Regulation of matrix reloading by tumor endothelial marker 1 protects against abdominal aortic aneurysm

Tumor endothelial marker 1 (TEM1), an activated mesenchymal cell marker, is implicated in tissue remodeling and repair. Herein, we investigated the role and therapeutic implications of TEM1 in abdominal aortic aneurysm (AAA), a potentially life-threatening aortic disease characterized by vascular inflammation and matrix turnover. Characterization of human AAA revealed increased TEM1 expression derived mainly from medial vascular smooth muscle cells (VSMCs) and adventitial fibroblasts. Bioinformatics analysis demonstrated the association between TEM1-expressing VSMCs and fibroblasts and collagen gene expression. Consistently, collagen content and TEM1 expressed by VSMCs and fibroblasts were increased during CaCl2-induced AAA formation in mice. TEM1 silencing in VSMCs and fibroblasts inhibited transforming growth factor-β1-induced phenotypic change, SMAD2 phosphorylation, and COL1A1 gene expression. Also, Tem1 deficiency reduced collagen synthesis and exacerbated CaCl2-induced AAA formation in mice without disturbing elastin destruction and inflammatory responses. In contrast, rTEM1 promoted phenotypic change and COL1A1 gene expression through SMAD2 phosphorylation in VSMCs and fibroblasts. Treatment with rTEM1 enhanced collagen synthesis, attenuated elastin fragmentation, and inhibited CaCl2-induced and angiotensin II-infused AAA formation. In summary, TEM1 in resident stromal cells regulates collagen synthesis to counteract aortic wall failure during AAA formation. Matrix integrity restored by rTEM1 treatment may hold therapeutic potential against AAA.