Group II muscarinic acetylcholine receptors attenuate hepatic injury via Nrf2/ARE pathway.

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.

Muscarinic receptor mediated signaling pathways in hepatocytes from CCL4 - induced liver fibrotic rat.

The pathological changes of parasympathetic nerves are considered as an independent prognostic factor of the survival rate for patients with chronic liver disease. The non-selective muscarinic acetylcholine receptors (mAchR) agonists and antagonists can affect the proliferation of hepatocytes, but little is known about the role of mAChR in hepatocytes and hepatic fibrosis and the signaling pathway of this receptor in regulation of hepatocytes remains elusive. Here, 3ml/kg 40% carbon tetrachloride (CCL4) was given to induce hepatic fibrosis in rats and the hepatocytes were isolated to investigate the expression of mAchR and the cell signaling pathways which were involved in. Compared with the normal state, the expression levels of m1, 3, 5 in fibrotic hepatocytes (FHC) and the cells treated with 10µM pilocarpine (Pi) were obviously increased, while decreased in m2,4. Pi could increase the value of alanine aminotransferase (ALT), hydroxyproline (Hyp), decrease albumin (ALB) and cell viability, while atropine could ameliorate fibrotic hepatocytes fuction. The p-AKT, p-ERK, p- JNK and p-P38 increased in Pi group or FHC group, but the inhibitors of PI3K, MAPK and PKC could reverse the Pi action and improve the FHC fuction. In this study we found that mAchR played an important role in the regulation of hepatic fibrosis process and the PKC, ERK, P38 and PI3K/AKT signaling pathways involved in the parasympathetic excitation mediated by mAchR.

Expression of muscarinic acetylcholine receptors in hepatocytes from rat fibrotic liver.

The pathological changes of parasympathetic nerve are considered as an independent prognostic factor of the survival rate of patients with chronic liver disease. The non-selective muscarinic acetylcholine receptors (mAchR) agonists and antagonists can affect the proliferation of hepatocytes and hepatic stellate cells, but the subtypes of mAchR expressions in HCs are still uncertain. Here, we investigate the expression of mAchR in hepatic fibrosis on rats. 3ml/kg 40% carbon tetrachloride (CCL4) was given to induce hepatic fibrosis on rats and the hepatocytes were isolated. Compared to the normal state, the expression levels of m1, 3, 5 in fibrotic liver tissues or hepatocytes were obviously increased, while m2, 4 decreased. 10µM pilocarpine or 10µM acetylcholine could increase the alanine aminotransferase (ALT), hydroxyproline (Hyp), collagen I, III in the hepatocytes, and decreased albumin (ALB). They also changed the expressions of mAchR similarly as the fibrotic hepatocytes and livers. However, atropine could ameliorate the state of fibrotic hepatocytes. These data indicate that mAchR played an important role in the regulation of hepatic fibrosis process. Targeting mAchR would have therapeutic potential for hepatic fibrosis.