ENHANCED HEPATIC COLLAGEN TYPE-I MESSENGER-RNA EXPRESSION INTO FAT-STORING CELLS IN A RODENT MODEL OF HEMOCHROMATOSIS

recent years, identifying the hepatic cell type responsible for collag en synthesis in experimental models of postnecrotic or inflammatory fi brosis has been the subject of active investigation. In primary iron o verload states, however, hepatic fibrosis and cirrhosis occur without accompanying necroinflammatory phenomena. In this study, we combined m orphological, immunological, cell isolation and purification and molec ular biological techniques to identify the hepatic cell responsible fo r enhanced collagen type I gene expression during chronic enteral iron overload in the rat. Ultrastructural analysis of liver tissue section s from iron-loaded rats specifically revealed an altered appearance of fat-storing cells, which showed few if any fat droplets left and incr eased rough endoplasmic reticulum. In situ hybridization analysis with specific complementary RNA probes identified enhanced signal for coll agen type I into nonparenchymal cells in zones 1 and 2, without signal over the background onto iron-laden hepatocytes. Immunocytochemistry with desmin antibodies combined with in situ hybridization on the same tissue sections identified the cells expressing high level of collage n type I transcripts as fat-storing cells. Northern-blot analysis on R NA extracted from various purified cell isolates, confirmed the presen ce of collagen type I mRNA signal only into the fat-storing cells isol ate. Our study shows that in an experimental model of metabolic fibros is in which the hepatotoxin selectively accumulates into parenchymal c ells, fat-storing cells are the main source of enhanced collagen type I gene expression.