The molecular mechanism of mechanical stress-induced receptor activator of nuclear factor kappa B ligand expression in human periodontal ligament cells

Abstract

Mechanical stress such as orthodontic forces or abnormal mastication produce inflammation and damage of periodontium including alveolar bone resorption. The receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG) are two key proteins important in bone homeostasis. This study aimed to examine the influence of mechanical stress on the expression and regulation of RANKL as well as the signaling pathway involved in human periodontal ligament (HPDL) cells. Continuous compressive force was applied on cultured HPDL cells. The released adenosine triphosphate (ATP) was measured using luciferin-luciferase bioluminescence. The level of mRNA and protein of RANKL expression in HPDL cells were examined by reverse transcription polymerase chain reaction (RT-PCR) and western analysis. Intracellular signal transduction was investigated using inhibitors and antagonists. The results of this study demonstrated that mechanical stress-induced ATP release through connexin 43 (Cx43) hemichannel. The mechanism of ATP release may depend on intracellular Ca2+ signaling pathway. In addition, extracellular ATP stimulates RANKL expression through P2Y1 receptor. In conclusion, this study showed that HPDL cells responded to mechanical stress by increasing the release of ATP, as well as the expression of RANKL. These finding suggests that ATP and P2Y1 receptor play an important role in regulating bone resorption and bone homeostasis.