Mediation Analysis of the Molecular Phenotypes in a Severe MASH-like Liver Injury Mouse Model.

Metabolic dysfunction-associated steatohepatitis (MASH), a severe form of fatty liver disease, is a leading cause of cirrhosis and lacks effective therapies. Understanding the molecular mediators of disease progression remains a critical gap. This study aimed to investigate the roles of molecular phenotypes as mediators of MASH disease features in a diet-induced mouse model. Data used for these analyses was from a previous study where male and female CC042 mice were fed either a control or high-fat, high-sucrose (HF/HS) diet for 20, 40, or 60 weeks. Associations and mediated relationships between molecular and metabolic phenotypes, and histopathologic markers of liver injury, inflammation, and lipid accumulation were assessed using regression modeling and causal mediation analyses. We observed strong associations between the HF/HS diet and duration of treatment and liver pathology, with limited effect of sex. Mediation analysis revealed that liver lipid phenotypes, particularly monounsaturated and polyunsaturated fatty acids, consistently mediated the effects of diet on liver disease scores. TNF-α and Cxcl10, despite being treatment-induced, showed modest evidence of mediation on MASH or specific liver disease outcomes. Serum insulin showed modest mediation of inflammation and osmium staining, while serum glucose and triglycerides were not significant mediators. These findings highlight evidence that liver lipid metabolism may act as primary mediators of MASH progression in this mouse model. The study underscores the value of mediation analysis for improved characterization of metabolic pathways in disease pathogenesis and supports the use of serum lipids as accessible biomarkers for clinical risk stratification and therapeutic targeting in MASH.