Peptide growth factors regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts

Assessment of the nitrofen model of congenital diaphragmatic hernia and of the dysregulated factors involved in pulmonary hypoplasia

PURPOSE

To study pulmonary hypoplasia (PH) associated with congenital diaphragmatic hernia (CDH), investigators have been employing a fetal rat model based on nitrofen administration to dams. Herein, we aimed to: (1) investigate the validity of the model, and (2) synthesize the main biological pathways implicated in the development of PH associated with CDH.

METHODS

Using a defined strategy, we conducted a systematic review of the literature searching for studies reporting the incidence of CDH or factors involved in PH development. We also searched for PH factor interactions, relevance to lung development and to human PH.

RESULTS

Of 335 full-text articles, 116 reported the incidence of CDH after nitrofen exposure or dysregulated factors in the lungs of nitrofen-exposed rat fetuses. CDH incidence: 54% (27-85%) fetuses developed a diaphragmatic defect, whereas the whole litter had PH in varying degrees. Downregulated signaling pathways included FGF/FGFR, BMP/BMPR, Sonic Hedgehog and retinoid acid signaling pathway, resulting in a delay in early epithelial differentiation, immature distal epithelium and dysfunctional mesenchyme.

CONCLUSIONS

The nitrofen model effectively reproduces PH as it disrupts pathways that are critical for lung branching morphogenesis and alveolar differentiation. The low CDH rate confirms that PH is an associated phenomenon rather than the result of mechanical compression alone.

REGULATION OF INSULIN-LIKE GROWTH FACTOR (IGF)-BINDING PROTEIN EXPRESSION BY GROWTH FACTORS AND CYTOKINES ALTERS IGF-MEDIATED PROLIFERATION OF POSTNATAL LUNG FIBROBLASTS

Postnatal day 5 is the beginning of septation and the peak of postnatal fibroblast proliferation. The author and colleagues studied fibroblasts from this developmental time period to determine factors that regulate cell proliferation. Exposure of cells to insulin-like growth factor (IGF)-I for 48 hours increased cell number whereas exposure to epithelial growth factor (EGF), platelet-derived growth factor (PDGF)-BB, fibroblast growth factor (FGF)-7, FGF-2, tumor necrosis factor-alpha (TNF-alpha), or interleukin (L)-1beta did not alter cell number. Long[R3]IGF-I (a synthetic IGF analog with reduced affinity for IGF-binding proteins [IGFBPs]) was more potent than IGF-I, with half-maximal stimulation at a dose of 0.6 nM for long[R3]IGF-I compared to 1.5 nM for IGF-I, suggesting that IGFBPs in the conditioned medium (CM) inhibit IGF activity. Addition of exogenous IGFBP-3 inhibited the IGF-stimulated increase in cell number. Addition of IGFBP-4 did not alter IGF activity because IGF-I stimulated proteolysis of IGFBP-4. The expression of mRNA for PAPP-A (a known IGFBP-4 protease) suggests that the clearance of IGFBP-4 is mediated by pregnancy-associated plasma protein (PAPP)-A. Exposure of cells to TNF-alpha or IL-1beta increased IGFBP-3 mRNA abundance and IGFBP-3 protein in CM. PDGF-BB and IL-1beta increased IGFBP-4 protein abundance and PDGF-BB and dibutyryl cAMP increased IGFBP-4 mRNA. The increase in CM IGFBP-3 following TNF-alpha exposure blocked IGF-mediated cell proliferation, suggesting that the growth factor- and cytokine-mediated changes in IGFBP abundance regulate postnatal fibroblast cell proliferation.

Relationship between pregnancy-associated plasma protein-A and lung cancer

BACKGROUND

: Pregnancy-associated plasma protein-A (PAPP-A) has insulin-like growth factor (IGF)-dependent IGFBP-4 protease activity and plays an important role in amplifying local IGF-1 activity in wound healing, vascular repair, and bone remodeling. We postulated that PAPP-A may contribute to the availability and activity of IGFs, which affect lung cancer. Therefore, we determined the levels of PAPP-A in patients with lung cancer and their possible clinical significance.

METHODS

: The study population consisted of 83 patients with lung cancer and 33 healthy subjects as a control group. Serum PAPP-A levels were determined using an ultrasensitive enzyme-linked immunosorbent assay.

RESULTS

: The serum PAPP-A levels were higher in patients with lung cancer [median (interquartile range) 10.7 (7.6-14.2) ng/mL] than in the control group [6.2 (5.2-9.8) ng/mL, P < 0.001]. There was a significant negative correlation between the serum PAPP-A levels and Karnofsky performance status (r = -0.330; P < 0.001) and a positive correlation with patient age (r = 0.358; P < 0.001).

CONCLUSION

: PAPP-A is a proatherosclerotic metalloproteinase that is also thought to be an inflammatory marker. We found that the serum PAPP-A levels increased in patients with lung cancer and postulated that PAPP-A levels may be a prognostic factor in such cases.

Fetal intestinal fibroblasts respond to insulin-like growth factor (IGF)-II better than adult intestinal fibroblasts

Background

We compared IGF responses of fetal and adult intestinal fibroblasts to identify a developmental difference in the IGF-axis. Intestinal fibroblasts were isolated from maternal and fetal jejunum. Media was conditioned at confluence and one week afterwards. The proliferative response at confluence to 5 nM IGF-I or -II was compared.

Results

There were no significant differences in IGFBP expression at confluence. Post-confluence, fetal fibroblasts had no significant changes in IGFBP-2 and IGFBP-3 expression. Post-confluent maternal fibroblasts had increased IGFBP-3 levels that were significant compared to the fetal fibroblasts. IGF-I increased in post-confluent fetal fibroblasts, while in maternal fibroblasts it decreased (p < 0.001). IGF-II secretion decreased significantly in post-confluent maternal fibroblasts (p < 0.05). Maternal fibroblasts proliferated more with IGF-I than IGF-II (p < 0.001). Fetal fibroblasts responded to IGF-II slightly better than IGF-I and significantly greater than maternal cells (p < 0.001).

Conclusion

Fetal intestinal fibroblasts respond to IGF-II with greater proliferation and do not have the increased IGFBPs seen post-confluence in adult intestinal fibroblasts.

Growth factors in lung development

Organized and coordinated lung development follows transcriptional regulation of a complex set of cell-cell and cell-matrix interactions resulting in a blood-gas interface ready for physiologic gas exchange at birth. Transcription factors, growth factors, and various other signaling molecules regulate epithelial-mesenchymal interactions by paracrine and autocrine mechanisms. Transcriptional control at the earliest stages of lung development results in cell differentiation and cell commitment in the primitive lung bud, in essence setting up a framework for pattern formation and branching morphogenesis. Branching morphogenesis results in the formation of the conductive airway system, which is critical for alveolization. Lung development is influenced at all stages by spatial and temporal distribution of various signaling molecules and their receptors and also by the positive and negative control of signaling by paracrine, autocrine, and endocrine mechanisms. Lung bud formation, cell differentiation, and its interaction with the splanchnic mesoderm are regulated by HNF-3beta, Shh, Nkx2.1, HNF-3/Forkhead homolog-8 (HFH-8), Gli, and GATA transcription factors. HNF-3beta regulates Nkx2.1, a transcription factor critical to the formation of distal pulmonary structures. Nkx2.1 regulates surfactant protein genes that are important for the development of alveolar stability at birth. Shh, produced by the foregut endoderm, regulates lung morphogenesis signaling through Gli genes expressed in the mesenchyme. FGF10, produced by the mesoderm, regulates branching morphogenesis via its receptors on the lung epithelium. Alveolization and formation of the capillary network are influenced by various factors that include PDGF, vascular endothelial growth factor (VEGF), and retinoic acid. Epithelial-endothelial interactions during lung development are important in establishing a functional blood-gas interface. The effects of various growth factors on lung development have been demonstrated by gain- or loss-of-function studies in null mutant and transgenic mice models. Understanding the role of growth factors and various other signaling molecules and their cellular interactions in lung development will provide us with new insights into the pathogenesis of bronchopulmonary dysplasia and disorders of lung morphogenesis.

Epidermal growth factor receptor regulates aberrant expression of insulin-like growth factor-binding protein 3

Epidermal growth factor receptor (EGFR) is frequently overexpressed in esophageal carcinoma and its precursor lesions. To gain insights into how EGFR overexpression affects cellular functions in primary human esophageal cells, we performed gene expression profiling and identified insulin-like growth factor-binding protein (IGFBP)-3 as the most up-regulated gene. IGFBP-3 regulates cell proliferation through both insulin-like growth factor-dependent and independent mechanisms. We found that IGFBP-3 mRNA and protein expression was increased in EGFR-overexpressing primary and immortalized human esophageal cells. IGFBP-3 was also up-regulated in EGFR-overexpressing cells in organotypic culture and in EGFR transgenic mice. Furthermore, IGFBP-3 mRNA was overexpressed in 80% of primary esophageal squamous cell carcinomas and 60% of primary esophageal adenocarcinomas. Concomitant up-regulation of EGFR and IGFBP-3 was observed in 60% of primary esophageal squamous cell carcinomas. Immunohistochemistry revealed cytoplasmic localization of IGFBP-3 in the preponderance of preneoplastic and neoplastic esophageal lesions. IGFBP-3 was also overexpressed in esophageal cancer cell lines at both mRNA (60%) and protein (40%) levels. IGFBP-3 secreted by cancer cells was capable of binding to insulin-like growth factor I. Functionally, epidermal growth factor appeared to regulate IGFBP-3 expression in esophageal cancer cell lines. Finally, suppression of IGFBP-3 by small interfering RNA augmented cell proliferation, suggesting that IGFBP-3 may inhibit tumor cell proliferation as a negative feedback mechanism. In aggregate, we have identified for the first time that IGFBP-3 is an aberrantly regulated gene through the EGFR signaling pathway and it may modulate EGFR effects during carcinogenesis.

Pro- and anti-inflammatory cytokines regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts

The inflammatory response of the lung to noxious factors contributes to the pathogenesis of chronic lung injury. Inflammatory mediators regulate the insulin-like growth factor (IGF) system, a key modulator of lung fibroblast proliferation. The activity of IGFs is regulated by IGF-binding proteins (IGFBPs) secreted by lung cells. To investigate the regulation of lung fibroblast IGFBPs by cytokines, we exposed 19-d fetal rat lung fibroblasts to various pro- and anti-inflammatory mediators. IGFBP abundance in conditioned medium (CM) was measured by ligand blot and RNA transcript abundance by RNase protection assays. Fetal rat lung fibroblasts exposed to interleukin (IL)-1beta or tumor necrosis factor (TNF)-alpha for 48 h demonstrated increased abundance of CM IGFBP-3 (5.9- and 4.7-fold increases for IL-1beta and TNF-alpha, respectively) and IGFBP-4 (5.7- and 7.4-fold increases for IL-1beta and TNF-alpha, respectively) that was accompanied by a small increase in IGFBP-4 mRNA and a larger increase in IGFBP-3 mRNA abundance. IGFBP-4 specific proteolysis was examined in CM collected from fetal rat lung fibroblasts after incubation with serum-free medium (SFM), IL-1beta, or TNF-alpha for 48 h. Cell-free aliquots of SFM-CM incubated at 37C for 24 h showed a 65% decrease in IGFBP-4 abundance that was inhibited by 1,10-phenanthroline. In contrast, CM from cells exposed to IL-1beta or TNF-alpha incubated at 37 degrees C for 24 h did not show a significant decrease in IGFBP-4 abundance unless IGF-I was present during the cell-free incubation. Addition of IGFBP-3 to aliquots of SFM-CM reversed the IGF-I-mediated acceleration of IGFBP-4 proteolysis. Similarly, addition of IGFBP-3 to cells in culture increased the accumulation of CM IGFBP-4. These results demonstrate that cytokines regulate IGFBP production and clearance by fetal lung cells and suggest a mechanism by which cytokines regulate cell proliferation following lung injury.

Epidermal growth factor and lung development in the offspring of the diabetic rat

Fetuses of diabetic mothers who were exposed to excessive glucose show delayed maturation. Under these conditions, altered growth factor expression or signaling may have important regulatory influences. We examined the role of epidermal growth factor (EGF) in lung development and maternal diabetes in the rat. In order to evaluate the possible role of glucose for the expression of EGF and the growth of lung tissue, we performed in vitro studies with organotypic cultures of fetal alveolar cells obtained from control rats. Compared to pups of normal rats, the newborn rats of untreated diabetic rats had reduced body weight, but normal lung weight relative to body weight. The air:mesenchyme ratio and the average size of alveoli per mm(2) lung tissue were reduced. The immunoreactivity (IR) of EGF, which was quantified using a computerized image analysis system, appeared with increased intensity and was associated with a reduced intensity of surfactant protein A-IR. The only difference observed between pups of treated diabetic rats and controls was a decrease in the lung weight:body weight ratio. In organotypic cultures, the presence of 13 mmol/L glucose in the cell media increased immunoreactive staining against EGF, but decreased the incorporation of thymidine as compared to the results obtained with alveolar cells grown in a normophysiological concentration of glucose (3 mmol/L). Addition of EGF increased the thymidine incorporation only in cells grown in 3 mM glucose. These findings may indicate immaturity of the lungs of pups of untreated diabetic rats, and subtle alterations in the lungs of pups from treated diabetic rats. The results also suggest that glucose plays a role in the expression of EGF, and that cells exposed to high concentrations of glucose are less responsive to EGF.