Onset of Apoptosis in the Cystic Duct During Metamorphosis of a Japanese Lamprey, Lethenteron reissneri

Abstract

A nonparasitic lamprey in Japan, Lethenteron reissneri, stops feeding prior to the commencement of metamorphosis. Resumption of feeding cannot take place due to major alterations in the digestive system, including loss of the gall bladder (GB) and biliary tree in the liver. This degeneration of bile ducts is considered to depend on programmed cell death or apoptosis, but molecular evidence of apoptosis remains lacking. Using terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining and immunohistochemistry with an antibody against active caspase-3, we showed that epithelial cells of the cystic duct (CD) and GB became TUNELpositive by the early metamorphosing stage. Immunohistochemical staining of active caspase-3, a key mediator in the apoptotic cascade, showed that the apoptotic signal was initiated in the region around the CD in the late larval phase. In later stages, active caspase-3-positive epithelial cells were also observed in the large intrahepatic bile duct (IHBD) and peripheral small IHBDs. At the early metamorphosing stage, bile canaliculi between hepatocytes were dilated and displayed features resembling canaliculi in cholestasis. Onset of apoptosis around the CD, which is the pathway for the storage of bile juice, and progression of apoptosis towards the large IHBD, which is the pathway for the secretion of bile juice, may lead to temporary intrahepatic cholestasis. The present study represents the first precise spatial and temporal analysis of apoptosis in epithelial cells of the biliary tract system during metamorphosis of any lamprey species. Anat Rec, 293:1155Rec, 293: -1166

How Do Lampreys Avoid Cholestasis After Bile Duct Degeneration?

“…Moreover, the degeneration of bile ducts has been associated with the development of marked periductal fibrosis due to fibroblast activation caused by leaked biliary materials (Youson et al, 1987;Yamamoto et al, 1986). Our observation of apoptosis in biliary epithelial cells detected prior to changes in hepatocyte morphology (Morii et al, 2010) was consistent with the results of previous reports. Intrahepatic cholestasis may regulate the remodeling of hepatocytes by changing the way cholesterol is metabolized, the expression of transporters in the basolateral membrane and the disappearance of tight junctions in hepatocytes surrounding bile canaliculi.…”

“…Chronological TUNEL analysis of metamorphosing lampreys showed that apoptosis started in the region around the CD and then progressed towards both the periphery and the center (Morii et al, 2010). Figure 8 shows that the epithelial cells of the GB were positive for TUNEL staining.…”

“…We have previously demonstrated that apoptosis plays a significant role in the degeneration of lamprey bile ducts during metamorphosis (Morii et al, 2010). The involvement of apoptosis in both human BA and lamprey bile duct degeneration during metamorphosis indicates that lampreys could be used as a model animal for studying the etiology and underlying mechanisms of human BA.…”

“…Multiple reports have described a histological similarity between human and lamprey bile duct loss and suggested that the lamprey be used as an animal model in the study of BA (Youson & Sidon, 1978;Boomer et al, 2010;Morii et al, 2010). While the lamprey differs greatly from humans in both appearance and character, striking parallels exist between the behavior of their hepatocytes and biliary epithelial cells.…”

Biliary atresia in sea lampreys. What can it tell us about the disorder in human infants?

“…As might be expected, the degeneration of bile ducts occurs via programmed cell death or apoptosis in a related, nonparasitic lamprey, Lethenteron reissner, and in the sea lamprey, Petromyzon marinus. 14,15 Similar to the lamprey, several reports have documented cholangiocyte apoptosis as evidenced by positive transferasemediated dUTP nick end labeling (TUNEL) staining of cholangiocytes in the livers of patients with biliary atresia. Although apoptosis is a normal process in remodeling of the mammalian ductal plate during liver development, it would not be expected in the extrahepatic biliary system except as part of the process of immunologic ductal injury.…”