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Objective: To investigate the molecular mechanism of adiponectin inhibiting activation of hepatic stellate cells in non-alcoholic fatty liver fibrosis.
Methods: The rat models of non-alcoholic fatty liver fibrosis were successfully established by fat-rich diet administration. The expression of adiponectin mRNA and protein were respectively detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. LX-2 cells were cultured in an adipogenic differentiation mixture to induce quiescent adipocytic phenotypes, and then they were treated with TGFβ1, adiponectin and TGFβ1 + adiponectin, respectively. RT-PCR and Western blot were used to determine the expressions of mRNAs and proteins of a-smooth muscle actin (a-SMA), Collagen, adenosine monophosphate-activated protein kinase (AMPK), inducible nitric oxide synthase (iNOS), and endothelial NOS (eNOS). The results were analyzed using one-way ANOVA, Student-Newman-Keuls test, and linear correlation analysis. A P value of less than 0.05 was considered as statistically significant.
Results: In vivo, with the progress of non-alcoholic fatty liver fibrosis, the model rats gradually showed hepatic steatosis, inflammation, necrosis and fibrosis. Compared with the control group, the level of serum adiponectin (2.49 ± 0.86 vs 5.81 ± 0.87, P < 0.05) and hepatic expressions of adiponectin mRNA and protein (0.26 ± 0.04 vs 0.72 ± 0.08; 0.64 ± 0.07 vs 0.21 ± 0.07, all P < 0.05) were all decreased in the 24th week group, and were negatively correlated with the level of Collagen which increased gradually. In vitro, TGFβ1 could activate quiescent LX-2 cells by decreasing mRNA and protein expression of eNOS (0.30 ± 0.10 vs 0.44 ± 0.08; 0.30 ± 0.09 vs 0.46 ± 0.07, all P < 0.05) and increasing the expression of iNOS (0.53 ± 0.07 vs 0.37 ± 0.04; 0.55 ± 0.07 vs 0.39 ± 0.05, all P < 0.05). Recombinant adiponectin not only maintained the quiescent phenotype of LX-2 cells but also inhibited LX-2 cells activation due to TGFβ1 by increasing the expression of eNOS (0.43 ± 0.08 vs 0.30 ± 0.10; 0.42 ± 0.07 vs 0.30 ± 0.09, all P < 0.05) and phosphorylation of AMPK (0.43 ± 0.07 vs 0.24 ± 0.04, P < 0.05) and decreasing the expression of iNOS (0.44 ± 0.05 vs 0.53 ± 0.07; 0.46 ± 0.07 vs 0.55 ± 0.07, all P < 0.05).
Conclusions: Data suggested that adiponectin could play a protective role on the pathogenesis of non-alcoholic fatty liver fibrosis by inhibiting the activation of hepatic stellate cells via up-regulating the expression of eNOS, which might associate with increased phosphorylation of AMPK.
