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Respiratory tract infections (RTIs) are amongst the leading causes of hospitalizations in children with Down syndrome (DS). Their elevated susceptibility likely stems from structural differences in the airways and immune system abnormalities. The aim of this study was to characterize immune cells in prenatal Trisomy 21 (T21) lungs, potentially explaining vulnerability to RTIs. Single-cell RNA sequencing was used to profile immune cells in prenatal T21 (n = 5) and non-T21 (n = 4) prenatal lungs. Spatial phenotypes were assessed via fluorescent in situ hybridization and immunofluorescent staining on prenatal lung tissue sections. Gene expression analysis was also performed on isolated immune cells from lung single-cell suspensions. Several major immune cell populations were identified. A total of 84 DEGs were identified in at least 1 of the 14 different clusters. A significant decrease in the percentage of B cells was observed in T21 lungs (FDR = 0.0037, * p < 0.05). Furthermore, qRT-PCR demonstrated B cell markers were significantly decreased in T21, including those associated with B cell maturation (* p < 0.05 and ** p < 0.01). Several of these markers were also decreased at the protein level (i.e., CD20 and CD38; * p < 0.05 and ** p < 0.01). Our data demonstrate changes in the T21 pulmonary immune system in utero, primarily within the B cell population, which may contribute to the increased susceptibility to RTIs observed in children with DS.

The Hedgehog (HH) signaling pathway plays an essential role in mouse lung development. We hypothesize that the HH pathway is necessary for branching during human lung development and is impaired in pulmonary hypoplasia. Single-cell, bulk RNA-sequencing data, and human fetal lung tissues were analyzed to determine the spatiotemporal localization of HH pathway actors. Distal human lung segments were cultured in an air-liquid interface and treated with an SHH inhibitor (5E1) to determine the effect of HH inhibition on human lung branching, epithelial-mesenchymal markers, and associated signaling pathways in vitro. Our results showed an early and regulated expression of HH pathway components during human lung development. Inhibiting HH signaling caused a reduction in branching during development and dysregulated epithelial (SOX2, SOX9) and mesenchymal (ACTA2) progenitor markers. FGF and Wnt pathways were also disrupted upon HH inhibition. Finally, we demonstrated that HH signaling elements were downregulated in lung tissues of patients with a congenital diaphragmatic hernia (CDH). In this study, we show for the first time that HH signaling inhibition alters important genes and proteins required for proper branching of the human developing lung. Understanding the role of the HH pathway on human lung development could lead to the identification of novel therapeutic targets for childhood pulmonary diseases.

Patients with Apert syndrome (AS) display a wide range of congenital malformations including tracheal stenosis, which is a disease characterized by a uniform cartilaginous sleeve in place of a normally ribbed cartilagenous trachea. We have studied the cellular and molecular basis of this phenotype in a mouse model of AS ( Fgfr2c +/Δ mice), which shows ectopic expression of Fgfr2b in mesenchymal tissues. Here we report that tracheal stenosis is associated with increased proliferation of mesenchymal cells, where the expression of Fgf10 and its upstream regulators Tbx4 and Tbx5 are abnormally elevated. We show that Fgf10 has a critical inductive role in tracheal stenosis, as genetic knockdown of Fgf10 in Fgfr2c +/Δ mice rescues this phenotype. These novel findings demonstrate a regulatory role for Fgf10 in tracheal development and shed more light on the underlying cause of tracheal defects in AS.

The signaling pathways that are essential for gastric organogenesis have been studied in some detail; however, those that regulate the maintenance of the gastric epithelium during adult homeostasis remain unclear. In this study, we investigated the role of Fibroblast growth factor 10 (FGF10) and its main receptor, Fibroblast growth factor receptor 2b (FGFR2b), in adult glandular stomach homeostasis. We first showed that mouse adult glandular stomach expressed Fgf10, its receptors, Fgfr1b and Fgfr2b, and most of the other FGFR2b ligands (Fgf1, Fgf7, Fgf22) except for Fgf3 and Fgf20. Fgf10 expression was mesenchymal whereas FGFR1 and FGFR2 expression were mostly epithelial. Studying double transgenic mice that allow inducible overexpression of Fgf10 in adult mice, we showed that Fgf10 overexpression in normal adult glandular stomach increased epithelial proliferation, drove mucous neck cell differentiation, and reduced parietal and chief cell differentiation. Although a similar phenotype can be associated with the development of metaplasia, we found that Fgf10 overexpression for a short duration does not cause metaplasia. Finally, investigating double transgenic mice that allow the expression of a soluble form of Fgfr2b, FGF10's main receptor, which acts as a dominant negative, we found no significant changes in gastric epithelial proliferation or differentiation in the mutants. Our work provides evidence, for the first time, that the FGF10-FGFR2b signaling pathway is not required for epithelial proliferation and differentiation during adult glandular stomach homeostasis.

Branching morphogenesis underlies organogenesis in vertebrates and invertebrates, yet is incompletely understood. Here, we show that the sarco-endoplasmic reticulum Ca2+ reuptake pump (SERCA) directs budding across germ layers and species. Clonal knockdown demonstrated a cell-autonomous role for SERCA in Drosophila air sac budding. Live imaging of Drosophila tracheogenesis revealed elevated Ca2+ levels in migratory tip cells as they form branches. SERCA blockade abolished this Ca2+ differential, aborting both cell migration and new branching. Activating protein kinase C (PKC) rescued Ca2+ in tip cells and restored cell migration and branching. Likewise, inhibiting SERCA abolished mammalian epithelial budding, PKC activation rescued budding, while morphogens did not. Mesoderm (zebrafish angiogenesis) and ectoderm (Drosophila nervous system) behaved similarly, suggesting a conserved requirement for cell-autonomous Ca2+ signaling, established by SERCA, in iterative budding.

Myofibroblasts (MYFs) are generally considered the principal culprits in excessive extracellular matrix deposition and scar formation in the pathogenesis of lung fibrosis. Lipofibroblasts (LIFs), on the other hand, are defined by their lipid-storing capacity and are predominantly found in the alveolar regions of the lung. They have been proposed to play a protective role in lung fibrosis. We previously reported that a LIF to MYF reversible differentiation switch occurred during fibrosis formation and resolution. In this study, we tested whether WI-38 cells, a human embryonic lung fibroblast cell line, could be used to study fibroblast differentiation towards the LIF or MYF phenotype and whether this could be relevant for idiopathic pulmonary fibrosis (IPF). Using WI-38 cells, Fibroblast (FIB) to MYF differentiation was triggered using TGF-β1 treatment and FIB to LIF differentiation using Metformin treatment. We also analyzed the MYF to LIF and LIF to MYF differentiation by pre-treating the WI-38 cells with TGF-β1 or Metformin respectively. We used IF, qPCR and bulk RNA-Seq to analyze the phenotypic and transcriptomic changes in the cells. We correlated our transcriptome data from WI-38 cells (obtained via bulk RNA sequencing) with the transcriptomic signature of LIFs and MYFs derived from the IPF cell atlas as well as with our own single-cell transcriptomic data from IPF patients-derived lung fibroblasts (LF-IPF) cultured . We also carried out alveolosphere assays to evaluate the ability of the proposed LIF and MYF cells to support the growth of alveolar epithelial type 2 cells. : WI-38 cells and LF-IPF display similar phenotypical and gene expression responses to TGF-β1 and Metformin treatment. Bulk RNA-Seq analysis of WI-38 cells and LF-IPF treated with TGF-β1, or Metformin indicate similar transcriptomic changes. We also show the partial conservation of the LIF and MYF signature extracted from the Habermann scRNA-seq dataset in WI-38 cells treated with Metformin or TGF-β1, respectively. Alveolosphere assays indicate that LIFs enhance organoid growth, while MYFs inhibit organoid growth. Finally, we provide evidence supporting the MYF to LIF and LIF to MYF reversible switch using WI-38 cells. WI-38 cells represent a versatile and reliable model to study the intricate dynamics of fibroblast differentiation towards the MYF or LIF phenotype associated with lung fibrosis formation and resolution, providing valuable insights to drive future research.

IntroductionSingle-cell RNA-sequencing analyses have revealed the existence of two distinct capillary cell populations in the human lung: general capillary cells (CAP1) and alveolar capillary cells (CAP2). Studies in mouse have shown that the splicing of Vegf-a evolves during embryonic development, creating a temporal pattern of expression for different isoforms, which contributes to the formation of pulmonary capillaries. Moreover, it was demonstrated that murine Vegf-a188 isoform promotes the emergence of CAP2 in vitro. Human homologs of these VEGF-A isoforms exist; however, their role in this process remains elusive. This study investigates the role of VEGF-A and its isoforms in the differentiation of lung capillaries during human prenatal development.MethodsA cohort of human prenatal tissues, aged from the late pseudoglandular to early canalicular stages of development (10–20 weeks of gestation), was used to study the emergence of CAP2 markers (TBX2, SOSTDC1, EDNRB, HPGD, APLN) in correlation with the expression of the different VEGF-A isoforms (VEGF-A121, VEGF-A145, VEGF-A165, VEGF-A189).ResultsRT-qPCR analyses revealed a simultaneous expression of certain VEGF-A isoforms with several CAP2 markers, which peaked at around 18–20 weeks of gestation. Human prenatal lung explants were then treated with recombinant proteins of the different VEGF-A isoforms to study their impact on EC proliferation, as well as on the expression of CAP2 markers. While most of the isoforms did not impact EC proliferation, except for VEGF-A189 which downregulated it, almost all of them upregulated the expression of APLN, a major CAP2 marker. By using fluorescence in situ hybridization, we showed that this increase of expression was specific to the ECs. However, most of the isoforms induced a downregulation of EDNRB and HPGD. They also did not impact the expression of SOSTDC1 and TBX2.DiscussionOur study shows that the different VEGF-A isoforms do not have the same effect on human lung capillary differentiation as those observed with their homologs in mice, highlighting the importance of studying this process in the human model. Moreover, while it demonstrated that VEGF-A isoforms can induce APLN expression in ECs, it also revealed that CAP2 differentiation is most likely a multifactorial process, not only involving VEGF-A.

Fibroblast growth factor (FGF) signaling is necessary for proper lung branching morphogenesis, alveolarization, and vascular development. Dysregulation of FGF activity has been implicated in various lung diseases. Recently, we showed that FGF18 promotes human lung branching morphogenesis by regulating mesenchymal progenitor cells. However, the underlying mechanisms remain unclear. Thus, we aimed to determine the role of FGF18 and its receptors (FGFR) in regulating mesenchymal cell proliferation, migration, and differentiation from pseudoglandular to canalicular stage. We performed siRNA assays to identify the specific FGFR(s) associated with FGF18-induced biological processes. We found that FGF18 increased proliferation and migration in human fetal lung fibroblasts (HFLF) from both stages. FGFR2/FGFR4 played a significant role in pseudoglandular stage. HFLF proliferation, while FGFR3/FGFR4 were involved in canalicular stage. FGF18 enhanced HFLF migration through FGFR2 and FGFR4 in pseudoglandular and canalicular stage, respectively. Finally, we provide evidence that FGF18 treatment leads to reduced expression of myofibroblast markers (ACTA2 and COL1A1) and increased expression of lipofibroblast markers (ADRP and PPARγ) in both stages HFLF. However, the specific FGF18/FGFR complex involved in this process varies depending on the stage. Our findings suggest that in context of human lung development, FGF18 tends to associate with distinct FGFRs to initiate specific biological processes on mesenchymal cells.

Cystic fibrosis (CF)-related bone disease has emerged as a significant comorbidity of CF and is characterized by decreased bone formation and increased bone resorption. Both osteoblast and osteoclast differentiations are impacted by cystic fibrosis transmembrane conductance regulator (CFTR) mutations. The defect of CFTR chloride channel or the loss of CFTR’s ability to interact with other proteins affect several signaling pathways involved in stem cell differentiation and the commitment of these cells toward bone lineages. Specifically, TGF-β, nuclear factor-kappa B (NF-κB), PI3K/AKT, and MAPK/ERK signaling are disturbed by CFTR mutations, thus perturbing stem cell differentiation. High inflammation in patients changes myeloid lineage secretion, affecting both myeloid and mesenchymal differentiation. In osteoblast, Wnt signaling is impacted, resulting in consequences for both bone formation and resorption. Finally, CFTR could also have a direct role in osteoclast’s resorptive function. In this review, we summarize the existing literature on the role of CFTR mutations on the commitment of induced pluripotent stem cells to bone cells.