Emphysema is a component of Chronic Obstructive Pulmonary Disease (COPD) and is characterized by alveolar wall destruction. Microvascular endothelial cell dysfunction is thought to contribute to emphysema development. We aimed to study the interactions of human pulmonary microvascular endothelial cells with alveolar cells in repair and regeneration.

CD31⁺ endothelial cells and HTII-280⁺ alveolar epithelial type 2 cells (AEC2) were isolated from resected peripheral human lung tissue and expanded in vitro. AEC2 were seeded in hydrogel in the insert and organoid formation was assessed in the presence or absence of endothelial cells. Endothelial cells were repeatedly exposed (every 2 days, 4 times in total, with 0.5 AU/ml for 15 min) to cigarette smoke extract (CSE) or medium, as controls. In another model, AEC2 were cultured in a monolayer in the insert, before a circular wound was created, followed by transferring inserts into a plate with a monolayer of endothelial cells in the bottom well.

Co-culture of AEC2 with lung endothelial cells increased (4-fold) alveolar organoid numbers after 12 days (n=6) and repeated CSE exposures significantly decreased the alveolar organoid numbers (3-fold; n=4). Endothelial expression of genes involved in alveolar support (TMEM100, ALK1, BMPR1, MMP14, TSP-1) was reduced upon exposure to CSE. In the second model, the presence of endothelial cells reduced the residual wound area by 19% at day 7. The closed wound area had cells with an AEC1 morphology and  lacked AEC2 markers.

These data indicate that pulmonary endothelial cells support alveolar repair and regeneration, while cigarette smoke exposure inhibits the alveolar support function of endothelial cells.