AOAH-mediated LPS inactivation limits macrophage endotoxin tolerance and promotes inflammation and fibrosis in MASH.

BACKGROUND & AIMS: Metabolic dysfunction-associated steatohepatitis (MASH), a chronic liver disease, is characterized by persistent low-grade inflammation, partially driven by gut-derived lipopolysaccharide (LPS). Although repeated LPS exposure can induce endotoxin tolerance in innate immune cells, its role in chronic liver diseases remains unclear. Acyloxyacyl hydrolase (AOAH) is an endogenous enzyme that inactivates LPS, potentially modulating this process. We aimed to investigate how AOAH regulates endotoxin tolerance in Kupffer cells (KCs) and how this affects hepatic inflammation and fibrosis during MASH progression. METHODS: AOAH-deficient (AOAH-/-) mice and wild-type controls were subjected to multiple dietary MASH models. Inflammatory responses, fibrosis, and transcriptomic changes in liver tissues and isolated KCs were analyzed. Endotoxin tolerance was modulated through β-glucan administration or LPS preconditioning. LPS bioactivity was assessed using TLR4-reporter cell assays. RESULTS: LPS-preconditioned KCs exhibited reduced pro-inflammatory cytokine production and transcriptional suppression of inflammatory pathways, indicating tolerance. Despite slight elevation of plasma LPS levels in MASH, upregulation of hepatic AOAH positively correlated with disease severity, suggesting enhanced LPS inactivation but impaired establishment of tolerance. In contrast, AOAH-deficient KCs displayed reinforced endotoxin tolerance, leading to diminished hepatic inflammation and fibrosis. Reversal of tolerance using β-glucan reactivated inflammatory and fibrogenic responses in AOAH-deficient mice, whereas tolerance induction by low-dose LPS preconditioning mitigated MASH pathology, supporting the protective role of macrophage tolerance in chronic liver injury. CONCLUSIONS: Endotoxin tolerance in KCs represents a protective mechanism against chronic liver inflammation and fibrosis. AOAH regulates this state by limiting bioactive LPS, thereby modulating the establishment of endotoxin tolerance and downstream inflammatory and fibrotic responses. Enhancing macrophage tolerance by utilizing LPS may offer a novel therapeutic avenue to control the progression of MASH.