Mutations In Fibrillin-1 Research Articles

Glycoproteomic Analysis of the Aortic Extracellular Matrix in Marfan Patients.

Marfan syndrome (MFS) is caused by mutations in FBN1 (fibrillin-1), an extracellular matrix (ECM) component, which is modified post-translationally by glycosylation. This study aimed to characterize the glycoproteome of the aortic ECM from patients with MFS and relate it to aortopathy. Approach and Results: ECM extracts of aneurysmal ascending aortic tissue from patients with and without MFS were enriched for glycopeptides. Direct N-glycopeptide analysis by mass spectrometry identified 141 glycoforms from 47 glycosites within 35 glycoproteins in the human aortic ECM. Notably, MFAP4 (microfibril-associated glycoprotein 4) showed increased and more diverse N-glycosylation in patients with MFS compared with control patients. MFAP4 mRNA levels were markedly higher in MFS aortic tissue. MFAP4 protein levels were also increased at the predilection (convexity) site for ascending aorta aneurysm in bicuspid aortic valve patients, preceding aortic dilatation. In human aortic smooth muscle cells, MFAP4 mRNA expression was induced by TGF (transforming growth factor)-β1 whereas siRNA knockdown of MFAP4 decreased FBN1 but increased elastin expression. These ECM changes were accompanied by differential gene expression and protein abundance of proteases from ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family and their proteoglycan substrates, respectively. Finally, high plasma MFAP4 concentrations in patients with MFS were associated with a lower thoracic descending aorta distensibility and greater incidence of type B aortic dissection during 68 months follow-up. Our glycoproteomics analysis revealed that MFAP4 glycosylation is enhanced, as well as its expression during the advanced, aneurysmal stages of MFS compared with control aneurysms from patients without MFS.

Analysis of FBN1 gene mutations in two pedigrees affected with Marfan syndrome

To detect mutations of fibrillin-1 (FBN1) gene in two pedigrees affected with Marfan syndrome (MFS). Peripheral blood samples were collected from MFS patients and their healthy family members for extracting genomic DNA. All of the 65 exons of the FBN1 gene were analyzed by next-generation sequencing. PolyPhen-2 and SIFT was used to predict structural and functional changes in FBN1 protein. Patients from both pedigrees presented ocular and skeletal manifestations suggestive of MFS. Two novel heterozygous mutations of the FBN1 gene, including c.1879C>T (p.R627C) in exon 16 and c.2584T>C (p.C862R) in exon 22, were identified. The same mutations were not found among unaffected members. By bioinformatic analysis, the mutations may affect the structure and function of the FBN1 protein. The c.1879C>T and c.2584T>C mutations of the FBN1 gene probably account for the disease in the two pedigrees, respectively. Identification of the c.2584T>C has enriched the spectrum of FBN1 gene mutations.

Systems pharmacology-based integration of human and mouse data for drug repurposing to treat thoracic aneurysms.

Marfan syndrome (MFS) is associated with mutations in fibrillin-1 that predispose afflicted individuals to progressive thoracic aortic aneurysm (TAA) leading to dissection and rupture of the vessel wall. Here we combined computational and experimental approaches to identify and test FDA-approved drugs that may slow or even halt aneurysm progression. Computational analyses of transcriptomic data derived from the aortas of MFS patients and MFS mice (Fbn1mgR/mgR mice) predicted that subcellular pathways associated with reduced muscle contractility are key TAA determinants that could be targeted with the GABAB receptor agonist baclofen. Systemic administration of baclofen to Fbn1mgR/mgR mice validated our computational prediction by mitigating arterial disease progression at the cellular and physiological levels. Interestingly, baclofen improved muscle contraction-related subcellular pathways by upregulating a different set of genes than those downregulated in the aorta of vehicle-treated Fbn1mgR/mgR mice. Distinct transcriptomic profiles were also associated with drug-treated MFS and wild-type mice. Thus, systems pharmacology approaches that compare patient- and mouse-derived transcriptomic data for subcellular pathway-based drug repurposing represent an effective strategy to identify potential new treatments of human diseases.

Accelerated Marfan syndrome model recapitulates established signaling pathways

ObjectiveMarfan syndrome (MFS) represents a genetic disorder with a range of clinical features, including proximal aortic aneurysms. Extensive research has revealed an abundance of transforming growth factor beta from a mutation in fibrillin-1 to be the key biochemical mechanism of aneurysm formation. Many important signaling pathways downstream of transforming growth factor beta have been further characterized. Our laboratory has previously demonstrated a unique murine model of MFS resulting in the accelerated formation of ascending aortic aneurysms and dilated cardiomyopathies. This study aims to characterize the relevance of this model to known signaling mechanisms in MFS. MethodsFibrillin 1C1039G/+ heterozygous mice (ie, MFS), with a mutation in fibrillin-1, were supplemented with 4.5 mg/kg/d angiotensin II to accelerate aneurysm formation. Four mouse groups were analyzed: wild type with or without angiotensin II and MFS with or without angiotensin II. Aortic tissue from these samples were subjected to western blotting and phosphoimaging to query various signaling pathways. ResultsMice with MFS displayed downstream regulation in both the canonical (Smad2) and noncononical (extracellular signal-regulated kinases and P38) pathways characteristic of MFS. However, these downstream signals were exaggerated in the MFS mice supplemented with angiotensin II (accelerated model), matching the observed phenotypic severity of this model. ConclusionsThe murine MFS model depicted here accelerates ascending aortic aneurysm formation and cardiomyopathies via well-characterized MFS signaling cascades. The mechanistic relevance of the accelerated murine MFS model suggests that it could be an important tool in future studies hoping to characterize MFS signaling in an expedited experimental design.

Sildenafil Prevents Marfan-Associated Emphysema and Early Pulmonary Artery Dilation in Mice

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in fibrillin-1 (Fbn1). Although aortic rupture is the major cause of mortality in MFS, patients also experience pulmonary complications, which are poorly understood. Loss of basal nitric oxide (NO) production and vascular integrity has been implicated in MFS aortic root disease, yet their contribution to lung complications remains unknown. Because of its capacity to potentiate the vasodilatory NO/cyclic guanylate monophosphate signaling pathway, we assessed whether the phosphodiesterase-5 inhibitor, sildenafil (SIL), could attenuate aortic root remodeling and emphysema in a mouse model of MFS. Despite increasing NO-dependent vasodilation, SIL unexpectedly elevated mean arterial blood pressure, failed to inhibit MFS aortic root dilation, and exacerbated elastic fiber fragmentation. In the lung, early pulmonary artery dilation observed in untreated MFS mice was delayed by SIL treatment, and the severe emphysema-like alveolar destruction was prevented. In addition, improvements in select parameters of lung function were documented. Subsequent microarray analyses showed changes to gene signatures involved in the inflammatory response in the MFS lung treated with SIL, without significant down-regulation of connective tissue or transforming growth factor-β signaling genes. Because phosphodiesterase-5 inhibition leads to improved lung histopathology and function, the effects of SIL against emphysema warrant further investigation in the settings of MFS despite limited efficacy on aortic root remodeling.

Aortic Strain Correlates with Elastin Fragmentation in Fibrillin-1 Hypomorphic Mice.

Background: High-frequency ultrasound has facilitated in vivo measurement of murine ascending aorta, allowing aortic strain to be determined from 2-D imaging. Thoracic aortic aneurysms associated with mutations in fibrillin-1 (FBN1) display elastin fragmentation, which may affect aortic strain. In this study, we determined the relationship between elastin fragmentation and aortic circumferential strain in wild-type (WT) and fibrillin-1 hypomorphic (FBN1mgR/mgR) mice.Methods and Results: Luminal diameter of the ascending aorta from WT and FBN1mgR/mgR mice was measured in systole and diastole. Expansion of the ascending aorta during systole in male and female WT mice was 0.21±0.02 mm (16.3%) and 0.21±0.01 mm (17.0%), respectively, while expansion in male and female FBN1mgR/mgR mice was 0.11±0.04 mm (4.9%) and 0.07±0.02 mm (4.5%), respectively. Reduced circumferential strain was observed in FBN1mgR/mgR mice compared with WT littermates. Elastin fragmentation was inversely correlated to circumferential strain (R2=0.628, P=0.004) and significantly correlated with aortic diameter (systole, R2=0.397, P=0.038; diastole, R2=0.515, P=0.013).Conclusions: FBN1mgR/mgR mice had increased aortic diameter, reduced circumferential strain, and increased elastin fragmentation. Elastin fragmentation in FBN1mgR/mgR and their WT littermates was correlated with reduced circumferential strain.

Human Marfan and Marfan-like Syndrome associated mutations lead to altered trafficking of the Type II TGFβ receptor in Caenorhabditis elegans.

The transforming growth factor-β (TGFβ) family plays an important role in many developmental processes and when mutated often contributes to various diseases. Marfan syndrome is a genetic disease with an occurrence of approximately 1 in 5,000. The disease is caused by mutations in fibrillin, which lead to an increase in TGFβ ligand activity, resulting in abnormalities of connective tissues which can be life-threatening. Mutations in other components of TGFβ signaling (receptors, Smads, Schnurri) lead to similar diseases with attenuated phenotypes relative to Marfan syndrome. In particular, mutations in TGFβ receptors, most of which are clustered at the C-terminal end, result in Marfan-like (MFS-like) syndromes. Even though it was assumed that many of these receptor mutations would reduce or eliminate signaling, in many cases signaling is active. From our previous studies on receptor trafficking in C. elegans, we noticed that many of these receptor mutations that lead to Marfan-like syndromes overlap with mutations that cause mis-trafficking of the receptor, suggesting a link between Marfan-like syndromes and TGFβ receptor trafficking. To test this hypothesis, we introduced three of these key MFS and MFS-like mutations into the C. elegans TGFβ receptor and asked if receptor trafficking is altered. We find that in every case studied, mutated receptors mislocalize to the apical surface rather than basolateral surface of the polarized intestinal cells. Further, we find that these mutations result in longer animals, a phenotype due to over-stimulation of the nematode TGFβ pathway and, importantly, indicating that function of the receptor is not abrogated in these mutants. Our nematode models of Marfan syndrome suggest that MFS and MFS-like mutations in the type II receptor lead to mis-trafficking of the receptor and possibly provides an explanation for the disease, a phenomenon which might also occur in some cancers that possess the same mutations within the type II receptor (e.g. colon cancer).

Histologic differences between the ascending and descending aortas in young adults with fibrillin-1 mutations

ObjectivesThis study aimed to review the clinical results of young adult patients with aortic disease associated with mutations in the fibrillin-1 gene (FBN1) and disclose the histologic differences between the ascending and descending aortas. MethodsBetween 2012 and 2015, 94 patients aged less than 50 years underwent surgery for thoracic aortic diseases. Forty-two patients (44.7%) had FBN-1 mutations. Of these, 40 patients (42.5%) with surgical specimens for histologic evaluation were included in the study. With the histologic results including the specimen sampled at their previous operations, cystic medial necrosis was classified into 3 grades according to the degree of the cystic area. ResultsThirty-nine patients (97.5%) had aortic root dilatation (Z ≥2), and 13 patients (32.5%) had ectopia lentis. Thirty-nine patients (97.5%) fulfilled the diagnostic criteria for Marfan syndrome. There were no in-hospital deaths. The majority (27/29: 93.1%) of the specimens of the ascending aorta revealed cystic medial necrosis pattern. With grade III being the most severe condition, these cases were classified into grade I (n = 2), grade II (n = 5), and grade III (n = 20). In contrast, only 6 specimens (6/17: 35.3%) of the descending aorta showed a cystic medial necrosis pattern that was classified into grade I (n = 2) and grade III (n = 4), (P < .00001). ConclusionsFewer specimens of the descending aorta revealed cystic medial necrosis compared with those of the ascending aorta. This difference might influence the characteristic aortic disease in Marfan syndrome associated with FBN-1 mutations.

Limb- and tendon-specific Adamtsl2 deletion identifies a role for ADAMTSL2 in tendon growth in a mouse model for geleophysic dysplasia

Geleophysic dysplasia is a rare, frequently lethal condition characterized by severe short stature with progressive joint contractures, cardiac, pulmonary, and skin anomalies. Geleophysic dysplasia results from dominant fibrillin-1 (FBN1) or recessive ADAMTSL2 mutations, suggesting a functional link between ADAMTSL2 and fibrillin microfibrils. Mice lacking ADAMTSL2 die at birth, which has precluded analysis of postnatal limb development and mechanisms underlying the skeletal anomalies of geleophysic dysplasia. Here, detailed expression analysis of Adamtsl2 using an intragenic lacZ reporter shows strong Adamtsl2 expression in limb tendons. Expression in developing and growing bones is present in regions that are destined to become articular cartilage but is absent in growth plate cartilage. Consistent with strong tendon expression, Adamtsl2 conditional deletion in limb mesenchyme using Prx1-Cre led to tendon anomalies, albeit with normal collagen fibrils, and distal limb shortening, providing a mouse model for geleophysic dysplasia. Unexpectedly, conditional Adamtsl2 deletion using Scx-Cre, a tendon-specific Cre-deleter strain, which does not delete in cartilage, also impaired skeletal growth. Recombinant ADAMTSL2 is shown here to colocalize with fibrillin microfibrils in vitro, and enhanced staining of fibrillin-1 microfibrils was observed in Prx1-Cre Adamtsl2 tendons. The findings show that ADAMTSL2 specifically regulates microfibril assembly in tendons and that proper microfibril composition in tendons is necessary for tendon growth. We speculate that reduced bone growth in geleophysic dysplasia may result from external tethering by short tendons rather than intrinsic growth plate anomalies. Taken together with previous work, we suggest that GD results from abnormal microfibril assembly in tissues, and that ADAMTSL2 may limit the assembly of fibrillin microfibrils.

Targeted deletion of fibrillin-1 in the mouse eye results in ectopia lentis and other ocular phenotypes associated with Marfan syndrome.

ABSTRACTFibrillin is an evolutionarily ancient protein that lends elasticity and resiliency to a variety of tissues. In humans, mutations in fibrillin-1 cause Marfan and related syndromes, conditions in which the eye is often severely affected. To gain insights into the ocular sequelae of Marfan syndrome, we targeted Fbn1 in mouse lens or non-pigmented ciliary epithelium (NPCE). Conditional knockout of Fbn1 in NPCE, but not lens, profoundly affected the ciliary zonule, the system of fibrillin-rich fibers that centers the lens in the eye. The tensile strength of the fibrillin-depleted zonule was reduced substantially, due to a shift toward production of smaller caliber fibers. By 3 months, zonular fibers invariably ruptured and mice developed ectopia lentis, a hallmark of Marfan syndrome. At later stages, untethered lenses lost their polarity and developed cataracts, and the length and volume of mutant eyes increased. This model thus captures key aspects of Marfan-related syndromes, providing insights into the role of fibrillin-1 in eye development and disease.

Prevalence of renal, hepatic, and pulmonary cysts in Marfan syndrome and matched controls: Interest of a cystic score

Recently an increased prevalence of renal cysts has been reported in patients with aortic aneurysm or dissection. The Marfan Syndrome (MFS) is associated with severe aortic disease. Some cases of cystic lungs have been associated with MFS and one series reported an increased prevalence of hepatic cysts in MFS patients. However, no study focused on multi-organ cystic disease in this particular population. The aims of this paper were to evaluate the prevalence of renal, hepatic, and pulmonary cysts in MFS patients with FBN1 mutations as compared to matched controls without MFS and analyze the link between a cystic score, defined as 1 point for each organ with at least one cyst, and aortic surgery in MFS patients. All consecutive MFS patients with a mutation in the Fibrillin-1 ( FBN1 ) gene who underwent a CT scan were included in the study. They were matched 1:1 for age and sex with controls without MFS. Between 2010 and 2016, 264 patients were included in this study. The prevalence of cysts was significantly increased in MFS patients as compared with controls: 40% for renal cysts in MFS patients versus 23% in controls; P = 0.003, 21% for hepatic cysts in MFS patients versus 8% in controls; P = 0.003, and 28% for pulmonary cysts in MFS patients versus 4% in controls; P < 0.0001. Among the 132 MFS patients, the cystic score was significantly increased in the 96 patients with aortic surgery as compared with the 36 patients free of surgery: 1.07 ± 0.9 versus 0.72 ± 0.8 points, P = 0.04 ( Fig. 1 ). This study reports for the first time an increased prevalence of renal, hepatic, and pulmonary cysts in MFS patients with FBN1 mutation as compared with matched controls. About 2 out of 3 MFS patients exhibited at least 1 cyst in any of these organs, a prevalence 2 fold higher as compared with controls. In MFS patients, a higher cystic score was associated with aortic surgery and could represent a marker of severity of the disease.

Anesthetic Management of an Adolescent With Marfan Syndrome During Anterior Spinal Fusion

Marfan syndrome (MFS) is an autosomal dominant disorder resulting from a mutation of the gene encoding fibrillin-1 (FBN1) on chromosome 15. Fibrillin-1 is a matrix glycoprotein essential for the formation of microfibrils that regulate the formation and repair of connective tissue throughout the body. This primary cellular defect results in a multisystem disorder of connective tissue. Given the multisystem involvement of MFS, anesthetic care is frequently required during surgical or orthopedic procedures. We present a 15-year-old adolescent who required anesthetic care during spinal fusion. The perioperative implications of MFS are reviewed and options for anesthetic care presented. J Med Cases. 2018;9(11):366-370 doi: https://doi.org/10.14740/jmc3181

A FBN1 3′UTR mutation variant is associated with endoplasmic reticulum stress in aortic aneurysm in Marfan syndrome

Marfan syndrome (MFS) is caused by mutations in the protein fibrillin-1 (FBN1) which affects the integrity of connective tissue elastic fibres. The most severe clinical outcome is the formation of ascending aortic aneurysms. FBN1 mutations are extremely variable and the prediction of disease phenotype and aortic risk is challenging under the prevailing mutation type classification. Finding a better correlation between mutation type and disease development is crucial for patient treatment. By mRNA sequencing of cultured vascular smooth muscle cells derived from control subjects and from the dilated and non-dilated aortic tunica media of MFS patients, we found a scarcely described FBN1 3′UTR mutation. This mutation was accompanied by a clear gene ontological endoplasmic reticulum (ER) stress response in the non-dilated aortic zone, which was confirmed by the increased transcriptional expression of MANF, HSPA5, SEL1L, DDIT3/CHOP and CRELD2 as well as protein expression levels of BiP/GRP78, CHOP and sXBP1. Moreover, the ER stress response was accompanied by a decrease in the phosphorylation levels of the protein translation regulator elF2α. In conclusion, we here identify a 3′UTR mutation of FBN1 in MFS patients, whose molecular mechanism suggest the involvement of the ER stress response in the formation of the aortic aneurysm. Our results emphasise the importance of mutations in non-coding regions and their resulting molecular mechanisms in the development of connective tissue diseases with impact on the cardiovascular system.

Type A aortic dissection in pregnant patients with fibrillin-1 gene mutations: Two case reports and a literature review.

In acute aortic dissection (AD) in pregnancy, increased cardiovascular stress due to pregnancy is an important factor leading to an emergent aortic event. It is rare but often results in a devastating event for both the pregnant patient and the foetus. Two cases of acute AD (Stanford type A) in pregnant females are presented in the present study. The patients were diagnosed via echocardiography, and the diagnosis was confirmed with computed tomography angiography prior to aortic surgery. Up to 50% of ADs in pregnancy occur in patients with fibrillin-1 (FBN1) gene mutations. The FBN1 gene was sequenced in both patients, and notable, novel pathogenic mutations of FBN1 were identified in both patients. A literature review was also performed on available diagnostic imaging and other measurements regarding AD during pregnancy. The authors suggest that the relevant content may have important clinical implications in raising disease awareness, arranging test rationally and choosing an intervention method.

ADAMTS10-mediated tissue disruption in Weill-Marchesani syndrome.

Fibrillin microfibrils are extracellular matrix assemblies that form the template for elastic fibres, endow blood vessels, skin and other elastic tissues with extensible properties. They also regulate the bioavailability of potent growth factors of the TGF-β superfamily. A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)10 is an essential factor in fibrillin microfibril function. Mutations in fibrillin-1 or ADAMTS10 cause Weill–Marchesani syndrome (WMS) characterized by short stature, eye defects, hypermuscularity and thickened skin. Despite its importance, there is poor understanding of the role of ADAMTS10 and its function in fibrillin microfibril assembly. We have generated an ADAMTS10 WMS mouse model using Clustered Regularly Spaced Interspaced Short Palindromic Repeats and CRISPR associated protein 9 (CRISPR-Cas9) to introduce a truncation mutation seen in WMS patients. Homozygous WMS mice are smaller and have shorter long bones with perturbation to the zones of the developing growth plate and changes in cell proliferation. Furthermore, there are abnormalities in the ciliary apparatus of the eye with decreased ciliary processes and abundant fibrillin-2 microfibrils suggesting perturbation of a developmental expression switch. WMS mice have increased skeletal muscle mass and more myofibres, which is likely a consequence of an altered skeletal myogenesis. These results correlated with expression data showing down regulation of Growth differentiation factor (GDF8) and Bone Morphogenetic Protein (BMP) growth factor genes. In addition, the mitochondria in skeletal muscle are larger with irregular shape coupled with increased phospho-p38 mitogen-activated protein kinase (MAPK) suggesting muscle remodelling. Our data indicate that decreased SMAD1/5/8 and increased p38/MAPK signalling are associated with ADAMTS10-induced WMS. This model will allow further studies of the disease mechanism to facilitate the development of therapeutic interventions.

Fibrillin microfibrils and proteases, key integrators of fibrotic pathways.

Supramolecular networks composed of multi-domain ECM proteins represent intricate cellular microenvironments which are required to balance tissue homeostasis and direct remodeling. Structural deficiency in ECM proteins results in imbalances in ECM-cell communication resulting often times in fibrotic reactions. To understand how individual components of the ECM integrate communication with the cell surface by presenting growth factors or providing fine-tuned biomechanical properties is mandatory for gaining a better understanding of disease mechanisms in the quest for new therapeutic approaches. Here we provide an overview about what we can learn from inherited connective tissue disorders caused primarily by mutations in fibrillin-1 and binding partners as well as by altered ECM processing leading to defined structural changes and similar functional knock-in mouse models. We will utilize this knowledge to propose new molecular hypotheses which should be tested in future studies.

Fibrillin-1 mutant mice (tight skin) show increased spontaneous and trauma-induced osteoarthritis development

Purpose: Osteoarthritis development is a major chronic disorder affected >8million British people. Despite the high prevalence of OA, there are currently no therapies to slow disease progression. Fibrillin-1 is an extracellular matrix protein found in elastic fibres. One of its main roles is to control growth factor bioavailability, which play vital functions in joint homeostasis. Fibrillin-1 mutations, as those found in Tight Skin mice (TSK), can increase TGFß signalling, and leads to tight skin, myocardial hypertrophy, marfan-like skeletal phenotype and lung emphysema. The aim of this study is to assess OA development in TSK mice in spontaneous and in trauma-induced models. Methods: Immunohistochemistry for Fibrillin-1 was performed in CBA and Str/ort mice (spontaneous OA), and in trauma-induced OA. For the ageing model, knees from 35wk-old TSK and littermate control male mice were collected, microCT scanned and used for histology. The non-invasive loading model was used and the right knee of male TSK and WT mice were loaded i) a single time at 7 or 9N loads and joints analysed 1 weeks later; or ii) repetitively for 2 weeks to induce OA progression, and joints assessed 6 weeks after the last loading episode. Histology was performed on these joints after decalcification (10% formic acid), serial sections cut across the whole joint at 6μm, and AC degradation severity assessed (OARSI grading system). Results: Fibrillin-1 was found in the pericellular matrix of chondrocytes in both the growth plate (resting and hypertrophic cells) and in the uncalcified articular cartilage in healthy CBA mice. During the development of OA in Str/ort mice and in response to mechanical trauma, Fibrillin-1 immunolabelling was decreased. TSK mice showed spontaneous increased joint space mineralised tissue volume (including meniscus and ligament calcification) and increased AC degradation compared to WT at 35wks of age. In contrast, no significant differences were seen in tibial epiphyseal bone (medial and lateral; BV/TV, Trabecular Thickness, Trabecular Separation, Trabecular number). A single loading episode at both 9 and 7N produced AC lesions in the lateral femur in both WT and TSK mice, however severity of lesions created were more severe in TSK mice (preliminary data). Repetitive loading episodes lead to slight increase in mineralised joint space tissue between TSK and litter mate WT controls (preliminary data), which from our previous studies has shown to be correlated with OA severity. Conclusions: This study shows that Fibrillin-1 is decreased from the pericellular matrix during OA development in spontaneous and trauma-induced OA, suggesting increased Fibrillin-1 degradation. In addition, mutations in Fibrillin-1 in the TSK mouse lead to increased spontaneous and trauma-induced OA development. These data suggest that normal Fibrillin-1 expression and function may play an important role in joint homeostasis and that abnormal expression or mutations promote OA development initiation and progression.

Participation of Arachidonic Acid Metabolism in the Aortic Aneurysm Formation in Patients with Marfan Syndrome.

Marfan syndrome (MFS) is a pleiotropic genetic disease involving the cardiovascular system where a fibrillin-1 mutation is present. This mutation is associated with accelerated activation of transforming growth factor β (TGFβ1) which contributes to the formation of aneurysms in the root of the aorta. There is an imbalance in the synthesis of thromboxane A2 (TXA2) and prostacyclin, that is a consequence of a differential protein expression of the isoforms of cyclooxygenases (COXs), suggesting an alteration of arachidonic acid (AA) metabolism. The aim of this study was to analyze the participation of AA metabolism associated with inflammatory factors in the dilation and dissection of the aortic aneurysm in patients with MFS. A decrease in AA (p = 0.02), an increase in oleic acid (OA), TGFβ1, tumor necrosis factor alpha (TNFα), prostaglandin E2 (PGE2) (p < 0.05), and COXs activity (p = 0.002) was found. The expressions of phospholipase A2 (PLA2), cytochrome P450 (CYP450 4A), 5-lipoxygenase (5-LOX), COX2 and TXA2R (p < 0.05) showed a significant increase in the aortic aneurysm of patients with MFS compared to control subjects. COX1, 6-keto-prostaglandin 1 alpha (6-keto-PG1α) and 8-isoprostane did not show significant changes. Histological examination of the aortas showed an increase of cystic necrosis, elastic fibers and collagen in MFS. The results suggest that there are inflammatory factors coupled to genetic factors that predispose to aortic endothelial dysfunction in the aortic tissue of patients with MFS. There is a decrease in the percentage of AA, associated with an increase of PLA2, COX2/TXA2R, CYP450 4A, and 5-LOX which leads to a greater synthesis of PGE2 than of 6-keto-PGF1α, thus contributing to the formation of the aortic aneurysm. The evident loss of the homeostasis in these mechanisms confirms that there is a participation of the AA pathway in the aneurysm progression in MFS.

The Effect of a Nonpeptide Angiotensin II Type 2 Receptor Agonist, Compound 21, on Aortic Aneurysm Growth in a Mouse Model of Marfan Syndrome.

Introduction:Available evidence suggests that the renin–angiotensin–aldosterone (RAA) system is a good target for medical intervention on aortic root dilatation in Marfan syndrome (MFS). The effect of Compound 21 (C21), a nonpeptide angiotensin II type 2 receptor agonist, on aneurysm progression was tested.Methods:Mice with a mutation in fibrillin-1 (Fbn1C1039G/+) and wild-type mice were treated with vehicle, losartan, C21, enalapril, or a combination. Blood pressure, aortic root diameter, and histological slides were evaluated.Results:All groups had a comparable blood pressure. Echographic evaluation of the aortic root diameter revealed a protective effect of angiotensin II type 1 receptor antagonist (losartan) and no effect of C21 treatment. None of the treatments had a beneficial effect on the histological changes in MFS.Discussion:This study confirms that angiotensin II type 1 receptor antagonism (losartan) decreases aortic aneurysm growth in a mouse model of MFS. A nonpeptide angiotensin II type 2 receptor agonist (C21), at the doses studied, was ineffective. Future studies are warranted to further elucidate the exact role of the RAA system in aneurysm formation in MFS and identify alternative targets for intervention.

Aortic dilatation in Marfan syndrome: role of arterial stiffness and fibrillin-1 variants.

Marfan syndrome (MFS) is an autosomal dominant genetic disorder characterized by aortic root dilation and dissection and an abnormal fibrillin-1 synthesis. In this observational study, we evaluated aortic stiffness in MFS and its association with ascending aorta diameters and fibrillin-1 genotype. A total of 116 Marfan adult patients without history of cardiovascular surgery, and 144 age, sex, blood pressure and heart rate matched controls were enrolled. All patients underwent arterial stiffness evaluation through carotid-femoral pulse wave velocity (PWV) and central blood pressure waveform analysis (PulsePen tonometer). Fibrillin-1 mutations were classified based on the effect on the protein, into 'dominant negative' and 'haploinsufficient' mutations. PWV and central pulse pressure were significantly higher in MFS patients than in controls [respectively 7.31 (6.81-7.44) vs. 6.69 (6.52-6.86) m/s, P = 0.0008; 41.3 (39.1-43.5) vs. 34.0 (32.7-35.3) mmHg, P < 0.0001], with a higher age-related increase of PWV in MFS (β 0.062 vs. 0.036). Pressure amplification was significantly reduced in MFS [18.2 (15.9-20.5) vs. 33.4 (31.6-35.2)%, P < 0.0001]. Central pressure profile was altered even in MFS patients without aortic dilatation. Multiple linear regression models showed that PWV independently predicted aortic diameters at the sinuses of Valsalva (ß = 0.243, P = 0.002) and at the sinotubular junction (ß = 0.186, P = 0.048). PWV was higher in 'dominant negative' than 'haploinsufficient' fibrillin-1 mutations [7.37 (7.04-7.70) vs. 6.60 (5.97-7.23) m/s, P = 0.035], although this difference was not significant after adjustment. Aortic stiffness is increased in MFS, independently from fibrillin-1 genotype and is associated with diameters of ascending aorta. Alterations in central hemodynamics are present even when aortic diameter is within normal limits. Our findings suggest an accelerated arterial aging in MFS.