Epithelial-stromal cell interactions and ECM mechanics drive the formation of airway-mimetic tubular morphology in lung organoids

The complex cellular organisation of the human airway tract where interaction between epithelial and stromal lineages and the extracellular matrix (ECM) make it a difficult organ to study in vitro. Current in vitro lung models focus on modelling the lung epithelium such as air-liquid interface (ALI) cultures and bronchospheres, do not model the complex morphology and the cell-ECM interaction seen in vivo. Models that include stromal populations often separate them via a semipermeable barrier, which precludes the effect of cell-cell interaction or do not include the ECM or the effect of ECM mechanics such as viscoelasticity and stiffness. Here we investigated the effect of stromal cells on basal epithelial cell-derived bronchosphere structure and function through a triple culture of bronchial epithelial, lung fibroblast and airway smooth muscle cells. Epithelial-stromal cross talk enabled formation of epithelial cell-driven branching tubules consisting of luminal epithelial cells surrounded by stromal cells termed bronchotubules. Addition of agarose to the Matrigel scaffold (Agrigel) created a mechanically tunable ECM, where viscoelasticity and stiffness could be altered to enable long term tubule survival. Bronchotubule models enable the investigation of how epithelial-stromal cell and cell-ECM communication drive tissue patterning, repair and development of disease.