Novel lung organoid model reveals crucial role of lung resident mesenchymal stromal cells in COPD pathogenesis

Introduction
Despite impressive progress in development of human pulmonary organoid models, majority of these models are comprised predominantly of epithelial cells, with just a few reporting presence of supporting mesenchymal cells. These organoids do not yet recapitulate the complex structure and cellular interactions of the highly vascularized alveolar region. Therefore, more complex models utilizing the entirety of the lung architecture are required.

Objective
Here we aimed to develop an organoid model representative of human distal lung tissue comprised of primary human pulmonary epithelial, mesenchymal and endothelial cells.

Methods
Primary human distal lung epithelial (Promocell), endothelial (Promocell) and lung mesenchymal stromal cells (MSCs) directly isolated from human lung tissue were co-cultured in Matrigel for 21 day. The morphology, size and cellular composition of the resultant structures were assessed by confocal and transmission electron microscopy. We compared organoids seeded with MSCs isolated from healthy and COPD donor lungs. Secretion levels of hepatocyte growth factor (HGF) were assessed by ELISA.

Results
At 21 days organoids reach 1000 µm in size and develop multiple budding spherical structures with a lumen approx. 150–200 µm diameter. These structures are composed of alveolar epithelial cells (SPC+ ATII-like, AQP5+ ATI-like, and SPC+AQP5+ cells indicating intermediate phenotype). Presence of Krt5+, p63+ and MUC5+ epithelial cells is also observed. Interconnected network of endothelial cells is observed throughout the organoid (figure 1). Presence of endothelial cells is critical for organoid reaching 1000 µm size, while presence of lung MSCs is critical for structural symmetry. Organoids seeded with MSCs derived from COPD lungs are characterised by non-symmetrical morphology and smaller size compared to organoids seeded with MSCs isolated from lungs of healthy donors and were unable to support endothelial cells, recapitulating loss of vasculature in emphysema. Both COPD lung MSCs and COPD organoids had lower levels of HGF secretion expression compared to their healthy lung counterparts.