calpain and Cholestasis

Alterations in apical junctional complexes (AJCs) have been reported in genetic or acquired biliary diseases. The vitamin D nuclear receptor (VDR), predominantly expressed in biliary epithelial cells in the liver, has been shown to regulate AJCs. The aim of our study was thus to investigate the role of VDR in the maintenance of bile duct integrity in mice challenged with biliary-type liver injury. Vdr(-/-) mice subjected to bile duct ligation (BDL) displayed increased liver damage compared to wildtype BDL mice. Adaptation to cholestasis, ascertained by expression of genes involved in bile acid metabolism and tissue repair, was limited in Vdr(-/-) BDL mice. Furthermore, evaluation of Vdr(-/-) BDL mouse liver tissue sections indicated altered E-cadherin staining associated with increased bile duct rupture. Total liver protein analysis revealed that a truncated form of E-cadherin was present in higher amounts in Vdr(-/-) mice subjected to BDL compared to wildtype BDL mice. Truncated E-cadherin was also associated with loss of cell adhesion in biliary epithelial cells silenced for VDR. In these cells, E-cadherin cleavage occurred together with calpain 1 activation and was prevented by the silencing of calpain 1. Furthermore, VDR deficiency led to the activation of the epidermal growth factor receptor (EGFR) pathway, while EGFR activation by EGF induced both calpain 1 activation and E-cadherin cleavage in these cells. Finally, truncation of E-cadherin was blunted when EGFR signaling was inhibited in VDR-silenced cells.. Biliary-type liver injury is exacerbated in Vdr(-/-) mice by limited adaptive response and increased bile duct rupture. These results indicate that loss of VDR restricts the adaptation to cholestasis and diminishes bile duct integrity in the setting of biliary-type liver injury.

Topics: Amino Acid Sequence; Animals; Bile Ducts; Biliary Tract; Cadherins; Calpain; Cholestasis; Disease Models, Animal; Epithelial Cells; ErbB Receptors; Intercellular Junctions; Ligation; Liver; Mice; Mice, Knockout; Molecular Sequence Data; Receptors, Calcitriol

Cholestasis leading to retention and accumulation of toxic hydrophobic bile salts within hepatocytes may cause hepatocyte toxicity by inducing apoptosis. Calpains have been found to be involved in apoptosis of many cell systems. This study is designed with the aim of evaluating the possible effect of Z-LLY-FMK (a calpain inhibitor) on hepatocyte apoptosis after bile duct ligation in rat.. Male Sprague-Dawley rats were randomized to five groups. Group 1 (C) underwent sham operation. Group 2 (CDMSO) underwent Sham operation and simultaneous treatment with dimethylsulfoxide (DMSO). Group 3 (OB) underwent common bile duct ligation. Group 4 (OBZLLY) underwent common bile duct ligation and simultaneous treatment with Z-LLY-FMK. Group 5 (OBZFA) underwent common bile duct ligation and simultaneous treatment with ZFA-FMK. After 3 days, liver tissue was harvested for histopathologic analysis and apoptosis measurements.. When compared with sham operation groups, increased hepatocyte apoptosis (P < 0.001) and ductular proliferation (P < 0.001) occurred after common bile duct ligation. Following administration of Z-LLY-FMK, the increased hepatocyte apoptosis and ductular proliferation after common bile duct ligation were significantly diminished (P < 0.001 and P < 0.001). Moreover, administration of ZFA failed to show the same phenomenon (P = 0.9 and 0.987).. Significantly increased hepatocyte apoptosis and ductular proliferation occurred after common bile duct ligation. The administration of Z-LLY-FMK could effectively diminish the hepatocyte apoptosis and ductular proliferation after common bile duct ligation, whereas the administration of ZFA-FMK failed to show the same effect.

Topics: Animals; Apoptosis; Bile Ducts; Calpain; Cell Proliferation; Cholestasis; Disease Models, Animal; Hepatocytes; Jaundice, Obstructive; Ligation; Male; Rats; Rats, Sprague-Dawley

As part of this thematic series on mitochondria in cell death, we would like to review our data on: (1) the role of the mitochondrial permeability transition (MPT) in hepatocyte necrosis during cholestasis; and (2) the concept that endogenous mitochondrial protease activity may lead to the MPT. Many chronic human liver diseases are characterized by cholestasis, an impairment in bile flow. During cholestasis an accumulation of toxic hydrophobic bile salts in the hepatocyte causes necrosis. We tested the hypothesis that toxic hydrophobic bile salt, glycochenodeoxycholate (GCDC), causes hepatocyte necrosis by inducing the MPT. GCDC induces a rapid, cyclosporin A-sensitive MPT. The hydrophilic bile salt, ursodeoxycholate (UDCA), prevents the GCDC-induced MPT and hepatocyte necrosis providing an explanation for its beneficial effect in human liver disease. We have also demonstrated that the calcium-dependent MPT is associated with an increase in calpain-like protease activity and inhibited by calpain inhibitors. In an experimental model of cholestasis, mitochondrial calpain-like protease activity increases 1.6-fold. We propose for the first time that activation of mitochondrial proteases may initiate the MPT and cell necrosis during cholestasis.

Topics: Animals; ATP-Dependent Proteases; Calcium Channels; Calpain; Cholestasis; Enzyme Activation; Glycochenodeoxycholic Acid; Liver; Mitochondria, Liver; Necrosis; Permeability; Serine Endopeptidases; Ursodeoxycholic Acid