Lung collagen: more than scaffolding

Local fractal dimension of collagen detects increased spatial complexity in fibrosis

Increase of collagen content and reorganization characterizes fibrosis but quantifying the latter remains challenging. Spatially complex structures are often analyzed via the fractal dimension; however, established methods for calculating this quantity either provide a single dimension for an entire object or a spatially distributed dimension that only considers binary images. These neglect valuable information related to collagen density in images of fibrotic tissue. We sought to develop a fractal analysis that can be applied to 3-dimensional (3D) images of fibrotic tissue. A fractal dimension map for each image was calculated by determining a single fractal dimension for a small area surrounding each image pixel, using fiber thickness as the third dimension. We found that this local fractal dimension increased with age and with progression of fibrosis regardless of collagen content. Our new method of distributed 3D fractal analysis can thus distinguish between changes in collagen content and organization induced by fibrosis.

Bronchial obstruction in osteogenesis imperfecta can be detected by forced oscillation technique

Introduction

Respiratory insufficiency is a leading cause of death in individuals with osteogenesis imperfecta (OI). However, evaluating pulmonary function in OI presents challenges. Commonly used pulmonary function tests such as spirometry and body plethysmography are sometimes difficult to perform for OI patients, and reference intervals are not always applicable. The forced oscillation technique (FOT) is a patient-friendly method for detecting respiratory abnormalities that requires no effort from the patient.

Objective

This study investigates the feasibility of FOT in the evaluation of respiratory function in the clinical management of OI patients.

Methods

Twelve OI patients, comprising eight with Sillence OI I, two with OI IV, and two with OI III, underwent spirometry, body plethysmography, and FOT, both pre-and post-administration of salbutamol.

Results

FOT measurements exhibited consistent trends that aligned with spirometry and body plethysmography findings. The resistance at 8 Hz decreased after the administration of salbutamol, indicating that FOT is able to detect bronchial obstruction and its alleviation by medication (p < 0.05). The resonant frequency during expiration was higher than during inspiration in nearly all patients, suggesting obstructive disease. The technique gives insight into both inspiratory and expiratory impairment of pulmonary ventilation. The main FOT parameters showed a relatively high repeatability in duplicate measurements.

Conclusion

Bronchial obstruction can be detected by FOT in patients with OI during quiet breathing, making it an easily executable alternative to other lung function measurements. The technique can detect the bronchodilator effect of sympathomimetic medication. It has the potential to provide information on expiratory flow limitation, pulmonary restriction, and reduced lung compliance.

The Regenerative Power of Stem Cells: Treating Bleomycin-Induced Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease with no known cure, characterized by the formation of scar tissue in the lungs, leading to respiratory failure. Although the exact cause of IPF remains unclear, the condition is thought to result from a combination of genetic and environmental factors. One of the most widely used animal models to study IPF is the bleomycin-induced lung injury model in mice. In this model, the administration of the chemotherapeutic agent bleomycin causes pulmonary inflammation and fibrosis, which closely mimics the pathological features of human IPF. Numerous recent investigations have explored the functions of various categories of stem cells in the healing process of lung injury induced by bleomycin in mice, documenting the beneficial effects and challenges of this approach. Differentiation of stem cells into various cell types and their ability to modulate tissue microenvironment is an emerging aspect of the regenerative therapies. This review article aims to provide a comprehensive overview of the role of stem cells in repairing bleomycin-induced lung injury. It delves into the mechanisms through which various types of stem cells, including mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells, and lung resident stem cells, exert their therapeutic effects in this specific model. We have also discussed the unique set of intermediate markers and signaling factors that can influence the proliferation and differentiation of alveolar epithelial cells both during lung repair and homeostasis. Finally, we highlight the challenges and opportunities associated with translating stem cell therapy to the clinic for IPF patients. The novelty and implications of this review extend beyond the understanding of the potential of stem cells in treating IPF to the broader field of regenerative medicine. We believe that the review paves the way for further advancements in stem cell therapies, offering hope for patients suffering from this debilitating and currently incurable disease.

The interplay of cells, polymers, and vascularization in three-dimensional lung models and their applications in COVID-19 research and therapy

Millions of people have been affected ever since the emergence of the corona virus disease of 2019 (COVID-19) outbreak, leading to an urgent need for antiviral drug and vaccine development. Current experimentation on traditional two-dimensional culture (2D) fails to accurately mimic the in vivo microenvironment for the disease, while in vivo animal model testing does not faithfully replicate human COVID-19 infection. Human-based three-dimensional (3D) cell culture models such as spheroids, organoids, and organ-on-a-chip present a promising solution to these challenges. In this report, we review the recent 3D in vitro lung models used in COVID-19 infection and drug screening studies and highlight the most common types of natural and synthetic polymers used to generate 3D lung models.

Distinct type I collagen alterations cause intrinsic lung and respiratory defects of variable severity in mouse models of osteogenesis imperfecta

Type I collagen alterations cause osteogenesis imperfecta (OI), a connective tissue disorder characterized by severe bone fragility. Patients with OI can suffer from significant pulmonary manifestations including severe respiratory distress in the neonatal period and a progressive decline in respiratory function in adulthood. We and others have shown intrinsic lung defects in some mouse models of OI. In this large study, we performed histological, histomorphometric, microcomputed tomography and invasive studies on oim/+, Col1a2+/G610C , CrtapKO and oim/oim mice, mimicking mild to moderate to severe OI, with the overall goal of determining the extent of their pulmonary and respiratory mechanics defects and whether these defects correlate with the skeletal disease severity and affect each sex equally. Although with variable severity, OI lung histology consistently showed alveolar simplification with enlarged acinar airspace and reduced alveolar surface. Numerous respiratory mechanics parameters, including respiratory system resistance and elastance, tissue damping, inspiratory capacity, total lung capacity, and others, were significantly and similarly impacted in CrtapKO and oim/oim but not in oim/+ or Col1a2+/G610C compared to control mice. Our data indicate that the impact of type I collagen alterations and OI on lung morphology and function positively correlate with the severity of the extracellular matrix deficiency. Moreover, the respiratory defects were more pronounced in male compared to female mice. It will be important to determine whether our observations in mice translate to OI patients and to dissect the respective contribution of intrinsic lung defects vs. extrinsic skeletal defects to impaired lung function in OI. KEY POINTS: Different type I collagen alterations in mouse models of osteogenesis imperfecta (OI) cause similar abnormal lung histology, with alveolar simplification and reduced alveolar surface, reminiscent of emphysema. Several respiratory mechanics parameters are altered in mouse models of OI. The impact of type I collagen alterations and OI on lung morphology and function positively correlate with the severity of the extracellular matrix deficiency. Respiratory defects were more pronounced in male compared to female mice. It will be important to determine whether our observations in mice translate to OI patients and to dissect the respective contribution of intrinsic lung defects vs. extrinsic skeletal defects to impaired lung function in OI.

Ogerin mediated inhibition of TGF-β(1) induced myofibroblast differentiation is potentiated by acidic pH

Transforming growth factor beta (TGF-β) induced myofibroblast differentiation is central to the pathological scarring observed in Idiopathic Pulmonary Fibrosis (IPF) and other fibrotic diseases. Our lab has recently identified expression of GPR68 (Ovarian Cancer Gene Receptor 1, OGR1), a pH sensing G-protein coupled receptor, as a negative regulator of TGF-β induced profibrotic effects in primary human lung fibroblasts (PHLFs). We therefore hypothesized that small molecule activators of GPR68 would inhibit myofibroblast differentiation. Ogerin is a positive allosteric modulator (PAM) of GPR68, inducing a leftward shift of the dose response curve to proton induced signaling. Using PHLFs derived from patients with both non-fibrotic and IPF diagnoses, we show that Ogerin inhibits, and partially reverses TGF-β induced myofibroblast differentiation in a dose dependent manner. This occurs at the transcriptional level without inhibition of canonical TGF-β induced SMAD signaling. Ogerin induces PKA dependent CREB phosphorylation, a marker of Gαs pathway activation. The ability of Ogerin to inhibit both basal and TGF-β induced collagen gene transcription, and induction of Gαs signaling is enhanced at an acidic pH (pH 6.8). Similar findings were also found using fibroblasts derived from dermal, intestinal, and orbital tissue. The biological role of GPR68 in different tissues, cell types, and disease states is an evolving and emerging field. This work adds to the understanding of Gαs coupled GPCRs in fibrotic lung disease, the ability to harness the pH sensing properties of GPR68, and conserved mechanisms of fibrosis across different organ systems.

Differential roles for lysyl oxidase (like), family members in chronic obstructive pulmonary disease; from gene and protein expression to function

Chronic obstructive pulmonary disease (COPD) is characterized by long-term airflow obstruction with cigarette smoke as a key risk factor. Extracellular matrix (ECM) alterations in COPD may lead to small airway wall fibrosis. Altered collagen cross-linking, potentially mediated by the lysyl oxidase (LO) family of enzymes (LOX, LOXL1-4), orchestrates disturbed ECM homeostasis. In this study, we investigated the effects of smoking status and presence and severity of COPD on LOs gene and protein expression in the airways and the impact of LOs inhibition on airway contraction in an ex vivo mouse model. We used gene expression data from bronchial brushings, airway smooth muscle (ASM) cells in vitro and immunohistochemistry in lung tissue to assess smoke- and COPD-associated differences in LOs gene and protein expression in the small airways. We found higher LOX expression in current- compared to ex-smokers and higher LOXL1 expression in COPD compared to non-COPD patients. LOX and LOXL2 expression were upregulated in COPD ASM cells treated with cigarette smoke extract. LOXL1 and LOXL2 protein levels were higher in small airways from current- compared to non-smokers. In COPD patients, higher LOXL1 and lower LOX protein levels were observed, but no differences for LOXL2, LOXL3, and LOXL4 protein were detected in small airways. Inhibiting LOs activity increased airway contraction in murine lung slices. COPD-associated changes in LOs, in particular LOX and LOXL1, may be related to smoking and contribute to impaired airway function, providing potential novel targets for preventing or treating small airways changes in COPD.

Cell Inertia: Predicting Cell Distributions in Lung Vasculature to Optimize Re-endothelialization

We created a transient computational fluid dynamics model featuring a particle deposition probability function that incorporates inertia to quantify the transport and deposition of cells in mouse lung vasculature for the re-endothelialization of the acellular organ. Our novel inertial algorithm demonstrated a 73% reduction in cell seeding efficiency error compared to two established particle deposition algorithms when validated with experiments based on common clinical practices. We enhanced the uniformity of cell distributions in the lung vasculature by increasing the injection flow rate from 3.81 ml/min to 9.40 ml/min. As a result, the cell seeding efficiency increased in both the numerical and experimental results by 42 and 66%, respectively.

Air pollution particles hijack peroxidasin to disrupt immunosurveillance and promote lung cancer

Although fine particulate matter (FPM) in air pollutants and tobacco smoke is recognized as a strong carcinogen and global threat to public health, its biological mechanism for inducing lung cancer remains unclear. Here, by investigating FPM's bioactivities in lung carcinoma mice models, we discover that these particles promote lung tumor progression by inducing aberrant thickening of tissue matrix and hampering migration of antitumor immunocytes. Upon inhalation into lung tissue, these FPM particles abundantly adsorb peroxidasin (PXDN) - an enzyme mediating type IV collagen (Col IV) crosslinking - onto their surface. The adsorbed PXDN exerts abnormally high activity to crosslink Col IV via increasing the formation of sulfilimine bonds at the NC1 domain, leading to an overly dense matrix in the lung tissue. This disordered structure decreases the mobility of cytotoxic CD8+ T lymphocytes into the lung and consequently impairs the local immune surveillance, enabling the flourishing of nascent tumor cells. Meanwhile, inhibiting the activity of PXDN abolishes the tumor-promoting effect of FPM, indicating the key impact of aberrant PXDN activity on the tumorigenic process. In summary, our finding elucidates a new mechanism for FPM-induced lung tumorigenesis and identifies PXDN as a potential target for treatment or prevention of the FPM-relevant biological risks.

Stiffness reduction and collagenase resistance of aging lungs measured using scanning acoustic microscopy

Lung tissue stiffness is altered with aging. Quantitatively evaluating lung function is difficult using a light microscope (LM) alone. Scanning acoustic microscope (SAM) calculates the speed-of-sound (SOS) using sections to obtain histological images by plotting SOS values on the screen. As SOS is positively correlated with stiffness, SAM has a superior characteristic of simultaneously evaluating tissue stiffness and structure. SOS images of healthy bronchioles, arterioles, and alveoli were compared among young, middle-aged, and old lung sections. Formalin-fixed, paraffin-embedded (FFPE) sections consistently exhibited relatively higher SOS values than fresh-frozen sections, indicating that FFPE became stiffer but retained the relative stiffness reflecting fresh samples. All lung components exhibited gradually declining SOS values with aging and were associated with structural alterations such as loss of smooth muscles, collagen, and elastic fibers. Moreover, reaction to collagenase digestion resulted in decreased SOS values. SOS values of all components were significantly reduced in young and middle-aged groups, whereas no significant reduction was observed in the old group. Protease damage in the absence of regeneration or loss of elastic components was present in old lungs, which exbited dilated bronchioles and alveoli. Aging lungs gradually lose stiffness with decreasing structural components without exposure to specific insults such as inflammation.

Collagen fibril assembly: New approaches to unanswered questions

Collagen fibrils are essential for metazoan life. They are the largest, most abundant, and most versatile protein polymers in animals, where they occur in the extracellular matrix to form the structural basis of tissues and organs. Collagen fibrils were first observed at the turn of the 20th century. During the last 40 years, the genes that encode the family of collagens have been identified, the structure of the collagen triple helix has been solved, the many enzymes involved in the post-translational modifications of collagens have been identified, mutations in the genes encoding collagen and collagen-associated proteins have been linked to heritable disorders, and changes in collagen levels have been associated with a wide range of diseases, including cancer. Yet despite extensive research, a full understanding of how cells assemble collagen fibrils remains elusive. Here, we review current models of collagen fibril self-assembly, and how cells might exert control over the self-assembly process to define the number, length and organisation of fibrils in tissues.

Pathophysiology of respiratory failure in patients with osteogenesis imperfecta: a systematic review

INTRODUCTION

Respiratory failure is a major cause of death in patients with Osteogenesis Imperfecta. Moreover, respiratory symptoms seem to have a dramatic impact on their quality of life. It has long been thought that lung function disorders in OI are mainly due to changes in the thoracic wall, caused by bone deformities. However, recent studies indicate that alterations in the lung itself can also undermine respiratory health.

OBJECTIVES

Is there any intrapulmonary alteration in Osteogenesis Imperfecta that can explain decreased pulmonary function? The aim of this systematic literature review is to investigate to what extent intrapulmonary or extrapulmonary thoracic changes contribute to respiratory dysfunction in Osteogenesis Imperfecta.

METHODS

A literature search (in PubMed, Embase, Web of Science, and Cochrane), which included articles from inception to December 2020, was performed in accordance with the PRISMA guidelines.

RESULTS

Pulmonary function disorders have been described in many studies as secondary to scoliosis or to thoracic skeletal deformities. The findings of this systematic review suggest that reduced pulmonary function can also be caused by a primary pulmonary problem due to intrinsic collagen alterations.

CONCLUSIONS

Based on the most recent studies, the review indicates that pulmonary defects may be a consequence of abnormal collagen type I distorting the intrapulmonary structure of the lung. Lung function deteriorates further when intrapulmonary defects are combined with severe thoracic abnormalities. This systematic review reveals novel findings of the underlying pathological mechanism which have clinical and diagnostic implications for the assessment and treatment of pulmonary function disorders in Osteogenesis Imperfecta.KEY MESSAGESDecreased pulmonary function in Osteogenesis Imperfecta can be attributed to primary pulmonary defects due to intrapulmonary collagen alterations and not solely to secondary problems arising from thoracic skeletal dysplasia.Type I collagen defects play a crucial role in the development of the lung parenchyma and defects, therefore, affect pulmonary function. More awareness is needed among physicians about pulmonary complications in Osteogenesis Imperfecta to develop novel concepts on clinical and diagnostic assessment of pulmonary functional disorders.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Second harmonic generation imaging of collagen scaffolds within the alveolar ducts of healthy and emphysematous mouse lungs

The alveolar ducts are connected to peripheral septal fibers which extend from the visceral pleura into interlobular septa, and are anchored to axial fibers in the small airways. Together these axial and septal fibers constitute a fiber continuum that provides tension and integrity throughout the lung. Building on the observations that alveolar ducts associated with sub-pleural alveoli are orientated perpendicular to the visceral pleura, and in parallel to each other, the goal of the present study was to investigate the nature of the collagen fiber organization within sub-pleural alveolar ducts in healthy control and elastase-induced emphysema murine lungs. Employing three-dimensional second harmonic generation imaging, the structural arrangement of fibrilar collagen fibers could be visualized in cleared murine lungs. In healthy control lungs, fibrilar collagen fibers within alveolar mouths formed the coiled collagen structure within the alveolar duct. In the elastase-treated emphysema lungs, there was loss of fibrilar collagen fibers (p < 0.01) and disruption of collagens structural organization as measured by the fibrillar collagen length (p < 0.01) and entropy (p < 0.01). Compared to the alveolar ducts from healthy controls, there was a significant increase in the area of cells (nm², p < 0.001), and area of cells with cytoplasmic granules (nm², p < 0.001) compared to emphysematous lungs. These results are consistent with the idea that one of the major contributors to the progressive loss of alveolar surfaces and elastic recoil in the emphysematous lung is loss of the structural integrity of the collagen scaffold that maintains the spatial relationships important for cell survival and lung function.

HSP47: a potential target for fibrotic diseases and implications for therapy

Introduction: Chronic fibrotic disorders are challenging clinical problems. The major challenge is the identification of specific targets expressed selectively in fibrotic tissues. Collagen accumulation is the hallmark fibrosis. HSP47 is a collagen-specific chaperon with critical role in collagen folding. This review discusses the anti-fibrotic potential of HSP47. Areas covered: This review compiles data retrieved from the PubMed database with keywords 'HSP47+fibrosis' from 01/2005 to 06/2020. We examined 1) collagen biology and its role in fibrotic diseases, 2) HSP47 role in fibrosis, 3) HSP47 inhibition strategies and 4) clinical investigations. The identification of the HSP47-collagen binding site led to the development of methods to screen HSP47 inhibitors with anti-fibrotic potential. Specific in vivo  delivery systems of HSP47 siRNA to fibrotic tissue reduced collagen production/secretion associated with fibrosis inhibition in preclinical models. This strategy is about to be tested in clinical trials. Expert opinion: As a collagen-specific chaperon, HSP47 is a promising therapeutic target in fibrosis. Preclinical models have shown encouraging anti-fibrotic results. Anti-HSP47 strategies need to be further evaluated in clinical trials. The increase in circulating-HSP47 in lung fibrosis patients highlights the potential of HSP47 as a noninvasive biomarker and may represent an important step toward personalized medicine in fibrotic disorders.

Compact portable multiphoton microscopy reveals histopathological hallmarks of unprocessed lung tumor tissue in real time

During lung cancer operations a rapid and reliable assessment of tumor tissue can reduce operation time and potentially improve patient outcomes. We show that third harmonic generation (THG), second harmonic generation (SHG) and two-photon excited autofluorescence (2PEF) microscopy reveals relevant, histopathological information within seconds in fresh unprocessed human lung samples. We used a compact, portable microscope and recorded images within 1 to 3 seconds using a power of 5 mW. The generated THG/SHG/2PEF images of tumorous and nontumorous tissues are compared with the corresponding standard histology images, to identify alveolar structures and histopathological hallmarks. Cellular structures (tumor cells, macrophages and lymphocytes) (THG), collagen (SHG) and elastin (2PEF) are differentiated and allowed for rapid identification of carcinoid with solid growth pattern, minimally enlarged monomorphic cell nuclei with salt-and-pepper chromatin pattern, and adenocarcinoma with lipidic and micropapillary growth patterns. THG/SHG/2PEF imaging is thus a promising tool for clinical intraoperative assessment of lung tumor tissue.

Respiratory impairment impacts QOL in osteogenesis imperfecta independent of skeletal abnormalities

Respiratory insufficiency is the leading cause death in people with osteogenesis imperfecta (OI). Adults with OI reported that respiratory symptoms negatively impacted psychosocial wellbeing and limited daily physical activities, irrespective of OI type, age, stature, or scoliosis. The impact of respiratory status on quality of life in this population warrants further investigation.

PURPOSE

Respiratory insufficiency is the leading cause of mortality in osteogenesis imperfecta (OI), a heterogeneous group of heritable connective tissue disorders characterized by fractures, bone fragility, and scoliosis. There is little research on how respiratory health influences daily life in this population. This study explores the relationship between respiratory function and quality of life in adults with OI.

METHODS

One hundred fifty-seven adults with OI completed the St. George's Respiratory Questionnaire (SGRQ) and provided demographic and health information through REDCap. SGRQ scores were compared to reference scores for the general population, and comparisons were made between OI type, presence of scoliosis, stature, and other factors such as age or comorbidities.

RESULTS

Average age was 45.87 years (range 19-81). Respondents scored worse on average (32 ± 23) than the normative data (6 ± 1). Those with type I OI scored better than those with type IV (p = 0.002) or type III (p = 0.024). Total scores correlated with age, activity level, assistive device use, and presence of pulmonary or cardiac comorbidities but did not correlate with stature or degree of scoliosis.

CONCLUSION

Respiratory symptoms negatively impact both psychosocial wellbeing in the OI population and limit daily physical activity. These limitations occur irrespective of their OI type, age, stature, or scoliosis and reflect the dramatic impact of respiratory status on quality of life for people with OI. Future studies should examine the etiology of respiratory insufficiency in this population so guidelines for management can be established.

ADAM10 is indispensable for longitudinal bone growth in mice

Skeletal development is a highly sophisticated process in which the expression of a variety of growth factors, signaling molecules, and extracellular matrix proteins is spatially and temporally orchestrated. In the present study, we show that ADAM10, a transmembrane protease that is critically involved in the functional regulation of various membrane-bound molecules, plays an essential role in the longitudinal growth of long bones and in skeletal development. We found that mutant mice lacking ADAM10 in osteochondroprogenitors exhibited marked growth retardation and had shorter long bones than the control mice. Histomorphometric analysis revealed that the mutant mice had a shorter hypertrophic zone and that their hypertrophic chondrocytes were smaller in size than those of the control mice. Unexpectedly, we found that the mRNA expression of the chemokine CXCL12 and its receptor CXCR4 were significantly reduced in cartilage tissues lacking ADAM10. Further, exogenous supplementation of recombinant CXCL12 rescued the defect in the ADAM10-deficient growth plate in an ex vivo culture model. Taken together, our data show a previously unknown role for ADAM10 in skeletal development that involves its regulation of the CXCL12 and CXCR4 signaling pathway.

Respiratory defects in the CrtapKO mouse model of osteogenesis imperfecta

Respiratory disease is a leading cause of mortality in patients with osteogenesis imperfecta (OI), a connective tissue disease that causes severely reduced bone mass and is most commonly caused by dominant mutations in type I collagen genes. Previous studies proposed that impaired respiratory function in OI patients was secondary to skeletal deformities; however, recent evidence suggests the existence of a primary lung defect. Here, we analyzed the lung phenotype of Crtap knockout (KO) mice, a mouse model of recessive OI. While we confirm changes in the lung parenchyma that are reminiscent of emphysema, we show that CrtapKO lung fibroblasts synthesize type I collagen with altered posttranslation modifications consistent with those observed in bone and skin. Unrestrained whole body plethysmography showed a significant decrease in expiratory time, resulting in an increased ratio of inspiratory time over expiratory time and a concomitant increase of the inspiratory duty cycle in CrtapKO compared with WT mice. Closed-chest measurements using the forced oscillation technique showed increased respiratory system elastance, decreased respiratory system compliance, and increased tissue damping and elasticity in CrtapKO mice compared with WT. Pressure-volume curves showed significant differences in lung volumes and in the shape of the curves between CrtapKO mice and WT mice, with and without adjustment for body weight. This is the first evidence that collagen defects in OI cause primary changes in lung parenchyma and several respiratory parameters and thus negatively impact lung function.

Defective Fibrillar Collagen Organization by Fibroblasts Contributes to Airway Remodeling in Asthma

Rationale: Histologic stains have been used as the gold standard to visualize extracellular matrix (ECM) changes associated with airway remodeling in asthma, yet they provide no information on the biochemical and structural characteristics of the ECM, which are vital to understanding alterations in tissue function.Objectives: To demonstrate the use of nonlinear optical microscopy (NLOM) and texture analysis algorithms to image fibrillar collagen (second harmonic generation) and elastin (two-photon excited autofluorescence), to obtain biochemical and structural information on the remodeled ECM environment in asthma.Methods: Nontransplantable donor lungs from donors with asthma (n = 13) and control (n = 12) donors were used for the assessment of airway collagen and elastin fibers by NLOM, and extraction of lung fibroblasts for in vitro experiments.Measurements and Main Results: Fibrillar collagen is not only increased but also highly disorganized and fragmented within large and small asthmatic airways compared with control subjects, using NLOM imaging. Furthermore, such structural alterations are present in pediatric and adult donors with asthma, irrespective of fatal disease. In vitro studies demonstrated that asthmatic airway fibroblasts are deficient in their packaging of fibrillar collagen-I and express less decorin, important for collagen fibril packaging. Packaging of collagen fibrils was found to be more disorganized in asthmatic airways compared with control subjects, using transmission electron microscopy.Conclusions: NLOM imaging enabled the structural assessment of the ECM, and the data suggest that airway remodeling in asthma involves the progressive accumulation of disorganized fibrillar collagen by airway fibroblasts. This study highlights the future potential clinical application of NLOM to assess airway remodeling in vivo.

Collagen type-V is a danger signal associated with primary graft dysfunction in lung transplantation

BACKGROUND

Primary graft dysfunction (PGD) is the leading cause of early mortality after lung transplantation. Anti-collagen type-V (col(V)) immunity has been observed in animal models of ischemia-reperfusion injury (IRI) and in PGD. We hypothesized that collagen type-V is an innate danger signal contributing to PGD pathogenesis.

METHODS

Anti-col(V) antibody production was detected by flow cytometric assay following cultures of murine CD19+ splenic cells with col.(V). Responding murine B cells were phenotyped using surface markers. RNA-Seq analysis was performed on murine CD19+ cells. Levels of anti-col(V) antibodies were measured in 188 recipients from the Lung Transplant Outcomes Group (LTOG) after transplantation.

RESULTS

Col(V) induced rapid production of anti-col(V) antibodies from murine CD19+ B cells. Subtype analysis demonstrated innate B-1 B cells bound col.(V). Col(V) induced a specific transcriptional signature in CD19+ B cells with similarities to, yet distinct from, B cell receptor (BCR) stimulation. Rapid de novo production of anti-col(V) Abs was associated with an increased incidence of clinical PGD after lung transplant.

CONCLUSIONS

This study demonstrated that col.(V) is an rapidly recognized by B cells and has specific transcriptional signature. In lung transplants recipients the rapid seroconversion to anti-col(V) Ab is linked to increased risk of grade 3 PGD.

Pulmonary environmental cues drive group 2 innate lymphoid cell dynamics in mice and humans

Group 2 innate lymphoid cells (ILC2s) are enriched in mucosal tissues (e.g., lung) and respond to epithelial cell-derived cytokines initiating type 2 inflammation. During inflammation, ILC2 numbers are increased in the lung. However, the mechanisms controlling ILC2 trafficking and motility within inflamed lungs remain unclear and are crucial for understanding ILC2 function in pulmonary immunity. Using several approaches, including lung intravital microscopy, we demonstrate that pulmonary ILC2s are highly dynamic, exhibit amoeboid-like movement, and aggregate in the lung peribronchial and perivascular spaces. They express distinct chemokine receptors, including CCR8, and actively home to CCL8 deposits located around the airway epithelium. Within lung tissue, ILC2s were particularly motile in extracellular matrix-enriched regions. We show that collagen-I drives ILC2 to markedly change their morphology by remodeling their actin cytoskeleton to promote environmental exploration critical for regulating eosinophilic inflammation. Our study provides previously unappreciated insights into ILC2 migratory patterns during inflammation and highlights the importance of environmental guidance cues in the lung in controlling ILC2 dynamics.

Integrated lung tissue mechanics one piece at a time: Computational modeling across the scales of biology

The lung is a delicately balanced and highly integrated mechanical system. Lung tissue is continuously exposed to the environment via the air we breathe, making it susceptible to damage. As a consequence, respiratory diseases present a huge burden on society and their prevalence continues to rise. Emergent function is produced not only by the sum of the function of its individual components but also by the complex feedback and interactions occurring across the biological scales - from genes to proteins, cells, tissue and whole organ - and back again. Computational modeling provides the necessary framework for pulling apart and putting back together the pieces of the body and organ systems so that we can fully understand how they function in both health and disease. In this review, we discuss models of lung tissue mechanics spanning from the protein level (the extracellular matrix) through to the level of cells, tissue and whole organ, many of which have been developed in isolation. This is a vital step in the process but to understand the emergent behavior of the lung, we must work towards integrating these component parts and accounting for feedback across the scales, such as mechanotransduction. These interactions will be key to unlocking the mechanisms occurring in disease and in seeking new pharmacological targets and improving personalized healthcare.

Infrared micro-spectroscopy of human tissue: principles and future promises

This article summarizes the methods employed, and the progress achieved over the past two decades in applying vibrational (Raman and IR) micro-spectroscopy to problems of medical diagnostics and cellular biology. During this time, several research groups have verified the enormous information contained in vibrational spectra; in fact, information on protein, lipid and metabolic composition of cells and tissues can be deduced by decoding the observed vibrational spectra. This decoding process is aided by the availability of computer workstations and advanced algorithms for data analysis. Furthermore, commercial instrumentation for the fast collection of both Raman and infrared micro-spectral data has enabled the collection of images of cells and tissues based solely on vibrational spectroscopic data. The progress in the field has been manifested by a steady increase in the number and quality of publications submitted by established and new research groups in vibrational spectroscopy in the biological and biomedical arenas.

Pulmonary Function and Sleep Breathing: Two New Targets for Type 2 Diabetes Care

Population-based studies showing the negative impact of type 2 diabetes (T2D) on lung function are overviewed. Among the well-recognized pathophysiological mechanisms, the metabolic pathways related to insulin resistance (IR), low-grade chronic inflammation, leptin resistance, microvascular damage, and autonomic neuropathy are emphasized. Histopathological changes are exposed, and findings reported from experimental models are clearly differentiated from those described in humans. The accelerated decline in pulmonary function that appears in patients with cystic fibrosis (CF) with related abnormalities of glucose tolerance and diabetes is considered as an example to further investigate the relationship between T2D and the lung. Furthermore, a possible causal link between antihyperglycemic therapies and pulmonary function is examined. T2D similarly affects breathing during sleep, becoming an independent risk factor for higher rates of sleep apnea, leading to nocturnal hypoxemia and daytime sleepiness. Therefore, the impact of T2D on sleep breathing and its influence on sleep architecture is analyzed. Finally, the effect of improving some pathophysiological mechanisms, primarily IR and inflammation, as well as the optimization of blood glucose control on sleep breathing is evaluated. In summary, the lung should be considered by those providing care for people with diabetes and raise the central issue of whether the normalization of glucose levels can improve pulmonary function and ameliorate sleep-disordered breathing. Therefore, patients with T2D should be considered a vulnerable group for pulmonary dysfunction. However, further research aimed at elucidating how to screen for the lung impairment in the population with diabetes in a cost-effective manner is needed.

Target-Specific Delivery of an Antibody That Blocks the Formation of Collagen Deposits in Skin and Lung

Regardless of the cause of organ fibrosis, its main unwanted consequence is the formation of collagen fibril-rich deposits that hamper the structure and function of affected tissues. Although many strategies have been proposed for the treatment of fibrotic diseases, no therapy has been developed, which can effectively block the formation of collagen fibril deposits. With this in mind, we recently developed an antibody-based therapy to block key interactions that drive collagen molecules into fibrils. In this study, we analyzed target specificity, which is a main parameter that defines the safe use of all antibody-based therapies in humans. We hypothesized that, regardless of the route of administration, our antibody would preferentially bind to free collagen molecules synthesized at the sites of fibrosis and have minimal off-target interactions when applied in various tissues. To test this hypothesis, we used two experimental models of organ fibrosis: (1) a keloid model, in which antibody constructs were directly implanted under the skin of nude mice and (2) an experimental model of pulmonary fibrosis, in which our antibody was administered systemically by intravenous injection. Following administration, we studied the distribution of our antibody within target and off-target sites as well as analyzed its effects on fibrotic tissue formation. We found that local and systemic application of our antibody had high specificity for targeting collagen fibrillogenesis and also appeared safe and therapeutically effective. In summary, this study provides the basis for further testing our antifibrotic antibody in a broad range of disease conditions and suggests that this treatment approach will be effective if delivered by local or systemic administration.

Increased deposition of glycosaminoglycans and altered structure of heparan sulfate in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by aberrant deposition of extracellular matrix (ECM) constituents, including glycosaminoglycans (GAGs), that may play a role in remodelling processes by influencing critical mediators such as growth factors. We hypothesize that GAGs may be altered in IPF and that this contribute to create a pro-fibrotic environment. The aim of this study was therefore to examine the fine structure of heparan sulfate (HS), chondroitin/dermatan sulfate (CS/DS) and hyaluronan (HA) in lung samples from IPF patients and from control subjects. GAGs in lung samples from severe IPF patients and donor lungs were analyzed with HPLC. HS was assessed by immunohistochemistry and collagen was quantified as hydroxyproline content. The total amount of HS, CS/DS and HA was increased in IPF lungs but there was no significant difference in the total collagen content. We found a relative increase in total sulfation of HS due to increment of 2-O, 6-O and N-sulfation and a higher proportion of sulfation in CS/DS. Highly sulfated HS was located in the border zone between denser areas and more normal looking alveolar parenchyma in basement membranes of blood vessels and airways, that were immuno-positive for perlecan, as well as on the cell surface of spindle-shaped cells in the alveolar interstitium. These findings show for the first time that both the amount and structure of glycosaminoglycans are altered in IPF. These changes may contribute to the tissue remodelling in IPF by altering growth factor retention and activity, creating a pro-fibrotic ECM landscape.

Lung-Restricted Antibodies Mediate Primary Graft Dysfunction and Prevent Allotolerance after Murine Lung Transplantation

Over one-third of lung recipients have preexisting antibodies against lung-restricted antigens: collagen (Col) type V and K-α1 tubulin (KAT). Although clinical studies have shown association of these antibodies with primary graft dysfunction (PGD), their biological significance remains unclear. We tested whether preexisting lung-restricted antibodies can mediate PGD and prevent allotolerance. A murine syngeneic (C57BL/6) or allogeneic (C57BL/6 to BALB/c) left lung transplantation model was used. Rabbit polyclonal antibodies were produced against KAT and Col-V and injected pretransplantation. T cell frequency was analyzed using enzyme-linked immunospot, whereas alloantibodies were determined using flow cytometry. Wet:dry ratio, arterial oxygenation, and histology were used to determine PGD. Preexisting Col-V or KAT, but not isotype control, antibodies lead to dose-dependent development of PGD after syngeneic lung transplantation, as evidenced by poor oxygenation and increased wet:dry ratio. Histology confirmed alveolar and capillary edema. The native right lung remained unaffected. Epitope spreading was observed where KAT antibody treatment led to the development of IL-17-producing CD4⁺ T cells and humoral response against Col-V, or vice versa. In contrast, isotype control antibody failed to induce Col-V- or KAT-specific cellular or humoral immunity. In addition, none of the mice developed immunity against a non-lung antigen, collagen type II. Preexisting lung-restricted antibodies, but not isotype control, prevented development of allotolerance using the MHC-related 1 and cytotoxic T-lymphocyte-associated protein 4-Ig regimen. Lung-restricted antibodies can induce both early and delayed lung graft dysfunction. These antibodies can also cause spreading of lung-restricted immunity and promote alloimmunity. Antibody-directed therapy to treat preexisting lung-restricted antibodies might reduce PGD after lung transplantation.

Drug-Induced Lung Toxicity

The number of blood-borne chemotherapeutic agents implicated in drug-induced lung toxicity continues to increase, although problems in detection remain. The initiation of drug-induced lung injury can have an immunologic or nonimmunologic basis. If endothelial cells are injured, interstitial pulmonary edema may result. Regardless of the source of injury, the progression of drug-induced lung toxicity is often quite similar, involving (1) parenchymal damage, (2) recruitment of inflammatory cells, and (3) progression of the inflammatory process. If the inflammatory reponse is sufficiently severe and disperse, increased collagen can be deposited in interstitial and intra-alveolar areas. The resulting attenuation of gas exchange can induce dyspnea and possibly death. Recent research suggests mediation of the fibrogenic process via cytokines such as transforming growth factor-β and tumor necrosis factor. Preliminary results demonstrating amelioration of cytokine mediated lung-induced fibrosis in animal models with appropriate antibodies suggest a possible future modality of therapy. Certain amphiphilic drugs are capable of eliciting a more specific form of lung toxicity. This class of drugs can interfere with phospholipid metabolism in pulmonary macrophages. In these cases, phospholipidosis results from phospholipid accumulation. The physiologic sequelae in human phospholipidosis is still uncertain.

NMR spectroscopy-based metabolomic study of serum in sulfur mustard exposed patients with lung disease

Sulfur mustard (SM) is a vesication chemical warfare agent for which there is currently no antidote. Despite years of research, there is no common consensus about the pathophysiological basis of chronic pulmonary disease caused by this chemical warfare agent. In this study, we combined chemometric techniques with nuclear magnetic resonance (NMR) spectroscopy to explore the metabolic profile of sera from SM-exposed patients. A total of 29 serum samples obtained from 17 SM-injured patients, and 12 healthy controls were analyzed by Random Forest. Increased concentrations of seven amino acids, glycerol, dimethylamine, ketone bodies, lactate, acetate, citrulline and creatine together with the decreased very low-density lipoproteins (VLDL) levels were observed in patients compared with control subjects. Our study reveals the metabolic profile of sera from SM-injured patients and indicates that NMR-based methods can distinguish these patients from healthy controls.

Postural variation of pulmonary diffusing capacity as a marker of lung microangiopathy in Indian patients with type 2 diabetes mellitus

INTRODUCTION

Diabetes mellitus (DM) is characterized by the presence of chronic hyperglycemia and formation of advanced glycation end products (AGEs). Interaction between AGE and its receptor leads to endothelial damage and microangiopathy. This study was undertaken to investigate the possibility of using a postural variation of diffusing capacity as an early marker of lung microangiopathy and its correlation with the level of adhesion molecules, HbA1c, duration of diabetes, and insulin resistance in type 2 DM (T2DM) patients with and without microangiopathy.

MATERIALS AND METHODS

Forty patients having T2DM without any microangiopathy (n = 20) as well as with microangiopathy (n = 20), and 22 age and sex matched healthy controls were enrolled in this cross-sectional study. Measurement of lung volumes and capacities were done. DLco was measured in sitting and supine position. Levels of vascular cell adhesion molecule-1 (VCAM-1), E-selectin, fasting glucose, and insulin were estimated in plasma of the patients and compared with controls.

RESULTS

Restrictive type of ventilatory change was observed in DM patients. Diffusing capacity (% predicted) in the supine position (P < 0.0001), postural change in DLco (P < 0.0001), and coefficient of diffusion were significantly less in DM patients as compared to controls. Plasma levels of VCAM-1 were significantly higher in DM patients without microangiopathy and negatively correlated (r = -0.4054, P = 0.0094) with Δ DLco in all diabetic subjects. All patients had significantly higher insulin resistance.

CONCLUSION

Lack of postural increase in diffusing capacity in type 2 diabetic patients along with increased VCAM-1 levels could reflect the presence of an early microangiopathy of the small pulmonary vessels.

Mesenchymal stem cells and serelaxin synergistically abrogate established airway fibrosis in an experimental model of chronic allergic airways disease

This study determined if the anti-fibrotic drug, serelaxin (RLN), could augment human bone marrow-derived mesenchymal stem cell (MSC)-mediated reversal of airway remodeling and airway hyperresponsiveness (AHR) associated with chronic allergic airways disease (AAD/asthma). Female Balb/c mice subjected to the 9-week model of ovalbumin (OVA)-induced chronic AAD were either untreated or treated with MSCs alone, RLN alone or both combined from weeks 9-11. Changes in airway inflammation (AI), epithelial thickness, goblet cell metaplasia, transforming growth factor (TGF)-β1 expression, myofibroblast differentiation, subepithelial and total lung collagen deposition, matrix metalloproteinase (MMP) expression, and AHR were then assessed. MSCs alone modestly reversed OVA-induced subepithelial and total collagen deposition, and increased MMP-9 levels above that induced by OVA alone (all p<0.05 vs OVA group). RLN alone more broadly reversed OVA-induced epithelial thickening, TGF-β1 expression, myofibroblast differentiation, airway fibrosis and AHR (all p<0.05 vs OVA group). Combination treatment further reversed OVA-induced AI and airway/lung fibrosis compared to either treatment alone (all p<0.05 vs either treatment alone), and further increased MMP-9 levels. RLN appeared to enhance the therapeutic effects of MSCs in a chronic disease setting; most likely a consequence of the ability of RLN to limit TGF-β1-induced matrix synthesis complemented by the MMP-promoting effects of MSCs.

Fate of distal lung epithelium cultured in a decellularized lung extracellular matrix

Type II cells are the defenders of the alveolus. They produce surfactant to prevent alveolar collapse, they actively transport water to prevent filling of the air sacs that would otherwise prevent gas exchange, and they differentiate to type I epithelial cells. They are an indispensable component of functional lung tissue. To understand the functionality of type II cells in isolation, we sought to track their fate in decellularized matrices and to assess their ability to contribute to barrier function by differentiation to type I alveolar epithelial cells. Rat type II cells were isolated from neonatal rat lungs by labeling with the RTII-70 surface marker and separation using a magnetic column. This produced a population of ∼50% RTII-70-positive cells accompanied by few type I epithelial cells or α-actin-positive mesenchymal cells. This population was seeded into decellularized rat lung matrices and cultured for 1 or 7 days. Culture in Dulbecco's modified Eagle's medium +10% fetal bovine serum (FBS) resulted in reduced expression of epithelial markers and increased expression of mesenchymal markers. By 7 days, no epithelial markers were visible by immunostaining; nearly all cells were α-actin positive. Gene expression for the mesenchymal markers, α-actin, vimentin, and TGF-βR, was significantly upregulated on day 1 (p=0.0005, 0.0005, and 2.342E-5, respectively). Transcript levels of α-actin and TGF-βR remained high at 7 days (p=1.364E-10 and 0.0002). Interestingly, human type II cells cultured under the same conditions showed a similar trend in the loss of epithelial markers, but did not display high expression of mesenchymal markers. Rat cells additionally showed the ability to produce and degrade the basement membrane and extracellular matrix components, such as fibronectin, collagen IV, and collagen I. Quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) showed significant increases in expression of the fibronectin and matrix metalloprotease-2 (MMP-2) genes after 1 day in culture (p=0.0135 and 0.0128, respectively) and elevated collagen I expression at 7 days (p=0.0016). These data suggest that the original type II-enriched population underwent a transition to increased expression of mesenchymal markers, perhaps as part of a survival or wound-healing program. These results suggest that additional medium components and/or the application of physiologically appropriate stimuli such as ventilation may be required to promote lung-specific epithelial phenotypes.

Extracellular matrix as a driver for lung regeneration

Extracellular matrix has manifold roles in tissue mechanics, guidance of cellular behavior, developmental biology, and regenerative medicine. Over the past several decades, various pre-clinical and clinical studies have shown that many connective tissues may be replaced and/or regenerated using suitable extracellular matrix scaffolds. More recently, decellularization of lung tissue has shown that gentle removal of cells can leave behind a "footprint" within the matrix that may guide cellular adhesion, differentiation and homing following cellular repopulation. Fundamental issues like understanding matrix composition and micro-mechanics remain difficult to tackle, largely because of a lack of available assays and tools for systematically characterizing intact matrix from tissues and organs. This review will critically examine the role of engineered and native extracellular matrix in tissue and lung regeneration, and provide insights into directions for future research and translation.

The role of miR-29 in pulmonary fibrosis

Pulmonary fibrosis is a pathological condition in which lungs become scarred due to the excess extracellular matrix (ECM) deposition and structural alterations in the interstitium of lung parenchyma. Many patients with interstitial lung diseases (ILDs) caused by long-term exposure to toxic substances, chronic infections, or autoimmune responses develop fibrosis. Etiologies for many ILDs are unknown, such as idiopathic pulmonary fibrosis (IPF), a devastating, relentless form of pulmonary fibrosis with a median survival of 2-3 years. Despite several decades of research, factors that initiate and sustain the fibrotic response in lungs remain unclear and there is no effective treatment to block progression of fibrosis. Here we summarize recent findings on the antifibrotic activity of miR-29, a small noncoding regulatory RNA, in the pathogenesis of fibrosis by regulating ECM production and deposition, and epithelial-mesenchymal transition (EMT). We also describe interactions of miR-29 with multiple profibrotic and inflammatory pathways. Finally, we review the antifibrotic activity of miR-29 in animal models of fibrosis and highlight miR-29 as a promising therapeutic reagent or target for the treatment of pulmonary fibrosis.

Cryptococcus gattii in North American Pacific Northwest: whole-population genome analysis provides insights into species evolution and dispersal

The emergence of distinct populations of Cryptococcus gattii in the temperate North American Pacific Northwest (PNW) was surprising, as this species was previously thought to be confined to tropical and semitropical regions. Beyond a new habitat niche, the dominant emergent population displayed increased virulence and caused primary pulmonary disease, as opposed to the predominantly neurologic disease seen previously elsewhere. Whole-genome sequencing was performed on 118 C. gattii isolates, including the PNW subtypes and the global diversity of molecular type VGII, to better ascertain the natural source and genomic adaptations leading to the emergence of infection in the PNW. Overall, the VGII population was highly diverse, demonstrating large numbers of mutational and recombinational events; however, the three dominant subtypes from the PNW were of low diversity and were completely clonal. Although strains of VGII were found on at least five continents, all genetic subpopulations were represented or were most closely related to strains from South America. The phylogenetic data are consistent with multiple dispersal events from South America to North America and elsewhere. Numerous gene content differences were identified between the emergent clones and other VGII lineages, including genes potentially related to habitat adaptation, virulence, and pathology. Evidence was also found for possible gene introgression from Cryptococcus neoformans var. grubii that is rarely seen in global C. gattii but that was present in all PNW populations. These findings provide greater understanding of C. gattii evolution in North America and support extensive evolution in, and dispersal from, South America.

Cryptococcus gattii emerged in the temperate North American Pacific Northwest (PNW) in the late 1990s. Beyond a new environmental niche, these emergent populations displayed increased virulence and resulted in a different pattern of clinical disease. In particular, severe pulmonary infections predominated in contrast to presentation with neurologic disease as seen previously elsewhere. We employed population-level whole-genome sequencing and analysis to explore the genetic relationships and gene content of the PNW C. gattii populations. We provide evidence that the PNW strains originated from South America and identified numerous genes potentially related to habitat adaptation, virulence expression, and clinical presentation. Characterization of these genetic features may lead to improved diagnostics and therapies for such fungal infections. The data indicate that there were multiple recent introductions of C. gattii into the PNW. Public health vigilance is warranted for emergence in regions where C. gattii is not thought to be endemic.

Lung collagens perpetuate pulmonary fibrosis via CD204 and M2 macrophage activation

Idiopathic pulmonary fibrosis is characterized by abundant collagen production and accumulation of alternatively activated macrophages (M2) in the lower respiratory tract. Mechanisms as to how alveolar macrophages are activated by collagen breakdown products are unknown. Alveolar macrophages were obtained by bronchoalveolar lavage from 30 patients with idiopathic pulmonary fibrosis (IPF) and 37 healthy donors (HD). Alveolar macrophages were cultured in the presence of collagen type I, III, IV and V monomers w/wo a neutralizing antibody against scavenger receptor I class A (CD204). Culture supernatants were assayed for the M2 markers CCL18, CCL2, and interleukin-1 receptor antagonist (IL-1ra) by ELISA. Furthermore, expression of phospho-Akt was measured using ELISA and expression of CD204 by RT-PCR and flow cytometry. Stimulation with collagen type I and III monomers significantly up-regulated CCL18, IL-1ra production of alveolar macrophages. Furthermore, expression of CCL2 and CD204 were up-regulated by collagen type I exposure. In addition, collagen type I stimulation increased pospho-Akt expression. Collagen type I effects were abrogated by neutralizing antiCD204 and a non-selective Phosphatidylinositide 3-kinase inhibitor (LY294002). Spontaneous CD204 expression of alveolar macrophages was significantly increased in patients with IPF. In conclusion, our findings demonstrate that monomeric collagen type I via CD204 induces phospho-Akt expression shifting alveolar macrophages to the profibrotic M2 type. Innate immune responses induced by collagen monomers might perpetuate pulmonary fibrosis.

Structure and composition of pulmonary arteries, capillaries, and veins

The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in general, this vasculature is thin-walled, structure is nonetheless complex. Contributions to structure (and thus potentially to function) from cells other than endothelial and smooth muscle cells as well as those from the extracellular matrix should be considered. This review is multifaceted, bringing together information regarding (i) classification of pulmonary vessels, (ii) branching geometry in the pulmonary vascular tree, (iii) a quantitative view of structure based on morphometry of the vascular wall, (iv) the relationship of nerves, a variety of interstitial cells, matrix proteins, and striated myocytes to smooth muscle and endothelium in the vascular wall, (v) heterogeneity within cell populations and between vascular compartments, (vi) homo- and heterotypic cell-cell junctional complexes, and (vii) the relation of the pulmonary vasculature to that of airways. These issues for pulmonary vascular structure are compared, when data is available, across species from human to mouse and shrew. Data from studies utilizing vascular casting, light and electron microscopy, as well as models developed from those data, are discussed. Finally, the need for rigorous quantitative approaches to study of vascular structure in lung is highlighted.

Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis

Pulmonary fibrosis is a vexing clinical problem with no proven therapeutic options. In the normal lung there is continuous collagen synthesis and collagen degradation, and these two processes are precisely balanced to maintain normal tissue architecture. With lung injury there is an increase in the rate of both collagen production and collagen degradation. The increase in collagen degradation is critical in preventing the formation of permanent scar tissue each time the lung is exposed to injury. In pulmonary fibrosis, collagen degradation does not keep pace with collagen production, resulting in extracellular accumulation of fibrillar collagen. Collagen degradation occurs through both extracellular and intracellular pathways. The extracellular pathway involves cleavage of collagen fibrils by proteolytic enzyme including the metalloproteinases. The less-well-described intracellular pathway involves binding and uptake of collagen fragments by fibroblasts and macrophages for lysosomal degradation. The relationship between these two pathways and their relevance to the development of fibrosis is complex. Fibrosis in the lung, liver, and skin has been associated with an impaired degradative environment. Much of the current scientific effort in fibrosis is focused on understanding the pathways that regulate increased collagen production. However, recent reports suggest an important role for collagen turnover and degradation in regulating the severity of tissue fibrosis. The objective of this review is to evaluate the roles of the extracellular and intracellular collagen degradation pathways in the development of fibrosis and to examine whether pulmonary fibrosis can be viewed as a disease of impaired matrix degradation rather than a disease of increased matrix production.

What drives the peripheral lung-remodeling process in chronic obstructive pulmonary disease?

The smaller airways (<2 mm in diameter) offer little resistance in normal lungs but become the major site of obstruction in chronic obstructive pulmonary disease (COPD). We examined bronchiolar remodeling in COPD by combining quantitative histology, micro-computed tomography (CT), and gene expression studies. Volumes of bronchiolar tissue, total collagen, collagen-1, and collagen-3 were measured in lung tissue from 52 patients with different levels of COPD severity. Micro-CT was used to measure the number and lumen area of terminal bronchioles in four lungs removed before lung transplantation and in four donor lungs that served as controls. Laser capture microdissection provided 136 paired samples of bronchiolar and surrounding lung tissue from 63 patients and the gene expression of a cluster of tissue repair genes was compared. This study shows that total bronchiolar tissue decreased with progression of COPD and was associated with a reduction in total collagen and relative increase in collagen-3 over collagen-1. The micro-CT studies showed a 10-fold reduction in terminal bronchiolar number and a 100-fold reduction in lumen area. Interestingly, most genes associated with tissue accumulation during repair decreased their expression in both airways and in the surrounding lung as FEV(1) declined, but eight genes previously associated with COPD increased expression in the surrounding lung tissue. Our study shows that small airway remodeling is associated with narrowing and obliteration of the terminal bronchioles that begins before emphysematous destruction in COPD and in relation to differential expression of tissue repair genes in the airways and surrounding lung.

Asthma therapy and airway remodeling

Asthma is characterized by variable degrees of chronic inflammation and structural alterations in the airways. The most prominent abnormalities include epithelial denudation, goblet cell metaplasia, subepithelial thickening, increased airway smooth muscle mass, bronchial gland enlargement, angiogenesis, and alterations in extracellular matrix components, involving large and small airways. Chronic inflammation is thought to initiate and perpetuate cycles of tissue injury and repair in asthma, although remodeling may also occur in parallel with inflammation. In the absence of definite evidence on how different remodeling features affect lung function in asthma, the working hypothesis should be that structural alterations can lead to the development of persistent airway hyperresponsiveness and fixed airway obstruction. It is still unanswered whether and when to begin treating patients with asthma to prevent or reverse deleterious remodeling, which components of remodeling to target, and how to monitor remodeling. Consequently, efforts are being made to understand better the effects of conventional anti-inflammatory therapies, such as glucocorticosteroids, on airway structural changes. Animal models, in vitro studies, and some clinical studies have advanced present knowledge on the cellular and molecular pathways involved in airway remodeling. This has encouraged the development of biologicals aimed to target various components of airway remodeling. Progress in this area requires the explicit linking of modern structure-function analysis with innovative biopharmaceutical approaches.

Localization of precursor proteins and mRNA of type I and III collagens in usual interstitial pneumonia and sarcoidosis

The aim of this study was to assess and compare the accumulation and distribution of newly synthesized type I and III collagens in usual interstitial pneumonia (UIP) and pulmonary sarcoidosis. Lung biopsies from 10 patients with UIP and 13 patients with sarcoidosis were investigated by immunohistochemical technique and mRNA in situ hybridization. The antibodies for the aminoterminal propeptide of type I procollagen and the aminoterminal propeptide of type III procollagen (PINP and PIIINP, respectively) were used. When compared to healthy lung, levels of type I pN- and type III pN-collagens were increased in both of these disorders. Type I procollagen was mostly present as intracellular spots in newly formed fibrosis in UIP while type III pN-collagen was expressed extracellularly underneath metaplastic alveolar epithelium. Type I procollagen was present intracellularly within and around the granulomas of sarcoidosis, whereas type III pN-collagen was expressed extracellularly, mainly around the granulomas. mRNAs of both collagens colocalized with the precursor proteins. We conclude that the expression of precursor proteins and mRNA of type I and type III collagens is increased in UIP and sarcoidosis, reflecting mainly active synthesis of these collagens in different areas of the lung.

Pediatric lung disease: from proteinases to pulmonary fibrosis

One distinctive outcome of interstitial lung diseases in childhood is the abnormal accumulation of pulmonary extracellular matrix. The clinical consequence of such excessive connective tissue accumulation is known as pulmonary fibrosis. While numerous aspects of its pathogenesis have become familiar, many key events involved in its inception and progression still remain unclear. There is now compelling evidence that lung damage due to uncontrolled proteolysis may help drive critical processes that regulate fibrotic matrix remodeling. In this regard, a number of proteinases have been implicated in promoting both the initial lung injury and the fibroproliferative repair that follows. This review summarizes the knowledge of how different matrix-targeting enzymes may act to influence the development of pediatric pulmonary fibrosis. Understanding the scientific basis of this complex process may highlight opportunities to limit unwanted proteolysis and the intensity of its fibrotic sequelae.

Lung tissue mechanics and extracellular matrix composition in a murine model of silicosis

The dynamic mechanical properties of lung tissue and its contents of collagen and elastic fibers were studied in strips prepared from mice instilled intratracheally with saline (C) or silica [15 (S15) and 30 days (S30) after instillation]. Resistance, elastance, and hysteresivity were studied during oscillations at different frequencies on S15 and S30. Elastance increased from C to silica groups but was similar between S15 and S30. Resistance was augmented from C to S15 and S30 and was greater in S30 than in S15 at higher frequencies. Hysteresivity was higher in S30 than in C and S15. Silica groups presented a greater amount of collagen than did C. Elastic fiber content increased progressively along time. This increment was related to the higher amount of oxytalan fibers at 15 and 30 days, whereas elaunin and fully developed elastic fibers were augmented only at 30 days. Silicosis led not only to pulmonary fibrosis but also to fibroelastosis, thus assigning a major role to the elastic system in the silicotic lung.

Collagen metabolism disturbances are accompanied by an increase in prolidase activity in lung carcinoma planoepitheliale

One of the consequences of neoplastic transformation is deregulation of tissue collagen metabolism. Although metalloproteinases initiate the breakdown of collagen in lung carcinoma, the final step of collagen degradation is mediated by prolidase (E.C.3.4.13.9). We investigated whether prolidase activity could reflect disturbances of collagen metabolism in human lung carcinoma planoepitheliale (Ca pl.). Ten human lung Ca pl. and 10 samples of normal lung parenchyma were compared with respect to prolidase activity and expression (western immunoblot), the content of collagen and collagen degradation products (free and bound hydroxyproline determination), beta1 integrin subunit expression (western immunoblot) and collagenolytic activity (zymography). An increase in collagen content (66%, P < 0.05), free proline pool (50%, P < 0.05) and collagenolytic activity was accompanied by a significant increase in the prolidase activity (106%, P < 0.05) and its expression in Ca pl. No differences were found between Ca pl. and the control lung tissue with respect to beta1 integrin expression. Prolidase activity may reflect disturbances in tissue collagen metabolism in lung Ca pl. and it may, therefore, serve as a sensitive marker of the disease.

Influence of alternatively and classically activated macrophages on fibrogenic activities of human fibroblasts

Activated macrophages regulate fibrogenesis by providing cytokines and growth factors that modulate the proliferation and collagen synthesis of fibroblasts. However, macrophages can be activated in a classical pathway induced by LPS or IFN-gamma and an alternative pathway induced by IL-4 or glucocorticoid. Differently activated macrophages display distinct biological features. To clarify the difference between these two subsets of macrophages in the regulatory mechanisms controlling fibrogenesis, human peripheral blood monocytes were used as the source of macrophages and cocultivation of differently activated macrophages and a fibroblast cell line, WI-38, was performed. Alternatively activated macrophages increased the proliferation index and collagen synthesis of cocultivated WI-38 cells in comparison to untreated monocytes, while classically activated macrophages markedly reduced collagen production of cocultivated WI-38 cells. Additionally, mRNA expression and protein production of TGF-beta(1), PDGF-AA, and PDGF-BB were elevated in alternatively activated macrophages in parallel to their profibrogenic effects. In contrast, expression and production of TNF-alpha, as well as MMP-7, were enhanced in classically activated macrophages. These findings suggested that alternatively activated macrophages enhance fibrogenesis of fibroblasts by providing profibrogenic factors, while classically activated macrophages inhibit fibrogenesis of fibroblasts by releasing antifibrogenic or fibrolytic factors.