Runx1 negatively regulates inflammatory cytokine production by neutrophils in response to Toll-like receptor signaling: HP scRNA-seq

RUNX1 is frequently mutated in myeloid and lymphoid malignancies. It has been shown to negatively regulate Toll-like receptor 4 (TLR4) signaling through nuclear factor kappa-B (NF-κB) in lung epithelial cells. Here we show that RUNX1 regulates TLR1/2 and TLR4 signaling and inflammatory cytokine production by neutrophils. Hematopoietic-specific RUNX1 loss increased the production of pro-inflammatory mediators, including tumor necrosis factor α (TNF-α), by bone marrow (BM) neutrophils in response to TLR1/2 and TLR4 agonists. Hematopoietic RUNX1 loss also resulted in profound damage to the lung parenchyma following inhalation of the TLR4 ligand lipopolysaccharide (LPS). However, neutrophils with neutrophil-specific RUNX1 loss lacked the inflammatory phenotype caused by pan-hematopoietic RUNX1 loss, indicating that dysregulated TLR4 signaling is not due to loss of RUNX1 in neutrophils per se, and single cell RNA sequencing indicates the dysregulation originates in a neutrophil precursor.  Enhanced inflammatory cytokine production by neutrophils following pan-hematopoietic RUNX1 loss correlated with increased degradation of the inhibitor of NF-κB signaling (IκBα), and RUNX1-deficient neutrophils displayed broad transcriptional upregulation of many of the core components of the TLR4 signaling pathway.  Hence early, pan-hematopoietic RUNX1 loss de-represses an innate immune signaling transcriptional program that is maintained in terminally differentiated neutrophils, resulting in their hyper-inflammatory state. We hypothesize that inflammatory cytokine production by neutrophils may contribute to leukemia associated with inherited RUNX1 mutations. 12 samples were analzyed including 3 replicates each of Control and Runx1 KO neutrophils treated with vehicle or 100 ng/mL LPS. The Control sample includes LKS- cells of pooled BM from 1 Runx1f/f and 1 Runx1f/- mouse (i.e. with a monoallelic germline Runx1 mutation).