Mechanisms and Limits of Induced Postnatal Lung Growth

Localization and stretch-dependence of lung elastase activity in development and compensatory growth

Synthesis and remodeling of the lung matrix is necessary for primary and compensatory lung growth. Because cyclic negative force is applied to developing lung tissue during the respiratory cycle, we hypothesized that stretch is a critical regulator of lung matrix remodeling. By using quantitative image analysis of whole-lung and whole-lobe elastin in situ zymography images, we demonstrated that elastase activity increased twofold during the alveolar stage of postnatal lung morphogenesis in the mouse. Remodeling was restricted to alveolar walls and ducts and was nearly absent in dense elastin band structures. In the mouse pneumonectomy model of compensatory lung growth, elastase activity increased threefold, peaking at 14 days postpneumonectomy and was higher in the accessory lobe compared with other lobes. Remodeling during normal development and during compensatory lung growth was different with increased major airway and pulmonary arterial remodeling during development but not regeneration, and with homogenous remodeling throughout the parenchyma during development, but increased remodeling only in subpleural regions during compensatory lung growth. Left lung wax plombage prevented increased lung elastin during compensatory lung growth. To test whether the adult lung retains an innate capacity to remodel elastin, we developed a confocal microscope-compatible stretching device. In ex vivo adult mouse lung sections, lung elastase activity increased exponentially with strain and in peripheral regions of lung more than in central regions. Our study demonstrates that lung elastase activity is stretch-dependent and supports a model in which externally applied forces influence the composition, structure, and function of the matrix during periods of alveolar septation.

Repair and regeneration of the respiratory system: complexity, plasticity, and mechanisms of lung stem cell function

Respiratory disease is the third leading cause of death in the industrialized world. Consequently, the trachea, lungs, and cardiopulmonary vasculature have been the focus of extensive investigations. Recent studies have provided new information about the mechanisms driving lung development and differentiation. However, there is still much to learn about the ability of the adult respiratory system to undergo repair and to replace cells lost in response to injury and disease. This Review highlights the multiple stem/progenitor populations in different regions of the adult lung, the plasticity of their behavior in injury models, and molecular pathways that support homeostasis and repair.

Prenatal programming of pulmonary hypertension induced by chronic hypoxia or ductal ligation in sheep

Pulmonary hypertension of the newborn is caused by a spectrum of functional and structural abnormalities of the cardiopulmonary circuit. The existence of multiple etiologies and an incomplete understanding of the mechanisms of disease progression have hindered the development of effective therapies. Animal models offer a means of gaining a better understanding of the fundamental basis of the disease. To that effect, a number of experimental animal models are being used to generate pulmonary hypertension in the fetus and newborn. In this review, we compare the mechanisms associated with pulmonary hypertension caused by two such models: in utero ligation of the ductus arteriosus and chronic perinatal hypoxia in sheep fetuses and newborns. In this manner, we make direct comparisons between ductal ligation and chronic hypoxia with respect to the associated mechanisms of disease, since multiple studies have been performed with both models in a single species. We present evidence that the mechanisms associated with pulmonary hypertension are dependent on the type of stress to which the fetus is subjected. Such an analysis allows for a more thorough evaluation of the disease etiology, which can help focus clinical treatments. The final part of the review provides a clinical appraisal of current treatment strategies and lays the foundation for developing individualized therapies that depend on the causative factors.

Growth of alveoli during postnatal development in humans based on stereological estimation

Alveolarization in humans and nonhuman primates begins during prenatal development. Advances in stereological counting techniques allow accurate assessment of alveolar number; however, these techniques have not been applied to the developing human lung. Based on the recent American Thoracic Society guidelines for stereology, lungs from human autopsies, ages 2 mo to 15 yr, were fractionated and isometric uniform randomly sampled to count the number of alveoli. The number of alveoli was compared with age, weight, and height as well as growth between right and left lungs. The number of alveoli in the human lung increased exponentially during the first 2 yr of life but continued to increase albeit at a reduced rate through adolescence. Alveolar numbers also correlated with the indirect radial alveolar count technique. Growth curves for human alveolarization were compared using historical data of nonhuman primates and rats. The alveolar growth rate in nonhuman primates was nearly identical to the human growth curve. Rats were significantly different, showing a more pronounced exponential growth during the first 20 days of life. This evidence indicates that the human lung may be more plastic than originally thought, with alveolarization occurring well into adolescence. The first 20 days of life in rats implies a growth curve that may relate more to prenatal growth in humans. The data suggest that nonhuman primates are a better laboratory model for studies of human postnatal lung growth than rats.

DA-Raf-dependent inhibition of the Ras-ERK signaling pathway in type 2 alveolar epithelial cells controls alveolar formation

Alveolar formation is coupled to the spatiotemporally regulated differentiation of alveolar myofibroblasts (AMYFs), which contribute to the morphological changes of interalveolar walls. Although the Ras-ERK signaling pathway is one of the key regulators for alveolar formation in developing lungs, the intrinsic molecular and cellular mechanisms underlying its role remain largely unknown. By analyzing the Ras-ERK signaling pathway during postnatal development of lungs, we have identified a critical role of DA-Raf1 (DA-Raf)-a dominant-negative antagonist for the Ras-ERK signaling pathway-in alveolar formation. DA-Raf-deficient mice displayed alveolar dysgenesis as a result of the blockade of AMYF differentiation. DA-Raf is predominantly expressed in type 2 alveolar epithelial cells (AEC2s) in developing lungs, and DA-Raf-dependent MEK1/2 inhibition in AEC2s suppresses expression of tissue inhibitor of matalloprotienase 4 (TIMP4), which prevents a subsequent proteolytic cascade matrix metalloproteinase (MMP)14-MMP2. Furthermore, MMP14-MMP2 proteolytic cascade regulates AMYF differentiation and alveolar formation. Therefore, DA-Raf-dependent inhibition of the Ras-ERK signaling pathway in AEC2s is required for alveolar formation via triggering MMP2 activation followed by AMYF differentiation. These findings reveal a pivotal role of the Ras-ERK signaling pathway in the dynamic regulation of alveolar development.

Dynamic expression of chymotrypsin-like elastase 1 over the course of murine lung development

Postnatal lung development requires coordination of three processes (surface area expansion, microvascular growth, and matrix remodeling). Because normal elastin structure is important for lung morphogenesis, because physiological remodeling of lung elastin has never been defined, and because elastin remodeling is angiogenic, we sought to test the hypothesis that, during lung development, elastin is remodeled in a defined temporal-spatial pattern, that a novel protease is associated with this remodeling, and that angiogenesis is associated with elastin remodeling. By elastin in situ zymography, lung elastin remodeling increased 24-fold between embryonic day (E) 15.5 and postnatal day (PND) 14. Remodeling was restricted to major vessels and airways on PND1 with a sevenfold increase in alveolar wall elastin remodeling from PND1 to PND14. By inhibition assays and literature review, we identified chymotrypsin-like elastase 1 (CELA1) as a potential mediator of elastin remodeling. CELA1 mRNA levels increased 12-fold from E15.5 to PND9, and protein levels increased 3.4-fold from E18.5 to PND9. By costaining experiments, the temporal-spatial pattern of CELA1 expression matched that of elastin remodeling, and 58-85% of CELA1(+) cells were <10 μm from an elastase signal. An association between elastin remodeling and angiogenesis was tested by similar methods. At PND7 and PND14, 60-95% of angiogenin(+) cells were associated with elastin remodeling. Both elastase inhibition and CELA1 silencing impaired angiogenesis in vitro. Our data defines the temporal-spatial pattern of elastin remodeling during lung development, demonstrates an association of this remodeling with CELA1, and supports a role for elastin remodeling in regulating angiogenesis.

Abnormal spirometry after the Fontan procedure is common and associated with impaired aerobic capacity

Impaired exercise capacity is common after the Fontan procedure and is attributed to cardiovascular limits. The Fontan circulation, however, is also distinctively vulnerable to unfavorable lung mechanics. This study aimed to define the prevalence and physiological relevance of pulmonary dysfunction in patients with Fontan physiology. We analyzed data from the Pediatric Heart Network Fontan Cross-Sectional Study to assess the prevalence and pattern of abnormal spirometry in Fontan patients (6-18 yr old) and investigated the relationship between low forced vital capacity (FVC) and maximum exercise variables, including peak O2 consumption (Vo2peak), among those who demonstrated adequate effort (n = 260). Average ages at the time of exercise testing and Fontan completion were 13.2 ± 3.0 and 3.5 ± 2.2 yr old, respectively. Aerobic capacity was reduced (Vo2peak: 67.3 ± 15.6% predicted). FVC averaged 79.0 ± 14.8% predicted, with 45.8% having a FVC less then the lower limit of normal. Only 7.8% demonstrated obstructive spirometry. Patients with low FVC had lower Vo2peak (64.4 ± 15.9% vs. 69.7 ± 14.9% predicted, P < 0.01); low FVC independently predicted lower Vo2peak after adjusting for relevant covariates. Among those with Vo2peak < 80% predicted (n = 204/260), 22.5% demonstrated a pulmonary mechanical contribution to exercise limitation (breathing reserve < 20%). Those with both low FVC and ventilatory inefficiency (minute ventilation/CO2 production > 40) had markedly reduced Vo2peak (61.5 ± 15.3% vs. 72.0 ± 14.9% predicted, P < 0.01) and a higher prevalence of pulmonary mechanical limit compared with patients with normal FVC and efficient ventilation (36.1% vs. 4.8%). In conclusion, abnormal FVC is common in young patients after the Fontan procedure and is independently associated with reduced exercise capacity. A large subset has a pathologically low breathing reserve, consistent with a pulmonary mechanical contribution to exercise limitation.

Kelch-like ECT2-interacting protein KLEIP regulates late-stage pulmonary maturation via Hif-2α in mice

Respiratory distress syndrome (RDS) caused by preterm delivery is a major clinical problem with limited mechanistic insight. Late-stage embryonic lung development is driven by hypoxia and the hypoxia-inducible transcription factors Hif-1α and Hif-2α, which act as important regulators for lung development. Expression of the BTB-and kelch-domain-containing (BTB-kelch) protein KLEIP (Kelch-like ECT2-interacting protein; also named Klhl20) is controlled by two hypoxia response elements, and KLEIP regulates stabilization and transcriptional activation of Hif-2α. Based on the available data, we hypothesized an essential role for KLEIP in murine lung development and function. Therefore, we have performed a functional, histological, mechanistic and interventional study in embryonic and neonatal KLEIP^−/− mice. Here, we show that about half of the KLEIP^−/− neonates die due to respiratory failure that is caused by insufficient aeration, reduced septal thinning, reduced glycogenolysis, type II pneumocyte immaturity and reduced surfactant production. Expression analyses in embryonic day (E) 18.5 lungs identified KLEIP in lung capillaries, and showed strongly reduced mRNA and protein levels for Hif-2α and VEGF; such reduced levels are associated with embryonic endothelial cell apoptosis and lung bleedings. Betamethasone injection in pregnant females prevented respiratory failure in KLEIP^−/− neonates, normalized lung maturation, vascularization, aeration and function, and increased neonatal Hif-2α expression. Thus, the experimental study shows that respiratory failure in KLEIP^−/− neonates is determined by insufficient angiocrine Hif-2α–VEGF signaling and that betamethasone activates this newly identified signaling cascade in late-stage embryonic lung development.

Antenatal hypoxia and pulmonary vascular function and remodeling

This review provides evidence that antenatal hypoxia, which represents a significant and worldwide problem, causes prenatal programming of the lung. A general overview of lung development is provided along with some background regarding transcriptional and signaling systems of the lung. The review illustrates that antenatal hypoxic stress can induce a continuum of responses depending on the species examined. Fetuses and newborns of certain species and specific human populations are well acclimated to antenatal hypoxia. However, antenatal hypoxia causes pulmonary vascular disease in fetuses and newborns of most mammalian species and humans. Disease can range from mild pulmonary hypertension, to severe vascular remodeling and dangerous elevations in pressure. The timing, length, and magnitude of the intrauterine hypoxic stress are important to disease development, however there is also a genetic-environmental relationship that is not yet completely understood. Determining the origins of pulmonary vascular remodeling and pulmonary hypertension and their associated effects is a challenging task, but is necessary in order to develop targeted therapies for pulmonary hypertension in the newborn due to antenatal hypoxia that can both treat the symptoms and curtail or reverse disease progression.

Lung regeneration and translational implications of the postpneumonectomy model

Lung regeneration research is yielding data with increasing translational value. The classical models of lung development, postnatal alveolarization, and postpneumonectomy alveolarization have contributed to a broader understanding of the cellular participants including stem-progenitor cells, cell-cell signaling pathways, and the roles of mechanical deformation and other physiologic factors that have the potential to be modulated in human and animal patients. Although recent information is available describing the lineage fate of lung fibroblasts, genetic fate mapping, and clonal studies are lacking in the study of lung regeneration and deserve further examination. In addition to increasing knowledge concerning classical alveolarization (postnatal, postpneumonectomy), there is increasing evidence for remodeling of the adult lung after partial pneumonectomy. Though limited in scope, compelling data have emerged describing restoration of lung tissue mass in the adult human and in large animal models. The basis for this long-term adaptation to pneumonectomy is poorly understood, but investigations into mechanisms of lung regeneration in older animals that have lost their capacity for rapid re-alveolarization are warranted, as there would be great translational value in modulating these mechanisms. In addition, quantitative morphometric analysis has progressed in conjunction with developments in advanced imaging, which allow for longitudinal and nonterminal evaluation of pulmonary regenerative responses in animals and humans. This review focuses on the cellular and molecular events that have been observed in animals and humans after pneumonectomy because this model is closest to classical regeneration in other mammalian systems and has revealed several new fronts of translational research that deserve consideration.

Effect of unilateral diaphragmatic paralysis on postpneumonectomy lung growth

Respiratory muscle-associated stretch has been implicated in normal lung development (fetal breathing movements) and postpneumonectomy lung growth. To test the hypothesis that mechanical stretch from diaphragmatic contraction contributes to lung growth, we performed left phrenic nerve transections (PNT) in mice with and without ipsilateral pneumonectomy. PNT was demonstrated by asymmetric costal margin excursion and confirmed at autopsy. In mice with two lungs, PNT was associated with a decrease in ipsilateral lung volume (P<0.05) and lung weight (P<0.05). After pneumonectomy, PNT was not associated with a change in activity level, measureable hypoxemia, or altered minute ventilation; however, microCT scanning demonstrated altered displacement and underinflation of the cardiac lobe within the first week after pneumonectomy. Coincident with the altered structural realignment, lung impedance measurements, fitted to the constant-phase model, demonstrated elevated airway resistance (P<0.05), but normal peripheral tissue resistance (P>0.05). Most important, PNT appeared to abrogate compensatory lung growth after pneumonectomy; the weight of the lobes of the right lung was significantly less than pneumonectomy alone (P<0.001) and indistinguishable from nonsurgical controls (P>0.05). We conclude that the cyclic stretch associated with diaphragmatic muscle contraction is a controlling factor in postpneumonectomy compensatory lung growth.

Gene network analysis in a pediatric cohort identifies novel lung function genes

Lung function is a heritable trait and serves as an important clinical predictor of morbidity and mortality for pulmonary conditions in adults, however, despite its importance, no studies have focused on uncovering pediatric-specific loci influencing lung function. To identify novel genetic determinants of pediatric lung function, we conducted a genome-wide association study (GWAS) of four pulmonary function traits, including FVC, FEV₁, FEV₁/FVC and FEF_25–75% in 1556 children. Further, we carried out gene network analyses for each trait including all SNPs with a P-value of <1.0×10⁻³ from the individual GWAS. The GWAS identified SNPs with notable trends towards association with the pulmonary function measures, including the previously described INTS12 locus association with FEV1 (p_meta = 1.41×10⁻⁷). The gene network analyses identified 34 networks of genes associated with pulmonary function variables in Caucasians. Of those, the glycoprotein gene network reached genome-wide significance for all four variables. P-value range p_meta = 6.29×10⁻⁴ - 2.80×10⁻⁸ on meta-analysis. In this study, we report on specific pathways that are significantly associated with pediatric lung function at genome-wide significance. In addition, we report the first loci associated with lung function in both pediatric Caucasian and African American populations.

Early lung development: lifelong effect on respiratory health and disease

Interest in the contribution of changes in lung development during early life to subsequent respiratory morbidity is increasing. Most evidence of an association between adverse intrauterine factors and structural effects on the developing lung is from animal studies. Such evidence has been augmented by epidemiological studies showing associations between insults to the developing lung during prenatal and early postnatal life and adult respiratory morbidity or reduced lung function, and by physiological studies that have elucidated mechanisms underlying these associations. The true effect of early insults on subsequent respiratory morbidity can be understood only if the many prenatal and postnatal factors that can affect lung development are taken into account. Adverse factors affecting lung development during fetal life and early childhood reduce the attainment of maximum lung function and accelerate lung function decline in adulthood, initiating or worsening morbidity in susceptible individuals. In this Review, we focus on factors that adversely affect lung development in utero and during the first 5 years after birth, thereby predisposing individuals to reduced lung function and increased respiratory morbidity throughout life. We focus particularly on asthma and COPD.

Mechanisms of acute respiratory distress syndrome in children and adults: a review and suggestions for future research

OBJECTIVES

To provide a current overview of the epidemiology and pathophysiology of acute respiratory distress syndrome in adults and children, and to identify research questions that will address the differences between adults and children with acute respiratory distress syndrome.

DATA SOURCES

Narrative literature review and author-generated data.

DATA SELECTION

The epidemiology of acute respiratory distress syndrome in adults and children, lung morphogenesis, and postnatal lung growth and development are reviewed. The pathophysiology of acute respiratory distress syndrome is divided into eight categories: alveolar fluid transport, surfactant, innate immunity, apoptosis, coagulation, direct alveolar epithelial injury by bacterial products, ventilator-associated lung injury, and repair.

DATA EXTRACTION AND SYNTHESIS

Epidemiologic data suggest significant differences in the prevalence and mortality of acute respiratory distress syndrome between children and adults. Postnatal lung development continues through attainment of adult height, and there is overlap between the regulation of postnatal lung development and inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms. Therefore, there is a different biological baseline network of gene and protein expression in children as compared with adults.

CONCLUSIONS

There are significant obstacles to performing research on children with acute respiratory distress syndrome. However, epidemiologic, clinical, and animal studies suggest age-dependent differences in the pathophysiology of acute respiratory distress syndrome. In order to reduce the prevalence and improve the outcome of patients with acute respiratory distress syndrome, translational studies of inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms are needed. Understanding the differences in pathophysiologic mechanisms in acute respiratory distress syndrome between children and adults should facilitate identification of novel therapeutic interventions to prevent or modulate lung injury and improve lung repair.

Early life influences on the development of chronic obstructive pulmonary disease

There is increasing evidence that chronic obstructive pulmonary disease (COPD) is not simply a disease of old age that is largely restricted to heavy smokers, but may be associated with insults to the developing lung during foetal life and the first few years of postnatal life, when lung growth and development are rapid. A better understanding of the long-term effects of early life factors, such as intrauterine growth restriction, prenatal and postnatal exposure to tobacco smoke and other pollutants, preterm delivery and childhood respiratory illnesses, on the subsequent development of chronic respiratory disease is imperative if appropriate preventive and management strategies to reduce the burden of COPD are to be developed. The extent to which insults to the developing lung are associated with increased risk of COPD in later life depends on the underlying cause, timing and severity of such derangements. Suboptimal conditions in utero result in aberrations of lung development such that affected individuals are born with reduced lung function, which tends to remain diminished throughout life, thereby increasing the risk both of wheezing disorders during childhood and subsequent COPD in genetically susceptible individuals. If the current trend towards the ever-increasing incidence of COPD is to be reversed, it is essential to minimize risks to the developing lung by improvements in antenatal and neonatal care, and to reduce prenatal and postnatal exposures to environmental pollutants, including passive tobacco smoke. Furthermore, adult physicians need to recognize that lung disease is potentially associated with early life insults and provide better education regarding diet, exercise and avoidance of smoking to preserve precious reserves of lung function in susceptible adults. This review focuses on factors that adversely influence lung development in utero and during the first 5 years of life, thereby predisposing to subsequent COPD.

Fragility of pulmonary capillaries

Although the pulmonary capillaries were discovered in 1661, the ultrastructure of the wall was not elucidated until 60 years ago. Electron micrographs then showed that only 0.2 μm of tissue separated the capillary endothelium from the alveolar space over much of the area. In retrospect this vanishingly small protective layer should have alerted physiologists to the potential fragility of the capillaries, but this was not appreciated until almost 40 years later. This predicament is unique to pulmonary capillaries. No other capillaries in the body are shielded from the outside environment by such a minute amount of tissue. Reasons why the fragility of the capillaries was not recognized earlier include an inappropriate comparison with the properties of systemic capillaries, the mistaken view that the pulmonary capillary pressure is always low, and a misleading use of the Laplace equation. Evidence for the fragility comes from physiological, pathological, and laboratory observations. As expected from evolutionary considerations, the fragility only becomes evident in the normal lung under exceptional conditions. These include elite human athletes at maximal exercise and animals that have developed the capacity for extreme aerobic activity. However, lung and heart diseases frequently cause capillary disruption. Remodeling of pulmonary capillaries occurs in humans in whom the capillary pressure rises over a long period. Neonatal capillaries are extremely fragile, presumably because they have never been exposed to increased transmural pressures. The capillaries conform to the general biological rule that tissue adapts its structure to carry out its required function.

Migration of CD11b+ accessory cells during murine lung regeneration

In many mammalian species, the removal of one lung leads to growth of the remaining lung to near-baseline levels. In studying post-pneumonectomy mice, we used morphometric measures to demonstrate neoalveolarization within 21 days of pneumonectomy. Of note, the detailed histology during this period demonstrated no significant pulmonary inflammation. To identify occult blood-borne cells, we used a parabiotic model (wild-type/GFP) of post-pneumonectomy lung growth. Flow cytometry of post-pneumonectomy lung digests demonstrated a rapid increase in the number of cells expressing the hematopoietic membrane molecule CD11b; 64.5% of the entire GFP(+) population were CD11b(+). Fluorescence microscopy demonstrated that the CD11b(+) peripheral blood cells migrated into both the interstitial tissue and alveolar airspace compartments. Pneumonectomy in mice deficient in CD11b (CD18(-/-) mutants) demonstrated near-absent leukocyte migration into the airspace compartment (p<.001) and impaired lung growth as demonstrated by lung weight (p<.05) and lung volume (p<.05). Transcriptional activity of the partitioned CD11b(+) cells demonstrated significantly increased transcription of Angpt1, Il1b, and Mmp8, Mmp9, Ncam1, Sele, Sell, Selp in the alveolar airspace and Adamts2, Ecm1, Egf, Mmp7, Npr1, Tgfb2 in the interstitial tissue (>4-fold regulation; p<.05). These data suggest that blood-borne CD11b(+) cells represent a population of accessory cells contributing to post-pneumonectomy lung growth.

Long-term pulmonary outcomes of patients with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the commonest cause of chronic lung disease in infancy. The incidence of BPD has remained unchanged despite many advances in neonatal care. BPD starts in the neonatal period but its effects can persist long term. Premature infants with BPD have a greater incidence of hospitalization, and continue to have a greater respiratory morbidity and need for respiratory medications, compared to those without BPD. Lung function abnormalites, especially small airway abnormalities, often persist. Even in the absence of clinical symptoms, BPD survivors have persistent radiological abnormalities and presence of emphysema has been reported on chest computed tomography scans. Concern regarding their exercise tolerance remains. Long-term effects of BPD are still unknown, but given reports of a more rapid decline in lung function and their suspectibility to develop chronic obstructive pulmonary disease phenotype with aging, it is imperative that lung function of survivors of BPD be closely monitored.

Alveolar epithelial dynamics in postpneumonectomy lung growth

The intimate anatomic and functional relationship between epithelial cells and endothelial cells within the alveolus suggests the likelihood of a coordinated response during postpneumonectomy lung growth. To define the population dynamics and potential contribution of alveolar epithelial cells to alveolar angiogenesis, we studied alveolar Type II and I cells during the 21 days after pneumonectomy. Alveolar Type II cells were defined and isolated by flow cytometry using a CD45(-) , MHC class II(+) , phosphine(+) phenotype. These phenotypically defined alveolar Type II cells demonstrated an increase in cell number after pneumonectomy; the increase in cell number preceded the increase in Type I (T1α(+) ) cells. Using a parabiotic wild type/GFP pneumonectomy model, <3% of the Type II cells and 1% of the Type I cells were positive for GFP-a finding consistent with the absence of a blood-borne contribution to alveolar epithelial cells. The CD45(-) , MHC class II(+) , phosphine(+) Type II cells demonstrated the active transcription of angiogenesis-related genes both before and after pneumonectomy. When the Type II cells on Day 7 after pneumonectomy were compared to nonsurgical controls, 10 genes demonstrated significantly increased expression (P<0.05). In contrast to the normal adult Type II cells, there was notable expression of inflammation-associated genes (Ccl2, Cxcl2, Ifng) as well as genes associated with epithelial growth (Ereg, Lep). Together, the data suggest an active contribution of local alveolar Type II cells to alveolar growth.

Hepatocyte growth factor, a determinant of airspace homeostasis in the murine lung

The alveolar compartment, the fundamental gas exchange unit in the lung, is critical for tissue oxygenation and viability. We explored hepatocyte growth factor (HGF), a pleiotrophic cytokine that promotes epithelial proliferation, morphogenesis, migration, and resistance to apoptosis, as a candidate mediator of alveolar formation and regeneration. Mice deficient in the expression of the HGF receptor Met in lung epithelial cells demonstrated impaired airspace formation marked by a reduction in alveolar epithelial cell abundance and survival, truncation of the pulmonary vascular bed, and enhanced oxidative stress. Administration of recombinant HGF to tight-skin mice, an established genetic emphysema model, attenuated airspace enlargement and reduced oxidative stress. Repair in the TSK/+ mouse was punctuated by enhanced akt and stat3 activation. HGF treatment of an alveolar epithelial cell line not only induced proliferation and scattering of the cells but also conferred protection against staurosporine-induced apoptosis, properties critical for alveolar septation. HGF promoted cell survival was attenuated by akt inhibition. Primary alveolar epithelial cells treated with HGF showed improved survival and enhanced antioxidant production. In conclusion, using both loss-of-function and gain-of-function maneuvers, we show that HGF signaling is necessary for alveolar homeostasis in the developing lung and that augmentation of HGF signaling can improve airspace morphology in murine emphysema. Our studies converge on prosurvival signaling and antioxidant protection as critical pathways in HGF–mediated airspace maintenance or repair. These findings support the exploration of HGF signaling enhancement for diseases of the airspace.

The airspace compartment of the mammalian lung, comprised of spherical sacs termed alveoli, harbors the architecture, cellular composition, and molecular armamentarium to perform the critical function of gas exchange or oxygen uptake. Despite the necessity of this alveolar compartment for organismal viability, the mechanism by which alveoli are formed and maintained is obscure. Furthermore, no treatments are currently available that can regenerate the airspace once damaged. In this manuscript, we sought to determine whether hepatocyte growth factor, a cytokine with a functional armamentarium that subserves the critical events of alveolar formation (epithelial proliferation, migration, resistance from apoptosis and angiogenesis), could be an important mediator of alveolar formation and airspace maintenance. Our simple paradigm was that critical homeostatic pathways for the lung should operate both in lung formation and in lung maintenance/regeneration. Using an informative battery of mouse models and cell lines, we show that hepatocyte growth factor is a determinant of alveolar formation and that the enhancement of hepatocyte growth factor signaling can both protect and repair the airspace from pathologic airspace enlargement or emphysema.

Separating in vivo mechanical stimuli for postpneumonectomy compensation: imaging and ultrastructural assessment

Following right pneumonectomy (PNX), the remaining lung expands and its perfusion more than doubles. Tissue and microvascular mechanical stresses are putative stimuli for compensatory lung growth and remodeling, but their relative contribution remains uncertain. To temporally separate expansion- and perfusion-related stimuli, we replaced the right lung of adult dogs with a customized inflated prosthesis. Four months later, the prosthesis was either acutely deflated (DEF) or kept inflated (INF). Thoracic high-resolution computed tomography (HRCT) was performed pre- and post-PNX before and after prosthesis deflation. Lungs were fixed for morphometric analysis ∼12 mo post-PNX. The INF prosthesis prevented mediastinal shift and lateral lung expansion while allowing the remaining lung to expand 27-38% via caudal elongation, associated with reversible capillary congestion in dependent regions at low inflation and 40-60% increases in the volumes of alveolar sepal cells, matrix, and fibers. Delayed prosthesis deflation led to further significant increases in lung volume, alveolar tissue volumes, and alveolar-capillary surface areas. At postmortem, alveolar tissue volumes were 33% higher in the DEF than the INF group. Lateral expansion explains ∼65% of the total post-PNX increase in left lung volume assessed in vivo or ex vivo, ∼36% of the increase in HRCT-derived (tissue + microvascular blood) volume, ∼45% of the increase in ex vivo septal extravascular tissue volume, and 60% of the increase in gas exchange surface areas. This partition agrees with independent physiological measurements obtained in these animals. We conclude that in vivo signals related to lung expansion and perfusion contribute separately and nearly equally to post-PNX growth and remodeling.

Low birth weight and very low birth weight neonates with congenital heart disease: timing of surgery, reasons for delaying or not delaying surgery

Conventional management of low birth weight and very low birth weight neonates was composed of deferring corrective surgery by aggressive medical management or palliative surgery which does not require cardiopulmonary bypass. However, while waiting for weight gain, these neonates are at risk for various comorbidities. In the current era, this "wait and let the baby grow" approach has not been shown to result in better clinical outcomes. Early primary repair hence has become the standard strategy for congenital heart disease requiring surgery in these neonates. However, there still exist some circumstances, which are considered to be unfavorable for corrective surgery due to medical, physiologic, surgeon's technical and institutional-systemic factors. We reviewed the recent literature and examined the reasons for delaying or not delaying surgery.

Early onset scoliosis: current concepts and controversies

Early Onset Scoliosis (EOS) may be associated with long-term pulmonary morbidity, which is not commonly seen in Adolescent Idiopathic Scoliosis. Initial evaluation is based on determining any underlying etiology related to congenital or syndromic conditions. Assessing the impact of scoliosis on thoracic development may help guide treatment, which is often required at a young age in these children to prevent irreversible pulmonary insufficiency. Treatment is based on multiple factors but may include non-surgical strategies, such as casting or bracing, along with growth-sparing surgical procedures using growing rods or chest wall expansion. Definitive fusion is rarely indicated in young patients. This chapter will cover the diagnosis, evaluation, and treatment of children with EOS.

Mechanostructural adaptations preceding postpneumonectomy lung growth

In many species, pneumonectomy results in compensatory growth in the remaining lung. Although the late mechanical consequences of murine pneumonectomy are known, little is known about the anatomic adaptations and respiratory mechanics during compensatory lung growth. To investigate the structural and mechanical changes during compensatory growth, mice were studied for 21 days after left pneumonectomy using microCT and respiratory system impedance (FlexiVent). Anatomic changes after left pneumonectomy included minimal mediastinal shift or chestwall remodeling, but significant displacement of the heart and cardiac lobe. Mean displacement of the cardiac lobe centroid was 5.2 ± 0.8 mm. Lung impedance measurements were used to investigate the associated changes in respiratory mechanics. Quasi-static pressure-volume loops demonstrated progressive increase in volumes with decreased distensibility. Measures of quasi-static compliance and elastance were increased at all time points postpneumonectomy (P < .01). Oscillatory mechanics demonstrated a significant change in tissue impedance on the third day after pneumonectomy. The input impedance on day 3 after pneumonectomy demonstrated a significant increase in tissue damping (5.8 versus 4.3 cm H(2)O/mL) and elastance (36.7 versus 26.6 cm H(2)O/mL) when compared to controls. At all points, hysteresivity was unchanged (0.17). We conclude that the timing and duration of the mechanical changes was consistent with a mechanical signal for compensatory growth.

Detection of murine post-pneumonectomy lung regeneration by 18FDG PET imaging

BACKGROUND

An intriguing biologic process in most adult mammals is post-pneumonectomy lung regeneration, that is, the removal of one lung (pneumonectomy) results in the rapid compensatory growth of the remaining lung. The spatial dependence and metabolic activity of the rodent lung during compensatory lung regeneration is largely unknown.

METHODS

To determine if murine lung regeneration could be detected in vivo, we studied inbred mice 3, 7, 14, and 21 days after left pneumonectomy. The remaining lung was imaged using microCT as well as the glucose tracer 2-deoxy-2-[18 F]fluoro-d-glucose (18FDG) and positron-emission tomography (PET). Because of the compliance of the murine chest wall, reproducible imaging required orotracheal intubation and pressure-controlled ventilation during scanning.

RESULTS

After left pneumonectomy, the right lung progressively enlarged over the first 3 weeks. The cardiac lobe demonstrated the greatest percentage increase in size. Dry weights of the individual lobes largely mirrored the increase in lung volume. PET/CT imaging was used to identify enhanced metabolic activity within the individual lobes. In the cardiac lobe, 18FDG uptake was significantly increased in the day 14 cardiac lobe relative to preoperative values (p < .05). In contrast, the 18FDG uptake in the other three lobes was not statistically significant at any time point.

CONCLUSIONS

We conclude that the cardiac lobe is the dominant contributor to compensatory growth after murine pneumonectomy. Further, PET/CT scanning can detect both the volumetric increase and the metabolic changes associated with the regenerative growth in the murine cardiac lobe.

Computational analysis of lung deformation after murine pneumonectomy. [corrected]

In many mammalian species, the removal of one lung (pneumonectomy) is associated with the compensatory growth of the remaining lung. To investigate the hypothesis that parenchymal deformation may trigger lung regeneration, we used microCT scanning to create 3D finite element geometric models of the murine lung pre- and post-pneumonectomy (24 h). The structural correspondence between models was established using anatomic landmarks and an iterative computational algorithm. When compared with the pre-pneumonectomy lung, the post-pneumonectomy models demonstrated significant translation and rotation of the cardiac lobe into the post-pneumonectomy pleural space. 2D maps of lung deformation demonstrated significant heterogeneity; the areas of greatest deformation were present in the subpleural regions of the lobe. Consistent with the previously identified growth patterns, subpleural regions of enhanced deformation are compatible with a mechanical signal - likely involving parenchymal stretch - triggering lung growth.

LRP5 regulates development of lung microvessels and alveoli through the angiopoietin-Tie2 pathway

Angiogenesis is crucial for lung development. Although there has been considerable exploration, the mechanism by which lung vascular and alveolar formation is controlled is still not completely understood. Here we show that low-density lipoprotein receptor-related protein 5 (LRP5), a component of the Wnt ligand-receptor complex, regulates angiogenesis and alveolar formation in the lung by modulating expression of the angiopoietin (Ang) receptor, Tie2, in vascular endothelial cells (ECs). Vascular development in whole mouse lungs and in cultured ECs is controlled by LRP5 signaling, which is, in turn, governed by a balance between the activities of the antagonistic Tie2 ligands, Ang1 and Ang2. Under physiological conditions when Ang1 is dominant, LRP5 knockdown decreases Tie2 expression and thereby, inhibits vascular and alveolar development in the lung. Conversely, when Ang2 dominates under hyperoxia treatment in neonatal mice, high LRP5 and Tie2 expression suppress angiogenesis and lung development. These findings suggest that the LRP5-Tie2-Ang signaling axis plays a central role in control of both angiogenesis and alveolarization during postnatal lung development, and that deregulation of this signaling mechanism might lead to developmental abnormalities of the lung, such as are observed in bronchopulmonary dysplasia (BPD).

Evidence for adult lung growth in humans

A 33-year-old woman underwent a right-sided pneumonectomy in 1995 for treatment of a lung adenocarcinoma. As expected, there was an abrupt decrease in her vital capacity, but unexpectedly, it increased during the subsequent 15 years. Serial computed tomographic (CT) scans showed progressive enlargement of the remaining left lung and an increase in tissue density. Magnetic resonance imaging (MRI) with the use of hyperpolarized helium-3 gas showed overall acinar-airway dimensions that were consistent with an increase in the alveolar number rather than the enlargement of existing alveoli, but the alveoli in the growing lung were shallower than in normal lungs. This study provides evidence that new lung growth can occur in an adult human.

What can imaging tell us about physiology? Lung growth and regional mechanical strain

The interplay of mechanical forces transduces diverse physico-biochemical processes to influence lung morphogenesis, growth, maturation, remodeling and repair. Because tissue stress is difficult to measure in vivo, mechano-sensitive responses are commonly inferred from global changes in lung volume, shape, or compliance and correlated with structural changes in tissue blocks sampled from postmortem-fixed lungs. Recent advances in noninvasive volumetric imaging technology, nonrigid image registration, and deformation analysis provide valuable tools for the quantitative analysis of in vivo regional anatomy and air and tissue-blood distributions and when combined with transpulmonary pressure measurements, allow characterization of regional mechanical function, e.g., displacement, strain, shear, within and among intact lobes, as well as between the lung and the components of its container-rib cage, diaphragm, and mediastinum-thereby yielding new insights into the inter-related metrics of mechanical stress-strain and growth/remodeling. Here, we review the state-of-the-art imaging applications for mapping asymmetric heterogeneous physical interactions within the thorax and how these interactions permit as well as constrain lung growth, remodeling, and compensation during development and following pneumonectomy to illustrate how advanced imaging could facilitate the understanding of physiology and pathophysiology. Functional imaging promises to facilitate the formulation of realistic computational models of lung growth that integrate mechano-sensitive events over multiple spatial and temporal scales to accurately describe in vivo physiology and pathophysiology. Improved computational models in turn could enhance our ability to predict regional as well as global responses to experimental and therapeutic interventions.

Pentoxifylline and prevention of hyperoxia-induced lung -injury in neonatal rats

INTRODUCTION

Oxygen exposure plays an important role in the pathogenesis of bronchopulmonary dysplasia (BPD). The phosphodiesterase inhibitor pentoxifylline (PTX) has anti-inflammatory and antifibrotic effects in multiple organs. It was hypothesized that PTX would have a protective effect on hyperoxia-induced lung injury (HILI).

METHODS

Newborn Sprague-Dawley rats were exposed to >95% oxygen (O(2)) and injected subcutaneously with normal saline (NS) or PTX (75 mg/kg) twice a day for 9 d. NS-injected, room air-exposed pups were controls. At days 4 and 9, lung tissue was collected to assess edema, antioxidant enzyme (AOE) activities, and vascular endothelial growth factor (VEGF) expression. At day 9, pulmonary macrophage infiltration, vascularization, and alveolarization were also examined.

RESULTS

At day 9, treatment with PTX significantly increased survival from 54% to 88% during hyperoxia. Treatment with PTX significantly decreased lung edema and macrophage infiltration. PTX treatment increased lung AOE activities including those of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). Furthermore, PTX treatment also increased the gene expression of VEGF189 and VEGF165, increased VEGF protein expression, and improved pulmonary vascularization.

DISCUSSION

These data indicate that the reduced lung edema and inflammation, increased AOE activities, and improved vascularization may be responsible for the improved survival with PTX during hyperoxia. PTX may be a potential therapy in reducing some of the features of BPD in preterm newborns.

Evidence for a causal relationship between respiratory syncytial virus infection and asthma

Respiratory syncytial virus (RSV) infects all children early in life, is the most common cause of infant lower respiratory tract infections, and causes disease exacerbations in children with asthma. Episodes of lower respiratory tract infection in early life are associated with asthma development. Whether RSV infection early in life directly causes asthma or simply identifies infants who are genetically predisposed to develop subsequent wheezing is debatable. Recent studies suggest that these two explanations are not mutually exclusive, and are likely both important in asthma development. An open-label study of RSV immunoprophylaxis administered to preterm infants reduced recurrent wheezing by 50%. Clinical trials of infant RSV prevention, delay or severity reduction on the outcome of childhood asthma would confirm the causal relationship between RSV infection and asthma, and offer a primary prevention strategy.

Animal models of human respiratory syncytial virus disease

Infection with the human pneumovirus pathogen, respiratory syncytial virus (hRSV), causes a wide spectrum of respiratory disease, notably among infants and the elderly. Laboratory animal studies permit detailed experimental modeling of hRSV disease and are therefore indispensable in the search for novel therapies and preventative strategies. Present animal models include several target species for hRSV, including chimpanzees, cattle, sheep, cotton rats, and mice, as well as alternative animal pneumovirus models, such as bovine RSV and pneumonia virus of mice. These diverse animal models reproduce different features of hRSV disease, and their utilization should therefore be based on the scientific hypothesis under investigation. The purpose of this review is to summarize the strengths and limitations of each of these animal models. Our intent is to provide a resource for investigators and an impetus for future research.

Progressive adaptation in regional parenchyma mechanics following extensive lung resection assessed by functional computed tomography

In adult canines following major lung resection, the remaining lobes expand asymmetrically, associated with alveolar tissue regrowth, remodeling, and progressive functional compensation over many months. To permit noninvasive longitudinal assessment of regional growth and function, we performed serial high-resolution computed tomography (HRCT) on six male dogs (∼9 mo old, 25.0 ± 4.5 kg, ±SD) at 15 and 30 cmH(2)O transpulmonary pressure (Ptp) before resection (PRE) and 3 and 15 mo postresection (POST3 and POST15, respectively) of 65-70% of lung units. At POST3, lobar air volume increased 83-148% and tissue (including microvascular blood) volume 120-234% above PRE values without further changes at POST15. Lobar-specific compliance (Cs) increased 52-137% from PRE to POST3 and 28-79% from POST3 to POST15. Inflation-related parenchyma strain and shear were estimated by detailed registration of corresponding anatomical features at each Ptp. Within each lobe, regional displacement was most pronounced at the caudal region, whereas strain was pronounced in the periphery. Regional three-dimensional strain magnitudes increased heterogeneously from PRE to POST3, with further medial-lateral increases from POST3 to POST15. Lobar principal strains (PSs) were unchanged or modestly elevated postresection; changes in lobar maximum PS correlated inversely with changes in lobar air and tissue volumes. Lobar shear distortion increased in coronal and transverse planes at POST3 without further changes thereafter. These results establish a novel use of functional HRCT to map heterogeneous regional deformation during compensatory lung growth and illustrate a stimulus-response feedback loop whereby postresection mechanical stress initiates differential lobar regrowth and sustained remodeling, which in turn, relieves parenchyma stress and strain, resulting in progressive increases in lobar Cs and a delayed increase in whole lung Cs.

Unilateral absence of pulmonary artery in children: bronchovascular anatomy, natural course and effect of treatment on lung growth

BACKGROUND

Unilateral absence of pulmonary artery (UAPA) is a rare congenital anomaly with few published studies focusing on anatomy and outcome.

OBJECTIVE

To assess the bronchovascular anatomy, lung volume and growth in treated and untreated patients with UAPA.

MATERIALS AND METHODS

Eighteen children with UAPA (isolated: n = 12; associated with congenital heart disease: n = 6) were retrospectively studied to assess the vascularization and lung segmentation and to appraise lung volume evolution in treated and untreated patients. Age at presentation: 1 day to 6 years; mean follow-up duration 13.6 years. Reperfusion of the affected pulmonary artery was attempted in 10 children (younger than 6 months: n = 7; older than 6 months: n = 3).

RESULTS

Bronchovascular lung segmentation was complete in all cases. In children treated before 6 months of age, lung volume normalized in 3 and remained normal in 3, and hypoplasia progression was noted in 1. Hypoplasia persisted in children treated after 6 months of age. In untreated children, lung hypoplasia was unchanged in cases diagnosed after 7 months of age (n = 4) and progressive in cases diagnosed before 3 months (n = 4).

CONCLUSION

In UAPA, lung anatomy and volume are normal at birth. Revascularization of the affected pulmonary artery before 6 months of age seems to allow optimal lung growth and prevent postnatal lung hypoplasia and development of collaterals.

The Transition from Bronchopulmonary Dysplasia to Childhood Chronic Lung Disease

The impact of a preterm birth on lung function in later life is not always predictable and the variability of lung phenotype in these children can be striking even among children of the same gestational age. Although many children with a history of bronchopulmonary dysplasia (BPD) improve with age, others continue to manifest significant pulmonary abnormalities. Several different lung phenotypes have been described in older children with a history of BPD. These descriptions have been based in part on chronic respiratory symptoms, pulmonary function abnormalities, and response to respiratory illnesses. These lung phenotypes include large and/or small airway dysfunction, impaired alveolar growth characterized by decreased pulmonary reserve, and pulmonary hypertension found primarily in children with severe chronic lung disease. Children with a history of BPD can manifest 1 or more of these lung phenotypes with varying degrees of severity. Currently, treatment of respiratory symptoms is primarily supportive and symptom based. Although many children improve with age, others continue to have chronic respiratory symptoms into adult life. The development of standardized guidelines for the care of children after discharge from the neonatal intensive care unit may help direct appropriate therapy, limit lung injury, and maximize lung growth potential in this vulnerable group of children.

Asthma in childhood: a complex, heterogeneous disease

Asthma in childhood is a heterogeneous disease with different phenotypes and variable clinical manifestations, which depend on the age, gender, genetic background, and environmental influences of the patients. Several longitudinal studies have been conducted to classify the phenotypes of childhood asthma, on the basis of the symptoms, triggers of wheezing illness, or pathophysiological features of the disease. These studies have provided us with important information about the different wheezing phenotypes in young children and about potential mechanisms and risk factors for the development of chronic asthma. The goal of these studies was to provide a better insight into the causes and natural course of childhood asthma. It is well-known that complicated interactions between genes and environmental factors contribute to the development of asthma. Because childhood is a period of rapid growth in both the lungs and the immune system, developmental factors should be considered in the pathogenesis of childhood asthma. The pulmonary system continues to grow and develop until linear growth is completed. Longitudinal studies have reported significant age-related immune development during postnatal early life. These observations suggest that the phenotypes of childhood asthma vary among children and also in an individual child over time. Improved classification of heterogeneous conditions of the disease will help determine novel strategies for primary and secondary prevention and for the development of individualized treatment for childhood asthma.

Airway administration of dexamethasone, 3'-5'-cyclic adenosine monophosphate, and isobutylmethylxanthine facilitates compensatory lung growth in adult mice

The combination of dexamethasone, 8-bromo-3'-5'-cyclic adenosine monophosphate, and isobutylmethylxanthine, referred to as DCI, has been reported to optimally induce cell differentiation in fetal lung explants and type II epithelial cells. DCI administration is also known to modulate the expression levels of many genes known to be involved in the facilitation of lung growth. Recently, we found that RNA silencing of thyroid transcription factor 1 (TTF-1) delayed compensatory lung growth. DCI is also known to induce TTF-1 expression in pulmonary epithelial cells. From these findings, we hypothesized that DCI administration may facilitate compensatory lung growth. In the present study, using a postpneumonectomy lung growth model in 9-wk-old male mice, we found that compensatory lung growth was significantly facilitated by airway administration of DCI immediately following left pneumonectomy, as indicated by the increase in the residual right lung dry weight index. TTF-1 expression was significantly elevated by DCI administration, and transient knockdown of TTF-1 attenuated the facilitation of compensatory lung growth by DCI. These results suggested that DCI facilitated compensatory lung growth, at least in part, through the induction of TTF-1. Morphological analyses suggested that DCI administration increased the number of alveoli, made each of them smaller, and produced a net increase in the calculated surface area of the alveoli per volume of lung. The effect of a single administration was maintained during the observation period, which was 28 days. DCI with further modifications may provide the material to potentially augment residual lung function after resection.

In vitro and in vivo assessment of pulmonary risk associated with exposure to combustion generated fine particles

Strong correlations exist between exposure to PM(2.5) and adverse pulmonary effects. PM(2.5) consists of fine (70% of the total particles. Environmentally persistent free radicals (EPFRs) have recently been identified in airborne PM(2.5). To determine the adverse pulmonary effects of EPFRs associated with exposure to elevated levels of PM(2.5), we engineered 2.5 mum surrogate EPFR-particle systems. We demonstrated that EPFRs generated greater oxidative stress in vitro, which was partly responsible for the enhanced cytotoxicity following exposure. In vivo studies using rats exposed to EPFRs containing particles demonstrated minimal adverse pulmonary effects. Additional studies revealed that fine particles failed to reach the alveolar region. Overall, our study implies qualitative differences between the health effects of PM size fractions.

Lethal skeletal dysplasia in mice and humans lacking the golgin GMAP-210

BACKGROUND

Establishing the genetic basis of phenotypes such as skeletal dysplasia in model organisms can provide insights into biologic processes and their role in human disease.

METHODS

We screened mutagenized mice and observed a neonatal lethal skeletal dysplasia with an autosomal recessive pattern of inheritance. Through genetic mapping and positional cloning, we identified the causative mutation.

RESULTS

Affected mice had a nonsense mutation in the thyroid hormone receptor interactor 11 gene (Trip11), which encodes the Golgi microtubule-associated protein 210 (GMAP-210); the affected mice lacked this protein. Golgi architecture was disturbed in multiple tissues, including cartilage. Skeletal development was severely impaired, with chondrocytes showing swelling and stress in the endoplasmic reticulum, abnormal cellular differentiation, and increased cell death. Golgi-mediated glycosylation events were altered in fibroblasts and chondrocytes lacking GMAP-210, and these chondrocytes had intracellular accumulation of perlecan, an extracellular matrix protein, but not of type II collagen or aggrecan, two other extracellular matrix proteins. The similarities between the skeletal and cellular phenotypes in these mice and those in patients with achondrogenesis type 1A, a neonatal lethal form of skeletal dysplasia in humans, suggested that achondrogenesis type 1A may be caused by GMAP-210 deficiency. Sequence analysis revealed loss-of-function mutations in the 10 unrelated patients with achondrogenesis type 1A whom we studied.

CONCLUSIONS

GMAP-210 is required for the efficient glycosylation and cellular transport of multiple proteins. The identification of a mutation affecting GMAP-210 in mice, and then in humans, as the cause of a lethal skeletal dysplasia underscores the value of screening for abnormal phenotypes in model organisms and identifying the causative mutations.

Recent advances and new opportunities in lung mechanobiology

Lung function is inextricably linked to mechanics. On short timescales every breath generates dynamic cycles of cell and matrix stretch, along with convection of fluids in the airways and vasculature. Perturbations such airway smooth muscle shortening or surfactant dysfunction rapidly alter respiratory mechanics, with profound influence on lung function. On longer timescales, lung development, maturation, and remodeling all strongly depend on cues from the mechanical environment. Thus mechanics has long played a central role in our developing understanding of lung biology and respiratory physiology. This concise review focuses on progress over the past 5 years in elucidating the molecular origins of lung mechanical behavior, and the cellular signaling events triggered by mechanical perturbations that contribute to lung development, homeostasis, and injury. Special emphasis is placed on the tools and approaches opening new avenues for investigation of lung behavior at integrative cellular and molecular scales. We conclude with a brief summary of selected opportunities and challenges that lie ahead for the lung mechanobiology research community.

Rhinovirus and the initiation of asthma

PURPOSE OF REVIEW

Virus-induced wheezing in infancy is a risk factor for asthma, and recent studies have highlighted the role of rhinoviruses in causing acute illnesses and as a possible contributing factor to chronic asthma.

RECENT FINDINGS

Human rhinoviruses (HRVs) have long been known as the most common cause of common cold in infants and children. Recent developments in molecular diagnostics have led to the discovery of new viruses and have also provided data to implicate HRV as an important cause of lower respiratory infections and acute virus-induced wheezing in preschool children. In addition, HRV-induced wheezing episodes appear to identify children who are at increased risk for the subsequent development of childhood asthma.

SUMMARY

Collectively, these findings raise the possibility that lower respiratory infections with pathogens such as HRV and respiratory syncytial virus could participate in the causation of asthma, especially in children with suboptimal antiviral defenses. A variety of experimental models and clinical studies have been used to identify possible mechanisms related to the infection and the ensuing host response that could disturb normal lung and immunologic development to promote asthma. Defining these relationships could lead to new therapeutic and preventive approaches to common forms of childhood asthma.

Pulmonary epithelial neuropilin-1 deletion enhances development of cigarette smoke-induced emphysema

RATIONALE

Cigarette smoke (CS) exposure is an important risk factor for chronic obstructive pulmonary disease; however, not all smokers develop disease, suggesting that other factors influence disease development.

OBJECTIVES

We sought to determine whether neuropilin-1 (Nrp1), an integral component of receptor complexes mediating alveolar septation and vascular development, was involved in maintenance of normal alveolar structure, and/or altered susceptibility to the effects of CS.

METHODS

Transgenic mice were generated to achieve inducible lung-specific deletion of epithelial Nrp1. We determined whether conditional Nrp1 deletion altered airspace size, then compared the effects of chronic CS or filtered air exposure on airspace size, inflammation, and the balance between cell death and proliferation in conditionally Nrp1-deficient adult mice and littermate controls. Finally, we evaluated the effects of Nrp1 silencing on cell death after acute exposure of A549 cells to cigarette smoke extract or short chain ceramides.

MEASUREMENTS AND MAIN RESULTS

Genetic deletion of epithelial Nrp1 in either postnatal or adult lungs resulted in a small increase in airspace size. More notably, both airspace enlargement and apoptosis of type I and type II alveolar epithelial cells were significantly enhanced following chronic CS exposure in conditionally Nrp1-deficient adult mice. Silencing of Nrp1 in A549 cells did not alter cell survival after vehicle treatment but significantly augmented apoptosis after exposure to cigarette smoke extract or ceramide.

CONCLUSIONS

These data support a role for epithelial Nrp1 in the maintenance of normal alveolar structure and suggest that dysregulation of Nrp1 expression may promote epithelial cell death in response to CS exposure, thereby enhancing emphysema development.

Characterization and expression of bone morphogenetic protein 4 gene in postnatal pigs

Bone morphogenetic protein 4 (BMP4) is involved in animal embryonic development and reproductive physiology. The human and murine BMP4 genes have been isolated and characterized. The objectives of this study were to: (1) characterize the full mRNA and genomic sequence for porcine BMP4, and (2) examine BMP4 gene expression in 10 tissues of postnatal female pigs. Using RT-PCR, RACE and general PCR techniques, a 1,626 bp DNA including the full coding region of BMP4 was isolated and identified as a homologue of human BMP4 transcript variant (TV)-c. The porcine TV-c contained 3 exons and astride 3.6 kb in the isolated 7.8 kb porcine BMP4 genome. The In silicon cloning identified other three forms of mRNAs, including the homologues of human TV-1, TV-a and a novel variant related to human TV-3 (TV-3p). The porcine TV-c, TV-1 and TV-3p bear internal ribosome entry sites (IRES) in 5' untranslated region (UTR), while there are two ARE elements in the 3'UTR. The full genomic sequence of porcine BMP4 gene showed 81.38, 76.23 and 64.00% identity with that of bovine, human and murine, respectively. The expression of BMP4 mRNA was determined by RT-PCR in 7, 14, and 28 day old female piglets and non-gestational sows. The results showed that porcine BMP4 occurred in all 10 examined tissues (heart, lung, liver, kidney, ovary, spleen, spinal medulla, brain, duodenum and thymus). The mRNA expression levels were relatively higher in lung and kidney in 7 day old piglets, thymus in 14 day old piglets, and spleen in 28 day old piglets, respectively, while the higher expressions were detected in liver of non-gestational pigs (P < 0.05). Moreover, the mRNA amounts both in 7 day old piglets and sows were generally higher than those in 14 and 28 day old piglets in nearly all examined tissues, except in thymus. It is concluded that the structure of porcine BMP4 gene is highly conservative with other mammalian BMP4 genes, but some differences may present in the regulation of gene expression. BMP4 mRNAs are expressed in postnatal pigs, and is spatiotemporally regulated.