title: Claudin 2 deficiency reduces bile flow and increases susceptibility to cholesterol gallstone disease in mice.
abstract: OBJECTIVE
  Bile formation and secretion are essential functions of the hepatobiliary system. Bile flow is generated by transepithelial transport of water and ionic/nonionic solutes via transcellular and paracellular pathways that is mainly driven by osmotic pressure. We examined the role of tight junction-based paracellular transport in bile secretion. Claudins are cell-cell adhesion molecules in tight junctions that create the paracellular barrier. The claudin family has 27 reported members, some of which have paracellular ion- and/or water-channel-like functions. Claudin 2 is a paracellular channel-forming protein that is highly expressed in hepatocytes and cholangiocytes; we examined the hepatobiliary system of claudin 2 knockout (Cldn2(-/-)) mice.
  
  
  METHODS
  We collected liver and biliary tissues from Cldn2(-/-) and Cldn2(+/+) mice and performed histologic, biochemical, and electrophysiologic analyses. We measured osmotic movement of water and/or ions in Cldn2(-/-) and Cldn2(+/+) hepatocytes and bile ducts. Mice were placed on lithogenic diets for 4 weeks and development of gallstone disease was assessed.
  
  
  RESULTS
  The rate of bile flow in Cldn2(-/-) mice was half that of Cldn2(+/+) mice, resulting in significantly more concentrated bile in livers of Cldn2(-/-) mice. Consistent with these findings, osmotic gradient-driven water flow was significantly reduced in hepatocyte bile canaliculi and bile ducts isolated from Cldn2(-/-) mice, compared with Cldn2(+/+) mice. After 4 weeks on lithogenic diets, all Cldn2(-/-) mice developed macroscopically visible gallstones; the main component of the gallstones was cholesterol (>98%). In contrast, none of the Cldn2(+/+) mice placed on lithogenic diets developed gallstones.
  
  
  CONCLUSIONS
  Based on studies of Cldn2(-/-) mice, claudin 2 regulates paracellular ion and water flow required for proper regulation of bile composition and flow. Dysregulation of this process increases susceptibility to cholesterol gallstone disease in mice.
authors: Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan; Department of Gastroenterology and Hepatology, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Kengo
authors: K
authors: Matsumoto
authors: Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Mitsunobu
authors: M
authors: Imasato
authors: Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Yuji
authors: Y
authors: Yamazaki
authors: Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Hiroo
authors: H
authors: Tanaka
authors: Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan; Graduate School of Media and Governance, Faculty of Environment and Information Studies, Keio University, Kanagawa, Japan.
authors: Mitsuhiro
authors: M
authors: Watanabe
authors: Department of Surgery, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Hidetoshi
authors: H
authors: Eguchi
authors: Department of Surgery, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Hiroaki
authors: H
authors: Nagano
authors: Department of Gastroenterology and Hepatology, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Hayato
authors: H
authors: Hikita
authors: Department of Gastroenterology and Hepatology, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Tomohide
authors: T
authors: Tatsumi
authors: Department of Gastroenterology and Hepatology, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors: Tetsuo
authors: T
authors: Takehara
authors: Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan. Electronic address: atamura@biosci.med.osaka-u.ac.jp.
authors: Atsushi
authors: A
authors: Tamura
authors: Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan. Electronic address: atsukita@biosci.med.osaka-u.ac.jp.
authors: Sachiko
authors: S
authors: Tsukita
mesh_terms: D000368:Aged; D000818:Animals; D001646:Bile / Q000378:metabolism*; D016022:Case-Control Studies; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D057167:Claudins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D005704:Gallbladder / Q000378:metabolism* / Q000473:pathology; D042882:Gallstones / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008875:Middle Aged; D009997:Osmotic Pressure; D010539:Permeability; D019108:Tight Junctions / Q000378:metabolism* / Q000473:pathology; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: C491875:CLDN2 protein, human; D057167:Claudins; C113371:Cldn2 protein, mouse; D014867:Water; D002784:Cholesterol
keywords: Claudin 2; Hepatic Microcirculation; Mouse Model; TJ