INFLUENCE OF OXYGEN ON THE RESPONSE OF HUMAN PERIODONTAL LIGAMENT CELLS TO MECHANICAL STRESS

Abstract

Mechanical force, i.e. occlusal trauma was shown to promote insulin like growth factor-1 (IGF-1) and osteopontin (OPN) expression in periodontal ligament both in vitro and in vivo. IGF-1 plays a role in various cellular activity, including survival, proliferation, and differentiation while OPN is one of the intermediate protein for bone remodeling. Occlusal force and hypoxic condition are considered as the facilitating factors for periodontitis which is a worldwide disease resulting in the destruction of the periodontium. However, the mechanism by which force and hypoxia contributing to periodontal destruction is yet unclear. Thus, this study investigated the influence of the intermittent mechanical stress on IGF-1 and OPN expression by human periodontal ligament cells (HPDLs) under normoxia and hypoxia. The intermittent mechanical stress was applied to HPDLs with or without cobalt chloride (CoCl2) for 24 hours. The gene expression was examined by conventional and real-time polymerase chain reaction. The protein expression was examined by ELISA assay. The signaling pathways regulating gene expression were investigated using chemical inhibitors. The results showed that both IGF-1 and OPN mRNA expression increased in the intermittent mechanical stress treated group and CoCl2 synergistically enhanced the intermittent mechanical stress-induced OPN expression. In opposite to IGF-1, CoCl2 attenuated the intermittent mechanical stress-induced IGF-1 expression. The TGF-β receptor I inhibitor (SB431542) abolished IGF-1 and OPN mRNA expression induced by intermittent mechanical stress with and without CoCl2. Furthermore, the intermittent mechanical stress could induce TGF-β1 protein release in the presence and absence of CoCl2. HPDLs treated with recombinant transforming growth factor-beta1 (rhTGF-β1) significantly upregulated both IGF-1 and OPN mRNA levels. However, the combination of rhTGF-β1 and CoCl2 significantly downregulated IGF-1 expression while, this condition could upregulate OPN expression. In conclusion, the results suggested that intermittent mechanical stress induced IGF-1 and OPN expression in HPDLs through TGF-β1. The level of oxygen influenced to this phenomenon in HPDLs.