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 Fbn1mgR/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.

Altered Integrin Signaling in Thoracic Aortopathy

“…These results implicate a detrimental fibronectin/α 5 /NF-κb (nuclear factor kappa B) pathway that is specific to α 5 . Taken together, results from Nakamura et al 8 and Chen et al 17 demonstrate that multiple pathways of aberrant integrin signaling can exacerbate aortopathy in Marfan syndrome (Figure) and integrin targeting should be considered, although as noted by Nakamura et al, such targeting will need to be guided by lineage-specific expression and signaling.…”

“…Supporting a pathological role for altered integrin signaling in TAAs, our recent work in Arteriosclerosis, Thrombosis, and Vascular Biology reported excessive fibronectin accumulation in syndromic and nonsyndromic human TAAs and in Fbn1 mgR/mgR Marfan TAAs. 17 Fibronectin binds multiple α V integrins, though preferentially α 5 β 1 . Genetic replacement of the α 5 cytosolic domain with that of α 2 , which alters signaling without affecting the structural linkage, markedly improved survival and attenuated the TAA phenotype in mice.…”

Development of a methodological framework to probe regional mechanics of the aneurysmal ascending thoracic aorta

“…models including the Fbn1 mgR/mgR and Fbn1 C1041G/+ [253,57,82,65,252,83]. Aortic tissue from mg∆ loxP neo mice displayed a similar Marfan phenotype characterized by a change in the shape of the pressure-diameter curve towards a more collagen driven response, as well as a loss of axial extensibility.…”

“…TAA progression was also attenuated by caspase inhibition in F bn1 C1041G/+ [80], and also by the absence of latent transforming growth factor-beta binding protein-3 (LTBP-3) in F bn1 mgR/mgR [81,82]. Whereas, fibronectin-integrin α5 signaling exacerbated TAAs in mice [83]. As such, beyond exploring the mechanisms of existing treatment approaches, these various mouse studies have provided invaluable insight into disease pathways and possible therapeutic targets that warrant further investigation in a clinical MFS population.…”

“…To probe vSMC vasoactivity, and endothelium-dependent and -independent relaxation, phenylephrine, carbamylcholine chloride/acetylcholine, and sodium nitroprusside are used, respectively. L-arginine methyl ester (L-NAME) may also be used to investigate the nitric-oxide synthase-mediated component of the endotheliumdependent relaxation [287,288,160,243,83]. These tests can be performed using the same set-up for passive mechanical testing described in Chapter 5, however they require the tissue to be tested fresh before cell apoptosis has occurred.…”