Metabolic Control of Erythroid Differentiation

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Project summary: Anemia is a significant human health problem that is caused by multiple etiologies and has negative impact on quality of life. Standard treatments for anemia are transfusion therapy and treatment with erythropoiesis stimulating agents, which can be effective in the short-term, but are not without risk. Treatment of chronic anemia with transfusion therapy is complicated by the risk of allo-immunization and the potential for infection. While, erythropoiesis stimulating agents are not effective treatments for all anemia and their immunomodulatory properties can compromise other treatments. These observations point to a need in the field to identify new treatments for anemia. One possibility is to characterize the physiological response to anemic stress. Previous work in my lab showed that in response to hypoxic stress, bone marrow steady state erythropoiesis is unable to maintain homeostasis. At these times, stress erythropoiesis predominates. Stress erythropoiesis is best understood in the murine system where it is extra-medullary, occurring in the adult spleen and liver and in the fetal liver during development. Stress erythropoiesis utilizes a different strategy than steady state erythropoiesis. Instead of generating new erythrocytes at a constant rate, stress erythropoiesis generates a bolus of new erythrocytes designed to alleviate anemia until steady state erythropoiesis can resume. This strategy relies on the ability of immature stress erythroid progenitors to proliferate without differentiating. The expansion of this transient amplifying population is an essential step in stress erythropoiesis. If too few early progenitors are generated or if they differentiate prematurely, insufficient erythrocytes will be produced to alleviate the anemia. In this proposal submitted under the SHINE II program announcement, we will focus on the mechanisms that regulate the expansion of early stress progenitors and the mechanisms that inhibit their differentiation during this expansion phase. We hypothesize that stress erythroid progenitors adopt a pro-inflammatory metabolism characterized by increased glucose and glutamine metabolism, which results in the production of anabolic intermediates needed to produce lipids, nucleotides and amino acids necessary for cell proliferation. In addition, this metabolic program produces metabolites that promote the activity of histone methylases that maintain repression of the erythroid differentiation program. This model demonstrates how metabolic regulation can coordinate the proliferation and differentiation of stress erythroid progenitors during the recovery from anemic stress.