Intracytoplasmic retention of type VII collagen and dominant dystrophic epidermolysis bullosa: reversal of defect following cessation of or marked improvement in disease activity

Self-improving dystrophic epidermolysis bullosa with a novel heterozygous missense variant in the COL7A1 gene in a Taiwanese family

Self-improving dystrophic epidermolysis bullosa (DEB) is a genodermatosis that is inherited autosomal dominantly or recessively, and its clinical symptoms may improve or subside spontaneously. Herein, we report a case of self-improving DEB with COL7A1 p.Gly2025Asp variant. The diagnosis was made through histopathological, electron microscopic examination, and genetic testing. The same variant is also noted on his father, who presents with dystrophic toenails without any blisters. This study highlights that idiopathic nail dystrophy could be linked to congenital or hereditary disease. Furthermore, we conducted a review of the literature on the characteristics of reported cases of self-improving DEB with a personal or family history of nail dystrophy. The results supported our findings that nail dystrophy may be the sole manifestation in some family members. We suggest that individuals suffering from idiopathic nail dystrophy may seek genetic counselling when planning pregnancy to early evaluate the potential risk of hereditary diseases.

Self-improving dystrophic epidermolysis bullosa: First report of clinical, molecular, and genetic characterization of five patients from Southeast Asia

Self-improving dystrophic epidermolysis bullosa is a rare subtype of dystrophic epidermolysis bullosa (DEB) characterized by significant improvement in skin fragility within the first few years of life. Genetic inheritance has previously been reported as autosomal dominant or recessive with both forms harboring mutations in COL7A1. To date, there have been no reports of this rare clinical entity from various Southeast Asian ethnicities. Here, we describe the clinical and molecular features of five patients from the Southeast Asia region who presented with predominantly acral-distributed blisters and erosions in the first few days of life. Blistering resolved over several months, without appearance of new blisters. By immunofluorescence, intraepidermal retention of Type VII collagen was observed in all patient skin biopsies when investigated with antibody staining. Genetic analysis of four patients revealed pathogenic variants in COL7A1 which have not been previously reported. The clinical diagnosis in these rare patients is confirmed with molecular histology and genetic characterization.

Intraepidermal Type VII Collagen by Immunofluorescence Mapping: A Specific Finding for Bullous Dermolysis of the Newborn

BACKGROUND

Bullous dermolysis of the newborn (BDN) is a subtype of dystrophic epidermolysis bullosa (DEB) characterized by skin fragility and blister formation at birth that typically resolves within the first year of life. Abnormal intraepidermal retention of type VII collagen (C7) has been reported as a characteristic feature of BDN, but few studies have investigated the specificity of this finding.

METHODS

We retrospectively reviewed pathology reports of patients diagnosed with DEB using immunofluorescence mapping from January 2001 to January 2015. For cases describing intraepidermal accumulation of C7, we collected information on patient characteristics, including genetic testing results, clinical outcome, and concurrent electron microscopy findings, where available.

RESULTS

Of the 143 cases of DEB with immunofluorescence mapping, eight patients had intracytoplasmic epidermal retention of C7. Of these eight patients, two were lost to follow-up, four had complete resolution of bullae, and two had marked improvement with rare residual bullae. Concurrent electron microscopic findings available for three patients were consistent with BDN.

CONCLUSIONS

Our review of immunofluorescence mapping findings in patients with DEB found that 5.6% had abnormal intracytoplasmic epidermal retention of C7, a finding previously reported in BDN. All such patients with clinical outcomes available had resolution or marked improvement of bullae, consistent with clinical outcomes expected in BDN.

Antisense Oligonucleotide-mediated Exon Skipping as a Systemic Therapeutic Approach for Recessive Dystrophic Epidermolysis Bullosa

The "generalized severe" form of recessive dystrophic epidermolysis bullosa (RDEB-gen sev) is caused by bi-allelic null mutations in COL7A1, encoding type VII collagen. The absence of type VII collagen leads to blistering of the skin and mucous membranes upon the slightest trauma. Because most patients carry exonic point mutations or small insertions/deletions, most exons of COL7A1 are in-frame, and low levels of type VII collagen already drastically improve the disease phenotype, this gene seems a perfect candidate for antisense oligonucleotide (AON)-mediated exon skipping. In this study, we examined the feasibility of AON-mediated exon skipping in vitro in primary cultured keratinocytes and fibroblasts, and systemically in vivo using a human skin-graft mouse model. We show that treatment with AONs designed against exon 105 leads to in-frame exon 105 skipping at the RNA level and restores type VII collagen protein production in vitro. Moreover, we demonstrate that systemic delivery in vivo induces de novo expression of type VII collagen in skin grafts generated from patient cells. Our data demonstrate strong proof-of-concept for AON-mediated exon skipping as a systemic therapeutic strategy for RDEB.

Dystrophic epidermolysis bullosa: a review

Dystrophic epidermolysis bullosa is a rare inherited blistering disorder caused by mutations in the COL7A1 gene encoding type VII collagen. The deficiency and/or dysfunction of type VII collagen leads to subepidermal blistering immediately below the lamina densa, resulting in mucocutaneous fragility and disease complications such as intractable ulcers, extensive scarring, malnutrition, and malignancy. The disease is usually diagnosed by immunofluorescence mapping and/or transmission electron microscopy and subsequently subclassified into one of 14 subtypes. This review provides practical knowledge on the disease, including new therapeutic strategies.

Recessive bullous dermolysis of the newborn in preterm siblings with a missense mutation in type VII collagen

Bullous dermolysis of the newborn is a dominant or recessive inherited subtype of dystrophic epidermolysis bullosa characterized by the tendency to spontaneously stop blistering within the first months of life. Here we report two siblings with bullous dermolysis of the newborn who were born prematurely and have a novel recessive mutation, p.Pro2259Leu, in the triple helix domain of type VII collagen. We discuss the possible relationship between genotype and prematurity and clinical manifestations in these patients.

Bullous dermolysis of the newborn: four new cases and clinical review

Bullous dermolysis of the newborn (BDN) is a subtype of dystrophic epidermolysis bullosa caused by mutations in type VII collagen resulting in disorganized anchoring fibrils and sublamina densa blister formation. Disease activity is usually confined to the first year of life, with restoration of physiologic type VII collagen localization. We report four new cases of BDN and review the utility of immunofluorescence mapping in establishing the diagnosis.

Mutation analysis and characterization of COL7A1 mutations in dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is inherited in both an autosomal dominant DEB and autosomal recessive manner RDEB, both of which result from mutations in the type VII collagen gene (COL7A1). To date, 324 pathogenic mutations have been detected within COL7A1 in different variants of DEB; many mutations are clustered in exon 73 (10.74%) which is close to the 39 amino acid interruption region. Dominant dystrophic epidermolysis bullosa usually involves glycine substitutions within the triple helix of COL7A1 although other missense mutations, deletions or splice-site mutations may underlie some cases. In recessive dystrophic epidermolysis bullosa, the mutations include nonsense, splice site, deletions or insertions, 'silent' glycine substitutions within the triple helix and non-glycine missense mutations within the triple helix or non-collagenous NC-2 domain. The nature of mutations in COL7A1 and their positions correlate reasonably logically with the severity of the resulting phenotypes.

Transient bullous dermolysis of the newborn in three generations

Transient bullous dermolysis of the newborn (TBDN) is a rare form of dystrophic epidermolysis bullosa (DEB) that presents with neonatal skin blistering but which usually improves markedly during early life or even remits completely. Skin biopsies reveal abnormal intraepidermal accumulation of type VII collagen which results in poorly constructed anchoring fibrils and a sublamina densa plane of blister formation. The reason for the spontaneous clinical improvement is not known, but there is a gradual recovery in type VII collagen secretion from basal keratinocytes to the dermal-epidermal junction, with subsequent improvement or correction of anchoring fibril morphology. In this report, we describe TBDN occurring in three generations of the same family. Blistering occurred only during the first few months after birth, and all affected individuals were found to have a heterozygous glycine substitution mutation in exon 45 of the type VII collagen gene, COL7A1, designated G1522E. This mutation represents the third report of a pathogenic COL7A1 mutation in TBDN. Despite limited understanding of the disease mechanism in TBDN, this distinct form of DEB is important to recognize as it typically has a benign and self-limiting course. However, not all cases of DEB associated with intraepidermal type VII collagen are 'transient'. Genetic counselling in such patients therefore should be guarded until the pathophysiology of TBDN is better understood.

Transcriptional Control of the Mouse Col7a1 Gene in Keratinocytes: Basal and Transforming Growth Factor-β Regulated Expression

Anchoring fibrils at the cutaneous basement membrane zone of the stratified squamous epithelia are essential to maintaining skin integrity, as absence of these structures leads to the chronic blistering disease, dystrophic epidermolysis bullosa. Type VII collagen, the major component of anchoring fibrils, is synthesized primarily by basal keratinocytes and to a lesser degree by dermal fibroblasts. To elucidate the transcriptional control elements of the type VII collagen gene (Col7a1), 3 kb of 5' flanking sequence of the mouse gene was cloned, sequenced, and fused to the chloramphenicol acetyltransferase reporter gene. Promoter deletion analyses revealed that 560 bp of Col7a1 5' flanking sequence was sufficient and necessary for basal level of transcription in cultured murine keratinocytes. Mutagenesis of DNA sequences with similarity to consensus binding sites for transcription factors, including Sp1/Sp3, AP2, AP1, and Smads, within the p-560Col7a1 promoter/chloramphenicol acetyltransferase construct, coupled with DNA binding assays, revealed the importance of these sites for basal Col7a1 expression. The effect of transforming growth factor beta, an activator of Col7a1 expression in keratinocytes and dermal fibroblasts, was examined using the same Col7a1 promoter/chloramphenicol acetyltransferase constructs. These analyses demonstrated that transforming growth factor beta1 stimulation of Col7a1 transcription is dependent on a putative interaction between Smads and AP1. Interestingly, the Smad-like binding site was essential for both basal and transforming growth factor beta1 stimulated Col7a1 transcription. Collectively, these findings attest to the complex regulation of Col7a1 transcription in epidermal keratinocytes.

Initial experience with a composite autologous skin substitute

Patients with large burns are surviving in increasing numbers, but there remains no durable and reliable permanent skin replacement. After initial favorable small animal experiments, a pilot trial of a composite skin replacement was performed in patients with massive burns. A composite skin replacement (CSR) was developed by culturing autologous keratinocytes on acellular allogenic dermis. This material was engrafted in patients with massive burns and compared to a matched wound covered with split thickness autograft. With human studies committee approval, 12 wounds in 7 patients were grafted with CSR while a matched control wound was covered with split thickness autograft. These 7 children had an average age of 6.4+/-1.4 yr and burn size of 75.9+/-5.0% of the body surface. Nine wounds were acute burns and three were reconstructive releases. Successful vascularization at 14 days averaged 45.7+/-14.2% (range 0-100%) in the study wounds and 98+/-1% (range 90-100%) in the control sites (P<0.05). Reduced CSR take seemed to correlate with wound colonization. All children survived. While CSR did not engraft with the reliability of standard autograft, this pilot experience is encouraging in that successful wound closure with this material is possible, if not yet dependable. It is hoped that a more mature epidermal layer may facilitate engraftment, and trials to explore this possibility are in progress.

Basement membrane zone remodeling during appendageal development in human fetal skin. The absence of type VII collagen is associated with gelatinase-A (MMP2) activity

Epithelial cell adhesion, migration, and differentiation are controlled by interactions at the basement membrane zone (BMZ). Type VII collagen is the major collagenous component of anchoring fibrils that are essential for the attachment of the epidermis to the dermis. Gelatinase A (MMP-2) is believed to be necessary for the degradation of type VII collagen. In this study we have examined the in vivo distribution of type VII collagen and gelatinase A (Gel A) in the developing human epidermis and its appendages. At 13-15 wk of gestation a marked decrease in type VII collagen immunoreactivity was seen in the BMZ surrounding invading appendageal buds; however, type VII collagen mRNA was strongly expressed in the budding epidermal keratinocytes adjacent to the BMZ. At these stages, Gel A-positive mesenchymal-like cells were found scattered throughout the stroma with numerous Gel A-containing cells in direct contact with the developing appendageal buds. In situ zymography was used to show Gel A-activity in vivo. Gel A-mediated lysis was present at the interface between the appendageal buds and the underlying BMZ. By 20-25 wk of gestational age, immunostaining for type VII collagen protein was absent from the BMZ surrounding the distal portion of invading appendageal epithelial cords of both hair follicles and sweat glands. In contrast, type VII collagen mRNA was present in the basal keratinocytes adjacent to the BMZ surrounding the distal portion of these invading appendageal epithelial cords. At these stages Gel A-positive cells were present in the stroma directly adjacent to the distal portion of developing appendageal cords that lacked type VII collagen. In situ zymography showed zones of Gel A-mediated stromal lysis at the distal portion of developing appendageal cords. Interestingly, no differences were seen in the distribution of type IV collagen in the BMZ of both budding and resting fetal epidermis. These observations suggest that the absence of type VII collagen protein correlates directly with the presence of Gel A-activity at the BMZ. Gel A appears to play a major role in appendageal development and contributes to remodeling of the BMZ during fetal skin morphogenesis.

In vitro characteristics of early epidermal progenitors isolated from keratin 14 (K14)-deficient mice: insights into the role of keratin 17 in mouse keratinocytes

Keratin 14 (K14) is believed to play a pivotal role in the maintenance of epidermal cell shape and contributing to their resistance to mechanical trauma, thereby protecting the cells from lysing. Mice harboring a K14 null mutation produce phenotypic characteristics of epidermolysis bullosa simplex, a skin blistering disease (Lloyd et al., 1995, J Cell Biol 129:1329-1344). K14 null animals die several days after birth, making the detailed study of the consequences of K14 deletion in epidermal cell physiology in vivo particularly difficult. To define the consequences of K14 loss more precisely, we used an in vitro approach by isolating K14-/- cell lines and studying epidermal differentiation in the K14 null background. Several keratinocyte cell lines were generated from 6-day-old mice homozygous for a targeted disruption of the K14 gene (lines designated MKC-5, MKC-23, and MKC-33) and from their wild-type littermates (lines designated MKC-1 and MKC-6). Under low Ca2+ (0.066 mM) and low serum (2%) conditions, both wild-type and mutant cells were able to adhere to collagen type I-coated dishes and form epithelial sheets. They maintained basal epidermal cell characteristics and continued to proliferate without obvious signs of terminal differentiation; however, K14-/- cells proliferated two- to threefold slower than did their wild-type counterparts. The distribution of K5, the natural partner of K14, at the immunofluorescence level was also normal looking in the K14-/- MKC-5 cells, but with fewer filaments detectable, consistent with the approximately 20% reduction in K5 detectable on immunoblots. K17 expression was increased approximately 40% in the K14-/- cells. The levels of K15 and K16 were not different in the MKC-5 and MKC-6 cell lines, suggesting that they are not contributing factors to the stabilization of K5 in the mutant cells. K8, K19, and vimentin were undetectable in both lines. Both MKC-5 and MKC-6 cells underwent morphological and biochemical differentiation in response to a switch to high Ca2+ medium. These findings indicate that K14-/- MKC-5 cells preserve the morphological, biochemical, and physiological characteristics of epidermal cells for an extensive period of time in vitro, likely due to the compensatory expression of K17. The culturing capacity of these cells also permits the analysis of keratinocyte growth and differentiation in the absence of K14. In addition, the culturing methods we describe will be useful for the generation of epithelial cell lines from a wealth of increasingly available knockout mouse strains with early lethality.

Three new cases of transient bullous dermolysis of the newborn

We present 3 new patients with transient bullous dermolysis of the newborn (TBDN), which is a form of dystrophic epidermolysis bullosa. TBDN may be diagnosed by electron microscopy showing a sublamina densa cleavage; immunofluorescence antigenic mapping demonstrating bullous pemphigoid antigen, laminin- 1, and type IV collagen along the epidermal roof of subepidermal clefts; and indirect immunofluorescence with monoclonal antibodies revealing intraepidermal type VII collagen. Although intraepidermal type VII collagen has been reported in other forms of dystrophic epidermolysis bullosa, we believe that the presence of type VII collagen in a striking intraepidermal granular array is a finding unique to TBDN. Our cases demonstrate the importance of immunodermatologic studies in the diagnosis of bullous disorders that are seen at birth because accurate diagnosis carries prognostic implications. This variant of epidermolysis bullosa, in contrast to other forms of dystrophic epidermolysis bullosa, is a benign, self-limited disease.

Intraepidermal expression of basement membrane components in the lesional skin of a patient with dystrophic epidermolysis bullosa

The patient was a 15-year-old male. Since birth, he had developed blistering and erosion of the skin. Biopsy skin specimen of the bullous lesions showed subepidermal blister formation. Electron microscopic examination revealed that tissue separation had occurred at the sublamina densa level. By indirect immunofluorescence using antibodies specific for alpha 6 integrin, laminin 5, type IV collagen, and type VII collagen, all of these basement membrane components were detected as coarse granular intracytoplasmic deposits only in the basal and suprabasal cells of the blister roof. In the non-blistered regions, these basement membrane components showed a linear pattern similar to that seen in normal skin. These findings suggest that intraepidermal expression of basement membrane components was closely related to the blister formation. The biological meaning of intraepidermal expression of basement membrane components were also discussed.

Transient bullous dermolysis of the newborn associated with compound heterozygosity for recessive and dominant COL7A1 mutations

The neonatal skin blistering disorder transient bullous dermolysis of the newborn (TBDN) heals spontaneously or improves dramatically within the first months and years of life. TBDN is characterized by subepidermal blisters, reduced or abnormal anchoring fibrils at the dermo-epidermal junction, and electron-dense inclusions in keratinocytes. These features are partly similar to those in dystrophic epidermolysis bullosa, which is caused by defects in COL7A1 gene encoding collagen VII, the main anchoring fibril protein. TBDN has been grouped separately from dystrophic epidermolysis bullosa based on the pronounced morphologic features and the self-limiting course of the disorder; however, it remains unclear whether it represents a distinct clinical entity with a single etiology. We now report a TBDN patient who is compound heterozygous for a recessive and a dominant glycine substitution mutation in COL7A1. Two point mutations caused amino acid substitutions G1519D and G2251E in the triple helical domain of collagen VII. In the heterozygous state G1519D was silent, and G2251E led to nail dystrophy, but not to skin blistering. In the proband, compound heterozygosity for the mutations caused massive, transitory retention of collagen VII in the epidermis, its reduced deposition at the basement membrane zone, and extensive dermo-epidermal separation at birth. Accordingly, TBDN keratinocytes in vitro accumulated collagen VII intracellularly in the rough endoplasmic reticulum.

Genetic basis of dominantly inherited transient bullous dermolysis of the newborn: a splice site mutation in the type VII collagen gene

Transient bullous dermolysis of the newborn (TBDN) is a blistering disease evident at birth or shortly thereafter, but the blistering tendency decreases with advancing age. The tissue separation in TBDN is below the lamina densa, and electron microscopy has revealed abnormalities in anchoring fibrils. Immunofluorescence staining demonstrates intracellular accumulation of type VII collagen. In this study, we report a G-to-C transversion mutation in the last nucleotide of intron 35 of the type VII collagen gene (COL7A1) in a family with autosomal dominant TBDN in three generations. This nucleotide substitution abolishes the obligatory consensus 3'-acceptor splice site, predicting in-frame skipping of exon 36. Thus, TBDN in this family is caused by a mutation in COL7A1, and is therefore allelic with other variants of dominant dystrophic epidermolysis bullosa.

Spontaneous disappearance of intraepidermal type VII collagen in a patient with dystrophic epidermolysis bullosa

Recently, a peculiar self-healing neonatal blistering disease has been reported, which is characterized by perinuclear stellate inclusions within basilar keratinocytes, representing abnormal retention of type VII collagen. We report a Japanese patient with this condition, in whom we studied the expression of a variety of basement membrane zone (BMZ)-related antigens. Skin biopsy specimens at 3 days of age showed abundant accumulation of both the NC-1 domain and the collagenous part of type VII collagen within the basal and suprabasal keratinocytes, in addition to patchy and weak staining along the BMZ. In contrast, at 4 years of age, when the disease activity was markedly attenuated, a second biopsy showed complete linear staining of type VII collagen along the BMZ, with no detectable intracytoplasmic deposits. Expression of other BMZ-related antigens, including laminin 5, alpha 6 and beta 4 integrins, bullous pemphigoid antigens 1 and 2, and type IV collagen, was normal in both the biopsy specimens. Our observations further confirm that the perinuclear stellate bodies seen in this peculiar condition are composed of both collagenous and non-collagenous domains of type VII collagen retained within the epidermis, and that these bodies disappear when the disease activity remits.

Assessment of sulfur mustard interaction with basement membrane components

Bis-2-chloroethyl sulfide (sulfur mustard, HD) is a bifunctional alkylating agent which causes severe vesication characterized by slow wound healing. Our previous studies have shown that the vesicant HD disrupts the epidermal-dermal junction at the lamina lucida of the basement membrane. The purpose of this study was to examine whether HD directly modifies basement membrane components (BMCs), and to evaluate the effect of HD on the cell adhesive activity of BMCs. EHS laminin was incubated with [14C]HD, and extracted by gel filtration. Analysis of the [14C]HD-conjugated laminin fraction by a reduced sodium dodecyl sulfate-polyacrylaminde gel electrophoresis (SDS-PAGE) revealed the incorporation of radioactivity into both laminin subunits and a laminin trimer resistant to dissociation in reduced SDS-PAGE sample buffer, suggesting direct alkylation and cross-linking of EHS laminin by [14C]HD. Normal human foreskin epidermal keratinocytes were biosynthetically labeled with [35S]cysteine. 35S-labeled laminin isoforms, Ae.B1e.B2e. laminin and K.B1e.B2e. laminin (using the nomenclature of Engel), fibronectin, and heparan sulfate proteoglycan were isolated by immunoprecipitation from the cell culture medium, treated with HD or ethanol as control, and then analyzed by SDS-PAGE. On reduced SDS gels, these three BMCs not treated with HD showed the typical profile of dissociated subunits. However, HD treatment caused the appearance of higher molecular weight bands indicative of cross-linking of subunits within these BMCs. The HD scavengers sodium thiosulfate and cysteine prevented the cross-linking of BMC subunits by HD. Finally, tissue culture dishes coated with laminin or fibronectin were treated with HD or ethanol as a control, and human keratinocytes were plated on the BMC-coated surfaces. After 20 h of incubation, it was observed that cell adhesion was decreased significantly on the BMC-coated surfaces treated with HD. As expected, the preincubation of HD with cysteine diminished the HD inhibition of cell adhesion. Thus, HD alkylates adhesive macromolecules of the basement membrane zone and inhibits their cell adhesive activity. These findings support the hypothesis that the alkylation of basement membrane components by HD destabilizes the epidermal-dermal junction in the process of HD-induced vesication. The failure of the HD-alkylated BMCs to support the attachment of keratinocytes might also contribute to the slow reepithelialization of the wound site which is characteristic of HD-induced blistering.

The National Epidermolysis Bullosa Registry

Since its inception in 1986, the NEBR has proved to be an excellent example of how a relatively small allocation of federal research funds for the development of a registry of cases of a single rare disease can have a major impact on the rapid expansion in the depth of knowledge of not only the disease itself but of a number of associated biologic principles, including keratinization and epithelial cell-extracellular matrix interactions. At present, the NEBR is generating extensive clinical, laboratory, and demographic data, both from cross-sectional and longitudinal perspectives, as well as establishing a centralized cell and tissue bank that will serve the scientific community at large as a valuable resource for future basic research on this oftentimes devastating genetic disease.