Keratin-dependent thymic stromal lymphopoietin expression suggests a link between skin blistering and atopic disease

Interleukin-18 as a severity marker and novel potential therapeutic target for epidermolytic ichthyosis

BACKGROUND

Epidermolytic ichthyosis (EI) is a major form of nonsyndromic inherited ichthyosis, characterized by erythroderma, marked hyperkeratosis and scale, bulla and erosion at birth, associated with KRT1/KRT10 mutations. The cytokine and chemokine profiles in EI are poorly understood, and specific treatment options have not been established.

AIM

To explore novel biomarkers and therapeutic targets in patients with EI.

METHODS

We analysed cytokine levels in serum and skin samples from 10 patients with inherited ichthyosis, including seven patients with EI. Wild-type and mutant KRT1 constructs were established and transfected into HaCaT cells, an immortalized keratinocyte cell line, for in vitro immunoblotting and immunocytochemistry analyses.

RESULTS

Multiplex cytokine/chemokine analysis revealed that 10 cytokines/chemokines [interleukin (IL)-1β, IL-4, IL-17A, IL-16, IL-18, IL-1 receptor-α, macrophage colony-stimulating factor, interferon-α2, basic fibroblast growth factor and monocyte chemotactic protein-3] were significantly increased in patients with EI. Furthermore, IL-18 levels were significantly higher in patients with EI [n = 7; 2714.1 (1438.0) pg mL-1] than in healthy controls [n = 11; 218.4 (28.4) pg mL-1, P < 0.01]. Immunohistochemical analyses showed that IL-18 expression was elevated in skin samples from patients with EI. Serum IL-18 levels correlated with the severity of ichthyosis, as measured by the Ichthyosis Scoring System. Immunoblotting analysis revealed that mature IL-18 levels were increased in the supernatant of mutant KRT1 expressing HaCaT cells. Additionally, these cells showed NLRP3 aggregation in the cytoplasm and ASC clustered around mutant keratin aggregations. These findings suggest that mutant keratin might promote the activation of the NLRP3 inflammasome and its downstream caspase-1-mediated IL-18 release in keratinocytes from patients with EI.

CONCLUSIONS

Our results suggest that serum IL-18 is a severity marker released from the skin of patients with EI. Blockade of IL-18 may be a useful novel therapeutic option for patients with EI.

Improving Polysaccharide-Based Chitin/Chitosan-Aerogel Materials by Learning from Genetics and Molecular Biology

Improved wound healing of burnt skin and skin lesions, as well as medical implants and replacement products, requires the support of synthetical matrices. Yet, producing synthetic biocompatible matrices that exhibit specialized flexibility, stability, and biodegradability is challenging. Synthetic chitin/chitosan matrices may provide the desired advantages for producing specialized grafts but must be modified to improve their properties. Synthetic chitin/chitosan hydrogel and aerogel techniques provide the advantages for improvement with a bioinspired view adapted from the natural molecular toolbox. To this end, animal genetics provide deep knowledge into which molecular key factors decisively influence the properties of natural chitin matrices. The genetically identified proteins and enzymes control chitin matrix assembly, architecture, and degradation. Combining synthetic chitin matrices with critical biological factors may point to the future direction with engineering materials of specific properties for biomedical applications such as burned skin or skin blistering and extensive lesions due to genetic diseases.

Keratins as an Inflammation Trigger Point in Epidermolysis Bullosa Simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited keratinopathies that, in most cases, arise due to mutations in keratins and lead to intraepidermal ruptures. The cellular pathology of most EBS subtypes is associated with the fragility of the intermediate filament network, cytolysis of the basal layer of the epidermis, or attenuation of hemidesmosomal/desmosomal components. Mutations in keratins 5/14 or in other genes that encode associated proteins induce structural disarrangements of different strengths depending on their locations in the genes. Keratin aggregates display impaired dynamics of assembly and diminished solubility and appear to be the trigger for endoplasmic reticulum (ER) stress upon being phosphorylated by MAPKs. Global changes in cellular signaling mainly occur in cases of severe dominant EBS mutations. The spectrum of changes initiated by phosphorylation includes the inhibition of proteasome degradation, TNF-α signaling activation, deregulated proliferation, abnormal cell migration, and impaired adherence of keratinocytes. ER stress also leads to the release of proinflammatory danger-associated molecular pattern (DAMP) molecules, which enhance avalanche-like inflammation. Many instances of positive feedback in the course of cellular stress and the development of sterile inflammation led to systemic chronic inflammation in EBS. This highlights the role of keratin in the maintenance of epidermal and immune homeostasis.

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.

Structural heterogeneity of cellular K5/K14 filaments as revealed by cryo-electron microscopy

Keratin intermediate filaments are an essential and major component of the cytoskeleton in epithelial cells. They form a stable yet dynamic filamentous network extending from the nucleus to the cell periphery, which provides resistance to mechanical stresses. Mutations in keratin genes are related to a variety of epithelial tissue diseases. Despite their importance, the molecular structure of keratin filaments remains largely unknown. In this study, we analyzed the structure of keratin 5/keratin 14 filaments within ghost mouse keratinocytes by cryo-electron microscopy and cryo-electron tomography. By averaging a large number of keratin segments, we have gained insights into the helical architecture of the filaments. Two-dimensional classification revealed profound variations in the diameter of keratin filaments and their subunit organization. Computational reconstitution of filaments of substantial length uncovered a high degree of internal heterogeneity along single filaments, which can contain regions of helical symmetry, regions with less symmetry and regions with significant diameter fluctuations. Cross-section views of filaments revealed that keratins form hollow cylinders consisting of multiple protofilaments, with an electron dense core located in the center of the filament. These findings shed light on the complex and remarkable heterogenic architecture of keratin filaments, suggesting that they are highly flexible, dynamic cytoskeletal structures.

Epidermolysis bullosa

Epidermolysis bullosa (EB) is an inherited, heterogeneous group of rare genetic dermatoses characterized by mucocutaneous fragility and blister formation, inducible by often minimal trauma. A broad phenotypic spectrum has been described, with potentially severe extracutaneous manifestations, morbidity and mortality. Over 30 subtypes are recognized, grouped into four major categories, based predominantly on the plane of cleavage within the skin and reflecting the underlying molecular abnormality: EB simplex, junctional EB, dystrophic EB and Kindler EB. The study of EB has led to seminal advances in our understanding of cutaneous biology. To date, pathogenetic mutations in 16 distinct genes have been implicated in EB, encoding proteins influencing cellular integrity and adhesion. Precise diagnosis is reliant on correlating clinical, electron microscopic and immunohistological features with mutational analyses. In the absence of curative treatment, multidisciplinary care is targeted towards minimizing the risk of blister formation, wound care, symptom relief and specific complications, the most feared of which - and also the leading cause of mortality - is squamous cell carcinoma. Preclinical advances in cell-based, protein replacement and gene therapies are paving the way for clinical successes with gene correction, raising hopes amongst patients and clinicians worldwide.

A novel mutation of keratin 5 in epidermolysis bullosa simplex with migratory circinate erythema

Epidermolysis bullosa simplex migratory circinate erythema (EBS-Migr) is an uncommon subtype of EBS. We report a case of EBS-MIGR with a novel heterozygous pathogenic mutation in exon 9 (frameshift deletion c.1650delC) and likely benign heterozygous mutation in exon 2 (missense c.591C > A) of keratin 5. This novel pathogenic mutation in KRT5 expands the molecular spectrum of this rare subtype of EBS.

A proinflammatory role of KLK6 protease in Netherton syndrome

BACKGROUND

Netherton syndrome (NS) is a rare but severe type of ichthyosis characterized by atopy, allergies, and potentially lethal skin overdesquamation associated with highly elevated proteolytic activities in LEKTI-deficient epidermis. NS symptoms are recapitulated in Spink5^-/- mouse where the gene encoding Lekti has been invalidated. Spink5^-/- mice die within 5h from birth due to their severe skin barrier defect leading to dehydration. Spink5^-/- mice also serve as a model for atopic dermatitis. The KLK6 protease is expressed by epidermal keratinocytes and shown in vitro to cleave desmosomal components.

OBJECTIVE

To investigate in vivo whether KLK6 is implicated in epidermal overdesquamation and/or inflammation associated with NS.

METHODS

The role of KLK6 was evaluated by generating Spink5^-/-Klk6^-/- double knockout mice. The phenotype was assessed by macroscopic observation, immunohistochemistry for differentiation markers, in situ zymography for proteolysis, and quantification of proinflammatory cytokines.

RESULTS

Elimination of Klk6 in Spink5^-/- remarkably suppresses the expression of Tslp, a major itching-inducing factor and driver of allergic reactions. Tnfα and the Th17 promoting cytokine Il-23 were also suppressed. Spink5^-/-Klk6^-/- mice display normalized keratinocyte differentiation, nevertheless, epidermal proteolytic activities and the associated overdesquamation were not ameliorated, and Spink5^-/-Klk6^-/- still died from a severe epidermal barrier defect as the Spink5^-/-.

CONCLUSIONS

Ablation of Klk6 largely suppresses epidermal inflammation but cannot rescue overdesquamation leading to the lethal NS phenotype. Nonetheless, our findings demonstrate for the first time that KLK6 is implicated in skin inflammation and may represent a novel druggable target for NS and other inflammatory conditions e.g. atopic dermatitis.

Newer Treatment Modalities in Epidermolysis Bullosa

The term epidermolysis bullosa (EB) refers to a group of hereditary skin blistering diseases. The group is clinically and genetically heterogeneous, but all EB forms are associated with mechanically induced skin blistering and fragility. The causative gene mutations of most EB types are known. The current international consensus classification contains four main types: EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler syndrome (KS). The classification is based on the morphological level of blister formation. In EBS, the split is intra-epidermal, in JEB along the basement membrane and in DEB below the basement membrane. In Kindler syndrome, the dermal-epidermal junction is disorganized, and blisters can occur on all three levels. Each major EB type has further subtypes which may differ in terms of their genetic, biological or clinical characteristics. Traditionally, EB treatments have been symptomatic, but increasing understanding of disease etio-pathogenesis is facilitating development of novel evidence-based therapy approaches. First gene- and cell-based therapies are being tested at preclinical level and in clinical trials. New knowledge on secondary disease mechanisms has led to development and clinical testing of urgently needed symptom-relief therapies using small molecules and biologicals.

Epithelial Keratins Modulate cMet Expression and Signaling and Promote InlB-Mediated Listeria monocytogenes Infection of HeLa Cells

The host cytoskeleton is a major target for bacterial pathogens during infection. In particular, pathogens usurp the actin cytoskeleton function to strongly adhere to the host cell surface, to induce plasma membrane remodeling allowing invasion and to spread from cell to cell and disseminate to the whole organism. Keratins are cytoskeletal proteins that are the major components of intermediate filaments in epithelial cells however, their role in bacterial infection has been disregarded. Here we investigate the role of the major epithelial keratins, keratins 8 and 18 (K8 and K18), in the cellular infection by Listeria monocytogenes. We found that K8 and K18 are required for successful InlB/cMet-dependent L. monocytogenes infection, but are dispensable for InlA/E-cadherin-mediated invasion. Both K8 and K18 accumulate at InlB-mediated internalization sites following actin recruitment and modulate actin dynamics at those sites. We also reveal the key role of K8 and K18 in HGF-induced signaling which occurs downstream the activation of cMet. Strikingly, we show here that K18, and at a less extent K8, controls the expression of cMet and other surface receptors such TfR and integrin β1, by promoting the stability of their corresponding transcripts. Together, our results reveal novel functions for major epithelial keratins in the modulation of actin dynamics at the bacterial entry sites and in the control of surface receptors mRNA stability and expression.

Atopic Dermatitis-like Graft-versus-host Disease and Lichen Planus-like Graft-versus-host Disease: Alterations in Skin Barrier Function and Related Molecules

Background:

Graft-versus-host disease (GVHD) is a common complication of hematopoietic stem cell transplantation. Skin barrier disruption could induce thymic stromal lymphopoietin (TSLP) expression, and the expression of TSLP was increased in lesions of atopic dermatitis (AD)-like GVHD and lichen planus (LP)-like GVHD. This study attempted to investigate the skin barrier function of AD-like GVHD and LP-like GVHD and possible mechanisms.

Methods:

Eighteen AD-like GVHD patients, 12 LP-like GVHD patients, and 14 healthy volunteers were enrolled in this study. Skin biopsy was done in five AD-like GVHD patients, eight LP-like GVHD patients, and eight healthy volunteers. The intensity of pruritus was assessed by visual analog scale itch score and detailed pruritus score. Transepidermal water loss (TEWL) was measured using Tewameter^® TM 300. Immunohistochemistry was used to observe the expression of loricrin, involucrin, LL37, and human β-defensins 2 (hBD2) in skin lesions. Western blot analysis was used for analyzing the protein levels of loricrin and involucrin in skin lesions. Real-time polymerase chain reaction was performed to assess the mRNA levels of LL37 and hBD2 in skin lesions.

Results:

Pruritus score was higher in patients with AD-like GVHD (11.33 ± 5.35) than that of patients with LP-like GVHD (2.58 ± 3.09, P < 0.001). Compared with healthy controls (HCs, 4.52 ± 1.24 g·m⁻²·h⁻¹), TEWL was increased in AD-like GVHD (26.72 ± 9.02 g·m⁻²·h⁻¹, P < 0.001) and LP-like GVHD patients (18.78 ± 4.57 g·m⁻²·h⁻¹, P < 0.001), and expressions of loricrin and involucrin were also increased in skin lesions of AD-like GVHD and LP-like GVHD patients (all P < 0.05). LL37 mRNA expression was decreased in lesions of AD-like GVHD and LP-like GVHD patients (P = 0.005 and P = 0.008, vs. HCs, respectively). hBD2 mRNA expression was increased in skin lesions of AD-like GVHD and LP-like GVHD patients (P = 0.002 and P < 0.001, vs. HCs, respectively).

Conclusions:

Skin barrier dysfunction is present in AD-like GVHD and LP-like GVHD. The immunoreactions, but not the congenital defect, are considered to be the primary cause of skin barrier impairment in AD-like GVHD and LP-like GVHD.

EB2017-Progress in Epidermolysis Bullosa Research toward Treatment and Cure

Epidermolysis bullosa, a group of heritable blistering disorders, shows extensive phenotypic variability due to mutations in as many as 20 distinct genes. There is no cure for this devastating group of disorders; however, a number of preclinical developments show promise, and some approaches have already reached the stage of early clinical trials. Dystrophic Epidermolysis Bullosa Research Association (DEBRA) International, a global coalition of national patient organizations advocating on behalf of the patients and families with epidermolysis bullosa, supports research and organizes periodic scientific and clinical meetings on this disease. The most recent meeting, EB2017, was held in Salzburg in September 2017. This report summarizes some of the recent research and clinical developments that have identified promising avenues toward treatment and perhaps eventual cure, with improved quality of life for patients with epidermolysis bullosa.

Desmosomes and Intermediate Filaments: Their Consequences for Tissue Mechanics

Adherens junctions (AJs) and desmosomes connect the actin and keratin filament networks of adjacent cells into a mechanical unit. Whereas AJs function in mechanosensing and in transducing mechanical forces between the plasma membrane and the actomyosin cytoskeleton, desmosomes and intermediate filaments (IFs) provide mechanical stability required to maintain tissue architecture and integrity when the tissues are exposed to mechanical stress. Desmosomes are essential for stable intercellular cohesion, whereas keratins determine cell mechanics but are not involved in generating tension. Here, we summarize the current knowledge of the role of IFs and desmosomes in tissue mechanics and discuss whether the desmosome-keratin scaffold might be actively involved in mechanosensing and in the conversion of chemical signals into mechanical strength.