Mechanism Study On The Relationship Between ALDH2 Function And Liver Injury

Alcohol abuse is the leading cause of morbidity and mortality worldwide,and the liver is not only the dominating metabolic site of ethanol but also the major target organ for ethanol intoxication.ALDH2 in the hepatic mitochondria is the key enzyme responsible for the clearance of acetaldehyde,the highly toxic and carcinogenic intermediate metabolite of ethanol metabolism,while it exits both inactive and active forms in human.Subjects who carry inactive ALDH2 show extremely high acetaldehyde levels after ethanol consumption.Moreover,ALDH2 mutation has also been correlated with cell imunity.How ALDH2 and acetaldehyde influence T cell hepatitis in the presence of chronic ethanol consumptions is unclear.Moreover,whether liver injury and inflammation alter hepatic ethanol and acetaldehyde metabolism should be explored as co-existence of liver injury and excessive alcohol drinking is commonly observed in clinical practice.Part 1:Viral hepatitis and alcohol abuse usually coexist and synergistically contribute to the development of chronic hepatic disorders,while underlying mechanisms are not fully understood yet.The hallmark of viral hepatitis is the activation of T cells for viral clearance.ALDH2 is critical for the overall process of alcohol metabolism.About 40% of East Asian population have the ALDH2 variant,which leads to acetaldehyde accumulation and subsequent adverse effects after alcohol consumption.Since ALDH2 deficiency could aggravate alcohol intoxication,it's meaningful to check whether individuals with ALDH2 deficiency are more suspectable to T cell hepatitis.In the current study,we used Con A injection to stimulate T cell activation and induce hepatitis in both WT and ALDH2 KO mice under chronic alcohol diet feeding.Blood biochemistry and IHC were implied to compare the injury and inflammation levels of two groups.ELISA,flow cytometry,q PCR and western blots were used for mechanism studies.Results of Part 1:Alcohol feeding promoted T cell hepatitis caused by Con A injection in WT mice while startlingly improved Con A-induced hepatitis in ALDH2 knockout mice,although they had higher acetaldehyde levels.Cytokine production and downstream signaling pathways in the liver with Con A treatment were also suppressed in ethanol-fed ALDH2 knockout mice compared with WT controls.Acetaldehyde incubation inhibited cytokine production ability of mouse primary splenocytes or human T cells in vitro induced by Con A or PHA treatment.Mechanistically,acetaldehyde dampened T cell glucose metabolism by downregulating aerobic glycolysis signals.Last but not least,ALDH2 knockout mice showed higher corticosterone levels after ethanol feeding compared to WT mice and blocking corticosterone in vivo partially restored Con A hepatitis in ethanol-fed ALDH2 knockout mice.In conclusion,ALDH2 deficiency relates to high acetaldehyde and corticosteroids levels after ethanol consumption,which accordingly interferes with T cell function and hepatitis.Part 2:The disruptive role of alcohol toxicity in the development of various liver diseases have been well studied,as polymorphisms of major enzymes involved in alcohol metabolism have been shown participating in live disease progression.While,the extent to which the specific steps of alcohol metabolism is affected by hepatic injury and what influence it could pose on mouse drinking pattern still need to be explored.In the current study,we utilized three commonly used mouse models of acute or chronic liver injury to explore the influence of hepatic lesion and inflammation on ethanol metabolisms and mouse drinking patterns.We measured enzymatic activities,gene expressions and protein levels of hepatic ADH1 and ALDH2.Using GC-MS,in vivo acetaldehyde levels were determined as direct evidence of impaired ethanol metabolism.Two behavior models,two-bottle paradigm and the drinking in the dark binge-like model,were used to study drinking behaviors of mice.Results of Part 2:Acute LPS,and acute/chronic CCl4 induced liver injury inhibited hepatic ALDH2 expression and activity,which consequently led to elevated acetaldehyde concentrations in mouse liver and circulation.Moreover,LPS and chronic CCl4 induced liver injury suppressed ADH1 activity and expression and subsequently increased blood and liver ethanol concentrations.All injured mice showed reduced drinking behaviors,in line with damaged alcohol metabolism.Mechanistically,oxidative stress could inhibit ADH1 and ALDH2 activity of hepatocytes post-transcriptionally in vitro,while proinflammatory cytokines caused transcriptional suppression of ADH1 and ALDH2,via influencing transcription factor HNF4?.In all,we conclude that inflammation and oxidative stress during liver injury sufficiently repress alcohol metabolism,further decreases drinking behavior.