Biology of anchoring fibrils: lessons from dystrophic epidermolysis bullosa

Practical considerations relevant to treatment with the gene therapy beremagene geperpavec-svdt for dystrophic epidermolysis bullosa

BACKGROUND/PURPOSE

Dystrophic epidermolysis bullosa (DEB), a rare genetic skin disease caused by loss-of-function mutations in COL7A1, the gene encoding type VII collagen (COL7), is characterized by skin blistering, scarring, and extracutaneous manifestations that markedly reduce patient quality-of-life. Beremagene geperpavec-svdt ('B-VEC') is a gene therapy employing a non-integrating, replication-defective herpes simplex virus type 1 (HSV-1)-based vector encoding two copies of full-length human COL7A1 to restore COL7 protein after topical administration to DEB wounds. B-VEC was approved in the United States in 2023 as the first topical gene therapy and the first approved treatment for DEB. However, few providers have experience with use of this gene therapy.

METHODS

Data was obtained through literature review and the experience of providers who participated in the B-VEC clinical study or initiated treatment after B-VEC approval.

RESULTS

This review discusses the burden of disease, describes the clinical trial outcomes of B-VEC, and provides physician and patient/caregiver recommendations as a practical guide for the real-world use of B-VEC, which can be administered in-office or at the patient's home.

CONCLUSIONS

By continuing to optimize the practical aspects of B-VEC administration, the focus will continue to shift to patient-centric considerations and improved patient outcomes.

Stem Cell Therapies for Epidermolysis Bullosa Treatment

Epidermolysis bullosa (EB) includes a group of rare skin diseases characterized by skin fragility with bullous formation in the skin, in response to minor mechanical injury, as well as varying degrees of involvement of the mucous membranes of the internal organs. EB is classified into simplex, junctional, dystrophic and mixed. The impact of the disease on patients is both physical and psychological, with the result that their quality of life is constantly affected. Unfortunately, there are still no approved treatments available to confront the disease, and treatment focuses on improving the symptoms with topical treatments to avoid complications and other infections. Stem cells are undifferentiated cells capable of producing, maintaining and replacing terminally differentiated cells and tissues. Stem cells can be isolated from embryonic or adult tissues, including skin, but are also produced by genetic reprogramming of differentiated cells. Preclinical and clinical research has recently greatly improved stem cell therapy, making it a promising treatment option for various diseases in which current medical treatments fail to cure, prevent progression, or alleviate symptoms. So far, stem cells from different sources, mainly hematopoietic and mesenchymal, autologous or heterologous have been used for the treatment of the most severe forms of the disease each one of them with some beneficial effects. However, the mechanisms through which stem cells exert their beneficial role are still unknown or incompletely understood and most importantly further research is required to evaluate the effectiveness and safety of these treatments. The transplantation of skin grafts to patients produced by gene-corrected autologous epidermal stem cells has been proved to be rather successful for the treatment of skin lesions in the long term in a limited number of patients. Nevertheless, these treatments do not address the internal epithelia-related complications manifested in patients with more severe forms.

Analysis of COL7A1 pathogenic variants in a large cohort of dystrophic epidermolysis bullosa patients from Argentina reveals a new genotype-phenotype correlation

Dystrophic epidermolysis bullosa (DEB) is a clinically heterogeneous heritable skin disorder, characterized by blistering of the skin and mucous membranes following minor trauma. Dominant (DDEB) and recessive (RDEB) forms are caused by pathogenic variants in COL7A1 gene. Argentina's population has a heterogeneous genetic background, and little is known about the molecular basis of DEB in our country or in native South American populations. In this study, we present the prevalence and geographical distribution of pathogenic variants found in 181 patients from 136 unrelated families (31 DDEB and 105 RDEB). We detected 95 different variants, 59 of them were previously reported in the literature and 36 were novel, nine of which were detected in more than one family. The most prevalent pathogenic variants were identified in exon 73 in DDEB patients and in exon 3 in RDEB patients. We also report a new phenotype-genotype correlation found in 10 unrelated families presenting mild blistering and severe mucosal involvement. Molecular studies in populations with an unexplored genetic background like ours revealed a diversity of pathogenic variants, and we hope that these findings will contribute to the definition of targets for new gene therapies.

Patient-reported outcomes and quality of life in dominant dystrophic epidermolysis bullosa: A global cross-sectional survey

INTRODUCTION

Dystrophic epidermolysis bullosa is a debilitating skin condition, without curative treatment. Previous research has focused on the recessive variant, which is known to cause severe disease. Limited work focusing on the clinical manifestations and outcomes of dominant dystrophic epidermolysis bullosa is found (DDEB).

METHODS

Analysis of an online survey of 42 DDEB patients.

RESULTS

Self-reported severity of disease did not correlate with size of the wound or number of dressing changes, but did correlate with severity of pain reported in the last 12 months (3.4 mild vs 6.8 severe disease, P = 0.0002). Patients with severe DDEB also reported more severe internal disease symptoms, such as difficulty swallowing (62.5%, P = 0.01) and greater analgesic use during dressing changes (4.4% mild vs 81.3% severe, P = <0.001).

DISCUSSION

Patient perception of disease severity in DDEB appears to be most impacted by pain, presence of chronic open wounds, difficulty swallowing, difficulty walking, and anal strictures. As research on DDEB increases, future studies focused on these symptoms might be the most impactful for DDEB patients. However, distinguishing DDEB from other subtypes remains a challenge.

The Role of Dermal Regenerative Templates in Complex Lower Extremity Wounds

Dermal regenerative templates (DRTs) provide an option for management of complex lower extremity wounds. DRTs may be used to achieve definitive wound closure by serving as a scaffold for local tissue infiltration. Healing with a DRT interface leads to histologic and structural properties similar to native skin. DRTs can be applied over deep wounds with exposed critical structures that may have required a local or free flap. DRTs are a valuable option for lower extremity limb reconstruction.

Epidermolysis bullosa

Epidermolysis bullosa (EB) is an inherited, heterogeneous group of rare genetic dermatoses characterized by mucocutaneous fragility and blister formation, inducible by often minimal trauma. A broad phenotypic spectrum has been described, with potentially severe extracutaneous manifestations, morbidity and mortality. Over 30 subtypes are recognized, grouped into four major categories, based predominantly on the plane of cleavage within the skin and reflecting the underlying molecular abnormality: EB simplex, junctional EB, dystrophic EB and Kindler EB. The study of EB has led to seminal advances in our understanding of cutaneous biology. To date, pathogenetic mutations in 16 distinct genes have been implicated in EB, encoding proteins influencing cellular integrity and adhesion. Precise diagnosis is reliant on correlating clinical, electron microscopic and immunohistological features with mutational analyses. In the absence of curative treatment, multidisciplinary care is targeted towards minimizing the risk of blister formation, wound care, symptom relief and specific complications, the most feared of which - and also the leading cause of mortality - is squamous cell carcinoma. Preclinical advances in cell-based, protein replacement and gene therapies are paving the way for clinical successes with gene correction, raising hopes amongst patients and clinicians worldwide.

Composition, structure and function of the corneal stroma

No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma. The precise arrangement and orientation of collagen fibrils, lamellae and keratocytes that occurs during development and is needed in adults to maintain stromal function is dependent on the regulated interaction of multiple ECM components that contribute to attain the unique properties of the cornea: transparency, shape, mechanical strength, and avascularity. This review summarizes the contribution of different ECM components, their structure, regulation and function in modulating the properties of the corneal stroma. Fibril forming collagens (I, III, V), fibril associated collagens with interrupted triple helices (XII and XIV), network forming collagens (IV, VI and VIII) as well as small leucine-rich proteoglycans (SLRP) expressed in the stroma: decorin, biglycan, lumican, keratocan, and fibromodulin are some of the ECM components reviewed in this manuscript. There are spatial and temporal differences in the expression of these ECM components, as well as interactions among them that contribute to stromal function. Unique regions within the stroma like Bowman's layer and Descemet's layer are discussed. To define the complexity of corneal stroma composition and structure as well as the relationship to function is a daunting task. Our knowledge is expanding, and we expect that this review provides a comprehensive overview of current knowledge, definition of gaps and suggests future research directions.

Patent landscape of molecular and cellular targeted therapies for recessive dystrophic epidermolysis bullosa

INTRODUCTION

Recessive Dystrophic Epidermolysis Bullosa (RDEB) is a monogenetic inherited genodermatosis associated with deleterious mutations in the gene encoding type VII collagen (COL7A1). COL7A1 is essential for promoting attachment of the epidermis to the dermis, and its dysfunction may lead to generalized mucosal and cutaneous blistering associated to severe deformities. Currently, management of RDEB patients is limited to supportive care, being aimed at treating and preventing common complications associated with this condition. There is a great demand to develop targeted therapies for this devastating disease and RDEB research advances are currently being translated into clinical trials.

AREAS COVERED

Based on the literature and patent search, the authors have grouped the RDEB targeted therapies into five categories: a) cell-based therapies; b) gene therapy; c) protein replacement therapy; d) molecular therapy based on exon skipping; and e) drug-mediated premature termination codon read-through. The patent searching strategy involved inquiring Google and USPTO patent databases to reveal companies and institutions that are active in the area of RDEB targeted therapies.

EXPERT OPINION

The patent landscape related to targeted therapies for RDEB is quite heterogeneous, with each targeted therapeutic approach being associated with its own challenges in achieving robust patent protection and identifying opportunities for future development.

Single stem cell gene therapy for genetic skin disease

Stem cell gene therapy followed by transplantation into damaged regions of the skin has been successfully used to treat genetic skin blistering disorder. Usually, many stem cells are virally transduced to obtain a sufficient number of genetically corrected cells required for successful transplantation, as genetic insertion in every stem cell cannot be precisely defined. In this issue of EMBO Molecular Medicine, Droz-Georget Lathion et al developed a new strategy for ex vivo single cell gene therapy that allows extensive genomic and functional characterization of the genetically repaired individual cells before they can be used in clinical settings.

A single epidermal stem cell strategy for safe ex vivo gene therapy

There is a widespread agreement from patient and professional organisations alike that the safety of stem cell therapeutics is of paramount importance, particularly for ex vivo autologous gene therapy. Yet current technology makes it difficult to thoroughly evaluate the behaviour of genetically corrected stem cells before they are transplanted. To address this, we have developed a strategy that permits transplantation of a clonal population of genetically corrected autologous stem cells that meet stringent selection criteria and the principle of precaution. As a proof of concept, we have stably transduced epidermal stem cells (holoclones) obtained from a patient suffering from recessive dystrophic epidermolysis bullosa. Holoclones were infected with self-inactivating retroviruses bearing a COL7A1 cDNA and cloned before the progeny of individual stem cells were characterised using a number of criteria. Clonal analysis revealed a great deal of heterogeneity among transduced stem cells in their capacity to produce functional type VII collagen (COLVII). Selected transduced stem cells transplanted onto immunodeficient mice regenerated a non-blistering epidermis for months and produced a functional COLVII. Safety was assessed by determining the sites of proviral integration, rearrangements and hit genes and by whole-genome sequencing. The progeny of the selected stem cells also had a diploid karyotype, was not tumorigenic and did not disseminate after long-term transplantation onto immunodeficient mice. In conclusion, a clonal strategy is a powerful and efficient means of by-passing the heterogeneity of a transduced stem cell population. It guarantees a safe and homogenous medicinal product, fulfilling the principle of precaution and the requirements of regulatory affairs. Furthermore, a clonal strategy makes it possible to envision exciting gene-editing technologies like zinc finger nucleases, TALENs and homologous recombination for next-generation gene therapy.

Polymeric Nanoparticles to Combat Squamous Cell Carcinomas in Patients with Dystrophic Epidermolysis Bullosa

Skin cancer is the leading cause of malignancy in the United States, with Basal Cell Carcinoma, Squamous Cell Carcinoma , and Melanoma being the three most common diagnoses, respectively. Squamous Cell Carcinoma (SCC) is a particular concern for patients suffering from Dystrophic Epidermolysis Bullosa (DEB), a disease that affects the production and function of collagen VII, a protein that forms the anchoring fibrils which bind the epidermis to the dermis. Patients with DEB suffer from chronic blistering and wounds that have impaired healing capabilities, often leading to the development of SCC and eventual mortality. Nanomedicine is playing an increasing role in the delivery of effective therapeutics to combat a wide range of diseases, including the imaging and treatment of SCC. In this review, we discuss the role of nanoparticles in the treatment of SCC with an emphasis on PLGA nanoparticles and SCCs found in patients suffering from DEB, and address recent patents that are pertinent to the development of novel nanomedical therapeutics.

Collagen VII plays a dual role in wound healing

Although a host of intracellular signals is known to contribute to wound healing, the role of the cell microenvironment in tissue repair remains elusive. Here we employed 2 different mouse models of genetic skin fragility to assess the role of the basement membrane protein collagen VII (COL7A1) in wound healing. COL7A1 secures the attachment of the epidermis to the dermis, and its mutations cause a human skin fragility disorder coined recessive dystrophic epidermolysis bullosa (RDEB) that is associated with a constant wound burden. We show that COL7A1 is instrumental for skin wound closure by 2 interconnected mechanisms. First, COL7A1 was required for re-epithelialization through organization of laminin-332 at the dermal-epidermal junction. Its loss perturbs laminin-332 organization during wound healing, which in turn abrogates strictly polarized expression of integrin α6β4 in basal keratinocytes and negatively impacts the laminin-332/integrin α6β4 signaling axis guiding keratinocyte migration. Second, COL7A1 supported dermal fibroblast migration and regulates their cytokine production in the granulation tissue. These findings, which were validated in human wounds, identify COL7A1 as a critical player in physiological wound healing in humans and mice and may facilitate development of therapeutic strategies not only for RDEB, but also for other chronic wounds.

Targeted gene addition in human epithelial stem cells by zinc-finger nuclease-mediated homologous recombination

Preclinical and clinical studies showed that autologous transplantation of epidermis derived from genetically modified epithelial stem cells (EpSCs) leads to long-term correction of inherited skin adhesion defects. These studies were based on potentially genotoxic retroviral vectors. We developed an alternative gene transfer strategy aimed at targeting a "safe harbor" locus, the adeno-associated virus integration site 1 (AAVS1), by zinc-finger nuclease (ZFN)-induced homologous recombination (HR). Delivery of AAVS1-specific ZFNs and a GFP-expressing HR cassette by integration-defective lentiviral (LV) vectors (IDLVs) or adenoviral (Ad) vectors resulted in targeted gene addition with an efficiency of > 20% in a human keratinocyte cell line, > 10% in immortalized keratinocytes, and < 1% in primary keratinocytes. Deep sequencing of the AAVS1 locus showed that ZFN-induced double-strand breaks are mostly repaired by nonhomologous end joining (NHEJ) in primary cells, indicating that poor induction of the HR-dependent DNA repair pathway may be a significant limitation for targeted gene integration. Skin equivalents derived from unselected keratinocyte cultures coinfected with a GFP-IDLV and a ZFN-Ad vector were grafted onto immunodeficient mice. GFP-positive clones were observed in all grafts up to 18 weeks post-transplantation. By histological and molecular analysis, we were able to demonstrate highly efficient targeting of the AAVS1 locus in human repopulating EpSCs.

Diagnosing epidermolysis bullosa type and subtype in infancy using immunofluorescence microscopy: the Stanford experience

The natural history of inherited epidermolysis bullosa (EB) varies significantly across subtypes. When confronted with an infant suspected to have EB, rapidly determining the type and subtype is critical in counselling families accurately about the infant's diagnosis and prognosis. Although transmission electron microscopy (TEM) has been considered the criterion standard for EB diagnosis, immunofluorescence microscopy (IFM) using monoclonal antibodies (mAbs) to EB-specific basement membrane zone proteins has several advantages, but few studies have evaluated the diagnostic utility of IFM. We sought to evaluate the clinical utility of IFM using an expanded panel of EB-specific mAbs. This was a retrospective review of pathology reports from infants younger < 1 year old with suspected EB primarily analyzed with IFM by the Stanford Dermatopathology service. Seventy-seven cases were identified for analysis, of which 20 were suboptimal for IFM analysis. Fifty-five cases were diagnosed with EB and classified as follows: EB simplex (n = 5), junctional EB (n = 31), dystrophic EB (n = 19). TEM was available in 36 of 55 cases (65%). IFM with an expanded panel of EB-specific mAbs should be considered the first-line diagnostic test to evaluate infants with clinically suspected EB.

De Novo COL7A1 mutation in a patient with trisomy 21: coexistence of dystrophic epidermolysis bullosa and Down syndrome

BACKGROUND

Down syndrome (DS) is the most common autosomal chromosomal disorder. Epidermolysis bullosa (EB) is a rare genodermatosis characterized by skin and mucous membrane fragility, with formation of blisters and erosions after minor trauma. Dystrophic EB (DEB) is inherited as an autosomal dominant (DDEB) or recessive (RDEB) trait. Both forms are caused by mutations in COL7A1, the gene coding for the type VII collagen. We report a patient affected by both conditions: DS and DDEB.

METHODS

A patient with DS developed generalized blisters at the age of three months. Cytogenetic study was performed to confirm DS. Skin biopsies were examined with immunohistochemical and electron microscopy techniques to determine EB subtype. Genomic DNA was extracted from peripheral blood samples. COL7A1 mutations were screened by heteroduplex analysis using conformation-sensitive gel electrophoresis and sequencing.

RESULTS

Karyotype analysis revealed trisomy 21. Histological study agreed with a DEB diagnosis. Mutational analysis showed a heterozygous c.6127G>T mutation in COL7A1, which is compatible with DDEB. Parental study suggests that c.6127G>T arises as a de novo mutation.

CONCLUSIONS

This report demonstrates that EB can be associated with other common conditions and reports the case of a patient who suffered two de novo independent genetic conditions. It also contributes to expanding the knowledge and database of clinical and molecular aspects of DDEB.

Folding delay and structural perturbations caused by type IV collagen natural interruptions and nearby Gly missense mutations

The standard collagen triple helix requires Gly as every third residue in the amino acid sequence, yet all nonfibrillar collagens contain sites where this repeating pattern is interrupted. To explore the effects of such natural interruptions on the triple helix, a 4- or 15-residue sequence from human basement membrane type IV collagen was introduced between (Gly-Xaa-Yaa)(n) domains within a recombinant bacterial collagen. The interruptions had little effect on melting temperature, consistent with the high thermal stability reported for nonfibrillar collagens. Although the 4-residue interruption cannot be accommodated within a standard triple helix, trypsin and thermolysin resistance indicated a tightly packed structure. Central residues of the 15-residue interruption were protease-susceptible, whereas residues near the (Gly-Xaa-Yaa)(n) boundary were resistant, supporting a transition from an alternate conformation to a well packed triple helix. Both interruptions led to a delay in triple-helix folding, with the 15-residue interruption causing slower folding than the 4-residue interruption. These results suggest that propagation through interruptions represents a slow folding step. To clarify the relation between natural interruptions and pathological mutations, a Gly to Ser missense mutation was placed three triplets away from the 4-residue interruption. As a result of this mutation, the 4-residue interruption and nearby triple helix became susceptible to protease digestion, and an additional folding delay was observed. Because Gly missense mutations that cause disease are often located near natural interruptions, structural and folding perturbations arising from such proximity could be a factor in collagen genetic diseases.

The COL7A1 mutation database

Dystrophic Epidermolysis Bullosa (DEB) is a genetic disease caused by mutations in the COL7A1 gene that is inherited in the autosomal dominant or recessive mode. We have developed a curated, freely accessible COL7A1 specific database (http://www.col7.info), which contains more than 730 reported and unpublished sequence variants of the gene. Molecular defects are reported according to HGVS recommendation. The clinical description module is provided with an advanced search tool together with a CSV (comm. separated values) data format download option. This compilation of COL7A1 data and nomenclature is aimed at assisting molecular and clinical geneticists to enhance the collaboration between researchers worldwide.

Correction of dog dystrophic epidermolysis bullosa by transplantation of genetically modified epidermal autografts

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin blistering condition caused by mutations in the gene coding for collagen type VII. Genetically engineered RDEB dog keratinocytes were used to generate autologous epidermal sheets subsequently grafted on two RDEB dogs carrying a homozygous missense mutation in the col7a1 gene and expressing baseline amounts of the aberrant protein. Transplanted cells regenerated a differentiated and vascularized auto-renewing epidermis progressively repopulated by dendritic cells and melanocytes. No adverse immune reaction was detected in either dog. In dog 1, the grafted epidermis firmly adhered to the dermis throughout the 24-month follow-up, which correlated with efficient transduction (100%) of highly clonogenic epithelial cells and sustained transgene expression. In dog 2, less efficient (65%) transduction of primary keratinocytes resulted in a loss of the transplanted epidermis and graft blistering 5 months after transplantation. These data provide the proof of principle for ex vivo gene therapy of RDEB patients with missense mutations in collagen type VII by engraftment of the reconstructed epidermis, and demonstrate that highly efficient transduction of epidermal stem cells is crucial for successful gene therapy of inherited skin diseases in which correction of the genetic defect confers no major selective advantage in cell culture.

The extracellular matrix of the dermis: flexible structures with dynamic functions

The current understanding of the role of extracellular matrix proteins is mainly based on their structural properties and their assembly into complex networks. The multiplicity of interactions between cells, cytokines and growth factors within the networks determines functional units dictating the biophysical properties of tissues. This review focuses on the understanding how alterations in the genes, modifying enzymes or biological functions of extracellular matrix molecules, lead to inborn or acquired skin disorders. Analysis of the disease mechanisms provides the basis for the emerging concept that not solely structural defects of single extracellular matrix proteins are at fault, but rather that the functional unit as a whole is not working properly, causing similar clinical symptoms although the causative genes are entirely different. The understanding of these disease-causing pathways has already led to surprising new therapeutic developments applied to rare inborn disorders. They now permit to design new concepts for the treatment of more common diseases associated with the accumulation of connective tissue and alterations of the biomechanical properties of the extracellular matrix.

The radial growth phase of malignant melanoma: multi-phase modelling, numerical simulations and linear stability analysis

Cutaneous melanoma is disproportionately lethal despite its relatively low incidence and its potential for cure in the early stages. The aim of this study is to foster understanding of the role of microstructure on the occurrence of morphological changes in diseased skin during melanoma evolution. The authors propose a biomechanical analysis of its radial growth phase, investigating the role of intercellular/stromal connections on the initial stages of epidermis invasion. The radial growth phase of a primary melanoma is modelled within the multi-phase theory of mixtures, reproducing the mechanical behaviour of the skin layers and of the epidermal-dermal junction. The theoretical analysis takes into account those cellular processes that have been experimentally observed to disrupt homeostasis in normal epidermis. Numerical simulations demonstrate that the loss of adhesiveness of the melanoma cells both to the basal laminae, caused by deregulation mechanisms of adherent junctions, and to adjacent keratynocytes, consequent to a downregulation of E-cadherin, are the fundamental biomechanical features for promoting tumour initiation. Finally, the authors provide the mathematical proof of a long wavelength instability of the tumour front during the early stages of melanoma invasion. These results open the perspective to correlate the early morphology of a growing melanoma with the biomechanical characteristics of its micro-environment.

Basement membranes in development and disease

Basement membranes (BMs) are specializations of the extracellular matrix that act as key mediators of development and disease. Their sheet like protein matrices typically serve to separate epithelial or endothelial cell layers from underlying mesenchymal tissues, providing both a biophysical support to overlying tissue as well as a hub to promote and regulate cell-cell and cell-protein interactions. In the latter context, the BM is increasingly being recognized as a mediator of growth factor interactions during development. In this review, we discuss recent findings regarding the structure of the BM and its roles in mediating the normal development of the embryo, and we examine congenital diseases affecting the BM which impact embryonic development and health in later life.

Dystrophic epidermolysis bullosa: pathogenesis and clinical features

Dystrophic epidermolysis bullosa (DEB) is relatively well understood. Potential therapies are in development. This article describes the pathogenesis and clinical features of DEB. It also describes therapeutic options and the future of molecular therapies.

Design and validation of a conformation-sensitive capillary electrophoresis system for mutation identification of the COL7A1 gene with automated peak comparison

Dystrophic epidermolysis bullosa is a heritable skin disease in which blisters occur because of a defect in type VII collagen resulting from mutations in the COL7A1 gene that is composed of 118 exons. Although a few mutations are specific to certain populations owing to founder effects, and although a few mutational hotspots exist, most mutations are unique to families and can be found scattered throughout the entire COL7A1 gene. This emphasizes the need for a sensitive, reliable, and efficient mutation scanning technique. Therefore, we developed a conformation-sensitive capillary electrophoresis (CSCE) system for COL7A1 mutation scanning. Here we report on the design and validation of this system. The CSCE technique is based on the principle of heteroduplex formation when polymerase chain reaction-amplified DNA fragments containing heterozygous sequence changes are slowly reannealed. These fluorescently labeled fragments have different migration characteristics and can be detected on a multi-capillary automated sequencer. Validation was performed by analysis of 29 known COL7A1 sequence changes, covering 33% of amplicons. After optimization of the conditions, all 29 sequence changes were detected by the CSCE system, irrespective of length or CG-content of amplicons and position of sequence changes, reflecting an analytical sensitivity of 90.2-100% (95% confidence interval). We conclude that this CSCE system is a rapid, reliable, cost-effective, and highly sensitive way of mutation scanning for COL7A1 in a molecular genetics service laboratory.

Forty-two novel COL7A1 mutations and the role of a frequent single nucleotide polymorphism in the MMP1 promoter in modulation of disease severity in a large European dystrophic epidermolysis bullosa cohort

BACKGROUND

Dystrophic epidermolysis bullosa (DEB) is a severe genetic skin blistering disorder caused by mutations in the gene COL7A1, encoding collagen VII. Recently, the MMP1 promoter single nucleotide polymorphism (SNP) rs1799750, designated as 1G 2G, was shown to be involved in modulation of disease severity in patients with recessive DEB (RDEB), and was proposed as a genetic modifier.

OBJECTIVES

To identify the molecular basis of DEB in 103 individuals and to replicate the results of the MMP1 promoter SNP analysis in an independent patient group, as verification is necessary in such a rare and heterogeneous disorder.

METHODS

To determine the molecular basis of the disease, we performed COL7A1 mutation screening, reverse transcription-polymerase chain reaction (PCR) and real-time quantitative PCR. The status of the MMP1 SNP was analysed by PCR and restriction enzyme digestion and verified by sequencing.

RESULTS

We disclosed 42 novel COL7A1 mutations, including the first large genomic deletion of 4 kb affecting only the COL7A1 gene, and three apparently silent mutations affecting splicing. Even though the frequency of the high-risk allele was increased in patients with RDEB, no statistically significant correlation between disease severity and genotype could be made. Also, no correlation was observed with development of squamous cell carcinoma, a severe complication of DEB.

CONCLUSIONS

Taken together, the results suggest that the MMP1 SNP is not the sole disease modifier in different forms of DEB, and other genetic and environmental factors contribute to the clinical phenotype.

Supramolecular interactions in the dermo-epidermal junction zone: anchoring fibril-collagen VII tightly binds to banded collagen fibrils

The dermis and the epidermis of normal human skin are functionally separated by a basement membrane but, together, form a stable structural continuum. Anchoring fibrils reinforce this connection by insertion into the basement membrane and by intercalation with banded collagen fibrils of the papillary dermis. Structural abnormalities in collagen VII, the major molecular constituent of anchoring fibrils, lead to a congenital skin fragility condition, dystrophic epidermolysis bullosa, associated with skin blistering. Here, we characterized the molecular basis of the interactions between anchoring fibrils and banded collagen fibrils. Suprastructural fragments of the dermo-epidermal junction zone were generated by mechanical disruption and by separation with magnetic Immunobeads. Anchoring fibrils were tightly attached to banded collagen fibrils. In vitro binding studies demonstrated that a von Willebrand factor A-like motif in collagen VII was essential for binding of anchoring fibrils to reconstituted collagen I fibrils. Since collagen I and VII molecules reportedly undergo only weak interactions, the attachment of anchoring fibrils to collagen fibrils depends on supramolecular organization of their constituents. This complex is stabilized in situ and resists dissociation by strong denaturants.

Differential localization profile of Fras1/Frem proteins in epithelial basement membranes of newborn and adult mice

The Fras1/Frem gene family encodes for structurally similar proteins of the extracellular matrix, functionally correlated with embryonic dermal-epidermal adhesion as deduced from the appearance of sub-epidermal blisters in mouse mutants compromising the function of Fras1, Frem1 and Frem2 proteins. Mutations in the human counterparts FRAS1 and FREM2 have been detected in patients suffering from Fraser syndrome. So far, Fras1/Frem proteins have been shown to be strictly colocalized in the sublamina densa of mouse epithelial basement membranes during development. Here, we focused on the characterization of the localization pattern of the aforementioned proteins, in various parts of the adult mouse skin as well as a range of organs and tissues. Frem3 was present in a broad range of epithelial basement membranes where Fras1, Frem1 and Frem2 were missing. The localization profile of Frem3 coincided with that of collagen VII in all skin basement membranes but differed in that Frem3 was additionally found in the basement membrane of several internal epithelia, where collagen VII was absent. Fras1 and Frem2 were colocalized with Frem3 in the basement membrane of certain skin parts, underlying the thin-layer, of rapidly proliferating keratinocytes, whereas Frem1 was detected only in the basement membrane of the tail. The localization pattern of Fras1 and Frem2 was indistinguishable, while both proteins along with Frem3 could be detected even in the absence of Frem1.

[Localised de novo dominant dystrophic epidermolysis bullosa]

INTRODUCTION

Dystrophic epidermolysis bullosa is a hereditary heterogeneous blistering disease. Clinical examination and additional tests are not always sufficient to identify the subtype or mode of transmission. We describe a case of de novo dominant inherited dystrophic epidermolysis bullosa localised strictly to the knees.

CASE REPORT

A 3-year-old boy presented symmetrical lesions on the anterior aspect of the knees since starting to walk. No nail, dental or mucous dystrophy was observed and the parents presented no clinical abnormalities. Optical microscopy, electron microscopy and immunofluorescence analysis suggested dystrophic epidermolysis bullosa. The genealogical tree allowed no distinction between the dominant de novo and mitis recessive forms. Genetic analysis identified a missense G 1776W mutation at exon 61 of gene COL 7A1 in the child's DNA but not the parents'.

DISCUSSION

Dystrophic epidermolysis bullosa may present in generalized or localized forms and the disease may be inherited in either autosomal dominant or recessive mode. Genetic analysis shows mutations in COL 7A1. While the clinical features often allow different types to be distinguished when the parents do not have the disease (with the recessive forms being more severe), genetic analysis is essential to confirm the mode of inheritance. In the dominant forms, and more recently in recessive cases, glycine substitutions have been implicated, although the precise role of glycine substitution has yet to be clarified. Localised involvement of the skin alone, as seen in our case report, is very rare.

CONCLUSION

Genetic analysis is important for genetic counselling and determination of risk of recurrence.

The Fras1/Frem family of extracellular matrix proteins: structure, function, and association with Fraser syndrome and the mouse bleb phenotype

Fras1 and the structurally related proteins Frem1, Frem2, and Frem3, comprise a novel family of extracellular matrix proteins, which localize in a similar fashion underneath the lamina densa of epithelial basement membranes. They are involved in the structural adhesion of the skin epithelium to its underlying mesenchyme. Deficiency in the individual murine Fras1/Frem genes gives rise to the bleb phenotype, which is equivalent to the human hereditary disorder Fraser syndrome, characterized by cryptophthalmos (hidden eyes), embryonic skin blistering, renal agenesis, and syndactyly. Recent studies revealed a functional cooperation between the Fras1/Frem gene products, in which Fras1, Frem1 and Frem2 are simultaneously stabilized at the lowermost region of the basement membrane by forming a macromolecular ternary complex. Loss of any of these proteins results in the collapse of the protein assembly, thus providing a molecular explanation for the highly similar phenotypic defects displayed by the respective mutant mice. Here, we summarize the current knowledge regarding the structure, function, and interplay between the proteins of the Fras1/Frem family and further propose a possible scenario for the evolution of the corresponding genes.

Development of Tissue-Targeting Hemagglutinating Virus of Japan Envelope Vector for Successful Delivery of Therapeutic Gene to Mouse Skin

We report a novel strategy for constructing a tissue-targeting hemagglutinating virus of Japan (HVJ; Sendai virus) envelope vector (HVJ-E), and its application in gene therapy of a mouse model of genetic skin disease. Chimeric genes encoding viral F protein and green fluorescent protein (GFP) were constructed on the basis of various deletion mutants. The product of one chimeric gene, containing signal peptide, transmembrane domain, and the cytoplasmic tail of F protein, was transported to the cell surface and incorporated into new viruses released from HVJ-infected LLC-MK2 cells. For tissue targeting, in the preceding construct GFP was replaced with single-chain antibody (scFv) against mouse desmoglein 3 (mDsg3), a desmosomal cadherin found in basal layer keratinocytes of the skin. HVJ encoding scFv-F chimeric protein bound to mDsg3-coated plates much more efficiently than did wild-type HVJ. When chimeric HVJ was injected into a skin blister of a mouse model of epidermolysis bullosa, in which defective expression of type VII collagen results in a failure to secure epidermis to the underlying dermis, viral F protein expression was detected in most of the basal keratinocytes. Furthermore, chimeric HVJ-E introduced type VII collagen expression more efficiently compared with wild-type HVJ in basal keratinocytes of type VII collagen-deficient mouse skin, resulting in efficient amelioration of the genetic defect. Thus, a novel tissue-targeting HVJ-E could be used to successfully target epidermal keratinocytes both in vitro and in vivo.

Ultrastructural localization of Fras1 in the sublamina densa of embryonic epithelial basement membranes

Fras1 is the first identified member of a protein family comprising Fras1 and the related extracellular matrix proteins Frem1, Frem2 and Frem3. Mutations in Fras1, Frem1 and Frem2 have been associated with the bleb phenotype in mouse, whereas mutations in the human orthologs FRAS1 and FREM2 have been implicated in the pathogenesis of the human Fraser syndrome. Bleb mutant mice are characterized by embryonic sub-epidermal blistering, unilateral or bilateral renal agenesis or dysgenesis, cutaneous syndactyly and fused eyelids. As revealed by immunofluorescence, Fras1 co-localizes with the markers of epithelial basement membranes and is ultrastructurally detected underneath the lamina densa of embryonic mouse epithelia. Since the loss of Fras1 mainly affects the cohesiveness of the embryonic skin basement membrane with its underlying mesenchyme, we compared here the ultrastructural localization of Fras1 in the dermal-epidermal junction and in the basement membrane of other embryonic epithelia that do not show any overt phenotype using preembedding immunocytochemistry. Fras1 immunoreactivity was detected in all epithelia examined, within the sublamina densa adjacent to stromal tissue, as clustered gold/silver enhanced depositions, usually attached to anchoring fibrils. Interestingly, clusters corresponding to Fras1 were frequently detected in close proximity to mesenchymal cells, indicating that Fras1 could serve as a direct link between the sublamina densa and mesenchyme. The localization of Fras1 is consistent with previous results indicating that Fras1 exerts its function below the lamina densa and that Fras1 displays the same localization pattern in all epithelial basement membranes.

Patients with recessive dystrophic epidermolysis bullosa develop squamous-cell carcinoma regardless of type VII collagen expression

Recent data suggest that individuals with recessive dystrophic epidermolysis bullosa (RDEB) only develop squamous-cell carcinoma (SCC) in the presence of the NC1 domain of type VII collagen. This conclusion was based on experimental work in which cryosections of SCCs from 10 people with RDEB all showed positive type VII collagen immunostaining and observations in a murine model of SCC development in which tumors only occurred using keratinocytes from RDEB subjects that expressed detectable levels of the NC1 domain of the type VII collagen protein. To assess whether the clinical interpretation was valid in another cohort of RDEB patients, we examined expression of type VII collagen in 17 SCC tumors excised from 11 patients. Indirect immunofluorescent staining of SCC cryosections and Western blotting of cultured keratinocyte lysates identified two RDEB individuals who did not express detectable levels of type VII collagen. Mutation analysis revealed that these two patients harbor compound heterozygous nonsense mutations within the region of the COL7A1 gene encoding the NC1 domain. These data suggest that individuals with RDEB can develop SCC regardless of type VII collagen expression and that additional factors have a role in explaining the high incidence of tumors complicating this genodermatosis.

Spatiotemporal distribution of Fras1/Frem proteins during mouse embryonic development

The Fras1/Frem gene family encodes for structurally similar, developmentally regulated extracellular matrix proteins. Mutations in Fras1, Frem1 and Frem2 have been identified in different classes of mouse bleb mutants, while defects in the human orthologs FRAS1 and FREM2 are causative for Fraser syndrome. The hallmark phenotypic feature of bleb mice is embryonic skin blistering due to dermal-epidermal detachment. The similarity of the phenotypic characteristics among the bleb mouse mutants, together with the fact that Fras1/Frem proteins are co-localized in embryonic epithelial basement membranes, suggest that they operate in a common pathway. Here, we report for the first time the immunofluorescence pattern of Frem3 and provide a comparative analysis of the spatiotemporal localization of all Fras1/Frem proteins during mouse embryonic development. We demonstrate their overall co-localization in embryonic epithelial basement membranes, with emphasis on areas of phenotypic interest such as eyelids, limbs, kidneys, lungs and organs of the gastrointestinal tract and the central nervous system. We further studied collagen VII, impairment of which produces dystrophic epidermolysis bullosa, a postnatal skin blistering disorder. We show that basement membrane levels of collagen VII rise at late embryonic life, concomitant with descending Fras1/Frem immunolabeling.

Molecular and diagnostic aspects of genetic skin fragility

Genetic syndromes with skin fragility represent a heterogeneous group of very rare disorders caused by mutations in genes encoding proteins or protein subunits important for the mechanical resistance of keratinocytes and for cell-cell or cell-extracellular matrix adhesion. The common symptoms are skin blistering or peeling, with various degrees of severity and distribution, ranging from localized to generalized forms. Associated features include involvement of skin annexes, mucous membranes, teeth, muscles or the digestive tract. Morphological investigation of skin samples provides evidence for the tissue level of blister formation, while immunostainings may reveal defective proteins, providing clues concerning the genetic origin of the disease. Extensive mutation analysis and subsequent identification of new gene defects provide accurate diagnostics, and lead to better understanding of the functions of the respective proteins, with the potential for new therapeutic strategies.

Expanding the COL7A1 Mutation Database: Novel and Recurrent Mutations and Unusual Genotype – Phenotype Constellations in 41 Patients with Dystrophic Epidermolysis Bullosa

Dystrophic epidermolysis bullosa (DEB), a heterogeneous hereditary skin disorder characterized by trauma-induced blistering and scarring, affects thousands of families worldwide. The clinical manifestations extend from minor nail dystrophy to severe life-threatening blistering, making early molecular diagnosis and prognostication of utmost importance for the affected families. DEB is caused by mutations in the COL7A1 gene encoding collagen VII in the skin. Molecular diagnostics and genotype-phenotype correlations in DEB remain complex owing to the gene structure, large variety of mutations, high rate of novel mutations, complex protein structure and assembly, and the heterogeneity of phenotypes. Here, we report an efficient strategy for COL7A1 mutation detection using direct automated DNA sequencing and implementation of software tools. With this approach, COL7A1 mutations of 41 DEB families were disclosed. Twenty-four mutations were novel and two recurrent. Elucidation of biological consequences of the mutations helped define disease mechanisms, but also revealed several unusual genotypic and/or phenotypic constellations, which impeded the diagnostics and prognostication. In addition, the studies disclosed a de novo mutation in recessive DEB and two new polymorphisms in the COL7A1 gene.

Developmental roles of the BMP1/TLD metalloproteinases

The astacin family (M12A) of the metzincin subclan MA(M) of metalloproteinases has been detected in developing and mature individuals of species that range from hydra to humans. Functions of this family of metalloproteinase vary from digestive degradation of polypeptides, to biosynthetic processing of extracellular proteins, to activation of growth factors. This review will focus on a small subgroup of the astacin family; the bone morphogenetic protein 1 (BMP1)/Tolloid (TLD)-like metalloproteinases. In vertebrates, the BMP1/TLD-like metalloproteinases play key roles in regulating formation of the extracellular matrix (ECM) via biosynthetic processing of various precursor proteins into mature functional enzymes, structural proteins, and proteins involved in initiating mineralization of the ECM of hard tissues. Roles in ECM formation include: processing of the C-propeptides of procollagens types I-III, to yield the major fibrous components of vertebrate ECM; proteolytic activation of the enzyme lysyl oxidase, necessary to formation of covalent cross-links in collagen and elastic fibers; processing of NH2-terminal globular domains and C-propeptides of types V and XI procollagen chains to yield monomers that are incorporated into and control the diameters of collagen type I and II fibrils, respectively; processing of precursors for laminin 5 and collagen type VII, both of which are involved in securing epidermis to underlying dermis; and maturation of small leucine-rich proteoglycans. The BMP1/TLD-related metalloproteinases are also capable of activating the vertebrate transforming growth factor-beta (TGF-beta)-like "chalones" growth differentiation factor 8 (GDF8, also known as myostatin), and GDF11 (also known as BMP11), involved in negative feedback inhibition of muscle and neural tissue growth, respectively; by freeing them from noncovalent latent complexes with their cleaved prodomains. BMP1/TLD-like proteinases also liberate the vertebrate TGF-beta-like morphogens BMP2 and 4 and their invertebrate ortholog decapentaplegic, from latent complexes with the vertebrate extracellular antagonist chordin and its invertebrate ortholog short gastrulation (SOG), respectively. The result is formation of the BMP signaling gradients that form the dorsal-ventral axis in embryogenesis. Thus, BMP1/TLD-like proteinases appear to be key to regulating and orchestrating formation of the ECM and signaling by various TGF-beta-like proteins in morphogenetic and homeostatic events.

Type VII collagen is required for Ras-driven human epidermal tumorigenesis

Type VII collagen defects cause recessive dystrophic epidermolysis bullosa (RDEB), a blistering skin disorder often accompanied by epidermal cancers. To study the role of collagen VII in these cancers, we examined Ras-driven tumorigenesis in RDEB keratinocytes. Cells devoid of collagen VII did not form tumors in mice, whereas those retaining a specific collagen VII fragment (the amino-terminal noncollagenous domain NC1) were tumorigenic. Forced NC1 expression restored tumorigenicity to collagen VII-null epidermis in a non-cell-autonomous fashion. Fibronectin-like sequences within NC1 (FNC1) promoted tumor cell invasion in a laminin 5-dependent manner and were required for tumorigenesis. Tumor-stroma interactions mediated by collagen VII thus promote neoplasia, and retention of NC1 sequences in a subset of RDEB patients may contribute to their increased susceptibility to squamous cell carcinoma.

Construction of skin equivalents for gene therapy of recessive dystrophic epidermolysis bullosa

We have shown that retroviral vectors efficiently transfer the 9-kb collagen type VII cDNA into keratinocytes of dogs with recessive dystrophic epidermolysis bullosa (RDEB) and achieve correction of the RDEB phenotype in vitro. As a next step toward gene therapy applications, we have assessed the suitability of retroviral vectors to transduce human collagen type VII cDNA into primary human RDEB keratinocytes and generate transplantable autologous skin equivalents. The transduced RDEB keratinocytes permanently express high levels of recombinant collagen type VII that assembles into functional homotrimers readily secreted into the extracellular matrix. The recombinant collagen type VII reverts the migration and invasion potential of the transduced RDEB keratinocytes in vitro and is efficiently deposited at the dermal epidermal junction of artificial skin prepared with the reverted cells and artificial dermis made of biomaterial sponges embedded with dermal RDEB fibroblasts. Transplantable fibrin-based skin equivalents made with the transduced RDEB keratinocytes and grafted onto SCID mice either orthotopically or in accordance with the flap method generated cohesive and orderly stratified epithelia with all the characteristics of normal human epidermis, including rapid formation of anchoring fibrils. Because transplantable epithelia are routinely used to cure patients suffering from large skin or mucosal defects, the full phenotypic reversion of primary RDEB epidermal clonogenic cells mediated by recombinant retroviral vectors opens new perspectives in the long-term treatment of genodermatoses.