Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Louisville, Louisville, Kentucky, USA.
Department of Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA.
Alcohol Clin Exp Res. 2022 Aug;46(8):1371-1383. doi: 10.1111/acer.14893. Epub 2022 Jul 3.
Chronic heavy alcohol consumption is a major risk factor for the development of liver steatosis, fibrosis, and cirrhosis, but the mechanisms by which alcohol causes liver damage remain incompletely elucidated. This group has reported that α4 nicotinic acetylcholine receptors (α4 nAChRs) act as sensors for alcohol in lung cells. This study tested the hypothesis that α4 nAChRs mediate the effects of alcohol in the liver.
Expression of acetylcholine receptor subunits in mouse liver was determined by RNA sequencing (RNA-seq). α4 nAChR knockout (α4 KO) mice were generated in C57BL/6J mice by introducing a mutation encoding an early stop codon in exon 4 of Chrna4, the gene encoding the α4 subunit of the nAChR. The presence of the inactivating mutation was established by polymerase chain reaction and genomic sequencing, and the lack of α4 nAChR function was confirmed in primary fibroblasts isolated from the α4 KO mice. Wild-type (WT) and α4 KO mice were fed the Lieber-DeCarli diet (with 36% of calories from alcohol) or pair fed an isocaloric maltose-dextrin control diet for a 6-week period that included a ramping up phase of increasing dietary alcohol.
Chrna4 was the most abundantly expressed nAChR subunit gene in mouse livers. After 6 weeks of alcohol exposure, WT mice had elevated serum transaminases and their livers showed increased fat accumulation, decreased Sirt1 protein levels, and accumulation of markers of oxidative stress and inflammation including Cyp2E1, Nos2, Sod1, Slc7a11, TNFα, and PAI1. All these responses to alcohol were either absent or significantly attenuated in α4 KO animals.
Together, these observations support the conclusion that activation of α4 nAChRs by alcohol or one of its metabolites is one of the initial events promoting the accumulation of excess fat and expression of inflammatory mediators. Thus, α4 nAChRs may represent viable targets for intervention in chronic alcohol-related liver disease.
慢性大量饮酒是导致肝脂肪变性、纤维化和肝硬化的主要危险因素，但酒精引起肝损伤的确切机制仍不完全清楚。本研究组曾报道α4 型烟碱型乙酰胆碱受体（α4 nAChR）可作为肺细胞中酒精的传感器。本研究旨在验证α4 nAChR 是否介导酒精对肝脏的作用。
采用 RNA 测序（RNA-seq）方法检测小鼠肝脏中的乙酰胆碱受体亚基表达。利用 Chrna4 基因（编码 nAChR 的α4 亚基）第 4 外显子中的一个提前终止密码子突变，在 C57BL/6J 小鼠中生成α4 nAChR 敲除（α4 KO）小鼠。通过聚合酶链反应和基因组测序确定失活突变的存在，并通过对α4 KO 小鼠原代成纤维细胞中α4 nAChR 功能缺失的确认。将野生型（WT）和α4 KO 小鼠分别用 Lieber-DeCarli 饮食（36%的热量来自酒精）或等热量麦芽糖-糊精对照饮食喂养 6 周，包括逐渐增加饮食中酒精的阶段。
Chrna4 是小鼠肝脏中表达最丰富的 nAChR 亚基基因。在酒精暴露 6 周后，WT 小鼠血清转氨酶升高，肝脏脂肪堆积增加，Sirt1 蛋白水平降低，氧化应激和炎症标志物如 Cyp2E1、Nos2、Sod1、Slc7a11、TNFα 和 PAI1 蓄积。α4 KO 动物对酒精的所有这些反应均不存在或显著减弱。
综上所述，这些观察结果支持以下结论：酒精或其代谢物激活α4 nAChR 是促进脂肪堆积和炎症介质表达的初始事件之一。因此，α4 nAChR 可能是治疗慢性酒精相关性肝病的可行靶点。
