Functional definition of endothelial progenitors by PROCR and PDGFRA co-expression

Abstract

The functional and molecular definition of progenitors giving rise to blood vessel endothelium in vivo remains disputed. Upon investigating the overlap of seemingly divergent reports currently defining putative endothelial progenitor cells (EPCs) using single-cell RNA-sequencing and flow cytometry, Protein C Receptor (PROCR) and Platelet-Derived Growth Factor Receptor Alpha (PDGFRA) largely overlapped with previously characterized murine aorta’s CD34⁺CD31^low endovascular progenitors (EVPs). Functional assays and lineage tracing in homeostatic aorta and excisional wounds demonstrated increased clonogenic capacity, engraftment potential, and ability to form differentiated endothelial (D) cells of PROCR⁺ PDGFRA⁺ EPCs, termed as refined endothelial progenitor cell (rEPC), as compared to PROCR^negPDGFRA^neg EVPs. Similar PROCR and PDGFRA expression in normal human aorta, and increased clonogenic capacity of CD34⁺CD31^lowPROCR⁺ endothelial cells from freshly isolated human term placenta were observed as compared to controls. Functional validation of human rEPCs is supported by PROCR enrichment, while PDGFRA co‑expression in human endothelial progenitor–like cells is supported at the transcriptomic level only. Thus, overlapping PROCR and PDGFRA expression in EVPs narrows the population with true functional progenitor capacity.