Objectives Circulating microRNAs (miRNAs) are gaining more substantial research in recent years. They may serve as biomarker of certain diseases, and they are also biological active in disease progression. High density lipoprotein (HDL) was proved to be an novel endogenous circulating miRNA transporters. Low density lipoprotein (LDL) is similar to HDL in molecular structure, can also transport miRNAs in plasma. The aim of the study was to prove the existence of miRNAs in LDL, and reveal the changes in patients in coronary artery disease.

Methods Samples from 3 patients with coronary angiography diagnosed CAD and 3 healthy controls. LDL (1.019-1.063 g/ml) was isolated from the plasma by sequential ultracentrifugation, followed by desalting and dehydration by ultrafiltration. The LDL was then further purified by fast protein liquid chromatography. The expression of Ago2, NPM1 and CD63 in plasma and LDL were detected by western-blot methods. Total RNA was isolated from the highly purified LDL by mirVana^TM miRNA isolation kit. The miRNA expression profiles were analysed by miRCURY ^TM LNA Array (v.18.0) chip.

Results Ultracentrifugation and FPLC can separate the LDL from other miRNA protein transporters. The apolipoprotein in highly purified LDL was apoB100, without any HDL components (apoAI). The miRNA chip revealed that LDL contains up to 280 miRNAs. LDL from CAD patients contains more miR-4778-5p than that from the healthies. Biological imformation studies reveal that the potential target genes of miR-4778-5p is ABCA1 and ABCG1. miR-4778-5p might regulate cholesterol efflux by regulating ABCA1 and ABCG1 directly.

Conclusions LDL is an novel endogenous miRNA transporter. The expression profiles were significantly changed in CAD patients. The miRNAs in LDL might be biological active in atherosclerosis.