Effects of elevated circulating IGF-1 on the extracellular matrix in "high-growth" C57BL/6J mice

Collagen biosynthesis was analyzed in C57BL/6J mice homozygous for the high-growth locus. Plasma levels of insulin-like growth factor-1 (IGF-1) were significantly elevated in high-growth mice at all ages studied (3 wk-6 mo); IGF-binding proteins were also elevated. Skin biopsies were obtained from mice aged 3, 6, and 9 wk under halothane anesthesia. Mice were killed at 6 mo of age. Collagen, expressed per weight of tissue, was significantly increased in all tissues from high-growth mice, as was collagen cross-linking, expressed as moles of cross-link per mole of collagen. Expression of types I and III collagen, lysyl oxidase, and lysyl hydroxylase was increased in all tissues analyzed. There was a preferential increase in type III expression relative to type I expression. Rate and extent of accumulation of collagen in granulation tissue were measured in polyvinyl alcohol sponges implanted subcutaneously; collagen accumulation was significantly greater in the high-growth mice. These results suggest that 1) elevated circulating IGF-1 may increase collagen deposition both in normal tissue as well as in granulation tissue by increasing collagen gene expression, 2) IGF-1 may increase collagen cross-linking by stimulating expression of lysyl oxidase, and 3) the preferential increase in dihydroxylated cross-links observed in high-growth mice may be due to the stimulation of lysyl hydroxylase expression by IGF-1. In summary, elevated levels of IGF-1 appear to affect collagen both quantitatively and qualitatively, primarily through their effects on gene expression of collagen and of those enzymes responsible for posttranslational modifications of collagen.