DDX41 heterozygosity impairs hematopoietic progenitor cell fitness and cooperates with p53 mutation to drive malignancy [LSK]

Germline heterozygous mutations in DDX41 predispose individuals to hematologic malignancies in adulthood. Most of these DDX41 mutations result in a truncated protein, leading to loss of protein function. To investigate the impact of these mutations on hematopoiesis, we generated mice with hematopoietic-specific knockout of one Ddx41 allele. Under normal steady-state conditions, there was minimal effect on lifelong hematopoiesis, resulting in a mild yet persistent reduction in red blood cell counts. However, stress induced by transplantation of the Ddx41+/- BM resulted in hematopoietic stem/progenitor cell (HSPC) defects and onset of hematopoietic failure upon aging. Transcriptomic analysis of HSPC subsets from the transplanted BM revealed activation of cellular stress responses, including upregulation of p53 target genes in erythroid progenitors. To understand how the loss of p53 affects the phenotype of Ddx41+/- HSPCs, we generated mice with combined Ddx41 and Trp53 heterozygous deletions. The reduction in p53 expression rescued the fitness defects in HSPC caused by Ddx41 heterozygosity. However, the combined Ddx41 and Trp53 mutant mice were prone to developing hematologic malignancies that resemble human myelodysplastic syndrome and acute myeloid leukemia. In conclusion, DDX41 heterozygosity causes dysregulation of the response to hematopoietic stress, which increases the risk of transformation with a p53 mutation. We transplanted lethally-irradiated BoyJ mice with bone marrow cells from Ddx41+/flox or Ddx41+/+ RosaCreERT2 mice and immediately treated the mice with tamoxifen to excise the floxed alleles. At 8 weeks post-transplant, we harvested the bone marrow from these mice and then sorted Lin-Sca1+cKit+ cells by flow cytometry. We harvested RNA from approximately 20K LSK cells from each mouse, and then isolated the RNA. We conducted gene expression analysis by RNA-seq on these samples.