| Co-Investigator(Kenkyū-buntansha) |
INAO Mie Saitama Medical School, Faculty of Medicine, Assistant, 医学部, 助手 (70286037)
MATSUI Atsushi Saitama Medical School, Faculty of Medicine, Assistant, 医学部, 助手 (40260484)
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| Research Abstract |
Macrophage infiltration into the liver is assumed to be a critical event in the development of fulminant hepatic failure, since massive liver necrosis can develop as a result of microcirculatory disturbance due to sinusoidal fibrin deposition caused by activated macrophages. However, the precise mechanisms of such macrophage infiltration are to be elucidated. Osteopontin, an extracellular matrix with RGD sequence, has been shown to act as a chemokine that can induce macrophage migration. The possibility that osteopontin can play a role in infiltration of macrophages into the liver was investigated in rats and mice. Northern blot analysis revealed that osteopontin mRNA expression was minimal in Kupffer cells and hepatocytes immediately after isolation from normal rats, but slight in stellate cells cultured for 3 days on plastic dishes. When rats received carbon tetrachloride or heat-killed Propionibacterium acnes (P.acnes), osteopontin mRNA expression assessed by competitive RT-PCR was
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increased in the liver preceding the occurrence of macrophage infiltration. Kupffer cells and hepatic macrophages and stellate cells isolated from such liver showed marked expression of osteopontin mRNA on Northern blotting. Immunohistochemical examination disclosed that osteopontin was stained in the Golgi apparatus of macrophages including Kupffer cells and hepatic stellate cells in these rats. In P.acnes-treated rats, both mRNA expressions of MIC-1 and MIP-1α were increased in the liver. Although mice with allele B osteopontin gene, in which osteopontin expression was absent, showed similar increase of both chemokine expressions, hepatic macrophage infiltration was minimal in such mice following P.acnes administration. Osteopontin may play a central role in hepatic macrophage infiltration among various chemokines. Kupffer cells and hepatic macrophages and stellate cells may contribute to hepatic macrophage infiltration by expressing osteopontin.
Regulation mechanisms of osteopontin expression in the liver were examined using rat stellate cells and hepatocytes in primary culture. In both cells, mRNA and protein expressions of osteopontin were upregulated following stimulation by TGF-β in a dose-dependant manner. Immunohistochemical examination revealed that osteopontin was expressed in hepatocytes and stellate cells in the liver of patients with liver cirrhosis. Also, the expression was found in well-differentiated hepatocellular carcinoma cells in these patients. Thus, osteopontin might be involved in the process of liver fibrosis and carcinogenesis as well as massive liver necrosis. To clarify the role of osteopontin in the development of liver diseases, we established transgenic mice expressing osteopontin abundantly in the liver. Less
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