Thesis (Ph.D.)--Chulalongkorn University, 2007

Thrombin influences the biological behavior of human periodontal ligament cells (HPDL) and plays multiple roles in the early stage of bone healing. Osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) are two key molecules that regulate bone homeostasis. The balance of RANKL and OPG in the tissue is one of the factors significant in the mechanism of hard tissue destruction and remodeling. However, the specific role of thrombin on balance of RANKL and OPG has not been studied. In the present study, we investigated the effect of thrombin on RANKL and OPG synthesis. The participation of PAR-1 and the signaling pathways mediate by thrombin are focused. Our result showed that thrombin profoundly induced protein synthesis of OPG at 0.1 U/ml. The inductive effect was inhibited by cycloheximide, but not by indomethacin. Phosphatidylinositol 3’kinase (PI3K) inhibitor, LY294002 and mammalian target of rapamycin (mTOR) inhibitor, rapamycin, exerted the inhibitory effect on the thrombin induced OPG synthesis. In addition, the thrombin-induced OPG synthesis was inhibited by protease-activated receptor (PAR) -1 antagonist. Activation of phospho-Akt (p-Akt) was observed and the effect was abolished by LY294002. In conclusion, this study was the first to demonstrate that thrombin induce OPG synthesis in HPDL cells post-transcriptionally, possibly through PAR-1. The regulation was through PI3K/Akt and mTOR pathway. This finding suggests that thrombin may play a significant role in alveolar bone repair and homeostasis of periodontal tissue, partly through RANKL/OPG system.