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Human adipose-derived stem cells(hASC)are routinely isolated from the stromal vascular fraction(SVF)of homogenized fat tissue.They have been found to be a suitable and an easily accessible source for adipose-derived mesenchymal stem cell(MSC)isolation.In the past years the use of MSC in tissue engineering has gained of importance and has opened new possibilities for the reconstruction of large bone defects.An important hurdle for the successful application of MSC in bone regeneration is to obtain an appropriate vascularisation of the tissue.Endothelial cells(EC)are involved in the processes of angiogenesis and vasculogenesis.The capability of MSC to contribute to the formation of endothelial cells during bone regeneration is not yet completely clarified.Aim: The main goals of this study were(I)to evaluate and to characterize the capacity of adipose-derived stem cells to differentiate into EC.(Ⅱ)to identify characteristic EC markers for the identification of Hasc derived EC.Materials and Methods: hASCs were harvested from subcutaneous fat tissues samples.Hasc were characterized by FACS and immunohistochemistry.22 Hasc to EC differentiation experiments were performed and Hasc were cultured in endothelial cells differentiation medium for up to 4 weeks.We analyzed the differentiation potential and messenger RNA expression of selected genes.We further monitored vasculogenesis and expression changes of endothelial markers during the differentiation process.Results: The obtained EC showed cobblestone morphology and expressed EC markers including CD31,von Willebrand factor,CD146,CD54.Flowcytometry result showed that the MFI increased with CD31,Cd34,CD105 and CD146 and the obtained cells have positive fraction for the endothelial markers CD31,CD54 and CD146.We examined the expression of EC-specific genes by semi-quantitative PCR analysis after 4 weeks of induction.PCR showed Vwf,VEGF-R,Ang1,agged1,Tie2 expression up-regulation of EC specific markers.In vitro differentiation experiment by using Matrigel re-plate Hasc diifer.Cells indicated that the cells formed tubes and capillary-like structures,an indication that vasculogenesis is occurring under these culture conditions.Conclusion: In conclusion,our experiments demonstrate that Hasc have endothelial cell differentiation ability and that CD31 and von Willebrand factor represent good markers for monitoring the Hasc to EC conversion.