Auta James, Zhang Huaibo, Pandey Subhash C, Guidotti Alessandro
Center for Alcohol Research in Epigenetics , Department of Psychiatry, College of Medicine, University of Illinois at Chicago, Chicago, Illinois.
Jesse Brown VA Medical Center , Chicago, Illinois.
Alcohol Clin Exp Res. 2017 Jun;41(6):1105-1111. doi: 10.1111/acer.13382. Epub 2017 Apr 25.
Epigenetic mechanisms such as DNA methylation play an important role in regulating the pathophysiology of alcoholism. Chronic alcohol exposure leads to behavioral changes as well as decreased expression of genes associated with synaptic plasticity. In the liver, it has been documented that chronic alcohol exposure impairs methionine synthase (Ms) activity leading to a decrease in S-adenosyl methionine/S-adenosyl homocysteine (SAM/SAH) ratio which results in DNA hypomethylation; however, it is not known whether similar alterations of SAM and SAH levels are also produced in brain.
Male adult Sprague Dawley rats were fed chronically with Lieber-DeCarli ethanol (EtOH) (9% v/v) or control diet. The EtOH-diet-fed rats were withdrawn for 0 and 24 hours. The cerebellum and liver tissues were dissected and used to investigate changes in one-carbon metabolism, SAM, and SAH levels.
We found that chronic EtOH exposure decreased SAM levels, SAM/SAH ratio, Ms, methylene tetrahydrofolate reductase, and betaine homocysteine methyltransferase (Bhmt) expression and increased methionine adenosyltransferase-2b (Mat2b) but not Mat2a expression in the liver. In contrast, chronic EtOH exposure decreased SAH levels, increased SAM/SAH ratio and the expression of Mat2a and S-adenosyl homocysteine hydrolase, while the levels of SAM or Bhmt expression in cerebellum remained unaltered. However, in both liver and cerebellum, chronic EtOH exposure decreased the expression of Ms and increased Mat2b expression. All chronic EtOH-induced changes of one-carbon metabolism in cerebellum, but not liver, returned to near-normal levels during EtOH withdrawal.
These results indicate a decreased "methylation index" in liver and an increased "methylation index" in cerebellum. The opposing changes of the "methylation index" suggest altered DNA methylation in liver and cerebellum, thus implicating one-carbon metabolism in the pathophysiology of alcoholism.
DNA甲基化等表观遗传机制在调节酒精中毒的病理生理过程中起着重要作用。长期酒精暴露会导致行为改变以及与突触可塑性相关基因的表达降低。在肝脏中，已有文献记载长期酒精暴露会损害甲硫氨酸合成酶（Ms）的活性，导致S-腺苷甲硫氨酸/ S-腺苷同型半胱氨酸（SAM/SAH）比值降低，从而引起DNA低甲基化；然而，尚不清楚大脑中是否也会产生类似的SAM和SAH水平变化。
成年雄性Sprague Dawley大鼠长期喂食Lieber-DeCarli乙醇（EtOH）（9% v/v）或对照饮食。喂食乙醇饮食的大鼠分别戒断0小时和24小时。解剖小脑和肝脏组织，用于研究一碳代谢、SAM和SAH水平的变化。
我们发现，长期乙醇暴露会降低肝脏中SAM水平、SAM/SAH比值、Ms、亚甲基四氢叶酸还原酶和甜菜碱同型半胱氨酸甲基转移酶（Bhmt）的表达，并增加甲硫氨酸腺苷转移酶-2b（Mat2b）的表达，但不会增加Mat2a的表达。相比之下，长期乙醇暴露会降低小脑的SAH水平，增加SAM/SAH比值以及Mat2a和S-腺苷同型半胱氨酸水解酶的表达，而小脑的SAM水平或Bhmt表达保持不变。然而，在肝脏和小脑中，长期乙醇暴露都会降低Ms的表达并增加Mat2b的表达。在戒断期间，所有长期乙醇诱导的小脑（而非肝脏）一碳代谢变化都恢复到接近正常水平。
这些结果表明肝脏中的“甲基化指数”降低，而小脑中的“甲基化指数”增加。“甲基化指数”的相反变化表明肝脏和小脑中的DNA甲基化发生了改变，从而提示一碳代谢参与了酒精中毒的病理生理过程。
