Stem cells have been a recent focus of regenerative medicine research, and dental pulp cells are considered as a source of stem cells. Cell proliferation and differentiation of dental pulp cells in deciduous teeth are greater than those of dental pulp cells in permanent teeth. Some reports indicate that hypoxia upregulates the proliferation and differentiation of stem cells. In this study, we examined the effect of hypoxia on human dental pulp cells of deciduous teeth. Hypoxia at 2% O₂ for 2 days did not affect cell proliferation of human dental pulp cells from deciduous teeth. However, it increased the gene expression of hypoxia inducible factor-1-1α, Oct3/4, Sox2, and C-Myc, and enhanced adipogenic differentiation. These results suggest that hypoxia enhances the differentiation ability of dental pulp cells in deciduous teeth.

In general, cell viability decreases as the concentration of chemicals increases. However, the survival rates of cells exposed to trace amounts of chemicals increases in many cases. Few reports have been published on such phenomenon. In addition, cells damaged by chemical exposure are known to recover when the chemicals are washed away and the medium is replaced with fresh medium. The relationship between the increased cell viability and the cell recovery rates after exposure to trace amounts chemicals remain unclear.

In the present study, a three-dimensional culture with collagen gel was employed to examine the cell viability rates by exposing cells to copper, silver, tin, and zinc solutions at low concentrations. In addition, the collagen gel containing cells was vertically cut to examine the decreased cell recovery rates of the cut surface after 7 days of culture based on the amount of dye penetration. As a result, the cell survival rates increased by a trace amount of zinc ion, with the highest cell recovery rate. Also, the cell survival rates were slightly increased by exposing the cells to trace amounts of other metal ions. These results may provide useful basic data for applying metal ions to regenerative medicine in the future.

Mesenchymal stem cells (MSCs)　have limited capacity to proliferate in vitro, making it very difficult to acquire sufficient cell numbers for implantation. The objective of this study was to induce MSC-like cells (MSLCs) derived from human gingival induced pluripotent stem (HG-iPSCs) into osteoblast-like cells. We derived MSLCs from HG-iPSCs under feeder-free conditions. MSLCs expressing MSC-specific markers treated with osteoblast differentiation factor expressed osteoblast-specific mRNA and protein level when cultured with or without bone morphogenetic protein (BMP). BMP-2 had a positive effect on the expression of early indicators of osteogenic differentiation. However, the medium without BMP-2 promoted calcium deposition, which occurs at the terminal stage of osteogenic differentiation. MSLCs are likely to have higher proliferative capacity, and hence, in vitro-differentiated osteoblast-like cells and appropriate scaffolds can be used for bone tissue engineering.

Adiponectin, an adipocyte-derived biologically active molecule, is an abundant plasma protein and has various biological functions. Two types of adiponectin receptors (AdipoR1 and AdipoR2) have been cloned and found to be expressed ubiquitously. More recently, T-cadherin (CDH13) has been characterized as a novel adiponectin receptor on vascular endothelial cells and smooth muscle. In this study, we investigated the effects of adiponectin on gene expression during osteoblast differentiation using DNA microarray analysis and performed pathway analysis of the clusters including adiponectin receptors.

Osteoblastic differentiation of a murine pro-osteoblastic cell line MC3T3-E1 was induced by ascorbic acid and β-glycerophosphate with or without recombinant murine adiponectin. Three days after stimulation, gene expression profiles were obtained by DNA microarray analysis and used for hierarchical clustering with correlation centered similarity metrics. Functional cluster annotations for selected clusters were generated based on significant gene ontology terms, and the relationship among genes was visualized by pathway analysis.

Genes significantly upregulated by differentiation medium were related to osteoblast differentiation and cell growth. The genes included in cluster AdipoR1 were downregulated by differentiation medium, but those in cluster AdipoR2 were upregulated by the medium. The genes included in cluster CDH13 were also upregulated during osteoblastic differentiation.

Our study suggests that AdipoR2 and CDH13, rather than AdipoR1, may be involved in osteoblastic differentiation.

In 2014, we discovered that bone phosphoproteins, which are collectively called SIBULING family of proteins, are equipped with titanium-binding ability. Furthermore, the titanium implant devices which were coated with titanium-bound SIBLING induced more than 100 times faster bone formation of early stage when implanted into rat calvaria. These findings led us to an explanation why titanium implants could be fixed into living bone. Several other phosphoproteins including, phosvitin, caseins and phosphophoryn (a dentin phosphoprotein) were also found to bind with titanium by use of a chromatographic column packed with titanium beads. In this study we demonstrated that a typical phosphoprotein, phosvitin lost its titanium-binding ability in a time-dependent manner by the reaction with λ-protein phosphatase. The fact confirmed that certain specific phosphoserines λresidues in this protein were responsible for the titanium-protein interaction. For an additional confirmation of SIBLING-titanium interaction, we extracted bone and dentin proteins with a new and simple method of acidic condition and applied them to the chromatographic column packed with titanium beads. The results showed that definite portions of the acid soluble proteins from both bone and dentin were retained in the column. Electrophoretic analysis showed the retained fractions were Stains-all positive, indicating that both bone and dentin contain multiple phosphoproteins which have affinity with titanium. The titanium-bound fraction of acid extract was again coated on the titanium device and implanted into rat calvaria. After one week, histology showed that in addition to definite pattern of bone formation, process of endochondral ossification was clearly observed. In the control implant of uncoated titanium device, only collagenous tissues were observed, without any cartilage nor bone formation. Based upon these findings we reconfirmed that the core biochemical mechanisms underlying the strong bond between the titanium and living bone is based upon the interaction between the implanted titanium and multiple bone phosphoproteins in the host tissue.