Vascularization of the adult mouse lung grafted onto the chick chorioallantoic membrane.

In the later stages of angiogenesis, the vascular sprout transitions into a functional vessel by fusing with a target vessel. Although this process appears to routinely occur in embryonic tissue, the biologic rules for sprout fusion and lumenization in adult regenerating tissue are unknown. To investigate this process, we grafted portions of the regenerating post-pneumonectomy lung onto the chick chorioallantoic membrane (CAM). Grafts from all 4 lobes of the post-pneumonectomy right lung demonstrated peri-graft angiogenesis as reflected by fluorescent plasma markers; however, fluorescent microsphere perfusion primarily occurred in the lobe of the lung that is the dominant site of post-pneumonectomy angiogenesis-namely, the cardiac lobe. Vascularization of the cardiac lobe grafts was confirmed by active tissue growth (p < .05). Functional vascular connections between the cardiac lobe and the CAM vascular network were demonstrated by confocal fluorescence microscopy as well as corrosion casting and scanning electron microscopy (SEM). Bulk transcriptional profiling of the cardiac lobe demonstrated the enhanced expression of many genes relative to alveolar epithelial cell (CD11b/CD31) control cells, but only the upregulation of Ereg and Fgf6 compared to the less well-vascularized right upper lobe. The growth of actively regenerating non-neoplastic adult tissue on the CAM demonstrates that functional lumenization can occur between species (mouse and chick) and across the developmental spectrum (adult and embryo).