| Periodontal tissue is the physiological foundation of prosthodontic work. The proper occlusion force is healthful to the periodontal tissue, whereas inappropriate force does harm to the periodontal tissue of abutment if we design the denture improperly. Despite extensive research over many decades, the intracellular mechanisms and the role of trauma from occlusion in the progression of alveolar bone loss and damage of periodontal ligament tissue remain unclear. There is growing evidence that human periodontal ligament fibroblasts (HPLF) are involved in this process.HPLF are the predominant cells of the periodontal ligament and have important roles in the development, function, and regeneration of the tooth support apparatus. In response to applied mechanical forces, they can synthesize a wide range of cytokines to induce bone resorption and matrix degradation. The ability of HPLF to synthesize and secrete such regulatory molecules is an essential component of tissue remodeling and periodontalligament homeostasis.Mitogen-activated protein kinase (MAPK) are a group of serine/threonine-specific protein kinases which have important function of transduce extracellular siganals to intracellular response. p38 MAPK is one of the subgroup of these MAPK family, and recent work has showed that it can modulate the expression of several kinds of proinflamation cytokines.To identify whether the p38 MAPK is involved in the mechanotransduction process and to determine the effect of the p38 MAPK on down-stream gene expression, we stimulated HPLF by employing an established invitro model of continuous pressure application.Methods and Results:The whole thesis can be divided into two parts. In the 1st section, we used two experiments to identify if the p38 MAPK is involved in the mechanotransduction of the HPLF. In the 2nd section, the other two experiments were used to clarify the mechanism of how the p38 MAPK modulate the expression of IL-6 induced by mechanical pressure in HPLF.The 1st section:Firstly, we treated the HPLF with the continuance pressure of 100kPa, 150kPa, 200kPa respectively. Then the p38 MAPK activation after the loading of mechanical pressure was demonstrated by western-blot for the active kinase (tyrosine/threonine phosphorylated) in whole cell extracts using phospho-specific antibodies. Our data suggested that the activity of p38 MAPK was increased from 5 min, peaked at 30 min, and returned to the original level at 60 min after stimulated with 200kPa pressure. But neither pressure of lOOkPa and 150 kPa could activate p38 MAPK in HPLF.Immunohistochemistry was further used to check the distribution and intensity of p38 MAPK in cultured HPLF exposed to mechanical pressure. Compared with the 1st experiment, we got the same result that when the pressure rose to 200kPa, the p38 MAPK was activated in response to mechanical stress, translocated to nuclear at 30 min, and returned to the level before stimulation at 60 min.The 2nd section:The role of p38 MAPK of HPLF in response to mechanical pressure is investigated by use of a pyridinyl imidazole compound (SB203580),which specifically inhibits the enzyme.We pretreated HPLF with SB203580 for 60 minutes, and then examined both mRNA and protein levels of IL-6 induced by 200kPa mechanical pressure. IL-6-mRNA levels were measured by competitive PCR, and IL-6 levels both in the cell and culture media were measured by enzyme-linked immunosorbent assay(ELISA). We found that SB203580 significantly inhibited the expression of IL-6 stimulated by mechanical pressure in HPLF, but not the level of IL-6 mRNA.Conclusions:1. Our data underscore the role of p38 MAPK as signal transduction molecule under mechanical pressure in HPLF; The pressure should reach some threshold, otherwise the p38 MAPK in the HPLF can not be activated; The mechanotransduction that the p38 MAPK involved in is a dynamic process.2. p38 MAPK acts as important cooprative mechanism to regulate IL-6 synthesis induced by mechanical pressure, and the mediation was primary...
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