INTRODUCTION: Dental mesenchymal stem cells (dMSCs) might differentiate into odontoblast-like cells and form mineralized nodules. In the current study, we investigated the effects of senescence on odontogenic differentiation of dMSCs. METHODS: dMSCs were serially subcultured until senescence. Telomere lengths and telomerase activities were determined by quantitative polymerase chain reaction. Expression of genes involved in cell proliferation and differentiation, eg, Bmi-1, p16(INK4A), osteocalcin (OC), dentin sialoprotein (DSP), bone sialoprotein (BSP), and dentin matrix protein-1 (DMP-1) were assayed by Western blotting and quantitative reverse transcription polymerase chain reaction. Exogenous Bmi-1 was expressed in dMSCs by using retroviral vectors. Odontogenic differentiation was assayed by alkaline phosphatase activity. RESULTS: Subculture-induced replicative senescence of dMSCs led to reduced expression of Bmi-1, OC, DSP, and BSP compared with rapidly proliferating cells, whereas p16(INK4A) level increased. The cells exhibited progressive loss of telomeric DNA during subculture, presumably as a result of lack of telomerase activity. Bmi-1 transduction did not affect proliferation of cells but enhanced the expression of OC and DSP in the late passage cultures. Bmi-1-transduced cells also demonstrated enhanced alkaline phosphatase activity and mineralized nodule formation. CONCLUSIONS: These results indicate that dMSCs lose their odontogenic differentiation potential during senescence, in part by reduced Bmi-1 expression.
INTRODUCTION: Dental mesenchymal stem cells (dMSCs) might differentiate into odontoblast-like cells and form mineralized nodules. In the current study, we investigated the effects of senescence on odontogenic differentiation of dMSCs. METHODS:dMSCs were serially subcultured until senescence. Telomere lengths and telomerase activities were determined by quantitative polymerase chain reaction. Expression of genes involved in cell proliferation and differentiation, eg, Bmi-1, p16(INK4A), osteocalcin (OC), dentin sialoprotein (DSP), bone sialoprotein (BSP), and dentin matrix protein-1 (DMP-1) were assayed by Western blotting and quantitative reverse transcription polymerase chain reaction. Exogenous Bmi-1 was expressed in dMSCs by using retroviral vectors. Odontogenic differentiation was assayed by alkaline phosphatase activity. RESULTS: Subculture-induced replicative senescence of dMSCs led to reduced expression of Bmi-1, OC, DSP, and BSP compared with rapidly proliferating cells, whereas p16(INK4A) level increased. The cells exhibited progressive loss of telomeric DNA during subculture, presumably as a result of lack of telomerase activity. Bmi-1 transduction did not affect proliferation of cells but enhanced the expression of OC and DSP in the late passage cultures. Bmi-1-transduced cells also demonstrated enhanced alkaline phosphatase activity and mineralized nodule formation. CONCLUSIONS: These results indicate that dMSCs lose their odontogenic differentiation potential during senescence, in part by reduced Bmi-1 expression.
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