Immunohistologic abnormalities of the microfibrillar-fiber system in the Marfan syndrome

Role of mechanotransduction in vascular biology: focus on thoracic aortic aneurysms and dissections

Thoracic aortic diseases that involve progressive enlargement, acute dissection, or rupture are influenced by the hemodynamic loads and mechanical properties of the wall. We have only limited understanding, however, of the mechanobiological processes that lead to these potentially lethal conditions. Homeostasis requires that intramural cells sense their local chemomechanical environment and establish, maintain, remodel, or repair the extracellular matrix to provide suitable compliance and yet sufficient strength. Proper sensing, in turn, necessitates both receptors that connect the extracellular matrix to intracellular actomyosin filaments and signaling molecules that transmit the related information to the nucleus. Thoracic aortic aneurysms and dissections are associated with poorly controlled hypertension and mutations in genes for extracellular matrix constituents, membrane receptors, contractile proteins, and associated signaling molecules. This grouping of factors suggests that these thoracic diseases result, in part, from dysfunctional mechanosensing and mechanoregulation of the extracellular matrix by the intramural cells, which leads to a compromised structural integrity of the wall. Thus, improved understanding of the mechanobiology of aortic cells could lead to new therapeutic strategies for thoracic aortic aneurysms and dissections.

Beneficial Outcome of Losartan Therapy Depends on Type of FBN1 Mutation in Marfan Syndrome

BACKGROUND

It has been shown that losartan reduces aortic dilatation in patients with Marfan syndrome. However, treatment response is highly variable. This study investigates losartan effectiveness in genetically classified subgroups.

METHODS AND RESULTS

In this predefined substudy of COMPARE, Marfan patients were randomized to daily receive losartan 100 mg or no losartan. Aortic root dimensions were measured by MRI at baseline and after 3 years. FBN1 mutations were classified based on fibrillin-1 protein effect into (1) haploinsufficiency, decreased amount of normal fibrillin-1, or (2) dominant negative, normal fibrillin-1 abundance with mutant fibrillin-1 incorporated in the matrix. A pathogenic FBN1 mutation was found in 117 patients, of whom 79 patients were positive for a dominant negative mutation (67.5%) and 38 for a mutation causing haploinsufficiency (32.5%). Baseline characteristics between treatment groups were similar. Overall, losartan significantly reduced aortic root dilatation rate (no losartan, 1.3±1.5 mm/3 years, n=59 versus losartan, 0.8±1.4 mm/3 years, n=58; P=0.009). However, losartan reduced only aortic root dilatation rate in haploinsufficient patients (no losartan, 1.8±1.5 mm/3 years, n=21 versus losartan 0.5±0.8 mm/3 years, n=17; P=0.001) and not in dominant negative patients (no losartan, 1.2±1.7 mm/3 years, n=38 versus losartan 0.8±1.3 mm/3 years, n=41; P=0.197).

CONCLUSIONS

Marfan patients with haploinsufficient FBN1 mutations seem to be more responsive to losartan therapy for inhibition of aortic root dilatation rate compared with dominant negative patients. Additional treatment strategies are needed in Marfan patients with dominant negative FBN1 mutations.

CLINICAL TRIAL REGISTRATION

http://www.trialregister.nl/trialreg/index.asp; Unique Identifier: NTR1423.

Corneal stroma microfibrils

Elastic tissue was first described well over a hundred years ago and has since been identified in nearly every part of the body. In this review, we examine elastic tissue in the corneal stroma with some mention of other ocular structures which have been more thoroughly described in the past. True elastic fibers consist of an elastin core surrounded by fibrillin microfibrils. However, the presence of elastin fibers is not a requirement and some elastic tissue is comprised of non-elastin-containing bundles of microfibrils. Fibers containing a higher relative amount of elastin are associated with greater elasticity and those without elastin, with structural support. Recently it has been shown that the microfibrils, not only serve mechanical roles, but are also involved in cell signaling through force transduction and the release of TGF-β. A well characterized example of elastin-free microfibril bundles (EFMBs) is found in the ciliary zonules which suspend the crystalline lens in the eye. Through contraction of the ciliary muscle they exert enough force to reshape the lens and thereby change its focal point. It is believed that the molecules comprising these fibers do not turn-over and yet retain their tensile strength for the life of the animal. The mechanical properties of the cornea (strength, elasticity, resiliency) would suggest that EFMBs are present there as well. However, many authors have reported that, although present during embryonic and early postnatal development, EFMBs are generally not present in adults. Serial-block-face imaging with a scanning electron microscope enabled 3D reconstruction of elements in murine corneas. Among these elements were found fibers that formed an extensive network throughout the cornea. In single sections these fibers appeared as electron dense patches. Transmission electron microscopy provided additional detail of these patches and showed them to be composed of fibrils (∼10 nm diameter). Immunogold evidence clearly identified these fibrils as fibrillin EFMBs and EFMBs were also observed with TEM (without immunogold) in adult mammals of several species. Evidence of the presence of EFMBs in adult corneas will hopefully pique an interest in further studies that will ultimately improve our understanding of the cornea's biomechanical properties and its capacity to repair.

Early fibrillin-1 assembly monitored through a modifiable recombinant cell approach

Fibrillin proteins constitute the backbone of extra-cellular macromolecular microfibrils. Mutations in fibrillins cause heritable connective tissue disorders, including Marfan syndrome, dominant Weill-Marchesani syndrome, and stiff skin syndrome. Fibronectin provides a critical scaffold for microfibril assembly in cell culture models. Full length recombinant fibrillin-1 was expressed by HEK 293 cells, which deposited the secreted protein in a punctate pattern on the cell surface. Cocultured fibroblasts consistently triggered assembly of recombinant fibrillin-1, which was dependent on a fibronectin network formed by the fibroblasts. Deposition of recombinant fibrillin-1 on fibronectin fibers occurred first in discrete packages that subsequently extended along fibronectin fibers. Mutant fibrillin-1 harboring either a cysteine 204 to serine mutation or a RGD to RGA mutation which prevents integrin binding, did not affect fibrillin-1 assembly. In conclusion, we developed a modifiable recombinant full-length fibrillin-1 assembly system that allows for rapid analysis of critical roles in fibrillin assembly and functionality. This system can be used to study the contributions of specific residues, domains, or regions of fibrillin-1 to the biogenesis and functionality of microfibrils. It provides also a method to evaluate disease-causing mutations, and to produce microfibril-containing matrices for tissue engineering applications, for example, in designing novel vascular grafts or stents.

Surgical management of lens subluxation in Marfan syndrome

PURPOSE

To review the literature on the surgical management, describe a simplified surgical technique, and to report the postoperative clinical course of ectopia lentis removal in patients with Marfan syndrome.

METHODS

The medical records of patients with a clinical diagnosis of Marfan syndrome and clinically significant lens subluxation were retrospectively reviewed. Patients underwent lens extraction by a single surgeon via a simplified anterior segment approach. The pre- and postoperative best-corrected visual acuity, biometric measurements, intraocular pressure, and incidence of surgery-related complications were reviewed.

RESULTS

A total of 42 eyes of 22 patients were included. Mean postoperative follow-up was 4.9 ± 2.9 years (range, 1-10 years). Average age at surgery was 10.2 ± 9.2 years (range, 2-37 years), with 18 patients (36 eyes) ≤ 18 years of age. The average preoperative best-corrected visual acuity was 20/80, and the average postoperative best-corrected visual acuity at last follow-up was 20/25, with an average improvement of 6 lines on the Snellen chart. All eyes had a best-corrected visual acuity > 20/30 at last follow-up with aphakic correction. One eye of 1 patient developed a retinal detachment following blunt trauma. No other intra- or postoperative complications were reported.

CONCLUSIONS

Anterior lensectomy and limited vitrectomy with aphakic correction is safe and provides a consistent visual outcome in patients with lens subluxation secondary to Marfan syndrome. This is especially important in pediatric patients, in whom long-term follow-up for iris- and scleral-fixated intraocular lenses is limited.

The microfibril hypothesis of glaucoma: implications for treatment of elevated intraocular pressure

Microfibrils are macromolecular aggregates located in the extracellular matrix of both elastic and nonelastic tissues that have essential functions in formation of elastic fibers and control of signaling through the transforming growth factor beta (TGFβ) family of cytokines. Elevation of systemic TGFβ and chronic activation of TGFβ signal transduction are associated with diseases caused by mutations in microfibril-associated genes, including FBN1. A role for microfibrils in glaucoma is suggested by identification of risk alleles in LOXL1 for exfoliation glaucoma and mutations in LTBP2 for primary congenital glaucoma, both of which are microfibril-associated genes. Recent identification of a mutation in another microfibril-associated gene, ADAMTS10, in a dog model of primary open-angle glaucoma led us to form the microfibril hypothesis of glaucoma, which in general states that defective microfibrils may be an underlying cause of glaucoma. Microfibril defects could contribute to glaucoma through alterations in biomechanical properties of tissue and/or through effects on signaling through TGFβ, which is well established to be elevated in the aqueous humor of glaucoma patients. Recent work has shown that diseases caused by microfibril defects are associated with increased concentrations of TGFβ protein and chronic activation of TGFβ-mediated signal transduction. In analogy with other microfibril-related diseases, defective microfibrils could provide a mechanism for the elevation of TGFβ2 in glaucomatous aqueous humor. If glaucoma shares mechanisms with other diseases caused by defective microfibrils, such as Marfan syndrome, therapeutic interventions to inhibit chronic activation of TGFβ signaling used in those diseases may be applied to glaucoma.

Immunolocalisation of fibrillin microfibrils in the calf metacarpal and vertebral growth plate

Overgrowth of limbs and spinal deformities are typical clinical manifestations of Marfan syndrome (MFS) and congenital contractural arachnodactyly (CCA), caused by mutations of the genes encoding fibrillin-1 (FBN1) and fibrillin-2 (FBN2), respectively. FBN1 mutations are also associated with acromicric (AD) and geleophysic dysplasias (GD), and with Weill-Marchesani syndrome (WMS), which is characterised by short stature. The mechanisms leading to such abnormal skeletal growth and the involvement of the fibrillins are not understood. Postnatal longitudinal bone growth mainly occurs in the epiphyseal growth plate. Here we investigated the organisation of fibrillin microfibrils in the growth plate of the long bone and vertebra immunohistochemically. Fibrillin-1 was dual-immunostained with elastin, with fibrillin-2 or with collagen X. We report that fibrillin microfibrils are distributed throughout all regions of the growth plate, and that fibrillin-1 and fibrillin-2 were differentially organised. Fibrillin-1 was more abundant in the extracellular matrix of the resting and proliferative zones of the growth plate than in the hypertrophic zone. More fibrillin-2 was found in the calcified region than in the other regions. No elastin fibres were observed in either the proliferative or hypertrophic zones. This study indicates that, as fibrillin microfibrils are involved in growth factor binding and may play a mechanical role, they could be directly involved in regulating bone growth. Hence, mutations of the fibrillins could affect their functional role in growth and lead to the growth disorders seen in patients with MFS, CCA, AD, GD and WMS.

ADAMTSL4, a secreted glycoprotein widely distributed in the eye, binds fibrillin-1 microfibrils and accelerates microfibril biogenesis

PURPOSE

ADAMTSL4 mutations cause autosomal recessive isolated ectopia lentis (IEL) and ectopia lentis et pupillae. Dominant FBN1 mutations cause IEL or syndromic ectopia lentis (Marfan syndrome and Weill-Marchesani syndrome). The authors sought to characterize recombinant ADAMTSL4 and the ocular distribution of ADAMTSL4 and to investigate whether ADAMTSL4 influences the biogenesis of fibrillin-1 microfibrils, which compose the zonule.

METHODS

ADAMTSL4 was expressed by the transfection of HEK293F cells. Protein extracts and paraffin sections from human eyes were analyzed by Western blot analysis and by immunoperoxidase staining, respectively. Immunofluorescence was used to evaluate fibrillin-1 deposition in the ECM of fetal bovine nuchal ligament cells after culture in ADAMTSL4-conditioned medium or control medium. Confocal microscopy was performed to investigate ADAMTSL4 and fibrillin-1 colocalization in these cultures.

RESULTS

Western blot analysis identified ADAMTSL4 as a glycoprotein in HEK293F cells and as a major band of 150 kDa in ocular tissues including ciliary body, sclera, cornea, and retina. Immunoperoxidase staining showed a broad ocular distribution of ADAMTSL4, associated with both cells and fibrillar ECM. When cultured in ADAMTSL4-containing medium, fetal bovine nuchal ligament cells showed accelerated fibrillin-1 deposition in ECM. ADAMTSL4 colocalized with fibrillin-1 microfibrils in the ECM of these cells.

CONCLUSIONS

ADAMTSL4 is a secreted glycoprotein that is widely distributed in the human eye. Enhanced fibrillin-1 deposition in the presence of ADAMTSL4 and colocalization of ADAMTSL4 with fibrillin-1 in the ECM of cultured fibroblasts suggest a potential role for ADAMTSL4 in the formation or maintenance of the zonule.

Microenvironmental regulation by fibrillin-1

Fibrillin-1 is a ubiquitous extracellular matrix molecule that sequesters latent growth factor complexes. A role for fibrillin-1 in specifying tissue microenvironments has not been elucidated, even though the concept that fibrillin-1 provides extracellular control of growth factor signaling is currently appreciated. Mutations in FBN1 are mainly responsible for the Marfan syndrome (MFS), recognized by its pleiotropic clinical features including tall stature and arachnodactyly, aortic dilatation and dissection, and ectopia lentis. Each of the many different mutations in FBN1 known to cause MFS must lead to similar clinical features through common mechanisms, proceeding principally through the activation of TGFβ signaling. Here we show that a novel FBN1 mutation in a family with Weill-Marchesani syndrome (WMS) causes thick skin, short stature, and brachydactyly when replicated in mice. WMS mice confirm that this mutation does not cause MFS. The mutation deletes three domains in fibrillin-1, abolishing a binding site utilized by ADAMTSLIKE-2, -3, -6, and papilin. Our results place these ADAMTSLIKE proteins in a molecular pathway involving fibrillin-1 and ADAMTS-10. Investigations of microfibril ultrastructure in WMS humans and mice demonstrate that modulation of the fibrillin microfibril scaffold can influence local tissue microenvironments and link fibrillin-1 function to skin homeostasis and the regulation of dermal collagen production. Hence, pathogenetic mechanisms caused by dysregulated WMS microenvironments diverge from Marfan pathogenetic mechanisms, which lead to broad activation of TGFβ signaling in multiple tissues. We conclude that local tissue-specific microenvironments, affected in WMS, are maintained by a fibrillin-1 microfibril scaffold, modulated by ADAMTSLIKE proteins in concert with ADAMTS enzymes.

The microenvironment is specified by cell-surface molecules, growth factors, and the extracellular matrix. Here we report genetic evidence that implicates fibrillin-1, a ubiquitous extracellular matrix molecule that sequesters latent growth factor complexes, as a key determinant in the local control of musculoskeletal and skin microenvironments. A novel mutation in fibrillin-1 demonstrates that modulation of the fibrillin microfibril scaffold can influence tissue microenvironments and result in the clinical features of Weill-Marchesani syndrome (WMS), including thick skin, short stature, and brachydactyly. Dysregulated WMS microenvironments diverge from Marfan pathogenetic mechanisms, which lead to broad activation of TGFβ signaling in multiple tissues.

Essential role of microfibrillar-associated protein 4 in human cutaneous homeostasis and in its photoprotection

UVB-induced cutaneous photodamage/photoaging is characterized by qualitative and quantitative deterioration in dermal extracellular matrix (ECM) components such as collagen and elastic fibers. Disappearance of microfibrillar-associated protein 4 (MFAP-4), a possible limiting factor for cutaneous elasticity, was documented in photoaged dermis, but its function is poorly understood. To characterize its possible contribution to photoprotection, MFAP-4 expression was either augmented or inhibited in a human skin xenograft photodamage murine model and human fibroblasts. Xenografted skin with enhanced MFAP-4 expression was protected from UVB-induced photodamage/photoaging accompanied by the prevention of ECM degradation and aggravated elasticity. Additionally, remarkably increased or decreased fibrillin-1-based microfibril development was observed when fibroblasts were treated with recombinant MFAP-4 or with MFAP-4-specific siRNA, respectively. Immunoprecipitation analysis confirmed direct interaction between MFAP-4 and fibrillin-1. Taken together, our findings reveal the essential role of MFAP-4 in photoprotection and offer new therapeutic opportunities to prevent skin-associated pathologies.

The role of the elastic fiber system in the pathogenesis of osteoarthritis and knee joint laxity

Osteoarthritis (OA) is a disease of synovial joints in which all articular structures are affected. Evidence suggests that a decreased density in the elastic fiber concentration of the knee capsule is associated with joint hypermobility, a condition associated with OA. However, there is no study that shows a direct relationship between the elastic fiber system and knee OA. The purpose of this study is to determine if there is a correlation between the elastic fiber density in medial (MCL) and lateral (LCL) collateral ligaments and the severity of OA. The elastic fiber concentration in MCL and LCL were examined in cadaver knees (n = 10; 4 M, 6 F). The elastic fiber density, measured as the concentration of elastic fibers per unit area, was correlated with the severity of OA, which was graded on a 0-16 scale using histologic and macroscopic markers. Among all subjects, elastic fiber concentrations between MCL (mean 15.49% ± 2.49) and LCL (mean 13.93 ± 3.63) showed a significant difference (P = 0.023). There were no inter-gender differences between the elastic fiber concentration in either MCL or LCL. Among all subjects, the severity of OA was found to be correlated negatively with the elastic fiber concentration in both MCL (r = -0.693, P ≤ 0.05) and LCL (r = -0.718, P ≤ 0.05). This is the first study to show a correlation between the elastic fiber system and knee OA.

Fibrillin-1 and fibrillin-2 are essential for formation of thick oxytalan fibers in human nonpigmented ciliary epithelial cells in vitro

The ciliary zonule, also known as Zinn's zonule, is composed of oxytalan fibers. However, the mechanism by which epithelial cells in the ciliary body form these fibers in not fully understood. We examined human nonpigmented ciliary epithelial cells to determine the appearance and amount of oxytalan fibers in terms of positivity for their major components, fibrillin-1 and fibrillin-2. Examination of fibrillin-1 and fibrillin-2 expression by immunofluorescence revealed that thin fibers positive for fibrillin-1 on Day 2 changed to thick fibers by Day 8. The fibers positive for fibrillin-2 appeared on the thick fibrillin-1-positive fibers after Day 4. Northern blot analysis revealed that the level of fibrillin-1 did not change markedly, while induction of fibrillin-2 gene was evident on Day 5. Western blot analysis showed that fibrillin-1 deposition increased gradually, while that of fibrillin-2 increased markedly from Day 5 to Day 8. Fibrillin-1 suppression did not lead to the formation of fibrillin-2-positive thick fibers, whereas fibrillin-2 suppression led to the formation of fibrillin-1-positive thin fibers, but not thick fibers. These results suggest that both fibrillin-1 and fibrillin-2 are essential for the formation of thick oxytalan fibers in the ciliary zonule and are informative for clarifying the mechanism of homeostasis of the ocular matrix.

Classical and neonatal Marfan syndrome mutations in fibrillin-1 cause differential protease susceptibilities and protein function

Mutations in fibrillin-1 give rise to Marfan syndrome (MFS) characterized by vascular, skeletal, and ocular abnormalities. Fibrillins form the backbone of extracellular matrix microfibrils in tissues including blood vessels, bone, and skin. They are crucial for regulating elastic fiber biogenesis and growth factor bioavailability. To compare the molecular consequences of mutations causing the severe neonatal MFS with mutations causing the milder classical MFS, we introduced representative point mutations from each group in a recombinant human fibrillin-1 fragment. Structural effects were analyzed by circular dichroism spectroscopy and analytical gel filtration chromatography. Proteolytic susceptibility was probed with non-physiological and physiological proteases, including plasmin, thrombin, matrix metalloproteinases, and cathepsins. All mutant proteins showed a similar gross secondary structure and no differences in heat stability as compared with the wild-type protein. Proteins harboring neonatal mutations were typically more susceptible to proteolytic cleavage compared with those with classical mutations and the wild-type protein. Proteolytic neo-cleavage sites were found both in close proximity and distant to the mutations, indicating small but significant structural changes exposing cryptic cleavage sites. We also report for the first time that cathepsin K and V cleave non-mutated fibrillin-1 at several domain boundaries. Compared with the classical mutations and the wild type, the group of neonatal mutations more severely affected the ability of fibrillin-1 to interact with heparin/heparan sulfate, which plays a role in microfibril assembly. These results suggest differential molecular pathogenetic concepts for neonatal and classical MFS including enhanced proteolytic susceptibility for physiologically relevant enzymes and loss of function for heparin binding.

Obstructive sleep apnea syndrome: from phenotype to genetic basis

Obstructive sleep apnea syndrome (OSAS) is a complex chronic clinical syndrome, characterized by snoring, periodic apnea, hypoxemia during sleep, and daytime hypersomnolence. It affects 4-5% of the general population. Racial studies and chromosomal mapping, familial studies and twin studies have provided evidence for the possible link between the OSAS and genetic factors and also most of the risk factors involved in the pathogenesis of OSAS are largely genetically determined. A percentage of 35-40% of its variance can be attributed to genetic factors. It is likely that genetic factors associated with craniofacial structure, body fat distribution and neural control of the upper airway muscles interact to produce the OSAS phenotype. Although the role of specific genes that influence the development of OSAS has not yet been identified, current researches, especially in animal model, suggest that several genetic systems may be important. In this chapter, we will first define the OSAS phenotype, the pathogenesis and the risk factors involved in the OSAS that may be inherited, then, we will review the current progress in the genetics of OSAS and suggest a few future perspectives in the development of therapeutic agents for this complex disease entity.

ADAMTS10 protein interacts with fibrillin-1 and promotes its deposition in extracellular matrix of cultured fibroblasts

Autosomal recessive and autosomal dominant forms of Weill-Marchesani syndrome, an inherited connective tissue disorder, are caused by mutations in ADAMTS10 (encoding a secreted metalloprotease) and FBN1 (encoding fibrillin-1, which forms tissue microfibrils), respectively, yet they are clinically indistinguishable. This genetic connection prompted investigation of a potential functional relationship between ADAMTS10 and fibrillin-1. Specifically, fibrillin-1 was investigated as a potential ADAMTS10 binding partner and substrate, and the role of ADAMTS10 in influencing microfibril biogenesis was addressed. Using ligand affinity blotting and surface plasmon resonance, recombinant ADAMTS10 was found to bind to fibrillin-1 with a high degree of specificity and with high affinity. Two sites of ADAMTS10 binding to fibrillin-1 were identified, one toward the N terminus and another in the C-terminal half of fibrillin-1. Confocal microscopy and immunoelectron microscopy localized ADAMTS10 to fibrillin-1-containing microfibrils in human tissues. Furin-activated ADAMTS10 could cleave fibrillin-1, but innate resistance of ADAMTS10 zymogen to propeptide excision by furin was observed, suggesting that, unless activated, ADAMTS10 is an inefficient fibrillinase. To investigate the role of ADAMTS10 in microfibril biogenesis, fetal bovine nuchal ligament cells were cultured in the presence or absence of ADAMTS10. Exogenously added ADAMTS10 led to accelerated fibrillin-1 microfibril biogenesis. Conversely, fibroblasts obtained from a Weill-Marchesani syndrome patient with ADAMTS10 mutations deposited fibrillin-1 microfibrils sparsely compared with unaffected control cells. Taken together, these findings suggest that ADAMTS10 participates in microfibril biogenesis rather than in fibrillin-1 turnover.

Obstructive sleep apnea syndrome: natural history, diagnosis, and emerging treatment options

Sleep apnea is an entity characterized by repetitive upper airway obstruction resulting in nocturnal hypoxia and sleep fragmentation. It is estimated that 2%-4% of the middle-aged population has sleep apnea with a predilection in men relative to women. Risk factors of sleep apnea include obesity, gender, age, menopause, familial factors, craniofacial abnormalities, and alcohol. Sleep apnea has been increasingly recognized as a major health burden associated with hypertension and increased risk of cardiovascular disease and death. Increased airway collapsibility and derangement in ventilatory control responses are the major pathological features of this disorder. Polysomnography (PSG) is the gold-standard method for diagnosis of sleep apnea and assessment of sleep apnea severity; however, portable sleep monitoring has a diagnostic role in the setting of high pretest probability sleep apnea in the absence of significant comorbidity. Positive pressure therapy is the mainstay therapy of sleep apnea. Other treatment modalities, such as upper airway surgery or oral appliances, may be used for the treatment of sleep apnea in select cases. In this review, we focus on describing the sleep apnea definition, risk factor profile, underlying pathophysiologic mechanisms, associated adverse consequences, diagnostic modalities, and treatment strategies.

In vivo studies of mutant fibrillin-1 microfibrils

In humans, mutations in fibrillin-1 result in a variety of genetic disorders with distinct clinical phenotypes. While most of the known mutations in fibrillin-1 cause Marfan syndrome, a number of other mutations lead to clinical features unrelated to Marfan syndrome. Pathogenesis of Marfan syndrome is currently thought to be driven by mechanisms due to haploinsufficiency of wild-type fibrillin-1. However, haploinsufficiency-driven mechanisms cannot explain the distinct phenotypes found in other fibrillinopathies. To test the hypothesis that mutations in fibrillin-1 cause disorders through primary effects on microfibril structure, two different mutations were generated in Fbn1 in mice. One mutation leads to a truncated fibrillin-1 molecule that is tagged with green fluorescent protein, allowing visualization of mutant fibrillin-1 incorporated into microfibrils. In heterozygosity, these mutant mice demonstrate progressive fragmentation of the aortic elastic lamellae and also display fragmentation of microfibrils in other tissues. Fibrillin-2 epitopes are also progressively revealed in these mice, suggesting that fibrillin-2 immunoreactivity can serve as a marker for microfibril degradation. In contrast, a second mutation (in-frame deletion of the first hybrid domain) in fibrillin-1 results in stable microfibrils, demonstrating that fibrillin-1 molecules are not required to be in perfect register for microfibril structure and function and that the first hybrid domain is dispensable for microfibril assembly. Taken together, these results suggest that perturbation of microfibril structure may underlie one of the major features of the Marfan syndrome: fragmentation of aortic elastic lamellae.

Outcomes of iris-claw anterior chamber versus iris-fixated foldable intraocular lens in subluxated lens secondary to Marfan syndrome

PURPOSE

To compare the outcome of phacoemulsification using 2 different iris-fixation techniques for intraocular lens (IOL) replacement, a foldable posterior chamber IOL (PCIOL; AcrySof MA60AC, Alcon Laboratories Inc, Fort Worth, TX) and an iris-claw anterior chamber IOL (ACIOL; Artisan, Ophtec BV), for treatment of subluxated lenses in patients with Marfan syndrome (MFS).

DESIGN

Randomized, controlled trial.

PARTICIPANTS

A total of 31 eyes of 16 patients with subluxated lenses associated with MFS and a preoperative corrected visual acuity (CVA) < or =20/40 based on the Early Treatment Diabetic Retinopathy Study chart.

METHODS

Patients were enrolled and the eye with worse visual acuity was randomly assigned to 1 of 2 study arms: phacoemulsification and iris-fixated PCIOL or phacoemulsification and iris-claw ACIOL; the second eye of the same patient received the other IOL type. Preoperative and postoperative ophthalmologic examination, optical coherence tomography, and endothelial cell counts were performed.

MAIN OUTCOME MEASURES

We recorded CVA results at 3, 6, and 12 months, complications, endothelial cell loss, and central retinal thickness.

RESULTS

In the iris-fixated PCIOL group, CVA was significantly improved at 3 (P = 0.011; n = 16), 6 (P = 0.006; n = 16), and 12 months (P = 0.002; n = 16). In the iris-claw ACIOL group, CVA was significantly improved at 3 (P = 0.001; n=15), 6 (P = 0.001; n = 15), and 12 months (P = 0.009; n = 12). The CVA results did not differ significantly between groups. Dislocation of the IOL occurred in 3 of 16 (18.75%) eyes in the PCIOL group. Retinal detachment occurred in 3 eyes (2 in the PCIOL group and 1 in the ACIOL group) and was successfully repaired. Postoperative foveal tomograms in both groups revealed a decrease in the mean foveal thickness (MFT; < or =172 microm) in 54.16% of the patients.

CONCLUSIONS

The iris-sutured PCIOL and iris-claw ACIOL produced comparable improvements in CVA at 3, 6, and 12 months postoperatively. Although IOL dislocation tended to occur more frequently in the iris-fixated PCIOL group, the difference was not significant. At 6 months postoperatively, all study patients tended to have a thinner MFT. None of the patients in either group developed cystoid macular edema.

Microfibril structure masks fibrillin-2 in postnatal tissues

Fibrillin microfibrils are polymeric structures present in connective tissues. The importance of fibrillin microfibrils to connective tissue function has been demonstrated by the multiple genetic disorders caused by mutations in fibrillins and in microfibril-associated molecules. However, knowledge of microfibril structure is limited, largely due to their insolubility. Most previous studies have focused on how fibrillin-1 is organized within microfibril polymers. In this study, an immunochemical approach was used to circumvent the insolubility of microfibrils to determine the role of fibrillin-2 in postnatal microfibril structure. Results obtained from studies of wild type and fibrillin-1 null tissues, using monoclonal and polyclonal antibodies with defined epitopes, demonstrated that N-terminal fibrillin-2 epitopes are masked in postnatal microfibrils and can be revealed by enzymatic digestion or by genetic ablation of Fbn1. From these studies, we conclude that fetal fibrillin polymers form an inner core within postnatal microfibrils and that microfibril structure evolves as growth and development proceed into the postnatal period. Furthermore, documentation of a novel cryptic site present in EGF4 in fibrillin-1 underscores the molecular complexity and tissue-specific differences in microfibril structure.

Biogenesis and function of fibrillin assemblies

Fibrillin-1 and fibrillin-2 are large cysteine-rich glycoproteins that serve two key physiological functions: as supporting structures that impart tissue integrity and as regulators of signaling events that instruct cell performance. The structural role of fibrillins is exerted through the temporal and hierarchical assembly of microfibrils and elastic fibers, whereas the instructive role reflects the ability of fibrillins to sequester transforming growth factor beta (TGFbeta) and bone morphogenetic protein (BMP) complexes in the extracellular matrix. Characterization of fibrillin mutations in human patients and in genetically engineered mice has demonstrated that perturbation of either function manifests in disease. More generally, these studies have indicated that fibrillins are integral components of a broader biological network of extracellular, cell surface, and signaling molecules that orchestrate morphogenetic and homeostatic programs in multiple organ systems. They have also suggested that the relative composition of fibrillin-rich microfibrils imparts contextual specificity to TGFbeta and BMP signaling by concentrating the ligands locally so as to regulate cell differentiation within a spatial context during organ formation (positive regulation) and by restricting their bioavailability so as to modulate cell performance in a timely fashion during tissue remodeling/repair (negative regulation). Correlative evidence suggests functional coupling of the cell-directed assembly of microfibrils and targeting of TGFbeta and BMP complexes to fibrillins. Hence, the emerging view is that fibrillin-rich microfibrils are molecular integrators of structural and instructive signals, with TGFbeta and BMPs as the nodal points that convert extracellular inputs into discrete and context-dependent cellular responses.

[Interactions between fibrillin-1 and tgf-beta: consequences and human pathology]

Fibrillin-1 (FBN-1) is the main component of the 10-12 nm microfibrils found in the extracellular matrix (ECM). ECM displays a structural role in the tissue-specific organization and takes part in the regulation of various cytokines and growth factors. A growing body of evidences supports a narrow relationship between FBN-1 and TGF-beta. Homology between FBN-1 and latent TGF-beta (LTGF) allows microfibrills to be a reservoir for this cytokine. The Marfan syndrome (MFS), a prototypic fibrillinopathy, highlights these relationships as it relates to 2 major genes that are FBN1 and TGF-beta type II receptor (TGFBR2) genes. In a mouse model of MFS, an up-regulation of the TGF-beta pathway is partly responsible for the phenotype. This FBN-1/TGF-beta relationship may play also a role in systemic sclerosis (SSc), a multigenic disease characterized by excessive generalised ECM deposit. Indeed, two related animal models results from both gene mutations: the Tight Skin 1 mouse is due to a partial in-frame duplication of the Fbn1 gene and another model conditionally overexpresses TGF-beta type I receptor. A better understanding of FBN-1/TGF-beta relationship appears of great importance in fibrillinopathies: it may allow reconsidering the nosologic framework of these diseases including the TGF-beta signalopathies and could lead to innovative therapeutic strategies.

Comparative and morphological analysis of commonly used autografts for anterior cruciate ligament reconstruction with the native ACL: an electron, microscopic and morphologic study

Ligaments and tendons are similar in composition but differ in proportion and arrangement. Tendons are being used as grafts for the ACL reconstruction. Their microscopic structure has not been sufficiently studied and compared to the native ACL. A null hypothesis was declared stating that the anterior cruciate ligament should be histological, morphologically and functionally different from the tendon grafts used for ACL reconstruction. We investigated similarities and differences of the structure of ACL and tendons used as a graft tissue for ACL reconstruction. In this study, standardized samples of quadriceps, hamstrings (semitendinosus and gracilis) and patellar tendons, and the ACL were harvested from 26 autopsies (average age 36.4) and were investigated using light and electron microscopy, immunohistochemistry and morphometry. The thickness of the collagen fibrils, collagen organization and diameter, the fibril/interstitium ratio, density of fibroblasts and blood vessels, and distribution of the collagen type I, III and V fibrils were analyzed. The semitendinosus showed the highest density of fibroblasts and blood vessels, while the gracilis the highest fibril/interstitium ratio. No differences regarding the thickness of collagen fibrils and distribution of fibrils were found. The ACL had the highest concentration of type III and V collagen fibrils as well as elastic fibers. The histological and ultrastructural appearance of the ACL differs from those of the tendons used as graft, for ACL reconstruction. Its ultrastructure is varied and complex, with its collagen fibers bundles lying in many directions.

Fibrillin assembly requires fibronectin

Fibrillins constitute the major backbone of multifunctional microfibrils in elastic and nonelastic extracellular matrices. Proper assembly mechanisms are central to the formation and function of these microfibrils, and their properties are often compromised in pathological circumstances such as in Marfan syndrome and in other fibrillinopathies. Here, we have used human dermal fibroblasts to analyze the assembly of fibrillin-1 in dependence of other matrix-forming proteins. siRNA knockdown experiments demonstrated that the assembly of fibrillin-1 is strictly dependent on the presence of extracellular fibronectin fibrils. Immunolabeling performed at the light and electron microscopic level showed colocalization of fibrillin-1 with fibronectin fibrils at the early stages of the assembly process. Protein-binding assays demonstrated interactions of fibronectin with a C-terminal region of fibrillin-1, -2, and -3 and with an N-terminal region of fibrillin-1. The C-terminal half of fibrillin-2 and -3 had propensities to multimerize, as has been previously shown for fibrillin-1. The C-terminal of all three fibrillins interacted strongly with fibronectin as multimers, but not as monomers. Mapping studies revealed that the major binding interaction between fibrillins and fibronectin involves the collagen/gelatin-binding region between domains FNI(6) and FNI(9).

Targeting of bone morphogenetic protein growth factor complexes to fibrillin

Both latent transforming growth factor-beta (TGF-beta)-binding proteins fibrillins are components of microfibril networks, and both interact with members of the TGF-beta family of growth factors. Interactions between latent TGF-beta-binding protein-1 and TGF-beta and between fibrillin-1 and bone morphogenetic protein-7 (BMP-7) are mediated by the prodomain of growth factor complexes. To extend this information, investigations were performed to test whether stable complexes are formed by additional selected TGF-beta family members. Using velocity sedimentation in sucrose gradients as an assay, complex formation was demonstrated for BMP-7 and growth and differentiation factor-8 (GDF-8), which are known to exist in prodomain/growth factor complexes. Comparison of these results with complex formation by BMP-2, BMP-4 (full-length and shortened propeptides), BMP-10, and GDF-5 allowed us to conclude that all, except for BMP-2 and the short BMP-4 propeptides, formed complexes with their growth factors. Using surface plasmon resonance, binding affinities between fibrillin and all propeptides were determined. Binding studies revealed that the N-terminal end of fibrillin-1 serves as a universal high affinity docking site for the propeptides of BMP-2, -4, -7, and -10 and GDF-5, but not GDF-8, and located the BMP/GDF binding site within the N-terminal domain in fibrillin-1. Rotary shadowing electron microscopy of molecules of BMP-7 complex bound to fibrillin-1 confirmed these findings and also showed that prodomain binding targets the growth factor to fibrillin. Immunolocalization of BMP-4 demonstrated fibrillar staining limited to certain tissues, indicating tissue-specific targeting of BMP-4. These data implicate the fibrillin microfibril network in the extracellular control of BMP signaling and demonstrate differences in how prodomains target their growth factors to the extracellular space.

Aberrant fibrillin-1 expression in early emphysematous human lung: a proposed predisposition for emphysema

Parenchymal destruction, airspace enlargement, and loss of elasticity are hallmarks of pulmonary emphysema. Although the basic mechanism is unknown, there is a consensus that malfunctioning of the extracellular matrix is a major contributor to the pathogenesis of emphysema. In this study, we analyzed the expression of the elastic fiber protein fibrillin-1 in a large number (n=69) of human lung specimens with early-onset emphysema. Specimens were morphologically characterized by the Destructive Index, the Mean Linear Intercept, and the Panel Grading. We observed a strong correlation (P<0.001) of aberrant fibrillin-1 staining with the degree of destruction of lung parenchyma (r=0.71), airspace enlargement (r=0.47), and emphysema-related morphological abnormalities (r=0.69). There were no obvious correlations with age and smoking behavior. Staining for three other extracellular matrix components (type I collagen, type IV collagen, and laminin) was not affected. The aberrant fibrillin-1 staining observed in this study is similar to that observed in Marfan syndrome, a syndrome caused by mutations in the gene encoding fibrillin-1. Strikingly, emphysema is noticed in a number of Marfan patients. This, together with the notion that disruption of the fibrillin-1 gene in mice results in emphysematous lesions, makes fibrillin-1 a strong candidate to be involved in the etiology and pathogenesis of emphysema.

Therapy of Marfan Syndrome

Marfan syndrome is a common inherited disorder of connective tissue caused by deficiency of the matrix protein fibrillin-1. Effective surgical therapy for the most life-threatening manifestation, aortic root aneurysm, has led to a nearly normal lifespan for affected individuals who are appropriately recognized and treated. Traditional medical therapies, such as beta-adrenergic receptor blockade, are used to slow pathologic aortic growth and decrease the risk of aortic dissection by decreasing hemodynamic stress. New insights regarding the pathogenesis of Marfan syndrome have developed from investigation of murine models of this disorder. Fibrillin-1 deficiency is associated with excess signaling by transforming growth factor beta (TGFbeta). TGFbeta antagonists have shown great success in improving or preventing several manifestations of Marfan syndrome in these mice, including aortic aneurysm. These results highlight the potential for development of targeted therapies based on discovery of disease genes and interrogation of pathogenesis in murine models.

Fibrillin-rich microfibrils: Structural determinants of morphogenetic and homeostatic events

Fibrillin-rich microfibrils are specialized extracellular matrix assemblies that endow connective tissues with mechanical stability and elastic properties, and that participate in the regulation of organ formation, growth and homeostasis. Their physiological importance is underscored by the complex spectrum of clinical manifestations associated with mutations of fibrillin-1 and fibrillin-2 in Marfan syndrome (MFS) and congenital contractural arachnodactyly, respectively. Early evidence suggested that fibrillin-1 mutations in MFS lead to loss of tissue integrity by perturbing microfibril assembly and function. Recent studies in genetically targeted mice have however revealed that fibrillin-1 and fibrillin-2 mutations perturb signaling events mediated by TGF-beta superfamily members. As such, these studies have established a new biological paradigm whereby fibrillin-rich microfibrils are structural networks that specify the local concentration and timely release of signaling molecules during morphogenesis and tissue remodeling. This review summarizes our current understanding of the role of fibrillin-rich microfibrils in development and disease, as well as exciting new applications in the clinical management of MFS and related connective tissue disorders.

Elastin gene mutations in transgenic mice

We have constructed several rat tropoelastin minigene recombinants encoding the complete sequence of rat tropoelastin, two isoforms of rat tropoelastin and a truncated tropoelastin lacking the domains encoded by exons 19-31 of the rat gene. Coding and non-coding domains in all these recombinants were placed under the transcriptional control of 3 kb of the promoter domain of the rat tropoelastin gene. These minigenes were used to prepare a total of 28 separate founder lines of transgenic mice. A species-specific reverse-transcriptase polymerase chain reaction (RT-PCR) assay was established to demonstrate the synthesis of rat and mouse tropoelastin mRNA in several tissues obtained from both neonatal and adult transgenic mice. Thermolytic digestion of insoluble elastin isolated from several neonatal mouse tissues revealed the presence of rat tropoelastin peptides in progeny from all those founder mice in which detectable levels of rat tropoelastin mRNA were noted. Phenotypic and histopathological assessment of transgenic and non-transgenic animals revealed the development of two diverse elastic tissue disorders. The progeny of two separate founder lines overexpressing the rat tropoelastin isoform lacking exon 33, developed an emphysematous phenotype in early adulthood. In contrast, transgenic mice, in which expression of the truncated rat tropoelastin minigene lacking exons 19-31 had been observed, died of a ruptured ascending aortic aneurysm. Tropoelastin gene mutations, therefore, will result in heritable disorders of elastic tissue. Moreover, different mutations in the tropoelastin gene will be responsible for very different abnormalities in elastic tissue function.

Marfan syndrome: from molecular pathogenesis to clinical treatment

Marfan syndrome is a connective tissue disorder with ocular, musculoskeletal and cardiovascular manifestations that are caused by mutations in fibrillin-1, the major constituent of extracellular microfibrils. Mouse models of Marfan syndrome have revealed that fibrillin-1 mutations perturb local TGFbeta signaling, in addition to impairing tissue integrity. This discovery has led to the identification of a new syndrome with overlapping Marfan syndrome-like manifestations that is caused by mutations in TGFbeta receptor types I and II. It has also prompted the idea that TGFbeta antagonism will be a productive treatment strategy in Marfan syndrome and perhaps in other related disorders. More generally, these studies have established that Marfan syndrome is part of a group of developmental disorders with broad and complex effects on morphogenesis, homeostasis and organ function.

Current concepts of ocular manifestations in Marfan syndrome

Marfan syndrome is a widespread disorder of connective tissue. It is characterized by systemic and ocular features due to mutations in the fibrillin gene. Awareness and prompt recognition of the ocular complications of Marfan syndrome may enable improvement and preservation of sight. Studies have been performed in the last few years that enable a better understanding of the genetics of the syndrome, earlier diagnosis, and improvement in the surgical techniques and options.

Effects of fibrillin-1 degradation on microfibril ultrastructure

Current models of the elastic properties and structural organization of fibrillin-containing microfibrils are based primarily on microscopic analyses of microfibrils liberated from connective tissues after digestion with crude collagenase. Results presented here demonstrate that this digestion resulted in the cleavage of fibrillin-1 and loss of specific immunoreactive epitopes. The proline-rich region and regions near the second 8-cysteine domain in fibrillin-1 were easily cleaved by crude collagenase. Other sites that may also be cleaved during microfibril digestion and extraction were identified. In contrast to collagenase-digested microfibrils, guanidine-extracted microfibrils contained all fibrillin-1 epitopes recognized by available antibodies. The ultrastructure of guanidine-extracted microfibrils differed markedly from that of collagenase-digested microfibrils. Fibrillin-1 filaments splayed out, extending beyond the width of the periodic globular beads. Both guanidine-extracted and collagenase-digested microfibrils were subjected to extensive digestion by crude collagenase. Collagenase digestion of guanidine-extracted microfibrils removed the outer filaments, revealing a core structure. In contrast to microfibrils extracted from tissues, cell culture microfibrils could be digested into short units containing just a few beads. These data suggest that additional cross-links stabilize the long beaded microfibrils in tissues. Based on the microfibril morphologies observed after these experiments, on the crude collagenase cleavage sites identified in fibrillin-1, and on known antibody binding sites in fibrillin-1, a model is proposed in which fibrillin-1 molecules are staggered in microfibrils. This model further suggests that the N-terminal half of fibrillin-1 is asymmetrically exposed in the outer filaments, whereas the C-terminal half of fibrillin-1 is present in the interior of the microfibril.

Genetic Basis of Thoracic Aortic Aneurysms and Dissections: Potential Relevance to Abdominal Aortic Aneurysms

Ascending thoracic aortic aneurysms leading to type A dissections (TAAD) have long been known to occur in association with a genetic syndrome such as Marfan syndrome (MFS). More recently, TAAD has also been demonstrated to occur as an autosomal dominant disorder in the absence of syndromic features, termed familial TAAD. Familial TAAD demonstrates genetic heterogeneity, and linkage studies have identified TAAD loci at 5q13-14 (TAAD1), 11q23 (FAA1), 3p24-25 (TAAD2), and 16p12.2-13.13. The genetic heterogeneity of TAAD is reflected by variation in disease in terms of the age of onset, progression, penetrance, and association with additional cardiac and vascular features. The underlying genetic heterogeneity of TAAD is reflected in the phenotypic variation associated with familial TAAD with respect to age of onset, progression, penetrance, and association with additional cardiac and vascular features. Mutations in the TGFBR2 gene have been identified as the cause of disease linked to the 3p24-25 locus, implicating dysregulation of TGF-beta signaling in TAAD. Mutations in myosin heavy chain (MYH11), a smooth muscle cell-specific contractile protein, have been identified in familial TAAD associated with patent ductus arteriosus (PDA) linked to 16p12.2-12.13. The identification of these novel disease pathways has led to new directions for future research addressing the pathology and treatment of TAAD.

The molecular genetics of Marfan syndrome and related disorders

Marfan syndrome (MFS), a relatively common autosomal dominant hereditary disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular systems, is caused by mutations in the gene for fibrillin-1 (FBN1). The leading cause of premature death in untreated individuals with MFS is acute aortic dissection, which often follows a period of progressive dilatation of the ascending aorta. Recent research on the molecular physiology of fibrillin and the pathophysiology of MFS and related disorders has changed our understanding of this disorder by demonstrating changes in growth factor signalling and in matrix-cell interactions. The purpose of this review is to provide a comprehensive overview of recent advances in the molecular biology of fibrillin and fibrillin-rich microfibrils. Mutations in FBN1 and other genes found in MFS and related disorders will be discussed, and novel concepts concerning the complex and multiple mechanisms of the pathogenesis of MFS will be explained.

Determinants of rapid progression of aortic root dilatation and complications in Marfan syndrome

BACKGROUND

Progressive aortic dilatation has prognostic significance in the Marfan syndrome.

METHODS

To identify which patients were at high risk of rapid progression, we echocardiographically studied 43 patients (age 22 +/- 14 years) with the mean follow-up period of 5.2 +/- 3.2 years. Aortic diameters, left ventricular (LV) size, fractional shortening, and the severity of aortic and mitral regurgitation were assessed. Transmitral peak early and atrial flow velocities, their ratio and the deceleration time of peak early velocity were also obtained.

RESULTS

Mean annual increases of aortic diameters were 0.4 +/- 0.3 mm at the annulus, 1.5 +/- 1.3 mm at the sinuses of Valsalva, 0.7 +/- 0.6 mm at the supraaortic ridge and 0.4 +/- 0.4 mm at the proximal ascending aorta. Patients were divided into 2 groups according to the aortic growth rate at the sinuses of Valsalva level: rapid (R, >3% per year, 15 patients) or slow (S, < or =3% per year, 28 patients) progression groups. Measured variables did not show significant differences between the 2 groups except older age, higher blood pressure and more severe aortic regurgitation in group R. Multiple regression analysis identified prolonged deceleration time as the most important variable predicting aortic complications. Aortic dissection occurred more frequently in group R (7 patients, 47%) than in group S (0%, P < 0.001).

CONCLUSIONS

Marfan patients at older age, with higher blood pressure, and with significant aortic regurgitation were at high risk of progression of aortic dilatation, with the most remarkable increase at the sinuses of Valsalva. Prolonged deceleration time may relate to an increased risk for aortic complications.

Marfan's syndrome

Marfan's syndrome is a systemic disorder of connective tissue caused by mutations in the extracellular matrix protein fibrillin 1. Cardinal manifestations include proximal aortic aneurysm, dislocation of the ocular lens, and long-bone overgrowth. Important advances have been made in the diagnosis and medical and surgical care of affected individuals, yet substantial morbidity and premature mortality remain associated with this disorder. Progress has been made with genetically defined mouse models to elucidate the pathogenetic sequence that is initiated by fibrillin-1 deficiency. The new understanding is that many aspects of the disease are caused by altered regulation of transforming growth factor beta (TGFbeta), a family of cytokines that affect cellular performance, highlighting the potential therapeutic application of TGFbeta antagonists. Insights derived from studying this mendelian disorder are anticipated to have relevance for more common and non-syndromic presentations of selected aspects of the Marfan phenotype.

Genetic basis of thoracic aortic aneurysms and aortic dissections

Ascending thoracic aortic aneurysms leading to type A dissections (TAAD) can occur in association with a genetic syndrome, such as Marfan syndrome (MFS), or as an autosomal dominant disorder in the absence of syndromic features, termed familial TAAD. Familial TAAD demonstrates genetic heterogeneity, and linkage studies have identified three TAAD loci at 5q13-14 (TAAD1), 11q23 (FAA1), and 3p24-25 (TAAD2). The underlying genetic heterogeneity of TAAD is reflected in the phenotypic variation associated with familial TAAD with respect to age of onset, progression, penetrance, and association with additional cardiac and vascular features. Recently, mutations in the TGFBR2 gene have been identified as the cause of disease linked to the TAAD2 locus, supporting the hypothesis that dysregulation of TGFbeta signaling is a mechanism leading to aneurysms and dissections. The recent identification of the TGFbeta pathway as a key target in the molecular pathogenesis of TAAD has opened new avenues for future genetic and therapeutic research.

Surgical treatment for scoliosis in Marfan syndrome

STUDY DESIGN

Review of results of patients with Marfan syndrome treated with instrumented posterior fusion alone for scoliosis.

OBJECTIVE

To analyze the results of surgical treatment for scoliosis in Marfan syndrome.

SUMMARY OF BACKGROUND DATA

Few studies have been reported in the literature on surgical treatment for scoliosis in Marfan syndrome, analyzing long-term results of posterior instrumented fusion.

METHODS

Twenty-three patients with Marfan syndrome with a mean age of 17 years (range, 11-31 years) were treated surgically from 1982 to 1995 for scoliosis, using a posterior instrumented fusion alone (Harrington rod with sublaminar wires in the first 16 cases, and a more recent hybrid instrumentation in the remaining 7 cases). All of the patients received a long posterior instrumented fusion, including 12.3 levels on average (range, 9-17), extending the fusion area to vertebrae that were neutral and stable in both coronal and sagittal planes before surgery. Patients were analyzed as two different groups (Group 1 and Group 2) according to the different posterior instrumentations employed: Group 1 included 16 patients treated by the Harrington distraction rod technique with sublaminar wires, while Group 2 included 7 patients treated using more recent hybrid instrumentations. Presentation features, complications, and results were analyzed.

RESULTS

At a minimum follow-up of 7 years (maximum, 18 years), all 23 patients were reviewed. The mean age was 26.8 years (range, 20-38 years). The average preoperative scoliosis value of 69.91 degrees was initially corrected to 38.17 degrees, averaged 40.89 degrees 1 year after surgery, and was finally equal to 44.09 degrees at the last follow-up. Differences in terms of scoliosis correction achieved with different instrumentations (Groups 1 and 2) did not reach statistical significance. In Group 2 patients, the percentage of postoperative correction was slightly lower (44.23%) than that of Group 1 (46.55%) but remained more stable at the last follow-up (40.97% vs. 36.38% of Group 1). There were 11 complications in 10 of the 23 patients (43.4%); two complications occurred in 1 patient. Intraoperatively, dural tears occurred in 2 cases (8.6%). Pseudarthrosis with instrumentation failure in 2 cases (8.6%) required revision surgery. Five (21.7%) distal hook dislodgements with moderate loss of scoliosis correction, 1 (4.3%) mild loss of correction without instrumentation failure, and 1 asymptomatic cervicothoracic junctional kyphosis. did not require surgery. All complications occurred among the 16 Group 1 patients, treated using the Harrington rod instrumentation with sublaminar wires.

CONCLUSIONS

These results seemed to demonstrate that a satisfactory stabilization of scoliosis can be achieved by posterior instrumentation alone in patients with Marfan syndrome. Instrumented posterior fusion should be extended to include vertebrae that are neutral and stable in both coronal and sagittal planes before surgery, in order to ensure stabilization of the deformity and reduce the risks of decompensation of the spine.

The elastic fiber network of the anulus fibrosus of the normal and scoliotic human intervertebral disc

STUDY DESIGN

Immunohistochemical study of elastic fibers in human intervertebral discs (IVD) collected at surgery from patients with scoliosis.

OBJECTIVES

To compare the elastic fiber network in scoliotic discs (idiopathic scoliosis or neuromuscular scoliosis) to that of control (normal) discs. To study whether the change in elastic fiber organization could contribute to the progression of spinal deformity.

SUMMARY OF BACKGROUND DATA

Elastin and elastic fibers have been identified previously in human IVD but were believed to contribute little to the tissue's mechanical properties. However, a recent immunohistochemical study has revealed an abundant and organized elastic fiber network in bovine IVD, indicating that elastic fibers could play an important mechanical role. This article reports the organization of elastic fibers in human IVD and the changes of elastic fiber organization in scoliosis.

METHODS

Intact wedges of IVD were obtained from patients undergoing surgery for scoliosis (aged 12-22 years). Control discs were obtained from a patient (aged 12 years) with a spinal tumor and a trauma patient (aged 17 years). The discs were dissected to give radial slices and were snap frozen. Frozen sections were cut and digested with hyaluronidase to remove glycosaminoglycans. Micrographs of the sections were examined by polarized light to visualize collagen organization. The elastic fiber network was visualized immunohistochemically or by histochemical staining with orcein.

RESULTS

A highly organized elastic fiber network, similar to that described in bovine discs, was revealed in the control human discs. In the anulus fibrosus of control discs, dense elastic fibers were located between adjacent lamellae, with fibers also present within individual lamellae. Elastic fibers appeared to be long (>200 microm) and straight in outer anulus, whereas in inner anulus, they nearly ran parallel to each other and at an angle of approximately 60 degrees or 120 degrees to those in adjacent lamellae. However, in scoliotic discs, elastic fibers were sparse, and the collagen and elastic fiber networks were disorganized with loss of lamellar structure. Cell clusters, one of typical degenerative feature, were seen in scoliotic discs but not in age-matched control discs.

CONCLUSIONS

Our results reveal an abundant and organized network of elastic fibers in the adolescent (12 and 17-year-olds) human IVD, and suggest that elastic fiber network plays a significant biomechanical role. This network is sparse and disrupted in scoliotic discs, and could be involved in the progression of the spinal deformity.