Blockade of Hedgehog Signaling Attenuates Biliary Cystogenesis in the Polycystic Kidney (PCK) Rat

Caroli disease represents a hepatic manifestation of autosomal recessive polycystic kidney disease, and belongs to a class of cholangiociliopathies. The role of Hedgehog signaling, a major pathway regulated by primary cilia, in biliary cystogenesis in Caroli disease remains unknown. Using the polycystic kidney (PCK) rat as an animal model of Caroli disease, this study investigated the involvement of Hedgehog signaling in its pathogenesis. In vitro experiments revealed that PCK cholangiocytes overexpressed Smoothened, Gli1, and Gli1's target molecule cyclin D1. The nuclear expression of Gli1, Gli2, and Gli3 was observed in PCK cholangiocytes by immunocytochemistry. An immunohistochemical analysis using liver sections confirmed the overexpression of Smoothened and cyclin D1, and the nuclear expression of the Gli proteins in the biliary epithelium of PCK rats as well as human Caroli disease. The treatment of PCK cholangiocytes with cyclopamine inhibited cell proliferative activity that was associated with the inhibition of nuclear translocation of Gli1 and Gli2, and reduced cyclin D1 expression. The in vivo administration of cyclopamine to PCK rats decreased abnormally elevated serum liver enzymes, and significantly attenuated bile duct dilation as well as kidney cyst formation. These results suggest that cholangiocyte hyperproliferation is causally associated with the aberrant activation of Hedgehog signaling, and the inhibition of the signaling has potential as a therapeutic strategy for biliary cystogenesis in Caroli disease.