Micromolar sodium fluoride promotes osteo/odontogenic differentiation in dental pulp stem cells by inhibiting PI3K/AKT pathway

Dental pulp stem cells - A basic research and future application in regenerative medicine

Dental pulp is a valuable and accessible source of stem cells (DPSCs) with characteristics similar to mesenchymal stem cells. DPSCs can regenerate a range of tissues and their potential for clinical application in regenerative medicine is promising. DPSCs have been found to express low levels of Class II HLA-DR (MHC) molecules, making them potential candidates for allogeneic transplantation without matching the donor's tissue. Research on the correlation between non-coding RNAs (ncRNAs) and human dental pulp stem cells (DPSCs) provides promising insights into the use of these cells in clinical settings for a wide range of medical conditions. It is possible to use a number of ncRNAs in order to restore the functional role of downregulated ncRNAs that are correlated with osteoblastogenesis, or to suppress the functional role of overexpressed ncRNAs associated with osteoclast differentiation in some cases.

Landscape of Differentiation Potentials as a "Hallmark" in Oral-derived MSCs

Background

Mesenchymal stem cells (MSCs) offer clinical promise for use in cell therapy approaches for regenerative medicine. A therapeutic challenge is that MSCs from different tissues are phenotypically and functionally distinct. Therefore, this study aims to molecularly characterize oral-derived MSCs by defining one of the three hallmarks of MSCs, differentiation potential, to discern their true molecular identities.

Methods

Three different populations of oral tissue MSCs (from alveolar bone-aBMSCs; from dental pulp-DPSCs; and from gingiva-GMSCs) from three different patients were isolated and cultured. These MSCs were characterized for their stemness by flow cytometry and multi-differentiation potential, and their RNA was also isolated and analyzed quantitatively with RNA sequencing. Total mRNA-seq was performed and differentially expressed genes (DEGs) were identified in pairwise (DPSCs vs. aBMSCs, GMSCs vs. aBMSCs, and GMSCs vs. DPSCs) and tissue-specific comparisons (aBMSCs vs. Others, DPSCs vs. Others, GMSCs vs. Others) (FDR, p<0.05 ). Further, these DEGs, either common between MSC populations or unique to a specific MSC population, were evaluated for pathways and biological processes.

Results

aBMSCs, DPSCs, and GMSCs were successfully isolated and characterized. The tissue-specific comparison revealed that DEGs were most numerous in DPSCs (693 genes) as compared to aBMSCs (103 genes) or DPSCs (232 genes). Statistically significant DEGs through pairwise comparisons present higher numbers in GMSCs vs. DPSCs (627) as compared to either DPSCs vs aBMSCs (286) or GMSCs vs. aBMSCs (82). Further analysis found that RUNX2, IBSP, SOX6, ACAN, and VCAM1 were significantly upregulated in aBMSCs. In DPSCs, BMP4 and IL6 were significantly downregulated, whereas AXL and NES were significantly upregulated. In GMSCs, AGPT1, SEMA4D, and PGDFA were significantly downregulated. Additionally, MAPK, PI3-AKT, and RAS signaling pathways were significantly regulated in GMSCs. Interestingly, aBMSCs and DPSCs revealed positive regulation of osteoblast differentiation, whereas GMSCs revealed negative regulation of osteoblast differentiation. DPSCs also revealed negative regulation of angiogenesis.

Conclusions

Oral-derived MSCs have an inherent "landscape" of differentiation defined by their tissue of origin; yet this differentiation potential can be modulated by their microenvironment.

Effects of different signaling pathways on odontogenic differentiation of dental pulp stem cells: a review

Dental pulp stem cells (DPSCs) are a type of mesenchymal stem cells that can differentiate into odontoblast-like cells and protect the pulp. The differentiation of DPSCs can be influenced by biomaterials or growth factors that activate different signaling pathways in vitro or in vivo. In this review, we summarized six major pathways involved in the odontogenic differentiation of DPSCs, Wnt signaling pathways, Smad signaling pathways, MAPK signaling pathways, NF-kB signaling pathways, PI3K/AKT/mTOR signaling pathways, and Notch signaling pathways. Various factors can influence the odontogenic differentiation of DPSCs through one or more signaling pathways. By understanding the interactions between these signaling pathways, we can expand our knowledge of the mechanisms underlying the regeneration of the pulp-dentin complex.

Stimulation phosphatidylinositol 3-kinase/protein kinase B signaling by Porphyromonas gingivalis lipopolysacch aride mediates interleukin-6 and interleukin-8 mRNA/protein expression in pulpal inflammation

BACKGROUND/PURPOSE

The signaling mechanisms for Porphyromonas gingivalis lipopolysaccharide (PgLPS)-induced inflammation in human dental pulp cells are not fully clarified. This in vitro study aimed to evaluate the involvement of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway in PgLPS-induced pulpal inflammation.

METHODS

Human dental pulp cells (HDPCs) were challenged with PgLPS with or without pretreatment and coincubation with a PI3K/Akt inhibitor (LY294002). The gene or protein levels of PI3K, Akt, interleukin (IL)-6, IL-8, alkaline phosphatase (ALP), osteocalcin and osteonectin were analyzed by reverse transcription polymerase chain reaction (PCR), real-time PCR, western blotting, and immunofluorescent staining. In addition, an enzyme-linked immunosorbent assay was used to analyze IL-6 and IL-8 levels in culture medium.

RESULTS

In response to 5 μg/ml PgLPS, IL-6, IL-8, and PI3K, but not Akt mRNA expression of HDPCs, was upregulated. IL-6, IL-8, PI3K, and p-Akt protein levels were stimulated by 10-50 μg/ml of PgLPS in HDPCs. PgLPS also induced IL-6 and IL-8 secretion at concentrations higher than 5 μg/ml. Pretreatment and co-incubation by LY294002 attenuated PgLPS-induced IL-6 and IL-8 mRNA expression in HDPCs. The mRNA expression of ALP, but not osteocalcin and osteonectin, was inhibited by higher concentrations of PgLPS in HDPCs.

CONCLUSION

P. gingivalis contributes to pulpal inflammation in HDPCs by dysregulating PI3K/Akt signaling pathway to stimulate IL-6 and IL-8 mRNA/protein expression and secretion. These results are useful for understanding the pulpal inflammation and possible biomarkers of inflamed pulp diagnosis and treatment.

Biphasic Functions of Sodium Fluoride (NaF) in Soft and in Hard Periodontal Tissues

Sodium fluoride (NaF) is widely used in clinical dentistry. However, the administration of high or low concentrations of NaF has various functions in different tissues. Understanding the mechanisms of the different effects of NaF will help to optimize its use in clinical applications. Studies of NaF and epithelial cells, osteoblasts, osteoclasts, and periodontal cells have suggested the significant roles of fluoride treatment. In this review, we summarize recent studies on the biphasic functions of NaF that are related to both soft and hard periodontal tissues, multiple diseases, and clinical dentistry.