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RESEARCH PRODUCT

Dexamethasone modulates α2-macroglobulin and apolipoprotein E gene expression in cultured rat liver fat-storing (Ito) cells

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Fat-storing (Ito) cells are perisinusoidal liver cells thought to play a central role in vitamin A metabolism and fibrogenesis. Glucocorticoids have been shown to be beneficial in the treatment of certain types of liver diseases by delaying the development of cirrhosis. To study the regulatory effects of dexamethasone on Ito cell gene expression, Ito cells were isolated from normal rat liver and primary cultures were established. The effect of dexamethasone on the synthesis of α2-macroglobulin, apolipoprotein E, fibronectin and actin was examined. Protein synthesis was studied both at the protein level and at the RNA level by means of biosynthetic labeling, immunoprecipitation followed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and by Northern blot analysis of total RNA. After exposure to dexamethasone for 20 hr, α2-macroglobulin protein synthesis was increased threefold, whereas apolipoprotein E expression was decreased 80%. Biosynthesis of fibronectin remained unaffected by hormone treatment. The dexamethasone effect became detectable 5 hr after beginning the exposure. Deinduction kinetic experiments showed that the glucocorticoid effect was detectable more than 12 hr after the replacement of the dexamethasonecontaining culture medium by medium without the hormone. Corresponding to the data obtained at the protein level, dexamethasone increased the steady-state levels of α2-macroglobulin–specific messenger RNA and reduced apolipoprotein E–specific transcripts, whereas fibronectin and actin messenger mRNA remained unchanged. These findings indicate that glucocorticoids can affect the Ito-cell gene expression in a differentiated manner. Because dexamethasone not only stimulates α2-macroglobulin but also fibronectin and apolipoprotein E gene expression in rat hepatocytes, it will be interesting to study the difference in regulation of those genes in both cell populations. (HEPATOLOGY 1991;14:875–882).