Emergency Myelopoiesis in the Pathogenesis of Myeloid Malignancies

PROJECT DESCRIPTION Our overall goals are to understand how emergency myelopoiesis contributes to the pathogenesis of myeloid malignancies, dissect the underlying metabolic and epigenetic mechanisms driving aberrant self-re- newal and differentiation properties in malignant hematopoietic stem and progenitor cells (HSPC), and identify potential vulnerabilities to target therapeutically. At steady-state, blood production reflects the differential pro- duction by rare quiescent hematopoietic stem cells (HSC) of a small number of myeloid-biased multipotent pro- genitors (MPP2/3) and a large number of lymphoid-biased multipotent progenitors (MPP4), which both give rise to granulocyte/macrophage progenitors (GMP) and contribute to limited myeloid output. In contrast, during re- generation, activated HSCs overproduce myeloid-biased MPP2/3, lymphoid-biased MPP4 are reprogrammed towards myelopoiesis, and GMP expand in the bone marrow (BM) cavity as GMP clusters (cGMP), driving burst production of myeloid cells. This remodeling of the HSPC compartment reflects the engagement of emergency myelopoiesis pathways, which are transiently activated during regeneration but are co-opted and constantly triggered in myeloid malignancies such as myeloproliferative neoplasms (MPN). However, the regulatory mech- anisms controlling emergency myelopoiesis remain poorly understood, and the relationships between leukemic myelopoiesis, which is continuously fueled by pre-leukemic HSCs in MPNs, and regenerative myelopoiesis, which is an acute stress response, are still largely unexplored. Furthermore, the role of emergency myelopoiesis in the development of acute myeloid leukemia (AML), where HSPC differentiation is blocked and leukemic stem cells (LSC) emerges from transformed HSPCs, remains unknown. Our objective is to identify how HSPCs adapt in these different situations and adjust both self-renewal and differentiation properties during regenerative and leukemic myelopoiesis. In Aim 1, we will take advantage of our newly generated single-cell RNA sequencing atlas of 5-fluorouracil (5FU)-mediated regeneration and Scl-tTA:TRE-BCR/ABL (BAtTA) MPN malignancy to iden- tify changes in cell-state and differentiation trajectories driving activation of emergency myelopoiesis pathways. In Aim 2, we will investigate the role of two key regulatory processes (metabolic adaptation and epigenetic remodeling) in driving emergency myelopoiesis during regenerative and malignancy. In particular, we will test the central role of the MYC transcription factor, the metabolite alpha-ketoglutarate (?KG) and the process of glutaminolysis in remodeling the HSPC compartment. In Aim 3, we will test whether activation of emergency myelopoiesis pathways cooperates with epigenetic driver mutations like TET2 loss in pre-leukemic HSCs to promote clonal selection and LSC emergence from an expanded and remodeled HSPC compartment. Collec- tively, these approaches will uncover the mechanisms driving emergency myelopoiesis that are critical for dis- ease development, and provide new insights into the epigenetic and metabolic states associated with enhanced myelopoiesis that could potentially be targeted for leukemia treatment.