Ehlers–Danlos syndrome: A showcase of conditions that lead to understanding matrix biology

En route towards a personalized medicine approach: Innovative therapeutic modalities for connective tissue disorders

Connective tissue disorders can be caused by pathogenic variants (mutations) in genes encoding extracellular matrix (ECM) proteins. Such disorders typically manifest during development or postnatal growth and result in significant morbidity and mortality. The development of curative treatments for connective tissue disorders is hampered in part by the inability of many mature connective tissues to efficiently regenerate. To be most effective, therapeutic strategies designed to preserve or restore tissue function will likely need to be initiated during phases of significant endogenous connective tissue remodeling and organ sculpting postnatally and directly target the underlying ECM protein mutations. With recent advances in whole exome sequencing, in-vitro and in-vivo disease modeling, and the development of mutation-specific molecular therapeutic modalities, it is now feasible to directly correct disease-causing mutations underlying connective tissue disorders and ameliorate their pathogenic consequences. These technological advances may lead to potentially curative personalized medicine approaches for connective tissue disorders that have previously been considered incurable. In this review, we highlight innovative therapeutic modalities including gene replacement, exon skipping, DNA/mRNA editing, and pharmacological approaches that were used to preserve or restore tissue function in the context of connective tissue disorders. Inherent to a successful application of these approaches is the need to deepen the understanding of mechanisms that regulate ECM formation and homeostasis, and to decipher how individual mutations in ECM proteins compromise ECM and connective tissue development and function.

Patient-derived extracellular matrix demonstrates role of COL3A1 in blood vessel mechanics

Vascular Ehlers-Danlos Syndrome (vEDS) is a rare autosomal dominant disease caused by mutations in the COL3A1 gene, which renders patients susceptible to aneurysm and arterial dissection and rupture. To determine the role of COL3A1 variants in the biochemical and biophysical properties of human arterial ECM, we developed a method for synthesizing ECM directly from vEDS donor fibroblasts. We found that the protein content of the ECM generated from vEDS donor fibroblasts differed significantly from ECM from healthy donors, including upregulation of collagen subtypes and other proteins related to ECM structural integrity. We further found that ECM generated from a donor with a glycine substitution mutation was characterized by increased glycosaminoglycan content and unique viscoelastic mechanical properties, including increased time constant for stress relaxation, resulting in a decrease in migratory speed of human aortic endothelial cells when seeded on the ECM. Collectively, these results demonstrate that vEDS patient-derived fibroblasts harboring COL3A1 mutations synthesize ECM that differs in composition, structure, and mechanical properties from healthy donors. These results further suggest that ECM mechanical properties could serve as a prognostic indicator for patients with vEDS, and the insights provided by the approach demonstrate the broader utility of cell-derived ECM in disease modeling. STATEMENT OF SIGNIFICANCE: The role of collagen III ECM mechanics remains unclear, despite reported roles in diseases including fibrosis and cancer. Here, we generate fibrous, collagen-rich ECM from primary donor cells from patients with vascular Ehlers-Danlos syndrome (vEDS), a disease caused by mutations in the gene that encodes collagen III. We observe that ECM grown from vEDS patients is characterized by unique mechanical signatures, including altered viscoelastic properties. By quantifying the structural, biochemical, and mechanical properties of patient-derived ECM, we identify potential drug targets for vEDS, while defining a role for collagen III in ECM mechanics more broadly. Furthermore, the structure/function relationships of collagen III in ECM assembly and mechanics will inform the design of substrates for tissue engineering and regenerative medicine.

Strategic outline of interventions targeting extracellular matrix for promoting healthy longevity

The extracellular matrix (ECM), composed of interlinked proteins outside of cells, is an important component of the human body that helps maintain tissue architecture and cellular homeostasis. As people age, the ECM undergoes changes that can lead to age-related morbidity and mortality. Despite its importance, ECM aging remains understudied in the field of geroscience. In this review, we discuss the core concepts of ECM integrity, outline the age-related challenges and subsequent pathologies and diseases, summarize diagnostic methods detecting a faulty ECM, and provide strategies targeting ECM homeostasis. To conceptualize this, we built a technology research tree to hierarchically visualize possible research sequences for studying ECM aging. This strategic framework will hopefully facilitate the development of future research on interventions to restore ECM integrity, which could potentially lead to the development of new drugs or therapeutic interventions promoting health during aging.

Salt-wasting congenital adrenal hyperplasia phenotype as a result of the TNXA/TNXB chimera 1 (CAH-X CH-1) and the pathogenic IVS2-13A/C > G in CYP21A2 gene

BACKGROUND

Genetic diversity of mutations in the CYP21A2 gene is the main cause of the monogenic congenital adrenal hyperplasia (CAH) disorder. On chromosome 6p21.3, the CYP21A2 gene is partially overlapped by the TNXB gene, the two residing in tandem with their highly homologous corresponding pseudogenes (CYP21A1P and TNXA), which leads to recurrent homologous recombination.

METHODS AND RESULTS

In the present study, the genetic status of an ethnic Greek-Cypriot family, with a female neonate that was originally classified as male and manifested the salt-wasting (SW) form, is presented. Genetic defects in the CYP21A2 and TNXB genes were investigated by Sanger sequencing multiplex ligation-dependent probe amplification (MLPA) and a real-time PCR assay. The neonate carried in compound heterozygosity the TNXA/TNXB chimeric gene complex (termed CAH-X CH-1) that results in a contiguous CYP21A2 and TNXB deletion and in her second allele the pathogenic IVS2-13A/C > G (c.655A/C > G) in CYP21A2.

CONCLUSIONS

The classic SW-CAH due to 21-hydroxylase (21-OH) deficiency may result from various complex etiological mechanisms and, as such, can involve the formation of monoallelic TNXA/TNXB chimeras found in trans with other CYP21A2 pathogenic variants. This is a rare case of CAH due to 21-hydroxylase deficiency, which elucidates the role of the complex RCCX CNV structure in the development of the disease. Identification of the correct CAH genotypes for a given phenotype is of considerable value in assisting clinicians in prenatal diagnosis, appropriate treatment, and genetic counseling.

Novel regulatory roles of small leucine-rich proteoglycans in remodeling of the uterine cervix in pregnancy

The cervix undergoes rapid and dramatic shifts in collagen and elastic fiber structure to achieve its disparate physiological roles of competence during pregnancy and compliance during birth. An understanding of the structure-function relationships of collagen and elastic fibers to maintain extracellular matrix (ECM) homeostasis requires an understanding of the mechanisms executed by non-structural ECM molecules. Small-leucine rich proteoglycans (SLRPs) play key functions in biology by affecting collagen fibrillogenesis and regulating enzyme and growth factor bioactivities. In the current study, we evaluated collagen and elastic fiber structure-function relationships in mouse cervices using mice with genetic ablation of decorin and/or biglycan genes as representative of Class I SLRPs, and lumican gene representative of Class II SLRP. We identified structural defects in collagen fibril and elastic fiber organization in nonpregnant mice lacking decorin, or biglycan or lumican with variable resolution of defects noted during pregnancy. The severity of collagen and elastic fiber defects was greater in nonpregnant mice lacking both decorin and biglycan and defects were maintained throughout pregnancy. Loss of biglycan alone reduced tissue extensibility in nonpregnant mice while loss of both decorin and biglycan manifested in decreased rupture stretch in late pregnancy. Collagen cross-link density was similar in the Class I SLRP null mice as compared to wild-type nonpregnant and pregnant controls. A broader range in collagen fibril diameter along with an increase in mean fibril spacing was observed in the mutant mice compared to wild-type controls. Collectively, these findings uncover functional redundancy and hierarchical roles of Class I and Class II SLRPs as key regulators of cervical ECM remodeling in pregnancy. These results expand our understating of the critical role SLRPs play to maintain ECM homeostasis in the cervix.

Increased Risk of Aortic Dissection with Perlecan Deficiency

Perlecan (HSPG2), a basement membrane-type heparan sulfate proteoglycan, has been implicated in the development of aortic tissue. However, its role in the development and maintenance of the aortic wall remains unknown. Perlecan-deficient mice (Hspg2^−/−-Tg: Perl KO) have been found to show a high frequency (15–35%) of aortic dissection (AD). Herein, an analysis of the aortic wall of Perl KO mice revealed that perlecan deficiency caused thinner and partially torn elastic lamina. Compared to the control aortic tissue, perlecan-deficient aortic tissue showed a significant decrease in desmosine content and an increase in soluble tropoelastin levels, implying the presence of immature elastic fibers in Perl KO mice. Furthermore, the reduced expression of the smooth muscle cell contractile proteins actin and myosin in perlecan-deficient aortic tissue may explain the risk of AD. This study showed that a deficiency in perlecan, which is localized along the elastic lamina and at the interface between elastin and fibrillin-1, increased the risk of AD, largely due to the immaturity of extracellular matrix in the aortic tissue. Overall, we proposed a new model of AD that considers the deficiency of extracellular molecule perlecan as a risk factor.

Roles of Two Small Leucine-Rich Proteoglycans Decorin and Biglycan in Pregnancy and Pregnancy-Associated Diseases

Two small leucine-rich proteoglycans (SLRP), decorin and biglycan, play important roles in structural–functional integrity of the placenta and fetal membranes, and their alterations can result in several pregnancy-associated diseases. In this review, we briefly discuss normal placental structure and functions, define and classify SLRPs, and then focus on two SLRPs, decorin (DCN) and biglycan (BGN). We discuss the consequences of deletions/mutations of DCN and BGN. We then summarize DCN and BGN expression in the pregnant uterus, myometrium, decidua, placenta, and fetal membranes. Actions of these SLRPs as ligands are then discussed in the context of multiple binding partners in the extracellular matrix and cell surface (receptors), as well as their alterations in pathological pregnancies, such as preeclampsia, fetal growth restriction, and preterm premature rupture of membranes. Lastly, we raise some unanswered questions as food for thought.

Type V Collagen Regulates the Structure and Biomechanics of TMJ Condylar Cartilage: A Fibrous-Hyaline Hybrid

This study queried the role of type V collagen in the post-natal growth of temporomandibular joint (TMJ) condylar cartilage, a hybrid tissue with a fibrocartilage layer covering a secondary hyaline cartilage layer. Integrating outcomes from histology, immunofluorescence imaging, electron microscopy and atomic force microscopy-based nanomechanical tests, we elucidated the impact of type V collagen reduction on TMJ condylar cartilage growth in the type V collagen haploinsufficiency and inducible knockout mice. Reduction of type V collagen led to significantly thickened collagen fibrils, decreased tissue modulus, reduced cell density and aberrant cell clustering in both the fibrous and hyaline layers. Post-natal growth of condylar cartilage involves the chondrogenesis of progenitor cells residing in the fibrous layer, which gives rise to the secondary hyaline layer. Loss of type V collagen resulted in reduced proliferation of these cells, suggesting a possible role of type V collagen in mediating the progenitor cell niche. When the knockout of type V collagen was induced in post-weaning mice after the start of physiologic TMJ loading, the hyaline layer exhibited pronounced thinning, supporting an interplay between type V collagen and occlusal loading in condylar cartilage growth. The phenotype in hyaline layer can thus be attributed to the impact of type V collagen on the mechanically regulated progenitor cell activities. In contrast, knee cartilage does not contain the progenitor cell population at post-natal stages, and develops normal structure and biomechanical properties with the loss of type V collagen. Therefore, in the TMJ, in addition to its established role in regulating the assembly of collagen I fibrils, type V collagen also impacts the mechanoregulation of progenitor cell activities in the fibrous layer. We expect such knowledge to establish a foundation for understanding condylar cartilage matrix development and regeneration, and to yield new insights into the TMJ symptoms in patients with classic Ehlers-Danlos syndrome, a genetic disease due to autosomal mutation of type V collagen.

Orthopaedic Conditions Associated with Aneurysms

Orthopaedic surgeons are sometimes the first specialists encountered by patients with inherited conditions that predispose them to aneurysms. The skeletal features are evident, but the aneurysm is silent. Early recognition of the conditions associated with aneurysms can lead to effective treatment and minimize risks of morbidity and death. Marfan syndrome is characterized by abnormal fibrillin-1 protein and has a broad range of skeletal manifestations, including scoliosis, hindfoot deformity, arachnodactyly, pectus excavatum or carinatum deformity, dural ectasia, and acetabular protrusio. Aneurysm-associated complications are the leading cause of early morbidity and death in patients with Marfan syndrome. Ehlers-Danlos syndrome is caused by a disturbance in collagen biosynthesis most commonly resulting in joint hypermobility and skin abnormalities. Among the types of Ehlers-Danlos syndrome, vascular Ehlers-Danlos syndrome presents the highest risk of vascular complications. Clubfoot and joint dislocations are common presenting symptoms in vascular Ehlers-Danlos syndrome. Loeys-Dietz syndrome is a connective tissue disorder resulting in aortic root dilation and several skeletal manifestations, including scoliosis, cervical malformations, joint contractures, and foot deformities.

Physical therapy treatment of hypermobile Ehlers-Danlos syndrome: A systematic review

Physiotherapy techniques are regularly prescribed in the hypermobile type Ehlers-Danlos syndrome (hEDS) and they are appreciated by the patients. The objective of this systematic review was to investigate the effect of the different physiotherapy techniques related to the children and adult patients with hEDS. PubMed, SPORTDiscus, Cochrane Library, PEDro, Scopus, and Embase databases were analyzed from inception to April 2020. Characteristics of the studies (authors), patients (sample size, sex, age, Beighton score), and nonpharmacological treatment (length of the program, number of session, duration of the session, and type of intervention), and the results with the dropout rate were extracted. From the 1045 retrieved references, 6 randomized controlled trial with a sample size ranging from 20 to 57 patients were included in the systematic review. There was a huge heterogeneity in the interventions. The durations of the program were from 4 to 8 weeks. Pain or proprioception demonstrated significant improvements in the intervention group regardless of the type of intervention. A benefit of the inspiratory muscle training was observed on functional exercise capacity. The quality of life was systematically improved. Physiotherapy benefits on proprioception and pain in patients with hEDS even if robust randomized control studies are missing.

Ehlers-Danlos syndrome: what the radiologist needs to know

Ehlers-Danlos syndrome is a real diagnosis that is erroneously used to explain multiple fractures in suspected child abuse. This paper reviews the clinical and molecular diagnostic criteria for Ehlers-Danlos syndrome. This knowledge can help prevent misdiagnosis and support clinicians when evaluating infants and young children with multiple fractures.

The Ehlers-Danlos syndromes

The Ehlers-Danlos syndromes (EDS) are a heterogeneous group of hereditary disorders of connective tissue, with common features including joint hypermobility, soft and hyperextensible skin, abnormal wound healing and easy bruising. Fourteen different types of EDS are recognized, of which the molecular cause is known for 13 types. These types are caused by variants in 20 different genes, the majority of which encode the fibrillar collagen types I, III and V, modifying or processing enzymes for those proteins, and enzymes that can modify glycosaminoglycan chains of proteoglycans. For the hypermobile type of EDS, the molecular underpinnings remain unknown. As connective tissue is ubiquitously distributed throughout the body, manifestations of the different types of EDS are present, to varying degrees, in virtually every organ system. This can make these disorders particularly challenging to diagnose and manage. Management consists of a care team responsible for surveillance of major and organ-specific complications (for example, arterial aneurysm and dissection), integrated physical medicine and rehabilitation. No specific medical or genetic therapies are available for any type of EDS.

Mechanics of Mineralized Collagen Fibrils upon Transient Loads

Collagen is a key structural protein in the human body, which undergoes mineralization during the formation of hard tissues. Earlier studies have described the mechanical behavior of bone at different scales, highlighting material features across hierarchical structures. Here we present a study that aims to understand the mechanical properties of mineralized collagen fibrils upon tensile/compressive transient loads, investigating how the kinetic energy propagates and it is dissipated at the molecular scale, thus filling a gap of knowledge in this area. These specific features are the mechanisms that nature has developed to passively dissipate stress and prevent structural failures. In addition to the mechanical properties of the mineralized fibrils, we observe distinct nanomechanical behaviors for the two regions (i.e., overlap and gap) of the D-period to highlight the effect of the mineralization. We notice decreasing trends for both wave speeds and Young's moduli over input velocity with a marked strengthening effect in the gap region due to the accumulation of the hydroxyapatite. In contrast, the dissipative behavior is not affected by either loading conditions or the mineral percentage, showing a stronger damping effect upon faster inputs compatible to the bone behavior at the macroscale. Our results offer insights into the dissipative behavior of mineralized collagen composites to design and characterize bioinspired composites for replacement devices (e.g., prostheses for sound transmission or conduction) or optimized structures able to bear transient loads, for example, impact, fatigue, in structural applications.

Wave Propagation and Energy Dissipation in Collagen Molecules

Collagen is the key protein of connective tissue (i.e., skin, tendons and ligaments, and cartilage, among others), accounting for 25-35% of the whole-body protein content and conferring mechanical stability. This protein is also a fundamental building block of bone because of its excellent mechanical properties together with carbonated hydroxyapatite minerals. Although the mechanical resilience and viscoelasticity have been studied both in vitro and in vivo from the molecular to tissue level, wave propagation properties and energy dissipation have not yet been deeply explored, in spite of being crucial to understanding the vibration dynamics of collagenous structures (e.g., eardrum, cochlear membranes) upon impulsive loads. By using a bottom-up atomistic modeling approach, here we study a collagen peptide under two distinct impulsive displacement loads, including longitudinal and transversal inputs. Using a one-dimensional string model as a model system, we investigate the roles of hydration and load direction on wave propagation along the collagen peptide and the related energy dissipation. We find that wave transmission and energy-dissipation strongly depend on the loading direction. Also, the hydrated collagen peptide can dissipate five times more energy than dehydrated one. Our work suggests a distinct role of collagen in term of wave transmission of different tissues such as tendon and eardrum. This study can step toward understanding the mechanical behavior of collagen upon transient loads, impact loading and fatigue, and designing biomimetic and bioinspired materials to replace specific native tissues such as the tympanic membrane.

Recognition and nursing management of abusive head trauma in children

Abusive head trauma (AHT) describes an injury to the head caused by a deliberate impact or shaking by a parent or carer. It can cause significant morbidity and mortality in infants, and is most commonly seen in those aged under 2 years. The initial presentation of AHT can include vague symptoms and the correct diagnosis may be missed by health professionals. Subdural haematoma, brain oedema and retinal haemorrhages are well-known features associated with AHT. However, other conditions such as birth trauma, accidental falls in infants and bleeding disorders can all mimic AHT, thus making its recognition difficult. Suspicion of AHT should lead to initiation of safeguarding procedures alongside organising neurological imaging to identify skull fracture and/or intracranial lesions. This article highlights different aspects of the clinical presentation of AHT and its management. Safeguarding and recognising child abuse is vital and requires every member of the multidisciplinary team to remain vigilant. An illustrative case study is included to highlight some of the challenges that health professionals working in different clinical set-ups are likely to come across while managing an infant with AHT.

Therapeutic education program for patients with hypermobile Ehlers-Danlos syndrome: feasibility and satisfaction of the participants

Objectives: To describe a therapeutic education program for patients with hypermobile Ehlers-Danlos syndrome, called PrEduSED and to evaluate its feasibility and efficiency in terms of satisfaction and impact on disease management in daily life. Methods: Prospective observational study. Evaluation before, after and 6 months after PrEduSED, consisted in: CSQ-F, SF-12, HAD, QIC, FIS, Zarit, Quiz and Vignettes (knowledge and skills about the disease), satisfaction questionnaire, Goal Attainment Scales. Results: Nineteen (19) patients (89% women, mean age: 39.2) were included and 9 relatives (78% men, mean age: 44.1). Participants were generally highly satisfied with the content and the organization of PrEduSED. Knowledge about the EDS and skills significantly improved (p < 0.001 for patients, p = 0.016 for relatives). QIC score improved significantly (p = 0.047) and FIS score also for the relationships domain (p = 0.05). At the end of the program, 69% of participants thought they had achieved their goals (mainly about acquiring knowledge and managing their treatment) beyond what they had hoped for; at 6 months, 54% felt they had achieved them beyond what they hoped for. Conclusions: Real success of PrEduSED for patients with hypermobile EDS in terms of recognition, satisfaction, increase of knowledge about the disease and adaptative skills.

Understanding the basis of Ehlers-Danlos syndrome in the era of the next-generation sequencing

Ehlers-Danlos syndrome (EDS) is a clinically and genetically heterogeneous group of heritable connective tissue disorders (HCTDs) defined by joint laxity, skin alterations, and joint hypermobility. The latest EDS classification recognized 13 subtypes in which the clinical and genetic phenotypes are often overlapping, making the diagnosis rather difficult and strengthening the importance of the molecular diagnostic confirmation. New genetic techniques such as next-generation sequencing (NGS) gave the opportunity to identify the genetic bases of unresolved EDS types and support clinical counseling. To date, the molecular defects have been identified in 19 genes, mainly in those encoding collagen, its modifying enzymes or other constituents of the extracellular matrix (ECM). In this review we summarize the contribution of NGS technologies to the current knowledge of the genetic background in different EDS subtypes.

Ehlers-Danlos syndrome with infective endocarditis: A case report with literature review

We report a patient with Ehlers-Danlos syndrome and mitral valve infective endocarditis. The case was complicated due to multiorgan involvement and initially diagnosed as hand-foot-and-mouth disease. The patient was transferred to our hospital with cerebral septic emboli and bilateral lower extremity emboli requiring early surgery. Complications of this syndrome and surgical risks are discussed in this report.

Inspiratory muscle strength training improves lung function in patients with the hypermobile Ehlers-Danlos syndrome: A randomized controlled trial

As exertional inspiratory dyspnea is a common disabling complaint in hypermobile Ehlers-Danlos syndrome (hEDS) often also known as joint hypermobility syndrome (JHS), we investigated inspiratory muscle (IM) strength in patients with hEDS, and we assessed the effects of IM training (IMT) on IM strength, lung function, and exercise capacity. A prospective evaluation of IM strength followed by a randomized controlled trial of IMT was performed in women with hEDS. Sniff nasal inspiratory pressure (SNIP) was used to routinely measure IM strength and IMT was carried out using a pressure threshold device. IM strength (main outcome), cardiopulmonary function, exercise capacity, and emotional distress of both the treated and control groups were evaluated at the start and at the end of the 6-week training period. IM strength was reduced (<80% of predicted) in 77% of patients (80/104). Lung function was normal, although 24% of patients had a higher forced expiratory vital capacity (FVC) than normal and 12% of patients had a higher total lung capacity (TLC) than normal. Both the IMT and control groups (n = 20) had similar baseline characteristics. Significant changes were noted only in the IMT group after IMT. At the end of the program, IMT improved SNIP (20%) (before: 41 ± 17 cm H₂ O [28, 53] vs. after: 49 ± 18 cm H₂ O [34;65]), six-minute walking distance (6MWD) (60 m) (455 ± 107 m [379,532] vs. 515 ± 127 m [408, 621]), and forced expiratory volume in one second (FEV1) (285 mL) (94 ± 14% pred [84,104] vs. 103 ± 11% pred [94, 112]). IM strength is significantly reduced in patients with hEDS. IMT improved IM strength, lung function, and exercise capacity. Our findings suggest that IMT should be added to usual care.

Histopathological and electron microscopic study in dogs with patellar luxation and skin hyperextensibility

Patellar luxation is abnormal displacement of the patella from the femoral trochlear groove. It is seen primarily in small breed dogs and causes pain and limited mobility of the stifle joint. This study aimed to investigate the relationship among patellar luxation, skin extension, and skin collagen fibril diameter. Nine dogs with patellar luxation and five clinically normal dogs were enrolled in the study. We measured the skin extension and investigated the ultrastructure of the skin and patellofemoral ligament by histopathology and transmission electron microscopy. The mean skin extension in dogs with patellar luxation was 18.5 ± 5.5% which is greater than the reference value (14.5%). Mean skin extension in controls was 8.8 ± 1.7% and was within the normal range. In dogs with patellar luxation, histopathology of the skin and patellofemoral ligament showed sparse and unevenly distributed collagen fibers. Transmission electron microscopy identified poorly organized, irregularly shaped, thin collagen fibrils. Collagen fibril thickness in dogs with patellar luxation was significantly less than fibril thickness in controls (P<0.001). There was a significant negative correlation (ρ= −0.863; P<0.001) between skin collagen fibril diameter and skin extension. Skin extension was correlated with patellar luxation and disease severity. Dogs with patellar luxation, joint dysplasia, and hyperextensible skin appear to be pathologically related. This might represent a phenotype of the Ehlers–Danlos syndrome, a hereditary connective tissue disorder in humans.

Vascular aspects of the Ehlers-Danlos Syndromes

The Ehlers-Danlos Syndromes comprise a heterogeneous group of rare monogenic conditions that are characterized by joint hypermobility, skin and vascular fragility and generalized connective tissue friability. The latest classification recognizes 13 clinical subtypes, with mutations identified in 19 different genes. Besides defects in fibrillar collagens (collagen types I, III and V), their modifying enzymes (ADAMTS-2, lysylhydroxylase 1 (LH1)), and molecules involved in collagen folding (FKBP22), defects have recently been identified in other constituents of the extracellular matrix (e.g. Tenascin-X, collagen type XII), enzymes involved in glycosaminoglycan biosynthesis (β4GalT7 and β3GalT6), dermatan 4-O-sulfotransferase-1 (D4ST1), dermatan sulfate epimerase (DSE)), (putative) transcription factors (ZNF469, PRDM5), components of the complement pathway (C1r, C1s) and an intracellular Zinc transporter (ZIP13). Easy bruising is, to a variable degree, present in all subtypes of EDS. A variable bleeding tendency, manifesting e.g. as gum bleeding, menometrorraghia, postnatal or peri-operative hemorrhage is observed in many EDS-patients of varying EDS subtypes. Life-threatening arterial aneurysms, dissections and ruptures of medium-sized and large arteries are a hallmark of the vascular subtype of EDS, caused by a molecular defect in collagen type III, an important constituent of blood vessel walls and hollow organs. They may however also occur in other EDS subtypes, especially in classical EDS, caused by defects in type V collagen or, rarely, type I collagen, and in kyphoscoliotic EDS, caused by defects in LH1 or FKBP22. These manifestations of vascular fragility and bleeding are usually attributed to fragility of the blood vessel walls and the perivascular connective tissues, but the molecular pathomechanisms underlying these complications are poorly studied. This review summarizes current knowledge on manifestations of vascular fragility in the different EDS subtypes.

Discovering Cell-Adhesion Peptides in Tissue Engineering: Beyond RGD

As an alternative to natural extracellular matrix (ECM) macromolecules, cell-adhesion peptides (CAPs) have had tremendous impact on the design of cell culture platforms, implants, and wound dressings. However, only a handful of CAPs have been utilized. The discrepancy in ECM composition strongly affects cell behavior, so it is paramount to reproduce such differences in synthetic systems. This Opinion article presents strategies inspired from high-throughput screening techniques implemented in drug discovery to exploit the potential of a growing CAP library. These strategies are expected to promote the use of a broader spectrum of CAPs, which in turn could lead to improved cell culture models, implants, and wound dressings.

Mobile Cecum in a Young Woman with Ehlers-Danlos Syndrome Hypermobility type: A Case Report and Review of the Literature

Ehlers-Danlos syndrome, hypermobility type (EDS-HT) is unexpectedly common and is associated with a high rate of gastrointestinal manifestations. We herein report the first documented case of mobile cecum associated with EDS-HT. A 21-year-old woman with repeated right lower abdominal pain was initially diagnosed with EDS-HT. Abdominal examinations performed in the supine position, such as CT and ultrasonography, showed no gross abnormalities. In contrast, oral barium gastrointestinal transit X-ray images obtained with changes in the patient's body position revealed position-dependent cecal volvulus with mobile cecum. She was finally discharged with a dramatic resolution of her symptoms after laparoscopic cecopexy for mobile cecum.

Meprin metalloproteases: Molecular regulation and function in inflammation and fibrosis

The zinc-endopeptidases meprin α and meprin β are extracellular proteases involved in connective tissue homeostasis, intestinal barrier function and immunological processes. Meprins are unique among other extracellular proteases with regard to cleavage specificity and structure. Meprin α and meprin β have a strong preference for negatively charged amino acids around the scissile bond, reflected by cleavage sites identified in procollagen I, the amyloid precursor protein (APP) and the interleukin-6 receptor (IL-6R). In this review we report on recent findings that summarize the complex molecular regulation of meprins, particular folding, activation and shedding. Dysregulation of meprin α and meprin β is often associated with pathological conditions such as neurodegeneration, inflammatory bowel disease and fibrosis. Based on mouse models and patient data we suggest meprins as possible key regulators in the onset and progression of fibrotic disorders, leading to severe diseases such as pulmonary hypertension. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Disentangling mechanisms involved in collagen pyridinoline cross-linking: The immunophilin FKBP65 is critical for dimerization of lysyl hydroxylase 2

Collagens are subjected to extensive posttranslational modifications, such as lysine hydroxylation. Bruck syndrome (BS) is a connective tissue disorder characterized at the molecular level by a loss of telopeptide lysine hydroxylation, resulting in reduced collagen pyridinoline cross-linking. BS results from mutations in the genes coding for lysyl hydroxylase (LH) 2 or peptidyl-prolyl cis-trans isomerase (PPIase) FKBP65. Given that the immunophilin FKBP65 does not exhibit LH activity, it is likely that LH2 activity is somehow dependent on FKPB65. In this report, we provide insights regarding the interplay between LH2 and FKBP65. We found that FKBP65 forms complexes with LH2 splice variants LH2A and LH2B but not with LH1 and LH3. Ablating the catalytic activity of FKBP65 or LH2 did not affect complex formation. Both depletion of FKBP65 and inhibition of FKBP65 PPIase activity reduced the dimeric (active) form of LH2 but did not affect the binding of monomeric (inactive) LH2 to procollagen Iα1. Furthermore, we show that LH2A and LH2B cannot form heterodimers with each other but are able to form heterodimers with LH1 and LH3. Collectively, our results indicate that FKBP65 is linked to pyridinoline cross-linking by specifically mediating the dimerization of LH2. Moreover, FKBP65 does not interact with LH1 and LH3, explaining why in BS triple-helical hydroxylysines are not affected. Our results provide a mechanistic link between FKBP65 and the loss of pyridinolines and may hold the key to future treatments for diseases related to collagen cross-linking anomalies, such as fibrosis and cancer.

Abdominal wall hernias-A local manifestation of systemically impaired quality of the extracellular matrix

BACKGROUND

Throughout life, inguinal hernia develops in approximately every fourth man, some of whom develop multiple hernias. If patients at risk of developing multiple hernias could be identified by a serologic biomarker, treatment might be able to be tailored and improved. Evidence suggests that abdominal wall hernia formation is associated with altered collagen metabolism. The aim of this study was to evaluate biomarkers for type IV and V collagen turnover in patients with multiple hernias and control subjects without hernia.

METHODS

Venous blood was collected from 88 men (mean age, 62 years) with a history of more than 3 hernia repairs and 86, age-matched men without hernias. Biomarkers for synthesis of collagen type IV (P4NP) and type V (P5CP) as well as breakdown (C4M and C5M) were measured in serum by validated, solid-phase, competitive assays. Collagen turnover was indicated by the ratio between the biomarker for synthesis and breakdown.

RESULTS

Type IV collagen turnover was 1.4-fold increased in patients with multiple hernias compared to control subjects (P < .001), whereas type V collagen turnover was 1.7-fold decreased (P < .001). Diagnostic power of P5CP was 0.83 (95%C.I.:0.77-0.89), P < .001.

CONCLUSION

Patients with multiple hernias exhibit increased turnover of type IV collagen and a decreased turnover of type V collagen, demonstrating systemically altered collagen turnover. Biomarkers for type V collagen turnover may be used to identify patients at risk for or with multiple hernias.

Collagen-mediated hemostasis

Collagens mediate essential hemostasis by maintaining the integrity and stability of the vascular wall. Imbalanced turnover of collagens by uncontrolled formation and/or degradation may result in pathologic conditions such as fibrosis. Thickening of the vessel wall because of accumulation of collagens may lead to arterial occlusion or thrombosis. Thinning of the wall because of collagen degradation or deficiency may lead to rupture of the vessel wall or aneurysm. Preventing excessive hemorrhage or thrombosis relies on collagen-mediated actions. Von Willebrand factor, integrins and glycoprotein VI, as well as clotting factors, can bind collagen to restore normal hemostasis after trauma. This review outlines the essential roles of collagens in mediating hemostasis, with a focus on collagens types I, III, IV, VI, XV, and XVIII.

Ptbp1 and Exosc9 knockdowns trigger skin stability defects through different pathways

In humans, genetic diseases affecting skin integrity (genodermatoses) are generally caused by mutations in a small number of genes that encode structural components of the dermal-epidermal junctions. In this article, we first show that inactivation of both exosc9, which encodes a component of the RNA exosome, and ptbp1, which encodes an RNA-binding protein abundant in Xenopus embryonic skin, impairs embryonic Xenopus skin development, with the appearance of dorsal blisters along the anterior part of the fin. However, histological and electron microscopy analyses revealed that the two phenotypes are distinct. Exosc9 morphants are characterized by an increase in the apical surface of the goblet cells, loss of adhesion between the sensorial and peridermal layers, and a decrease in the number of ciliated cells within the blisters. Ptbp1 morphants are characterized by an altered goblet cell morphology. Gene expression profiling by deep RNA sequencing showed that the expression of epidermal and genodermatosis-related genes is also differentially affected in the two morphants, indicating that alterations in post-transcriptional regulations can lead to skin developmental defects through different routes. Therefore, the developing larval epidermis of Xenopus will prove to be a useful model for dissecting the post-transcriptional regulatory network involved in skin development and stability with significant implications for human diseases.

Complex Scapular Winging following Total Shoulder Arthroplasty in a Patient with Ehlers-Danlos Syndrome

This is a unique case of a female patient with features of classical and hypermobile types of Ehlers-Danlos syndrome (EDS) who developed complex scapular winging from spinal accessory and long thoracic neuropathies. These neurological problems became manifest after an uncomplicated total shoulder arthroplasty (TSA). The patient had a complex postoperative course with extensive work-up in addition to revision shoulder surgery and manipulations to treat shoulder stiffness. It was eventually suspected that the periscapular nerve impairments occurred during physical therapy sessions after her TSA. This interpretation was further supported by genetic evidence that, in addition to EDS, the patient had an unrecognized genetic propensity for nerve palsies from stretch or pressure (“hereditary neuropathy with liability to pressure palsies” (HNPP)). By two years after the TSA the neuropathies had only partially improved, leaving the patient with persistent scapular winging and shoulder weakness. With this case we alert surgeons and physical therapists that patients with EDS can have not only a complicated course after TSA, but rare concurrent conditions that can further increase the propensity of neurological injuries that result in compromised shoulder function.

Genetic heterogeneity and clinical variability in musculocontractural Ehlers-Danlos syndrome caused by impaired dermatan sulfate biosynthesis

Bi-allelic variants in CHST14, encoding dermatan 4-O-sulfotransferase-1 (D4ST1), cause musculocontractural Ehlers-Danlos syndrome (MC-EDS), a recessive disorder characterized by connective tissue fragility, craniofacial abnormalities, congenital contractures, and developmental anomalies. Recently, the identification of bi-allelic variants in DSE, encoding dermatan sulfate epimerase-1 (DS-epi1), in a child with MC-EDS features, suggested locus heterogeneity for this condition. DS-epi1 and D4ST1 are crucial for biosynthesis of dermatan sulfate (DS) moieties in the hybrid chondroitin sulfate (CS)/DS glycosaminoglycans (GAGs). Here, we report four novel families with severe MC-EDS caused by unique homozygous CHST14 variants and the second family with a homozygous DSE missense variant, presenting a somewhat milder MC-EDS phenotype. The glycanation of the dermal DS proteoglycan decorin is impaired in fibroblasts from D4ST1- as well as DS-epi1-deficient patients. However, in D4ST1-deficiency, the decorin GAG is completely replaced by CS, whereas in DS-epi1-deficiency, still some DS moieties are present. The multisystemic abnormalities observed in our patients support a tight spatiotemporal control of the balance between CS and DS, which is crucial for multiple processes including cell differentiation, organ development, cell migration, coagulation, and connective tissue integrity.

Proteoglycan form and function: A comprehensive nomenclature of proteoglycans

We provide a comprehensive classification of the proteoglycan gene families and respective protein cores. This updated nomenclature is based on three criteria: Cellular and subcellular location, overall gene/protein homology, and the utilization of specific protein modules within their respective protein cores. These three signatures were utilized to design four major classes of proteoglycans with distinct forms and functions: the intracellular, cell-surface, pericellular and extracellular proteoglycans. The proposed nomenclature encompasses forty-three distinct proteoglycan-encoding genes and many alternatively-spliced variants. The biological functions of these four proteoglycan families are critically assessed in development, cancer and angiogenesis, and in various acquired and genetic diseases where their expression is aberrant.

Spondylocheirodysplastic Ehlers-Danlos syndrome (SCD-EDS) and the mutant zinc transporter ZIP13

The zinc transporter protein ZIP13 plays crucial roles in bone, tooth, and connective tissue development, and its dysfunction is responsible for the spondylocheirodysplastic form of Ehlers-Danlos syndrome (SCD-EDS, OMIM 612350). We recently reported that the pathogenic mutations in ZIP13 reduce its functional protein level by accelerating the protein degradation via the VCP-linked ubiquitin proteasome pathway, resulting in the disturbance of intracellular zinc homeostasis that appears to contribute to SCD-EDS pathogenesis. Finally, we implicate that possible therapeutic approaches for SCD-EDS would be based on regulating the degradation of the pathogenic mutant ZIP13 proteins.

Pulse-chase analysis of procollagen biosynthesis by azidohomoalanine labeling

Disruptions in procollagen synthesis, trafficking and secretion by cells occur in multiple connective tissue diseases. Traditionally, these disruptions are studied by pulse-chase labeling with radioisotopes. However, significant DNA damage, excessive accumulation of reactive oxygen species and formation of other free radicals have been well documented in the literature at typical radioisotope concentrations used for pulse-chase experiments. Therefore, it is important to keep in mind that the resulting cell stress response might affect interpretation of the data, particularly with respect to abnormal function of procollagen-producing cells. In this study, we describe an alternative method of pulse-chase procollagen labeling with azidohomoalanine, a noncanonical amino acid that replaces methionine in newly synthesized protein chains and can be detected via highly selective click chemistry reactions. At least in fibroblast culture, this approach is more efficient than traditional radioisotopes and has fewer, if any, unintended effects on cell function. To illustrate its applications, we demonstrate delayed procollagen folding and secretion by cells from an osteogenesis imperfecta patient with a Cys substitution for Gly766 in the triple helical region of the α1(I) chain of type I procollagen.

Structure of human peptidyl-prolyl cis-trans isomerase FKBP22 containing two EF-hand motifs

The FK506-binding protein (FKBP) family consists of proteins with a variety of protein-protein interaction domains and versatile cellular functions. It is assumed that all members are peptidyl-prolyl cis-trans isomerases with the enzymatic function attributed to the FKBP domain. Six members of this family localize to the mammalian endoplasmic reticulum (ER). Four of them, FKBP22 (encoded by the FKBP14 gene), FKBP23 (FKBP7), FKBP60 (FKBP9), and FKBP65 (FKBP10), are unique among all FKBPs as they contain the EF-hand motifs. Little is known about the biological roles of these proteins, but emerging genetics studies are attracting great interest to the ER resident FKBPs, as mutations in genes encoding FKBP10 and FKBP14 were shown to cause a variety of matrix disorders. Although the structural organization of the FKBP-type domain as well as of the EF-hand motif has been known for a while, it is difficult to conclude how these structures are combined and how it affects the protein functionality. We have determined a unique 1.9 Å resolution crystal structure for human FKBP22, which can serve as a prototype for other EF hand-containing FKBPs. The EF-hand motifs of two FKBP22 molecules form a dimeric complex with an elongated and predominantly hydrophobic cavity that can potentially be occupied by an aliphatic ligand. The FKBP-type domains are separated by a cleft and their putative active sites can catalyze isomerazation of two bonds within a polypeptide chain in extended conformation. These structural results are of prime interest for understanding biological functions of ER resident FKBPs containing EF-hand motifs.

Next generation diagnostics of heritable connective tissue disorders

Finding pathogenic mutations in monogenic diseases represents one of the significant milestones of late 20th century molecular genetics. Mutation data can improve genetic counseling, assist disease modeling and provide a basis for translational research and therapeutics. The logistics of detecting disease mutations, however, has not always been easy or straightforward. Traditional approaches using genetic linkage or candidate gene analysis have often been laborious and expensive, but the advent of next generation sequencing technologies is changing the very nature of modern-day gene discovery and mutation detection. The application of whole-exome and whole-genome sequencing has demonstrated how these new approaches can improve diagnostic sensitivity as well as disclose completely novel and unsuspected disease-gene associations. Use of next generation sequencing in inherited diseases that display genetic heterogeneity is already a cost-effective methodology for mutation detection. Further reductions in sequencing costs and machine run time, as well as improved bioinformatics, are likely to lead to the incorporation of next generation sequencing into routine diagnostics within clinical genetics. In the short term, the impact of next generation sequencing on the genetically diverse and clinically protean heritable connective tissue disorders is likely to mean more comprehensive documentation of individual mutations. Longer term, dissection of bioinformatics data may lead to further insight into individual prognosis and an era of new personal therapeutics.