptor. ATP-stimulated IL-1 expression was also diminished by intracellular calcium inhibitors. Conclusion Our work clearly indicates the capability of HPDL cells to respond directly to mechanical stimulation. The results signified the important roles of ATP/P2 purinergic receptors, as well as intracellular calcium signaling, in mechanical stress-induced inflammation via up-regulation of the proinflammatory cytokine, IL-1, in HPDL cells.