Wnt7b-induced Sox11 functions enhance self-renewal and osteogenic commitment of bone marrow mesenchymal stem cells

As a profoundly anabolic regulator of bone, Wnt7b is well acknowledged to enhance osteoblast activities. Here, we report that bone marrow mesenchymal stem cells (BMSCs) are another important populations responding to Wnt7b. In this study, we systematically investigate the in vivo role of Wnt7b in BMSCs using transgenic mice, high-throughput RNA-seq, immunohistochemistry, RT-qPCR, and in situ hybridization. These methods lead us to uncover that Sox11 is induced via Wnt7b in BMSCs. Colony formation assay, flow cytometry, EdU incorporation labeling, RT-qPCR, and Western blot are conducted to detect the self-renewal capacity of BMSCs. Alkaline phosphatase staining, alizarin red staining, and ex vivo BMSCs transplantation are utilized to detect the osteogenic ability of BMSCs. ChIP-qPCR, shRNAs, and immunofluorescence staining are utilized to investigate underlying mechanisms. Consequently, bone-derived Wnt7b is found to decrease in osteoporosis and elevate in bone fracture healing. During bone fracture healing, Wnt7b is particularly expressed in the mesenchymal cells residing within healing frontiers. RNA-seq data of Wnt7b-overexpressed bones uncover the significant upregulation of Sox11. Histological results further unveil that Sox11 is specifically increased in BMSCs. Wnt7b-induced Sox11 is demonstrated to reinforce both self-renewal and osteogenic differentiation of BMSCs. Mechanistically, Wnt7b activates the Ca2+-dependent Nfatc1 signaling to directly induce Sox11 transcription, which in turn activates the transcriptions of both proliferation-related transcription factors (Ccnb1 and Sox2) and osteogenesis-related factors (Runx2, Sp7) in BMSCs. It is intriguing that this Wnt7b-Sox11 signaling in BMSCs is beta-Catenin-independent. Overall, this study provides brand new insights of Wnt7b in bone formation, namely, Wnt7b can enhance both self-renewal and osteogenic differentiation of BMSCs via inducing Sox11. These findings present a new crosstalk between Wnt and Sox signaling in BMSCs.