Fibulin-4 Deficiency Results in Ascending Aortic Aneurysms A Potential Link Between Abnormal Smooth Muscle Cell Phenotype and Aneurysm Progression

Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Circulation Research (Impact Factor: 11.02). 12/2009; 106(3):583-92. DOI: 10.1161/CIRCRESAHA.109.207852
Source: PubMed

ABSTRACT Loss of fibulin-4 during embryogenesis results in perinatal lethality because of aneurysm rupture, and defective elastic fiber assembly has been proposed as an underlying cause for the aneurysm phenotype. However, aneurysms are never seen in mice deficient for elastin, or for fibulin-5, which absence also leads to compromised elastic fibers.
We sought to determine the mechanism of aneurysm development in the absence of fibulin-4 and establish the role of fibulin-4 in aortic development.
We generated germline and smooth muscle cell (SMC)-specific deletion of the fibulin-4 gene in mice (Fbln4(GKO) and Fbln4(SMKO), respectively). Fbln4(GKO) and Fbln4(SMKO) aortic walls fail to fully differentiate, exhibiting reduced expression of SM-specific contractile genes and focal proliferation of SMCs accompanied by degenerative changes of the medial wall. Marked upregulation of extracellular signal-regulated kinase 1/2 signaling pathway was observed in the aneurysmal wall of Fbln4(GKO) and Fbln4(SMKO) mice and both mutants developed aneurysm predominantly in the ascending thoracic aorta. In vitro, Fbln4(GKO) SMCs exhibit an immature SMC phenotype with a marked reduction of SM-myosin heavy chain and increased proliferative capacity.
The vascular phenotype in Fbln4 mutant mice is remarkably similar to a subset of human thoracic aortic aneurysms caused by mutations in SMC contractile genes. Our study provides a potential link between the intrinsic properties of SMCs and aneurysm progression in vivo and supports the dual role of fibulin-4 in the formation of elastic fibers as well as terminal differentiation and maturation of SMCs in the aortic wall.

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    • "SMCs secrete a large amount of the blood vessel ECM, consisting mainly of Laminin, Collagen IV, Nidogen, Perlecan, and Fibulins. Secretion of ECM from vSMCs is vital, as loss of the collagen Col4a1 leads to perinatal hemorrhage [19], while loss of Fibulin4 leads to aneurysms [20], [21]. "
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    ABSTRACT: Mural cells of the vascular system include vascular smooth muscle cells (SMCs) and pericytes whose role is to stabilize and/or provide contractility to blood vessels. One of the earliest markers of mural cell development in vertebrates is α smooth muscle actin (acta2; αsma), which is expressed by pericytes and SMCs. In vivo models of vascular mural cell development in zebrafish are currently lacking, therefore we developed two transgenic zebrafish lines driving expression of GFP or mCherry in acta2-expressing cells. These transgenic fish were used to trace the live development of mural cells in embryonic and larval transgenic zebrafish. acta2:EGFP transgenic animals show expression that largely mirrors native acta2 expression, with early pan-muscle expression starting at 24 hpf in the heart muscle, followed by skeletal and visceral muscle. At 3.5 dpf, expression in the bulbus arteriosus and ventral aorta marks the first expression in vascular smooth muscle. Over the next 10 days of development, the number of acta2:EGFP positive cells and the number of types of blood vessels associated with mural cells increases. Interestingly, the mural cells are not motile and remain in the same position once they express the acta2:EGFP transgene. Taken together, our data suggests that zebrafish mural cells develop relatively late, and have little mobility once they associate with vessels.
    PLoS ONE 03/2014; 9(3):e90590. DOI:10.1371/journal.pone.0090590 · 3.23 Impact Factor
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    • "Increased TGFbeta activity was demonstrated in aortic walls of both LDS and MFS patients. Subsequently, dysregulated TGFbeta signaling was found in other syndromic and non-syndromic forms of TAAD [Coucke et al., 2006; Zhu et al., 2006; Guo et al., 2007; Hanada et al., 2007; Gomez et al., 2009; Guo et al., 2009; Huang et al., 2010; Wang et al., 2010; Renard et al., 2011] and it was hypothesized that different molecular defects in TAAD may account for different pathogenetic mechanisms of enhanced TGFbeta signaling [Renard et al., 2011]. "
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    ABSTRACT: Recently, mutations in the SMAD3 gene were found to cause a new autosomal dominant aneurysm condition similar to Loeys-Dietz syndrome (LDS), mostly with osteoarthritis, called aneurysms-osteoarthritis syndrome (AOS). Our 3-year-old propositus underwent correction of an inguinal hernia at 3 months and substitution of the ascending aorta for pathologic dilation at 12 months of age. Family history reveals aortic dilation in his mother at 30 years, death due to aortic dissection of an 18-year-old maternal aunt, surgical replacement of the ascending aorta because of aneurysm in a maternal uncle at 19 years, postpartum death of the maternal grandmother at 24 years and surgical intervention because of thoracic aortic aneurysm in a brother of the propositus' grandmother at 54 years. The affected individuals present with several other signs of connective tissue disease, but the two adult patients evaluated revealed no radiologic evidence of osteoarthritis. Molecular testing of the TGFBR1 and TGFBR2 genes, involved in LDS, resulted negative, but analysis of SMAD3 disclosed the novel heterozygous loss-of-function mutation c.1170_1179del (p.Ser391AlafsX7) in exon 9 in all affected family members, confirming the diagnosis of AOS. SMAD3 mutations should be considered in patients of all ages with LDS-like phenotypes and negative TGFBR1/2 molecular tests, especially in the presence of aortic root or ascending aortic aneurysms, even though signs of early onset osteoarthritis are absent. © 2013 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 05/2013; 161(5). DOI:10.1002/ajmg.a.35852 · 2.16 Impact Factor
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    • "Huang et al. observed that while Fbln4 null mice develop lethal aortic aneurysms, deficiency of other elastic elements like fibulin-5 and elastin were not associated with as severe aneurysm formation or lethality. They postulated a dual role for fibulin-4, in elastic fiber formation, as well as terminal differentiation and maturation of SMC (smooth muscle cells) in aortic wall [32]. "
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    ABSTRACT: Background: Vascular elasticity is crucial for maintaining hemodynamics. Molecular mechanisms involved in human elastogenesis are incompletely understood. We describe a syndrome of lethal arteriopathy associated with a novel, identical mutation in the fibulin 4 gene (FBLN4) in a unique cohort of infants from South India. Methods: Clinical characteristics, cardiovascular findings, outcomes and molecular genetics of twenty-two infants from a distinct population subgroup, presenting with characteristic arterial dilatation and tortuosity during the period August 2004 to June 2011 were studied. Results: Patients (11 males, 11 females) presented at median age of 1.5 months, belonging to unrelated families from identical ethno-geographical background; eight had a history of consanguinity. Cardiovascular features included aneurysmal dilatation, elongation, tortuosity and narrowing of the aorta, pulmonary artery and their branches. The phenotype included a variable combination of cutis laxa (52%), long philtrum-thin vermillion (90%), micrognathia (43%), hypertelorism (57%), prominent eyes (43%), sagging cheeks (43%), long slender digits (48%), and visible arterial pulsations (38%). Genetic studies revealed an identical c.608A > C (p. Asp203Ala) mutation in exon 7 of the FBLN4 gene in all 22 patients, homozygous in 21, and compound heterozygous in one patient with a p. Arg227Cys mutation in the same conserved cbEGF sequence. Homozygosity was lethal (17/21 died, median age 4 months). Isthmic hypoplasia (n = 9) correlated with early death (≤4 months). Conclusions: A lethal, genetic disorder characterized by severe deformation of elastic arteries, was linked to novel mutations in the FBLN4 gene. While describing a hitherto unreported syndrome in this population subgroup, this study emphasizes the critical role of fibulin-4 in human elastogenesis.
    Orphanet Journal of Rare Diseases 09/2012; 7(1):61. DOI:10.1186/1750-1172-7-61 · 3.36 Impact Factor
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