766 Hypothalamic Expression of Galanin Is Dysregulated During Cholestatic Liver Injury and Contributes to Hyperplastic Cholangiocyte Proliferation

Abstract

During the course of cholestatic liver diseases, cholangiocytes exhibit marked proliferative capacity followed by cholangiocyte loss. A hallmark feature of cholestasis is increased concentrations of serum bile acids. We have previously shown alteration of hypothalamic-derived hormones during cholestatic liver injury as a result of aberrant bile acid signaling in the hypothalamus via an ASBT/FXR-dependent mechanism. This dysregulated signaling may regulate the proliferative response of cholangiocytes in a paracrine manner. Galanin is a hypothalamic neuropeptide that controls the growth hormone releasing hormone (GHRH)/ growth hormone (GH) axis. AIMS: The aims of this study were to i) assess the expression of Galanin in the hypothalamus during cholestatic liver injury, ii) determine the effects of bile acid signaling on hypothalamic expression of Galanin and iii) evaluate the effects of central activation of Galanin signaling on cholangiocyte proliferation. Methods: Male Sprague-Dawley rats underwent sham or BDL surgery. In parallel, central administration of the bile acids cholic acid (CA), deoxycholic acid (DCA) and taurocholic acid (TCA; all at 10 pmol icv) were performed and tissue was collected after 3 hr. The expression of Galanin and GHRH in the hypothalamus and GH in the pituitary was assessed by real time PCR and immnunofluorescence. In vitro, hypothalamic neurons (m-hypo-A) were treated with the above-mentioned bile acids as well as the FXR agonist fexaramine (10 and 100 nM) for 4 hr, and galanin expression was assessed. Lastly, a synthetic Galanin analogue (M617) was infused into the brain (100 pmol/day icv) of sham and BDL rats; intrahepatic bile duct mass (IBDM) was assessed by real time PCR and immunohistochemistry using cytokeratin 19 as a cholangiocyte marker. Results: Hypothalamic Galanin expression was upregulated 1 to 7 days after BDL surgery, paralleled by an increase in GHRH and GH expression. Treatment of hypothalamic neurons with DCA, CA, or TCA increased Galanin mRNA expression in vitro and in vivo, with DCA having the greatest effect. Furthermore, treatment of m-hypoA cells with fexaramine increased Galanin expression to a similar degree. Lastly, central administration of M617 increased the expression of GHRH and GH in the hypothalamus and pituitary, respectively, and increased CK-19 mRNA expression and IBDM in sham and BDL animals. Conclusions: Our data provide further evidence for dysregulation of hypothalamic peptides during cholestatic liver injury. Specifically, the hypothalamic expression of Galanin and subsequent activation of the GHRH/GH axis is upregulated via a mechanism involving bile acid signaling. This Galanin/GHRH/GH axis may contribute to cholangiocyte proliferation during cholestatic liver injury and may be an effective therapeutic target for the maintenance of biliary mass during cholestatic liver diseases.