Effects of nicotine on microRNA-124 expression in bile duct ligation-induced liver fibrosis in rats

Nicotine, the main compound of smoking may exert its effects by changing the expression of microRNAs (miRNAs). This study was conducted to further investigate the molecular mechanisms of miRNA-dependent effects of nicotine in an animal model of liver fibrosis. The bile duct ligation (BDL) approach was used to create a model of liver fibrosis. Twenty-four male Wistar rats were used in the study. The effects of nicotine administration on miRNA-124 expression, as well as alpha-smooth muscle actin (liver fibrosis marker) and chemokine ligand 2 (an inflammatory chemokine), were investigated using RT-qPCR. In addition, the mRNA and protein expression of signal transducer and activator of transcription 3 (STAT-3; as a potential target for miRNA-124) were investigated by RT-qPCR and immunofluorescence, respectively. Liver enzyme activity levels were measured using a colorimetric assay. In addition, the effects of nicotine on the process of liver fibrosis were investigated with histological studies. The development of liver fibrosis in BDL rats and nicotine administration led to a decrease in miRNA-124 expression. The decrease in the expression is accompanied by the increase in the expression of fibrotic and proinflammatory genes. Also, an increase in STAT-3 mRNA and protein expression was observed in the fibrotic rats that received nicotine. In addition, the significant increase in bilirubin and liver enzymes in fibrotic rats worsens with nicotine administration. The results of histological studies also confirm these results. Considering that miRNA-124 is an anti-inflammatory miRNA, it can be concluded that the decrease in its expression due to nicotine exposure leads to an increase in inflammatory processes and subsequently to an increase in liver fibrosis.