ALDH2 deficiency promotes alcohol-associated liver cancer by activating oncogenic pathways via oxidized DNA enriched extracellular vesicles

Abstract Background & Aims Excessive alcohol drinkingis one of the major causes of hepatocellular carcinoma ( HCC). Approximately 30-40% Asian population are deficient for aldehyde dehydrogenase2 ( ALDH2), a key enzyme to detoxify the ethanol metabolite acetaldehyde. However, how ALDH2deficiency affects alcohol-related HCCremains obscure. Methods ALDH2polymorphism in 646 patients with viral hepatitis B (HBV) infection with or without alcohol drinkingwas studied. A new model of HCCinduced by chronic carbon tetrachloride (CCl 4 ) and alcohol administration was developed and studied in three lines of Aldh2-deficient mice: including Aldh2global knockout (KO) mice, Aldh2* 1/ * 2 knock-in mutant mice, and liver-specific Aldh2KO mice. Results We demonstrated that ALDH2deficiency was not associated with liver disease progression but was associated with an increased risk of HCCdevelopment in cirrhotic HBV patients with excessive alcohol consumption. The mechanisms underlying HCCdevelopment associated with cirrhosis and alcohol consumption were studied in Aldh2-deficient mice. We found that all three lines of Aldh2-deficient mice were more susceptible to CCl 4 plus alcohol-associated liver fibrosis and HCCdevelopment. Furthermore, our results from in vivo and in vitro mechanistic studies revealed that after CCl 4 plus ethanol exposure, Aldh2-deficient hepatocytes produced a large amount of harmful oxidized mtDNA via extracellular vesicles(EVs) , which were then transferred into neighboring HCCcells and together with acetaldehyde activated multiple oncogenic pathways (JNK, STAT3, BCL-2, and TAZ), thereby promoting HCC. Conclusions ALDH2deficiency is associated with an increased risk of alcohol related- HCCdevelopment from fibrosis in patients and in mice. Mechanistic studies reveal a novel mechanism that Aldh2-deficient hepatocytes promote alcohol-associated HCCby transferring harmful oxidized mtDNA-enriched EVs into HCCand subsequently activating multiple oncogenic pathways in HCC. Lay Summary Alcoholics with ALDH2polymorphism have an increased risk of digestive track cancer development, however, the link between ALDH2deficiency and HCCdevelopment has not been well established. In this study, we show that ALDH2deficiency exacerbates alcohol-associated HCCdevelopment both in patients and mouse models. Mechanistic studies revealed that after chronic alcohol exposure, Aldh2-deficient hepatocytes produce a large amount of harmful oxidized mitochondrial DNA via extracellular vesicles, which can be delivered into neighboring HCCcells and subsequently activate multiple oncogenic pathways, thereby promoting HCC.