Alveolar Hypoplasia Research Articles

Altered alveolar cell signature in pre- and post-natal Trisomy 21 lung

Rationale: Pulmonary and cardiovascular disorders result in 75% of the mortality observed in individuals with Down Syndrome (DS). However, little is known about the pulmonary anomalies observed in DS, as they are often considered a secondary condition to congenital heart defects. However, we and others have demonstrated that lungs from patients with trisomy 21 (T21) may present alveolar abnormalities, such as pulmonary alveolar hypoplasia, regardless of congenital heart disease. Therefore, the etiology of alveolar defects in T21 lungs remains elusive. The aim of our study is to define the molecular and cellular defects underlying alveolar defects in T21 developing lungs. Methods: Single cell RNA sequencing data was generated from 5 T21 and 4 non-T21 human fetal lungs (18 weeks gestation). T21 and non-T21 human fetal lung tissues (aged 18 to 22 weeks gestation), and postnatal human lung tissues from 2 months to 6 years old were processed to compare and determine the localization and expression of alveolar cells and their markers by RT-qPCR, fluorescence in situ hybridization (FISH) and immunofluorescent staining (IF). Results: Our single cell data showed an increase in the proportion of mature fetal AT2 cells in T21 as compared to non-T21 samples, whereas a decrease was observed in the intermediate and progenitor cell populations. When comparing fetal T21 to non-T21 samples, RT-qPCR results demonstrated significantly increased expression of both alveolar type II markers (SFTPD, ABCA3, SCGB3A2, LAMP3) and the alveolar type I marker AGER. Furthermore, FISH showed a significant increase in SFTPC and SFTPB in fetal T21 lungs. Conversely, when comparing postnatal T21 to non-T21 samples, RT-qPCR results demonstrated reduced expression of alveolar type II markers (SFTPB, SFTPD, ABCA3, SCGB3A2, LAMP3) and alveolar type I markers (HOPX, AGER, PODOPLANIN). Our IF staining in postnatal T21 vs non-T21 showed a significant increase in the number KRT8 and KRT8+/SFTPC+ cells, markers of an intermediate progenitor cell population, accompanied by a decrease in proliferating AT2 cells (SFTPC+/Ki67+). Conclusion: While our single cell data, RT-qPCR, FISH and IF results show an accelerated maturation during T21 lung fetal pre-alveolar development, postnatal T21 lungs display a decrease in mature AT2 cell numbers. This could likely be due to an accelerated maturation early on in development, that suppresses proper proliferation necessary to expand the pool of AT2 cells to a normal range. This suppression seems to persist into the postnatal period. 3R21HL165411-02S1. NIH/NHLBI Offce of The Director, National Institutes of Health (OD) R01HL155104 (SD). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

FOXF1 Regulates Alveolar Epithelial Morphogenesis through Transcriptional Activation of Mesenchymal WNT5A.

Mutations in the FOXF1 (forkhead box F1) gene, encoding the mesenchymal FOX (forkhead box) transcription factor, are linked to alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV), a severe congenital disorder associated with the loss of alveolar capillaries and lung hypoplasia. Although proangiogenic functions of FOXF1 have been extensively studied, the role of FOXF1 in mesenchymal-epithelial signaling during lung development remains uncharacterized. Herein, we used murine lung organoids to demonstrate that the S52F FOXF1 mutation (found in patients with ACDMPV) stimulates canonical WNT/β-catenin signaling in type 2 alveolar epithelial cells (AEC2s), leading to increased proliferation of AEC2s and decreased differentiation of AEC2s into type 1 alveolar epithelial cells (AEC1s). Alveolar organoids containing Foxf1WT/S52F lung fibroblasts and wild-type epithelial cells grew faster on Matrigel and exhibited AEC2 hyperplasia. AEC2 hyperplasia and loss of AEC1s were found in the lungs of Foxf1WT/S52F embryos, a mouse model of ACDMPV. Activation of canonical WNT/β-catenin signaling in AEC2s of lung organoids and Foxf1WT/S52F mice was associated with decreased expression of noncanonical WNT5A (Wnt family member 5A) ligand in lung fibroblasts. Mechanistically, FOXF1 directly activates the Wnt5a gene transcription through an evolutionarily conserved +6320/+6326 region located in the first intron of the Wnt5a gene. Site-directed mutagenesis of the +6320/+6326 region prevented the transcriptional activation of the Wnt5a enhancer by FOXF1. Treatment with exogenous WNT5A ligand inhibited the effects of the S52F FOXF1 mutation on canonical WNT/β-catenin signaling in alveolar organoids, preventing aberrant AEC2 expansion and restoring differentiation of AEC1s. Activation of either FOXF1 or WNT5A may provide an attractive strategy to improve lung function in patients with ACDMPV.

Thrombospondin-1 Plays a Major Pathogenic Role in Experimental and Human Bronchopulmonary Dysplasia.

Rationale: Extremely preterm infants develop bronchopulmonary dysplasia (BPD), a chronic lung injury that lacks effective treatment. TSP-1 (thrombospondin-1) is an antiangiogenic protein that activates TGF-β1 (transforming growth factor-β1), a cytokine strongly linked to both experimental and human BPD. Objectives:1) To examine effects of inhibiting TSP-1-mediated TGF-β1 activation (LSKL [leucine-serine-lysine-leucine]) in neonatal rats with bleomycin-induced lung injury; 2) to examine effects of a TSP-1 mimic (ABT-510) on lung morphology; and 3) to determine whether TSP-1 and related signaling peptides are increased in lungs of human preterm infants at risk for BPD. Methods: From Postnatal Days 1 to 14, rat pups received daily intraperitoneal bleomycin (1 mg/kg) or vehicle and were treated with daily subcutaneous LSKL (20 mg/kg) or vehicle alone. Separate animals were treated with vehicle or ABT-510 (30 mg/kg/d). Paraffin-embedded lung tissues from 47 autopsies (controls; death <28 d, n = 30 and BPD at risk; death ⩾28 d, n = 17) performed on infants born <29 completed weeks' gestation were semiquantified for injury markers (collagen, macrophages, and 3-nitrotyrosine), TSP-1, and TGF-β1. Measurements and Main Results: Bleomycin or ABT-510 increased lung TGF-β1 activity and macrophage influx, caused pulmonary hypertension, and led to alveolar and microvascular hypoplasia. Treatment with LSKL partially prevented abnormal lung morphology secondary to bleomycin. Lungs from human infants at risk for BPD had increased contents of TSP-1 and TGF-β1 when compared with controls. TGF-β1 content correlated with markers of lung injury. Conclusions: TSP-1 inhibits alveologenesis in neonatal rats, in part via the upregulated activity of TGF-β1. Observations in human lungs suggest a similar pathogenic role for TSP-1 in infants at risk for BPD.

Insight Into the Roles of Non-coding RNA in Bronchopulmonary Dysplasia.

Bronchopulmonary dysplasia (BPD) is a chronic lung disease most commonly occurring in premature infants, and its pathological manifestations are alveolar hypoplasia and dysregulation of pulmonary vasculature development. The effective treatment for BPD has not yet been established. Non-coding RNAs, including microRNAs and long non-coding RNAs do not encode proteins, but can perform its biological functions at the RNA level. Non-coding RNAs play an important role in the incidence and development of BPD by regulating the expression of genes related to proliferation, apoptosis, angiogenesis, inflammation and other cell activities of alveolar epithelial cells and vascular endothelial cells. Here we summarize the role of non-coding RNAs in BPD, which provides possible molecular marker and therapeutic target for the diagnosis and treatment of BPD.

Insufficient development of vessels and alveoli in lungs of infants with trisomy 18-Features of pulmonary histopathological findings from lung biopsy.

The aim of this study was to evaluate the features of pulmonary histopathological changes in cases of trisomy 18 complicated with congenital heart disease and pulmonary arterial hypertension. Twenty-eight patients with trisomy 18 underwent open lung biopsy at the time of primary operation in our hospital between 2008 and 2019. We compared these histopathological findings with those from previously described groups without trisomy 18. Mean age at primary cardiac surgery was 37 days (range, 9-69 days). According to the Heath-Edwards (HE) classification, 1, 8, 12, and 5 patients were graded as 0, 1, 2, and 3, respectively, whereas 2 patients were not classifiable due to medial defects in the small pulmonary arteries (MD). Four (14.3%) and 13 (46.4%) patients presented with MD and hypoplasia of the small pulmonary arteries (HS). Fifteen (53.6%) and 21 (75.0%) patients presented with alveolar hypoplasia (AH) and alveolar wall thickening (AT). MD, HS, and AH in trisomy 18 were present frequently, differing significantly from previous reports. These findings might be associated with congenital inadequate development of vessels and alveoli in the lung, contributing to a high risk of PAH in trisomy 18.

Accelerated tooth movement in Rsk2-deficient mice with impaired cementum formation

Coffin–Lowry–Syndrome (CLS) is a X-linked mental retardation characterized by skeletal dysplasia and premature tooth loss. We and others have previously demonstrated that the ribosomal S6 kinase RSK2, mutated in CLS, is essential for bone and cementum formation; however, it remains to be established whether RSK2 plays also a role in mechanically induced bone remodeling during orthodontic tooth movement (OTM). We, therefore, performed OTM in wild-type (WT) mice and Rsk2-deficient mice using Nitinol tension springs that were fixed between the upper left molars and the incisors. The untreated contralateral molars served as internal controls. After 12 days of OTM, the jaws were removed and examined by micro-computed tomography (µCT), decalcified histology, and immunohistochemistry. Our analysis of the untreated teeth confirmed that the periodontal phenotype of Rsk2-deficient mice is characterized by alveolar bone loss and hypoplasia of root cementum. Quantification of OTM using µCT revealed that OTM was more than two-fold faster in Rsk2-deficient mice as compared to WT. We also observed that OTM caused alveolar bone loss and root resorptions in WT and Rsk2-deficient mice. However, quantification of these orthodontic side effects revealed no differences between WT and Rsk2-deficient mice. Taken together, Rsk2 loss-of-function accelerates OTM in mice without causing more side effects.

Deficiency of the SMOC2 matricellular protein impairs bone healing and produces age-dependent bone loss

Secreted extracellular matrix components which regulate craniofacial development could be reactivated and play roles in adult wound healing. We report a patient with a loss-of-function of the secreted matricellular protein SMOC2 (SPARC related modular calcium binding 2) presenting severe oligodontia, microdontia, tooth root deficiencies, alveolar bone hypoplasia, and a range of skeletal malformations. Turning to a mouse model, Smoc2-GFP reporter expression indicates SMOC2 dynamically marks a range of dental and bone progenitors. While germline Smoc2 homozygous mutants are viable, tooth number anomalies, reduced tooth size, altered enamel prism patterning, and spontaneous age-induced periodontal bone and root loss are observed in this mouse model. Whole-genome RNA-sequencing analysis of embryonic day (E) 14.5 cap stage molars revealed reductions in early expressed enamel matrix components (Odontogenic ameloblast-associated protein) and dentin dysplasia targets (Dentin matrix acidic phosphoprotein 1). We tested if like other matricellular proteins SMOC2 was required for regenerative repair. We found that the Smoc2-GFP reporter was reactivated in adjacent periodontal tissues 4 days after tooth avulsion injury. Following maxillary tooth injury, Smoc2−/− mutants had increased osteoclast activity and bone resorption surrounding the extracted molar. Interestingly, a 10-day treatment with the cyclooxygenase 2 (COX2) inhibitor ibuprofen (30 mg/kg body weight) blocked tooth injury-induced bone loss in Smoc2−/− mutants, reducing matrix metalloprotease (Mmp)9. Collectively, our results indicate that endogenous SMOC2 blocks injury-induced jaw bone osteonecrosis and offsets age-induced periodontal decay.

Bronchopulmonary Dysplasia Patients Have Preserved CT‐Measured Central Airway Luminal Area

ObjectiveBronchopulmonary dysplasia (BPD) is a condition of neonatal chronic lung disease due to disruption or dysregulation of pulmonary development. It is associated with decreased septation, alveolar hypoplasia, and abnormal disruption of pulmonary alveolar capillaries resulting in increased pulmonary resistance. However, the pathophysiology of BPD in the large conducting airways is not fully understood. The objective of our study was to determine if the luminal area of the central airways, measured by imaging, are altered in patients with a history of BPD. We hypothesized that compared to age‐ and sex‐matched controls, BPD patients would have a decreased luminal area of the central conducting airways and lung volume.MethodsFourteen BPD patients (8M/6F; Age=5.7±5.5 yrs) who had undergone a chest computed tomography (CT) scan were retrospectively identified. Age and sex matched controls (8M/6F, Age=5.6±5.3 yrs) who had undergone a CT scan for trauma were used for comparison. Measurement and analysis were performed by a single investigator using commercially available software (Aquarius, TeraRecon Inc.) that reconstructs the airways into 3D. Measurements of luminal airway area were conducted at three points based on anatomic bifurcations (corresponding to the beginning, middle and end of the airway) for each of the following structures: trachea, left main bronchus, left upper lobe, left lower lobe, right main bronchus, intermediate bronchus, and right upper lobe. Each airway’s luminal area was calculated based on the averages of the three measures obtained for each anatomic airway structure. Independent Student’s t‐test was used for statistical analysis.ResultsAirway luminal area was not different between BPD patients and matched controls (trachea: 89.8±57.1 vs 87.4±58.6 mm2; right main bronchus: 58.8±40.8 vs 64.0±44.5 mm2; intermediate bronchus: 33.6±21.2 vs 41.0±28.9 mm2; left main bronchus: 39.3±27.1 vs 46.6±36.5 mm2; left lower lobe: 22.7±14.6 vs 29.9±18.9 mm2; p&gt;0.05 for all comparisons; BPD and controls, respectively). Total lung volume detected in the CT scans was not different between BPD patients and matched controls (3069±1073 vs 3215±984 cm3, p&gt;0.05).ConclusionsOur results suggest the luminal areas of the large conducting airways in patients with BPD are not different from matched controls. Given the degree of respiratory complications and sequelae associated with BPD, our findings suggest future research should focus on alveolar and vascular impaired physiological and anatomic developments versus the large conducting airways.Support or Funding InformationNational Institutes of Health Grants R35‐HL139854 (MJJ), F32 HL‐131151 (SEB), T32 DK‐007352‐39 (CCW) and Mayo Clinic Internal Funding and Natural Science and Engineering Council of Canada RGPIN‐2019‐04615 (PBD)

Subphenotyping and Classification of Cleft Lip and Alveolus in Adult Unoperated Patients: A New Embryological Approach.

Previously, a new embryological classification was introduced subdividing oral clefts into fusion and/or differentiation defects. This subdivision was used to classify all subphenotypes of cleft lip with or without alveolus (CL±A). Subsequently, it was investigated whether further morphological grading of incomplete CLs is clinically relevant, and which alveolar part is deficient in fusion/differentiation defects. Observational cohort study. Three hundred fifty adult unoperated Indonesian cleft patients presented themselves for operation. Cephalograms, dental casts, and intraoral and extraoral photographs-eligible for the present study-were used to determine morphological severity of CL±A. Patients with unilateral or bilateral clefts of the primary palate only were included. Clefts were classified-according to developmental mechanisms and timing in embryogenesis-as fusion and/or differentiation defects. Grades of incomplete CLs were related to the severity of alveolar clefts (CAs) and hypoplasia, and permanent dentition was used to investigate which alveolar part is deficient in fusion/differentiation defects. One hundred eight adult patients were included. All subphenotypes-96 unilateral and 12 bilateral clefts-could be classified into differentiation (79%), fusion (17%), fusion-differentiation (2%), or fusion and differentiation (2%) defects. The various grades of incomplete CLs were related to associated CAs and hypoplasia, and all alveolar deformities were located in the premaxillae. This study showed that all CL±A including the Simonart bands can be classified, that further morphological grading of incomplete CLs is clinically relevant, and that the premaxilla forms the deficient part in alveolar deformities.

Upper lip tie wrapping into the hard palate and anterior premaxilla causing alveolar hypoplasia

Bony anomaly caused by lip tie is not many reported yet. There was a case of upper lip tie wrapping into the anterior premaxilla. We represent a case of severe upper lip tie of limited lip motion, upper lips curling inside, and alveolar hypoplasia. Male patient was born on June 3, 2016. He had a deep philtral sulcus, low vermilion border and deep cupid’s bow of upper lip due to tension of short, stout and very tight frenulum. His upper lip motion was severely restricted in particular lip eversion. There was anterior alveolar hypoplasia with deep sulcus in anterior maxilla. Resection of frenulum cord with Z-plasty was performed at anterior premaxilla and upper lip sulcus. Frenulum was tightly attached to gingiva through gum and into hard palate. Width of frenulum cord was about 1 cm, and length was about 3 cm. He gained upper lip contour including cupid’s bow and normal vermilion border after the surgery. This case is severe upper lip tie showing the premaxillary hypoplasia, abnormal lip motion and contour for child. Although there is mild limitation of feeding with upper lip tie child, early detection and treatment are needed to correct bony growth.

Differential Expression of Angiogenic Gene Networks during Post-natal Lung Alveolarization

Prematurity of birth is the leading cause of death in children under 5 years of age. Preterm birth rates are steadily increasing across the globe due to advancements in medical knowledge and procedures that allow progressively earlier fetuses to survive outside of the mother’s womb. Bronchopulmonary dysplasia is a chronic lung disorder that can result from mechanical ventilation and long-term oxygen use in preterm neonates. This condition is characterized by disrupted pulmonary alveolar septation, alveolar hypoplasia, and fewer, larger alveoli that lead to decreased surface area available for gas exchange. Despite notable advances in preterm care, bronchopulmonary dysplasia results in a large number of short- and long-term morbidities, thus more advanced treatments that facilitate lung development in this subset of pediatric patients are sorely needed. In this study, we examined alterations in the gene expression profiles of 81 genes involved in angiogenesis during the process of normal alveolarization in mouse lungs. Our data revealed that alveolarization can be largely divided into early (1 week postnatal) and late (4 to 8 weeks postnatal) stages based on angiogenic gene expression profiles. In summary, our findings provide molecularlevel data illustrating the dynamic alterations in pulmonary angiogenesis during postnatal alveolarization. This knowledge can be used to provide a better understanding of normal lung development, and set the stage for discovering targeted therapies that can assist in pulmonary functioning for preterm infants.

Rare combination of congenital heart disease and pulmonary alveolar proteinosis

Here, we describe a case of total anomalous pulmonary venous return with coarctation of the aorta that was diagnosed as pulmonary alveolar proteinosis at autopsy in a male infant. Surgical repair was performed at 1 day of age, but the infant died on postoperative day 51 due to respiratory insufficiency without any evidence of pulmonary venous obstruction. He had been unexpectedly diagnosed with pulmonary alveolar proteinosis and pulmonary hypoplasia on autopsy. Congenital pulmonary alveolar proteinosis is a serious condition with a high mortality rate, which should be considered in the differential diagnosis in patients with a clinical picture of pulmonary venous obstruction, because most patients are unable to survive without proper treatment. In this report, we address specific issues that should be discussed in such cases based on our recent experience.

Adding glutathione to parenteral nutrition prevents alveolar loss in newborn Guinea pig

Bronchopulmonary dysplasia, a main complication of prematurity, is characterized by an alveolar hypoplasia. Oxidative stress is suspected to be a trigger event in this population who has a low level of glutathione, a main endogenous antioxidant, and who receives high oxidative load, particularly ascorbylperoxide from their parenteral nutrition. Hypothesis: the addition of glutathione (GSSG) in parenteral nutrition improves detoxification of ascorbylperoxide by glutathione peroxidase and therefore prevents exaggerated apoptosis and loss of alveoli.Methods: Ascorbylperoxide is assessed as substrate for glutathione peroxidase in Michaelis-Menten kinetics. Three-days old guinea pig pups were divided in 6 groups to receive, through a catheter in jugular vein, the following solutions: 1) Sham (no infusion); 2) PN(-L): parenteral nutrition protected against light (low ascorbylperoxide); 3) PN(+L): PN without photo-protection (high ascorbylperoxide); 4) 180μM ascorbylperoxide; 5) PN(+L)+10μM GSSG; 6) ascorbylperoxyde+10μM GSSG. After 4 days, lungs were sampled and prepared for histology and biochemical determinations. Data were analysed by ANOVA, p<0.05Results: The Km of ascorbylperoxide for glutathione peroxidase was 126±6μM and Vmax was 38.4±2.5nmol/min/ U. The presence of GSSG in intravenous solution has prevented the high GSSG, oxidized redox potential of glutathione, activation of caspase-3 (apoptosis marker) and loss of alveoli induced by PN(+L) or ascorbylperoxide.Conclusion: A correction of the low glutathione levels observed in newborn animal on parenteral nutrition, protects lungs from toxic effect of ascorbylperoxide. Premature infants having a low level of glutathione, this finding is of high importance because it provides hope in a possible prevention of bronchopulmonary dysplasia.

Caffeine induces alveolar apoptosis in the hyperoxia-exposed developing mouse lung

BackgroundCaffeine is a nonspecific adenosine receptor antagonist used in premature neonates to treat apnea of prematurity. While its use may reduce the incidence of bronchopulmonary dysplasia (BPD), the precise mechanisms remain unknown. Evidence of increased adenosine levels are noted in chronic lung diseases including tracheal aspirates of infants with BPD. Utilizing a well characterized newborn mouse model of alveolar hypoplasia, we hypothesized that hyperoxia-induced alveolar inflammation and hypoplasia is associated with alterations in the adenosine signaling pathway.MethodsNewborn murine pups were exposed to a 14-day period of hyperoxia and daily caffeine administration followed by a 14-day recovery period in room air. Lungs were collected at both time points for bronchoalveolar fluid (BAL) analysis as well as histopathology and mRNA and protein expression.ResultsCaffeine treatment increased inflammation and worsened alveolar hypoplasia in hyperoxia exposed newborn mice. These changes were associated with decreased alveolar type II cell numbers, increased cell apoptosis, and decreased expression of A2A receptors. Following discontinuation of caffeine and hyperoxia, lung histology returned to baseline levels comparable to hyperoxia exposure alone.ConclusionResults of this study suggest a potentially adverse role of caffeine on alveolar development in a murine model of hyperoxia-induced alveolar hypoplasia.

Prosthodontic Rehabilitation in Patient With Ectodermal Dysplasia Combining Preprosthetic Techniques

Oral manifestations in ectodermal dysplasia include oligodontia, alveolar ridges hypoplasia, and others. Due to the special conditions in terms of unhealthy teeth and lack of bone, implant-supported rehabilitation seems to offer the most satisfactory outcome. A 27-year-old male diagnosed with ectodermal dysplasia was referred to our department for oral rehabilitation. Oral manifestations included oligodontia, maxillary and mandibular atrophy, mandibular alveolar ridge with knife-edge morphology, and conical teeth. Treatment planning consisted of a Le Fort I osteotomy with interpositional grafts, bilateral sinus lift, and placement of maxillary and mandibular inlay and onlay corticocancellous grafts, using autologous iliac crest bone. In the second surgery, all remaining teeth were removed and 11 endosteal implants were placed. Six months after implant placement, a bimaxillary fixed implant-supported prosthesis was delivered, maintaining a satisfactory esthetic and functional result after a 2-year follow-up. The use of combined preprosthetic techniques allows the placement of endosteal implants and a fixed implant-supported prosthesis in patients with oligodontia and ectodermal dysplasia, providing an esthetic and functional oral rehabilitation.

Chronic Lung Disease in the Preterm Infant. Lessons Learned from Animal Models

Neonatal chronic lung disease, also known as bronchopulmonary dysplasia (BPD), is the most common complication of premature birth, affecting up to 30% of very low birth weight infants. Improved medical care has allowed for the survival of the most premature infants and has significantly changed the pathology of BPD from a disease marked by severe lung injury to the "new" form characterized by alveolar hypoplasia and impaired vascular development. However, increased patient survival has led to a paucity of pathologic specimens available from infants with BPD. This, combined with the lack of a system to model alveolarization in vitro, has resulted in a great need for animal models that mimic key features of the disease. To this end, a number of animal models have been created by exposing the immature lung to injuries induced by hyperoxia, mechanical stretch, and inflammation and most recently by the genetic modification of mice. These animal studies have 1) allowed insight into the mechanisms that determine alveolar growth, 2) delineated factors central to the pathogenesis of neonatal chronic lung disease, and 3) informed the development of new therapies. In this review, we summarize the key findings and limitations of the most common animal models of BPD and discuss how knowledge obtained from these studies has informed clinical care. Future studies should aim to provide a more complete understanding of the pathways that preserve and repair alveolar growth during injury, which might be translated into novel strategies to treat lung diseases in infants and adults.

Intra-amniotic LPS amplifies hyperoxia-induced airway hyperreactivity in neonatal rats.

Background:We previously showed that intra-amniotic lipopolysaccharide (LPS) amplifies alveolar hypoplasia induced by postnatal hyperoxia. We determined whether the priming effect of intra-amniotic LPS amplifies hyperoxia-induced airway hyperreactivity (AHR).Methods:LPS or normal saline was injected into the amniotic cavities of pregnant rats at the 20th day of gestation. After birth, rat pups were exposed to 60% O2 or air for 14 d. On postnatal day 14, rat pups underwent forced oscillometry, which included a challenge with nebulized methacholine, and the lungs were harvested for morphological studies.Results:Hyperoxia significantly increased airway reactivity and decreased compliance. Intra-amniotic LPS further increased hyperoxia-induced AHR but did not further impair respiratory system compliance. Hyperoxia-induced changes in lung parenchymal and small airway morphology were not further altered by intra-amniotic LPS. However, combined exposure to intra-amniotic LPS and hyperoxia increased the proportion of degranulating mast cells in the hilar airways.Conclusion:Intra-amniotic LPS amplified postnatal hyperoxia-induced AHR. This was associated with increased airway mast cell degranulation, which has previously been linked with hyperoxia-induced AHR. There were no morphologic changes of parenchyma or airways that would account for the LPS augmentation of hyperoxia-induced AHR.

Retinoic Acid Rescues Alveolar Hypoplasia in the Calorie-Restricted Developing Rat Lung

Infants born with intrauterine growth retardation (IUGR) are at increased risk of adverse pulmonary outcomes at birth, including meconium aspiration and persistent pulmonary hypertension. Preterm infants with IUGR are at especially high risk of developing bronchopulmonary dysplasia (BPD), a disease hallmarked by alveolar hypoplasia. Although vitamin A supplementation has been shown to decrease the incidence of BPD or death in preterm very low birth weight infants, its potential to reduce BPD or death in preterm infants with IUGR remains unknown. We used a well-characterized rat model of caloric restriction to mimic IUGR and determine the impact of IUGR on lung development. We hypothesized that retinoic acid treatment would preserve alveolar formation through increases in key signaling molecules of the retinoic acid signaling pathway. Our results showed that alveolar hypoplasia caused by caloric restriction can be reversed with refeeding, and that retinoic acid prevents the alveolar hypoplasia coincident with the increased expression of elastin and retinoic acid receptor-α and decreased transforming growth factor-β activity in developing rat lungs. These findings suggest that alveolar hypoplasia attributable to caloric restriction is reversible, and raises the possibility that retinoic acid therapy may prove a useful strategy to prevent adverse pulmonary sequelae such as BPD in preterm infants with IUGR.

Timing and expression of the Angiopoietin-1/Tie-2 pathway in murine lung development and congenital diaphragmatic hernia (CDH)

SUMMARYCongenital diaphragmatic hernia (CDH) is one of the most common congenital abnormalities. Children born with CDH suffer a number of co-morbidities, the most serious of which is respiratory insufficiency from a combination of alveolar hypoplasia and pulmonary vascular hypertension. All children born with CDH display some degree of pulmonary hypertension, the severity of which has been correlated with mortality. The molecular mechanisms responsible for the development of pulmonary hypertension in CDH remain poorly understood. Angiopoitein-1 (Ang-1), a central mediator in angiogenesis, participates in the vascular development of many tissues, including the lung. Although previous studies have demonstrated that Ang-1 might play an important role in the development of familial pulmonary hypertension, the role of Ang-1 in the development of the pulmonary hypertension associated with CDH is poorly understood. The aim of this study was to examine the role of the Ang-1 pathway in a murine model of CDH. Here, we report that Ang-1 appears important in normal murine lung development, and have established its tissue-level expression and localization patterns at key time-points. Additionally, our data from a nitrofen and bisdiamine-induced murine model of CDH suggests that altered expression patterns of Ang-1, its receptor Tie-2 and one of its transcription factors (epithelium-specific Ets transcription factor 1) might be responsible for development of the pulmonary vasculopathy seen in the setting of CDH.

Conditional deletion of epithelial IKKβ impairs alveolar formation through apoptosis and decreased VEGF expression during early mouse lung morphogenesis

BackgroundAlveolar septation marks the beginning of the transition from the saccular to alveolar stage of lung development. Inflammation can disrupt this process and permanently impair alveolar formation resulting in alveolar hypoplasia as seen in bronchopulmonary dysplasia in preterm newborns. NF-κB is a transcription factor central to multiple inflammatory and developmental pathways including dorsal-ventral patterning in fruit flies; limb, mammary and submandibular gland development in mice; and branching morphogenesis in chick lungs. We have previously shown that epithelial overexpression of NF-κB accelerates lung maturity using transgenic mice. The purpose of this study was to test our hypothesis that targeted deletion of NF-κB signaling in lung epithelium would impair alveolar formation.MethodsWe generated double transgenic mice with lung epithelium-specific deletion of IKKβ, a known activating kinase upstream of NF-κB, using a cre-loxP transgenic recombination strategy. Lungs of resulting progeny were analyzed at embryonic and early postnatal stages to determine specific effects on lung histology, and mRNA and protein expression of relevant lung morphoreulatory genes. Lastly, results measuring expression of the angiogenic factor, VEGF, were confirmed in vitro using a siRNA-knockdown strategy in cultured mouse lung epithelial cells.ResultsOur results showed that IKKβ deletion in the lung epithelium transiently decreased alveolar type I and type II cells and myofibroblasts and delayed alveolar formation. These effects were mediated through increased alveolar type II cell apoptosis and decreased epithelial VEGF expression.ConclusionsThese results suggest that epithelial NF-κB plays a critical role in early alveolar development possibly through regulation of VEGF.