Heterozygous <i>ddx41</i> Mutation Drive Age-Dependent Hematopoietic Stem and Progenitor Cell Dysfunction

Myelodysplastic syndromes (MDS) are a group of blood cancers characterized by hematopoietic stem and progenitor cell (HSPC) expansion, ineffective hematopoiesis, myeloid cell dysplasia, cytopenia, and inflammation. Driving events for MDS are largely unknown, but clinically relevant to improve monitoring for at-risk patients and generate preventative therapies. Heterozygous, loss-of-function mutations in the ATPase DEAD-box Helicase 41 (DDX41) gene are common in inherited late-onset adult MDS, providing a compelling model to study the mechanisms preceding MDS. We established ddx41 heterozygous loss-of-function mutant zebrafish as an in vivo model that develops age-associated MDS features to study progressive changes in the hematopoietic system leading to disease. By 12-14 months, ddx41 heterozygous animals displayed erythroid dysplasia, HSPC expansion, and increased NFkB-active myeloid cells compared to wildtype siblings. Based on prior work, we hypothesized that the innate immune sensing cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) pathway that can respond to many damage-associated molecular patterns could be driving HSPC expansion. Indeed, HSPC frequency in 14-month-old ddx41 heterozygous; cgas homozygous mutants was significantly reduced compared to ddx41 heterozygous; cgas heterozygous mutants. To identify early arising deregulation that contributes to later MDS features in ddx41 heterozygous animals, we performed scRNA-seq on total marrow cells from 3-, 6-, and 14-month-old ddx41 wildtype and heterozygous animals. We identified gene signatures indicative of elevated cellular stress in HSPC in ddx41 heterozygous animals as early as 3 months. Our findings suggest that Ddx41 insufficiency promotes cellular distress that triggers age-associated cGAS-mediated HSPC expansion. These results have the potential to uncover new ways to prevent MDS progression and will also provide valuable insight into fundamental mechanisms controlling HSPC homeostasis.