Increased cytoprotective function in the liver of transgenic mice expressing osteopontin in hepatocytes.

Osteopontin is a crucial factor for initiation of Th1 immune reaction. Previously, we established transgenic mice expressing osteopontin in hepatocytes, in which lymphocyte infiltration occurred spontaneously at 12 weeks of age and liver necrosis at 24 weeks of age. This liver necrosis may develop through provocation by excessive Th1 immune reaction, but it is also possible that hepatocytes become fragile under abundant osteopontin in the cytoplasm. Thus, gene expression profiles in the liver were evaluated to seek such contributing factors in the transgenic mice. On DNA microarray analysis of 3774 mouse genes, 16 genes were selected as hepatic genes significantly up-regulated in the transgenic mice aged 8 weeks than in the negative littermate, which included mRNAs of cytoprotective metallothionein and glutathione S-transferase (GST). Hepatic up-regulations of both genes were also seen by Western blotting. Liver necrosis in the centrilobular areas developed after carbon tetrachloride treatment, but its histological extent and plasma ALT activities were significantly smaller in the transgenic mice aged 8 weeks than in the wild-type C57BL/6 control mice. We conclude that cytoprotective function of the liver is increased through up-regulated expressions of metallothionein and GST, and thereby susceptibility of hepatocytes to the stress may be less possible, if any, in the development of spontaneous liver necrosis in transgenic mice expressing osteopontin in hepatocytes.

Extrahepatic manifestations in transgenic mice of osteopontin in hepatocytes-A clue to advent of pathological state in various organs of chronic hepatitis C patients.

Osteopontin is a cytokine essential for initiation of Th1 immune reaction. We established transgenic mice expressing osteopontin in hepatocyte, in which liver necrosis with lymphocyte infiltration developed gradually from 12 weeks of age with up-regulated osteopontin levels in the circulation, suggesting that extrahepatic manifestations might also occur as a result of excessive Th1 immune reaction. We examined histological and immunohistochemical features of various organs in these mice. Splenomegaly and enlargement of lymph nodes around the liver and intestine became apparent with marked infiltration of small lymphocytes in the transgenic mice later than 24 weeks of age. Immunostaining revealed that lymphocytes in the spleen and lymph nodes were positive for either CD3 or CD20, suggesting that the infiltrating lymphocytes were both B and T cells. Similar lymphocyte infiltration was found in the lung, kidney and submandibular gland. Alveolar septa became hypertrophic with lymphocyte infiltration, and the lung showed the appearance of interstitial pneumonia. These lesions are similar to extrahepatic manifestations in chronic hepatitis C patients, suggesting that augmented Th1 immune reaction to hepatitis C virus (HCV) proteins or the proteins with molecular mimicry of HCV may be a contributing factor for the formation of the pathological state not only in the liver but also in various organs under chronic infection of hepatitis C virus.

Massive liver necrosis after provocation of imbalance between Th1 and Th2 immune reactions in osteopontin transgenic mice.

BACKGROUND: Massive liver necrosis can develop as a consequence of imbalance between T-helper (Th)1 and Th2 immune reactions in the liver. Osteopontin is a glycoprotein secreted for the initiation of the Th1 immune reaction, as well as for extracellular matrix formation and calcium deposition in the bone and kidney. Osteopontin is overexpressed in Kupffer cells, macrophages, and stellate cells activated in injured livers. We established transgenic mice expressing osteopontin exclusively in hepatocytes, using a vector containing human serum amyloid P component promoter. The relation of Th1/Th2 immune imbalance to massive liver necrosis was studied using these transgenic mice. METHODS: Transgenic mice and C27BL/6 mice, wild-type controls of the transgenic mice, were given an intravenous injection of concanavalin-A, and the histological extent of liver injuries and plasma cytokine levels were evaluated. RESULTS: When the transgenic mice received concanavalin-A, massive necrosis and mononuclear cell infiltration developed in the liver, the extent of which was greater in the female mice than in the male mice. This treatment produced minimal liver injury and focal liver necrosis in male and female C57BL/6 mice. In these transgenic and control mice, plasma concentrations of interleukin (IL)-10 and interferon (IFN)-gamma were increased after concanavalin-A treatment. However, the upregulation of plasma IL-10 concentration was smaller in the male and female transgenic mice than in the control mice, and the upregulation of the IFN-gamma concentration was greater in the female transgenic mice than in the female control mice. CONCLUSIONS: Th1 and Th2 immune reactions were deranged after concanavalin-A treatment, with Th1 immunity predominating in transgenic mice expressing osteopontin in hepatocytes; this immunological imbalance may contribute to massive liver necrosis.

Transgenic mice expressing osteopontin in hepatocytes as a model of autoimmune hepatitis.

Osteopontin, a crucial factor for Th1 immune response, is expressed in stellate cells and macrophages activated in injured liver. To clarify the role of osteopontin in inflammatory changes in the liver, we attempted to establish transgenic mice expressing osteopontin in hepatocytes. Mouse osteopontin cDNA, cloned from concanavalin-A-stimulated spleen cells in C57BL/6 mice, was constructed into the vector containing serum amyloid-P component promoter. This construction was microinjected into fertilized eggs of C57BL/6 mice, and 4 lines of the transgenic mice were obtained. Western blotting and immunohistochemistry revealed that osteopontin was expressed in hepatocytes, but not in non-parenchymal cells, in the transgenic mice. The mean osteopontin concentrations in the liver and plasma in the mice were 13 and 2.6 times higher than those in negative littermates. Antinuclear antibody was positive in the plasma in 50% of the transgenic mice. In the transgenic mice later than 12 weeks of age, mononuclear cell infiltration in the liver developed, and these cells were positive for CD8 and HLA-DR. Plasma ALT activity was increased with focal necrosis in hepatic lobules in the transgenic mice later than 24 weeks of age. The transgenic mice expressing osteopontin in hepatocytes may be useful as a model of autoimmune hepatitis.