RESEARCH ARTICLE Possible Dual Role of Decorin in Abdominal

Abdominal aortic aneurysm (AAA) is characterized by chronic inflammation, which leads to pathological remodeling of the extracellular matrix. Decorin, a small leucine-rich repeat pro-teoglycan, has been suggested to regulate inflammation and stabilize the extracellular ma-trix. Therefore, the present study investigated the role of decorin in the pathogenesis of AAA. Decorin was localized in the aortic adventitia under normal conditions in both mice and humans. AAA was induced in mice using CaCl2 treatment. Initially, decorin protein lev-els decreased, but as AAA progressed decorin levels increased in all layers. Local adminis-tration of exogenous decorin prevented the development of CaCl2-induced AAA. However, decorin was highly expressed in the degenerative lesions of human AAA walls, and this ex-pression positively correlated with matrix metalloproteinase (MMP)-9 expression. In cell cul-ture experiments, the addition of decorin inhibited secretion of MMP-9 in vascular smooth muscle cells, but had the opposite effect in macrophages. The results suggest that decorin plays a dual role in AAA. Adventitial decorin in normal aorta may protect against the devel-opment of AAA, but macrophages expressing decorin in AAA walls may facilitate the pro-gression of AAA by up-regulating MMP-9 secretion