Models of alveolar remodeling in chronic lung disease

Sammanfattning: Lung function is highly dependent on the structure of the lung parenchyma. Remodeling of the alveolar compartment is a central part of the pathology of chronic lung disease such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Pathological lung remodeling occurs as an interplay between cells and the extracellular matrix (ECM) which in addition to its structural role influence most aspects of cell behavior. This thesis aimed to improve on the available in vitro methods for studies of cell-ECM interaction in the alveolar compartment of the human lung. A technique to produce acellular lung slices for cell culture from clinical lung resection material with preservation of native 3-dimensional structure and ECM composition was established and evaluated. Protein turnover in cell cultures in decellularized lung slices (DLS) was analyzed by mass spectrometry implementing amino acids labeled with stable heavy isotopes to distinguish between cell and DLS derived ECM proteins. The work entailed study of ECM production of primary human lung fibroblasts and primary human alveolar epithelial type II cells (AECII) in DLS from derived from human lungs. In addition, a device for mechanical stretching of lungs slice cultures have been designed and evaluated. Fibroblasts and AECII cultured in DLS secreted ECM components that were incorporated in structure of the lung slices. Fibroblasts showed to be highly responsive to their extracellular milieu and when cultured in IPF derived ECM, they produced ECM recapitulating pathological alterations of the ECM scaffold. In a comparison with fibroblast culture on standard plastic tissue culture surfaces the deposition of ECM proteins was hampered compared DLS culture. DLS culture of AECII showed that these cells produced a wide array of ECM proteins including interstitial matrix components mostly associated with cells of mesenchymal origin. AECII from explanted healthy and end stage COPD lungs were almost indistinguishable in a proteomic evaluation and with limited transcriptomic differences. Healthy AECII did however display a significant plasticity in ECM production when stimulated with the profibrotic growth factor TGF-ß1, upregulating many markers of IPF remodeling. Finally, the novel stretch device proved to be compatible with lung slice culture and capable to induce a cellular stretch responses. This thesis provide insight into how lung ECM can dictate cellular function and presents new techniques for the study of interactions of cells and ECM lung parenchyma. The presented model systems have potential to improve on the in vivo relevance of preclinical experimental research by better representing normal and pathophysiological conditions. Finally, the description of a broad capacity for ECM production by alveolar epithelial cells raises interesting questions about their importance in alveolar ECM homeostasis pathological remodeling.