title: Impaired odontogenic differentiation of senescent dental mesenchymal stem cells is associated with loss of Bmi-1 expression.
abstract: BACKGROUND
  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.
authors.affiliation: UCLA School of Dentistry, Los Angeles, CA, USA.
authors.forename: Shebli
authors.initials: S
authors.lastname: Mehrazarin
authors.forename: Ju Eun
authors.initials: JE
authors.lastname: Oh
authors.forename: Christine L
authors.initials: CL
authors.lastname: Chung
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Reuben H
authors.initials: RH
authors.lastname: Kim
authors.forename: Songtao
authors.initials: S
authors.lastname: Shi
authors.forename: No-Hee
authors.initials: NH
authors.lastname: Park
authors.forename: Mo K
authors.initials: MK
authors.lastname: Kang
mesh_terms: D000469:Alkaline Phosphatase / Q000032:analysis; D015415:Biomarkers / Q000032:analysis; D002113:Calcification, Physiologic / Q000235:genetics; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation; D048430:Cell Shape; D016922:Cellular Senescence / Q000235:genetics*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D003782:Dental Pulp / Q000166:cytology*; D016326:Extracellular Matrix Proteins / Q000235:genetics; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D058574:Integrin-Binding Sialoprotein / Q000235:genetics; D059630:Mesenchymal Stem Cells / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics*; D009805:Odontogenesis / Q000235:genetics*; D015675:Osteocalcin / Q000235:genetics; D010486:Periapical Tissue / Q000166:cytology*; D010750:Phosphoproteins / Q000235:genetics; D063150:Polycomb Repressive Complex 1; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics*; D012795:Sialoglycoproteins / Q000235:genetics; D019098:Telomerase / Q000235:genetics; D016615:Telomere / Q000235:genetics / Q000648:ultrastructure; D014161:Transduction, Genetic; D016335:Zinc Fingers / Q000235:genetics*; D000099311:Dentin Sialophosphoprotein
chemical_list: D000469:Alkaline Phosphatase; D015415:Biomarkers; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016326:Extracellular Matrix Proteins; D058574:Integrin-Binding Sialoprotein; D009687:Nuclear Proteins; D015675:Osteocalcin; D010750:Phosphoproteins; D063150:Polycomb Repressive Complex 1; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D012795:Sialoglycoproteins; D019098:Telomerase; D000099311:Dentin Sialophosphoprotein; C069077:BMI1 protein, human; C513309:DMP1 protein, human