Clearance of matrix metalloproteinase-9 is dependent on low-density lipoprotein receptor-related protein-1 expression downregulated by microRNA-205 in human abdominal aortic aneurysm.

Objective: Low-density lipoprotein receptor-related protein-1 (LRP1) has been suggested to be a crucial regulator in the pathogenesis of abdominal aortic aneurysm (AAA) from previous genome association and animal studies. Our prior study using human aortic samples has further revealed a significant reduction of LRP1 protein expression associated with AAA. However, the downregulation of LRP1 in the pathophysiology of AAA remained unresolved. We hypothesized that LRP1 downregulation may be mediated by microRNA (miR) and that LRP1 may function as a scavenger of matrix metalloproteinase-9 (MMP-9), a well-known protease for degradation of extracellular matrix proteins at the aortic wall for AAA pathogenesis. This study investigated the cause of LRP1 downregulation and its potential effect on AAA pathogenesis.

Methods: An observational study of LRP1 protein, LRP1 messenger RNA (mRNA), and its three predicted miR candidates (miR-205, miR-338-5p, and miR-545-3p) was first performed in AAA compared with nonaneurysmal tissues from humans, followed by a functional study testing the effect on LRP1 expression of miR-205 overexpression and knockdown in human vascular smooth muscle cells (VSMCs) explant cultured from human abdominal aortic tissues. Lastly, another functional study was performed to test for the clearance of exogenous MMP-9 upon silencing of LRP1 in human VSMCs.

Results: From the observational study, significantly higher miR-205 (P < .001) and lower LRP1 protein (P < .001) expressions were found in human AAA tissues compared with nonaneurysmal aortic tissues, and no significant difference in LRP1 mRNA expression was observed. Further statistical analysis showed a significant negative correlation between miR-205 and LRP1 protein expressions (r = -0.65; P < .01). For the functional study, a significant downregulation of LRP1 protein expression was shown in miR-205-overexpressing VSMCs (P < .05), without any alteration in LRP1 mRNA expression. Moreover, a significantly reduced clearance of exogenous MMP-9 was observed in LRP1-silenced VSMCs (P < .05), and this difference in MMP-9 clearance was completely abolished with a pretreatment of anti-LRP1 antibody.

Conclusions: Our study revealed the downregulation of LRP1 protein expression may be tightly regulated by miR-205 through translational inhibition in human VSMCs. Also, such LRP1 down-regulation in VSMCs may hinder the removal of pericellular MMP-9, leading to excess MMP-9 remaining in the extracellular matrix. Hence, the integrity of the vascular wall may be disrupted, promoting AAA formation.