Loss of Histone Deacetylase 9 in Hepatocytes Attenuated Alcohol-Induced Hepatic Injury in Male Mice

Objectives: Excessive alcohol consumption leads to the development of alcohol-related liver disease (ALD). As alcohol can lead to epigenetic modifications to alter gene expression, we investigated whether the hepatocyte-specific deletion of histone deacetylase 9 (HDAC9), a class IIa HDAC, plays a role in the pathogenesis of ALD. Methods: Male and female (n=10/ group) Hdac9 floxed control (Hdac9fl/fl) and hepatocyte-specific Hdac9 knockout (Hdac9HKO) mice were pair-fed a Lieber-DeCarli (LD) control diet or LD containing 5% ethanol for 10 days, followed by a single binge (the chronic-binge model of ALD developed by the National Institute on Alcohol Abuse and Alcoholism). Blood and liver samples were collected for serum, gene, and protein analysis and NAD+ measurement. Results: Ethanol consumption increased hepatic cytochrome P450 2E1 (CYP2E1) protein regardless of genotypes in males and females. There was a decreasing trend of CYP2E1 protein in male and female Hdac9HKO mice compared to Hdac9fl/fl mice on the ethanol diet. With ethanol intake, Hdac9HKO mice displayed significantly less fat mass, serum triglycerides, and serum alanine transaminase activity than Hdac9fl/fl mice in males. A similar trend, albeit less, was also observed in females. Male Hdac9HKO mice on the ethanol diet exhibited significantly lower liver tissue weight, lipids, and pro-inflammatory gene expression than Hdac9fl/fl mice; however, no significant differences were detected between female genotypes. Moreover, ethanol exposure markedly reduced hepatic NAD+ levels in Hdac9fl/fl mice compared to its pair-fed control. In contrast, Hdac9 deletion in hepatocytes significantly increased hepatic NAD+ and the expression of genes involved in the NAD+ salvage pathway compared to Hdac9fl/fl mice in both males and females consuming ethanol. Conclusions: The loss of hepatocyte Hdac9 mitigated the development of ALD in males but not females. The decreased CYP2E1 and elevated NAD+ levels in the liver of Hdac9HKO mice may help attenuate the progression of hepatic steatosis and inflammation upon ethanol challenge, especially in male mice. Further studies are required to dissect the molecular mechanism to explain the sex-dependent role of hepatocyte Hdac9 in ALD development. Funding Sources: Supported by the funds from the College of Agriculture, Health and Natural Resources at the University of Connecticut.