D109-01 Single-Cell Insight into a Transitional Aerocyte Subtype Bridging Aerocytes and General Capillary Endothelial Cells

Rationale Aerocytes (aCaps) facilitate gas exchange, while general capillary endothelial cells (gCaps) support immune and barrier functions. Although gCaps show transcriptional diversity, the heterogeneity of aCaps and its connection to injury responses remain unclear. We hypothesize that aerocytes have an intermediate state that appears during development and re-emerges under stress. Methods We analyzed single-cell RNA sequencing profiles of endothelial cells from rat lungs collected at 2, 6, and 12 weeks postnatal under normal and hypoxic conditions, and from human lungs. Standard Seurat workflows were used for quality control, normalization, dimensionality reduction, clustering, and differential expression analysis. Cell states were identified by canonical markers and mapped in UMAP space at the aCap-gCap interface. Results Across species, we identified two aerocyte clusters. Both expressed canonical aCap markers (Car4, Ednrb, Sostdc1, Tbx2), but a second cluster, Aerocyte 2, also expressed gCap-linked genes (Kit, Aplnr, Ptprb, Gpihbp1), placing it transcriptionally between aCaps and gCaps and forming a distinct boundary cluster in UMAP. In a developmental time course, Aerocyte 2 marker expression were more prevalent at early postnatal stages and declined as the animals reached maturity. Notably, Aerocyte 2 shared signatures with the reported “iCap” (injury-induced capillary) population; yet, we observed it under normal postnatal conditions, suggesting that iCaps likely recapitulate a physiological repair program to restore mature aerocytes rather than representing a purely disease-specific state. Under hypoxia, total aerocytes decreased in rats, but the proportion of Aerocyte 2 increased; in human pulmonary hypertension model, both total aerocytes and Aerocyte 2 declined. Conclusions We define a conserved intermediate aerocyte (iCap-like) endothelial state that 1) is prevalent during postnatal lung growth, 2) diminishes with maturation, and 3) expands under stress. Its developmental presence supports a model in which injury triggers a developmental repair program to rebuild the aerocyte compartment. These findings clarify the role of iCaps, explain aerocyte lineage dynamics, and identify potential targets to influence capillary repair and remodeling during development and disease. This abstract is funded by: NIH