The role of xdh and hprt1 on purine metabolism in hematopoiesis and leukemia

Abstract In mammalian cells, purine metabolism is essential for nucleic acid synthesis, redox balance, and energy homeostasis, involving denovo synthesis, salvage, and catabolism pathways. The purine metabolite hypoxanthine links salvage and catabolism pathways, yet its role in hematopoiesis and leukemia progression remains unclear. Using low-input targeted metabolomics, we characterized purine metabolism across murine hematopoietic stem/progenitor cells (HSPCs). Hematopoietic stem cells (HSCs) exhibited the highest intracellular uric acid levels and expressed abundant xanthine dehydrogenase (Xdh), the sole enzyme producing uric acid. Conditional knockout of Xdh in the hematopoietic compartment increased adenosine monophosphate (AMP) and guanosine monophosphate (GMP) while inosine monophosphate (IMP) remained unchanged, elevating AMP-to-IMP and GMP-to-IMP ratios and reducing hypoxanthine-to-IMP ratios. This shift towards the salvage pathway resulted in impaired HSC function, as evidenced by reduced reconstitution of myeloid and lymphoid cells upon transplantation. The salvage pathway of hypoxanthine is regulated by hypoxanthine phosphoribosyltransferase 1 (HPRT1). Conditional knockout of Hprt1 led to significantly reduced reconstitution capacity upon transplantation, with increased ratios of hypoxanthine to IMP and decreased ratios of AMP to IMP and GMP to IMP, suggesting reduced sources for nucleic acid synthesis from the salvage pathway. Granulocyte-monocyte progenitors (GMPs) displayed high intracellular uric acid levels and Xdh expression. In MLL-AF9-driven acute myeloid leukemia (AML), leukemia stem cells (LSCs) shared immunophenotype with GMPs and accumulated uric acid at the expense of nucleotides and hypoxanthine, suggesting leukemia-associated metabolic diversion. Conditional knockout of Xdh in the hematopoietic compartment reduced hyperuricemia and prolonged survival, whereas knockout of Hprt1 accelerated leukemia progression and worsened survival in the AML model. In summary, our data identify XDH and HPRT1 as opposing molecular switches in purine metabolism: XDH promotes catabolism and maintains HSC quiescence, while HPRT1 enables nucleotide synthesis for HSC proliferation. In leukemia, XDH suppresses LSC expansion, whereas HPRT1 promotes it. These findings highlight the potential of targeting purine metabolism in hematopoietic diseases.