Abstract 16783: Discovery and Characterization of Transient Endothelial Stem-Like Cells Responsible for Rapid Lung Microvascular Regeneration Post Endothelial Ablation

Abstract

Background: Single-cell RNA sequencing (scRNA-seq) has revealed two main types of alveolar capillary endothelial cells (ECs): aCap ECs (or aerocytes) express typical aCap markers, including apelin, whereas general (gCap) ECs express apelin receptor, Aplnr /APJ. Aerocytes constitute the air-blood barrier and are incapable of proliferation, unlike smaller gCap ECs that can proliferate. Hypothesis: After lung microvascular injury, gCap ECs give rise to stem-like ECs that can regenerate depleted lung EC populations, including highly specialized aerocytes. Approach: scRNA-seq was used to study depletion and regeneration of lung EC populations after intratracheal instillation of diphtheria toxin (DT) in transgenic mice harboring an EC-targeted human DT receptor. Results: DT resulted in ~80% loss of lung microvascular EC populations including aerocytes, associated with severe acute lung injury (ALI), and there was full spontaneous recovery by day 7. Interestingly, a novel EC population appeared at day 3 post injury in a transitional gCap EC cluster characterized by paradoxical expression of ‘aCap’ marker, apelin, together with endothelial progenitor/stem cell markers, Cd34 and endothelial protein C receptor ( Procr /EPCR). These ‘transient endothelial stem-like cells’ (TESCs) transitioned to highly proliferative progenitor-like FoxM1 + cells ultimately repopulating all depleted EC populations by day 7. Using flow cytometry of lung cells harvested at 3 days post DT instillation, TESCs were identified by unique co-expression of CD34 and EPCR (Figure), thereby allowing isolation and culture in vitro for further characterization of their proliferation and differentiation potential. Conclusions: Lung microvascular repair is orchestrated by the emergence of stem-like, gCap ECs (TESCs), transiently expressing aCap/aerocyte marker, apelin, together with Procr /EPCR, which have the capacity to regenerate lung microvasculature rapidly and efficiently.