| In recent years,mesenchymal stem cells(MSCs) have been considered as an ideal source for cell therapy strategies.Bone marrow has been considered as the main source of MSCs until later studies demonstrate that MSCs exist in the stroma of other tissues. Recently,several groups have succeeded in isolating MSCs from umbilical cord and have shown that the biological similarity between BM-MSCs and UC-MSCs.Because umbilical cord is a postnatal organ discarded after birth,the collection of cells does not require an invasive and painful procedure nor involves ethical issues.However,there is still a lack of definitive cell markers for specific isolation and identification of MSCs. Thus MSCs are always studied as a heterogeneous cell population,which will prohibit further studying their therapeutic potential and complicate the interpretation of data from different laboratories with regard to the true nature of these cells.Therefore,there is an urgent need for novel markers and methods to isolate a pure MSCs population.Recently a novel surface marker neural ganglioside GD2 has been reported to be expressed on human BM- MSCs,which appears to be the first reported single surface marker that uniquely distinguishes MSCs from other marrow elements.Here,we aimed to analyze the expression of GD2 on UC-MSCs and further demonstrate whether we can establish an efficient method to isolate a homogenous cell population from early-passage cultures of UC-MSCs by GD2 immunosorting.Meanwhile,we analyzed the expression of GD2 on murine bone marrow MSCs(mBM-MSCs) and further demonstrated whether GD2 may be a conserved marker for MSC from various mammalian species in addition to humans.In the first part of this paper,we found that MSCs derived from umbilical cord (UC-MSCs) also expressed this marker at early-passages.More importantly,UC-MSCs were the only cells within umbilical cord expressing this marker.Compared to unsorted cells,GD2~+-sorted cells not only possessed much higher clonogenicity and proliferation capacity but also had significantly stronger multi-differentiation potentials.Flow cytometric analysis revealed that GD2~+-sorted cells showed increased expression of SSEA-4,Oct-4,Sox-2 and Nanog,the typical markers expressed in embryonic stem cells, in comparison to unsorted or GD2-negative MSCs.Take together,our data demonstrate that the cells selected by GD2 are a subpopulation of MSCs with feature of primitive precursor cells and provide evidence that GD2 can be a cell surface marker suitable for the isolation and purification of UC-MSCs in early-passage culture.In the second part,we found that murine bone marrow MSC(mBM-MSCs) expressed a novel surface marker the neural ganglioside GD2.More importantly, mBM-MSCs were the only cells within bone marrow that expressed this marker.Further studies demonstrated that a homogenous population of MSCs could be obtained from bone marrow cultures in early passages by GD2 immunosorting.Compared to parental cells,GD2~+-sorted cells not only possessed much higher clonogenic and proliferative capabilities but also had significantly stronger differentiation potential to adipocytes and osteoblasts.Furthermore,GD2~+-sorted cells have enhanced the expression of SSEA-1 and Nanog,the embryonic stem cells markers.Take together,our observations provide the first demonstration that GD2 can serve as a single definitive maker for the identification and purification of mBM-MSCs.Meanwhile,our study indicates that the cells selected by GD2 are a subpopulation of MSCs with feature of primitive precursor cells.In conclusion,the results of this study demonstrate that GD2 can be used as a novel marker for isolating UC-MSCs and identifies a primitive subpopulation of UC-MSCs with high specificity.It suggests that GD2 may be a conserved marker for MSCs from various mammalian species in addition to humans.These findings may have a significant impact on the studies of isolation and purification of MSCs and help in better understanding the biology of these cells.
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