g., after pinealectomy and exposure to dark to stimulate melatonin release from the pineal gland) in the regulation of biliary functions are ongoing. Having demonstrated that AANAT is expressed by cholangiocytes and that AANAT expression is up-regulated by BDL and melatonin administration, we proposed to demonstrate that reduction of biliary AANAT expression (by Vivo-Morpholino) increases cholangiocyte proliferation and IBDM as well as the expression of SR, CFTR, and Cl−/HCO AE2 in cholangiocytes. After BDL, the increase of biliary proliferation and IBDM is followed

by the extension of the peribiliary plexus and the increase of surrounding connective tissue, which is organized Ruxolitinib around bile ducts and vessels.10 In our model, we only observed a slight CH5424802 chemical structure difference in collagen tissue content in BDL rats treated with mismatch Morpholino versus BDL rats treated with AANAT Vivo-Morpholino. This low increase of connective tissue cannot determine a clear hepatic fibrosis in our model of short time of BDL. Further studies are needed to evaluate the long-term effects of BDL on the modulation of melatonin synthesis on liver fibrosis. Also, the novel concept that AANAT regulates SRCFTRCl−/HCO AE2 expression is supported by our previous study16 showing that in vivo administration of melatonin to BDL rats decreases secretin-induced choleresis. To determine that the effects of down-regulation of AANAT

on biliary growth depend on direct effects on bile ducts, cholangiocytes Thalidomide were treated in vitro with melatonin that decreased the biliary proliferation and expression of SR, CFTR, and Cl−/HCO AE2. We overexpressed AANAT in cholangiocytes and demonstrated a decrease

in biliary proliferation and secretin-stimulated cAMP levels and Cl− efflux. In vitro, overexpression of AANAT in cholangiocytes leading to decreased biliary proliferation and secretin receptor-dependent ductal secretion (in the absence of intestinal secretin supply) was likely the result of the fact that cholangiocytes express SR and express the message for secretin and secrete secretin,7, 39, 40 which (similar to what is observed in vivo) is an important autocrine factor sustaining biliary proliferation. We propose that the modulation of biliary melatonin secretion (by chronic administration of melatonin or changes in AANAT expression; Fig. 6) may be a valuable therapeutic approach for regulating the balance between biliary growth/apoptosis. In support of this view, we have shown that in the first stage of primary biliary cirrhosis, there is an increase of cholangiocyte proliferation that resulted in a positive balance between growth and apoptosis.41 By contrast, the end stage is characterized by the collapse of the proliferative capacity of cholangiocytes, resulting in the reduction (high apoptosis rate) of the number of bile ducts (vanishing bile duct syndrome).