Expression of extracellular matrix genes in cultured hepatic oval cells: an origin of hepatic stellate cells through transforming growth factor beta?

BACKGROUND: Hepatic oval cells, progenitor cells in the liver, can differentiate into hepatocytes and bile duct cells both in vitro and in vivo. Although hepatic stellate cells are another important cell component in the liver, less attention has been focused on the relationship between hepatic oval cells and hepatic stellate cells.

METHODS: Hepatic oval cells were isolated from rats fed a choline-deficient diet supplemented with 0.1% ethionine for 6 weeks and characterized by electron microscopy, flow cytometry, reverse transcription polymerase chain reaction, Western blot and bi-direction differentiation. After treatment with transforming growth factor-beta1 (TGF-beta1), changes in cell viability, morphology, extracellular matrix (ECM) expression and immune phenotype were analysed in these cultured and adherent hepatic oval cells.

RESULTS: The primary cultured hepatic oval cells were positive for the oval cell-specific markers OV-6, BD-1/BD-2 and M2PK as well as the hepatocyte markers albumin and alpha-foetoprotein. These hepatic oval cells differentiated bipotentially into hepatocytes or bile duct-like cells under appropriate conditions. It is noteworthy that these bipotential hepatic oval cells expressed ECM genes stably, including collagens, matrix metalloproteinases and tissue inhibitor of mellatoproteinase. Furthermore, except for growth inhibition and morphological changes in the hepatic oval cells after exposure to TGF-beta1, there was an increased expression of ECM genes, the onset expression of snail and loss expression of E-cadherin. During this process, TGF-beta1 treatment induced an upregulation of marker genes for hepatic stellate cells in hepatic oval cells, such as desmin and GFAP.

CONCLUSION: Except for the expression of ECM, the cultured hepatic oval cells could induce an increased expression of hepatic stellate cell markers by TGF-beta1 through an epithelial-mesenchymal transition process, which might indicate the contribution of hepatic oval cells to liver fibrosis.