Reduction of osteocalcin expression in aged human dental pulp

CDKN2A/p16INK4a expression is associated with vascular progeria in chronic kidney disease

Patients with chronic kidney disease (CKD) display a progeric vascular phenotype linked to apoptosis, cellular senescence and osteogenic transformation. This has proven intractable to modelling appropriately in model organisms. We have therefore investigated this directly in man, using for the first time validated cellular biomarkers of ageing (CDKN2A/p16INK4a, SA-β-Gal) in arterial biopsies from 61 CKD patients undergoing living donor renal transplantation. We demonstrate that in the uremic milieu, increased arterial expression of CDKN2A/p16INK4a associated with vascular progeria in CKD, independently of chronological age. The arterial expression of CDKN2A/p16INK4a was significantly higher in patients with coronary calcification (p=0.01) and associated cardiovascular disease (CVD) (p=0.004). The correlation between CDKN2A/p16INK4a and media calcification was statistically significant (p=0.0003) after correction for chronological age. We further employed correlate expression of matrix Gla protein (MGP) and runt-related transcription factor 2 (RUNX2) as additional pathognomonic markers. Higher expression of CDKN2A/p16INK4a, RUNX2 and MGP were observed in arteries with severe media calcification. The number of p16INK4a and SA-β-Gal positive cells was higher in biopsies with severe media calcification. A strong inverse correlation was observed between CDKN2A/p16INK4a expression and carboxylated osteocalcin levels. Thus, impaired vitamin K mediated carboxylation may contribute to premature vascular senescence.

Chitosan/Carboxymethyl Cellulose Polyelectrolyte Complex Scaffolds for Pulp Cells Regeneration

Novel polyelectrolyte complex (PEC) chitosan/carboxymethyl cellulose (CMC) scaffolds are prepared using a freeze-dry process. The microstructure is characterized by SEM and the average pore diameters and internal porosities are calculated. The morphology and distribution of pulp cells on these three-dimensional scaffolds are investigated by SEM and confocal laser scanning microscopy (CLSM). The expression of osteonectin (ON) and dentin sialophosphoprotein (DSPP) is detected by reverse transcription polymerase chain reaction (RT-PCR). The scaffolds are then implanted subcutaneously into BALB/c mice. The addition of CMC to chitosan decreases the pore diameter and increases internal porosity. The pulp cells co-cultured in these PEC scaffolds show improved adhesion, spreading, cell capacity, and three-dimensional configurations compared to pure chitosan scaffolds. Based on the data obtained, the chitosan/CMC complex provides an improved scaffold material for pulp tissue engineering.

Vital pulp therapy

Vital pulp therapy is performed to preserve the health status of the tooth and its ultimate position in the arch. These procedures are performed routinely in primary and permanent teeth. This review is divided into 2 parts: the first aims to illustrate the basic biology of the pulp and the effects on the pulp due to various procedures; the second focuses on the clinical aspects of treatment and the use of various dental materials during different vital pulp therapy procedures performed in the primary and permanent teeth.

Increased autophagic activity in senescent human dental pulp cells

AIM

To establish whether autophagy is involved in dental pulp cell (DPC) senescence, so as to better understand the mechanism of the ageing process within the dental pulp.

METHODOLOGY

Human DPCs obtained from intact molars and premolars were cultured and serially passaged. Senescence-β-galactosidase (SA-β-gal) staining was performed to assess DPC senescence, which is considered to be the senescence of cells in culture after a series of passages. Autophagic activity was analysed by Western blot for major autophagic proteins and transmission electron microscopy (TEM) for autophagic vacuoles in both young and senescent cells. Statistical analyses were performed using the Student's t-test.

RESULTS

Senescence-β-galactosidase staining was higher in senescent DPC than in young cells (P = 0.011). Western blot revealed senescent DPCs had greater expression of autophagic proteins (microtubule-associated protein light chain 3 and Beclin 1) than young cells (P = 0.04, P = 0.001). Transmission electron microscopy revealed more autophagic vacuoles in senescent DPCs compared to young cells (P = 0.029).

CONCLUSIONS

Expression of autophagic proteins (microtubule-associated protein light chain 3 and Beclin 1) increased in senescent DPCs compare to young cells. More autophagic vacuoles were observed in senescent DPCs by TEM. Collectively, these data imply that autophagic activity increased in senescent DPCs.

Impaired odontogenic differentiation of senescent dental mesenchymal stem cells is associated with loss of 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.

Analysis of side population cells derived from dental pulp tissue

AIM

To investigate the characteristics of side population (SP) cells derived from the dental pulp of young and aged rats.

METHODOLOGY

Maxillary and mandibular incisors were extracted from 5-week-old (young) rats and 60- to 80-week-old (aged) rats. Coronal pulp tissue was removed mechanically, and single-cell suspensions were prepared using collagenase and dispase. Cells were stained with Hoechst 33342 and sorted with an fluorescence-activated cell sorter (FACS). Isolated SP and main population (MP) cells were analysed by real-time reverse transcription polymerase chain reaction, immunohistochemical localization and cell cycle determination. Two-way analysis of variance and the multiple comparison Scheffè test were used for statistical analysis (P<0.05).

RESULTS

Approximately 0.40% of pulp cells in young rats and 0.11% in aged rats comprised SP cells. SP cells expressed a higher mRNA level of ATP-binding cassette transporter G2 (ABCG2), but lower mRNA levels of nestin, alkaline phosphatase, p16 and p57 than MP cells in both age groups. Immunohistochemical observation revealed ABCG2-positive cells localized in the cell-rich zone and nestin in the odontoblastic layer in both groups. Furthermore, the majority of both young and aged SP and MP cells were in growth arrest of the G(0) /G(1) phase.

CONCLUSION

The FACS analysis revealed a decrease in the proportion of SP cells with age, whilst p16 mRNA expression indicated an increase in cell senescence. The cell cycles of SP and MP cells from both young and aged dental pulp were generally in the G0/G1 phase.

Gene-enhanced tissue engineering for dental hard tissue regeneration: (2) dentin-pulp and periodontal regeneration

Potential applications for gene-based tissue engineering therapies in the oral and maxillofacial complex include the delivery of growth factors for periodontal regeneration, pulp capping/dentin regeneration, and bone grafting of large osseous defects in dental and craniofacial reconstruction. Part 1 reviewed the principals of gene-enhanced tissue engineering and the techniques of introducing DNA into cells. This manuscript will review recent advances in gene-based therapies for dental hard tissue regeneration, specifically as it pertains to dentin regeneration/pulp capping and periodontal regeneration.

Gene-enhanced tissue engineering for dental hard tissue regeneration: (1) overview and practical considerations

Gene-based therapies for tissue regeneration involve delivering a specific gene to a target tissue with the goal of changing the phenotype or protein expression profile of the recipient cell; the ultimate goal being to form specific tissues required for regeneration. One of the principal advantages of this approach is that it provides for a sustained delivery of physiologic levels of the growth factor of interest.

This manuscript will review the principals of gene-enhanced tissue engineering and the techniques of introducing DNA into cells. Part 2 will review recent advances in gene-based therapies for dental hard tissue regeneration, specifically as it pertains to dentin regeneration/pulp capping and periodontal regeneration.