Thy1+ Periosteal Osteoprogenitors Contribute to Mandibular Bone Defect Healing in Mice

Objective: To investigate the distribution, lineage fate, and reparative function of Thy1 lineage cells in the mouse mandible.

Methods: Single-cell transcriptomic analysis was used to identify osteogenic subpopulations within mandibular mesenchymal stem cells. Lineage tracing in Thy1-CreERT2;Rosa26-tdTomato mice was employed to map the localization and osteogenic contribution of Thy1 lineage cells, while a critical-sized mandibular defect model was established to assess their reparative dynamics. Loss- and gain-of-function experiments were performed using Thy1-CreERT2;Rosa26-DTR mice and transplantation of purified tdTomato⁺ periosteal cells within hydrogel scaffolds.

Results: Single-cell analysis identified a Thy1-enriched osteoprogenitor subpopulation preferentially localized to the periosteum. Lineage tracing revealed that Thy1-lineage cells constituted a major proportion of periosteal osteogenic cells and exhibited clonogenic expansion and ectopic bone formation. Following mandibular injury, tdTomato⁺ cells progressively accumulated within the callus and represented the predominant osteogenic cell population at later stages. Genetic ablation of Thy1-lineage cells markedly impaired bone repair, whereas transplantation of purified tdTomato⁺ periosteal cells enhanced bone formation within the defect.

Conclusions: Thy1 lineage periosteal cells represent a functionally important osteoprogenitor population in mandibular bone regeneration, providing a cellular framework for future mechanistic and translational studies.