Regional Heterogeneity in Murine Lung Fibroblasts from Normal Mice or Mice Exposed Once to Cigarette Smoke

Chronic obstructive lung disease (COPD) is characterized by matrix deposition in the small airways but matrix loss from the parenchyma, phenomena which must depend on the ability of local fibroblasts to produce matrix after smoke exposure. To investigate this idea, we exposed C57Bl/6 mice once to cigarette smoke or to air (control) and prepared primary cultures of lung fibroblasts by microdissecting large airways (trachea, LAF), medium size airways (major bronchi, MAF) and parenchyma (PF). Control PF showed the lowest rate of wound closure and wound closure was depressed in all lines by a single in vivo smoke exposure. Gene expression of matrix proteins differed considerably among the sites; decorin, which may sequester TGFβ, was markedly higher in PF. PF showed higher intrinsic ratios of pSmad2/Smad2. Smoke caused much greater increases in secreted and matrix deposited collagens 1 and 3 in PF than in LAF or MAF. Expression of Thy-1, a gene that suppresses myofibroblast differentiation, was increased by smoke in PF. We conclude that there is considerable regional heterogeneity in murine lung fibroblasts in terms of matrix production, either basally or after in vivo smoke exposure; that PF have lower ability to repair wounds and higher intrinsic TGFβ signaling; and that a single exposure to smoke produces lasting changes in the pattern of matrix production and wound repair, changes that may be mediated in part by smoke-induced release of TGFβ. However, PF still retain the ability to repair by producing new matrix after a single in vivo smoke exposure

Comparison of Two Quantitative Methods of Discerning Airspace Enlargement in Smoke-Exposed Mice

In this work, we compare two methods for evaluating and quantifying pulmonary airspace enlargement in a mouse model of chronic cigarette smoke exposure. Standard stereological sample preparation, sectioning, and imaging of mouse lung tissues were performed for semi-automated acquisition of mean linear intercept (Lm) data. After completion of the Lm measurements, D2, a metric of airspace enlargement, was measured in a blinded manner on the same lung images using a fully automated technique developed in-house. An analysis of variance (ANOVA) shows that although Lm was able to separate the smoke-exposed and control groups with statistical significance (p = 0.034), D2 was better able to differentiate the groups (p<0.001) and did so without any overlap between the control and smoke-exposed individual animal data. In addition, the fully automated implementation of D2 represented a time savings of at least 24x over semi-automated Lm measurements. Although D2 does not provide 3D stereological metrics of airspace dimensions as Lm does, results show that it has higher sensitivity and specificity for detecting the subtle airspace enlargement one would expect to find in mild or early stage emphysema. Therefore, D2 may serve as a more accurate screening measure for detecting early lung disease than Lm

Linking Microscopic Spatial Patterns of Tissue Destruction in Emphysema to Macroscopic Decline in Stiffness Using a 3D Computational Model

Pulmonary emphysema is a connective tissue disease characterized by the progressive destruction of alveolar walls leading to airspace enlargement and decreased elastic recoil of the lung. However, the relationship between microscopic tissue structure and decline in stiffness of the lung is not well understood. In this study, we developed a 3D computational model of lung tissue in which a pre-strained cuboidal block of tissue was represented by a tessellation of space filling polyhedra, with each polyhedral unit-cell representing an alveolus. Destruction of alveolar walls was mimicked by eliminating faces that separate two polyhedral either randomly or in a spatially correlated manner, in which the highest force bearing walls were removed at each step. Simulations were carried out to establish a link between the geometries that emerged and the rate of decline in bulk modulus of the tissue block. The spatially correlated process set up by the force-based destruction lead to a significantly faster rate of decline in bulk modulus accompanied by highly heterogeneous structures than the random destruction pattern. Using the Karhunen-Loève transformation, an estimator of the change in bulk modulus from the first four moments of airspace cell volumes was setup. Simulations were then obtained for tissue destruction with different idealized alveolar geometry, levels of pre-strain, linear and nonlinear elasticity assumptions for alveolar walls and also mixed destruction patterns where both random and force-based destruction occurs simultaneously. In all these cases, the change in bulk modulus from cell volumes was accurately estimated. We conclude that microscopic structural changes in emphysema and the associated decline in tissue stiffness are linked by the spatial pattern of the destruction process

Role of IL-18 in second-hand smoke-induced emphysema

Item does not contain fulltextChronic second-hand smoke (SHS) exposure comprises the main risk factor for nonsmokers to develop chronic obstructive pulmonary disease (COPD). However, the mechanisms behind the chronic inflammation and lung destruction remain incompletely understood. In this study, we show that chronic exposure of Sprague-Dawley rats to SHS results in a significant increase of proinflammatory cytokine IL-18 and chemokine (C-C motif) ligand 5 in the bronchoalveolar lavage fluid (BALF) and a significant decrease of vascular endothelial growth factor (VEGF) in the lung tissue. SHS exposure resulted in progressive alveolar airspace enlargement, cell death, pulmonary vessel loss, vessel muscularization, collagen deposition, and right ventricular hypertrophy. Alveolar macrophages displayed a foamy phenotype and a decreased expression of the natural inhibitor of IL-18, namely, IL-18 binding protein (IL-18BP). Moreover, IL-18 down-regulated the expression of VEGF receptor-1 and VEGFR receptor-2, and induced apoptosis in pulmonary microvascular endothelial cells in vitro. We also observed a trend toward increased concentrations of IL-18 in the BALF of patients with COPD. Our findings suggest that IL-18-mediated endothelial cell death may contribute to vascular destruction and disappearance in SHS-induced COPD. Moreover, IL-18 and IL-18BP are potential new targets for therapeutics