Unraveling the role of sex in endothelial cell dysfunction – Evidence from lineage tracing mice and cultured cells

Background: Biological-sex differences play a vital role in cardiovascular diseases, including atherosclerosis. The endothelium is a critical contributor to cardiovascular pathologies since endothelial cells (EC) regulate vascular tone, redox balance, and inflammatory reactions. Although EC activation and dysfunction play an essential role in the early and late stages of atherosclerosis development, little is known about sex-dependent differences in EC. Methods: We used aortic EC that was isolated from 13-week-old female and male mice as well as EC-lineage tracing (Cdh5-CreERT2 Rosa-YFP) atherosclerotic Apoe-/- mice to investigate the biological sexual dimorphism of the EC functions in vitro and in vivo. RNA sequencing (RNAseq) analyses were performed on male and female mouse aortic EC and human lung EC. Results: In vitro, female mouse aortic EC (F_MAEC) showed more apoptosis and higher cellular ROS levels, lower mitochondrial membrane potential (??m), and lower levels of mitochondrial transcription factor A (TFAM) than male aortic EC (M_MAEC). Additionally, F_MAEC had decreased angiogenic potential (tube formation, cell viability, and proliferation) compared to M_MAEC. In vivo, female mice had significantly higher lipid accumulation within the aortas, less efficient outward vessel remodeling, and lower endothelial-mediated vasorelaxation than males. Using the EC-lineage tracing approach, we found that female lesions had significantly lower rates of intraplaque neovascularization and Endothelial-to-Mesenchymal (EndoMT) transition within advanced atherosclerotic lesions but higher incidents of missing EC lumen coverage and higher levels of oxidative products and apoptosis. RNAseq analyses revealed that both mouse and human female EC had higher expression of genes associated with inflammation and apoptosis and lower expression of genes related to angiogenesis and oxidative phosphorylation than male EC. Conclusions: Our study delineates critical sex-specific differences in EC relevant to pro-inflammatory, pro-oxidant, and angiogenic characteristics, which are entirely consistent with a vulnerable phenotype in females. Our results provide a biologic basis for sex-specific pro-atherosclerotic mechanisms. Overall design: To investigate the sexual dimorphism of endothelial cells, we isolated endothelial cells from male and female mouse aortas. We established mouse aortic primary cultured endothelial cells. We then performed gene expression profiling analysis of RNA-seq data for sexual dimorphism of endothelial cells.