Osteopontin expression in normal and fibrotic liver. Altered liver healing in osteopontin-deficient mice

Background/Aims Osteopontin has been implicated in numerous physiopathological events. Osteopontin expression in normal and fibrotic liver and liver fibrogenesis in osteopontin-deficient mice were studied. Methods Fibrosis was induced in mice and rats by carbon tetrachloride (CCl4) treatment or bile duct ligation. The liver was used for conventional histology, osteopontin immunohistochemistry and in situ hybridization, or protein and RNA extraction. In mice, necrotic areas and fibrosis were evaluated by quantitative image analysis. Results In normal liver, osteopontin mRNA expression was very low. After CCl4 treatment or bile duct ligation, osteopontin mRNA expression was increased. Osteopontin was expressed by biliary epithelial cells in normal and fibrotic liver. Soon after the beginning of the CCl4 treatment, osteopontin was also present in inflammatory cells of the necrotic areas. In osteopontin-deficient mice, necrotic areas after a single dose of CCl4, and fibrosis after chronic CCl4 treatment were significantly increased as compared with wild-type treated mice. Conclusions Our results show that osteopontin expression increases during liver fibrogenesis. Furthermore, osteopontin-deficient mice were more susceptible to CCl4 treatment, displaying more necrosis during the initial steps (probably due to a deficiency in nitric oxide production) and more fibrosis thereafter. The increase in osteopontin expression observed during liver fibrogenesis may play a protective role.