OBJECTIVETo investigate the effects of Osterix (Osx) overexpression on the osteogenic differentiation of human periodontal ligament cells in response to mechanical force.

METHODSHuman periodontal ligament cells were isolated and cultured in vitro with explant method. Cells were transfected with either an Osx expression vector pcDNA3.1 flag-Osx or the mock control vector pcDNA3.1 flag. Then, cells were centrifuged for 6 h. After transfection and centrification, the expression of Osx mRNA and protein in untransfected cells, mock-transfected cells and Osx-transfected cells were measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot respectively. Furthermore, the changes of mRNA expressions of core-binding factor cal (Cbfal), alkaline phosphatase (ALP), osteopontin (OPN), osteocalcin (OC), bone sialoprotein(BSP) and collagen protein al (Col I ) genes were measured to assess the differentiation of human periodontal ligament cells.

RESULTSAt 24 h after transfection, Osx mRNA and protein level increased significantly in Osx-transfected cells (P < 0.01), while there were no significant difference in Osx mRNA and protein levels between mock-transfected cells and untransfected cells(P > 0.05). Simultaneously, the upregulated mRNA expressions of all the five osteogenic genes were observed (P < 0.05, P < 0.01). After 6 h of mechanical stimulation, a significant increase in Osx expression was shown in all three groups. However, compared to mock-transfected and untransfected cells, Osx-transfected cells further showed the highest Osx mRNA and protein expression level. Furthermore, the mRNA expressions of all five osteogenic markers in Osx-transfected cells also exhibited the greater increase and showed the highest levels.

CONCLUSIONThe overexpression of Osx promotes the mechanical stress-induced osteogenic differentiation of human periodontal ligament cells. Osx may be essential for mechanical stress-induced differentiation of human periodontal ligament cells to osteoblas tic-like cells and be involved in orthodontic osteogenic remodeling.