Up-regulation of exosomal miR-106a may play a significant role in abdominal aortic aneurysm by inducing vascular smooth muscle cell apoptosis and targeting TIMP-2, an inhibitor of metallopeptidases that suppresses extracellular matrix degradation.

Abstract

Abdominal aortic aneurysm (AAA) rupture is a dramatic and lethal clinical condition with a high risk of death. Emerging evidence indicates a role for miRNAs in AAA pathogenesis, therefore we aimed to identify miRNAs that differently expressed in exosomes from AAA patients and explore the underlying mechanisms of how miR-106a plays its role in this disease. Exosomes were isolated from plasma of AAA patients, as well as from the tissue-conditioned culture medium. The exosomal expression profiles of several miRNAs including miR-106a were analyzed by quantitative RT-PCR. To determine the potential role of miR-106a in the pathogenesis of AAA, miR-106a was overexpressed in vascular smooth muscle cells (VSMCs), and then cell viability and apoptosis were evaluated by performing CCK-8 assay and flow cytometry, respectively. Afterwards, enzyme-linked immunosorbent assay (ELISA) was applied to assess the expression levels of some proteins involved in the modulation of extracellular matrix (ECM) homeostasis. Furthermore, the target gene of miR-106a was predicted and verified through Dual-Luciferase reporter assay. MiR-106a was up-regulated in exosomes from plasma of those patients with AAA as compared with healthy peers. Likely, increased level of miR-106a was observed in exosomes released from AAA tissue in comparison to those from adjacent normal tissues. Enhanced expression of miR-106a in VSMCs suppressed cell viability but promoted cellular apoptosis, whereas inhibition of miR-106a in VSMCs resulted in a significant decrease in the percentage of apoptotic cells compared to the control group. In addition, the protein levels of matrix metalloproteinases (MMPs, including MMP-2 and MMP-12) secreted from VSMCs were significantly up-regulated, while their inhibitor TIMP-2 was down-regulated due to miR-106a overexpression. Finally, TIMP-2 was validated subsequently as the direct target of miR-106a through Dual-Luciferase reporter assay. In aggregate, our results suggest that increased expression of miR-106a promotes VSMC cell apoptosis and down-regulates TIMP-2 through directly targeting its 3'-UTR, which in turn restores MMP production and ultimately accelerates ECM degradation. Therefore miR-106a is proposed to play a crucial role in AAA development and this will provide an update on the understanding of the clinical value of miRNAs as novel therapeutic targets for the treatment of this disease.