A compound heterozygous one amino-acid insertion/nonsense mutation in the plectin gene causes epidermolysis bullosa simplex with plectin deficiency

Plectin Deficiency in Fibroblasts Deranges Intermediate Filament and Organelle Morphology, Migration, and Adhesion

Plectin, a highly versatile and multifunctional cytolinker, has been implicated in several multisystemic disorders. Most sequence variations in the human plectin gene (PLEC) cause epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), an autosomal recessive skin-blistering disorder associated with progressive muscle weakness. In this study, we performed a comprehensive cell biological analysis of dermal fibroblasts from three different patients with EBS-MD, where PLEC expression analyses revealed preserved mRNA levels in all cases, whereas full-length plectin protein content was significantly reduced or completely absent. Downstream effects of pathogenic PLEC sequence alterations included massive bundling of vimentin intermediate filament networks, including the occurrence of ring-like nuclei-encasing filament bundles, elongated mitochondrial networks, and abnormal nuclear morphologies. We found that essential fibroblast functions such as wound healing, migration, or orientation upon cyclic stretch were significantly impaired in the cells of patients with EBS-MD. Finally, EBS-MD fibroblasts displayed reduced adhesion capacities, which could be attributed to smaller focal adhesion contacts. Our study not only emphasizes plectin's functional role in human skin fibroblasts, it also provides further insights into the understanding of EBS-MD-associated disease mechanisms.

Mutation update: The spectra of PLEC sequence variants and related plectinopathies

Plectin, encoded by PLEC, is a cytoskeletal linker of intermediate filaments expressed in many cell types. Plectin consists of three main domains that determine its functionality: the N-terminal domain, the Rod domain, and the C-terminal domain. Molecular defects of PLEC correlating with the functional aspects lead to a group of rare heritable disorders, plectinopathies. These multisystem disorders include an autosomal dominant form of epidermolysis bullosa simplex (EBS-Ogna), limb-girdle muscular dystrophy (LGMD), aplasia cutis congenita (ACC), and an autosomal recessive form of EBS, which may associate with muscular dystrophy (EBS-MD), pyloric atresia (EBS-PA), and/or congenital myasthenic syndrome (EBS-MyS). In this study, genotyping of over 600 Iranian patients with epidermolysis bullosa by next-generation sequencing identified 15 patients with disease-causing PLEC variants. This mutation update analyzes the clinical spectrum of PLEC in our cohort and in the literature and demonstrates the relationship between PLEC genotype and phenotypic manifestations. This study has integrated our seven novel PLEC variants and phenotypic findings with previously published data totaling 116 variants to provide the most complete overview of pathogenic PLEC variants and related disorders.

Muscle-Related Plectinopathies

Plectin is a giant cytoskeletal crosslinker and intermediate filament stabilizing protein. Mutations in the human plectin gene (PLEC) cause several rare diseases that are grouped under the term plectinopathies. The most common disorder is autosomal recessive disease epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), which is characterized by skin blistering and progressive muscle weakness. Besides EBS-MD, PLEC mutations lead to EBS with nail dystrophy, EBS-MD with a myasthenic syndrome, EBS with pyloric atresia, limb-girdle muscular dystrophy type R17, or EBS-Ogna. In this review, we focus on the clinical and pathological manifestations caused by PLEC mutations on skeletal and cardiac muscle. Skeletal muscle biopsies from EBS-MD patients and plectin-deficient mice revealed severe dystrophic features with variation in fiber size, degenerative myofibrillar changes, mitochondrial alterations, and pathological desmin-positive protein aggregates. Ultrastructurally, PLEC mutations lead to a disorganization of myofibrils and sarcomeres, Z- and I-band alterations, autophagic vacuoles and cytoplasmic bodies, and misplaced and degenerating mitochondria. We also summarize a variety of genetically manipulated mouse and cell models, which are either plectin-deficient or that specifically lack a skeletal muscle-expressed plectin isoform. These models are powerful tools to study functional and molecular consequences of PLEC defects and their downstream effects on the skeletal muscle organization.

Identifying Plectin Isoform Functions through Animal Models

Plectin, a high-molecular-weight cytoskeletal linker protein, binds with high affinity to intermediate filaments of all types and connects them to junctional complexes, organelles, and inner membrane systems. In addition, it interacts with actomyosin structures and microtubules. As a multifunctional protein, plectin has been implicated in several multisystemic diseases, the most common of which is epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). A great part of our knowledge about plectin’s functional diversity has been gained through the analysis of a unique collection of transgenic mice that includes a full (null) knockout (KO), several tissue-restricted and isoform-specific KOs, three double KOs, and two knock-in lines. The key molecular features and pathological phenotypes of these mice will be discussed in this review. In summary, the analysis of the different genetic models indicated that a functional plectin is required for the proper function of striated and simple epithelia, cardiac and skeletal muscle, the neuromuscular junction, and the vascular endothelium, recapitulating the symptoms of humans carrying plectin mutations. The plectin-null line showed severe skin and muscle phenotypes reflecting the importance of plectin for hemidesmosome and sarcomere integrity; whereas the ablation of individual isoforms caused a specific phenotype in myofibers, basal keratinocytes, or neurons. Tissue-restricted ablation of plectin rendered the targeted cells less resilient to mechanical stress. Studies based on animal models other than the mouse, such as zebrafish and C. elegans, will be discussed as well.

Epigenetic and metabolic regulation of epidermal homeostasis

Continuous exposure of the skin to environmental, mechanical and chemical stress necessitates constant self‐renewal of the epidermis to maintain its barrier function. This self‐renewal ability is attributed to epidermal stem cells (EPSCs), which are long‐lived, multipotent cells located in the basal layer of the epidermis. Epidermal homeostasis – coordinated proliferation and differentiation of EPSCs – relies on fine‐tuned adaptations in gene expression which in turn are tightly associated with specific epigenetic signatures and metabolic requirements. In this review, we will briefly summarize basic concepts of EPSC biology and epigenetic regulation with relevance to epidermal homeostasis. We will highlight the intricate interplay between mitochondrial energy metabolism and epigenetic events – including miRNA‐mediated mechanisms – and discuss how the loss of epigenetic regulation and epidermal homeostasis manifests in skin disease. Discussion of inherited epidermolysis bullosa (EB) and disorders of cornification will focus on evidence for epigenetic deregulation and failure in epidermal homeostasis, including stem cell exhaustion and signs of premature ageing. We reason that the epigenetic and metabolic component of epidermal homeostasis is significant and warrants close attention. Charting epigenetic and metabolic complexities also represents an important step in the development of future systemic interventions aimed at restoring epidermal homeostasis and ameliorating disease burden in severe skin conditions.

Much More Than a Scaffold: Cytoskeletal Proteins in Neurological Disorders

Recent observations related to the structure of the cytoskeleton in neurons and novel cytoskeletal abnormalities involved in the pathophysiology of some neurological diseases are changing our view on the function of the cytoskeletal proteins in the nervous system. These efforts allow a better understanding of the molecular mechanisms underlying neurological diseases and allow us to see beyond our current knowledge for the development of new treatments. The neuronal cytoskeleton can be described as an organelle formed by the three-dimensional lattice of the three main families of filaments: actin filaments, microtubules, and neurofilaments. This organelle organizes well-defined structures within neurons (cell bodies and axons), which allow their proper development and function through life. Here, we will provide an overview of both the basic and novel concepts related to those cytoskeletal proteins, which are emerging as potential targets in the study of the pathophysiological mechanisms underlying neurological disorders.

GPR56/ADGRG1 regulates development and maintenance of peripheral myelin

This study identifies GPR56/ADGRG1 as a conserved regulator of peripheral nervous system myelination and defines a novel interacting partner of GPR56: plectin. This study is directly relevant to human health because mutations in GPR56 and PLECTIN cause diseases with neuropathic symptoms.

Myelin is a multilamellar sheath generated by specialized glia called Schwann cells (SCs) in the peripheral nervous system (PNS), which serves to protect and insulate axons for rapid neuronal signaling. In zebrafish and rodent models, we identify GPR56/ADGRG1 as a conserved regulator of PNS development and health. We demonstrate that, during SC development, GPR56-dependent RhoA signaling promotes timely radial sorting of axons. In the mature PNS, GPR56 is localized to distinct SC cytoplasmic domains, is required to establish proper myelin thickness, and facilitates organization of the myelin sheath. Furthermore, we define plectin—a scaffolding protein previously linked to SC domain organization, myelin maintenance, and a series of disorders termed “plectinopathies”—as a novel interacting partner of GPR56. Finally, we show that Gpr56 mutants develop progressive neuropathy-like symptoms, suggesting an underlying mechanism for peripheral defects in some human patients with GPR56 mutations. In sum, we define Gpr56 as a new regulator in the development and maintenance of peripheral myelin.

Loss of interaction between plectin and type XVII collagen results in epidermolysis bullosa simplex

Plectin is a linker protein that interacts with intermediate filaments and β4 integrin in hemidesmosomes of the epidermal basement membrane zone (BMZ). Type XVII collagen (COL17) has been suggested as another candidate plectin binding partner in hemidesmosomes. Here, we demonstrate that plectin-COL17 binding helps to maintain epidermal BMZ organization. We identified an epidermolysis bullosa (EB) simplex patient as having markedly diminished expression of plectin and COL17 in skin. The patient is compound heterozygous for sequence variants in the plectin gene (PLEC); one is a truncation and the other is a small in-frame deletion sequence variant. The in-frame deletion is located in the putative COL17-binding domain of plectin and abolishes the plectin-COL17 interaction in vitro. These results imply that disrupted interaction between plectin and COL17 is involved in the development of EB. Our study suggests that protein-protein binding defects may underlie EB in patients with unidentified disease-causing sequence variants.

Epidermolysis bullosa simplex with muscular dystrophy. Review of the literature and a case report

BACKGROUND

Epidermolysis bullosa simplex associated with muscular dystrophy is a genetic skin disease caused by plectin deficiency. A case of a 19-year-old Czech patient affected with this disease and a review all previously published clinical cases are presented.

MAIN OBSERVATIONS

In our patient, skin signs of the disease developed after birth. Bilateral ptosis at the age of 8 years was considered as the first specific symptom of muscular dystrophy. Since then, severe scoliosis, urological and psychiatric complication have quickly developed. The signs of plectin deficiency were found by histopathological studies, electron microscopy and antigen mapping of the skin and muscular samples. Two autosomal recessive mutations in the plectin gene leading to premature termination codon were disclosed by mutation analysis. By review of all published clinical cases, 49 patients with this disease were found. 54 different mutations in the plectin gene were published, p.(Arg2319*) in exon 31 being the most frequently found. Median age of muscular dystrophy development was 9.5 years. Hoarseness and respiratory complications were the most often complications beside skin involvement.

CONCLUSION

Epidermolysis bullosa simplex with muscular dystrophy was diagnosed based on clinical, histopathological (skin and muscle biopsy) and mutation analysis of the plectin gene. Overview of the genetic and clinical characteristic of this disease could be presented by review of all previously published clinical cases.

Plectin reinforces vascular integrity by mediating crosstalk between the vimentin and the actin networks

Mutations in the cytoskeletal linker protein plectin result in multisystemic diseases affecting skin and muscle with indications of additional vascular system involvement. To study the mechanisms underlying vascular disorders, we established plectin-deficient endothelial cell and mouse models. We show that apart from perturbing the vimentin cytoskeleton of endothelial cells, plectin deficiency leads to severe distortions of adherens junctions (AJs), as well as tight junctions, accompanied by an upregulation of actin stress fibres and increased cellular contractility. Plectin-deficient endothelial cell layers were more leaky and showed reduced mechanical resilience in fluid-shear stress and mechanical stretch experiments. We suggest that the distorted AJs and upregulated actin stress fibres in plectin-deficient cells are rooted in perturbations of the vimentin cytoskeleton, as similar phenotypes could be mimicked in wild-type cells by disruption of vimentin filaments. In vivo studies in endothelium-restricted conditional plectin-knockout mice revealed significant distortions of AJs in stress-prone aortic arch regions and increased pulmonary vascular leakage. Our study opens a new perspective on cytoskeleton-controlled vascular permeability, where a plectin-organized vimentin scaffold keeps actomyosin contractility ‘in-check’ and maintains AJ homeostasis.

Summary: Plectin-arranged vimentin scaffolds keep actomyosin contractility ‘in-check’ and maintain cell–cell junction homeostasis, providing a new perspective on cytoskeleton-controlled vascular permeability.

Plectin-related skin diseases

Plectin has been characterized as a linker protein that is expressed in many cell types and is distinctive in various isoforms in the N-terminus and around the rod domain due to complicated alternative splicing of PLEC, the gene encoding plectin. Plectin deficiency causes autosomal recessive epidermolysis bullosa simplex (EBS) with involvement of the skin and other organs, such as muscle and gastrointestinal tract, depending on the expression pattern of the defective protein. In addition, a point mutation in the rod domain of plectin leads to autosomal dominant EBS, called as EBS-Ogna. Plectin can be targeted by circulating autoantibodies in subepidermal autoimmune blistering diseases. This review summarizes plectin-related skin diseases, from congenital to autoimmune disorders.

Mitochondrial dysfunction: a neglected component of skin diseases

Aberrant mitochondrial structure and function influence tissue homeostasis and thereby contribute to multiple human disorders and ageing. Ten per cent of patients with primary mitochondrial disorders present skin manifestations that can be categorized into hair abnormalities, rashes, pigmentation abnormalities and acrocyanosis. Less attention has been paid to the fact that several disorders of the skin are linked to alterations of mitochondrial energy metabolism. This review article summarizes the contribution of mitochondrial pathology to both common and rare skin diseases. We explore the intriguing observation that a wide array of skin disorders presents with primary or secondary mitochondrial pathology and that a variety of molecular defects can cause dysfunctional mitochondria. Among them are mutations in mitochondrial- and nuclear DNA-encoded subunits and assembly factors of oxidative phosphorylation (OXPHOS) complexes; mutations in intermediate filament proteins involved in linking, moving and shaping of mitochondria; and disorders of mitochondrial DNA metabolism, fatty acid metabolism and heme synthesis. Thus, we assume that mitochondrial involvement is the rule rather than the exception in skin diseases. We conclude the article by discussing how improving mitochondrial function can be beneficial for aged skin and can be used as an adjunct therapy for certain skin disorders. Consideration of mitochondrial energy metabolism in the skin creates a new perspective for both dermatologists and experts in metabolic disease.

Epidermolysis bullosa simplex with PLEC mutations: new phenotypes and new mutations

BACKGROUND

Genetic mutations in the plectin gene (PLEC) cause autosomal recessive forms of epidermolysis bullosa simplex (EBS) associated with either muscular dystrophy (EBS-MD) or pyloric atresia (EBS-PA). Phenotype-genotype analysis has suggested that EBS-MD is due mostly to genetic mutations affecting the central rod domain of plectin, and EBS-PA to mutations outside this domain.

OBJECTIVES

This study aimed to describe new phenotypes of patients with EBS-MD and EBS-PA, to identify novel PLEC mutations and to establish genotype-phenotype correlations.

METHODS

Seven patients with a suspicion of EBS linked to PLEC mutations were included. A standardized clinical questionnaire was sent to the physicians in charge of each patient. Immunofluorescence studies of skin biopsies followed by molecular analysis of PLEC were performed in all patients.

RESULTS

We report the first case of nonlethal EBS-PA improving with age, the first multisystemic involvement in a patient with lethal EBS-PA, and the first patients with EBS-MD with involvement of either the bladder or oesophagus. Eleven novel PLEC mutations are also reported.

CONCLUSIONS

Our results confirm that EBS-PA is linked to mutations in the distal exons 1-30 and 32 of PLEC. Long-term survival is possible, with skin improvement, but a delayed onset of MD is probable. While EBS-MD is linked to PLEC mutations in all exons, in most cases one of the mutations affects exon 31. The precocity of MD seems to be linked to the type and localization of the PLEC mutation(s), but no correlation with mucosal involvement has been found.

Stabilization of the dystroglycan complex in Cajal bands of myelinating Schwann cells through plectin-mediated anchorage to vimentin filaments

Previous studies have unmasked plectin, a uniquely versatile intermediate filament-associated cytolinker protein, to be essential for skin and skeletal muscle integrity. Different sets of isoforms of the protein were found to stabilize cells mechanically, regulate cytoskeletal dynamics, and serve as a scaffolding platform for signaling molecules. Here, we investigated whether a similar scenario prevails in myelinating Schwann cells. Using isoform-specific antibodies, the two plectin variants predominantly expressed in the cytoplasmic compartment (Cajal bands) of Schwann cells were identified as plectin (P)1 and P1c. Coimmunoprecipitation and immunolocalization experiments revealed complex formation of Cajal band plectin with β-dystroglycan, the core component of the dystrophin glycoprotein complex that in Schwann cells is crucial for the compartmentalization and stabilization of the myelin sheath. To study the functional implications of Schwann cell-specific plectin-β-dystroglycan interaction, we generated conditional (Schwann cell-restricted) plectin knockout mice. Ablation of plectin in myelinating Schwann cells (SCs) was found not to affect myelin sheath formation but to abrogate the tight association of the dystroglycan complex with the intermediate filament cytoskeleton. We show that the disruption of this association leads to the destabilization of the dystroglycan complex combined with increased myelin sheath deformations observed in the peripheral nerve during ageing of the animal.

Plectin-intermediate filament partnership in skin, skeletal muscle, and peripheral nerve

Plectin is a large, 500-kDa, intermediate filament (IF)-associated protein. It acts as a cytoskeletal crosslinker and signaling scaffold, affecting mechanical as well as dynamic properties of the cytoskeleton. As a member of the plakin family of cytolinker proteins, plectin has a multidomain structure that is responsible for its vast binding portfolio. It not only binds to all types of IFs, actin filaments and microtubules, but also to transmembrane receptors, proteins of the subplasma membrane protein skeleton, components of the nuclear envelope, and several kinases with known roles in migration, proliferation, and energy metabolism of cells. Due to alternative splicing, plectin is expressed as various isoforms with differing N-terminal heads that dictate their differential subcellular targeting. Through specific interactions with other proteins at their target sites and their ability to bind to all types of IFs, plectin molecules provide strategically located IF anchorage sites within the cytoplasm of cells. In this review, we will present an overview of the structural features and functional properties of plectin and discuss recent progress in defining the role of its isoforms in stress-prone tissues and the implicated diseases, with focus on skin, skeletal muscle, and Schwann cells of peripheral nerve.

The many faces of plectin and plectinopathies: pathology and mechanisms

Plectin, a giant multifunctional cytolinker protein, plays a crucial role in stabilizing and orchestrating intermediate filament networks in cells. Mutations in the human plectin gene result in multiple diseases manifesting with muscular dystrophy, skin blistering, and signs of neuropathy. The most common disease caused by plectin deficiency is epidermolysis bullosa simplex (EBS)-MD, a rare autosomal-recessive skin blistering disorder with late-onset muscular dystrophy. EBS-MD patients and plectin-deficient mice display pathologic desmin-positive protein aggregates, degenerated myofibrils, and mitochondrial abnormalities, the hallmarks of myofibrillar myopathies. In addition to EBS-MD, plectin mutations have been shown to cause EBS-MD with a myasthenic syndrome, limb-girdle muscular dystrophy type 2Q, EBS with pyloric atresia, and EBS-Ogna. This review focuses on clinical and pathological manifestations of these plectinopathies. It addresses especially plectin's role in skeletal muscle, where a loss of muscle fiber integrity and profound changes of myofiber cytoarchitecture are observed in its absence. Furthermore, the highly complex genetic and molecular structure of plectin is discussed; a high number of differentially spliced exons give rise to a variety of different isoforms, which fulfill distinct functions in different cell types and tissues. Plectin's abilities to act as a dynamic organizer of intermediate filament networks and to interact with a multitude of different interaction partners are the basis for its function as a scaffolding platform for proteins involved in signaling. Finally, the article addresses a series of genetically manipulated mouse lines that were generated to serve as powerful models to study functional and molecular consequences of plectin gene defects.

Epidermolysis bullosa - a group of skin diseases with different causes but commonalities in gene expression

Epidermolysis bullosa (EB) is a group of hereditary skin disorders. Although each subtype is caused by mutations in genes encoding differentially located components of the skin, the resulting phenotype is similar. In this study, we investigated similarities in the gene expression profiles of each subtype on mRNA level. Type XVI collagen (COL16A1), G0/G1 switch 2 (G0S2), fibronectin (FN1), ribosomal protein S27A (RPS27A) and low density lipoprotein receptor (LDLR) were shown to exhibit corresponding changes in gene expression in all three EB subtypes. While COL16A1, G0S2 and FN1 are up-regulated, LDLR and RPS27A mRNA levels are decreased. These data indicate that EB cells seem to take measures increasing their mechanical stability. Apoptosis is likely to be exacerbated, and migratory potential appears to be elevated. Protein degradation is hampered, and the release of fatty acids and glycerol is restricted, probably to save energy. These commonalities might benefit existing EB treatment strategies or could help to reveal new starting points for the treatment of EB in the future.

Epidermolysis bullosa simplex associated with muscular dystrophy and cardiac involvement

We report a new clinical variant of epidermolysis bullosa simplex with muscular dystrophy (EBS-MD) that was associated with cardiac involvement. A 33-year-old patient had atrial fibrillation, pericardial effusion, and hypokinetic left ventricular cardiac walls. The muscle biopsy material revealed diffuse endomysial fibrosis and small atrophic muscle fibers with rounded contours. A positive desmin expression with abnormal localization in the subsarcolemmal groups was observed. We concluded that patients with EBS-MD should be investigated carefully when there are associated cardiac findings.

Application of the procedural consolidation concept to surgical treatment of children with epidermolysis bullosa: a retrospective analysis

Aim

To assess the efficacy of the procedural consolidation concept (PCC) at reducing the number of sessions of general anesthesia necessary for treating children with epidermolysis bullosa (EB).

Methods

We examined the records of children treated at Children's Hospital of Zagreb between April 1999 and December 2007. Children treated before the introduction of PCC in January 2005 (n = 39) and after (n = 48) were analyzed in order to determine the effect of PCC on the occurrence of complications, days of hospitalization, and number of hospitalizations.

Results

During the study period, 53 patients underwent 220 sessions of general anesthesia for a total of 743 surgical interventions per session. Before the introduction of PCC (n = 39 patients, 83 sessions), the median number of interventions per session was 2 (range 1-5), and after the introduction of PCC (n = 48 patients, 137 sessions) it was 4 (range 3-7, P < 0.001). After the introduction of PCC, the median number of complications per anesthesia session increased from 2 (range 0-10) to 3 (range 0-10) (P = 0.027), but the median number of complications per surgical procedure decreased from 1 (range 0-10) to 0.6 (range 0-2.5) (P < 0.001). PCC lengthened each anesthesia session from a median of 65 minutes (range 35-655) to 95 minutes (range 50-405), (P < 0.001). Total length of hospitalization was similar before (median 1, range 1-4) and after (median 1, range 1-3) introduction of PCC (P = 0.169). The number of hospitalization days per procedure was 3 times lower after the introduction of PCC (median 0.3, range 0.2-3) than before (median 1, range 0.75-1.7) (P < 0.001).

Conclusion

PCC should be considered an option in the surgical treatment of children with EB.

Novel insertion mutation of ABCB1 gene in an ivermectin-sensitive Border Collie

P-glycoprotein (P-gp) is encoded by the ABCB1 gene and acts as an efflux pump for xenobiotics. In the Border Collie, a nonsense mutation caused by a 4-base pair deletion in the ABCB1 gene is associated with a premature stop to P-gp synthesis. In this study, we examined the full-length coding sequence of the ABCB1 gene in an ivermectin-sensitive Border Collie that lacked the aforementioned deletion mutation. The sequence was compared to the corresponding sequences of a wild-type Beagle and seven ivermectin-tolerant family members of the Border Collie. When compared to the wild-type Beagle sequence, that of the ivermectin-sensitive Border Collie was found to have one insertion mutation and eight single nucleotide polymorphisms (SNPs) in the coding sequence of the ABCB1 gene. While the eight SNPs were also found in the family members' sequences, the insertion mutation was found only in the ivermectin-sensitive dog. These results suggest the possibility that the SNPs are species-specific features of the ABCB1 gene in Border Collies, and that the insertion mutation may be related to ivermectin intolerance.

Myasthenic syndrome caused by plectinopathy

BACKGROUND

Plectin crosslinks intermediate filaments to their targets in different tissues. Defects in plectin cause epidermolysis bullosa simplex (EBS), muscular dystrophy (MD), and sometimes pyloric atresia. Association of EBS with a myasthenic syndrome (MyS) was documented in a single patient in 1999.

OBJECTIVES

To analyze the clinical, structural, and genetic aspects of a second and fatal case of EBS associated with a MyS and search for the genetic basis of the disease in a previously reported patient with EBS-MD-MyS.

METHODS

Clinical observations; histochemical, immunocytochemical, and electron microscopy studies of skeletal muscle and neuromuscular junction; and mutation analysis.

RESULTS

An African American man had EBS since early infancy, and progressive muscle weakness, hyperCKemia, and myasthenic symptoms refractory to therapy since age 3 years. Eventually he became motionless and died at age 42 years. At age 15 years, he had a marked EMG decrement, and a reduced miniature endplate potential amplitude. The myopathy was associated with dislocated muscle fiber organelles, structurally abnormal nuclei, focal plasmalemmal defects, and focal calcium ingress into muscle fibers. The neuromuscular junctions showed destruction of the junctional folds, and remodeling. Mutation analysis demonstrated a known p.Arg2319X and a novel c.12043dupG mutation in PLEC1. The EBS-MD-MyS patient reported in 1999 also carried c.12043dupG and a novel p.Gln2057X mutation. The novel mutations were absent in 200 Caucasian and 100 African American subjects.

CONCLUSIONS

The MyS in plectinopathy is attributed to destruction of the junctional folds and the myopathy to defective anchoring of muscle fiber organelles and defects in sarcolemmal integrity.

Plectin isoforms as organizers of intermediate filament cytoarchitecture

Intermediate filaments (IFs) form cytoplamic and nuclear networks that provide cells with mechanical strength. Perturbation of this structural support causes cell and tissue fragility and accounts for a number of human genetic diseases. In recent years, important additional roles, nonmechanical in nature, were ascribed to IFs, including regulation of signaling pathways that control survival and growth of the cells, and vectorial processes such as protein targeting in polarized cellular settings. The cytolinker protein plectin anchors IF networks to junctional complexes, the nuclear envelope and cytoplasmic organelles and it mediates their cross talk with the actin and tubulin cytoskeleton. These functions empower plectin to wield significant influence over IF network cytoarchitecture. Moreover, the unusual diversity of plectin isoforms with different N termini and a common IF-binding (C-terminal) domain enables these isoforms to specifically associate with and thereby bridge IF networks to distinct cellular structures. Here we review the evidence for IF cytoarchitecture being controlled by specific plectin isoforms in different cell systems, including fibroblasts, endothelial cells, lens fibers, lymphocytes, myocytes, keratinocytes, neurons and astrocytes, and discuss what impact the absence of these isoforms has on IF cytoarchitecture-dependent cellular functions.

Plectin expression patterns determine two distinct subtypes of epidermolysis bullosa simplex

Plectin is a cytoskeletal linker protein that has a dumbbell-like structure with a long central rod and N- and C-terminal globular domains. Mutations in the gene encoding plectin (PLEC1) cause two distinct autosomal recessive subtypes of epidermolysis bullosa (EB): EB simplex with muscular dystrophy (EBS-MD), and EB simplex with pyloric atresia (EBS-PA). Here, we demonstrate that normal human fibroblasts express two different plectin isoforms including full-length and rodless forms of plectin. We performed detailed analysis of plectin expression patterns in six EBS-MD and three EBS-PA patients. In EBS-PA, expression of all plectin domains was found to be markedly attenuated or completely lost; in EBS-MD, the expression of the N- and C-terminal domains of plectin remained detectable, although the expression of rod domains was absent or markedly reduced. Our data suggest that loss of the full-length plectin isoform with residual expression of the rodless plectin isoform leads to EBS-MD, and that complete loss or marked attenuation of full-length and rodless plectin expression underlies the more severe EBS-PA phenotype. These results also clearly account for the majority of EBS-MD PLEC1 mutation restriction within the large exon 31 that encodes the plectin rod domain, whereas EBS-PA PLEC1 mutations are generally outside exon 31.

Epidermolysis bullosa simplex with muscular dystrophy

Epidermolysis bullosa simplex (EBS) is an inherited skin disorder characterized by separation of the epidermis from the underlying dermis, with the cleavage plane lying within the basal-cell layer of the epithelium. The major clinical subtypes of EBS have a dominant inheritance and have been associated with genetic defects in specific domains of keratins K5 and K14 that result in abnormal organization of the keratin network and cell disruption. Autosomal recessive forms of EBS associated with extracutaneous manifestations, such as muscular dystrophy (MIM 226670) or pyloric atresia (MIM 612138), have been linked to genetic mutations in the gene for plectin (PLEC). PLEC mutations have also been found in 2 families with the rare dominant Ogna form of EBS. This article reviews current knowledge on EBS.

Plectin gene defects lead to various forms of epidermolysis bullosa simplex

Plectin is an important organizer of the keratin filament cytoskeleton in basal keratinocytes. It is essential for anchoring these filaments to the extracellular matrix via hemidesmosomal integrins. Loss of plectin or incorrect function of the protein due to mutations in its gene can lead to various forms of the skin blistering disease, epidermolysis bullosa simplex. Severity and subtype of the disease is dependent on the specific mutation and can be associated with (late-onset) muscular dystrophy or pyloric atresia. Mouse models mimicking the human phenotypes allow detailed study of plectin function.

Myofiber integrity depends on desmin network targeting to Z-disks and costameres via distinct plectin isoforms

Dysfunction of plectin, a 500-kD cytolinker protein, leads to skin blistering and muscular dystrophy. Using conditional gene targeting in mice, we show that plectin deficiency results in progressive degenerative alterations in striated muscle, including aggregation and partial loss of intermediate filament (IF) networks, detachment of the contractile apparatus from the sarcolemma, profound changes in myofiber costameric cytoarchitecture, and decreased mitochondrial number and function. Analysis of newly generated plectin isoform-specific knockout mouse models revealed that IF aggregates accumulate in distinct cytoplasmic compartments, depending on which isoform is missing. Our data show that two major plectin isoforms expressed in muscle, plectin 1d and 1f, integrate fibers by specifically targeting and linking desmin IFs to Z-disks and costameres, whereas plectin 1b establishes a linkage to mitochondria. Furthermore, disruption of Z-disk and costamere linkages leads to the pathological condition of epidermolysis bullosa with muscular dystrophy. Our findings establish plectin as the major organizer of desmin IFs in myofibers and provide new insights into plectin- and desmin-related muscular dystrophies.

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.

Epidermolysis bullosa naevi reveal a distinctive dermoscopic pattern

BACKGROUND

Large, asymmetrical and irregularly pigmented naevi in patients with epidermolysis bullosa (EB) have been reported often to mimic cutaneous melanoma clinically.

OBJECTIVES

As the biological course of these peculiar moles is benign, we assessed EB naevi with a dermatoscope to determine whether they could be reliably differentiated from cutaneous melanoma.

METHODS

We evaluated digital dermoscopic images of 23 EB naevi from 11 patients with EB and analysed these pigmented lesions according to pattern analysis, ABCD rule of dermoscopy and the seven-point checklist.

RESULTS

Melanoma-associated dermoscopic criteria such as multicomponent pattern (20 of 23), atypical pigment network (17 of 23), irregular dots/globules (16 of 23), irregular pigmentation (22 of 23) and an atypical vascular pattern (seven of 23) were frequently seen in EB naevi. In contrast, other criteria frequently associated with melanoma progression, such as irregular streaks, blue-whitish veil, regression structures (blue-whitish areas) or black dots, were rarely seen. Most lesions gave false-positive results when the scores of the dermoscopic diagnostic algorithms were calculated.

CONCLUSIONS

Recurring dermoscopic structures in EB naevi reveal a distinctive dermoscopic pattern of this recently defined entity. Although EB naevi represent an exception to dermoscopic diagnostic algorithms, their dermoscopic evaluation most often allows us to estimate their benign nature. Nevertheless, as an unequivocal discrimination from malignant melanoma in vivo is sometimes not possible, regular clinical follow up of EB naevi with histopathological evaluation of highly suspicious lesions is mandatory.

Plectin deficient epidermolysis bullosa simplex with 27-year-history of muscular dystrophy

BACKGROUND

Epidermolysis bullosa simplex associated with muscular dystrophy is caused by plectin deficiency.

OBJECTIVE

To report clinical, immunohistochemical, ultrastructural and molecular features of a 52-year-old Japanese patient affected with this disease, whose muscular disease had been followed-up for 27 years.

METHODS

We performed histopathological study, immunofluorescence, electron microscopic study and mutation detection analysis for plectin.

RESULTS

The patient developed blisters and erosions followed by nail deformity on the traumatized regions from birth. The skin lesions were continuously developed to date. The histopathological study showed subepidermal blister. Electron microscopic study showed blister formation inside the basal cells at the level just above the attachment plaque of hemidesmosome. Immunofluorescence showed complete loss of staining to plectin. The mutation analysis using protein truncation test and DNA sequencing revealed a C-to-T transition at nucleotide position 7006 of the plectin cDNA sequence, which lead a novel homozygous nonsense mutation (R2319X).

CONCLUSION

From the above results, the diagnosis of epidermolysis bullosa simplex associated with muscular dystrophy was made. Slight muscular dystrophy was noticed at the age of 25 years. The muscular dystrophy gradually progressed and she could not walk at the age of 46 years. However, she can still breathe and swallow by herself. This is the patient of this disease with the longest follow-up, and may indicate the slow progress of muscular condition of this disease.

Severe mucous membrane involvement in epidermolysis bullosa simplex with muscular dystrophy due to a novel plectin gene mutation

Epidermolysis bullosa simplex with muscular dystrophy (OMIM 226670) is an autosomal recessive disorder caused by mutations of the human plectin gene on chromosome 8q24. Here, we report a 3-year-old girl, offspring of a consanguineous Lebanese family, who presented with skin blistering and recurrent episodes of severe respiratory distress necessitating tracheotomy at the age of 2 years. Repeated examination did not provide any evidence of muscle involvement. Indirect immunofluorescence analysis of a diagnostic skin biopsy with four different domain specific plectin antibodies showed a complete absence of plectin staining. Mutation analysis revealed a novel homozygous single guanine insertion mutation (5588insG/5588insG) residing in the N-terminal part of exon 31 of the plectin gene.

CONCLUSION

The complete lack of protein expression, which may be attributed to a nonsense-mediated plectin mRNA decay, is likely to cause muscular dystrophy and other multisystem involvement later in life.

Identification of a Lethal Form of Epidermolysis Bullosa Simplex Associated with a Homozygous Genetic Mutation in Plectin

Genetic mutations in plectin, a cytoskeleton linker protein expressed in a large variety of tissues including skin, muscle, and nerves, cause epidermolysis bullosa simplex with muscular dystrophy, a recessive inherited disease characterized by blistering of the skin and late onset of muscular dystrophy, and Ogna epidermolysis bullosa simplex, a rare dominant inherited form of epidermolysis bullosa simplex with no muscular involvement. Here we report a novel homozygous genetic mutation (2727del14) in the plectin gene (PLEC1) associated with a lethal form of recessive inherited epidermolysis bullosa in a consanguineous family with three affected offspring. This new clinical variant of epidermolysis bullosa is characterized by general skin blistering, aplasia cutis of the limbs, developmental complications, and rapid demise after birth. Mutation 2727del14 is the first genetic defect described in PLEC1 that disrupts the plakin domain of plectin. The severe phenotype of the patients may be linked to the role of the N-terminal domain in the function of plectin and develops the understanding of the genotype-phenotype correlations in the genodermatoses affecting the dermal-epidermal junction.

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.

Disorganization of the desmin cytoskeleton and mitochondrial dysfunction in plectin-related epidermolysis bullosa simplex with muscular dystrophy

Mutations of the human plectin gene (Plec1) cause autosomal recessive epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). Here, we report on molecular mechanisms leading to severe dystrophic muscle alterations in EBS-MD. Analysis of a 25-yr-old EBS-MD patient carrying a novel homozygous 16-bp insertion mutation (13803ins16/13803ins16) close to the intermediate filament (IF) binding site of plectin showed severe disorganization of the myogenic IF cytoskeleton. Intermyofibrillar and subsarcolemmal accumulations of assembled but highly unordered desmin filaments may be attributed to impaired desmin binding capability of the mutant plectin. This IF pathology was also associated with severe mitochondrial dysfunction, suggesting that the muscle pathology of EBS-MD caused by IF disorganization leads not only to defects in mechanical force transduction but also to metabolic dysfunction. Beyond EBS-MD, our data may contribute to the understanding of other myopathies characterized by sarcoplasmic IF accumulations such as desminopathies or alpha-B-crystallinopathies.

A site-specific plectin mutation causes dominant epidermolysis bullosa simplex Ogna: two identical de novo mutations

Plectin is one of the largest and most versatile cytolinker proteins known. In basal keratinocytes it links the intermediate filament network to cell membrane-associated hemidesmosomes. Several mutations in its gene have been identified that lead to the recessive disease epidermolysis bullosa with muscular dystrophy. We report here a mutation that leads to a dominant form of the disease, epidermolysis bullosa simplex Ogna. We found that the epidermolysis bullosa simplex Ogna phenotype is due to a site-specific missense mutation within plectin's rod domain. Further, we show that epidermolysis bullosa simplex Ogna is not restricted to a single Norwegian kindred as previously believed. A German family with the phenotypic hallmarks of epidermolysis bullosa simplex Ogna was found to carry an identical de novo mutation. These two mutations arose about 200 y apart in time. Consistent with the absence of muscular symptoms in these patients, muscle biopsies from several epidermolysis bullosa simplex Ogna members of the Norwegian kindred showed normal staining patterns using antibodies to plectin. Skin changes in epidermolysis bullosa simplex Ogna patients are documented on the ultrastructural level.

Spotting the target: microarrays for disease gene discovery

Microarray technologies enable genome-scale expression measurements. Already proved to be of value for the functional analysis of individual genes and biological processes, the application of expression profiling to disease gene discovery is now growing in importance and practicality.