Chronic Ethanol Metabolism Inhibits Hepatic Mitochondrial Superoxide Dismutase via Lysine Acetylation

Abstract

Background Chronic ethanol consumption is a major cause of liver disease worldwide. Oxidative stress is a known consequence of ethanol metabolism and is thought to contribute significantly to alcoholic liver disease (ALD). Therefore, elucidating pathways leading to sustained oxidative stress and downstream redox imbalances may reveal how ethanol consumption leads to ALD. Recent studies suggest that ethanol metabolism impacts mitochondrial antioxidant processes through a number of proteomic alterations, including hyperacetylation of key antioxidant proteins. Methods In order to elucidate mechanisms of ethanol-induced hepatic oxidative stress, we investigate a role for protein hyperacetylation in modulating mitochondrial superoxide dismutase (SOD2) structure and function in a 6-week Lieber-DeCarli murine model of ethanol consumption. Our experimental approach includes immunoblotting, immunohistochemistry, activity assays, mass spectrometry, and in silico modeling. Results We found that ethanol metabolism significantly increased the acetylation of SOD2 at two functionally relevant lysine sites, K68 and K122, resulting in a 40% decrease in enzyme activity while overall SOD2 abundance was unchanged. In vitro studies also reveal which lysine residues are more susceptible to acetylation. Immunohistochemical analysis demonstrates that SOD2 hyperacetylation occurs near zone 3 within the liver, which is the main ethanol-metabolizing region of the liver. Conclusion Overall, the findings presented in this study support a role for ethanol-induced lysine acetylation as an adverse post-translational modification within the mitochondria that directly impacts SOD2 charge-state and activity. Lastly, the data presented here indicate that protein hyperacetylation may be a major factor contributing to an imbalance in hepatic redox homeostasis due to chronic ethanol metabolism.

Mitochondrial Oxidative Stress and Antioxidants Balance in Fatty Liver Disease

“…Similar to the status of SOD2 in NAFLD, the role of alcohol on SOD2 regulation is controversial, with findings indicating increased expression, no change, or decreased expression . Moreover, recent findings underscore that chronic ethanol metabolism inhibits hepatic SOD2 through lysine acetylation, without change in SOD2 expression . Interestingly, the lysine acetylation–mediated inactivation of SOD2 was preferentially seen in zone 3 of the liver, where most of the ethanol metabolism takes place.…”

Alcohol Metabolizing Enzymes, Microsomal Ethanol Oxidizing System, Cytochrome P450 2E1, Catalase, and Aldehyde Dehydrogenase in Alcohol-Associated Liver Disease

“…ALD has been shown to be associated with increase in lipid peroxidation, formation of 1-hydroxyethyl radical and lipid radicals, and decrease in hepatic antioxidants, especially glutathione [67,82,124]. In addition to the role of CYP2E1-induced oxidative stress, alcohol can also acetylate mitochondrial superoxide dismutase and impact its antioxidant ability [125]. Changes in diets that either promote or reduce oxidative stress have an impact on the degree of liver injury.…”

Pathogenesis, Early Diagnosis, and Therapeutic Management of Alcoholic Liver Disease

“…Activation of antioxidant genes such as Nrf-2, [38] NF-κB, superoxide dismutase, [95,96] catalase, glutathione, peroxidase-1, metallothionein, and peroxiredoxin-1 [97,98] is the targeted treatment for ALD caused by oxidative stress. Furthermore, the drugs inhibit CYP2E1, reduce reactive oxygen species, promote PPARα and activate SIRT1, AMPK, [99] HO-1, [100] and other pathways that can be used for the treatment of ALD.…”