Alcohol and Liver Clock Disruption Increase Small Droplet Macrosteatosis, Alter Lipid Metabolism and Clock Gene mRNA Rhythms, and Remodel the Triglyceride Lipidome in Mouse Liver

Abstract

Heavy alcohol drinking dysregulates lipid metabolism, promoting hepatic steatosis-the first stage of alcohol-related liver disease (ALD). The molecular circadian clock plays a major role in synchronizing daily rhythms in behavior and metabolism and clock disruption can cause pathology, including liver disease. Previous studies indicate that alcohol consumption alters liver clock function, but the impact alcohol or clock disruption, or both have on the temporal control of hepatic lipid metabolism and injury remains unclear. Here, we undertook studies to determine whether genetic disruption of the liver clock exacerbates alterations in lipid metabolism and worsens steatosis in alcohol-fed mice. To address this question, male liver-specific Bmal1 knockout (LKO) and flox/flox (Fl/Fl) control mice were fed a control or alcohol-containing diet for 5 weeks. Alcohol significantly dampened diurnal rhythms of mRNA levels in clock genes Bmal1 and Dbp, phase advanced Nr1d1/ REV-ERBα, and induced arrhythmicity in Clock, Noct, and Nfil3/E4BP4, with further disruption in livers of LKO mice. Alcohol-fed LKO mice exhibited higher plasma triglyceride (TG) and different time-of-day patterns of hepatic TG and macrosteatosis, with elevated levels of small droplet macrosteatosis compared to alcohol-fed Fl/Fl mice. Diurnal rhythms in mRNA levels of lipid metabolism transcription factors (Srebf1, Nr1h2, and Ppara) were significantly altered by alcohol and clock disruption. Alcohol and/or clock disruption significantly altered diurnal rhythms in mRNA levels of fatty acid (FA) synthesis and oxidation (Acaca/b, Mlycd, Cpt1a, Fasn, Elovl5/6, and Fads1/2), TG turnover (Gpat1, Agpat1/2, Lpin1/2, Dgat2, and Pnpla2/3), and lipid droplet (Plin2/5, Lipe, Mgll, and Abdh5) genes, along with protein abundances of p-ACC, MCD, and FASN. Lipidomics analyses showed that alcohol, clock disruption, or both significantly altered FA saturation and remodeled Valcin et al.

Transcriptional Feedback Loops in the Caprine Circadian Clock System

“…This observation is inconsistent with a previous report on human chondrocytes, which showed nearly opposite phases of BMAL1 and NR1D1 proteins ( 50 ). The antiphase of BMAL1 and NR1D1 at the mRNA and protein levels was evident in goat liver and kidney tissues ( Figures 4 , 5 ), which is consistent with a previous report in mice ( 53 , 54 ). In addition, the expression profiles of CRY1 and CRY2 in goat liver and kidney tissues were consistent with previous reports in goat whole blood, showing low expression at 10:00 h and high expression at 22:00 h ( 49 ).…”

Metabolic Profile and Lipid Metabolism Phenotype in Mice with Conditional Deletion of Hepatic BMAL1

“…Liver-clock mutant mice exhibit impaired lipid homeostasis, which is partially regulated by BMAL1/LIPIN/DGAT signaling [ 16 , 17 ]. Combined with our previous research findings, we investigated hepatic lipid metabolism in Bmal1 hep− / − mice, focusing on changes in lipolysis, lipid uptake, and synthesis.…”

Circadian rhythms and the liver

“…In turn, genetic disruption of the liver clock worsens both abnormalities in lipid metabolism and steatosis in mice fed with alcohol. 60 Randomized clinical trials on the effects of modulating meal timing (chrononutrition) on weight, adiposity, energy expenditure and hormones/metabolites circadian profiles are sparse but promising, 61 and suggest that circadian hygiene, especially in relation to meal timing, may come to play an important role in preventing MAFLD, and in breaking the vicious circle through which abnormalities in the cross-talk between metabolism and the circadian timing system sustain the onset and progression of fatty liver and steatohepatitis (Figure 2). Finally, and as for the association between MAFLD and hepatocellular carcinoma (HCC) [also in the absence of significant liver fibrosis/cirrhosis 62 ], a single but large and apparently solid US study has documented that an increase in East to West longitude within a given time zone is associated with a statistically significant increase in HCC risk in individuals under 65 years of age, 63 adding HCC to the list of neoplasms for which misalignment seems to represent a risk factor.…”

“…Further, by use of unbiased high‐throughput proteomics, acetylomics and circadian transcriptomics, Gaucher and co‐workers 59 have shown how acute and chronic alcohol consumption differentially reprogram circadian gene expression in the mouse liver. In turn, genetic disruption of the liver clock worsens both abnormalities in lipid metabolism and steatosis in mice fed with alcohol 60 . Randomized clinical trials on the effects of modulating meal timing ( chrononutrition ) on weight, adiposity, energy expenditure and hormones/metabolites circadian profiles are sparse but promising, 61 and suggest that circadian hygiene, especially in relation to meal timing, may come to play an important role in preventing MAFLD, and in breaking the vicious circle through which abnormalities in the cross‐talk between metabolism and the circadian timing system sustain the onset and progression of fatty liver and steatohepatitis (Figure 2).…”