Abstract
Pluripotent stem cell-derived endothelial cells (ECs) have great potential to be used in vascular therapy or tissue engineering. It is also much desired to obtain arterial or venous ECs for specific applications. Factors that are critical for the proper arterial or venous differentiation from pluripotent stem cells still need to be understood. Here, we aim at investigating this problem deeper by examining neuropilin-1 (Nrp1), an early arterial marker that may be critical for arterial cell fate commitment. Using murine embryonic stem cells as the model system, this study investigates the neuropilin-1 (Nrp1) expression during the differentiation of pluripotent stem cells toward a vascular progenitor population. We hypothesize that Nrp1, an early arterial marker present in a developing embryo, may be more responsive when further induced in vitro toward an arterial fate. We developed a two-step differentiation approach that yielded a large percentage of Nrp1+ vascular progenitor cells (VPCs) and investigated their potential to become arterial ECs. We have defined the culture parameters that contribute greatly to the emergence of Nrp1+ VPCs: certain soluble factors, especially Wnt and BMP4, early cell-cell contact, and hypoxia. Subsequent isolation of this population demonstrated a highly proliferative and network-forming behavior. The Nrp1+ VPCs exhibited increased gene expression of several Notch pathway-related arterial markers compared with Nrp1- VPCs. Most importantly, Nrp1+ VPCs demonstrated a dramatically greater response to hemodynamic stimuli by upregulating many arterial markers whereas Nrp1- VPCs have very little response. Surprisingly, these differences between Nrp1+ and Nrp1- VPCs are not evident with vascular endothelial growth factor (VEGF) treatment. Our data suggest that Nrp1+ VPCs may serve as the arterial progenitor by enhanced response to hemodynamic flow but not to VEGF, whereas Nrp1- VPCs lack the plasticity to become arterial ECs. The findings of this research indicate that Nrp1+ VPCs in the murine model act as an important step in the arterial differentiation process.