Single-cell transcriptomics reveals critical role of CD74 in bone marrow-derived mesenchymal stem cells.

BACKGROUND: Human bone marrow aspirates have been widely used for skeletal tissue regeneration. However, clinical outcomes of the tissue repair after transplantation are variable. METHODS: In this study, we analyzed the molecular signatures and osteogenic differentiation potential of bone marrow-derived mesenchymal stromal cells (BMSCs) from different donors. RESULTS: Our results clearly showed that BMSCs isolated from different patients exhibited different osteogenic capacities and growth rates. Moreover, single-cell RNA sequencing revealed that these BMSCs expressed elevated levels of genes associated with early osteogenesis, chondrogenesis, and adipogenesis. Differentially expressed genes related to cell cycles were enriched in clusters from all 5 different samples, suggesting these genes play an important role in BMSC maintenance and differentiation. More importantly, the BMSCs with the lowest osteogenic differentiation potential showed a dramatic decrease in the expression of cell surface protein CD74 when compared to other osteogenic genes. Knockdown of CD74 in BMSCs with high osteogenic potential significantly reduced their osteogenic capacity. CONCLUSIONS: These findings suggest that CD74 is a novel predictive marker of outcomes following BMSC transplantation. Furthermore, CD74-high BMSCs may represent a subpopulation of bone marrow cells responsible for bone marrow aspirate-mediated tissue regeneration.