A Heterotopic Xenograft Model of Human Airways for Investigating Fibrosis in Asthma

Abstract

Limited in vivo models exist to investigate the lung airway epithelial role in repair, regeneration, and pathology of chronic lung diseases. Herein, we introduce a novel animal model in asthma-a xenograft system integrating a differentiating human asthmatic airway epithelium with an actively remodeling rodent mesenchyme in an immunocompromised murine host. Human asthmatic and nonasthmatic airway epithelial cells were seeded into decellularized rat tracheas. Tracheas were ligated to a sterile cassette and implanted subcutaneously in the flanks of nude mice. Grafts were harvested at 2, 4, or 6 weeks for tissue histology, fibrillar collagen, and transforming growth factor-b activation analysis. We compared immunostaining in these xenografts to human lungs. Grafted epithelial cells generated a differentiated epithelium containing basal, ciliated, and mucus-expressing cells. By 4 weeks postengraftment, asthmatic epithelia showed decreased numbers of ciliated cells and decreased E-cadherin expression compared with nonasthmatic grafts, similar to human lungs. Grafts seeded with asthmatic epithelial cells had three times more fibrillar collagen and induction of transforming growth factor-b isoforms at 6 weeks postengraftment compared with nonasthmatic grafts. Asthmatic epithelium alone is sufficient to drive aberrant mesenchymal remodeling with fibrillar collagen deposition in asthmatic xenografts. Moreover, this xenograft system represents an advance over current asthma models in that it permits direct assessment of the epithelial-mesenchymal trophic unit.Keywords: asthma; remodeling; lung Clinical RelevanceWe developed a human asthmatic airway epithelial xenograft system as an animal model in asthma and demonstrate that the asthmatic airway epithelium alone can drive airway remodeling. This xenograft model is an advance over current animal models for asthma in that it permits direct assessment of the epithelial-mesenchymal trophic unit.

Imaging Collagen in Scar Tissue: Developments in Second Harmonic Generation Microscopy for Biomedical Applications

“…The technique has also been used to identify differences in the collagen organization in emphysematous COPD lung tissues compared to control donors [ 114 , 115 ]. In terms of quantification of SHG, signal intensity has previously been used to quantify the fibrosis-related increase in fibrillar collagen in a mouse model of pulmonary fibrosis [ 112 ], a human-mouse xenograft model of airway epithelial-induced fibrosis in asthma [ 116 ] and an in vitro collagen-gel contraction model using lung fibroblasts from COPD patients [ 117 ]. The SHG signal intensity has also been used to compare the ratio of collagen and elastin (measured by TPEF) in COPD lungs [ 115 ].…”

Functional characterization of a novel 3D model of the epithelial-mesenchymal trophic unit

“…xenografts (7), ex vivo tissue explants (8), lung slices (9) or in vitro cultures of primary cells derived from airway disease patients (10). Such models have the advantage of using cells containing relevant genetic and epigenetic information that contribute to underlying pathogenetic processes, increasing confidence in results from mechanistic studies, including target identification and validation, as well as toxicological testing.…”

“…However, one of the main limitations of these models is the general absence of ECM components and the loss of proper cell-cell interactions that arises from the former. In recent years, the aspiration to recapitulate a 3D tissue micro-architecture has prompted the development of more innovative, integrated models using tissue engineering (25;26) or xenograft models (7). While co-culture models have been developed (27;28), they utilize bronchial epithelial cells and fibroblasts that have initially been cultured separately and co-cultured in a range of formats including Transwell ® systems (or similar synthetic polymer supports (28)), where the epithelial cells and fibroblasts are physically separated by porous supports.…”

“…Nonetheless, such a model has been used to investigate the effects whole smoke exposure with clear evidence of decreased cilia and increased goblet cell differentiation, but ECM remodeling was not explored (30). The alternative xenograft approach involves seeding human airway epithelial cells into decellularized rat tracheas and culturing in the flanks of nude mice (7). While grafts seeded with epithelial cells from asthmatic donors had three times more fibrillar collagen compared to non-asthmatic grafts, this presumably reflects migration of rodent mesenchymal cells into the graft.…”

“…6 Institute of Biomedicine and Molecular Immunology (IBIM), Italian National Research Council (CNR), Palermo, Italy. 7 Interventional Pulmonology Unit, La Maddalena Cancer Center, Palermo, Italy.…”