Our findings suggest that the effect of acute EtOH gavage on hepatic autophagy differs significantly from that after chronic EtOH feeding. Each regimen distinctly affects TFEB localization, which in turn, regulates hepatic autophagy and lysosome biogenesis.
Our findings demonstrate that ethanol metabolism generates oxidants, the levels of which differentially influence the activities of the proteasome and autophagy.
Background
Previous work demonstrated that the transcription factor, early growth response-1 (Egr-1) participates in the development of steatosis (fatty liver) after chronic ethanol administration. Here, we determined the extent to which Egr-1 is involved in fatty liver development in mice subjected to acute ethanol administration.
Methods
In acute studies, we treated both wild type and Egr-1 null mice with either ethanol or phosphate-buffered saline (PBS) by gastric intubation. At various times after treatment, we harvested sera and livers and quantified endotoxin, indices of liver injury, steatosis, and hepatic Egr-1 content. In chronic studies, groups of mice were fed liquid diets containing either ethanol or isocaloric maltose-dextrin for 7-8 weeks.
Results
Compared with controls, acute ethanol-treated mice showed a rapid, transient elevation in serum endotoxin beginning 30 minutes after treatment. One hour post-gavage, livers from ethanol-treated mice exhibited a robust elevation of both Egr-1 mRNA and protein. By three hours post-gavage, liver triglyceride increased in ethanol-treated mice as did lipid peroxidation. Acute ethanol treatment of Egr-1-null mice showed no Egr-1 expression, but these animals still developed elevated triglycerides, although significantly lower than ethanol-fed wild-type littermates. Despite showing decreased fatty liver, ethanol-treated Egr-1 null mice exhibited greater liver injury. After chronic ethanol feeding, steatosis and liver enlargement were clearly evident, but there was no indication of elevated endotoxin. Egr-1 levels in ethanol-fed mice were equal to those of pair-fed controls.
Conclusions
Acute ethanol administration induced the synthesis of Egr-1 in mouse liver. However, despite its robust increase, the transcription factor had a smaller, albeit significant, function in steatosis development after acute ethanol treatment. We propose that the rise in Egr-1 after acute ethanol is an hepatoprotective adaptation to acute liver injury from binge drinking that is triggered by ethanol metabolism and elevated levels of endotoxin.
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