Role of CHOP in Hepatic Apoptosis in the Murine Model of Intragastric Ethanol Feeding

Abstract

BACKGROUND: CHOP is a transcriptional regulator involved in apoptosis caused by endoplasmic reticulum (ER) stress. We previously reported that CHOP as well as other ER stress response genes is induced in the liver of a murine model of intragastric ethanol feeding. This study was undertaken to determine the role of CHOP in hepatocellular apoptosis and liver injury in this model. METHODS: CHOP wild-type (+/+) mice and CHOP null (-/-) mice were fed alcohol for four weeks with glucose as control. Hematoxylin-eosin staining, TUNEL, and caspase 3 staining of liver tissues were performed for assessment of fatty liver, necroinflammation, and apoptosis. Total RNA was extracted for microarray and reverse transcription-PCR analyses, and proteins were used for western blotting. RESULTS: Significant increased liver/body ratio, steatosis, liver triglyceride levels, and plasma homocysteine concentrations were observed in alcohol-fed mice as compared with controls in both genotypes. There was no significant difference between wild-type and CHOP null (-/-) mice in the parameters related to fatty liver. Alcohol-induced increased serum alanine aminotransferase levels and necroinflammatory foci were not significantly reduced in CHOP null (-/-) mice. However, apoptosis was present in alcohol-fed wild-type mice but virtually absent in alcohol-fed CHOP null (-/-) mice. The ER stress response indicated by increased Grp78 mRNA was observed in both types of mice fed alcohol. Of 12,423 transcripts analyzed for >or= two-fold changes, several related to apoptosis were influenced by CHOP: Gadd45 and cathepsin B were up-regulated in ethanol-fed wild-type mice but not in CHOP null (-/-) mice, whereas Jun D and Bcl-xL were down-regulated in ethanol-fed wild-type mice but not in ethanol-fed CHOP null (-/-) mice. CONCLUSIONS: CHOP null (-/-) mice have remarkable absence of hepatocellular apoptosis in response to alcohol feeding but no protection against hyperhomocysteinemia, ER stress, and fatty liver. Thus, CHOP up-regulation occurs downstream of and contributes to one manifestation of ER stress, namely, apoptosis. Microarray studies confirmed by PCR analysis and western blotting indicate that genes affected by CHOP are both proapoptotic and antiapoptotic and CHOP induction by ethanol may tip the balance of cell survival and death toward apoptosis.