Proteomic Analysis Reveals Intrinsic Differences between Phenotypically Identical Mesenchymal Stem Cells.

We have previously reported the isolation of Stro-1+, CD45-, GlyA-human MSC from human bone marrow (BM), liver (LV), and brain (BR). Despite their similar morphology and phenotype, these cells, upon in vivo transplantation into the pre-immune fetal sheep model, seemed to differentiate more efficiently into cells of their tissue of origin. For instance, all 3 sources of MSC gave rise to blood, with average levels of human CD45+ cells in chimeric animals of 8.7% for LVMSC, 3.3% for BRMSC, and 4.5%for BMMSC. Human neural cells were also detected in the brain of transplanted animals with the highest levels obtained with BRMSC (1.33%) and lowest with LVMSC (0.4%). However, BRMSC generated very few human hepatocytes (2–10 hepatocytes/section), while both LVMSC and BMMSC gave rise to much higher levels of hepatocytes. This led us to hypothesize that despite the similar phenotype, the proteome makeup of MSC from different tissues may be distinct. To test this hypothesis, we examined the commonalities and differences in the protein repertoire of cultured MSC from these 3 different sources. The eighty most prominent protein spots from the 2-D gel of each cell population were removed and identified by MOLDI-TOF/TOF mass spectroscopy after Trypsin digestion. Our results demonstrate that there are a large number of common proteins between the LV, BM and BR MSC (> 75%). Besides the cytoskeletal and associative proteins such as Vimentin, β-actin, cofilin, Tropomyosin and Lamin A/C, the cells contained a large quantity of proteins for protein processing such as Cyclophilin A, Endoplasmic reticulum protein ERp29, Disulfide-isomerase ER60 and Glucose-regulated proteins 75 and 78, which may be important for the broad differentiative potential of MSC. Despite these similarities, forty percent of the identified proteins showed significantly different expression levels between the three types of cells (> 300%), the majority of which were not proteins previously shown to be BM-, Liver or Brain-specific. Interestingly, however, LV-derived cells contained a 5-fold greater concentration of Albumin than BM or Brain cells, which may explain their greater tendency to form liver tissue in vivo. Likewise, since BMMSC were enriched in smooth muscle associated proteins, potentially they may constitute a better source to be used for muscle repair. Thus, the definition of the different MSC proteomes can lead not only to the discover of critical differences involved in differentiation/plasticit into different cell fates, but may also help us to identify distinct cell populations that are ideally suited for cell therapies for specific organs.