Exploring the Role of the DNA Damage Response in Hematopoiesis in ddx41 Mutant Zebrafish.

Abstract

Myelodysplastic syndrome (MDS) is a preleukemic conditions arising from mutations in hematopoietic stem and progenitor cells (HSPCs) resulting in an expansion of dysfunctional blasts and ineffective hematopoiesis. Germline mutations in DEAD-box Helicase 41 (DDX41) were identified in patients with MDS with inferior overall survival, suggesting a contribution to disease pathogenesis. Though a strong clinical correlation is found between mutations in DDX41 and MDS, the in vivo role of DDX41 in hematopoiesis has not been elucidated. ==== Previous work in our lab has shown that ddx41 loss-of-function homozygous mutants (ddx41 mutants) have developmental hematopoietic defects including megaloblastoid-like anemia and increased HSPC formation at 36 hours post-fertilization (hpf). Additionally, ddx41 mutant cells exhibit cell cycle arrest and apoptosis, phenotypes commonly mediated by the DNA damage response (DDR). DNA damage can trigger several signaling pathways via the activation of distinct kinases, such as Ataxia Telangiectasia Mutated (ATM) in response to double-strand breaks, and ATM and RAD3-related (ATR) in response to single-strand breaks or replication stress. It remains unclear if these DNA damage response kinases mediate apoptosis or the hematological defects in ddx41 mutants. ======= To address these questions, we pharmacologically inhibited the ATM and ATR kinases and then assessed levels of apoptotic cells, mature erythrocytes, and HSPCs in ddx41 mutants and sibling controls. ATM kinase inhibition led to a partial but significant suppression of apoptosis and anemia in ddx41 mutants as compared to DMSO vehicle-treated ddx41 mutants. In contrast, ATR kinase inhibition did not significantly impact either defect. Taken together, these results suggest that ATM, but not ATR, partially mediates the DDR and erythropoietic defect in ddx41 mutants. ========== In future studies, we aim to determine the involvement of ATM and ATR kinases in HSPC expansion and cell cycle arrest in ddx41 mutants. Additionally, we will explore which components downstream of ATM mediate its effects on apoptosis and erythroid differentiation. These results highlight the important role of Ddx41 as a protector of genomic integrity and the negative impact of the DNA damage response on erythropoiesis. These studies provide potential therapeutic targets for treating DDX41 mutated MDS and AML