Targeting Galanin Receptor Signaling as a Novel Therapeutic Strategy for the Treatment of Fatty Liver Disease

Abstract

BackgroundNon‐alcoholic fatty liver disease (NAFLD) is a common liver disease in the United States and is associated with dysregulated lipid metabolism and fat accumulation in hepatocytes (i.e. steatosis) leading to inflammation and fibrosis and cirrhosis. Galanin (Gal) is a neuropeptide with a role in food intake behavior and chronic upregulation of Gal is associated with increases in serum triglycerides, hyperinsulinemia, impaired glucose tolerance and hepatic steatosis. Targeting Gal receptor (GalR) signaling has been shown to have antifibrotic in models of cholestatic liver disease although the effects in NAFLD is unknown. The aim of this study was to evaluate the Gal/GalR axis in NAFLD and determined the effects of Gal Inhibition on the pathogenesis of NAFLD.MethodsC57Bl6 mice were fed a western diet (WD) consisting of high fat/high sugar/high cholesterol for a total of 16 weeks. At the 4 week time point, mice were treated with the GalR1/GalR2 antagonist, M40 (1 nmol, 3X per week for the duration of the experiment), or corresponding vehicle control. Serum and liver assays of Gal, triglycerides, and cholesterol were performed using commercially available kits. The expression of Gal, GalR1, GalR2, markers of steatosis (perilipin 2, PLIN2), biliary hyperplasia (cytokeratin 19, CK19), fibrosis (collagen type 1A1, Col1A1; α‐smooth muscle actin, α‐SMA) and inflammation (chemokine C‐C motif ligand 2, CCL2; tumor necrosis factor‐α, TNFα) by qPCR and immunostaining. Liver macrophages CD11b+ and CD68+ were quantified by immunohistochemistry (IHC). Liver lipid droplets (LD) were stained with Oil Red O. In vitro, HepG2 cells were used to assess the effects of M40 on palmitate (PA)‐induced LD formation.ResultsGal was significantly increased in the serum and liver of WD‐fed mice, with a corresponding increase in GalR1 and GalR2 expression. WD‐mice exhibited significant increase in serum transaminases, triglycerides and cholesterol compared to control mice, and M40 significantly reduced these indicators of liver injury. A drastic decrease in liver steatosis was also observed in M40‐treated WD‐mice compared to vehicle‐treated WD‐mice. M40 treatment also ameliorated WD‐induced increase in ductular reaction, fibrosis and liver inflammation in NAFLD mice. In vitro experiments confirmed that M40 decreased PA‐induced steatosis of HepG2.ConclusionsThe expression of Gal and its receptors GalR1 and GalR2, is enhanced in livers of mice on a WD. Treatment of WD‐fed mice with M40 reduces steatosis, intrahepatic biliary mass, fibrosis and inflammation. Therefore, targeting GalR1 and GalR2 may be a novel therapeutic option for the treatment of NAFLD.