Genetic Ablation of miR-146a Induces Abdominal Aortic Aneurysm Formation by Intensifying Inflammatory M1-Like Macrophages Polarization and Vascular Smooth Muscle Cell Phenotypic Switching

Abstract

Background: Abdominal aortic aneurysm (AAA), a pathological dilation of the abdominal aorta, is primarily driven by chronic aortic wall inflammation. The well-established anti-inflammatory microRNA 146a (miR-146a) has been implicated as a key regulator in various chronic inflammatory pathologies. However, its potential functional role in the pathogenesis of AAA remains to be elucidated.

Methods: We constructed Ang II (angiotensin II)-induced and PPE (porcine pancreatic elastase)-induced models in global miR-146a knockout mice, vascular smooth muscle cell (VSMC)-specific miR-146a knockout mice, and macrophage-specific miR-146a knockout mice, respectively, to explore the role of miR-146a in AAA. Western blot, quantitative polymerase chain reaction, and immunohistochemistry were used to detect the levels of aortic proinflammatory markers and VSMC contractile proteins, whereas flow cytometry was used to assess M1/M2-like macrophage polarization. To validate the downstream mechanism, dibenzazepine was intraperitoneally injected to inhibit the Notch1 pathway in rescue experiments.

Results: In the Ang II-induced and PPE-induced model, global knockout of miR-146a promoted AAA development, increased maximal aortic diameter, exacerbated medial elastin degradation, and upregulated aortic proinflammatory markers (COX2 [cyclooxygenase 2], MMP [matrix metalloproteinase] 2, MMP9, and CCL2 [chemokine (C-C motif) ligand 2]). Flow cytometry analysis revealed that global miR-146a deficiency also induced macrophage polarization toward the inflammatory M1 phenotype. Conditional deletion of miR-146a in VSMCs and macrophages largely replicated AAA formation and proinflammatory effects. Furthermore, AAV9-mediated miR-146a knockdown significantly reduced VSMC contractile proteins CNN1 (calponin 1), SM22α (smooth muscle 22α), and α-SMA (α-smooth muscle actin) in mouse aortas at 7 days post-Ang II perfusion. Mechanistically, Notch1 antagonist dibenzazepine effectively rescued AAA characteristics and M1 biomarkers while enhancing M2 biomarkers in global miR-146a knockout mice.

Conclusions: The absence of miR-146a potentiates AAA formation by promoting VSMC phenotypic switching, Notch1 signaling-mediated aortic inflammation, and macrophage M1 polarization. Thus, miR-146a plays a critical role in maintaining aortic structural integrity to prevent aneurysmal pathogenesis.

Keywords: aortic aneurysm, abdominal; inflammation; knockout, mice; macrophages; muscle, smooth, vascular.