Oxygen Tension Controls the Expansion and Differentiation of Normal and Tumor-derived Human Neural Stem Cells. Role of oxygen in BMP responsiveness

During neural development the generation of diverse cell types involves the response of precursor cells to a wide variety of environmental cues, like soluble factors, the extracellular matrix and oxygen tension. Among these, oxygen tension and oxidation state in particular are important biophysical parameters that control neural precursor proliferation, survival and fate determination, so the dynamic control of oxygen availability regulates self renewal and the generation of cell diversity during development and throughout the life of the organism. However, the mechanisms by which oxygen acts in this manner are poorly understood. Current evidence suggests that oxygen levels in both developing and mature brain are much lower than the 20% oxygen used in standard mammalian cell culture (Erecinska M. et al. 2001). Previously it has been found that the sensitivity to oxygen tension is greater in mouse than in rat cells. Precursor survival and expansion is greatly improved at an oxygen tension (2-5%) closer to that measured in vivo and far lower than conditions typically used (20%) in culture studies. In the last decade much research has focused on the detrimental effect of anoxia during ischemic episodes and these results indicate that atmospheric oxygenation is incompatible with long-term precursors cell survival. Furthermore, one of the main effort is directed to maximize the culture efficiency of neural precursors for replacement therapies and also in vitro fertilization research has focused on oxygenation in order to optimize viability of the early post-fertilization embryo. It will be very important to understand the signals that control survival, proliferation and fate choice of precursor cells and it will also be necessary to investigate what subtypes of precursors are preferentially selected under normal in vitro condition. Indeed, the addition of antioxidants and other free radical scavengers is likely to be no more than a sub-optimal surrogate for culturing in lowered oxygen. Moreover, it has been recently shown that hypoxia is a crucial component of the brain tumor niche as it positively correlates with tumor aggressiveness and over-activity of Hypoxia Inducible Factor-1? (HIF-1?) reinforces tumor progression. Thus, the main aim of the project is to understand the role of oxygen tension in proliferation and lineage determination of Human CNS (Central Nervous System) and brain tumor derived precursor cells. We sought to understand if a lower oxygen tension (2-5%), compared to environmental 20% oxygen, promotes the expansion of a more premature and actively proliferating subtype of precursor cells, affecting cell multipotency, and which could be the molecular pathways modulated by oxygen tension. Our results indicate that dynamic control of oxygen tension regulates different steps in fate and maturation and may be crucial for treating neurodegenerative diseases (i.e. demyelinating diseases). They also suggest that the maintenance of brain tumors stem-ness, particularly in high Grade Glioma (HGG) tumors, is correlated to a hypoxic microenvironment in which BMP signaling pathway and the pro-differentiating effects mediated by BMP are down-regulated.