Alveolar epithelial cells are competent producers of interstitial extracellular matrix with disease relevant plasticity in a human in vitro 3D model

Abstract

Background The structure of alveoli is critical for normal lung function and when maintenance of the underlying extracellular matrix (ECM) that forms these delicate structures fails, patients may develop emphysema or lung fibrosis via pathological processes that are not fully understood. The alveolar walls are lined by alveolar epithelial cells (AEC), these cells have so far been implicated in pathological remodeling through signaling that alters the activity of mesenchymal and immune cells. We set out to examine the capacity of AEC to produce ECM and thereby directly contribute towards the ECM remodeling in chronic lung diseases. Methods Cryopreserved type 2 AEC (AEC2) isolated from healthy lungs and chronic obstructive pulmonary disease (COPD) afflicted lungs were cultured in decellularized human lung slices over a period of 13 days. AEC2 from healthy lungs were treated with transforming growth factor ß1 (TGF-β1) to evaluate the plasticity of their ECM production. Evaluation of phenotypic markers and expression of matrisome genes and proteins were performed by RNA-sequencing, mass spectrometry and immunohistochemistry. Results AEC2 in our model displayed an AEC marker profile similar to freshly isolated AEC2 throughout the 13 day culture period. Cultured COPD-derived AEC2 retained expression of known disease markers, as HLA-A. AEC2 expressed basement membrane components but also a complex set of structural proteins found in interstitial ECM. TGF-β1 stimuli of AEC2 from healthy lungs induced a change in ECM production from AEC2 resembling what has previously been documented in mesenchymal cells, without loss of specific AEC marker expression. Conclusions This study reveals a previously unexplored potential of AEC to directly contribute to ECM turnover, motivating a re-evaluation of the role of AEC2 in pathological lung remodeling.