Involvement of G protein-coupled receptor kinase 2 (GRK2) in the development of non-alcoholic steatosis and steatohepatitis in mice and humans

Insulin resistance (IR) and obesity are important risk factors for non-alcoholic fatty liver disease (NAFLD). G protein-coupled receptor kinase 2 (GRK2) is involved in the development of IR and obesity in vivo. However, its possible contribution to NAFLD and/or non-alcoholic steatohepatitis (NASH) independently of its role on IR or fat mass accretion has not been explored. Here, we used wild-type (WT) or GRK2 hemizygous (GRK2 +/-) mice fed a high-fat diet (HFD) or a methionine and choline-deficient diet (MCD) as a model of NASH independent of adiposity and IR. GRK2 +/- mice were protected from HFD-induced NAFLD. Moreover, MCD feeding caused an increased in triglyceride content and liver-to-body weight ratio in WT mice, features that were attenuated in GRK2 +/- mice. According to their NAFLD activity score, MCD-fed GRK2 +/- mice were diagnosed with simple steatosis and not overt NASH. They also showed reduced expression of lipogenic and lipid-uptake markers and less signs of inflammation in the liver. GRK2 +/- mice preserved hepatic protective mechanisms as enhanced autophagy and mitochondrial fusion and biogenesis, together with reduced endoplasmic reticulum stress. GRK2 protein was increased in MCD-fed WT but not in GRK2 +/- mice, and enhanced GRK2 expression potentiated palmitic acid-triggered lipid accumulation in human hepatocytes directly relating GRK2 levels to steatosis. GRK2 protein and mRNA levels were increased in human liver biopsies from simple steatosis or NASH patients in two different human cohorts. Our results describe a functional relationship between GRK2 levels and hepatic lipid accumulation and implicate GRK2 in the establishment and/or development of NASH.