TET1 and sex differences in alcohol associated liver tumorigenesis - Project summary: Men have a high incidence of hepatocellular carcinoma (HCC) development, likely due to elevated interleukin-6 (IL-6), but clinical data suggests that women have a strong risk of HCC development if they drink alcohol heavily. Interestingly, the sex difference that females have a higher global DNA methylation than males was previously observed in the liver, suggesting the enzymes regulating DNA methylation may be involved in the said phenotype switch. The family of Ten-eleven translocation methylcytosine dioxygenases (TETs), which include (TET)1, TET2, and TET3, are suggested to participate in catalyzing DNA demethylation. Our preliminary studies reaffirmed that females have higher hepatic DNA methylation than males in mice, likely due to decreased TET1. Interestingly, TET1 was further downregulated in alcohol associated liver disease (ALD) mice with a much greater extent of reduction in females than males. These findings are unsurprised given the reasons that female sex hormones transcriptionally downregulate TET1 expression and that estrogen levels are highly elevated in patients drinking alcohol, with a 7-times higher elevation in females than males. To investigate how TET1 affects ALD, TET1 KO mice were generated and fed with an alcoholic liquid (EtOH) diet chronically. It was unexpectedly found that only female TET1 KO mice developed alcohol-associated liver fibrosis, possibly contributing to ALD-associated HCC development in the female sex. In line with this finding, liver specific TET1 KO (TET1∆Hep) female mice also developed fibrosis upon chronic alcohol feeding. Besides, it was reported that liver specific TP53 KO mice developed liver cancer in a sex dependent manner, 52.3% in male mice and 9.1% in female ones. Intriguingly, liver specific TET1 and TP53 double KO resulted in early liver tumor development without a sex difference. We also found that female TET1 KO mice have a significant downregulation of the dual specificity protein phosphatase 1 (Dusp1), which is an important suppressor in ALD/HCC development. In addition, hepatic and serum IL-6 levels were not significantly different between male and female mice fed with an EtOH diet. IL-6 was increased in TET1∆Hep female mice fed with an EtOH diet. Based on these findings, we form our central hypothesis that alcohol consumption would cause estrogen elevation in the female sex, resulting in the decreased TET1 signaling cascade, in turn contributing to ALD/HCC development. Our long-term goal is to determine the role of TET1 and sex differences in ALD with a specific focus on liver tumorigenesis. Three specific aims are proposed to achieve this goal. 1) We will determine the role of female sex and TET1 in alcohol-associated liver fibrosis in vivo. 2) We will investigate the role of TET1 and female sex hormones in alcohol-associated HCC in vivo. 3) We will decipher the mechanisms by which the estrogen-mediated TET1 downregulation alters hepatic stellate cell changes involving ALD/HCC. As TET1 is involved in sex differences in ALD injuries, the accomplishment of this study may identify TET1 as a preventive target for ALD/HCC.
