Daiki Mizuno

Composite implantation of mesenchymal stem cells with endothelial progenitor cells enhances tissue-engineered bone formation

For successful tissue engineering, neovascularization of the implanted tissue is critical. Factors generated by endothelial cells are also considered crucial for the process of osteogenesis. The direct effects of supplementing tissue engineered constructs with cultured endothelial progenitor cells (EPCs) for enhancing bone regeneration have not been reported. In this study, we investigated the potential of EPCs to facilitate neovascularization in implants and evaluated their influence on bone regeneration. The influence of EPC soluble factors on osteogenic differentiation of mesenchymal stem cells (MSCs) was tested by adding EPC culture supernatant to MSC culture medium. To evaluate the influence of EPCs on MSC osteogenesis, canine MSCs-derived osteogenic cells and EPCs were seeded independently onto collagen fiber mesh scaffolds and co-transplanted to nude mice subcutaneously. Results from coimplant experiments were compared to implanted cells absent of EPCs 12 weeks after implantation. Factors from the culture supernatant of EPCs did not influence MSC differentiation. Coimplanted EPCs increased neovascularization and the capillary score was 1.6-fold higher as compared to the MSC only group (p < 0.05). Bone area was also greater in the MSC + EPC group (p < 0.05) and the bone thickness was 1.3-fold greater in the MSC + EPC group than the MSC only group (p < 0.05). These results suggest that soluble factors generated by EPCs may not facilitate the osteogenic differentiation of MSCs; however, newly formed vasculature may enhance regeneration of tissue-engineered bone.

Limited but heterogeneous osteogenic response of human bone marrow mesenchymal stem cells to bone morphogenetic protein-2 and serum.

Although there are numerous reports describing the in vivo bone forming capability of recombinant human bone morphogenetic proteins-2 (rhBMP-2), studies have reported limited effects on human mesenchymal stem cells (hMSCs). However, the reasons for these discrepancies are not well understood. The aim of this study was to investigate the responsiveness of hMSCs to osteoinductive signals, focusing on rhBMP-2 and the effect of serum on that responsiveness. Human MSCs from six donors were analysed. When those cells were treated with osteoinduction medium including dexamethasone (Dex), alkaline phosphatase (ALP) activities increased in all cell lines. On the other hand, rhBMP-2-containing medium failed to increase ALP activity. When five different sera were used for cultivation and induction with rhBMP-2, ALP activities increased in two of them, but not in the others. The expression of BMP-2 antagonist noggin was induced in almost all combinations regardless of the responsiveness to rhBMP-2. On the other hand, the expression of follistatin showed significant variations depending on the serum and cell line. However, the expression did not correlate with the responsiveness to rhBMP-2. The results from this study showed limited but heterogeneous osteogenic response of hMSCs to rhBMP-2 and that the results are affected by the choice of serum. This fact should be concerned for the successful and effective clinical application of rhBMP-2.