Pulmonary Surfactant Metabolism Research Articles

ABCA3 c.838C>T (p.Arg280Cys, R280C) and c.697C>T (p.Gln233Ter, Q233X, Q233*) as Causative Variants for RDS: A Family Case Study and Literature Review.

Background: Respiratory distress syndrome (RDS) is the primary cause of respiratory failure in preterm infants, but it also affects 5-7% of term infants. Dysfunctions in pulmonary surfactant metabolism, resulting from mutations of the lung surfactant genes, are rare diseases, ranging from fatal neonatal RDS to interstitial lung disease, associated with increased morbidity and mortality. This study aims to clarify the clinical significance of ABCA3 variants found in a specific family case, as existing data in the literature are inconsistent. Material and Methods: A family case report was conducted; targeted panel genetic testing identified a variant of the SFTPB gene and two variants of ABCA3 genes. Comprehensive research involving a systematic review of PubMed, Google Scholar databases, and genome browsers was used to clarify the pathogenicity of the two ABCA3 variants found in the index patient. Advanced prediction tools were employed to assess the pathogenicity of the two ABCA3 variants, ensuring the validity and reliability of our findings. Results: The index case exhibited fatal neonatal RDS. Genetic testing revealed the presence of the SFTPB p.Val267Ile variant, which was not previously reported but is a benign variant based on family genetic testing and history. Additionally, two ABCA3 gene variants were identified: c.697C>T, not yet reported, and c.838C>T. These variants were found to affect ABCA3 protein function and were likely associated with neonatal RDS. Prediction tools and data from nine other cases in the literature supported this conclusion. Conclusions: Based on in silico predictors, an analysis of the presented family, and cases described in the literature, it is reasonable to consider reclassifying the two ABCA3 variants identified in the index case as pathogenic/pathogenic. Reclassification will improve genetic counseling accuracy and facilitate correct diagnosis.

Activation of alveolar epithelial ER stress by β-coronavirus infection disrupts surfactant homeostasis in mice: implications for COVID-19 respiratory failure.

COVID-19 syndrome is characterized by acute lung injury, hypoxemic respiratory failure, and high mortality. Alveolar type 2 (AT2) cells are essential for gas exchange, repair, and regeneration of distal lung epithelium. We have shown that the causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and other members of the β-coronavirus genus induce an endoplasmic reticulum (ER) stress response in vitro; however, the consequences for host AT2 cell function in vivo are less understood. To study this, two murine models of coronavirus infection were used-mouse hepatitis virus-1 (MHV-1) in A/J mice and a mouse-adapted SARS-CoV-2 strain. MHV-1-infected mice exhibited dose-dependent weight loss with histological evidence of distal lung injury accompanied by elevated bronchoalveolar lavage fluid (BALF) cell counts and total protein. AT2 cells showed evidence of both viral infection and increased BIP/GRP78 expression, consistent with activation of the unfolded protein response (UPR). The AT2 UPR included increased inositol-requiring enzyme 1α (IRE1α) signaling and a biphasic response in PKR-like ER kinase (PERK) signaling accompanied by marked reductions in AT2 and BALF surfactant protein (SP-B and SP-C) content, increases in surfactant surface tension, and emergence of a reprogrammed epithelial cell population (Krt8+ and Cldn4+). The loss of a homeostatic AT2 cell state was attenuated by treatment with the IRE1α inhibitor OPK-711. As a proof-of-concept, C57BL6 mice infected with mouse-adapted SARS-CoV-2 demonstrated similar lung injury and evidence of disrupted surfactant homeostasis. We conclude that lung injury from β-coronavirus infection results from an aberrant host response, activating multiple AT2 UPR stress pathways, altering surfactant metabolism/function, and changing AT2 cell state, offering a mechanistic link between SARS-CoV-2 infection, AT2 cell biology, and acute respiratory failure.NEW & NOTEWORTHY COVID-19 syndrome is characterized by hypoxemic respiratory failure and high mortality. In this report, we use two murine models to show that β-coronavirus infection produces acute lung injury, which results from an aberrant host response, activating multiple epithelial endoplasmic reticular stress pathways, disrupting pulmonary surfactant metabolism and function, and forcing emergence of an aberrant epithelial transition state. Our results offer a mechanistic link between SARS-CoV-2 infection, AT2 cell biology, and respiratory failure.

The Synthetic Surfactant CHF5633 Restores Lung Function and Lung Architecture in Severe Acute Respiratory Distress Syndrome in Adult Rabbits

PurposeAcute respiratory distress syndrome (ARDS) is a major cause of hypoxemic respiratory failure in adults. In ARDS extensive inflammation and leakage of fluid into the alveoli lead to dysregulation of pulmonary surfactant metabolism and function. Altered surfactant synthesis, secretion, and breakdown contribute to the clinical features of decreased lung compliance and alveolar collapse. Lung function in ARDS could potentially be restored with surfactant replacement therapy, and synthetic surfactants with modified peptide analogues may better withstand inactivation in ARDS alveoli than natural surfactants.MethodsThis study aimed to investigate the activity in vitro and the bolus effect (200 mg phospholipids/kg) of synthetic surfactant CHF5633 with analogues of SP‐B and SP‐C, or natural surfactant Poractant alfa (Curosurf®, both preparations Chiesi Farmaceutici S.p.A.) in a severe ARDS model (the ratio of partial pressure arterial oxygen and fraction of inspired oxygen, P/F ratio ≤ 13.3 kPa) induced by hydrochloric acid instillation followed by injurious ventilation in adult New Zealand rabbits. The animals were ventilated for 4 h after surfactant treatment and the respiratory parameters, histological appearance of lung parenchyma and levels of inflammation, oxidative stress, surfactant dysfunction, and endothelial damage were evaluated.ResultsBoth surfactant preparations yielded comparable improvements in lung function parameters, reductions in lung injury score, pro-inflammatory cytokines levels, and lung edema formation compared to untreated controls.ConclusionsThis study indicates that surfactant replacement therapy with CHF5633 improves lung function and lung architecture, and attenuates inflammation in severe ARDS in adult rabbits similarly to Poractant alfa. Clinical trials have so far not yielded conclusive results, but exogenous surfactant may be a valid supportive treatment for patients with ARDS given its anti-inflammatory and lung-protective effects.

Mucopolysaccharidosis (MPS IIIA) mice have increased lung compliance and airway resistance, decreased diaphragm strength, and no change in alveolar structure.

Mucopolysaccharidosis type IIIA (MPS IIIA) is characterized by neurological and skeletal pathologies caused by reduced activity of the lysosomal hydrolase, sulfamidase, and the subsequent primary accumulation of undegraded heparan sulfate (HS). Respiratory pathology is considered secondary in MPS IIIA and the mechanisms are not well understood. Changes in the amount, metabolism, and function of pulmonary surfactant, the substance that regulates alveolar interfacial surface tension and modulates lung compliance and elastance, have been reported in MPS IIIA mice. Here we investigated changes in lung function in 20-wk-old control and MPS IIIA mice with a closed and open thoracic cage, diaphragm contractile properties, and potential parenchymal remodeling. MPS IIIA mice had increased compliance and airway resistance and reduced tissue damping and elastance compared with control mice. The chest wall impacted lung function as observed by an increase in airway resistance and a decrease in peripheral energy dissipation in the open compared with the closed thoracic cage state in MPS IIIA mice. Diaphragm contractile forces showed a decrease in peak twitch force, maximum specific force, and the force-frequency relationship but no change in muscle fiber cross-sectional area in MPS IIIA mice compared with control mice. Design-based stereology did not reveal any parenchymal remodeling or destruction of alveolar septa in the MPS IIIA mouse lung. In conclusion, the increased storage of HS which leads to biochemical and biophysical changes in pulmonary surfactant also affects lung and diaphragm function, but has no impact on lung or diaphragm structure at this stage of the disease.NEW & NOTEWORTHY Heparan sulfate storage in the lungs of mucopolysaccharidosis type IIIA (MPS IIIA) mice leads to changes in lung function consistent with those of an obstructive lung disease and includes an increase in lung compliance and airway resistance and a decrease in tissue elastance. In addition, diaphragm muscle contractile strength is reduced, potentially further contributing to lung function impairment. However, no changes in parenchymal lung structure were observed in mice at 20 wk of age.

Biochemical criteria for pulmonary surfactant damage in tuberculosis patients with previous work in dusty conditions

Introduction. Among the mechanisms of pathogenesis of tuberculosis is damage to the pulmonary surfactant. In patients with tuberculosis who previously worked in an industrial dusty environment, the pulmonary surfactant system is affected by two damaging factors simultaneously.The aim of the work was to determine the role of biochemical criteria of pulmonary surfactant damage as early molecular markers of the sub-radiological stage of pneumoconiosis in pulmonary tuberculosis patients.Materials and methods. The object of the study was 91 patients with pulmonary tuberculosis, of whom 59 patients had contact with industrial quartz-containing dust in the course of their work (the main group) and 32 patients − with an unburdened professional route (the control group). The content of total protein (TP), total phospholipids (TPL), phospholipid spectrum by thin-layer chromatography as criteria of pulmonary surfactant damage were studied biochemically in bronchoalveolar flushes (BAF).Results. It was found that in bronchoalveolar flushes of patients with tuberculosis of dust-hazardous professions, in group 1, the content of total protein increases, while the level of total phospholipids does not statistically significantly change in comparison with patients with an unburdened professional route. Among the phospholipids of BAF, phosphatidylcholine (PC), phosphatidiylethanolamine (PEA) and cardiolipin (CL) are the most common. In the BAF of the 1st group of patients, a frequent combination of fractions of PC and CL was found, in the 2nd group − PC, PEA and CL. Combinations containing sphingomyelin (SPM), PC and CL were found only in groups 1 and 2. It was also found that the level of total protein in BAF varies depending on the activity of the process, so in patients of group 1 with the presence of areas of destruction of lung tissue, the content of total protein significantly exceeded that in patients with specific inflammation subsiding.Discussion. Patients with pulmonary tuberculosis with dust exposure develop sub-radiological manifestations of pneumoconiosis in the form of impaired metabolism and biochemical composition of pulmonary surfactant, which is caused both by the dust factor and the influence of specific inflammation.Conclusion The role of biochemical criteria of pulmonary surfactant damage as early molecular markers of the sub-radiological stage of pneumoconiosis in pulmonary tuberculosis patients was determined.

Chronic Rhinosinusitis with Nasal Polyposis in an Adult with Homozygous Variants of Uncertain Significance in ABCA3 Gene

IntroductionThe role of surfactant proteins in pulmonary diseases has been studied extensively. However, little is known about its contribution in diseases involving the nasal mucosa. Chronic rhinosinusitis with nasal polyps (CRSwNP) is a common disease characterized by persistent inflammation of the nasal passage and paranasal sinuses. We present a case of CRSwNP and interstitial lung disease (ILD) with variants of uncertain significance (VUS) in adenosine triphosphate binding cassette subfamily A member 3 (ABCA3) identified as potential genetic etiology. Case DescriptionPatient was a 42-year-old female with chronic obstructive pulmonary disease (COPD) with oxygen-dependance, bronchiectasis, history of hospitalization for bronchiolitis obliterans organizing pneumonia (BOOP) in infancy, who presented for evaluation of CRSwNP and anosmia. Nasal polyps were first discovered around three years of age, requiring more than 25 nasal polypectomies in her lifetime. Evaluation for cystic fibrosis during childhood was unremarkable. She reported only one episode of wheezing and denied aspirin sensitivity. Despite her significant history of BOOP in infancy, the patient remained without pulmonary infections until four years prior to presentation. Since then, she had two episodes of pneumonia and was diagnosed with COPD, leading to chronic oxygen use. Recent spirometry showed severe airflow obstruction, hyperinflation and decreased diffusing capacity for carbon monoxide. Chest CT revealed diffuse bronchiectasis, mucous plugging, and mild ground glass opacity. Patient had negative sweat test and normal alpha-1 antitrypsin level. Genetic testing with Invitae PCD panel and Neonatal Respiratory Distress panel revealed homozygous VUS [c.155C>T (p. Pro52Leu)] in ABCA3 gene. ConclusionOur patient had an atypical course of ILD, remaining asymptomatic most of her life, and CRSwNP. ABCA3 variants are associated with autosomal recessive pulmonary diseases, such as pulmonary surfactant metabolism dysfunction, pediatric ILD and pulmonary fibrosis1. Surfactant phospholipids are known to lower the surface tension in the alveoli, but they also decrease mucus viscosity and help to eliminate inhaled pathogens2,3,4. The pathophysiology of CRSwNP is unclear and the clinical phenotype of the disease varies widely. While the pathogenicity of the variant is not defined, this case raises a possibility that patient’s ABCA3 genotype may contribute to CRSwNP with recalcitrant nasal polyps.

Role of GM-CSF in lung balance and disease.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic growth factor originally identified as a stimulus that induces the differentiation of bone marrow progenitor cells into granulocytes and macrophages. GM-CSF is now considered to be a multi-origin and pleiotropic cytokine. GM-CSF receptor signals activate JAK2 and induce nuclear signals through the JAK-STAT, MAPK, PI3K, and other pathways. In addition to promoting the metabolism of pulmonary surfactant and the maturation and differentiation of alveolar macrophages, GM-CSF plays a key role in interstitial lung disease, allergic lung disease, alcoholic lung disease, and pulmonary bacterial, fungal, and viral infections. This article reviews the latest knowledge on the relationship between GM-CSF and lung balance and lung disease, and indicates that there is much more to GM-CSF than its name suggests.

Profound Effect of Pulmonary Surfactant on the Treatment of Preterm Infants with Respiratory Distress Syndrome.

Inherited diseases caused by dysfunction of pulmonary surfactant metabolism or surfactant dysfunction have recently been considered the underlying causes of neonatal and pediatric respiratory diseases. Respiratory distress syndrome in premature infants is a common respiratory disease in pediatrics. It is caused by underdeveloped lungs in infants and a lack of active substances on the surface of the alveoli, which leads to insufficiency of lung function, which can lead to difficulty breathing, increased heart rate, facial bruising, and more. Neonatal Respiratory Distress Syndrome is a very dangerous disease with a high mortality rate and a great threat to children's lives and health. Therefore, enough attention and treatment should be caused in clinical practice. Natural pulmonary surfactant (PS) has achieved positive effects in the treatment of neonatal respiratory distress syndrome (RDS), reducing neonatal mortality, the application of mechanical ventilation, and the occurrence of late complications. To further explore the role of pulmonary surfactants in the treatment of neonatal respiratory distress syndrome, to analyze the best time to use PS to prevent RDS, this paper has selected premature infants with RDS received by the neonatal department of a hospital in a province from March 2019 to October 2020 to compare the efficacy of pulmonary surfactant (PS) in preterm infants with respiratory distress syndrome (RDS). The experiment has found that the average mechanical ventilation time (5.1 d) and oxygen therapy time (7.3 d) in the early group are shorter than the average mechanical ventilation time (6.4 d) and oxygen therapy time (10.6 d) in the late group. It has been demonstrated that early administration of pulmonary surfactant (PS) therapy is of great help in improving respiratory distress syndrome in premature infants.

Abstract 14272: Whole Exome Sequence Analysis of Pulmonary Hypertension in the UK Biobank

Introduction: Pulmonary hypertension (PH) is a progressive disease characterized by adverse remodeling of the lung vasculature and right ventricular failure. While BMPR2 mutations account for the majority of familial pulmonary arterial hypertension (PAH), the predisposing genetic factors in non-familial PH are not well understood. Whole exome sequencing (WES) data from individuals in the UK Biobank (UKB) provides a unique opportunity to interrogate the genetic factors underlying this rare disease. Hypothesis: Rare disruptive coding variants associated with sporadic PH will provide novel mechanistic insights. Methods: Exome sequences were aligned to the GRCh38 reference genome and variants annotated using Variant Effect Predictor. We identified rare (minor allele frequency <1%) high confidence loss-of-function variants using LOFTEE and deleterious missense variants using MetaSVM. We then performed a rare variant burden association study using logistic regression in REGENIE adjusting for age, sex, array, smoking status, and principal components 1-10. These analyses were performed on unrelated individuals identified based on kinship (kinship > 0.0884). We secondarily curated a list of 58 candidate PAH genes based on recent publications of rare variants identified in PAH, as well as the ClinVar database. PH was defined utilizing ICD codes 416.0 (ICD-9), I27.0, I27.2 (ICD-10). Results: 185,586 UKB participants were included; 665 with PH (age 62 years (+/-6), 46% female) and 184,921 controls (age 56 years (+/-8), 55% female). Rare variant association testing did not identify exome-significantly associated genes (p<2.5x10 -7 ), nor nominal associations in candidate PAH genes. Four novel genes with p<0.01 were identified, which included genes important in mitochondrial function ( ACADM ), nicotinic acetylcholine receptor signaling ( MYO18A ), pulmonary surfactant metabolism ( SFTPA1 ) and smooth muscle function ( BEST2 ). Conclusions: We identified putative genes associated with PH in the population which have not been previously implicated in familial PAH. If additional evidence supports the roles of these genes in PH, these findings may provide new therapeutic insights.

A novel synonymous ABCA3 variant identified in a Chinese family with lethal neonatal respiratory failure

BackgroundLethal respiratory failure is primarily caused by a deficiency of pulmonary surfactant, and is the main cause of neonatal death among preterm infants. Pulmonary surfactant metabolism dysfunction caused by variants in the ABCA3 gene is a rare disease with very poor prognosis. Currently, the mechanisms associated with some ABCA3 variants have been determined, including protein mistrafficking and impaired phospholipid transport. However, some novel variants and their underlying pathogenesis has not been fully elucidated yet. In this study we aimed to identify the genetic features in a family with lethal respiratory failure.MethodsWe studied members of two generations of a Chinese family, including a female proband, her parents, her monozygotic twin sister, and her older sister. Trio whole exome sequencing (WES) were used on the proband and her parents to identify the ABCA3 variants. Sanger sequencing and real-time quantitative polymerase chain reaction (PCR) were used on the monozygotic twin sister of proband to validate the ABCA3 synonymous variant and exon deletion, respectively. The potential pathogenicity of the identified synonymous variant was predicted using the splice site algorithms dbscSNV11_AdaBoost, dbscSNV11_RandomForest, and Human Splicing Finder (HSF).ResultsAll patients showed severe respiratory distress, which could not be relieved by mechanical ventilation, supplementation of surfactant, or steroid therapy, and died at an early age. WES analysis revealed that the proband had compound heterozygous ABCA3 variants, including a novel synonymous variant c.G873A (p.Lys291Lys) in exon 8 inherited from the mother, and a heterozygous deletion of exons 4–7 inherited from the father. The synonymous variant was consistently predicted to be a cryptic splice donor site that may lead to aberrant splicing of the pre-mRNA by three different splice site algorithms. The deletion of exons 4–7 of the ABCA3 gene was determined to be a likely pathogenic variant. The variants were confirmed in the monozygotic twin sister of proband by Sanger sequencing and qPCR respectively. The older sister of proband was not available to determine if she also carried both ABCA3 variants, but it is highly likely based on her clinical course.ConclusionsWe identified a novel synonymous variant and a deletion in the ABCA3 gene that may be responsible for the pathogenesis in patients in this family. These results add to the known mutational spectrum of the ABCA3 gene. The study of ABCA3 variants may be helpful for the implementation of patient-specific therapies.

Metabolic labelling of choline phospholipids probes ABCA3 transport in lamellar bodies

In the metabolism of pulmonary surfactant, the ATP-binding cassette sub-family A member 3 (ABCA3) is a crucial protein in the formation of the storage compartment for surfactant, the lamellar body (LB), and the transport of phospholipids in it. Mutations in ABCA3 not only disturb surfactant metabolism but also cause chronic interstitial lung diseases. Assays for ABCA3 transport function are needed to investigate pathophysiology of the mutations and treatment options for the patients.We metabolically labeled choline (Cho) head phospholipids with the Cho analogue, propargyl-Cho. The universal incorporation of propargyl-Cho was confirmed by mass spectrometry and labeled lipids were visualized in confocal microscopy by click reaction with an azide fluorophore. After pulse-labeling propargyl-Cho labeled lipids accumulated in ABCA3+ vesicles in a time and concentration dependent manner. When treated with the choline kinase inhibitor MN58b during the first 12 h, the lipids intensity inside ABCA3+ vesicles decreased, whereas intensity was unchanged when treated after 12 h. Miltefosine, a substrate of ABCA3, decreased the incorporation of labeled lipids in ABCA3+ vesicles at all time points. The lipids intensity inside the mutated (p.N568D or p.L1580P) ABCA3+ vesicles was decreased compared to wild type, while the intensity outside of vesicles showed no difference.Propargyl-Cho can metabolically pulse-label Cho phospholipids. Visualization and quantification of fluorescence intensity of the labeled lipids inside ABCA3+ vesicles at equilibrium can specifically assess the transport function of ABCA3.

ABCG1 regulates pulmonary surfactant metabolism in mice and men

Idiopathic pulmonary alveolar proteinosis (PAP) is a rare lung disease characterized by accumulation of surfactant. Surfactant synthesis and secretion are restricted to epithelial type 2 (T2) pneumocytes (also called T2 cells). Clearance of surfactant is dependent upon T2 cells and macrophages. ABCG1 is highly expressed in both T2 cells and macrophages. ABCG1-deficient mice accumulate surfactant, lamellar body-loaded T2 cells, lipid-loaded macrophages, B-1 lymphocytes, and immunoglobulins, clearly demonstrating that ABCG1 has a critical role in pulmonary homeostasis. We identify a variant in the ABCG1 promoter in patients with PAP that results in impaired activation of ABCG1 by the liver X receptor α, suggesting that ABCG1 basal expression and/or induction in response to sterol/lipid loading is essential for normal lung function. We generated mice lacking ABCG1 specifically in either T2 cells or macrophages to determine the relative contribution of these cell types on surfactant lipid homeostasis. These results establish a critical role for T2 cell ABCG1 in controlling surfactant and overall lipid homeostasis in the lung and in the pathogenesis of human lung disease.

Abstract 172: Abcg1 Regulates Pulmonary Surfactant Metabolism in Mice and Men

Inflammation is a hallmark characteristic of many diseases, including atherosclerosis and respiratory distress, and it is also a stereotypical response of the innate immune system to pathogens. Given the central role both inflammation and lipid homeostasis play in disease progression, defining the immune and lipid signaling pathways is key in identifying new strategies for therapeutic intervention. The ATP Binding Cassette (ABC) transporter ABCG1 is highly expressed in pulmonary type 2 cells, alveolar macrophages and immune cells. We, and others, have demonstrated that loss of ABCG1 attenuates atherosclerotic lesion progression, and profoundly impacts B cell and natural antibody homeostasis. ABCG1-deficient mice accumulate pulmonary surfactant, lamellar-body loaded type 2 cells, lipid-loaded macrophages, B-1 lymphocytes and immunoglobulins, clearly demonstrating the ABCG1 has a critical role in pulmonary homeostasis. We have identified a variant in the ABCG1 promoter in patients with pulmonary alveolar proteinosis, that results in impaired activation of ABCG1 by the liver X receptor alpha. We have generated mice that lack ABCG1 specifically in either type 2 cells or macrophages, and show that loss of ABCG1 from both cell types has specific effects on pulmonary lipid and immune homeostasis. These results establish a critical role for type 2 cell ABCG1 in controlling surfactant and lipid homeostasis in the lung and in the pathogenesis of human lung disease.

Pulmonary surfactant homeostasis associated genetic abnormalities and lung diseases

Pulmonary surfactant (PS) is synthesized and secreted by alveolar epithelial type II (AEII) cells, which is a complex compound formed by proteins and lipids. Surfactant participates in a range of physiological processes such as reducing the surface tension, keeping the balance of alveolar fluid, maintaining normal alveolar morphology and conducting host defense. Genetic disorders of the surfactant homeostasis genes may result in lack of surfactant or cytotoxicity, and lead to multiple lung diseases in neonates, children and adults, including neonatal respiratory distress syndrome, interstitial pneumonia, pulmonary alveolar proteinosis, and pulmonary fibrosis. This paper has provided a review for the functions and processes of pulmonary surfactant metabolism, as well as the connection between disorders of surfactant homeostasis genes and lung diseases.

A disorder of surfactant metabolism without identified genetic mutations

BackgroundSurfactant metabolism disorders may result in diffuse lung disease in children.Case presentationWe report a 3-years-old boy with dry cough, progressive hypoxemia, dyspnea and bilateral ground glass opacities at chest high-resolution computed tomography (HRCT) who had no variants in genes encoding surfactant proteins or transcription factors. Lung histology strongly suggested an abnormality of surfactant protein. A 7-month course of pulse intravenous high-dose methylprednisolone plus oral hydroxychloroquine and azithromycin led to gradual weaning from oxygen and oral steroids, and to improvement of cough and dyspnea. Over the follow-up period, hydroxychloroquine and azithromycin were not withdrawn as cough and dyspnea re-appeared at each attempt and disappeared at re-start. At 6 years of age chest HRCT still appeared unchanged, but clinical symptoms or signs were absent.ConclusionsIn children suspected of inborn errors of pulmonary surfactant metabolism who do not have a recognized genetic mutation, lung biopsy with consistent histology may help physicians to address the definitive diagnosis.

Abstract 19020: ABCG1 Regulates Pulmonary Surfactant Homeostasis and the Lung Microbiome

Chronic respiratory diseases are the 3rd leading cause of death, and individuals suffering from respiratory distress are at risk for cardiovascular complications. Changes in the commensal bacteria in the lung have been associated with the development of chronic lung conditions including asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. The lung is a dynamic environment, constantly subject to influx of debris and microbes. The clearance of pathogens and adaptation to changes in commensal flora are mediated by innate and acquired immune responses that minimize inflammation and maintain pulmonary homeostasis. Surfactant proteins are essential for the structure and function of pulmonary surfactant, produced solely by pulmonary type 2 cells, and have their own intrinsic innate immune properties. The ATP Binding Cassette Transporter G1 (ABCG1) is highly expressed in pulmonary type 2 cells, alveolar macrophages and immune cells. We have recently demonstrated that ABCG1 regulates pulmonary B cell and natural antibody homeostasis. Here we show that mice lacking ABCG1 specifically in pulmonary type 2 cells have altered lamellar body and surfactant homeostasis. Additionally, we show that mice lacking ABCG1 have disturbances in the commensal bacteria that populate the lungs. Abcg1-/- mice may represent a novel model in which to study the interaction between pulmonary surfactant metabolism, pulmonary innate immune responses and the lung microbiome.

Inactivation of Peroxiredoxin 6 by the Pla Protease of Yersinia pestis.

Pneumonic plague represents the most severe form of disease caused by Yersinia pestis due to its ease of transmission, rapid progression, and high mortality rate. The Y. pestis outer membrane Pla protease is essential for the development of pneumonic plague; however, the complete repertoire of substrates cleaved by Pla in the lungs is not known. In this study, we describe a proteomic screen to identify host proteins contained within the bronchoalveolar lavage fluid of mice that are cleaved and/or processed by Y. pestis in a Pla-dependent manner. We identified peroxiredoxin 6 (Prdx6), a host factor that contributes to pulmonary surfactant metabolism and lung defense against oxidative stress, as a previously unknown substrate of Pla. Pla cleaves Prdx6 at three distinct sites, and these cleavages disrupt both the peroxidase and phospholipase A2 activities of Prdx6. In addition, we found that infection with wild-type Y. pestis reduces the abundance of extracellular Prdx6 in the lungs compared to that after infection with Δpla Y. pestis, suggesting that Pla cleaves Prdx6 in the pulmonary compartment. However, following infection with either wild-type or Δpla Y. pestis, Prdx6-deficient mice exhibit no differences in bacterial burden, host immune response, or lung damage from wild-type mice. Thus, while Pla is able to disrupt Prdx6 function in vitro and reduce Prdx6 levels in vivo, the cleavage of Prdx6 has little detectable impact on the progression or outcome of pneumonic plague.

Null ABCA3 in humans: Large homozygous ABCA3 deletion, correlation to clinical–pathological findings

A study was undertaken to analyze the clinical presentation, pulmonary function, and pathological features in two female siblings with neonatal pulmonary surfactant metabolism dysfunction, type 3 (MIM 610921). The clinical records of the siblings were examined; the genes encoding surfactant protein B (SFTPB), surfactant protein C (SFTPC), and ATP-binding cassette transporter 3 protein (ABCA3) were analyzed with direct sequencing and Southern blotting. The infants were homozygous for a 5,983 bp deletion in ABCA3 including exons 2-5 as well as the start AUG codon and a putative Golgi exit signal motif. Dense abnormalities of lamellar bodies at electron microscopy and absence of ABCA3 at immunohistochemical staining were in agreement with the presence of two null alleles. In addition, an increased lipid synthesis suggested a compensatory mechanism. The clinical course in the two sisters was influenced by different environmental factors like the time needed for molecular confirmation, the ventilatory assistance adopted, the occurrence of infections. A less aggressive clinical approach did not improve the course of the disease; the prognosis was always poor. Development of a fast molecular test, able to detect also structural variants, is needed.

Large ABCA3 and SFTPC Deletions Resulting in Lung Disease

Mutations in genes encoding proteins important in the function and metabolism of pulmonary surfactant are recognized causes of lung disease. Clinical genetic testing is available for these disorders, but children with phenotypes consistent with surfactant dysfunction and no identifiable mutations in the known causative genes have been reported. To identify the mechanism(s) for lung disease in two children with the phenotype of surfactant dysfunction who had negative testing in clinical laboratories for gene mutations causing surfactant dysfunction. Amplicons spanning multiple exons of candidate genes were generated by polymerase chain reaction and sequenced. A 4,335-base deletion that included all of exon 12 of the gene encoding member A3 of the adenosine triphosphate-binding cassette transporter was identified in a full-term infant with respiratory failure. A 333-base deletion involving part of exon 4 and the adjacent intron of the gene encoding surfactant protein C was identified in a child with interstitial lung disease. Large deletions are a cause of surfactant dysfunction disorders and may need to be sought for specifically in children whose phenotypes suggest these syndromes but in whom clinical genetic testing is unrevealing.

Local delivery of Granulocyte/Macrophage Colony Stimulating Factor protects mice from lethal pneumococcal pneumonia

Introduction: The growth factor granulocyte/macrophage-colony stimulating factor (GM-CSF) has an important role in pulmonary surfactant metabolism and the regulation of antibacterial activities of lung sentinel cells. However, the potential of intra-alveolar GM-CSF to augment lung protective immunity against inhaled bacterial pathogens has not been defined in preclinical infection models. We hypothesized that transient overexpression of GM-CSF in the lungs of mice by adenoviral gene transfer (Ad-GM-CSF) would protect mice from subsequent lethal pneumococcal pneumonia.