Influence Of Mechanical Stress On Proliferation And Differentiation Of Human Dental Pulp Stem Cells And Stem Cells From Human Apical Papilla In Vitro

Chronic parafunctional forces from clenching and bruxism cause pulpal inflammation and elevated intra-pulpal pressure which influence the dynamic balance of the pulp cells. During the orthodontic treatment,when mechanical force pull out the delayed eruption of immature permanent tooth,we will observe the phenomena of root elongation and development,such as the apical foramina narrows gradually and the length of root becomes long.Therefore, in recent years, more and more scholars pay close attention to the inflammatory micro environment of dental pulp regeneration, and some also began to study the hypoxia environment. However, it remains unclear whether mechanical forces stimulation can affect the proliferation and differentiation of human DPSCs or SCAP. This subject is based on centrifugal force pressure mode in vitro, we will compare the effect of different cyclic mechanical stress stimulation on proliferation and differentiation ability of DPSCs, SCAP. In order to find a suitable way of mechanical stress applied to the DPSCs, SCAP, provides the reference for the basic study and clinical application of the future.Methods:Human DPSCs and SCAP were isolated and subjected to cyclic mechanical stress(170g,210 g,250g) for 30 min everyday. Untreated DPSCs and SCAP as control groups. After that, cells ultrastructure were observated by the transmission electron microscope.Cells proliferation ability were examined by cell counting kit-8(CCK-8). ALP activity was detected by AKP kit and BCIP/NBT ALP kit. The formation of mineralized nodules were determined using half-quantitative Alizarin Red S assay. Real-time quantitative PCR detected the gene expression of DSPP, RUNX-2, OCN, BSP,OSX and DMP-1 in 14 days.Results:1.cyclic mechanical stress effect the proliferation activity of DPSCs, SCAP: Compared with the control group, cyclic mechanical stress stimulation can significantly inhibit the proliferation ability of DPSCs and SCAP. However, cell apoptosis detection results show that a short time of mechanical stress had no significant effect on cell activity. 2.cyclic mechanical stress effect the differentiation of DPSCs: In the research of cyclic mechanical stress effect on differentiation ability of DPSCs, the ALP activity and the formation of mineralized nodules of stress-treated groups were decreased significantly, further more, the 250 g group had the most significant inhibition. RT-PCR results showed that, the bone / odontoblast related gene expression of stress-treated groups were significantly down-regulated. It showed direct ratio between the formation of mineralized nodules and the degree of cyclic mechanical stress. 3.cyclic mechanical stress effect the differentiation of SCAP: For cultured of two-dimensional plane of SCAP in vitro, compared with the control group, cyclic mechanical stress increased the activity of ALP significantly. The formationof mineralized nodules of stress-treated groups were significantly raised, in addition the promoting effect on 210 g group is the most significant. RT-PCR results also show, the bone / odontoblast related gene expression of stress-treated SCAP were up-regulated. That cyclic mechanical stress can promote the bone / odontoblast differentiation of SCAP.Conclusion:Cyclic mechanical stress may play an important role in regulating the proliferation and osteogenic / odontoblast differentiation of stem cells from the apical papilla and human dental pulp stem cells.