Regulation of insulin-like growth factor-I and of insulin-like growth factor binding protein-1, -3 and -4 in cocultures of rat hepatocytes and Kupffer cells by interleukin-6

Abstract

Background/Aims : Catabolism is associated with decreased serum concentrations of insulin-like growth factor (IGF)-I and insulin-like growth factor binding protein (IGFBP)-3 associated with elevated IGFBP-3 protease activity and increased concentrations of IGFBP-1 and -4. The effects of the acute phase mediators interleukin (IL)-6, IL-1 β and tumor necrosis factor α (TNF α) on the biosynthesis of IGF-I and IGFBPs were studied in primary rat liver cells. Methods : mRNA levels of IGF-I and of IGFBPs were analyzed by Northern blotting, secretion of IGFBPs by [ 125 I]IGF-I ligand blotting. Proteolytic activity was measured using iodinated recombinant IGFBP-3 as the substrate. Results : In hepatocytes, Kupffer cells (KC) and cocultures of hepatocytes with KC, IL-6 reduced IGF-I biosynthesis dose-dependently. IL-6 stimulated mRNA expression and protein secretion of IGFBP-1 and -4 in hepatocytes and that of IGFBP-3 in KC, respectively. In cocultures, biosynthesis of IGFBP-1, -3 and -4 was increased dose-dependently by IL-6, while the effects of IL-1 β or TNF α were less prominent. At neutral pH, proteolytic activity against IGFBP-3 was not detected in media of cocultures treated with IL-6. Conclusions : The alterations of IGF-I, IGFBP-1 and -4 observed in catabolism correlate with the effects of IL-6 on the biosynthesis of these components in primary rat liver cells, while a neutral IGFBP-3 protease was not detectable.