O-GlcNAcylation in Gli1 Mesenchymal Stem Cells Is Indispensable for Bone Formation and Fracture Healing.

Adult mesenchymal stem cells (MSCs) play a crucial role in maintaining bone health and promoting regeneration. In our previous research, we identified Gli1 MSCs as key contributors to the formation of most trabecular bone in adulthood and as essential for healing bicortical fractures. However, the mechanisms behind the maintenance and differentiation of Gli1 MSCs are still not fully understood. O-linked N-acetylglucosamine modification (O-GlcNAcylation), mediated by O-GlcNAc glycosyltransferase (OGT), is involved in various biological processes and diseases. Our earlier work also demonstrated that O-GlcNAcylation is necessary for Wnt-stimulated bone formation. Nonetheless, the specific functions of O-GlcNAcylation in MSCs have not been completely elucidated. In this study, we found that the absence of OGT in Gli1 MSCs led to a decrease in O-GlcNAcylation, which impaired both the bone formation and regeneration following fractures. Mechanistically, the Hedgehog signaling pathway induced O-GlcNAcylation through the insulin-like growth factor (Igf)-mTORC2 axis. This process stabilized the Gli2 protein at a specific site Ser355 and promoted osteogenesis in MSCs in vitro. Our findings reveal a significant mechanism by which O-GlcNAcylation regulates bone development and repair in mammals.