Low oxygen concentrations within various tissues of the embryo and adult play a physiological role in the development and growth of the stem cells for the blood system. In our LSBR funded-studies we examined the mouse embryo to determine whether the Hypoxia-Inducible Factor (HIF)-1α and its downstream effectors play a role in the generation of these potent adult stem cells. We found that the vascular region of the embryo, where the first blood stem cells are made, is low in oxygen concentration. In mouse embryos lacking HIF-1α (a factor that is activated at low oxygen concentrations and expressed in blood stem cells and their ancestor cells), very few or no blood stem cells were found and progenitor numbers were reduced, thus revealing the requirement for this factor in stem cell development. When another factor, PHD2 (which normally degrades HIF-1α) was deleted, we found that there is a trend towards the production of more blood progenitor cells. We are now examining whether the generation of blood stem cells is also enhanced.

In establishing an accessible culture system to further study blood progenitor and stem cell generation we created useful fluorescent reporter (GATA2Venus) pluripotent stem cell lines. The human cells when cultured at low oxygen concentrations showed a 3- to 10-fold increase in the frequency of blood progenitors. Explant culture systems were established to study the role of other factors such as BMP4 and Hh in blood stem cell generation. The results of these studies demonstrated that they act to positively affect stem cell generation, and in fact the growth of two types of blood stem cells. Together the results of these studies show that hypoxia, the HIF-1α protein and downstream effectors and factors are positive regulators of HSC generation, beginning at the earliest embryonic stages. These studies provide new insights, reagents and screening approaches for drug discovery so as to manipulate the hypoxic response for ex vivo blood stem cell generation.

Thesis 2017: Gata2 in Hematopoietic Cell Generation, Mari-Liss Kauts