Nonbone Marrow CD34 + Cells Are Crucial for Endothelial Repair of Injured Artery

Rationale: Endothelial cells play a critical role in multiple cardiovascular diseases. Circulating CD34+ cells are believed to be endothelial progenitors that have been used to treat cardiovascular diseases. However, the exact identity and the role of CD34+ cells in vascular regeneration remains unclear.Objective: We aimed to investigate the exact identity and the role of CD34+ cells in vascular regeneration.Methods and Results: Compared with healthy arteries, CD34 expression percentage was significantly increased in diseased femoral arteries from patients. Using a guidewire-induced endothelial denudation model, we reported the transcriptional profiling of over 30 000 cells by single-cell RNA sequencing analysis and provided a cell atlas of normal and lesioned arteries in mouse, in which a heterogeneous population of CD34+ cells was revealed. Combining the inducible lineage tracingCd34 -CreERT2 ;R26-tdTomato mouse model and bone marrow transplantation experiments, we showed that nonbone marrow CD34+ mesenchymal cells acquired endothelial cell fate in the injured femoral artery rather than preexiting endothelial cells, while bone marrow-derived CD34+ cells differentiated into immune cells locally after vessel injury. Depletion of nonbone marrow CD34+ cells using diphtheria toxin-induced cell ablation models exacerbate neointimal lesions of the injured vessel. Furthermore, isolated vascular adventitia CD34+ cells displayed endothelial differentiation, in which microRNA-21-Smad7-pSmad2/3 pathway regulated endothelial gene expression and function during differentiation.Conclusions: Our study provides a transcriptional and cellular landscape of vessels after endothelial denudation. Our findings suggest heterogeneous CD34+ cells serve as a contributor not only to endothelial regeneration but also an inflammatory response that may provide therapeutic insights into vascular diseases.