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Acute coronary syndrome (ACS) is characterized by atherosclerotic plaque rupture with a high incidence of recurrent ischemic events. Several microRNAs are found to be aberrantly expressed in atherosclerotic plaques. This study aims to investigate the effects of microRNA‐9 (miR‐9) on vulnerable atherosclerotic plaque and vascular remodeling in ACS and underlying mechanisms. Microarray‐based gene expression profiling was used to identify differentially expressed genes related to ACS and regulatory miRNAs. Oxidized low‐density lipoprotein (lectin‐like) receptor 1 (OLR1) was identified to be aberrantly activated in ACS and regulated by miR‐9. OLR1 was verified as a target gene of miR‐9 by bioinformatics prediction and dual luciferase reporter gene assay. The atherosclerotic models were induced in ApoE−/− mice, in which the agomir or antagomir of miR‐9, or small interfering RNA (siRNA) against OLR1 were separately introduced. Serum lipid levels and expression of vascular remodeling and inflammatory response‐related factors were determined, respectively. On the basis of the obtained results, in the atherosclerosis mice treated with the agomir of miR‐9 and siRNA against OLR1, the p38‐mitogen‐activated protein kinase (p38MAPK) pathway was inhibited; levels of triglyceride, total cholesterol, low‐density lipoprotein cholesterol, tumor necrosis factor‐α, interleukin‐6, and vascular endothelial growth factor were reduced, but the high‐density lipoprotein cholesterol level was increased, along with decreased vulnerable atherosclerotic plaque area and enhanced vascular remodeling. Taken together, these findings suggested an inhibitory role miR‐9 acts in the formation of vulnerable atherosclerotic plaques in ACS mice, along with a promoted vascular remodeling, via a negative feedback regulation of OLR1‐mediated p38MAPK pathway.

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