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A6108 - How Fibroblast Growth Factors Critical to Mouse Lung Branching Morphogenesis Functionally Compare in Early Human Lung Development
Author Block: S. Danopoulos1, S. Bellusci2, D. Warburton1, D. Al Alam1; 1Surgery, Children's Hospital Los Angeles, Los Angeles, CA, United States, 2University of Giessen Lung Center and Member of the German Lung Center, Giessen, Germany.
Rationale: Fibroblast Growth Factor (FGF) signaling plays an important role in lung organogenesis. Over the last decades, FGF signaling in lung development have been extensively studied in animal models. Genetic studies in mouse have shown that perturbation of one or more FGF ligand and/or receptors at specific developmental stages can lead to branching defects. However, little is known about their expression, localization and functional roles in human fetal lung development. In this study, we aimed to determine the expression and function of several FGF ligands and receptors in human lung development. Methods: Using in situ hybridization (ISH) and RNA-sequencing, we assessed the expression and distribution of several FGFs in native human fetal lung. Human fetal lung explants derived from 10-12 weeks gestation lungs were treated with human recombinant FGFs (FGF7, FGF9 or FGF10) in air liquid interface culture for 48 hours. Explants were analyzed grossly to observe differences in branching pattern, as well as at the cellular and molecular level via qRT-PCR and histological analyses. Complementary experiments were performed using neutralizing recombinant chimera proteins for FGFR2b and FGFR3b. Results: ISH determined that FGF9 is mainly localized in the distal epithelium, whereas FGF10 demonstrated weak expression throughout the parenchyma with some expression in the smooth muscle cells (SMCs). However, we did not identify high FGF10 expression domains in the distal mesenchyme near the tip of epithelial branches as seen in mouse lung. FGFR2 expression was high in both proximal and distal epithelial cells as well as the SMCs. FGFR3 was expressed mostly in the epithelial cells, with lower expression in the mesenchyme. Through the use of recombinant protein FGFs, we demonstrated that FGF7 and FGF9 had similar effects on human fetal lung as on mouse; however, FGF10 caused the human explants to expand and cyst as opposed to inducing epithelial branching as in mouse. In conjunction with decreased branching, treatment with recombinant FGF7, FGF9 and FGF10 also resulted in decreased SMC expression as well as a decreased double positive SOX2/SOX9 progenitor cell population, which are normally present only in the distal epithelial tips of early human fetal lung, as compared to control explants. Conclusion: Although FGF ligand localization may be somewhat comparable between developing mouse and human lungs, their contributing functional roles may differ substantially. Whilst in mouse it is known that Fgf10 is the main morphogen regulating branching morphogenesis, our data indicate that this is not true in humans.