3026 – METABOLIC ADAPTATION IN HEMATOPOIETIC STEM AND PROGENITOR CELLS DURING EMERGENCY MYELOPOIESIS

Abstract

Under conditions of stress, hematopoietic stem cells (HSC) respond to inflammatory cytokines by activating emergency myelopoiesis pathways to rapidly regenerate myeloid cells and maintain blood system homeostasis. Emergency myelopoiesis pathways involve the overproduction of myeloid-biased multipotent progenitors (MPP), the myeloid reprogramming of lymphoid-biased MPP, and the formation of granulocyte-macrophage progenitor (GMP) clusters in the bone marrow microenvironment, which serve as hubs of myeloid cell differentiation and overproduction. However, the molecular mechanisms that remodel hematopoietic stem and progenitor cells (HSPC) remain poorly understood and little is known about the role of emergency myelopoiesis pathways in the genesis of functional heterogeneity in mature myeloid cells. Here we have generated a single-cell RNA sequencing atlas of myeloid regeneration by kinetic profiling of hematopoietic regeneration following myeloablative 5-fluorouracil treatment. Analysis of regenerative HSPCs reveals suppression of both myeloid and lymphoid lineage commitment genes and metabolic activation throughout the hematopoietic hierarchy. Notably, we observe an increase in mitochondrial biogenesis, aerobic glycolysis, and other MYC target genes and usage of a MYC-EGFP reporter demonstrates increased levels of MYC in regenerative HSPCs. Immunofluorescence reveals increased levels of mitochondria in regenerative HSPCs, in accordance with increased basal mitochondrial respiration and maximal respiratory capacity. Regenerative HSPCs also have increased metabolic flexibility and the capacity to utilize aerobic glycolysis under conditions of mitochondrial stress. Like upstream HSPCs, mature monocytes and neutrophils that develop through the emergency myelopoiesis pathway have increased mitochondria, activated metabolism, and display altered effector functions. Emergency neutrophils also have increased oxidative burst capacity and extended survival. We hypothesize the activated metabolic state of HSPCs during emergency myelopoiesis is propagated through the differentiation hierarchy, resulting in mature myeloid cells with altered metabolism and effector functions. Work is ongoing to investigate the role of activated metabolism in driving epigenetic remodeling in HSPCs, overproduction of myeloid cells, and acquisition of altered myeloid effector functions.