PROJECT SUMMARY: Loss of function mutations in the transcription factor RUNX1 often occur in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Patients carrying inherited RUNX1 mutations are predisposed to developing clonal hematopoiesis, myelodysplastic syndrome, and leukemia. Interestingly, patients with inherited RUNX1 mutations are predisposed to developing inflammatory disorders such as asthma and eczema. RUNX1 mutations and their contributions to oncogenesis are well described. However, the broader effects of RUNX1 mutations on inflammatory responses are poorly understood. Our lab recently demonstrated that RUNX1 has a significant role in regulating inflammatory responses in mouse neutrophils. Pan- hematopoietic RUNX1 loss activated an inflammatory transcriptional program that primed neutrophils to hyperactivate in response to toll-like receptor 4 (TLR4) stimulation. Since neutrophils are an important component of the bone marrow niche, we hypothesize that increased inflammatory cytokine and chemokine production by neutrophils may contribute to the elevated risk of clonal hematopoiesis and leukemia in patients with RUNX1 mutations. The goal of this proposal is to understand the mechanisms by which RUNX1 regulates inflammation in neutrophils. I hypothesize that alterations in the TLR4 signaling pathway are established in a neutrophil precursor by an alteration in the progenitor epigenome that is then propagated to differentiated neutrophils, causing them to hyper-respond to TLR4 ligands. The first goal of my proposal is to test this hypothesis. The second goal is to determine whether RUNX1 directly regulates the expression of TLR4 pathway genes in neutrophil precursors, or if RUNX1 loss in other hematopoietic cells contributes to the inflammatory neutrophil response.