Impaired Odontogenic Differentiation of Senescent Dental Mesenchymal Stem Cells Is Associated with Loss of Bmi-1 Expression

Abstract

Introduction Dental mesenchymal stem cells (dMSCs) may 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 PCR. Expression of genes involved in cell proliferation and differentiation, e.g., Bmi-1, p16INK4A, osteocalcin (OC), dentin sialoprotein (DSP), bone sialoprotein (BSP), and dentin matrix protein-1 (DMP-1) were assayed by Western blotting and quantitative reverse transcription PCR. Exogenous Bmi-1 was expressed in dMSC using retroviral vectors. Odontogenic differentiation was assayed by alkaline phosphatase (ALP) activity. Results Subculture-induced replicative senescence of dMSCs led to reduced expression of Bmi-1, OC, DSPP, and BSP compared with rapidly proliferating cells, while p16INK4A level increased. The cells exhibited progressive loss of telomeric DNA during subculture, presumably due to lack of telomerase activity. Bmi-1 transduction did not affect proliferation of cells, but enhanced the expression of OC and DSPP in the late passage cultures. Bmi-1-transduced cells also demonstrated enhanced ALP 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.

The induction of cellular senescence in dental follicle cells inhibits the osteogenic differentiation

“…Previous studies with bone marrow-derived mesenchymal stem cells and dental pulp stem cells showed a progressive and rapid loss of differentiation potentials with prolonged culture [11][12][13][14]25]. We obtained similar results with DFCs.…”

Smad 1/5 Is Involved in Bone Morphogenetic Protein-2–induced Odontoblastic Differentiation in Human Dental Pulp Cells

“…For example, TGF-b2 was found to inhibit the differentiation of DPCs through activation of the ALK/Smad2/3 signal transduction pathway (20). Bmi-1 plays an important role in maintaining the odontogenic differentiation capacity in dental mesenchymal stem cells during senescence (21). Multiple signaling molecules, including BMPs, fibroblast growth factors, Shh, and Wnts, appear to regulate the early steps of tooth morphogenesis, and some transcription factors associated with these pathways have been shown to be required for tooth development (22,23).…”

Therapeutic Potential of Mesenchymal Stem Cells for Oral and Systemic Diseases

“…Upon serial subculture in vitro dMSCs have been shown to develop morphological changes consistent with cellular senescence, losing their spindle shape and exhibiting flattened, enlarged morphology [13]. Although they exhibit a universal morphology, MSCs originate from different tissue sources, and not all cells collected from these tissues are MSCs.…”

“…The osteogenic/odontoblastic lineage is among the most well characterized found in MSCs, and BMMSCs and dMSCs have been found to express common osteogenic/odontoblastic markers, such as collagen type I, alkaline phosphatase, and bone sialoprotein [11]. Altered gene expression of these markers has been used to investigate adverse effects of senescence in MSCs [13]. …”

“…MSCs have been shown to possess limited lifespan and ultimately undergo replicative senescence or aging in vitro [11, 13]. Self-renewal has been documented as ranging from 30–50 population doublings (PDs) in BMMSCs to more than 120 PDs in DPSC [11].…”