Inducing expansion of hematopoietic stem cells by HMG box proteins
Loh, Shuzk Cheng
Date of Issue2014
School of Biological Sciences
Hematopoietic stem cells (HSCs) are rare multipotent stem cells that give rise to all blood lineages, and its development is tightly regulated at all stages to ensure retention of full hematopoietic functionality throughout life. The aim of this work was to learn about genetic modifications that allow HSC expansion in vitro and hence to provide us with alternative avenues to expand these cells in vitro for clinical use. To tackle the challenge of improving HSC expansion and self-renewal in vitro, we turned to two transcription factors of the High Mobility Group (HMG) superfamily that are involved in hematopoietic regulation and test the functionality of the genetically modified murine HSCs. First, Sox17 was shown to be required for the maintenance and self-renewal of fetal-HSCs, and high Sox17 expression in fetal-HSCs maintains its high proliferative states. We found that overexpression of Sox17 in adult HSCs not only induced extensive self-renewal ability in vitro, but also resulted in abnormal leukemia-like phenotype in vivo. This leukemic phenotype is characterized by a skewed myeloerythroid development in the expense of lymphopoiesis during the early stages, which eventually manifested into erythroid-like leukemia with a latency of less than 5 months. Interestingly, we found that Sox17 overexpression induced expression of key genes of primitive and definitive erythropoiesis as well as endothelial signatures involved in blood specification and fetal hematopoiesis. Second, a truncated HMGA2 was shown to immortalize myeloid-biased clones that cured a patient with severe -thalassaemia, without developing leukemia. We found that overexpression of truncated-HMGA2 increased the expansion of adult HSCs in vitro. When transplanted in vivo, these cells retained multilineage reconstitution ability in the absence of competitor cells, but eventually generated a myeloid-biased leukemia-like phenotype with long latency.