CHARACTERIZATION OF INSULIN-LIKE GROWTH-FACTOR (IGF)-I-RECEPTOR BINDING-SITES DURING IN-VITRO TRANSFORMATION OF RAT HEPATIC STELLATE CELLS TO MYOFIBROBLASTS

Insulin-like growth factors are growth-promoting peptides structurally related to insulin which possess autocrine and paracrine activities. IGF-I is mainly synthesized in hepatocytes, but little is known about its paracrine action on hepatocyte-adjacent perisinusoidal hepatic ste llate cells, the principal matrix producing precursor cell type in the liver. IGF-I might stimulate proliferation and phenotypical transform ation of hepatic stellate cells into myofibroblasts, the cell type res ponsible for the excessive production of connective tissue elements du ring fibrogenesis. In this study we investigated the expression and fu nction of the IGF-I receptor during transformation of isolated and cul tured hepatic stellate cells. The respective stages of transformation of hepatic stellate cells were defined by determination of cellular sm ooth muscle iso-cr-actin and retinyl-palmitate content, respectively. IGF-I receptor protein decreased stage-dependently down to 0.5 at the 4th day and about 0.17 at the 8th day. The number of IGF-I receptors w as determined to be initially 1.3 x 10(5)/cell. Their quantity decreas ed to 0.8 x 10(5) sites/cell (4th day) down to 0.5 x 10(5) sites/cell at the 7th day and remained constant thereafter at 0.7 x 10(5) sites/c ell. Dissociation constants (KD) for IGF-I range from 0.32-0.57 nmol/l showing constantly high receptor affinity. Northern blot analyses rev ealed distinct upregulation of IGF-I receptor mRNA level during cultur e. It is concluded that hepatocyte-generated IGF-I and/or IGF-I bindin g proteins are candidate mediators of hepatic stellate cell activation during the initial period of transformation to myofibroblasts. After completion of transformation the cell becomes relatively refractory to the action of IGF-I as judged from receptor density.