Regulation Of Gene Expression Of OPG And Rankl In Cementoblasts By Mechanical Stress In Vitro

Background and objective: Orthodontic tooth movement is achieved by remodeling of periodontal tissue triggered by orthodontic force. The remodeling of periodontal tissue includes remodeling of alveolar bone,periodontal ligament and cementum. The remodeling of periodontal tissue aligns teeth and improves occlusion, but it also results in root resorption. The pathogenesis of root resorption is still not clear. Cementoblast plays a central role in repair root resorption by synthesizing cementum matrix. And it also regulates root resorption by expression of OPG and RANKL, which influence osteoclastogenesis directly. However, it is not known how orthodontic force influences the function of cementoblast and what is the relationship between the function change of cementoblast with root resorption. So we studied the effect of mechanical stimuli on root resoption by examining the expression OPG and RANKL and exploring the related signal transduction pathway in cementoblast.Methods: Cementoblasts OCCM30 were cultured in DMEM with 10% FBS for 48 hours and starved in DMEM with no FBS for 24 hours, then subjected to mechanical strain by four-point bending system with tension and compression stress at 2000μstrain at 0.5Hz frequency. The flow cytometry(FCM) was used to examine the cell cycle and proliferation activity after 3h, 6h, 12h, 24h loading respectively. OPG and RANKL mRNA were analysed with real time quantitive RT-PCR after the same loading period as FCM. The phosphorylation level of ERKl/2 and P38MAPK after 5min, 15min, 30min, 60min loading were measured by Western Blotting. Statistical significance was determined for each comparison using the one-way ANOVA, and p<0.05 was statistically considered significant.Results:1. 2000μstrain tension and compression both depressed proliferation activity of Cementoblasts after 31k 6h loading. The inhibitory effect declined with time prolonged. After 24h loading, the proliferation activity resumed to the level of controls. There was no significant difference between tension and compression in the influence on proliferation.2. 2000μstrain tension and compression both suppressed mRNA expression of OPG and RANKL of Cementoblasts. Tension stress suppressed OPG expression stronger than compression stress, while compression stress suppressed RANKL expression stronger than tension stress.3. The RANKL/OPG ratio of Cementoblasts was increased after tension loading.4. The RANKL/OPG ratio of Cementoblasts was decreased after 3h,6h compression loading, but there was no significant difference compared with controls after 12h,24h loading.5. 2000μstrain tension and compression both activated ERK1,2 signals in Cementoblasts and the effect of tension strain is more significant.6. 2000μstrain tension and compression could not induce P38MAPK signals in Cementoblasts. Conclusion:1. 2000μstrain tension and compression both depressed proliferation activity of Cementoblasts reversiblely.2. 2000μstrain tension loading increased the RANKL/OPG ratio of Cementoblasts and might accelerate osteoclastogenesis.3. 2000μstrain compression loading decreased the RANKL/OPG ratio of Cementoblasts early and might not affect osteoclastogenesis long-termly.4. ERK1/2, not P38MAPK, was activated after 2000μstrain tension and compression loading and it may be a signal transduction pathway for the regulation of OPG and RANKL expression after stress loading.