Abstract 15509: “Root” Endothelial Cells: A Novel Population That Regulates Lung Capillary and Artery Maintenance and Repair

Abstract

Introduction: Pulmonary capillary endothelial cells (ECs) are vital for various lung functions, such as maintaining the capillary network, promoting angiogenesis and facilitating gas and nutrient exchange. Recent advancements in single-cell transcriptomics have uncovered novel populations of general capillary ECs (gCaps) in the lungs. Understanding specialized EC types provides valuable insights into pulmonary vascular diseases. We aimed to challenge current understanding of the regenerative capabilities of lung resident ECs. Methods: Highly enriched ECs isolated from rat and mouse lungs underwent single-cell transcriptomics to explore EC population diversity. Results: UMAP annotation of ECs identified five novel general capillary cell populations (gCaps A-E). Lineage confirmation was achieved by Apelin receptor expression. Two distinct zonations (AV-zonation) were observed between pulmonary artery and vein ECs, with specific gCaps phenotypes (A: Clic4+, B: Flot1+, D: Scn7a+, E: Lingo2+), indicating a gradual phenotypic transition from arterial to vein ECs. Within the AV-zonation, a small population of gCapB (Flot1+) cells, resided at the interface of small artery ECs and gCap A and D, exhibiting characteristics of Root cells. RNA velocity analysis suggested Root cells as the origin of capillary and arterial cell lineages. PAGA analysis revealed high transcriptional similarity between gCapB and gCaps A, D, E and arterial cells, suggesting gCapB's role in capillary and arteriole formation and repair. Root cells exhibited upregulation of transcription factors Fos and Jun, promoting EC proliferation and angiogenesis, along with the Foxo and associated cell cycle regulation pathways. Root cells also displayed high G2M and S scores, indicating mitotic activity, supporting their role as the origin of capillary and arterial ECs. Elevated expression of CDKn1a and 1c, crucial for stem cell maintenance and differentiation further implied the repair potential of Root cells. Conclusions: Root Cells (gCapB) play a crucial role in regulating capillary and arteriole formation and repair by serving as a source of capillary and arterial ECs. These findings enhance our understanding of pulmonary vascular maintenance and repair mechanisms.