Impact of lung remodelling on respiratory mechanics in a model of severe allergic inflammation

A theoretical model of inflammation- and mechanotransduction-driven asthmatic airway remodelling

Inflammation, airway hyper-responsiveness and airway remodelling are well-established hallmarks of asthma, but their inter-relationships remain elusive. In order to obtain a better understanding of their inter-dependence, we develop a mechanochemical morphoelastic model of the airway wall accounting for local volume changes in airway smooth muscle (ASM) and extracellular matrix in response to transient inflammatory or contractile agonist challenges. We use constrained mixture theory, together with a multiplicative decomposition of growth from the elastic deformation, to model the airway wall as a nonlinear fibre-reinforced elastic cylinder. Local contractile agonist drives ASM cell contraction, generating mechanical stresses in the tissue that drive further release of mitogenic mediators and contractile agonists via underlying mechanotransductive signalling pathways. Our model predictions are consistent with previously described inflammation-induced remodelling within an axisymmetric airway geometry. Additionally, our simulations reveal novel mechanotransductive feedback by which hyper-responsive airways exhibit increased remodelling, for example, via stress-induced release of pro-mitogenic and pro-contractile cytokines. Simulation results also reveal emergence of a persistent contractile tone observed in asthmatics, via either a pathological mechanotransductive feedback loop, a failure to clear agonists from the tissue, or a combination of both. Furthermore, we identify various parameter combinations that may contribute to the existence of different asthma phenotypes, and we illustrate a combination of factors which may predispose severe asthmatics to fatal bronchospasms.

Inflammatory and Oxidative Stress Markers in Experimental Allergic Asthma

Ovalbumin-induced allergic lung inflammation (ALI) is a condition believed to be mediated by cytokines, extracellular matrix remodeling, and redox imbalance. In this study, we evaluated pulmonary function together with inflammatory markers as interleukin-4 (IL-4), myeloperoxidase (MPO), eosinophil cells, and redox markers in the lungs of BALB/c mice after ovalbumin (OVA) sensitization and challenge. Our results showed an increase in bronchial hyperresponsiveness stimulated by methacholine (Mch), inflammatory cell influx, especially eosinophils together with an increase of high mobility group box 1 (HMGB1) and altered lipid peroxidation (LP) and antioxidant defenses in the OVA group compared to the control group (p ≤ 0.5). Thus, we demonstrated that OVA-induced ALI altered redox status concomitantly with impaired lung function, which was associated with HMGB1 expression and proteolytic remodeling. Taken together all results found here, we may suggest HMGB1 is an important therapeutic target for asthma, once orchestrates the redox signaling, inflammation, and remodeling that contribute to the disease development.

Human adipose tissue mesenchymal stromal cells and their extracellular vesicles act differentially on lung mechanics and inflammation in experimental allergic asthma

Background

Asthma is a chronic inflammatory disease that can be difficult to treat due to its complex pathophysiology. Most current drugs focus on controlling the inflammatory process, but are unable to revert the changes of tissue remodeling. Human mesenchymal stromal cells (MSCs) are effective at reducing inflammation and tissue remodeling; nevertheless, no study has evaluated the therapeutic effects of extracellular vesicles (EVs) obtained from human adipose tissue-derived MSCs (AD-MSC) on established airway remodeling in experimental allergic asthma.

Methods

C57BL/6 female mice were sensitized and challenged with ovalbumin (OVA). Control (CTRL) animals received saline solution using the same protocol. One day after the last challenge, each group received saline, 10⁵ human AD-MSCs, or EVs (released by 10⁵ AD-MSCs). Seven days after treatment, animals were anesthetized for lung function assessment and subsequently euthanized. Bronchoalveolar lavage fluid (BALF), lungs, thymus, and mediastinal lymph nodes were harvested for analysis of inflammation. Collagen fiber content of airways and lung parenchyma were also evaluated.

Results

In OVA animals, AD-MSCs and EVs acted differently on static lung elastance and on BALF regulatory T cells, CD3⁺CD4⁺ T cells, and pro-inflammatory mediators (interleukin [IL]-4, IL-5, IL-13, and eotaxin), but similarly reduced eosinophils in lung tissue, collagen fiber content in airways and lung parenchyma, levels of transforming growth factor-β in lung tissue, and CD3⁺CD4⁺ T cell counts in the thymus. No significant changes were observed in total cell count or percentage of CD3⁺CD4⁺ T cells in the mediastinal lymph nodes.

Conclusions

In this immunocompetent mouse model of allergic asthma, human AD-MSCs and EVs effectively reduced eosinophil counts in lung tissue and BALF and modulated airway remodeling, but their effects on T cells differed in lung and thymus. EVs may hold promise for asthma; however, further studies are required to elucidate the different mechanisms of action of AD-MSCs versus their EVs.

A HuR/TGF-β1 feedback circuit regulates airway remodeling in airway smooth muscle cells

Background

Asthma is a worldwide health burden with an alarming prevalence. For years, asthma-associated airway injury remains elusive. Transforming growth factor β1 (TGF-β1) is a pleiotropic cytokine that has been shown to be involved in the synthesis of the matrix molecules associated with airway remodeling. Human antigen R (HuR), the member of the Hu RNA-binding protein family, can bind to a subset of short-lived mRNAs in their 3′ untranslated regions (UTR). However, the functional roles and relevant signaling pathways of HuR in airway remodeling have not been well illustrated. Thus, we aim to explore the relationship between HuR and TGF-β1 in platelet derived growth factor(PDGF)-induced airway smooth muscle (ASM) cells and asthmatic animal.

Methods

Cultured human ASM cells were stimulated by PDGF for 0, 6, 12 and 24 h. Western blotting, RT-PCR and immunofluoresence were used to detect the expression of HuR, TGF-β1, α-smooth muscle actins (α-SMA) and collagen type I (Col-I). Then knockdown of HuR, flow cytomerty was used to detect the morphological change and western blotting for functionally change of ASM cells. Furthermore, the interference of TGF-β1 and exogenous TGF-β1 were implemented to testify the influence on HuR. A murine OVA-driven allergic model based on sensitization and challenge was developed. The inflammatory response was measured by bronchoalveolar lavage fluid (BALF), airway damage was analyzed by hematoxylin and eosin staining, airway remodeling was assessed by sirius red staining and periodic acid-schiff staining, the expression level of HuR, TGF-β1 and α-SMA were measured by RT-PCR, western blotting and immunohistochemistry.

Results

Here, we found that PDGF elevated HuR expression both at mRNA and protein level in cultured ASM cells at a time-dependent manner, which was simultaneously accompanied by the enhanced expression of TGF-β1, α-SMA and Col-I. Further study revealed that the knockdown of HuR significantly increased the apoptosis of ASM cells and dampened TGF-β1, Col-I and α-SMA expression. However, interfering TGF-β1 with siRNA or extra addition of TGF-β1, HuR could restore its production as well as Col-I. Compared with normal mice stimulating with PBS, OVA-induced mice owned high amount of inflammatory cells, such as eosinophils, lymphocytes and neutrophils except macrophages. HE staining showed accumulation of inflammatory cells surrounding bronchiole and sirius red staining distinguished collagen type I and III deposition around the bronchiole. Higher abundance of HuR, TGF-β1 and α-SMA were verified in OVA-induced mice than PBS-induced mice by RT-PCR, western blotting and immunohistochemistry.

Conclusions

A HuR/TGF-β1 feedback circuit was established to regulate airway remodeling in vivo and in vitro and targeting this feedback has considerable potential for the intervention of asthma.

The effect of angiotensin-converting enzyme inhibition by captopril on respiratory mechanics in healthy rats

CONTEXT

Angiotensin stimulates smooth-muscle contraction. Accordingly, angiotensin-converting enzyme (ACE) inhibition is expected to decrease airway resistance.

OBJECTIVES

To measure the effects of ACE inhibition on respiratory mechanics in healthy mammals.

MATERIALS AND METHODS

We measured respiratory mechanics before and after i.p. ACE inhibitor captopril (100 mg/kg) in normal anaesthetised rats. The end-inflation occlusion method allowed the measurements of respiratory system elastance and ohmic and viscoelastic pressure dissipations. Respiratory system hysteresis and the elastic and resistive work of breathing were calculated.

RESULTS

Captopril induced a reduction of the ohmic and the total respiratory system resistances, while respiratory system hysteresis and elastance did not change. Accordingly, a reduction of the resistive and of the total work of breathing was observed.

CONCLUSIONS

The captopril-induced reduction of airway resistance indicates that angiotensin modulates bronchomotor tone in basal conditions. ACE inhibition may positively affect respiratory system mechanics and work of breathing.

Integrin αvβ5-mediated TGF-β activation by airway smooth muscle cells in asthma

Severe asthma is associated with airway remodeling, characterized by structural changes including increased smooth muscle mass and matrix deposition in the airway, leading to deteriorating lung function. TGF-β is a pleiotropic cytokine leading to increased synthesis of matrix molecules by human airway smooth muscle (HASM) cells and is implicated in asthmatic airway remodeling. TGF-β is synthesized as a latent complex, sequestered in the extracellular matrix, and requires activation for functionality. Activation of latent TGF-β is the rate-limiting step in its bioavailability. This study investigated the effect of the contraction agonists LPA and methacholine on TGF-β activation by HASM cells and its role in the development of asthmatic airway remodeling. The data presented show that LPA and methacholine induced TGF-β activation by HASM cells via the integrin αvβ5. Our findings highlight the importance of the β5 cytoplasmic domain because a polymorphism in the β5 subunit rendered the integrin unable to activate TGF-β. To our knowledge, this is the first description of a biologically relevant integrin that is unable to activate TGF-β. These data demonstrate that murine airway smooth muscle cells express αvβ5 integrins and activate TGF-β. Finally, these data show that inhibition, or genetic loss, of αvβ5 reduces allergen-induced increases in airway smooth muscle thickness in two models of asthma. These data highlight a mechanism of TGF-β activation in asthma and support the hypothesis that bronchoconstriction promotes airway remodeling via integrin mediated TGF-β activation.

Epigen is induced during the interleukin-13-stimulated cell proliferation in murine primary airway epithelial cells

Airway remodeling in bronchial asthma is characterized by epithelial detachment and proliferation, subepithelial fibrosis, increased smooth muscle mass, and goblet cell hyperplasia. These features are mediated by T-helper type 2 (Th2) cytokines including interleukin (IL)-13. However, the direct effects of IL-13 on the functions of airway epithelial cells are not fully understood. Murine primary airway epithelial (MPAE) cells were cultured in an air-liquid interface (ALI) culture system. AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase, was used to examine whether EGFR was involved in the IL-13-stimulated proliferation of MPAE cells. The expressions of EGFR ligands were investigated by reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemical analyses. The cell counting in cross-sections and [(3)H]thymidine incorporation assays revealed a significant increase in the number of MPAE cells cultured with IL-13 compared with a phosphate-buffered saline (PBS) control. AG1478 abolished the IL-13-stimulated proliferation of MPAE cells. The expression of epigen, one of the EGFR ligands, was enhanced in MPAE cells cultured with IL-13. The findings suggest that EGFR is involved in the IL-13-stimulated proliferation of MPAE cells, and that epigen is important for the proliferation process in airway remodeling.

Effects of cysteinyl-leukotriene receptors' antagonism by montelukast on lung mechanics and olfactory system histology in healthy mice

CONTEXT

At variance with steroid administration, the possible effects of leukotrienes inhibition on basal respiratory mechanics and olfactory system function are still unclear.

OBJECTIVE

To investigate if interference with the leukotrienes activity may influence basal lung mechanics in healthy mammals, as well as the olfactory system.

MATERIALS AND METHODS

We measured lung mechanics by the end-inflation occlusion method in control and in montelukast i.p. treated anaesthetised healthy mice (10 mg/kg/die for a week). A study of olfactory system histology was also conducted.

RESULTS

Elastance and resistive properties of the lung were not affected by montelukast, while a significant increment of lung hysteresis was observed. The analysis of olfactory system histology revealed no significant effects of montelukast compared to controls.

DISCUSSION AND CONCLUSIONS

Leukotrienes' antagonism does not affect respiratory mechanics in basal conditions, except for a hysteresis increment, which might counteract the increase in expiratory flow in asthmatic subjects assuming montelukast.

Impact of obesity on airway and lung parenchyma remodeling in experimental chronic allergic asthma

The impact of obesity on the inflammatory process has been described in asthma, however little is known about the influence of diet-induced obesity on lung remodeling. For this purpose, 56 recently weaned A/J mice were randomly divided into 2 groups. In the C group, mice were fed a standard chow diet, while OB animals received isocaloric high-fat diet to reach 1.5 of the mean body weight of C. After 12 weeks, each group was further randomized to be sensitized and challenged with ovalbumin (OVA) or saline. Twenty-four hours after the last challenge, collagen fiber content in airways and lung parenchyma, the volume proportion of smooth muscle-specific actin in alveolar ducts and terminal bronchiole, and the number of eosinophils in bronchoalveolar lavage fluid were higher in OB-OVA than C-OVA. In conclusion, diet-induced obesity enhanced lung remodeling resulting in higher airway responsiveness in the present experimental chronic allergic asthma.

Sex-specific lung remodeling and inflammation changes in experimental allergic asthma

There is evidence that sex and sex hormones influence the severity of asthma. Airway and lung parenchyma remodeling and the relationship of ultrastructural changes to airway responsiveness and inflammation in male, female, and oophorectomized mice (OVX) were analyzed in experimental chronic allergic asthma. Seventy-two BALB/c mice were randomly divided into three groups (n=24/each): male, female, and OVX mice, whose ovaries were removed 7 days before the start of sensitization. Each group was further randomized to be sensitized and challenged with ovalbumin (OVA) or saline. Twenty-four hours after the last challenge, collagen fiber content in airways and lung parenchyma, the volume proportion of smooth muscle-specific actin in alveolar ducts and terminal bronchiole, the amount of matrix metalloproteinase (MMP)-2 and MMP-9, and the number of eosinophils and interleukin (IL)-4, IL-5, and transforming growth factor (TGF)-β levels in bronchoalveolar lavage fluid were higher in female than male OVA mice. The response of OVX mice was similar to that of males, except that IL-5 remained higher. Nevertheless, after OVA provocation, airway responsiveness to methacholine was higher in males compared with females and OVX mice. In conclusion, sex influenced the remodeling process, but the mechanisms responsible for airway hyperresponsiveness seemed to differ from those related to remodeling.

Effect of parenchymal stiffness on canine airway size with lung inflation

Although airway patency is partially maintained by parenchymal tethering, this structural support is often ignored in many discussions of asthma. However, agonists that induce smooth muscle contraction also stiffen the parenchyma, so such parenchymal stiffening may serve as a defense mechanism to prevent airway narrowing or closure. To quantify this effect, specifically how changes in parenchymal stiffness alter airway size at different levels of lung inflation, in the present study, we devised a method to separate the effect of parenchymal stiffening from that of direct airway narrowing. Six anesthetized dogs were studied under four conditions: baseline, after whole lung aerosol histamine challenge, after local airway histamine challenge, and after complete relaxation of the airways. In each of these conditions, we used High resolution Computed Tomography to measure airway size and lung volume at five different airway pressures (0, 12, 25, 32, and 45 cm H(2)O). Parenchymal stiffening had a protective effect on airway narrowing, a fact that may be important in the airway response to deep inspiration in asthma. When the parenchyma was stiffened by whole lung aerosol histamine challenge, at every lung volume above FRC, the airways were larger than when they were directly challenged with histamine to the same initial constriction. These results show for the first time that a stiff parenchyma per se minimizes the airway narrowing that occurs with histamine challenge at any lung volume. Thus in clinical asthma, it is not simply increased airway smooth muscle contraction, but perhaps a lack of homogeneous parenchymal stiffening that contributes to the symptomatic airway hyperresponsiveness.

The olfactory system is affected by steroid aerosol treatment in mice

Asthma needs continuous treatment often for years. In humans, some drugs are administered via aerosol, therefore they come in contact with both respiratory and olfactory mucosa. We explored the possibility that antiasthma corticosteroid treatment could influence the olfactory function by passage through the nose. A group of mice was exposed twice daily for 42 days to fluticasone propionate aerosol and was compared with a control group. Olfactory behavior, respiratory mechanics, histology, and immunoreactivity in the olfactory system were assessed. Fluticasone-treated mice were slower in retrieving a piece of hidden food, but both groups were similarly fast when the food was visible. When a clearly detectable odor was present in the environment, all mice behaved in a similar way. Respiratory mechanics indices were similar in all mice except for the viscose resistance, which was reduced in fluticasone-treated mice. Olfactory mucosa of fluticasone-treated mice was thicker than that of controls. Slight but consistent differences in staining were present for Olfactory Marker Protein but not for other proteins. A mild impairment of olfactory function is present in mice chronically treated with fluticasone aerosol, apparently accompanied by slight modifications of the olfactory receptor cells, and suggests monitoring of olfactory function modifications in long-term steroid users.