Acetylation of TIR domains in the TLR4-Mal-MyD88 complex regulates immune responses in sepsis

Activation of the Toll-like receptor 4 (TLR4) by bacterial endotoxins in macrophages plays a crucial role in the pathogenesis of sepsis. However, the mechanism underlying TLR4 activation in macrophages is still not fully understood. Here, we reveal that upon lipopolysaccharide (LPS) stimulation, lysine acetyltransferase CBP is recruited to the TLR4 signalosome complex leading to increased acetylation of the TIR domains of the TLR4 signalosome. Acetylation of the TLR4 signalosome TIR domains significantly enhances signaling activation via NF-κB rather than IRF3 pathways. Induction of NF-κB signaling is responsible for gene expression changes leading to M1 macrophage polarization. In sepsis patients, significantly elevated TLR4-TIR acetylation is observed in CD16+ monocytes combined with elevated expression of M1 macrophage markers. Pharmacological inhibition of HDAC1, which deacetylates the TIR domains, or CBP play opposite roles in sepsis. Our findings highlight the important role of TLR4-TIR domain acetylation in the regulation of the immune responses in sepsis, and we propose this reversible acetylation of TLR4 signalosomes as a potential therapeutic target for M1 macrophages during the progression of sepsis. Synopsis Activation of macrophage TLR4 by bacterial endotoxins is important for the progression of sepsis, but the underlying mechanisms remain unknown. This study demonstrates that lipopolysaccharide (LPS) stimulation induces acetylation of the TLR4 signalosome TIR domains, which plays an important role in M1 macrophage polarization. LPS induces CBP-mediated acetylation of the TIR domains of TLR4, Mal, and MyD88 in the TLR4 signalosome complex. TIR domain acetylation in the TLR4 complex enhances NF-κB activation, leading to pro-inflammatory gene expression in M1 macrophages during sepsis. Inhibition of the primary TIR domain acetyltransferase CBP or deacetylase HDAC1 has opposite effects on the progression of sepsis. LPS-induced acetylation of the TLR4 complex TIR domains induces NF-κB signaling, leading to macrophage polarization.