Expression of the oncofetal marker Nope in the regenerating adult murine liver after disruption of interhepatocytic gap junctions via bile duct ligation

Background: Neighbor of Punc E11 (Nope) is strongly expressed in fetal and adult hepatic stem/progenitor cells and in hepatocellular carcinoma but not in terminally differentiated and normally polarized hepatocytes. We here investigated the expression pattern of the oncofetal marker Nope in adult mice after bile duct ligation leading to disruption of interhepatocytic gap junctions.

Methods: Liver tissue was extracted from adult C57Bl6 mice 24 hours up to 4 weeks after bile duct ligation (BDL). Liver tissue was tested for expression levels of Nope via quantitative RT-PCR and for Nope and the gap junction protein Connexin 26 via Western blotting. Costainings were performed for Nope in combination with Connexin 26, CK19 (biliary), E-cadherin (epithelial) or the canalicular marker dipeptidylpeptidase (DPP) IV.

Results: Bile duct ligation leads to a significantly increasing expression level of Nope (after 1 week 87-fold vs. adult liver, p < 0.0001, after 4 weeks 676-fold vs. adult liver, p < 0.001).

In Western blot, this high expression level of Nope after BDL can be confirmed, while the expression level of Connexin 26 is markedly downregulated. In immunohistochemistry, almost all of the hepatocytes stain positive for Nope at later stages after BDL. Costainings with E-cadherin and DPPIV demonstrate a regular sinusoidal expression pattern of Nope on hepatocytes, but no expression on CK19-positive cholangiocytes. Costainings with Connexin 26, that is equally distributed in normal adult liver, reveal a substantial overlap and staining for Connexin 26 is almost restricted to Nope-positive hepatocytes.

Conclusion: We here report the expression of the oncofetal marker Nope on adult hepatocytes after disruption of interhepatocytic gap junctions via BDL, while the expression of Connexin 26 is markedly downregulated and mainly limited to Nope-positive hepatocytes.

With regard to its structural similarity to axonal guidance receptors, the induction of Nope might be a compensatory mechanism of "disorientated" hepatocytes to regain hepatocellular polarization within the regenerating parenchymal liver network.