Expression and significance of fat mass and obesity associated gene and forkhead transcription factor O1 in non-alcoholic fatty liver disease

Abstract

Background Non-alcoholic fatty liver disease (NAFLD) is a complex disorder and has been closely linked to obesity. The fat mass and obesity-associated (FTO) gene is a newly discovered gene related to obesity, which enhances oxidative stress and lipogenesis in NAFLD. The forkhead transcription factor O1 (FoxO1) is another important gene involved in NAFLD, which causes lipid disorders when insulin resistance appears in the liver. However, the interactions between FTO and FoxO1 during the pathogenesis of NAFLD have not been fully elucidated. This study was designed to identify the relationship between these two factors that are involved in the development of NAFLD. Methods This study includes two parts referred to as animal and cell experiments. Twelve female SPF C57BL/6 mice were fed a high-fat diet to serve as an NAFLD animal model. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), total triglyceride (TG), total cholesterol (TC), alkaline phosphatase (ALP), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) were measured. Immunohistochemical analysis was used to detect the expression and histological localization of FTO, FoxO1, and adenosine monophosphate (AMP)-activated protein kinase (AMPK). The L02 cells were exposed to high fat for 24, 48, or 72 hours. Oil red O staining was used to detect intracellular lipid droplets. Reverse transcription-polymerase chain reaction was used for analyzing the levels of FTO and FoxO1 mRNA. Results At the end of 10 weeks, ALP, ALT, AST, and LDL were significantly increased (P <0.01), while TC and TG were also significantly higher (P <0.05). In addition, HDL was significantly decreased (P <0.05). The FTO and FoxO1 proteins were weakly expressed in the control group, but both FTO and FoxO1 were expressed significantly higher (P <0.01) in the experimental group, and the expression of the two factors was significantly correlated. AMPK in the high-fat group showed a low level of correlation with FTO, but not with FoxO1. Oil Red O staining results showed that the cells cultured in 50% fetal bovine serum for 24, 48, or 72 hours exhibited steatosis. FTO and FoxO1 mRNA were increased in the high-fat group compared with the normal group (P <0.01). The expression levels of FTO and FoxO1 mRNA were the highest at 48 hours (P <0.05). Conclusions A high-fat diet leads to higher expression of FTO, phosphorylation of FoxO1, and decreased phosphorylation of AMPK. These results suggest that the interactions between FTO and FoxO1 are closely related to the pathogenesis of NAFLD.