Abstract 12969: High Density Lipoprotein Bound Circulating microRNAs in Patients with Coronary Disease

Abstract

MicroRNAs (miRs) are small non-coding RNAs that regulate gene expression patterns. Recent studies demonstrate that miRs can be released and circulate in the blood in a remarkably stable form being protected by extracellular vesicles, proteins or high density lipoprotein (HDL). In our study we evaluated the regulation and function of HDL-bound miRs in patients with coronary disease compared to healthy subjects. HDL-bound miRs were detected in HDL isolated from healthy subjects (HS; n=10), patients with stable coronary artery disease (CAD; n=10) or an acute coronary syndrome (ACS; n=10) by quantitative real-time PCR. In HDL from HS, the liver-derived miR-223 was detected at >10.000 copies/µg HDL and the vascular miR-126 and miR-92a at about 3000 copies/µg HDL. The smooth muscle miR-145, the inflammation associated miR-146 and miR-155 and the metabolically controlled miR-378 were detected at levels below 120 copies/µg. HDL-miRs significantly correlated with the total copy numbers detected in plasma (r=0.5852; p<0.0001). MiR signatures only slightly varied in patient-derived HDL, which showed a reduction of HDL-bound miR-92a (67+14 % ACS compared to HC, p<0.05). To investigate whether circulating HDL-bound miRs are taken up by endothelial cells (EC), HDL was artificially loaded with C. elegans specific miR and incubated with EC. However, only low copy numbers (<50 copies C. elegans miR/EC) were detected in EC. In addition, incubation of EC with native HDL significantly reduced the endogenous expression of miR-223 (44+19% reduction, p<0.05), miR-92a (28+12 % reduction, p<0.05) and miR-126 (44+16% reduction, p<0.05) suggesting that HDL reduces the biosynthesis or enhances the export of miRs from EC. Interestingly, HDL from patients with CAD or ACS did not reduce endothelial miRs but induced a significant up-regulation (miR-223: 135+11%, miR-92a:133+9%, miR-126:144+15% EC with ACS-HDL compared to control EC). In conclusion we could detect circulating miRs in HDL. However, HDL-bound miRs are not efficiently taken up by EC in vitro. HDL from healthy subjects even transiently reduced several endothelial miRs, whereas patient-derived HDL significantly augmented endothelial miRs suggesting a disease-specific regulation of miR biosynthesis by HDL in EC.