Prolonged ER stress has been known to be one of the major drivers of impaired lipid homeostasis during the pathogenesis of non‐alcoholic liver disease (NAFLD). However, the downstream mediators of ER stress pathway in promoting lipid accumulation remain poorly understood. Here, we present data showing the b‐ZIP transcription factor E4BP4 in both the hepatocytes and the mouse liver is potently induced by the chemical ER stress inducer tunicamycin or by high‐fat, low‐methionine, and choline‐deficient (HFLMCD) diet. We showed that such an induction is partially dependent on CHOP, a known mediator of ER stress and requires the E‐box element of the E4bp4 promoter. Tunicamycin promotes the lipid droplet formation and alters lipid metabolic gene expression in primary mouse hepatocytes from E4bp4flox/flox but not E4bp4 liver‐specific KO (E4bp4‐LKO) mice. Compared with E4bp4flox/flox mice, E4bp4‐LKO female mice exhibit reduced liver lipid accumulation and partially improved liver function after 10‐week HFLMCD diet feeding. Mechanistically, we observed elevated AMPK activity and the AMPKβ1 abundance in the liver of E4bp4‐LKO mice. We have evidence supporting that E4BP4 may suppress the AMPK activity via promoting the AMPKβ1 ubiquitination and degradation. Furthermore, acute depletion of the Ampkβ1 subunit restores lipid droplet formation in E4bp4‐LKO primary mouse hepatocytes. Our study highlighted hepatic E4BP4 as a key factor linking ER stress and lipid accumulation in the liver. Targeting E4BP4 in the liver may be a novel therapeutic avenue for treating NAFLD.

Fructose over-consumption contributes to the development of liver steatosis in part by stimulating ChREBPα-driven de novo lipogenesis. However, the mechanisms by which fructose activates ChREBP pathway remain largely undefined. Here we performed affinity purification of ChREBPα followed by mass spectrometry and identified DDB1 as a novel interaction protein of ChREBPα in the presence of fructose. Depletion and overexpression of Ddb1 showed opposite effects on the ChREBPα stability in hepatocytes. We next tested the impact of hepatic Ddb1 deficiency on the fructose-induced ChREBP pathway. After 3-week high-fructose diet feeding, both Ddb1 liver-specific knockout and AAV-TBG-Cre-injected Ddb1 flox/flox mice showed significantly reduced ChREBPα, lipogenic enzymes, as well as triglycerides in the liver. Mechanistically, DDB1 stabilizes ChREBPα through CRY1, a known ubiquitination target of DDB1 E3 ligase. Finally, overexpression of a degradation-resistant CRY1 mutant (CRY1–585KA) reduces ChREBPα and its target genes in the mouse liver following high-fructose diet feeding. Our data revealed DDB1 as an intracellular sensor of fructose intake to promote hepatic de novo lipogenesis and liver steatosis by stabilizing ChREBPα in a CRY1-dependent manner.

Acetaminophen (N‐acetyl‐para‐aminophenol [APAP]) overdose is the most common cause of drug‐induced liver injury in the Western world and has limited therapeutic options. As an important dietary component intake, fructose is mainly metabolized in liver, but its impact on APAP‐induced liver injury is not well established. We aimed to examine whether fructose supplementation could protect against APAP‐induced hepatotoxicity and to determine potential fructose‐sensitive intracellular mediators. We found that both high‐fructose diet feeding before APAP injection and fructose gavage after APAP injection reduced APAP‐induced liver injury with a concomitant induction of the hepatic carbohydrate‐response element‐binding protein α (ChREBPα)–fibroblast growth factor 21 (FGF21) pathway. In contrast, Chrebpα liver‐specific‐knockout (Chrebpα‐LKO) mice failed to respond to fructose following APAP overdose, suggesting that ChREBPα is the essential intracellular mediator of fructose‐induced hepatoprotective action. Primary mouse hepatocytes with deletion of Fgf21 also failed to show fructose protection against APAP hepatotoxicity. Furthermore, overexpression of FGF21 in the liver was sufficient to reverse liver toxicity in APAP‐injected Chrebpα‐LKO mice. Conclusion: Fructose protects against APAP‐induced hepatotoxicity likely through its ability to activate the hepatocyte ChREBPα–FGF21 axis.