Characterization of Levels and Cellular Transfer of Circulating Lipoprotein-Bound MicroRNAs

Objective-MicroRNAs are important intracellular regulators of gene expression, but also circulate in the blood being protected by extracellular vesicles, proteins, or high-density lipoprotein (HDL). Here, we evaluate the regulation and potential function of HDL-andlow-density lipoprotein-bound miRs isolated from healthy subjects and patients with coronary artery disease. Approach and Results-HDL-bound miRs with known effects in the cardiovascular system were analyzedin HDL isolated from healthy subjects (n= 10), patients with stable coronary artery disease (n= 10), and patients with an acute coronary syndrome (n= 10). In HDL from healthy subjects, miR-223 was detected at concentrations > 10 000 copies/mu g HDL, and miR-126 and miR-92a at about 3000 copies/mu g HDL. Concentrations of most miRs were substantially higher in HDL as compared with low-density lipoprotein. However, HDL-bound miR-223 contributed to only 8% of the total circulating miRs. The signatures of miRs varied only slightly in HDL derived from patients with coronary artery disease. We did not observe a significant uptake of HDL-bound miRs into endothelial cells, smooth muscle cells, or peripheral blood mononuclear cells. However, patient-derived HDL transiently reduced miR expression particularly when incubated with smooth muscle and peripheral blood mononuclear cells. Conclusions-Circulating miRs are detected in HDL and to a lesser extent in low-density lipoprotein, and the miR-signatures are only slightly altered in patients with coronary artery disease. Lipoprotein-bound miRs were not efficiently delivered to endothelial, smooth muscle, and peripheral blood mononuclear cells suggesting that the lipoprotein-associated pool of miRs is not regulating the function of the studied cells in vitro.