Aging and DNA damage are associated with the development of endothelial cell clonal expansion

Endothelial dysfunction is a hallmark of vascular aging and a key contributor to cardiovascular disease. Although senescence has been widely studied as a terminal endothelial cell fate, recent evidence suggests that clonal expansion, the proliferative expansion of genetically identical cells, may also occur in aged tissues. We sought to determine whether endothelial clonal expansion increases with age, specifically at the atheroprone regions of the aorta, and to evaluate whether DNA damage promotes endothelial cell clonal expansion. Tamoxifen-inducible, endothelial-specific Cdh5-CreERT2 male and female mice were used to quantify clonal expansion in endothelial cells (ECs) across the aortic region in both young (4 mo) and aged (24 mo) mice. We further examined the effect of DNA damage by administering systemic doxorubicin (DOXO) to assess clonal dynamics in different aortic regions. Aging significantly increased EC clone size and the percentage of clonal ECs in atheroprone regions, particularly the minor arch, whereas only clone size increased in nonatheroprone regions. Systemic DOXO administration increased clone size across the aortic region without altering clonal recruitment, indicating selective amplification of preexisting clones. These findings suggest that clonal expansion is promoted by both aging and DNA damage. Clonal expansion may represent an underrecognized mechanism contributing to endothelial homogeneity and vascular remodeling during aging and in response to sublethal genomic stress.NEW & NOTEWORTHY Aging reshapes the vascular endothelium in unexpected ways. Using lineage tracing in mice, we show that endothelial cells undergo age-dependent clonal expansion, particularly in atheroprone regions exposed to disturbed blood flow. This process is amplified by DNA damage and reflects the selective expansion of preexisting clones rather than increased recruitment. Endothelial clonal expansion may represent an underrecognized mechanism driving vascular remodeling during aging and genotoxic stress.