Nonalcoholic Fatty Liver Disease is Associated with Dysfunction in Hepatic Circadian Rhythm
Authors: Larion Sebastian , Mintz James D. , Fulton David J. , Khurana Sandeep , Stepp David W. 
Published: November 2023

Adaption to daily changes in the environment requires an active molecular clock anticipating circadian rhythms. Many diseases are associated with changes in clock performance, the nature and impact of which are incompletely understood. Nonalcoholic fatty liver disease (NAFLD) is associated with hepatic dysregulation of energy metabolism, lipid accumulation and hepatic inflammation. The effect of NAFLD on the hepatic clock mechanism and circadian gene expression is not well understood. This study investigates whether obesity induces alterations in daily pattern of food intake, hepatic clock function, and circadian gene expression in a mouse model of NAFLD.Adult male control and obese db/db mice were sacrificed and the development of NAFLD was assessed using biochemical and histological indices of disease. Diurnal feeding behavior was evaluated using metabolic chambers. Hepatic circadian clock functioning was evaluated using transgenic Per2‐luciferase reporter assay in control and db/db transgenic mice. Gene expression at 12PM and 12AM was assessed by microarray and evaluated using Ingenuity pathway analysis.Obese mice had significantly increased total and night time food intake, body mass, serum glucose, plasma lipids, insulin and hemoglobin A1c than control mice (n≥8; p<0.05). Obese mice also had significantly increased serum AST, ALT, bilirubin and alkaline phosphatase (p<0.05), with greater histological evidence of steatosis. Hepatic per2 expression, as assessed by luciferase reporter assay, was significantly increased at 12AM than 12PM in control, but not obese, mice. In addition, peak per2 expression at 12AM was significantly attenuated in obese mice versus control. While nocturnal food intake was increased in obese mice, diurnal intake was similar, implying a normal circadian rhythm of ingestion and indicating that changes in food intake do not explain depression of the hepatic molecular clock. Microarray revealed greater circadian variation (fold change>2) of hepatic gene expression in obese (328 genes) mice compared to controls (158 genes; p<0.001). Interestingly, pathway analysis revealed RAR‐related orphan receptor‐alpha (RORα), a potent transcriptional activator of BMAL1, as the top upstream regulator differentially expressed at 12PM in obese vs control mice (p<10‐47). Of genes involved in inflammation, 55 showed circadian variation in diurnal gene expression in obese mice compared to only 14 in control mice (p<0.001).Transgenic mouse models of NAFLD are associated with hepatic clock dysfunction and alterations in circadian gene expression including those involved in inflammatory pathways. Taken together, these data suggest that the hepatic molecular clock plays a key role in suppressing inflammation and loss of clock function is associated with increased activation of inflammatory genes in the liver. Risk factors that impair the clock may increase the risk for NAFLD.Support or Funding InformationWork supported by NHLBI 092446 and 124773 and the Department of Medicine Research Residency Program.