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 osteoblasts (OBs) 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 labelling, 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 (OP) 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 up-regulation 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 Ca(2+) -dependent Nfatc1 signaling to induce directly 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. (c) AlphaMed Press 2020 SIGNIFICANCE STATEMENT: In this study we first of time report brand new deterministic mechanisms of BMSCs selfrenewal and osteogenesis via Wnt7b-induced Sox11 signaling. This signaling manipulates crucial fate-decisive genes transcription to support BMSCs long-term amplification and lineage commitment, finally contributing to enhanced bone formation and regeneration. These results provide insights that Wnt7b-Sox11 signaling in BMSCs may be explored to develop a viable bone anabolic therapy.