Distribution of fibroblast growth factor (FGF)-2 and FGF receptor-1 messenger RNA expression and protein presence in the mid-trimester human fetus

Administration of antenatal glucocorticoids upregulates peptide growth factor gene expression in nitrofen-induced congenital diaphragmatic hernia in rats

BACKGROUND/PURPOSE

There is increasing evidence to suggest that various growth factors play a crucial role in fetal lung growth and morphogenesis. An array of peptide growth factors regulate cell proliferation, differentiation, and various other cell functions in the developing lung. The aim of this study was to investigate the effect of antenatal glucocorticoids administration on gene expression of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta1 in nitrofen-induced congenital diaphragmatic hernia (CDH) in rats.

METHODS

A CDH model was induced in pregnant rats after administration of nitrofen. Dexamethasone (Dex; 0.25 mg/kg) was given intraperitoneally on day 18.5 and 19.5 of gestation (term, day 22). Cesarean section was performed on day 21 of gestation. mRNA was extracted from left lung and reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate mRNA expression of each growth factors. Relative levels of mRNA were expressed as a ratio of the band density divided by that of beta-actin, a housekeeping gene known to be expressed at a constant level.

RESULTS

Relative mRNA levels of bFGF and TGF-beta1 were decreased significantly in CDH lung compared with controls. Antenatal Dex treatment up-regulated gene expression of bFGF, PDGF, and TGF-beta1 in the hypoplastic CDH lung.

CONCLUSIONS

The authors' findings suggest that decreased gene expression of bFGF, PDGF, and TGF-beta1 in the CDH lung may suppress lung growth and development. Increased gene expression of bFGF, PDGF, and TGF-beta1 in Dex-treated lung suggests that antenatal glucocorticoid administration may accelerate fetal lung growth by up-regulating these growth factors.

Expression and localization of fibroblast growth factors and fibroblast growth factor receptors in the developing rat kidney

Expression and localization of fibroblast growth factors and fibroblast growth factor receptors in the developing rat kidney.

BACKGROUND

The permanent kidney, or metanephros, develops through a complex series of reciprocal inductive events and involves branching morphogenesis, tubulogenesis, angiogenesis, and tissue remodeling. Fibroblast growth factors (FGFs) are a family of growth and differentiation factors that have been implicated in metanephric development. FGFs exert their actions through tyrosine kinase receptors, FGFRs, which are encoded by four FGFR genes (FGFR1 through FGFR4).

METHODS

Reverse transcriptase-polymerase chain reaction was used to detect the expression of FGFs and FGFRs in rat metanephroi from embryonic day (E) 14 to E21. Nonradioactive in situ hybridization was used to localize FGF1 mRNA in E20 rat metanephroi, and immunohistochemistry was used to localize FGFRs in E15 and E20 rat metanephroi.

RESULTS

We detected the expression of mRNAs for FGF1 through FGF5, FGF7 through FGF10, and FGFR1 through FGFR4 (IIIb and IIIc splice variants) in rat metanephroi from E14 to E21. By in situ hybridization, FGF1 mRNA was detected in the nephrogenic zone, ureteric epithelium, and developing nephron elements. FGFR proteins were localized in a distinct pattern that altered with maturation. FGFR1 was widely distributed in developing metanephric epithelia and mesenchyme, but not in developing interstitium. FGFR2 was also widely distributed in nephron epithelia, particularly in proximal convoluted tubules, but was not detected in metanephric mesenchyme, mesenchymal condensates, or developing interstitium. FGFR3 was localized to mesenchymal condensates, nephron elements, and medullary interstitium but not proximal convoluted tubules. FGFR4 was localized mostly to maturing nephron structures and was not detected in nephrogenic mesenchyme, mesenchymal condensates, or developing interstitium.

CONCLUSIONS

These results indicate that FGFs and FGFRs are expressed in the developing rat metanephros from at least E14 and that they likely play important roles in metanephric development and maturation.

Elevated platelet-derived growth factor-B in congenital cystic adenomatoid malformations requiring fetal resection

BACKGROUND

During lung development, platelet-derived growth factor-BB (PDGF-BB) is maximal during the canalicular stage and decreases by the saccular stage. PDGF-BB stimulates lung growth by increasing cell proliferation. Fetal CCAMs have been shown to have an elevated proliferative index, but it is not known why some CCAMs rapidly enlarge in utero and cause fetal hydrops. The authors hypothesized that the high proliferative index and rapid enlargement of some fetal CCAMs may be caused by persistently elevated PDGF-BB production compared with normal fetal lung.

METHODS

To test this hypothesis, tissue was obtained at the time of resection from two fetal CCAMs (22 weeks), three full-term CCAMs, and three normal fetal lungs (21 to 22 weeks). PDGF-BB production by fetal CCAMs was compared with normal age-matched fetal lung using immunohistochemistry, reverse transcriptionase-polymerase chain reaction (RT-PCR), and Western blot analysis.

RESULTS

CCAMs resulting in fetal hydrops and requiring fetal resection had strong mesenchymal immunostaining for PDGF-BB next to epithelial lined cysts, increased PDGF-B gene expression by RT-PCR, and elevated PDGF-BB protein by Western blot, compared with normal age-matched fetal lung. Term CCAMs had minimal PDGF-BB staining, PDGF-B gene expression, and PDGF-BB protein production.

CONCLUSIONS

CCAMs that grew rapidly and progressed to hydrops, requiring in utero resection, demonstrated increased mesenchymal PDGF-B gene expression and PDGF-BB protein production compared with age-matched normal fetal lung, which may, in part, be responsible for the autonomous growth and proliferation seen in hydropic fetal CCAMs.

Differential expression of fibroblast growth factor receptor-1, -2, and -3 and syndecan-1, -2, and -4 in neonatal rat mandibular condyle and calvaria during osteogenic differentiation in vitro

Fibroblast growth factors (FGFs) play important roles in the control of skeletal cell growth and differentiation. To identify the mechanisms of regulation of FGF actions during chondrogenesis and osteogenesis, we investigated, by immunohistochemistry, the spatiotemporal expression of the high-affinity FGF receptors (FGFR-1, -2, and -3) and coreceptors (syndecans-1, -2, and -4) in newborn rat condyle and calvaria during chondrogenesis and osteogenesis in vitro. During chondrogenesis at 4 days of culture, condyle chondrocytes showed weak FGFR-1, FGFR-2, and syndecan-1 immunoreactivity; stronger syndecan-2 expression; and marked FGFR-3 and syndecan-4 immunolabeling. At a later stage (i.e., 9 days of culture), FGFR-1, -2, and -3 were coexpressed with syndecan-4 in chondrocytes. Condyle progenitor cells located in the condyle perichondrium initially expressed strong syndecan-2 and -4 and weak syndecan-1 labeling, whereas no FGFR was detectable. When these cells differentiated into osteoblasts, they expressed syndecan-2 and -4 coincidently with FGFR-1, -2, and -3 at 9 days of culture. In newborn rat calvaria, syndecan-1, -2, and -4 were coexpressed mainly with FGFR-1 and -2 in osteoblasts. In the two models, treatment with FGF-2 (100 ng/mL) at 4-9 days of culture increased cell growth and decreased glycosaminoglycan or collagen synthesis, respectively, suggesting interactions of FGF-2 with distinct FGFRs and syndecans during chondrogenesis and osteogenesis. The coincident or distinct spatiotemporal expression pattern of FGFRs and syndecans in chondrocytes, progenitor cells, and osteoblasts represents a dynamic mechanism by which FGF effects on skeletal cells may be controlled in a coordinate manner during cartilage and bone formation in vitro.

Control of Bone Growth by Fibroblast Growth Factors

Fibroblast growth factors (FGFs) and their receptors (FGFRs) negatively regulate longitudinal bone growth. Activating FGFR3 mutations impair growth, causing human skeletal dysplasias, whereas inactivating mutations stimulate growth. Systemic administration of FGF-2 to mice stimulates bone growth at low doses but inhibits growth at high doses. In organ culture, FGF-2 inhibits growth by decreasing growth plate chondrocyte proliferation, hypertrophy and cartilage matrix synthesis. Local FGF-2 infusion accelerates ossification of growth plate cartilage. Thus, FGFs may regulate both growth plate chondrogenesis and ossification.

FGF-2 induces surfactant protein gene expression in foetal rat lung epithelial cells through a MAPK-independent pathway

Fibroblast growth factors (FGFs) play important roles in diverse aspects of animal development including mammalian lung epithelial cell proliferation, differentiation, and branching morphogenesis. We developed an in vitro lung epithelial cell culture system to study functions and mechanisms of FGFs in regulating growth and differentiation of primary foetal rat lung epithelial cells. In comparison with other growth factors such as IGF-I, EGF, and HGF, FGFs were the most potent mitogens in stimulating lung epithelial cell proliferation. In the presence of FGF-1, 2, or 7, the primary lung epithelial cells could be propagated for generations and grown for more than two mo in vitro. Among the three FGFs tested, FGF-7 showed the strongest stimulation in cell growth. FGF-2, on the other hand, is the most effective inducer of lung epithelial cell-specific surfactant protein gene expression (SP-A, -B, and -C). FGF-2 upregulated SP-C expression in a dose-dependent manner. More interestingly, the induction of surfactant protein gene expression by FGF-2 appeared to be independent of MAPK pathway, since the SP-C expression was not inhibited but rather augmented by MEK1 inhibitor which inhibited MAPK activation and cell proliferation. Similar effects were observed for the expressions of surfactant protein genes SP-A and SP-B. In contrast to MAPK, FGF-2-induced SP-C expression was partially inhibited by PI 3-kinase inhibitor wortmannin. These data suggest dynamic roles and complex signalling mechanisms of FGFs in regulating lung epithelial cell proliferation and differentiation. While a MAPK-dependent pathway is essential for all three FGFs to stimulate cell proliferation, a MAPK-independent pathway may be responsible for the FGF-2-induced surfactant protein gene expression. PI 3-kinase may play an important role in mediating FGF-2-induced lung epithelial cell differentiation during development.

Spatio-temporal expression of FGFR 1, 2 and 3 genes during human embryo-fetal ossification

Mutations in FGFR 1-3 genes account for various human craniosynostosis syndromes, while dwarfism syndromes have been ascribed exclusively to FGFR 3 mutations. However, the exact role of FGFR 1-3 genes in human skeletal development is not understood. Here we describe the expression pattern of FGFR 1-3 genes during human embryonic and fetal endochondral and membranous ossification. In the limb bud, FGFR 1 and FGFR 2 are initially expressed in the mesenchyme and in epidermal cells, respectively, but FGFR 3 is undetectable. At later stages, FGFR 2 appears as the first marker of prechondrogenic condensations. In the growing long bones, FGFR 1 and FGFR 2 transcripts are restricted to the perichondrium and periosteum, while FGFR 3 is mainly expressed in mature chondrocytes of the cartilage growth plate. Marked FGFR 2 expression is also observed in the periarticular cartilage. Finally, membranous ossification of the skull vault is characterized by co-expression of the FGFR 1-3 genes in preosteoblasts and osteoblasts. In summary, the simultaneous expression of FGFR 1-3 genes in cranial sutures might explain their involvement in craniosynostosis syndromes, whereas the specific expression of FGFR 3 in chondrocytes does correlate with the involvement of FGFR 3 mutations in inherited defective growth of human long bones.

Fibroblast growth factor-2 and fibroblast growth factor receptor-1 mRNA expression and peptide localization in placentae from normal and diabetic pregnancies

Fibroblast growth factor-2 (FGF-2) is a potent mitogen expressed widely during embryogenesis and in tissues of the human fetus. It is recognized as an endothelial cell mitogen and is angiogenic in vivo. Expression of FGF-2 mRNA has also been shown within the human term placenta, and FGF-2 isolated from placental tissue, suggesting a role in placental growth including angiogenesis. The purpose of this study was to quantify and localize the sites of expression of FGF-2 and its high-affinity receptor, FGFR1, within placentae from normal term human pregnancies (n=8, 39-42 weeks), and pregnancies complicated by pregestational, type 1 diabetes (n=8, 36-40 weeks). Tissues were collected immediately following delivery and were either snap-frozen for RNA isolation, or fixed for either in situ hybridization using a 35S-labelled cRNAs encoding human FGF-2 or FGFR1, or immunocytochemistry using antibodies against human FGF-2 or FGFR1. Northern blot hybridization showed a significantly increased abundance of mRNAs for both FGF-2 and FGFR1 in placentae from diabetic women compared to those from normal women. In normal term placenta FGF-2 mRNA was present at low abundance in fetal villous tissue, in the vascular endothelium of blood vessels, and in the syncytiotrophoblast. FGF-2 mRNA was considerably more abundant in the syncytiotrophoblast and villous tissue of placentae from diabetic patients. Messenger RNA for FGFR1 was similarly distributed to that encoding FGF-2. Immunocytochemistry revealed abundant FGF-2 and FGFR1 peptides in villous vascular endothelial cells, and associated with the cell membranes of stromal tissues in placentae from control pregnancies. Little immunoreactive FGF-2 was present in the syncytiotrophoblast at term. In pregnancies complicated by diabetes intense staining for immunoreactive FGF-2 and for FGFR1 additionally existed in syncytiotrophoblast. The results suggest that FGF-2 acting as an autocrine agent contributes to placental angiogenesis, but may be released from the syncytium into the maternal circulation. Expression is elevated in placentae from diabetic pregnancies, and is particularly associated with the syncytiotrophoblast. This suggests a placental source for the elevated circulating maternal FGF-2 previously described in diabetic pregnancy.