Effects Of Mechanical Strain On Osteogenic Differentiation Of Bone Marrow Stromal Cell Line ST2

Background:Mechanicalloads play a key role in orthodontic tooth movement, Duringorthodontic tooth movement, the applied forces lead to strain in the PDL,then thepower was transmittedto the alveolar bone, where the strain was conversed intobiochemical signaling. Adequate mechanical stimulus is critical for bone remodeling,and various cells, including MSCs, OBs, and OCs participate in this process, amongwhich MSCs is most important. The effects of mechanical strain on MSCs have beenextensively studied, however, the conversion of mechanical loads to biochemicalresponse is not fully understood.Consequently, further study in the mechanism ofeffects of mechanical strain in bone remodeling not only has great theoreticalsignificance in recognizing the differentiation process of MSCs and deepenunderstanding of the nature of bone remodeling, but also has great practicalsignificance in promoting the further improve of orthodontic treatment technologyand contributing to improve the efficiency of orthodontic treatment.Bone marrow mesenchymal stem cells have potential of multidirectionaldifferentiation, during the differentiation process to the osteoblast, the expression ofRunx2, Sp7, ColⅠ, Alp and so on genes which further promoted osteoblastogenesisare necessary. EphrinB2/EphB4bidirectional axis plays an important role inangiogenesis and neural development, in recent years, studies have shown that cellinteractionsignal path have involved in bone remodeling. Mediated by ephrinB2ligand on osteoclasts and EphB4receptor on osteoblasts generates bidirectionalanti-osteoclastogenic and pro-osteoblastogenic signals into respective cells, thenfacilitates transition from bone resorption to bone formation.However, whetherephrinB2/EphB4bidirectional axis involved in mechanical stress stimulationsignaltransduction, the reports have not been found at home and abroad literature. Inthis experiment,we observed the osteogenic differentiation of ST2in vitro under mechanical strain, meanwhile, the change of ephrinB2/EphB4bidirectional axis aftermechanical load.We cultured ST2cell in vitro, using a four-point bending apparatus respectivelyapplied to the cell1h,2h,4h periodic mechanical strain (2000μstrains,0.5Hz). Cellproliferation ability after mechanical strain1-5day was determined by MTTexamination, The mRNAexpression change of osteoblastogenesis-relating genesRunx2, Sp7, ColⅠ, Alp expression and ephrinB2/EphB4bidirectional axiswereanalyzed by Real-time PCR immediately after mechanical loads.1. Compare with the control,the proliferation of1h group,2h group and4hgroup was significantly increasedat the first day and second day after the mechanicalstrain, and the peak at4h group（P<0.05）,at3-5day, each group is similar to thecontrol.2. ST2in vitro undergo mechanical strain without mineralization fluid, comparedwith their own control: mRNA level of Runx2significant increase in1h group（P<0.05）and2h group（P<0.01）, peak in the2h group; Sp7mRNAwas decreasedin each group(P<0.05),2h groupexpression level is higher than1h group;ColⅠmRNA was significantly increased in1h group(P<0.05);Alp mRNA was significantlyincreased in1h group（P<0.01）,2h group（P<0.01）and4h group（P<0.01）, peakin the2h group; ephrinB2mRNA was significantly increased in1h group（P<0.05）,2h group（P<0.01）,peak in the2h group; EphB4mRNA was significantly increased in1h group（P<0.01）,2h group（P<0.01）,peak in the2h group.3. ST2in vitro undergo mechanical strain with mineralization fluid，comparedwith their own control: mRNA level of Runx2was suppressed at1h group（P<0.01）,but significantly increased at2h group（P<0.01）,4h group (p<0.05) and the peak inthe4h group; each group Sp7mRNA level was significantly increased(P<0.05), andpeakinthe4h group; Col Ⅰ mRNA was significantly increased in1hgroup(P<0.05);Alp mRNA was significantly increased in each group（P<0.05）, peakin the4h group; ephrinB2mRNA was significantly increased in1h group（P<0.01）,2h group（P<0.01）,4h group（P<0.05）, peak in the4h group; EphB4mRNA wassignificantly increased in4h group(P<0.01). Conclusion:1. The proliferation of ST2was significantly increased by the mechanical strain inthe early stage;2. Mechanical strain promoted ST2differentiation into osteoblast, but withoutmineralization fluid the cells were suppressed differentiation into mature osteoblast;3. Mechanical strain increased the ephrinB2/EphB4signals in ST2, which could promotebone formation.