Blocking MOXD1-derived ACOX1 peroxisome trafficking suppresses metabolic dysfunction-associated steatohepatitis

BACKGROUND: Metabolic dysfunction-associated steatohepatitis (MASH) has become a major global health burden yet effective pharmacological treatments remain scarce. Lipotoxicity is one of the central drivers of MASH, but the molecular regulators that control lipid metabolism homeostasis in MASH remain incompletely defined. OBJECTIVE: To discover and characterise key regulators of hepatic lipotoxicity that drive MASH progression and to delineate their mechanistic and therapeutic relevance. DESIGN: We integrated multiple RNA-seq datasets from murine and human MASH to identify candidate genes linked to disease-associated metabolic signatures. Functional and mechanistic studies were performed using primary hepatocytes, hepatocyte-specific transgenic and knockout mice and an AAV8-based post-onset knockdown model. Protein interactions and subcellular dynamics were evaluated using co-immunoprecipitation-mass spectrometry, structural modelling and colocalisation analysis. The small molecule of monooxygenase DBH like 1 (MOXD1) inhibitor candidates was screened by the artificial intelligence (AI) model, and their anti-MASH capacity was evaluated in vitro and in vivo. RESULTS: We identified MOXD1 as a previously unrecognised gene tightly associated with MASH transcriptional programmes. Hepatocyte MOXD1 significantly exacerbated MASH phenotypes. Mechanistically, MOXD1 directly interacted with the ACOX1-PEX5 translocation complex, promoting ACOX1 trafficking to peroxisomes to block lipolysis, lipophagy. We further identified four key MOXD1 residues required for ACOX1 binding and resultant pro-MASH capacity. Importantly, based on the AI model and interacting details of MOXD1-ACOX1, we identified a small molecule rM15 that directly binds to MOXD1 and blocks its interaction with ACOX1. Notably, rM15 robustly protected against hepatocyte lipid accumulation and suppressed diet-induced MASH progression in vivo. CONCLUSION: This study identifies MOXD1 as a previously unrecognised regulator of hepatic fatty-acid homeostasis and a key driver of MASH pathogenesis. Targeting the MOXD1-ACOX1 axis offers a promising therapeutic strategy for MASH.