Novel and recurrent mutations in the laminin-5 genes causing lethal junctional epidermolysis bullosa: molecular basis and clinical course of Herlitz disease

Extracellular matrix-derived materials for tissue engineering and regenerative medicine: A journey from isolation to characterization and application

Biomaterial choice is an essential step during the development tissue engineering and regenerative medicine (TERM) applications. The selected biomaterial must present properties allowing the physiological-like recapitulation of several processes that lead to the reestablishment of homeostatic tissue or organ function. Biomaterials derived from the extracellular matrix (ECM) present many such properties and their use in the field has been steadily increasing. Considering this growing importance, it becomes imperative to provide a comprehensive overview of ECM biomaterials, encompassing their sourcing, processing, and integration into TERM applications. This review compiles the main strategies used to isolate and process ECM-derived biomaterials as well as different techniques used for its characterization, namely biochemical and chemical, physical, morphological, and biological. Lastly, some of their applications in the TERM field are explored and discussed.

The Interaction of LAMA2 and Duration of Illness Affects the Thickness of the Right Transverse Temporal Gyrus in Major Depressive Disorder

Background

Depression is a heritable brain disorder. Laminin genes were recently identified to affect the brain's overall thickness through neurogenesis, differentiation, and migration in depression. This study aims to explore the effects of the LAMA2's single nucleotide polymorphisms (SNP), a subunit gene of laminin, on the detected brain regions of patients with major depressive disorder (MDD).

Methods

The study included 89 patients with MDD and 60 healthy controls with T1-weighted structural magnetic resonance imaging and blood samples for genotyping. The interactions between LAMA2 gene SNPs and diagnosis as well as duration of illness (DOI) were explored on brain measures controlled for age, gender, and site.

Results

The right transverse temporal gyrus and right parahippocampal gyrus showed reduced thickness in MDD. Almost all seven LAMA2 SNPs showed significant interactions with diagnosis on both gyrus (corrected p < 0.05 or trending). In MDD, rs6569604, rs2229848, rs2229849, rs2229850, and rs2784895 interacted with DOI on the right transverse temporal gyrus (corrected p < 0.05), but not the right parahippocampal gyrus.

Conclusion

The thickness of the right transverse temporal gyrus in patients with MDD may be affected by LAMA2 gene and DOI.

Chromosome-level Dinobdella ferox genome provided a molecular model for its specific parasitism

BACKGROUND

Dinobdella ferox is the most frequently reported leech species parasitizing the mammalian nasal cavity. However, the molecular mechanism of this special parasitic behavior has remained largely unknown.

METHODS

PacBio long-read sequencing, next-generation sequencing (NGS), and Hi-C sequencing were employed in this study to generate a novel genome of D. ferox, which was annotated with strong certainty using bioinformatics methods. The phylogenetic and genomic alterations of D. ferox were then studied extensively alongside the genomes of other closely related species. The obligatory parasitism mechanism of D. ferox was investigated using RNA-seq and proteomics data.

RESULTS

PacBio long-read sequencing and NGS yielded an assembly of 228 Mb and contig N50 of 2.16 Mb. Along Hi-C sequencing, 96% of the sequences were anchored to nine linkage groups and a high-quality chromosome-level genome was generated. The completed genome included 19,242 protein-coding genes. For elucidating the molecular mechanism of nasal parasitism, transcriptome data were acquired from the digestive tract and front/rear ends of D. ferox. Examining secretory proteins in D. ferox saliva helped to identify intimate connections between these proteins and membrane proteins in nasal epithelial cells. These interacting proteins played important roles in extracellular matrix (ECM)-receptor interaction, tight junction, focal adhesion, and adherens junction. The interaction between D. ferox and mammalian nasal epithelial cells included three major steps of pattern recognition, mucin connection and breakdown, and repair of ECM. The remodeling of ECM between epithelial cells of the nasal mucosa and epithelial cells of D. ferox may produce a stable adhesion environment for parasitism.

CONCLUSIONS

Our study represents the first-ever attempt to propose a molecular model for specific parasitism. This molecular model may serve as a practical reference for parasitism models of other species and a theoretical foundation for a molecular process of parasitism.

Junctional epidermolysis bullosa: genotype-phenotype correlations

Junctional epidermolysis bullosa most commonly results from mutations in theLAMA3, LAMB3, LAMC2, COL17A1, ITGA6 and ITGB4genes. Junctional epidermolysis bullosa is characterized by clinical heterogeneity. To date, scientific findings allow to evaluate correlations between the severity of clinical manifestations and genetic defects underlying in the development of the disease. A systematic literature search was performed using PubMed and RSCI, and keywords including junctional epidermolysis bullosa, laminin 332, collagen XVII, 64 integrin. The review includes description of clinical findings of junctional epidermolysis bullosa, mutation location and types, its impact on protein production and functions. To evaluate the impact of gene mutation on protein functions, this review explores the structure and functions of lamina lucida components, including laminin 332, collagen XVII and 64 integrin, which are frequently associated with the development of junctional epidermolysis bullosa. The correlation between severe types of junctional epidermolysis bullosa and mutations resulting in premature stop codon generation and complete absence of protein expression has been described. Although, genotype-phenotype correlations should be analyzed carefully due to mechanisms which enable to improve protein expression.

Molecular and Clinical Outcomes After Intravenous Gentamicin Treatment for Patients With Junctional Epidermolysis Bullosa Caused by Nonsense Variants

IMPORTANCE

Junctional epidermolysis bullosa (JEB) is an incurable blistering skin disorder with high infant mortality often caused by nonsense variants in the genes that encode laminin 332.

OBJECTIVE

To evaluate the safety and outcomes following intravenous gentamicin readthrough therapy and subsequent laminin 332 expression in patients with JEB.

DESIGN, SETTING, AND PARTICIPANTS

This open-label, pilot nonrandomized clinical trial assessed 1 course of low- or high-dose intravenous gentamicin, including follow-up at 30 and 90 days after treatment. Five pediatric patients with JEB (2 with intermediate JEB and 3 with severe JEB) and confirmed nonsense variants in LAMA3 or LAMB3 in 1 or 2 alleles and decreased expression of laminin 332 at the dermal-epidermal junction of their skin participated in the study, which was performed at a single institution in collaboration with physicians and home infusion services near the patients from April 1, 2019, to February 28, 2021, with follow-up until May 31, 2021.

INTERVENTIONS

Three patients received gentamicin at 7.5 mg/kg daily for 14 days, and 2 patients received gentamicin at 10 mg/kg daily for 24 days.

MAIN OUTCOMES AND MEASURES

Primary outcomes were change in expression of laminin 332 in patients' skin and assessments for safety (ototoxic effects, nephrotoxic effects, and autoimmune response). Secondary outcomes included wound healing in monitored wounds and Epidermolysis Bullosa Disease Activity and Scarring Index (EBDASI) score.

RESULTS

After gentamicin treatment, all 5 patients (age range, 3 months to 10 years, 4 [80%] female) exhibited increased laminin 332 in the dermal-epidermal junction. By 1 month, 7 of 9 wounds in patients receiving low-dose intravenous gentamicin and all wounds in patients receiving high-dose intravenous gentamicin exhibited at least 50% wound closure. By 3 months, 8 of 9 wounds in patients receiving low-dose gentamicin and all wounds in patients receiving high-dose intravenous gentamicin exhibited greater than 85% closure. All 3 patients who were evaluated with EBDASI showed a decrease in total activity scores that met minimal clinically important differences 1 month after treatment. All 5 patients completed the study, and no ototoxic effects, nephrotoxic effects, or anti-laminin 332 antibodies were detected.

CONCLUSIONS AND RELEVANCE

In this nonrandomized clinical trial, intravenous gentamicin therapy was associated with induced readthrough of nonsense variants in patients with JEB, restored functional laminin 332 in their skin, and wound closure during the 3-month study period. Although long-term safety and efficacy requires further evaluation, a single cycle of intravenous gentamicin may be a safe and readily available therapy in the short term for this population of patients with JEB.

TRIAL REGISTRATION

ClinicalTrials.gov Identifiers: NCT03526159 and NCT04140786.

Novel variants in LAMA3 and COL7A1 and recurrent variant in KRT5 underlying epidermolysis bullosa in five Chinese families

Epidermolysis bullosa (EB) is a group of clinically and genetically heterogeneous diseases characterized by trauma-induced mucocutaneous fragility and blister formation. Here, we investigated five Chinese families with EB, and eight variants including a novel nonsense variant (c.47G>A, p.W16*) in LAMA3, a known recurrent variant (c.74C>T, p.P25L) in KRT5, 2 novel (c.2531T>A, p.V844E; c.6811_6814del, p.R2271fs) and 4 known (c.6187C>T, p.R2063W; c.7097G>A, p.G2366D; c.8569G>T, p.E2857*; c.3625_3635del, p.S1209fs) variants in COL7A1 were detected. Notably, this study identified a nonsense variant in LAMA3 that causes EB within the Chinese population and revealed that this variant resulted in a reduction in LAMA3 mRNA and protein expression levels by nonsense-mediated mRNA decay. Our study expands the mutation spectra of Chinese patients with EB.

Gentamicin Induces Laminin 332 and Improves Wound Healing in Junctional Epidermolysis Bullosa Patients with Nonsense Mutations

Generalized severe junctional epidermolysis bullosa (GS-JEB) is an incurable and fatal autosomal recessively inherited blistering skin disease caused by mutations in the LAMA3, LAMB3, or LAMC2 genes. Most of these mutations are nonsense mutations that create premature termination codons that lead to impaired production of functional laminin 332, a protein needed for epidermal-dermal adherence. Gentamicin induces readthrough of nonsense mutations and restores the full-length protein in various genetic diseases. Using primary keratinocytes from three GS-JEB patients, we showed that gentamicin induced functional laminin 332 that reversed a JEB-associated, abnormal cell phenotype. In a subsequent open-label trial involving the same patients, we examined whether 0.5% gentamicin ointment applied topically to open skin wounds could promote nonsense mutation readthrough and create new laminin 332 in the patients' skin. Gentamicin-treated wounds exhibited increased expression of laminin 332 at the dermal-epidermal junction for at least 3 months and were associated with improved wound closure. There were no untoward side effects from topical gentamicin. The newly induced laminin 332 did not generate anti-laminin 332 autoantibodies in either the patients' blood or skin. Gentamicin readthrough therapy may be a treatment for GS-JEB patients with nonsense mutations.

Attenuation of Severe Generalized Junctional Epidermolysis Bullosa by Systemic Treatment with Gentamicin

Severe generalized junctional epidermolysis bullosa (JEB), a lethal genodermatosis, is mainly caused by premature termination codons (PTCs) in one of the three genes encoding the anchoring protein laminin-332. Only symptomatic treatment has been established; overcoming PTCs by aminoglycosides may represent an interesting alternative. This retrospective study aimed at assessing for the first time the clinical effects of systemic gentamicin application in infants with severe generalized JEB. Five patients, homozygous or compound-heterozygous for PTCs in the gene LAMB3, were treated with gentamicin which was administered intravenously or by intramuscular injection at doses of 7.5 mg/kg/d for three weeks. Skin biopsies were investigated by immunofluorescence analyses. Clinical effects of the medication were recorded with a parent questionnaire and by assessing weight-for-age charts. Gentamicin application was well tolerated, long hospitalization was not required. Low levels of laminin-332 could be detected in a skin sample obtained after treatment. Gentamicin had a positive impact on skin fragility and daily life in four patients but did not influence weight gain and failed to reverse the lethal course of the disease. Gentamicin injections should be considered regularly in cases of severe generalized JEB caused by PTCs as they may attenuate JEB symptoms without impeding quality of life.

Targeted next-generation sequencing identifies a novel mutation of LAMB3 in a Chinese neonatal patient presented with junctional epidermolysis bullosa

RATIONALE

Epidermolysis bullosa (EB) refers to a group of rare inherited mechanobullous disorders that present with great clinical and genetic heterogeneity. Its severity ranges from mild blistering to life-threatening. However, the clinical symptoms of different types of EB overlap significantly, especially at an early stage. Thus it is important to clarify the diagnosis for prognostic implications, patient management, and genetic counseling.

PATIENT CONCERNS

Here, we report a 10-day-old male neonate from a nonconsanguineous Chinese family. He showed a bulla on the left lower limb lasting for 3 days, erosions around fingertips and toe tips at birth (predominantly on fingers), with the progressive spread of generalized blisters over the body as well as the development of the illness.

DIAGNOSIS

The patient was diagnosed with suspected epidermolysis bullosa according to the blisters and erosions of the body as well as the pyogenic fingernails and toenails.

INTERVENTIONS

The patient was performed targeted next-generation sequencing (NGS) with 9 candidate known genes, subsequently, his parents were screened for the mutations identified in the patient by Sanger sequencing. Then, prenatal diagnosis with amniotic fluid was performed in the subsequent pregnancy by Sanger sequencing.

OUTCOMES

Targeted NGS revealed a previously unreported splice site variant c.822+1G>A (IVS 8) and a known recurrent nonsense variant c.124C>T (p.Arg42Ter, exon 3) in LAMB3 gene. The patient's father possessed a heterozygous c.822+1G>A mutation, his mother possessed a heterozygous c.124C>T mutation. For the subsequent pregnancy, the analyses of amniotic fluid sample indicated that the fetus carried neither of the mutations.

LESSONS

Our finding will further enlarge LAMB3 genotype-phenotype correlations spectrum. Targeted capture sequencing is a valuable method to illustrate precise molecular pathology in patients with EB disorders, especially at an early stage of the clinical evaluation of complex disorders to avoid unnecessary and economically wasteful tests.

Gentamicin induces LAMB3 nonsense mutation readthrough and restores functional laminin 332 in junctional epidermolysis bullosa

Herlitz junctional epidermolysis bullosa (H-JEB) is an incurable, devastating, and mostly fatal inherited skin disease for which there is only supportive care. H-JEB is caused by loss-of-function mutations in LAMA3, LAMB3, or LAMC2, leading to complete loss of laminin 332, the major component of anchoring filaments, which mediate epidermal-dermal adherence. LAMB3 (laminin β3) mutations account for 80% of patients with H-JEB, and ∼95% of H-JEB-associated LAMB3 mutations are nonsense mutations leading to premature termination codons (PTCs). In this study, we evaluated the ability of gentamicin to induce PTC readthrough in H-JEB laminin β3-null keratinocytes transfected with expression vectors encoding eight different LAMB3 nonsense mutations. We found that gentamicin induced PTC readthrough in all eight nonsense mutations tested. We next used lentiviral vectors to generate stably transduced H-JEB cells with the R635X and C290X nonsense mutations. Incubation of these cell lines with various concentrations of gentamicin resulted in the synthesis and secretion of full-length laminin β3 in a dose-dependent and sustained manner. Importantly, the gentamicin-induced laminin β3 led to the restoration of laminin 332 assembly, secretion, and deposition within the dermal/epidermal junction, as well as proper polarization of α6β4 integrin in basal keratinocytes, as assessed by immunoblot analysis, immunofluorescent microscopy, and an in vitro 3D skin equivalent model. Finally, newly restored laminin 332 corrected the abnormal cellular phenotype of H-JEB cells by reversing abnormal cell morphology, poor growth potential, poor cell-substratum adhesion, and hypermotility. Therefore, gentamicin may offer a therapy for H-JEB and other inherited skin diseases caused by PTC mutations.

Application of whole exome sequencing in elucidating the phenotype and genotype spectrum of junctional epidermolysis bullosa: A preliminary experience of a tertiary care centre in India

BACKGROUND

Junctional epidermolysis bullosa (JEB) is a diverse group of genodermatoses associated with extreme skin fragility. Despite several well-characterized genetic studies, molecular diagnosis of this heterogeneous group is still challenging. Recent advances in the field of genomics have seen the successful implementation of whole exome sequencing (WES) as a fast and efficient diagnostic strategy in several genodermatoses.

OBJECTIVE

In view of the scarcity and need of molecular studies for JEB in India, we sought to explore the potential of WES in understanding the mutational spectrum of this rare, in certain subtypes lethal, sub-group of EB.

METHODS

WES was performed using genomic DNA from each case of EB, followed by massively parallel sequencing. Resulting reads were mapped to the human reference genome hg19. Sanger sequencing subsequently confirmed the potentially pathogenic mutations.

RESULTS

Overall, four unrelated families (6 patients) of JEB with a highly variable clinical presentation including a rare case of LOC syndrome were studied. WES revealed 4 variations in 3 genes (LAMA3, LAMB3 and COL17A1) that are implicated in JEB. None of the variations were recurrent. In addition we proposed the probable molecular consequence of a missense mutation on the structure-function relationship of lamininβ3 protein through computational modeling studies.

CONCLUSIONS

Being the first report documenting the phenotype-genotype correlations of JEB patients from India, our preliminary experience with WES is clearly encouraging and serves as a nidus for future large-scale molecular studies to actively identify and understand JEB patients in Indian population.

Genotype, Clinical Course, and Therapeutic Decision Making in 76 Infants with Severe Generalized Junctional Epidermolysis Bullosa

Severe generalized junctional epidermolysis bullosa, a lethal hereditary blistering disorder, is usually treated by palliative care. Allogeneic stem cell transplantation (SCT) has been proposed as a therapeutic approach, yet without clinical evidence. Decision making was evaluated retrospectively in 76 patients with severe generalized junctional epidermolysis bullosa born in the years 2000-2015. The diagnosis was based on the absence of laminin-332 in skin biopsies. With an incidence of 1 of 150,000, severe generalized junctional epidermolysis bullosa occurred more often than published previously. Eleven as yet unreported mutations in the laminin-332 genes were detected. Although patients homozygous for the LAMB3 mutation c.1903C>T lived longer than the others, life expectancy was greatly diminished (10.8 vs. 4.6 months). Most patients failed to thrive. In two patients with initially normal weight gain, the decision for SCT from haploidentical bone marrow or peripheral blood was made. Despite transiently increasing skin erosions, the clinical status of both subjects stabilized for several weeks after SCT, but finally deteriorated. Graft cells, but no laminin-332, were detected in skin biopsies. The patients died 96 and 129 days after SCT, respectively, one of them after receiving additional skin grafts. Treatment of severe generalized junctional epidermolysis bullosa by SCT is a last-ditch attempt still lacking proof of efficacy.

Extracellular matrix structure

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network composed of collagens, proteoglycans/glycosaminoglycans, elastin, fibronectin, laminins, and several other glycoproteins. Matrix components bind each other as well as cell adhesion receptors forming a complex network into which cells reside in all tissues and organs. Cell surface receptors transduce signals into cells from ECM, which regulate diverse cellular functions, such as survival, growth, migration, and differentiation, and are vital for maintaining normal homeostasis. ECM is a highly dynamic structural network that continuously undergoes remodeling mediated by several matrix-degrading enzymes during normal and pathological conditions. Deregulation of ECM composition and structure is associated with the development and progression of several pathologic conditions. This article emphasizes in the complex ECM structure as to provide a better understanding of its dynamic structural and functional multipotency. Where relevant, the implication of the various families of ECM macromolecules in health and disease is also presented.

Laminins: Roles and Utility in Wound Repair

Significance: Laminins are complex extracellular macromolecules that are major players in the control of a variety of core cell processes, including regulating rates of cell proliferation, differentiation, adhesion, and migration. Laminins, and related extracellular matrix components, have essential roles in tissue homeostasis; however, during wound healing, the same proteins are critical players in re-epithelialization and angiogenesis. Understanding how these proteins influence cell behavior in these different conditions holds great potential in identifying new strategies to enhance normal wound closure or to treat chronic/nonhealing wounds. Recent Advances: Laminin-derived bioactive peptides and, more recently, laminin-peptide conjugated scaffolds, have been designed to improve tissue regeneration after injuries. These peptides have been shown to be effective in decreasing inflammation and granulation tissue, and in promoting re-epithelialization, angiogenesis, and cell migration. Critical Issues: Although there is now a wealth of knowledge concerning laminin form and function, there are still areas of some controversy. These include the relative contribution of two laminin-based adhesive devices (focal contacts and hemidesmosomes) to the re-epithelialization process, the impact and implications of laminin proteolytic processing, and the importance of laminin polymer formation on cell behavior. In addition, the roles in wound healing of the laminin-related proteins, netrins, and LaNts are still to be fully defined. Future Directions: The future of laminin-based therapeutics potentially lies in the bioengineering of specific substrates to support laminin deposition for ex vivo expansion of autologous cells for graft formation and transplantation. Significant recent advances suggest that this goal is within sight.

Epidermolysis bullosa in Danish Hereford calves is caused by a deletion in LAMC2 gene

BACKGROUND

Heritable forms of epidermolysis bullosa (EB) constitute a heterogeneous group of skin disorders of genetic aetiology that are characterised by skin and mucous membrane blistering and ulceration in response to even minor trauma. Here we report the occurrence of EB in three Danish Hereford cattle from one herd.

RESULTS

Two of the animals were necropsied and showed oral mucosal blistering, skin ulcerations and partly loss of horn on the claws. Lesions were histologically characterized by subepidermal blisters and ulcers. Analysis of the family tree indicated that inbreeding and the transmission of a single recessive mutation from a common ancestor could be causative. We performed whole genome sequencing of one affected calf and searched all coding DNA variants. Thereby, we detected a homozygous 2.4 kb deletion encompassing the first exon of the LAMC2 gene, encoding for laminin gamma 2 protein. This loss of function mutation completely removes the start codon of this gene and is therefore predicted to be completely disruptive. The deletion co-segregates with the EB phenotype in the family and absent in normal cattle of various breeds. Verifying the homozygous private variants present in candidate genes allowed us to quickly identify the causative mutation and contribute to the final diagnosis of junctional EB in Hereford cattle.

CONCLUSIONS

Our investigation confirms the known role of laminin gamma 2 in EB aetiology and shows the importance of whole genome sequencing in the analysis of rare diseases in livestock.

A truncating mutation in the laminin-332α chain highlights the role of the LG45 proteolytic domain in regulating keratinocyte adhesion and migration

BACKGROUND

Altered function of laminin-332 (α3β3γ2) consequent to mutations in the LAMA3, LAMB3 and LAMC2 genes causes junctional epidermolysis bullosa non-Herlitz (JEB-nH). JEB-nH patients suffer from skin blistering and have an increased risk of developing aggressive skin carcinomas in adulthood. Laminin-332 is proteolytically processed and its extracellular mature form lacks the α3 chain C-terminal globules 4 and 5 (LG45). The LG45 tandem has cell adhesion and protumorigenic properties. However, mutations that affect this domain are very rare and their functional effects in patients have not been explored to date.

OBJECTIVE

To characterize molecularly an adult patient with JEB-nH and altered laminin-332 expression presenting multiple skin carcinomas, and to analyse LG45-mediated biological functions using keratinocytes from the patient.

METHODS

A mutational search in laminin-332 genes was performed by hetero-duplex analysis. LAMA3 mRNA and laminin-332 protein levels in patient keratinocytes were investigated by real-time reverse transcriptase polymerase chain reaction and radioimmunoprecipitation assay, respectively. Keratinocyte migration was examined by scratch and Boyden chamber assays.

RESULTS

We identified a homozygous LAMA3 mutation, p.Leu1648TrpfsX32, which truncates the last 45 amino acids of the carboxyl terminal LG5 subdomain. Gene expression studies revealed that the mutant transcripts were stable and even increased, precursor laminin-332 molecules were retained intracellularly and the amount of mature extracellular heterotrimers was reduced to about 50%. Finally, the patient's keratinocytes migrated faster than normal keratinocytes.

CONCLUSIONS

Structural disruption of LG5 highlights the critical functions of the LG45 proteolytic region in precursor laminin-332 secretion and keratinocyte adhesion and migration. Perturbation of LG45 function might explain the non-aggressive behaviour of carcinomas in this patient.

Molecular identification of collagen 17a1 as a major genetic modifier of laminin gamma 2 mutation-induced junctional epidermolysis bullosa in mice

Epidermolysis Bullosa (EB) encompasses a spectrum of mechanobullous disorders caused by rare mutations that result in structural weakening of the skin and mucous membranes. While gene mutated and types of mutations present are broadly predictive of the range of disease to be expected, a remarkable amount of phenotypic variability remains unaccounted for in all but the most deleterious cases. This unexplained variance raises the possibility of genetic modifier effects. We tested this hypothesis using a mouse model that recapitulates a non-Herlitz form of junctional EB (JEB) owing to the hypomorphic jeb allele of laminin gamma 2 (Lamc2). By varying normally asymptomatic background genetics, we document the potent impact of genetic modifiers on the strength of dermal-epidermal adhesion and on the clinical severity of JEB in the context of the Lamc2(jeb) mutation. Through an unbiased genetic approach involving a combination of QTL mapping and positional cloning, we demonstrate that Col17a1 is a strong genetic modifier of the non-Herlitz JEB that develops in Lamc2(jeb) mice. This modifier is defined by variations in 1-3 neighboring amino acids in the non-collagenous 4 domain of the collagen XVII protein. These allelic variants alter the strength of dermal-epidermal adhesion in the context of the Lamc2(jeb) mutation and, consequentially, broadly impact the clinical severity of JEB. Overall the results provide an explanation for how normally innocuous allelic variants can act epistatically with a disease causing mutation to impact the severity of a rare, heritable mechanobullous disorder.

Laminin 332 in junctional epidermolysis bullosa

Laminin 332 is an essential component of the dermal-epidermal junction, a highly specialized basement membrane zone that attaches the epidermis to the dermis and thereby provides skin integrity and resistance to external mechanical forces. Mutations in the LAMA3, LAMB3 and LAMC2 genes that encode the three constituent polypeptide chains, α3, β3 and γ2, abrogate or perturb the functions of laminin 332. The phenotypic consequences are diminished dermal-epidermal adhesion and, as clinical symptoms, skin fragility and mechanically induced blistering. The disorder is designated as junctional epidermolysis bullosa (JEB). This article delineates the signs and symptoms of the different forms of JEB, the mutational spectrum, genotype-phenotype correlations as well as perspectives for future molecular therapies.

Inherited junctional epidermolysis bullosa (Herlitz type) in German black-headed mutton sheep

This report describes the microscopical, immunohistochemical and ultrastructural findings in the first ovine cases of the Herlitz type of inherited junctional epidermolysis bullosa. Sixteen German black-headed mutton lambs and one crossbred lamb had blisters and ulceration of the skin and mucous membranes in addition to alterations of the horn of the hooves. Microscopically, there was separation of the dermoepidermal junction, which was confirmed to be located in the lamina lucida of the basement membrane by electron microscopy. In areas of subepidermal splitting the hemidesmosomes were missing and in adjacent areas they appeared to be rudimentary and reduced in number. Immunohistochemistry for laminin 5 revealed a markedly reduced expression of this molecule on the dermal side of the blisters, while expression of collagen VII was normal.

Early intra-amniotic gene transfer using lentiviral vector improves skin blistering phenotype in a murine model of Herlitz junctional epidermolysis bullosa

Mutations of the LAMB3 gene cause a lethal form of junctional epidermolysis bullosa (JEB). We hypothesized that early intra-amniotic gene transfer in a severe murine model of JEB would improve or correct the skin phenotype. Time-dated fetuses from heterozygous LAMB3(IAP) breeding pairs underwent ultrasound guided intra-amniotic injection of lentiviral vector encoding the murine LAMB3 gene at embryonic day 8 (E8). Gene expression was monitored by immunohistochemistry. The transgenic laminin-β3 chain was shown to assemble with its endogenous partner chains, resulting in detectable amounts of laminin-332 in the basement membrane zone of skin and mucosa. Ultrastructually, the restoration of ∼60% of hemidesmosomal structures was also noted. Although we could correct the skin phenotype in 11.9% of homozygous LAMB3(IAP) mice, none survived beyond 48 h. However, skin transplants from treated E18 homozygous LAMB3(IAP) fetuses maintained normal appearance for 6 months with persistence of normal assembly of laminin-332. These results demonstrate for the first time long-term phenotypic correction of the skin pathology in a severe model of JEB by in vivo prenatal gene transfer. Although survival remained limited due to the limitations of this mouse model, this study supports the potential for treatment of JEB by prenatal gene transfer.

Herlitz junctional epidermolysis bullosa: diagnostic features, mutational profile, incidence and population carrier frequency in the Netherlands

BACKGROUND

Junctional epidermolysis bullosa, type Herlitz (JEB-H) is a lethal, autosomal recessive blistering disease caused by null mutations in the genes coding for the lamina lucida/densa adhesion protein laminin-332 (LAMB3, LAMA3 and LAMC2).

OBJECTIVES

To present the diagnostic features and molecular analyses of all 22 patients with JEB-H in the Dutch Epidermolysis Bullosa Registry between 1988 and 2011, and to calculate the disease incidence and carrier frequency in the Netherlands.

METHODS

All patients were analysed with immunofluorescence antigen mapping (IF), electron microscopy (EM) and molecular analysis.

RESULTS

The mean lifespan of our patients with JEB-H was 5·8 months (range 0·5-32·6). IF showed absent (91%) or strongly reduced (9%) staining for laminin-332 with monoclonal antibody GB3. In EM the hemidesmosomes and sub-basal dense plates were hypoplastic or absent. We identified mutations in all 22 patients: in 19 we found LAMB3 mutations, in two LAMA3 mutations, and in one LAMC2 mutations. We found three novel splice site mutations in LAMB3: (i) c.29-2A>G resulting in an out-of-frame skip of exon 3 and a premature termination codon (PTC); (ii) c.1289-2_1296del10 leading to an out-of-frame skip of exon 12 and a PTC; and (iii) c.3228+1G>T leading to an exon 21 skip.

CONCLUSIONS

All diagnostic tools should be evaluated to clarify the diagnosis of JEB-H. We have identified 11 different mutations in 22 patients with JEB-H, three of them novel. In the Netherlands the incidence rate of JEB-H is 4·0 per one million live births. The carrier frequency of a JEB-H mutation in the Dutch population is 1 in 249.

Type XVII collagen (BP180) can function as a cell-matrix adhesion molecule via binding to laminin 332

Collagen XVII (COL17) is a transmembrane glycoprotein that is expressed on the basal surface of basal epidermal keratinocytes. Previous observations have led to the hypothesis that an interaction between COL17 and laminin 332, an extracellular matrix protein, contributes to the attachment of the basal keratinocyte to the basement membrane. In order to isolate and manipulate COL17 interactions with ECM components, we induced COL17 expression in two cells lines, SK-MEL1 and K562, that exhibit little or no capacity to attach to our test substrates, including laminin 332, types I and IV collagen, and fibronectin. Cells expressing high levels of COL17 preferentially adhered to a laminin 332 matrix, and, to a lesser extent, type IV collagen, while showing little or no binding to type I collagen or fibronectin. A quantitative analysis of cell adhesive forces revealed that, compared with COL17-negative cells, COL17-positive cells required over 7-fold greater force to achieve 50% detachment from a laminin 332 substrate. When a cell preparation (either K562 or SK-MEL1) with heterogeneous COL17 expression levels was allowed to attach to a laminin 332 matrix, the COL17-positive and COL17-negative cells differentially sorted to the bound and unbound cell fractions, respectively. COL17-dependent attachment to laminin 332 could be reduced or abolished by siRNA-mediated knock-down of COL17 expression or by adding to the assay wells specific antibodies against COL17 or laminin 332. These findings provide strong support for the hypothesis that cell surface COL17 can interact with laminin 332 and, together, participate in the adherence of a cell to the extracellular matrix.

A Japanese-specific recurrent mutation and a novel splice site mutation in the LAMC2 gene identified in two Japanese families with Herlitz junctional epidermolysis bullosa

BACKGROUND

Herlitz junctional epidermolysis bullosa (H-JEB) is an extremely rare genodermatosis characterized by lethality owing to severe blister formation. We report two unrelated Japanese patients with H-JEB. Genetic analyses detected a single nonsense mutation on the LAMC2 gene in these two patients.

AIM

To identify the mutation involved and describe the first reported Japanese recurrent mutation in the LAMC2 gene.

METHODS

Direct sequencing was performed of DNA from either peripheral blood or fetal cells in amniotic fluid. Reverse transcriptase PCR was used to confirm that an aberrant transcript resulted from the splice site mutation. A haplotype analysis was performed to define the origin of the recurrent mutation.

RESULTS

Both patients had blisters and erosions on the trunk and limbs at birth, with nail dystrophy. Patient 1 died as a result of sepsis at 30 weeks of age, and patient 2 died as a result of disseminated intravascular coagulation at 20 weeks of age. Mutation analysis of the LAMC2 gene revealed that patient 1 was compound heterozygous for a nonsense mutation (p.Cys553X) and a novel splice site mutation (c.2868+1delG), and patient 2 was a homozygous for p.Cys553X. Prenatal diagnosis performed during a subsequent pregnancy in family 2 revealed that this second child was heterozygous for p.Cys553X, and was thus not affected. Haplotype analysis suggested that a p.Cys553X allele derived from the same origin had been independently inherited by these two unrelated families.

CONCLUSIONS

p.Cys553X in the LAMC2 gene may be a Japanese-specific recurrent mutation as a result of a founder effect, and it may therefore be useful for initial screening in the mutation analysis of H-JEB.

Basement membranes in development and disease

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

Physiological and pathological implications of laminins: From the gene to the protein

The extracellular matrix plays an important role in modulating the behavior of cells with which it interacts. There are a number of families of extracellular matrix (ECM) proteins including collagens, proteoglycans and laminins (LM). LM are the major component of the basal lamina (BL). Here, we review the current knowledge on their structure, self-assembly, binding mechanisms, diverse tissue-expression patterns and its impact on pathology. Studies and hypothesis exploring the role of LM and their polymorphic genes on autoimmune diseases (AIDs) such as systemic lupus erythematosus and Sjögren's syndrome (SS) are also discussed.

Biological function of laminin-5 and pathogenic impact of its deficiency

The basement membrane glycoprotein laminin-5 is a key component of the anchoring complex connecting keratinocytes to the underlying dermis. It is secreted by keratinocytes as a cross-shaped heterotrimer of alpha3, beta3 and gamma2 chains and serves as a ligand of various transmembrane receptors, thereby regulating keratinocyte adhesion, motility and proliferation. In intact skin, laminin-5 provides essential links to both the hemidesmosomal alpha6beta4 integrin and the collagen type VII molecules which form the anchoring fibrils inserting into the dermis. If the basement membrane is injured, laminin-5 production increases rapidly. It then serves as a scaffold for cell migration, initiates the formation of hemidesmosomes and accelerates basement membrane restoration at the dermal-epidermal junction. Mutations of the laminin-5 genes or auto-antibodies against one of the subunits of laminin-5 may lead to a significant lack of this molecule in the epidermal basement membrane zone. The major contributions of laminin-5 to the resistance of the epidermis against frictional stress but also for basement membrane regeneration and repair of damaged skin are reflected by the phenotype of Herlitz junctional epidermolysis bullosa, which is caused by an inherited absence of functional laminin-5. This lethal disease becomes manifest in widespread blistering of skin and mucous membranes, impaired wound healing and chronic erosions containing exuberant granulation tissue. Here, we discuss current understanding of the biological functions of laminin-5, the pathogenic impact of its deficiency and implications on molecular approaches towards a therapy of junctional epidermolysis bullosa.

Laminin-5-deficient human keratinocytes: defective adhesion results in a saltatory and inefficient mode of migration

Laminin-5 is a major adhesion protein of the skin basement membrane and crucially involved in integrin-mediated cell substrate attachment of keratinocytes, which is important for hemidesmosomal anchorage as well as for keratinocyte migration during epidermal wound healing. To investigate its role in keratinocyte migration, we analyzed laminin-5-deficient cells of patients with a lethal variant of junctional epidermolysis bullosa. Normal migrating keratinocytes adopted monopolar morphology with a distinct front lamella and employed a continuous mode of translocation. In contrast, laminin-5-deficient cells assumed a stretched bipolar shape with two lamella regions and migrated in a discontinuous, saltatory manner characterized by significantly decreased directional persistence and reduced migration velocity. The distinct morphology as well as the migratory phenotype apparently resulted from a defect in the formation of cell substrate adhesions that were completely missing in the cell body and less stable in the lamella regions. Accordingly in normal keratinocytes, a bipolar shape and a saltatory migration mode were inducible by blocking laminin-5-mediated substrate adhesion. Our findings clearly point to an essential role of laminin-5 in forming dynamic cell substrate adhesion during migration of epidermal keratinocytes and provide an explanation for the cellular mechanisms that underlie the lethal form of junctional epidermolysis bullosa.

The β3 chain short arm of laminin-332 (laminin-5) induces matrix assembly and cell adhesion activity of laminin-511 (laminin-10)

The basement membrane (BM) protein laminin-332 (Lm332) (laminin-5) has unique activity and structure as compared with other laminins: it strongly promotes cellular adhesion and migration, and its alpha3, beta3, and gamma2 chains are all truncated in their N-terminal regions (short arms). In the present study, we investigated the biological function of the laminin beta3 chain. When the beta3 chain short arm (beta3SA) was overexpressed in HEK293 cells (beta3SA-HEK), they deposited a large amount of beta3SA and a small amount of laminin-511 (Lm511) (laminin-10) on culture plates. Control HEK293 cells secreted Lm511 but failed to deposit it. The extracellular matrix (ECM) deposited by beta3SA-HEK cells strongly promoted cell attachment and spreading. The beta3SA-HEK ECM did not directly bind Lm511, but it stimulated control HEK293 cells to deposit Lm511 on the culture plates. Although purified beta3SA did not support cell adhesion by itself, it enhanced the cell adhesion activity of Lm511. Experiments with anti-integrin antibodies also suggested that the strong cell adhesion activity of the beta3SA-HEK ECM was derived from the synergistic action of beta3SA and Lm511. It has previously been found that beta3SA binds an unknown cell surface receptor. Taken together, the present study suggests that the short arm of the laminin beta3 chain enhances the matrix assembly of Lm511 and its cell adhesion activity by interacting with its receptor.

Molecular and diagnostic aspects of genetic skin fragility

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

Evaluation of prenatal intra-amniotic LAMB3 gene delivery in a mouse model of Herlitz disease

Prenatal gene therapy has been considered for Herlitz junctional epidermolysis bullosa (H-JEB), a lethal genodermatosis caused by the absence of any of the three subunits of laminin-5, resulting from birth in widespread blistering and erosions of skin and mucosae. To investigate this strategy in an animal model, adenovirus type 5- and adeno-associated virus (AAV) type 2-derived vectors carrying a beta-galactosidase reporter gene or LAMB3 cDNA encoding the beta3 chain of laminin-5 were generated, tested for stability in amniotic fluid and evaluated in vitro on murine H-JEB keratinocytes, and in vivo by prenatal injection into the amniotic cavities of laminin-5 beta3-deficient mice. The different vectors were administered individually or combined at maximum doses on day 14 post coitum. Adenoviral vectors infected preferentially the foetal epidermis, whereas AAV delivered the transgene mainly to mucous membranes of the airways and the upper digestive tract. The LAMB3 transgene was expressed in target epithelia of newborn laminin-5 beta3-deficient mice, and the transgenic beta3 chain was shown to assemble with its endogenous partner chains, resulting in detectable amounts of laminin-5 in the basement membranes of skin and mucosae and in a lower extent of tissue separation in the skin. However, only combined delivery of the two vector types led to a minor increase of the life span of H-JEB mice. Failure to rescue diseased animals was, at least in part, due to abandonment of any conspicuous pup by the heterozygous mother. This is the first study of a prenatal gene therapy approach to a heritable blistering disorder. Although our findings indicate that prenatal combined administration of adenoviral and adeno-associated LAMB3 vectors provides therapeutic benefit to H-JEB mice, this animal model appears unsuitable for long-term investigations of the therapeutic concept.

Epidermal basement membrane: its molecular organization and blistering disorders

The epidermal basement membrane is a specialized structure localized between the epidermis and the dermis. Recent studies have elucidated the biological roles of the basement membrane and its pathophysiological involvement in bullous diseases. To understand the functions of the basement membrane, it is essential to have clear and precise information regarding the ultrastructural molecular organization of the epidermal basement membrane. Immunoelectron microscopy is a powerful technique and the only method available for the clarification of the ultrastructural localization or orientation of molecules. This review summarizes the latest information regarding the molecular organization of the epidermal basement membrane as determined by immunoelectron microscopy as well as the blistering diseases that occur in the epidermal basement membrane zone.

In utero gene therapy: current challenges and perspectives

Over the past few years, considerable progress in prenatal diagnosis and surgery combined with improvements in vector design vindicate a reappraisal of the feasibility of in utero gene therapy for serious monogenetic diseases. As adult gene therapy gathers pace, several apparent obstacles to its application as a treatment may be overcome by pre- or early postnatal treatment. This review will examine the concepts and practice of prenatal vector administration. We aim to highlight the advantages of early therapeutic intervention focusing on diseases that could benefit greatly from a prenatal gene therapy approach. We will pay special attention to the strategies and vectors that are most likely to be used for this application and will speculate on their expected developments for the near future.