Mice deficient in involucrin, envoplakin, and periplakin have a defective epidermal barrier

Metabolic dysfunction mediated by HIF-1α contributes to epithelial differentiation defects in eosinophilic esophagitis

BACKGROUND

Investigating the contributory role that epithelial cell metabolism plays in allergic inflammation is a key factor to understanding what influences dysfunction and the pathogenesis of the allergic disease eosinophilic esophagitis (EoE). We previously highlighted that the absence of hypoxia signaling through hypoxia-inducible factor (HIF)-1α in EoE contributes to esophageal epithelial dysfunction. However, metabolic regulation by HIF-1α has not been explored in esophageal allergy.

OBJECTIVES

We sought to define the role of HIF-1α-mediated metabolic dysfunction in esophageal epithelial differentiation processes and barrier function in EoE.

METHODS

In RNA sequencing of EoE patient biopsy samples, we observed the expression pattern of key genes involved in mitochondrial metabolism/oxidative phosphorylation (OXPHOS) and glycolysis. Seahorse bioenergetics analysis was performed on EPC2-hTERT cells to decipher the metabolic processes involved in epithelial differentiation processes. In addition, air-liquid interface cultures were used to delineate metabolic dependency mechanisms required for epithelial differentiation.

RESULTS

Transcriptomic analysis identified an increase in genes associated with OXPHOS in patients with EoE. Epithelial origin of this signature was confirmed by complex V immunofluorescence of patient biopsy samples. Bioenergetic analysis in vitro revealed that differentiated epithelium was less reliant on OXPHOS compared with undifferentiated epithelium. Increased OXPHOS potential and reduced glycolytic capacity was mirrored in HIF1A-knockdown EPC2-hTERT cells that exhibited a significant absence of terminal markers of epithelial differentiation, including involucrin. Pharmacologic glucose transport inhibition phenocopied this, while rescue of the HIF-1α-deficient phenotype using the pan-prolyl hydroxylase inhibitor dimethyloxalylglycine resulted in restored expression of epithelial differentiation markers.

CONCLUSIONS

An OXPHOS-dominated metabolic pattern in EoE patients, brought about largely by the absence of HIF-1α-mediated glycolysis, is linked with the deficit in esophageal epithelial differentiation.

C. elegans epicuticlins define specific compartments in the apical extracellular matrix and function in wound repair

The apical extracellular matrix (aECM) of external epithelia often contains lipid-rich outer layers that contribute to permeability barrier function. The external aECM of nematodes is known as the cuticle and contains an external lipid-rich layer - the epicuticle. Epicuticlins are a family of tandem repeat cuticle proteins of unknown function. Here, we analyze the localization and function of the three C. elegans epicuticlins (EPIC proteins). EPIC-1 and EPIC-2 localize to the surface of the cuticle near the outer lipid layer, as well as to interfacial cuticles and adult-specific struts. EPIC-3 is expressed in dauer larvae and localizes to interfacial aECM in the buccal cavity. Skin wounding in the adult induces epic-3 expression, and EPIC proteins localize to wound sites. Null mutants lacking EPIC proteins are viable with reduced permeability barrier function and normal epicuticle lipid mobility. Loss of function in EPIC genes modifies the skin blistering phenotypes of Bli mutants and reduces survival after skin wounding. Our results suggest EPIC proteins define specific cortical compartments of the aECM and promote wound repair.

Diminished γδ T Cells during Murine Allergic Skin Inflammation Is Mediated by IL-4 Signaling in Keratinocytes

Atopic dermatitis results in diminished barrier function and altered production of antimicrobial peptides. Dendritic epidermal T cells (DETCs) play an important role in the wound repair and inflammation process. Our previous work identified an IL-4-dependent loss of DETCs in Stat6VT mice and in the MC903-induced skin inflammation mouse model. However, the mechanisms through which IL-4 mediates the loss of DETCs are unclear. In this study, we show that IL-4Rα germline knockout mice (Il4ra-/-) have increased DETCs, faster wound healing, and increased epidermal differentiation complex gene and fibronectin expression. The absence of IL-4Rα minimized the MC903-induced loss of DETCs, and reciprocal bone marrow chimera experiments in Il4ra-/- and wild-type mice demonstrated structural nonhematopoietic IL-4-responsive cell-mediated DETC homeostasis. Skin keratinocyte-derived IL-15 decreased dramatically in the MC903 model, while injection of IL-15 rescued DETC loss by promoting DETC proliferation and limiting apoptosis. Conditional deletion of IL-4Rα from keratinocytes using Il4rafl/fl K14-Cre mice showed an increase of DETCs, increased IL-15 production, and diminished skin inflammation following wounding. These results suggest that IL-4-dependent effects on DETCs in allergic skin inflammation are mediated by the IL-4Rα receptor of keratinocytes.

Plakins are involved in the regulation of centrosome position in polarized epithelial cells

BACKGROUND INFORMATION

The control of epithelial cell polarity is key to their function. Its dysregulation is a major cause of tissue transformation. In polarized epithelial cells,the centrosome is off-centred toward the apical pole. This asymmetry determines the main orientation of the microtubule network and intra-cellular traffic. However, the mechanism regulating centrosome positioning at the apical pole of polarized epithelial cells is still poorly undertood.

RESULTS

In this study we used transcriptomic data from breast cancer cells to identify molecular changes associated with the different stages of tumour transformation. We correlated these changes with variations in centrosome position or with cell progression along the epithelial-to-mesenchymal transition (EMT), a process that involves centrosome repositioning. We found that low levels of epiplakin, desmoplakin and periplakin correlated with centrosome mispositioning in cells that had progressed through EMT or tissue transformation. We further tested the causal role of these plakins in the regulation of centrosome position by knocking down their expression in a non-tumorigenic breast epithelial cell line (MCF10A). The downregulation of periplakin reduced the length of intercellular junction, which was not affected by the downregulation of epiplakin or desmoplakin. However, down-regulating any of them disrupted centrosome polarisation towards the junction without affecting microtubule stability.

CONCLUSIONS

Altogether, these results demonstrated that epiplakin, desmoplakin and periplakin are involved in the maintenance of the peripheral position of the centrosome close to inter-cellular junctions. They also revealed that these plakins are downregulated during EMT and breast cancer progression, which are both associated with centrosome mispositioning.

SIGNIFICANCE

These results revealed that the down-regulation of plakins and the consequential centrosome mispositioning are key signatures of disorganised cytoskeleton networks, inter-cellular junction weakening, shape deregulation and the loss of polarity in breast cancer cells. These metrics could further be used as a new readouts for early phases of tumoral development.

Dihydromyrcenol Modulates Involucrin Expression through the Akt Signaling Pathway

The epidermis serves as a protective barrier against external threats and is primarily composed of keratinocytes, which ultimately form corneocytes. Involucrin, a protein integral to the cornified envelope, plays a pivotal role in preserving the functional integrity of the skin barrier. Previous studies have shown that Akt plays an important role in keratinocyte differentiation and skin barrier development. This study investigated whether dihydromyrcenol (DHM), a plant-derived terpene, could increase involucrin production in keratinocytes and sought to elucidate the possible underlying mechanisms. To accomplish this objective, we assessed the alterations in involucrin by DHM through quantitative PCR and Western blot on the HaCaT cell line. The changes in the promoter levels were investigated using luciferase assays. Furthermore, upstream mechanisms were explored through the use of siRNA and inhibitors. To strengthen our findings, the results were subsequently validated in primary cells and 3D skin equivalents. DHM significantly increased involucrin mRNA and protein levels in a concentration-dependent manner. In addition, the Fyn-Akt signaling pathway was found to be required for DHM-induced involucrin expression, as inhibition of Fyn or Akt blocked the increase in involucrin mRNA induced by DHM. The transcription factor Sp1, which is recognized as one of the transcription factors for involucrin, was observed to be activated in response to DHM treatment. Moreover, DHM increased epidermal thickness in a 3D human skin model. These findings suggest that the modulation of involucrin expression with DHM could improve skin barrier function and highlight the importance of manipulating the Akt pathway to achieve this improvement.

C. elegans epicuticlins define specific compartments in the apical extracellular matrix and function in wound repair

The apical extracellular matrix (aECM) of external epithelia often contains lipid-rich outer layers that contribute to permeability barrier function. The external aECM of nematode is known as the cuticle and contains an external lipid-rich layer, the epicuticle. Epicuticlins are a family of tandem repeat proteins originally identified as components of the insoluble fraction of the cuticular aECM and thought to localize in or near epicuticle. However, there has been little in vivo analysis of epicuticlins. Here, we report the localization analysis of the three C. elegans epicuticlins (EPIC proteins) using fluorescent protein knock-ins to visualize endogenously expressed proteins, and further examine their in vivo function using genetic null mutants. By TIRF microscopy, we find that EPIC-1 and EPIC-2 localize to the surface of the cuticle in larval and adult stages in close proximity to the outer lipid layer. EPIC-1 and EPIC-2 also localize to interfacial cuticles and adult-specific cuticle struts. EPIC-3 expression is restricted to the stress-induced dauer stage, where it localizes to interfacial aECM in the buccal cavity. Strikingly, skin wounding in the adult induces epic-3 expression, and EPIC-3::mNG localizes to wound scars. Null mutants lacking one, two, or all three EPIC proteins display reduced survival after skin wounding yet are viable with low penetrance defects in epidermal morphogenesis. Our results suggest EPIC proteins define specific aECM compartments and have roles in wound repair.

Keratinocyte proline-rich protein modulates immune and epidermal response in imiquimod-induced psoriatic skin inflammation

Psoriasis is a persistent inflammatory skin disease thought to arise as a result of the infiltration of inflammatory cells and activation of keratinocytes. Recent advances in basic research and clinical experience revealed that the interleukin (IL)-23/IL-17 axis has been identified as a major immune pathway in psoriasis. However, it remains unclear how keratinocyte factors contribute to the pathology of psoriasis. Keratinocyte proline-rich protein (KPRP) is a proline-rich insoluble protein, which is present in the epidermis and is likely to be involved in the skin barrier function. Here, to investigate the potential roles of KPRP in psoriatic skin inflammation, Kprp-modified mice were applied in the imiquimod (IMQ)-induced skin inflammation model, which develops psoriasis-like epidermal hyperplasia and cutaneous inflammation features. Then, heterozygous knockout (Kprp+/- ) but not homozygous knockout (Kprp-/- ) mice displayed attenuated skin erythema compared to control wild-type mice. In addition, RNA sequencing, quantitative PCR and/or histological analysis detected changes in the expression of several molecules related to psoriatic inflammation or keratinocyte differentiation in Kprp+/- mice, but not Kprp-/- mice. Further analysis exhibited reduced IL-17-producing γδlow T cells and amplified epidermal hyperplasia in Kprp+/- mice, which were implied to be related to decreased expression of β-defensins and increased expression of LPAR1 (Lysophosphatidic acid receptor 1), respectively. Thus, our results imply that KPRP has the potential as a therapeutic target in psoriatic skin inflammation.

Targeting lymphoid-derived IL-17 signaling to delay skin aging

Skin aging is characterized by structural and functional changes that contribute to age-associated frailty. This probably depends on synergy between alterations in the local niche and stem cell-intrinsic changes, underscored by proinflammatory microenvironments that drive pleotropic changes. The nature of these age-associated inflammatory cues, or how they affect tissue aging, is unknown. Based on single-cell RNA sequencing of the dermal compartment of mouse skin, we show a skew towards an IL-17-expressing phenotype of T helper cells, γδ T cells and innate lymphoid cells in aged skin. Importantly, in vivo blockade of IL-17 signaling during aging reduces the proinflammatory state of the skin, delaying the appearance of age-related traits. Mechanistically, aberrant IL-17 signals through NF-κB in epidermal cells to impair homeostatic functions while promoting an inflammatory state. Our results indicate that aged skin shows signs of chronic inflammation and that increased IL-17 signaling could be targeted to prevent age-associated skin ailments.

Involucrin Modulates Vitamin D Receptor Activity in the Epidermis

Terminally differentiated keratinocytes are critical for epidermal function and are surrounded by involucrin (IVL). Increased IVL expression is associated with a near-selective sweep in European populations compared with those in Africa. This positive selection for increased IVL in the epidermis identifies human adaptation outside of Africa. The functional significance is unclear. We hypothesize that IVL modulates the environmentally sensitive vitamin D receptor (VDR) in the epidermis. We investigated VDR activity in Ivl‒/‒ and wild-type mice using vitamin D agonist (MC903) treatment and comprehensively determined the inflammatory response using single-cell RNA sequencing and associated skin microbiome changes using 16S bacterial phylotyping. VDR activity and target gene expression were reduced in Ivl‒/‒ mouse skin, with decreased MC903-mediated skin inflammation and significant reductions in CD4+ T cells, basophils, macrophages, monocytes, and type II basal keratinocytes and an increase in suprabasal keratinocytes. Coinciding with the dampened MC903-mediated inflammation, the skin microbiota of Ivl‒/‒ mice was more stable than that of the wild-type mice, which exhibited an MC903-responsive increase in Bacteroidetes and a decrease in Firmicutes. Together, our studies in Ivl‒/‒ mice identify a functional role for IVL to positively impact VDR activity and suggest an emerging IVL/VDR paradigm for adaptation in the human epidermis.

An integrative analysis of enhancer of yellow 2 homolog (ENY2) as a molecular biomarker in pan-cancer

ENY2 (Enhancer of yellow 2 transcription factor) is a transcription nuclear protein and primarily participates in the course of mRNA export and histone deubiquitination to influence gene expression. Current studies have shown that the expression of ENY2 is significantly upregulated in multiple cancers. However, the exact association between ENY2 and pan-cancers has not been fully established. Here, we comprehensively analyzed ENY2 from the online public database and The Cancer Genome Atlas (TCGA) database, including gene expression level in pan-cancer, comparison of ENY2 expression in different molecular and immune subtypes of pan-cancer, targeted protein, biological functions, molecular signatures, diagnostic and prognostic value in pan-cancer. Moreover, we focused on head and neck squamous cell carcinoma (HNSC) and explored ENY2 from the perspective of the correlations with clinical characteristics, prognosis, co-expression genes, differentially expressed genes (DEGs) and immune Infiltration. Our findings showed that the expression of ENY2 differed enormously not only in most cancer types but also in different molecular and immune subtypes of cancers. High accuracy in predicting cancers and notable correlations with prognosis of certain cancers suggested that ENY2 might be a potential diagnostic and prognostic biomarker of cancers. In addition, ENY2 was identified to be significantly correlated with clinical stage, gender, histologic grade and lymphovascular invasion in HNSC. Overexpression of ENY2 could lead to a worse overall survival (OS), disease-specific survival (DSS), and progression-free interval (PFI) in HNSC, especially in different clinical subgroups of HNSC. Taken together, ENY2 showed strong correlation with the diagnosis and prognosis of pan-cancer, and was an independent prognostic risk factor of HNSC, which may serve as a potential target for cancer management.

The Biological Role of Dead Sea Water in Skin Health: A Review

Applying natural mineral water to skin care is a popular tendency and many cosmetics products based on thermal spring water have been developed. The special location and environmental conditions provide Dead Sea water (DSW) with unique ion composition and concentrations, which bring comprehensive positive effects on skin health. This article reviews two potential action modes of DSW, and the biological function of DSW and its related complex in dermatology and skin care. Previous studies have proved the functions of skin moisturization, anti-inflammation, skin barrier repair, and anti-pollution. Especially, the anti-aging effect of DSW and related complexes can act in three different ways: keratinocyte rejuvenation, photo-protection, and cellular energy elevation. Additionally, the issues that need further investigation are also discussed. We hope that this review will help to improve the understanding of DSW and its related complex, and further contribute to product development in the skincare industry.

Thermostable Proteins from HaCaT Keratinocytes Identify a Wide Breadth of Intrinsically Disordered Proteins and Candidates for Liquid-Liquid Phase Separation

Intrinsically disordered proteins (IDPs) move through an ensemble of conformations which allows multitudinous roles within a cell. Keratinocytes, the predominant cell type in mammalian epidermis, have had only a few individual proteins assessed for intrinsic disorder and its possible contribution to liquid-liquid phase separation (LLPS), especially in regard to what functions or structures these proteins provide. We took a holistic approach to keratinocyte IDPs starting with enrichment via the isolation of thermostable proteins. The keratinocyte protein involucrin, known for its resistance to heat denaturation, served as a marker. It and other thermostable proteins were identified by liquid chromatography tandem mass spectrometry and subjected to extensive bioinformatic analysis covering gene ontology, intrinsic disorder, and potential for LLPS. Numerous proteins unique to keratinocytes and other proteins with shared expression in multiple cell types were identified to have IDP traits (e.g., compositional bias, nucleic acid binding, and repeat motifs). Among keratinocyte-specific proteins, many that co-assemble with involucrin into the cell-specific structure known as the cornified envelope scored highly for intrinsic disorder and potential for LLPS. This suggests intrinsic disorder and LLPS are previously unrecognized traits for assembly of the cornified envelope, echoing the contribution of intrinsic disorder and LLPS to more widely encountered features such as stress granules and PML bodies.

MAB21L4 Deficiency Drives Squamous Cell Carcinoma via Activation of RET

Epithelial squamous cell carcinomas (SCC) most commonly originate in the skin, where they display disruptions in the normally tightly regulated homeostatic balance between keratinocyte proliferation and terminal differentiation. We performed a transcriptome-wide screen for genes of unknown function that possess inverse expression patterns in differentiating keratinocytes compared with cutaneous SCC (cSCC), leading to the identification of MAB21L4 (C2ORF54) as an enforcer of terminal differentiation that suppresses carcinogenesis. Loss of MAB21L4 in human cSCC organoids increased expression of RET to enable malignant progression. In addition to transcriptional upregulation of RET, deletion of MAB21L4 preempted recruitment of the CacyBP-Siah1 E3 ligase complex to RET and reduced its ubiquitylation. In SCC organoids and in vivo tumor models, genetic disruption of RET or selective inhibition of RET with BLU-667 (pralsetinib) suppressed SCC growth while inducing concomitant differentiation. Overall, loss of MAB21L4 early during SCC development blocks differentiation by increasing RET expression. These results suggest that targeting RET activation is a potential therapeutic strategy for treating SCC.

SIGNIFICANCE

Downregulation of RET mediated by MAB21L4-CacyBP interaction is required to induce epidermal differentiation and suppress carcinogenesis, suggesting RET inhibition as a potential therapeutic approach in squamous cell carcinoma.

Identification of Biomarkers Associated With CD4+ T-Cell Infiltration With Gene Coexpression Network in Dermatomyositis

Background

Dermatomyositis is an autoimmune disease characterized by damage to the skin and muscles. CD4⁺ T cells are of crucial importance in the occurrence and development of dermatomyositis (DM). However, there are few bioinformatics studies on potential pathogenic genes and immune cell infiltration of DM. Therefore, this study intended to explore CD4⁺ T-cell infiltration–associated key genes in DM and construct a new model to predict the level of CD4⁺ T-cell infiltration in DM.

Methods

GSE46239, GSE142807, GSE1551, and GSE193276 datasets were downloaded. The WGCNA and CIBERSORT algorithms were performed to identify the most correlated gene module with CD4⁺ T cells. Matascape was used for GO enrichment and KEGG pathway analysis of the key gene module. LASSO regression analysis was used to identify the key genes and construct the prediction model. The correlation between the key genes and CD4⁺ T-cell infiltration was investigated. GSEA was performed to research the underlying signaling pathways of the key genes. The key gene-correlated transcription factors were identified through the RcisTarget and Gene-motif rankings databases. The miRcode and DIANA-LncBase databases were used to build the lncRNA-miRNA-mRNA network.

Results

In the brown module, 5 key genes (chromosome 1 open reading frame 106 (C1orf106), component of oligomeric Golgi complex 8 (COG8), envoplakin (EVPL), GTPases of immunity-associated protein family member 6 (GIMAP6), and interferon-alpha inducible protein 6 (IFI6)) highly associated with CD4⁺ T-cell infiltration were identified. The prediction model was constructed and showed better predictive performance in the training set, and this satisfactory model performance was validated in another skin biopsy dataset and a muscle biopsy dataset. The expression levels of the key genes promoted the CD4⁺ T-cell infiltration. GSEA results revealed that the key genes were remarkably enriched in many immunity-associated pathways, such as JAK/STAT signaling pathway. The cisbp_M2205, transcription factor-binding site, was enriched in C1orf106, EVPL, and IF16. Finally, 3,835 lncRNAs and 52 miRNAs significantly correlated with key genes were used to build a ceRNA network.

Conclusion

The C1orf106, COG8, EVPL, GIMAP6, and IFI6 genes are associated with CD4⁺ T-cell infiltration. The prediction model constructed based on the 5 key genes may better predict the level of CD4⁺ T-cell infiltration in damaged muscle and lesional skin of DM. These key genes could be recognized as potential biomarkers and immunotherapeutic targets of DM.

Loricrin at the Boundary between Inside and Outside

Cornification is a specialized mode of the cell-death program exclusively allowed for terrestrial amniotes. Recent investigations suggest that loricrin (LOR) is an important cornification effector. As the connotation of its name (“lorica” meaning an armor in Latin) suggests, the keratin-associated protein LOR promotes the maturation of the epidermal structure through organizing covalent cross-linkages, endowing the epidermis with the protection against oxidative injuries. By reviewing cornification mechanisms, we seek to classify ichthyosiform dermatoses based on their function, rather than clinical manifestations. We also reviewed recent mechanistic insights into the Kelch-like erythroid cell-derived protein with the cap “n” collar homology-associated protein 1/nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway in skin health and diseases, as LOR and NRF2 coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of cross-talking between keratinocytes and epidermal resident leukocytes, dissecting an LOR immunomodulatory function.

Loricrin and NRF2 Coordinate Cornification

Cornification involves cytoskeletal cross-linkages in corneocytes (the brick) and the secretion of lipids/adhesion structures to the interstitial space (the mortar). Because the assembly of lipid envelopes precedes corneocyte maturation, loricrin is supposed to be dispensable for the protection against desiccation. Although the phenotypes of Lor knockout (LKO) mice are obscure, the antioxidative response on the KEAP1/NRF2 signaling pathway compensates for the structural defect in utero. In this study, we asked how the compensatory response is evoked after the defects are repaired. To this end, the postnatal phenotypes of LKO mice were analyzed with particular attention to the permeability barrier function primarily maintained by the mortar. Ultrastructural analysis revealed substantially thinner cornified cell envelopes and increased numbers of lamellar granules in LKO mice. Superficial epidermal damages triggered the adaptive repairing responses that evoke the NRF2-dependent upregulation of genes associated with lamellar granule secretion in LKO mice. We also found that corneodesmosomes are less degraded in LKO mice. The observation suggests that loricrin and NRF2 are important effectors of cornification, in which proteins need to be secreted, cross-linked, and degraded in a coordinated manner.

γδ T Cells in Skin Inflammation

Gamma delta (γδ) T cells are a subset of T lymphocytes that express T cell receptor γ and 5 chains and display structural and functional heterogeneity. γδ T cells are typically of low abundance in the body and account for 1-5% of the blood lymphocytes and peripheral lymphoid tissues. As a bridge between innate and adaptive immunity, γδ T cells are uniquely poised to rapidly respond to stimulation and can regulate immune responses in peripheral tissues. The dendritic epidermal T cells in the skin epidermis can secrete growth factors to regulate skin homeostasis and re-epithelization and release inflammatory factors to mediate wound healing during skin inflammatory responses. Dermal γδ T cells can regulate the inflammatory process by producing interleukin-17 and other cytokines or chemokines. Here, we offer a review of the immune functions of γδ T cells, intending to understand their role in regulating skin barrier integrity and skin wound healing, which may be crucial for the development of novel therapeutics in skin diseases like atopic dermatitis and psoriasis.

The Epidermis: Redox Governor of Health and Diseases

A functional epithelial barrier necessitates protection against dehydration, and ichthyoses are caused by defects in maintaining the permeability barrier in the stratum corneum (SC), the uppermost protective layer composed of dead cells and secretory materials from the living layer stratum granulosum (SG). We have found that loricrin (LOR) is an essential effector of cornification that occurs in the uppermost layer of SG (SG1). LOR promotes the maturation of corneocytes and extracellular adhesion structure through organizing disulfide cross-linkages, albeit being dispensable for the SC permeability barrier. This review takes psoriasis and AD as the prototype of impaired cornification. Despite exhibiting immunological traits that oppose each other, both conditions share the epidermal differentiation complex as a susceptible locus. We also review recent mechanistic insights on skin diseases, focusing on the Kelch-like erythroid cell-derived protein with the cap "n" collar homology-associated protein 1/NFE2-related factor 2 signaling pathway, as they coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of thiol-mediated crosstalk between keratinocytes and leukocytes in the epidermis that was put forward earlier.

Molecular Mechanisms of Eosinophilic Esophagitis

Food hypersensitivity is a group of diseases arising from a specific immune response that reproduces on exposure to a given food. The current understanding of molecular mechanisms and immunopathology of non-IgE-mediated/mixed food hypersensitivity, e.g., eosinophilic esophagitis, contains many gaps in knowledge. This review aims to provide a modern classification and identify the primary diseases of non-IgE-mediated/mixed food hypersensitivity reactions, delineate the distinctive molecular features, and discuss recent findings in the immunopathology of eosinophilic esophagitis that may become a basis to develop valid biomarkers and novel therapies for this disease. Eosinophilic esophagitis is a recently recognized allergic-mediated disease with eosinophil-predominant esophagus inflammation. Its pathogenesis is a complicated network of interactions and signaling between epithelial, mesenchymal, and immune cells on molecular and intercellular levels. Alterations produced by overactivation of some cytokine signaling pathways, e.g., IL-13 or thymic stromal lymphopoietin (TSLP), were evolved and observed in this review from the viewpoints of molecular, genetic, epigenetic, and transcriptomic changes. Despite substantial experimental data, the reliable and representative mechanism of eosinophilic esophagitis pathogenesis has yet to show itself. So, the place of esophagitis between mixed and non-IgE-mediated allergic disorders and between eosinophilic gastrointestinal disorders currently seems vague and unclear.

Desmoplakin and periplakin genetically and functionally contribute to eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a chronic allergic inflammatory disease with a complex underlying genetic etiology. Herein, we conduct whole-exome sequencing of a multigeneration EoE pedigree (discovery set) and 61 additional multiplex families with EoE (replication set). A series of rare, heterozygous, missense variants are identified in the genes encoding the desmosome-associated proteins DSP and PPL in 21% of the multiplex families. Esophageal biopsies from patients with these variants retain dilated intercellular spaces and decrease DSP and PPL expression even during disease remission. These variants affect barrier integrity, cell motility and RhoGTPase activity in esophageal epithelial cells and have increased susceptibility to calpain-14-mediated degradation. An acquired loss of esophageal DSP and PPL is present in non-familial EoE. Taken together, herein, we uncover a pathogenic role for desmosomal dysfunction in EoE, providing a deeper mechanistic understanding of tissue-specific allergic responses.

Impact of chlorogenic acid on modulation of significant genes in dermal fibroblasts and epidermal keratinocytes

Chlorogenic acid is one of the most abundant polyphenols found in human diet. It is well-documented that chlorogenic acid has a significant impact on human cells, especially in the regulation of inflammation and metabolic processes. However, its role in regulating skin functions, especially with respect to the dermal collagen network or epidermal skin barrier, has not yet been elucidated. Here, we report that chlorogenic acid treatment can induce production of procollagen type I in human dermal fibroblast, Hs68 cell lines. Moreover, this treatment can stimulate upregulation of skin barrier genes, including the ones encoding filaggrin (FLG), involucrin (IVL), and envoplakin (EVPL), in epidermal keratinocytes. Chlorogenic acid also triggered a multifaceted response in the cytokine profile of keratinocytes. Therefore, we suggest that chlorogenic acid can be used to restore the impaired dermal matrix network as well as the epidermal skin barrier.

Commensal-Related Changes in the Epidermal Barrier Function Lead to Alterations in the Benzo[a]Pyrene Metabolite Profile and Its Distribution in 3D Skin

Polycyclic aromatic hydrocarbons (PAH) such as benzo[a]pyrene (B[a]P) are among the most abundant environmental pollutants, resulting in continuous exposure of human skin and its microbiota. However, effects of the latter on B[a]P toxicity, absorption, metabolism, and distribution in humans remain unclear. Here, we demonstrate that the skin microbiota does metabolize B[a]P on and in human skin in situ, using a recently developed commensal skin model. In this model, microbial metabolism leads to high concentrations of known microbial B[a]P metabolites on the surface as well as in the epidermal layers. In contrast to what was observed for uncolonized skin, B[a]P and its metabolites were subject to altered rates of skin penetration and diffusion, resulting in up to 58% reduction of metabolites recovered from basal culture medium. The results indicate the reason for this altered behavior to be a microbially induced strengthening of the epidermal barrier. Concomitantly, colonized models showed decreased formation and penetration of the ultimate carcinogen B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), leading, in consequence, to fewer BPDE-DNA adducts being formed. Befittingly, transcript and expression levels of key proteins for repairing environmentally induced DNA damage such as xeroderma pigmentosum complementation group C (XPC) were also found to be reduced in the commensal models, as was expression of B[a]P-associated cytochrome P450-dependent monooxygenases (CYPs). The results show that the microbiome can have significant effects on the toxicology of external chemical impacts. The respective effects rely on a complex interplay between microbial and host metabolism and microbe-host interactions, all of which cannot be adequately assessed using single-system studies.

Comparison of Epidermal Barrier Integrity in Adults with Classic Atopic Dermatitis, Atopic Prurigo and Non-Atopic Prurigo Nodularis

A deficient epidermal barrier is a key feature of atopic dermatitis (AD) and comprises altered lipid and protein content and composition of the stratum corneum resulting in disturbed water balance. Clinically, eczematous lesions on dry skin and pruritus develop. Pruritic nodules occur in prurigo nodularis (PN), another chronic skin disease, which can be associated with atopy. We aimed at comparing the three clinical pictures, classic AD, atopic prurigo (AP), and non-atopic PN, to healthy controls regarding the epidermal barrier. We determined clinical parameters and performed biophysical measurements, histology/immunohistochemistry, electron microscopy, and molecular biological analysis. We found distinctively elevated clinical scores, reduced hydration and increased transepidermal water loss, epidermal hyperplasia and inflammation reduced filaggrin and increased loricrin and involucrin expression, as well as reduced intercellular lipid lamellae in all three disease groups. These findings show a severe disruption in epidermal barrier structure and function in all three disorders so that epidermal barrier impairment is now proven not only for AD but also for PN.

Unbound Corneocyte Lipid Envelopes in 12R-Lipoxygenase Deficiency Support a Specific Role in Lipid-Protein Cross-Linking

Loss-of-function mutations in arachidonate lipoxygenase 12B (ALOX12B) are an important cause of autosomal recessive congenital ichthyosis (ARCI). 12R-lipoxygenase (12R-LOX), the protein product of ALOX12B, has been proposed to covalently bind the corneocyte lipid envelope (CLE) to the proteinaceous corneocyte envelope, thereby providing a scaffold for the assembly of barrier-providing, mature lipid lamellae. To test this hypothesis, an in-depth ultrastructural examination of CLEs was performed in ALOX12B-/- human and Alox12b-/- mouse epidermis, extracting samples with pyridine to distinguish covalently attached CLEs from unbound (ie, noncovalently bound) CLEs. ALOX12B--/- stratum corneum contained abundant pyridine-extractable (ie, unbound) CLEs, compared with normal stratum corneum. These unbound CLEs were associated with defective post-secretory lipid processing, and were specific to 12R-LOX deficiency, because they were not observed with deficiency of the related ARCI-associated proteins, patatin-like phospholipase 1 (Pnpla1) or abhydrolase domain containing 5 (Abhd5). These results suggest that 12R-LOX contributes specifically to CLE-corneocyte envelope cross-linking, which appears to be a prerequisite for post-secretory lipid processing, and provide insights into the pathogenesis of 12R-LOX deficiency in this subtype of ARCI, as well as other conditions that display a defective CLE.

Grainyhead-like transcription factors: guardians of the skin barrier

There has been selective pressure to maintain a skin barrier since terrestrial animals evolved 360 million years ago. These animals acquired an unique integumentary system with a keratinized, stratified, squamous epithelium surface barrier. The barrier protects against dehydration and entry of microbes and toxins. The skin barrier centres on the stratum corneum layer of the epidermis and consists of cornified envelopes cemented by the intercorneocyte lipid matrix. Multiple components of the barrier undergo cross-linking by transglutaminase (TGM) enzymes, while keratins provide additional mechanical strength. Cellular tight junctions also are crucial for barrier integrity. The grainyhead-like (GRHL) transcription factors regulate the formation and maintenance of the integument in diverse species. GRHL3 is essential for formation of the skin barrier during embryonic development, whereas GRHL1 maintains the skin barrier postnatally. This is achieved by transactivation of Tgm1 and Tgm5, respectively. In addition to its barrier function, GRHL3 plays key roles in wound repair and as an epidermal tumour suppressor. In its former role, GRHL3 activates the planar cell polarity signalling pathway to mediate wound healing by providing directional migration cues. In squamous epithelium, GRHL3 regulates the balance between proliferation and differentiation, and its loss induces squamous cell carcinoma (SCC). In the skin, this is mediated through increased expression of MIR21, which reduces the expression levels of GRHL3 and its direct target, PTEN, leading to activation of the PI3K-AKT signalling pathway. These data position the GRHL family as master regulators of epidermal homeostasis across a vast gulf of evolutionary history.

"Structural imprinting" of the cutaneous immune effector function

Keratinization provides tolerance to desiccation and mechanical durability. Loricrin, which is an epidermal thiol-rich protein, efficiently stabilizes terminally differentiated keratinocytes and maintains redox homeostasis. The discovery of the largely asymptomatic loricrin knockout (LKO) phenotype decades ago was rather unpredicted. Nevertheless, when including redox-driven, NF-E2-related factor 2-mediated backup responses, LKO mice provide opportunities for the observation of altered or "quasi-normal" homeostasis. Specifically, given that the tissue structure, as well as the local metabolism, transmits immunological signals, we sought to dissect the consequence of truncated epidermal differentiation program from immunological perspectives. Through a review of the aggregated evidence, we have attempted to generate an integrated view of the regulation of the peripheral immune system, which possibly occurs within the squamous epithelial tissue with truncated differentiation. This synthesis might not only provide insights into keratinization but also lead to the identification of factors intrinsic to the epidermis that imprint the immune effector function.

Biomimetic and estrogenic fibers promote tissue repair in mice and human skin via estrogen receptor β

The dynamic changes in estrogen levels throughout aging and during the menstrual cycle influence wound healing. Elevated estrogen levels during the pre-ovulation phase accelerate tissue repair, whereas reduced estrogen levels in post-menopausal women lead to slow healing. Although previous reports have shown that estrogen may potentiate healing by triggering the estrogen receptor (ER)-β signaling pathway, its binding to ER-α has been associated with severe collateral effects and has therefore limited its use as a therapeutic agent. To this end, soy phytoestrogens, which preferentially bind to the ER-β, are currently being explored as a safer therapeutic alternative to estrogen. However, the development and evaluation of phytoestrogen-based materials as local ER-β modulators remains largely unexplored. Here, we engineered biomimetic and estrogenic nanofiber wound dressings built from soy protein isolate (SPI) and hyaluronic acid (HA) using immersion rotary jet spinning. These engineered scaffolds were shown to successfully recapitulate the native dermal architecture, while delivering an ER-β-triggering phytoestrogen (genistein). When tested in ovariectomized mouse and ex vivo human skin tissues, HA/SPI scaffolds outperformed controls (no treatment or HA only scaffolds) towards promoting cutaneous tissue repair. These improved healing outcomes were prevented when the ER-β pathway was genetically or chemically inhibited. Our findings suggest that estrogenic fibrous scaffolds facilitate skin repair by ER-β activation.

Human stratum corneum proteomics reveals cross-linking of a broad spectrum of proteins in cornified envelopes

Defects in keratinocyte transglutaminase (TGM1), resulting in an improper protein scaffold for deposition of the lipid barrier, comprise a major source of autosomal recessive congenital ichthyosis. For that reason, the composition and formation of the cornified (cross-linked) protein envelope of the epidermis have been of considerable interest. Since the isopeptide cross-linked protein components are not individually isolable once incorporated, purified envelopes were analysed by mass spectrometry after trypsin digestion. Quantitative estimates of the identified components revealed some 170 proteins, each comprising at least 0.001% of the total, of which keratins were major constituents accounting for ≈74% of the total. Some prevalent non-keratin constituents such as keratinocyte proline-rich protein, loricrin and late envelope protein-7 were preferentially incorporated into envelopes. The results suggest a model where, as previously observed in hair shaft and nail plate, a diversity of cellular proteins are incorporated. They also help rationalize the minimal effect on epidermis of ablating genes for specific single envelope structural components. The quantitative profile of constituent proteins provides a foundation for future exploration of envelope perturbations that may occur in pathological conditions.

SDR9C7 catalyzes critical dehydrogenation of acylceramides for skin barrier formation

The corneocyte lipid envelope, composed of covalently bound ceramides and fatty acids, is important to the integrity of the permeability barrier in the stratum corneum, and its absence is a prime structural defect in various skin diseases associated with defective skin barrier function. SDR9C7 encodes a short-chain dehydrogenase/reductase family 9C member 7 (SDR9C7) recently found mutated in ichthyosis. In a patient with SDR9C7 mutation and a mouse Sdr9c7-KO model, we show loss of covalent binding of epidermal ceramides to protein, a structural fault in the barrier. For reasons unresolved, protein binding requires lipoxygenase-catalyzed transformations of linoleic acid (18:2) esterified in ω-O-acylceramides. In Sdr9c7-/- epidermis, quantitative liquid chromatography-mass spectometry (LC-MS) assays revealed almost complete loss of a species of ω-O-acylceramide esterified with linoleate-9,10-trans-epoxy-11E-13-ketone; other acylceramides related to the lipoxygenase pathway were in higher abundance. Recombinant SDR9C7 catalyzed NAD+-dependent dehydrogenation of linoleate 9,10-trans-epoxy-11E-13-alcohol to the corresponding 13-ketone, while ichthyosis mutants were inactive. We propose, therefore, that the critical requirement for lipoxygenases and SDR9C7 is in producing acylceramide containing the 9,10-epoxy-11E-13-ketone, a reactive moiety known for its nonenzymatic coupling to protein. This suggests a mechanism for coupling of ceramide to protein and provides important insights into skin barrier formation and pathogenesis.

LSD1 Inhibition Promotes Epithelial Differentiation through Derepression of Fate-Determining Transcription Factors

Self-renewing somatic tissues depend upon the proper balance of chromatin-modifying enzymes to coordinate progenitor cell maintenance and differentiation, disruption of which can promote carcinogenesis. As a result, drugs targeting the epigenome hold significant therapeutic potential. The histone demethylase, LSD1 (KDM1A), is overexpressed in numerous cancers, including epithelial cancers; however, its role in the skin is virtually unknown. Here we show that LSD1 directly represses master epithelial transcription factors that promote differentiation. LSD1 inhibitors block both LSD1 binding to chromatin and its catalytic activity, driving significant increases in H3K4 methylation and gene transcription of these fate-determining transcription factors. This leads to both premature epidermal differentiation and the repression of squamous cell carcinoma. Together these data highlight both LSD1’s role in maintaining the epidermal progenitor state and the potential of LSD1 inhibitors for the treatment of keratinocyte cancers, which collectively outnumber all other cancers combined.

Egolf et al. demonstrate that inhibition of the epigenetic regulator and histone demethylase, LSD1, promotes activation of the epidermal differentiation transcriptional program and, in turn, represses the invasion of cutaneous squamous cell carcinoma, one of the most common of all human cancers.

The KEAP1/NRF2 Signaling Pathway in Keratinization

Keratinization is a tissue adaptation, but aberrant keratinization is associated with skin disorders such as ichthyoses, atopic dermatitis, psoriasis, and acne. The disease phenotype stems from the interaction between genes and the environment; therefore, an understanding of the adaptation machinery may lead to a new appreciation of pathomechanisms. The KEAP1/NRF2 signaling pathway mediates the environmental responses of squamous epithelial tissue. The unpredicted outcome of the Keap1-null mutation in mice allowed us to revisit the basic principle of the biological process of keratinization: sulfur metabolism establishes unparalleled cytoprotection in the body wall of terrestrial mammals. We summarize the recent understanding of the KEAP1/NRF2 signaling pathway, which is a thiol-based sensor-effector apparatus, with particular focuses on epidermal differentiation in the context of the gene-environment interaction, the structure/function principles involved in KEAP1/NRF2 signaling, lessons from mouse models, and their pathological implications. This synthesis may provide insights into keratinization, which provides physical insulation and constitutes an essential innate integumentary defense system.

Regulatory CDH4 Genetic Variants Associate With Risk to Develop Capecitabine-Induced Hand-Foot Syndrome

Capecitabine-induced hand-foot syndrome (CiHFS) is a common dermatological adverse reaction affecting around 30% of patients with capecitabine-treated cancer, and the main cause of dose reductions and chemotherapy delays. To identify novel genetic factors associated with CiHFS in patients with cancer, we carried out an extreme-phenotype genomewide association study in 166 patients with breast and colorectal capecitabine-treated cancer with replication in a second cohort of 85 patients. We discovered and replicated a cluster of four highly correlated single-nucleotide polymorphisms associated with susceptibility to CiHFS at 20q13.33 locus (top hit = rs6129058, hazard ratio = 2.40, 95% confidence interval = 1.78-3.20; P = 1.2 × 10^-8 ). Using circular chromosome conformation capture sequencing, we identified a chromatin contact between the locus containing the risk alleles and the promoter of CDH4, located 90 kilobases away. The risk haplotype was associated with decreased levels of CDH4 mRNA and the protein it encodes, R-cadherin (RCAD), which mainly localizes in the granular layer of the epidermis. In human keratinocytes, CDH4 downregulation resulted in reduced expression of involucrin, a protein of the cornified envelope, an essential structure for skin barrier function. Immunohistochemical analyses revealed that skin from patients with severe CiHFS exhibited low levels of RCAD and involucrin before capecitabine treatment. Our results uncover a novel mechanism underlying individual genetic susceptibility to CiHFS with implications for clinically relevant risk prediction.

Unraveling the molecular pathobiology of vocal fold systemic dehydration using an in vivo rabbit model

Vocal folds are a viscoelastic multilayered structure responsible for voice production. Vocal fold epithelial damage may weaken the protection of deeper layers of lamina propria and thyroarytenoid muscle and impair voice production. Systemic dehydration can adversely affect vocal function by creating suboptimal biomechanical conditions for vocal fold vibration. However, the molecular pathobiology of systemically dehydrated vocal folds is poorly understood. We used an in vivo rabbit model to investigate the complete gene expression profile of systemically dehydrated vocal folds. The RNA-Seq based transcriptome revealed 203 differentially expressed (DE) vocal fold genes due to systemic dehydration. Interestingly, function enrichment analysis showed downregulation of genes involved in cell adhesion, cell junction, inflammation, and upregulation of genes involved in cell proliferation. RT-qPCR validation was performed for a subset of DE genes and confirmed the downregulation of DSG1, CDH3, NECTIN1, SDC1, S100A9, SPINK5, ECM1, IL1A, and IL36A genes. In addition, the upregulation of the transcription factor NR4A3 gene involved in epithelial cell proliferation was validated. Taken together, these results suggest an alteration of the vocal fold epithelial barrier independent of inflammation, which could indicate a disruption and remodeling of the epithelial barrier integrity. This transcriptome provides a first global picture of the molecular changes in vocal fold tissue in response to systemic dehydration. The alterations observed at the transcriptional level help to understand the pathobiology of dehydration in voice function and highlight the benefits of hydration in voice therapy.

Caffeoyl-Pro-His amide relieve DNCB-Induced Atopic Dermatitis-Like phenotypes in BALB/c mice

The main factors involved in the pathogenesis of atopic dermatitis (AD) are skin barrier abnormality, allergy/immunology, and pruritus. Considering how oxidative stress influences these factors, antioxidant agents may be effective candidates in the treatment of AD. To evaluate the effect of Caffeoyl–Pro–His amide (CA-PH), an antioxidant agent, on 2,4-dinitrochlorobenzene (DNCB)-induced AD-like phenotypes in BALB/c mice. Topical sensitization and challenge by DNCB were performed on the dorsal skin of BALB/c mice to induce AD-like cutaneous lesions, phenotypes, and immunologic response. CA-PH was applied topically for 2 weeks to assess its effects on DNCB-induced AD-like phenotypes. As a result, CA-PH relieved DNCB-induced AD-like phenotypes quantified by dermatitis severity score, scratching duration, and trans-epidermal water loss. Histopathological analysis showed that CA-PH decreased epidermal thickening, the number of mast cells, and eosinophil infiltration in dermis. Immunohistochemical staining revealed that CA-PH recovered skin barrier-related proteins: filaggrin, involucrin, and loricrin. As for the immunologic aspects, CA-PH treatment lowered mRNA or protein levels of interleukin (IL)-4, IL-6, IL-17a, IL-1b, IL-31, and IL-33 levels and thymic stromal lymphopoietin (TSLP) levels in cutaneous tissue, reducing the DNCB-induced serum IgE level elevation. In conclusion, topical CA-PH may be a therapeutic option for the treatment of AD.

HPV16 E7-impaired keratinocyte differentiation leads to tumorigenesis via cell cycle/pRb/involucrin/spectrin/adducin cascade

Here, we used codon usage technology to generate two codon-modified human papillomavirus (HPV)16 E7 genes and, together with wild-type E7, to construct three HPV16 E7 gene plasmids: Wt-E7, HB1-E7, and HB2-E7. The three HPV 16 E7 plasmids were used to investigate how HPV16 E7 protein was expressed in different cells and how this oncoprotein deregulated cellular and molecular events in human keratinocytes to induce carcinogenesis. We discovered that codon usage of HPV16 E7 gene played a key role in determining expression of E7 oncoprotein in all tested cells. HPV16 E7 inhibited significantly expression of pRb to impair keratinocyte differentiation and disrupted development of skin epidermis in mice. HPV16 E7 increased substantially the number of G0/G1 cells associated with upregulation of cyclin D2 and downregulation of cyclin B1 in keratinocytes. HPV16 E7 not only inhibited expression of involucrin and α-spectrin but also disrupted the organization of involucrin filaments and spectrin cytoskeleton. Furthermore, HPV16 E7 inhibited expression of β-adducin, destroyed its cytoskeletal structure and induced phosphorylation of β-adducin^(Ser662) in keratinocytes. Importantly, HPV16 E7 induced carcinogenesis in mice associated with expression of phosphorylated β-adducin^(Ser662) and its nucleus-translocation. In conclusion, we provided evidence that HPV16 E7 oncoprotein inhibited keratinocyte differentiation in vitro and in vivo leading to carcinogenesis through cell cycle arrest and disruption of pRb/involucrin/spectrin/adducin cascade.

Loricrin: Past, Present, and Future

The terminal differentiation of the epidermis is a complex physiological process. During the past few decades, medical genetics has shown that defects in the stratum corneum (SC) permeability barrier cause a myriad of pathological conditions, ranging from common dry skin to lethal ichthyoses. Contrarily, molecular phylogenetics has revealed that amniotes have acquired a specialized form of cytoprotection cornification that provides mechanical resilience to the SC. This superior biochemical property, along with desiccation tolerance, is attributable to the proper formation of the macromolecular protein-lipid complex termed cornified cell envelopes (CE). Cornification largely depends on the peculiar biochemical and biophysical properties of loricrin, which is a major CE component. Despite its quantitative significance, loricrin knockout (LKO) mice have revealed it to be dispensable for the SC permeability barrier. Nevertheless, LKO mice have brought us valuable lessons. It is also becoming evident that absent loricrin affects skin homeostasis more profoundly in many more aspects than previously expected. Through an extensive review of aggregate evidence, we discuss herein the functional significance of the thiol-rich protein loricrin from a biochemical, genetic, pathological, metabolic, or immunological aspect with some theoretical and speculative perspectives.

Analysis of zebrafish periderm enhancers facilitates identification of a regulatory variant near human KRT8/18

Genome-wide association studies for non-syndromic orofacial clefting (OFC) have identified single nucleotide polymorphisms (SNPs) at loci where the presumed risk-relevant gene is expressed in oral periderm. The functional subsets of such SNPs are difficult to predict because the sequence underpinnings of periderm enhancers are unknown. We applied ATAC-seq to models of human palate periderm, including zebrafish periderm, mouse embryonic palate epithelia, and a human oral epithelium cell line, and to complementary mesenchymal cell types. We identified sets of enhancers specific to the epithelial cells and trained gapped-kmer support-vector-machine classifiers on these sets. We used the classifiers to predict the effects of 14 OFC-associated SNPs at 12q13 near KRT18. All the classifiers picked the same SNP as having the strongest effect, but the significance was highest with the classifier trained on zebrafish periderm. Reporter and deletion analyses support this SNP as lying within a periderm enhancer regulating KRT18/KRT8 expression.

Epidermal mammalian target of rapamycin complex 2 controls lipid synthesis and filaggrin processing in epidermal barrier formation

BACKGROUND

Perturbation of epidermal barrier formation will profoundly compromise overall skin function, leading to a dry and scaly, ichthyosis-like skin phenotype that is the hallmark of a broad range of skin diseases, including ichthyosis, atopic dermatitis, and a multitude of clinical eczema variants. An overarching molecular mechanism that orchestrates the multitude of factors controlling epidermal barrier formation and homeostasis remains to be elucidated.

OBJECTIVE

Here we highlight a specific role of mammalian target of rapamycin complex 2 (mTORC2) signaling in epidermal barrier formation.

METHODS

Epidermal mTORC2 signaling was specifically disrupted by deleting rapamycin-insensitive companion of target of rapamycin (Rictor), encoding an essential subunit of mTORC2 in mouse epidermis (epidermis-specific homozygous Rictor deletion [Ric^EKO] mice). Epidermal structure and barrier function were investigated through a combination of gene expression, biochemical, morphological and functional analysis in Ric^EKO and control mice.

RESULTS

Ric^EKO newborns displayed an ichthyosis-like phenotype characterized by dysregulated epidermal de novo lipid synthesis, altered lipid lamellae structure, and aberrant filaggrin (FLG) processing. Despite a compensatory transcriptional epidermal repair response, the protective epidermal function was impaired in Ric^EKO mice, as revealed by increased transepidermal water loss, enhanced corneocyte fragility, decreased dendritic epidermal T cells, and an exaggerated percutaneous immune response. Restoration of Akt-Ser473 phosphorylation in mTORC2-deficient keratinocytes through expression of constitutive Akt rescued FLG processing.

CONCLUSION

Our findings reveal a critical metabolic signaling relay of barrier formation in which epidermal mTORC2 activity controls FLG processing and de novo epidermal lipid synthesis during cornification. Our findings provide novel mechanistic insights into epidermal barrier formation and could open up new therapeutic opportunities to restore defective epidermal barrier conditions.

Dry skin management: practical approach in light of latest research on skin structure and function

Dry skin is a common condition that is attributed to a lack of water in the stratum corneum. With the availability of new technologies, light has been shed on the pathophysiology of dry skin at the molecular level. With the aim to discuss implications of this latest research for the optimal formulation of emollients designed to treat dry skin, five specialists met in November 2017. Research on three topics thereby provided particularly detailed new insights on how to manage dry skin: research on the lipid composition and organization of the stratum corneum, research on natural moisturizing factors, and research on the peripheral nervous system. There was consensus that latest research expands the rationale to include physiological lipids in an emollient used for dry skin, as they were found to be essential for an adequate composition and organization in the stratum corneum but are reduced in dry skin. Latest findings also confirmed the incorporation of carefully selected humectants into a topical emollient for dry skin, given the reduced activity of enzymes involved in the synthesis of moisturizing factors when skin is dry. Overall, the group of specialists concluded that the previous concept of the five components for an ideal emollient for dry skin is well in accordance with latest research.

The ciliary GTPase Arl3 maintains tissue architecture by directing planar spindle orientation during epidermal morphogenesis

Arl/ARF GTPases regulate ciliary trafficking, but their tissue-specific functions are unclear. Here, we demonstrate that ciliary GTPase Arl3 is required for mitotic spindle orientation of mouse basal stem cells during skin development. Arl3 loss diminished cell divisions within the plane of the epithelium, leading to increased perpendicular divisions, expansion of progenitor cells and loss of epithelial integrity. These observations suggest that an Arl3-dependent mechanism maintains cell division polarity along the tissue axis, and disruption of planar spindle orientation has detrimental consequences for epidermal architecture. Defects in planar cell polarity (PCP) can disrupt spindle positioning during tissue morphogenesis. Upon Arl3 loss, the PCP signaling molecules Celsr1 and Vangl2 failed to maintain planar polarized distributions, resulting in defective hair follicle angling, a hallmark of disrupted PCP. In the absence of Celsr1 polarity, frizzled 6 lost its asymmetrical distribution and abnormally segregated to the apical cortex of basal cells. We propose that Arl3 regulates polarized endosomal trafficking of PCP components to compartmentalized membrane domains. Cell-cell communication via ciliary GTPase signaling directs mitotic spindle orientation and PCP signaling, processes that are crucial for the maintenance of epithelial architecture.

Pulling force deforms hair follicle root sheath nuclei and surrounding dermal collagen matrix differently at infundibulum, isthmus and suprabulbar regions

The biomechanical properties of the collagenous dermal matrix are well described but responses to mechanical force by the hair follicles have not been characterised so far. We applied a pulling force on hair follicles to visualise and quantify changes in the keratin-14 and involucrin-positive cell layers of the follicles using nuclear dimensions as an indicator of tissue deformation. Moreover, we used second-harmonic generation imaging to visualise changes in the dermal collagen. We report how the anatomical regions of the follicle respond to the force. Nuclei of the isthmus region were most affected. The nuclei in both K14-positive outer root sheath cells and in involucrin-positive cells were significantly compressed, whereas the response in the infundibulum and suprabulbar regions was more variable. The deformation of the nuclei did not correlate with lamin A/C expression. The changes in the collagenous matrix were distinct at different depths of the dermis as collagen fibrils were compressed closer to each other in the region adjacent to upper suprabulbar follicle and pulled apart near the infundibulum. Thus, the responses to the force are locally defined and the cells in the permanent and cycling parts of the follicle behave differently.

Depilatory chemical thioglycolate affects hair cuticle and cortex, degrades epidermal cornified envelopes and induces proliferation and differentiation responses in keratinocytes

Thioglycolate is a potent depilatory agent. In addition, it has been proposed to be useful as a penetration enhancer for transepidermal drug delivery. However, the effects on hair structure and stress responses it elicits in epidermal keratinocytes have not been fully characterised. We have used label-free confocal and fluorescence lifetime imaging supported by electron microscopy to demonstrate how thioglycolate damages hair cuticle cells by generating breakages along the endocuticle and leading to swelling of cortex cells. Maleimide staining of free SH-groups and a decrease in the average fluorescence lifetime of endogenous fluorophores demonstrate a specific change in protein structure in both hair cuticle and cortex. We found that the thioglycolate damages cornified envelopes isolated from the stratum corneum of the epidermis. However, thioglycolate-treated epidermal equivalent cultures recover within 48 hours, which highlights the reversibility of the damage. HaCaT keratinocytes respond to thioglycolate by increased proliferation, onset of differentiation and expression of the chaperone protein Hsp 70, but not Hsp 27. Up-regulation of involucrin can be blocked by an application of c-Jun N-terminal kinase (JNK) inhibitor, but the up-regulation of Hsp 70 takes place regardless of the presence of the JNK inhibitor.

Possible Role of Single Stranded DNA Binding Protein 3 on Skin Hydration by Regulating Epidermal Differentiation

Background

Skin hydration is a common problem both in elderly and young people as dry skin may cause irritation, dermatological disorders, and wrinkles. While both genetic and environmental factors seem to influence skin hydration, thorough genetic studies on skin hydration have not yet been conducted.

Objective

We used a genome-wide association study (GWAS) to explore the genetic elements underlying skin hydration by regulating epidermal differentiation and skin barrier function.

Methods

A GWAS was conducted to investigate the genetic factors influencing skin hydration in 100 Korean females along with molecular studies of genes in human epidermal keratinocytes for functional study in vitro.

Results

Among several single nucleotide polymorphisms identified in GWAS, we focused on Single Stranded DNA Binding Protein 3 (SSBP3) which is associated with DNA replication and DNA damage repair. To better understand the role of SSBP3 in skin cells, we introduced a calcium-induced differentiation keratinocyte culture system model and found that SSBP3 was upregulated in keratinocytes in a differentiation dependent manner. When SSBP3 was overexpressed using a recombinant adenovirus, the expression of differentiation-related genes such as loricrin and involucrin was markedly increased.

Conclusion

Taken together, our results suggest that genetic variants in the intronic region of SSBP3 could be determinants in skin hydration of Korean females. SSBP3 represents a new candidate gene to evaluate the molecular basis of the hydration ability in individuals.

Recent evolution of the human skin barrier

The skin is the first line of defense against the environment, with the epidermis as the outermost tissue providing much of the barrier function. Given its direct exposure to and encounters with the environment, the epidermis must evolve to provide an optimal barrier for the survival of an organism. Recent advances in genomics have identified a number of genes for the human skin barrier that have undergone evolutionary changes since humans diverged from chimpanzees. Here, we highlight a selection of key and innovative genetic findings for skin barrier evolution in our divergence from our primate ancestors and among modern human populations.

Corneocyte proteomics: Applications to skin biology and dermatology

Advances in mass spectrometry-based proteomics now permit analysis of complex cellular structures. Application to epidermis and its appendages (nail plate, hair shaft) has revealed a wealth of information about their protein profiles. The results confirm known site-specific differences in levels of certain keratins and add great depth to our knowledge of site specificity of scores of other proteins, thereby connecting anatomy and pathology. An example is the evident overlap in protein profiles of hair shaft and nail plate, helping rationalize their sharing of certain dystrophic syndromes distinct from epidermis. In addition, interindividual differences in protein level are manifest as would be expected. This approach permits characterization of altered profiles as a result of disease, where the magnitude of perturbation can be quantified and monitored during treatment. Proteomic analysis has also clarified the nature of the isopeptide cross-linked residual insoluble material after vigorous extraction with protein denaturants, nearly intractable to analysis without fragmentation. These structures, including the cross-linked envelope of epidermal corneocytes, are comprised of hundreds of protein constituents, evidence for strengthening the terminal structure complementary to disulphide bonding. Along with other developing technologies, proteomic analysis is anticipated to find use in disease risk stratification, detection, diagnosis and prognosis after the discovery phase and clinical validation.