Reduced Filaggrin Expression Research Articles

195 Reduced filaggrin expression reduces ERK signalling and disrupts desmosomes in atopic eczema

195 Reduced filaggrin expression reduces ERK signalling and disrupts desmosomes in atopic eczema

563 - Dupilumab improves skin lipid composition in atopic dermatitis irrespective of patient filaggrin (FLG) mutation status

Abstract Introduction/Background Type 2 inflammatory cytokines interleukin 4 (IL-4) and IL-13 play an important role in skin barrier disruption in atopic dermatitis (AD). Filaggrin and ceramides play a crucial role in skin barrier integrity. Loss of function mutations in the FLG gene are associated with the impaired skin barrier function and more severe AD.1,2 FLG mutations only affect a minority of AD patients; however, increased IL-4 and IL-13 cytokines are a common cause of reduced filaggrin expression in patients with AD, independent of FLG genotype. Objectives To explore whether dupilumab treatment improves skin barrier function in patients with or without FLG mutations. Methods In the BArrier function and LIpidomics STudy in Atopic Dermatitis (BALISTAD; NCT04447417), a 16-week study in patients with AD aged 12 to 65 years, adult patients with AD received dupilumab 300 mg every 2 weeks; adolescent patients with AD received dupilumab 200 mg every 2 weeks if their baseline weight was <60 kg and 300 mg if ≥60 kg. FLG mutations were evaluated in DNA from blood samples of consenting patients with AD and healthy volunteers. Transepidermal water loss (TEWL) was assessed longitudinally after 5 skin tape strippings (STS) from AD lesions (n = 26) and from the skin of healthy participants (n =26) (age: 12 to 63 years) over a 16-week course of dupilumab treatment. Quantitative N(C18)S-ceramide analysis of STS samples collected on Days 1, 15, 29, 57, and 85, and at Week 16 from AD lesions and from the skin of healthy participants was performed using liquid chromatography tandem mass spectrometry. Results At baseline, mean TEWL after 5 STS (TEWL5) was significantly higher in AD lesional skin than healthy skin (p<0.0001). The mean TEWL5 in AD lesions in subjects with FLG mutations (n = 6/19) was significantly higher at baseline than in AD subjects without mutations (P < 0.0001). Dupilumab treatment significantly reduced TEWL5 in AD lesional skin as early as Week 2 with a progressive decrease through Week 16 (P < 0.0001). Reduction in mean TEWL5 was similar from Week 2 to Week 16 in AD patients with and without FLG mutations. At Week 16, TEWL5 was comparable to healthy skin in the lesional skin of AD patients with and without FLG mutations (P > 0.05). AD skin lesions had increased levels of N(C18)S-ceramides at baseline (P < 0.0001); but no differences were noted in subjects with or without FLG mutations (P > 0.05). Dupilumab treatment significantly reduced levels of N(C18)S-ceramides in AD lesional skin as early as Week 2 with a progressive decrease through Week 16 (P < 0.0001). Dupilumab treatment decreased levels of N(C18)S-ceramides in STS samples similarly in subjects with and without FLG mutations from Week 2 to Week 16. Conclusions Dupilumab treatment normalizes TEWL5 and decreases levels of N(C18)S-ceramides in AD lesional skin of subjects with and without FLG mutations.

Epicutaneous Sensitization to the Phytocannabinoid β-Caryophyllene Induces Pruritic Inflammation.

In recent years, there has been increased accessibility to cannabis for recreational and medicinal use. Incidentally, there has been an increase in reports describing allergic reactions to cannabis including exacerbation of underlying asthma. Recently, multiple protein allergens were discovered in cannabis, yet these fail to explain allergic sensitization in many patients, particularly urticaria and angioedema. Cannabis has a rich chemical profile including cannabinoids and terpenes that possess immunomodulatory potential. We examined whether major cannabinoids of cannabis such as cannabidiol (CBD) and the bicyclic sesquiterpene beta-caryophyllene (β-CP) act as contact sensitizers. The repeated topical application of mice skin with β-CP at 10 mg/mL (50 µL) induced an itch response and dermatitis at 2 weeks in mice, which were sustained for the period of study. Histopathological analysis of skin tissues revealed significant edema and desquamation for β-CP at 10 mg/mL. For CBD and β-CP, we observed a dose-dependent increase in epidermal thickening with profound thickening observed for β-CP at 10 mg/mL. Significant trafficking of CD11b cells was observed in various compartments of the skin in response to treatment with β-CP in a concentration-dependent manner. Mast cell trafficking was restricted to β-CP (10 mg/mL). Mouse proteome profiler cytokine/chemokine array revealed upregulation of complement C5/5a (anaphylatoxin), soluble intracellular adhesion molecule-1 (sICAM-1) and IL-1 receptor antagonist (IL-1RA) in animals dosed with β-CP (10 mg/mL). Moreover, we observed a dose-dependent increase in serum IgE in animals dosed with β-CP. Treatment with β-CP (10 mg/mL) significantly reduced filaggrin expression, an indicator of barrier disruption. In contrast, treatment with CBD at all concentrations failed to evoke scratching and dermatitis in mice and did not result in increased serum IgE. Further, skin tissues were devoid of any remarkable features, although at 10 mg/mL CBD we did observe the accumulation of dermal CD11b cells in skin tissue sections. We also observed increased filaggrin staining in mice repeatedly dosed with CBD (10 mg/mL). Collectively, our studies indicate that repeated exposure to high concentrations of β-CP can induce dermatitis-like pathological outcomes in mice.

P102 Severe atopic eczema is associated with reduced acne vulgaris in Bangladeshi children and young adults: a retrospective analysis from a cross-sectional study

Abstract Atopic eczema (AE) is the most common inflammatory dermatosis, affecting up to 20% of children. Loss of function (LoF) mutations in FLG are the most strongly implicated genetic risk factor for eczema. To understand the effect of FLG on the pathobiology of AE, we knocked down FLG in primary keratinocytes using short hairpin RNA and performed phosphoproteomic analysis, which showed downregulation of the AKT signalling pathway, confirmed using Western blotting to phospho-AKT and immunostaining of biopsies from patients with AE. Given that AKT signalling is increased in acne vulgaris, we hypothesized that loss of FLG may protect patients with AE from acne. The Tower Hamlets Eczema Assessment (THEA) study is a cross-sectional study that aims to phenotype and genotype 1000 Bangladeshi children and young adults with AE. So far, 620 participants have undergone genotyping, 37% of whom have LoF mutations in FLG. We selected patients from this cohort who were older than 12 years of age. In total, 204 patients (99 FLG wild type, 86 heterozygotes, 19 compound heterozygotes) were included. We identified a diagnosis of acne or previous prescription of topical acne therapies or tetracycline antibiotics from the patients’ general practice e-health records. We stratified the patients by genotype, Eczema Area and Severity Index (EASI) score, Patient Oriented Eczema Measure (POEM) score, transepidermal water loss (TEWL) and palmar hyperlinearity groups. The χ2-test was used to determine differences between groups. A lower proportion of patients with AE with FLG mutations had acne (27% wild type vs. 19% FLG mutations), which was more pronounced, but not statistically significant, in the compound heterozygote group (16%). We saw a nonsignificant reduction in acne in patients who had the top 25% of TEWL measurements, those with the most severe form of hyperlinearity and those with higher POEM scores. Patients with severe AE, measured as an EASI score > 21, had a more reduced incidence of acne than those with lower EASI scores (9% vs. 26%; P = 0.04). Overall, this suggests that patients with more severe AE are protected from developing acne. There was insufficient evidence to establish if this was mediated by a reduction in filaggrin (FLG) and AKT signalling. This may be because the groups were too small to determine this. Given that all patients with severe AE have reduced FLG expression regardless of genotype, it is possible that this is mediated through FLG–AKT signalling.

Mouse models of atopic dermatitis: a critical reappraisal.

Mouse models for atopic dermatitis (AD) are an indispensable preclinical research tool for testing new candidate AD therapeutics and for interrogating AD pathobiology in vivo. In this Viewpoint, we delineate why, unfortunately, none of the currently available so-called "AD" mouse models satisfactorily reflect the clinical complexity of human AD, but imitate more "allergic" or "irriant" contact dermatitis conditions. This limits the predictive value of AD models for clinical outcomes of new tested candidate AD therapeutics and the instructiveness of mouse models for human AD pathophysiology research. Here, we propose to initiate a rational debate on the minimal criteria that a mouse model should meet in order to be considered relevant for human AD. We suggest that valid AD models should at least meet the following criteria: (a) an AD-like epidermal barrier defect with reduced filaggrin expression along with hyperproliferation, hyperplasia; (b) increased epidermal expression of thymic stromal lymphopoietin (TSLP), periostin and/or chemokines such as TARC (CCL17); (c) a characteristic dermal immune cell infiltrate with overexpression of some key cytokines such as IL-4, IL-13, IL-31 and IL-33; (d) distinctive "neurodermatitis" features (sensory skin hyperinnervation, defective beta-adrenergic signalling, neurogenic skin inflammation and triggering or aggravation of AD-like skin lesions by perceived stress); and (e) response of experimentally induced skin lesions to standard AD therapy. Finally, we delineate why humanized AD mouse models (human skin xenotransplants on SCID mice) offer a particularly promising preclinical research alternative to the currently available "AD" mouse models.

Immunohistochemical expression of filaggrin is decreased in proton pump inhibitor non-responders compared with proton pump inhibitor responders of eosinophilic esophagitis.

Eosinophilic esophagitis (EoE) is an allergic gastrointestinal disease that features eosinophilic infiltration of esophageal mucosa, but the role of barrier dysfunction of the epithelium in its pathogenesis remains to be elucidated. Clinically, EoE is divided into proton pump inhibitor-non-responders (PPI-NR) and PPI-responders (PPI-R). Our main aims were to investigate the differences of expression of epidermal differential complex (EDC) proteins and desmoglein that are considered to play important roles in formation of the epidermal skin barrier between these two conditions and to seek the usefulness of the differences in pathological diagnosis. Conventional histopathological findings and allergic background were also compared. Twenty-nine PPI-NR and 44 PPI-R were recruited, and 35 reflux esophagitis patients were also enrolled. After clinical information and histopathological findings were reviewed, immunohistochemical expression of EDC proteins (filaggrin, loricrin, and involucrin) and desmoglein in all three groups were examined and semi-quantitatively scored. Regarding allergic conditions, the prevalence of asthma was significantly higher in PPI-NR than in PPI-R. Other allergic conditions showed no differences. Histopathological findings did not exhibit the statistical difference between PPI-NR and PPI-R. However, immunostaining score of filaggrin in PPI-NR was significantly lower than in PPI-R, although the expressions of involucrin, loricrin and desmoglein demonstrated no differences. The results suggest a role of reduced filaggrin expression in the difference of effectiveness of PPI treatment between PPI-NR and PPI-R. Moreover, immunohistochemical determination of filaggrin expression in EoE patients could be informative in the clinical decision of how to treat the patients.

Expression of Skin Barrier Protein Filaggrin in Skin Diseases without Atopic Dermatitis

The epidermis represents an essential barrier versus a broad range of exogenous stimuli. To form a functional epidermis, keratinocytes express filaggrin which plays a vital role in atopic dermatitis. However the relationship between filaggrin and other skin diseases remains unknown. In our study we chose 5 different common skin diseases and analyzed the expression of filaggrin in the skin using immunohistochemistry. Imiquimod (IMQ)-induced mouse model was used for detecting the filaggrin level and barrier function. The results indicated that the expression of filaggrin is reduced in psoriasis compared to the other skin diseases. Furthermore in vivo study showed that the skin barrier is defected with a decreased expression of filaggrin in IMQ-induced psoriasis mouse model, which is accompanied with an increased level of IL-17/IL-23. In conclusion, the defective skin barrier is involved in the development of psoriasis in human and mice with a reduced expression of filaggrin which may be regulated by the increased level of IL-17/IL-23 in the skin.

Hypoxia-Inducible Factors Regulate Filaggrin Expression and Epidermal Barrier Function

A functional epidermal skin barrier requires the formation of a cornified envelope from terminally differentiating keratinocytes. During this process, multiple genetic and environmental signals coordinately regulate protein expression and tissue differentiation. Here we describe a critical role for hypoxia-inducible factors (HIFs) in the regulation of filaggrin expression and skin barrier formation. Similar to other mammalian tissues, fetal epidermis in mice is normally O2-deprived. Simultaneous deletion of Hif1a and Hif2a in murine epidermis revealed defects in keratinocyte terminal differentiation and epidermal barrier formation. Mice lacking Hif1a and Hif2a in the epidermis exhibited dry flaky skin, impaired permeability barrier, and enhanced sensitivity to cutaneous allergens. These defects were correlated with stratum granulosum attenuation and reduced filaggrin expression. Hypoxic treatment of primary keratinocytes induced filaggrin (Flg) gene expression in a HIF1α- and HIF2α-dependent manner, suggesting that one mechanism by which Hif1a and Hif2a loss causes epidermal barrier defects in mice lies in Flg dysregulation. Therefore, low O2 tension is an essential component of the epidermal environment that contributes to skin development and function.

Reduced filaggrin expression is accompanied by increased Staphylococcus aureus colonization of epidermal skin models.

Atopic dermatitis is an inflammatory skin disease that is characterized by a reduced skin barrier function, reduced filaggrin (FLG) expression as well as increased colonization by Staphylococcus aureus. This study focused on the possible involvement of FLG in epidermal colonization by S. aureus and/or whether it affects the epidermal defence mechanisms, including the expression of antimicrobial peptides (AMPs) and enzymes involved in stratum corneum barrier lipid synthesis. Furthermore, IL-31 has been shown to reduce FLG expression, but its effects on bacterial colonization and on the expression of AMPs and enzymes involved in the barrier lipid synthesis are not known. We established N/TERT-based epidermal models (NEMs), after FLG knockdown (FLG-KD) and/or cultured with IL-31, that were colonized with S. aureus for 24 h. Both FLG-KD and IL-31 supplementation resulted in significantly increased epidermal S. aureus colonization, as well as in an up-regulation of S. aureus-induced IL-8 expression. IL-31, but not FLG-KD, prevented S. aureus-induced up-regulation of mRNA expression for the AMPs human β-defensin 2 and -3 and RNAse7, whereas psoriasin expression remained unchanged. Furthermore, the S. aureus colonization induced changes in mRNA expression of ELOVL4 was not affected by FLG-KD, but was blocked by IL-31. Expression of SCD-1 and Gcase mRNA was reduced by IL-31, but not by FLG-KD. This study shows that NEMs, with FLG-KD and/or cultured in the presence of IL-31, mimic the skin of patients with atopic dermatitis in several aspects, including enhanced bacterial colonization, increased inflammatory and reduced protective responses.

TNF-α and Th2 Cytokines Induce Atopic Dermatitis–Like Features on Epidermal Differentiation Proteins and Stratum Corneum Lipids in Human Skin Equivalents

Atopic dermatitis (AD) is a chronic inflammatory skin disease in which the skin barrier function is disrupted. In this inflammatory AD environment, cytokines are upregulated, but the cytokine effect on the AD skin barrier is not fully understood. We aimed to investigate the influence of Th2 (IL-4, IL-13, IL-31) and pro-inflammatory (tumor necrosis factor alpha (TNF-α)) cytokines on epidermal morphogenesis, proliferation, differentiation, and stratum corneum lipid properties. For this purpose, we used the Leiden epidermal model (LEM) in which the medium was supplemented with these cytokines. Our results show that IL-4, IL-13, IL-31, and TNF-α induce spongiosis, augment TSLP secretion by keratinocytes, and alter early and terminal differentiation-protein expression in LEMs. TNF-α alone or in combination with Th2 cytokines decreases the level of long chain free fatty acids (FFAs) and ester linked ω-hydroxy (EO) ceramides, consequently affecting the lipid organization. IL-31 increases long chain FFAs in LEMs but decreases relative abundance of EO ceramides. These findings clearly show that supplementation with TNF-α and Th2 cytokines influence epidermal morphogenesis and barrier function. As a result, these LEMs show similar characteristics as found in AD skin and can be used as an excellent tool for screening formulations and drugs for the treatment of AD.

Epidermal Nerve Fibers Modulate Keratinocyte Growth via Neuropeptide Signaling in an Innervated Skin Model

Atopic eczema is a chronic inflammatory skin disease characterized by cutaneous nerve fiber sprouting and epidermal hyperplasia, pointing to an involvement of the peripheral nervous system in cutaneous homeostasis. However, the interaction of sensory neurons and skin cells is poorly understood. Using an innervated skin model, we investigated the influence of sensory neurons on epidermal morphogenesis. Neurons induced the proliferation of keratinocytes, resulting in an increase in the epidermal thickness. Inhibition of calcitonin gene-related peptide (CGRP), but not substance P (SP) signaling, reversed this effect. Human CGRP enhanced keratinocyte proliferation and epidermal thickness in skin models, demonstrating a key role of CGRP in modulating epidermal morphogenesis, whereas SP had only a moderate effect. Innervated skin models composed of atopic skin cells showed increased neurite outgrowth, accompanied by elevated CGRP release. As atopic keratinocytes were sensitized to CGRP owing to higher expression levels of the CGRP receptor components, receptor activity-modifying protein 1 (RAMP1) and receptor component protein (RCP), atopic innervated skin models displayed a thicker epidermis than did healthy controls. We conclude that neural CGRP controls local keratinocyte growth. Our results show that the crosstalk of the cutaneous peripheral nervous system and skin cells significantly influences epidermal morphogenesis and homeostasis in healthy and atopic skin.

Filaggrin Null Mutations Are Not a Protective Factor for Acne Vulgaris

Filaggrin Null Mutations Are Not a Protective Factor for Acne Vulgaris

Cytokine modulation of atopic dermatitis filaggrin skin expression

Atopic dermatitis (AD) is a chronic inflammatory skin disease that is characterized by a defective skin barrier function. Recent studies have reported mutations of the skin barrier gene encoding filaggrin in a subset of patients with AD. We investigated whether reduced filaggrin expression was found in patients with AD who were not carriers of known filaggrin mutations and whether filaggrin expression was modulated by the atopic inflammatory response. Filaggrin expression was measured in skin biopsies and cultured keratinocytes using real-time RT-PCR and immunohistochemistry. Filaggrin loss-of-function mutations were screened in a total of 69 subjects. Compared with normal skin, filaggrin expression was significantly reduced (P < .05) in acute AD skin, with further reduction seen in acute lesions from 3 European American subjects with AD who were heterozygous for the 2282del4 mutation. This was confirmed by using immunohistochemistry. AD skin is characterized by the overexpression of IL-4 and IL-13. Keratinocytes differentiated in the presence of IL-4 and IL-13 exhibited significantly reduced filaggrin gene expression (0.04 +/- 0.01 ng filaggrin/ng glyceraldehyde 3-phosphate dehydrogenase; P < .05) compared with media alone (0.16 +/- 0.03). Patients with AD have an acquired defect in filaggrin expression that can be modulated by the atopic inflammatory response. The atopic immune response contributes to the skin barrier defect in AD; therefore, neutralization of IL-4 and IL-13 could improve skin barrier integrity.

Specific Filaggrin Mutations Cause Ichthyosis Vulgaris and Are Significantly Associated with Atopic Dermatitis in Japan

Mutations in the gene encoding filaggrin (FLG) have been identified as the cause of ichthyosis vulgaris (IV) and shown to be major predisposing factors for atopic dermatitis (AD). However, these studies have been mainly carried out in European populations. In early 2007, we identified two Oriental-specific FLG mutations in four Japanese families with IV and reported that filaggrin mutations were also significant predisposing factors for AD in Japan. However, the frequency of FLG mutations observed in our Japanese AD cohort (5.6%), was much lower than that seen in Europeans (up to 48%). Here, we studied a further seven Japanese families with IV and identified two additional nonsense mutations in FLG, S2889X, and S3296X. We found that more than 20% of patients in our Japanese AD case series carry FLG mutations, and there is significant statistical association between the four mutations and AD (chi(2) P=8.4 x 10(-6); heterozygote odds ratio 7.57, 95% CI 2.84-23.03). These data emphasize that skin-barrier impairment due to reduced filaggrin expression plays an important role in the pathogenesis of AD and sheds further light on the genetic architecture of atopy in Japan.

Barrier Function, Epidermal Differentiation, and Human β-Defensin 2 Expression in Tinea Corporis

Barrier Function, Epidermal Differentiation, and Human β-Defensin 2 Expression in Tinea Corporis

Cytokine modulation of atopic dermatitis filaggrin skin expression

Atopic dermatitis (AD) is a chronic inflammatory skin disease that is characterized by a defective skin barrier function. Recent studies have reported mutations of the skin barrier gene encoding filaggrin in a subset of patients with AD. We investigated whether reduced filaggrin expression was found in patients with AD who were not carriers of known filaggrin mutations and whether filaggrin expression was modulated by the atopic inflammatory response. Filaggrin expression was measured in skin biopsies and cultured keratinocytes using real-time RT-PCR and immunohistochemistry. Filaggrin loss-of-function mutations were screened in a total of 69 subjects. Compared with normal skin, filaggrin expression was significantly reduced (P < .05) in acute AD skin, with further reduction seen in acute lesions from 3 European American subjects with AD who were heterozygous for the 2282del4 mutation. This was confirmed by using immunohistochemistry. AD skin is characterized by the overexpression of IL-4 and IL-13. Keratinocytes differentiated in the presence of IL-4 and IL-13 exhibited significantly reduced filaggrin gene expression (0.04 +/- 0.01 ng filaggrin/ng glyceraldehyde 3-phosphate dehydrogenase; P < .05) compared with media alone (0.16 +/- 0.03). Patients with AD have an acquired defect in filaggrin expression that can be modulated by the atopic inflammatory response. The atopic immune response contributes to the skin barrier defect in AD; therefore, neutralization of IL-4 and IL-13 could improve skin barrier integrity.