There is considerable evidence learn more that activation

of inflammation targeting the biliary system plays an important role in both extrahepatic and intrahepatic aspects of BA.44 Studies examining the importance of the inflammatory process have strengthened the argument for an infectious pathogenesis to BA, but there is evidence from other diseases that noninfectious etiologies may lead to inflammatory activation, including activation of IFN-γ.45 Here we demonstrate that developmental defects in biliary anatomy and activation of IFN-γ-stimulated genes can be elicited by genetic and pharmacologic inhibition of DNA methylation. IFN-γ activation in biliary cells may lead to cell damage via activation of IFN-γ downstream pathways, or potentially by inhibition of transforming growth factor β (TGF-β). Activation of IFN-γ inhibits TGF-β signaling in several model systems.46 TGF-β exerts a positive effect on the development

of bile duct cells,28 and thus inhibition of TGF-β would be expected to have a negative effect on biliary development. Such a mechanism is attractive in the developing liver, as the differentiation of hepatoblasts into bile duct cells is probably not present in the healthy mature liver. Thus, the specificity of this mechanism would be due to pathways that are developmentally limited. Although there are similarities between our zebrafish with inhibition of DNA methylation and BA, there are also key differences. We did Hydroxychloroquine solubility dmso not observe extrahepatic biliary defects in dtp, azaC-treated

larvae, or dnmt1 morphants, whereas extrahepatic biliary abnormalities are clearly important in BA. Of note, we have not observed extrahepatic defects in any of our models of abnormal biliary development in zebrafish, including hnf6 morphants, whereas targeted deletion of Hnf6 in mice clearly leads to extrahepatic biliary defects.29 This discrepancy may be due to a lack of evolutionary conservation in development of the extrahepatic biliary tree, or may be due to other factors such as timing of knockdown with respect to development or technical difficulties in observing the extrahepatic biliary tree in developing zebrafish. We also did not observe inflammatory medchemexpress infiltration of the liver or biliary tree in our models, although we did observe activation of inflammatory genes. This activation of IFN-γ-responsive genes in particular was attenuated by prednisone, which also led to rescue of the biliary defects in our fish and has been shown to be of some benefit for patients with BA post-portoenterostomy.47, 48 These results suggest that the gene expression changes elicited by prednisone may be responsible for the rescue of biliary defects, but other possible mechanisms, such as altered expression of non-IFN-γ pathway genes that lead to biliary growth and development, may be functioning as well.