Thy1+ Progenitors Drive Mandibular Repair Through Localized Osteogenic Activation

To clarify the contribution of Thy1+ cells to in situ osteogenesis in mandibular defect repair and define a new population of osteoprogenitor cells. Mandibles from 10-week-old male C57BL/6 mice underwent scRNA-seq (GEO:GSM8311031). Thy1-CreER;tdTomato mice received intraperitoneal tamoxifen (1/3/8 weeks) for lineage tracing, with tdTomato+ cells tracked at 2d/1w via immunofluorescence. Critical-size mandibular defects (1.5mm) were generated, monitoring tdTomato+ cell recruitment at 1w/2w. Co-localization with Runx2+ osteoblasts was confirmed by dual staining. Thy1-CreER;DTR mice received diphtheria toxin (5μg/g) for Thy1+ cell ablation, and bone healing was assessed by micro-CT at 2 weeks. Statistical significance (p<0.05) was assessed by two-tailed t-tests. scRNA-seq results showed that Thy1+ cells were concentrated in an independent osteoprogenitor cluster, and 54.17% of Thy1+ cells co-expressed Postn, a marker of periosteal cells. Lineage tracing revealed that Thy1+ cells were mainly located in the periosteum and all of them co-localized with osteoblasts. During the healing process of mandibular injury, Thy+ cells are activated and actively respond, and significantly accumulate in the injured area. Local ablation of Thy1+ cells significantly delayed the healing process of mandibular defects. Thy1+ skeletal stem cells are indispensable for craniofacial bone regeneration, with their spatiotemporal activation and osteogenic differentiation tightly coupled to defect microenvironmental cues. The anatomical localization and niche interaction patterns of these progenitors warrant further investigation to delineate their collaborative networks in bone repair.