Involvement of macrophage-derived exosomes in abdominal aortic aneurysms development

Background and aims: Abdominal aortic aneurysm (AAA) is characterized by infiltration of inflammatory cells, extracellular matrix (ECM) degradation, and dysfunction of vascular smooth muscle cells (VSMCs). Recent studies reported that exosomes mediate intercellular communication and are involved in different diseases. Whether exosomes play a role in AAA is poorly understood. Hence, this study evaluated the function of exosomes in AAA development. Methods: The presence of exosomes in human and calcium phosphate (CaPO4)-induced AAA tissues was determined by immunofluorescence staining of CD63 and Alix. GW4869, an inhibitor of exosome biogenesis, was intraperitoneally injected into CaPO4-induced AAA tissues to evaluate the effects of exosomal inhibition on AAA development. To explore the underlying mechanisms, the human monocytic cell line THP-1 was differentiated into macrophages, and exosomes were collected from macrophages. VSMCs were treated with macrophagederived exosomes, and the expression of matrix metalloproteinase-2 (MMP-2) was evaluated. The activation of mitogen-activated protein kinases (MAPKs) pathways was also investigated in vitro and in vivo. Results: Exosomes were detected in the adventitia of aneurysmal tissues obtained from humans and mice. They were mainly expressed in clusters of macrophages. Intraperitoneal injection of GW4869 for two weeks significantly attenuated the progression of CaPO4-induced AAA, preserved elastin integrity and decreased MMP-2 expression. Similarly, administration of GW4869 suppressed the systemic and aneurysmal exosome generation. In vitro, treatment with macrophage-derived exosomes elevated MMP-2 expression in human VSMCs, while pretreatment with GW4869 abolished these effects. It was also found that JNK and p38 pathways mediated the production of MMP-2 in VSMCs following treatment with macrophage-derived exosomes. Conclusions: This study suggests that exosomes derived from macrophages are involved in the pathogenesis of AAA. Macrophage-derived exosomes trigger MMP-2 expression in VSMC via JNK and p38 pathways. GW4869 supplementation attenuates CaPO4-induced AAA in mice.