Transforming growth factor-β regulates endothelin-1 signaling in the newborn mouse lung during hypoxia exposure

LungElast-an open-source, flexible, low-cost, microprocessor-controlled mouse lung elastometer

The study of mouse lung mechanics provides essential insights into the physiological mechanisms of pulmonary disease. Consequently, investigators assemble custom systems comprising infusion-withdrawal syringe pumps and analog pressure sensors to investigate the lung function of these animals. But these systems are expensive and require ongoing regulation, making them challenging to use. Here I introduce LungElast, an open-source, inexpensive, and self-contained instrument that can experimentally determine lung elasticity and volumes even in immature mice. It is assembled using custom 3D printed parts and readily available or easily constructed components. In this device, a microprocessor-controlled stepper motor automatically regulates lung volume by precisely driving a syringe piston whose position is determined using time-of-flight LIDAR technology. The airway pressures associated with the lung volumes are determined using compact sensor-on-chip technology, retrieved in a digital format, and stored by the microcontroller. The instrument software is modular, which eases device testing, calibration, and use. Data are also provided here that specify the accuracy and precision of the elastometer's sensors and volume delivery and demonstrate its use with lung models and mouse pups. This instrument has excellent potential for research and educational work.

MicroRNA 219-5p inhibits alveolarization by reducing platelet derived growth factor receptor-alpha

BACKGROUND

MicroRNA (miR) are small conserved RNA that regulate gene expression post-transcription. Previous genome-wide analysis studies in preterm infants indicate that pathways of miR 219-5p are important in infants with Bronchopulmonary Dysplasia (BPD).

METHODS

Here we report a prospective cohort study of extremely preterm neonates wherein infants diagnosed with severe BPD expressed increased airway miR-219-5p and decreased platelet derived growth factor receptor alpha (PDGFR-α), a target of mir-219-5p and a key regulator of alveolarization, compared to post-conception age-matched term infants.

RESULTS

miR-219-5p was highly expressed in the pulmonary epithelial lining in lungs of infants with BPD by in situ hybridization of human infant lungs. In both in vitro and in vivo (mouse) models of BPD, miR-219-5p was increased on exposure to hyperoxia compared with the normoxia control, with a complementary decrease of PDGFR-α. To further confirm the target relationship between miR-219 and PDGFR-α, pulmonary epithelial cells (MLE12) and lung primary fibroblasts were treated with a mimic of miR-219-5p and a locked nucleic acid (LNA) based inhibitor of miR-219-5p. In comparison with the control group, the level of miR-219 increased significantly after miR-219 mimic treatment, while the level of PDGFR-α declined markedly. LNA exposure increased PDGFR-α. Moreover, in BPD mouse model, over-expression of miR-219-5p inhibited alveolar development, indicated by larger alveolar spaces accompanied by reduced septation.

CONCLUSIONS

Taken together, our results demonstrate that increased miR-219-5p contributes to the pathogenesis of BPD by targeting and reducing PDGFR-α. The use of specific miRNA antagonists may be a therapeutic strategy for preventing the development of BPD.

Halogen exposure injury in the developing lung

Owing to a high-volume industrial usage of the halogens chlorine (Cl₂ ) and bromine (Br₂ ), they are stored and transported in abundance, creating a risk for accidental or malicious release to human populations. Despite extensive efforts to understand the mechanisms of toxicity upon halogen exposure and to develop specific treatments that could be used to treat exposed individuals or large populations, until recently, there has been little to no effort to determine whether there are specific features and or the mechanisms of halogen exposure injury in newborns or children. We established a model of neonatal halogen exposure and published our initial findings. In this review, we aim to contrast and compare the findings in neonatal mice exposed to Br₂ with the findings published on adult mice exposed to Br₂ and the neonatal murine models of bronchopulmonary dysplasia. Despite remarkable similarities across these models in overall alveolar architecture, there are distinct functional and apparent mechanistic differences that are characteristic of each model. Understanding the mechanistic and functional features that are characteristic of the injury process in neonatal mice exposed to halogens will allow us to develop countermeasures that are appropriate for, and effective in, this unique population.

CFTR dysfunction increases endoglin and TGF-β signaling in airway epithelia

Endoglin (ENG) regulates signaling by transforming growth factor‐β (TGF‐β), a genetic modifier of cystic fibrosis (CF) lung disease severity. We hypothesized that ENG mediates TGF‐β pathobiology in CF airway epithelia. Comparing CF and non‐CF human lungs, we measured ENG by qPCR, immunoblotting and ELISA. In human bronchial epithelial cell lines (16HBE), we used CFTR siRNA knockdown and functional inhibition (CFTR_INH‐172) to connect loss of CFTR to ENG synthesis. Plasmid overexpression of ENG assessed the direct effect of ENG on TGF‐β transcription and signal amplification in 16HBE cells. We found ENG protein to be increased more than fivefold both in human CF bronchoalveolar fluid (BALF) and human CF lung homogenates. ENG transcripts were increased threefold in CF, with a twofold increase in TGF‐β signaling. CFTR knockdown in 16HBE cells tripled ENG transcription and doubled protein levels with corresponding increases in TGF‐β signaling. Plasmid overexpression of ENG alone nearly doubled TGF‐β1 mRNA and increased TGF‐β signaling in 16HBE cells. These experiments identify that loss of CFTR function increases ENG expression in CF epithelia and amplifies TGF‐β signaling. Targeting ENG may offer a novel therapeutic opportunity to address TGF‐β associated pathobiology in CF.

Qingxuan Jiangya Decoction () Prevents Blood Pressure Elevation and Ameliorates Vascular Structural Remodeling via Modulating TGF-β 1/Smad Pathway in Spontaneously Hypertensive Rats

OBJECTIVE

To elevate the effects of Qingxuan Jiangya Decoction (, QXJYD) on hypertension and vascular structural remodeling (VSR) in spontaneously hypertensive rats (SHRs), and investigate the underlying mechanisms.

METHODS

SHRs (n=8) were given intra-gastric administration with 60 mg/kg of QXJYD or saline, daily for 8 weeks, while rats in SHR-control (n=8) and WKY (n=8) groups were received equal volumes of saline solution. Systolic blood pressures (SBP), diastolic blood pressures (DBP) and mean blood pressures (MBP) were measured once a week. The levels of angiotensin II (Ang II), endothelin 1 (ET-1) and plasma renin activity (PRA) were tested by enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay, respectively. The effect of QXJYD on VSR was determined by examining the media thickness and the ex vivo contractility of thoracic aortic. The proliferation and fibrosis of vascular smooth muscle cells (VSMCs) were examined via immunohistochemical (IHC) staining for proliferating cell nuclear antigen (PCNA), collagen I and collagen III, respectively. The mRNA and protein expressions of transforming growth factor β 1 (TGF-β 1), Smad3 and phosphorylation of Smad3 in thoracic aorta tissues were determined by real-time polymerase chain reaction (PCR) and Western blot assay, respectively.

RESULTS

QXJYD treatment led to a significant decrease of the elevation of blood pressure in SHRs and reduced the levels of Ang II, ET-1 and PRA in the serum (P<0.05). In addition, QXJYD treatment remarkably ameliorated VSR and vascular function in SHRs. Moreover, QXJYD inhibited VSMC proliferation and fibrosis by suppressing the expression of PCNA, collagen I and collagen III in thoracic aortic. Furthermore, QXJYD inhibited the expression of TGF-β 1, Smad3 and the phosphorylation of Smad3, respectively (P<0.05).

CONCLUSION

QXJYD reversed VSR by inhibiting VSMC proliferation and collagen deposition via regulation of TGF-β 1/Smad signaling pathway, which may, in part, illuminate its anti-hypertensive activities.

The effects of a graded increase in chronic hypoxia exposure duration on healthy rats at high-altitude

To investigate the effects of chronic hypoxia exposure at high altitude on the formation of pulmonary edema in rats, we randomized rats into normoxic control groups and hypoxic 24, 48, and 72-hour exposure groups. In the hypoxic exposure group, the arterial blood gas, wet-dry weight ratio (W/D), lung tissue permeability index (LPI), bronchoalveolar lavage fluid (BALF) and plasma levels of the inflammatory factors were measured after continuous, chronic hypoxic exposure for a corresponding time, and the pathological changes in the lung tissue and the expression of tight junction-associated protein occludin were observed. We found that the contents of arterial blood gas, W/D, LPI, BALF and plasma IL-6, TNF-α, and IL-10 in the hypoxic exposure group were significantly different from the contents of arterial blood gas in the normoxic control group. H&E staining showed tissue effusion, a marked thickening of the pulmonary septum, interstitial inflammatory cells, and erythrocytic infiltration. Compared with the normoxic control group, the pulmonary edema score was significantly increased in the hypoxic 48-hour group. Toluidine blue staining showed that the mast cell count and degranulation rate were significantly increased in the hypoxic 48-hour and 72-hour groups, but massone staining showed no significant pulmonary interstitial fibrosis in the 4 groups. Occludin expression was significantly higher in the normoxic control group than it was in the hypoxic exposure group. These results indicated that different chronic hypoxic exposure durations at the plateau all caused high-altitude pulmonary edema in rats, but there was no significant difference in some indicators among the groups.

Transforming Growth Factor-β-Neutralizing Antibodies Improve Alveolarization in the Oxygen-Exposed Newborn Mouse Lung

Abnormal alveolar formation and excessive disordered elastin accumulation are key pathological features in bronchopulmonary dysplasia. Transforming growth factor (TGF)-β is an important regulator of the extracellular matrix in the developing lung. To determine if increased TGF-β would injure alveolar development by activating TGF-β signaling and by influencing the expression of elastogenesis-related protein, we performed intraperitoneal injection of newborn mice with the TGF-β-neutralizing antibody 1D11 and observed whether 1D11 had a protective role in the oxygen (O₂)-exposed newborn mouse lung. The newborn mice were exposed to 85% O₂ for 14 and 21 days. 1D11 was administered by intraperitoneal injection every day from postnatal days 3 to 20. Alveolar morphology was assessed by hematoxylin and eosin staining. The expression and distribution of elastin were evaluated by immunohistochemistry. The level of TGF-β signaling-related proteins were measured by immunohistochemistry, enzyme-linked immunosorbent assay, and Western blot. The expression levels of elastogenesis-related proteins, including tropoelastin, fibulin-5, and neutrophil elastase (NE), which participate in the synthesis, assembly, and degradation of elastin, were detected by real-time PCR and Western blot. In this research, impaired alveolar development and elastin deposition as well as the excessive activation of TGF-β signaling were observed in the newborn mouse lung exposed to hyperoxia. 1D11 improved alveolarization as well as the distribution of elastin in the newborn lung with hyperoxia exposure. The expression levels of tropoelastin, fibulin-5, and NE, which are important components of elastogenesis, were decreased by treatment with 1D11 in the injured newborn lung. These data demonstrate that 1D11 improved alveolarization by blocking the TGF-β signaling pathway and by reducing the abnormal expression of elastogenesis-related proteins in the O₂-exposed newborn mouse lung. 1D11 may become a new therapeutic method to prevent the development of bronchopulmonary dysplasia.

Redox Mechanisms Influencing cGMP Signaling in Pulmonary Vascular Physiology and Pathophysiology

The soluble form of guanylate cyclase (sGC) and cGMP signaling are major regulators of pulmonary vasodilation and vascular remodeling that protect the pulmonary circulation from hypertension development. Nitric oxide, reactive oxygen species, thiol and heme redox, and heme biosynthesis control mechanisms regulating the production of cGMP by sGC. In addition, a cGMP-independent mechanism regulates protein kinase G through thiol oxidation in manner controlled by peroxide metabolism and NADPH redox. Multiple aspects of these regulatory processes contribute to physiological and pathophysiological regulation of the pulmonary circulation, and create potentially novel therapeutic targets for the treatment of pulmonary vascular disease.

[Methods for establishing animal model of bronchopulmonary dysplasia and their evaluation]

With the development of treatment, the survival rate of premature infants has significantly increased, especially extremely premature infants and very low birth weight infants. This has led to an increase in incidence of bronchopulmonary dysplasia (BPD) year by year. BPD has been one of the most common respiratory system diseases in premature infants, especially the small premature infants. Arrested alveolar development is an important cause of BPD. Therefore, the mechanism of arrested alveolar development and the intervention measures for promoting alveolar development are the focuses of research on BPD. Selecting the appropriate animal model of BPD is the key to obtaining meaningful results in the basic research on BPD. Based on above, several common methods for establishing an animal model of BPD and the corresponding changes in pathophysiology are summarized and evaluated in order to provide a reference for selecting the appropriate animal model in studies on the pathogenesis, pathophysiology, and prevention and control strategies of BPD.

The role of PSMB9 upregulated by interferon signature in the pathophysiology of cutaneous lesions of dermatomyositis and systemic lupus erythematosus

BACKGROUND

Dermatomyositis (DM) and systemic lupus erythematosus (SLE) have common skin features, including dermal mucin deposition and interferon signature, although their roles are unknown.

OBJECTIVES

To identify common or specific molecular changes in DM and SLE skin.

METHODS

Proteomic analysis was performed using DM and healthy skin. Glycosaminoglycans were analysed by high-performance liquid chromatography.

RESULTS

The expression of 60 proteins was upregulated or downregulated in DM skin compared with healthy skin in the proteomic analysis. Among those proteins, PSMB9, an immunoproteasome subunit, was upregulated in the epidermis of DM and SLE, but not in other skin diseases. Furthermore, versican V1, a core protein for glycosaminoglycans, was upregulated, while type I collagen was downregulated in the dermis of DM and SLE skin. Interferon stimulated PSMB9 expression in cultured keratinocytes and reduced collagen expression in dermal fibroblasts, but did not affect versican expression. The PSMB9 knock-down in keratinocytes led to significant suppression of transforming growth factor (TGF)-β2 and TGF-β3, inducers of versican synthesis. TGF-β3 expression was upregulated in both DM and SLE, while TGF-β2 expression was increased only in the DM epidermis. ΔDiHS-diS1, a component of heparan sulfate, was significantly increased only in DM. TGF-β2 expression significantly increased the ΔDiHS-diS1 expression in dermal fibroblasts in vitro.

CONCLUSIONS

The interferon signature in DM and SLE skin reduces collagen in dermal fibroblasts, whereas overexpression of PSMB9 induced by interferon stimulates versican inducers in epidermal keratinocytes. In addition, the TGF-β2-ΔDiHS-diS1 pathway may be responsible for the specific molecular change in DM skin.

Regulation of alveolar septation by microRNA-489

MicroRNAs (miRs) are small conserved RNA that regulate gene expression. Bioinformatic analysis of miRNA profiles during mouse lung development indicated a role for multiple miRNA, including miRNA-489. miR-489 increased on completion of alveolar septation [postnatal day 42 (P42)], associated with decreases in its conserved target genes insulin-like growth factor-1 (Igf1) and tenascin C (Tnc). We hypothesized that dysregulation of miR-489 and its target genes Igf1 and Tnc contribute to hyperoxia-induced abnormal lung development. C57BL/6 mice were exposed to normoxia (21%) or hyperoxia (85% O2) from P4 to P14, in combination with intranasal locked nucleic acid against miR-489 to inhibit miR-489, cytomegalovirus promoter (pCMV)-miR-489 to overexpress miR-489, or empty vector. Hyperoxia reduced miR-489 and increased Igf1 and Tnc. Locked nucleic acid against miR-489 improved lung development during hyperoxia and did not alter it during normoxia, whereas miR-489 overexpression inhibited lung development during normoxia. The 3' untranslated region in vitro reporter studies confirmed Igf1 and Tnc as targets of miR-489. While miR-489 was of epithelial origin and present in exosomes, its targets Igf1 and Tnc were produced by fibroblasts. Infants with bronchopulmonary dysplasia (BPD) had reduced lung miR-489 and increased Igf1 and Tnc compared with normal preterm or term infants. These results suggest increased miR-489 is an inhibitor of alveolar septation. During hyperoxia or BPD, reduced miR-489 and increased Igf1 and Tnc may be inadequate attempts at compensation. Further inhibition of miR-489 may permit alveolar septation to proceed. The use of specific miRNA antagonists or agonists may be a therapeutic strategy for inhibited alveolarization, such as in BPD.

IGF-1 signaling in neonatal hypoxia-induced pulmonary hypertension: Role of epigenetic regulation

Pulmonary hypertension is a fatal disease characterized by a progressive increase in pulmonary artery pressure accompanied by pulmonary vascular remodeling and increased vasomotor tone. Although some biological pathways have been identified in neonatal hypoxia-induced pulmonary hypertension (PH), little is known regarding the role of growth factors in the pathogenesis of PH in neonates. In this study, using a model of hypoxia-induced PH in neonatal mice, we demonstrate that the growth factor insulin-like growth factor-1 (IGF-1), a potent activator of the AKT signaling pathway, is involved in neonatal PH. After exposure to hypoxia, IGF-1 signaling is activated in pulmonary endothelial and smooth muscle cells in vitro, and the IGF-1 downstream signal pAKT(S473) is upregulated in lungs of neonatal mice. We found that IGF-1 regulates ET-1 expression in pulmonary endothelial cells and that IGF-1 expression is regulated by histone deacetylases (HDACs). In addition, there is a differential cytosine methylation site in the IGF-1 promoter region in response to neonatal hypoxia. Moreover, inhibition of HDACs with apicidin decreases neonatal hypoxia-induced global DNA methylation levels in lungs and specific cytosine methylation levels around the pulmonary IGF-1 promoter region. Finally, HDAC inhibition with apicidin reduces chronic hypoxia-induced activation of IGF-1/pAKT signaling in lungs and attenuates right ventricular hypertrophy and pulmonary vascular remodeling. Taken together, we conclude that IGF-1, which is epigenetically regulated, is involved in the pathogenesis of pulmonary hypertension in neonatal mice. This study implicates a novel HDAC/IGF-1 epigenetic pathway in the regulation of hypoxia-induced PH and warrants further study of the role of IGF-1 in neonatal pulmonary hypertensive disease.

Epigenetic contributions to the developmental origins of adult lung disease

Perinatal insults, including intrauterine growth restriction, preterm birth, maternal exposure to toxins, or dietary deficiencies produce deviations in the epigenome of lung cells. Occurrence of perinatal insults often coincides with the final stages of lung development. The result of epigenome disruptions in response to perinatal insults during lung development may be long-term structural and functional impairment of the lung and development of lung disease. Understanding the contribution of epigenetic mechanisms to life-long lung disease following perinatal insults is the focus of the developmental origins of adult lung disease field. DNA methylation, histone modifications, and microRNA changes are all observed in various forms of lung disease. However, the perinatal contribution to such epigenetic mechanisms is poorly understood. Here we discuss the developmental origins of adult lung disease, the interplay between perinatal events, lung development and disease, and the role that epigenetic mechanisms play in connecting these events.

Animal models of bronchopulmonary dysplasia. The term mouse models

The etiology of bronchopulmonary dysplasia (BPD) is multifactorial, with genetics, ante- and postnatal sepsis, invasive mechanical ventilation, and exposure to hyperoxia being well described as contributing factors. Much of what is known about the pathogenesis of BPD is derived from animal models being exposed to the environmental factors noted above. This review will briefly cover the various mouse models of BPD, focusing mainly on the hyperoxia-induced lung injury models. We will also include hypoxia, hypoxia/hyperoxia, inflammation-induced, and transgenic models in room air. Attention to the stage of lung development at the timing of the initiation of the environmental insult and the duration of lung injury is critical to attempt to mimic the human disease pulmonary phenotype, both in the short term and in outcomes extending into childhood, adolescence, and adulthood. The various indexes of alveolar and vascular development as well as pulmonary function including pulmonary hypertension will be highlighted. The advantages (and limitations) of using such approaches will be discussed in the context of understanding the pathogenesis of and targeting therapeutic interventions to ameliorate human BPD.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Transglutaminase 2: a new player in bronchopulmonary dysplasia?

Aberrant remodelling of the extracellular matrix in the developing lung may underlie arrested alveolarisation associated with bronchopulmonary dysplasia (BPD). Transglutaminases are regulators of extracellular matrix remodelling. Therefore, the expression and activity of transglutaminases were assessed in lungs from human neonates with BPD and in a rodent model of BPD. Transglutaminase expression and localisation were assessed by RT-PCR, immunoblotting, activity assay and immunohistochemical analyses of human and mouse lung tissues. Transglutaminase regulation by transforming growth factor (TGF)-β was investigated in lung cells by luciferase-based reporter assay and RT-PCR. TGF-β signalling was neutralised in vivo in an animal model of BPD, to determine whether TGF-β mediated the hyperoxia-induced changes in transglutaminase expression. Transglutaminase 2 expression was upregulated in the lungs of preterm infants with BPD and in the lungs of hyperoxia-exposed mouse pups, where lung development was arrested. Transglutaminase 2 localised to the developing alveolar septa. TGF-β was identified as a regulator of transglutaminase 2 expression in human and mouse lung epithelial cells. In vivo neutralisation of TGF-β signalling partially restored normal lung structure and normalised lung transglutaminase 2 mRNA expression. Our data point to a role for perturbed transglutaminase 2 activity in the arrested alveolarisation associated with BPD.

Endothelin-1 directs airway remodeling and hyper-reactivity in a murine asthma model

Background

The current paradigm describing asthma pathogenesis recognizes the central role of abnormal epithelial function in the generation and maintenance of the disease. However, the mechanisms responsible for the initiation of airway remodeling, which contributes to decreased lung function, remain elusive. Therefore, we aimed to determine the role of altered pulmonary gene expression in disease inception and identify proremodeling mediators.

Methods

Using an adenoviral vector, we generated mice overexpressing smad2, a TGF-β and activin A signaling molecule, in the lung. Animals were exposed to intranasal ovalbumin (OVA) without systemic sensitization.

Results

Control mice exposed to inhaled OVA showed no evidence of pulmonary inflammation, indices of remodeling, or airway hyper-reactivity. In contrast, local smad2 overexpression provoked airway hyper-reactivity in OVA-treated mice, concomitant with increased airway smooth muscle mass and peribronchial collagen deposition. Pulmonary eosinophilic inflammation was not evident, and there was no change in serum IgE or IgG1 levels. The profound remodeling changes were not mediated by classical pro-inflammatory Th2 cytokines. However, uric acid and interleukin-1β levels in the lung were increased. Epithelial-derived endothelin-1 and fibroblast growth factor were also augmented in smad2-expressing mice. Blocking endothelin-1 prevented these phenotypic changes.

Conclusions

Innate epithelial-derived mediators are sufficient to drive airway hyper-reactivity and remodeling in response to environmental insults in the absence of overt Th2-type inflammation in a model of noneosinophilic, noninflammed types of asthma. Targeting potential asthma therapies to epithelial cell function and modulation of locally released mediators may represent an effective avenue for therapeutic design.

Recent advances in late lung development and the pathogenesis of bronchopulmonary dysplasia

In contrast to early lung development, a process exemplified by the branching of the developing airways, the later development of the immature lung remains very poorly understood. A key event in late lung development is secondary septation, in which secondary septa arise from primary septa, creating a greater number of alveoli of a smaller size, which dramatically expands the surface area over which gas exchange can take place. Secondary septation, together with architectural changes to the vascular structure of the lung that minimize the distance between the inspired air and the blood, are the objectives of late lung development. The process of late lung development is disturbed in bronchopulmonary dysplasia (BPD), a disease of prematurely born infants in which the structural development of the alveoli is blunted as a consequence of inflammation, volutrauma, and oxygen toxicity. This review aims to highlight notable recent developments in our understanding of late lung development and the pathogenesis of BPD.

Ambrisentan reduces pulmonary arterial hypertension but does not stimulate alveolar and vascular development in neonatal rats with hyperoxic lung injury

Ambrisentan, an endothelin receptor type A antagonist, may be a novel therapeutic agent in neonatal chronic lung disease (CLD) by blocking the adverse effects of the vasoconstrictor endothelin-1, especially pulmonary arterial hypertension (PAH)-induced right ventricular hypertrophy (RVH). We determined the cardiopulmonary effects of ambrisentan treatment (1-20 mg·kg(-1)·day(-1)) in neonatal rats with CLD in 2 models: early treatment during continuous exposure to hyperoxia for 10 days and late treatment starting on day 6 in rat pups exposed postnatally to hyperoxia for 9 days, followed by a 9-day recovery period in room air. Parameters investigated included survival, lung and heart histopathology, right ventricular function, fibrin deposition, and differential mRNA expression in the lungs. In the early treatment model, we investigated the role of nitric oxide synthase (NOS) inhibition with N(ω)-nitro-L-arginine methyl ester (L-NAME; 25 mg·kg(-1)·day(-1)) during ambrisentan treatment. In the early treatment model, ambrisentan improved survival with reduced lung fibrin and collagen III deposition, arterial medial wall thickness, and RVH. These changes were not affected by L-NAME administration. Ambrisentan did not reduce the influx of macrophages and neutrophils or prevent reduced irregular elastin expression. In the late treatment model, ambrisentan diminished PAH, RVH, and right ventricular peak pressure, demonstrating that RVH is reversible in the neonatal period. Alveolarization and vascularization were not affected by ambrisentan. In conclusion, ambrisentan prolongs survival and reduces lung injury, PAH, and RVH via a NOS-independent mechanism but does not affect inflammation and alveolar and vascular development in neonatal rats with CLD.

Titanium oxide nanoparticle instillation induces inflammation and inhibits lung development in mice

Nanoparticles are used in an increasing number of biomedical, industrial, and food applications, but their safety profiles in developing organisms, including the human fetus and infant, have not been evaluated. Titanium oxide (TiO(2)) nanoparticles, which are commonly used in cosmetics, sunscreens, paints, and food, have been shown to induce emphysema and lung inflammation in adult mice. We hypothesized that exposure of newborn mice to TiO(2) would induce lung inflammation and inhibit lung development. C57BL/6 mice were exposed to TiO(2) (anatase; 8-10 nm) nanoparticles by intranasal instillation as a single dose on postnatal day 4 (P4) or as three doses on postnatal days 4, 7, and 10 (each dose = 1 μg/g body wt). Measurements of lung function (compliance and resistance), development (morphometry), inflammation (histology; multiplex analysis of bronchoalveolar lavage fluid for cytokines; PCR array and multiplex analysis of lung homogenates for cytokines) was performed on postnatal day 14. It was observed that a single dose of TiO(2) nanoparticles led to inflammatory cell influx, and multiple doses led to increased inflammation and inhibition of lung development without significant effects on lung function. Macrophages were noted to take up the TiO(2) nanoparticles, followed by polymorphonuclear infiltrate. Multiple cytokines and matrix metalloproteinase-9 were increased in lung homogenates, and VEGF was reduced. These results suggest that exposure of the developing lung to nanoparticles may lead to ineffective clearance by macrophages and persistent inflammation with resulting effects on lung development and may possibly impact the risk of respiratory disorders in later life.