Parasympathetic nervous system dysfunction is common in patients with liver disease. We have previously shown that muscarinic acetylcholine receptors (mAchRs) play an important role in the regulation of hepatic fibrosis and that the receptor agonists and antagonists affect hepatocyte proliferation. However, little is known about the impact of the different mAchR subtypes and associated signaling pathways on liver injury. Here, we treated the human liver cell line HL7702 with 10 mmol/L carbon tetrachloride (CCL4) to induce hepatocyte damage. We found that CCL4 treatment increased the protein levels of group I mAchRs (M1, M3, M5) but reduced the expression of group II mAchRs (M2, M4) and activated the Nrf2/ARE and MAPK signaling pathways. Although overexpression of M1, M3, or M5 led to hepatocyte damage with an intact Nrf2/ARE pathway, overexpression of M2 or M4 increased, and siRNA-mediated knockdown of either M2 or M4 decreased the protein levels of Nrf2 and its downstream target genes. Moreover, CCL4 treatment increased serum ALT levels more significantly, but only induced slight changes in the expression of mAchRs, NQO1 and HO1, while reducing the expression of M2 and M4 in liver tissues of Nrf2−/− mice compared to wild type mice. Our findings suggest that group II mAchRs, M2 and M4, activate the Nrf2/ARE signaling pathway, which regulates the expression of M2 and M4, to protect the liver from CCL4-induced injury.

副交感神经系统功能障碍在肝病患者中很常见。以前我们已经证明毒蕈碱型乙酰胆碱受体（mAchRs）在肝纤维化的调节中起着重要作用，并且受体激动剂和拮抗剂会影响肝细胞的增殖。但是，关于不同的mAchR亚型和相关的信号通路对肝损伤的影响知之甚少。在这里，我们用10 mmol / L四氯化碳（CCL4）处理人肝细胞系HL7702，以诱导肝细胞损伤。我们发现，CCL4处理可增加I类mAchRs（M1，M3，M5）的蛋白水平，但降低II类mAchRs（M2，M4）的表达并激活Nrf2 / ARE和MAPK信号通路。尽管M1，M3或M5的过度表达导致了完整的Nrf2 / ARE途径对肝细胞的损害，M2或M4的过表达增加，并且siRNA介导的M2或M4的敲低降低Nrf2及其下游靶基因的蛋白质水平。此外，与野生型小鼠相比，CCL4处理更明显地提高了血清ALT水平，但仅引起mAchRs，NQO1和HO1表达的轻微变化，同时降低了Nrf2-/-小鼠肝脏组织中M2和M4的表达。我们的发现表明，II类mAchRs，M2和M4激活Nrf2 / ARE信号通路，调节N2和M4的表达，以保护肝脏免受CCL4诱导的损伤。但是与野生型小鼠相比，Nchf2-/-小鼠肝脏组织中的Mach和M4和M4的表达却降低了，但是只诱导了mAchRs，NQO1和HO1的表达发生了细微的变化。我们的发现表明，II类mAchRs，M2和M4激活Nrf2 / ARE信号通路，调节N2和M4的表达，以保护肝脏免受CCL4诱导的损伤。但是与野生型小鼠相比，Nchf2-/-小鼠肝脏组织中的Mach和M4和M4的表达却降低了，但是只诱导了mAchRs，NQO1和HO1的表达发生了细微的变化。我们的发现表明，II类mAchRs，M2和M4激活Nrf2 / ARE信号通路，调节N2和M4的表达，以保护肝脏免受CCL4诱导的损伤。