Pathological Mechanisms Involved in Epidermolysis Bullosa Simplex: Current Knowledge and Therapeutic Perspectives.

Epidermolysis bullosa (EB) is a clinically and genetically heterogeneous group of mechanobullous diseases characterized by non-scarring blisters and erosions on the skin and mucous membranes upon mechanical trauma. The simplex form (EBS) is characterized by recurrent blister formation within the basal layer of the epidermis. It most often results from dominant mutations in the genes coding for keratin (K) 5 or 14 proteins (KRT5 and KRT14). A disruptive mutation in KRT5 or KRT14 will not only structurally impair the cytoskeleton, but it will also activate a cascade of biochemical mechanisms contributing to EBS. Skin lesions are painful and disfiguring and have a significant impact on life quality. Several gene expression studies were accomplished on mouse model and human keratinocytes to define the gene expression signature of EBS. Several key genes associated with EBS were identified as specific immunological mediators, keratins, and cell junction components. These data deepened the understanding of the EBS pathophysiology and revealed important functional biological processes, particularly inflammation. This review emphasizes the three EBS subtypes caused by dominant mutations on either KRT5 or KRT14 (localized, intermediate, and severe). It aims to summarize current knowledge about the EBS expression profiling pattern and predicted molecular mechanisms involved and to outline progress in therapy.

Allele-specific CRISPR-Cas9 editing of dominant epidermolysis bullosa simplex in human epidermal stem cells.

Epidermolysis bullosa simplex (EBS) is a rare skin disease inherited mostly in an autosomal dominant manner. Patients display a skin fragility that leads to blisters and erosions caused by minor mechanical trauma. EBS phenotypic and genotypic variants are caused by genetic defects in intracellular proteins whose function is to provide the attachment of basal keratinocytes to the basement membrane zone and most EBS cases display mutations in keratin 5 (KRT5) and keratin 14 (KRT14) genes. Besides palliative treatments, there is still no long-lasting effective cure to correct the mutant gene and abolish the dominant negative effect of the pathogenic protein over its wild-type counterpart. Here, we propose a molecular strategy for EBS01 patient's keratinocytes carrying a monoallelic c.475/495del21 mutation in KRT14 exon 1. Through the CRISPR-Cas9 system, we perform a specific cleavage only on the mutant allele and restore a normal cellular phenotype and a correct intermediate filament network, without affecting the epidermal stem cell, referred to as holoclones, which play a crucial role in epidermal regeneration.

Negative pressure wound treatment in a neonate with epidermolysis bullosa simplex severe generalized: A case report.

Negative pressure wound treatment (NPWT) is very useful for the treatment of chronic or deep wounds and in the setting of skin grafting. Due to the need for adhesive dressings, this treatment is rarely attempted in patients with skin fragility secondary to hereditary epidermolysis bullosa (EB). We present a neonate with EB simplex, severe generalized in a critical clinical state where NPWT was successfully applied and describe the measures taken to avoid any further skin damage. This case is of clinical importance to physicians and health care staff treating patients with this rare disease where additional therapeutic measures for the treatment of chronic wounds are scarce.

An ex vivo RNA trans-splicing strategy to correct human generalized severe epidermolysis bullosa simplex.

BACKGROUND: Generalized severe epidermolysis bullosa simplex (EBS-gen sev) is a genetic blistering skin disease in which autosomal dominant mutations in either the keratin KRT5 or KRT14 genes lead to impaired function of the intermediate filament cytoskeleton in the basal epidermis. Here we present an ex vivo RNA trans-splicing-based therapeutic approach to correct the phenotype. OBJECTIVES: To correct a mutation within exon 1 of the KRT14 gene, using a 5'-trans-splicing approach, where any mutation within the first seven exons could be replaced by a single therapeutic molecule. METHODS: A therapeutic RNA trans-splicing molecule containing wild-type exons 1-7 was stably transduced into an EBS patient-derived keratinocyte line. Trans-splicing was confirmed via reverse-transcriptase polymerase chain reaction, Western blotting and immunofluorescence microscopy. Skin equivalents generated from corrected keratinocytes were grafted onto nude mice and analysed about 8 weeks post-transplantation for regular epidermal stratification, trans-splicing-induced green fluorescent protein expression and blistering. RESULTS: Transplanted skin equivalents generated from trans-splicing-corrected patient keratinocytes showed a stable and blister-free epidermis. KRT14 correction disrupted EBS-gen sev-associated proinflammatory signalling, as shown at the mRNA and protein levels. Disruption of the pathogenic feedback loop in addition to overall downregulation of KRT14 expression highlighted the effect of KRT14 correction on the EBS pathomechanism. CONCLUSIONS: Our data demonstrate that trans-splicing-mediated mRNA therapy is an effective method for the correction of dominantly inherited KRT14 mutations at the transcriptional level. This results in the rescue of the EBS-gen sev phenotype and stabilization of the epidermis in a xenograft mouse model.

Cut and Paste: Efficient Homology-Directed Repair of a Dominant Negative KRT14 Mutation via CRISPR/Cas9 Nickases.

With the ability to induce rapid and efficient repair of disease-causing mutations, CRISPR/Cas9 technology is ideally suited for gene therapy approaches for recessively and dominantly inherited monogenic disorders. In this study, we have corrected a causal hotspot mutation in exon 6 of the keratin 14 gene (KRT14) that results in generalized severe epidermolysis bullosa simplex (EBS-gen sev), using a double-nicking strategy targeting intron 7, followed by homology-directed repair (HDR). Co-delivery into EBS keratinocytes of a Cas9 D10A nickase (Cas9n), a predicted single guide RNA pair specific for intron 7, and a minicircle donor vector harboring the homology donor template resulted in a recombination efficiency of >30% and correction of the mutant KRT14 allele. Phenotypic correction of EBS-gen sev keratinocytes was demonstrated by immunofluorescence analysis, revealing the absence of disease-associated K14 aggregates within the cytoplasm. We achieved a promising safety profile for the CRISPR/Cas9 double-nicking approach, with no detectable off-target activity for a set of predicted off-target genes as confirmed by next generation sequencing. In conclusion, we demonstrate a highly efficient and specific gene-editing approach for KRT14, offering a causal treatment option for EBS.

A prospective, split-face, double-blinded, randomized study of the efficacy and safety of a fractional 1064-nm Q-switched Nd:YAG laser for photoaging-associated mottled pigmentation in Asian skin.

BACKGROUND: Laser toning using low-fluence 1064-nm Q-switched neodymium-doped yttrium aluminum laser (QSNY) has gained popularity in the treatment of photoaging-associated mottled pigmentation (PMP). However, hypopigmentation or lack of efficacy has been reported depending on the fluences used. OBJECTIVE: To compare a novel fractional 1064-nm QSNY with conventional 1064-nm QSNY for the treatment of photoaging-associated mottled pigmentary lesions except epidermal lesions of lentigines and freckles through a randomized, split-face, double-blind study. MATERIALS AND METHODS: Thirteen Asian women were treated every week for 6 weeks with fractional 1064-nm QSNY on one side of the face and conventional 1064-nm QSNY on the other side. We evaluated the pigmentation area and severity index (PSI), melanin index, erythema index, and the patient's global assessment of improvement. RESULTS: At three months post-treatment, the PSI score improved compared with baseline, by 14.48% on the conventional 1064-nm QSNY side and 21.81% on the fractional 1064-nm QSNY side. Both groups showed improvements in the melanin index. CONCLUSION: Both fractional 1064-nm QSNY and strictly low-fluence conventional 1064-nm QSNY are moderately effective against PMP and other photoaging signs. Fractional laser toning shows better subjective outcomes than conventional toning.

Development of allele-specific therapeutic siRNA for keratin 5 mutations in epidermolysis bullosa simplex.

Epidermolysis bullosa simplex (EBS) is an incurable, inherited skin-blistering disorder predominantly caused by dominant-negative mutations in the genes encoding keratins K5 or K14. RNA interference, particularly in the form of small interfering RNA (siRNA), offers a potential therapy route for EBS and related keratin disorders by selectively silencing the mutant allele. Here, using a systemic screening system based on a luciferase reporter gene assay, we have developed mutant-specific siRNAs for two independent EBS-causing missense mutations in the K5 gene (p.Ser181Pro and p.Asn193Lys). The specificity of the allele-specific inhibitors identified in the screen was subsequently confirmed at the protein level, where the lead inhibitors were shown to strongly knock down the expression of mutant proteins with negligible effect on wild-type K5 expression. In a cell-based model system, the lead inhibitors were able to significantly reverse the cytoskeletal aggregation phenotype. Overall, this approach shows promise for the treatment of EBS and paves the way for future clinical trials.

Keratin 14-null cells as a model to test the efficacy of gene therapy approaches in epithelial cells.

Skin fragility disorders caused by keratin mutations are incurable, and a better understanding of their etiology is needed to find new ways to improve and treat these conditions. The best-studied skin fragility disorder is epidermolysis bullosa simplex (EBS), an autosomal dominant condition caused by mutations in keratin 5 (K5) or K14. To analyze disease mechanisms and develop gene therapy strategies, we have used keratinocyte cell lines derived from EBS patients as model systems. Here, we describe two cell lines established from EBS patients with K14-null mutations. We analyze the responses of these cells to stress assays previously shown to discriminate between wild-type and keratin-mutant keratinocytes, to directly evaluate the efficacy of rescuing K14-null cells by supplementation with wild-type K14 complementary DNA (cDNA). The K14-null cells show elevated levels of stress correlating with reduced normal keratin function. By transfecting wild-type K14 into these cells, we demonstrate "proof of principle" that an add-back approach can significantly rescue the normal keratinocyte behavior profile. These K14-null cell lines provide a disease model for studying the effects of keratin ablation in EBS patients and to test the efficacy of gene add-back and other therapy approaches in keratinocytes.

K14 mRNA reprogramming for dominant epidermolysis bullosa simplex.

The major challenge to a successful gene therapy of autosomal dominant genetic diseases is a highly efficient and specific knock-down or repair of the disease-causing allele. In epidermolysis bullosa simplex-type Dowling-Meara (EBS-DM), a single amino acid exchange in exon 1 of the keratin 14 gene (K14) triggers a severe skin phenotype, characterized by blistering of the skin and mucous membranes after minor trauma. We chose spliceosome-mediated RNA trans-splicing to specifically replace exons 1-7 of the K14 gene. In this approach, the mutated coding region is replaced by an RNA-trans-splicing molecule (RTM) that incorporates a binding domain (BD) and the wild-type sequence of K14. Since the BD is crucial for the trans-splicing functionality, we developed a fluorescence-based RTM screen consisting of an RTM library containing random BDs. Co-transfection of the library with a target molecule enabled us to identify highly functional RTMs. The best RTMs were adapted for endogenous trans-splicing in an EBS-DM patient cell line. In this cell line, we were able to detect functional, efficient and correct trans-splicing on RNA and protein levels. Scratch assays confirmed phenotypic reversion in vitro. Owing to concomitant knock-down and repair of the mutated allele, we assume that trans-splicing is a promising tool for the treatment of autosomal dominant genetic disease.

Efficient KRT14 targeting and functional characterization of transplanted human keratinocytes for the treatment of epidermolysis bullosa simplex.

Inherited skin blistering conditions collectively named epidermolysis bullosa (EB) cause significant morbidity and mortality due to the compromise of the skin's barrier function, the pain of blisters, inflammation, and in some cases scaring and cancer. The simplex form of EB is usually caused by dominantly inherited mutations in KRT5 or KRT14. These mutations result in the production of proteins with dominant-negative activity that disrupt polymerization of intermediate filaments in the basal keratinocyte layer and result in a weak epidermal-dermal junction. The genome of adeno-associated virus (AAV) vectors can recombine with chromosomal sequence so that mutations can be corrected, or production of proteins with dominant-negative activity can be disrupted. We demonstrate a clinically feasible strategy for efficient targeting of the KRT14 gene in normal and EB-affected human keratinocytes. Using a gene-targeting vector with promoter trap design, targeted alteration of one allele of KRT14 occurred in 100% of transduced cells and transduction frequencies ranged from 0.1 to 0.6% of total cells. EBS patient keratinocytes with precise modifications of the mutant allele are preferentially recovered from targeted cell populations. Single epidermal stem cell clones produced histologically normal skin grafts after transplantation to athymic mice and could generate a sufficient number of cells to transplant the entire skin surface of an individual.

Epidermolysis bullosa in Australia and New Zealand.

This article describes the clinical services for EB in Australia and New Zealand. The history and epidemiology of EB in Australia is described. Current treatment and research achievements are described.

Epidermolysis bullosa simplex.

The prevalence of epidermolysis bullosa simplex (EBS) is estimated to be approximately 6 to 30 per 1 million live births. The disease is usually caused by missense mutations in KRT5 and KRT14, encoding keratins mostly expressed in the epidermal basal layer. Major advances in understanding of the molecular basis of EBS and other keratin disorders have led to the development of DNA-based prenatal testing.

Case of mistaken identity: bullous congenital ichthyosiform erythroderma mistaken as epidermolysis bullosa simplex.

Distinguishing clinically similar dermatologic disorders can be challenging and the differential diagnosis of a blistering eruption in the newborn period can be extensive. Several genodermatosis, such as bullous congenital ichthyosiform erythroderma (BCIE) and epidermolysis bullosa simplex (EBS), autoimmune bullous disorders, infectious diseases, sucking blisters, and bullous mastocytosis must be considered. We present a case of BCIE misdiagnosed as EBS and review characteristic clinical and histopathological features of each disorder as well as the basic approach to treatment.

Epidermolysis bullosa simplex: a paradigm for disorders of tissue fragility.

Epidermolysis bullosa (EB) simplex is a rare genetic condition typified by superficial bullous lesions that result from frictional trauma to the skin. Most cases are due to dominantly acting mutations in either keratin 14 (K14) or K5, the type I and II intermediate filament (IF) proteins tasked with forming a pancytoplasmic network of 10-nm filaments in basal keratinocytes of the epidermis and in other stratified epithelia. Defects in K5/K14 filament network architecture cause basal keratinocytes to become fragile and account for their trauma-induced rupture. Here we review how laboratory investigations centered on keratin biology have deepened our understanding of the etiology and pathophysiology of EB simplex and revealed novel avenues for its therapy.

Otorhinolaryngological and esophageal manifestations of epidermolysis bullosa.

UNLABELLED: Epidermolysis bullosa (EB) is a group of skin diseases with different clinical manifestations and varied inheritance patterns. Blisters may appear spontaneously or following minimal trauma to the skin or mucosa. AIM: this paper aims to describe the otorhinolaryngological manifestations and esophageal complications related to EB, and the experience in treating patients with esophageal stenosis secondary to this disease. MATERIALS AND METHOD: this descriptive study enrolled 60 patients with EB seen from June 1999 to December 2006 at the Head and Neck Surgery Service of X Hospital, a reference center for EB. RESULTS: the patients' mean age was 14.5 years. Twenty-eight (46.6%) were females and 32 (53.4%) were males. Eight (13.4%) were diagnosed with epidermolysis bullosa simplex, while 51 (85%) had epidermolysis bullosa dystrophica; one (1.6%) patient had one acquired EB. Lips, mouth, tongue and ears were the most frequently involved sites (32 patients - 53.3%). Dysphagia was found in 28 patients (46.6%). After esophageal dilatation the symptoms subsided. CONCLUSION: EB is a rare disease and patients must be sent for treatment at reference centers. Physicians treating patients for EB must be aware of the measures required to improve the quality of the treatment provided without putting the patients in harm's way.

Manifestações otorrinolaringológicas e esofágicas da epidermólise bolhosa / Otorhinolaryngological and esophageal manifestations of epidermolysis bullosa

Epidermólise bolhosa (EB) é um conjunto de afecções bolhosas, de caráter hereditário, com diferentes quadros clínicos e diferentes modos de transmissão genética. Os indivíduos evoluem com bolhas na pele e mucosas, que surgem espontaneamente ou após mínimos traumatismos. OBJETIVO: Descrever as manifestações otorrinolaringológicas, as complicações esofágicas relacionadas à EB e a experiência na conduta de pacientes com estenose esofágica decorrente da EB. CASUÍSTICA E MÉTODO: Estudo descritivo de 60 pacientes com EB, atendidos de 1999 a 2006, no serviço de Otorrinolaringologia e Cirurgia de Cabeça e Pescoço do Hospital X, centro de referência para EB. RESULTADOS: Dos 60 pacientes com idade média de 14,5 anos, 28 (46,6 por cento) eram mulheres e 32 (53,4 por cento) homens. Oito (13,4 por cento) tinham o diagnóstico de EB simples, 51 (85 por cento) EB distrófica e um (1,6 por cento) caso de EB adquirida. Lábios, boca, língua e pavilhão auricular foram os locais mais acometidos (32 pacientes - 53,3 por cento). Disfagia foi encontrada em 28 pacientes (46,6 por cento). Após dilatação do esôfago todos apresentaram remissão do sintoma. CONCLUSÃO: EB é uma doença rara e os pacientes devem ser encaminhados para tratamento em centros de referência. Portanto, é fundamental que os médicos envolvidos com os cuidados de pacientes com EB conheçam as condutas necessárias para melhorar a qualidade do tratamento sem prejuízos adicionais.

Epidermolysis bullosa (EB) is a group of skin diseases with different clinical manifestations and varied inheritance patterns. Blisters may appear spontaneously or following minimal trauma to the skin or mucosa. AIM: this paper aims to describe the otorhinolaryngological manifestations and esophageal complications related to EB, and the experience in treating patients with esophageal stenosis secondary to this disease. MATERIALS AND METHOD: this descriptive study enrolled 60 patients with EB seen from June 1999 to December 2006 at the Head and Neck Surgery Service of X Hospital, a reference center for EB. RESULTS: the patients' mean age was 14.5 years. Twenty-eight (46.6 percent) were females and 32 (53.4 percent) were males. Eight (13.4 percent) were diagnosed with epidermolysis bullosa simplex, while 51 (85 percent) had epidermolysis bullosa dystrophica; one (1.6 percent) patient had one acquired EB. Lips, mouth, tongue and ears were the most frequently involved sites (32 patients - 53.3 percent). Dysphagia was found in 28 patients (46.6 percent). After esophageal dilatation the symptoms subsided. CONCLUSION: EB is a rare disease and patients must be sent for treatment at reference centers. Physicians treating patients for EB must be aware of the measures required to improve the quality of the treatment provided without putting the patients in harm's way.

SMaRT technology enables gene expression repair in skin gene therapy.

In this issue, Wally et al. (2008) report successful gene expression repair by spliceosome-mediated RNA trans-splicing (SMaRT), a novel achievement in molecular medicine. In their model, SMaRT was able to replace a mutation of the plectin gene in epidermolysis bullosa simplex with muscular dystrophy. This approach is particularly attractive for skin gene therapy of dominant-negative mutations present in a number of blistering genodermatoses.

5' trans-splicing repair of the PLEC1 gene.

The efficient treatment of hereditary disorders, especially of those caused by dominant-negative mutations still remains an obstacle to be overcome. Allele specificity is a critical aspect that must be addressed by silencing therapies such as small interfering RNA, which has the potential risk of also reducing expression of the normal allele. To overcome this hurdle, we used spliceosome-mediated RNA trans-splicing (SMaRT) to replace mRNA exon segments in an in vitro disease model. In this model, a heterozygous insertion of a leucine codon into exon 9 of the plectin gene (PLEC1) leads to aggregation of plectin peptide chains and subsequent protein degradation recapitulating, together with a nonsense mutation on the other allele, the blistering skin disease epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). Transient transfection of EBS-MD fibroblasts with a 5' pre-trans-splicing molecule encoding wild-type exons 2-9 led to specific replacement of the mutated 5' portion of the endogenous PLEC1 transcript through trans-splicing. This treatment reduced the levels of mutant mRNA and restored a wild-type pattern of plectin expression as revealed by immunofluorescence microscopy. When EBS-MD fibroblasts were transfected with retroviral constructs, the level of full-length plectin protein in the corrected fibroblasts increased by 58.7%. Thus, SMaRT may be a promising new tool for treatment of autosomal-dominant genetic diseases.

Gene therapy for autosomal dominant disorders of keratin.

Dominant mutations that interfere with the assembly of keratin filaments cause painful and disfiguring epidermal diseases like pachyonychia congenita and epidermolysis bullosa simplex. Genetic therapies for such diseases must either suppress the production of the toxic proteins or correct the genetic defect in the chromosome. Because epidermal skin cells may be genetically modified in tissue culture or in situ, gene correction is a legitimate goal for keratin diseases. In addition, recent innovations, such as RNA interference in animals, make an RNA knockdown approach plausible in the near future. Although agents of RNA reduction (small interfering RNA, ribozymes, triplex oligonucleotides, or antisense DNA) can be delivered as nucleotides, the impermeability of the skin to large charged molecules presents a serious impediment. Using viral vectors to deliver genes for selective inhibitors of gene expression presents an attractive alternative for long-term treatment of genetic disease in the skin.