Chronic Ethanol Consumption Disrupts the Core Molecular Clock and Diurnal Rhythms of Metabolic Genes in the Liver without Affecting the Suprachiasmatic Nucleus

Abstract

Chronic ethanol consumption disrupts several metabolic pathways including β-oxidation and lipid biosynthesis, facilitating the development of alcoholic fatty liver disease. Many of these same metabolic pathways are directly regulated by cell autonomous circadian clocks, and recent studies suggest that disruption of daily rhythms in metabolism contributes to multiple common cardiometabolic diseases (including non-alcoholic fatty liver disease). However, it is not known whether ethanol disrupts the core molecular clock in the liver, nor whether this, in turn, alters rhythms in lipid metabolism. Herein, we tested the hypothesis that chronic ethanol consumption disrupts the molecular circadian clock in the liver and potentially changes the diurnal expression patterns of lipid metabolism genes. Consistent with previous studies, male C57BL/6J mice fed an ethanol-containing diet exhibited higher levels of liver triglycerides compared to control mice, indicating hepatic steatosis. Further, the diurnal oscillations of core clock genes (Bmal1, Clock, Cry1, Cry2, Per1, and Per2) and clock-controlled genes (Dbp, Hlf, Nocturnin, Npas2, Rev-erbα, and Tef) were altered in livers from ethanol-fed mice. In contrast, ethanol had only minor effects on the expression of core clock genes in the suprachiasmatic nucleus (SCN). These results were confirmed in Per2Luciferase knock-in mice, in which ethanol induced a phase advance in PER2::LUC bioluminescence oscillations in liver, but not SCN. Further, there was greater variability in the phase of PER2::LUC oscillations in livers from ethanol-fed mice. Ethanol consumption also affected the diurnal oscillations of metabolic genes, including Adh1, Cpt1a, Cyp2e1, Pck1, Pdk4, Ppargc1a, Ppargc1b and Srebp1c, in the livers of C57BL/6J mice. In summary, chronic ethanol consumption alters the function of the circadian clock in liver. Importantly, these results suggest that chronic ethanol consumption, at levels sufficient to cause steatosis, disrupts the core hepatic clock as well as the diurnal rhythms of key lipid metabolism genes.

Chronic Alcohol Consumption in Rats Leads to Desynchrony in Diurnal Rhythms and Molecular Clocks

“…Diurnal rhythms of blood glucose, lactic acid, and cholesterol were also shifted following chronic alcohol (Rajakrishnan et al, 1999). Last, changes in the expression of clock and clock-controlled genes in the liver have been observed after chronic alcohol (Farnell et al, 2008;Filiano et al, 2013;Zhou et al, 2014). In the present study, we found multiple changes in rhythms within the HPA axis after chronic alcohol.…”

“…Pituitary: Con, U = 229, p < 0.01; Alc, U = 242.5, p < 0.01. Adrenal: Con, U = 252.2, p < 0.01; Alc, U = 170, p < 0.1. report that chronic alcohol did not affect the molecular clock in the SCN (as measured by Per2 expression) while advancing clocks in the liver (Filiano et al, 2013). Other groups have reported alterations in the rhythmic expression of clock genes in the SCN after alcohol (Chen et al, 2004(Chen et al, , 2006Farnell et al, 2008).…”

Chronic ethanol consumption disrupts diurnal rhythms of hepatic glycogen metabolism in mice

“…Eight-week-old male C57BL/6J mice were purchased from Jackson Laboratories and allowed to acclimate for at least 1 wk before they were divided into control and ethanol feeding groups. For the feeding studies, each ethanol-fed mouse was weight-matched to a control-fed mouse partner to establish the pairfeeding regimen (13). Mice were singly housed in standard husbandry boxes with bedding and kept in a temperature-and humidity-controlled environment under a 12:12-h light-dark cycle.…”

Bile Acid Signaling in Metabolic Disease and Drug Therapy

“…Alcohol treatment increased hepatic triglycerides in clock mutant mice more than in wildtype mice and altered lipogenic gene expression in clock mutant mouse liver (Kudo et al, 2009). The diurnal rhythm of many primary clock genes (Bmal1, Clock, Cry1/2, and Per1/2) and CCGs (Dbp, Npas2, and Rev-erba) were altered in alcohol-fed mouse livers (Filiano et al, 2013) and caused phase shifting of diurnal rhythm of hepatic triglycerides, cholesterol, and bile acid levels (Zhou et al, 2014). Alcohol also alters the NAD/ NADH ratio, which regulates sirtuin SIRT1 activity and downstream target genes Bmal1/Npas2/Clock (Nakahata et al, 2009).…”

“…The methylated/nonmethylated DNA ratios in CpG islands in the PGC-1a gene promoter in diabetic patients is correlated with serum insulin and a homeostasis model of assessment of insulin resistance. Chronic alcohol consumption disrupts clock genes and diurnal rhythms of liver metabolic genes (Filiano et al, 2013). However, the mechanism of ethanol effect on circadian clock expression is not clear.…”