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The ADAMTS superfamily is composed of secreted metalloproteases and structurally related non-catalytic ADAMTS-like proteins. A subset of this superfamily, including ADAMTS6, ADAMTS10 and ADAMTSL2, are involved in elastic fiber assembly and bind to fibrillin and other matrix molecules that regulate the extracellular bioavailability of the potent growth factor TGFβ. Fibrillinopathies, that can also result from mutation of these ADAMTS/L proteins, have been linked to disrupted TGFβ homeostasis. ADAMTS6 and ADAMTS10 are homologous metalloproteases with poorly characterized substrates where ADAMTS10 is thought to process fibrillin-2 and ADAMTS6 latent TGFβ-binding protein (LTBP)-1. In order to understand the contribution of ADAMTS6, and these other members of the ADAMTS/L family, to TGFβ homeostasis, we have analyzed the effects of ADAMTS6, ADAMTS10 and ADAMTSL2 expression on TGFβ activation. We found that their expression increases TGFβ activation in a dose dependent manner, following stimulation with mature TGFβ1. For ADAMTS6, the catalytically active protease is required for effective TGFβ activation, where ADAMTS6 cleaves LTBP3 as well as LTBP1, and binds to the large latent TGFβ complexes of LTBP1 and LTBP3. Furthermore, ADAMTS6 expression increases the mechanotension of cells which results in inactivation of the Hippo Pathway, resulting in an increased translocation of YAP/TAZ complex to the nucleus. Together these findings suggest that when the balance of TGFβ is perturbed ADAMTS6 can influence TGFβ activation via two mechanisms. It directly cleaves the latent TGFβ complexes and also acts indirectly, along with ADAMTS10 and ADAMTSL2, by altering the mechanotension of cells. Together this increases activation of TGFβ from large latent complexes which may contribute to disease pathogenesis.

Glaucoma is a neurodegenerative disease that causes irreversible blindness due to loss of retinal ganglion cells (RGCs) and their axons. We previously identified a G661R mutation of ADAMTS10 (A Disintegrin And Metalloproteinase with ThromboSpondin type 1 motif 10) as the disease-causing mutation in a beagle model of glaucoma. ADAMTS10 is a secreted matrix metalloproteinase that belongs to the ADAMTS family which is involved in extracellular matrix (ECM) turnover. Previous studies have shown that ADAMTS10 binds fibrillin microfibrils, promotes their formation, and influences their fibrillin isoform composition. Here, we established a mouse model carrying the G661R mutation of ADAMTS10 (ADAMTS10

This study aimed to develop objective diagnostic criteria for early onset Marfan syndrome (eoMFS) to facilitate early diagnosis and timely interventions.On the basis of an extensive literature review and the responses from a survey distributed among providers with expertise in the diagnosis and management of eoMFS, we developed an age-based, diagnostic scoring system encompassing 10 features common to eoMFS (9 clinical + 1 laboratory) and divided them into cardiac, systemic, and FBN1 (on the basis of the location of the pathogenic FBN1 variant) scores.In total, 77 individuals with eoMFS (13 newly reported) and 49 individuals diagnosed with classical Marfan syndrome during early childhood were used to validate the criteria. Median cardiac (8 vs 0, P.001), systemic (11 vs 3, P.001), FBN1 (5 vs 0, P.001), and total (23 vs 4, P.001) scores were significantly higher in individuals with eoMFS than in those without. A proposed clinical score (cardiac + systemic) cutoff of ≥14 points showed excellent sensitivity (100%), specificity (92%), and reliability (correctly classified = 94%).Distinct from classical Marfan syndrome in phenotype and morbidity, eoMFS can be diagnosed clinically using an objective scoring system encompassing the typical physical features and cardiac disease manifestations. Although genetic testing can be suggestive of eoMFS, genetic testing alone is insufficient for diagnosis.

A disproportionate tall stature is the most evident manifestation in Marfan syndrome (MFS), a multisystem condition caused by mutations in the extracellular protein and TGFβ modulator, fibrillin-1. Unlike cardiovascular manifestations, there has been little effort devoted to unravel the molecular mechanism responsible for long bone overgrowth in MFS. By combining the Cre-LoxP recombination system with metatarsal bone cultures, here we identify the outer layer of the perichondrium as the tissue responsible for long bone overgrowth in MFS mice. Analyses of differentially expressed genes in the fibrillin-1-deficient perichondrium predicted that loss of TGFβ signaling may influence chondrogenesis in the neighboring epiphyseal growth plate (GP). Immunohistochemistry revealed that fibrillin-1 deficiency in the outer perichondrium is associated with decreased accumulation of latent TGFβ-binding proteins (LTBPs)-3 and -4, and reduced levels of phosphorylated (activated) Smad2. Consistent with these findings, mutant metatarsal bones grown in vitro were longer and released less TGFβ than the wild-type counterparts. Moreover, addition of recombinant TGFβ1 normalized linear growth of mutant metatarsal bones. We conclude that longitudinal bone overgrowth in MFS is accounted for by diminished sequestration of LTBP-3 and LTBP-4 into the fibrillin-1-deficient matrix of the outer perichondrium, which results in less TGFβ signaling locally and improper GP differentiation distally.

Fibrillins (FBNs) are a family of genes in cyanobacteria, algae, and plants. The proteins they encode possess a lipid-binding motif, exist in various types of plastids, and are associated with lipid bodies called plastoglobules, implicating them in lipid metabolism. FBNs present in the thylakoid and stroma are involved in the storage, transport, and synthesis of lipid molecules for photoprotective functions against high-light stress. In this review, the diversity of subplastid locations in the evolution of FBNs, regulation of FBNs expression by various stresses, and the role of FBNs in plastid lipid metabolism are comprehensively summarized and directions for future research are discussed.

Background: Diverse extracellular matrix (ECM) proteins physically interact with stem cells and regulate stem cell function. However, the large molecular weight of the natural ECM renders large-scale fabrication of a similar functional structure challenging. Objective: The objective of this study was to construct a low molecular weight and multifunctional chimeric form of recombinant ECM to stimulate mesenchymal stem cell (MSC) for tissue repair. We engineered Fibrillin-1PF14 fused to an elastin-like polypeptide to develop a new biomimetic ECM for stem cell differentiation and investigated whether this recombinant chimeric Fibrillin-Elastin fragment (rcFE) was effective on human nasal inferior turbinate-derived mesenchymal stem cells (hTMSCs). Methods: hTMSCs were grown in the medium supplemented with rcFE, then the effect of the protein was confirmed through cell adhesion assay, proliferation assay, and real-time PCR. Results: rcFE enhanced the adhesion activity of hTMSCs by 2.7-fold at the optimal concentration, and the proliferation activity was 2.6-fold higher than that of the control group (non-treatment rcFE). In addition, when smooth muscle cell differentiation markers were identified by real-time PCR, Calponin increased about 6-fold, α-actin about 9-fold, and MYH11 about 10-fold compared to the control group. Conclusion: Chimeric rcFE enhanced cellular functions such as cell adhesion, proliferation, and smooth muscle differentiation of hTMSCs, suggesting that the rcFE can facilitate the induction of tissue regeneration.

Mutations of fibrillin-1 (FBN1) have been associated with Marfan syndrome and pleiotropic connective tissue disorders, collectively termed as "type I fibrillinopathy". However, few genotype-phenotype correlations are known in the ocular system. Patients with congenital ectopia lentis (EL) received panel-based next-generation sequencing, complemented with multiplex ligation-dependent probe amplification. In a total of 125 probands, the ocular phenotypes were compared for different types of FBN1 mutations. Premature termination codons were associated with less severe EL and a thinner central corneal thickness (CCT) than the inframe mutations. The eyes of patients with mutations in the C-terminal region had a higher incidence of posterior staphyloma than those in the middle and N-terminal regions. Mutations in the TGF-β-regulating sequence had larger horizontal corneal diameters (white-to-white [WTW]), higher incidence of posterior staphyloma, but less severe EL than those with mutations in other regions. Mutations in the neonatal region were associated with thinner CCT. Longer axial length (AL) was associated with mutations in the C-terminal region or TGF-β regulating sequence after adjusting for age, EL severity, and corneal curvature radius. FBN1 genotype-phenotype correlations were established for some ocular features, including EL severity, AL, WTW, CCT, and so forth, providing novel perspectives and directions for further mechanistic studies.

Background Marfan syndrome (MFS) is a rare autosomal dominant connective tissue disorder. Diagnosing MFS can be challenging as the disease's severity and clinical manifestations differ between pathogenic variants, and because a lack of published information currently exists on phenotype-genotype correlations. This report aims to underline the clinical manifestations associated with fibrillin-1 (FBN1) gene mutations by assessing MFS in 6 families from China. Methods We diagnosed 6 patients and their relatives with MFS by combining a clinical examination (based on the 2010 revised Ghent nosology criteria) with a targeted next-generation sequencing analysis. The functional analysis of the causal mutations and clinical details of the affected patients were then assessed. Results We identified 6 pathogenic mutations in FBN1, including 1 novel frameshift, 1 nonsense, and 4 missense mutations. Most uniquely, mitral valve prolapses (MVP) and ectopia lentis (EL) were found in the cysteine-related mutations. Typically, facial symptoms of MFS are observed in frameshift or nonsense mutants, not in cysteine-related ones. Furthermore, the patients with premature terminal codons had a more serious skin condition than patients with missense mutations, partly indicating the important effect FBN1 has on skin. Conclusions This study expands the mutation spectrum of MFS and highlights possible genotype-phenotype correlations, thereby improving the early diagnosis and symptomatic treatment of the disease.

Marfan syndrome is an autosomal dominant genetic disorder of the fibrous connective tissue caused by pathogenic mutations in the fibrillin-1 gene. Neonatal Marfan syndrome is a rare type of Marfan syndrome that is genotypically and phenotypically different from classical Marfan syndrome and has a poor prognosis. Most patients with neonatal Marfan syndrome die during infancy due to severe and rapidly progressive cardiovascular disorders. Here, we present a case of an 11-year-old girl with neonatal Marfan syndrome due to a novel missense mutation in exon 27 of the fibrillin-1 gene. Her condition was critical due to progressive mitral and tricuspid regurgitation. Mitral valve replacement, performed at the age of 6 months, improved her critical condition. Our case suggests that early mitral valve replacement may lead to better outcomes in patients with neonatal Marfan syndrome.

Marfan syndrome ([MS], OMIM 154700) is a connective tissue disorder that exhibits an autosomal dominant pattern of inheritance, whose clinical characteristics can affect multiple systems or organs in a variable way. It is caused by mutations in the FBN1 gene (OMIM 134797) located at 15q21.1. Neonatal MS is an uncommon variety of the entity associated with missense mutation between exons 23-33 and truncating mutations, exhibits a more severe phenotype and high percentage of mortality in the first years of life. The case of male adolescent with neonatal MS and missense mutation (c.3037GA; p.Gly225Arg) in exon 24 of the FBN1 gene is presented. Given these findings, interfamilial phenotype variation, the early interdisciplinary medical evaluation necessary for the management of possible complications, as well as the appropriate family genetic counseling were studied.El síndrome de Marfan ([SM], OMIM 154700) es un trastorno del tejido conectivo que exhibe un patrón de herencia autosómico dominante, cuyas características clínicas pueden afectar de forma variable múltiples sistemas u órganos. Es causado por mutaciones en el gen FBN1 (OMIM 134797) localizado en 15q21.1. El SM neonatal es una variedad infrecuente de la entidad asociado con mutaciones en el cambio de sentido entre los exones 23-33 y mutaciones truncadas, exhibe un fenotipo más severo y alto porcentaje de mortalidad en los primeros años de vida. Se presenta el caso de adolescente masculino con SM neonatal y mutaciones en el cambio de sentido (c.3037GA; p.Gly225Arg) en el exón 24 del gen FBN1. Ante estos hallazgos se estudió la variación fenotípica interfamiliar, la evaluación médica interdisciplinaria precoz necesaria para el manejo de las posibles complicaciones, así como el oportuno asesoramiento genético familiar.

Extracellular matrix (ECM) remodeling is crucial in the regulation of gastric cancer (GC) progression. This work aims to reveal novel posttranslational modifications and their relevant mechanisms in GC. In 3D matrix culture and animal models, it is found that fibrillin 1 (FBN1) expression is increased in advanced GC and has succinylation modification. The succinylation modification of FBN1 blocks its degradation by matrix metalloproteinases (MMPs). The long-term accumulation and deposition of FBN1 enhance tumor progression by activating TGF-β1 and intracellular PI3K/Akt pathway. The FBN1 succinylation site monoclonal antibody can effectively intervene the effect of succinylation modification and inhibit GC progression. FBN1 is specifically upregulated in the progression of GC compared with other tumors. In conclusion, FBN1 is widely present in the form of K672-succinylated modifications in GC. Besides, the succinyl group of FBN1 blocks its binding to MMP2, inhibits its degradation by MMP2, and leads to the accumulation of FBN1, which poses a long-term risk to the poor prognosis of GC.

Elastic fibers are essential components of the arterial extracellular matrix. They consist of the protein elastin and an array of microfibrils that support the protein and connect it to the surrounding matrix. The elastin gene encodes tropoelastin, a protein that requires extensive cross-linking to become elastin. Tropoelastin is expressed throughout human life, but its expression levels decrease with age, suggesting that the potential to synthesize elastin persists during lifetime although declines with aging. The initial abnormality documented in human atherosclerosis is fragmentation and loss of the elastic network in the medial layer of the arterial wall, suggesting an imbalance between elastic fiber injury and restoration. Damaged elastic structures are not adequately repaired by synthesis of new elastic elements. Progressive collagen accumulation follows medial elastic fiber disruption and fibrous plaques are formed, but advanced atherosclerosis lesions do not develop in the absence of prior elastic injury. Aging is associated with arterial extracellular matrix anomalies that evoke those present in early atherosclerosis. The reduction of elastic fibers with subsequent collagen accumulation leads to arterial stiffening and intima-media thickening, which are independent predictors of incident hypertension in prospective community-based studies. Arterial stiffening precedes the development of hypertension. The fundamental role of the vascular elastic network to arterial structure and function is emphasized by congenital disorders caused by mutations that disrupt normal elastic fiber production. Molecular changes in the genes coding tropoelastin, lysyl oxidase (tropoelastin cross-linking), and elastin-associated microfibrils, including fibrillin-1, fibulin-4, and fibulin-5 produce severe vascular injury due to absence of functional elastin.

The tooth is stabilized by fiber-rich tissue called the periodontal ligament (PDL). The narrow space of the PDL does not calcify in the physiological state even thought it exists between two calcified tissues, namely, the cementum of the root and alveolar bone. Two situations that require PDL regeneration are periodontitis and dental trauma. Periodontitis induces the loss of PDL and alveolar bone due to inflammation related to infection. Conversely, in PDLs damaged by dental trauma, accelerating bone formation as an overreaction of the healing process is induced, thereby inducing dentoalveolar ankylosis at the tooth root surface. PDL regeneration following dental trauma must therefore be considered separately from periodontitis. Therefore, PDL regeneration in dental trauma must be considered separately from periodontitis. This review focuses on the components involved in avoiding dentoalveolar ankylosis, including oxytalan fibers, aggregated microfibrils, epithelial cell rests of Malassez (ERM), and TGF-β signaling. During root development, oxytalan fibers produced by PDL cells work in collaboration with the epithelial components in the PDL (e.g., Hertwig's root sheath [HERS] and ERM). We herein describe the functions of oxytalan fibers, ERM, and TGF-β signals which are involved in the avoidance of bone formation.

Intercellular lipids comprise mainly ceramides, known to enhance the barrier function of the stratum corneum. However, the activities of ceramides inside the skin have not yet been fully elucidated. Here we examined how the human ceramide mixture (HC123) functions in the dermis. We treated human skin fibroblasts with HC123-expressed fibroblast growth factor (FGF), transforming growth factor-β (TGF-β), collagen I, and fibrillin. We found that HC123 promoted the formation of collagen fibers and microfibrils (fibrillin) which affect the elasticity of the skin. We also confirmed that the gene expression of collagen and fibrillin is promoted via TGF-β and FGF2, respectively. We then investigated the permeability of HC123 for external use, in pursuit of evidence that HC123 may exert an anti-aging effect by penetrating into the dermis, activating fibroblasts, and promoting the production of collagen fibers and elastin-related microfibrils.

Collagens, elastin, fibrillin, decorin, and laminin are key constituents of the extracellular matrix and basement membrane of mammalian organs. Thus, changes in their quantities may influence the mechanochemical regulation of resident cells. Since maintenance of a native stromal composition is a requirement for three-dimensional (3D) matrix-based recellularization techniques in tissue engineering, we studied the influence of the decellularization detergents on these proteins in porcine kidney, liver, pancreas, and skin. Using a quick thawing/quick microwave-assisted decellularization protocol and two different detergents, sodium dodecyl sulfate (SDS) vs Triton X-100 (TX100), at identical concentration, variations in matrix conservation of stromal proteins were detected by liquid chromatography-mass spectrometry coupled to light and scanning electron microscopies, in dependence on each detergent. In all organs tested except pancreas, collagens were retained to a statistically significant level using the TX100-based protocol. In contrast fibrillin, elastin (except in kidney), and decorin (only in liver) were better preserved with the SDS-dependent protocol. Irrespective of the detergent used, laminin always remained at an irrelevant level. Our results prompt attention to the type of detergent in organ decellularization, suggesting that its choice may influence morphoregulatory inputs peculiar to the type of 3D bioartificial mammalian organ to be reconstructed. Impact statement Simple change of the protocol's main detergent leads to a very substantial difference in the panel of the stromal proteins detected by qualitative and semiquantitative mass spectrometry in acellular porcine matrices. This remarkable methodological variable promises to yield proteomic reference panels in a number of different species-specific acellular matrices allowing for selective retainment of peculiar mechanochemical inputs, to differently address the development of the seeded cells in relation to the type of organ to be bioartificially reconstructed.

Cranial cruciate ligament disease (CCLD) is the most common cause of pelvic limb lameness in dogs but its precise aetiopathogenesis is uncertain. Fibrillin microfibrils (FM) are complex macro-molecular assemblies found in many tissues including ligaments, where they are thought to play an important mechanical role. We hypothesised that FM ultrastructural variation correlates with the differing predisposition of canine breeds to CCLD. Non-diseased cranial and caudal cruciate ligaments (CCLs and CaCLs) were obtained from Greyhound (GH) and Staffordshire Bull Terrier (SBT) cadavers. Fibrillin microfibrils were extracted from the ligaments by bacterial collagenase digestion, purified by size-exclusion chromatography and subsequently visualized by atomic force microscopy (AFM). With AFM, FMs have a characteristic beads-on-a-string appearance. For each FM, periodicity (bead-bead distance) and length (number of beads/FM) was measured. Fibrillin microfibril length was found to be similar for GH and SBT, with non-significant inter-breed and inter-ligament differences. Fibrillin microfibril periodicity varied when comparing GH and SBT for CCL (GH 60.2 ± 1.4 nm; SBT 56.2 ± 0.8 nm) and CaCL (GH 55.5 ± 1.6 nm; SBT 61.2 ± 1.2 nm). A significant difference was found in the periodicity distribution when comparing CCL for both breeds (P 0.00001), further, intra-breed differences in CCL vs CaCL were statistically significant within both breeds (P 0.00001). The breed at low risk of CCLD exhibited a periodicity profile which may be suggestive of a repair and remodelling within the CCL.

TGFβ superfamily members are potent growth factors in the extracellular matrix with essential roles in all aspects of cellular behaviour. Latent TGFβ binding proteins (LTBPs) are co-expressed with TGFβ, essential for correct folding and secretion of the growth factor, to form large latent complexes. These large latent complexes bind extracellular proteins such as fibrillin for sequestration of TGFβ in the matrix, essential for normal tissue function, and dysregulated TGFβ signalling is a hallmark of many fibrillinopathies. Transglutaminase-2 (TG2) cross-linking of LTBPs is known to play a role in TGFβ activation but the underlying molecular mechanisms are not resolved. Here we show that fibrillin is a matrix substrate for TG2 and that TG2 cross-linked complexes can be formed between fibrillin and LTBP-1 and -3, and their latent TGFβ complexes. The structure of the fibrillin-LTBP1 complex shows that the two elongated proteins interact in a perpendicular arrangement which would allow them to form distal interactions between the matrix and the cell surface. Formation of the cross-link with fibrillin does not change the interaction between latent TGFβ and integrin αVβ6 but does increase TGFβ activation in cell-based assays. The activating effect may be due to direction of the latent complexes to the cell surface by fibrillin, as competition with heparan sulphate can ameliorate the activating effect. Together, these data support that TGFβ activation can be enhanced by covalent tethering of LTBPs to the matrix via fibrillin.

AIM: To identify pathogenic rare coding Mendelian/high-effect size variant(s) by whole-exome sequencing in familial PCOS patients to elucidate PCOS related pathways. METHODS: Twenty women and their affected available relatives diagnosed with polycystic ovary syndrome according to Rotterdam Criteria were recruited. Whole-exome sequencing on germ-line DNA from 31 polycystic ovary syndrome probands and their affected relatives were performed. Whole-exome sequencing data was further evaluated by pathway and chemogenomics analyses. In-slico analysis of candidate variants were done by VarCards for functional predictions and VarSite for impact on 3D structures in the candidate proteins. RESULTS: Two heterozygous rare FBN3 missense variants in three patients, and one FN1 missense variant in one patient from three different PCOS families were identified. CONCLUSIONS: We identified three novel FBN3 and FN1 variants for the first time in the literature and linked with polycystic ovary syndrome. Further functional studies may identify causality of these newly discovered PCOS related variants, and their role yet remain to be investigated. Our findings may improve our understanding of the biologic pathways affected and identify new drug targets

Elastin represents the structural component of the extracellular matrix providing elastic recoil to tissues such as skin, blood vessels and lungs. Elastogenic cells secrete soluble tropoelastin monomers into the extracellular space where these monomers associate with other matrix proteins (e.g., microfibrils and glycoproteins) and are crosslinked by lysyl oxidase to form insoluble fibres. Once elastic fibres are formed, they are very stable, highly resistant to degradation and have an almost negligible turnover. However, there are circumstances, mainly related to inflammatory conditions, where increased proteolytic degradation of elastic fibres may lead to consequences of major clinical relevance. In severely affected COVID-19 patients, for instance, the massive recruitment and activation of neutrophils is responsible for the profuse release of elastases and other proteolytic enzymes which cause the irreversible degradation of elastic fibres. Within the lungs, destruction of the elastic network may lead to the permanent impairment of pulmonary function, thus suggesting that elastases can be a promising target to preserve the elastic component in COVID-19 patients. Moreover, intrinsic and extrinsic factors additionally contributing to damaging the elastic component and to increasing the spread and severity of SARS-CoV-2 infection are reviewed.

PURPOSE In a large cohort of 373 pediatric patients with Marfan syndrome (MFS) with a severe cardiovascular phenotype, we explored the proportion of patients with MFS with a pathogenic FBN1 variant and analyzed whether the type/location of FBN1 variants was associated with specific clinical characteristics and response to treatment. Patients were recruited on the basis of the following criteria: aortic root z-score > 3, age 6 months to 25 years, no prior or planned surgery, and aortic root diameter < 5 cm. METHODS Targeted resequencing and deletion/duplication testing of FBN1 and related genes were performed. RESULTS We identified (likely) pathogenic FBN1 variants in 91% of patients. Ectopia lentis was more frequent in patients with dominant-negative (DN) variants (61%) than in those with haploinsufficient variants (27%). For DN FBN1 variants, the prevalence of ectopia lentis was highest in the N-terminal region (84%) and lowest in the C-terminal region (17%). The association with a more severe cardiovascular phenotype was not restricted to DN variants in the neonatal FBN1 region (exon 25-33) but was also seen in the variants in exons 26 to 49. No difference in the therapeutic response was detected between genotypes. CONCLUSION Important novel genotype-phenotype associations involving both cardiovascular and extra-cardiovascular manifestations were identified, and existing ones were confirmed. These findings have implications for prognostic counseling of families with MFS.

Item does not contain fulltext Marfan Syndrome is an autosomal dominant connective tissue disorder caused by mutations in the FBN1 gene. Early Onset Marfan Syndrome is at the severe end of the Marfan syndrome spectrum and is frequently associated with variants in exons 24-32 of the FBN1 gene. To the best of our knowledge, this is the first molecularly confirmed patient from Sub-Saharan Africa with Early Onset Marfan Syndrome who presented with tall stature, arachnodactyly, multivalvular insufficiency and ectopia lentis. Sequencing analysis of FBN1 gene revealed a pathogenic (class 5) heterozygous recurrent variant in exon 61 (c.7606G > A p.0NM_000138.3), which was up to now not associated with rapidly progressive Marfan syndrome with multivalvular insufficiency and congestive cardiac failure. This further supports the notion that the interplay of the given FBN1 mutation, one or more genetic modifiers and epigenetic and environmental factors defines the disease phenotype. 01 november 2022

Acromelic dysplasias are a group of rare musculoskeletal disorders that collectively present with short stature, pseudomuscular build, stiff joints, and tight skin. Acromelic dysplasias are caused by mutations in genes (FBN1, ADAMTSL2, ADAMTS10, ADAMTS17, LTBP2, and LTBP3) that encode secreted extracellular matrix proteins, and in SMAD4, an intracellular coregulator of transforming growth factor-β (TGF-β) signaling. The shared musculoskeletal presentations in acromelic dysplasias suggest that these proteins cooperate in a biological pathway, but also fulfill distinct roles in specific tissues that are affected in individual disorders of the acromelic dysplasia group. In addition, most of the affected proteins directly interact with fibrillin microfibrils in the extracellular matrix and have been linked to the regulation of TGF-β signaling. Together with recently developed knockout mouse models targeting the affected genes, novel insights into molecular mechanisms of how these proteins regulate musculoskeletal development and homeostasis have emerged. Here, we summarize the current knowledge highlighting pathogenic mechanisms of the different disorders that compose acromelic dysplasias and provide an overview of the emerging biological roles of the individual proteins that are compromised. Finally, we develop a conceptual model of how these proteins may interact and form an "acromelic dysplasia complex" on fibrillin microfibrils in connective tissues of the musculoskeletal system.

Fibrillins (FBNs) form mesh‐like structures of microfibrils in various elastic tissues. RECK and FBN1 are co‐expressed in many human tissues, suggesting a functional relationship. We found that dermal FBN1 fibers show atypical morphology in mice with reduced RECK expression (RECK‐Hypo mice). Dermal FBN1 fibers in mice‐lacking membrane‐type 1‐matrix metalloproteinase (MT1‐MMP) show a similar atypical morphology, despite the current notion that MT1‐MMP (a membrane‐bound protease) and RECK (a membrane‐bound protease inhibitor) have opposing functions. Our experiments using dermal fibroblasts indicated that RECK promotes pro‐MT1‐MMP activation, increases cell‐associated gelatinase/collagenase activity, and decreases diffusible gelatinase/collagenase activity, while MT1‐MMP stabilizes RECK in these cells. Experiments using purified proteins indicate that RECK and its binding partner ADAMTS10 keep the proteolytic activity of MT1‐MMP within a certain range. These findings suggest that RECK, ADAMTS10, and MT1‐MMP cooperate to support the formation of robust FBN1 fibers., Fibrillin‐1 fibers in the skin of mice with reduced RECK or membrane‐type 1‐matrix metalloproteinase (MT1‐MMP) deficiency show atypical morphology. Our experiments in vitro indicated that RECK, ADAMTS10, and MT1‐MMP cooperate to support the formation of robust fibrillin‐1 fibers.

Marfan Syndrome (MFS) is an autosomal dominant connective tissue disorder with a wide range of severities. Ninety-five percent of MFS probands have a mutation in the fibrillin-1 gene (FBN1); however, there are a high number of unique mutations complicating attempts at establishing any phenotype-genotype correlations for this disease (Tiecke et al., European Journal of Human Genetics, 2001, 9, 13-21). One of the few extant genotype-phenotype correlations is in exon 24-32 which have been associated with a severe pediatric presentation of neonatal MFS with predominately cardiovascular symptoms. We present a 24-year-old male patient with a heterozygous de novo variant NM_000138.4: c.3037G>A (p.G1013R) located in exon 25 of the FBN1 gene. The patient was found to have dysplastic mitral and tricuspid valves with dilated aortic root at 9 months of age. This is a notable case in that the location of this patient's mutation and his age of symptom onset would indicate a guarded prognosis. Further, this mutation, FBN1 G1013R, has been reported in the literature in four other unrelated patients all of whom presented at a young age with cardiac involvement and all of whom had relative longevity when compared to other patients with mutations in this exon 24-32 hot spot. These findings may represent a more specific genotype-phenotype correlation within this mutational hot spot.

Arabidopsis thaliana contains 13 fibrillins (FBNs), which are all localized to chloroplasts. FBN1 and FBN2 are involved in photoprotection of photosystem II, and FBN4 and FBN5 are thought to be involved in plastoquinone transport and biosynthesis, respectively. The functions of the other FBNs remain largely unknown. To gain insight into the function of FBN6, we performed coexpression and Western analyses, conducted fluorescence and transmission electron microscopy, stained reactive oxygen species (ROS), measured photosynthetic parameters and glutathione levels, and applied transcriptomics and metabolomics. Using coexpression analyses, FBN6 was identified as a photosynthesis‐associated gene. FBN6 is localized to thylakoid and envelope membranes, and its knockout results in stunted plants. The delayed‐growth phenotype cannot be attributed to altered basic photosynthesis parameters or a reduced CO2 assimilation rate. Under moderate light stress, primary leaves of fbn6 plants begin to bleach and contain enlarged plastoglobules. RNA sequencing and metabolomics analyses point to an alteration in sulfate reduction in fbn6. Indeed, glutathione content is higher in fbn6, which in turn confers cadmium tolerance of fbn6 seedlings. We conclude that loss of FBN6 leads to perturbation of ROS homeostasis. FBN6 enables plants to cope with moderate light stress and affects cadmium tolerance.

LTBP1 is a large extracellular matrix protein and an associated ligand of fibrillin-microfibrils. Knowledge of LTBP1 functions is largely limited to its role in targeting and sequestering TGFβ growth factors within the extracellular matrix, thereby regulating their bioavailability. However, the recent description of a wide spectrum of phenotypes in multiple tissues in patients harboring LTBP1 pathogenic variants suggests a multifaceted role of the protein in the homeostasis of connective tissues. To better understand the human pathology caused by LTBP1 deficiency it is important to investigate its functional role in extracellular matrix formation. In this study, we show that LTBP1 coordinates the incorporation of fibrillin-1 and -2 into the extracellular matrix in vitro. We also demonstrate that this function is differentially exerted by the two isoforms, the short and long forms of LTBP1. Thereby our findings uncover a novel TGFβ-independent LTBP1 function potentially contributing to the development of connective tissue disorders.

Collagens are the most abundant components of the extracellular matrix (ECM) and many types of soft tissues. Elastin is another major component of certain soft tissues, such as arterial walls and ligaments. It is an insoluble polymer of the monomeric soluble precursor tropoelastin, and the main component of elastic fibers in matrix tissue where it provides elastic recoil and resilience to a variety of connective tissues, e.g., aorta and ligaments. Elastic fibers regulate activity of transforming growth factors β (TGFβ) through their association with fibrillin microfibrils. Elastin also plays a role in cell adhesion, cell migration, and has the ability to participate in cell signaling. Mutations in the elastin gene lead to cutis laxa. Many other molecules, though lower in quantity, function as essential, structural and/or functional components of the extracellular matrix in soft tissues. Some of these are reviewed in this chapter. Besides their basic structure, biochemistry and physiology, their roles in disorders of soft tissues are discussed only briefly as most chapters in this volume deal with relevant individual compounds. Fibronectin with its multidomain structure plays a role of "master organizer" in matrix assembly as it forms a bridge between cell surface receptors, e.g., integrins, and compounds such collagen, proteoglycans and other focal adhesion molecules. It also plays an essential role in the assembly of fibrillin-1 into a structured network. Though the primary role of fibrinogen is in clot formation, after conversion to fibrin by thrombin it also binds to a variety of compounds, particularly to various growth factors, and as such, fibrinogen is a player in cardiovascular and extracellular matrix physiology. Laminins contribute to the structure of the ECM and modulate cellular functions such as adhesion, differentiation, migration, stability of phenotype, and resistance towards apoptosis. Fibrillins represent the predominant core of microfibrils in elastic as well as non-elastic extracellular matrixes, and interact closely with tropoelastin and integrins. Not only do microfibrils provide structural integrity of specific organ systems, but they also provide basis for elastogenesis in elastic tissues. Fibrillin is important for the assembly of elastin into elastic fibers. Mutations in the fibrillin-1 gene are closely associated with Marfan syndrome. Latent TGFβ binding proteins (LTBPs) are included here as their structure is similar to fibrillins. Several categories of ECM components described after fibrillins are sub-classified as matricellular proteins, i.e., they are secreted into ECM, but do not provide structure. Rather they interact with cell membrane receptors, collagens, proteases, hormones and growth factors, communicating and directing cell-ECM traffic. Fibulins are tightly connected with basement membranes, elastic fibers and other components of extracellular matrix and participate in formation of elastic fibers. Matrilins have been emerging as a new group of supporting actors, and their role in connective tissue physiology and pathophysiology has not been fully characterized. Tenascins are ECM polymorphic glycoproteins found in many connective tissues in the body. Their expression is regulated by mechanical stress both during development and in adulthood. Tenascins mediate both inflammatory and fibrotic processes to enable effective tissue repair and play roles in pathogenesis of Ehlers-Danlos, heart disease, and regeneration and recovery of musculo-tendinous tissue. One of the roles of thrombospondin 1 is activation of TGFβ. Increased expression of thrombospondin and TGFβ activity was observed in fibrotic skin disorders such as keloids and scleroderma. Cartilage oligomeric matrix protein (COMP) or thrombospondin-5 is primarily present in the cartilage. High levels of COMP are present in fibrotic scars and systemic sclerosis of the skin, and in tendon, especially with physical activity, loading and post-injury. It plays a role in vascular wall remodeling and has been found in atherosclerotic plaques as well.

Fibrillin-1 is an extracellular glycoprotein present throughout the body. Mutations in fibrillin-1 cause a wide spectrum of type I fibrillinopathies, including Marfan syndrome characterized by clinical manifestations in adipose tissues, among others. This study addresses the hypothesis that fibrillin-1 regulates adipocyte development and plays a vital role in adipose tissue homeostasis. We employed two mouse models - Fbn1

Marfan syndrome (MFS) is an autosomal dominant, age-related but highly penetrant condition with substantial intrafamilial and interfamilial variability. MFS is caused by pathogenetic variants in FBN1, which encodes fibrillin-1, a major structural component of the extracellular matrix that provides support to connective tissues, particularly in arteries, the pericondrium and structures in the eye. Up to 25% of individuals with MFS have de novo variants. The most prominent manifestations of MFS are asymptomatic aortic root aneurysms, aortic dissections, dislocation of the ocular lens (ectopia lentis) and skeletal abnormalities that are characterized by overgrowth of the long bones. MFS is diagnosed based on the Ghent II nosology; genetic testing confirming the presence of a FBN1 pathogenetic variant is not always required for diagnosis but can help distinguish MFS from other heritable thoracic aortic disease syndromes that can present with skeletal features similar to those in MFS. Untreated aortic root aneurysms can progress to life-threatening acute aortic dissections. Management of MFS requires medical therapy to slow the rate of growth of aneurysms and decrease the risk of dissection. Routine surveillance with imaging techniques such as transthoracic echocardiography, CT or MRI is necessary to monitor aneurysm growth and determine when to perform prophylactic repair surgery to prevent an acute aortic dissection.