The role of ascorbate in myelopoiesis and infection

PROJECT SUMMARY:
We have developed methods to profile the metabolome of hematopoietic stem cells (HSCs) and other rare cell
types purified from tissues. Each hematopoietic cell type had a distinct metabolite identity. Most metabolites
were enriched or depleted in specific cell types, suggesting they may have novel cell-type specific roles. HSCs
and multipotent progenitors (MPPs) in mouse and human bone marrow had high levels of ascorbate (Vitamin
C), which promoted the activity of the enzyme TET2, a suppressor of HSC function. Hematopoietic-specific
ascorbate deficiency promoted HSC function, myelopoiesis and the generation of inflammatory myeloid cells,
and caused early lethality. Ascorbate deficiency is common in the human population because in early primate
evolution we lost the ability to synthesize ascorbate. Ascorbate deficiency in healthy people is associated with
increased risk of mortality for unknown reasons. Hematopoietic TET2 loss of function mutations are also
common in humans, and drive a clonal expansion of mutant blood cells termed clonal hematopoiesis. TET2-
deficient blood cells may contribute to an increased risk of mortality. This application’s objective is to
understand the role of ascorbate in the regulation of myelopoiesis. Our central hypothesis is that ascorbate
suppresses myelopoiesis, and that ascorbate deficiency increases myelopoiesis and inflammation after
plasmodium infection. To test this hypothesis, we will use genetically engineered ascorbate deficient mice, to
mimic the human condition, and Tet2-deficient mice. In Aim 1 we will test if ascorbate suppresses the
generation of inflammatory myeloid cells by acting on HSCs or restricted myeloid progenitors, and if this is
mediated by Tet2. In Aim 2 we will determine the effects of ascorbate deficiency or Tet2 deficiency on the
myelopoietic response to Plasmodium infection in a mouse model of malaria. In Aim 3 we will investigate the
mechanisms by which ascorbate deficiency and Tet2 deficiency promote morbidity and mortality in
Plasmodium infection. These experiments may have significant public health implications. They could identify
physiological situations, such as infection, in which the presence of ascorbate deficiency and Tet2-deficient
clonal hematopoiesis are deleterious to the organism. They may also identify mechanisms by which aberrant
myelopoiesis contributes to the pathogenesis of malaria which afflicts more than 200 million people worldwide.

Grant Number: 5R01DK125713-05
NIH Institute/Center: NIH
Principal Investigator: Michalis Agathocleous