Hepatocyte cholesterol content modulates glucagon receptor signalling

Glucagon decreases liver fat, and non-alcoholic fatty liver disease (NAFLD) is associated with hepatic glucagon resistance. Increasingly it is recognised that the function of G protein-coupled receptors can be regulated by their local plasma membrane lipid environment. The aim of this study was to evaluate the effects of experimentally modulating hepatocyte cholesterol content on the function of the glucagon receptor (GCGR). We found that glucagon-mediated cAMP production is inversely proportional to cholesterol content of human hepatoma and primary mouse hepatocytes after treatment with cholesterol-depleting and loading agents, with ligand internalisation showing the opposite trend. Mice fed a high cholesterol diet had increased hepatic cholesterol and a blunted hyperglycaemic response to glucagon, both of which were partially reversed by simvastatin. Molecular dynamics simulations identified potential membrane-exposed cholesterol binding sites on the GCGR. Overall, our data suggest that increased hepatocyte membrane cholesterol could directly contribute to glucagon resistance in NAFLD.