Chronic ethanol-mediated hepatocyte apoptosis links to decreased TET1 and 5-hydroxymethylcytosine formation

The 5-hydroxymethylcytosine (5hmc) is a newly identified epigeneticmodification thought to be regulated by the TET family of proteins. Little information is available about how ethanol consumption may modulate 5hmC formation and alcoholic liver disease (ALD) progression. A rat ALD model was used to study 5hmC in relationship to hepatocyte apoptosis. Human ALD liver samples were also used to validate these findings. It was found that chronic ethanol feedingsignificantlyreduced5hmCformationinaratALDmodel.TherewerenosignificantchangesinTET2and TET3between the control- andethanol-fed animals. In contrast,methylcytosinedioxygenaseTET1(TET1) expressionwas substantially reduced in the ethanol-fed rats and was accompanied by increased hepatocyte apoptosis. Similarly, knockdown of TET1 in human hepatocyte-like cells also significantly promoted apoptosis. Down-regulation of TET1 resulted in elevated expression of the DNA damage marker, suggesting a role for 5hmc in hepatocyte DNA damage as well. Mechanistic studies revealed that inhibition ofTET1 promoted apoptotic gene expression. Similarly, targetingTET1 activity by removing cosubstrate promoted apoptosis and DNA damage. Furthermore, treatment with 5-azacitidine significantlymimics these effects, suggesting that chronic ethanol consumption promotes hepatocyte apoptosis andDNA damageby diminishingTET1-mediated5hmCformation andDNAmethylation. In summary, the current study providesa novel molecular insight that TET1-mediated 5hmC is involved in hepatocyte apoptosis in ALD progression.