Fibronectin-integrin α5 signaling promotes thoracic aortic aneurysm in a mouse model of Marfan syndrome

ABSTRACT Background Marfan syndrome, caused by mutations in the gene for the extracellular matrix (ECM) glycoprotein fibrillin-1, leads to thoracic aortic aneurysms (TAAs). Phenotypic modulation of vascular smooth muscle cells (SMCs) and ECM remodeling are characteristics of both non-syndromic and Marfan aneurysms. The ECM protein fibronectin (FN) is elevated in the tunica media of TAAs and amplifies inflammatory signaling in endothelial and SMCs through its main receptor, integrin α5β1. We investigated the role of integrin α5-specific signals in Marfan mice in which the cytoplasmic domain of integrin α5 was replaced with that of integrin α2 (denoted α5/2 chimera). Methods We used α5/2 chimera mouse crossed with Fbn1 mgR/mgR genetic background (mgR, a mouse model of Marfan syndrome) to compare the survival rate and pathogenesis of TAAs among wild type, α5/2, mgR and α5/2; mgR mice. Further biochemical and microscopic analysis of porcine and mouse aortic SMCs allowed us to identify the molecular mechanisms by which FN affects SMCs and subsequent development of TAAs. Results FN was elevated in the thoracic aortas from Marfan patients, in non-syndromic aneurysms and in the mgR mouse model of Marfan syndrome. The α5/2 mutation greatly prolonged survival of Marfan mice, with improved elastic fiber integrity, mechanical properties, SMC density, and SMC contractile gene expression. Furthermore, in vitro, plating of wild-type, but not α5/2, SMCs on FN decreased contractile gene expression and activated inflammatory pathways. These effects correlated with increased NF-kB activation and immune cell infiltration in the mgR aortas, which was rescued in the α5/2 mgR aortas. Conclusions FN-integrin α5 signaling is a significant driver of TAA in the mgR mouse model. This pathway warrants further investigation as a therapeutic target.