Honokiol inhibits epithelial-mesenchymal transition and hepatic fibrosis via activation of Ecadherin/GSK3β/JNK and inhibition of AKT/ERK/p38/β-catenin/TMPRSS4 signaling axis

Though Honokiol was known to have anti-inflammatory, antioxidant, anticancer, antithrombotic, anti-viral, metabolic, antithrombotic, and neurotrophic activities, the underlying mechanisms of Honokiol on epithelial-mesenchymal transition (EMT) mediated liver fibrosis still remain elusive so far. Anti-EMT and antifibrotic effects of Honokiol were explored in murine AML-12 hepatocyte cells by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, wound healing assay, Western blotting and also in CCl4-induced liver injury mouse model by immunohistochemistry. Honokiol significantly suppressed transforming growth factor beta 1 (TGF-beta 1)-induced EMT and migration of AML-12 cells along with decreased EMT phenotypes such as loss of cell adhesion and formation of fibroblast like mesenchymal cells in TGF beta 1-treated AML-12 cells. Consistently, Honokiol suppressed the expression of Snail and transmembrane protease serine 4 (TMPRSS4), but not p-Smad3, and activated Ecadherin in TGF-beta 1-treated AML-12 cells. Additionally, Honokiol reduced the expression of beta-catenin, p-AKT, p-ERK, p-p38 and increased phosphorylation of glycogen synthase kinase 3 beta (GSK3 beta) and JNK in TGF-beta 1-treated AML-12 cells via TGF-beta 1/ nonSmad pathway. Conversely, GSK3 beta inhibitor SB216763 reversed the ability of Honokiol to reduce Snail, beta-catenin and migration and activate E-cadherin in TGF beta 1-treated AML-12 cells. Also, Honokiol suppressed hepatic steatosis and necrosis by reducing the expression of TGF-beta 1 and a-SMA in liver tissues of CCl4 treated mice. These findings provide scientific evidence that Honokiol suppresses EMT and hepatic fibrosis via activation of E-cadherin/GSK3 beta/JNK and inhibition of AKT/ERK/p38/ beta-catenin/TMPRSS4 signaling axis.