Transforming growth factor‐β1 (TGF‐β1) induces mouse precartilaginous stem cell differentiation through TGFRII‐CK1ε‐β‐catenin signalling

Precartilaginous stem cells (PSCs) are adult stem cells which could self‐renew or differentiate into chondrocytes to promote bone growth. In this study, we aimed to understand the role of transforming growth factor‐β1 (TGF‐β1) in precartilaginous stem cell (PSC) differentiation and to study the mechanisms that underlie this role. We purified PSCs from the neonatal murine perichondrial mesenchyme using immunomagnetic beads, and primary cultured them. Their phenotype was confirmed by the PSC marker fibroblast growth factor receptor‐3 (FGFR‐3) overexpression. TGF‐β1 was added to induce PSCs differentiation. TGF‐β1 increased mRNA expression of chondrogenesis‐related genes (collagen type II, Sox 9 and aggrecan) in the cultured PSCs. This was abolished by TGF‐β receptor II (TGFRII) and Casein kinase 1 epsilon (CK1ε) lentiviral shRNA depletion. Meanwhile, we found that TGF‐β1 induced CK1ε activation, glycogen synthase kinase‐3β (GSK3β) phosphorylation and β‐catenin nuclear translocation in the mouse PSCs, which was almost completely blocked by TGFRII and CK1ε shRNA knockdown. Based on these results, we suggest that TGF‐β1 induces CK1ε activation to promote β‐catenin nuclear accumulation, which then regulates chondrogenesis‐related gene transcription to eventually promote mouse PSC differentiation.