Nitric Acid-Induced Bronchiolitis in Rats Mimics Childhood Bronchiolitis obliterans

Transcriptome analysis reveals the impact of NETs activation on airway epithelial cell EMT and inflammation in bronchiolitis obliterans

Bronchiolitis obliterans (BO) is a chronic airway disease that was often indicated by the pathological presentation of narrowed and irreversible airways. However, the molecular mechanisms of BO pathogenesis remain unknown. Although neutrophil extracellular traps (NETs) can contribute to inflammatory disorders, their involvement in BO is unclear. This study aims to identify potential signaling pathways in BO by exploring the correlations between NETs and BO. GSE52761 and GSE137169 datasets were downloaded from gene expression omnibus (GEO) database. A series of bioinformatics analyses such as differential expression analysis, gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG), and gene set enrichment analysis (GSEA) were performed on GSE52761 and GSE137169 datasets to identify BO potential signaling pathways. Two different types of BO mouse models were constructed to verify NETs involvements in BO. Additional experiments and bioinformatics analysis using human small airway epithelial cells (SAECs) were also performed to further elucidate differential genes enrichment with their respective signaling pathways in BO. Our study identified 115 differentially expressed genes (DEGs) that were found up-regulated in BO. Pathway enrichment analysis revealed that these genes were primarily involved in inflammatory signaling processes. Besides, we found that neutrophil extracellular traps (NETs) were formed and activated during BO. Our western blot analysis on lung tissue from BO mice further confirmed NETs activation in BO, where neutrophil elastase (NE) and myeloperoxidase (MPO) expression were found significantly elevated. Transcriptomic and bioinformatics analysis of NETs treated-SAECs also revealed that NETs-DEGs were primarily associated through inflammatory and epithelial-to-mesenchymal transition (EMT) -related pathways. Our study provides novel clues towards the understanding of BO pathogenesis, in which NETs contribute to BO pathogenesis through the activation of inflammatory and EMT associated pathways. The completion of our study will provide the basis for potential novel therapeutic targets in BO treatment.

Identification of Hub Genes in the Pathogenesis of Bronchiolitis Obliterans via Bioinformatic Analysis and Experimental Verification

Background

Bronchiolitis obliterans (BO) is a chronic disease that can arise as a complication of severe childhood pneumonia and can also impact the long-term survival of patients after lung transplantation. However, the precise molecular mechanism underlying BO remains unclear. We aimed to identify BO-associated hub genes and their molecular mechanisms.

Methods

BO-associated transcriptome datasets (GSE52761, GSE137169, and GSE94557) were downloaded from the Gene Expression Omnibus (GEO) database to identify differentially expressed genes (DEGs). Additional bioinformatics analyses, such as Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Protein-Protein Interaction (PPI) analyses, were performed to determine functional roles and DEG-associated regulatory networks. Prediction of hub genes using the 12 algorithms available in the Cytohubba plugin of Cytoscape software was also performed. Verification was performed using the BO mouse model.

Results

Our results revealed 57 DEGs associated with BO, of which 18 were down-regulated and 39 were up-regulated. The Cytohubba plugin data further narrowed down the 57 DEGs into 9 prominent hub genes (CCR2, CD1D, GM2A, TFEC, MPEG1, CTSS, GPNMB, BIRC2, and CTSZ). Genes such as CCR2, TFEC, MPEG1, CTSS, and CTSZ were dysregulated in 2,3-butanedione-induced BO mice, whereas TFEC, CTSS, and CTSZ were dysregulated in nitric acid-induced BO mouse models.

Conclusion

Our study identified and validated four novel BO biomarkers, which may allow further investigation into the development of distinct BO diagnostic markers and novel therapeutic avenues.

Overexpression of miR‑200a‑3p promoted inflammation in sepsis‑induced brain injury through ROS‑induced NLRP3

Sepsis, a systemic inflammatory response syndrome induced by infection, is a common complication of trauma, burns, postoperative infection and critical disease, and is characterized by an acute onset and high fatality rate. The aim of the present study was to explore the possible molecular mechanisms of microRNA-200a-3p (miRNA-200a-3p) on inflammation during sepsis. Reverse transcription-quantitative PCR and gene microarray were used to measure the expression of miRNA-200a-3p. Tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-18 were searched by ELISA. The related proteins expression was measured using western blotting. The expression of miRNA-200a-3p was markedly higher in the sepsis model when compared with the normal control group. In addition, the expression of miRNA-200a-3p was upregulated by the miRNA-200a-3p plasmid in human brain microvascular endothelial cells treated with lipopolysaccharide, which further induced inflammation via the induction of NLR family pyrin domain containing 3 (NLRP3) and suppression of Kelch like ECH associated protein (Keap)-1/nuclear factor erythroid 2 like 2 (Nrf2)/heme oxygenase (HO)-1. The inhibition of Keap1/Nrf2/HO-1 attenuated the effects of anti-miRNA-200a-3p on inflammation. However, the inhibition of NLRP3 attenuated the effects of miRNA-200a-3p on inflammation. In conclusion, to the best of our knowledge, the results of the present study demonstrated for the first time that overexpression of miRNA-200a-3p promoted inflammation in sepsis-induced brain injury through reactive oxygen species-induced NLRP3.

Bronchiolitis obliterans murine model induced by nitric acid aerosol inhalation: An economical and reproducible model

PURPOSE

Bronchiolitis obliterans (BO) is a highly debilitative and fatal syndrome associated with a series of severe lower airway disorders. The pathogenesis of BO is complicated and not entirely understood. An appropriate animal model of BO may aid research into its pathogenesis. Here, we establish a mouse model of BO to provide insight into this disease.

MATERIALS AND METHODS

6-8 week old BABL/c mice were exposed to 5% nitric acid (NA) aerosol through a nebulizer for 3 hours, and controls were exposed to distilled water instead. Symptoms, airway resistance and pathological process were observed dynamically. The levels of matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), 8-isoprostane and myeloperoxidase (MPO) in lung tissue and bronchoalveolar lavage fluids (BLAF) were determined by ELISA on day 3, 7, 14, 28 and 56 after the aerosol nebulization.

RESULTS

Typical BO lesions were observed in NA nebulized mice characterized histologically by initial necrotizing bronchiolitis and final airway fibrosis at day 28 after the aerosol nebulization. NA nebulized mice also exhibited labored breathing and significantly increased airway resistance. Expression of MMP-2, MMP-9, TIMP-1, 8-isoprostane and MPO were significantly elevated in NA nebulized mice in different time frame.

CONCLUSION

A murine BO model was established by NA aerosol inhalation. It provides an easy, economic, and reproducible mice model for BO research.

Use of macrolides in lung diseases: recent literature controversies

OBJECTIVE

To review the mechanisms of action of macrolides in pediatric respiratory diseases and their clinical indications.

SOURCES

Review in the PubMed database, comprising the following terms in English: "macrolide and asthma"; "macrolide and cystic fibrosis"; "macrolide bronchiolitis and viral acute"; "macrolide and bronchiolitis obliterans" and "macrolide and non-CF bronchiectasis".

SUMMARY OF THE FINDINGS

The spectrum of action of macrolides includes production of inflammatory mediators, control of mucus hypersecretion, and modulation of host-defense mechanisms. The potential benefit of macrolide antibiotics has been studied in a variety of lung diseases, such as cystic fibrosis (CF), bronchiectasis, asthma, acute bronchiolitis, and non-CF bronchiectasis. Several studies have evaluated the benefits of macrolides in asthma refractory to therapy, but the results are controversial and indications should be limited to specific phenotypes. In viral bronchiolitis, there is no consistent benefit in acute conditions, although recent data have shown an effect in recurrent wheezing prevention. In patients with CF results are also contradictory, but the consensus states there is a small clinical benefit, especially for patients infected with P. aeruginosa. There was also no positive action of macrolides in patients with post-infectious bronchiolitis obliterans. Children with non-CF bronchiectasis seem to have clear benefits regarding the use of macrolides, which showed clinical advantages in parenchyma protection and lung function.

CONCLUSIONS

The long-term use of macrolides should be limited to highly selected situations, especially in patients with bronchiectasis. Careful evaluation of the benefits and potential damage are tools for their indication in specific groups.

Modeling the lung: Design and development of tissue engineered macro- and micro-physiologic lung models for research use

Respiratory tract specific cell populations, or tissue engineered in vitro grown human lung, have the potential to be used as research tools to mimic physiology, toxicology, pathology, as well as infectious diseases responses of cells or tissues. Studies related to respiratory tract pathogenesis or drug toxicity testing in the past made use of basic systems where single cell populations were exposed to test agents followed by evaluations of simple cellular responses. Although these simple single-cell-type systems provided good basic information related to cellular responses, much more can be learned from cells grown in fabricated microenvironments which mimic in vivo conditions in specialized microfabricated chambers or by human tissue engineered three-dimensional (3D) models which allow for more natural interactions between cells. Recent advances in microengineering technology, microfluidics, and tissue engineering have provided a new approach to the development of 2D and 3D cell culture models which enable production of more robust human in vitro respiratory tract models. Complex models containing multiple cell phenotypes also provide a more reasonable approximation of what occurs in vivo without the confounding elements in the dynamic in vivo environment. The goal of engineering good 3D human models is the formation of physiologically functional respiratory tissue surrogates which can be used as pathogenesis models or in the case of 2D screening systems for drug therapy evaluation as well as human toxicity testing. We hope that this manuscript will serve as a guide for development of future respiratory tract model systems as well as a review of conventional models.

Loss of basal cells precedes bronchiolitis obliterans-like pathological changes in a murine model of chlorine gas inhalation

Bronchiolitis obliterans (BO) is a major cause of chronic airway dysfunction after toxic chemical inhalation. The pathophysiology of BO is not well understood, but epithelial cell injury has been closely associated with the development of fibrotic lesions in human studies and in animal models of both toxin-induced and transplant-induced BO. However, whereas almost all cases and models of BO include epithelial injury, not all instances of epithelial injury result in BO, suggesting that epithelial damage per se is not the critical event leading to the development of BO. Here, we describe a model of chlorine-induced BO in which mice develop tracheal and large airway obliterative lesions within 10 days of exposure to high (350 parts per million [ppm]), but not low (200 ppm), concentrations of chlorine gas. Importantly, these lesions arise only under conditions and in areas in which basal cells, the resident progenitor cells for large airway epithelium, are eliminated by chlorine exposure. In areas of basal cell loss, epithelial regeneration does not occur, resulting in persistent regions of epithelial denudation. Obliterative airway lesions arise specifically from regions of epithelial denudation in a process that includes inflammatory cell infiltration by Day 2 after exposure, fibroblast infiltration and collagen deposition by Day 5, and the ingrowth of blood vessels by Day 7, ultimately leading to lethal airway obstruction by Days 9-12. We conclude that the loss of epithelial progenitor cells constitutes a critical factor leading to the development of obliterative airway lesions after chemical inhalation.

Severe airway epithelial injury, aberrant repair and bronchiolitis obliterans develops after diacetyl instillation in rats

BACKGROUND

Bronchiolitis obliterans (BO) is a fibrotic lung disease that occurs in a variety of clinical settings, including toxin exposures, autoimmunity and lung or bone marrow transplant. Despite its increasing clinical importance, little is known regarding the underlying disease mechanisms due to a lack of adequate small animal BO models. Recent epidemiological studies have implicated exposure to diacetyl (DA), a volatile component of artificial butter flavoring, as a cause of BO in otherwise healthy factory workers. Our overall hypothesis is that DA induces severe epithelial injury and aberrant repair that leads to the development of BO. Therefore, the objectives of this study were 1) to determine if DA, delivered by intratracheal instillation (ITI), would lead to the development of BO in rats and 2) to characterize epithelial regeneration and matrix repair after ITI of DA.

METHODS AND MAIN RESULTS

Male Sprague-Dawley rats were treated with a single dose of DA (125 mg/kg) or sterile water (vehicle control) by ITI. Instilled DA resulted in airway specific injury, followed by rapid epithelial regeneration, and extensive intraluminal airway fibrosis characteristic of BO. Increased airway resistance and lung fluid neutrophilia occurred with the development of BO, similar to human disease. Despite rapid epithelial regeneration after DA treatment, expression of the normal phenotypic markers, Clara cell secretory protein and acetylated tubulin, were diminished. In contrast, expression of the matrix component Tenascin C was significantly increased, particularly evident within the BO lesions.

CONCLUSIONS

We have established that ITI of DA results in BO, creating a novel chemical-induced animal model that replicates histological, biological and physiological features of the human disease. Furthermore, we demonstrate that dysregulated epithelial repair and excessive matrix Tenacin C deposition occur in BO, providing new insights into potential disease mechanisms and therapeutic targets.

Bronchiolitis obliterans in children

PURPOSE OF REVIEW

In this review, we discuss recent advances in our understanding of the etiology, pathology and pathogenesis, clinical presentation, diagnosis, treatment, and outcome of bronchiolitis obliterans in the nontransplant, pediatric population.

RECENT FINDINGS

The diagnosis of bronchiolitis obliterans in children can be made with confidence based on clinical presentation, particularly with a history of adenovirus bronchiolitis or pneumonia, fixed obstructive lung disease on pulmonary function testing, and characteristic changes of mosaic perfusion, vascular attenuation, and central bronchiectasis on chest high-resolution computed tomography, thus avoiding the need for lung biopsy in most patients. Patients with postinfectious bronchiolitis obliterans generally have chronic, nonprogressive disease; in contrast, patients with bronchiolitis obliterans from Stevens-Johnson syndrome often have progressive disease that may require lung transplantation.

SUMMARY

Bronchiolitis obliterans is a rare form of chronic obstructive lung disease that follows a severe insult to the lower respiratory tract, resulting in fibrosis of the small airways. In the nontransplant pediatric population, adenovirus infection is the most common cause. Treatment is largely supportive and prognosis is mainly related to the underlying cause and to the severity of the initial insult.

Challenges in pulmonary fibrosis. 2: Bronchiolocentric fibrosis

Bronchiolocentric fibrosis is essentially represented by the pathological pattern of constrictive fibrotic bronchiolitis obliterans. The corresponding clinical condition (obliterative bronchiolitis) is characterised by dyspnoea, airflow obstruction at lung function testing and air trapping with characteristic mosaic features on expiratory high resolution CT scans. Bronchiolitis obliterans may result from many causes including acute diffuse bronchiolar damage after inhalation of toxic gases or fumes, alloimmune chronic processes after lung or haematopoietic stem cell transplantation, or connective tissue disease (especially rheumatoid arthritis). Airway-centred interstitial fibrosis and bronchiolar metaplasia are other features of bronchiolocentric fibrosis.

Immune Cell Infiltration and Broncovascular Remodeling After Nitric Acid Nasal Instillation in a Mouse Bronchiolitis Obliterans Model

Immune cell airway infiltration and the bronchovascular remodeling process have shown to be promising in the understanding of bronchiolitis obliterans (BO) pathogenesis. In this study we sought to validate the importance of immune cells, whether diffusely distributed or forming lymphoid follicles, collagen density, and vascular factors. Eight weeks after a single nitric acid (NA) nasal instillation, lung changes were characterized by lumen distortion, epithelial layer folding, reduction or total obliteration of terminal bronchiole (TB) lumen, and wall thickness increase. The morphologic changes in the TB and TA (terminal artery) lumen coincide with the measurement difference in the three groups. The TB diameter and lumen were significantly decreased in BO when compared with non-BO lungs (0.76 +/- 0.05 microm vs. 0.81 +/- 0.05 microm and 12,286.13 +/- 378.83 microm vs. 18,182.27 +/- 5,593.98 microm, p = 0.05 and p = 0.01, respectively). Equally significant was the increase in TB thickness in BO when compared with the non-BO group (201.72 +/- 35.75 microm vs. 149.75 +/- 40.61 microm, p = 0.007). The morphologic changes in immune cells seen in TB, TA, and bronchus-associated lymphoid tissue (BALT) also coincide with the quantification differences observed in the three groups. We concluded that immune cell infiltration and collagen/vascular remodeling are related to the spectrum of histologic changes in a BO nasal-induced model in mice and may be an appropriate target for prospective studies of human bronchiolitis.