FN (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 fibrillin-1, leads to thoracic aortic aneurysms (TAAs). Phenotypic modulation of vascular smooth muscle cells (SMCs) and ECM (extracellular matrix) remodeling are characteristic of both nonsyndromic and Marfan aneurysms. The ECM protein FN (fibronectin) 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 crossed α5/2 chimeric mice with Fbn1 mgR/mgR mice (mgR model of Marfan syndrome) to evaluate 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 investigated molecular mechanisms by which FN affects SMCs and subsequent development of TAAs. RESULTS: FN was elevated in the thoracic aortas from Marfan patients, in nonsyndromic aneurysms, and in mgR mice. 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, plating of wild-type SMCs on FN decreased contractile gene expression and activated inflammatory pathways whereas α5/2 SMCs were resistant. These effects correlated with increased NF-kB activation in cultured SMCs and mgR aortas, which was alleviated by the α5/2 mutation or NF-kB inhibition. CONCLUSIONS: FN-integrin α5 signaling is a significant driver of TAA in the mgR mouse model. This pathway thus warrants further investigation as a therapeutic target.

Computational modelling distinguishes diverse contributors to aneurysmal progression in the Marfan aorta

“…At the tissue scale, it remains difficult to delineate the interplay between cellular mechanosensing and mechanoregulation, as seen in the correlations between the optimal insult parameters over multiple trials. Compromised mechanosensing has been conjectured based on the diverse mutations that predispose to TAAs [16] and is supported by the observed loss of intra-and inter-lamellar elastin [53] and recent studies showing altered integrin signalling in the Marfan aorta [37][38][39]. These diverse observational and experimental results are now supported by our computational results herein.…”

“…Hence, rates of turnover and mechanoregulation of newly deposited matrix become critical parameters [35,36]. Furthermore, increasing evidence for altered integrin signalling in Marfan syndrome suggests compromised actomyosin activity in vascular cells may play a major role in disease progression [37][38][39]. Motivated thus, in this paper we model progressive changes in aortic structure and function of the Marfan aorta in Fbn1 C1041G/+ and Fbn1 mgR/mgR mice.…”

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.…”

A novel genetic mouse model of fatal aortic dissection reveals massive inflammatory cell infiltration in the thoracic aorta

“…The upregulation of fibronectin in the subendothelial space represents an early indicator of vascular alterations, potentially contributing to the pathogenesis of atherosclerosis 48 . Indeed, research using genetically modified mice in which the intracellular domain of integrin α5β1, a fibronectin receptor, is replaced with that of α2β1 collagen receptor, modulates the fibronectin-mediated signaling and attenuates aneurysm formation and improves the survival of Fbn1 mgR/mgR mice 49 . Interestingly, fibronectin was also elevated in subendothelial lesions and medial layers in AD mice and upregulation of laminin and collagen IV was detected, indicating the alteration of ECM composition due to an alteration of fibrillin-1 microfibrils in the subendothelial matrix.…”