| Tissue engineering offers unique therapeutic opportunities for the repair of tissues damaged by disease or injury. Despite many advances in cell-based tissue engineering, significant challenges remain with respect to cell sourcing, expansion, and differentiation for application to engineered tissue repair. Various stem cells that retain the capability to differentiate into multiple cell types has been a critical step in providing potential cell sources for tissue engineering.The aim of first part was to used an in vitro analytical approach which, although not necessarily predictive of the'in vivo'cell behavior, would provide information on the clone-forming and differentiation ability of human mesenchymal stem cell. The method will be useful for both basic and applied studies aimed at human MSCs. The method can be used to compare different cell and to compare different culture medium. Our findings provide evidence against the notion that the differentiation of MSC cells due to the presence of a mixed lineage-specific population of progenitor cells residing within adult tissue. Here we experimentally provide clear evidence that a single clone of the MSCs that has the potential differentiating along two or more of lineages. The second part is aimed to delineate whether the effect of MSCs on liver fibroblast cells is achieved by their inhibition on HSCs'activation and proliferation, thereby extend our knowledge on the antifibrotic properties of MSCs. In conclusion, we show here that MSCs interfere with proliferation and activation at least through TGF-βand HGF, ERK respectively. These observations provide new insights in the mechanisms of the antifibrotic effects of MSCs and support the suggestion that MSCs can be used as a novel therapeutic for fibrosis.In the third part, we tried to find pluripotent stem cells in human placenta. We isolated Flkl+CD31-CD34- cells from placenta mesenchymal cells. They had the potential to differentiate not only into neural cells, hepatocyte-like cells and endothelial lineages at the single-cell level according to the culture conditions. Morphologically, these cells were polygonal or fibroblast-like. Interestingly, the phenotype of these progenitor cells was similar to human bone marrow-derived MSCs:Flkl, CD105, CD29 and CD44 positive; CD31, CD34, CD45 and HLA-DR negative, and they were negative for markers of epithelial cells. These stem cells had the capacity for self-renewal and the multilineage differentiation even after being expanded for more than 30 population doublings in vitro. So they may be an ideal source of stem cells for clinical therapy.
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