Differential Dependence On Aerobic Glycolysis In Normal and Malignant Hematopoietic Stem and Progenitor Cells To Sustain Daughter Cell Production

How glucose is metabolized can influence cell function, but whether differences in glucose metabolism reflect, or dictate, cell state is not clear and is of particular interest given the association of cancer with aerobic glycolysis. Studies on cancer cell lines have indicated that increased glucose uptake with lactate production regardless of oxygen concentration, a phenomenon also known as the Warburg effect, is promoted in part by expression of the M2 isoform of pyruvate kinase (PKM2) and the muscle form of lactate dehydrogenase A (LDHA). Normal somatic cells thought to also preferentially use glycolytic metabolism are tissue stem cells, particularly the self-renewing hematopoietic stem cells (HSC) resident in the hypoxic microenvironment of the bone marrow. It remains to be defined, however whether proliferating hematopoietic progenitor cells rely on aerobic glycolysis and whether malignant and normal hematopoietic cells are dependent on the same metabolic regulation. We observed that PKM2 and LDHA are the predominant isoforms expressed by all BM hematopoietic cells. To further understand the role of glycolytic metabolism in hematopoiesis and hematological malignancy, we utilized a mouse strain that allows conditional deletion of the PKM2 specific exon 10. Deletion of PKM2 in hematopoetic cells leads to expression of PKM1, accompanied with partial inhibition of lactate production and decreased glycolytic intermediates in the hematopoietic stem/progenitor cell (HSPC) population. Loss of PKM2 compromises the long-term repopulation capacity of HSPCs as revealed by serial transplantation assay. Interestingly, the repopulating defects resulting from PKM2 depletion appear to involve progenitors, perhaps due to inadequate biomass generation necessary for robust cell proliferation. To confirm that the effect of PKM2 deletion on HSPC function is due to metabolic changes rather than other putative PKM2 functions, we engineered a mouse strain that allowed conditional knockout of LDHA to more potently impair aerobic glycolysis. LDHA deletion completely inhibited lactate production, enhanced ROS levels in hematopoietic cells and impaired long-term BM repopulating activity. In contrast to PKM2 deletion that affects progenitor but not stem cells, LDHA depletion impacts both stem cell maintenance and progenitor cell proliferation. Deletion of either PKM2 or LDHA markedly suppressed leukemia initiation by either putative stem cell (BCR-ABL) or progenitor (MLL-AF9) transforming alleles. Therefore, modulating aeroblic glycolysis has effects on normal hematopoietic cells that depend upon cell state and negatively impacts leukemic growth regardless of cell state. The differential sensitivity of normal and malignant cells to modulation of aerobic glycolysis suggests a potential therapeutic opportunity for leukemia intervention.