Identification of biomarkers indicative of functional skeletal stem cells.

OBJECTIVES

Skeletal stem cells (SSCs) are characterized by expression of cell surface biomarkers and their ability to differentiate into bone, cartilage and fat. However, the current biomarkers used to identify these cell populations are not cell-type-specific or indicative of the differentiation status of these cells and are therefore unreliable. Our objective was to identify alternative cell surface biomarkers and transcription factors shared between SSCs isolated from the bone marrow (BM) and those derived from pluripotent stem cells (PSC).

MATERIALS AND METHODS

Human PSCs were induced into SSCs. FACS and qRT-PCR were used to determine differences in expression of cell surface biomarkers and transcription factors between SSCs derived from PSCs and isolated from BM, in differentiating cells, in cells from early and late passage, and in fibroblasts.

RESULTS

A significant reduction in proliferation and capacity of SSCs to differentiate into adipocytes and osteoblasts was observed after 3 passages. Protein and mRNA analysis indicated that commonly used biomarkers remain highly expressed in cells that lost capacity for differentiation. However, integrin α6 (CD49f) and transcription factors GATA6, PRDM16, SIM2 and SOX11 were significantly upregulated in SSCs compared to fibroblasts. In early stages of adipogenic and osteogenic differentiation, the expression of CD49f, GATA6 and SIM2 was reduced in later passage cells, which have limited proliferation and differentiation capabilities.

CONCLUSIONS

Our results suggest that CD49f and transcription factors GATA6 and SIM2 identify functional SSCs.