IGF-I stimulates tropoelastin synthesis in neonatal rat pulmonary fibroblasts

We have examined the effect of IGF-I on tropoelastin (TE) synthesis in cultured rat neonatal pulmonary fibroblasts, because this growth factor has been shown to stimulate TE synthesis in vascular smooth muscle cells. IGF-I stimulated TE and total protein synthesis in a dose-dependent manner even when cells were cultured in the medium supplemented with 0.5% FCS. The maximal stimulation was at IGF-I concentration 500 ng/mL and was an increase of 86 +/- 14 and 35 +/- 5% for TE and estimated total protein synthesis, respectively. There was a corresponding 95 +/- 20% increase in the TE mRNA/beta-actin mRNA ratio assessed by densitometry of the Northern blot analysis. At this low concentration of FCS, however, there was neither TE stimulation by dexamethasone alone nor in combination with IGF-I. We conclude that IGF-I stimulation of TE synthesis may occur in cells other than vascular smooth muscle cells and that there is no additive stimulation by glucocorticoids.