Novel role for carbohydrate responsive element binding protein in the control of ethanol metabolism and susceptibility to binge drinking

Abstract

Carbohydrate responsive element binding protein (ChREBP) is central for de novo fatty acid synthesis under physiological conditions and in the context of nonalcoholic fatty liver disease. We explored its contribution to alcohol-induced steatosis in a mouse model of binge drinking as acute ethanol (EtOH) intoxication has become an alarming health problem. Within 6 hours, ChREBP acetylation and its recruitment onto target gene promoters were increased in liver of EtOH-fed mice. Acetylation of ChREBP was dependent on alcohol metabolism because inhibition of alcohol dehydrogenase (ADH) activity blunted ChREBP EtOH-induced acetylation in mouse hepatocytes. Transfection of an acetylation-defective mutant of ChREBP (ChREBP K672A ) in HepG2 cells impaired the stimulatory effect of EtOH on ChREBP activity. Importantly, ChREBP silencing in the liver of EtOH-fed mice prevented alcohol-induced triglyceride accumulation through an inhibition of the lipogenic pathway but also led, unexpectedly, to hypothermia, increased blood acetaldehyde concentrations, and enhanced lethality. This phenotype was associated with impaired hepatic EtOH metabolism as a consequence of reduced ADH activity. While the expression and activity of the NAD 1 dependent deacetylase sirtuin 1, a ChREBP-negative target, were down-regulated in the liver of alcohol-fed mice, they were restored to control levels upon ChREBP silencing. In turn, ADH acetylation was reduced, suggesting that ChREBP regulates EtOH metabolism and ADH activity through its direct control of sirtuin 1 expression. Indeed, when sirtuin 1 activity was rescued by resveratrol pretreatment in EtOH-treated hepatocytes, a significant decrease in ADH protein content and/or acetylation was observed. Conclusion: Our study describes a novel role for ChREBP in EtOH metabolism and unravels its protective effect against severe intoxication in response to binge drinking. (HEPATOLOGY 2015;62:1086-1100 Abbreviations: ADH; alcohol dehydrogenase; ALD, alcoholic liver disease; ALDH, acetaldehyde dehydrogenase; ALT, alanine aminotransferase; AST, aspartate aminotransferase; ChIP, chromatin immunoprecipitation; ChoRE, carbohydrate responsive element; ChREBP, carbohydrate responsive element binding protein; CoA, coenzyme A; CYP2E1, cytochrome P450 2E1 enzyme; DM, dextrin-maltose; Elvol6, elongase 6; EtOH, ethanol; FAS, fatty acid synthase; [G5]/[G25], 5 mM and 25 mM glucose concentration; GPAT, glycerol phosphate acyltransferase; L-PK, liver-pyruvate kinase; 4MP, 4-methylpyrazole; mRNA, messenger RNA; NAD 1 , oxidized form of reduced nicotinamide adenine dinucleotide; NADH, reduced nicotinamide adenine dinucleotide; PGC1a, peroxisome proliferator-activated receptor gamma coactivator 1-a; qPCR, quantitative real-time polymerase chain reaction; Re-ChIP, sequential chromatin immunoprecipitation; SCD1, stearoyl-CoA desaturase 1; SEM, standard error of the mean; sh, short hairpin; SIRT1, deacetylase sirtuin 1; SREBP-1c, sterol regulatory element binding protein-1c; TG, triglyceride.From the

Ethanol-induced hepatic steatosis is modulated by glycogen level in the liver

“…that controls transcription of a range of genes involved in free fatty acid transport and oxidation. Recently, it was discovered that the activity ChREBP, an important transcription factor for de novo fatty acid synthesis ( 22 ), is elevated by alcohol exposure ( 24,25 ). In our experimental setting, we found that the mRNA level of ChREBP was not increased by EtOH treatment.…”

The hepatic BMAL1/AKT/lipogenesis axis protects against alcoholic liver disease in mice via promoting PPARα pathway

“…SREBP‐1c has been implicated as a direct downstream effector of AKT‐mTORC1 signaling in insulin‐induced de novo lipogenesis, whereas ChREBP has been more associated with high carbohydrate feeding, in particular, fructose feeding . A recent study showed loss of Chrebp may sensitize mice from binge‐drinking‐induced liver injury . We observed that L‐pk , the hallmark target of ChREBP, was reduced in the liver of both Bmal1‐LKO and mice with liver specific depletion of Bmal1 but induced in Ad‐ Bmal1 liver (Fig.…”

Lipogenic transcription factor ChREBP mediates fructose-induced metabolic adaptations to prevent hepatotoxicity

“…ChREBP deficiency in diabetic mice alleviates liver steatosis and improves glucose metabolism (9,10). In addition, ChREBP was found to regulate ethanol metabolism and modulate the degree of ethanol-induced liver injury (11). These studies suggest that ChREBP may regulate liver pathophysiology in a context-dependent manner.…”

“…These data highlight the importance of the proper control of UPR and ER stress activity in hepatocytes in the presence of fructose influx and highlight the essential role of ChREBP in maintaining normal liver functions by suppressing the PERK-CHOP branch of the UPR. Recent work from the Postic group demonstrated that ChREBP is important for protecting the liver by regulating ethanol metabolism via sirtuin 1 (SIRT1) (11). It will be interesting to examine the role of the ChREBP-controlled UPR pathway in alcohol-induced liver injury models.…”