Endothelialized Bronchioalveolar Lung Organoids Model Endothelial Cell Responses to Injury

Organoid three-dimensional systems are powerful platforms to study development and disease. Recently, the complexity of lung organoid models derived from adult mouse and human stem cells has increased substantially in terms of cellular composition and structural complexity. However, a murine lung organoid system with a clear integrated endothelial compartment is still missing. Here, we describe a novel method that adds another level of intricacy to our published bronchioalveolar lung organoid (BALO) model by microinjection of FACS-sorted lung endothelial cells (ECs) into differentiated organoid cultures. Before microinjection, ECs obtained from the lung homogenate of young mice expressed typical EC markers such as CD31 and vascular endothelial cadherin and showed tube formation capacity. Following microinjection, ECs surrounded the BALO's alveolar-like compartment, aligning with type I and type II alveolar epithelial cells, as demonstrated by confocal and electron microscopy. Notably, expression of Car4 and Aplnr was as well detected, suggesting the presence of EC microvascular phenotypes in the cultured ECs. Moreover, upon epithelial cell injury by LPS and influenza A virus, endothelialized BALOs released proinflammatory cytokines, leading to the upregulation ICAM-1 (intercellular adhesion molecule 1) in ECs. In summary, we characterized for the first time an organoid model that incorporates ECs into the alveolar structures of lung organoids, not only increasing our previous model's cellular and structural complexity but also providing a suitable niche to model lung endothelium responses to injury <i>ex vivo</i>.