Adult stem cell-based apexogenesis

Strontium (Sr) elicits odontogenic differentiation of human dental pulp stem cells (hDPSCs): A therapeutic role for Sr in dentine repair?

Strontium (Sr) forms a significant component of dental restorative materials and although it is widely used in toothpastes, the biological effects of Sr on the dentine-pulp complex have not been investigated. In this first study, we characterise the Sr elicited effects on human dental pulp stem cells (hDPSC) in vitro using exogenously Sr added to culture medium, and bioavailable Sr derived from a novel bioactive glass (BG). The related mechanisms were also investigated. Our results indicate that low dose Sr (between 0.1 and 2.5mM) induces proliferation and alkaline phosphatase (ALP) activity of hDPSCs, but has no effect on colony formation or cell migration. Sr at specific concentrations (1 and 2.5mM) stimulated collagen formation and mineralisation of the hDPSC generated matrix. In addition, qRT-PCR, Western blotting and immunocytochemistry revealed that Sr regulates gene expression and the protein secretion of the odontogenic markers: dentine sialophosphoprotein (DSPP) and dentine matrix protein 1 (DMP-1) and protein localisation (DSPP was localised to the Golgi, while no apparent changes occur in DMP-1 distribution which remains in both cytosol and the nucleus). Additionally, the calcium sensing receptor (CaSR) and downstream pathway MAPK/ERK signalling pathway in hDPSCs were activated by Sr. Bioavailable Sr from the BG revealed novel biological insights of regulating metabolic and ALP activities in hDPSCs. Taken together, these results suggest that Sr at specific doses significantly influences proliferation, odontogenic differentiation and mineralisation of hDPSCs in vitro via the CaSR using a pathway with similarities to osteoblast differentiation. These are the first such studies and indicate that Sr treatment of hDPSCs could be a promising therapeutic agent in dental applications. In conclusion, we propose that Sr from a substituted BG could be used more effectively in biomaterials designed for dental applications.

STATEMENT OF SIGNIFICANCE

Despite the fact that strontium (Sr) is used widely in dental practise, its potential effects on odontoblasts have been ignored. Our study provides the first evidence that Sr (exogenous and that derived from a bioglass (BG)) can stimulate dentinogenesis in human dental pulp stem cells (hDPSCs) by promoting their proliferation, differentiation and mineralisation in vitro. Therefore, while previously unrecognised, Sr BG is likely to be beneficial in atraumatic dentistry practise and maintenance of a competent tooth in conditions such as caries. Repair of defected dentine is still one of the main challenges in dental research and annually untreated caries results in the loss of productivity equivalent to US$ 27 billion. Advances in tissue engineering technology, alongside the use of dental pulp stem cells provide an approach to achieve dentine regeneration. Understanding the actions of Sr will permit a more controlled application of Sr in the clinic. These data are thus likely to be of great interest to the material scientists, biological researchers, clinicians and manufacturers of dental products.

Conditioned medium from human bone marrow stromal cells attenuates initial inflammatory reactions in dental pulp tissue

AIM

To evaluate the effect of MSC-conditioned medium (CM) on the secretion of pro- and anti-inflammatory cytokines from dental pulp cells (hDPC) in vitro, and on the gene expression in vivo after replantation of rat molars.

MATERIALS AND METHODS

hDPC were cultured in CM for 24 h, and the concentration of interleukin IL-10, IL-4, IL-6, and IL-8, regulated on activation, normal T Cell expressed and secreted (RANTES), and prostaglandin E₂ (PGE₂ ) in the media were measured by multiplex assay and ELISA, respectively. Expression of cyclooxygenase-2 (COX-2) was also examined by Western blot analysis after 24 h. Left and right maxillary first rat molars (n = 20) were elevated for 2 min and then replanted with or without application of CM into the tooth sockets. Levels of IL-1β, IL-10, IL-4, IL-6, and IL-8, and tumor necrosis factor-alpha (TNF-α) mRNA were evaluated by real-time qRT-PCR 3 and 14 days following tooth replantation.

RESULTS

The production of IL-8, IL-10, and IL-6, RANTES and PGE₂ by cells cultured in CM was significantly higher than production by cells cultured in standard medium (DMEM). At day 3 following replantation in vivo, the levels of IL-1β and IL-6, and TNF-α mRNA were significantly lower in the CM-treated replanted teeth compared with control teeth. Further, at day 3, the IL-6/IL-10 ratio was significantly lower in the CM-treated replanted teeth compared with control. At day 14 following replantation, no differences in the mRNA ratios were detected between the pulp tissues of replanted and control teeth.

CONCLUSIONS

These findings indicated that CM promotes secretion of pro- and anti-inflammatory cytokines from hDPCin vitro and attenuates the initial inflammatory response in the rat dental pulp in vivo following tooth replantation.