UNRAVELING A NOVEL TRANSCRIPTION FACTOR CODE INDUCTIVE FOR THE HUMAN ARTERIAL-SPECIFIC ENDOTHELIAL CELL SIGNATURE

Endothelial cells (EC) lining arteries and veins have distinct molecular and functional signatures. The (epi)genetic regulatory mechanisms underlying this heterogeneity in human EC are incompletely understood. Using genome-wide microarray screening we established a specific fingerprint of freshly isolated arterial (HUAEC) and venous EC (HUVEC) from human umbilical cord comprising 64 arterial and 12 venous genes, representing distinct functions and pathways. Among the arterial genes were 8 transcription factors, including HEY2, a downstream target of Notch signaling and the current ‘golden standard’ pathway for arterial EC specification. Short-term culture of HUAEC or HUVEC abrogated differential gene expression resulting in a default state. Erasure of arterial gene expression was at least in part due to loss of canonical Notch activity and HEY2 expression. Notably, nCounter analysis revealed that restoring HEY2 expression or Delta-like 4 (Dll4)-induced Notch signaling in cultured HUVEC or HUAEC only partially reinstated the arterial EC gene signature while combined overexpression of the 8 transcription factors restored this fingerprint much more robustly. Each transcription factor had a different impact on gene regulation, with some stimulating only few and others boosting a large proportion of arterial genes. Interestingly, although there was some overlap and cross-regulation, the transcription factors largely complemented each other in regulating the arterial EC gene profile. Thus, our study showed that Notch signaling determines only part of the arterial EC signature and identified additional novel and complementary transcriptional players in the complex regulation of human arteriovenous EC identity To identify an arteriovenous (AV) fingerprint in human endothelial cells (EC) across different vascular beds, we used microarrays on RNA from 38 EC samples corresponding to 6 cultured human arterial-EC types (hepatic artery EC or HHAEC, N=3; aorta EC or HAEC, N=2; coronary artery EC or HCAEC, N=2; iliac artery EC or HIAEC, N=2; pulmonary artery EC or HPAEC, N=3; and umbilical artery EC or HUAEC-C, N=5), 4 cultured human venous-EC types (hepatic vein EC or HHVEC, N=3; iliac vein EC or HIVEC, N=3; pulmonary vein EC or HPVEC, N=2; and umbilical vein EC or HUVEC-C, N=5), freshly isolated HUAEC (HUAEC-F, N=4) and freshly isolated HUVEC (HUVEC-F, N=4). Due to the difficulty to obtain biopsies from healthy donors, we did not have access to freshly isolated aEC or vEC matched for all cultured EC types.