Gestational vitamin D deficiency impairs fetal lung development through suppressing type II pneumocyte differentiation

Gestational vitamin D deficiency is associated with pulmonary diseases. This study aimed to investigate the effect of gestational vitamin D deficiency on fetal lung development in mice. Absolute and relative weights of fetal lungs were reduced in vitamin D deficient (VDD) group. Incrassate mesenchyme, measured by septal wall thickness, accompanied by lessened saccular space, was shown in VDD group. Numerous immature type II pneumocytes, as determined by PAS staining, were observed in VDD group. Moreover, increased Ki67-positive cells, a marker of cell proliferation, was detected in VDD group. The additional experiments showed that Sftpa, Sftpb, Sftpc and Sftpd, four surfactant genes, were downregulated and pro-surfactant protein B was reduced in VDD group. FoxA1, FoxA2 and TTF-1, three transcription factors that regulate surfactant genes, and VEGF, a key regulator for pulmonary maturation, were downregulated in VDD group. These results suggest that gestational vitamin D deficiency impairs fetal lung development partially through suppressing type II pneumocyte differentiation.

Long Non-Coding RNA NANCI/NKX2-1 Duplex Impacts Prognosis in Stage I Non-Small-Cell Lung Cancer

BACKGROUND

NANCI, an intergenic long non-coding RNA (lncRNA) is essential for buffering NKX2-1 expression during embryonic development and in adult tissue. We analyzed NANCI and NKX2-1 in human lung embryonic samples and adult lung tissues and evaluated their potential as prognostic markers in stage I non-small cell lung cancer (NSCLC).

METHODS AND RESULTS

NANCI and NKX2-1 expression was assessed by TaqMan assays in 18 human embryonic samples from 8 to 13 weeks, 59 non-tumoral (NT) lung tissue samples, and 98 stage I NSCLC tumor samples. NANCI and NKX2-1 expression in embryonic and NSCLC samples were downregulated in comparison to adult NT tissue. Patients with low expression of NANCI had shorter disease-free survival (DFS) and overall survival (OS) than those with high levels (47.6 vs 69.3 months, P=0.032 and 57.7 vs 77.6 months, P=0.021, respectively). When the expression levels of NANCI and NKX2-1 were evaluated in combination, four groups were identified (high NANCI/high NKX2-1, low NANCI/high NKX2-1, high NANCI/low NKX2-1 and low NANCI/low NKX2-1) with differential impact on DFS (P=0.042) and OS (P=0.024). Interestingly, the high NANCI/high NKX2-1 duplex group had longer DFS and OS than the other three groups (71.25 vs 46.3 months, P=0.009 and 81.3 vs 56.1 months, P=0.004, respectively). In the multivariate analysis, the high NANCI/high NKX2-1 duplex was identified as an independent prognostic factor for longer DFS (HR 0.346, 95% CI, 0.169-0.709; P=0.004) and OS (HR 0.309, 95% CI, 0.121-0.786; P=0.014).

CONCLUSIONS

NANCI and the NANCI-NKX2-1 duplex impacts prognosis in stage I NSCLC patients.

Circular RNAs are abundant and dynamically expressed during the embryonic lung development of C57BL/6 mice

Circular RNAs (circRNAs), a novel type of endogenous RNAs, can function as microRNA (miRNA) sponges capable of regulating gene transcription, binding to RNA-associated proteins, and even encoding proteins. CircRNAs are involved in various cell behaviors, such as proliferation and apoptosis. The mouse model has also been demonstrated to be similar to that of humans in many studies. To explore the profile of circRNAs during embryonic lung development and their potential functions in lung development-related diseases, mouse embryos at the pseudoglandular phase, canalicular phase, saccular phase, and alveolar phase were collected. High-throughput sequencing was then used to identify a total of 1,735 circRNAs (junction reads ≥5 and p < 0.05). It is well known that the functions of circRNAs are related to host genes. In our study, bioinformatics analysis indicated that the screened host genes were closely associated with lung development and included the Hippo signaling pathway, PI3K-Akt signaling pathways, and TGF-β signaling pathways. Moreover, miRNA sponges are another mechanism involved in lung development. Therefore, we predicted many miRNAs binding to circRNAs, such as miR-17 and miR-20, using the TargetScan and miRanda databases. Previously, miRNAs were proven to be necessary for lung development. The peak expression of circRNAs is distributed at different time points, suggesting their involvement in different stages of embryonic mouse lung development.

Preterm birth impairs postnatal lung development in the neonatal rabbit model

Background

Bronchopulmonary dysplasia continues to cause important respiratory morbidity throughout life, and new therapies are needed. The common denominator of all BPD cases is preterm birth, however most preclinical research in this area focusses on the effect of hyperoxia or mechanical ventilation. In this study we investigated if and how prematurity affects lung structure and function in neonatal rabbits.

Methods

Pups were delivered on either day 28 or day 31. For each gestational age a group of pups was harvested immediately after birth for lung morphometry and surfactant protein B and C quantification. All other pups were hand raised and harvested on day 4 for the term pups and day 7 for the preterm pups (same corrected age) for lung morphometry, lung function testing and qPCR. A subset of pups underwent microCT and dark field imaging on day 0, 2 and 4 for terms and on day 0, 3, 5 and 7 for preterms.

Results

Preterm pups assessed at birth depicted a more rudimentary lung structure (larger alveoli and thicker septations) and a lower expression of surfactant proteins in comparison to term pups. MicroCT and dark field imaging revealed delayed lung aeration in preterm pups, in comparison to term pups. Preterm birth led to smaller pups, with smaller lungs with a lower alveolar surface area on day 7/day 4. Furthermore, preterm birth affected lung function with increased tissue damping, tissue elastance and resistance and decreased dynamic compliance. Expression of vascular endothelial growth factor (VEGFA) was significantly decreased in preterm pups, however in the absence of structural vascular differences.

Conclusions

Preterm birth affects lung structure and function at birth, but also has persistent effects on the developing lung. This supports the use of a preterm animal model, such as the preterm rabbit, for preclinical research on BPD. Future research that focuses on the identification of pathways that are involved in in-utero lung development and disrupted by pre-term birth, could lead to novel therapeutic strategies for BPD.

Bone marrow stem cells accelerate lung maturation and prevent the LPS-induced delay of morphological and functional fetal lung development in the presence of ErbB4

ErbB4 is a regulator in lung development and disease. Prenatal infection is an important risk factor for the delay of morphologic lung development, while promoting the maturation of the surfactant system. Bone marrow-derived mesenchymal stem cells (BMSCs) have the potential to prevent lung injury. We hypothesized that BMSCs in comparison with hematopoietic control stem cells (HPSCs) minimize the lipopolysaccharide (LPS)-induced lung injury only when functional ErbB4 receptor is present. We injected LPS and/or murine green fluorescent protein-labeled BMSCs or HPSCs into the amniotic cavity of transgenic ErbB4^heart mothers at gestational day 17. Fetal lungs were analyzed 24 h later. BMSCs minimized significantly LPS-induced delay in morphological lung maturation consisting of a stereologically measured increase in mesenchyme and septal thickness and a decrease of future airspace and septal surface. This effect was more prominent and significant in the ErbB4^heart+/- lungs, suggesting that the presence of functioning ErbB4 signaling is required. BMSC also diminished the LPS induced increase in surfactant protein (Sftp)a mRNA and decrease in Sftpc mRNA is only seen if ErbB4 is present. The reduction of morphological delay of lung development and of levels of immune-modulating Sftp was more pronounced in the presence of the ErbB4 receptor. Thus, ErbB4 may be required for the protective signaling of BMSCs.

Stem Cells in Lungs

The respiratory system plays an essential role for human life. This system (like all others) undergoes physiological regeneration due to many types of stem cells found both in the respiratory tract itself and in the alveoli. The stem cell hierarchy is very extensive due to their variety in the lungs and is still not completely understood.The best described lung stem cells are alveolar type II cells, which as progenitor lung stem cells are precursors of alveolar type I cells, i.e., cells that perform gas exchange in the lungs. These progenitor stem cells, which reside in alveoli corners, express high levels of surfactant protein C (SFTPC). Despite the fact that type II pneumocytes occupy only 7-10% of the lung surface, there are almost twice as many as alveolar type I cells occupying almost 95% of the surface.Other stem cells making up the lung regenerative potential have also been identified in the lungs. Both endothelial, mesodermal, and epithelial stem cells are necessary for the lungs to function properly and perform their physiological functions.The lungs, like all other organs, undergo an aging process. As a result of this process, not only the total number of cells changes, the percentage of particular types of cells, but also their efficiency is reduced. With age, the proliferative potential of lung stem cells also decreases, not just their number. This brings about the need to increase the intensity of research in the field of regenerative medicine.

The roles and regulation of TBX3 in development and disease

TBX3, a member of the ancient and evolutionary conserved T-box transcription factor family, is a critical developmental regulator of several structures including the heart, mammary glands, limbs and lungs. Indeed, mutations in the human TBX3 lead to ulnar mammary syndrome which is characterized by several clinical malformations including hypoplasia of the mammary and apocrine glands, defects of the upper limb, areola, dental structures, heart and genitalia. In contrast, TBX3 has no known function in adult tissues but is frequently overexpressed in a wide range of epithelial and mesenchymal derived cancers. This overexpression greatly impacts several hallmarks of cancer including bypass of senescence, apoptosis and anoikis, promotion of proliferation, tumour formation, angiogenesis, invasion and metastatic capabilities as well as cancer stem cell expansion. The debilitating consequences of having too little or too much TBX3 suggest that its expression levels need to be tightly regulated. While we have a reasonable understanding of the mutations that result in low levels of functional TBX3 during development, very little is known about the factors responsible for the overexpression of TBX3 in cancer. Furthermore, given the plethora of oncogenic processes that TBX3 impacts, it must be regulating several target genes but to date only a few have been identified and characterised. Interestingly, while there is compelling evidence to support oncogenic roles for TBX3, a few studies have indicated that it may also have tumour suppressor functions in certain contexts. Together, the diverse functional elasticity of TBX3 in development and cancer is thought to involve, in part, the protein partners that it interacts with and this area of research has recently received some attention. This review provides an insight into the significance of TBX3 in development and cancer and identifies research gaps that need to be explored to shed more light on this transcription factor.

Identification of a FGF18-expressing alveolar myofibroblast that is developmentally cleared during alveologenesis

Alveologenesis is an essential developmental process that increases the surface area of the lung through the formation of septal ridges. In the mouse, septation occurs postnatally and is thought to require the alveolar myofibroblast (AMF). Though abundant during alveologenesis, markers for AMFs are minimally detected in the adult. After septation, the alveolar walls thin to allow efficient gas exchange. Both loss of AMFs or retention and differentiation into another cell type during septal thinning have been proposed. Using a novel Fgf18:CreERT2 allele to lineage trace AMFs, we demonstrate that most AMFs are developmentally cleared during alveologenesis. Lung mesenchyme also contains other poorly described cell types, including alveolar lipofibroblasts (ALF). We show that Gli1:CreERT2 marks both AMFs as well as ALFs, and lineage tracing shows that ALFs are retained in adult alveoli while AMFs are lost. We further show that multiple immune cell populations contain lineage-labeled particles, suggesting a phagocytic role in the clearance of AMFs. The demonstration that the AMF lineage is depleted during septal thinning through a phagocytic process provides a mechanism for the clearance of a transient developmental cell population.

Alveolar Airspace Size in Healthy and Diseased Infant Lungs Measured via Hyperpolarized 3He Gas Diffusion Magnetic Resonance Imaging

BACKGROUND

Alveolar development and lung parenchymal simplification are not well characterized in vivo in neonatal patients with respiratory morbidities, such as bronchopulmonary dysplasia (BPD). Hyperpolarized (HP) gas diffusion magnetic resonance imaging (MRI) is a sensitive, safe, nonionizing, and noninvasive biomarker for measuring airspace size in vivo but has not yet been implemented in young infants.

OBJECTIVE

This work quantified alveolar airspace size via HP gas diffusion MRI in healthy and diseased explanted infant lung specimens, with comparison to histological morphometry.

METHODS

Lung specimens from 8 infants were obtained: 7 healthy left upper lobes (0-16 months, post-autopsy) and 1 left lung with filamin-A mutation, closely representing BPD lung disease (11 months, post-transplantation). Specimens were imaged using HP 3He diffusion MRI to generate apparent diffusion coefficients (ADCs) as biomarkers of alveolar airspace size, with comparison to mean linear intercept (Lm) via quantitative histology.

RESULTS

Mean ADC and Lm were significantly increased throughout the diseased specimen (ADC = 0.26 ± 0.06 cm2/s, Lm = 587 ± 212 µm) compared with healthy specimens (ADC = 0.14 ± 0.03 cm2/s, Lm = 133 ± 37 µm; p < 1 × 10-7); increased values reflect enlarged airspaces. Mean ADCs in healthy specimens were significantly correlated to Lm (r = 0.69, p = 0.041).

CONCLUSIONS

HP gas diffusion MRI is sensitive to healthy and diseased regional alveolar airspace size in infant lungs, with good comparison to quantitative histology in ex vivo specimens. This work demonstrates the translational potential of gas MRI techniques for in vivo assessment of normal and abnormal alveolar development in neonates with pulmonary disease.

TBX2-positive cells represent a multi-potent mesenchymal progenitor pool in the developing lung

Background

In the embryonic mammalian lung, mesenchymal cells act both as a signaling center for epithelial proliferation, differentiation and morphogenesis as well as a source for a multitude of differentiated cell types that support the structure of the developing and mature organ. Whether the embryonic pulmonary mesenchyme is a homogenous precursor pool and how it diversifies into different cell lineages is poorly understood. We have previously shown that the T-box transcription factor gene Tbx2 is expressed in the pulmonary mesenchyme of the developing murine lung and is required therein to maintain branching morphogenesis.

Methods

We determined Tbx2/TBX2 expression in the developing murine lung by in situ hybridization and immunofluorescence analyses. We used a genetic lineage tracing approach with a Cre line under the control of endogenous Tbx2 control elements (Tbx2^cre), and the R26^mTmG reporter line to trace TBX2-positive cells in the murine lung. We determined the fate of the TBX2 lineage by co-immunofluorescence analysis of the GFP reporter and differentiation markers in normal murine lungs and in lungs lacking or overexpressing TBX2 in the pulmonary mesenchyme.

Results

We show that TBX2 is strongly expressed in mesenchymal progenitors in the developing murine lung. In differentiated smooth muscle cells and in fibroblasts, expression of TBX2 is still widespread but strongly reduced. In mesothelial and endothelial cells expression is more variable and scattered. All fetal smooth muscle cells, endothelial cells and fibroblasts derive from TBX2⁺ progenitors, whereas half of the mesothelial cells have a different descent. The fate of TBX2-expressing cells is not changed in Tbx2-deficient and in TBX2-constitutively overexpressing mice but the distribution and abundance of endothelial and smooth muscle cells is changed in the overexpression condition.

Conclusion

The fate of pulmonary mesenchymal progenitors is largely independent of TBX2. Nevertheless, a successive and precisely timed downregulation of TBX2 is necessary to allow proper differentiation and functionality of bronchial smooth muscle cells and to limit endothelial differentiation. Our work suggests expression of TBX2 in an early pulmonary mesenchymal progenitor and supports a role of TBX2 in maintaining the precursor state of these cells.

E3 ubiquitin ligase MDM2 acts through p53 to control respiratory progenitor cell number and lung size

The respiratory lineage initiates from the specification of NKX2-1⁺ progenitor cells that ultimately give rise to a vast gas-exchange surface area. How the size of the progenitor pool is determined and whether this directly impacts final lung size remains poorly understood. Here, we show that epithelium-specific inactivation of Mdm2, which encodes an E3 ubiquitin ligase, led to lethality at birth with a striking reduction of lung size to a single vestigial lobe. Intriguingly, this lobe was patterned and contained all the appropriate epithelial cell types. The reduction of size can be traced to the progenitor stage, when p53, a principal MDM2 protein degradation target, was transiently upregulated. This was followed by a brief increase of apoptosis. Inactivation of the p53 gene in the Mdm2 mutant background effectively reversed the lung size phenotype, allowing survival at birth. Together, these findings demonstrate that p53 protein turnover by MDM2 is essential for the survival of respiratory progenitors. Unlike in the liver, in which genetic reduction of progenitors triggered compensation, in the lung, respiratory progenitor number is a key determinant factor for final lung size.

New insights on congenital pulmonary airways malformations revealed by proteomic analyses

Background

Congenital Pulmonary Airway Malformation (CPAM) has an estimated prevalence between 0.87 and 1.02/10,000 live births and little is know about their pathogenesis. To improve our knowledge on these rare malformations, we analyzed the cellular origin of the two most frequent CPAM, CPAM types 1 and 2, and compared these malformations with adjacent healthy lung and human fetal lungs.

Methods

We prospectively enrolled 21 infants undergoing surgical resection for CPAM. Human fetal lung samples were collected after termination of pregnancy. Immunohistochemistry and proteomic analysis were performed on laser microdissected samples.

Results

CPAM 1 and 2 express mostly bronchial markers, such as cytokeratin 17 (Krt17) or α-smooth muscle actin (ACTA 2). CPAM 1 also expresses alveolar type II epithelial cell markers (SPC). Proteomic analysis on microlaser dissected epithelium confirmed these results and showed distinct protein profiles, CPAM 1 being more heterogeneous and displaying some similarities with fetal bronchi.

Conclusion

This study provides new insights in CPAM etiology, showing clear distinction between CPAM types 1 and 2, by immunohistochemistry and proteomics. This suggests that CPAM 1 and CPAM 2 might occur at different stages of lung branching. Finally, the comparison between fetal lung structures and CPAMs shows clearly different protein profiles, thereby arguing against a developmental arrest in a localized part of the lung.

Paradigms that define lung epithelial progenitor cell fate in development and regeneration

Purpose of Review

Throughout the lifespan, lung injury impedes the primary critical function essential for life-respiration. To repair quickly and efficiently is critical and is orchestrated by a diverse repertoire of progenitor cells and their niche. This review incorporates knowledge gained from early studies in lung epithelial morphogenesis and cell fate and explores its relevance to more recent findings of lung progenitor and stem cells in development and regeneration.

Recent Findings

Cell fate in the lung is organized into an early specification phase and progressive differentiation phase in lung development. The advent of single cell analysis combined with lineage analysis and projections is uncovering new functional cell types in the lung providing a topographical atlas for progenitor cell lineage commitment during development, homeostasis, and regeneration.

Summary

Lineage commitment of lung progenitor cells is spatiotemporally regulated during development. Single cell sequencing technologies have significantly advanced our understanding of the similarities and differences between developmental and regenerative cell fate trajectories. Subsequent unraveling of the molecular mechanisms underlying these cell fate decisions will be essential to manipulating progenitor cells for regeneration.

Discovering myeloid cell heterogeneity in the lung by means of next generation sequencing

The lung plays a vital role in maintaining homeostasis, as it is responsible for the exchange of oxygen and carbon dioxide. Pulmonary homeostasis is maintained by a network of tissue-resident cells, including epithelial cells, endothelial cells and leukocytes. Myeloid cells of the innate immune system and epithelial cells form a critical barrier in the lung. Recently developed unbiased next generation sequencing (NGS) has revealed cell heterogeneity in the lung with respect to physiology and pathology and has reshaped our knowledge. New phenotypes and distinct gene signatures have been identified, and these new findings enhance the diagnosis and treatment of lung diseases. Here, we present a review of the new NGS findings on myeloid cells in lung development, homeostasis, and lung diseases, including acute lung injury (ALI), lung fibrosis, chronic obstructive pulmonary disease (COPD), and lung cancer.

Postnatal morphological lung development of wild type and CD26/DPP4 deficient rat pups in dependency of LPS exposure

BACKGROUND

Rodents are born with morphological immature lungs and an intact surfactant system. CD26/DPP4 is a multifactorial transmembrane integral type II protein, which is involved in physiological and pathophysiological processes and is already expressed during development. CD26/DPP4, called CD26 in the following, is able to enhance or dampen differently triggered inflammation. LPS exposure often used to simulate perinatal infection delays lung development.

OBJECTIVE

A perinatal LPS rat model was used to test the hypothesis that CD26 deficiency modulates LPS-induced retardation in morphological lung development.

METHODS

New born Fischer CD26 positive (CD26⁺) and deficient (CD26^-) rats were exposed to LPS on postnatal day (day post partum, dpp) 3 and 5. Morphological parameters of lung development were determined stereologically. Lung development was analysed in 7, 10 14 and 21day old rats.

RESULTS

Compared to controls LPS application resulted (1) in a mild inflammation independent of the strain, (2) in significantly lower total surface and volume of alveolar septa combined with significantly higher total volume of airspaces and alveolar size on dpp 7 in both substrains. However, compared to controls in LPS treated CD26^- rats significant lower values of total septal surface and volume combined with higher values of total parenchymal airspaces and alveolar size were found until the end of classical alveolarization (dpp14). In LPS treated CD26⁺ rat pups the retardation was abolished already on dpp 10.

CONCLUSION

In absence of CD26, LPS enhances the delay of morphological lung development. Morphological recovery was slower after the end of LPS exposure in CD26 deficient lungs.

Time-lapse Imaging of Alveologenesis in Mouse Precision-cut Lung Slices

Alveoli are the gas-exchange units of lung. The process of alveolar development, alveologenesis, is regulated by a complex network of signaling pathways that act on various cell types including alveolar type I and II epithelial cells, fibroblasts and the vascular endothelium. Dysregulated alveologenesis results in bronchopulmonary dysplasia in neonates and in adults, disrupted alveolar regeneration is associated with chronic lung diseases including COPD and pulmonary fibrosis. Therefore, visualizing alveologenesis is critical to understand lung homeostasis and for the development of effective therapies for incurable lung diseases. We have developed a technique to visualize alveologenesis in real-time using a combination of widefield microscopy and image deconvolution of precision-cut lung slices. Here, we describe this live imaging technique in step-by-step detail. This time-lapse imaging technique can be used to capture the dynamics of individual cells within tissue slices over a long time period (up to 16 h), with minimal loss of fluorescence or cell toxicity.

Secondary crest myofibroblast PDGFRα controls the elastogenesis pathway via a secondary tier of signaling networks during alveologenesis

Postnatal alveolar formation is the most important and the least understood phase of lung development. Alveolar pathologies are prominent in neonatal and adult lung diseases. The mechanisms of alveologenesis remain largely unknown. We inactivated Pdgfra postnatally in secondary crest myofibroblasts (SCMF), a subpopulation of lung mesenchymal cells. Lack of Pdgfra arrested alveologenesis akin to bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease. The transcriptome of mutant SCMF revealed 1808 altered genes encoding transcription factors, signaling and extracellular matrix molecules. Elastin mRNA was reduced, and its distribution was abnormal. Absence of Pdgfra disrupted expression of elastogenic genes, including members of the Lox, Fbn and Fbln families. Expression of EGF family members increased when Tgfb1 was repressed in mouse. Similar, but not identical, results were found in human BPD lung samples. In vitro, blocking PDGF signaling decreased elastogenic gene expression associated with increased Egf and decreased Tgfb family mRNAs. The effect was reversible by inhibiting EGF or activating TGFβ signaling. These observations demonstrate the previously unappreciated postnatal role of PDGFA/PDGFRα in controlling elastogenic gene expression via a secondary tier of signaling networks composed of EGF and TGFβ.

Pericytes in the Lung

The lung has numerous roles, including gas exchange, immune surveillance, and barrier function. Being a highly vascularized organ, the lung receives dual blood supply from both the pulmonary and bronchial circulation. Therefore, pericytes likely play a prominent role in lung physiology given their localization in the perivascular niche. New genetic approaches have increased our understanding of the origin and the diverse functions of lung pericytes. Lung pericytes are myofibroblast progenitors, contributing to development of fibrosis in mouse models. Lung pericytes are also capable of responding to danger signals and amplify the inflammatory response through elaboration of cytokines and adhesion molecules. In this chapter, we describe the molecular, anatomical, and phenotypical characterization of lung pericytes. We further highlight their potential roles in the pathogenesis of lung diseases including pulmonary fibrosis, asthma, and pulmonary hypertension. Finally, current gaps in knowledge and areas of ongoing investigation in lung pericyte biology are also discussed.

Clinical phenotypes and management concepts for severe, established bronchopulmonary dysplasia

With advances in care, the bronchopulmonary dysplasia phenotypes have evolved, so that infants who would have died in previous eras are now surviving with significant pulmonary and neurologic morbidities. The spectrum of bronchopulmonary dysplasia phenotypes is broad, however, ranging from very mild to very severe disease, and management strategies used in previous eras of care may not be appropriate for the most severe phenotypes. The pathophysiology depends largely on the gestational age at birth, but disease progression and long-term outcome depends on the net sum of antenatal, perinatal and postnatal exposures. There is no single management strategy for the wide spectrum of clinical presentations of BPD; care must be individualized. Regardless of the phenotype, the support apparatus should match the disease physiology. Here we describe an interdisciplinary approach to management in terms of achieving clinical stability and progress along a continuum, from diagnosis at 36 weeks of corrected gestational age to convalescence. The clinical trajectory depends on the balance of factors related to support of respiration, healing of the lungs, and return of organ growth and development. The overall treatment strategy should optimize positive influences that lead to a pro-growth state, while minimizing exposures that interfere with lung growth and development. This is best achieved by use of a multi-disciplinary team, with feedback loops that inform clinical decision-making regarding respiratory stability, tolerance for cares and activities, the clinical response to changes in the care plan, and progress in growth and development.

Yap and its subcellular localization have distinct compartment-specific roles in the developing lung

Although the Hippo-yes-associated protein (Yap) pathway has been implicated in lung development, the specific roles for Yap and its nucleocytoplasmic shuttling in the developing airway and alveolar compartments remain elusive. Moreover, conflicting results from expression studies and differences in the lung phenotypes of Yap and Hippo kinase null mutants caused controversy over the dynamics and significance of Yap subcellular localization in the developing lung. Here, we show that the aberrant morphogenesis of Yap-deficient lungs results from the disruption of developmental events specifically in distal epithelial progenitors. We also show that activation of nuclear Yap is enough to fulfill the Yap requirements to rescue abnormalities in these lungs. Remarkably, we found that Yap nucleocytoplasmic shuttling is largely dispensable in epithelial progenitors for both branching morphogenesis and sacculation. However, if maintained transcriptionally active in airways, nuclear Yap profoundly alters proximal-distal identity and halts epithelial differentiation. Taken together, these observations provide novel insights into the crucial importance of Hippo-Yap signaling in the lung prenatally.

The role of miR-431-5p in regulating pulmonary surfactant expression in vitro

Background

Pulmonary surfactant is the complex mixture of lipid and protein that covers the alveolar surface. Pulmonary surfactant deficiency is one of the main causes of neonatal respiratory distress. Recent studies showed that miRNA plays an important role in lung development, but research into miR-431 regulation of pulmonary surfactant are sparse. In this study, we explored the regulatory role of miR-431-5p in the expression of pulmonary surfactant and identified its potential target gene, Smad4.

Methods

The bioinformatics tool TargetScan was used to predict the targets of miR-431. The expression of miR-431-5p was achieved via transfection of miR-431-5p mimics, an miR-431-5p inhibitor and corresponding negative control. The level of miR-431-5p was determined using quantitative real-time PCR. The CCK8 assay was conducted to confirm cell growth 12 h after transfection with miR-431-5p mimics, inhibitor or NC. Smad4 and surfactant-associated proteins in A549 were analyzed using western blot and quantitative real-time PCR.

Results

Smad4 was validated as a target of miR-431 in A549 cells. Overexpression of miR-431 accelerated A549 proliferation and inhibited A549 apoptosis. The mRNA and protein levels for the surfactant proteins (SP-A, SP-B, SP-C and SP-D) were found to be differentially expressed in A549 cells over- or under-expressing miR-431-5p.

Conclusion

Our results show that miR-431-5p is critical for pulmonary surfactant expression and that its regulation is closely related to the TGF-β/Smad4 pathway. These results will help us to study the pathophysiological mechanism of lung developmental diseases.

Receptor for advanced glycation end-products modulates lung development and lung sensitivity to hyperoxic injury in newborn mice

The receptor for advanced glycation end-products is mainly expressed in type I alveolar epithelial cells but its importance in lung development and response to neonatal hyperoxia is unclear. Therefore, our study aimed at the analysis of young wildtype and RAGE knockout mice which grew up under normoxic or hyperoxic air conditions for the first 14 days followed by a longer period of normoxic conditions. Lung histology, expression of lung-specific proteins, and respiratory mechanics were analyzed when the mice reached an age of 2 or 4 months. These analyses indicated less but larger and thicker alveoli in RAGE knockout mice, reverse differences in the mRNA and protein amount of pro-surfactant proteins (pro-SP-B, pro-SP-C) and aquaporin-5, and differences in the amount of elastin and CREB, a pro-survival transcription factor, as well as higher lung compliance. Despite this potential disadvantages, RAGE knockout lungs showed less long-term damages mediated by neonatal hyperoxia. In detail, the hyperoxia-mediated reduction in alveoli, enlargement of airspaces, fragmentation of elastic fibers, and increased lung compliance combined with reduced peak airflows was less pronounced in RAGE knockout mice. In conclusion, RAGE supports the alveolarization but makes the lung more susceptible to hyperoxic injury shortly after birth. Blocking RAGE function could still be a helpful tool in reducing hyperoxia-mediated lung pathologies during alveolarization.

Epigenetic impacts of maternal tobacco and e-vapour exposure on the offspring lung

In utero exposure to tobacco products, whether maternal or environmental, have harmful effects on first neonatal and later adult respiratory outcomes. These effects have been shown to persist across subsequent generations, regardless of the offsprings' smoking habits. Established epigenetic modifications induced by in utero exposure are postulated as the mechanism underlying the inherited poor respiratory outcomes. As e-cigarette use is on the rise, their potential to induce similar functional respiratory deficits underpinned by an alteration in the foetal epigenome needs to be explored. This review will focus on the functional and epigenetic impact of in utero exposure to maternal cigarette smoke, maternal environmental tobacco smoke, environmental tobacco smoke and e-cigarette vapour on foetal respiratory outcomes.

Presence of N-acetylglucosamine residues on the surface coating of bronchioloalveolar cells during rat postnatal development: What is their purpose?

Mammalian lung development is a complex process that is partially accomplished during the postnatal period. Surface carbohydrates are crucial in many biological and pathological phenomena and are key partners during development. The outer surface of lung epithelial cells, which is rich in carbohydrate components, plays a pivotal role throughout the developmental process. However, systematic studies on the sugar residue content of the cell surface coating during postnatal rat lung development are scarce. The aim of the present study was to identify and determine the localization of N-acetylglucosamine residues on the bronchioloalveolar cell surface during rat lung development using light and pre-embedding transmission electron microscopy methodologies, and to associate these data with the components underlying postnatal lung growth. Strong binding sites for the lectin Triticum vulgare (common name Wheat Germ, WGA) are present on the luminal surface of adult rat bronchioloalveolar cells throughout the entire postnatal period and have been identified as N-acetylglucosamine residues. The consistent positive reaction observed on the surface coating of bronchioloalveolar lining cells before and after neuraminidase treatment suggests that aside from possible terminal sialic acids, the lectin specificity for N-acetylglucosamine residues is still evident. Our results also suggest a stronger positive reaction on the bronchioloalveolar cell surface when compared with endothelial cell surface. N-acetylglucosamine residues for lectin binding can be present in glycoproteins in the membrane and also within heparin sulfate chains of glycosaminoglycans, which are crucial for lung development. The work described here has sought to highlight the presence and possible importance of N-acetylglucosamine residues on the glycocalyx of bronchioloalveolar cells, during postnatal lung development.

Maternal high fat diet compromises survival and modulates lung development of offspring, and impairs lung function of dams (female mice)

Background

Epidemiological studies have identified strong relationships between maternal obesity and offspring respiratory dysfunction; however, the causal direction is not known. We tested whether maternal obesity alters respiratory function of offspring in early life.

Methods

Female C57Bl/6 J mice were fed a high or low fat diet prior to and during two rounds of mating and resulting pregnancies with offspring lung function assessed at 2 weeks of age. The lung function of dams was measured at 33 weeks of age.

Results

A high fat diet caused significant weight gain prior to conception with dams exhibiting elevated fasting glucose, and glucose intolerance. The number of surviving litters was significantly less for dams fed a high fat diet, and surviving offspring weighed more, were longer and had larger lung volumes than those born to dams fed a low fat diet. The larger lung volumes significantly correlated in a linear fashion with body length. Pups born from the second pregnancy had reduced tissue elastance compared to pups born from the first pregnancy, regardless of the dam’s diet. As there was reduced offspring survival born to dams fed a high fat diet, the statistical power of lung function measures of offspring was limited. There were signs of increased inflammation in the bronchoalveolar lavage fluid of dams (but not offspring) fed a high fat diet, with more tumour necrosis factor-α, interleukin(IL)-5, IL-33 and leptin detected. Dams that were fed a high fat diet and became pregnant twice had reduced fasting glucose immediately prior to the second mating, and lower levels of IL-33 and leptin in bronchoalveolar lavage fluid.

Conclusions

While maternal high fat diet compromised litter survival, it also promoted somatic and lung growth (increased lung volume) in the offspring. Further studies are required to examine downstream effects of this enhanced lung volume on respiratory function in disease settings.