Abstract
Hypertrophic chondrocytes (HCs) could transform into osteoblastic lineage cells while the pathophysiological implications of HC transformation remain largely unknown. Here, we generated a mouse line utilizing Col10a1-Cre to induce DTA expression to genetically ablate HCs and their descendants. Col10a1-Cre; R26DTA/+ mice displayed dwarf phenotype, abnormal spongy bone, and significantly delayed drill-hole injuries healing, suggesting an indispensable role of HC lineage extension in bone growth and injury repair. Intriguingly, single-cell RNA sequencing analysis revealed the most significant loss of a cell cluster expressing multiple angiogenic factors (Pro-Angiogenic Descendants of HCs, PADs) among cells derived from Col10a1-Cre; R26DTA/+ and control femurs. In silico analysis of cell-cell communication supported Thrombospondin 4 (THBS4) as a specific angiogenic factor mediating the crosstalk between PADs and vascular endothelial cells. Concordantly, analyses using immunostaining combined with tissue clearing revealed that PADs physically contacted with endothelial cells, whereas Col10a1-Cre; R26DTA/+ mice showed defective metaphyseal and cortical vessel formation and post-injury angiogenesis along with a significant loss of THBS4. Moreover, in vitro assays showed that supplying THBS4 was sufficient to promote proliferation and tube formation of endothelial cells and rescue defective angiogenesis of Col10a1-Cre; R26DTA/+ metatarsal explants. Collectively, these findings demonstrate a critical role of PADs in bone growth and injury repair by secreting THBS4 to regulate angiogenesis.