Co-ordinated targeting of galanin receptors on cholangiocytes and hepatic stellate cells ameliorates liver fibrosis in Mdr2-knockout mice

Galanin (Gal) is a peptide with a role in neuroendocrine regulation of the liver. In this study we assessed the role of Gal and its receptors GalR1 and GalR2 in cholangiocyte proliferation and liver fibrosis in Mdr2-knockout (KO) mice as a model of chronic hepatic cholestasis. The distribution of Gal, GalR1, and GalR2 in specific liver cell types was assessed by laser-capture microdissection and confocal microscopy. Galanin immunoreactivity was detected in cholangiocytes, hepatic stellate cells (HSC), and hepatocytes. Cholangiocytes expressed GalR1, whereas HSC and hepatocytes expressed GalR2. Strategies were used to either stimulate or block GalR1 and GalR2 in FVB/N (wild type) and Mdr2KO mice, and measure biliary hyperplasia and hepatic fibrosis by qPCR and immuno-staining of specific markers. Galanin treatment increased cholangiocyte proliferation and fibrogenesis in both FVB/N and Mdr2KO mice. Suppression of GalR1, GalR2, or both receptors in Mdr2KO mice resulted in reduced bile duct mass and hepatic fibrosis. In vitro knockdown of GalR1 in cholangiocytes reduced αSMA expression in LX-2 cells treated with cholangiocyte-conditioned media. A GalR2 antagonist inhibited HSC activation when Gal was administered directly to LX-2 cells, but not via cholangiocyte-conditioned media. These data demonstrate that Gal contributes not only to cholangiocyte proliferation but also to liver fibrogenesis via the coordinate activation of GalR1 in cholangiocytes, and GalR2 in HSC.