Kristina Rydell-Törmänen

Mice Lacking 12/15-Lipoxygenase Have Attenuated Airway Allergic Inflammation and Remodeling

Arachidonate 15-lipoxygenase (LO)-1 has been implicated in allergic inflammation and asthma. The overall effect of 15-LO in allergic inflammation in vivo is, however, unclear. This study investigates systemic allergen sensitization and local allergic airway inflammation and remodeling in mice lacking the murine 12/15-LO, the ortholog to human 15-LO-1. Upon systemic sensitization with intraperitoneal ovalbumin, 12/15-LO-/- mice produced elevated levels of allergen-specific immunoglobulin E compared with wild-type (Wt) controls. However, when challenged with repeated aerosolized allergen, sensitized 12/15-LO-/- mice had an impaired development of airway allergic inflammation compared with Wt controls, as indicated by reduced bronchoalveolar lavage fluid leukocytes (eosinophils, lymphocytes, macrophages) and Th2 cytokines (IL-4, IL-5, IL-13), as well as tissue eosinophils. Allergen-induced airway epithelial proliferation was also significantly attenuated in 12/15-LO-/- mice, whereas goblet cell hyperplasia was unaffected. However, 12/15-LO-/- mice had significantly reduced luminal mucus secretions compared with Wt controls. The repeated allergen challenges resulted in a dramatic increase of alpha-smooth muscle actin-positive alveolar cells in the peripheral airways, a phenomenon that was significantly less developed in 12/15-LO-/- mice. In conclusion, our data suggest that 12/15-LO-/- mice, although having a fully developed systemic sensitization, did not establish a fully developed allergic airway inflammation and associated manifestations of central and peripheral airway remodeling. These data suggest that 12/15-LO-derived metabolites play an important pathophysiologic role in allergen-induced inflammation and remodeling. Hence, pharmacologic targeting of the human 15-LO-1 may represent an attractive therapeutic strategy to control inflammation and remodeling in asthma.

Induction of Vascular Remodeling in the Lung by Chronic House Dust Mite Exposure.

Structural changes to the lung are associated with chronic asthma. In addition to alterations to the airway wall, asthma is associated with vascular modifications, although this aspect of remodeling is poorly understood. We sought to evaluate the character and kinetics of vascular remodeling in response to chronic aeroallergen exposure. Because many ovalbumin-driven models used to investigate allergic airway disease do so in the absence of persistent airway inflammation, we used a protocol of chronic respiratory exposure to house dust mite extract (HDME), which has been shown to induce persistent airway inflammation consistent with that seen in humans with asthma. Mice were exposed to HDME intranasally for 7 or 20 consecutive weeks, and resolution of the inflammatory and remodeling response to allergen was investigated 4 weeks after the end of a 7-week exposure protocol. Measures of vascular remodeling, including total collagen deposition, procollagen I production, endothelial and smooth muscle cell proliferation, smooth muscle area, and presence of myofibroblasts, were investigated histologically in lung vessels of different sizes and locations. We observed an increase in total collagen content, which did not resolve upon cessation of allergen exposure. Other parameters were significantly increased after 7 and/or 20 weeks of allergen exposure but returned to baseline after allergen withdrawal. We conclude that respiratory HDME exposure induces airway remodeling and pulmonary vascular remodeling, and, in accordance with airway remodeling, some components of these structural changes may be irreversible.

Direct evidence of secondary necrosis of neutrophils during intense lung inflammation

Several pulmonary inflammatory conditions are characterised by infiltration of neutrophils. Normally, neutrophils are silently removed by apoptosis, followed by phagocytosis. However, if phagocytosis fails, apoptotic cells undergo secondary necrosis. Recent findings of increased levels of the pan-necrosis marker lactate dehydrogenase in bronchoalveolar lavage from lipopolysaccharide-exposed mice implies potential involvement of secondary necrosis. Using a similar model, this study aimed to identify the source of lactate dehydrogenase and to search for direct histological evidence of secondary necrosis. Lipopolysaccharide (LPS) was administered to the lungs of BALB/c mice, and bronchoalveolar lavage and tissue samples were collected 4, 12, 24, 36, 48, 60 and 72 h after administration. LPS induced a patchy neutrophil-rich lung inflammation, where the numbers of terminal deoxynucleotide transferase-mediated dUTP nick-end labelling-positive neutrophils were increased at 12 h and onwards. Lavage levels of neutrophils and lactate dehydrogenase increased significantly at 4 and 24 h, respectively. Detailed electron microscopic assessment of neutrophil activation and death modes revealed that up to 14% of the neutrophils were undergoing secondary necrosis, whereas apoptotic or primary necrotic structural cells were rarely found. In summary, this study provides direct evidence that secondary necrosis of neutrophils is a common process during intense lung inflammation. This implies that neutrophil apoptosis may cause rather than resolve airway inflammation.

Anti-Fas mAb-induced apoptosis and cytolysis of airway tissue eosinophils aggravates rather than resolves established inflammation.

BackgroundFas receptor-mediated eosinophil apoptosis is currently forwarded as a mechanism resolving asthma-like inflammation. This view is based on observations in vitro and in airway lumen with unknown translatability to airway tissues in vivo. In fact, apoptotic eosinophils have not been detected in human diseased airway tissues whereas cytolytic eosinophils abound and constitute a major mode of degranulation of these cells. Also, Fas receptor stimulation may bypass the apoptotic pathway and directly evoke cytolysis of non-apoptotic cells. We thus hypothesized that effects of anti-Fas mAb in vivo may include both apoptosis and cytolysis of eosinophils and, hence, that established eosinophilic inflammation may not resolve by this treatment.MethodsWeeklong daily allergen challenges of sensitized mice were followed by airway administration of anti-Fas mAb. BAL was performed and airway-pulmonary tissues were examined using light and electron microscopy. Lung tissue analysis for CC-chemokines, apoptosis, mucus production and plasma exudation (fibrinogen) were performed.ResultsAnti-Fas mAb evoked apoptosis of 28% and cytolysis of 4% of eosinophils present in allergen-challenged airway tissues. Furthermore, a majority of the apoptotic eosinophils remained unengulfed and eventually exhibited secondary necrosis. A striking histopathology far beyond the allergic inflammation developed and included degranulated eosinophils, neutrophilia, epithelial derangement, plasma exudation, mucus-plasma plugs, and inducement of 6 CC-chemokines. In animals without eosinophilia anti-Fas evoked no inflammatory response.ConclusionAn efficient inducer of eosinophil apoptosis in airway tissues in vivo, anti-Fas mAb evoked unprecedented asthma-like inflammation in mouse allergic airways. This outcome may partly reflect the ability of anti-Fas to evoke direct cytolysis of non-apoptotic eosinophils in airway tissues. Additionally, since most apoptotic tissue eosinophils progressed into the pro-inflammatory cellular fate of secondary necrosis this may also explain the aggravated inflammation. Our data indicate that Fas receptor mediated eosinophil apoptosis in airway tissues in vivo may cause severe disease exacerbation due to direct cytolysis and secondary necrosis of eosinophils.

Neutrophil cannibalism--a back up when the macrophage clearance system is insufficient.

BackgroundDuring a lipopolysaccharide-induced lung inflammation, a massive accumulation of neutrophils occurs, which is normally cleared by macrophage phagocytosis following neutrophil apoptosis. However, in cases of extensive apoptosis the normal clearance system may fail, resulting in extensive neutrophil secondary necrosis. The aim of this study was to explore the hypothesis that neutrophils, in areas of the lung with extensive cellular infiltration, contribute to clearance by phagocytosing apoptotic cells and/or cell debris derived from secondary necrosis.MethodsIntranasal lipopolysaccharide administration was used to induce lung inflammation in mice. The animals were sacrificed at seven time points following administration, bronchoalveolar lavage was performed and tissue samples obtained. Electron microscopy and histochemistry was used to assess neutrophil phagocytosis.ResultsElectron microscopic studies revealed that phagocytosing neutrophils was common, at 24 h after LPS administration almost 50% of the total number of neutrophils contained phagosomes, and the engulfed material was mainly derived from other neutrophils. Histochemistry on bronchoalvolar lavage cells further showed phagocytosing neutrophils to be frequently occurring.ConclusionNeutrophils are previously known to phagocytose invading pathogens and harmful particles. However, this study demonstrates that neutrophils are also able to engulf apoptotic neutrophils or cell debris resulting from secondary necrosis of neutrophils. Neutrophils may thereby contribute to clearance and resolution of inflammation, thus acting as a back up system in situations when the macrophage clearance system is insufficient and/or overwhelmed.

Versican in inflammation and tissue remodeling: The impact on lung disorders

Versican is a proteoglycan that has many different roles in tissue homeostasis and inflammation. The biochemical structure comprises four different types of the core protein with attached glycosaminoglycans (GAGs) that can be sulfated to various extents and has the capacity to regulate differentiation of different cell types, migration, cell adhesion, proliferation, tissue stabilization and inflammation. Versicans regulatory properties are of importance during both homeostasis and changes that lead to disease progression. The GAGs that are attached to the core protein are of the chondroitin sulfate/dermatan sulfate type and are known to be important in inflammation through interactions with cytokines and growth factors. For a more complex understanding of versican, it is of importance to study the tissue niche, where the wound healing process in both healthy and diseased conditions take place. In previous studies, our group has identified changes in the amount of the multifaceted versican in chronic lung disorders such as asthma, chronic obstructive pulmonary disease, and bronchiolitis obliterans syndrome, which could be a result of pathologic, transforming growth factor β driven, on-going remodeling processes. Reversely, the context of versican in its niche is of great importance since versican has been reported to have a beneficial role in other contexts, e.g. emphysema. Here we explore the vast mechanisms of versican in healthy lung and in lung disorders.

Extracellular matrix alterations and acute inflammation; developing in parallel during early induction of pulmonary fibrosis.

Pulmonary fibrosis is a hallmark of several systemic diseases such as systemic sclerosis. Initiation and early development is not well characterized, as initiation usually is unnoticed in patients, yet fibrosis has been considered a late event, occurring after an inflammatory phase. By utilizing an animal model, the starting point can be defined and the initiation process and early development thoroughly investigated. To investigate these processes from a systemic perspective, we choose a systemic administration route, instead of the more commonly used local administration. The aim of this work was to study the initiation of pulmonary fibrosis in an animal model and to investigate early alterations in connective tissue, cell turnover and acute immune response in lung parenchyma. Animals were injected subcutaneously with bleomycin, three times a week (w) for 1–4w (controls received saline). Total collagen was histologically assessed by Picro Sirius Red and Massons Trichrome, collagen production by antibodies directed against N-terminal of procollagens I and III, proliferation by labeling with proliferating cell nuclear antigen, apoptosis by TUNEL and innate immunity by detecting neutrophils and macrophages. Total collagen was significantly increased at 1, 2 and 4w compared with controls. Procollagen I, was increased at 1w and remained increased, whereas procollagen III-staining was increased at 2w, compared with controls. Myofibroblasts were increased at all times as were proliferation, whereas apoptosis was increased from 2w. Neutrophils peaked at 1w (2779±820 cells/mm2) and gradually decreased, whereas macrophages peaked at 2w (135±29 cells/mm2). Subcutaneously administered bleomycin induces rapid alterations in connective tissue and cell turnover, suggesting a plasticity of the connective tissue. A transient neutrophilia is detected and increased number of macrophages likely represents a clearance process of said neutrophils. The study suggests fibrosis initiation and acute inflammation to occur in parallel in this model.

Effects of steroid treatment on lung CC chemokines, apoptosis and transepithelial cell clearance during development and resolution of allergic airway inflammation.

Background Steroid treatment of allergic eosinophilic airway diseases is considered to attenuate cell recruitment by inhibiting several chemokines and to cause eosinophil clearance through inducement of apoptosis of these cells. However, roles of these mechanisms in the actions of steroids in vivo have not been fully established. Also, as regards clearance of tissue eosinophils other mechanisms than apoptosis may operate in vivo.

Remodeling of extra-bronchial lung vasculature following allergic airway inflammation

BackgroundWe previously observed that allergen-exposed mice exhibit remodeling of large bronchial-associated blood vessels. The aim of the study was to examine whether vascular remodeling occurs also in vessels where a spill-over effect of bronchial remodeling molecules is less likely.MethodsWe used an established mouse model of allergic airway inflammation, where an allergic airway inflammation is triggered by inhalations of OVA. Remodeling of bronchial un-associated vessels was determined histologically by staining for α-smooth muscle actin, procollagen I, Ki67 and von Willebrand-factor. Myofibroblasts were defined as and visualized by double staining for α-smooth muscle actin and procollagen I. For quantification the blood vessels were divided, based on length of basement membrane, into groups; small (≤250 μm) and mid-sized (250–500 μm).ResultsWe discovered marked remodeling in solitary small and mid-sized blood vessels. Smooth muscle mass increased significantly as did the number of proliferating smooth muscle and endothelial cells. The changes were similar to those previously seen in large bronchial-associated vessels. Additionally, normally poorly muscularized blood vessels changed phenotype to a more muscularized type and the number of myofibroblasts around the small and mid-sized vessels increased following allergen challenge.ConclusionWe demonstrate that allergic airway inflammation in mice is accompanied by remodeling of small and mid-sized pulmonary blood vessels some distance away (at least 150 μm) from the allergen-exposed bronchi. The present findings suggest the possibility that allergic airway inflammation may cause such vascular remodeling as previously associated with lung inflammatory conditions involving a risk for development of pulmonary hypertension.

Smooth muscle in tissue remodeling and hyper-reactivity: Airways and arteries.

Smooth muscle comprises a key functional component of both the airways and their supporting vasculature. Dysfunction of smooth muscle contributes to and exacerbates a host of breathing-associated pathologies such as asthma, chronic obstructive pulmonary disease and pulmonary hypertension. These diseases may be marked by airway and/or vascular smooth muscle hypertrophy, proliferation and hyper-reactivity, and related conditions such as fibrosis and extracellular matrix remodeling. This review will focus on the contribution of airway or vascular smooth dysfunction to common airway diseases.