Circulating Endothelial Cells as Vascular Aging Sensors

Endothelial cells (ECs) line all blood vessels in our body. As we grow older, these tissue- resident ECs become dysfunctional, which increases our risk of developing cardiovascular diseases. Right now, we do not have a good understanding of what really happens to ECs in terms of their function and molecular characteristics during the process of aging. Moreover, obtaining tissue-resident ECs requires invasive biopsy sampling, which substantially hampers our ability to obtain an all-encompassing view of the diverse makeup and function of aging ECs throughout the human body. In that light, a small fraction of human blood is made up of circulating endothelial cells (CECs) involved in the maintenance and repair of our blood vessels. In principle, CECs can be extracted non-invasively and thus represent an ideal candidate to indirectly probe the health status of the blood vessels in our body. Yet, their translational use has been very limited thus far, as we currently lack an in-depth understanding of their molecular profile. We hypothesize that CEC-derived gene expression signatures in human blood mirror characteristics of aging-associated dysfunction of tissue-resident ECs. To study this, we leverage a technology called single-cell RNA-sequencing (scRNA-seq), with which the gene expression patterns of thousands of (C)ECs can be studied at once, one cell at a time. By mining a large body of publicly available scRNA-seq datasets, we will establish a high- resolution single-cell atlas of tissue-resident ECs across human organs and ages. This effort will help us chart aging-associated EC gene expression diversity throughout the body in a cost- effective, high-resolution setup. Moreover, we will freshly collect CECs from healthy young, middle-aged, and aged human blood donors, and subject these to scRNA-seq. This will result in the first-of-its-kind deep characterization of this cell type at single-cell resolution in healthy aging, to aid the uncovering of its full translational potential in a vascular aging context. By combining both scRNA-seq efforts, we aim to discover gene expression patterns in CECs that can predict their tissue-of-origin. Lastly, using liver fibrosis as a proof-of-concept, we will investigate the potential of CECs to also reflect the disease status of our tissue-resident endothelium. Altogether, our investigations are intended to set the stage for a fundamental change in the way we detect and investigate human vascular aging and aging-associated disease.