Identification of LRP1 and CD13 expressing human periosteal cells for stem cell-mediated bone repair
Human periosteal skeletal stem cells (P-SSCs) are critical for cortical bone maintenance and repair. However, their in vivo identity, molecular characteristics, and specific markers remain unknown. Here, single-cell sequencing revealed human periosteum contains SSC clusters  expressing known SSC markers, PDPN and PDGFRA. Notably, human P-SSCs, but not bone marrow SSCs (BM-SSCs), selectively expressed newly identified markers, LRP1 and CD13. Single-cell analysis of mouse periosteum further supported the preferential expression of LRP1 and CD13 in Prx1? P-SSCs. These LRP1?CD13? human P-SSCs were perivascular cells with high osteochondrogenic but minimal adipogenic potential. In addition, LRP1?CD13? human P-SSCs are maintained in vitro and self-renew in vivo upon transplantation into bone injuries in mice. When Lrp1 was conditionally deleted in Prx1-lineage cells, it led to severe bone deformity, short statue, and periosteal defects. By contrast, local treatment with a LRP1 agonist at the injury sites induced early P-SSC proliferation and bone healing. Thus, human periosteum contains unique osteochondrogenic stem cell subsets, and these P-SSCs express specific markers, LRP1 and CD13, with regulatory mechanism through LRP1 that enhances P-SSC function and bone repair. Overall design: Non-hematopoietic and non-endothelial cells from mouse long bone periosteum were isolated by Fluorescence-activated cell sorting and analyzed by 10x scRNA-seq