A keratin 14 'knockout' mutation in recessive epidermolysis bullosa simplex resulting in less severe disease

Dynamic changes in protein concentrations of keratins in crop milk and related gene expression in pigeon crops during different incubation and chick rearing stages

1. The objective of this study was to examine the keratin composition of crop milk, the variation of epithelial thickness and keratin (K) gene expression in samples from young pigeon during incubation and chick rearing.2. Crop milk was collected from 1-, 3- and 5-day-old squab crops for keratin content analysis. Results showed that K4 accounted for the highest proportion of all detected keratins.3. In total, 42 pairs of adult pigeons were allocated to seven groups according to different stages to collect crop samples. Gene expression studies showed that the K3 gene expression was maximised at rearing Day 15 (15) and R1 in males and females, respectively. K6a gene level was the greatest at R15 in females, whereas it peaked at incubation Day 4 (I4) in males. The K12, K13, K23 and K80 gene levels were inhibited at the peak period of crop milk formation in comparison with I4. In females, K cochleal expression peaked at I10, whereas it was the greatest at R25 in males. K4 and K14 gene expression was the highest at I10 in females, while K4 and K14 were minimised at I17 and R7 in males, respectively. Gene expressions of K5, K8, K19 and K20 in males and K19 in females were maximised at R1. The K5, K20 and K75 gene levels in females peaked at R7. K75 and K8 expressions in males and females reached a maximum value at R25 and I17, respectively.4. The epithelial thickness of male and female crops reached their greatest levels at R1 and had the highest correlation with K19.5. These results emphasised the importance of keratinisation in crop milk formation, and different keratins probably play various roles during this period. The K19 was probably a marker for pigeon crop epithelium development. The sex of the parent pigeon affected keratin gene expression profiles.

Keratins as an Inflammation Trigger Point in Epidermolysis Bullosa Simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited keratinopathies that, in most cases, arise due to mutations in keratins and lead to intraepidermal ruptures. The cellular pathology of most EBS subtypes is associated with the fragility of the intermediate filament network, cytolysis of the basal layer of the epidermis, or attenuation of hemidesmosomal/desmosomal components. Mutations in keratins 5/14 or in other genes that encode associated proteins induce structural disarrangements of different strengths depending on their locations in the genes. Keratin aggregates display impaired dynamics of assembly and diminished solubility and appear to be the trigger for endoplasmic reticulum (ER) stress upon being phosphorylated by MAPKs. Global changes in cellular signaling mainly occur in cases of severe dominant EBS mutations. The spectrum of changes initiated by phosphorylation includes the inhibition of proteasome degradation, TNF-α signaling activation, deregulated proliferation, abnormal cell migration, and impaired adherence of keratinocytes. ER stress also leads to the release of proinflammatory danger-associated molecular pattern (DAMP) molecules, which enhance avalanche-like inflammation. Many instances of positive feedback in the course of cellular stress and the development of sterile inflammation led to systemic chronic inflammation in EBS. This highlights the role of keratin in the maintenance of epidermal and immune homeostasis.

A nonsense variant in the KRT14 gene in a domestic shorthair cat with epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is a hereditary blistering disease affecting the skin and mucous membranes. It has been reported in humans, cattle, buffaloes and dogs, but so far not in cats. In humans, EBS is most frequently caused by variants in the KRT5 or KRT14 genes. Here, we report a case of feline epidermolysis bullosa simplex and describe the causative genetic variant. An 11-month-old male domestic shorthair cat presented with a history of sloughed paw pads and ulcerations in the oral cavity and inner aspect of the pinnae, starting a few weeks after birth. Clinical and histopathological findings suggested a congenital blistering disease with a split formation within the basal cell layer of the epidermis and oral mucous epithelium. The genetic investigation revealed a homozygous nonsense variant in the KRT14 gene (c.979C>T, p.Gln327*). Immunohistochemistry showed a complete absence of keratin 14 staining in all epithelia present in the biopsy. To the best of our knowledge, this is the first report of feline EBS, and the first report of a spontaneous pathogenic KRT14 variant in a non-human species. The homozygous genotype in the affected cat suggests an autosomal recessive mode of inheritance.

Biallelic KRT5 mutations in autosomal recessive epidermolysis bullosa simplex, including a complete human keratin 5 "knock-out"

Epidermolysis bullosa simplex (EBS) is usually inherited as an autosomal dominant disease due to monoallelic gain-of-function mutations in KRT5 or KRT14. Although autosomal recessive forms of EBS have been associated with mutations in at least 10 genes, recessive EBS due to homozygous biallelic KRT5 mutations has not been reported previously; it has been hypothesized that it would result in prenatal lethality. We sought the genetic causes of EB in a cohort of 512 distinct EB families by performing whole exome sequencing (WES) and using an EB-targeting next-generation sequencing (NGS) panel of 21 genes. The pathogenicity and consequences of the mutations were determined by expression profiling and at tissue and ultrastructural levels. Two pathogenic, homozygous missense variants of KRT5 in two patients with generalized EBS and a homozygous null mutation in a patient who died as a neonate from complications of EB were found. The two missense mutations disrupted keratin 5 expression on immunofluorescence microscopy, and the human "knock-out" of KRT5 showed no RNA and protein expression. Collectively, these findings identify biallelic KRT5 mutations with a phenotypic spectrum varying from mild, localized and generalized to perinatal lethal, expanding the genotypic profile of autosomal recessive EBS.

Sequence variants in nine different genes underlying rare skin disorders in 10 consanguineous families

BACKGROUND

Genodermatoses represent genetic anomalies of skin tissues including hair follicles, sebaceous glands, eccrine glands, nails, and teeth. Ten consanguineous families segregating various genodermatosis phenotypes were investigated in the present study.

METHODS

Homozygosity mapping, exome, and Sanger sequencing were employed to search for the disease-causing variants in the 10 families.

RESULTS

Exome sequencing identified seven homozygous sequence variants in different families, including: c.27delT in FERMT1; c.836delA in ABHD5; c.2453C>T in ERCC5; c.5314C>T in COL7A1; c.1630C>T in ALOXE3; c.502C>T in PPOX; and c.10G>T in ALDH3A2. Sanger sequencing revealed three homozygous variants: c.1718 + 2A>G in FERMT1; c.10459A>T in FLG; and c.92delT in the KRT14 genes as the underlying genetic cause of skin phenotypes.

CONCLUSION

This study supports the use of exome sequencing as a powerful, efficient tool for identifying genes that underlie rare monogenic skin disorders.

Gene therapy for keratin genodermatoses: striving forward but obstacles persist

D'Alessandro and colleagues have investigated stress responses in keratinocyte cell lines lacking keratin 14 (K14-null mutation). In this issue, they describe the use of this model to assess the extent of phenotypic rescue achievable by wild-type K14 in the absence of a dominant negative mutation. This work provides proof that, in principle, transfection of wild-type K14 on a null background can significantly normalize the cell and reduce stress responses. However, hurdles to gene therapy in vivo persist because the majority of patients with keratin genodermatoses have heterozygous dominant negative mutations, which are more disruptive than those of the null state. Although correction in the laboratory is now relatively routine, gene delivery to the skin of patients and stable correction of mutations remain major challenges.

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.

Extremely Low Frequency 7 Hz 100 µT Electromagnetic Radiation Promotes Differentiation in the Human Epithelial Cell Line HaCaT

Electromagnetic therapy is a treatment method in which an electromagnetic or magnetic stimulus is used to achieve physiological changes in the body. The specific aim of the present work concerns the effectiveness of low frequency electromagnetic fields to modify the biochemical properties of human keratinocytes (HaCaT). Cells exposed to a 7 Hz 100 microT electromagnetic field for one hour (twice daily), indicated modification in shape and morphology. These modifications were also associated with different actin distribution as revealed by phalloidin fluorescence analysis. Indirect immunofluorescence with fluorescent antibodies against involucrin and beta-Catenin, both differentiation and adhesion markers, revealed an increase in involucrin and beta-Catenin expression, supporting the conclusion that exposure to electromagnetic field carries keratinocytes to an upper differentiation level. This study confirms our previous observation and supports the hypothesis that 7 Hz electromagnetic field, may modify cell biochemistry interfering in the differentiation and cellular adhesion of normal keratinocytes.

KRT14 haploinsufficiency results in increased susceptibility of keratinocytes to TNF-alpha-induced apoptosis and causes Naegeli-Franceschetti-Jadassohn syndrome

Naegeli-Franceschetti-Jadassohn syndrome (NFJS) is a rare autosomal dominant disorder characterized by loss of dermatoglyphics, reticulate hyperpigmentation of the skin, palmoplantar keratoderma, abnormal sweating, and other developmental anomalies of the teeth, hair, and skin. We recently demonstrated that NFJS is caused by heterozygous nonsense or frameshift mutations in the E1/V1-encoding region of KRT14, but the mechanisms for their deleterious effects in NFJS remain elusive. In this study, we further expand the spectrum of NFJS-causing mutations and demonstrate that these mutations result in haploinsufficiency for keratin 14 (K14). As increased apoptotic activity was observed in the epidermal basal cell layer in NFJS patients and as previous data suggested that type I keratins may confer resistance to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis in epithelial tissues, we assessed the effect of down-regulation of KRT14 expression on apoptotic activity in keratinocytes. Using a HaCaT cell-based assay, we found that decreased KRT14 expression is associated with increased susceptibility to TNF-alpha-induced apoptosis. This phenomenon was not observed when cells were cultured in the presence of doxycycline, a known negative regulator of TNF-alpha-dependant pro-apoptotic signaling. Collectively, our results indicate that NFJS results from haploinsufficiency for K14 and suggest that increased susceptibility of keratinocytes to pro-apoptotic signals may be involved in the pathogenesis of this ectodermal dysplasia syndrome.

Structural and regulatory functions of keratins

The diversity of epithelial functions is reflected by the expression of distinct keratin pairs that are responsible to protect epithelial cells against mechanical stress and to act as signaling platforms. The keratin cytoskeleton integrates these functions by forming a supracellular scaffold that connects at desmosomal cell-cell adhesions. Multiple human diseases and murine knockouts in which the integrity of this system is destroyed testify to its importance as a mechanical stabilizer in certain epithelia. Yet, surprisingly little is known about the precise mechanisms responsible for assembly and disease pathology. In addition to these structural aspects of keratin function, experimental evidence accumulating in recent years has led to a much more complex view of the keratin cytoskeleton. Distinct keratins emerge as highly dynamic scaffolds in different settings and contribute to cell size determination, translation control, proliferation, cell type-specific organelle transport, malignant transformation and various stress responses. All of these properties are controlled by highly complex patterns of phosphorylation and molecular associations.

A Heterozygous Frameshift Mutation in the V1 Domain of Keratin 5 in a Family with Dowling–Degos Disease

Dowling-Degos disease (DDD) is an autosomal-dominant genodermatosis characterized by reticulate pigmentation of the flexures. By direct DNA sequencing, we have identified a frameshift mutation in exon 1 of KRT5 in the proband from an extended Spanish DDD kindred. Cloning of PCR products confirmed that this was a 2-bp deletion mutation, designated c.442delAG, leading to a premature termination codon in the V1 domain of the K5 polypeptide, designated p.S148fsX30. These data confirm that haploinsufficiency for K5 causes DDD and points to a prominent role for the keratin intermediate filament cytoskeleton within basal keratinocytes in epidermal pigment biology.

Preservation of phenotype in an organotypic cell culture model of a recessive keratinization defect of Norfolk terrier dogs

The purpose of this study is to reproduce in vitro a recessive keratinization defect of Norfolk terrier dogs characterized by a lack of keratin 10 (K10) production. Keratinocytes from skin biopsy samples of four normal dogs and two affected dogs were cultured organotypically with growth factor-supplemented media in order to stimulate cornification. The cultured epidermis from the normal dogs closely resembled the normal epidermis in vivo and cornified. The cultured epidermis from the affected dogs displayed many phenotypic alterations identified in skin biopsies from dogs with this heritable defect. Immunohistochemistry and immunoblotting showed a marked decrease in K10 from the cultures of the affected keratinocytes, compared to that in K10 from the cultures of the normal keratinocytes. Real-time reverse transcription polymerase chain reaction quantitation showed a 31-fold decrease in K10, a 1.75-fold increase in K1 and a 136-fold increase in K2e between the affected and the normal epidermis. Organotypic keratinocytes showed a 241-fold decrease in K10, a 31-fold decrease in K1 and a 1467-fold decrease in K2e between the affected and normal cultures. Although in vitro keratin expression did not precisely simulate in vivo, the morphology of the normal and the affected epidermis was largely preserved; thus, this culture system may provide an alternative to in vivo investigations for cutaneous research involving cornification.

Epidermolysis bullosa simplex: recurrent and de novo mutations in the KRT5 and KRT14 genes, phenotype/genotype correlations, and implications for genetic counseling and prenatal diagnosis

Epidermolysis bullosa simplex (EBS) is a mechano-bullous disorder characterized by intraepidermal blistering within the basal keratinocytes as a result of trauma to the skin. As part of the DNA diagnostics program, our laboratory has analyzed a cohort of 57 patients with the initial referral diagnosis of EBS. Among these patients, 18 were found to harbor heterozygous mutations in the keratin 5 or keratin 14 genes, KRT5 and KRT14, respectively, whereas in 14 cases, the disease was associated with mutations in both alleles of the plectin gene. Among the keratin mutations, 12 were distinct and six were novel, and in most cases there was no family history of a blistering disease. Prenatal diagnosis of eight pregnancies with keratin gene mutations, at risk for EBS either because one of the parents was affected (three cases) or history of a previously affected child as a result of a de novo mutation (five cases), predicted two fetuses being affected and six being normal. No recurrence of the de novo mutations in these pregnancies was disclosed. Collectively, the data suggest that a significant number of cases diagnosed as EBS are due to plectin mutations, and many cases result from de novo mutations in KRT5 and KRT14 genes. These findings have implications for genetic counseling and prenatal diagnosis for EBS.

Progress in epidermolysis bullosa: the phenotypic spectrum of plectin mutations

Plectin, a large multidomain adhesive protein with versatile binding functions, is expressed in a number of tissues and cell types. In the skin, plectin is a critical component of hemidesmosomes, interacting with keratin intermediate filaments and beta4 integrin. Mutations in the plectin gene (PLEC1) result in fragility of skin, demonstrating blister formation at the level of hemidesmosomes. These blistering disorders belong to the spectrum of epidermolysis bullosa (EB) phenotypes, and three distinct variants because of plectin mutations have been identified. First, EB with muscular dystrophy, an autosomal recessive syndrome, is frequently caused by premature termination codon-causing mutations leading to the absence of plectin both in the skin and in the muscle. Second, a heterozygous missense mutation (R2110W) in PLEC1 has been documented in patients with EB simplex of the Ogna type, a rare autosomal dominant disorder. Finally, recent studies have disclosed plectin mutations in patients with EB with pyloric atresia, an autosomal recessive syndrome, frequently with lethal consequences. Collectively, these observations attest to the phenotypic spectrum of plectin mutations, and provide the basis for accurate genetic counselling with prognostic implications, as well as for prenatal diagnosis in families at the risk of recurrence of the disease.

Progress in epidermolysis bullosa: Genetic classification and clinical implications

Epidermolysis bullosa (EB), a heterogenous group of genodermatoses, is characterized by fragility and blistering of the skin associated with extracutaneous manifestations. Based on clinical severity, constellation of the phenotypic manifestations, and the level of tissue separation within the cutaneous basement membrane zone (BMZ), EB has been divided into distinct subcategories. Traditionally, these include the simplex, junctional, and dystrophic forms of EB, and recently attention has been drawn to hemidesmosomal variants demonstrating tissue separation at the level of the hemidesmosomes. Specific mutations in ten distinct genes expressed within the cutaneous BMZ have been delineated in >500 families with different variants of EB. The types of mutations, their positions along the affected genes, and their consequences at the mRNA and protein levels provide explanation for the phenotypic variability and genetic heterogeneity of this group of genodermatoses. Elucidation of mutations in different forms of EB has direct translational applications for improved diagnosis and molecularly based classification with prognostic implications as well as for genetic counseling and DNA-based prenatal testing in families with EB.

Novel Mechanism of Revertant Mosaicism in Dowling–Meara Epidermolysis Bullosa Simplex

The severe Dowling-Meara form of epidermolysis bullosa simplex is caused by dominant-negative mutations in keratins 5 and 14, which are specifically expressed in the basal keratinocytes of the epidermis. The most common mutation in the Dowling-Meara form of epidermolysis bullosa simplex patients is the missense mutation R125C in exon 1 of the K14 gene. We made a primary keratinocyte cell line from a sporadic case known to carry the R125C mutation as part of an ongoing gene therapy initiative. The full-length K14 cDNA was sequenced using keratinocyte mRNA. Unexpectedly, a second mutation was identified in K14: a heterozygous 1 bp insertion mutation (242insG) upstream of the R125C mutation. This frameshift mutation creates a premature termination codon immediately downstream, thereby nullifying the dominant-negative allele. The second mutation was only present in DNA derived from keratinocytes and was absent from lymphocyte DNA. This case represents a novel mechanism of revertant mosaicism and is an example of "natural gene therapy".

Low electromagnetic field (50 Hz) induces differentiation on primary human oral keratinocytes (HOK)

This work concerns the effect of low frequency electromagnetic fields (ELF) on biochemical properties of human oral keratinocytes (HOK). Cells exposed to a 2 mT, 50 Hz, magnetic field, showed by scanning electron microscopy (SEM) modification in shape and morphology; these modifications were also associated with different actin distribution, revealed by phalloidin fluorescence analysis. Moreover, exposed cells had a smaller clonogenic capacity, and decreased cellular growth. Indirect immunofluorescence with fluorescent antibodies against involucrin and beta-catenin, both differentiation and adhesion markers, revealed an increase in involucrin and beta-catenin expression. The advance in differentiation was confirmed by a decrease of expression of epidermal growth factor (EGF) receptor in exposed cells, supporting the idea that exposure to electromagnetic field carries keratinocytes to higher differentiation level. These observations support the hypothesis that 50 Hz electromagnetic fields may modify cell morphology and interfere in differentiation and cellular adhesion of normal keratinocytes.

Recessive epidermolysis bullosa simplex phenotype reproduced in vitro: ablation of keratin 14 is partially compensated by keratin 17

Recessive epidermolysis bullosa simplex (REBS) is characterized by generalized cutaneous blistering in response to mechanical trauma. This results from fragility of the basal keratinocytes that lack keratin tonofilaments because of homozygote null mutation in the keratin 14 gene. REBS patients display in addition focal dyskeratotic skin lesions with histology of epidermolytic hyperkeratosis (EHK) and tonofilament clumping in the suprabasal layers of the epidermis. In this study we examined whether it is possible to mimic in vitro the bullous and dyskeratotic cellular phenotype. For this purpose, fibroblasts from nondyskeratotic (K14-/-) and dyskeratotic (K14-/-) skin of a REBS patient and fibroblasts from a healthy donor (K14+/+) were isolated and incorporated into collagen matrices. Subsequently, fresh biopsies originating from the nondyskeratotic and dyskeratotic skin of the patient and from a healthy donor were placed onto the collagen matrices and cultured at the air-liquid interface. Epidermal morphogenesis was evaluated on the basis of tissue morphology and the expression of a series of keratins. The results of the present study indicate that basal cell vacuolization in REBS can be mimicked in vitro but not the EHK. Fibroblasts seem to play an important regulatory role in establishing the REBS phenotype. These findings suggest that wild-type fibroblasts may enhance the stability of K14-/- keratinocytes in vitro.

Functional complexity of intermediate filament cytoskeletons: from structure to assembly to gene ablation

The cell biology of intermediate filament (IF) proteins and their filaments is complicated by the fact that the members of the gene family, which in humans amount to at least 65, are differentially expressed in very complex patterns during embryonic development. Thus, different tissues and cells express entirely different sets and amounts of IF proteins, the only exception being the nuclear B-type lamins, which are found in every cell. Moreover, in the course of evolution the individual members of this family have, within one species, diverged so much from each other with regard to sequence and thus molecular properties that it is hard to envision a unifying kind of function for them. The known epidermolytic diseases, caused by single point mutations in keratins, have been used as an argument for a role of IFs in mechanical "stress resistance," something one would not have easily ascribed to the beaded chain filaments, a special type of IF in the eye lens, or to nuclear lamins. Therefore, the power of plastic dish cell biology may be limited in revealing functional clues for these structural elements, and it may therefore be of interest to go to the extreme ends of the life sciences, i.e., from the molecular properties of individual molecules including their structure at the atomic level to targeted inactivation of their genes in living animals, mouse, and worm to define their role more precisely in metazoan cell physiology.

The molecular genetics of keratin disorders

Keratins are the type I and II intermediate filament proteins which form a cytoskeletal network within all epithelial cells. They are expressed in pairs in a tissue- and differentiation-specific fashion. Epidermolysis bullosa simplex (EBS) was the first human disorder to be associated with keratin mutations. The abnormal keratin filament aggregates observed in basal cell keratinocytes of some EBS patients are composed of keratins K5 and K14. Dominant mutations in the genes encoding these proteins were shown to disrupt the keratin filament cytoskeleton resulting in cells that are less resilient and blister with mild physical trauma. Identification of mutations in other keratin genes soon followed with attention focussed on disorders showing abnormal clumping of keratin filaments in specific cells. For example, in bullous congenital ichthyosiform erythroderma, clumping of filaments in the suprabasal cells led to the identification of mutations in the suprabasal keratins, K1 and K10. Mutations have now been identified in 18 keratins, all of which produce a fragile cell phenotype. These include ichthyosis bullosa of Siemens (K2e), epidermolytic palmoplantar keratoderma (K1, K9), pachyonychia congenita (K6a, K6b, K16, K17), white sponge nevus (K4, K13), Meesmann's corneal dystrophy (K3, K12), cryptogenic cirrhosis (K8, K18) and monilethrix (hHb6, hHb1).In general, these disorders are inherited as autosomal dominant traits and the mutations act in a dominant-negative manner. Therefore, treatment in the form of gene therapy is difficult, as the mutant gene needs to be inactivated. Ways of achieving this are actively being studied. Reliable mutation detection methods from genomic DNA are now available. This enables rapid screening of patients for keratin mutations. For some of the more severe phenotypes, prenatal diagnosis may be requested and this can now be performed from chorionic villus samples at an early stage of the pregnancy. This review article describes the discovery of, to date, mutations in 18 keratin genes associated with inherited human diseases.

Prenatal diagnosis for epidermolysis bullosa: a study of 144 consecutive pregnancies at risk

Epidermolysis bullosa (EB) is a group of inherited disorders characterized by increased skin fragility, resulting in blisters and erosions after minor trauma. Mutations in 10 structural genes expressed in the cutaneous basement membrane zone have been reported. The DebRA Molecular Diagnostics Laboratory at Jefferson Medical College has performed 144 DNA-based prenatal diagnoses since 1993 in families at risk for recurrence of the most severe forms of EB, including the recessive dystrophic EB (RDEB), junctional EB (JEB), EB with pyloric atresia (EB-PA), and EB simplex (EBS). A mutation-detection strategy using either conformation-sensitive gel electrophoresis (CSGE) or denaturing high-performance liquid chromatography (dHPLC) scanning analysis, followed by nucleotide sequencing, was applied to most cases with DEB and to all JEB, EB-PA, and EBS families. For some RDEB families, linkage analysis was performed, either alone when the inheritance pattern was clear or in combination with one mutation. Among the 144 prenatal diagnoses, 63 were for RDEB, 69 for JEB, 6 for EB-PA, and 6 for EBS. Twenty-eight normal, 73 heterozygous carrier, and 28 affected RDEB, JEB, and EB-PA pregnancies were reported in these recessively inherited diseases. Two affected and four normal pregnancies were predicted in dominantly inherited EBS. Among the 144 pregnancies, 9 were terminated without confirmation, 13 cases were lost to follow-up, and 6 pregnancies are ongoing. There were 6 families with inconclusive results due either to recombination events between flanking markers, absence of informative markers for one allele, or lack of sample from the previously affected child. There were three discordant results, one that was explained by maternal contamination of the chorionic villus sample and two that were unresolved. Overall, the availability, relative ease, and over 98% success rate make molecular DNA-based prenatal diagnosis a viable option for EB families at risk.

Phenotypes, genotypes and their contribution to understanding keratin function

A large number of mutations in keratin genes underlie inherited tissue fragility disorders of epithelia. The genotype-phenotype correlations emerging from these studies provide a rich source of information about the function of keratins that would have taken decades to achieve by a purely transgenic approach. Human disease studies are being supplemented by engineered mouse mutant studies, which give access to the effects of genetic alterations unlikely to occur naturally. Evidence is emerging that the great diversity of keratins might be required to enable cells to adapt their structure in response to different signalling pathways.

A novel homozygous nonsense deletion/insertion mutation in the keratin 14 gene (Y248X; 744delC/insAG) causes recessive epidermolysis bullosa simplex type Köbner

We report the sixth case of a human keratin 14 'knockout' mutation resulting in recessive epidermolysis bullosa simplex (EBS). A novel, homozygous nonsense mutation resulting from a deletion/insertion mutation (744delC/insAG) leads to a premature termination codon in the KRT14 gene (Y248X). The patient suffers from generalized cutaneous blistering since birth, mild nail dystrophy, involvement of mucous membranes and multiple epidermolysis bullosa naevi. The clinical variability noted in K14-deficient EBS patients suggests phenotypic modulation by additional genetic and/or epigenetic factors.

Genética Molecular das Epidermólises Bolhosas

O estudo das alterações moleculares das epidermólises bolhosas tem contribuído para que se compreenda melhor essas enfermidades. Na epidermólise bolhosa simples a maioria dos casos está associada com alteração nas citoqueratinas basais 5 (gen KRT5) e 14 (gen KRT14), o que modifica o citoesqueleto na camada basal da epiderme, levando à degeneração dessa camada, formando bolha intra-epidérmica. Mutações na plectina (gen PLEC1), componente da placa interna do hemidesmossoma, levam também à clivagem intra-epidérmica. Na epidermólise bolhosa juncional vários gens estão envolvidos, em decorrência da complexidade da zona da membrana basal, todos levando ao descolamento dos queratinócitos basais na lâmina lúcida, pela disfunção da aderência entre esses e a lâmina densa. Alterações na laminina 5 (gens LAMA3, LAMB3 e LAMC2), integrina alfa6beta4 (gens ITGA6 e ITGB4) e colágeno XVII (gen COL17A1) foram descritas. Por fim, na epidermólise bolhosa distrófica apenas um gen está mutado, alterando o colágeno VII (gen COL7A1), principal componente das fibrilas ancorantes, produzindo clivagem abaixo da lâmina densa, variando fenotipicamente de acordo com a conseqüência da mutação. Outra aplicação importante dessas informações refere-se ao diagnóstico pré-natal, com a perspectiva no futuro da terapia gênica.

The molecular basis of hereditary palmoplantar keratodermas

In recent years, the gene defects causing many types of hereditary palmoplantar keratoderma have been discovered. These genes encode a variety of proteins involved in the terminal differentiation of keratinocytes and the formation of the cornified cell envelope. In this article, we review the molecular defects underlying various palmoplantar keratodermas with particular attention to the role of these molecules in the terminal differentiation of palmoplantar epidermis. Of the proteins involved in keratodermas, loricrin, keratins, and desmosomal proteins provide the protein structure of the cornified cell envelope. Connexins form intercellular gap junctions, which regulate ionic calcium signals necessary for the expression of the proteins that form the cornified cell envelope. Cathepsins likely mediate enzymatic processes necessary for the formation and dissolution of the cornified cell envelope. The clinical phenotypes produced by various mutations affecting these proteins are discussed vis-à-vis data from genetic, cellular, and molecular experiments.

Effects of extremely low frequency (50 Hz) magnetic field on morphological and biochemical properties of human keratinocytes

We investigated the effects on human keratinocytes (HaCaT) of exposure to a sinusoidal magnetic field of 2 mT (50 Hz). These cells are a good model for studying interaction of nonionising radiation, because they are not shielded from fields in vivo and also because they are resistant to both mechanical and thermal stimuli. We performed scanning microscopy which showed modification in shape and morphology in exposed cells. This modification is related to differential actin distribution as revealed by phalloidin fluorescence analysis. Moreover, the exposed cells show increased clonogenic capacity, as well as increased cellular growth as showed by clonogenicity assays and growth curves. Indirect immunofluorescence analysis using a fluorescent antibody against involucrin and beta4 integrin, which are respectively differentiation and adhesion markers, revealed an increase of involucrin expression and segregation of beta4 integrin in the cell membrane in cells exposed to 50 Hz; a higher percentage of the exposed cells shows a modified pattern of adhesion and differentiation markers. We also present evidence that exposure of HaCaT cells can interfere with protein kinase activity. Our observations confirm the hypothesis that electromagnetic fields at 50 Hz may modify cell membrane morphology and interfere with initiation of the signal cascade pathway and cellular adhesion.

A novel nonsense mutation at E106 of the 2B rod domain of keratin 14 causes dominant epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is classified into three main types and is caused, in most cases, by missense mutations in the genes encoding keratin (K) 5 and K14. In this study, we clinically, ultrastructurally, immunohistochemically, and molecularly studied a patient with a dominant EBS, Köbner type. Using sequence analysis of genomic DNA, a novel K14 nonsense mutation was identified. A heterozygous mutation G1231T of KRT14 was found to be associated with the disease in the patient. The mutation created a premature stop codon (amino acid codon 411, residue 106 of the 2B helix) in the K14 molecule. This residue lies in a highly conserved region and was recently found to be absolutely required for molecular stability and intermediate filament assembly in K5 and K14. The E411X (E106X) heterozygous ablation, missing the last 16 amino acid residues of the 2B and the entire tail domain of K14, led to disease but did not result in clumping of keratin filaments. It is the first premature stop codon mutation of K14 found in dominant EBS.

'Hard' and 'soft' principles defining the structure, function and regulation of keratin intermediate filaments

Keratins make up the largest subgroup of intermediate filament proteins and represent the most abundant proteins in epithelial cells. They exist as highly dynamic networks of cytoplasmic 10-12 nm filaments that are obligate heteropolymers involving type I and type II keratins. The primary function of keratins is to protect epithelial cells from mechanical and nonmechanical stresses that result in cell death. Other emerging functions include roles in cell signaling, the stress response and apoptosis, as well as unique roles that are keratin specific and tissue specific. The role of keratins in a number of human skin, hair, ocular, oral and liver diseases is now established and meshes well with the evidence gathered from transgenic mouse models. The phenotypes associated with defects in keratin proteins are subject to significant modulation by functional redundancy within the family and modifier genes as well. Keratin filaments undergo complex regulation involving post-translational modifications and interactions with self and with various classes of associated proteins.

Formation of a normal epidermis supported by increased stability of keratins 5 and 14 in keratin 10 null mice

The expression of distinct keratin pairs during epidermal differentiation is assumed to fulfill specific and essential cytoskeletal functions. This is supported by a great variety of genodermatoses exhibiting tissue fragility because of keratin mutations. Here, we show that the loss of K10, the most prominent epidermal protein, allowed the formation of a normal epidermis in neonatal mice without signs of fragility or wound-healing response. However, there were profound changes in the composition of suprabasal keratin filaments. K5/14 persisted suprabasally at elevated protein levels, whereas their mRNAs remained restricted to the basal keratinocytes. This indicated a novel mechanism regulating keratin turnover. Moreover, the amount of K1 was reduced. In the absence of its natural partner we observed the formation of a minor amount of novel K1/14/15 filaments as revealed by immunogold electron microscopy. We suggest that these changes maintained epidermal integrity. Furthermore, suprabasal keratinocytes contained larger keratohyalin granules similar to our previous K10T mice. A comparison of profilaggrin processing in K10T and K10(-/-) mice revealed an accumulation of filaggrin precursors in the former but not in the latter, suggesting a requirement of intact keratin filaments for the processing. The mild phenotype of K10(-/-) mice suggests that there is a considerable redundancy in the keratin gene family.

Complete cytolysis and neonatal lethality in keratin 5 knockout mice reveal its fundamental role in skin integrity and in epidermolysis bullosa simplex

In human patients, a wide range of mutations in keratin (K) 5 or K14 lead to the blistering skin disorder epidermolysis bullosa simplex. Given that K14 deficiency does not lead to the ablation of a basal cell cytoskeleton because of a compensatory role of K15, we have investigated the requirement for the keratin cytoskeleton in basal cells by inactivating the K5 gene in mice. We report that the K5(-/-) mice die shortly after birth, lack keratin filaments in the basal epidermis, and are more severely affected than K14(-/-) mice. In contrast to the K14(-/-) mice, we detected a strong induction of the wound-healing keratin K6 in the suprabasal epidermis of cytolyzed areas of postnatal K5(-/-) mice. In addition, K5 and K14 mice differed with respect to tongue lesions. Moreover, we show that in the absence of K5 and other type II keratins, residual K14 and K15 aggregated along hemidesmosomes, demonstrating that individual keratins without a partner are stable in vivo. Our data indicate that K5 may be the natural partner of K15 and K17. We suggest that K5 null mutations may be lethal in human epidermolysis bullosa simplex patients.