Single‐Cell Transcriptome Decoding Umbilical Cord‐Derived Mesenchymal Stem Cell Heterogeneity Reveals a Unique IL1R1^HighPDGFRA^High Ultroser‐G‐MSC With Osteogenesis and Chondrogenesis Signatures

The heterogeneity of human umbilical cord mesenchymal stem cells (hUC-MSCs) is culturing-dependent, resulting in functional non-uniformness. To achieve the best clinical benefit, a comprehensive understanding of the origin of the heterogeneity in different culture systems can identify functional subgroups to direct the precise application of hUC-MSCs. Here, we create a single-cell transcriptome atlas of hUC-MSC in different culture systems for the identification of a subgroup of Ultroser-G-MSCs with high osteogenic and chondrogenic potentials featured by high expressions of IL1R1 and PDGFRA. Further experimental validations surprisingly reveal that IL1R1^highPDGFRA^high Ultroser-G-MSCs possess advantages over "traditional" hUC-MSCs in the treatments of modeled osteoarthritis, leading to a cell-cell communication network centered in Clusters 0 and 2. Moreover, we found that Wnt5 signaling is the key pathway for the dynamic transformation of osteogenic and chondrogenic phenotypes in hUC-MSC. Overall, the present study paves the way for the clarification of heterogenetic nature of hUC-MSC in different culture systems for the selection of optimal MSC types to achieve the precision on clinical treatments.