Gut microbial DL-endopeptidase protects against alcohol-associated liver disease via hepatocyte NOD2 signaling

Chronic alcohol consumption disrupts gut-liver homeostasis not only by inducing direct hepatotoxic injury, but also by perturbing host-microbial defense mechanisms that normally protect the liver from metabolic and inflammatory stress. We show that hepatocyte-specific deletion of Nod2 exacerbates ethanol-induced steatosis, oxidative stress, and mitochondrial dysfunction, establishing NOD2 as a critical protective factor in alcohol-associated liver disease (ALD). Importantly, beyond its direct hepatotoxic effects, ethanol exposure simultaneously diminishes this protective NOD2 pathway by limiting microbiota-derived ligand availability. Guided by this functional deficit, clinical metagenomic analysis (n = 1516) revealed that alcohol consumption is associated with a selective depletion of gut microbial DL-endopeptidase, a rate-limiting enzyme for NOD2 ligand generation, which inversely correlated with liver injury severity. Mice receiving fecal microbiota from donors with low DL-endopeptidase activity showed increased susceptibility to ALD. Importantly, supplementation with a NOD2 ligand or its clinical analogue, mifamurtide, restored mitochondrial homeostasis and alleviated liver injury. Together, these findings identify the gut microbial DL-endopeptidase-NOD2 axis as a key protective mechanism against ethanol-induced liver injury and a promising therapeutic target in alcohol-associated liver disease.