Alveolar repair following LPS-induced injury requires cell-ECM interactions

During alveolar repair, alveolar type 2 (AT2) epithelial cell progenitors rapidly proliferate and differentiate into flat AT1 epithelial cells. Failure of normal alveolar repair mechanisms can lead to loss of alveolar structure (emphysema) or development of fibrosis, depending on the type and severity of injury. To test if β1-containing integrins are required during repair following acute injury, we administered E. coli lipopolysaccharide (LPS) by intratracheal injection to mice with a postdevelopmental deletion of β1 integrin in AT2 cells. While control mice recovered from LPS injury without structural abnormalities, β1-deficient mice had more severe inflammation and developed emphysema. In addition, recovering alveoli were repopulated with an abundance of rounded epithelial cells coexpressing AT2 epithelial, AT1 epithelial, and mixed intermediate cell state markers, with few mature type 1 cells. AT2 cells deficient in β1 showed persistently increased proliferation after injury, which was blocked by inhibiting NF-κB activation in these cells. Lineage tracing experiments revealed that β1-deficient AT2 cells failed to differentiate into mature AT1 epithelial cells. Together, these findings demonstrate that functional alveolar repair after injury with terminal alveolar epithelial differentiation requires β1-containing integrins.

Ligand-independent integrin β1 signaling supports lung adenocarcinoma development

Integrins - the principal extracellular matrix (ECM) receptors of the cell - promote cell adhesion, migration, and proliferation, which are key events for cancer growth and metastasis. To date, most integrin-targeted cancer therapeutics have disrupted integrin-ECM interactions, which are viewed as critical for integrin functions. However, such agents have failed to improve cancer patient outcomes. We show that the highly expressed integrin β1 subunit is required for lung adenocarcinoma development in a carcinogen-induced mouse model. Likewise, human lung adenocarcinoma cell lines with integrin β1 deletion failed to form colonies in soft agar and tumors in mice. Mechanistically, we demonstrate that these effects do not require integrin β1-mediated adhesion to ECM but are dependent on integrin β1 cytoplasmic tail-mediated activation of focal adhesion kinase (FAK). These studies support a critical role for integrin β1 in lung tumorigenesis that is mediated through constitutive, ECM binding-independent signaling involving the cytoplasmic tail.

A single-cell atlas of mouse lung development

Lung organogenesis requires precise timing and coordination to effect spatial organization and function of the parenchymal cells. To provide a systematic broad-based view of the mechanisms governing the dynamic alterations in parenchymal cells over crucial periods of development, we performed a single-cell RNA-sequencing time-series yielding 102,571 epithelial, endothelial and mesenchymal cells across nine time points from embryonic day 12 to postnatal day 14 in mice. Combining computational fate-likelihood prediction with RNA in situ hybridization and immunofluorescence, we explore lineage relationships during the saccular to alveolar stage transition. The utility of this publicly searchable atlas resource (www.sucrelab.org/lungcells) is exemplified by discoveries of the complexity of type 1 pneumocyte function and characterization of mesenchymal Wnt expression patterns during the saccular and alveolar stages - wherein major expansion of the gas-exchange surface occurs. We provide an integrated view of cellular dynamics in epithelial, endothelial and mesenchymal cell populations during lung organogenesis.

Neutrophilic inflammation during lung development disrupts elastin assembly and predisposes adult mice to COPD

Emerging evidence indicates that early life events can increase the risk for developing chronic obstructive pulmonary disease (COPD). Using an inducible transgenic mouse model for NF-κB activation in the airway epithelium, we found that a brief period of inflammation during the saccular stage (P3-P5) but not alveolar stage (P10-P12) of lung development disrupted elastic fiber assembly, resulting in permanent reduction in lung function and development of a COPD-like lung phenotype that progressed through 24 months of age. Neutrophil depletion prevented disruption of elastic fiber assembly and restored normal lung development. Mechanistic studies uncovered a role for neutrophil elastase (NE) in downregulating expression of critical elastic fiber assembly components, particularly fibulin-5 and elastin. Further, purified human NE and NE-containing exosomes from tracheal aspirates of premature infants with lung inflammation downregulated elastin and fibulin-5 expression by saccular-stage mouse lung fibroblasts. Together, our studies define a critical developmental window for assembling the elastin scaffold in the distal lung, which is required to support lung structure and function throughout the lifespan. Although neutrophils play a well-recognized role in COPD development in adults, neutrophilic inflammation may also contribute to early-life predisposition to COPD.

Standardization of methods for sampling the distal airspace in mechanically ventilated patients using heat moisture exchange filter fluid

Noninvasive sampling of the distal airspace in patients with acute respiratory distress syndrome (ARDS) has long eluded clinical and translational researchers. We recently reported that fluid collected from heat moisture exchange (HME) filters closely mirrors fluid directly aspirated from the distal airspace. In the current study, we sought to determine fluid yield from different HME types, optimal HME circuit dwell time, and reliability of HME fluid in reflecting the distal airspace. We studied fluid yield from four different filter types by loading increasing volumes of saline and measuring volumes of fluid recovered. We collected filters after 1, 2, and 4 h of dwell time for measurement of fluid volume and total protein from 13 subjects. After identifying 4 h as the optimal dwell time, we measured total protein and IgM in HME fluid from 42 subjects with ARDS and nine with hydrostatic pulmonary edema (HYDRO). We found that the fluid yield varies greatly by filter type. With timed sample collection, fluid recovery increased with increasing circuit dwell time with a median volume of 2.0 mL [interquartile range (IQR) 1.2-2.7] after 4 h. Total protein was higher in the 42 subjects with ARDS compared with nine with HYDRO [median 708 µg/mL (IQR 244-2017) vs. 364 µg/mL (IQR 136-578), P = 0.047], confirming that total protein concentration in HME is higher in ARDS compared with hydrostatic edema. These studies establish a standardized HME fluid collection protocol and confirm that HME fluid analysis is a novel noninvasive tool for the study of the distal airspace in ARDS.

Age-determined expression of priming protease TMPRSS2 and localization of SARS-CoV-2 in lung epithelium

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) novel coronavirus 2019 (COVID-19) global pandemic has led to millions of cases and hundreds of thousands of deaths. While older adults appear at high risk for severe disease, hospitalizations and deaths due to SARS-CoV-2 among children have been relatively rare. Integrating single-cell RNA sequencing (scRNA-seq) of developing mouse lung with temporally resolved immunofluorescence in mouse and human lung tissue, we found that expression of SARS-CoV-2 Spike protein primer TMPRSS2 was highest in ciliated cells and type I alveolar epithelial cells (AT1), and TMPRSS2 expression increased with aging in mice and humans. Analysis of autopsy tissue from fatal COVID-19 cases detected SARS-CoV-2 RNA most frequently in ciliated and secretory cells in airway epithelium and AT1 cells in peripheral lung. SARS-CoV-2 RNA was highly colocalized in cells expressing TMPRSS2. Together, these data demonstrate the cellular spectrum infected by SARS-CoV-2 in lung epithelium and suggest that developmental regulation of TMPRSS2 may underlie the relative protection of infants and children from severe respiratory illness.

Hyperoxia Injury in the Developing Lung Is Mediated by Mesenchymal Expression of Wnt5A

Rationale: Bronchopulmonary dysplasia (BPD) is a leading complication of preterm birth that affects infants born in the saccular stage of lung development at <32 weeks of gestation. Although the mechanisms driving BPD remain uncertain, exposure to hyperoxia is thought to contribute to disease pathogenesis.Objectives: To determine the effects of hyperoxia on epithelial-mesenchymal interactions and to define the mediators of activated Wnt/β-catenin signaling after hyperoxia injury.Methods: Three hyperoxia models were used: A three-dimensional organotypic coculture using primary human lung cells, precision-cut lung slices (PCLS), and a murine in vivo hyperoxia model. Comparisons of normoxia- and hyperoxia-exposed samples were made by real-time quantitative PCR, RNA in situ hybridization, quantitative confocal microscopy, and lung morphometry.Measurements and Main Results: Examination of an array of Wnt ligands in the three-dimensional organotypic coculture revealed increased mesenchymal expression of WNT5A. Inhibition of Wnt5A abrogated the BPD transcriptomic phenotype induced by hyperoxia. In the PCLS model, Wnt5A inhibition improved alveolarization following hyperoxia exposure, and treatment with recombinant Wnt5a reproduced features of the BPD phenotype in PCLS cultured in normoxic conditions. Chemical inhibition of NF-κB with BAY11-7082 reduced Wnt5a expression in the PCLS hyperoxia model and in vivo mouse hyperoxia model, with improved alveolarization in the PCLS model.Conclusions: Increased mesenchymal Wnt5A during saccular-stage hyperoxia injury contributes to the impaired alveolarization and septal thickening observed in BPD. Precise targeting of Wnt5A may represent a potential therapeutic strategy for the treatment of BPD.

Age-determined expression of priming protease TMPRSS2 and localization of SARS-CoV-2 infection in the lung epithelium

The SARS-CoV-2 novel coronavirus global pandemic (COVID-19) has led to millions of cases and hundreds of thousands of deaths around the globe. While the elderly appear at high risk for severe disease, hospitalizations and deaths due to SARS-CoV-2 among children have been relatively rare. Integrating single-cell RNA sequencing (scRNA-seq) of the developing mouse lung with temporally-resolved RNA-in-situ hybridization (ISH) in mouse and human lung tissue, we found that expression of SARS-CoV-2 Spike protein primer TMPRSS2 was highest in ciliated cells and type I alveolar epithelial cells (AT1), and TMPRSS2 expression was increased with aging in mice and humans. Analysis of autopsy tissue from fatal COVID-19 cases revealed SARS-CoV-2 RNA was detected most frequently in ciliated and secretory cells in the airway epithelium and AT1 cells in the peripheral lung. SARS-CoV-2 RNA was highly colocalized in cells expressing TMPRSS2. Together, these data demonstrate the cellular spectrum infected by SARS-CoV-2 in the lung epithelium, and suggest that developmental regulation of TMPRSS2 may underlie the relative protection of infants and children from severe respiratory illness.

β1 Integrin regulates adult lung alveolar epithelial cell inflammation

Integrins, the extracellular matrix receptors that facilitate cell adhesion and migration, are necessary for organ morphogenesis; however, their role in maintaining adult tissue homeostasis is poorly understood. To define the functional importance of β1 integrin in adult mouse lung, we deleted it after completion of development in type 2 alveolar epithelial cells (AECs). Aged β1 integrin-deficient mice exhibited chronic obstructive pulmonary disease-like (COPD-like) pathology characterized by emphysema, lymphoid aggregates, and increased macrophage infiltration. These histopathological abnormalities were preceded by β1 integrin-deficient AEC dysfunction such as excessive ROS production and upregulation of NF-κB-dependent chemokines, including CCL2. Genetic deletion of the CCL2 receptor, Ccr2, in mice with β1 integrin-deficient type 2 AECs impaired recruitment of monocyte-derived macrophages and resulted in accelerated inflammation and severe premature emphysematous destruction. The lungs exhibited reduced AEC efferocytosis and excessive numbers of inflamed type 2 AECs, demonstrating the requirement for recruited monocytes/macrophages in limiting lung injury and remodeling in the setting of a chronically inflamed epithelium. These studies support a critical role for β1 integrin in alveolar homeostasis in the adult lung.

Mouse models of preterm birth: suggested assessment and reporting guidelines

Preterm birth affects approximately 1 out of every 10 births in the United States, leading to high rates of mortality and long-term negative health consequences. To investigate the mechanisms leading to preterm birth so as to develop prevention strategies, researchers have developed numerous mouse models of preterm birth. However, the lack of standard definitions for preterm birth in mice limits our field's ability to compare models and make inferences about preterm birth in humans. In this review, we discuss numerous mouse preterm birth models, propose guidelines for experiments and reporting, and suggest markers that can be used to assess whether pups are premature or mature. We argue that adoption of these recommendations will enhance the utility of mice as models for preterm birth.

Successful Establishment of Primary Type II Alveolar Epithelium with 3D Organotypic Coculture

Alveolar type II (AT2) epithelial cells are uniquely specialized to produce surfactant in the lung and act as progenitor cells in the process of repair after lung injury. AT2 cell injury has been implicated in several lung diseases, including idiopathic pulmonary fibrosis and bronchopulmonary dysplasia. The inability to maintain primary AT2 cells in culture has been a significant barrier in the investigation of pulmonary biology. We have addressed this knowledge gap by developing a three-dimensional (3D) organotypic coculture using primary human fetal AT2 cells and pulmonary fibroblasts. Grown on top of matrix-embedded fibroblasts, the primary human AT2 cells establish a monolayer and have direct contact with the underlying pulmonary fibroblasts. Unlike conventional two-dimensional (2D) culture, the structural and functional phenotype of the AT2 cells in our 3D organotypic culture was preserved over 7 days of culture, as evidenced by the presence of lamellar bodies and by production of surfactant proteins B and C. Importantly, the AT2 cells in 3D cocultures maintained the ability to replicate, with approximately 60% of AT2 cells staining positive for the proliferation marker Ki67, whereas no such proliferation is evident in 2D cultures of the same primary AT2 cells. This organotypic culture system enables interrogation of AT2 epithelial biology by providing a reductionist in vitro model in which to investigate the response of AT2 epithelial cells and AT2 cell-fibroblast interactions during lung injury and repair.

Epithelial-Derived Inflammation Disrupts Elastin Assembly and Alters Saccular Stage Lung Development

The highly orchestrated interactions between the epithelium and mesenchyme required for normal lung development can be disrupted by perinatal inflammation in preterm infants, although the mechanisms are incompletely understood. We used transgenic (inhibitory κB kinase β transactivated) mice that conditionally express an activator of the NF-κB pathway in airway epithelium to investigate the impact of epithelial-derived inflammation during lung development. Epithelial NF-κB activation selectively impaired saccular stage lung development, with a phenotype comprising rapidly progressive distal airspace dilation, impaired gas exchange, and perinatal lethality. Epithelial-derived inflammation resulted in disrupted elastic fiber organization and down-regulation of elastin assembly components, including fibulins 4 and 5, lysyl oxidase like-1, and fibrillin-1. Fibulin-5 expression by saccular stage lung fibroblasts was consistently inhibited by treatment with bronchoalveolar lavage fluid from inhibitory κB kinase β transactivated mice, Escherichia coli lipopolysaccharide, or tracheal aspirates from preterm infants exposed to chorioamnionitis. Expression of a dominant NF-κB inhibitor in fibroblasts restored fibulin-5 expression after lipopolysaccharide treatment, whereas reconstitution of fibulin-5 rescued extracellular elastin assembly by saccular stage lung fibroblasts. Elastin organization was disrupted in saccular stage lungs of preterm infants exposed to systemic inflammation. Our study reveals a critical window for elastin assembly during the saccular stage that is disrupted by inflammatory signaling and could be amenable to interventions that restore elastic fiber assembly in the developing lung.

Epithelial β1 integrin is required for lung branching morphogenesis and alveolarization

Integrin-dependent interactions between cells and extracellular matrix regulate lung development; however, specific roles for β1-containing integrins in individual cell types, including epithelial cells, remain incompletely understood. In this study, the functional importance of β1 integrin in lung epithelium during mouse lung development was investigated by deleting the integrin from E10.5 onwards using surfactant protein C promoter-driven Cre. These mutant mice appeared normal at birth but failed to gain weight appropriately and died by 4 months of age with severe hypoxemia. Defects in airway branching morphogenesis in association with impaired epithelial cell adhesion and migration, as well as alveolarization defects and persistent macrophage-mediated inflammation were identified. Using an inducible system to delete β1 integrin after completion of airway branching, we showed that alveolarization defects, characterized by disrupted secondary septation, abnormal alveolar epithelial cell differentiation, excessive collagen I and elastin deposition, and hypercellularity of the mesenchyme occurred independently of airway branching defects. By depleting macrophages using liposomal clodronate, we found that alveolarization defects were secondary to persistent alveolar inflammation. β1 integrin-deficient alveolar epithelial cells produced excessive monocyte chemoattractant protein 1 and reactive oxygen species, suggesting a direct role for β1 integrin in regulating alveolar homeostasis. Taken together, these studies define distinct functions of epithelial β1 integrin during both early and late lung development that affect airway branching morphogenesis, epithelial cell differentiation, alveolar septation and regulation of alveolar homeostasis.

Interactions between NF-κB and SP3 connect inflammatory signaling with reduced FGF-10 expression

Inflammation inhibits normal lung morphogenesis in preterm infants. Soluble inflammatory mediators present in the lungs of patients developing bronchopulmonary dysplasia disrupt expression of multiple genes critical for development. However, the mechanisms linking innate immune signaling and developmental programs are not clear. NF-κB activation inhibits expression of the critical morphogen FGF-10. Here, we show that interactions between the RELA subunit of NF-κB and SP3 suppress SP1-mediated FGF-10 expression. SP3 co-expression reduced SP1-mediated Fgf-10 promoter activity, suggesting antagonistic interactions between SP1 and SP3. Chromatin immunoprecipitation of LPS-treated primary mouse fetal lung mesenchymal cells detected increased interactions between SP3, RELA, and the Fgf-10 promoter. Expression of a constitutively active IκB kinase β mutant not only decreased Fgf-10 promoter activity but also increased RELA-SP3 nuclear interactions. Expression of a dominant-negative IκB, which blocks NF-κB nuclear translocation, prevented inhibition of FGF-10 by SP3. The inhibitory functions of SP3 required sequences located in the N-terminal region of the protein. These data suggested that inhibition of FGF-10 by inflammatory signaling involves the NF-κB-dependent interactions between RELA, SP3, and the Fgf-10 promoter. NF-κB activation may therefore lead to reduced gene expression by recruiting inhibitory factors to specific gene promoters following exposure to inflammatory stimuli.

Nonmuscle myosin II regulation of lung epithelial morphology

BACKGROUND

The regulation of epithelial cell shape and orientation during lung branching morphogenesis is not clearly understood. Nonmuscle myosins regulate cell size, morphology, and planar cell polarity. Here, we test the hypothesis that nonmuscle myosin II (NM II) regulates lung epithelial morphology in a spatially restricted manner.

RESULTS

Epithelial cell orientation at airway tips in fetal mouse lungs underwent a significant transformation at embryonic day (E) E17. Treatment of E15 lung explants with the NM II inhibitor blebbistatin increased airway branching, epithelial cell size, and the degree of anisotropy in epithelial cells lining the airway stalks. In cultured MLE-12 lung epithelial cells, blebbistatin increased cell velocity, but left the migratory response to FGF-10 unchanged.

CONCLUSIONS

In the developing lung, NM II acts to constrain cell morphology and orientation, but may be suppressed at sites of branching and cell migration. The regulation of epithelial orientation may therefore undergo dynamic variations from E15 to E17.

Cytomegalovirus infection

Although commonly asymptomatic, congenital CMV infection is the leading cause of nonhereditary SNHL. Other sequelae that may be evident only after the neonatal period can include chorioretinitis, neurodevelopmental delay with mental or motor impairment, and microcephaly. (13) • Congenital CMV infection is confirmed by detection of the virus in urine, blood, or saliva within the first 3 weeks of life by culture or polymerase chain reaction. A positive test does not necessarily confirm symptomatic CMV disease or need for treatment. (13) • Postnatal CMV infections transmitted through human milk have been reported and may be clinically relevant in extremely premature infants; however, the risk-benefit ratio of pasteurizing human milk for the prevention of postnatal CMV infection is unclear. • Ganciclovir, valganciclovir, foscarnet, cidofovir, and CMV hyperimmune globulin are effective in treating or preventing CMV infections in the immunocompromised host, but require close monitoring for associated toxicities. Treatment for congenital CMV is associated with significant toxicity and uncertain effectiveness. • Based on strong evidence, anticipatory guidance for congenital CMV infection should include hearing tests and neurodevelopmental assessments until school age. (3) In patients with symptomatic congenital CMV infection, lifelong ophthalmologic screening should be included. (4) • Based primarily on consensus, owing to lack of relevant clinical studies, it is not recommended to withhold human milk produced by CMV-seropositive mothers from healthy term infants. (5)(6) • Based on some research evidence, as well as consensus, treatment for congenital CMV is recommended only in symptomatic infants with central nervous system involvement. (9)

NF-kappaB activation limits airway branching through inhibition of Sp1-mediated fibroblast growth factor-10 expression

Bronchopulmonary dysplasia (BPD) is a frequent complication of preterm birth. This chronic lung disease results from arrested saccular airway development and is most common in infants exposed to inflammatory stimuli. In experimental models, inflammation inhibits expression of fibroblast growth factor-10 (FGF-10) and impairs epithelial-mesenchymal interactions during lung development; however, the mechanisms connecting inflammatory signaling with reduced growth factor expression are not yet understood. In this study we found that soluble inflammatory mediators present in tracheal fluid from preterm infants can prevent saccular airway branching. In addition, LPS treatment led to local production of mediators that inhibited airway branching and FGF-10 expression in LPS-resistant C.C3-Tlr4(Lpsd)/J fetal mouse lung explants. Both direct NF-κB activation and inflammatory cytokines (IL-1β and TNF-α) that activate NF-κB reduced FGF-10 expression, whereas chemokines that signal via other inflammatory pathways had no effect. Mutational analysis of the FGF-10 promoter failed to identify genetic elements required for direct NF-κB-mediated FGF-10 inhibition. Instead, NF-κB activation appeared to interfere with the normal stimulation of FGF-10 expression by Sp1. Chromatin immunoprecipitation and nuclear coimmunoprecipitation studies demonstrated that the RelA subunit of NF-κB and Sp1 physically interact at the FGF-10 promoter. These findings indicate that inflammatory signaling through NF-κB disrupts the normal expression of FGF-10 in fetal lung mesenchyme by interfering with the transcriptional machinery critical for lung morphogenesis.

Validity of parental report of influenza vaccination in children 6 to 59 months of age

OBJECTIVE

The objective of this study was to assess the validity of parental report of influenza vaccinations.

PATIENTS AND METHODS

A cross-sectional study of children who were 6 to 59 months of age and presented to a large, pediatric residency clinic from February through April 2005 was performed. A standardized, parental questionnaire ascertained the influenza vaccination status of children during the 2004-2005 influenza season and was compared with the medical chart, the criterion standard. Children were classified as being at high risk when they had a specific influenza vaccine recommendation in 2004-2005 by age (6-23 months of age) or by chronic medical condition.

RESULTS

Of 218 parents approached in the pediatric residency clinic, 198 (95%) children who were 6 to 59 months of age were enrolled, and 84 (42%) were vaccinated according to the medical chart. More children who were 6 to 23 months than those who were 24 to 59 months of age were vaccinated (63% vs 21%). Children with chronic medical conditions were more likely to be vaccinated than healthy children who were 24 to 59 months of age (57% vs 11%), but no difference was observed for children who were 6 to 23 months of age (79% vs 60%). In comparison with the medical chart, parental report of influenza vaccination had a sensitivity of 88%, a specificity of 90%, and a kappa coefficient of 0.78. For children who were 6 to 23 months of age or had a chronic medical condition (n = 123), parental report had a sensitivity of 89%, a specificity of 81%, and a kappa coefficient of 0.71.

CONCLUSIONS

Parental report of influenza vaccination among children who were 6 to 59 months of age had reasonable sensitivity, specificity, and reliability as compared with the medical chart in this study population.