Search

The pathogenesis of acute leukemia involves interaction among genetic alterations. Mutations of IDH1/2and PHF6are common and co-exist in some patients of hematopoietic malignancies, but their cooperative effects remain unexplored. In this study, we addressed the question by characterizing the hematopoietic phenotypes of mice harboring neither, Phf6knockout, Idh2R172K, or combined mutations. We found that the combined Phf6KOIdh2R172Kmice showed biased hematopoietic differentiation toward myeloid lineages and reduced long-term hematopoietic stem cells. They rapidly developed neoplasms of myeloid and lymphoid lineages, with much shorter survival compared with single mutated and wild-type mice. The marrow and spleen cells of the combined mutated mice produced a drastically increased amount of 2-hydroxyglutarate compared with mice harboring Idh2R172K. Single-cell RNA sequencing revealed distinct patterns of transcriptome of the hematopoietic stem/progenitor cells from the combined mutated mice, including aberrant expression of metabolic enzymes, increased expression of several oncogenes, and impairment of DNA repairs, as confirmed by the enhanced γH2AX expression in the marrow and spleen cells. We conclude that Idh2and Phf6mutations are synergistic in leukemogenesis, at least through overproduction of 2-hydroxyglutarate and impairment of DNA repairs.

HOPX is a stem cell marker in hair follicles and intestines. It was shown critical for primitive hematopoiesis. We previously showed an association between higher HOPXexpression and clinical characteristics related to stemness and quiescence of leukemic cells in acute myeloid leukemia (AML) patients. To further explore its physiologic functions in hematopoietic system, we generated a mouse model with hematopoietic cell-specific knockout of Hopx(Hopx−/−). In young Hopx−/−mice, the hematopoietic stem cells (HSC) showed decreased reconstitution ability after serial transplantation. Further transcriptomic study revealed decreased HSC signatures in long-term HSCs from the Hopx−/−mice. At 18 months of age, half of the Hopx−/−mice developed cytopenia and splenomegaly. Bone marrow (BM) from the sick mice showed myeloid hyperplasia with predominant mature neutrophils, and decreased progenitor cells and lymphocytes. These phenotypes suggested critical functions of Hopx in maintaining HSC quiescence. Transcriptomic study of the Hopx−/−marrow cells showed significant downregulation of the Cxcl12-Cxcr4axis, which is critical for maintenance of HSC quiescence. We next examined the role of Hopx in AML by using the MN1overexpression murine leukemia model. Mice transplanted with MN1-overexpressed Hopx−/−BM cells developed AML with more aggressive phenotypes compared with those transplanted with MN1-overexpressed Hopx-wild cells. Hopx−/−MN1-overexpressed leukemia cells showed higher proliferation rate and downregulation of Cxcl12and Cxcr4. Furthermore, in human AML, BM plasma CXCL12 levels were lower in patients with lower HOPXexpression. In conclusion, our study highlights the roles of Hopx in maintenance of quiescence of the hematopoietic stem cells through CXCL12 pathway in vivo and provides implication of this protein in normal and malignant hematopoiesis.

Abstract 762