Role of CD56-expressing immature biliary epithelial cells in biliary atresia

AIM: To analyze the clinical and pathological parameters and expression of the neural cell adhesion molecule (CD56) in patients with biliary atresia (BA).

METHODS: Established clinical laboratory markers of hepatic function, including enzyme activity, protein synthesis, and bilirubin metabolism, were evaluated in patients with BA and compared with those in patients with choledochal cysts and neonatal hepatitis. Pathological changes in tissue morphology and fibrosis were examined by histological and tissue collagen staining. Immunohistochemical staining for the biliary epithelial cell markers CD56 and CK19 together with the Notch signaling related molecules Notch1 and Notch2 was performed in the context of alterations in the structure of intrahepatic biliary ducts.

RESULTS: Differences in some clinical laboratory parameters among the three diseases examined were observed, but they did not correlate with the pathological classification of fibrosis in BA. Immunohistochemical staining showed the presence of CD56-positive immature bile ducts in most patients (74.5%) with BA but not in patients with choledochal cysts or neonatal hepatitis. The number of CD56-expressing cells correlated with disease severity, with more positive cells present in the later stages of liver damage (81.8% vs 18.2%). Furthermore, bile plugs were mainly found in CD56-positive immature biliary ducts. Notch signaling was a key regulatory pathway in biliary duct formation and played a role in tissue fibrosis. Notch1 was co-expressed in CD56-positive cells, whereas Notch2 was found exclusively in blood vessels in the portal area of patients with BA.

CONCLUSION: The maturation of biliary epithelial cells and the expression of Notch may play a role in the pathogenesis of BA.

Asymmetric localization of Notch2 on the microvillous surface in choroid plexus epithelial cells

Notch family molecules are transmembrane receptors that play various roles in contact-dependent cell-cell interactions in a wide range of organs. In the brain, Notch2, but not the other members of Notch, is expressed in the choroid plexus at an exceptionally high level. We immunohistochemically examined the cellular and subcellular localization of Notch2 protein in the choroid plexus using confocal and electron microscopy. Unexpectedly, Notch2 was asymmetrically localized on the microvillous surface of epithelial cells in the choroid plexus of both postnatal and adult rats. This localization pattern of Notch2 suggests its novel and unknown role independent of contact with adjacent cells in the choroid plexus. In organotypic cultures of the choroid plexus, the addition of anti-Notch2 antibody resulted in deformation of microvilli in epithelial cells, which suggests a role of Notch2 in the maintenance of the microvillous structure in choroid plexus epithelial cells.

Evidence for differential expression of Notch receptors and their ligands in melanocytic nevi and cutaneous malignant melanoma

The Notch signaling has been implicated in the regulation of self-renewal of adult stem cells and differentiation of precursors along a specific cell lineage, in normal embryonic development and organogenesis. There is also evidence that signaling through Notch receptors regulate cell proliferation and cell survival in several types of cancer, with opposing results depending on tissue context. No data are available in the literature concerning modulation of the expression of Notch receptors, and their ligands, in human cutaneous malignant melanoma. Here, we have investigated, for the first time, the expression of Notch-1, Notch-2, Jagged-1, Jagged-2 and Delta-like 1 proteins, by immunohistochemistry, in a series of benign and malignant human melanocytic lesions: five common melanocytic nevi, five 'dysplastic nevi' and 20 melanomas (five in situ, five T1-T2, five T3-T4 and five metastatic melanomas). We found that the expression of Notch-1 and Notch-2, as well as Notch ligands, was upregulated in 'dysplastic nevi' and melanomas as compared with common melanocytic nevi. These results indicate that the activation of Notch may represent an early event in melanocytic tumor growth and upregulation of Notch signaling may sustain tumor progression.