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Purpose of Review: The rapid evolution of bronchoscopy equipment and technologies, from the introduction of the 1.1 mm flexible cryoprobe to the use of navigational and robotic bronchoscopy, has afforded unprecedented opportunities for pediatric advanced diagnostic and interventional bronchoscopy. While there is growing interest among pediatric pulmonologists to incorporate these new techniques into their practice, the current pediatric landscape is characterized by few practicing interventional bronchoscopists, scant published literature, and no formal training programs., Recent Findings: While the majority of the published literature consists of case reports and small case series, the increased application of new techniques is starting to yield larger and more structured studies that will be able to provide more objective commentary on the proposed indications, safety, and efficacy of such techniques in the pediatric population., Summary: For many decades, progress in pediatric advanced diagnostic and interventional bronchoscopy was slow and deliberate, limited by the lack of appropriately sized equipment and experienced interventional bronchoscopists. The current opportunities afforded require equal, or perhaps even more, vigilance as pediatric pulmonologists employ new equipment and technologies and define new practices and standards of care. Importantly, this review is meant to serve as a general conspectus of pediatric advanced diagnostic and interventional bronchoscopy and not a consensus guideline for the performance of advanced or even routine bronchoscopy in the pediatric population. For technical standards of pediatric bronchoscopy, refer to existing guidelines [1,2] ., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

For children with severe asthma, guideline-based management focuses on the escalation of anti-inflammatory and bronchodilatory medications while addressing comorbid conditions. Bronchoscopy, in this context, has been relegated to ruling out asthma mimickers. More recently, however, there have been questions surrounding the clinical utility of bronchoscopy in severe childhood asthma. In this solicited lecture summary, we discuss the past, present, and potential future applications of bronchoscopy in severe childhood asthma., (© 2019 Wiley Periodicals, Inc.)

Asthma encompasses numerous phenotypes that may require alternate approaches to diagnosis and therapy, particularly for patients whose symptoms remain poorly controlled despite escalating treatment. We describe 3 patients with apparent asthma who demonstrated unusual findings on cryobiopsy by flexible bronchoscopy and responded to therapy directed against autoimmune disease., Competing Interests: POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose., (Copyright © 2018 by the American Academy of Pediatrics.)

We report our use of cryotherapy delivered via flexible bronchoscopy in a 15-year old girl with granulomatosis with polyangiitis to both treat established airway stenosis and prevent multi-level progression of disease., (© 2017 Wiley Periodicals, Inc.)

Chronic lung disease of prematurity (CLD) is a frequent sequela of premature birth and oxygen toxicity is a major associated risk factor. Impaired alveolarization, scarring, and inflammation are hallmarks of CLD. Mast cell hyperplasia is a feature of CLD but the role of mast cells in its pathogenesis is unknown. We hypothesized that mast cell hyperplasia is a consequence of neonatal hyperoxia and contributes to CLD. Additionally, mast cell products may have diagnostic and prognostic value in preterm infants predisposed to CLD. To model CLD, neonatal wild-type and mast cell-deficient mice were placed in an O2 chamber delivering hyperoxic gas mixture [inspired O2 fraction (FiO2 ) of 0.8] (HO) for 2 wk and then returned to room air (RA) for an additional 3 wk. Age-matched controls were kept in RA (FiO2 of 0.21). Lungs from HO mice had increased numbers of mast cells, alveolar simplification and enlargement, and increased lung compliance. Mast cell deficiency proved protective by preserving air space integrity and lung compliance. The mast cell mediators β-hexosaminidase (β-hex), histamine, and elastase increased in the bronchoalveolar lavage fluid of HO wild-type mice. Tracheal aspirate fluids (TAs) from oxygenated and mechanically ventilated preterm infants were analyzed for mast cell products. In TAs from infants with confirmed cases of CLD, β-hex was elevated over time and correlated with FiO2 Mast cell exosomes were also present in the TAs. Collectively, these data show that mast cells play a significant role in hyperoxia-induced lung injury and their products could serve as potential biomarkers in evolving CLD., (Copyright © 2016 the American Physiological Society.)

Rationale: The treatment of children with severe-persistent asthma remains problematic. Recent studies suggest that stratification of this cohort by inflammatory type may be useful in designing effective treatment strategies. In this study, we examined the inflammatory profile in bronchoalveolar lavage fluid from children with severe-persistent asthma and compared this profile with serum IgE levels., Methods: The inflammatory profile in the bronchoalveolar fluid from 32 children who met criteria for severe-persistent asthma as defined by the Severe Asthma Research Program (SARP) were analyzed retrospectively. Inflammatory patterns were classified as neutrophilic, eosinophilic, mixed, or pauci-granulocytic. Serum total IgE was measured prior to bronchoscopy and determined by ELISA at each hospital's lab by standard procedures., Results: The most common pattern of inflammation in this cohort was neutrophilic (37.5%) followed by eosinophilic (28.1%), mixed (21.9%), and pauci-granulocytic (11.1%). The odds ratio of an eosinophilic BAL pattern for patients with an elevated serum IgE was 4.67 (CI 0.78-28, P = 0.12). A correlation between serum IgE levels and BAL eosinophil percentages was present (P = 0.04)., Conclusions: To our knowledge, ours is one of few studies to systematically investigate the pattern of lower airway inflammation in children with severe-persistent asthma. Our results differ from a recent investigation in children, showing more heterogeneity and a greater proportion of neutrophilic inflammation. Further investigation is required to determine whether specific inflammatory patterns are associated with specific etiologies, and whether individualized therapy is warranted., (© 2015 Wiley Periodicals, Inc.)

Alveolo-pleural fistula is a common complication of severe pulmonary infection. Some patients require long-term placement of chest tubes until spontaneous closure of the fistula takes place, whereas others require surgical intervention. We report a case of a patient with alveolo-pleural fistula secondary to Pneumocystis jirovecii pneumonia who was successfully treated with the use of intrabronchial unidirectional valves inserted using flexible bronchoscopy.

Rationale: Recent observations, especially in adults, suggest that asthma severity may be associated with fungal sensitization. Other studies suggest that some patients with severe asthma and fungal sensitization may benefit from anti-fungal therapy. Currently, the prevalence of fungal sensitization among children with severe asthma is not well characterized., Methods: We determined prevalence of fungal sensitization among children with moderate to severe persistent asthma and compared clinical characteristics between sensitized and non-sensitized children, including asthma severity, serum immunoglobulin E, and pulmonary function., Results: Of the 64 children enrolled, 25 (39%) had evidence of sensitization to one or more fungi. Nineteen of 25 (76%) children with fungal sensitization were categorized as severe persistent compared to 13 of 39 (33%) children without evidence of fungal sensitization (odds ratio = 6.33, 95% confidence interval 2.04-19.68, P = 0.0014). Of 32 severe persistent asthmatics, 19 (59%) demonstrated evidence of fungal sensitization. Serum immunoglobulin E was significantly higher (P < 0.001), and pulmonary function (including FEV1, FEV1/FVC, and FEF25-75%) significantly lower in the fungal-sensitized patients (P = 0.016, 0.0004, and 0.002, respectively). Bronchial biopsy of sensitized children revealed basement membrane thickening and eosinophil infiltration., Conclusions: Fungal sensitization in children with persistent asthma is associated with disease severity. Almost 60% of our severe persistent asthma patients had evidence of fungal sensitization and, based on our previous studies, may be potential candidates for anti-fungal therapy., (© 2013 Wiley Periodicals, Inc.)

Chitin, a polymer of N-acetylglucosamine, is an essential component of the fungal cell wall. Chitosan, a deacetylated form of chitin, is also important in maintaining cell wall integrity and is essential for Cryptococcus neoformans virulence. In their article, Gilbert et al. [N. M. Gilbert, L. G. Baker, C. A. Specht, and J. K. Lodge, mBio 3(1):e00007-12, 2012] demonstrate that the enzyme responsible for chitosan synthesis, chitin deacetylase (CDA), is differentially attached to the cell membrane and wall. Bioactivity is localized to the cell membrane, where it is covalently linked via a glycosylphosphatidylinositol (GPI) anchor. Findings from this study significantly enhance our understanding of cryptococcal cell wall biology. Besides the role of chitin in supporting structural stability, chitin and host enzymes with chitinase activity have an important role in host defense and modifying the inflammatory response. Thus, chitin appears to provide a link between the fungus and host that involves both innate and adaptive immune responses. Recently, there has been increased attention to the role of chitinases in the pathogenesis of allergic inflammation, especially asthma. We review these findings and explore the possible connection between fungal infections, the induction of chitinases, and asthma.

Background: Increasing evidence highlights the contribution of chitinases and fungal infection to the development of asthma., Objective: The purpose of this study was to characterize chitinase expression and serological markers of fungal infection in children with severe asthma., Methods: Bronchoalveolar lavage fluid (BALF) was collected from children undergoing clinically indicated flexible bronchoscopy. A diagnosis of asthma was confirmed by pulmonary function testing. BALF was tested for chitinase activity and YKL-40 (an enzymatically inactive chitinase) concentrations. Specimens were cultured for fungal organisms and tested for cryptococcal antigen by ELISA. IgG and IgA reactivity to whole extract fungal (Aspergillus fumigatus, Alternaria alternata, Cryptococcus neoformans and Candida albicans) proteins were determined by immunoblot assay., Results: Among the 37 patients studied, 30 were asthmatic and 7 were non-asthmatic. Asthmatics exhibited elevated serum IgE levels (median: 748 IU/mL, IQR: 219-1765 IU/mL). Chitinase activity was greater in the BALF of asthmatics (mean, 0.85 ± 1.2 U/mL) compared with non-asthmatics (mean: 0.23 ± 0.21 U/mL, P = 0.012). Likewise YKL-40 concentrations were higher in the BALF of asthmatics and correlated with chitinase activity. There was a trend towards increased fungal-specific IgG in the BALF of asthmatics compared with non-asthmatics and for C. albicans this difference reached statistical significance. IgA reactivity to C. neoformans and A. fumigatus was greater in the BALF of asthmatics compared with non-asthmatics., Conclusions and Clinical Relevance: Compared with non-asthmatics, asthmatic children exhibited increased chitinase activity and increased YKL-40 levels in BALF. Increased IgG and IgA reactivity to fungal proteins in the BALF of asthmatics may reflect a local response to fungal infection. Our findings are consistent with and suggest a role for chitinases in asthma pathogenesis among Bronx children and provide serological evidence of an association between fungal infection and severe asthma., (© 2011 Blackwell Publishing Ltd.)

Chitinases are necessary for fungal cell wall remodeling and cell replication. Methylxanthines have been shown to competitively inhibit family 18 chitinases in vitro. We sought to determine the effects of methylxanthines on fungal chitinases. Fungi demonstrated variable chitinase activity and incubation with methylxanthines (0.5-10 mM) resulted in a dose-dependent decrease in this activity. All fungi tested, except for Candida spp., demonstrated growth inhibition in the presence of methylxanthines at a concentration of 10 mM. India ink staining demonstrated impaired budding and decreased cell size for methylxanthine-treated Cryptococcus neoformans. C. neoformans and Aspergillus fumigatus treated with pentoxifylline also exhibited abnormal cell morphology. In addition, pentoxifylline-treated C. neoformans exhibited increased susceptibility to calcofluor and a leaky melanin phenotype consistent with defective cell wall function. Our data suggest that a variety of fungi express chitinases and that methylxanthines have antifungal properties related to their inhibition of fungal chitinases. Our results highlight the potential utility of targeting chitinases in the development of novel antifungal therapies.

Objective: To present a case of foreign body aspiration in a child with unilateral lung aplasia and successful removal of the foreign body by bedside flexible bronchoscopy., Data Source: Case details were obtained from medical records., Study Selection: Eighteen-month-old girl with unilateral lung aplasia., Data Extraction and Synthesis: Demographic details (age) and clinical and biochemical data (blood gas) were obtained from medical records. An 18-mo-old girl with the diagnosis of right lung aplasia, who underwent aortopexy in the newborn period for severe respiratory distress, presented with acute-onset respiratory distress. The patient was treated with bronchodilators and steroids without success and rapidly progressed to respiratory failure. Flexible bronchoscopy done at the bedside showed a foreign body completely obstructing the left main bronchus. The rigid bronchoscopy was unsuccessful in extracting the foreign body because of the complex airway anatomy. The foreign body was successfully extracted by basket forceps via a flexible bronchoscope, and the patient recovered remarkably within few hours of the procedure., Conclusions: Because foreign body aspiration in a child with a unilateral lung can result in abrupt respiratory compromise and death, a high index of suspicion is necessary when these children present with acute respiratory symptoms. Although rigid bronchoscopy is the procedure of choice for the removal of foreign bodies, flexible bronchoscopy may be necessary for patients with abnormal airway anatomy.

Background: Neutrophilic asthma is thought to be less responsive than eosinophilic asthma to anti-inflammatory therapies including corticosteroids. Chlamydia pneumoniae has been implicated in asthma, possibly by induction of interleukin (IL-8). We hypothesized that IL-8 is increased in the bronchoalveolar lavage (BAL) fluid from children with asthma and C. pneumoniae., Methods: BAL fluid was analyzed for C. pneumoniae and IL-8 using polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay from 2 asthma patient populations in the Bronx, NY and Massachusetts with an average age of 8 and 8.7 years old, respectively. For comparison, samples were also analyzed for C. trachomatis and Mycoplasma 16s DNA., Results: Of 18 Bronx samples analyzed, 6 (33%) were PCR-positive for C. pneumoniae, 10 (56%) for C. trachomatis, and 8 (44%) for Mycoplasma 16s DNA. IL-8 from C. pneumoniae-positive samples was 3.3-fold higher compared with negative samples (P = 0.003). There was no difference between patients tested for C. trachomatis or Mycoplasma. Of 84 Massachusetts samples analyzed, 42 (50%) were PCR-positive for C. pneumoniae, 42 (50%) for C. trachomatis, and 13 (16%) for Mycoplasma. IL-8 concentration from C. pneumoniae-positive samples was 10.49-fold higher compared with negative samples (P = 0.0001). As in the Bronx cohort, there were no differences between patients tested for C. trachomatis or Mycoplasma. Lastly, BAL neutrophilia predicted the presence of C. pneumoniae but not Mycoplasma or C. trachomatis., Conclusions: Children with asthma who were PCR-positive for C. pneumoniae demonstrated elevated concentrations of IL-8 and neutrophils in BAL fluid compared with similar patients who were positive for C. trachomatis or Mycoplasma organisms, but PCR-negative for C. pneumoniae. Undiagnosed C. pneumoniae infection in children may therefore contribute to poorly controlled asthma via induction of IL-8.

Fungi can exacerbate symptoms in patients with asthma. To our knowledge, genetic risk factors for fungal-associated asthma have not been described. We present here the cases of 6 children who carried the diagnosis of severe asthma with fungal sensitization, 3 of whom were treated with and responded clinically to itraconazole therapy. All 6 patients were heterozygous for a 24-base pair duplication in the CHIT1 gene, which has been associated with decreased levels of circulating chitotriosidase and susceptibility to fungal infection.

People with severe asthma with fungal sensitization may represent an underdiagnosed subset of patients with refractory disease. It is important to know that such patients may benefit from adjunct treatment with antifungal agents. We describe here the case of a child with refractory asthma, persistent airway obstruction, a serum immunoglobulin E level of >20000 IU/mL, and severe eosinophilic airway infiltration. Although he did not meet diagnostic criteria for allergic bronchopulmonary aspergillosis, he demonstrated evidence of sensitization to several fungi and responded dramatically to the addition of itraconazole therapy. We also discuss emerging hypotheses regarding fungal-induced asthma.

Although rigid bronchoscopy is the procedure of choice for interventional procedures of the proximal airway, flexible bronchoscopy can be used when lesions are not accessible by rigid equipment. We present an adolescent patient with tracheal stenosis whose airway was inaccessible through rigid bronchoscopy and thus required flexible bronchoscopy for all therapeutic procedures, including a stent placement. In addition, we describe our use of impulse oscillometry to monitor stent patency.

To date, major works on tracheomalacia have assumed a structural etiology and have proposed therapies as such. We describe a possible neurologic etiology for tracheomalacia in a child with clinically significant tracheomalacia that resolved in synchrony with each treatment of his recurring hydrocephalus. Endoscopy confirms remarkable expansion of tracheal diameter 7 days after decreasing intracranial pressure. The possibility of a neurologic etiology for tracheomalacia casts this condition in a new light with potential therapeutic implications.

Background: Permissive hypercapnia is increasingly utilized in the care of premature infants to prevent bronchopulmonary dysplasia. In a previous investigation, we described gene expression changes in the neonatal mouse lung exposed to chronic hypercapnia that might contribute to lung protection and accelerated maturation. However, it is unknown whether chronic hypercapnia increases alveolar formation, nor if it has detrimental effects in other developing organs such as the brain., Objective: To determine whether chronic hypercapnia accelerates early alveolar formation and increases neuronal cell injury in the developing mouse lung and brain, respectively., Design: Mouse pups were exposed to 8% CO(2) + 21% O(2) starting at postnatal day (P) 2 until P7. Control animals were maintained in room air. Animals were sacrificed at P4 or P7, and lungs and brains were excised and analyzed., Results: Exposure to 8% CO(2) resulted in an increased expression of alpha-smooth muscle actin (alpha-sma) which localized to the tips of developing alveolar buds, and also an increased number of alveolar buds at P7. Importantly, hypercapnic animals also demonstrated evidence of increased TUNEL-positive cells in the brain., Conclusions: Exposure to chronic hypercapnia may lead to early initiation of alveolar budding in the neonatal mouse, but may also lead to increased TUNEL-positive cells in the developing brain., ((c) 2009 Wiley-Liss, Inc.)

Objective: Demonstrate the benefits of a multidisciplinary pediatric airway team prepared to evaluate and treat otolaryngology patients with flexible bronchoscopy., Design: Case series., Setting: Tertiary, academic children's hospital., Patients: 10 children (5 male, 5 female age range 2 months-16 years) presenting with complex symptoms potentially referable to large airways., Intervention: Flexible bronchoscopy for diagnostic (bronchoalveolar lavage, ciliary biopsy, assess ongoing surgical intervention, and rule in or rule out foreign body; N=6) or therapeutic (evacuate bronchial mucus plug, laser subglottis when patient has fused cervical spine, and distal instillation [fibrin glue for bronchopleural fistula and dornase alpha for plastic bronchitis]; N=4)., Main Outcome Measure: Retrospectively ask if flexible bronchoscopy and interdisciplinary management improved patient care in these select otolaryngology cases., Results: 10/10 patients benefited from interdisciplinary management including flexible bronchoscopy., Conclusion: Our experience illustrates many uses for flexible bronchoscopy in otolaryngology patients, and suggests that an airway team prepared to use flexible bronchoscopy will create opportunities for improved patient care.

Background: We previously demonstrated that chronic pulmonary infection with Cryptococcus neoformans results in enhanced allergic inflammation and airway hyperreactivity in a rat model. Because the cell wall of C. neoformans consists of chitin, and since acidic mammalian chitinase (AMCase) has recently been implicated as a novel mediator of asthma, we sought to determine whether such infection induces chitinase activity and expression of AMCase in the rat., Methods: We utilized a previously-established model of chronic C. neoformans pulmonary infection in the rat to analyze the activity, expression and localization of AMCase., Results: Our studies indicate that intratracheal inoculation of C. neoformans induces chitinase activity within the lung and bronchoalveolar lavage fluid of infected rats. Chitinase activity is also elicited by pulmonary infection with other fungi (e.g. C. albicans), but not by the inoculation of dead organisms. Enhanced chitinase activity reflects increased AMCase expression by airway epithelial cells and alveolar macrophages. Systemic cryptococcosis is not associated with increased pulmonary chitinase activity or AMCase expression., Conclusion: Our findings indicate a possible link between respiratory fungal infections, including C. neoformans, and asthma through the induction of AMCase.

Although transforming growth factor-beta (TGF-beta) signaling negatively regulates branching morphogenesis in early lung development, few studies to date have addressed the role of this family of growth factors during late lung development. We describe here that the expression, tissue localization, and activity of components of the TGF-beta signaling machinery are dynamically regulated during late lung development in the mouse and human. Pronounced changes in the expression and localization of the TGF-beta receptors Acvrl1, Tgfbr1, Tgfbr2, Tgfbr3, and endoglin, and the intracellular messengers Smad2, Smad3, Smad4, Smad6, and Smad7 were noted as mouse and human lungs progressed through the canalicular, saccular, and alveolar stages of development. TGF-beta signaling, assessed by phosphorylation of Smad2, was detected in the vascular and airway smooth muscle, as well as the alveolar and airway epithelium throughout late lung development. These data suggest that active TGF-beta signaling is required for normal late lung development.

Purpose: To systematically assess the frequency and risk factors for atelectasis in children anesthetized for cardiothoracic magnetic resonance (MR)., Materials and Methods: We retrospectively identified 58 consecutive children (age range, 6 days to 21 years) who underwent cardiothoracic MR from January 2001 to December 2004 whose imaging and medical charts were available. One certificate of added qualification pediatric radiologist and 1 of 2 cardiothoracic radiologists, in consensus, evaluated the first and last set of axial images. Images were evaluated for cardiac, vascular and tracheobronchial abnormalities, and degree of atelectasis. Atelectasis was considered significant if the equivalent of 3 or more segments were involved. Patients received 1 or more of 7 anesthetic medications (n = 27), chloral hydrate alone (n = 4), or required no anesthesia (n = 27)., Results: Significant atelectasis developed only in those receiving anesthetic medications. Thirty-seven percent (10/27) of anesthetized children developed significant atelectasis in the first and/or last axial sequence. In 90% (9 /10) of patients, it developed in the first axial sequence. Strong risk factors were age younger than 1 year (80%, 8/10, P = 0.029) and MR evidence of tracheobronchial narrowing (50%, 5/10, P = 0.008). In patients with vascular ring, there was a trend toward significance (40%, 4/10, P = 0.09). None of the anesthesia factors were significant, including ventilation mode, anesthesia duration, or American Society of Anesthesiology risk (all P > 0.1)., Conclusions: Atelectasis may occur shortly after induction of anesthesia in children younger than 1 year of age or with tracheobronchial narrowing when anesthetized for cardiothoracic MR.

Despite the deleterious effects associated with elevated carbon dioxide (CO(2)) or hypercapnia, it has been hypothesized that CO(2) can protect the lung from injury. However, the effects of chronic hypercapnia on the neonatal lung are unknown. Hence, we investigated the effect of chronic hypercapnia on neonatal mouse lung to identify genes that could potentially contribute to hypercapnia-mediated lung protection. Newborn mouse litters were exposed to 8% CO(2), 12% CO(2), or room air for 2 wk. Lungs were excised and analyzed for morphometric alterations. The alveolar walls of CO(2)-exposed mice appeared thinner than those of controls. Analyses of gene expression differences by microarrays revealed that genes from a variety of functional categories were differentially expressed following hypercapnia treatment, including those encoding growth factors, chemokines, cytokines, and endopeptidases. In particular and of major interest, the expression level of genes encoding surfactant proteins A and D, as well as chloride channel calcium-activated 3, were significantly increased, but the expression of WNT1-inducible signaling pathway protein 2 was significantly decreased. The significant changes in gene expression occurred mostly at 8% CO(2), but only a few at 12% CO(2). Our results lead us to conclude that 1) there are a number of gene families that may contribute to hypercapnia-mediated lung protection; 2) the upregulation of surfactant proteins A and D may play a role as anti-inflammatory or antioxidant agents; and 3) the effects of CO(2) seem to depend on the level to which the lung is exposed.

Lung development is a highly orchestrated process characterized by timed expression and activation of growth factor and protease/antiprotease systems. This interplay is essential in regulating vasculogenesis, alveolarization, and epithelial to mesenchymal transition during lung development. Alterations in the proteolytic/antiproteolytic balance of the lung have been associated with several respiratory diseases characterized by changes in the lung extracellular matrix (ECM). Here, we characterized the expression pattern of matrix metalloproteases (MMP) and their inhibitors, the tissue inhibitors of metalloproteases (TIMP), in human and mouse lung development. Using MMP/TIMP expression arrays, RT-PCR, Western Blotting, and ELISA analyses, we demonstrate that fetal human lung is characterized by a dominant proteolytic profile with high MMP-2 and little TIMP-3 expression. Adult human lung, in contrast, exhibits a more anti-proteolytic profile with decreased MMP-2 and increased TIMP-3 expression. MMP-14, MMP-20, TIMP-1, and TIMP-2 were constitutively expressed, irrespective of the developmental stage. Similar results were obtained using mouse lungs of different developmental stages, with the addition that in mouse lung, TIMP-2 and TIMP-3 were upregulated as lung development progressed. Exposure of neonatal mice to chronic hypoxia (10% O2), a stimulus that leads to an arrest of lung development, resulted in upregulation of MMP-2 with a concomitant downregulation of TIMP-2. These results provide a comprehensive analysis of MMP and TIMP expression during human and mouse lung development. MMP-2, TIMP-2, and TIMP-3 may be key regulatory enzymes during lung development, possibly through their complex action on ECM components, membrane receptor ectodomain shedding, and growth factor bioactivity.

Research interest in bronchopulmonary dysplasia (BPD) has steadily increased, and numerous potential mediators have been implicated in the development of the disease. Among such mediators is transforming growth factor (TGF)-beta. Unfortunately, commonly utilized murine transgenic models are not optimal to investigate the effects of TGF-beta specifically during the 2-3 wk period of alveolar formation, the developmental stage that corresponds histologically to early alveolar development in humans, and the time frame during which BPD develops. In the current study, we utilized a triple-transgenic construct to overexpress bioactive TGF-beta1 in the neonatal mouse lung during the period of alveolar formation. Lungs were then examined by histologic, Western blot, and immunofluorescent methods. We found that overexpression of bioactive TGF-beta1 in neonatal mouse lungs resulted in structural changes that have been described in BPD. Included in those characteristics are abnormal alveolar structure, cellular composition, and vascular development. Our study indicates that TGF-beta1 overexpression in the neonatal mouse lung results in histologic alterations that have striking similarities to pathologic descriptions of BPD. We encourage the use of conditional transgenic models for the study of BPD, and hypothesize that the TGF-beta system is a central mediator for the histologic alterations described in association with the disease.

Long-term effects of hypoxia are largely due to its modulatory effects on proliferation and differentiation of epithelial and endothelial cells, processes also regulated by the transforming growth factor (TGF)-beta system. We investigated the effects of hypoxia on the TGF-beta system in rat lungs from different developmental stages. Sprague-Dawley rats were exposed to 9.5% oxygen during either the first 2 wk of life or adulthood. Analysis revealed an arrest of alveolarization in hypoxic postnatal day 14 rats. Bioactive TGF-beta levels in bronchoalveolar lavage fluid were increased in these animals, and Western blot analysis revealed upregulation of TGF-beta receptor (TbetaR) I and II. None of these changes was observed in hypoxic adults. Hypoxia did, however, lead to decreased expression of TbetaRIII in both postnatal day 14 and adult rats. Immunohistochemical analysis localized TbetaRI-III predominantly to bronchiolar and alveolar epithelium; these patterns did not change with hypoxia. Thus we observed changes in TGF-beta activity and TbetaR isotype expression in rat lung that parallel the arrest in alveolarization seen with chronic hypoxia in early development. These alterations may partly explain the morphological changes observed in hypoxia.