UCLA School of Dentistry, Los Angeles, CA, USA.
J Endod. 2011 May;37(5):662-6. doi: 10.1016/j.joen.2011.02.009.
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.
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.
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.
These results indicate that dMSCs lose their odontogenic differentiation potential during senescence, in part by reduced Bmi-1 expression.
牙髓间充质干细胞（dMSCs）可分化为成牙本质细胞样细胞并形成矿化结节。在本研究中，我们研究了衰老对 dMSCs 牙向分化的影响。
dMSCs 连续传代至衰老。通过定量聚合酶链反应测定端粒长度和端粒酶活性。通过 Western blot 和定量逆转录聚合酶链反应测定参与细胞增殖和分化的基因的表达，例如 Bmi-1、p16（INK4A）、骨钙素（OC）、牙本质涎蛋白（DSP）、骨涎蛋白（BSP）和牙本质基质蛋白-1（DMP-1）。通过逆转录病毒载体表达外源性 Bmi-1。碱性磷酸酶活性检测牙向分化。
dMSCs 的亚培养诱导的复制性衰老导致与快速增殖细胞相比，Bmi-1、OC、DSP 和 BSP 的表达降低，而 p16（INK4A）水平升高。细胞在传代过程中表现出端粒 DNA 的逐渐丢失，可能是由于缺乏端粒酶活性所致。Bmi-1 转导不影响细胞增殖，但增强了晚期传代培养物中 OC 和 DSP 的表达。Bmi-1 转导的细胞还表现出增强的碱性磷酸酶活性和矿化结节形成。
这些结果表明，dMSCs 在衰老过程中丧失了其牙向分化潜能，部分原因是 Bmi-1 表达降低。
