ALTERED EXPRESSION AND LOCALIZATION OF THE TIGHT JUNCTION PROTEIN ZO-1 AFTER COMMON BILE-DUCT LIGATION

Hepatocyte tight junctions form the intercellular barrier between bile and blood. Cholestasis due to common bile duct ligation (CBDL) results in structural changes in the tight junction (TJ) and an overt paracellular leak, although the molecular basis for these alterations is undefined. Using the epithelial isoform of the TJ protein ZO-1 (ZO-1alpha+) as a marker for molecular changes in hepatocyte TJs, we investigated the effects of CBDL on ZO-1alpha+ immunofluorescence (IF) localization and on ZO-1alpha+ mRNA and protein expression over 2 wk of CBDL. ZO-1alpha+ IF staining was altered after 2 days of CBDL and appeared to accumulate in pericanalicular regions after 7 and 9 days. Quantitative immunoblotting and ribonuclease protection revealed a marked increase in hepatic ZO-1alpha+ protein expression and ZO-1alpha+ mRNA levels, respectively. In contrast to changes in ZO-1alpha+ IF, which occurred throughout the lobule, and changes in mRNA and protein expression, which were maximal after 9 days of ligation, the maximal hepatocyte proliferation occurred within 2 days after CBDL and was confined to periportal regions. CBDL results in altered hepatic localization and increased expression of the TJ protein ZO-1alpha+ and appears to represent a specific response by hepatocytes to pathological junction injury independent of cell proliferation.