A combination of a common splice site mutation and a frameshift mutation in the COL7A1 gene: absence of functional collagen VII in keratinocytes and skin

Signatures of Dermal Fibroblasts from RDEB Pediatric Patients

The recessive form of dystrophic epidermolysis bullosa (RDEB) is a debilitating disease caused by impairments in the junctions of the dermis and the basement membrane of the epidermis. Mutations in the COL7A1 gene induce multiple abnormalities, including chronic inflammation and profibrotic changes in the skin. However, the correlations between the specific mutations in COL7A1 and their phenotypic output remain largely unexplored. The mutations in the COL7A1 gene, described here, were found in the DEB register. Among them, two homozygous mutations and two cases of compound heterozygous mutations were identified. We created the panel of primary patient-specific RDEB fibroblast lines (FEB) and compared it with control fibroblasts from healthy donors (FHC). The set of morphological features and the contraction capacity of the cells distinguished FEB from FHC. We also report the relationships between the mutations and several phenotypic traits of the FEB. Based on the analysis of the available RNA-seq data of RDEB fibroblasts, we performed an RT-qPCR gene expression analysis of our cell lines, confirming the differential status of multiple genes while uncovering the new ones. We anticipate that our panels of cell lines will be useful not only for studying RDEB signatures but also for investigating the overall mechanisms involved in disease progression.

Cord Blood-Derived Stem Cells Suppress Fibrosis and May Prevent Malignant Progression in Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin fragility disorder caused by mutations in the Col7a1 gene. Patients with RDEB suffer from recurrent erosions in skin and mucous membranes and have a high risk for developing cutaneous squamous cell carcinoma (cSCCs). TGFβ signaling has been associated with fibrosis and malignancy in RDEB. In this study, the activation of TGFβ signaling was demonstrated in col7a1^-/- mice as early as a week after birth starting in the interdigital folds of the paws, accompanied by increased deposition of collagen fibrils and elevated dermal expression of matrix metalloproteinase (MMP)-9 and MMP-13. Furthermore, human cord blood-derived unrestricted somatic stem cells (USSCs) that we previously demonstrated to significantly improve wound healing and prolong the survival of col7a1^-/- mice showed the ability to suppress TGFβ signaling and MMP-9 and MMP-13 expression meanwhile upregulating anti-fibrotic TGFβ3 and decorin. In parallel, we cocultured USSCs in a transwell with RDEB patient-derived fibroblasts, keratinocytes, and cSCC, respectively. The patient-derived cells were constitutively active for STAT, but not TGFβ signaling. Moreover, the levels of MMP-9 and MMP-13 were significantly elevated in the patient derived-keratinocytes and cSCCs. Although USSC coculture did not inhibit STAT signaling, it significantly suppressed the secretion of MMP-9 and MMP-13, and interferon (IFN)-γ from RDEB patient-derived cells. Since epithelial expression of these MMPs is a biomarker of malignant transformation and correlates with the degree of tumor invasion, these results suggest a potential role for USSCs in mitigating epithelial malignancy, in addition to their anti-inflammatory and anti-fibrotic functions. Stem Cells 2018;36:1839-12.

The autoantigen in anti-p200 pemphigoid is synthesized by keratinocytes and fibroblasts and is distinct from nidogen-2

Anti-p200 pemphigoid is a subepidermal immunobullous disorder associated with tissue-bound and circulating autoantibodies reactive with a 200 kDa protein on the dermal side of salt-split-skin. The autoantigen, named p200, is a non-collagenous glycoprotein located at the lamina lucida-lamina densa border of the epidermal basement membrane. However, its identity and cellular origin remain elusive. Here, we used biochemical and genetic approaches to characterize the autoantibody reactivity in three new patients with anti-p200 pemphigoid. We show that the target antigen p200 is synthesized by both keratinocytes and fibroblasts, is disulfide-bonded, and participates in calcium-dependent molecular interactions. Lack of collagen XVII (BP 180), collagen VII, or laminin 332 (laminin 5) from the dermal-epidermal junction does not destabilize p200. Colocalization within the basement membrane zone and an identical molecular weight suggested nidogen-2 as candidate autoantigen in anti-p200 pemphigoid, but biochemical analysis demonstrated that p200 is distinct from nidogen-2. In conclusion, the results define further the biochemical characteristics of p200 and demonstrate its in vitro-synthesis by keratinocytes and fibroblasts, thus providing a basis for identification and further characterization of this autoantigen.

Epidermolysis bullosa. II. Type VII collagen mutations and phenotype-genotype correlations in the dystrophic subtypes

BACKGROUND

The dystrophic forms of epidermolysis bullosa (DEB), a group of heritable blistering disorders, show considerable phenotypic variability, and both autosomal dominant and autosomal recessive inheritance can be recognised. DEB is derived from mutations in the type VII collagen gene (COL7A1), encoding a large collagenous protein that is the predominant, if not exclusive, component of the anchoring fibrils at the dermal-epidermal junction.

METHODS

The Dystrophic Epidermolysis Bullosa Research Association Molecular Diagnostics Laboratory (Philadelphia, Pennsylvania, USA), established in 1996, has analysed more than 1000 families with different forms of epidermolysis bullosa, among them 332 families with DEB. DNA specimens were subjected to mutation analysis by polymerase chain reaction (PCR) amplification of all 118 exons and flanking intronic sequences of COL7A1, followed either by heteroduplex scanning and sequencing of the PCR products demonstrating heteroduplexes or by direct nucleotide sequencing.

RESULTS

355 mutant alleles out of the anticipated 438 (81.1%) were disclosed. Among these mutations, a total of 242 mutations were distinct and 138 were novel, previously unreported mutations. No evidence of mutations in any other gene was obtained.

DISCUSSION

Examination of the mutation database suggested phenotype-genotype correlations, contributing to the improved subclassification of DEB with prognostic implications. The mutation information also forms the basis for accurate genetic counselling and prenatal diagnosis in families at risk for recurrence.

High frequency of the 425A-->G splice-site mutation and novel mutations of the COL7A1 gene in central Europe: significance for future mutation detection strategies in dystrophic epidermolysis bullosa

BACKGROUND

Mutations in the type VII collagen gene (COL7A1) are responsible for dominant and recessive forms of dystrophic epidermolysis bullosa (DEB). These mutations are usually specific for individual families; only a few cases of recurring mutations have been identified.

OBJECTIVES

Forty-three unrelated Hungarian and German patients with different DEB phenotypes were screened for novel and recurrent COL7A1 mutations.

METHODS

All patients were classified based on clinical and genetic findings, skin immunofluorescent antigen mapping, and electron microscopic studies. Mutation analysis was performed by amplification of genomic DNA with polymerase chain reaction using COL7A1-specific primers, heteroduplex analysis, and direct nucleotide sequencing. Restriction endonuclease digestion was used for family screening and mutation verification. Results In this group of patients, the splice-site mutation 425A-->G was observed frequently, in 11 of 86 alleles (12.8%), once in homozygous form and in nine cases in heterozygous form. One of 100 control alleles from clinically unaffected individuals also carried the mutation. We also identified three novel mutations: the 976-3C-->A splice-site mutation, and the 4929delT and 8441-15del20 deletions.

CONCLUSIONS

High recurrence of the splice-site mutation 425A-->G in central European patients with DEB should be taken into account when designing COL7A1 mutation detection strategies. Reporting of three novel COL7A1 mutations in this study further emphasizes the molecular heterogeneity of DEB and provides more information for studies on genotype-phenotype correlations in different DEB subtypes.

Dystrophic epidermolysis bullosa inversa with COL7A1 mutations and absence of GDA-J/F3 protein

Epidermolysis bullosa dystrophica inversa (DEB-I) is a very rare disease characterized by autosomal recessive inheritance that causes blistering and erosions on the trunk and extremities occurring in early infancy with a predilection for flexural and mucosal areas thereafter. Ultrastructural findings show dermolytic blistering and absent or rudimentary anchoring fibrils as in generalized forms of dystrophic epidermolysis bullosa. Immunoreactivity for type VII collagen, however, is preserved. We present two patients with DEB-I with compound heterozygosity for the two different COL7A1 mutations, one of them (Arg2069Cys in exon 74) carried by the heterozygous mother, the other one (Lys142Arg in exon 3) carried by the heterozygous father, accompanied by absence of the associated anchoring fibrils protein GDA-J/F3.

Genotype-phenotype correlation in italian patients with dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is a rare skin disorder that is clinically heterogeneous and is transmitted either in dominant (DDEB) or recessive (RDEB) mode. Nevertheless, all variants of DEB are caused by mutations in type VII collagen gene (COL7A1). We report an analysis of COL7A1 mutations in 51 Italian DEB patients, 27 affected with Hallopeau-Siemens RDEB, 19 with non Hallopeau-Siemens RDEB, two with DDEB, two with pretibial RDEB, and one with inversa RDEB. Forty-one mutations were identified, 18 of which are novel. Mutation consequences were analyzed at the mRNA and protein level and genotype-phenotype correlation was determined. Recessive inheritance of a new case of pretibial RDEB was also established. In RDEB patients, six recurrent mutations were identified: 7344G-->A, 425A-->G, 8441-14del21, 4783-1G-->A, 497insA, and G1664A, the last three being found only in Italian patients. Indeed, haplotype analysis supported propagation of ancestral mutated alleles within the Italian population for these particular mutations. Altogether recurrent mutations account for approximately 43% of RDEB alleles in Italian patients and therefore new DEB patients should first be screened for the presence of these mutations.

A microinjected COL7A1-PAC vector restores synthesis of intact procollagen VII in a dystrophic epidermolysis bullosa keratinocyte cell line

Dystrophic epidermolysis bullosa (DEB) comprises a family of inherited blistering skin disorders for which no corrective therapy currently exists. In the most severe form, the Hallopeau-Siemens subtype (RDEB-HS), the epidermal adhesion protein collagen VII is absent from the skin as a consequence of null mutations in the COL7A1 gene. In order to develop an ex vivo gene therapy approach for DEB, we aimed to restore expression of intact procollagen VII in RDEB-HS keratinocytes. The entire human COL7A1 locus in a P1-derived artificial chromosome (PAC) was transferred to RDEB-HS keratinocytes by microinjection, after which sustained biosynthesis and secretion of procollagen VII was detected for 1 year in vitro. Protein chemical analysis demonstrated that the chain composition, domain structure, N-glycosylation and protein folding of the newly produced procollagen VII were similar, if not identical, to its authentic counterpart, indicating that transgenic procollagen VII was structurally normal. These data demonstrate a "proof of principle" for genomic DNA vectors as a means of restoring collagen VII production in RDEB-HS skin and help develop future gene therapy protocols.

Three homozygous PTC mutations in the collagen type VII gene of patients affected by recessive dystrophic epidermolysis bullosa: analysis of transcript levels in dermal fibroblasts

The Hallopeau-Siemens variant of recessive dystrophic epidermolysis bullosa (HS-RDEB) is a severe inherited skin disease characterized by the absence of collagen type VII (COLVII) and anchoring fibrils (AF), caused by mutations in collagen type VII gene (COL7A1). Mutations leading to the formation of premature termination codons (PTCs) of translation are the characteristic genetic lesions in HS-RDEB patients; many PTC mutations have been found to be associated with a marked reduction or complete absence of COLVII mRNA. In this article, we report homozygosity for three different mutations in the COL7A1 of HS-RDEB patients. One mutation, the R2685X, falling in exon 109, is a novel mutation, whereas the other two, the 425A-->G falling in exon 3 and the 497insA in exon 4, have been previously identified in compound heterozygosity with different mutations in other unrelated RDEB patients. Haplotype analysis in three Italian families carrying the 497insA mutation suggested a common origin of this mutation and indicated that this is an ancestral Italian mutation. All these mutations generate PTCs and are associated with the absence of COLVII expression, as detected by immunofluorescence analysis of the patient's skin. Evaluation of the levels of the mutated COLVII mRNAs in cultured skin fibroblasts of the patients and of their parents showed that all the mutated transcripts were expressed at consistent levels. Therefore, our results indicate that a marked mRNA reduction is not a constant feature associated with PTC mutations in COL7A1.

Molecular basis of dystrophic epidermolysis bullosa: mutations in the type VII collagen gene (COL7A1)

Epidermolysis bullosa (EB), a group of heritable blistering diseases characterized by tissue separation within the cutaneous basement membrane zone, is inherited either in an autosomal dominant or autosomal recessive fashion. EB has been divided into four broad categories based on the precise level of tissue separation. In the dystrophic forms of EB (DEB), tissue separation occurs below the lamina densa within the upper papillary dermis at the level of anchoring fibrils, which are frequently altered in morphology, reduced in number, or entirely absent. Since type VII collagen is the major component of anchoring fibrils, the corresponding gene, COL7A1, was proposed as the candidate for DEB. Subsequent cloning of COL7A1 and elucidation of its genomic structure have led to identification of 53 distinct mutations in COL7A1 reported thus far. These mutations consist of nonsense mutations, small insertions or deletions resulting in frameshift and premature termination codons, splice site mutations, or missense mutations, particularly glycine substitutions within the collagenous domain of the protein. The types and combinations of these mutations and their positions along the type VII collagen molecule result in a spectrum of phenotypic severity and determine the mode of inheritance. Thus, examination of the mutation database has allowed genotype/phenotype predictions, with an impact on genetic counseling in this group of genodermatoses.

Comparative mutation detection screening of the type VII collagen gene (COL7A1) using the protein truncation test, fluorescent chemical cleavage of mismatch, and conformation sensitive gel electrophoresis

Mutations in the type VII collagen gene, COL7A1, give rise to the blistering skin disease, dystrophic epidermolysis bullosa. We have developed two new mutation detection strategies for the screening of COL7A1 mutations in patients with dystrophic epidermolysis bullosa and compared them with an established protocol using conformational sensitive gel electrophoresis. The first strategy consisted of an RNA based protein truncation test that amplified the entire coding region in only four overlapping nested reverse transcriptase-polymerase chain reaction assays. These fragments were transcribed and translated in vitro and analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We have used the protein truncation test procedure to characterize 15 truncating mutations in 13 patients with severe recessive dystrophic epidermolysis bullosa yielding a detection sensitivity of 58%. The second strategy was a DNA-based fluorescent chemical cleavage of mismatch (fl-CCM) procedure that amplified the COL7A1 gene in 21 polymerase chain reaction assays. Mismatches, formed between patient and control DNA, were identified using chemical modification and cleavage of the DNA. We have compared fl-CCM with conformational sensitive gel electrophoresis by screening a total of 50 dominant and recessive dystrophic epidermolysis bullosa patients. The detection sensitivity for fl-CCM was 81% compared with 75% for conformational sensitive gel electrophoresis (p = 0.37 chi2-test). Using a combination of the three techniques we have screened 93 dystrophic epidermolysis bullosa patients yielding an overall sensitivity of 87%, detecting 79 different mutations, 57 of which have not been reported previously. Comparing all three approaches, we believe that no single method is consistently better than the others, but that the fl-CCM procedure is a sensitive, semiautomated, high throughput system that can be recommended for COL7A1 mutation detection.

A recurrent frameshift mutation in exon 19 of the type VII collagen gene (COL7A1) in Mexican patients with recessive dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is an inherited blistering skin disorder caused by mutations in the type VII collagen gene (COL7A1). In this study, we determined the molecular basis of autosomal recessive DEB in a 19-year-old Hispanic Mexican woman by PCR amplification of genomic DNA, heteroduplex analysis, and automated sequencing of heteroduplex bandshifts. This approach revealed a homozygous frameshift mutation, 2470insG, in exon 19 of COL7A1 and resulted in attenuated basement membrane zone expression of type VII collagen, a reduced number of anchoring fibrils at the dermal-epidermal junction, and a sub-lamina densa level of blister formation. Clinically, the patient had widespread trauma-induced skin fragility and complete loss of the nails, but had less pseudosyndactyly of the fingers and toes and milder mucosal involvement compared to most patients with the generalized form of this genodermatosis. We also screened 7 other Hispanic-Mexican patients with recessive DEB, none of whom were known to be related to this individual, for the mutation 2470insG using heteroduplex analysis and direct sequencing and detected this mutation on 7/14 alleles. Haplotype analysis using intragenic COL7A1 and flanking polymorphisms and microsatellite markers revealed that all the mutant alleles had arisen on similar allelic backgrounds, consistent with propagation of a common Hispanic Mexican ancestral haplotype. In view of the high allelic frequency of the mutation 2470insG in the patients studied, we recommend initial screening for this mutation when attempting to identify the molecular pathology of recessive DEB in Hispanic Mexican patients.

A recurrent glycine substitution mutation, G2043R, in the type VII collagen gene (COL7A1) in dominant dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the type VII collagen gene (COL7A1). Nearly all cases of dominant DEB are caused by glycine substitution mutations occurring within the triple helical region of type VII collagen, and most of the mutations are unique to individual families. In this study, we identified a patient of Hispanic-Mexican origin with a mild form of DEB, which resulted from a de novo dominant glycine substitution, G2043R, in exon 73 of COL7A1. We also investigated a Scottish family with a three-generation pedigree of dominant DEB, in whom the same glycine to arginine substitution mutation was demonstrated. This particular mutation has also been detected previously in three other families with dominant DEB: one Italian, one Hungarian and one Norwegian. Given the widespread geographical distribution of this mutation and the demonstration of its occurrence as a de novo event, G2043R therefore represents the first example of a mutational hotspot in dominant DEB. Interestingly, although both the Mexican and Scottish families we studied had some clinical features in keeping with the Pasini form of the disorder, there was considerable interfamilial variability as well as intrafamilial diversity in the affected individuals.

Deletions within COL7A1 exons distant from consensus splice sites alter splicing and produce shortened polypeptides in dominant dystrophic epidermolysis bullosa

We describe two familial cases of dominant dystrophic epidermolysis bullosa (DDEB) that are heterozygous for deletions in COL7A1 that alter splicing, despite intact consensus splice-site sequences. One patient shows a 28-bp genomic deletion (6081del28) in exon 73 associated with the activation of a cryptic donor splice site within this exon; the combination of both defects restores the phase and replaces the last 11 Gly-X-Y repeats of exon 73 by a noncollagenous sequence, Glu-Ser-Leu. The second patient demonstrates a 27-bp deletion in exon 87 (6847del27), causing in-frame skipping of this exon; consensus splice sites, putative branch sites, and introns flanking exons 73 and 87 showed a normal sequence. Keratinocytes from the probands synthesized normal and shortened type VII collagen polypeptides and showed intracellular accumulation of type VII procollagen molecules. This first report of genomic deletions in COL7A1 in DDEB suggests a role for exonic sequences in the control of splicing of COL7A1 pre-mRNA and provides evidence that shortened type VII collagen polypeptides can alter, in a dominant manner, anchoring-fibril formation and can cause DDEB of differing severity.

Novel COL7A1 mutations in dystrophic forms of epidermolysis bullosa

Mutations in the type VII collagen gene (COL7A1) have been shown to underlie different variants of dystrophic epidermolysis bullosa (DEB). Examination of the genetic database indicates that most of the mutations are family specific, with few recurrent mutations. To facilitate further refinement of genotype/phenotype correlations in DEB, we have examined a cohort of nine families with DEB (seven recessively and two dominantly inherited) by a mutation detection strategy based on polymerase chain reaction amplification of COL7A1 genomic sequences, followed by heteroduplex scanning and direct nucleotide sequencing. The results revealed 16 allelic mutations, 11 of them being novel, previously unpublished. The genetic information was also used for prenatal testing in a family at risk for recurrence of a severe, Hallopeau-Siemens type of RDEB. These data contribute to the expanding database of COL7A1 mutations in DEB.

Some, but not all, glycine substitution mutations in COL7A1 result in intracellular accumulation of collagen VII, loss of anchoring fibrils, and skin blistering

COL7A1 gene mutations cause dystrophic epidermolysis bullosa, a skin blistering disorder. The phenotypes result from defects of collagen VII, the major component of the anchoring fibrils at the dermo-epidermal junction; however, the molecular mechanisms underlying the phenotypes remain elusive. We investigated naturally occurring COL7A1 mutations and showed that some, but not all, glycine substitutions in collagen VII interfered with biosynthesis of the protein in a dominant-negative manner. Three point mutations in exon 73 caused glycine substitutions G2006D, G2034R, and G2015E in the triple helical domain of collagen VII and interfered with its folding and secretion. Confocal laser scanning studies and semiquantitative immunoblotting determined that dystrophic epidermolysis bullosa keratinocytes retained up to 2.5-fold more procollagen VII within the rough endoplasmic reticulum than controls. Limited proteolytic digestions of mutant procollagen VII produced aberrant fragments and revealed reduced stability of the triple helix. In contrast, the glycine substitution G1519D in another segment of the triple helix affected neither procollagen VII secretion nor anchoring fibril function and remained phenotypically silent. These data demonstrate that collagen VII presents a remarkable exception among collagens in that not all glycine substitutions within the triple helix exert dominant-negative interference and that the biological consequences of the substitutions probably depend on their position within the triple helix.

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

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