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.

How high resolution 3-dimensional imaging changes our understanding of postnatal lung development

During the last 10 + years biologically and clinically significant questions about postnatal lung development could be answered due to the application of modern cutting-edge microscopic and quantitative histological techniques. These are in particular synchrotron radiation based X-ray tomographic microscopy (SRXTM), but also ³Helium Magnetic Resonance Imaging, as well as the stereological estimation of the number of alveoli and the length of the free septal edge. First, the most important new finding may be the following: alveolarization of the lung does not cease after the maturation of the alveolar microvasculature but continues until young adulthood and, even more important, maybe reactivated lifelong if needed to rescue structural damages of the lungs. Second, the pulmonary acinus represents the functional unit of the lung. Because the borders of the acini could not be detected in classical histological sections, any investigation of the acini requires 3-dimensional (imaging) methods. Based on SRXTM it was shown that in rat lungs the number of acini stays constant, meaning that their volume increases by a factor of ~ 11 after birth. The latter is very important for acinar ventilation and particle deposition.

Pre- and postnatal exposure of mice to concentrated urban PM2.5 decreases the number of alveoli and leads to altered lung function at an early stage of life

Gestational exposure to air pollution is associated with negative outcomes in newborns and children. In a previous study, we demonstrated a synergistic negative effect of pre- and postnatal exposure to PM_2.5 on lung development in mice. However, the means by which air pollution affects development of the lung have not yet been identified. In this study, we exposed pregnant BALB/c mice and their offspring to concentrated urban PM_2.5 (from São Paulo, Brazil; target dose 600 μg/m³ for 1 h daily). Exposure was started on embryonic day 5.5 (E5.5, time of placental implantation). Lung tissue of fetuses and offspring was submitted to stereological and transcriptomic analyses at E14.5 (pseudoglandular stage of lung development), E18.5 (saccular stage) and P40 (postnatal day 40, alveolarized lung). Additionally, lung function and cellularity of bronchoalveolar lavage (BAL) fluid were studied in offspring animals at P40. Compared to control animals that were exposed to filtered air throughout gestation and postnatal life, PM-exposed mice exhibited higher lung elastance and a lower alveolar number at P40 whilst the total lung volume and cellularity of BAL fluid were not affected. Glandular and saccular structures of fetal lungs were not altered upon gestational exposure; transcriptomic signatures, however, showed changes related to DNA damage and its regulation, inflammation and regulation of cell proliferation. A differential expression was validated at E14.5 for the candidates Sox8, Angptl4 and Gas1. Our data substantiate the in utero biomolecular effect of gestational exposure to air pollution and provide first-time stereological evidence that pre- and early life-postnatal exposure compromise lung development, leading to a reduced number of alveoli and an impairment of lung function in the adult mouse.

The artificial placenta: Continued lung development during extracorporeal support in a preterm lamb model

PURPOSE

An artificial placenta (AP) utilizing extracorporeal life support (ECLS) could avoid the harm of mechanical ventilation (MV) while allowing the lungs to develop.

METHODS

AP lambs (n = 5) were delivered at 118 days gestational age (GA; term = 145 days) and placed on venovenous ECLS (VV-ECLS) with jugular drainage and umbilical vein reinfusion. Lungs remained fluid-filled. After 10 days, lambs were ventilated. MV control lambs were delivered at 118 ("early MV"; n = 5) or 128 days ("late MV"; n = 5), and ventilated. Compliance and oxygenation index (OI) were calculated. After sacrifice, lungs were procured and H&E-stained slides scored for lung injury. Slides were also immunostained for PDGFR-α and α-actin; alveolar development was quantified by the area fraction of alveolar septal tips staining double-positive for both markers.

RESULTS

Compliance of AP lambs was 2.79 ± 0.81 C_dyn compared to 0.83 ± 0.19 and 3.04 ± 0.99 for early and late MV, respectively. OI in AP lambs was lower than early MV lambs (6.20 ± 2.10 vs. 36.8 ± 16.8) and lung injury lower as well (1.8 ± 1.6 vs. 6.0 ± 1.2). Double-positive area fractions were higher in AP lambs (0.012 ± 0.003) than early (0.003 ± 0.0005) and late (0.004 ± 0.002) MV controls.

CONCLUSIONS

Lung development continues and lungs are protected from injury during AP support relative to mechanical ventilation.

LEVEL OF EVIDENCE

n/a (basic/translational science).

Protective effect of electro-acupuncture at maternal different points on perinatal nicotine exposure-induced pulmonary dysplasia in offspring based on HPA axis and signal transduction pathway

Perinatal nicotine exposure can not only lead to lung dysplasia in offspring, but also cause epigenetic changes and induce transgenerational asthma. Previous studies have shown that electro-acupuncture (EA) applied to "Zusanli" (ST 36) can improve the lung morphology and correct abnormal expression of lung development-related protein in perinatal nicotine exposure offspring. However, it is still unclear whether ST 36 has a specific therapeutic effect and how maternal acupuncture can protect the offspring from pulmonary dysplasia. In this study, we compared the different effect of ST 36 and "Fenglong" (ST 40), which belong to the same meridian, in terms of lung pulmonary function and morphology, PPARγ, β-catenin, GR levels in the lung tissues and CORT in the serum of perinatal nicotine exposure offspring, and explored the mechanism of acupuncture based on the maternal hypothalamus-pituitary-adrenal (HPA) axis. It is shown that EA applied to ST 36 could restore the normal function of maternal HPA axis and alleviate maternal glucocorticoid overexposure in offspring, thereby it can up-regulate the PTHrP/PPARγ and down-regulate the Wnt/β-catenin signaling pathways, and protects perinatal nicotine exposure-induced pulmonary dysplasia in offspring. Its effect is better than that of ST 40. These results are of great significance in preventing perinatal nicotine exposure-induced pulmonary dysplasia in offspring.

FOXF1 transcription factor promotes lung morphogenesis by inducing cellular proliferation in fetal lung mesenchyme

Organogenesis is regulated by mesenchymal-epithelial signaling events that induce expression of cell-type specific transcription factors critical for cellular proliferation, differentiation and appropriate tissue patterning. While mesenchymal transcription factors play a key role in mesenchymal-epithelial interactions, transcriptional networks in septum transversum and splanchnic mesenchyme remain poorly characterized. Forkhead Box F1 (FOXF1) transcription factor is expressed in mesenchymal cell lineages; however, its role in organogenesis remains uncharacterized due to early embryonic lethality of Foxf1^-/- mice. In the present study, we generated mesenchyme-specific Foxf1 knockout mice (Dermo1-Cre Foxf1^-/-) and demonstrated that FOXF1 is required for development of respiratory, cardiovascular and gastrointestinal organ systems. Deletion of Foxf1 from mesenchyme caused embryonic lethality in the middle of gestation due to multiple developmental defects in the heart, lung, liver and esophagus. Deletion of Foxf1 inhibited mesenchyme proliferation and delayed branching lung morphogenesis. Gene expression profiling of micro-dissected distal lung mesenchyme and ChIP sequencing of fetal lung tissue identified multiple target genes activated by FOXF1, including Wnt2, Wnt11, Wnt5A and Hoxb7. FOXF1 decreased expression of the Wnt inhibitor Wif1 through direct transcriptional repression. Furthermore, using a global Foxf1 knockout mouse line (Foxf1^-/-) we demonstrated that FOXF1-deficiency disrupts the formation of the lung bud in foregut tissue explants. Finally, deletion of Foxf1 from smooth muscle cell lineage (smMHC-Cre Foxf1^-/-) caused hyper-extension of esophagus and trachea, loss of tracheal and esophageal muscle, mispatterning of esophageal epithelium and decreased proliferation of smooth muscle cells. Altogether, FOXF1 promotes lung morphogenesis by regulating mesenchymal-epithelial signaling and stimulating cellular proliferation in fetal lung mesenchyme.

Glucocorticoids influence versican and chondroitin sulphate proteoglycan levels in the fetal sheep lung

BACKGROUND

Prenatal glucocorticoid treatment decreases alveolar tissue volumes and facilitates fetal lung maturation, however the mechanisms responsible are largely unknown. This study examines whether changes in versican levels or sulphation patterns of chondroitin sulphate (CS) side chains, are associated with glucocorticoid-induced reductions in peri-alveolar tissue volumes.

METHODS

Lung tissue was collected from 1) fetal sheep at 131 ± 0.1 days gestational age (GA) infused with cortisol (122-131d GA) to prematurely induce a pre-parturient-like rise in circulating cortisol, 2) fetal sheep at 143d GA bilaterally adrenalectomised (ADX) at 112d GA to remove endogenous cortisol and 3) fetal sheep at 124d GA in which bolus doses (2 × 11.4 mg) of betamethasone were administered to the pregnant ewe. The level and distribution of versican and CS glycosaminoglycans (GAG) were determined using immunohistochemistry (IHC). Fluorophore assisted carbohydrate electrophoresis (FACE) was used to determine changes in CS sulphation patterns.

RESULTS

Cortisol infusion significantly decreased chondrotin-6-sulphate levels (C-6-S) to 16.4 ± 0.7 AU, compared with saline-infused fetuses (18.9 ± 0.7 AU: p = 0.04) but did not significantly alter the level of versican or chondroitin-4-sulphate (C-4-S). ADX significantly increased the level of C-4-S (28.2 ± 2.2 AU), compared with sham-operated fetuses (17.8 ± 2.0 AU; p = 0.006) without altering versican or C-6-S levels. Betamethasone significantly decreased versican, C-4-S and C-6-S in the fetal sheep lung (19.2 ± 0.9 AU, 24.9 ± 1.4 AU and 23.2 ± 1.0 AU, respectively), compared with saline-exposed fetuses (24.3 ± 0.4 AU, p = 0.0004; 33.3±0.6 AU, p = 0.0003; 29.8±1.3 AU, 0.03, respectively).

CONCLUSIONS

These results indicate that glucocorticoids alter versican levels and CS side chain microstructure in alveolar lung tissue. Betamethasone appears to have a greater impact on versican and CS side chains than cortisol.

Fetal lung transcriptome patterns in an ex vivo compression model of diaphragmatic hernia

BACKGROUND

The purpose of this study was to employ a novel ex vivo lung model of congenital diaphragmatic hernia (CDH) to determine how a mechanical compression affects early pulmonary development.

METHODS

Day-15 whole fetal rat lungs (n = 6-12/group) from nitrofen-exposed and normal (vehicle only) dams were explanted and cultured ex vivo in compression microdevices (0.2 or 0.4 kPa) for 16 h to mimic physiologic compression forces that occur in CDH in vivo. Lungs were evaluated with significance set at P < 0.05.

RESULTS

Nitrofen-exposed lungs were hypoplastic and expressed lower levels of surfactant protein C at baseline. Although compression alone did not alter the α-smooth muscle actin (ACTA2) expression in normal lungs, nitrofen-exposed lungs had significantly increased ACTA2 transcripts (0.2 kPa: 2.04 ± 0.15; 0.4 kPa: 2.22 ± 0.11; both P < 0.001). Nitrofen-exposed lungs also showed further reductions in surfactant protein C expression at 0.2 and 0.4 kPa (0.53 ± 0.04, P < 0.01; 0.69 ± 0.23, P < 0.001; respectively). Whereas normal lungs exposed to 0.2 and 0.4 kPa showed significant increases in periostin (POSTN), a mechanical stress-response molecule (1.79 ± 0.10 and 2.12 ± 0.39, respectively; both P < 0.001), nitrofen-exposed lungs had a significant decrease in POSTN expression (0.4 kPa: 0.67 ± 0.15, P < 0.001), which was confirmed by immunohistochemistry.

CONCLUSIONS

Collectively, these pilot data in a model of CDH lung hypoplasia suggest a primary aberration in response to mechanical stress within the nitrofen lung, characterized by an upregulation of ACTA2 and a downregulation in SPFTC and POSTN. This ex vivo compression system may serve as a novel research platform to better understand the mechanobiology and complex regulation of matricellular dynamics during CDH fetal lung development.

Cell type specific expression of Follistatin-like 1 (Fstl1) in mouse embryonic lung development

Follistatin like-1 (Fstl1) is a secreted glycoprotein and can be up-regulated by TGF-β1. To better study the function of Fstl1 in lung development, we examined Fstl1 expression in the developing lung, in a cell type specific manner, using a tamoxifen inducible Fstl1-reporter mouse strain. Our results show that Fstl1 is ubiquitously expressed at saccular stage in the developing lung. At E18.5, Fstl1 expression is robust in most type of mesenchymal cells, including airway smooth muscle cells surrounding airways, vascular smooth muscle cells, endothelial cells, and vascular pericytes from blood vessel, but not PDGFRα⁺ fibroblasts in the distal alveolar sacs. Meanwhile, relative weak and sporadic signals of Fstl1 expression are observed in epithelium, including a subgroup of club cells in proximal airways and a few type II alveolar epithelial cells in distal airways. Our data help to understand the critical role of Fstl1 in lung development and lung disease pathogenesis.

Effects of Hyperoxia on the Developing Airway and Pulmonary Vasculature

Although it is necessary and part of standard practice, supplemental oxygen (40-90% O₂) or hyperoxia is a significant contributing factor to development of bronchopulmonary dysplasia, persistent pulmonary hypertension, recurrent wheezing, and asthma in preterm infants. This chapter discusses hyperoxia and the role of redox signaling in the context of neonatal lung growth and disease. Here, we discuss how hyperoxia promotes dysfunction in the airway and the known redox-mediated mechanisms that are important for postnatal vascular and alveolar development. Whether in the airway or alveoli, redox pathways are important and greatly influence the neonatal lung.

β-Catenin maintains lung epithelial progenitors after lung specification

The entire lung epithelium arises from SRY box 9 (SOX9)-expressing progenitors that form the respiratory tree and differentiate into airway and alveolar cells. Despite progress in understanding their initial specification within the embryonic foregut, how these progenitors are subsequently maintained is less clear. Using inducible, progenitor-specific genetic mosaic mouse models, we showed that β-catenin (CTNNB1) maintains lung progenitors by promoting a hierarchical lung progenitor gene signature, suppressing gastrointestinal (GI) genes, and regulating NK2 homeobox 1 (NKX2.1) and SRY box 2 (SOX2) in a developmental stage-dependent manner. At the early, but not later, stage post-lung specification, CTNNB1 cell-autonomously maintained normal NKX2.1 expression levels and suppressed ectopic SOX2 expression. Genetic epistasis analyses revealed that CTNNB1 is required for fibroblast growth factor (Fgf)/Kirsten rat sarcoma viral oncogene homolog (Kras)-mediated promotion of the progenitors. In silico screening of Eurexpress and translating ribosome affinity purification (TRAP)-RNAseq identified a progenitor gene signature, a subset of which depends on CTNNB1. Wnt signaling also maintained NKX2.1 expression and suppressed GI genes in cultured human lung progenitors derived from embryonic stem cells.

Long Noncoding RNA RP11-380D23.2 Drives Distal-Proximal Patterning of the Lung by Regulating PITX2 Expression

Early lung development is a tightly orchestrated process encompassing (a) formation of definitive endoderm, (b) anteriorization of definitive endoderm, followed by (c) specification and maturation of both proximal and distal lung precursors. Several reports detailing the interaction of genes and proteins during lung development are available; however, studies reporting the role(s) of long noncoding RNAs (lncRNA) in lung morphogenesis are limited. To investigate this, we tailored a protocol for differentiation of human-induced pluripotent stem cells into distal and proximal lung progenitors to mimic in vivo lung development. The authenticity of differentiated cells was confirmed by expression of key lung markers such as FoxA2, Sox-17, Nkx2.1, Pitx2, FoxJ1, CC10, SPC, and via scanning as well as transmission electron microscopy. We employed next generation sequencing to identify lncRNAs and categorized them based on their proximity to genes essential for lung morphogenesis. In-depth bioinformatical analysis of the sequencing data enabled identification of a novel lncRNA, RP11-380D23.2, which is located upstream of PITX2 and includes a binding site for PARP1. Chromatin immunoprecipitation and other relevant studies revealed that PARP1 is a repressor for PITX2. Whole genome microarray analysis of RP11-380D23.2/PITX2 knockdown populations of progenitors demonstrated enrichment in proximal progenitors and indicated altered distal-proximal patterning. Dysregulation of WNT effectors in both knockdowns highlighted direct modulation of PITX2 by RP11-380D23.2. Most of these results were validated in four independent hiPSC lines (including a patient-specific CFTR mutant line). Taken together, these findings offer a mechanistic explanation underpinning the role of RP11-380D23.2 during lung morphogenesis via WNT signaling. Stem Cells 2018;36:218-229.

Regulation of vascular signalling by nuclear Sprouty2 in fetal lung epithelial cells: Implications for co-ordinated airway and vascular branching in lung development

Sprouty2 (Spry2) acts as a central regulator of tubular growth and branch patterning in the developing mammalian lung by controlling both magnitude and duration of growth factor signalling. To determine if this protein coordinates airway and vascular growth factor signalling, we tested the hypothesis that Spry2 links the primary cue for airway outgrowth, fibroblast growth factor-10 (FGF-10), to genomic events underpinning the expression and release of vascular endothelial growth factor-A (VEGF-A). Using primary fetal distal lung epithelial cells (FDLE) from rat, and immortalised human bronchial epithelial cells (16HBE14o-), we identified a nuclear sub-population of Spry2 which interacted with regions of the rat and human VEGF-A promoter spanning the hypoxia response element (HRE) and adjacent 3' sites. In FDLE cultured at the PO₂ of the fetal lung, FGF-10 relieved the Spry2 interaction at the HRE region by promoting clearance of a 39 kDa form and this was accompanied by histone-3 S10K14 phosphoacetylation, promoter de-methylation, hypoxia inducible factor-1α activation and VEGF-A expression. This repressive characteristic of nuclear Spry2 was relieved in 16HBE14o- by shRNA knockdown, and stable expression of mutants (C218A; C221A) that do not interact with the VEGF-A promoter HRE region. We conclude that nuclear Spry2 acts as a molecular link which co-ordinates airway and vascular growth of the cardiopulmonary system. This identifies Spry2 as a contributing determinant of design optimality in the mammalian lung.

Elastin in lung development and disease pathogenesis

Elastin is expressed in most tissues that require elastic recoil. The protein first appeared coincident with the closed circulatory system, and was critical for the evolutionary success of the vertebrate lineage. Elastin is expressed by multiple cell types in the lung, including mesothelial cells in the pleura, smooth muscle cells in airways and blood vessels, endothelial cells, and interstitial fibroblasts. This highly crosslinked protein associates with fibrillin-containing microfibrils to form the elastic fiber, which is the physiological structure that functions in the extracellular matrix. Elastic fibers can be woven into many different shapes depending on the mechanical needs of the tissue. In large pulmonary vessels, for example, elastin forms continuous sheets, or lamellae, that separate smooth muscle layers. Outside of the vasculature, elastic fibers form an extensive fiber network that originates in the central bronchi and inserts into the distal airspaces and visceral pleura. The fibrous cables form a looping system that encircle the alveolar ducts and terminal air spaces and ensures that applied force is transmitted equally to all parts of the lung. Normal lung function depends on proper secretion and assembly of elastin, and either inhibition of elastin fiber assembly or degradation of existing elastin results in lung dysfunction and disease.

Perfluorocarbons Prevent Lung Injury and Promote Development during Artificial Placenta Support in Extremely Premature Lambs

BACKGROUND

Extremely premature neonates suffer high morbidity and mortality. An artificial placenta (AP) using extracorporeal life support (ECLS) is a promising therapy.

OBJECTIVES

We hypothesized that intratracheal perfluorocarbon (PFC) instillation during AP support would reduce lung injury and promote lung development relative to intratracheal amniotic fluid or crystalloid.

METHODS

Lambs at an estimated gestational age (EGA) 116-121 days (term 145 days) were placed on venovenous ECLS with jugular drainage and umbilical vein reinfusion and intubated. Airways were managed by the instillation of amniotic fluid and tracheal occlusion (TO; n = 4), or lactated Ringer's (LR; n = 4) or perfluorodecalin (a PFC) without occlusion (n = 4). After 7 days, the animals were sacrificed. Early (EGA 116-121 days) and late (EGA 125-131 days) tissue control lambs were delivered and sacrificed. Lungs were formalin-inflated to 30 cm H2O and sectioned for histology. Injury was scored by an unbiased pathologist. Slides were immunostained for PDGFR-α and α-actin; development was quantified by the area fraction of double-positive tips. Surfactant protein-C (SP-C) concentration in bronchoalveolar lavage fluid was quantified using ELISA.

RESULTS

Total injury scores were lower in PFC lungs (1.8 ± 1.7) than in TO (6.5 ± 2.1; p = 0.01) and LR lungs (5.5 ± 2.4; p = 0.01). The area fraction of double-positive alveolar tips appeared higher in PFC lungs than in TO lungs (0.18 ± 0.007 vs. 0.008 ± 0.004; p = 0.07). SP-C concentration was higher in PFC lungs than in TO lungs (37.9 ± 7.6 vs. 20.0 ± 5.4 pg/mL; p = 0.005), and both early (12.4 ± 1.7 g/mL; p = 0.007) and late tissue control lungs (15.1 ± 5.0 pg/mL; p = 0.0008).

CONCLUSION

During AP support, intratracheal PFC prevents lung injury and promotes normal lung development better than crystalloid or amniotic fluid with TO.

Chronic Intermittent Hypoxia in Premature Infants: The Link Between Low Fat Stores, Adiponectin Receptor Signaling and Lung Injury

Premature infants have chronic intermittent hypoxia (CIH) that increases morbidity, and the youngest and the smallest premature infants are at the greatest risk. The combination of lung injury from inflammation/oxidative stress causing low functional residual capacity combined with frequent short apneas leads to CIH. Adiponectin (APN) is an adipose-derived adipokine that protects the lung from inflammation and oxidative stress. Premature and small for gestational age (SGA) infants have minimal body fat and low levels of circulating APN. To begin to understand the potential role of APN in lung protection during lung development, we characterized the developmental profile of APN and APN receptors (AdipoR1 and AdipoR2) protein and mRNA expression in the newborn rat lung at fetal day (FD) 19, and postnatal days (PD) 1, 4, 7, 10, 14, 21, and 28. Protein levels in lung homogenates were measured by western blot analyses; relative mRNA expression was detected by quantitative PCR (qPCR); and serum high molecular weight (HMW) APN was measured using enzyme-linked immunosorbent assay (ELISA). Results: APN protein and mRNA levels were lowest at FD19 and PD1, increased 2.2-fold at PD4, decreased at PD10, and then increased again at PD21. AdipoR1 protein and mRNA levels peaked at PD1, followed by a threefold drop by PD4, and remained low until PD21. AdipoR2 protein and mRNA levels also peaked at PD1, but remained high at PD4, followed by a 1.7-fold drop by PD10 that remained low by PD21. Serum APN levels detected by ELISA did not differ from PD4 to PD28. To date, this is the first report characterizing APN and APN receptor protein and mRNA expression in the rat lung during development. The developmental stage of the newborn rat lung models that of the premature human infant; both are in the saccular stage of lung development. In the newborn rat lung, alveolarization begins at PD4, peaks at PD10, and ends at PD21. Importantly, we found that AdipoR1 receptor protein and mRNA expression is lowest during lung alveolarization (PD4 to PD21). Thus, we speculate that low levels of AdipoR1 during lung alveolarization contributes to the increased susceptibility to developing acute lung edema and chronic lung injury such as bronchopulmonary dysplasia (BPD) in premature human infants.

FGF receptors control alveolar elastogenesis

Alveologenesis, the final step of lung development, is characterized by the formation of millions of alveolar septa that constitute the vast gas-exchange surface area. The genetic network driving alveologenesis is poorly understood compared with earlier steps in lung development. FGF signaling through receptors Fgfr3 and Fgfr4 is crucial for alveologenesis, but the mechanisms through which they mediate this process remain unclear. Here we show that in Fgfr3;Fgfr4 (Fgfr3;4) global mutant mice, alveolar simplification is first observed at the onset of alveologenesis at postnatal day 3. This is preceded by disorganization of elastin, indicating defects in the extracellular matrix (ECM). Although Fgfr3 and Fgfr4 are expressed in the mesenchyme and epithelium, inactivation in the mesenchyme, but not the epithelium, recapitulated the defects. Expression analysis of components of the elastogenesis machinery revealed that Mfap5 (also known as Magp2), which encodes an elastin-microfibril bridging factor, is upregulated in Fgfr3;4 mutants. Mfap5 mutation in the Fgfr3;4 mutant background partially attenuated the alveologenesis defects. These data demonstrate that, during normal lung maturation, FGF signaling restricts expression of the elastogenic machinery in the lung mesenchyme to control orderly formation of the elastin ECM, thereby driving alveolar septa formation to increase the gas-exchange surface.

14-3-3ζ loss leads to neonatal lethality by microRNA-126 downregulation-mediated developmental defects in lung vasculature

Background

The 14-3-3 family of proteins have been reported to play an important role in development in various mouse models, but the context specific developmental functions of 14-3-3ζ remain to be determined. In this study, we identified a context specific developmental function of 14-3-3ζ.

Results

Targeted deletion of 14-3-3ζ in the C57Bl/6J murine genetic background led to neonatal lethality due to respiratory distress and could be rescued by out-breeding to the CD-1 or backcrossing to the FVB/NJ congenic background. Histological analysis of lung sections from 18.5 days post coitum embryos (dpc) showed that 14-3-3ζ−/− lung development is arrested at the pseudoglandular stage and exhibits vascular defects. The expression of miR-126, an endothelial-specific miRNA known to regulate lung vascular integrity was down-regulated in the lungs of the 14-3-3ζ−/− embryos in the C57Bl/6J background as compared to their wild-type counterparts. Loss of 14-3-3ζ in endothelial cells inhibited the angiogenic capability of the endothelial cells as determined by both trans-well migration assays and tube formation assays and these defects could be rescued by re-expressing miR-126. Mechanistically, loss of 14-3-3ζ led to reduced Erk1/2 phosphorylation resulting in attenuated binding of the transcription factor Ets2 on the miR-126 promoter which ultimately reduced expression of miR-126.

Conclusion

Our data demonstrates that miR-126 is an important angiogenesis regulator that functions downstream of 14-3-3ζ and downregulation of miR-126 plays a critical role in 14-3-3ζ-loss induced defects in lung vasculature in the C57Bl/6J genetic background.

Electronic supplementary material

The online version of this article (10.1186/s13578-017-0186-y) contains supplementary material, which is available to authorized users.

Transcriptomic analysis comparing mouse strains with extreme total lung capacities identifies novel candidate genes for pulmonary function

BACKGROUND

Failure to attain peak lung function by early adulthood is a risk factor for chronic lung diseases. Previously, we reported that C3H/HeJ mice have about twice total lung capacity (TLC) compared to JF1/MsJ mice. We identified seven lung function quantitative trait loci (QTL: Lfnq1-Lfnq7) in backcross/intercross mice derived from these inbred strains. We further demonstrated, superoxide dismutase 3, extracellular (Sod3), Kit oncogene (Kit) and secreted phosphoprotein 1 (Spp1) located on these Lfnqs as lung function determinants. Emanating from the concept of early origin of lung disease, we sought to identify novel candidate genes for pulmonary function by investigating lung transcriptome in C3H/HeJ and JF1/MsJ mice at the completion of embryonic development, bulk alveolar formation and maturity.

METHODS

Design-based stereological analysis was performed to study lung structure in C3H/HeJ and JF1/MsJ mice. Microarray was used for lung transcriptomic analysis [embryonic day 18, postnatal days 28, 70]. Quantitative real time polymerase chain reaction (qRT-PCR), western blot and immunohistochemical analysis were used to confirm selected differences.

RESULTS

Stereological analysis revealed decreased alveolar number density, elastin to collagen ratio and increased mean alveolar volume in C3H/HeJ mice compared to JF1/MsJ. Gene ontology term "extracellular region" was enriched among the decreased JF1/MsJ transcripts. Candidate genes identified using the expression-QTL strategy include: ATP-binding cassette, sub-family G (WHITE), member 1 (Abcg1), formyl peptide receptor 1 (Fpr1), gamma-aminobutyric acid (GABA) B receptor, 1 (Gabbr1); histocompatibility 2 genes: class II antigen E beta (H2-Eb1), D region locus 1 (H2-D1), and Q region locus 4 (H2-Q4); leucine rich repeat containing 6 (testis) (Lrrc6), radial spoke head 1 homolog (Rsph1), and surfactant associated 2 (Sfta2). Noteworthy genes selected as candidates for their consistent expression include: Wnt inhibitor factor 1 (Wif1), follistatin (Fst), chitinase-like 1 (Chil1), and Chil3.

CONCLUSIONS

Comparison of late embryonic, adolescent and adult lung transcript profiles between mouse strains with extreme TLCs lead to the identification of candidate genes for pulmonary function that has not been reported earlier. Further mechanistic investigations are warranted to elucidate their mode of action in determining lung function.

Interstitial lung disease in newborns

The term 'interstitial lung disease' (ILD) refers to a group of disorders involving both the airspaces and tissue compartments of the lung, and these disorders are more accurately termed diffuse lung diseases. Although rare, they are associated with significant morbidity and mortality, with the prognosis depending upon the specific diagnosis. The major categories of ILD in children that present in the neonatal period include developmental disorders, growth disorders, surfactant dysfunction disorders, and specific conditions of unknown etiology unique to infancy. Whereas lung histopathology has been the gold standard for the diagnosis of ILD, as many of the disorders have a genetic basis, non-invasive diagnosis is feasible, and characteristic clinical and imaging features may allow for specific diagnosis in some circumstances. The underlying mechanisms, clinical, imaging, and lung pathology features and outcomes of ILD presenting in newborns are reviewed with an emphasis on genetic mechanisms and diagnosis.

Prenatal stress challenge impairs fetal lung development and asthma severity sex-specifically in mice

Allergic asthma is an increasing health problem worldwide. Interestingly, prenatal challenges such as stress have been associated with an increased risk for asthma during childhood. The underlying pathogenesis of how prenatal stress increases the risk for asthma still remains unclear. Potential targets could be that the fetal immune ontogeny or fetal lung development are compromised by prenatal challenges. Here, we aimed to identify whether prenatal stress challenge affects fetal lung development in mice. C57BL/6 pregnant mice were challenged with sound stress and fetal lung development was assessed histologically. Whilst prenatal stress challenge did not profoundly affect lung development in male fetuses, it resulted in less extensive terminal sacs, surrounded by thicker mesenchymal tissue in female fetuses. Thus, prenatal stress disrupted fetal lung development sex-specifically. Interestingly, upon prenatal stress challenge, the airway hyperresponsiveness and eosinophilic inflammation- two hallmarks of asthma - were significantly increased in adult female offspring, whilst regulatory CD4+ T cells were reduced. These findings strongly underpin the sex-specific association between s challenged fetal development and a sex-specific altered severity of asthma in adult offspring. Our model now allows to identify maternal markers through which the risk for asthma and possible other diseases is vertically transferred before birth in response to challenges. Such identification then opens avenues for primary disease prevention.

Genes involved in leukotriene synthesis pathway are dynamically regulated during lung development in Rhesus monkeys

BACKGROUND

Leukotrienes play critical roles in many inflammatory lung diseases and several antagonists of their receptors have been used in the clinical settings. However, the physiological functions of leukotrienes in lung development are still unclear.

METHOD

The expression levels of 34 genes involved in leukotriene synthesis and function pathway in the lungs of Rhesus monkey during different developmental time points were determined on a MiSeq platform and analyzed by the reads per kilobase of transcript per million mapped reads (RPKM) method.

RESULTS

The results showed that the expression levels of PLA2G1B, PLA2G10, PLA2G2D, ALOX5, and ALOX5AP increased dramatically in the lung of Rhesus monkey, reflecting the changes in the pulmonary environment after delivery. Additionally, the different expression patterns between molecules related to LTB4 and LTC4 synthesis suggested distinct roles of LTB4 and LTC4 in lung development. Finally, the constant expression of CysLT1 during the development process provided new information to the pharmaceutical basis of the use of leukotriene receptor antagonists in the clinical setting.

CONCLUSION

The expression levels of several key genes involved in leukotriene synthesis changed dramatically during lung development in Rhesus monkeys, suggesting the potential roles of leukotrienes in lung development in this animal model.

Vitamin C to Decrease the Effects of Smoking in Pregnancy on Infant Lung Function (VCSIP): Rationale, design, and methods of a randomized, controlled trial of vitamin C supplementation in pregnancy for the primary prevention of effects of in utero tobacco smoke exposure on infant lung function and respiratory health

Despite strong anti-smoking efforts, at least 12% of American women cannot quit smoking when pregnant resulting in >450,000 smoke-exposed infants born yearly. Smoking during pregnancy is the largest preventable cause of childhood respiratory illness including wheezing and asthma. Recent studies have shown a protective effect of vitamin C supplementation on the lung function of offspring exposed to in utero smoke in a non-human primate model and an initial human trial. Vitamin C to Decrease the Effects of Smoking in Pregnancy on Infant Lung Function (VCSIP) is a randomized, double-blind, placebo-controlled trial to evaluate pulmonary function at 3months of age in infants delivered to pregnant smokers randomized to 500mg/day of vitamin C versus placebo during pregnancy. Secondary aims evaluate the incidence of wheezing through 12months and pulmonary function testing at 12months of age. Women are randomized between 13 and 23weeks gestation from clinical sites in Portland, Oregon at Oregon Health & Science University and PeaceHealth Southwest Medical Center and in Indianapolis, Indiana at Indiana University and Wishard Hospital. Vitamin C supplementation occurs from randomization to delivery. Monthly contact with participants and monitoring of medical records is performed to document medication adherence, changes in smoking and medical history, and adverse events. Pulmonary function testing of offspring occurs at 3 and 12months of age and incidence of wheezing and respiratory illness through 12months is captured via at least quarterly questionnaires. Ancillary studies are investigating the impact of vitamin C on placental blood flow and DNA methylation.

Endothelial cells are not required for specification of respiratory progenitors

Crosstalk between mesenchymal and epithelial cells influences organogenesis in multiple tissues, such as lung, pancreas, liver, and the nervous system. Lung mesenchyme comprises multiple cell types, however, and precise identification of the mesenchymal cell type(s) that drives early events in lung development remains unknown. Endothelial cells have been shown to be required for some aspects of lung epithelial patterning, lung stem cell differentiation, and regeneration after injury. Furthermore, endothelial cells are involved in early liver and pancreas development. From these observations we hypothesized that endothelial cells might also be required for early specification of the respiratory field and subsequent lung bud initiation. We first blocked VEGF signaling in E8.5 cultured foreguts with small molecule VEGFR inhibitors and found that lung specification and bud formation were unaltered. However, when we examined E9.5 mouse embryos carrying a mutation in the VEGFR Flk-1, which do not develop endothelial cells, we found that respiratory progenitor specification was impeded. Because the E9.5 embryos were substantially smaller than control littermates, suggesting the possibility of developmental delay, we isolated and cultured foreguts from mutant and control embryos on E8.5, when no size differences were apparent. We found that both specification of the respiratory field and lung bud formation occurred in mutant and control explants. These observations were unaffected by the presence or absence of serum. We also observed that hepatic specification and initiation occurred in the absence of endothelial cells, and that expansion of the liver epithelium in culture did not differ between mutant and control explants. Consistent with previously published results, we also found that pancreatic buds were not maintained in cultured foreguts when endothelial cells were absent. Our observations support the conclusion that endothelial cells are not required for early specification of lung progenitors and bud initiation, and that the diminished lung specification seen in E9.5 Flk-/- embryos is likely due to developmental delay resulting from the insufficient delivery of oxygen, nutrients, and other factors in the absence of a vasculature.

Abnormal lung development in congenital diaphragmatic hernia

The outcomes of patients diagnosed with congenital diaphragmatic hernia (CDH) have recently improved. However, mortality and morbidity remain high, and this is primarily caused by the abnormal lung development resulting in pulmonary hypoplasia and persistent pulmonary hypertension. The pathogenesis of CDH is poorly understood, despite the identification of certain candidate genes disrupting normal diaphragm and lung morphogenesis in animal models of CDH. Defects within the lung mesenchyme and interstitium contribute to disturbed distal lung development. Frequently, a disturbance in the development of the pleuroperitoneal folds (PPFs) leads to the incomplete formation of the diaphragm and subsequent herniation. Most candidate genes identified in animal models have so far revealed relatively few strong associations in human CDH cases. CDH is likely a highly polygenic disease, and future studies will need to reconcile how disturbances in the expression of multiple genes cause the disease. Herein, we summarize the available literature on abnormal lung development associated with CDH.

The Role of Matrix Metalloproteinases in Development, Repair, and Destruction of the Lungs

Normal gas exchange after birth requires functional lung alveolar units that are lined with epithelial cells, parts of which are intricately fused with microvascular capillaries. A significant phase of alveolar lung development occurs in the perinatal period, continues throughout early stages in life, and requires activation of matrix-remodeling enzymes. Failure to achieve an optimum number of alveoli during lung maturation can cause several untoward medical consequences including disabling obstructive and/or restrictive lung diseases that limit physiological endurance and increase mortality. Several members of the matrix metalloproteinase (MMP) family are critical in lung remodeling before and after birth; however, their resurgence in response to environmental factors, infection, and injury can also compromise lung function. Therefore, temporal expression, regulation, and function of MMPs play key roles in developing and maintaining adequate oxygenation under steady state, as well as in diseased conditions. Broadly, with the exception of MMP2 and MMP14, most deletional mutations of MMPs fail to perturb lung development; however, their individual absence can alter the pathophysiology of respiratory diseases. Specifically, under stressed conditions such as acute respiratory infection and allergic inflammation, MMP2 and MMP9 can play a protective role through bacterial clearance and production of chemotactic gradient, while loss of MMP12 can protect mice from smoke-induced lung disease. Therefore, better understanding of the expression and function of MMPs under normal lung development and their resurgence in response respiratory diseases could provide new therapeutic options in the future.

Comparative analysis of the mechanical signals in lung development and compensatory growth

This review compares the manner in which physical stress imposed on the parenchyma, vasculature and thorax and the thoraco-pulmonary interactions, drive both developmental and compensatory lung growth. Re-initiation of anatomical lung growth in the mature lung is possible when the loss of functioning lung units renders the existing physiologic-structural reserves insufficient for maintaining adequate function and physical stress on the remaining units exceeds a critical threshold. The appropriate spatial and temporal mechanical interrelationships and the availability of intra-thoracic space, are crucial to growth initiation, follow-on remodeling and physiological outcome. While the endogenous potential for compensatory lung growth is retained and may be pharmacologically augmented, supra-optimal mechanical stimulation, unbalanced structural growth, or inadequate remodeling may limit functional gain. Finding ways to optimize the signal-response relationships and resolve structure-function discrepancies are major challenges that must be overcome before the innate compensatory ability could be fully realized. Partial pneumonectomy reproducibly removes a known fraction of functioning lung units and remains the most robust model for examining the adaptive mechanisms, structure-function consequences and plasticity of the remaining functioning lung units capable of regeneration. Fundamental mechanical stimulus-response relationships established in the pneumonectomy model directly inform the exploration of effective approaches to maximize compensatory growth and function in chronic destructive lung diseases, transplantation and bioengineered lungs.

Development of the lung

To fulfill the task of gas exchange, the lung possesses a huge inner surface and a tree-like system of conducting airways ventilating the gas exchange area. During lung development, the conducting airways are formed first, followed by the formation and enlargement of the gas exchange area. The latter (alveolarization) continues until young adulthood. During organogenesis, the left and right lungs have their own anlage, an outpouching of the foregut. Each lung bud starts a repetitive process of outgrowth and branching (branching morphogenesis) that forms all of the future airways mainly during the pseudoglandular stage. During the canalicular stage, the differentiation of the epithelia becomes visible and the bronchioalveolar duct junction is formed. The location of this junction stays constant throughout life. Towards the end of the canalicular stage, the first gas exchange may take place and survival of prematurely born babies becomes possible. Ninety percent of the gas exchange surface area will be formed by alveolarization, a process where existing airspaces are subdivided by the formation of new walls (septa). This process requires a double-layered capillary network at the basis of the newly forming septum. However, in parallel to alveolarization, the double-layered capillary network of the immature septa fuses to a single-layered network resulting in an optimized setup for gas exchange. Alveolarization still continues, because, at sites where new septa are lifting off preexisting mature septa, the required second capillary layer will be formed instantly by angiogenesis. The latter confirms a lifelong ability of alveolarization, which is important for any kind of lung regeneration.

Overview of Lung Development in the Newborn Human

In human neonates rapid adaptation from an aqueous intrauterine environment to permanent air breathing is the rate-limiting step for extrauterine life, failure of which justifies the existence of neonatal intensive care units. The lung develops at about 4-6 weeks' gestation in humans as a ventral outpouching of the primitive foregut into the surrounding ventral mesenchyme, termed the laryngotracheal groove. At its posterior end lie progenitor cells that form a pair of bronchial tubes, from which arise all the distal epithelial structures of the lung. In humans, formation of the distal gas exchange surfaces begins in utero at about 20 weeks' gestation and is substantially established by term. Stereotypic branching of the proximal airway ends relatively early at 16-18 weeks at the bronchoalveolar duct junctions. Distally, about 5 finger-like alveolar ducts arise from each bronchoalveolar duct junction and ramify outwards towards the pleura. The majority of alveolar air sacs arise from the sides of the alveolar ducts and each of these alveoli can have up to 5 daughter alveoli arising from the outer surface as subsequent buds. At the end of each alveolar duct lie the mouths of 5 interconnected alveoli. Each family of alveoli arising from each bronchoalveolar duct junction has a different shape depending upon the limitations imposed by the pleural surface as well as the interstitial fascial planes.

Pulmonary Effects of Maternal Smoking on the Fetus and Child: Effects on Lung Development, Respiratory Morbidities, and Life Long Lung Health

Maternal smoking during pregnancy is the largest preventable cause of abnormal in-utero lung development. Despite well known risks, rates of smoking during pregnancy have only slightly decreased over the last ten years, with rates varying from 5-40% worldwide resulting in tens of millions of fetal exposures. Despite multiple approaches to smoking cessation about 50% of smokers will continue to smoke during pregnancy. Maternal genotype plays an important role in the likelihood of continued smoking during pregnancy and the degree to which maternal smoking will affect the fetus. The primary effects of maternal smoking on offspring lung function and health are decreases in forced expiratory flows, decreased passive respiratory compliance, increased hospitalization for respiratory infections, and an increased prevalence of childhood wheeze and asthma. Nicotine appears to be the responsible component of tobacco smoke that affects lung development, and some of the effects of maternal smoking on lung development can be prevented by supplemental vitamin C. Because nicotine is the key agent for affecting lung development, e-cigarette usage during pregnancy is likely to be as dangerous to fetal lung development as is maternal smoking.

Developmental pathways in lung regeneration

The key processes of lung development have been elucidated in the past several decades, helping to identify and characterize the resident progenitor cells that ultimately generate the mature organ. The adult lung is a complex organ consisting in scores of different cell lineages that are remarkably quiescent in the absence of injury. Despite low cellular turnover, the lung can respond quickly and dramatically to acute damage, with spatially restricted stem and progenitor cells re-entering the cell cycle and differentiating to promote repair. The findings from lung developmental biology are now being used to examine the mechanisms that underlie lung regeneration. The use of in vitro models such as pluripotent stem cells and new methods of gene editing have provided models for understanding lung disease and exploring the mechanisms of lung regeneration and have raised the prospect of correcting lung dysfunction. We outline the way that basic studies into lung developmental biology are now being applied to lung regeneration, opening up new avenues of research that may ultimately be harnessed for treatments of lung disease.

Adamts18 deletion results in distinct developmental defects and provides a model for congenital disorders of lens, lung, and female reproductive tract development

The ADAMTS family comprises 19 secreted metalloproteinases that cleave extracellular matrix components and have diverse functions in numerous disease and physiological contexts. A number of them remain 'orphan' proteases and among them is ADAMTS18, which has been implicated in developmental eye disorders, platelet function and various malignancies. To assess in vivo function of ADAMTS18, we generated a mouse strain with inactivated Adamts18 alleles. In the C57Bl6/Ola background, Adamts18-deficient mice are born in a normal Mendelian ratio, and are viable but show a transient growth delay. Histological examination revealed a 100% penetrant eye defect resulting from leakage of lens material through the lens capsule occurring at embryonic day (E)13.5, when the lens grows rapidly. Adamts18-deficient lungs showed altered bronchiolar branching. Fifty percent of mutant females are infertile because of vaginal obstruction due to either a dorsoventral vaginal septum or imperforate vagina. The incidence of ovarian rete is increased in the mutant mouse strain. Thus, Adamts18 is essential in the development of distinct tissues and the new mouse strain is likely to be useful for investigating ADAMTS18 function in human disease, particularly in the contexts of infertility and carcinogenesis.

Lethal lung hypoplasia and vascular defects in mice with conditional Foxf1 overexpression

FOXF1 heterozygous point mutations and genomic deletions have been reported in newborns with the neonatally lethal lung developmental disorder, alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). However, no gain-of-function mutations in FOXF1 have been identified yet in any human disease conditions. To study the effects of FOXF1 overexpression in lung development, we generated a Foxf1 overexpression mouse model by knocking-in a Cre-inducible Foxf1 allele into the ROSA26 (R26) locus. The mice were phenotyped using micro-computed tomography (micro-CT), head-out plethysmography, ChIP-seq and transcriptome analyses, immunohistochemistry, and lung histopathology. Thirty-five percent of heterozygous R26-Lox-Stop-Lox (LSL)-Foxf1 embryonic day (E)15.5 embryos exhibit subcutaneous edema, hemorrhages and die perinatally when bred to Tie2-cre mice, which targets Foxf1 overexpression to endothelial and hematopoietic cells. Histopathological and micro-CT evaluations revealed that R26Foxf1; Tie2-cre embryos have immature lungs with a diminished vascular network. Neonates exhibited respiratory deficits verified by detailed plethysmography studies. ChIP-seq and transcriptome analyses in E18.5 lungs identified Sox11, Ghr, Ednrb, and Slit2 as potential downstream targets of FOXF1. Our study shows that overexpression of the highly dosage-sensitive Foxf1 impairs lung development and causes vascular abnormalities. This has important clinical implications when considering potential gene therapy approaches to treat disorders of FOXF1 abnormal dosage, such as ACDMPV.

Summary: Similar to Foxf1 loss, Foxf1 overexpression in mice is lethal. This finding highlights the need to consider alternatives beyond gene therapy to find a cure for alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV).

Targeted high-throughput sequencing of candidate genes for chronic obstructive pulmonary disease

Background

Reduced lung function in patients with chronic obstructive pulmonary disease (COPD) is likely due to both environmental and genetic factors. We report here a targeted high-throughput DNA sequencing approach to identify new and previously known genetic variants in a set of candidate genes for COPD.

Methods

Exons in 22 genes implicated in lung development as well as 61 genes and 10 genomic regions previously associated with COPD were sequenced using individual DNA samples from 68 cases with moderate or severe COPD and 66 controls matched for age, gender and smoking. Cases and controls were selected from the Obstructive Lung Disease in Northern Sweden (OLIN) studies.

Results

In total, 37 genetic variants showed association with COPD (p < 0.05, uncorrected). Several variants previously discovered to be associated with COPD from genetic genome-wide analysis studies were replicated using our sample. Two high-risk variants were followed-up for functional characterization in a large eQTL mapping study of 1,111 human lung specimens. The C allele of a synonymous variant, rs8040868, predicting a p.(S45=) in the gene for cholinergic receptor nicotinic alpha 3 (CHRNA3) was associated with COPD (p = 8.8 x 10⁻³). This association remained (p = 0.003 and OR = 1.4, 95 % CI 1.1-1.7) when analysing all available cases and controls in OLIN (n = 1,534). The rs8040868 variant is in linkage disequilibrium with rs16969968 previously associated with COPD and altered expression of the CHRNA5 gene. A follow-up analysis for detection of expression quantitative trait loci revealed that rs8040868-C was found to be significantly associated with a decreased expression of the nearby gene cholinergic receptor, nicotinic, alpha 5 (CHRNA5) in lung tissue.

Conclusion

Our data replicate previous result suggesting CHRNA5 as a candidate gene for COPD and rs8040868 as a risk variant for the development of COPD in the Swedish population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12890-016-0309-y) contains supplementary material, which is available to authorized users.

Marsupial tammar wallaby delivers milk bioactives to altricial pouch young to support lung development

Our research is exploiting the marsupial as a model to understand the signals required for lung development. Marsupials have a unique reproductive strategy, the mother gives birth to altricial neonate with an immature lung and the changes in milk composition during lactation in marsupials appears to provide bioactives that can regulate diverse aspects of lung development, including branching morphogenesis, cell proliferation and cell differentiation. These effects are seen with milk collected between 25 and 100days postpartum. To better understand the temporal effects of milk composition on postnatal lung development we used a cross-fostering technique to restrict the tammar pouch young to milk composition not extending beyond day 25 for 45days of its early postnatal life. These particular time points were selected as our previous study showed that milk protein collected prior to ~day 25 had no developmental effect on mouse embryonic lungs in culture. The comparative analysis of the foster group and control young at day 45 postpartum demonstrated that foster pouch young had significantly reduced lung size. The lungs in fostered young were comprised of large intermediate tissue, had a reduced size of airway lumen and a higher percentage of parenchymal tissue. In addition, expression of marker genes for lung development (BMP4, WNT11, AQP-4, HOPX and SPB) were significantly reduced in lungs from fostered young. Further, to identify the potential bioactive expressed by mammary gland that may have developmental effect on pouch young lungs, we performed proteomics analysis on tammar milk through mass-spectrometry and listed the potential bioactives (PDGF, IGFBP5, IGFBPL1 and EGFL6) secreted in milk that may be involved in regulating pouch young lung development. The data suggest that postnatal lung development in the tammar young is most likely regulated by maternal signalling factors supplied through milk.

Linking bronchopulmonary dysplasia to adult chronic lung diseases: role of WNT signaling

Bronchopulmonary dysplasia (BPD) is one of the most common chronic lung diseases in infants caused by pre- and/or postnatal lung injury. BPD is characterized by arrested alveolarization and vascularization due to extracellular matrix remodeling, inflammation, and impaired growth factor signaling. WNT signaling is a critical pathway for normal lung development, and its altered signaling has been shown to be involved in the onset and progression of incurable chronic lung diseases in adulthood, such as chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF). In this review, we summarize the impact of WNT signaling on different stages of lung development and its potential contribution to developmental lung diseases, especially BPD, and chronic lung diseases in adulthood.

CYP21A2 expression is localized in the developing distal epithelium of the human perinatal lung and is compatible with in situ production and intracrine actions of active glucocorticoids

Glucocorticoids play essential roles in lung development. We investigated for expression of CYP21A2 (21-hydroxylase) as well as for the presence of the corresponding protein and identification of CYP21A2-expressing cells in several human developing lungs. Expression of some related genes was also assessed. CYP21A2 and CYP17A1 (P450c17) mRNAs were found in all the 34 lung samples from 17 to 40 weeks' gestation at variable levels. No correlation was found according to sex but a correlation with age was detected for CYP17A1 only. In contrast, CYP11B1 (11β-hydroxylase)- and CYP11B2 (aldosterone synthase)-mRNAs were not detected. Significant levels of the CYP21A2 protein were detected in all the analyzed samples, while only very low signals were detected for CYP17A1 protein. In situ hybridization revealed that CYP21A2 was almost exclusively expressed in the distal epithelium. It was reported that the lung distal epithelium of human fetuses also express 11β-hydroxysteroid dehydrogenase type 2, which catalyzes cortisol inactivation into cortisone. Based on this information, intracrine glucocorticoid actions should take place from CYP21A2 products through the glucocorticoid receptor in the absence of cortisol. In contrast, mineralocorticoid receptor activation did not seem to depend on deoxycorticosterone produced from local activity of CYP21A2 because of the reported circulating amounts of aldosterone.

Inhaled Vitamin D: A Novel Strategy to Enhance Neonatal Lung Maturation

INTRODUCTION

The physiologic vitamin D (VD), 1α,25(OH)₂D₃ (1,25D) is a local paracrine/autocrine effecter of fetal lung maturation. By stimulating alveolar type II cell and lipofibroblast proliferation and differentiation, parenterally administered 1,25D has been shown to enhance neonatal lung maturation; but due to the potential systemic side effects of the parenteral route, the translational value of these findings might be limited. To minimize the possibility of systemic toxicity, we examined the effects of VD on neonatal lung maturation, when delivered directly to lungs via nebulization.

METHODS

One-day-old rat pups were administered three different doses of 1,25D and its physiologic precursor 25(OH)D (25D), or the diluent, via nebulization daily for 14 days. Pups were sacrificed for lung, kidneys, and blood collection to determine markers of lung maturation, and serum 25D and calcium levels.

RESULTS

Compared to controls, nebulized 25D and 1,25D enhanced lung maturation as evidenced by the increased expression of markers of alveolar epithelial (SP-B, leptin receptor), mesenchymal (PPARγ, C/EBPα), and endothelial (VEGF, FLK-1) differentiation, surfactant phospholipid synthesis, and lung morphology without any significant increases in serum 25D and calcium levels.

CONCLUSIONS

Inhaled VD is a potentially safe and effective novel strategy to enhance neonatal lung maturation.

A method for evaluating the murine pulmonary vasculature using micro-computed tomography

BACKGROUND

Significant mortality and morbidity are associated with alterations in the pulmonary vasculature. While techniques have been described for quantitative morphometry of whole-lung arterial trees in larger animals, no methods have been described in mice. We report a method for the quantitative assessment of murine pulmonary arterial vasculature using high-resolution computed tomography scanning.

METHODS

Mice were harvested at 2 weeks, 4 weeks, and 3 months of age. The pulmonary artery vascular tree was pressure perfused to maximal dilation with a radio-opaque casting material with viscosity and pressure set to prevent capillary transit and venous filling. The lungs were fixed and scanned on a specimen computed tomography scanner at 8-μm resolution, and the vessels were segmented. Vessels were grouped into categories based on lumen diameter and branch generation.

RESULTS

Robust high-resolution segmentation was achieved, permitting detailed quantitation of pulmonary vascular morphometrics. As expected, postnatal lung development was associated with progressive increase in small-vessel number and arterial branching complexity.

CONCLUSIONS

These methods for quantitative analysis of the pulmonary vasculature in postnatal and adult mice provide a useful tool for the evaluation of mouse models of disease that affect the pulmonary vasculature.

Ezh2 restricts the smooth muscle lineage during mouse lung mesothelial development

During development, the lung mesoderm generates a variety of cell lineages, including airway and vascular smooth muscle. Epigenetic changes in adult lung mesodermal lineages are thought to contribute towards diseases such as idiopathic pulmonary fibrosis and chronic obstructive pulmonary disease, although the factors that regulate early lung mesoderm development are unknown. We show in mouse that the PRC2 component Ezh2 is required to restrict smooth muscle differentiation in the developing lung mesothelium. Mesodermal loss of Ezh2 leads to the formation of ectopic smooth muscle in the submesothelial region of the developing lung mesoderm. Loss of Ezh2 specifically in the developing mesothelium reveals a mesothelial cell-autonomous role for Ezh2 in repression of the smooth muscle differentiation program. Loss of Ezh2 derepresses expression of myocardin and Tbx18, which are important regulators of smooth muscle differentiation from the mesothelium and related cell lineages. Together, these findings uncover an Ezh2-dependent mechanism to restrict the smooth muscle gene expression program in the developing mesothelium and allow appropriate cell fate decisions to occur in this multipotent mesoderm lineage.

Lung epithelial tip progenitors integrate glucocorticoid- and STAT3-mediated signals to control progeny fate

Insufficient alveolar gas exchange capacity is a major contributor to lung disease. During lung development, a population of distal epithelial progenitors first produce bronchiolar-fated and subsequently alveolar-fated progeny. The mechanisms controlling this bronchiolar-to-alveolar developmental transition remain largely unknown. We developed a novel grafting assay to test if lung epithelial progenitors are intrinsically programmed or if alveolar cell identity is determined by environmental factors. These experiments revealed that embryonic lung epithelial identity is extrinsically determined. We show that both glucocorticoid and STAT3 signalling can control the timing of alveolar initiation, but that neither pathway is absolutely required for alveolar fate specification; rather, glucocorticoid receptor and STAT3 work in parallel to promote alveolar differentiation. Thus, developmental acquisition of lung alveolar fate is a robust process controlled by at least two independent extrinsic signalling inputs. Further elucidation of these pathways might provide therapeutic opportunities for restoring alveolar capacity.

Temporal dynamics of the developing lung transcriptome in three common inbred strains of laboratory mice reveals multiple stages of postnatal alveolar development

To characterize temporal patterns of transcriptional activity during normal lung development, we generated genome wide gene expression data for 26 pre- and post-natal time points in three common inbred strains of laboratory mice (C57BL/6J, A/J, and C3H/HeJ). Using Principal Component Analysis and least squares regression modeling, we identified both strain-independent and strain-dependent patterns of gene expression. The 4,683 genes contributing to the strain-independent expression patterns were used to define a murine Developing Lung Characteristic Subtranscriptome (mDLCS). Regression modeling of the Principal Components supported the four canonical stages of mammalian embryonic lung development (embryonic, pseudoglandular, canalicular, saccular) defined previously by morphology and histology. For postnatal alveolar development, the regression model was consistent with four stages of alveolarization characterized by episodic transcriptional activity of genes related to pulmonary vascularization. Genes expressed in a strain-dependent manner were enriched for annotations related to neurogenesis, extracellular matrix organization, and Wnt signaling. Finally, a comparison of mouse and human transcriptomics from pre-natal stages of lung development revealed conservation of pathways associated with cell cycle, axon guidance, immune function, and metabolism as well as organism-specific expression of genes associated with extracellular matrix organization and protein modification. The mouse lung development transcriptome data generated for this study serves as a unique reference set to identify genes and pathways essential for normal mammalian lung development and for investigations into the developmental origins of respiratory disease and cancer. The gene expression data are available from the Gene Expression Omnibus (GEO) archive (GSE74243). Temporal expression patterns of mouse genes can be investigated using a study specific web resource (http://lungdevelopment.jax.org).

Vitamin A-retinoid signaling in pulmonary development and disease

Retinoic acid (RA), the active form of vitamin A, regulates key developmental processes in multiple organs. In the developing lung, RA is crucial for normal growth and differentiation of airways. Disruption in RA signaling or vitamin A deficiency (VAD) has been linked to aberrant development of the lung including alterations in the airway smooth muscle (SM) differentiation, development, and function. These alterations have been linked to disease states including asthma in both human and animal models.

Pathogenesis of bronchopulmonary dysplasia: when inflammation meets organ development

Bronchopulmonary dysplasia is a chronic lung disease of preterm infants. It is caused by the disturbance of physiologic lung development mainly in the saccular stage with lifelong restrictions of pulmonary function and an increased risk of abnormal somatic and psychomotor development. The contributors to this disease’s entity are multifactorial with pre- and postnatal origin. Central to the pathogenesis of bronchopulmonary is the induction of a massive pulmonary inflammatory response due to mechanical ventilation and oxygen toxicity. The extent of the pro-inflammatory reaction and the disturbance of further alveolar growth and vasculogenesis vary largely and can be modified by prenatal infections, antenatal steroids, and surfactant application.

This minireview summarizes the important recent research findings on the pulmonary inflammatory reaction obtained in patient cohorts and in experimental models. Unfortunately, recent changes in clinical practice based on these findings had only limited impact on the incidence of bronchopulmonary dysplasia.

Effect of Maternal Electroacupuncture on Perinatal Nicotine Exposure-Induced Lung Phenotype in Offspring

INTRODUCTION

Pregnant women exposed to tobacco smoke predispose the offspring to many adverse consequences including an altered lung development and function. There is no effective therapeutic intervention to block the effects of smoke exposure on the developing lung. Clinical and animal studies demonstrate that acupuncture can modulate a variety of pathophysiological processes, including those involving the respiratory system; however, whether acupuncture affects the lung damage caused by perinatal smoke exposure is not known.

METHODS

To determine the effect of acupuncture on perinatal nicotine exposure on the developing lung, pregnant rat dams were administered (1) saline, (2) nicotine, or (3) nicotine + electroacupuncture (EA). Nicotine was administered (1 mg/kg subcutaneously) once a day and EA was applied to both "Zusanli" (ST 36) points. Both interventions were administered from gestational day 6 to postnatal day 21 (PND21), following which pups were sacrificed. Lungs, blood, and brain were collected to examine markers of lung injury, repair, and hypothalamic pituitary adrenal (HPA) axis.

RESULTS

Concomitant EA application blocked nicotine-induced changes in lung morphology, lung peroxisome proliferator-activated receptor γ and wingless-int signaling, two key lung developmental signaling pathways, hypothalamic pituitary adrenal axis (hypothalamic corticotropic releasing hormone and lung glucocorticoid receptor levels), and plasma β-endorphin levels.

CONCLUSIONS

Electroacupuncture blocks the nicotine-induced changes in lung developmental signaling pathways and the resultant myogenic lung phenotype, known to be present in the affected offspring. We conclude that EA is a promising novel intervention against the smoke exposed lung damage to the developing lung.

Long-range enhancers modulate Foxf1 transcription in blood vessels of pulmonary vascular network

Intimate crosstalk occurs between the pulmonary epithelium and the vascular network during lung development. The transcription factor forkhead box f1 (Foxf1) is expressed in the lung mesenchyme and plays an indispensable role in pulmonary angiogenesis. Sonic hedgehog (Shh), a signalling molecule, is expressed in lung epithelium and is required to establish proper angiogenesis. It has been suggested that Foxf1, a downstream target of the Shh signalling pathway, mediates interaction between angiogenesis and the epithelium in lung. However, there has been no clear evidence showing the mechanism how Foxf1 is regulated by Shh signalling pathway during lung development. In this study, we investigated the lung-specific enhancers of Foxf1 and the Gli binding on the enhancers. At first, we found three evolutionarily conserved Foxf1 enhancers, two of which were long-range enhancers. Of the long-range enhancers, one demonstrated tissue-specific activity in the proximal and distal pulmonary blood vessels, while the other one demonstrated activity only in distal blood vessels. At analogous positions in human, these long-range enhancers were included in a regulatory region that was reportedly repeatedly deleted in alveolar capillary dysplasia with misalignment of pulmonary vein patients, which indicates the importance of these enhancers in pulmonary blood vessel formation. We also determined that Gli increased the activity of one of these long-range enhancers, which was specific to distal blood vessel, suggesting that Shh regulates Foxf1 transcription in pulmonary distal blood vessel formation.

Identification of vitamin D sensitive pathways during lung development

BACKGROUND

We have previously shown that vitamin D deficiency has a detrimental impact on lung development. In this study, we aimed to identify the mechanisms linking vitamin D with lung development using a mouse model of dietary manipulation.

METHODS

Female offspring were euthanized at different time-points; embryonic day (E)14.5, E17.5 or postnatal day (P)7. Lung tissue was collected for mass spectrometry-based proteomic analysis. Label-free quantitation was used to identify the differentially expressed proteins and ELISA confirmed the expression of selected proteins. Lungs from separate groups of mice were fixed and processed for stereological assessment of lung structure.

RESULTS

No differences in protein expression between vitamin D deficient and replete mice were detected at E14.5 and E17.5, whereas 66 proteins were differentially expressed in P7 lungs. The expression of pulmonary surfactant-associated protein B (SP-B) and peroxiredoxin 5 (PRDX5) were reduced in P7 lungs of vitamin D deficient mice, while the production of collagen type Ι alpha 1 (COL1A1) was higher in lungs of vitamin D deficient mice. There were no differences in lung volume, parenchymal volume, volume of airspaces or surface area of airspaces between vitamin D deficient and vitamin D replete mice across three time-points.

CONCLUSIONS

The difference in protein expression during the early postnatal time-point suggests that vitamin D deficiency may induce alterations of lung structure and function in later life during alveolarization stage through impaired pulmonary surfactant production and anti-oxidative stress ability as well as enhanced collagen synthesis. These data provided a plausible mechanism linking maternal vitamin D deficiency with altered postnatal lung function.

How to Grow a Lung: Applying Principles of Developmental Biology to Generate Lung Lineages from Human Pluripotent Stem Cells

The number and severity of diseases affecting human lung development and adult respiratory function has stimulated great interest in new in vitro models to study the human lung. This review summarizes the most recent breakthroughs deriving lung lineages in a dish by directing the differentiation of human pluripotent stem cells. A variety of culturing platforms have been developed, including two-dimensional and three-dimensional (organoid) culture platforms, to derive specific cell types and structures of the lung. These stem cell-derived lung models will further our understanding of human lung development, disease, and regeneration.

Ectopic expression of a small cell lung cancer transcription factor, INSM1 impairs alveologenesis in lung development

Background

Insulinoma associated-1 (INSM1) gene is expressed exclusively in early embryonic neuroendocrine tissues, but has been found highly re-activated in most of the neuroendocrine tumors including small cell lung carcinoma.

Methods

In order to elucidate the functional effects of INSM1 in normal lung development, we used a conditional lung-specific INSM1 transgenic mouse model. Transgenic (Tet-on system) CMV-INSM1 responder mice were bred with the lung-specific, club cell secretory protein (CCSP) promoter-rtTA activator mice to produce bi-transgenic progeny carrying both alleles, CCSP-rtTA and Tet-on-INSM1. Mice were fed with doxycycline containing food at the initial mating day to the postnatal day 21. Lung samples were collected at embryonic day 17.5, newborn, and postnatal day 21 for analyses.

Results

Northern blot, RT-PCR, and immunohistochemical analyses revealed that doxycycline induced respiratory epithelium-specific INSM1 expression in bi-transgenic mice. Samples from postnatal day 21 mice revealed a larger lung size in the bi-transgenic mouse as compared to the single-transgenic or wild-type littermates. The histopathology results showed that the alveolar space in the bi-transgenic mice were 4 times larger than those in the single transgenic or wild-type littermates. In contrast, the size was not significantly different in the lungs collected at E17.5 or newborn among the bi-transgenic, single transgenic, or wild type mice. The respiratory epithelium with INSM1 ectopic expression suppressed cyclin D1 signal. Further in vitro studies revealed that the ectopic expression of INSM1 suppresses cyclin D1 expression and delays cell cycle progression.

Conclusion

The current study suggests that CCSP promoter-driven INSM1 ectopic expression impairs normal lung development especially in postnatal alveologenesis.

Expression profile of androgen-modulated microRNAs in the fetal murine lung

Background

Androgens are known to delay lung development. As a consequence, the incidence and morbidity of respiratory distress syndrome of the neonate are higher for male than for female premature infants. We previously reported that many genes were expressed with a sex difference in the mouse developing lung and that several genes were under the control of androgens in the male fetal lung. microRNAs are small non-coding RNAs known to negatively regulate the expression of specific genes. In this study, we examined whether murine miRNAs are under the control of androgens in the male developing lung.

Methods

Expression profiling of microRNAs was performed by microarrays using RNA extracted from male fetal lungs isolated on gestational day (GD) 17.0 and GD 18.0 after daily injection of pregnant mice from GD 10.0 with the antiandrogen flutamide or vehicle only. To identify putative miRNA target genes, the data obtained here were combined with gene profiling data reported previously using the same RNA preparations. qPCR was used to confirm microarray data with fetal lungs from other litters than those used in microarrays.

Results

Flutamide induced downregulation and upregulation of several miRNAs on GD 17.0 and GD 18.0. Of the 43 mature miRNAs modulated by flutamide on GD 17.0, 60 % were downregulated, whereas this proportion was only of 34 % for the 35 mature miRNAs modulated on GD 18.0. For 29 and 26 flutamide-responsive miRNAs, we found a corresponding target inversely regulated by androgens on GD 17.0 and 18.0, respectively. The androgen-regulated target genes were involved in several biological processes (lipid metabolism, cell proliferation, and lung development) and molecular functions, mainly transcription factor binding.

Conclusions

Regulation of male lung development involves several miRNAs that are under androgen modulation in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0072-z) contains supplementary material, which is available to authorized users.