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.
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.
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.