Although haemopoietic stem cells (HSCs) represent one of the best-defined stem cell systems, the pathways regulating HSC development and maintenance are not fully understood. HSCs reside in the hypoxic niche and maintain intracellular hypoxia. Hypoxia and hypoxia signalling pathways are thought to play a vital role in HSC maintenance. Hypoxia inducible factors (Hifs) are evolutionarily conserved and are the key regulators of hypoxia. Hifs consist of an unstable, oxygen-dependent α-subunit and an oxygen-independent stable β-subunit. The two main isoforms of Hif-α, namely Hif-1α and Hif-2α, are critical for the response to hypoxia. Hif-mediated pathways have been extensively studied and have been shown to regulate metabolic adaptation and to influence various cellular mechanisms, including cell growth, survival, differentiation and apoptosis, erythropoiesis and angiogenesis. Hif-1α has been shown to be essential for maintenance of HSC functions under stressful conditions of serial transplantation and aging, but the role of Hif-2α and the interplay between Hif-1α and Hif-2α in regulating HSC functions and their niche is not known. Hence, in this study, I have investigated the role of Hif-α in HSC functions. Furthermore, published evidence suggested that leukaemic stem cells (LSC) share the hypoxic properties with HSCs. Cited2, a hypoxia-inducible Hif-1α and Hif-2α target gene, is critical for embryonic and adult haemopoiesis and possesses oncogenic properties. I have investigated the role of Cited2 in AML generation. The results demonstrate that Hif-2α is not essential for maintenance of HSC functions in a cell-autonomous manner under steady state and stressful conditions of serial transplantation and aging. It is also evident that HSCs lacking Hif-2α together with Hif-1α successfully maintain normal haemopoiesis. However, the data in this thesis show that Hif-2α is essential for non-cell-autonomous maintenance of HSC functions, particularly in males and current work also indicate that a previously unappreciated complex interplay between Hif-1α- and Hif-2α-dependent signalling is required for adult HSC maintenance in a non-cell-autonomous manner. Additionally, the data demonstrate that haemopoietic stem and progenitor cells (HSPCs) lacking Cited2 display reduced transformation potential and failure to generate transplantable AML in vivo. Overexpression of Mcl-1 (an anti-apoptotic gene), in Cited2Δ/Δ cells bypassed their defective transformation potential forming transformed colonies in vitro. Hence, the data in this thesis provide evidence that Cited2 is essential for leukaemic transformation at least in part via Mcl-1 regulation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:622019 |
| Date | January 2014 |
| Creators | Subramani, Chithra |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/5441/ |
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