Single‐cell transcriptomics of LepR‐positive skeletal cells reveals heterogeneous stress‐dependent stem and progenitor pools.

Leptin receptor (LepR)‐positive cells are key components of the bone marrow hematopoietic microenvironment, and highly enrich skeletal stem and progenitor cells that maintain homeostasis of the adult skeleton. However, the heterogeneity and lineage hierarchy within this population has been elusive. Using genetic lineage tracing and single‐cell RNA sequencing, we found that Lepr‐Cre labels most bone marrow stromal cells and osteogenic lineage cells in adult long bones. Integrated analysis of Lepr‐Cre‐traced cells under homeostatic and stress conditions revealed dynamic changes of the adipogenic, osteogenic, and periosteal lineages. Importantly, we discovered a Notch3+ bone marrow sub‐population that is slow‐cycling and closely associated with the vasculatures, as well as key transcriptional networks promoting osteo‐chondrogenic differentiation. We also identified a Sca‐1+ periosteal sub‐population with high clonogenic activity but limited osteo‐chondrogenic potential. Together, we mapped the transcriptomic landscape of adult LepR+ stem and progenitor cells and uncovered cellular and molecular mechanisms underlying their maintenance and lineage specification. SYNOPSIS: Leptin receptor (LepR) marks skeletal cells critical for the maintenance and regeneration of the bone. This expression profiling study dissects the heterogeneity of Lepr‐positive skeletal cell populations, suggesting coexisting stem and progenitor pools with context‐dependent function. Comparative analysis catalogs Prrx1‐Cre‐ and Lepr‐Cre‐traced cells in the adult mouse long bones under homeostatic and various stress conditions.Identification of a perivascular, quiescent Notch3+ bone marrow stromal cell subset.Hoxb2 and Npdc1 are osteo‐chondrogenic regulators promoting fracture repair in vivo.Identification of a Sca‐1+ periosteal cell population with increased adipogenic potential. [ABSTRACT FROM AUTHOR]