Insulin‐like growth factor‐I (IGF‐i) stimulates protein synthesis and collagen gene expression in monolayer and lattice cultures of fibroblasts

Abstract

Fibroblasts cultivated in three‐dimensional tissue‐like matrices are characterized by a slowed metabolism and a decrease of protein synthesis, unless they are submitted to physical tensions. We checked the effects of insulin like growth factor‐I (IGF‐I), known as a potent stimulator of mitogenesis and protein synthesis for many cell types, in various models of cultures: confluent monolayers, collagen lattices, non‐retracting or retracting fibrin lattices. IGF‐I (1–100 ng · ml⁻¹) had no effect on cell divisions in lattice cultures. It was able to stimulate collagen lattice retraction when the medium was supplemented with low concentrations of serum. IGF‐I at 10 or 100 ng · ml⁻¹ stimulated collagen and non‐collagen syntheses in all culture systems, but stimulation of collagen synthesis only began at the highest concentration (100 ng · ml⁻¹) in retracted lattices. Northern blot and dot‐olot analyses of mRNAs extracted from monolayer cultures of fibroblasts showed that IGF‐I stimulated pro α1(I) collagen synthesis at the pretranslational level. Cycloheximide (7.5 μg · ml⁻¹) completely inhibited pro α1(I) collagen gene expression induced by IGF‐I. These results show that IGF‐I is a potent stimulus for protein synthesis and collagen gene expression in monolayers and tridimensional cultures of fibroblasts, but that it exerts no mitogenic activity in tridimensional lattices. Synergistic associations of IGF‐I with other growth factors will have to be found in order to reverse the quiescent status of fibroblasts in lattices.