The differentiation-inducing effect of conditioned media obtained from dental pulp cells

Long-term culture of human odontoma-derived cells with a Rho kinase inhibitor

Because of cellular senescence/apoptosis, no effective culture systems are available to maintain replication of cells from odontogenic tumors especially for odontoma, and, thus, the ability to isolate human odontoma-derived cells (hODCs) for functional studies is needed. The current study was undertaken to develop an approach to isolate hODCs and fully characterize the cells in vitro. The hODCs were cultured successfully with a Rho-associated protein kinase inhibitor (Y-27632) for an extended period with stabilized lengths of the telomeres to sustain a similar phenotype/property as the primary tumoral cells. While the hODCs showed stable long-term expansion with expression of major dental epithelial markers including dentin sialophosphoprotein (DSPP) even in the three-dimensional microenvironment, they lack the specific markers for the characteristics of stem cells. Moreover, cells from dental pulp showed significant up-regulation of DSPP when co-cultured with the hODCs, while control fibroblasts with the hODCs did not. Taken together, we propose that the hODCs can be isolated and expanded over the long term with Y-27632 to investigate not only the development of the hODCs but also other types of benign human tumors.

EDTA soluble chemical components and the conditioned medium from mobilized dental pulp stem cells contain an inductive microenvironment, promoting cell proliferation, migration, and odontoblastic differentiation

Background

The critical challenge in tissue engineering is to establish an optimal combination of stem cells, signaling morphogenetic molecules, and extracellular matrix scaffold/microenvironment. The extracellular matrix components of teeth may be reconstituted as an inductive microenvironment in an ectopic tooth transplantation bioassay. Thus, the isolation and identification of the chemical components of the inductive microenvironment in pulp/dentin regeneration will accelerate progress towards the goal of tissue engineering of the tooth.

Methods

The teeth demineralized in 0.6 M hydrochloric acid were sequentially extracted by 4.0 M guanidine hydrochloride (GdnHCl), pH 7.4, and 0.5 M ethylenediaminetetraacetic acid (EDTA), pH 7.4. The extracted teeth were transplanted into an ectopic site in severe combined immunodeficiency (SCID) mice with mobilized dental pulp stem cells (MDPSCs). The unextracted tooth served as a positive control. Furthermore, the soluble components for the inductive microenvironment, the GdnHCl extracts, or the EDTA extracts together with or without MDPSC conditioned medium (CM) were reconstituted systematically with autoclaved teeth in which the chemical components were completely inactivated and only the physical microenvironment was preserved. Their pulp/dentin regenerative potential and angiogenic potential were compared 28 days after ectopic tooth transplantation by histomorphometry and real-time RT-PCR analysis.

Results

Expression of an odontoblastic marker, enamelysin, and a pulp marker, thyrotropin-releasing hormone degrading enzyme (TRH-DE), was lower, and expression of a periodontal cell marker, anti-asporin/periodontal ligament-associated protein 1 (PLAP-1), was higher in the transplant of the EDTA-extracted teeth compared with the GdnHCl-extracted teeth. The autoclaved teeth reconstituted with the GdnHCl extracts or the EDTA extracts have weak regenerative potential and minimal angiogenic potential, and the CM significantly increased this potential. Combinatorial effects of the EDTA extracts and the CM on pulp/dentin regeneration were demonstrated in vivo, consistent with their in-vitro effects on enhanced proliferation, migration, and odontoblastic differentiation.

Conclusions

The EDTA-extracted teeth demonstrated significantly lower pulp/dentin regenerative potential compared with the GdnHCl-extracted teeth. The EDTA soluble chemical components when reconstituted with the physical structure of autoclaved teeth serve as an inductive microenvironment for pulp/dentin regeneration, promoting cell proliferation, migration, and odontoblastic differentiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0334-z) contains supplementary material, which is available to authorized users.

Inhibition of odontogenic differentiation of human dental pulp cells by dental resin monomers

Background

Dental resin monomers that are leached from the resin matrix due to incomplete polymerization can affect the viability and various functions of oral tissues and cells. In this study, the effects of triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) on odontogenic differentiation of human dental pulp cells (HDPCs) were examined. To mimic clinical situations, dental pulp cells were treated with resin monomers for 24 h prior to the analysis of alkaline phosphatase (ALP) activity and mRNA expression of genes related to pulp cell differentiation. To elucidate the underlying signaling pathways, regulation of mitogen-activated protein (MAP) kinases by resin monomers was also investigated.

Results

The ALP activity of HDPCs was reduced by TEGDMA and HEMA at noncytotoxic concentrations. The mRNA expression of dentin sialophosphoprotein (DSPP), osteocalcin (OCN), and osteopontin (OPN) was also downregulated by resin monomers. However, DSPP expression was not affected by hydrogen peroxide (H₂O₂). Among the MAP kinases examined, ERK activation (ERK phosphorylation) was not affected by either resin monomers or H₂O₂, whereas JNK was phosphorylated by TEGDMA and HEMA. Phospho-p38 was upregulated by HEMA, while TEGDMA and H₂O₂ suppressed p38 phosphorylation.

Conclusions

Exposure to TEGDMA and HEMA for a limited period suppresses differentiation of HDPCs via different signaling pathways.

Conditioned medium from periapical follicle cells induces the odontogenic differentiation of stem cells from the apical papilla in vitro

INTRODUCTION

We investigated the biological effects of conditioned medium (CM) from periapical follicle cells (PAFCs) of root-developing tooth on the proliferation and differentiation of stem cells from the apical papilla (SCAP) in vitro.

METHODS

Human SCAP and PAFCs were isolated and expanded. CM from PAFCs was prepared with the primary cells. Cell cycle analysis, methyl-thiazol-diphenyltetrazolium assay, alkaline phosphatase activity, mineralization behavior, and gene expression of odontoblast phenotype SCAP cultured with or without CM from PAFCs were evaluated.

RESULTS

In the CM-treated group, the cell growth, alkaline phosphatase activity, and mineralization of SCAP were up-regulated. The expression of dentin sialophosphoprotein, alkaline phosphatase, and osteocalcin mRNA progressively increased in SCAP treated with CM from PAFCs.

CONCLUSIONS

Our findings suggest that CM from PAFCs is able to provide a favorable odontogenic microenvironment to induce differentiation of SCAP along the odontoblast lineage.

Ultrasonication and Genipin Cross-Linking to Prepare Novel Silk Fibroin–Gelatin Composite Hydrogel

Hydrogels are highly desirable tissue engineering scaffolds due to their high water content and structural similarity to a natural extra cellular matrix. However, the extensive use of hydrogels is limited by their low strength and facile degradation. By combining mechanical integrity and slow degradation of silk fibroin with excellent bioactivity of gelatin, a novel biocompatible protein-based composite hydrogel of silk fibroin and gelatin was developed. The gelation of silk fibroin aqueous solution was accelerated by ultrasonication, and gelatin derived from porcine skin was immobilized into the hydrogel network by the silk fibroin β-sheets. After that, genipin was used to post-cross-link the hydrogel to form a compact and stable hydrogel network. This hydrogel composite was a mechanically robust biomaterial with predictable long-term degradation characteristics. MG63 cells readily attached, spread, and proliferated on the surface of the hydrogels as demonstrated by fluorescein diacetate/propidium iodide staining and mitochondrial activity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. Furthermore, the physicochemical and biological properties of hydrogel were fine-tunable by altering the ratio of silk fibroin and gelatin. The silk fibroin/gelatin composite hydrogels are anticipated to have the potential as cartilage or non-load-bearing bone tissue engineering and regeneration.

Effects of N-acetylcysteine on TEGDMA- and HEMA-induced suppression of osteogenic differentiation of human osteosarcoma MG63 cells

Triethyleneglycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are major resinous components of dental restorative materials and dentin bonding adhesives. Resin monomers are known to cause cytotoxicity in mammalian cells via oxidative stress and inhibit differentiation of dental pulp cells and osteoblasts. This study was aimed to investigate whether oxidative stress was involved in the inhibition of TEGDMA- and HEMA-induced differentiation. TEGDMA and HEMA reduced alkaline phosphatase (ALP) activity and the mRNA expression of the osteopontin (OPN) gene in MG63 cells at noncytotoxic concentrations. On the other hand, N-acetylcysteine (NAC) did not affect ALP activity at concentrations below 10 mM. Reduced ALP activity and OPN mRNA expression by TEGDMA were partially recovered via cotreatment with NAC. However, NAC did not exhibit significant effects in HEMA-treated cells. Glutathione (GSH) levels were also down-regulated by both TEGDMA and HEMA. The addition of NAC induced the partial recovery of GSH in cells treated with 0.5 mM TEGDMA. On the other hand, the levels of GSH in HEMA-treated cells were not affected by NAC. These results suggest that oxidative stress is involved in the suppression of differentiation by TEGDMA. Translocation of Nrf2 from the cytoplasm to the nucleus has been known to play a role in the suppression of osteogenic differentiation by oxidative stress. However, Nrf2 did not move into the nucleus in resin monomer-treated MG63 cells, suggesting the contribution of other signaling pathways to the suppressive effects of resin monomers.