Characterization of Skeletal Stem Cells via Novel Biomarkers

Mesenchymal stem cells (MSCs), also called skeletal stem cells (SSCs), have been traditionally categorized by their ability to differentiate into bone, cartilage, and fat, combined with their expression of key cell surface biomarkers. One key problem that exists, however, is that these biomarkers are not cell-type specific and are not indicative of the stemness potential of these cells, and therefore are poorly reliable. To fill in the gap in literature, we attempted to identify alternative cell surface biomarkers and transcription factors present in skeletal stem cells that were extracted from the bone marrow and those derived from pluripotent stem cells. Our results confirmed a significant decline in the ability of skeletal stem cells derived from pluripotent stem cells to proliferate and differentiate into adipocytes and osteocytes after passage 3. Further, analysis of cell surface biomarkers and transcription factors showed that biomarkers commonly used to identify skeletal stem cells remain highly expressed in skeletal stem cells that had lost their ability to differentiate into the three lineages. However, it was found that integrin alpha-6 (CD49f) and the transcription factors GATA6, PRDM16, SIM2 and SOX11 were significantly upregulated in skeletal stem cells isolated from the bone marrow and cells derived from pluripotent stem cells when compared to fibroblasts. These transcription factors and CD49f also changed their expression in skeletal stem cells in later passages, which had lost their ability to proliferate and differentiate. Our results suggest that CD49f and the expression of transcription factors GATA6, PRMD16, SIM2 and SOX11 can be used to define skeletal stem cells derived from pluripotent stem cells.