Suppression of retinol-binding protein 4 with RNA oligonucleotide prevents high-fat diet-induced metabolic syndrome and non-alcoholic fatty liver disease in mice

Abstract

Conflicting data have been reported regarding the role of retinol-binding protein (RBP4) in insulin resistance, obesity, type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). In this study, we used pharmacological methods to investigate the role of RBP4. RNA oligonucleotide against RBP4 (anti-RBP4 oligo) was transfected into 3T3-L1 adipocytes. RT-PCR analysis showed that RBP4 mRNA expression decreased by 55% (p<0.01) compared with control cells. Validated RNA oligo was used in an in vivo study with high fat diet (HFD) fed — mice. 14weeks of HFD feeding increased RBP4 expression (associated with elevated serum levels measured with immunoblotting and ELISA) by 56% in adipose tissue (p<0.05) and 68% in the liver (p<0.01). Adipose RBP4 levels were significantly reduced after 4weeks treatment with anti-RBP4 oligo (25mg/kg, p<0.01) and rosiglitazone (RSG, 10mg/kg, p<0.05) compared with scrambled RNA oligo (25mg/kg) treated mice. Only anti-RBP4 oligo significantly inhibited RBP4 protein (p<0.01) and mRNA expression (p<0.01) in the liver and reduced serum RBP4 levels. Anti-RBP4 oligo and RSG showed comparable effects on impaired glucose tolerance, hyperinsulinaemia and hyperglycaemia. Anti-RBP4 oligo significantly enhanced adipose-GLUT4 expression (p<0.01) but did not increase muscle-GLUT4. Both RSG and anti-RBP4 oligo significantly reduced hepatic phosphoenolpyruvate carboxykinase expression (both p<0.05). Histological analysis revealed that anti-RBP4 oligo ameliorated hepatic steatosis and reduced lipid droplets associated with normalized liver function. Histological and pharmacological results of this study indicate that RBP4 is not only an adipocytokine, but also a hepatic cytokine leading to metabolic syndrome, NAFLD and type 2 diabetes.