Pulmonary Microvascular Endothelial Cells Support Alveolar Epithelial Growth via Bone Morphogenetic Protein 6 Secretion

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation and emphysema development, associated with enhanced tissue destruction and defective repair. Supporting cells in the alveolar niche play a crucial role in guiding the activation of alveolar epithelial progenitor cells during repair. Despite their close anatomical proximity, understanding of the supportive role of the pulmonary microvascular endothelium in adult alveolar epithelial repair remains limited. We hypothesized that factors secreted by pulmonary endothelial cells support alveolar epithelial cell growth. Here, we report that human pulmonary microvasculature endothelial cells (HPMECs) support murine and human alveolar organoid formation through paracrine signaling via the secretion of extracellular vesicles and soluble factors. Transcriptomic and proteomic analysis pinpointed HPMEC-derived bone morphogenetic protein 6 (BMP6) as a critical factor for alveolar organoid formation. BMP6 promoted alveolar epithelial cell growth, whereas function-blocking antibodies targeting BMP6 inhibited the beneficial effect of endothelial cells on murine alveolar organoid formation. Transcriptomic analysis revealed that BMP6 specifically enhances distal epithelial cell markers and increases Wnt signaling in epithelial progenitors. In contrast, BMP6 deficiency in mouse lungs was associated with reduced Wnt signaling and augmented oxidative stress signaling in murine lung tissue. Taken together, our findings highlight BMP6 as a key regulator of adult epithelial repair and suggest its potential as a therapeutic target for defective epithelial repair, particularly in individuals with early stages of COPD.