METTL3-mediated m6A mRNA methylation regulates neutrophil activation through targeting TLR4 signaling

N6-methyladenosine (m6A) modification accounts for the most prevalent mRNA internal modification and has emerged as a widespread regulatory mechanism in multiple physiological processes. We address a role of methyltransferase-like protein 3 (METTL3) in neutrophil activation. METTL3 controls neutrophil release from bone marrow to circulation through surface expression of CXC chemokine receptor 2 (CXCR2) in a Toll -like receptor 4 (TLR4) signaling-dependent manner in lipopolysaccharide (LPS)-induced endotoxemia. We show that the mRNA of TLR4 is modified by m6A, exhibiting increased translation and slowed degradation simultaneously, leading to elevated protein levels of TLR4, which eventually promotes the TLR4 signaling activation of neutrophil. The reduced expression of TLR4 lowers cytokine secretion in METTL3-deleted neu-trophils upon LPS stimulation through TLR4/Myd88/nuclear factor KB (NF-KB) signaling. Collectively, these data demonstrate that METTL3 modulation of TLR4 expression is a critical determinant of neutrophil activa-tion in endotoxemia.

Automated summary

N6-methyladenosine (m6A) modification is the most prevalent mRNA internal modification and serves as a widespread regulatory mechanism in various physiological processes. In this study, we found that methyltransferase-like protein 3 (METTL3) plays a crucial role in neutrophil activation. METTL3 controls the release of neutrophils from the bone marrow to circulation by regulating the surface expression of CXC chemokine receptor 2 (CXCR2) through Toll-like receptor 4 (TLR4) signaling in lipopolysaccharide (LPS)-induced endotoxemia. We discovered that the mRNA of TLR4 is modified by m6A, resulting in increased translation and decreased degradation, leading to elevated levels of TLR4 protein and subsequent activation of TLR4 signaling in neutrophils. The downregulation of TLR4 expression reduces cytokine secretion in METTL3-deleted neutrophils upon LPS stimulation through the TLR4/Myd88/nuclear factor KB (NF-KB) signaling pathway. Overall, these findings demonstrate that METTL3-mediated TLR4 expression is a critical determinant of neutrophil activation in endotoxemia.