IGF-I Stimulates Tropoelastin Synthesis in Neonatal Rat Pulmonary Fibroblasts

Abstract

ABSTRACT. 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 f 14 and 35 f 5% for TE and estimated total protein synthesis, respectively. There was a corresponding 95 f 20% increase in the TE mRNA/fi-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. (Pediatr Res 30: 248-251, 1991) Abbreviations RPF, rat pulmonary fibroblasts TE, tropoelastin DEX, dexamethasone An extracellular protein component, elastin, may play an important role in the formation of the terminal airsac/alveolus during perinatal lung morphogenesis in various animals and in humans (1-8).The pro-form protein, TE, is a soluble protein of approximately 72 000 to 75 000 molecular weight (9, lo), and the regulation of synthesis is poorly understood, partly because regulatory elements of the gene have not been fully defined (1 1). We have previously demonstrated that cultured RPF are elastogenic in early passaged cells and that TE expression is stimulated by DEX (12). To further understand the humoral factors that could stimulate TE synthesis in the developing lung, we have examined IGF-I in the present study. IGF-I has been shown to stimulate TE expression in vascular smooth muscle tissue and cells (13,14), but this effect on other cell types including RPF has not been reported. We found that IGF-I stimulates TE synthesis in the neonatal RPF in a dose-dependent manner. MATERIALS AND METHODSapolis, IN). The project was approved by the Animal Care Committee of St. Louis University. Postnatal d 1 was counted as the birth date, and RPF were isolated as described before (12). Selection of the ages and response to DEX stimulation was dependent on our previous finding that TE expression is maximum at 7 d (12). Pups from two or three litters were combined and were used for extraction of total RNA and isolation of pulmonary fibroblasts by the differential adhesion method (1 5). The cells were passaged once and maintained in RPMI 1640 supplemented with 10% FCS until just before confluency and then in RPMI 1640 with 0.5% FCS to minimize the IGF-I effects of the FCS (14). At this FCS concentration, the results were more consistent than with 0.1 % FCS. Twelve h after the medium switch, cells were treated with increasing concentrations of IGF-I for another 48 h, harvested by 0.25% trypsin and 0.0 1 % EDTA treatment, and processed for extraction of tot...

Fibroblast Growth Factor Receptors Control Epithelial–Mesenchymal Interactions Necessary for Alveolar Elastogenesis

“…One prominent study reported tissue specificity for the inductive effects of IGF1 on elastin expression, with a lack of response in lung fibroblasts (52). However, an earlier study suggested some potential elastogenic effects of IGF1 in lung fibroblasts (53). We observed an inductive response that was greater than that observed for other physiological inducers of lung fibroblast elastin gene expression, such as TGFb or retinoic acid (54,64).…”

“…Conversely, we found changes in the expression of multiple paracrine factors from AT2 cells, including the elastogenic molecule, Igf1 (53,73,74), and its binding protein, Igfbp2. Interestingly, lung expression of IGF1/IGF1R has been demonstrated (49), and deficiency in either IGF1 or IGF1R leads to abnormal lung development (50,64).…”

“…However, details regarding the histopathology of these mice are lacking. Conflicting data exist regarding the ability of IGF1 to promote lung fibroblast elastin expression (52,53). We attempted to reassess the regulatory effects of IGF1 on lung fibroblast elastin expression.…”

Global expression profiles from C57BL/6J and DBA/2J mouse lungs to determine aging-related genes

“…It is noteworthy that IGF-I signaling is a well-established determinant of longevity (29,57). While IGF-I is known to regulate antioxidant defense and cellular stress response systems, it is also known to stimulate Eln expression in neonatal pulmonary fibroblast cells (52). In the present study, differences in IGF-I signaling between B6 and D2 strains at 2 mo of age were observed with respect to the expression of Igfbp2, Igfbp4, and Pik3r1 (Supplemental Table S3).…”

Elastogenesis is linked to epithelial-stromal interactions in postnatal hamster bronchioles

“…Here, the controversy of IGF stimulation of pulmonary fibroblast elastogenesis and its functioning via epithelial-mesenchymal interactions is illustrative. Noguchi and Nelson (1991) have observed an elastogenic effect of IGF in pulmonary fibroblasts of 7-day-old rats (the period of optimal elastogenesis) but, unfortunately, they use supra-physiological concentrations, in the view of Rich et al (1992). In contrast, the latter have found no elastogenic response to physiological concentrations but, in their studies, fibroblasts are isolated from 2-to 3-day-old rats (Rich et al.…”