We examined the effects of insulin and insulin-like growth factor I (IGF-I) on the production of collagen by cultures of human embryonic lung fibroblasts. Insulin at 20 ng/ml increased collagen accumulation by 58% and total protein formation by 18%. At 2 micrograms/ml, insulin increased collagen production by 2- to 3-fold and total protein production by 2-fold. The mRNA levels for alpha 1(I) and alpha 1(III) collagen chains were elevated by insulin compared with untreated control values. IGF-I at 10 ng/ml increased collagen production 2-fold. IGF-I at 100 ng/ml maximally increased collagen production 3-fold. A specific antibody to the IGF-I receptor (alpha IR-3) caused a concentration-related decline in insulin-induced collagen formation. The addition of antibody at 1 micrograms/ml, resulted in 80% inhibition of insulin-induced collagen accumulation. Higher levels of antibody were required to inhibit IGF-I mediated collagen formation. The presence of antibody (alpha IR-3) also blocked fibroblast proliferation stimulated by epidermal growth factor plus insulin. These data show that insulin-induced collagen formation is mediated primarily through an interaction with the IGF-I receptor. The modulation of extracellular matrix production by insulin may influence the repair of tissue injury and the development of the accelerated atherosclerosis that accompanies the diabetic state in humans.

Transforming growth factor-beta (TGF-beta) stimulates alpha(1)(I) collagen mRNA synthesis in human lung fibroblasts through a mechanism that is partially sensitive to cycloheximide and that may involve synthesis of connective tissue growth factor (CTGF). Northern blot analyses indicate that TGF-beta stimulates time- and dose-dependent increases in CTGF mRNA. In TGF-beta-stimulated fibroblasts, maximal levels of CTGF mRNA (3.7-fold above baseline) occur at 6 h. The TGF-beta-stimulated increase in CTGF mRNA was not blocked by cycloheximide. Nuclear run-on analysis indicates that TGF-beta increases the CTGF transcription rate. The TGF-beta-stimulated increases in CTGF transcription and steady-state levels of CTGF mRNA are attenuated in prostaglandin E(2) (PGE(2))-treated fibroblasts. PGE(2) fails to attenuate luciferase activity induced by TGF-beta in fibroblasts transfected with the TGF-beta-responsive luciferase reporter construct p3TP-LUX. In amino acid-deprived fibroblasts, PGE(2) and insulin regulate alpha(1)(I) collagen mRNA levels without affecting CTGF mRNA levels. The data suggest that the regulation of alpha(1)(I) collagen mRNA levels by TGF-beta and PGE(2) may function through both CTGF-dependent and CTGF-independent mechanisms.