ADAMTSL2 mutations in geleophysic dysplasia demonstrate a role for ADAMTS-like proteins in TGF-beta bioavailability regulation

Multi-omics Data Integration for Identifying Osteoporosis Biomarkers and Their Biological Interaction and Causal Mechanisms

Osteoporosis is characterized by low bone mineral density (BMD). The advancement of high-throughput technologies and integrative approaches provided an opportunity for deciphering the mechanisms underlying osteoporosis. Here, we generated genomic, transcriptomic, methylomic, and metabolomic datasets from 119 subjects with high (n = 61) and low (n = 58) BMDs. By adopting sparse multiple discriminative canonical correlation analysis, we identified an optimal multi-omics biomarker panel with 74 differentially expressed genes (DEGs), 75 differentially methylated CpG sites (DMCs), and 23 differential metabolic products (DMPs). By linking genetic data, we identified 199 targeted BMD-associated expression/methylation/metabolite quantitative trait loci (eQTLs/meQTLs/metaQTLs). The reconstructed networks/pathways showed extensive biomarker interactions, and a substantial proportion of these biomarkers were enriched in RANK/RANKL, MAPK/TGF-β, and WNT/β-catenin pathways and G-protein-coupled receptor, GTP-binding/GTPase, telomere/mitochondrial activities that are essential for bone metabolism. Five biomarkers (FADS2, ADRA2A, FMN1, RABL2A, SPRY1) revealed causal effects on BMD variation. Our study provided an innovative framework and insights into the pathogenesis of osteoporosis.

The "other" 15-40%: The Role of Non-Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

Extracellular matrix (ECM) determines the physiological function of all tissues, including musculoskeletal tissues. In tendon, ECM provides overall tissue architecture, which is tailored to match the biomechanical requirements of their physiological function, that is, force transmission from muscle to bone. Tendon ECM also constitutes the microenvironment that allows tendon-resident cells to maintain their phenotype and that transmits biomechanical forces from the macro-level to the micro-level. The structure and function of adult tendons is largely determined by the hierarchical organization of collagen type I fibrils. However, non-collagenous ECM proteins such as small leucine-rich proteoglycans (SLRPs), ADAMTS proteases, and cross-linking enzymes play critical roles in collagen fibrillogenesis and guide the hierarchical bundling of collagen fibrils into tendon fascicles. Other non-collagenous ECM proteins such as the less abundant collagens, fibrillins, or elastin, contribute to tendon formation or determine some of their biomechanical properties. The interfascicular matrix or endotenon and the outer layer of tendons, the epi- and paratenon, includes collagens and non-collagenous ECM proteins, but their function is less well understood. The ECM proteins in the epi- and paratenon may provide the appropriate microenvironment to maintain the identity of distinct tendon cell populations that are thought to play a role during repair processes after injury. The aim of this review is to provide an overview of the role of non-collagenous ECM proteins and less abundant collagens in tendon development and homeostasis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:23-35, 2020.

Cell-Based Interaction Analysis of ADAMTS Proteases and ADAMTS-Like Proteins with Fibrillin Microfibrils

The extracellular matrix (ECM) is a composite biomaterial that serves as an anchor for cells and provides guidance cues for cell migration, proliferation, and differentiation. However, many details of the hierarchical ECM assembly process and the role of individual protein-protein interactions are not well understood. Here, I describe a cell-culture-based method that allows for determination of the ECM localization of recombinant ADAMTS proteases and ADAMTS-like (L) proteins in relationship to fibrillin microfibrils deposited by human dermal fibroblasts. The method can be readily adapted to study the localization of ECM components other than ADAMTS and ADAMTSL proteins to fibrillin microfibrils and other ECM networks.

ADAMTS Proteins: Concepts, Challenges, and Prospects

The ADAMTS superfamily comprises secreted metalloproteases (ADAMTS proteases) as well as structurally related secreted glycoproteins that lack catalytic activity (ADAMTS-like proteins). Members of both families participate in diverse morphogenetic processes during embryonic development, and connective tissue maintenance and hemostasis in the adult. Several ADAMTS proteins are heavily implicated in genetic and acquired human and animal disorders. Despite these indicators of a profound biological and medical importance, detailed knowledge about their molecular structures, substrates, biological pathways, and biochemical mechanisms is significantly limited by unique intrinsic characteristics, which have led to several technical challenges. As a group, they are larger, more heavily modified, and harder to purify than other secreted proteases. In addition, idiosyncratic aspects of individual members are deserving of further investigation but can complicate their analysis. Here, some of the key concepts, challenges, and prospects in ADAMTS research are discussed in the context of the knowledge accumulated over the past two decades. Individual chapters in this volume of Methods in Molecular Biology provide practical solutions for surmounting these challenges. Since the biology of a protease is actually the biology of its substrates, there is considerable emphasis on purification of recombinant ADAMTS proteins, identification of their substrates and assays for their proteolytic activity.

Adamts17 is involved in skeletogenesis through modulation of BMP-Smad1/5/8 pathway

Fibrillin microfibrils are ubiquitous elements of extracellular matrix assemblies that play crucial roles in regulating the bioavailability of growth factors of the transforming growth factor beta superfamily. Recently, several "a disintegrin and metalloproteinase with thrombospondin motifs" (ADAMTS) proteins were shown to regulate fibrillin microfibril function. Among them, ADAMTS17 is the causative gene of Weill-Marchesani syndrome (WMS) and Weill-Marchesani-like syndrome, of which common symptoms are ectopia lentis and short stature. ADAMTS17 has also been linked to height variation in humans; however, the molecular mechanisms whereby ADAMTS17 regulates skeletal growth remain unknown. Here, we generated Adamts17-/- mice to examine the role of Adamts17 in skeletogenesis. Adamts17-/- mice recapitulated WMS, showing shorter long bones, brachydactyly, and thick skin. The hypertrophic zone of the growth plate in Adamts17-/- mice was shortened, with enhanced fibrillin-2 deposition, suggesting increased incorporation of fibrillin-2 into microfibrils. Comprehensive gene expression analysis of growth plates using laser microdissection and RNA sequencing indicated alteration of the bone morphogenetic protein (BMP) signaling pathway after Adamts17 knockout. Consistent with this, phospho-Smad1 levels were downregulated in the hypertrophic zone of the growth plate and in Adamts17-/- primary chondrocytes. Delayed terminal differentiation of Adamts17-/- chondrocytes, observed both in primary chondrocyte and primordial metatarsal cultures, and was prevented by BMP treatment. Our data indicated that Adamts17 is involved in skeletal formation by modulating BMP-Smad1/5/8 pathway, possibly through inhibiting the incorporation of fibrillin-2 into microfibrils. Our findings will contribute to further understanding of disease mechanisms and will facilitate the development of therapeutic interventions for WMS.

Geleophysic dysplasia: novel missense variants and insights into ADAMTSL2 intracellular trafficking

Geleophysic dysplasia (GPHYSD1, MIM231050; GPHYSD2, MIM614185; GPHYSD3, MIM617809) is an autosomal disorder characterized by short-limb dwarfism, brachydactyly, cardiac valvular disease, and laryngotracheal stenosis. Mutations in ADAMTSL2, FBN1, and LTBP3 genes are responsible for this condition. We found that three previously described cases of GPHYSD diagnosed clinically were homozygote or compound heterozygotes for five ADAMTSL2 variants, four of which not being previously reported. By electron microscopy, skin fibroblasts available in one case homozygote for an ADAMTSL2 variant showed a defective intracellular localization of mutant ADAMTSL2 protein that did not accumulate within lysosome-like intra-cytoplasmic inclusions. Moreover, this mutant ADAMTSL2 protein was less secreted in medium and resulted in increased SMAD2 phosphorylation in transfected HEK293 cells.

Analyzing the Effects of O-Fucosylation on Secretion of ADAMTS Proteins Using Cell-Based Assays

Metalloproteinases of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin type 1 repeats) superfamily are extensively modified with glycan moieties. Glycosylation occurs as these enzymes are trafficked through the endoplasmic reticulum (ER) and Golgi apparatus on their way to the extracellular space and includes N-linked glycosylation, O-linked fucosylation and C-linked mannosylation. This chapter focuses on O-linked fucose, which is added to properly folded thrombospondin type 1 repeats (TSRs) in the ER by protein O-fucosyltransferase 2 (POFUT2) and elongated to a Glucoseβ1-3Fucose disaccharide by β3-glucosyltransferase (B3GLCT). Knockout of POFUT2 results in embryonic lethality in mice, and inactivating mutations in B3GLCT cause Peters plus syndrome, a congenital disorder of glycosylation in humans. Addition of the disaccharide by POFUT2 and B3GLCT stabilizes folded TSRs, enhancing folding in the ER and secretion efficiency of several ADAMTS proteins from cells. Thus, POFUT2 and B3GLCT both function as an ER quality control pathway for folding of TSRs in ADAMTS proteins. In this chapter we describe in detail the methods developed to analyze secretion defects of ADAMTS proteins upon loss of either POFUT2 or B3GLCT. The methods described include creation of CRISPR/Cas9-mediated knockout cell lines of POFUT2 and B3GLCT and use of these cell lines to analyze and quantify secretion defects of ADAMTS proteins.

Skin fibroblasts of patients with geleophysic dysplasia due to FBN1 mutations have lysosomal inclusions and losartan improves their microfibril deposition defect

Background

Geleophysic dysplasia (GPHYSD) is a disorder characterized by dysmorphic features, stiff joints and cardiac involvement due to defects of TGF‐β signaling. GPHYSD can be caused by mutations in FBN1, ADAMTLS2, and LTBP3 genes.

Methods and Results

Consistent with previous reports, we found intracellular inclusions of unknown material by electron microscopy (EM) in skin fibroblasts of two GPHYSD individuals carrying FBN1 mutations. Moreover, we found that the storage material is enclosed within lysosomes and is associated with the upregulation of several lysosomal genes. Treatment of GPHYSD fibroblasts carrying FBN1 mutations with the angiotensin II receptor type 1 inhibitor losartan that inhibits TGF‐β signaling did not reduce the storage but improved the extracellular deposition of fibrillin‐1 microfibrils.

Conclusion

Losartan is a promising candidate drug for treatment of GPHYSD due to FBN1 defects.

Fibrillin microfibrils and proteases, key integrators of fibrotic pathways

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

Disruption of the Extracellular Matrix Progressively Impairs Central Nervous System Vascular Maturation Downstream of β-Catenin Signaling

Supplemental Digital Content is available in the text.

Objective—

The Wnt/β-catenin pathway orchestrates development of the blood-brain barrier, but the downstream mechanisms involved at different developmental windows and in different central nervous system (CNS) tissues have remained elusive.

Approach and Results—

Here, we create a new mouse model allowing spatiotemporal investigations of Wnt/β-catenin signaling by induced overexpression of Axin1, an inhibitor of β-catenin signaling, specifically in endothelial cells (Axin1^iEC−^OE). AOE (Axin1 overexpression) in Axin1^iEC−^OE mice at stages following the initial vascular invasion of the CNS did not impair angiogenesis but led to premature vascular regression followed by progressive dilation and inhibition of vascular maturation resulting in forebrain-specific hemorrhage 4 days post-AOE. Analysis of the temporal Wnt/β-catenin driven CNS vascular development in zebrafish also suggested that Axin1^iEC−^OE led to CNS vascular regression and impaired maturation but not inhibition of ongoing angiogenesis within the CNS. Transcriptomic profiling of isolated, β-catenin signaling-deficient endothelial cells during early blood-brain barrier–development (E11.5) revealed ECM (extracellular matrix) proteins as one of the most severely deregulated clusters. Among the 20 genes constituting the forebrain endothelial cell-specific response signature, 8 (Adamtsl2, Apod, Ctsw, Htra3, Pglyrp1, Spock2, Ttyh2, and Wfdc1) encoded bona fide ECM proteins. This specific β-catenin-responsive ECM signature was also repressed in Axin1^iEC−^OE and endothelial cell-specific β-catenin–knockout mice (Ctnnb1-KO^iEC) during initial blood-brain barrier maturation (E14.5), consistent with an important role of Wnt/β-catenin signaling in orchestrating the development of the forebrain vascular ECM.

Conclusions—

These results suggest a novel mechanism of establishing a CNS endothelium-specific ECM signature downstream of Wnt-β-catenin that impact spatiotemporally on blood-brain barrier differentiation during forebrain vessel development.

Accommodative esotropia and Brown syndrome in a girl with recessive geleophysic dysplasia

Geleophysic dysplasia and Weill-Marchesani syndrome are acromelic dysplasias characterized by short stature, brachydactyly, and joint contractures. Recessive Weill-Marchesani syndrome typically includes spherophakia, but the ocular phenotype of recessive geleophysic dysplasia is not well defined. We describe the ocular phenotype of a girl with genetically confirmed recessive geleophysic dysplasia (biallelic ADAMTSL2 mutations). Features included high corneal astigmatism, accommodative esotropia, unilateral Brown syndrome, and no evidence for zonular disease at 12 years of age.

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

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

Protein O-fucosylation: structure and function

Fucose is a common terminal modification on protein and lipid glycans. Fucose can also be directly linked to protein via an O-linkage to Serine or Threonine residues located within consensus sequences contained in Epidermal Growth Factor-like (EGF) repeats and Thrombospondin Type 1 Repeats (TSRs). In this context, fucose is added exclusively to properly folded EGF repeats and TSRs by Protein O-fucosyltransferases 1 and 2, respectively. In both cases, the O-linked fucose can also be elongated with other sugars. Here, we describe the biological importance of these O-fucose glycans and molecular mechanisms by which they affect the function of the proteins they modify. O-Fucosylation of EGF repeats modulates the Notch signaling pathway, while O-fucosylation of TSRs is predicted to influence secretion of targets including several extracellular proteases. Recent data show O-fucose glycans mediate their effects by participating in both intermolecular and intramolecular interactions.

Impairment of chondrogenesis and microfibrillar network in Adamtsl2 deficiency

Mutations in the a disintegrin and metalloproteinase with thrombospondin motif-like 2 ( ADAMTSL2) gene are responsible for the autosomal recessive form of geleophysic dysplasia, which is characterized by short stature, short extremities, and skeletal abnormalities. However, the exact function of ADAMTSL2 is unknown. To elucidate the role of this protein in skeletal development, we generated complementary knockout (KO) mouse models with either total or chondrocyte Adamtsl2 deficiency. We observed that the Adamtsl2 KO mice displayed skeletal abnormalities reminiscent of the human phenotype. Adamtsl2 deletion affected the growth plate formation with abnormal differentiation and proliferation of chondrocytes. In addition, a TGF-β signaling impairment in limbs lacking Adamtsl2 was demonstrated. Further investigations revealed that Adamtsl2 KO chondrocytes failed to establish a microfibrillar network composed by fibrillin1 and latent TGF-β binding protein 1 fibrils. Chondrocyte Adamtsl2 KO mice also exhibited dwarfism. These studies uncover the function of Adamtsl2 in the maintenance of the growth plate ECM by modulating the microfibrillar network.-Delhon, L., Mahaut, C., Goudin, N., Gaudas, E., Piquand, K., Le Goff, W., Cormier-Daire, V., Le Goff, C. Impairment of chondrogenesis and microfibrillar network in Adamtsl2 deficiency.

Fibrillin protein pleiotropy: Acromelic dysplasias

The fibrillins are large extracellular matrix molecules that polymerize to form microfibrils. Fibrillin microfibrils are distinctive architectural elements that are both ubiquitous in the connective tissue space and also unique, displaying tissue-specific patterns. Mutations in the genes for fibrillin-1 (FBN1) result in multiple distinct pleiotropic disorders. Most of the more than 3000 mutations known today in FBN1 cause the Marfan syndrome. Marfan mutations can occur in any of the 56 domains that compose fibrillin-1. In contrast, rare mutations in FBN1 that are confined to only certain domains cause several different types of acromelic dysplasia. These genetic disorders demonstrate that specific domains of fibrillin-1 perform roles important to musculoskeletal growth. Many of the phenotypes of acromelic dysplasias are the opposite of those found in Marfan syndrome. Knowledge of the functions and structural organization of fibrillin molecules within microfibrils is required to understand how one protein and one gene can be the basis for multiple genetic disorders.

Geleophysic dysplasia: 48 year clinical update with emphasis on cardiac care

Geleophysic dysplasia is a rare skeletal dysplasia often complicated by progressive cardiac disease. Information about long-term outcomes is limited. A clinical update of the oldest surviving patient described with geleophysic dysplasia type 1 is provided. Special note is made in relation to the cardiac disease and interventions. Genetic testing of ADAMTSL2 revealed a previously reported missense mutation as well as a novel nonsense mutation, which can be added to the list of causative mutations in geleophysic dysplasia.

SLC10A7 mutations cause a skeletal dysplasia with amelogenesis imperfecta mediated by GAG biosynthesis defects

Skeletal dysplasia with multiple dislocations are severe disorders characterized by dislocations of large joints and short stature. The majority of them have been linked to pathogenic variants in genes encoding glycosyltransferases, sulfotransferases or epimerases required for glycosaminoglycan synthesis. Using exome sequencing, we identify homozygous mutations in SLC10A7 in six individuals with skeletal dysplasia with multiple dislocations and amelogenesis imperfecta. SLC10A7 encodes a 10-transmembrane-domain transporter located at the plasma membrane. Functional studies in vitro demonstrate that SLC10A7 mutations reduce SLC10A7 protein expression. We generate a Slc10a7^−/− mouse model, which displays shortened long bones, growth plate disorganization and tooth enamel anomalies, recapitulating the human phenotype. Furthermore, we identify decreased heparan sulfate levels in Slc10a7^−/− mouse cartilage and patient fibroblasts. Finally, we find an abnormal N-glycoprotein electrophoretic profile in patient blood samples. Together, our findings support the involvement of SLC10A7 in glycosaminoglycan synthesis and specifically in skeletal development.

The majority of skeletal dysplasia are caused by pathogenic variants in genes required for glycosaminoglycan (GAG) metabolism. Here, Dubail et al. identify genetic variants in the solute carrier family protein SLC10A7 in families with skeletal dysplasia and amelogenesis imperfecta that disrupt GAG synthesis.

Fibrillin microfibrils and elastic fibre proteins: Functional interactions and extracellular regulation of growth factors

Fibrillin microfibrils are extensible polymers that endow connective tissues with long-range elasticity and have widespread distributions in both elastic and non-elastic tissues. They act as a template for elastin deposition during elastic fibre formation and are essential for maintaining the integrity of tissues such as blood vessels, lung, skin and ocular ligaments. A reduction in fibrillin is seen in tissues in vascular ageing, chronic obstructive pulmonary disease, skin ageing and UV induced skin damage, and age-related vision deterioration. Most mutations in fibrillin cause Marfan syndrome, a genetic disease characterised by overgrowth of the long bones and other skeletal abnormalities with cardiovascular and eye defects. However, mutations in fibrillin and fibrillin-binding proteins can also cause short-stature pathologies. All of these diseases have been linked to dysregulated growth factor signalling which forms a major functional role for fibrillin.

Whole-genome resequencing of Ujumqin sheep to investigate the determinants of the multi-vertebral trait

The Ujumqin sheep is one of the most profitable breeds in China, with unique multi-vertebral characteristics. We performed high-throughput genome resequencing of five multi-vertebral and three non-multi-vertebral sheep in an Ujumqin population. We identified the genomic regions that correlated with the germplasm characteristics to establish the cause of the "multi-vertebral" phenotype in this breed. Sequencing generated a total of 314 952 000 000 bp of raw data. The alignment rate of all the samples was between 98.53% and 99.11%, and the mean depth of coverage relative to the reference genome was between 11.58× and 14.92×. After comparing the differences between the two groups, we identified 21 homozygous single nucleotide polymorphisms (SNPs) in the mutant exons of 14 genes. Nineteen loci of 10 genes contained nonsynonymous mutations, while two loci contained synonymous mutations. Resequencing revealed homozygous mutations comprised of 44 indels located within exons of 19 genes. These indels included 37 frameshift mutations, 6 non-frameshift mutations, and 1 stopgain single nucleotide variation (SNV). Finally, comparisons of genotypic variations revealed 17 genes with homozygous mutations in their coding regions, 5 of which have previously been associated with vertebral development and the remaining 12 genes were newly identified in this study.

The Clinical Cases of Geleophysic Dysplasia: One Gene, Different Phenotypes

Background

Geleophysic dysplasia is a rare multisystem disorder that principally affects the bones, joints, heart, and skin. This condition is inherited either in an autosomal dominant pattern due to FBN1 mutations or in an autosomal recessive pattern due to ADAMTSL2 mutations. Two patients with unaffected parents from unrelated families presented to their endocrinologist with severe short stature, resistant to growth hormone treatment. Routine endocrine tests did not reveal an underlying etiology. Exome sequencing was performed in each family. Our two patients, harboring de novo heterozygous FBN1 mutations p.Tyr1696Asp and p.Cys1748Ser, had common clinical symptoms such as severe short stature, characteristic facial features, short hands and feet, and limitation of joint movement. However, one patient had severe cardiac involvement whereas the other patient had tracheal stenosis requiring tracheostomy placement.

Conclusions

Patients with severe dwarfism, skeletal anomalies, and other specific syndromic features (e.g., tracheal stenosis and cardiac valvulopathy) should undergo genetic testing to exclude acromelic dysplasia syndromes.

Cardiac fibrosis in regenerative medicine: destroy to rebuild

The major limitations for cardiac regeneration in patients after myocardial infarction (MI) are the wide loss of cardiomyocytes and the adverse structural alterations of extracellular matrix (ECM). Cardiac fibroblast differentiation into myofibroblasts (MFB) leads to a huge deposition of ECM and to the subsequent loss of ventricular structural integrity. All these molecular events depict the fundamental features at the basis of the post-MI fibrosis and deserve in depth cellular and molecular studies to fill the gap in the clinical practice. Indeed, to date, there are no effective therapeutic approaches to limit the post-MI massive fibrosis development. In this review we describe the involvement of integrins and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)/ADAMTS-like (ADAMTSL) proteins in cardiac reparative pro-fibrotic response after MI, proposing some of them as novel potential pharmacological tools.

ADAMTS proteins in human disorders

ADAMTS proteins are a superfamily of 26 secreted molecules comprising two related, but distinct families. ADAMTS proteases are zinc metalloendopeptidases, most of whose substrates are extracellular matrix (ECM) components, whereas ADAMTS-like proteins lack a metalloprotease domain, reside in the ECM and have regulatory roles vis-à-vis ECM assembly and/or ADAMTS activity. Evolutionary conservation and expansion of ADAMTS proteins in mammals is suggestive of crucial embryologic or physiological roles in humans. Indeed, Mendelian disorders or birth defects resulting from naturally occurring ADAMTS2, ADAMTS3, ADAMTS10, ADAMTS13, ADAMTS17, ADAMTS20, ADAMTSL2 and ADAMTSL4 mutations as well as numerous phenotypes identified in genetically engineered mice have revealed ADAMTS participation in major biological pathways. Important roles have been identified in a few acquired conditions. ADAMTS5 is unequivocally implicated in pathogenesis of osteoarthritis via degradation of aggrecan, a major structural proteoglycan in cartilage. ADAMTS7 is strongly associated with coronary artery disease and promotes atherosclerosis. Autoantibodies to ADAMTS13 lead to a platelet coagulopathy, thrombotic thrombocytopenic purpura, which is similar to that resulting from ADAMTS13 mutations. ADAMTS proteins have numerous potential connections to other human disorders that were identified by genome-wide association studies. Here, we review inherited and acquired human disorders in which ADAMTS proteins participate, and discuss progress and prospects in therapeutics.

Biological functions of fucose in mammals

Fucose is a 6-deoxy hexose in the l-configuration found in a large variety of different organisms. In mammals, fucose is incorporated into N-glycans, O-glycans and glycolipids by 13 fucosyltransferases, all of which utilize the nucleotide-charged form, GDP-fucose, to modify targets. Three of the fucosyltransferases, FUT8, FUT12/POFUT1 and FUT13/POFUT2, are essential for proper development in mice. Fucose modifications have also been implicated in many other biological functions including immunity and cancer. Congenital mutations of a Golgi apparatus localized GDP-fucose transporter causes leukocyte adhesion deficiency type II, which results in severe developmental and immune deficiencies, highlighting the important role fucose plays in these processes. Additionally, changes in levels of fucosylated proteins have proven as useful tools for determining cancer diagnosis and prognosis. Chemically modified fucose analogs can be used to alter many of these fucose dependent processes or as tools to better understand them. In this review, we summarize the known roles of fucose in mammalian physiology and pathophysiology. Additionally, we discuss recent therapeutic advances for cancer and other diseases that are a direct result of our improved understanding of the role that fucose plays in these systems.

Interactions between lysyl oxidases and ADAMTS proteins suggest a novel crosstalk between two extracellular matrix families

The extracellular matrix (ECM) regulates numerous cellular events in addition to providing structural integrity. Among several protein and enzyme families implicated in functions of the ECM, the lysyl oxidases and ADAMTS proteins are known to participate in microfibril and elastic fiber formation as well as ECM-associated signaling. A yeast two-hybrid screen to identify lysyl oxidase (LOX) binding proteins identified ADAMTSL4 as a potential interactor. We demonstrate here that several members of the LOX and ADAMTS families interact with one another. Upon investigating the interaction between LOX and ADAMTSL2 we found that the absence or inhibition of Lox affected ADAMTSL2 molecular forms and reduced its tissue levels. Thus, ADAMTSL2 stability and inter-molecular complexes may depend on the activity of lysyl oxidases.

Spontaneous atopic dermatitis due to immune dysregulation in mice lacking Adamts2 and 14

Since its first description, ADAMTS14 has been considered as an aminoprocollagen peptidase based on its high similarity with ADAMTS3 and ADAMTS2. As its importance for procollagen processing was never experimentally demonstrated in vivo, we generated Adamts14-deficient mice. They are healthy, fertile and display normal aminoprocollagen processing. They were further crossed with Adamts2-deficient mice to evaluate potential functional redundancies between these two highly related enzymes. Initial characterizations made on young Adamts2-Adamts14-deficient animals showed the same phenotype as that of Adamts2-deficient mice, with no further reduction of procollagen processing and no significant aggravation of the structural alterations of collagen fibrils. However, when evaluated at older age, Adamts2-Adamts14-deficient mice surprisingly displayed epidermal lesions, appearing in 2 month-old males and later in some females, and then worsening rapidly. Immunohistological evaluations of skin sections around the lesions revealed thickening of the epidermis, hypercellularity in the dermis and extensive infiltration by immune cells. Additional investigations, performed on young mice before the formation of the initial lesions, revealed that the primary cause of the phenotype was not related to alterations of the epidermal barrier but was rather the result of an abnormal activation and differentiation of T lymphocytes towards a Th1 profile. However, the primary molecular defect probably does not reside in the immune system itself since irradiated Adamts2-Adamts14-deficient mice grafted with WT immune cells still developed lesions. While originally created to better characterize the common and specific functions of ADAMTS2 and ADAMTS14 in extracellular matrix and connective tissues homeostasis, the Adamts2-Adamts14-deficient mice revealed an unexpected but significant role of ADAMTS in the regulation of immune system, possibly through a cross-talk involving mesenchymal cells and the TGFβ pathways.

The ADAMTS5 Metzincin Regulates Zebrafish Somite Differentiation

The ADAMTS5 metzincin, a secreted zinc-dependent metalloproteinase, modulates the extracellular matrix (ECM) during limb morphogenesis and other developmental processes. Here, the role of ADAMTS5 was investigated by knockdown of zebrafish adamts5 during embryogenesis. This revealed impaired Sonic Hedgehog (Shh) signaling during somite patterning and early myogenesis. Notably, synergistic regulation of myod expression by ADAMTS5 and Shh during somite differentiation was observed. These roles were not dependent upon the catalytic activity of ADAMTS5. These data identify a non-enzymatic function for ADAMTS5 in regulating an important cell signaling pathway that impacts on muscle development, with implications for musculoskeletal diseases in which ADAMTS5 and Shh have been associated.

LTBPs in biology and medicine: LTBP diseases

The latent transforming growth factor (TGF) β binding proteins (LTBP) are crucial mediators of TGFβ function, as they control growth factor secretion, matrix deposition, presentation and activation. Deficiencies in specific LTBP isoforms yield discrete phenotypes representing defects in bone, lung and cardiovascular development mediated by loss of TGFβ signaling. Additional phenotypes represent loss of unique TGFβ-independent features of LTBP effects on elastogenesis and microfibril assembly. Thus, the LTBPs act as sensors for the regulation of both growth factor activity and matrix function.

A report of three families with FBN1-related acromelic dysplasias and review of literature for genotype-phenotype correlation in geleophysic dysplasia

Acromelic dysplasia is a heterogeneous group of rare skeletal dysplasias characterized by distal limb shortening. Weill-Marchesani syndrome (WMS), Geleophysic dysplasia (GD) and Acromicric dysplasia (AD) are clinically distinct entities within this group of disorders and are characterized by short stature, short hands, stiff joints, skin thickening, facial anomalies, normal intelligence and skeletal abnormalities. Mutations of the Fibrillin-1 (FBN1) gene have been reported to cause AD, GD and related phenotypes. We reported three families with acromelic short stature. FBN1 analysis showed that all affected individuals carry a heterozygous missense mutation c.5284G > A (p.Gly1762Ser) in exon 42 of the FBN1 gene. This mutation was previously reported to be associated with GD. We reviewed the literature and compared the clinical features of the patients with FBN1 mutations to those with A Distintegrin And Metalloproteinase with Thrombospondin repeats-like 2 gene (ADAMTSL2) mutations. We found that tip-toeing gait, long flat philtrum and thin upper upper lip were more consistently found in GD patients with ADAMTSL2 mutations than in those with FBN1 mutations. The results have shed some light on the phenotype-genotype correlation in this group of skeletal disorders. A large scale study involving multidisciplinary collaboration would be needed to consolidate our findings.

A chinese boy with geleophysic dysplasia caused by compound heterozygous mutations in ADAMTSL2

Geleophysic dysplasia, belonging to the group of acromelic dysplasia, is a rare genetic disease. Two genes, FBN1 and ADAMTSL2, were known to be linked to this disorder. The disorder presents as extreme short stature, short limbs, small hands and feet, stubby fingers and toes, joint stiffness, toe walking, skin thickening, progressive cardiac valvular thickening and characteristic facial features, including a round face with full cheeks. Here, we report the first Chinese case with geleophysic dysplasia type 1 based on clinical and genetic features. The boy was admitted because of severe physical growth retardation and mild motor retardation. Comprehensive medical evaluations were performed including metabolic studies, endocrine function examination, bone X-rays and echocardiography. Much delayed bone age and geleophysic dysplasia were found. Targeted next-generation sequencing was used to detect genetic mutations associated with skeletal dysplasia. Sanger sequencing was used to confirm the mutations in the patient. PCR amplification, cloing, and sequencing was used to determine the de novo mutation origin. Two compound heterozygous mutations were confirmed in the ADAMTSL2 gene of the patient. The c.340G > A (p.Glu114Lys) mutation was a de novo heterozygous mutation, and our results suggested that it was located on the paternal allele. While the c.234-2A > G inherited from his mother was a novel pathogenic heterozygous splicing mutation. Growth hormone deficiency had been observed in the patient. His growth velocity was improved by growth hormone supplementation. In conclusion, we have identified a novel splicing mutation of ADAMTSL2 carried by a Chinese boy with geleophysic dysplasia type 1. The patient was treated effectively with growth hormone supplementation.

Fell-Muir Lecture: Fibrillin microfibrils: structural tensometers of elastic tissues?

Fibrillin microfibrils are indispensable structural elements of connective tissues in multicellular organisms from early metazoans to humans. They have an extensible periodic beaded organization, and support dynamic tissues such as ciliary zonules that suspend the lens. In tissues that express elastin, including blood vessels, skin and lungs, microfibrils support elastin deposition and shape the functional architecture of elastic fibres. The vital contribution of microfibrils to tissue form and function is underscored by the heritable fibrillinopathies, especially Marfan syndrome with severe elastic, ocular and skeletal tissue defects. Research since the early 1990s has advanced our knowledge of biology of microfibrils, yet understanding of their mechanical and homeostatic contributions to tissues remains far from complete. This review is a personal reflection on key insights, and puts forward the conceptual hypothesis that microfibrils are structural 'tensometers' that direct cells to monitor and respond to altered tissue mechanics.

Cardiac complications of congenital disorders of glycosylation (CDG): a systematic review of the literature

Congenital disorders of glycosylation (CDG) are inborn errors of metabolism due to protein and lipid hypoglycosylation. This rapidly growing family of genetic diseases comprises 103 CDG types, with a broad phenotypic diversity ranging from mild to severe poly-organ -system dysfunction. This literature review summarizes cardiac involvement, reported in 20% of CDG. CDG with cardiac involvement were divided according to the associated type of glycosylation: N-glycosylation, O-glycosylation, dolichol synthesis, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, COG complex, V-ATPase complex, and other glycosylation pathways. The aim of this review was to document and interpret the incidence of heart disease in CDG patients. Heart disorders were grouped into cardiomyopathies, structural defects, and arrhythmogenic disorders. This work may contribute to improved early management of cardiac complications in CDG.

The ADAMTS hyalectanase family: biological insights from diverse species

The a disintegrin-like and metalloproteinase with thrombospondin type-1 motifs (ADAMTS) family of metzincins are complex secreted proteins that have diverse functions during development. The hyalectanases (ADAMTS1, 4, 5, 8, 9, 15 and 20) are a subset of this family that have enzymatic activity against hyalectan proteoglycans, the processing of which has important implications during development. This review explores the evolution, expression and developmental functions of the ADAMTS family, focusing on the ADAMTS hyalectanases and their substrates in diverse species. This review gives an overview of how the family and their substrates evolved from non-vertebrates to mammals, the expression of the hyalectanases and substrates in different species and their functions during development, and how these functions are conserved across species.

Raman microspectroscopy as a diagnostic tool for the non-invasive analysis of fibrillin-1 deficiency in the skin and in the in vitro skin models

Fibrillin microfibrils and elastic fibers are critical determinants of elastic tissues where they define as tissue-specific architectures vital mechanical properties such as pliability and elastic recoil. Fibrillin microfibrils also facilitate elastic fiber formation and support the association of epithelial cells with the interstitial matrix. Mutations in fibrillin-1 (FBN1) are causative for the Marfan syndrome, a congenital multisystem disorder characterized by progressive deterioration of the fibrillin microfibril/ elastic fiber architecture in the cardiovascular, musculoskeletal, ocular, and dermal system. In this study, we utilized Raman microspectroscopy in combination with principal component analysis (PCA) to analyze the molecular consequences of fibrillin-1 deficiency in skin of a mouse model (GT8) of Marfan syndrome. In addition, full-thickness skin models incorporating murine wild-type and Fbn1^GT8/GT8 fibroblasts as well as human HaCaT keratinocytes were generated and analyzed. Skin models containing GT8 fibroblasts showed an altered epidermal morphology when compared to wild-type models indicating a new role for fibrillin-1 in dermal-epidermal crosstalk. Obtained Raman spectra together with PCA allowed to discriminate between healthy and deficient microfibrillar networks in murine dermis and skin models. Interestingly, results obtained from GT8 dermis and skin models showed similar alterations in molecular signatures triggered by fibrillin-1 deficiency such as amide III vibrations and decreased levels of glycan vibrations. Overall, this study indicates that Raman microspectroscopy has the potential to analyze subtle changes in fibrillin-1 microfibrils and elastic fiber networks. Therefore Raman microspectroscopy may be utilized as a non-invasive and sensitive diagnostic tool to identify connective tissue disorders and monitor their disease progression.

STATEMENT OF SIGNIFICANCE

Mutations in building blocks of the fibrillin microfibril/ elastic fiber network manifest in disease conditions such as aneurysms, emphysema or lax skin. Understanding how structural changes induced by fibrillin-1 mutation impact the architecture of fibrillin microfibrils, which then translates into an altered activation state of targeted growth factors, represents a huge challenge in elucidating the genotype-phenotype correlations in connective tissue disorders such as Marfan syndrome. This study shows that Raman microspectroscopy is able to reveal structural changes in fibrillin-1 microfibrils and elastic fiber networks and to discriminate between normal and diseased networks in vivo and in vitro. Therefore Raman microspectroscopy may be utilized as a non-invasive and sensitive diagnostic tool to identify connective tissue disorders and monitor their disease progression.

Clinical Phenotype of Musladin-Lueke Syndrome in 2 Beagles

Musladin-Lueke syndrome (MLS), previously termed Chinese Beagle syndrome, is an autosomal-recessive connective tissue disorder characterized by extensive fibrosis of the skin and joints that was first identified in Beagles in the 1970s. Recent research identified a founder mutation (c.660C>T; p.R221C) in the ADAMTSL2 gene in Beagles with MLS. Here, we report the detailed clinical phenotype and laboratory findings in 2 Beagles affected with MLS. We discuss these findings in relation to the human disorder geleophysic dysplasia (GD), which also arises from recessive ADAMTSL2 mutations, and recent findings in Adamtsl2-deficient mice.

Three cases of Japanese acromicric/geleophysic dysplasia with FBN1 mutations: a comparison of clinical and radiological features

Acromicric dysplasia (AD) and geleophysic dysplasia (GD) are rare skeletal dysplasias characterized by short stature, acromelia, joint contracture, hepatomegaly, hoarseness and respiratory distress. Compared with GD, AD presents with milder clinical and radiological features. Radiological findings of AD and GD consist of shortened tubular bones of the hands and feet, and deformed capital femoral epiphyses. The genetic cause of AD and some cases of GD was shown to be mutations in the transforming growth factor (TGF) β-binding protein-like domain 5 of the fibrillin 1 gene (FBN1), which is also mutated in Marfan syndrome. In the present study, we report and compare the highly varied clinical and radiological features of three Japanese AD/GD children. Our patients, harboring FBN1 mutations p.Tyr1699Cys, p.Ser1750Arg, and p.Gly1762Ser, shared common clinical symptoms such as severe short stature, acromelia and hepatomegaly. Short tubular bones of hands and deformities of femur heads are common radiological features of our patients.

Lamin-B1 contributes to the proper timing of epicardial cell migration and function during embryonic heart development

Lamin proteins form a meshwork beneath the nuclear envelope and contribute to many different cellular processes. Mutations in lamins cause defective organogenesis in mouse models and human diseases that affect adipose tissue, brain, skeletal muscle, and the heart. In vitro cell culture studies have shown that lamins help maintain nuclear shape and facilitate cell migration. However, whether these defects contribute to improper tissue building in vivo requires further clarification. By studying the heart epicardium during embryogenesis, we show that Lb1-null epicardial cells exhibit in vivo and in vitro migratory delay. Transcriptome analyses of these cells suggest that Lb1 influences the expression of cell adhesion genes, which could affect cell migration during epicardium development. These epicardial defects are consistent with incomplete development of both vascular smooth muscle and compact myocardium at later developmental stages in Lb1-null embryos. Further, we found that Lb1-null epicardial cells have a delayed nuclear morphology change in vivo, suggesting that Lb1 facilitates morphological changes associated with migration. These findings suggest that Lb1 contributes to nuclear shape maintenance and migration of epicardial cells and highlights the use of these cells for in vitro and in vivo study of these classic cell biological phenomena.

DNA methylation at diagnosis is associated with response to disease-modifying drugs in early rheumatoid arthritis

AIM

A proof-of-concept study to explore whether DNA methylation at first diagnosis is associated with response to disease-modifying antirheumatic drugs (DMARDs) in patients with early rheumatoid arthritis (RA).

PATIENTS & METHODS

DNA methylation was quantified in T-lymphocytes from 46 treatment-naive patients using HumanMethylation450 BeadChips. Treatment response was determined in 6 months using the European League Against Rheumatism (EULAR) response criteria.

RESULTS

Initial filtering identified 21 cytosine-phosphate-guanines (CpGs) that were differentially methylated between responders and nonresponders. After conservative adjustment for multiple testing, six sites remained statistically significant, of which four showed high sensitivity and/or specificity (≥75%) for response to treatment. Moreover, methylation at two sites in combination was the strongest factor associated with response (80.0% sensitivity, 90.9% specificity, AUC 0.85).

CONCLUSION

DNA methylation at diagnosis is associated with disease-modifying antirheumatic drug treatment response in early RA.

Impaired ADAMTS9 secretion: A potential mechanism for eye defects in Peters Plus Syndrome

Peters Plus syndrome (PPS), a congenital disorder of glycosylation, results from recessive mutations affecting the glucosyltransferase B3GLCT, leading to congenital corneal opacity and diverse extra-ocular manifestations. Together with the fucosyltransferase POFUT2, B3GLCT adds Glucoseβ1-3Fucose disaccharide to a consensus sequence in thrombospondin type 1 repeats (TSRs) of several proteins. Which of these target proteins is functionally compromised in PPS is unknown. We report here that haploinsufficiency of murine Adamts9, encoding a secreted metalloproteinase with 15 TSRs, leads to congenital corneal opacity and Peters anomaly (persistent lens-cornea adhesion), which is a hallmark of PPS. Mass spectrometry of recombinant ADAMTS9 showed that 9 of 12 TSRs with the O-fucosylation consensus sequence carried the Glucoseβ1-3Fucose disaccharide and B3GLCT knockdown reduced ADAMTS9 secretion in HEK293F cells. Together, the genetic and biochemical findings imply a dosage-dependent role for ADAMTS9 in ocular morphogenesis. Reduced secretion of ADAMTS9 in the absence of B3GLCT is proposed as a mechanism of Peters anomaly in PPS. The functional link between ADAMTS9 and B3GLCT established here also provides credence to their recently reported association with age-related macular degeneration.

Cutaneous Expression of A Disintegrin-like and Metalloprotease domain containing Thrombospondin Type 1 motif-like 5 (ADAMTSL5) in Psoriasis goes beyond Melanocytes

A Disintegrin-like and Metalloprotease domain containing Thrombospondin type 1 motif-like 5 (ADAMTSL5) is a melanocyte-derived protein that has recently been implicated as an activating antigen for IL-17-producing T cells in psoriasis. There is a potential disconnect between the basal location of the melanocytes in the epidermis and the fact that T-cell infiltrates are seen mostly scattered in the epidermis with very large infiltrates in the dermis. Thus, we hypothesized that ADAMTSL5 may be expressed in other cells aside from melanocytes in skin. To further investigate the cutaneous expression of ADAMTSL5, we performed immunohistochemistry staining on lesional and nonlesional skin biopsies from psoriasis patients using three different commercially available antibodies. We confirmed that all ADAMTSL5 antibodies reacted with epidermal melanocytes. However, we also observed a strong expression of this protein in keratinocytes throughout the epidermis, and scattered expression in some dermal blood vessels and other perivascular dermal cells. Overall, the pattern of ADAMTSL5 expression is very similar to the infiltrating pattern of T-cells and dendritic cells in psoriasis lesions.

A novel biallelic splice site mutation of TECTA causes moderate to severe hearing impairment in an Algerian family

Congenital deafness is certainly one of the most common monogenic diseases in humans, but it is also one of the most genetically heterogeneous, which makes molecular diagnosis challenging in most cases. Whole-exome sequencing in two out of three Algerian siblings affected by recessively-inherited, moderate to severe sensorineural deafness allowed us to identify a novel splice donor site mutation (c.5272+1G > A) in the gene encoding α-tectorin, a major component of the cochlear tectorial membrane. The mutation was present at the homozygous state in the three affected siblings, and at the heterozygous state in their unaffected, consanguineous parents. To our knowledge, this is the first reported TECTA mutation leading to the DFNB21 form of hearing impairment among Maghrebian individuals suffering from congenital hearing impairment, which further illustrates the diversity of the genes involved in congenital deafness in the Maghreb.

FBN1: The disease-causing gene for Marfan syndrome and other genetic disorders

FBN1 encodes the gene for fibrillin-1, a structural macromolecule that polymerizes into microfibrils. Fibrillin microfibrils are morphologically distinctive fibrils, present in all connective tissues and assembled into tissue-specific architectural frameworks. FBN1 is the causative gene for Marfan syndrome, an inherited disorder of connective tissue whose major features include tall stature and arachnodactyly, ectopia lentis, and thoracic aortic aneurysm and dissection. More than one thousand individual mutations in FBN1 are associated with Marfan syndrome, making genotype-phenotype correlations difficult. Moreover, mutations in specific regions of FBN1 can result in the opposite features of short stature and brachydactyly characteristic of Weill-Marchesani syndrome and other acromelic dysplasias. How can mutations in one molecule result in disparate clinical syndromes? Current concepts of the fibrillinopathies require an appreciation of tissue-specific fibrillin microfibril microenvironments and the collaborative relationship between the structures of fibrillin microfibril networks and biological functions such as regulation of growth factor signaling.

ADAM and ADAMTS Family Proteins and Snake Venom Metalloproteinases: A Structural Overview

A disintegrin and metalloproteinase (ADAM) family proteins constitute a major class of membrane-anchored multidomain proteinases that are responsible for the shedding of cell-surface protein ectodomains, including the latent forms of growth factors, cytokines, receptors and other molecules. Snake venom metalloproteinases (SVMPs) are major components in most viper venoms. SVMPs are primarily responsible for hemorrhagic activity and may also interfere with the hemostatic system in envenomed animals. SVMPs are phylogenetically most closely related to ADAMs and, together with ADAMs and related ADAM with thrombospondin motifs (ADAMTS) family proteinases, constitute adamalysins/reprolysins or the M12B clan (MEROPS database) of metalloproteinases. Although the catalytic domain structure is topologically similar to that of other metalloproteinases such as matrix metalloproteinases, the M12B proteinases have a modular structure with multiple non-catalytic ancillary domains that are not found in other proteinases. Notably, crystallographic studies revealed that, in addition to the conserved metalloproteinase domain, M12B members share a hallmark cysteine-rich domain designated as the “ADAM_CR” domain. Despite their name, ADAMTSs lack disintegrin-like structures and instead comprise two ADAM_CR domains. This review highlights the current state of our knowledge on the three-dimensional structures of M12B proteinases, focusing on their unique domains that may collaboratively participate in directing these proteinases to specific substrates.

Mutations in LTBP3 cause acromicric dysplasia and geleophysic dysplasia

BACKGROUND

Acromelic dysplasias are a group of disorders characterised by short stature, brachydactyly, limited joint extension and thickened skin and comprises acromicric dysplasia (AD), geleophysic dysplasia (GD), Myhre syndrome and Weill-Marchesani syndrome. Mutations in several genes have been identified for these disorders (including latent transforming growth factor β (TGF-β)-binding protein-2 (LTBP2), ADAMTS10, ADAMSTS17 and fibrillin-1 (FBN1) for Weill-Marchesani syndrome, ADAMTSL2 for recessive GD and FBN1 for AD and dominant GD), encoding proteins involved in the microfibrillar network. However, not all cases have mutations in these genes.

METHODS

Individuals negative for mutations in known acromelic dysplasia genes underwent whole exome sequencing.

RESULTS

A heterozygous missense mutation (exon 14: c.2087C>G: p.Ser696Cys) in latent transforming growth factor β (TGF-β)-binding protein-3 (LTBP3) was identified in a dominant AD family. Two distinct de novo heterozygous LTPB3 mutations were also identified in two unrelated GD individuals who had died in early childhood from respiratory failure-a donor splice site mutation (exon 12 c.1846+5G>A) and a stop-loss mutation (exon 28: c.3912A>T: p.1304*Cysext*12).

CONCLUSIONS

The constellation of features in these AD and GD cases, including postnatal growth retardation of long bones and lung involvement, is reminiscent of the null ltbp3 mice phenotype. We conclude that LTBP3 is a novel component of the microfibrillar network involved in the acromelic dysplasia spectrum.

New insights into the structure, assembly and biological roles of 10–12 nm connective tissue microfibrils from fibrillin-1 studies

The 10–12 nm diameter microfibrils of the extracellular matrix (ECM) impart both structural and regulatory properties to load-bearing connective tissues. The main protein component is the calcium-dependent glycoprotein fibrillin, which assembles into microfibrils at the cell surface in a highly regulated process involving specific proteolysis, multimerization and glycosaminoglycan interactions. In higher metazoans, microfibrils act as a framework for elastin deposition and modification, resulting in the formation of elastic fibres, but they can also occur in elastin-free tissues where they perform structural roles. Fibrillin microfibrils are further engaged in a number of cell matrix interactions such as with integrins, bone morphogenetic proteins (BMPs) and the large latent complex of transforming growth factor-β (TGFβ). Fibrillin-1 (FBN1) mutations are associated with a range of heritable connective disorders, including Marfan syndrome (MFS) and the acromelic dysplasias, suggesting that the roles of 10–12 nm diameter microfibrils are pleiotropic. In recent years the use of molecular, cellular and whole-organism studies has revealed that the microfibril is not just a structural component of the ECM, but through its network of cell and matrix interactions it can exert profound regulatory effects on cell function. In this review we assess what is known about the molecular properties of fibrillin that enable it to assemble into the 10–12 nm diameter microfibril and perform such diverse roles.

Systematic data-querying of large pediatric biorepository identifies novel Ehlers-Danlos Syndrome variant

BACKGROUND

Ehlers Danlos Syndrome is a rare form of inherited connective tissue disorder, which primarily affects skin, joints, muscle, and blood cells. The current study aimed at finding the mutation that causing EDS type VII C also known as "Dermatosparaxis" in this family.

METHODS

Through systematic data querying of the electronic medical records (EMRs) of over 80,000 individuals, we recently identified an EDS family that indicate an autosomal dominant inheritance. The family was consented for genomic analysis of their de-identified data. After a negative screen for known mutations, we performed whole genome sequencing on the male proband, his affected father, and unaffected mother. We filtered the list of non-synonymous variants that are common between the affected individuals.

RESULTS

The analysis of non-synonymous variants lead to identifying a novel mutation in the ADAMTSL2 (p. Gly421Ser) gene in the affected individuals. Sanger sequencing confirmed the mutation.

CONCLUSION

Our work is significant not only because it sheds new light on the pathophysiology of EDS for the affected family and the field at large, but also because it demonstrates the utility of unbiased large-scale clinical recruitment in deciphering the genetic etiology of rare mendelian diseases. With unbiased large-scale clinical recruitment we strive to sequence as many rare mendelian diseases as possible, and this work in EDS serves as a successful proof of concept to that effect.

Two Patients with Severe Short Stature due to a FBN1 Mutation (p.Ala1728Val) with a Mild Form of Acromicric Dysplasia

BACKGROUND

Acromicric dysplasia (AD) and geleophysic dysplasia 2 (GD2) belong to the category of acromelic dysplasia syndromes, consisting of severe short stature, short hands and feet and skin thickening. Both can result from missense mutations in the transforming growth factor beta 5 domain of the fibrillin-1 gene (FBN1).

METHODS

Two patients (P1 age 10, and P2 age 7) from unrelated families presented to their endocrinologist with severe short stature (approx. -4 SDS). They were otherwise asymptomatic and only had mild facial dysmorphisms. Extensive endocrine work-up did not reveal an underlying etiology. Exome sequencing was performed in each family.

RESULTS

Exome sequencing identified the presence of the same heterozygous missense variant c.C5183T (p.Ala1728Val) in the FBN1 gene in both P1 and P2. This variant was previously reported in a patient with GD2 and associated cardiac valvulopathy and hepatomegaly. Detailed clinical re-examination, cardiac and skeletal imaging did not reveal any abnormalities in P1 or P2 other than mild hip dysplasia.

CONCLUSION

This report broadens the phenotypic spectrum of growth disorders associated with FBN1 mutations. Identical mutations give rise to a wide phenotypic spectrum, ranging from isolated short stature to a more classic picture of GD2 with cardiac involvement, distinct facial dysmorphisms and various skeletal anomalies.