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Mutations in the gene encoding collagen VII cause the devastating blistering disease recessive dystrophic epidermolysis bullosa (RDEB). RDEB is characterized by severe skin fragility and nonhealing wounds aggravated by scarring and fibrosis. We previously showed that TSP1 is increased in RDEB fibroblasts. Because transforming growth factor-β (TGF-β) signaling is also increased in RDEB, and TSP1 is known to activate TGF-β, we investigated the role of TSP1 in TGF-β signaling in RDEB patient cells. Knockdown of TSP1 reduced phosphorylation of smad3 (a downstream target of TGF-β signaling) in RDEB primary fibroblasts, whereas overexpression of collagen VII reduced phosphorylation of smad3. Furthermore, inhibition of TSP1 binding to the LAP/TGF-β complex decreased fibrosis in engineered extracellular matrix formed by RDEB fibroblasts, as evaluated by picrosirius red staining and analyses of birefringent collagen fibrillar deposits. We show that collagen VII binds TSP1, which could potentially limit TSP1-LAP association and subsequent TGF-β activation. Our study suggests a previously unreported mechanism for increased TGF-β signaling in the absence of collagen VII in RDEB patient skin. Moreover, these data identify TSP1 as a possible target for reducing fibrosis in the tumor-promoting dermal microenvironment of RDEB patients.

Keywords: epidermolysis bullosa; genetic diseases/mechanisms; genodermatoses.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare inherited skin and mucous membrane fragility disorder complicated by early-onset, highly malignant cutaneous squamous cell carcinomas (SCCs). The molecular etiology of RDEB SCC, which arises at sites of sustained tissue damage, is unknown. We performed detailed molecular analysis using whole-exome, whole-genome, and RNA sequencing of 27 RDEB SCC tumors, including multiple tumors from the same patient and multiple regions from five individual tumors. We report that driver mutations were shared with spontaneous, ultraviolet (UV) light–induced cutaneous SCC (UV SCC) and head and neck SCC (HNSCC) and did not explain the early presentation or aggressive nature of RDEB SCC. Instead, endogenous mutation processes associated with apolipoprotein B mRNA-editing enzyme catalytic polypeptide–like (APOBEC) deaminases dominated RDEB SCC. APOBEC mutation signatures were enhanced throughout RDEB SCC tumor evolution, relative to spontaneous UV SCC and HNSCC mutation profiles. Sixty-seven percent of RDEB SCC driver mutations was found to emerge as a result of APOBEC and other endogenous mutational processes previously associated with age, potentially explaining a >1000-fold increased incidence and the early onset of these SCCs. Human papillomavirus–negative basal and mesenchymal subtypes of HNSCC harbored enhanced APOBEC mutational signatures and transcriptomes similar to those of RDEB SCC, suggesting that APOBEC deaminases drive other subtypes of SCC. Collectively, these data establish specific mutagenic mechanisms associated with chronic tissue damage. Our findings reveal a cause for cancers arising at sites of persistent inflammation and identify potential therapeutic avenues to treat RDEB SCC.

Inherited epidermolysis bullosa (EB) comprises rare heterogeneous disorders characterized by cutaneous and mucosal fragility. Most of the 20 proteins affected have structural functions. Recently, a previously undescribed type of EB simplex (EBS), caused by gain-of-function mutations in KLHL24, encoding KLHL24 has been identified (He et al., 2016, Lin et al., 2016). This protein seems to be involved in protein ubiquitination. Patients carrying monoallelic mutations in the translation initiation codon of KLHL24 have a characteristic clinical phenotype, showing skin defects and blistering at birth and unusual stellate scarring, skin fragility, and whorled or macular hyperpigmentation or hypopigmentation in childhood (Figure 1a–e ). Although skin fragility improves by adulthood, nail dystrophy, anetoderma, and hair loss may occur (Figure 1f–h).

Purpose: This study describes ophthalmologic and systemic clinical findings in different subtypes of epidermolysis bullosa (EB) establishing genotype-phenotype correlations.

Methods: A cross-sectional study was conducted in 58 patients with EB together with the Dystrophic Epidermolysis Bullosa Research Association, Chile. Data were stratified by major subtypes such as «simplex epidermolysis bullosa» (EBS), «junctional epidermolysis bullosa» (JEB), «recessive and dominant dystrophic epidermolysis bullosa» and «dominant dystrophic epidermolysis bullosa» (DDEB), and «Kindler syndrome» (KS). The diagnosis was confirmed by skin immunofluorescence mapping and genetic testing. Best-corrected visual acuity, corneal erosions, corneal scarring, symblepharon, blepharitis, ectropion, limbal stem cell deficiency, and esophageal involvement were assessed. Clinical outcome was based on the presence of corneal involvement attributable to EB.

Results: The most common ocular manifestations were corneal erosion/scarring and recurrent erosions. Frequencies of the EB subtypes were as follows: 17% EBS, 12% JEB, 16% DDEB, 53% recessive and DDEB, and 2% KS. Patients with EBS and DDEB did not reveal ocular involvement. Patients with recessive dystrophic epidermolysis bullosa (RDEB) were most affected by the disease showing corneal involvement in 16 cases, whereas 2 patients with JEB and the single KS case also showed corneal disease. Before their visit, 24 patients had undergone esophageal dilation, 23 of them with RDEB and 1 with KS.

Conclusions: Although ophthalmic complications are common in EB, the incidence varied with the EB subtype. We also establish the correlation between esophageal and corneal involvement in RDEB.

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited skin disease characterized by epidermal fragility leading to chronic wounds (Fine et al., 2014). RDEB is complicated by other pathologies such as esophageal strictures, anemia, mitten deformity, and corneal abrasion, but poor wound healing has arguably the greatest impact on quality of life and ultimately leads to the development of highly aggressive squamous cell carcinoma (Fine et al., 2009). One of the defining features of RDEB wounds is that when they do heal, they do so with evident scarring. Because both scar formation and wound-induced cancer have previously been linked to microbial infection in murine studies (Canesso et al., 2014, Hoste et al., 2015), and because recent data suggest deficiencies in antibacterial immunity in RDEB patients (Nystrom et al., 2018), we sought to profile the microbiome of RDEB skin and wounds using shotgun whole-metagenome sequencing, a technique not previously used, to our knowledge, for analyzing this patient group.

Extracellular vesicles (EVs) are cell-derived membrane-bound vesicles that are important mediators of intercellular communication, and critical orchestrators of both physiological and pathologic processes. They are found in various biological fluids, including serum/plasma, breast milk, and urine (Carvalho and Oliveira, 2014,Ciardiello et al., 2016). EVs include both microvesicles, generated by outward budding from the plasma membrane, and exosomes, formed by inward budding into endosomes and released into the extracellular environment by subsequent fusion with the plasma membrane (Raposo and Stoorvogel, 2013). The molecular content of EVs includes proteins, lipids, DNA, and RNA, and collectively represents a fingerprint of the cell from which they originated. In this respect, and in the context of cancer, tumor-derived EVs that circulate in the blood represent a source of specific biomarkers that can be utilized for cancer detection and diagnosis, as well as to gain insight into the biology of the tumor (Becker et al., 2016). Recently, EVs have been implicated in the crosstalk between stromal fibroblasts and tumor cells, enhancing tumor-relevant signaling cascades in oral squamous cell carcinoma (SCC) cells (Languino et al., 2016). As such, deciphering the bioactive cargo of tumor-derived EVs and their impact on shaping the tumor microenvironment may offer fresh insight into pathophysiological tumor mechanisms and uncover previously unrecognized targets for therapy.

Keywords: epidermolysis bullosa; neuropathic pain; small fibre neuropathy.

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