Endothelial colony-forming cells show a mature transcriptional response to shear stress

Endothelial progenitor cells (EPC) play a central role in endothelial maintenance and repair. Endothelial colony-forming cells (ECFC) form a subpopulation of EPC. ECFC are readily attainable, can be easily isolated, possess a high proliferation potential, and are therefore a promising source of endothelial cells (EC) for future cardiovascular therapeutic applications. The extent to which these cells respond to shear stress as adult vascular EC remains to be elucidated. Here, we study the transcriptional response of ECFC induced by shear stress and compare it with the response of mature arterial and venous cells. ECFC, as well as human umbilical vein EC (HUVEC) and human umbilical artery EC (HUAEC), were subjected to low (0.5 Pa) and high (2.5 Pa) shear stress. The endothelial differentiation phenotype and transcriptional responses were analyzed using immunocytochemistry and quantitative polymerase chain reaction (Q-PCR). Performing absolute quantification of copy numbers by Q-PCR allows comparing the responses of cell types relative to each other. Our data show that isolated ECFC resemble mature EC in cobblestone morphology and endothelial marker expression. Absolute Q-PCR quantification revealed that although being truly endothelial, ECFC do not fully resemble HUVEC or HUAEC in the expression of specific differentiation markers. When subjected to shear stress, ECFC show a mature response to fluid flow, comparable to that of HUVEC and HUAEC. The capacity of endothelial progenitors to respond to fluid flow in a similar manner to HUVEC and HUAEC highlights the universal response of EC to fluid shear stress, independently of their endothelial differentiation status. This property supports the use of these cells as an EC source for tissue engineering applications.