Hypoxia in arterial and venous specification during vascular development

A developing embryo needs a constant supply of oxygen and nutrients in order to survive and grow into a functioning organism. During the earliest embryonic stages passive diffusion is enough to sustain the embryo. At later embryonic stages however, a system for delivering the necessary oxygen and nutrients to all parts of the embryo is needed. As a consequence, the vasculature is the earliest functional organ to form during embryonic development. The area of interest for my research has been vascular development, with a specific aim to uncover mechanisms of arterial and venous specification during embryogenesis. This research could be important for understanding underlying mechanisms behind several severe pathologies such as cancer, diabetes and atherosclerosis.

In the first study we developed a system for generating endothelial cells with arterial or venous characteristics from ESC (Embryonic stem cells). We showed that VEGF play a critical role in determining both arterial and venous fate. Differentiation of ESCs to endothelial cells using high levels of VEGF promoted arterial specification, while low levels of VEGF induced venous fate. In addition we could show that the VEGF signaling was dependent on Notch signaling for driving arterial fate.

In the second paper we characterized the promoter region of ephrinB2, a gene specifically expressed in arteries but not in veins, in order to identify transcription factors involved in arterial specification. In this study we identified the minimal promoter region of ephrinB2 and proved that the transcription factors MAZ, Meis1 and NFY bind to the promoter and induce EphrinB2 expression in MAE cells. In addition, a TATA-box necessary for ephrinB2 expression was identified.

In the third paper we showed that ephrinB2 is up regulated in response to hypoxia in mouse arterial endothelial (MAE) cells, and aimed to reveal the mechanism for hypoxic regulation of ephrinB2. We proved that neither hypoxia inducible factor (Hif) 1a nor Hif- 2a was responsible for inducing ephrinB2 expression in MAE cells. Instead we showed that Sp1 binds to the promoter during hypoxic conditions but not in normoxia, while the opposite is true for MAZ. Also, knocking down Sp1 proved to reduce ephrinB2 expression in hypoxic MAE cells.

In the fourth manuscript we used the in vitro ESC differentiation system developed in the first study to investigate how hypoxia affects arterial/venous differentiation of vascular progenitor cells. We showed that hypoxia activates an arterial transcriptional program and that this response is not driven by classic VEGF signaling, but rather by Notch and Adrenomedullin signaling.

List of scientific papers

I. Lanner F, Sohl M, Farnebo F (2007). Functional arterial and venous fate is determined by graded VEGF signaling and notch status during embryonic stem cell differentiation. Arterioscler Thromb Vasc Biol. 27(3): 487-93. Epub 2006 Dec 21
https://pubmed.ncbi.nlm.nih.gov/17185616

II. Sohl M, Lanner F, Farnebo F (2009). Characterization of the murine Ephrin-B2 promoter. Gene. 437(1-2): 54-9. Epub 2009 Mar 5
https://pubmed.ncbi.nlm.nih.gov/19268698

III. Sohl M, Lanner F, Farnebo F (2009). Hypoxia induced expression of ephrinB2 is independent of Hif-1. [Manuscript]

IV. Lanner F, Sohl M, Hansson E, Carmeliet P, Poellinger L, Lendahl U, Farnebo F (2009). Hypoxic induction of Adrenomedullin and Notch signaling promotes arterial differentiation of embryonic stem cells. [Manuscript]