18β-Glycyrrhetinic Acid Protectes Neonatal Rats with Hyperoxia Exposure Through Inhibiting ROS/NF-κB/NLRP3 Inflammasome

Bronchopulmonary dysplasia (BPD) is a common devastating pulmonary complication in preterm infants. Oxygen supplementation is a lifesaving therapeutic measure used for premature infants with pulmonary insufficiency. However, oxygen toxicity is a significant trigger for BPD, and oxidative stress-induced inflammatory responses, in turn, worsens the oxidative toxicity resulting in lung injury and arresting of lung development. Glycyrrhiza radix is commonly used in the medicine and food industries. 18β-Glycyrrhetinic acid (18β-GA), a primary active ingredient of Glycyrrhiza radix, has a powerful anti-oxidative and anti-inflammatory effects. This study aimed to determine whether 18β-GA has protective effects on neonatal rats with hyperoxia exposure. Newborn Sprague-Dawley rats were kept in either 21% (normoxia) or 80% O2 (hyperoxia) continuously from postnatal day (PN) 1 to 14. 18β-GA was injected intragastrically at 50 or 100 mg/kg body weight once a day from PN 1 to 14. We examined the body weights and alveolar development, and measured ROS level and the markers of pulmonary inflammation. Mature-IL-1β and NF-κB pathway proteins, and the NLRP3 inflammasome, were assessed; concurrently, caspase-1 activity was measured. Our results indicated that hyperoxia resulted in alveolar simplification and decreased bodyweight of neonatal rats. Hyperoxia exposure increased ROS level and pulmonary inflammation, and activated NF-κB and the NLRP3 inflammasome. 18β-GA treatment decreased ROS level, inhibited the activation of NF-κB and the NLRP3 inflammasome, decreased pulmonary inflammation, improved alveolar development, and increased the bodyweight of neonatal rats with hyperoxia exposure. Our study demonstrates that 18β-GA protects neonatal rats with hyperoxia exposure through inhibiting ROS/NF-κB/NLRP3 inflammasome.

Mice lacking DYRK2 exhibit congenital malformations with lung hypoplasia and altered Foxf1 expression gradient

Congenital malformations cause life-threatening diseases in pediatrics, yet the molecular mechanism of organogenesis is poorly understood. Here we show that Dyrk2-deficient mice display congenital malformations in multiple organs. Transcriptome analysis reveals molecular pathology of Dyrk2-deficient mice, particularly with respect to Foxf1 reduction. Mutant pups exhibit sudden death soon after birth due to respiratory failure. Detailed analyses of primordial lungs at the early developmental stage demonstrate that Dyrk2 deficiency leads to altered airway branching and insufficient alveolar development. Furthermore, the Foxf1 expression gradient in mutant lung mesenchyme is disrupted, reducing Foxf1 target genes, which are necessary for proper airway and alveolar development. In ex vivo lung culture system, we rescue the expression of Foxf1 and its target genes in Dyrk2-deficient lung by restoring Shh signaling activity. Taken together, we demonstrate that Dyrk2 is essential for embryogenesis and its disruption results in congenital malformation.

The Role of Hippo/YAP Signaling in Alveolar Repair and Pulmonary Fibrosis

Pulmonary fibrosis is characterized by loss of normal alveoli, accumulation of pathologic activated fibroblasts, and exuberant extracellular matrix deposition that over time can lead to progressive loss of respiratory function and death. This loss of respiratory function is associated with the loss of alveolar type 1 cells (AT1) that play a crucial role in gas exchange and the depletion of the alveolar type 2 cells (AT2) that act as progenitor cells to regenerate the AT1 and AT2 cell populations during repair. Understanding the mechanisms that regulate normal alveolar repair and those associated with pathologic repair is essential to identify potential therapeutic targets to treat or delay progression of fibrotic diseases. The Hippo/YAP developmental signaling pathway has been implicated as a regulator of normal alveolar development and repair. In idiopathic pulmonary fibrosis, aberrant activation of YAP/TAZ has been demonstrated in both the alveolar epithelium and activated fibroblasts associated with increased fibrotic remodeling, and there is emerging interest in this pathway as a target for antifibrotic therapies. In this review, we summarize current evidence as to the role of the Hippo-YAP/TAZ pathway in alveolar development, homeostasis, and repair, and highlight key questions that must be resolved to determine effective strategies to modulate YAP/TAZ signaling to prevent progressive pulmonary fibrosis and enhance adaptive alveolar repair.

Microvesicles Derived From Human Umbilical Cord Mesenchymal Stem Cells Enhance Alveolar Development and Attenuate Lung Inflammation in a Rat Model of Bronchopulmonary Dysplasia Induced by Antenatal Lipopolysaccharide

BackgroundAlthough it is known that exosomes derived from human umbilical cord mesenchymal stem cells (hUCMSCs) alleviate hyperoxic lung injury of bronchopulmonary dysplasia (BPD) in animal models, the role of microvesicles (MVs) derived from hUCMSCs in BPD is poorly defined. Furthermore, antenatal inflammation has been linked to high risk of BPD in preterm infants. The purpose of this study was to explore whether MVs derived from hUCMSCs can preserve lung structure and function in an antenatal lipopolysaccharide (LPS)-induced BPD rat model and to clarify the underlying mechanism.MethodsPregnant rats received intra-amniotic injections of LPS on day 20.5 of gestation (term=day 22.5 of gestion), and pups were delivered by cesarean section on embryonic day 22.5 (E22.5). MVs were isolated by ultracentrifugation and then were characterized. hUCMSCs and MVs were administered intratracheally on postnatal day 7 (PN7). On PN14, lung function was measured, and tissues were harvested to determine alveolarization. Immunofluorescence staining was used to determine the co-localization of MVs and lung cells. Cell proliferation was measured by Ki-67 staining, and apoptosis was determined by flow cytometry using 7-ADD and Annexin V. The expression levels of AKT, p38, JNK, ERK, and their phosphorylated forms, PTEN and VEGF, were measured by WB.ResultsAntenatal LPS induced alveolar simplification, altered lung function, and dysregulated pulmonary vasculature. Both hUCMSCs and MVs successfully promoted alveolar development and improved lung function. However, hUCMSCs but not MVs restored the loss of pulmonary microvascular vessels (<100 μm). Furthermore, MVs were mostly uptaken by alveolar epithelial type II cells (AT2) and macrophages. Compared with the LPS-exposed group, MVs restored the AT2 cell number and SP-C expression in vivo and promoted the proliferation of AT2 cells in vitro. MVs also restored the level of IL-6 and IL-10 in lung homogenate. Additionally, upregulated expression of p-AKT, downregulated expression of PTEN, as well as inhibition of MAPK pathway were observed in MVs-treated BPD rats.ConclusionsMVs derived from hUCMSCs improve lung architecture and function in an antenatal LPS-induced BPD rat model by promoting AT2 cell proliferation and attenuate lung inflammation; thus, MVs provide a promising therapeutic vehicle for BPD treatment.

The Specific Connexin 43–Inhibiting Peptide Gap26 Improved Alveolar Development of Neonatal Rats With Hyperoxia Exposure

Bronchopulmonary dysplasia (BPD) is a common devastating pulmonary complication in preterm infants. Alveolar maldevelopment is the crucial pathological change of BPD highly associated with oxidative stress–mediated excessive apoptosis. Cellular injury can be propagated and amplified by gap junction (GJ)–mediated intercellular communication. Connexin 43 (Cx43) is the most ubiquitous and critical GJ protein. Gap26 is a specific Cx43 mimic peptide, playing as a Cx43-GJ inhibitor. We hypothesized that Cx43-GJ was involved in alveolar maldevelopment of BPD via amplifying oxidative stress signaling and inducing excessive apoptosis. Neonatal Sprague Dawley rats were kept in either normoxia (21% O2) or hyperoxia (85% O2) continuously from postnatal day (PN) 1 to 14 in the presence or absence of Gap26. Moreover, RLE-6TN cells (type II alveolar epithelial cells of rats) were cultured in vitro under normoxia (21% O2) or hyperoxia (85% O2). RLE-6TN cells were treated by N-acetyl cysteine (NAC) (a kind of reactive oxygen species (ROS) scavenger) or Gap26. Morphological properties of lung tissue are detected. Markers associated with Cx43 expression, ROS production, the activity of the ASK1-JNK/p38 signaling pathway, and apoptotic level are detected in vivo and in vitro, respectively. In vitro, the ability of GJ-mediated intercellular communication was examined by dye-coupling assay. In vitro, our results demonstrated ROS increased Cx43 expression and GJ-mediated intercellular communication and Gap26 treatment decreased ROS production, inhibited ASK1-JNK/p38 signaling, and decreased apoptosis. In vivo, we found that hyperoxia exposure resulted in increased ROS production and Cx43 expression, activated ASK1-JNK/p38 signaling, and induced excessive apoptosis. However, Gap26 treatment reversed these changes, thus improving alveolar development in neonatal rats with hyperoxia exposure. In summary, oxidative stress increased Cx43 expression and Cx43-GJ–mediated intercellular communication. And Cx43-GJ–mediated intercellular communication amplified oxidative stress signaling, inducing excessive apoptosis via the ASK1-JNK/p38 signaling pathway. The specific connexin 43–inhibiting peptide Gap26 was a novel therapeutic strategy to improve the alveolar development of BPD.

Acquisition of alveolar fate and differentiation competence by human fetal lung epithelial progenitor cells

Variation in lung alveolar development is strongly linked to disease susceptibility. However, the cellular and molecular mechanisms underlying alveolar development are difficult to study in humans. Using primary human fetal lungs we have characterized a tip progenitor cell population with alveolar fate potential. These data allowed us to benchmark a self-organising organoid system which captures key aspects of lung lineage commitment and can be efficiently differentiated to alveolar type 2 cell fate. Our data show that Wnt and FGF signalling, and the downstream transcription factors NKX2.1 and TFAP2C, promote human alveolar or airway fate respectively. Moreover, we have functionally validated cell-cell interactions in human lung alveolar patterning. We show that Wnt signalling from differentiating fibroblasts promotes alveolar type 2 cell identity, whereas myofibroblasts secrete the Wnt inhibitor, NOTUM, providing spatial patterning. Our organoid system recapitulates key aspects of human lung development allowing mechanistic experiments to determine the underpinning molecular regulation.

Effects of Hyperoxia on Mitochondrial Homeostasis: Are Mitochondria the Hub for Bronchopulmonary Dysplasia?

Mitochondria are involved in energy metabolism and redox reactions in the cell. Emerging data indicate that mitochondria play an essential role in physiological and pathological processes of neonatal lung development. Mitochondrial damage due to exposure to high concentrations of oxygen is an indeed important factor for simplification of lung structure and development of bronchopulmonary dysplasia (BPD), as reported in humans and rodent models. Here, we comprehensively review research that have determined the effects of oxygen environment on alveolar development and morphology, summarize changes in mitochondria under high oxygen concentrations, and discuss several mitochondrial mechanisms that may affect cell plasticity and their effects on BPD. Thus, the pathophysiological effects of mitochondria may provide insights into targeted mitochondrial and BPD therapy.

CCR5 signaling promotes lipopolysaccharide-induced macrophage recruitment and alveolar developmental arrest

The pathogenesis of bronchopulmonary dysplasia (BPD), involves inflammatory, mechanisms that are not fully characterized. Here we report that overexpression of C-C chemokine receptor 5 (CCR5) and its ligands is associated with BPD development. Lipopolysaccharide-induced BPD rats have increased CCR5 and interleukin-1β (IL-1β) levels, and decreased alveolarization, while CCR5 or IL-1β receptor antagonist treatments decreased inflammation and increased alveolarization. CCR5 enhances macrophage migration, macrophage infiltration in the lungs, IL-1β levels, lysyl oxidase activity, and alveolar development arrest. CCR5 expression on monocytes, and its ligands in blood samples from BPD infants, are elevated. Furthermore, batyl alcohol supplementation reduced CCR5 expression and IL-1β production in lipopolysaccharide-exposed rat lungs. Moreover, receptor-interacting kinase 3 (RIP3) upstream regulator of CCR5-cultured RIP3−/− macrophages exhibited partly blocked lipopolysaccharide-induced CCR5 expression. We conclude that increased CCR5 expression is a key mechanism in BPD development and represents a novel therapeutic target for treatment.

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

<b><i>Background:</i></b> 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. <b><i>Objective:</i></b> This work quantified alveolar airspace size via HP gas diffusion MRI in healthy and diseased explanted infant lung specimens, with comparison to histological morphometry. <b><i>Methods:</i></b> 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 (<i>L</i>_m) via quantitative histology. <b><i>Results:</i></b> Mean ADC and <i>L</i>_m were significantly increased throughout the diseased specimen (ADC = 0.26 ± 0.06 cm²/s, <i>L</i>_m = 587 ± 212 µm) compared with healthy specimens (ADC = 0.14 ± 0.03 cm²/s, <i>L</i>_m = 133 ± 37 µm; <i>p</i> &#x3c; 1 × 10⁻⁷); increased values reflect enlarged airspaces. Mean ADCs in healthy specimens were significantly correlated to <i>L</i>_m (<i>r</i> = 0.69, <i>p</i> = 0.041). <b><i>Conclusions:</i></b> 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.