Identification of Postn + periosteal stem cells that orchestrate bone regeneration

Bone fracture healing requires skeletal stem cells (SSCs), which facilitate intramembranous ossification and endochondral ossification in long bone fractures. Although the periosteum is necessary for bone homeostasis and regeneration, the in vivo origin and regulatory mechanisms of periosteal SSCs (P-SSCs) remain unclear. Here, we identified Postn+ P-SSCs at the cambium layer of the periosteum that actively orchestrate regeneration in response to bone injury. Notably, the Postn+ P-SSCs that arise during bicortical fractures are likely derived from Gli1+ P-SSCs. In addition, Postn+ cell ablation compromises cortical bone homeostasis and bone regeneration. The IGF signal is indispensable in the regulatory effect of Postn+ P-SSCs on bicortical fractures since the genetic deletion of Igf1r in Postn+ cells dampens bone fracture healing. Taken together, adult Postn+ cells are region-specific P-SSCs that contribute to bone homeostasis and regeneration and are partially dependent upon IGF signaling. Bone callus was digested to isolate the periosteal cells within the callus at 7/10/14 day after femoral fracture. A CD45/CD31/Ter119 cocktail was used to exclude hematopoietic and endothelial cells by FACS, and mesenchymal lineages (referred to as the CD45-negative population) were selected for scRNA-seq via the 10x Genomics approach.