Background and Hypothesis: Extracellular vesicles (EVs) are membrane-bound particles shed from a variety of cell types. They contain molecular cargo from the parent cell including metabolites, proteins, and nucleic acids. EVs are present in biofluids and could be promising biomarkers for monitoring wellness. Total sedentary time is linearly associated with cardiovascular and coronary heart disease mortality risk among older women, indicating the intensive impact of sedentary behavior on the circulatory system. Endothelial cells (ECs) provide a barrier and maintain circulatory homeostasis in response to physical and biochemical stimuli. We hypothesize that EC-derived EV count and content changes with EC health and that EC-EVs play a role in bridging sedentary lifestyle with cardiovascular disease risk.
Materials and Results: Archival parent study data and plasma samples from a combined cohort of 518 women aged ≥55 years and BMI ≥25kg/m ² enrolled in the Metabolic, Exercise, and Nutrition at UCSD, Reach for Health, and Community of Mine studies were available to examine EV levels and contents associated with sitting time. Physical activity was measured objectively using accelerometers. Women in the lowest quartile of moderate-vigorous physical activity and who had the highest and lowest mean sitting bout duration across quartiles were indicated as Super Sitters and Interrupted Sitters, respectively. For EC-EV characterization, CD144 was shown to be a specific marker of EC-derived EVs and an anti-CD144 antibody specifically recognized EC-derived EVs from human plasma. EV biochemical markers (e.g., Hsp70, LAMP1, and CD63) were detected on the CD144 ⁺ EVs. Immune-gold staining identified CD81, CD63, LAMP1, and CD144 on individual EVs with a typical toroidal shape featuring phospholipid-bilayers using transmission electron microscopy. A protection assay showed CD144 ⁺ EVs protect miR-126, an EC-enriched miRNA, from RNase degradation. Study of EV levels and contents in plasma from Super Sitter and Interrupted Sitter groups is underway.
Conclusion: CD144 ⁺ EVs carrying molecular cargo from ECs. Hence, EVs and their cargo (e.g., miRNAs) are valuable for examination as novel biomarkers associated with sedentary behavior-induced cardiovascular risk.