The vWFA2 domain of type VII collagen is responsible for collagen binding

Clinical-Genomic Analysis of 1261 Patients with Ehlers-Danlos Syndrome Outlines an Articulo-Autonomic Gene Network (Entome)

Systematic evaluation of 80 history and 40 history findings diagnosed 1261 patients with Ehlers-Danlos syndrome (EDS) by direct or online interaction, and 60 key findings were selected for their relation to clinical mechanisms and/or management. Genomic testing results in 566 of these patients supported EDS relevance by their differences from those in 82 developmental disability patients and by their association with general rather than type-specific EDS findings. The 437 nuclear and 79 mitochondrial DNA changes included 71 impacting joint matrix (49 COL5), 39 bone (30 COL1/2/9/11), 22 vessel (12 COL3/8VWF), 43 vessel-heart (17FBN1/11TGFB/BR), 59 muscle (28 COL6/12), 56 neural (16 SCN9A/10A/11A), and 74 autonomic (13 POLG/25porphyria related). These genes were distributed over all chromosomes but the Y, a network analogized to an 'entome' where DNA change disrupts truncal mechanisms (skin constraint, neuromuscular support, joint vessel flexibility) and produces a mirroring cascade of articular and autonomic symptoms. The implied sequences of genes from nodal proteins to hypermobility to branching tissue laxity or dysautonomia symptoms would be ideal for large language/artificial intelligence analyses.

Missense Variant c.3301C>T (p.R1101W) in von Willebrand Factor A Sequence in a Patient with Recessive Dystrophic Epidermolysis Bullosa Pruriginosa with Compound Heterozygous COL7A1 Variants

Dystrophic epidermolysis bullosa (DEB) pruriginosa is a rare subtype of DEB characterized by multiple, violaceous, and severe pruritic lichenified nodules along with blisters. Here, we report the case of a Korean male who, since the age of 3 years, had multiple pruritic nodules with blisters on both lower extremities. Genetic testing is required to diagnose DEB pruriginosa because its clinical and histologic features are inconclusive. We identified compound heterozygous COL7A1 variants of c.5797C>T (p.R1933*) and c.3301C>T (p.R1101W) in the patient, leading to a diagnosis of recessive DEB pruriginosa. Among the variants identified, c.3301C>T is a novel missense variant that has not been reported previously. This variant is in exon 26, which encodes von Willebrand factor A (vWFA) in collagen type VII. vWFA is known to preserve normal dermal structures by interacting with dermal collagens and basement membranes. Considering that this variant contradicts the general concept that autosomal dominant inheritance is more common and that variants typically occur in the triple helical collagenous domain of COL7A1 in DEB pruriginosa, we focus on the rarity of this case and the possible pathogenic role of the c.3301C>T (p.R1101W) variant.

A Clinical Qualification Protocol Highlights Overlapping Genomic Influences and Neuro-Autonomic Mechanisms in Ehlers-Danlos and Long COVID-19 Syndromes

A substantial fraction of the 15% with double-jointedness or hypermobility have the traditionally ascertained joint-skeletal, cutaneous, and cardiovascular symptoms of connective tissue dysplasia and its particular manifestation as Ehlers-Danlos syndrome (EDS). The holistic ascertainment of 120 findings in 1261 EDS patients added neuro-autonomic symptoms like headaches, muscle weakness, brain fog, chronic fatigue, dyspnea, and bowel irregularity to those of arthralgia and skin laxity, 15 of these symptoms shared with those of post-infectious SARS-CoV-2 (long COVID-19). Underlying articulo-autonomic mechanisms guided a clinical qualification protocol that qualified DNA variants in 317 genes as having diagnostic utility for EDS, six of them identical (F2-LIFR-NLRP3-STAT1-T1CAM1-TNFRSF13B) and eighteen similar to those modifying COVID-19 severity/EDS, including ADAMTS13/ADAMTS2-C3/C1R-IKBKG/IKBKAP-PIK3C3/PIK3R1-POLD4/POLG-TMPRSS2/TMPRSS6-WNT3/WNT10A. Also, contributing to EDS and COVID-19 severity were forty and three genes, respectively, impacting mitochondrial functions as well as parts of an overlapping gene network, or entome, that are hypothesized to mediate the cognitive-behavioral, neuro-autonomic, and immune-inflammatory alterations of connective tissue in these conditions. The further characterization of long COVID-19 natural history and genetic predisposition will be necessary before these parallels to EDS can be carefully delineated and translated into therapies.

Structural and biophysical characterization of the type VII collagen vWFA2 subdomain leads to identification of two binding sites

Type VII collagen is an extracellular matrix protein, which is important for skin stability; however, detailed information at the molecular level is scarce. The second vWFA (von Willebrand factor type A) domain of type VII collagen mediates important interactions, and immunization of mice induces skin blistering in certain strains. To understand vWFA2 function and the pathophysiological mechanisms leading to skin blistering, we structurally characterized this domain by X-ray crystallography and NMR spectroscopy. Cell adhesion assays identified two new interactions: one with β1 integrin via its RGD motif and one with laminin-332. The latter interaction was confirmed by surface plasmon resonance with a K_D of about 1 mm. These data show that vWFA2 has additional functions in the extracellular matrix besides interacting with type I collagen.

Chemical shift assignments of the fibronectin III like domains 7-8 of type VII collagen

Type VII collagen (Col7) is important for skin stability. This is underlined by the severe skin blistering phenotype in the Col7 related diseases dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita (EBA). Col7 has a large N-terminal non-collagenous domain (NC1) that is followed by the triple helical collagenous domain. The NC1 domain has subdomains with homology to adhesion molecules and mediates important interactions within the extracellular matrix. An 185 amino acid long part of the NC1-subdomain termed fibronectin III like domains 7 and 8 (FNIII7-8) was investigated. Antibodies against this region are pathogenic in a mouse model of EBA and one reported missense mutations of Col7 lies within these domains. The nearly complete NMR resonance assignment of recombinant FNIII7-8 of Col7 is reported.

Radiosensitive Hematopoietic Cells Determine the Extent of Skin Inflammation in Experimental Epidermolysis Bullosa Acquisita

Animal models have enhanced our understanding of the pathogenesis of autoimmune diseases. For these models, genetically identical, inbred mice have commonly been used. Different inbred mouse strains, however, show a high variability in disease manifestation. Identifying the factors that influence this disease variability could provide unrecognized insights into pathogenesis. We established a novel Ab transfer-induced model of epidermolysis bullosa acquisita (EBA), an autoimmune disease characterized by (muco)-cutaneous blistering caused by anti-type VII collagen (COL7) autoantibodies. Blistering after anti-COL7 IgG (directed against the von Willebrand factor A-like domain 2) transfer showed clear variability among inbred mouse strains, that is, severe cutaneous blistering and inflammation in C57BL/6J and absence of skin lesions in MRL/MpJ mice. The transfer of anti-COL7 IgG into irradiated, EBA-resistant MRL/MpJ mice, rescued by transplantation with bone marrow from EBA-susceptible B6.AK-H2k mice, induced blistering. To the contrary, irradiated EBA-susceptible B6.AK-H2k mice that were rescued using MRL/MpJ bone marrow were devoid of blistering. In vitro, immune complex activation of neutrophils from C57BL/6J or MRL/MpJ mice showed an impaired reactive oxygen species release from the latter, whereas no differences were observed after PMA activation. This finding was paralleled by divergent expression profiles of immune complex-activated neutrophils from either C57BL/6J or MRL/MpJ mice. Collectively, we demonstrate that radiosensitive cells determine the varying extent of skin inflammation and blistering in the end-stage effector phase of EBA.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

From marrow to matrix: novel gene and cell therapies for epidermolysis bullosa

Epidermolysis bullosa encompasses a group of inherited connective tissue disorders that range from mild to lethal. There is no cure, and current treatment is limited to palliative care that is largely ineffective in treating the systemic, life-threatening pathology associated with the most severe forms of the disease. Although allogeneic cell- and protein-based therapies have shown promise, both novel and combinatorial approaches will undoubtedly be required to totally alleviate the disorder. Progress in the development of next-generation therapies that synergize targeted gene-correction and induced pluripotent stem cell technologies offers exciting prospects for personalized, off-the-shelf treatment options that could avoid many of the limitations associated with current allogeneic cell-based therapies. Although no single therapeutic avenue has achieved complete success, each has substantially increased our collective understanding of the complex biology underlying the disease, both providing mechanistic insights and uncovering new hurdles that must be overcome.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Advances in understanding and treating dystrophic epidermolysis bullosa

Epidermolysis bullosa is a group of inherited disorders that can be both systemic and life-threatening. Standard treatments for the most severe forms of this disorder, typically limited to palliative care, are ineffective in reducing the morbidity and mortality due to complications of the disease. Emerging therapies—such as the use of allogeneic cellular therapy, gene therapy, and protein therapy—have all shown promise, but it is likely that several approaches will need to be combined to realize a cure. For recessive dystrophic epidermolysis bullosa, each particular therapeutic approach has added to our understanding of type VII collagen (C7) function and the basic biology surrounding the disease. The efficacy of these therapies and the mechanisms by which they function also give us insight into developing future strategies for treating this and other extracellular matrix disorders.

The hinge region of type VII collagen is intrinsically disordered

Type VII collagen (Col7) is important for skin integrity. As a major component of the anchoring fibrils, Col7 is essential for linking different skin layers together. The central collagenous domain of Col7 contains several interruptions of the collagen triple helix. The longest interruption is 39 amino acids long and referred to as the hinge region. The hinge region is highly conserved between species. This region was predicted to adopt a coiled coil structure and to serve as the trimerization domain of Col7. To gain insight into the potential function of the hinge region we investigated a heterologous expressed peptide by CD and NMR spectroscopy. CD spectroscopy implies that the hinge region is intrinsically disordered. Resonance assignment was performed and allowed secondary structure analysis based on the chemical shift values. Seven amino acids in the N-terminal moiety show residual α-helical conformation. Subsequent investigation of temperature dependency of amide chemical shifts indicated participation in hydrogen bonding of amino acid residues in the C-terminal moiety of the hinge region. Therefore, the hinge region does not form a coiled coil structure under the employed experimental conditions. The intrinsic disorder of the hinge region might be desired for flexibility to serve as a "hinge" or the hinge region is an important interaction site as typically observed for intrinsically disordered proteins.

The cysteine-rich region of type VII collagen is a cystine knot with a new topology

Collagens are a group of extracellular matrix proteins with essential functions for skin integrity. Anchoring fibrils are made of type VII collagen (Col7) and link different skin layers together: the basal lamina and the underlying connective tissue. Col7 has a central collagenous domain and two noncollagenous domains located at the N and C terminus (NC1 and NC2), respectively. A cysteine-rich region of hitherto unknown function is located at the transition of the NC1 domain to the collagenous domain. A synthetic model peptide of this region was investigated by CD and NMR spectroscopy. The peptide folds into a collagen triple helix, and the cysteine residues form disulfide bridges between the different strands. The eight cystine knot topologies that are characterized by exclusively intermolecular disulfide bridges have been analyzed by molecular modeling. Two cystine knots are energetically preferred; however, all eight disulfide bridge arrangements are essentially possible. This novel cystine knot is present in type IX collagen, too. The conserved motif of the cystine knot is CX3CP. The cystine knot is N-terminal to the collagen triple helix in both collagens and therefore probably impedes unfolding of the collagen triple helix from the N terminus.

Clinical presentation, pathogenesis, diagnosis, and treatment of epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease. The pathogenic relevance of autoantibodies targeting type VII collagen (COL7) has been well-documented. Therefore, EBA is a prototypical autoimmune disease with a well-characterized pathogenic relevance of autoantibody binding to the target antigen. EBA is a rare disease with an incidence of 0.2 new cases per million and per year. The current treatment of EBA relies on general immunosuppressive therapy, which does not lead to remission in all cases. Therefore, there is a high, so far unmet medical need for the development of novel therapeutic options. During the last 10 years, several novel in vitro and in vivo models of EBA have been established. These models demonstrated a critical role of the genetic background, T cells, and cytokines for mediating the loss of tolerance towards COL7. Neutrophils, complement activation, Fc gamma receptor engagement, cytokines, several molecules involved in cell signaling, release of reactive oxygen species, and matrix metalloproteinases are crucial for autoantibody-induced tissue injury in EBA. Based on this growing understanding of the diseases' pathogenesis, several potential novel therapeutic targets have emerged. In this review, the clinical presentation, pathogenesis, diagnosis, and current treatment options for EBA are discussed in detail.