MMP-9 and CXCL8/IL-8 are potential therapeutic targets in epidermolysis bullosa simplex

Daily crowding stress has limited, yet detectable effects on skin and head kidney gene expression in surgically tagged atlantic salmon (Salmo salar)

To ensure welfare-friendly and effective internal tagging, the tagging process should not cause a long-term burden on individuals given that tagged fish serve as representatives for the entire population in telemetry applications. To some extent, stress is inevitable within regular aquaculture practices, and thus, the consequences of long-term stress should be described in terms of their effects on internal tagging. In fish, stressors activate the Hypothalamus-Pituitary-Interrenal (HPI) and Brain-Sympathetic-Chromaffin Cell (BSC) axes, leading to neuroimmunoendocrine communication and paracrine interactions among stress hormones. The interrelation between wound healing and stress is complex, owing to their shared components, pathways, and energy demands. This study assessed 14 genes (mmp9, mmp13, il-2, il-4, il-8a, il-10, il-12, il-17d, il-1b, tnfa, ifng, leg-3, igm, and crh) in the skin (1.5 cm from the wound) and head kidney over eight weeks. These genes, associated with cell signaling in immunity, wound healing, and stress, have previously been identified as influenced and regulated by these processes. Half of a group of Atlantic salmon (n = 90) with surgically implanted dummy smart-tags were exposed to daily crowding stress. The goal was to investigate how this gene panel responds to a wound alone and then to the combined effects of wounding and daily crowding stress. Our observations indicate that chronic stress impacts inflammation and impedes wound healing, as seen through the expression of matrix metalloproteinases genes in the skin but not in the head kidney. This difference is likely due to the ongoing internal wound repair, in contrast to the externally healed wound incision. Cytokine expression, when significant in the skin, was mainly downregulated in both treatments compared to control values, particularly in the study's first half. Conversely, the head kidney showed initial cytokine downregulation followed by upregulation. Across all weeks observed and combining both tissues, the significantly expressed gene differences were 12 % between the Wound and Stress+ groups, 28 % between Wound and Control, and 25 % between Stress+ and Control. Despite significant fluctuations in cytokines, sustained variations across multiple weeks are only evident in a few select genes. Furthermore, Stress+ individuals demonstrated the most cytokine correlations within the head kidney, which may suggest that chronic stress affects cytokine expression. This investigation unveils that the presence of stress and prolonged activation of the HPI axis in an eight weeklong study has limited yet detectable effects on the selected gene expression within immunity, wound healing, and stress, with notable tissue-specific differences.

A SUCTION BLISTER MODEL TO CHARACTERIZE EPIDERMAL WOUND HEALING AND EVALUATE THE EFFICACY OF THE TOPICAL WOUND HEALING AGENT INM-755 IN HEALTHY VOLUNTEERS

Non-healing wounds represent a substantial medical burden with few effective treatments available. To address this challenge, we developed a novel epidermal wound healing model using suction blisters in healthy volunteers. This model allowed for the comprehensive assessment of wound healing dynamics and the evaluation of INM-755, a topical cream containing cannabinol, as a potential therapeutic agent. Two clinical studies were conducted: an observational study and an interventional study. In both studies, healthy volunteers underwent a suction blister procedure on their lower back, creating open epidermal wounds. Wound healing parameters were assessed using advanced imaging systems. Skin barrier function and perfusion were evaluated through trans epidermal water loss (TEWL) and dynamic optical coherence tomography (D-OCT), respectively. The observational study demonstrated the successful and reproducible Induction of blisters and the removal of epidermal sheet, enabling quantifiable measurements of wound healing parameters over time. Re-epithelialization was observed, revealing recovery of skin barrier function and perfusion. In the interventional study, differences of treatments over time were quantified using the above-described techniques. Despite differences from disease-specific blistering, our developed model provides a valuable platform for studying wound healing mechanisms and assessing novel therapeutic interventions. The sensitivity to treatment effects demonstrated in our study underscores the potential utility of this model in early-phase clinical drug development programs targeting wound healing disorders.

Human iPSC-derived-keratinocytes, a useful model to identify and explore pathological phenotype of Epidermolysis Bullosa Simplex

Epidermolysis Bullosa Simplex (EBS), an autosomal dominant skin disorder, is characterized by skin fragility. Genetically, majority of cases are related to missense mutations in two keratin genes, KRT5 or KRT14, leading to cytolysis of basal keratinocytes and intraepidermal blistering. Progress towards identification of treatments have been hampered by incomplete understanding of the mechanisms underlying this disease, and availability of relevant and reliable in vitro models recapitulating the physiopathological mechanisms. Recent advances in stem cell field have fueled the prospect that these limitations could be overcome thanks to the availability of disease-specific human induced pluripotent stem cells (hiPSC). Here, we generated hiPSC-derived keratinocytes from patients carrying KRT5 dominant mutations and compared them to non-affected hiPSC-derived keratinocytes as well as their primary counterparts. Our results demonstrated that EBS hiPSC-derived keratinocytes displayed proliferative defects, increased capacity to migrate, alteration of ERK signaling pathway and cytoplasmic keratin filament aggregates as observed in primary EBS keratinocytes. Of interest, EBS hiPSC-derived keratinocytes exhibited a downregulation of hemidesmosomal proteins revealing the different effects of KRT5 mutations on keratin cytoskeletal organization. Combination of culture miniaturization and treatment with the chaperone molecule 4-PBA, our results demonstrated that hiPSC-derived keratinocytes represent a suitable model for identifying novel therapies for EBS.

Detrimental Effects of IFN-γ on an Epidermolysis Bullosa Simplex Cell Model and Protection by a Humanized Anti-IFN-γ Monoclonal Antibody

Epidermolysis bullosa is a group of severe skin blistering disorders, which currently have no cure. The pathology of epidermolysis bullosa is recognized as having an inflammatory component, but the role of inflammation in different epidermolysis bullosa disorders is unclear. Epidermolysis bullosa simplex (EBS) is primarily caused by sequence variants in keratin genes; its most severe form, EBS generalized severe, is characterized by aggregates of keratin proteins, and cell models of EBS generalized severe show constitutively elevated stress. IFN-γ is a major mediator of inflammation, and we show that the addition of IFN-γ alone to disease model keratinocytes promotes keratin aggregation, decreases cell-cell junctions, delays wound closure, and reduces cell proliferation. IFN-γ exposure weakens the intercellular cohesion of monolayers on mechanical stress, with IFN-γ-treated EBS monolayers more fragmented than IFN-γ-treated wild-type monolayers. A humanized monoclonal antibody to IFN-γ neutralized the detrimental effects on keratinocytes, restoring cell proliferation, increasing cell-cell adhesion, accelerating wound closure in the presence of IFN-γ, and reducing IFN-γ-mediated keratin aggregation in EBS cells. These suggest that treatment with IFN-γ blocking antibodies may constitute a promising new therapeutic strategy for patients with EBS and may also have ameliorating effects on other inflammatory skin diseases.

A cell-based drug discovery assay identifies inhibition of cell stress responses as a new approach to treatment of epidermolysis bullosa simplex

In the skin fragility disorder epidermolysis bullosa simplex (EBS), mutations in keratin 14 (K14, also known as KRT14) or keratin 5 (K5, also known as KRT5) lead to keratinocyte rupture and skin blistering. Severe forms of EBS are associated with cytoplasmic protein aggregates, with elevated kinase activation of ERK1 and ERK2 (ERK1/2; also known as MAPK3 and MAPK1, respectively), suggesting intrinsic stress caused by misfolded keratin protein. Human keratinocyte EBS reporter cells stably expressing GFP-tagged EBS-mimetic mutant K14 were used to optimize a semi-automated system to quantify the effects of test compounds on keratin aggregates. Screening of a protein kinase inhibitor library identified several candidates that reduced aggregates and impacted on epidermal growth factor receptor (EGFR) signalling. EGF ligand exposure induced keratin aggregates in EBS reporter keratinocytes, which was reversible by EGFR inhibition. EBS keratinocytes treated with a known EGFR inhibitor, afatinib, were driven out of activation and towards quiescence with minimal cell death. Aggregate reduction was accompanied by denser keratin filament networks with enhanced intercellular cohesion and resilience, which when extrapolated to a whole tissue context would predict reduced epidermal fragility in EBS patients. This assay system provides a powerful tool for discovery and development of new pathway intervention therapeutic avenues for EBS.

Transcriptomic Repositioning Analysis Identifies mTOR Inhibitor as Potential Therapy for Epidermolysis Bullosa Simplex

Expression-based systematic drug repositioning has been explored to predict novel treatments for a number of skin disorders. In this study, we utilize this approach to identify, to our knowledge, previously unreported therapies for epidermolysis bullosa simplex (EBS). RNA sequencing analysis was performed on skin biopsies of acute blisters (<1 week old) (n = 9) and nonblistered epidermis (n = 11) obtained from 11 patients with EBS. Transcriptomic analysis of blistered epidermis in patients with EBS revealed a set of 1,276 genes dysregulated in EBS blisters. The IL-6, IL-8, and IL-10 pathways were upregulated in the epidermis from EBS. Consistent with this, predicted upstream regulators included TNF-α, IL-1β, IL-2, IL-6, phosphatidylinositol 3-kinase, and mTOR. The 1,276 gene EBS blister signature was integrated with molecular signatures from cell lines treated with 2,423 drugs using the Connectivity Map CLUE platform. The mTOR inhibitors and phosphatidylinositol 3-kinase inhibitors most opposed the EBS signature. To determine whether mTOR inhibitors could be used clinically in EBS, we conducted an independent pilot study of two patients with EBS treated with topical sirolimus for painful plantar keratoderma due to chronic blistering. Both individuals experienced marked clinical improvement and a notable reduction of keratoderma. In summary, a computational drug repositioning analysis successfully identified, to our knowledge, previously unreported targets in the treatment of EBS.

A Pilot Clinical Study of Hyperacute Serum Treatment in Osteoarthritic Knee Joint: Cytokine Changes and Clinical Effects

The serum fraction of platelet-rich fibrin (hyperacute serum) has been shown to improve cartilage cell proliferation in in vitro osteoarthritic knee joint models. We hypothesize that hyperacute serum may be a potential regenerative therapeutic for osteoarthritic knees. In this study, the cytokine milieu at the synovial fluid of osteoarthritic knee joints exposed to hyperacute serum intraarticular injections was investigated. Patients with knee osteoarthritis received three injections of autologous hyperacute serum; synovial fluid was harvested before each injection and clinical monitoring was followed-up for 6 months. Forty osteoarthritic-related cytokines, growth factors and structural proteins from synovial fluid were quantified and analysed by Multivariate Factor Analysis. Hyperacute serum provided symptomatic relief regarding pain and joint stability for OA patients. Both patients "with" and "without effusion knees" had improved VAS, KOOS and Lysholm-Tegner scores 6 months after of hyperacute serum treatment. Synovial fluid analysis revealed two main clusters of proteins reacting together as a group, showing strong and significant correlations with their fluctuation patterns after hyperacute serum treatment. In conclusion, hyperacute serum has a positive effect in alleviating symptoms of osteoarthritic knees. Moreover, identified protein clusters may allow the prediction of protein expression, reducing the number of investigated proteins in future studies.

Immunological mechanisms underlying progression of chronic wounds in recessive dystrophic epidermolysis bullosa

Hereditary epidermolysis bullosa (EB) is a mechanobullous skin fragility disorder characterized by defective epithelial adhesion, leading to mechanical stress‐induced skin blistering. Based on the level of tissue separation within the dermal‐epidermal junction, EB is categorized into simplex (EBS), junctional (JEB), dystrophic (DEB) and Kindler syndrome. There is no cure for EB, and painful chronic cutaneous wounds are one of the major complications in recessive (RDEB) patients. Although RDEB is considered a cutaneous disease, recent data support the underlying systemic immunological defects. Furthermore, chronic wounds are often colonized with pathogenic microbiota, leading to excessive inflammation and altered wound healing. Consequently, patients with RDEB suffer from a painful sensation of chronic, cutaneous itching/burning and an endless battle with bacterial infections. To improve their quality of life and life expectancy, it is important to prevent cutaneous infections, dampen chronic inflammation and stimulate wound healing. A clear scientific understanding of the immunological events underlying the maintenance of chronic poorly healing wounds in RDEB patients is necessary to improve disease management and better understand other wound healing disorders. In this review, we summarize current knowledge of the role of professional phagocytes, such as neutrophils, macrophages and dendritic cells, the role of T‐cell‐mediated immunity in lymphoid organs, and the association of microbiota with poor wound healing in RDEB. We conclude that RDEB patients have an underlying immunity defect that seems to affect antibacterial immunity.

A Review of Acquired Autoimmune Blistering Diseases in Inherited Epidermolysis Bullosa: Implications for the Future of Gene Therapy

Gene therapy serves as a promising therapy in the pipeline for treatment of epidermolysis bullosa (EB). However, with great promise, the risk of autoimmunity must be considered. While EB is a group of inherited blistering disorders caused by mutations in various skin proteins, autoimmune blistering diseases (AIBD) have a similar clinical phenotype and are caused by autoantibodies targeting skin antigens. Often, AIBD and EB have the same protein targeted through antibody or mutation, respectively. Moreover, EB patients are also reported to carry anti-skin antibodies of questionable pathogenicity. It has been speculated that activation of autoimmunity is both a consequence and cause of further skin deterioration in EB due to a state of chronic inflammation. Herein, we review the factors that facilitate the initiation of autoimmune and inflammatory responses to help understand the pathogenesis and therapeutic implications of the overlap between EB and AIBD. These may also help explain whether corrections of highly immunogenic portions of protein through gene therapy confers a greater risk towards developing AIBD.

Modular design of a hybrid hydrogel for protease-triggered enhancement of drug delivery to regulate TNF-α production by pro-inflammatory macrophages

Systemic drug administration has conventionally been prescribed to alleviate persistent local inflammation which is prevalent in chronic diseases. However, this approach is associated with drug-induced toxicity, particularly when the dosage exceeds that necessitated by pathological conditions of diseased tissues. Herein, we developed a modular hybrid hydrogel which could be triggered to release an anti-inflammatory drug upon exposure to elevated protease activity associated with inflammatory diseases. Modular design of the hybrid hydrogel enabled independent optimization of its protease-cleavable and drug-loaded subdomains to facilitate hydrogel formation, cleavability by matrix-metalloprotease-9 (MMP-9), and tuning drug release rate. In vitro study demonstrated the protease-triggered enhancement of drug release from the hybrid hydrogel system for effective inhibition of TNF-α production by pro-inflammatory macrophages and suggested its potential to mitigate drug-induced cytotoxicity. Using non-invasive imaging to monitor the activity of reactive oxygen species in biomaterial-induced host response, we confirmed that the hybrid hydrogel and its constituent materials did not induce adverse immune response after 5 days following their subcutaneous injection in immuno-competent mice. We subsequently incorporated this hybrid hydrogel onto a commercial wound dressing which could release the drug upon exposure to MMP-9. Together, our findings suggested that this hybrid hydrogel might be a versatile platform for on-demand drug delivery via either injectable or topical application to modulate inflammation in chronic diseases.

Small molecule drug development for rare genodermatoses - evaluation of the current status in epidermolysis bullosa

Background

Hereditary epidermolysis bullosa (EB) comprises a heterogeneous group of rare genodermatoses, which are caused by mutations in genes involved in the maintenance of the structural and functional integrity of dermo-epidermal adhesion in various stratified epithelia. In severe variants, generalized skin disease, extracutaneous manifestations and multi-organ involvement cause considerable morbidity and mortality. Causal and early treatment by re-expression of a respective mutated gene is the major long-term goal in therapy development. However, characterization and targeted modulation of pathogenic molecular cascades in EB also holds great promise as a symptom-relieving approach to ameliorate phenotype, complications and quality of life. Small molecules are chemical structures of less than 900 Da that can diffuse across cell membranes and interfere with target biomolecules, thus influencing their function at different levels. They constitute the vast majority of active components of all approved drugs.

Methods

We performed PubMed and Google Scholar search for publications and screened FDA- and EMA-hosted clinical trial registries to identify studies using small molecule-based drugs for epidermolysis bullosa. Upon detailed analysis this resulted in the identification of a total of 84 studies.

Results

We identified 52 publications and 32 registered trials that investigate small molecules for their safety and efficacy as treatment for different aspects of epidermolysis bullosa. Further, a total of 38 different small molecules clinically used in EB were found. Most frequent outcome measures concerned wound healing, reduction in blister numbers, as well as reduction of itch and pain, predominantly for EBS and RDEB.

Conclusion

We provide a comprehensive summary of the current status of clinical small molecule development for EB and discuss prospects and limitations in orphan drug development for rare conditions like EB.

Epidermolysis bullosa: Advances in research and treatment

Epidermolysis bullosa (EB) is the umbrella term for a group of rare inherited skin fragility disorders caused by mutations in at least 20 different genes. There is no cure for any of the subtypes of EB resulting from different mutations, and current therapy only focuses on the management of wounds and pain. Novel effective therapeutic approaches are therefore urgently required. Strategies include gene-, protein- and cell-based therapies. This review discusses molecular procedures currently under investigation at the EB House Austria, a designated Centre of Expertise implemented in the European Reference Network for Rare and Undiagnosed Skin Diseases. Current clinical research activities at the EB House Austria include newly developed candidate substances that have emerged out of our translational research initiatives as well as already commercially available medications that are applied in off-licensed indications. Squamous cell carcinoma is the major cause of death in severe forms of EB. We are evaluating immunotherapy using an anti-PD1 monoclonal antibody as a palliative treatment option for locally advanced or metastatic squamous cell carcinoma of the skin unresponsive to previous systemic therapy. In addition, we are evaluating topical calcipotriol and topical diacerein as potential agents to improve the healing of skin wounds in EBS patients. Finally, the review will highlight the recent advancements of gene therapy development for EB.

Unraveling the ECM-Immune Cell Crosstalk in Skin Diseases

The extracellular matrix (ECM) is a complex network of proteins and proteoglycans secreted by keratinocytes, fibroblasts and immune cells. The function of the skin ECM has expanded from being a scaffold that provides structural integrity, to a more dynamic entity that is constantly remodeled to maintain tissue homeostasis. The ECM functions as ligands for cell surface receptors such as integrins, dystroglycans, and toll-like receptors (TLRs) and regulate cellular signaling and immune cell dynamics. The ECM also acts as a sink for growth factors and cytokines, providing critical cues during epithelial morphogenesis. Dysregulation in the organization and deposition of ECMs lead to a plethora of pathophysiological conditions that are exacerbated by aberrant ECM-immune cell interactions. In this review, we focus on the interplay between ECM and immune cells in the context of skin diseases and also discuss state of the art therapies that target the key molecular players involved.

Epidermolysis bullosa simplex generalized severe induces a T helper 17 response and is improved by apremilast treatment

BACKGROUND

Epidermolysis bullosa simplex generalized severe (EBS-gen sev) is a genetic disorder caused by mutation in the KRT5 or KRT14 genes. Although it is usually considered a mechanical disease, recent data argue for additional inflammatory mechanisms.

OBJECTIVES

To assess the inflammation in the skin of patients with EBS-gen sev.

METHODS

A first immunohistochemical retrospective study was performed on frozen skin samples from 17 patients with EBS-gen sev. A second multicentre prospective study was conducted on 10 patients with severe EBS-gen sev. Blister fluid and epidermis were processed for immunochemical analysis and quantitative real-time polymerase chain reaction. Cytokine expression was analysed in blister fluid and compared with that in controls.

RESULTS

Histological analysis showed a constant dermal perivascular CD4⁺ lymphocyte infiltrate in skin biopsies of both blister (n = 17) and rubbed skin (n = 5), an epidermal infiltration of neutrophils and eosinophils in 70% of cases, and increased immunostaining for CXCL9 and CXCL10 in blistering skin. High levels of T helper 17 cytokines were detected in lesional skin. Three adult patients with EBS-gen sev were treated with apremilast, with a dramatic improvement of skin blistering and good tolerance.

CONCLUSIONS

Our study demonstrates the importance of inflammation in patients with EBS-gen sev and underlines the key role for T helper 17 cells in its pathogenesis. In addition, this study provides promising new therapeutic approaches for this disabling disorder.

An ex vivo RNA trans-splicing strategy to correct human generalized severe epidermolysis bullosa simplex

Background

Generalized severe epidermolysis bullosa simplex (EBS‐gen sev) is a genetic blistering skin disease in which autosomal dominant mutations in either the keratin KRT5 or KRT14 genes lead to impaired function of the intermediate filament cytoskeleton in the basal epidermis. Here we present an ex vivo RNA trans‐splicing‐based therapeutic approach to correct the phenotype.

Objectives

To correct a mutation within exon 1 of the KRT14 gene, using a 5′‐trans‐splicing approach, where any mutation within the first seven exons could be replaced by a single therapeutic molecule.

Methods

A therapeutic RNA trans‐splicing molecule containing wild‐type exons 1–7 was stably transduced into an EBS patient‐derived keratinocyte line. Trans‐splicing was confirmed via reverse‐transcriptase polymerase chain reaction, Western blotting and immunofluorescence microscopy. Skin equivalents generated from corrected keratinocytes were grafted onto nude mice and analysed about 8 weeks post‐transplantation for regular epidermal stratification, trans‐splicing‐induced green fluorescent protein expression and blistering.

Results

Transplanted skin equivalents generated from trans‐splicing‐corrected patient keratinocytes showed a stable and blister‐free epidermis. KRT14 correction disrupted EBS‐gen sev‐associated proinflammatory signalling, as shown at the mRNA and protein levels. Disruption of the pathogenic feedback loop in addition to overall downregulation of KRT14 expression highlighted the effect of KRT14 correction on the EBS pathomechanism.

Conclusions

Our data demonstrate that trans‐splicing‐mediated mRNA therapy is an effective method for the correction of dominantly inherited KRT14 mutations at the transcriptional level. This results in the rescue of the EBS‐gen sev phenotype and stabilization of the epidermis in a xenograft mouse model.

What's already known about this topic?

RTM163, described in this study, was previously used in a transient in vitro transfection system, where the ability to correct KRT14 at the mRNA level was demonstrated.

What does this study add?

In this study, we stably transduced RTM163 in a second patient‐derived keratinocyte line.

Successful trans‐splicing was confirmed in this cell line.

The expression of disease‐related marker genes, which are characteristically deregulated in epidermolysis bullosa simplex, were analysed.

For the first time this study showed that RNA trans‐splicing molecule‐transduced patient keratinocytes can differentiate into a phenotypically normal and blister‐free epidermis in a xenograft mouse model.

What is the translational message?

This study shows the feasibility of using spliceosome‐mediated RNA trans‐splicing to generate a stable and blister‐free epidermis in vivo.

Combined with pre‐existing ex vivo gene therapeutic methods, this might be a valid option for future treatments of dominantly inherited genodermatoses.

Linked Comment: Bremer and van den Akker. Br J Dermatol 2019; 180:17–19.

CONGENITAL EPIDERMOLYSIS BULLOSA: PECULIARITIES OF EPIDERMIS REGENERATION AND METHODS OF TREATMENT

Congenital epidermolysis bullosa is a group of hereditary skin diseases caused by mutations in the genes of structural proteins of the dermoepidermal junction of the skin, characterized by formation of blisters and erosions at the smallest mechanical trauma. In patients with severe subtypes of borderline and dystrophic epidermolysis bullosa there are long-term erosive and ulcerative defects with disruption of the healing process. Factors that impede healing include: malnutrition, anemia, pain, inactivity, local factors (presence of infection, prolonged inflammation, extensive nature of the lesion, absence of skin appendages in the affected area, deficiency or lack of formation of type VII collagen). Elimination of healing impeding factors is the main challenge in treatment of severe subtypes of bullous epidermolysis. Modern promising treatment techniques are at the stage of development and have not yet been introduced into clinical practice, and, as of today, skin care and optimal topical treatment with modern non-adhesive dressings remain the most widespread treatment methods that facilitate accelerated healing.

Pro-Inflammatory Chemokines and Cytokines Dominate the Blister Fluid Molecular Signature in Patients with Epidermolysis Bullosa and Affect Leukocyte and Stem Cell Migration

Hereditary epidermolysis bullosa (EB) is associated with skin blistering and the development of chronic nonhealing wounds. Although clinical studies have shown that cell-based therapies improve wound healing, the recruitment of therapeutic cells to blistering skin and to more advanced skin lesions remains a challenge. Here, we analyzed cytokines and chemokines in blister fluids of patients affected by dystrophic, junctional, and simplex EB. Our analysis revealed high levels of CXCR1, CXCR2, CCR2, and CCR4 ligands, particularly dominant in dystrophic and junctional EB. In vitro migration assays demonstrated the preferential recruitment of CCR4⁺ lymphocytes and CXCR1⁺, CXCR2⁺, and CCR2⁺ myeloid cells toward EB-derived blister fluids. Immunophenotyping of skin-infiltrating leukocytes confirmed substantial infiltration of EB-affected skin with resting (CD45RA⁺) and activated (CD45RO⁺) T cells and CXCR2⁺ CD11b⁺ cells, many of which were identified as CD16b⁺ neutrophils. Our studies also showed that abundance of CXCR2 ligand in blister fluids also creates a favorable milieu for the recruitment of the CXCR2⁺ stem cells, as validated by in vitro and in-matrix migration assays. Collectively, this study identified several chemotactic pathways that control the recruitment of leukocytes to the EB-associated skin lesions. These chemotactic axes could be explored for the refinement of the cutaneous homing of the therapeutic stem cells.

Assays to Study Consequences of Cytoplasmic Intermediate Filament Mutations: The Case of Epidermal Keratins

The discovery of the causative link between keratin mutations and a growing number of human diseases opened the way for a better understanding of the function of the whole intermediate filament families of cytoskeleton proteins. This chapter describes analytical approaches to identification and interpretation of the consequences of keratin mutations, from the clinical and diagnostic level to cells in tissue culture. Intermediate filament pathologies can be accurately diagnosed from skin biopsies and DNA samples. The Human Intermediate Filament Database collates reported mutations in intermediate filament genes and their diseases, and can help clinicians to establish accurate diagnoses, leading to disease stratification for genetic counseling, optimal care delivery, and future mutation-aligned new therapies. Looking at the best-studied keratinopathy, epidermolysis bullosa simplex, the generation of cell lines mimicking keratinopathies is described, in which tagged mutant keratins facilitate live-cell imaging to make use of today's powerful enhanced light microscopy modalities. Cell stress assays such as cell spreading and cell migration in scratch wound assays can interrogate the consequences of the compromised cytoskeletal network. Application of extrinsic stresses, such as heat, osmotic, or mechanical stress, can enhance the differentiation of mutant keratin cells from wild-type cells. To bring the experiments to the next level, 3D organotypic human cultures can be generated, and even grafted onto the backs of immunodeficient mice for greater in vivo relevance. While development of these assays has focused on mutant K5/K14 cells, the approaches are often applicable to mutations in other intermediate filaments, reinforcing fundamental commonalities in spite of diverse clinical pathologies.