Taurochenodeoxycholic Acid Inhibits Hepatic Stellate Cell Activation To Alleviate Liver Fibrosis Through The Hippo/YAP Pathway

Liver disease is a common problem in animal production and pet rearing,and it has an important impact on the health and productivity of animals and chronic liver diseases are a major health problem worldwide,affecting approximately 800 million people globally and causing around 2 million deaths annually.In chronic liver disease,fibrosis is a common process and important feature of disease progression,which has a significant impact on patients’ quality of life and prognosis.Unfortunately,there are currently no officially approved specific drugs for the treatment of fibrosis.Hepatic stellate cells(HSC)are the key precursor cells of myofibroblasts and essential cells in liver fibrosis,and inhibiting the activation of HSCs is an important method for treating liver fibrosis.The Hippo/YAP signaling pathway has been considered an important factor in the activation of HSCs in some studies and can serve as a key target for inhibiting the activation of HSCs.Taurochenodeoxycholic Acid(TCDCA),a conjugated bile acid,is one of the main bioactive substances in animal bile synthesized from taurine and chenodeoxycholic acid in the liver,which has certain effects on antipyretic,analgesic,expectorant,antibacterial and immune regulation,but its effectiveness in the treatment of liver fibrosis is still poorly studied.In order to investigate the therapeutic effects and underlying mechanisms of TCDCA on liver fibrosis,we used biliary atresia induced fibrosis model rats and carbon tetrachloride induced fibrosis model mice as animal models and studied the efficacy of TCDCA on liver fibrosis.We also clarified the underlying mechanism by which TCDCA inhibits activation of hepatic stellate cells and alleviates liver fibrosis through regulation of Hippo/YAP pathway.The main results are as follows:1.TCDCA alleviates liver fibrosis in both rats and mice.Compared with the injury group,treatment with TCDCA in the biliary atresia induced fibrosis model rats and carbon tetrachloride induced fibrosis model mice resulted in less positive signals on Masson staining and α-SMA immunohistochemistry,lower hydroxyproline content in liver tissue,and decreased expression of fibrosis marker genes.These results indicate that TCDCA can alleviate liver fibrosis in both animal models.2.TCDCA inhibits the expression of YAP and its downstream target genes during liver fibrosis.The transcriptome sequencing results showed significant changes in Hippo/YAP pathway-related genes in both the treatment group and the injury group.q RT-PCR and Western blot detection results revealed that the core kinase Mst1 of the Hippo pathway was suppressed in the injury group,leading to significant upregulation of YAP and its downstream target genes.In contrast,the treatment group restored the activity of the Hippo pathway and inhibited the overexpression of YAP and its downstream target genes.These results suggest that TCDCA can inhibit the overexpression of YAP and its downstream target genes by activating the Hippo pathway.3.Downregulation of YAP expression inhibits the activation of hepatic stellate cells.Immunofluorescence and immunohistochemical detection were performed to further investigate the relationship between changes in YAP expression levels and the activation of hepatic stellate cells.The immunofluorescence results showed that there was a large number of activated hepatic stellate cells in the liver of the injury group,which spread to the area around the central vein.However,after TCDCA administration,the activation of hepatic stellate cells was reduced,and their spread from the portal vein to the region around the central vein was prevented.The immunohistochemical results showed that there was more co-localization of α-SMA and YAP in the hepatic stellate cells of the injury group,while only a small number of positive signals for α-SMA and YAP were found in the treatment group,and there was almost no co-localization.These results indicate that excessive activation of YAP in hepatic stellate cells in the injury group led to their differentiation into fibroblasts and ultimately resulted in severe liver fibrosis.In contrast,TCDCA administration inhibited the overexpression of YAP in the liver and reduced the activation of hepatic stellate cells,thereby alleviating the degree of liver fibrosis in rats.