Goal of regenerative medicine is to reconstruct tissues or organ in the needy part of the body. Discussions of what are the fundamental factors for creating artificially tissues or organ from cells require a certain biochemical and physiological knowledge, accompanying a deep insight into human body. Traditional triad for tissue engineering: (1) cells, (2) matrix and (3) cytokines seem no more enough now-a-day. We have been proposing the five factors: (1) cells, (2) matrices, (3) cytokines, (4) nutrients supply or vasculature and (5) mechano-dynamic factors, the last two of which, so far, has been poorly elucidated in vitro and in vivo situation. In the initial parts of this review, we recapitulate the history of the geometry of the artificial matrices", which are now understood to be closely related with nutrient supply or vasculature. Then we will step into an important issue of mechano-dynamic factors. So far, cell culture has been studied on static state on stable flat culture dishes. But in a living body, no single cell exists on such a motionless situation. Thus, various devices were invented for providing mechano-dynamic factors to the cells. The most of them are complex and highly expensive for many young researchers to approach. After reviewing several such devices, we introduce a simple application of gravitational forth, so-called "ceiling culture or anti-gravitational culture (anti-G-culture)". In this new culture system, it was shown that RNA of actin fibers increased 20 times higher than the conventional flat dish culture, meaning that in anti-G-culture system, general activities of cells highly enhanced due to a mechano-dynamic factor that is anti-G-force.
Statins, known as HMG-CoA reductase inhibitors, were reported to have osteogenic effects. However, the mechanism of the effect of dexamethasone on statin-induced osteogenesis remains elusive. This study investigated the effects of dexamethasone (Dex) on cell proliferation and osteoblastic differentiation of human mesenchymal stem cells (hMSCs) treated with fluvastatin (Flu). The addition of 10 nM Dex increased, by day 7, the growth of hMSCs treated with 0.5 µM Flu. Moreover, Dex of all tested concentrations increased the growth of hMSCs in the presence of 1.0 µM Flu by day 7. An alkaline phosphatase (ALP) activity assay showed the addition of Dex resulted in increased ALP activity of the hMSCs treated with 0.5 µM Flu in a concentration-independent manner, while Dex did not increase ALP levels in the presence of high Flu concentrations including 1.0 µM and 2.0 µM. These results suggest that the addition of 10 nM Dex may be necessary for cell proliferation and osteoblastic differentiation of hMSCs in the presence of 0.5 µM Flu.
Statins, the cholesterol-lowering drug, are known to activate the promoter of BMP-2 gene, and stimulate bone formation. In this study, we examine the effect of statin on the gene expression in human dental pulp cells.
Dental pulp cells were cultured in differential medium with simvastatin or mevastatin, and gene expression level was measured using real-time quantitative RT-PCR technique.
Both statins induced and significantly increased the gene expression of osteocalcin in the dental pulp cells, although they did not have influence on the expression of dentin sialophosphoprotein. Statins transiently promoted the gene expressions of BMP-2 and Runx2 in the dental pulp cells on day 3, and then they significantly suppressed Runx2 expression on day 16.
Hence, it is indicated that statins induce not only the initial osteogenic differentiation of human dental pulp stem cells but also final differentiation through the regulation of the transcription factor.
Coral is a porous material with rough surface, and physical strength that could be effectively used as scaffolding for bone growth. To compare the bioabsorbility and biocompatibility between cultured and natural coral, we examined the chemical characteristics and tissue affinity in vitro. The cultured and natural coral (montipora digitata) deproteinized with NaOH was used. The cultured and natural coral particles were soaked in calcium containing buffers (pH 6.0, pH 7.0, pH 8.0) for 10 days, and the calcium density in the buffer was then measured. The calcium density in a solution without these particles was measured as the control group. Human periodontal ligament fibroblast (HPLF) was multiplied. The cultured and natural coral particles were then seeded in the wells with HPLF. After 7 days of culture, the HPLF were stained with DAPI and 5-Ethynyl-2'-deoxyuridine (EdU), and the increase in cell number and S phase of the cell cycle were observed. Cells without these particles were cultured as a control. The density of calcium in the pH 6.0 buffer which soaked the cultured coral increased more than that which soaked the natural coral. On the other hand, the calcium density in the pH 8.0 seeded cultured coral was decreased compared with that which soaked the natural coral. After 7 days of culture, cells consisting of HPLF grew densely around the cultured coral particles compared with the natural coral. Thus, the cultured coral would provide a bioabsorbable and biocompatible scaffold.