Vitamin D nuclear receptor deficiency promotes cholestatic liver injury by disruption of biliary epithelial cell junctions in mice

Abstract

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. Conclusion: 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. (Hepatology 2013;58:1401–1412)

Pharmacology of bile acid receptors: Evolution of bile acids from simple detergents to complex signaling molecules

“…Administration of 1, 25 VD 3 did not significantly alter hepatic and plasma bile acid levels, but increased renal MRP2, MRP3 and MRP4 mRNA expression and increased renal bile acid secretion [114,130], suggesting VDR activation may also promote renal bile acid elimination under cholestasis conditions. VDR deficient mice were more susceptible to BDL-induced liver injury, which was accompanied by impaired adaptive induction of CYP3A, MDR2 and MRP3 [131]. Importantly, the higher susceptibility of vdr KO mice to bile acid-induced hepatotoxicity has also been attributed to VDR function in biliary epithelial cells to maintain bile duct integrity [131,132], similar to its role in regulating gut mucosal barrier function [123,124].…”

Nuclear Receptors in Acute and Chronic Cholestasis

“…BDL) by limiting the protection given by the epithelial barrier formed by BECs [41]. Mice submitted to a vitamin D-supplemented diet are protected from hepatic damage after BDL [41]. Furthermore, hepatic fibrosis is inversely correlated with vitamin D intake in mice invalidated for Abcb4, a well-known model of primary sclerosing cholangitis [42].…”

“…In mice, absence of VDR worsens hepatic damage due to acute obstructive cholestasis (i.e. BDL) by limiting the protection given by the epithelial barrier formed by BECs [41]. Mice submitted to a vitamin D-supplemented diet are protected from hepatic damage after BDL [41].…”

E-cadherin, guardian of liver physiology

“…We have recently shown that, during experimental bile duct obstruction, adherens junctions were altered by the expression of a truncated form of E-cadherin. Furthermore, our data indicate that liver injury was exacerbated when the truncated E-cadherin expression was increased [8]. Here, Nakagawa et al show that the absence of hepatic E-cadherin leads to a cholestatic phenotype evocative of PSC [3].…”

“…Furthermore, adherens junctions morphological analysis was performed in 2-month old animals while the cholestatic phenotype was evident at 8-month of age (ALP levels, histology). Thus, altered adherens junctions morphology may appear later in the CDH1 L mice as we have previously shown that E-cadherin alterations were increased when cholestasis was established in Vdr -/− mice [8].…”