Expression of the novel gene osteoactivin in rat and human liver tissue and isolated liver mononuclear phagocytes

Abstract

The transmembrane glycoprotein osteoactivin is found in osteoblasts, dendritic cells and tumor cells and is supposed to plays a role in osteoblast maturation and cell adhesion. Methods: Total RNA was extracted from rat organs, and from cultured liver cell populations (hepatocytes, Kupffer cells, sinusoidal endothelial cells, hepatic stellate cells, myofibroblasts), and analyzed by Northern blot hybridization. Moreover, inflammatory mononuclear phagocytes (MNP) were isolated from carbon tetrachloride (CCl4)-treated rats. Cultured Kupffer cells and MNP were treated with lipopolysaccharide (LPS) or dexamethasone (DEX). Total RNA was extracted from human liver (acute liver failure, liver cirrhosis from different origin). Results: Organ expression of osteoactivin showed high levels in lungs and spleen, less in kidney and colon. Trace osteoactivin expression was found in normal rat liver. High levels of osteoactivin mRNA were detected in normal Kupffer cells. LPS and DEX treatment of Kupffer cells led to a decrease of osteoactivin mRNA. In CCl4-treated animals osteoactivin mRNA was abundantly detected in total liver RNA and in isolated inflammatory MNP of the liver. DEX treatment of animals and of cultured inflammatory MNP decreased osteoactivin mRNA expression. Human liver total RNA extracts contained elevated osteoactivin mRNA levels in fulminant hepatitis. Conclusions: This is the first description of abundant osteoactivin expression in Kupffer cells as well as in liver inflammatory MNP. The inhibitory effect of glucocorticoids suggests a role of osteoactivin in inflammatory processes.