d-Amino Acids Suppress Macrophage IL-1β Release by Acetylating Gasdermin D, Attenuating Sepsis

Macrophage-associated inflammatory diseases are a significant health burden, with uncontrolled IL-1β release contributing to severe conditions like sepsis. Current anti-inflammatory strategies often lack specificity or have side effects. While d-amino acids are known to exist in various tissues, their role in modulating immune cell function, particularly macrophages, has remained largely unexplored. Understanding how these endogenous molecules influence inflammatory pathways, such as NF-κB signaling and IL-1β production, could unveil novel therapeutic targets for managing acute and chronic inflammatory states.

Researchers investigated the role of d-amino acids in macrophage function using both in vitro models and an in vivo lipopolysaccharide (LPS)-induced sepsis mouse model. They examined the expression of d-amino acid metabolizing enzymes, d-amino acid oxidase (DAAO) and d-aspartate oxidase (DDO), in inflammatory macrophages. The study involved inhibiting DAAO or DDO to observe changes in intracellular d-amino acid concentrations and IL-1β release. Mechanistic studies focused on gasdermin D (GSDMD) oligomerization and acetylation, as well as the activity of mitochondrial pyruvate dehydrogenase (PDH). Finally, mice were supplemented with d-Ala/d-Glu or engineered with myeloid-specific deletion of DDO to assess attenuation of LPS-induced sepsis.

Inflammatory macrophages significantly decreased mRNA expression of DAAO and DDO through activation of nuclear factor κB (NF-κB) signaling. Notably, inhibition of either DAAO or DDO led to an increase in intracellular d-amino acid concentrations, which consequently suppressed IL-1β release. Mechanistically, d-amino acids were found to directly inhibit the formation of gasdermin D (GSDMD) oligomers, a crucial step in pyroptosis, via GSDMD-K146 acetylation. This acetylation process was supported by d-amino acids directly binding to and increasing the enzyme activity of mitochondrial pyruvate dehydrogenase (PDH), resulting in enhanced acetyl-coenzyme A production. This acetyl-CoA then serves as a substrate for the observed acetylation events. Consistently, both d-Ala/d-Glu supplementation and myeloid-specific deletion of DDO robustly attenuated LPS-induced sepsis in mice. These findings collectively establish a novel regulatory mechanism:

d-amino acids mediate acetylation to restrain macrophage function and IL-1β release, offering a potential therapeutic avenue for inflammatory diseases.