Effect of circulating exosomal miRNA-122-3p on metabolic dysfunction-associated steatotic liver disease through impairing FGFR4 expression.

BACKGROUND: In metabolic dysfunction-associated steatotic liver disease (MASLD), exosome-encapsulated miRNAs mediate intercellular signaling pathways that drive dysregulated lipid metabolism, inflammation, and fibrosis. However, the cell-of-origin specificity and disease-modifying mechanisms of these microRNAs (miRNAs) remain poorly characterized. Here, we aimed to define the exosomal miRNA signatures originating from key MASLD microenvironments (liver and adipose tissue) and evaluate their causal roles in promoting hepatic steatosis and cellular damage.

METHODS: Plasma exosomes from patients with MASLD (n = 6) and healthy control volunteers (n = 6) were isolated, characterized, and profiled for miRNA expression. Subjects were enrolled from the Department of Gastroenterology at the First Affiliated Hospital of Shandong First Medical University. Oleic acid (OA)-treated HepG2 and Bel-7404 cells were used to model MASLD in vitro. Identified miRNAs were transfected into HepG2 and Bel-7404 cells to assess effects on triglyceride (TG) accumulation, reactive oxygen species (ROS), and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activity. Protein levels of key metabolic regulators-acyl-coenzyme A synthetase short-chain family member 2 (ACSS2), matrix metalloproteinase-12 (MMP12), fatty acid synthase (FASN), stearoyl-CoA desaturase-1 (SCD1), and sterol regulatory element-binding transcription factor 1 (SREBF1)-were evaluated using enzyme-linked immunosorbent assay, Oil Red O staining, Western blotting, and quantitative real-time polymerase chain reaction. Engineered exosomes-overexpressing miRNA mimics were used to validate target interactions.

RESULTS: Exosomal miR-122-3p and miR-3614-5p were significantly upregulated in patients with MASLD compared with healthy volunteers (P <0.05). Transfection of miR-122-3p-but not miR-3614-5p-into OA-treated HepG2 and Bel-7404 cells led to increased TG accumulation and ROS production, suppressed AMPK activity, and upregulated the expression of lipid metabolism genes ACSS2, FASN, SCD1, and SREBF1. These phenotypic effects were replicated using engineered exosomes-overexpressing miR-122-3p, with successful cellular uptake confirmed by luciferase assay. Mechanistically, fibroblast growth factor receptor 4 (FGFR4) was identified as a direct target of exosomal miR-122-3p: treatment with miR-122-3p-enriched exosomes reduced FGFR4 expression in wild-type hepatocytes but not in FGFR4-mutant models, confirming target specificity.

CONCLUSIONS: Exosomal miR-122-3p drives the progression of nonalcoholic fatty liver disease by promoting lipid accumulation, oxidative stress, and suppression of AMPK signaling, primarily through targeting FGFR4. These results identify the miR-122-3p/FGFR4 axis as a potential therapeutic target for treating this condition.