Extracellular Microfibrils Research Articles

Material and mechanical properties of bones deficient for fibrillin-1 or fibrillin-2 microfibrils

The contribution of non-collagenous components of the extracellular matrix to bone strength is largely undefined. Here we report that deficiency of fibrillin-1 or fibrillin-2 microfibrils causes distinct changes in bone material and mechanical properties. Morphometric examination of mice with hypomorphic or null mutations in fibrillin-1 or fibrillin-2, respectively, revealed appreciable differences in the postnatal shaping and growth of long bones. Fourier transform infrared imaging spectroscopy indicated that fibrillin-1 plays a predominantly greater role than fibrillin-2 in determining the material properties of bones. Biomechanical tests demonstrated that fibrillin-2 exerts a greater positive influence on the mechanical properties of bone than fibrillin-1 assemblies. Published evidence indirectly supports the notion that the above findings are mostly, if not exclusively, related to the differential control of TGFβ family signaling by fibrillin proteins. Our study therefore advances our understanding of the role that extracellular microfibrils play in bone physiology and implicitly, in the pathogenesis of bone loss in human diseases caused by mutations in fibrillin-1 or -2.

Fibrillin‐1 genetic deficiency leads to pathological ageing of arteries in mice

Fibrillin-1, the major component of extracellular microfibrils that associate with insoluble elastin in elastic fibres, is mainly synthesized during development and postnatal growth and is believed to guide elastogenesis. Mutations in the fibrillin-1 gene cause Marfan syndrome, a multisystem disorder characterized by aortic aneurysms and dissections. The recent finding that early deficiency of elastin modifies vascular ageing has raised the possibility that fibrillin-1 deficiency could also contribute to late-onset pathology of vascular remodelling. To address this question, we examined cardiovascular function in 3-week-old, 6-month-old, and 24-month-old mice that are heterozygous for a hypomorphic structural mutation of fibrillin-1 (Fbn1{+/mgΔ} mice). Our results indicate that Fbn1{+/mgΔ} mice, particularly those that are 24 months old, are slightly more hypotensive than wild-type littermates. Additionally, aneurysm and aortic insufficiency were more frequently observed in ageing Fbn1{+/mgΔ}$ mice than in the wild-type counterparts. We also noted substantial fragmentation and decreased number of elastic lamellae in the aortic wall of Fbn1{+/mgΔ} mice, which were correlated with an increase in aortic stiffness, a decrease in vasoreactivity, altered expression of elastic fibre-related genes, including fibrillin-1 and elastin, and a decrease in the relative ratio between tissue elastin and collagen. Collectively, our findings suggest that the heterozygous mgΔ mutation accelerates some aspects of vascular ageing and eventually leads to aortic manifestations resembling those of Marfan syndrome. Importantly, our data also indicate that vascular abnormalities in Fbn1{+/mgΔ} mice are opposite to those induced by elastin haploinsufficiency during ageing that affect blood pressure, vascular dimensions, and number of elastic lamellae.

The ECM protein LTBP‐2 is a suppressor of esophageal squamous cell carcinoma tumor formation but higher tumor expression associates with poor patient outcome

Our previous studies of chromosome 14 transfer into tumorigenic esophageal squamous cell carcinoma (ESCC) cell line, SLMT, suggested the existence of tumor suppressor genes on chromosome 14. Gene expression profiling of microcell hybrids and the tumor segregants identified an interesting gene, LTBP-2 (latent transforming growth factor β binding protein 2), which has been analyzed here for its role in ESCC. LTBP-2 maps to 14q24 and encodes a secreted protein, which is a component of the extracellular matrix microfibrils. LTBP-2 expression was downregulated in ESCC cell lines and tumor tissues. Promoter hypermethylation was found to be involved in LTBP-2 inactivation. Functional studies indicated its tumor-suppressive roles in ESCC. In the in vitro colony formation and Matrigel three-dimensional culture assays, LTBP-2 decreased the colony-forming abilities of ESCC cell lines. LTBP-2 expression was associated with reduction of cell migrating and invasive abilities. LTBP-2 could also reduce the tube-forming ability of endothelial cells. Moreover, LTBP-2 induced tumor suppression in in vivo nude mouse assays. Tissue microarray immunohistochemical staining analysis indicated that LTBP-2 expression is reduced in tumor tissues when compared to normal tissues, and LTBP-2 expression correlated significantly with the survival of ESCC patients. Thus, LTBP-2 appears to play an important role in ESCC.

Fibrillin-3 expression in human development

Fibrillin proteins are the major components of extracellular microfibrils found in many connective tissues. Fibrillin-1 and fibrillin-2 are well studied and mutations in these proteins cause a number of fibrillinopathies including Marfan syndrome and congenital contractural arachnodactyly, respectively. Fibrillin-3 was more recently discovered and is much less well characterized. Fibrillin-1 is expressed throughout life, whereas fibrillins-2 and -3 are thought to be primarily present during development. Here, we report detailed fibrillin-3 expression patterns in early human development.A polyclonal antiserum against a C-terminal recombinant half of human fibrillin-3 was produced in rabbit. Anti-fibrillin-3 antibodies were affinity-purified and antibodies cross-reacting with the other fibrillins were removed by absorption resulting in specific anti-fibrillin-3 antibodies. Immunohistochemical analyses with these purified antibodies demonstrate that fibrillin-3 is temporally expressed in numerous tissues relatively evenly from the 6th to the 12th gestational week. Fibrillin-3 was found spatially expressed in perichondrium, perineurium, perimysium, skin, developing bronchi, glomeruli, pancreas, kidney, heart and testis and at the prospective basement membranes in developing epithelia and endothelia. Double immunohistochemical analyses showed that all fibrillins are globally expressed in the same organs, with a number of differences on the tissue level in cartilage, perichondrium and developing bronchi. These results suggest that fibrillin-3, compared to the other fibrillins, fulfills both overlapping and distinct functions in human development.

Cytoskeleton-mediated templating of complex cellulose-scaffolded extracellular structure and its association with oikosins in the urochordate Oikopleura

Oriented cellulose deposition is critical to plant patterning and models suggest microtubules constrain cellulose synthase movements through the plasma membrane. Though widespread in plants, urochordates are the only animals that synthesize cellulose. We characterized the distinctive cellulose microfibril scaffold of the larvacean house and its interaction with house structural proteins (oikosins). Targeted disruption of cytoskeletal elements, secretory pathways, and plasma membrane organization, suggested a working model for templating extracellular cellulose microfibrils from animal cells that shows both convergence and differences to plant models. Specialized cortical F-actin arrays template microfibril orientation and glycosylphosphatidylinositol-anchored proteins in lipid rafts may act as scaffolding proteins in microfibril elongation. Microtubules deliver and maintain cellulose synthase complexes to specific cell membrane sites rather than orienting their movement through the membrane. Oikosins are incorporated into house compartments directly above their corresponding cellular field of expression and interact with the cellulose scaffold to a variable extent.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-010-0547-8) contains supplementary material, which is available to authorized users.

Extracellular Microfibrils Control Osteoblast-supported Osteoclastogenesis by Restricting TGFβ Stimulation of RANKL Production

Mutations in fibrillin-1 or fibrillin-2, the major structural components of extracellular microfibrils, cause pleiotropic manifestations in Marfan syndrome and congenital contractural arachnodactyly, respectively. We recently found that fibrillin-1 and fibrillin-2 control bone formation by regulating osteoblast differentiation through the differential modulation of endogenous TGFβ and bone morphogenetic protein signals. Here, we describe in vivo and ex vivo experiments that implicate the fibrillins as negative regulators of bone resorption. Adult Fbn2(-/-) mice display a greater than normal osteolytic response to locally implanted lipopolysaccharide-coated titanium particles. Although isolated cultures of Fbn2(-/-) preosteoclasts exhibited normal differentiation and activity, these features were substantially augmented when mutant or wild-type preosteoclasts were co-cultured with Fbn2(-/-) but not wild-type osteoblasts. Greater osteoclastogenic potential of Fbn2(-/-) osteoblasts was largely accounted for by up-regulation of the Rankl gene secondary to heightened TGFβ activity. This conclusion was based on the findings that blockade of TGFβ signaling blunts Rankl up-regulation in Fbn2(-/-) osteoblasts and bones and that systemic TGFβ antagonism improves locally induced osteolysis in Fbn2(-/-) mice. Abnormally high Rankl expression secondary to elevated TGFβ activity was also noted in cultured osteoblasts from Fbn1(-/-) mice. Collectively our data demonstrated that extracellular microfibrils balance local catabolic and anabolic signals during bone remodeling in addition to implying distinct mechanisms of bone loss in Marfan syndrome and congenital contractural arachnodactyly.

Fibrillin-1 and -2 differentially modulate endogenous TGF-β and BMP bioavailability during bone formation

Extracellular regulation of signaling by transforming growth factor (TGF)-β family members is emerging as a key aspect of organ formation and tissue remodeling. In this study, we demonstrate that fibrillin-1 and -2, the structural components of extracellular microfibrils, differentially regulate TGF-β and bone morphogenetic protein (BMP) bioavailability in bone. Fibrillin-2-null (Fbn2(-/-)) mice display a low bone mass phenotype that is associated with reduced bone formation in vivo and impaired osteoblast maturation in vitro. This Fbn2(-/-) phenotype is accounted for by improper activation of latent TGF-β that selectively blunts expression of osterix, the transcriptional regulator of osteoblast maturation, and collagen I, the structural template for bone mineralization. Cultured osteoblasts from Fbn1(-/-) mice exhibit improper latent TGF-β activation as well, but mature faster because of increased availability of otherwise matrix-bound BMPs. Additional in vitro evidence excludes a direct role of microfibrils in supporting mineral deposition. Together, these findings identify the extracellular microfibrils as critical regulators of bone formation through the modulation of endogenous TGF-β and BMP signaling.

The Extracellular Matrix Glycoprotein Elastin Microfibril Interface Located Protein 2: A Dual Role in the Tumor Microenvironment

We have recently reported that elastin microfibril interface located protein 2 (EMILIN2), an extracellular matrix (ECM) glycoprotein, triggers cell death through a direct binding to death receptors. EMILIN2 thus influences cell viability through a mechanism that is unique for an ECM molecule. In the present work, we report an additional function for this molecule. First, we identify the region responsible for the proapoptotic effects, a 90-amino acid residue-long coiled-coil fragment toward the N-terminus of the molecule. The fragment recapitulates EMILIN2 proapoptotic mechanisms. In addition, using either the full molecule or the active fragment, for the first time, we demonstrate a significant antitumoral effect in vivo, likely due to a decrease in tumor cell viability. Unexpectedly, tumors treated with EMILIN2 or the deletion mutant display a significant increase of tumor angiogenesis. In view of this novel finding, the cotreatment of the growing tumors with an antiangiogenic drug led, in most cases, to a complete regression of tumor growth. These results grant further support to recent findings that pinpoint the microenvironment as an important regulator of cell fate under both physiological and pathological conditions and disclose the possibility of using EMILIN2 fragments as potent antineoplastic tools for cancer treatment.

Mutations in fibrillin‐1 leading to classical and neonatal Marfan syndrome cause differential protease susceptibilities and protein function

Fibrillin‐1 constitutes the backbone of extracellular matrix microfibrils, which are crucial for regulating elastic fiber biogenesis and TGF‐beta bioavailability. Mutations in fibrillin‐1 give rise to the Marfan syndrome (MFS) characterized by vascular, skeletal and ocular symptoms. To investigate molecular consequences of mutations causing severe neonatal or the milder classical form of MFS, point mutations from each group were introduced in recombinant human fibrillin‐1 fragments. Proteolytic susceptibility was probed with physiological and non‐physiological proteases. The mutant proteins harboring neonatal mutations were typically more susceptible to proteolytic cleavage than those with classic mutations. The cleavage sites were found both in close proximity and distant to the mutations, indicating structural changes and the exposure of cryptic cleavage sites. 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. Fibroblasts attached less efficiently to the neonatal as compared to the classical mutant proteins. These results suggest new molecular pathogenetic concepts for MFS. In most cases the neonatal mutations resulted in more severe effects, and the biochemical variability correlates with the clinical variability observed in MFS. The work was funded by the Canadian CIHR.

The role of fibronectin in microfibril assembly and homeostasis

Fibrillins are members of a protein family that constitutes the backbone of extracellular microfibrils. Assembly of fibrillins into microfibrils is often compromised in pathological situations such as the Marfan syndrome and other fibrillinopathies. We have used a cellular model system to analyze assembly of fibrillin‐1 in dependence of fibronectin. Fibrillin‐1 assembly was strictly dependent on the presence of fibronectin fibers. Immunofluorescence and electron microscopy experiments showed that fibrillin‐1 and fibronectin colocalized to the same fiber system at early stages of the assembly of both proteins. Using a fibronectin assembly inhibiting peptide (FUD), we observed that homeostasis of fibrillin‐1 fibers is dependent on the constant availability of fibronectin fibers. Solid phase binding assays demonstrated that fibronectin interacted with the C‐terminal region of all fibrillins. We also demonstrated that multimerization of the C‐terminal half of fibrillins is required for interaction with fibronectin. Further interaction mapping studies revealed that fibrillins require the complete collagen/gelatin site in fibronectin. FUD inhibits the fibrillin‐1 interaction to fibronectin likely through conformational changes in the gelatin binding domain of fibronectin. In summary, our results show that fibrillin network formation and homeostasis requires fibronectin.

Functional specialization of cellulose synthase genes of prokaryotic origin in chordate larvaceans

Extracellular matrices play important, but poorly investigated, roles in morphogenesis. Extracellular cellulose is central to regulation of pattern formation in plants, but among metazoans only tunicates are capable of cellulose biosynthesis. Cellulose synthase (CesA) gene products are present in filter-feeding structures of all tunicates and also regulate metamorphosis in the ascidian Ciona. Ciona CesA is proposed to have been acquired by lateral gene transfer from a prokaryote. We identified two CesA genes in the sister-class larvacean Oikopleura dioica. Each has a mosaic structure of a glycoslyltransferase 2 domain upstream of a glycosyl hydrolase family 6 cellulase-like domain, a signature thus far unique to tunicates. Spatial-temporal expression analysis revealed that Od-CesA1 produces long cellulose fibrils along the larval tail, whereas Od-CesA2 is responsible for the cellulose scaffold of the post-metamorphic filter-feeding house. Knockdown of Od-CesA1 inhibited cellulose production in the extracellular matrix of the larval tail. Notochord cells either failed to align or were misaligned, the tail did not elongate properly and tailbud embryos also exhibited a failure to hatch. Knockdown of Od-CesA2 did not elicit any of these phenotypes and instead caused a mild delay in pre-house formation. Phylogenetic analyses including Od-CesAs indicate that a single lateral gene transfer event from a prokaryote at the base of the lineage conferred biosynthetic capacity in all tunicates. Ascidians possess one CesA gene, whereas duplicated larvacean genes have evolved distinct temporal and functional specializations. Extracellular cellulose microfibrils produced by the pre-metamorphic Od-CesA1 duplicate have a role in notochord and tail morphogenesis.

Association of Metalloproteinase Gene Polymorphisms with Systemic Sclerosis in the European Caucasian Population

Systemic sclerosis (SSc) is classified among the complex genetic disorders and is characterized by massive extracellular matrix deposits. These may be due to overactivation of transforming growth factor ss that may be in part a result of abnormal remodeling of extracellular matrix and microfibrils. Metalloproteinases (MMP) are a family of proteolytic enzymes, and MMP 2, 9, and 14 contribute to the degradation of microfibrils. Our aim was to determine whether polymorphisms of the MMP2, MMP9, and MMP14 genes confer susceptibility to SSc in a large population. A case-control study was performed in 659 SSc patients and 511 healthy matched controls from a European Caucasian population. Six Tag single-nucleotide polymorphisms (SNP) of the MMP2 gene and 2 SNP of MMP9 and MMP14 genes were genotyped. All SNP were in Hardy-Weinberg equilibrium in the control population. There was no association between the MMP2, MMP9, and MMP14 variants we investigated and SSc for allelic and genotype frequencies. No association was observed for the different subphenotypes of SSc patients. Our results in a large cohort of European Caucasian SSc patients do not support that MMP2, MMP9, and MMP14 genes are involved in the genetic background of SSc.

Computer construction and analysis of protein models of mutant fibrillin-1 gene in Marfan's syndrome

Fibrillin-1, the major constituent of extracellular microfibrils, plays an important role in the molecular pathogenesis of Marfan syndrome (MFS, #54700). The aim of this study was to analyze protein models of the mutation of the fibrillin-1 (FBN1) gene on Arg545Cys and Arg1530Cys which have been reported to cause predominant ectopia lentis in Chinese patients. We constructed and analyzed the protein models of the mutant FBN1 gene on Arg545Cys and Arg1530Cys. Fibrillin-1 protein structures were predicted by SWISS-MODEL. Models were viewed in Swiss-Pdb Viewer. Computer construction and analysis of protein models of the mutant FBN1 gene revealed that the mutant Arg545Cys FBN1 protein had various changes on protein's secondary structure with an absence of a helix, decreased hydrogen bond distance, different protein surface solvent-accessibility and decreased negative electrostatic potential. The mutant Arg1530Cys FBN1 showed lost of hydrogen bonds, different protein surface solvent-accessibility and increased negative electrostatic potential. Protein models of the mutant FBN1 gene shows significant alterations on the protein's secondary structure based on computer construction and analysis technology. This study provides further evidence for the important effect of the mutant FBN1 on the pathogenesis of human ectopia lentis.

Transcriptional regulation of fibrillin‐2 gene by E2F family members in chondrocyte differentiation

Mutation in fibrillin-2, a major structural component of extracellular microfibrils in connective tissue, results in the autosomal dominant disease congenital contractural arachnodactyly. This genetic disease is characterized by dolichostenomelia and arachnodactyly, in addition to contractures of the large joints and abnormal pinnae formation, thus indicating the significance of fibrillin-2 in chondrogenesis. In this study, we investigated the transcriptional regulation of fibrillin-2 in chondrogenic differentiation. Although mRNA expression of fibrillin-1, a highly homologous protein to fibrillin-2, remained almost unchanged during chondrogenesis of mouse ATDC5 cells, fibrillin-2 mRNA expression varied. Fibrillin-2 was highly expressed at the early stage and declined progressively during differentiation. The 5'-flanking region of the fibrillin-2 gene contains potential binding sites for E2F, Runx, AP-2, and Sox transcription factors. The promoter activity of fibrillin-2 decreased markedly following deletion and mutagenesis of the E2F binding site between -143 and -136 bp. Overexpression of E2F1 resulted in a marked increase in its promoter activity, whereas expression of other transcription factors including AP-2alpha and Runx2 had no effect. The increase in promoter activity by E2F1 was completely suppressed by the coexpression of E2F4. E2F2 and E2F3 had positive effects on the promoter activity. Although ATDC5 cells expressed transcripts for the E2F family genes at all stages of differentiation, the expression profiles differed. E2F1 expression remained almost unchanged, whereas E2F4 expression increased markedly at the late stage of differentiation. These results indicated that coordinated expression of the E2F family is critical for the transcriptional regulation of fibrillin-2 during chondrogenesis.

Integrin αvβ3 regulates microfibril assembly in human periodontal ligament cells

Fibrillin-1 is the major structural component of extracellular microfibrils. However, the mechanism by which extracellular fibrillin-1 assembles into microfibrils is not fully understood. Fibrillin-1 contains the Arg-Gly-Asp (RGD) motif, which may allow binding to RGD-recognizing integrins. We hypothesized that integrin αvβ3 on the cell surface of human periodontal ligament (PDL) fibroblasts may influence fibrillin-1 assembly into cell/matrix layers. We treated PDL fibroblasts with an integrin αvβ3-specific antagonist to examine fibrillin-1 assembly. Western blotting and immunofluorescence analysis showed that treatment with the integrin αvβ3 antagonist at 5 μM clearly abolished fibrillin-1 deposition. These results provide for the first time evidence that integrin αvβ3 regulates extracellular assembly of fibrillin-1, thereby modulating cell-mediated homeostasis of microfibrils.

Biogenesis of extracellular microfibrils: Multimerization of the fibrillin-1 C terminus into bead-like structures enables self-assembly

Microfibrils are essential elements in elastic and nonelastic tissues contributing to homeostasis and growth factor regulation. Fibrillins form the core of these multicomponent assemblies. Various human genetic disorders, the fibrillinopathies, arise from mutations in fibrillins and are frequently associated with aberrant microfibril assembly. These disorders include Marfan syndrome, Weill-Marchesani syndrome, Beals syndrome, and others. Although homotypic and heterotypic fibrillin self-interactions are considered to provide critical initial steps, the detailed mechanisms for microfibril assembly are unknown. We show here that the C-terminal recombinant half of fibrillin-1 assembles into disulfide-bonded multimeric globular structures with peripheral arms and a dense core. These globules are similar to the beaded structures observed in microfibrils isolated from tissues. Only these C-terminal fibrillin-1 multimers interacted strongly with the fibrillin-1 N terminus, whereas the monomers showed very little self-interaction activity. The multimers strongly inhibited microfibril formation in cell culture, providing evidence that these recombinant assemblies can also interact with endogenous fibrillin-1. The C-terminal self-interaction site was fine-mapped to the last three calcium-binding EGF domains in fibrillin-1. These results suggest a new mechanism for microfibril formation where fibrillin-1 first oligomerizes via its C terminus before the partially or fully assembled bead-like structures can further interact with other beads via the fibrillin-1 N termini.

Clinical diagnosis and surgical treatment of congenital contractural arachnodactyly: analysis of 6 cases

To discuss the clinical diagnosis and surgical treatment of congenital contractural arachnodactyly (CCA). The clinical data of 6 CCA patients, 1 male and 5 female, aged 7.5 (5-14) were analyzed. All cases had kyphoscoliosis, 2 in the thoracic segments and 4 in the thoracolumbar segments. The average scoliosis Cobb angle was 88.6 degrees (85 degrees-117 degrees). The average kyphosis Cobb angle was 93.6 degrees (75 degrees-123 degrees). All of the cases underwent internal fixation with pedicle screw and lamina hooks instrumentation, in which 4 cases underwent posterior Smith-Petersen osteotomy. The diagnosis was based on a constellation of clinical findings. The clinical manifestations included marfanoid habitus, flexion contractures of multiple joints (elbow, knee, hip, and finger), kyphoscoliosis, muscular hypoplasia, and abnormal pinnae ("crumpled" outer helices). Molecular genetic testing showed mutation in the fibrillin-2 (FBN2) gene encoding the extracellular matrix microfibril. Four cases were followed up for 6-9 months. After operation the average Cobb angle of the scoliosis and kyphosis were 37.6 degrees (35 degrees-52 degrees) and 38.6 degrees (28 degrees-54 degrees) immediately, with 62.3% and 68.7% curve correction respectively. Three cases got excellent synostosis of posterior lamina, 1 case underwent revision with lamina hook because the distal screw was loose and hurt the nerve root, and the other 2 cases lost follow-up. The patients' body appearance and pulmonary function were obviously improved. The characteristic clinical manifestation include severe and stiff kyphoscoliosis, difficult to correct , and enhanced Cobb angle, and pedicle dysplasia of vertebral pedicle leading to difficulty in installing screws. Smith-Petersen osteotomy is often necessary. CCA should be differentiated with Marfan syndrome (MFS), Stickler syndrome, Homocystinuria, and distal arthrogryposis, especially MFS.

A short ultraconserved sequence drives transcription from an alternate FBN1 promoter

FBN1, the gene mutated in Marfan syndrome, encodes fibrillin-1, a large glycoprotein component of the extracellular microfibrils. Human FBN1 has three untranslated upstream exons, and homologous sequences can be identified in a number of mammalian species.In this work, we have used functional assays to characterize the FBN1 upstream region. Sequences upstream of exon 1 and at least two of the upstream untranslated exons were shown to possess promoter activity in vitro. The strongest activity in luciferase assays was shown for sequences upstream of the untranslated exon A. Sequence analysis of the sequences in and upstream of exon A in humans and six other mammalian species demonstrated several highly conserved potential cis-acting sequences as well as a 66-basepair (bp) ultraconserved sequence with nearly perfect conservation in the seven species. The ultraconserved sequence contains an initiator element (Inr), a downstream promoter element (DPE), and a 10-bp palindromic element.Mutational assays showed that both the Inr and the DPE are critical for full promoter activity. A mutation of the 10-bp palindromic element completely abolished basal promoter activity. The element was shown to bind specifically to an unknown nuclear protein by electrophoretic mobility shift assay.Ultraconservation within an alternate promoter has not been previously reported. We suggest that the ultraconservation may reflect the importance of finely tuned regulation of alternate transcription of FBN1 and that the sequences involved have been under negative selective pressure for at least the last 180 million years of mammalian evolution.

Extracellular microfibrils in development and disease.

Fibrillins are the structural components of extracellular microfibrils that impart physical properties to tissues, alone or together with elastin as elastic fibers. Genetic studies in mice have revealed that fibrillin-rich microfibrils are also involved in regulating developmental programs and homeostatic processes through the modulation of TGF-beta/BMP signaling events. A new paradigm has thus emerged whereby the spatiotemporal organization of microfibrils dictates both the cellular activities and physical properties of connective tissues. These observations have paved the way to novel therapeutic approaches aimed at counteracting the life-threatening complications in human conditions caused by dysfunctions of fibrillin-rich microfibrils.

New Finding of Protrusio Acetabuli in Two Families with Congenital Contractural Arachnodactyly

Congenital contractural arachnodactyly is an autosomal dominant disorder of connective tissue and is associated with skeletal features similar to those seen with Marfan syndrome1. Congenital contractural arachnodactyly and Marfan syndrome are linked to mutations in the highly homologous but distinct genes FBN2 (5q23-q31) and FBN1 (15q15-q21), which encode fibrillin 2 and fibrillin 1, respectively2. Fibrillins are major components of extracellular matrix microfibrils, which play an essential role in the formation of elastic fiber and the deposition of tropoelastin and which perform anchoring functions in some tissues3. As a consequence of the abnormal microfibrillogenesis that is seen in association with congenital contractural arachnodactyly and Marfan syndrome, complications may be found in the mesodermal tissues (i.e., the ocular tissue, the skeletal, cardiovascular, pulmonary, and muscular systems, and the skin and integumentum). The phenotypic similarity at times makes it clinically difficult to differentiate congenital contractural arachnodactyly from Marfan syndrome. This is illustrated by the observation that Antoine Marfan's original patient may actually have had congenital contractural arachnodactyly and not what is known today as Marfan syndrome4. Contractures are seen in both syndromes. However, the contractures in patients with congenital contractural arachnodactyly are congenital and tend to improve spontaneously, whereas the contractures in Marfan syndrome are developmental and may be progressive1. Ectopia lentis was reported to occur in 60% of 160 patients with Marfan syndrome5. In contrast, to our knowledge, there has been only one report of ectopia lentis in association with congenital contractural arachnodactyly, in a patient with bilateral ectopia lentis6. The presence of a congenital heart defect strongly suggests the diagnosis of Marfan syndrome, although mitral valve prolapse7, atrial septal defects, and ventricular septal defects are also occasionally found in patients with congenital contractural arachnodactyly8 …