Transglutaminase function in epidermis

Mapping the Periostin splice isoforms in atopic dermatitis and an in vitro asthma model - A multi-platform analysis using mass spectrometry and RT-qPCR

Periostin is a matricellular protein known to be alternatively spliced to produce ten isoforms with a molecular weight of 78-91 kDa. Within the extracellular matrix, periostin attaches to cell surfaces to induce signaling via integrin-binding and actively participates in fibrillogenesis, orchestrating the arrangement of collagen in the extracellular environment. In atopic diseases such as atopic dermatitis (AD) and asthma, periostin is known to participate in driving the disease-causing type 2 inflammation. The periostin isoforms expressed in these diseases and the implication of the alternative splicing events are unknown. Here, we present two universal assays to map the expression of periostin isoforms at the mRNA (RT-qPCR) and protein (PRM-based mass spectrometry) levels. We use these assays to study the splicing profile of periostin in AD lesions as well as in in vitro models of AD and asthma. In these conditions, periostin displayed overexpression with isoforms 3 and 5 standing out as highly overexpressed. Notably, isoforms 9 and 10 exhibited a divergent pattern relative to the remaining isoforms. Isoforms 9 and 10 are often overlooked in periostin research and this paper presents the first evidence of their expression at the protein level. This underlines the necessity to include isoforms 9 and 10 in future research addressing periostin splice isoforms. The assays presented in this paper hold the potential to improve our insight into the splicing profile of periostin in tissues and diseases of interest. The application of these assays to AD lesions and in vitro models demonstrated their potential for identifying isoforms of particular significance, warranting a further in-depth investigation.

TGM1/3-mediated transamidation of Exo70 promotes tumor metastasis upon LKB1 inactivation

Exo70, a key exocyst complex component, is crucial for cell motility and extracellular matrix (ECM) remodeling in cancer metastasis. Despite its potential as a drug target, Exo70's post-translational modifications (PTMs) are poorly characterized. Here, we report that Exo70 is transamidated on Gln5 with Lys56 of cystatin A by transglutaminases TGM1 and TGM3, promoting tumor metastasis. This modification enhances Exo70's association with other exocyst subunits, essential for secreting matrix metalloproteinases, forming invadopodia, and delivering integrins to the leading edge. Tumor suppressor liver kinase B1 (LKB1), whose inactivation accelerates metastasis, phosphorylates TGM1 and TGM3 at Thr386 and Thr282, respectively, to inhibit their interaction with Exo70 and the following transamidation. Cantharidin, a US Food and Drug Administration (FDA)-approved drug, inhibits Exo70 transamidation to restrain tumor cell migration and invasion. Together, our findings highlight Exo70 transamidation as a key molecular mechanism and target and propose cantharidin as a therapeutic strategy with direct clinical translational value for metastatic cancers, especially those with LKB1 loss.

Dermal Injection of Recombinant Filaggrin-2 Ameliorates UVB-Induced Epidermal Barrier Dysfunction and Photoaging

The epidermal barrier is vital for protecting the skin from environmental stressors and ultraviolet (UV) radiation. Filaggrin-2 (FLG2), a critical protein in the stratum corneum, plays a significant role in maintaining skin barrier homeostasis. However, the precise role of FLG2 in mitigating the adverse effects of UV-induced barrier disruption and photoaging remains poorly understood. In this study, we revealed that UVB exposure resulted in a decreased expression of FLG2 in HaCaT keratinocytes, which correlated with a compromised barrier function. The administration of recombinant filaggrin-2 (rFLG2) enhanced keratinocyte differentiation, bolstered barrier integrity, and offered protection against apoptosis and oxidative stress induced by UVB irradiation. Furthermore, in a UV-induced photodamage murine model, the dermal injection of rFLG2 facilitated the enhanced restoration of the epidermal barrier, decreased oxidative stress and inflammation, and mitigated the collagen degradation that is typical of photoaging. Collectively, our findings suggested that targeting FLG2 could be a strategic approach to prevent and treat skin barrier dysfunction and combat the aging effects associated with photoaging. rFLG2 emerges as a potentially viable therapy for maintaining skin health and preventing skin aging processes amplified by photodamage.

Analysis on promotive effect of rocking culture on keratinocyte differentiation in 3-dimensional reconstitution human epidermis

A 3-dimensional culture system of keratinocytes achieves cornification as a terminal differentiation that can mimic the formation of stratified epidermis. At the onset of keratinocyte differentiation, air-exposure treatment is essential for promotion. We have previously reported that the stimulation of differentiation is accompanied by downregulation of the transcriptional activity of the hypoxia-inducible factor (HIF) and also found that rocking treatment of cultured keratinocytes in the submerged condition restored their differentiation. A comparative study of cultured keratinocytes with and without rocking was then carried out to investigate the characteristics of the recovered differentiation by morphological and biochemical analyses. In addition, transcriptome analysis revealed the expected similar pattern between air-exposed and rocking cultures, including HIF-regulating transcripts. Furthermore, the promotive effect of rocking treatment was impaired under hypoxic culture conditions (1% O2). We showed that the restored promotion of differentiation by rocking culture is mainly due to the abrogation of transcriptional events by hypoxia.

Plantar Skin Exhibits Altered Physiology, Constitutive Activation of Wound-Associated Phenotypes, and Inherently Delayed Healing

Wound research has typically been performed without regard for where the wounds are located on the body, despite well-known heterogeneities in physical and biological properties between different skin areas. The skin covering the palms and soles is highly specialized, and plantar ulcers are one of the most challenging and costly wound types to manage. Using primarily the porcine model, we show that plantar skin is molecularly and functionally more distinct from nonplantar skin than previously recognized, with unique gene and protein expression profiles, broad alterations in cellular functions, constitutive activation of many wound-associated phenotypes, and inherently delayed healing. This unusual physiology is likely to play a significant but underappreciated role in the pathogenesis of plantar ulcers as well as the last 25+ years of futility in therapy development efforts. By revealing this critical yet unrecognized pitfall, we hope to contribute to the development of more effective therapies for these devastating nonhealing wounds.

Integration of transcriptomics and spatial biology analyses reveals Galactomyces ferment filtrate promotes epidermal interconnectivity via induction of keratinocyte differentiation, proliferation and cellular bioenergetics

OBJECTIVE

Human skin is the first line of defence from environmental factors such as solar radiation and is susceptible to premature ageing, including a disruption in epidermal differentiation and homeostasis. We evaluated the impact of a Galactomyces Ferment Filtrate (GFF) on epidermal differentiation and response to oxidative stress.

METHODS

We used transcriptomics, both spatial and traditional, to assess the impact of GFF on epidermal biology and homeostasis in keratinocytes (primary or immortalized) and in ex vivo skin explant tissue. The effect of GFF on cell adhesion rates, cellular ATP levels and proliferation rates were quantitated. Oxidative phosphorylation and glycolytic rates were measured under normal and stress-induced conditions.

RESULTS

Transcriptomics from keratinocytes and ex vivo skin explants from multiple donors show GFF induces keratinocyte differentiation, skin barrier development and cell adhesion while simultaneously repressing cellular stress and inflammatory related processes. Spatial transcriptomics profiling of ex vivo skin indicated basal keratinocytes at the epidermal-dermal junction and cornifying keratinocytes in the top layer of the epidermis as the primary cell types influenced by GFF treatment. Additionally, GFF significantly increases crosstalk between suprabasal and basal keratinocytes. To support these findings, we show that GFF can significantly increase cell adhesion and proliferation in keratinocytes. GFF also protected overall cellular bioenergetics under metabolic or oxidative stress conditions.

CONCLUSION

Our findings provide novel insights into cellular differences and epidermal spatial localization in response to GFF, supporting previous findings that this filtrate has a significant impact on epidermal biology and homeostasis, particularly on spatially defined crosstalk. We propose that GFF can help maintain epidermal health by enhancing keratinocyte crosstalk and differentiation/proliferation balance as well as promoting an enhanced response to stress.

Immunolabeling for filaggrin and acidic keratins in the granular layer of mammalian epidermis indicates that an acidic-basic interaction is involved in cornification

The soft epidermis of mammals derives from the accumulation of keratohyaline granules in the granular layer, before maturing into corneocytes. Main proteins accumulated in the granular layer are pro-filaggrin and filaggrin that determine keratin clumping and later moisturization of the stratum corneum that remains flexible. This soft epidermis allows the high sensitivity of mammalian skin. Presence and thickness of the stratum granulosum varies among different species of mammals and even between different body regions of the same animal, from discontinuous to multilayered. These variations are evident using antibodies for filaggrin, a large protein that share common epitopes among placentals. Here we have utilized filaggrin antibodies (8959 and 466) and an acidic keratin antibody (AK2) for labeling placental, marsupial and monotreme epidermis. AK2 labeling appears mainly to detect K24 keratin, and less likely other acidic keratins. Immunoreactivity for filaggrin is absent in platypus, discontinuous in Echidna and in the tested marsupials. In placentals, it is inconstantly or hardly detected in the thin epidermis of bat, rodents, and lagomorphs with a narrow, mono-stratified and/or discontinuous granular layer. In contrast, where the granular layer is continuous or even stratified, both filaggrin and AK2 antibodies decorate granular cells. The ultrastructural analysis using the AK2 antibody on human epidermis reveals that a weak labeling is associated with keratohyalin granules and filamentous keratins of transitional keratinocytes and corneocytes. This observation suggests that basophilic filaggrin interacts with acidic keratins like K24 and determines keratin condensation into corneocytes of the stratum corneum.

Apelin-13 modulates the endometrial transcriptome of the domestic pig during implantation

BACKGROUND

The peri-implantation period is a critical time during pregnancy that mostly defines the overall litter size. Most authors agree that the highest percentage of embryo mortality occurs during this time. Despite the brevity of the peri-implantation period, it is the most dynamic part of pregnancy in which the sequential and uninterrupted course of several processes is essential to the animal's reproductive success. Also then, the maternal uterine tissues undergo an intensive remodelling process, and their energy demand dramatically increases. It is believed that apelin, a member of the adipokine family, is involved in the control of female reproductive functions in response to the current metabolic state. The verified herein hypothesis assumed the modulatory effect of apelin on the endometrial tissue transcriptome on days 15 to 16 of gestation (beginning of implantation).

RESULTS

The analysis of data obtained during RNA-seq (Illumina HiSeq2500) of endometrial slices treated and untreated with apelin (n = 4 per group) revealed changes in the expression of 68 genes (39 up-regulated and 29 down-regulated in the presence of apelin), assigned to 240 gene ontology terms. We also revealed changes in the frequency of alternative splicing events (397 cases), as well as single nucleotide variants (1,818 cases) in the presence of the adipokine. The identified genes were associated, among others, with the composition of the extracellular matrix, apoptosis, and angiogenesis.

CONCLUSIONS

The obtained results indicate a potential role of apelin in the regulation of uterine tissue remodelling during the peri-implantation period.

Biological Implications and Functional Significance of Transglutaminase Type 2 in Nervous System Tumors

Transglutaminase type 2 (TG2) is the most ubiquitously expressed member of the transglutaminase family. TG2 catalyzes the transamidation reaction leading to several protein post-translational modifications and it is also implicated in signal transduction thanks to its GTP binding/hydrolyzing activity. In the nervous system, TG2 regulates multiple physiological processes, such as development, neuronal cell death and differentiation, and synaptic plasticity. Given its different enzymatic activities, aberrant expression or activity of TG2 can contribute to tumorigenesis, including in peripheral and central nervous system tumors. Indeed, TG2 dysregulation has been reported in meningiomas, medulloblastomas, neuroblastomas, glioblastomas, and other adult-type diffuse gliomas. The aim of this review is to provide an overview of the biological and functional relevance of TG2 in the pathogenesis of nervous system tumors, highlighting its involvement in survival, tumor inflammation, differentiation, and in the resistance to standard therapies.

Hydroxychloroquine exacerbates imiquimod-induced psoriasis-like dermatitis through stimulating overexpression of IL-6 in keratinocytes

OBJECTIVE

Hydroxychloroquine (HCQ) is a US Food and Drug Administration (FDA)-approved treatment for systemic lupus erythematosus (SLE) through inhibition of antigen presentation and subsequent reduction in T cell activation. Psoriasis relapse after antimalarial therapy have been reported in up to 18% of patients with psoriasis. Here, we explored the role of HCQ on exacerbating dermatitis utilizing an imiquimod (IMQ)-induced psoriasis-like dermatitis mouse model.

METHODS

Thirty-six C57BL/6 female mice were divided into six groups: wild-type control, IMQ-Only, pre-treat HCQ (30 mg/kg and 60 mg/kg HCQ), and co-treat HCQ with IMQ (30 mg/kg and 60 mg/kg HCQ). Besides control, all were topically treated with IMQ for 5 days. Pharmacological effects and mechanisms of HCQ were assessed by clinical severity of dermatitis, histopathology, and flow cytometry. HaCaT cells were co-treated with both HCQ and recombinant IL-17A, followed by the detection of proinflammatory cytokine expression and gene profiles through enzyme-linked immunosorbent assay and next-generation sequencing.

RESULTS

In the pre-treated and co-treated HCQ groups, skin redness and scaling were significantly increased compared to the IMQ-Only group, and Th17 cell expression was also upregulated. Acanthosis and CD11b+IL23+ dendritic cell (DC) infiltration were observed in the HCQ treatment group. IL-6 overexpression was detected in both the HaCaT cells and skin from the experimental mice. Psoriasis-related genes were regulated after being co-treated with HCQ and recombinant IL-17A in HaCaT cells.

CONCLUSIONS

HCQ exacerbates psoriasis-like skin inflammation by increasing the expression of IL-6, stimulating DC infiltration, and promoting Th17 expression in the microenvironment of the skin.

KEY MESSAGES

This study provided possible mechanisms for inducing psoriasis during HCQ treatment through an animal model.

Construction of a dual-component hydrogel matrix for 3D biomimetic skin based on photo-crosslinked chondroitin sulfate/collagen

The main challenge in the field of 3D biomimetic skin is to search for a suitable hydrogel matrix with good biocompatibility, appropriate mechanical property and inner porosity that can support the adhesion and proliferation of skin cells. In this study, photocurable chondroitin sulfate methacrylate (CSMA) and collagen methacrylate (CoLMA) synthesized from chondroitin sulfate (CS) and type I collagen I (CoL) in the dermal matrix were used to construct a photo-crosslinked dual-component CSMA-CoLMA hydrogel matrix. Due to the toughening effect of the dual-component, the CSMA-CoLMA hydrogel improved the intrinsic brittleness of the single-component CSMA hydrogel, presented good mechanical tunability. The average storage and elasticity modulus could reach 3.3 KPa and 30.3 KPa, respectively, which were close to those of natural skin. The CSMA-CoLMA hydrogel with a ratio of 8/6 showed suitable porous structure and good biocompatibility, supporting the adhesion and proliferation of skin cells. Furthermore, the expression of characteristic marker proteins was detected in the epidermal and dermal bi-layered models constructed with the hydrogel containing keratinocytes and fibroblasts. These results suggest that the dual-component CSMA-CoLMA hydrogel has promising potential as a matrix to construct 3D biomimetic skin.

Adult dental epithelial stem cell-derived organoids deposit hydroxylapatite biomineral

Ameloblasts are specialized cells derived from the dental epithelium that produce enamel, a hierarchically structured tissue comprised of highly elongated hydroxylapatite (OHAp) crystallites. The unique function of the epithelial cells synthesizing crystallites and assembling them in a mechanically robust structure is not fully elucidated yet, partly due to limitations with in vitro experimental models. Herein, we demonstrate the ability to generate mineralizing dental epithelial organoids (DEOs) from adult dental epithelial stem cells (aDESCs) isolated from mouse incisor tissues. DEOs expressed ameloblast markers, could be maintained for more than five months (11 passages) in vitro in media containing modulators of Wnt, Egf, Bmp, Fgf and Notch signaling pathways, and were amenable to cryostorage. When transplanted underneath murine kidney capsules, organoids produced OHAp crystallites similar in composition, size, and shape to mineralized dental tissues, including some enamel-like elongated crystals. DEOs are thus a powerful in vitro model to study mineralization process by dental epithelium, which can pave the way to understanding amelogenesis and developing regenerative therapy of enamel.

ECM-Focused Proteomic Analysis of Ear Punch Regeneration in Acomys Cahirinus

In mammals, significant injury is generally followed by the formation of a fibrotic scar which provides structural integrity but fails to functionally restore damaged tissue. Spiny mice of the genus Acomys represent the first example of full skin autotomy in mammals. Acomys cahirinus has evolved extremely weak skin as a strategy to avoid predation and is able to repeatedly regenerate healthy tissue without scar after severe skin injury or full-thickness ear punches. Extracellular matrix (ECM) composition is a critical regulator of wound repair and scar formation and previous studies have suggested that alterations in its expression may be responsible for the differences in regenerative capacity observed between Mus musculus and A. cahirinus , yet analysis of this critical tissue component has been limited in previous studies by its insolubility and resistance to extraction. Here, we utilize a 2-step ECM-optimized extraction to perform proteomic analysis of tissue composition during wound repair after full-thickness ear punches in A. cahirinus and M. musculus from weeks 1 to 4 post-injury. We observe changes in a wide range of ECM proteins which have been previously implicated in wound regeneration and scar formation, including collagens, coagulation and provisional matrix proteins, and matricryptic signaling peptides. We additionally report differences in crosslinking enzyme activity and ECM protein solubility between Mus and Acomys. Furthermore, we observed rapid and sustained increases in CD206, a marker of pro-regenerative M2 macrophages, in Acomys, whereas little or no increase in CD206 was detected in Mus. Together, these findings contribute to a comprehensive understanding of tissue cues which drive the regenerative capacity of Acomys and identify a number of potential targets for future pro-regenerative therapies.

Effects of an Adipose Mesenchymal Stem Cell-Derived Conditioned medium and TGF-β1 on Human Keratinocytes In Vitro

Human keratinocytes play a crucial role during skin wound healing and in skin replacement therapies. The secretome of adipose-derived stem cells (ASCs) has been shown to secrete pro-healing factors, among which include TGF-β1, which is essential for keratinocyte migration and the re-epithelialization of cutaneous wounds during skin wound healing. The benefits of an ASC conditioned medium (ASC-CM) are primarily orchestrated by trophic factors that mediate autocrine and paracrine effects in keratinocytes. Here, we evaluated the composition and the innate characteristics of the ASC secretome and its biological effects on keratinocyte maturation and wound healing in vitro. In particular, we detected high levels of different growth factors, such as HGF, FGFb, and VEGF, and other factors, such as TIMP1 and 4, IL8, PAI-1, uPA, and IGFBP-3, in the ASC-CM. Further, we investigated, using immunofluorescence and flow cytometry, the distinct effects of a human ASC-CM and/or synthetic TGF-β1 on human keratinocyte proliferation, migration, and cell apoptosis suppression. We demonstrated that the ASC-CM increased keratinocyte proliferation as compared to TGF-β1 treatment. Further, we found that the ASC-CM exerted cell cycle progression in keratinocytes via regulating the phases G1, S, and G2/M. In particular, cells subjected to the ASC-CM demonstrated increased DNA synthesis (S phase) compared to the TGF-β1-treated KCs, which showed a pronounced G0/G1 phase. Furthermore, both the ASC-CM and TGF-β1 conditions resulted in a decreased expression of the late differentiation marker CK10 in human keratinocytes in vitro, whereas both treatments enhanced transglutaminase 3 and loricrin expression. Interestingly, the ASC-CM promoted significantly increased numbers of keratinocytes expressing epidermal basal keratinocyte markers, such DLL1 and Jagged2 Notch ligands, whereas those ligands were significantly decreased in TGF-β1-treated keratinocytes. In conclusion, our findings suggest that the ASC-CM is a potent stimulator of human keratinocyte proliferation in vitro, particularly supporting basal keratinocytes, which are crucial for a successful skin coverage after transplantation. In contrast, TGF-β1 treatment decreased keratinocyte proliferation and specifically increased the expression of differentiation markers in vitro.

Liquid biopsy: an examination of platelet RNA obtained from head and neck squamous cell carcinoma patients for predictive molecular tumor markers

Aim

Recently, a tumor cell-platelet interaction was identified in different tumor entities, resulting in a transfer of tumor-derived RNA into platelets, named further "tumor-educated platelets (TEP)". The present pilot study aims to investigate whether such a tumor-platelet transfer of RNA occurs also in patients suffering from head and neck squamous cell carcinoma (HNSCC).

Methods

Sequencing analysis of RNA derived from platelets of tumor patients (TPs) and healthy donors (HDs) were performed. Subsequently, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used for verification of differentially expressed genes in platelets from TPs and HDs in a second cohort of patients and HDs. Data were analyzed by applying bioinformatic tools.

Results

Sequencing of RNA derived from the tumor as well as from platelets of TPs and HDs revealed 426 significantly differentially existing RNA, at which 406 RNA were more and 20 RNA less abundant in platelets from TPs in comparison to that of HDs. In TPs' platelets, abundantly existing RNA coding for 49 genes were detected, characteristically expressed in epithelial cells and RNA, the products of which are involved in tumor progression. Applying bioinformatic tools and verification on a second TP/HD cohort, collagen type I alpha 1 chain (COL1A1) and zinc finger protein 750 (ZNF750) were identified as the strongest potentially platelet-RNA-sequencing (RNA-seq)-based biomarkers for HNSCC.

Conclusions

These results indicate a transfer of tumor-derived messenger RNA (mRNA) into platelets of HNSCC patients. Therefore, analyses of a patient's platelet RNA could be an efficient option for liquid biopsy in order to diagnose HNSCC or to monitor tumorigenesis as well as therapeutic responses at any time and in real time.

Spatial tissue proteomics reveals distinct landscapes of heterogeneity in cutaneous papillomavirus-induced keratinocyte carcinomas

Infection with certain cutaneous human papillomaviruses (HPV), in conjunction with chronic ultraviolet (UV) exposure, are the major cofactors of non-melanoma skin cancer (NMSC), the most frequent cancer type worldwide. Cutaneous squamous cell carcinomas (SCCs) as well as tumors in general represent three-dimensional entities determined by both temporal and spatial constraints. Whole tissue proteomics is a straightforward approach to understand tumorigenesis in better detail, but studies focusing on different progression states toward a dedifferentiated SCC phenotype on a spatial level are rare. Here, we applied an innovative proteomic workflow on formalin-fixed, paraffin-embedded (FFPE) epithelial tumors derived from the preclinical animal model Mastomys coucha. This rodent is naturally infected with its genuine cutaneous papillomavirus and closely mimics skin carcinogenesis in the context of cutaneous HPV infections in humans. We deciphered cellular networks by comparing diverse epithelial tissues with respect to their differentiation level and infection status. Our study reveals novel regulatory proteins and pathways associated with virus-induced tumor initiation and progression of SCCs. This approach provides the basis to better comprehend the multistep process of skin carcinogenesis.

Calcitriol, an Active Form of Vitamin D3, Mitigates Skin Barrier Dysfunction in Atopic Dermatitis NC/Nga Mice

Atopic dermatitis and psoriasis are prevalent chronic inflammatory skin diseases that are characterized by dysfunctional skin barriers and substantially impact patients' quality of life. Vitamin D3 regulates immune responses and keratinocyte differentiation and improves psoriasis symptoms; however, its effects on atopic dermatitis remain unclear. Here, we investigated the effects of calcitriol, an active form of vitamin D3, on an NC/Nga mouse model of atopic dermatitis. We observed that the topical application of calcitriol decreased the dermatitis scores and epidermal thickness of NC/Nga mice with atopic dermatitis compared to untreated mice. In addition, both stratum corneum barrier function as assessed by the measurement of transepidermal water loss and tight junction barrier function as evaluated by biotin tracer permeability assay were improved following calcitriol treatment. Moreover, calcitriol treatment reversed the decrease in the expression of skin barrier-related proteins and decreased the expression of inflammatory cytokines such as interleukin (IL)-13 and IL-33 in mice with atopic dermatitis. These findings suggest that the topical application of calcitriol might improve the symptoms of atopic dermatitis by repairing the dysfunctional epidermal and tight junction barriers. Our results suggest that calcitriol might be a viable therapeutic agent for the treatment of atopic dermatitis in addition to psoriasis.

ZFP750 affects the cutaneous barrier through regulating lipid metabolism

An essential function of the epidermis is to provide a physical barrier that prevents the loss of water. Essential mediators of this barrier function include ceramides, cholesterol, and very long chain fatty acids, and their alteration causes human pathologies, including psoriasis and atopic dermatitis. A frameshift mutation in the human ZNF750 gene, which encodes a zinc finger transcription factor, has been shown to cause a seborrhea-like dermatitis. Here, we show that genetic deletion of the mouse homolog ZFP750 results in loss of epidermal barrier function, which is associated with a substantial reduction of ceramides, nonpolar lipids. The alteration of epidermal lipid homeostasis is directly linked to the transcriptional activity of ZFP750. ZFP750 directly and/or indirectly regulates the expression of crucial enzymes primarily involved in the biosynthesis of ceramides. Overall, our study identifies the transcription factor ZFP750 as a master regulator epidermal homeostasis through lipid biosynthesis and thus contributing to our understanding of the pathogenesis of several human skin diseases.

Human epidermis organotypic cultures, a reproducible system recapitulating the epidermis in vitro

The translatability of research is highly dependent on models that recapitulate human tissues and organs. Here, we describe a procedure for the generation of human epidermis organotypic cultures (HEOCs) from primary keratinocytes isolated from foreskin and adult skin as well as from an immortalized keratinocyte cell line (KerTr). We tested several media conditions to develop a defined HEOC growing and expansion media. We characterized the HEOCs and show that in optimal culture conditions they express the proliferation marker Ki67, the basement membrane protein collagen 17 (col17) and the epidermal differentiation markers keratin 15 (K15), keratin 14 (K14), keratin 5 (K5), keratin 10 (K10), keratin 1 (K1), transglutaminase 1 (TGM1), transglutaminase 3 (TGM3) and filaggrin (FLG). Thus, they recapitulate the human epidermis and are stratified from the basal layer to the stratum corneum. These HEOC can be generated reproducibly on a large scale, making it an invaluable model for screening therapeutic compounds and also for the study of pathologies affecting the epidermis.

Transglutaminase-2 is critical for corneal epithelial barrier function via positive regulation of Claudin-1

PURPOSE

Transglutaminase (TG)-2 is a ubiquitous multi-functional protein expressed in all living cells. The purpose of the current study was to investigate the role of TG-2 in corneal barrier function and its potential regulation of epithelial junctional proteins and transcription factors.

METHODS

Corneal barrier function to ions in TG-2-/- and TG-2+/+ mice was assessed by Ussing chamber assay. Hypo-osmolar water or FITC-dextran was applied on top of mouse eyes to evaluate the corneal barrier function to water and macromolecules. Western blots, qPCR and immunofluorescent staining were used to investigate the expression of tight junction proteins in TG-2-/- and TG-2+/+ mouse corneas, and also in TG-2 knockdown human corneal epithelial cells.

RESULTS

Corneal explants from TG-2-/- mice had a lower trans-epithelial electrical resistance compared to TG-2+/+ mice. When challenged by hypo-osmolar water, the central corneal thickness of TG-2-/- mice increased faster, and these mice had a faster rise of fluorescence in the anterior chamber after ocular exposure to FITC-dextran, compared to TG-2+/+. Claudin-1 protein and transcript levels were reduced in the cornea of TG-2-/- mice and in TG-2 knockdown human corneal epithelial cells. Slug which previously reported suppressing Claudin-1 transcription, was increased at both protein and transcript level in TG-2 knockdown cells. TG-2 and Claudin-1 protein levels were unchanged in shRNA and shTG cells after MG132 treatment, while Slug accumulated in treated cells.

CONCLUSION

TG-2 may positively regulate Claudin-1 through repressing Slug at transcript level, and thus it is critical for normal corneal barrier function.

CD83 Regulates the Immune Responses in Inflammatory Disorders

Activating the immune system plays an important role in maintaining physiological homeostasis and defending the body against harmful infections. However, abnormalities in the immune response can lead to various immunopathological responses and severe inflammation. The activation of dendritic cells (DCs) can influence immunological responses by promoting the differentiation of T cells into various functional subtypes crucial for the eradication of pathogens. CD83 is a molecule known to be expressed on mature DCs, activated B cells, and T cells. Two isotypes of CD83, a membrane-bound form and a soluble form, are subjects of extensive scientific research. It has been suggested that CD83 is not only a ubiquitous co-stimulatory molecule but also a crucial player in monitoring and resolving inflammatory reactions. Although CD83 has been involved in immunological responses, its functions in autoimmune diseases and effects on pathogen immune evasion remain unclear. Herein, we outline current immunological findings and the proposed function of CD83 in inflammatory disorders.

Immunization with a Pneumococcal pep27 Mutant Strain Alleviates Atopic Dermatitis through the Upregulation of Regulatory T-Cell Activity and Epithelial Barrier Function and Suppressing TSLP Expression

Atopic dermatitis (AD) is an inflammatory disease driven in part by type 2 helper T (Th2) cytokines and skin barrier disruption alleviating the entry of allergens. Thymic stromal lymphopoietin (TSLP), an epithelial cell‒derived cytokine, is known to aggravate AD symptoms by activating Th2. In addition, regulatory T cells (Tregs) inhibit inflammatory cells such as Th2. However, the relationship between TSLP and Tregs in AD is unclear. A murine dermatitis model was induced by applying oxazolone to the ear skin of mice. Prophylactic and therapeutic responses were analyzed by immunizing mice intranasally with a pneumococcal pep27 mutant (Δpep27 mutant), attenuated strain by reducing the virulence of a pathogen. Intranasal immunization with a pneumococcal pep27 mutant could elicit anti-inflammatory Treg-relevant factors and epithelial barrier genes (loricrin, involucrin, filaggrin, and small proline-rich repeat proteins). Thus, pneumococcal pep27-mutant immunization suppressed epidermal collapse, IgE, TSLP, and upregulation of Th2 expression by upregulating Treg activity. In contrast, Treg inhibition aggravated AD symptoms through the upregulation of TSLP and Th2 and the repression of epithelial barrier function compared with that of the noninhibited pneumococcal Δpep27-mutant group. Taken together, immunization with pneumococcal Δpep27 mutant upregulated Treg and epithelial barrier function and inhibited TSLP and Th2 to relieve AD symptoms.

Fabricating a Novel Three-Dimensional Skin Model Using Silica Nonwoven Fabrics (SNF)

Silica nonwoven fabrics (SNF) prepared using electrospinning have high biocompatibility, thermal stability, and porosity that allows growing three-dimensional culture of cells. In this study, we used SNF to construct a three-dimensional artificial skin model consisting of epidermal and dermal layers with immortalized and primary human cell lines, creating a novel model that minimizes tissue shrinkage. As a result, SNF dermal/epidermal models have enhanced functions in the basement membrane, whereas Collagen dermal/epidermal models have advantages in keratinization and barrier functions. The SNF dermal/epidermal model with mechanical strength formed a basement membrane mimicking structure, suggesting the construction of a stable skin model. Next, we constructed three-dimensional skin models consisting of SNF and collagen. In the combination models, the expression of genes in the basement membrane was significantly increased compared with that in the Collagen dermal/epidermal model, and the gene for keratinization was increased compared with that in the SNF dermal/epidermal model. We believe that the combination model can be a biomimetic model that takes advantage of both SNF and collagen and can be applied to various basic research. Our new skin model is expected to be an alternative method for skin testing to improve the shrinkage of the collagen matrix gel.

Alpha-Keratin, Keratin-Associated Proteins and Transglutaminase 1 Are Present in the Ortho- and Parakeratinized Epithelium of the Avian Tongue

The lingual mucosa in birds is covered with two specific types of multilayered epithelia, i.e., the para- and orthokeratinized epithelium, that differ structurally and functionally. Comprehensive information on proteins synthesized in keratinocyte during their cytodifferentiation in subsequent layers of multilayered epithelia in birds concerns only the epidermis and are missing the epithelia of the lingual mucosa. The aim of the present study was to perform an immunohistochemical (IHC) and molecular analysis (WB) of bird-specific alpha-keratin, keratin-associated proteins (KAPs), namely filaggrin and loricrin, as well as transglutaminase 1 in the para- and orthokeratinized epithelium covering the tongue in the domestic duck, goose, and turkey. The results reveal the presence of alpha-keratin and KAPs in both epithelia, which is a sign of the cornification process. In contrast to the epidermis, the main KAPs involved in the cornification process of the lingual epithelia in birds is loricrin. Stronger expression with KAPs and transglutaminase 1 in the orthokeratinized epithelium than in the parakeratinized epithelium may determine the formation of a more efficient protective mechanical barrier. The presence of alpha-keratin, KAPs, and transglutaminase 1 epitopes characteristic of epidermal cornification in both types of the lingual epithelia may prove that they are of ectodermal origin.

Skin Minerals: Key Roles of Inorganic Elements in Skin Physiological Functions

As odd as it may seem at first glance, minerals, it is what we are all about…or nearly. Although life on Earth is carbon-based, several other elements present in the planet’s crust are involved in and often indispensable for functioning of living organisms. Many ions are essential, and others show supportive and accessory qualities. They are operative in the skin, supporting specific processes related to the particular situation of this organ at the interface with the environment. Skin bioenergetics, redox balance, epidermal barrier function, and dermal remodeling are amongst crucial activities guided by or taking advantage of mineral elements. Skin regenerative processes and skin ageing can be positively impacted by adequate accessibility, distribution, and balance of inorganic ions.

Type 2 Inflammation Contributes to Skin Barrier Dysfunction in Atopic Dermatitis

Skin barrier dysfunction, a defining feature of atopic dermatitis (AD), arises from multiple interacting systems. In AD, skin inflammation is caused by host-environment interactions involving keratinocytes as well as tissue-resident immune cells such as type 2 innate lymphoid cells, basophils, mast cells, and T helper type 2 cells, which produce type 2 cytokines, including IL-4, IL-5, IL-13, and IL-31. Type 2 inflammation broadly impacts the expression of genes relevant for barrier function, such as intracellular structural proteins, extracellular lipids, and junctional proteins, and enhances Staphylococcus aureus skin colonization. Systemic anti‒type 2 inflammation therapies may improve dysfunctional skin barrier in AD.

Decoy receptor 3 is involved in epidermal keratinocyte commitment to terminal differentiation via EGFR and PKC activation

Decoy receptor 3 (DcR3) is a soluble receptor for Fas ligand, LIGHT and TL1A, but it also exerts effector functions. Previously, we found that DcR3 is upregulated in the serum and lesional skin of patients with psoriasis and is upregulated by EGFR activation in proliferating primary human epidermal keratinocytes. However, the functional role of intracellular DcR3 in keratinocyte differentiation is still incompletely defined. Herein, primary cultured human epidermal keratinocytes were differentiated by phorbol 12-myristate 13-acetate (PMA) treatment, calcium treatment and cell confluence, which are three standard in vitro differentiation models. We found that the constitutive expression of the DcR3 gene and protein was progressively suppressed during terminal differentiation of keratinocytes. These changes were correlated with downregulation of EGFR activation during keratinocyte differentiation. EGFR inhibition by gefitinib further decreased confluence-induced suppression of DcR3 mRNA expression, and, vice versa, knocking down DcR3 expression attenuated EGFR and EGFR ligand expression as well as EGFR activation. Under conditions without a change in cell growth, DcR3 silencing reduced the expression of involucrin and transglutaminase 1 but enhanced the induction of the terminal differentiation markers keratin 10 and loricrin. Of note, DcR3 interacted with PKCα and PKCδ and enhanced PKC activity. In keratinocytes with PKCα and PKCδ silencing, differentiation markers were differentially affected. In conclusion, DcR3 expression in keratinocytes is regulated by EGFR and forms a positive feedback loop to orchestrate constitutive EGFR and PKC activity. During differentiation, DcR3 is downregulated and involved in modulating the pattern of terminal differentiation.

A protein linked to cancer and various inflammatory diseases may also be an important driver for the skin condition in psoriasis. The outer surface of the skin is formed by cells called keratinocytes, which transition from a highly proliferative state to a fully mature state where they no longer divide. This developmental process is disrupted in psoriasis. Researchers led by Wan-Wan Lin at National Taiwan University, Taipei, have now identified a prominent role for a protein called decoy receptor 3 (DcR3), which is a biomarker for a variety of disorders and is also abnormally expressed in keratinocytes in psoriatic lesions. Lin and colleagues demonstrated that DcR3 interacts with multiple cellular signaling pathways that coordinate cell differentiation. These findings reveal how aberrant DcR3 activity might lead to the abnormal keratinocyte developmental behavior observed in psoriasis.

The Discovery and Function of Filaggrin

Keratohyalin granules were discovered in the mid-19th century in cells that terminally differentiate to form the outer, cornified layer of the epidermis. The first indications of the composition of these structures emerged in the 1960s from a histochemical stain for histidine, followed by radioautographic evidence of a high incidence of histidine incorporation into newly synthesized proteins in cells containing the granules. Research during the next three decades revealed the structure and function of a major protein in these granules, which was initially called the ‘histidine-rich protein’. Steinert and Dale named the protein ‘filaggrin’ in 1981 because of its ability to aggregate keratin intermediate filaments. The human gene for the precursor, ‘profilaggrin,’ was reported in 1991 to encode 10, 11 or 12 nearly identical repeats. Remarkably, the mouse and rat genes encode up to 20 repeats. The lifetime of filaggrin is the time required for keratinocytes in the granular layer to move into the inner cornified layer. During this transition, filaggrin facilitates the collapse of corneocytes into ‘building blocks’ that become an impermeable surface barrier. The subsequent degradation of filaggrin is as remarkable as its synthesis, and the end-products aid in maintaining moisture in the cornified layer. It was apparent that ichthyosis vulgaris and atopic dermatitis were associated with the absence of this protein. McLean’s team in 2006 identified the cause of these diseases by discovering loss-of-function mutations in the profilaggrin gene, which led to dysfunction of the surface barrier. This story illustrates the complexity in maintaining a healthy, functional epidermis.

Transglutaminase 3 crosslinks the secreted gel-forming mucus component Mucin-2 and stabilizes the colonic mucus layer

The colonic mucus layer is organized as a two-layered system providing a physical barrier against pathogens and simultaneously harboring the commensal flora. The factors contributing to the organization of this gel network are not well understood. In this study, the impact of transglutaminase activity on this architecture was analyzed. Here, we show that transglutaminase TGM3 is the major transglutaminase-isoform expressed and synthesized in the colon. Furthermore, intrinsic extracellular transglutaminase activity in the secreted mucus was demonstrated in vitro and ex vivo. Absence of this acyl-transferase activity resulted in faster degradation of the major mucus component the MUC2 mucin and changed the biochemical properties of mucus. Finally, TGM3-deficient mice showed an early increased susceptibility to Dextran Sodium Sulfate-induced colitis. Here, we report that natural isopeptide cross-linking by TGM3 is important for mucus homeostasis and protection of the colon from inflammation, reducing the risk of colitis.

The colonic mucus layer is an organized system providing a physical barrier against pathogens and simultaneously harbouring the commensal flora. Here the authors report that transglutaminase 3 activity contributes to homeostasis of the colonic mucus layer and the lack of this enzymatic activity leads to increased susceptibility against DSS-induced colitis in mice.

Preventative effects of antioxidants on changes in sebocytes, outer root sheath cells, and Cutibacterium acnes-pretreated mice by particulate matter: No significant difference among antioxidants

OBJECTIVES

Particulate matter (PM) is an air pollutant that can damage human skin; antioxidants have shown some efficacy in alleviating PM-induced skin inflammation. We investigated the antioxidant effects of punicalagin, epigallocatechin-3-gallate (EGCG), and resveratrol on PM-induced changes in cultured human sebocytes, outer root sheath (ORS) cells, and Cutibacterium acnes-pretreated mice.

METHODS

Sebocytes and ORS cells were cultured with 100 μg/mL PM10 and 5 μM punicalagin, 1 μM EGCG, or 1 μM resveratrol for 24 h. In C. acnes-pretreated mice, inflammatory nodules were treated with 100 μg/mL PM10 and 5 μM punicalagin, 1 μM EGCG, or 1 μM resveratrol. Cell viability was measured using an MTT assay. Antioxidant effects were analyzed according to RNA expression, using real-time PCR, as well as reactive oxygen species (ROS) and sebum measurements.

RESULTS

Antioxidants inhibited the upregulation of inflammatory cytokines, matrix metalloproteinase, aryl hydrocarbon receptor, and NF-kB as well as the production of ROS induced by PM10 in cultured sebocytes and ORS cells. The preventative effects of punicalagin and EGCG on biomarker expression in cultured sebocytes and ORS cells were slightly greater than those of resveratrol, though the difference was not significant. In C. acnes-pretreated mice, the antioxidants inhibited inflammatory cytokine and matrix metalloproteinase expression as well as sebum production.

CONCLUSIONS

Antioxidants effectively reduced the expression of inflammatory biomarkers and sebum production in cultured sebocytes, ORS cells, and C. acnes-pretreated mice.

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.

Vertebrate keratinization evolved into cornification mainly due to transglutaminase and sulfhydryl oxidase activities on epidermal proteins: An immunohistochemical survey

The epidermis of vertebrates forms an extended organ to protect and exchange gas, water, and organic molecules with aquatic and terrestrial environments. Herein, the processes of keratinization and cornification in aquatic and terrestrial vertebrates were compared using immunohistochemistry. Keratins with low cysteine and glycine contents form the main bulk of proteins in the anamniote epidermis, which undergoes keratinization. In contrast, specialized keratins rich in cysteine-glycine and keratin associated corneous proteins rich in cysteine, glycine, and tyrosine form the bulk of proteins of amniote soft cornification in the epidermis and hard cornification in scales, claws, beak, feathers, hairs, and horns. Transglutaminase (TGase) and sulfhydryl oxidase (SOXase) are the main enzymes involved in cornification. Their evolution was fundamental for the terrestrial adaptation of vertebrates. Immunohistochemistry results revealed that TGase and SOXase were low to absent in fish and amphibian epidermis, while they increased in the epidermis of amniotes with the evolution of the stratum corneum and skin appendages. TGase aids the formation of isopeptide bonds, while SOXase forms disulfide bonds that generate numerous cross-links between keratins and associated corneous proteins, likely increasing the mechanical resistance and durability of the amniote epidermis and its appendages. TGase is low to absent in the beta-corneous layers of sauropsids but is detected in the softer but pliable alpha-layers of sauropsids, mammalian epidermis, medulla, and inner root sheath of hairs. SOXase is present in hard and soft corneous appendages of reptiles, birds, and mammals, and determines cross-linking among corneous proteins of scales, claws, beaks, hairs, and feathers.

Skewed inflammation is associated with aberrant interleukin-37 signaling pathway in atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a severe global burden on physical, physiological, and mental health. The role of IL-37, a fundamental inhibitor of immunity, in AD was herein explored.

METHOD

Serum levels of IL-37 and T helper (Th) 2-related inflammatory mediators were quantified in subjects with or without AD. The expression of IL-37 receptors was determined by flow cytometry. Proteomics was employed to explore the serum protein profile and novel biomarkers. In vitro cell model, 3D-keratinocytes mimicking skin model, and the serum of subjects with or without AD were investigated to verify the proteomic results.

RESULTS

AD patients were found to present with higher levels of total and specific IgE as well as Th2 inflammatory mediators compared with healthy controls (HC). IL-37 level and its receptor IL18Rɑ expression in AD patients were significantly decreased, together with increased population of eosinophils, indicating that the signaling of IL37/IL18Rɑ was dampened. In addition, proteomic analysis revealed a significantly differential protein profile of AD patients compared with HC. IL-37 showed the strongest negative correlation with involucrin, a keratinizing epithelia protein. IL-37 was verified to suppress induced involucrin expression in in vitro skin cell models. AD patients show a significantly higher serum concentration of involucrin compared with HC. Together, our results demonstrated that IL-37 plays a regulatory role in AD. Its deficiency may lead to the aberrant involucrin expression in AD.

CONCLUSIONS

The dysregulation of serum protein and skin disruption in AD is related to the insufficiency of IL-37 and its attenuated anti-inflammatory signaling.

NMDA Receptor Hypofunction in the Aging-Associated Malfunction of Peripheral Tissue

Glutamatergic transmission through NMDA receptors (NMDARs) is important for the function of peripheral tissues. In the bone, NMDARs and its co-agonist, D-serine participate in all the phases of the remodeling. In the vasculature, NMDARs exerts a tonic vasodilation decreasing blood perfusion in the corpus cavernosum and the filtration rate in the renal glomerulus. NMDARs are relevant for the skin turnover regulating the proliferation and differentiation of keratinocytes and the formation of the cornified envelope (CE). The interference with NMDAR function in the skin leads to a slow turnover and repair. As occurs with the brain and cognitive functions, the manifestations of a hypofunction of NMDARs resembles those observed during aging. This raises the question if the deterioration of the glomerular vasculature, the bone remodeling and the skin turnover associated with age could be related with a hypofunction of NMDARs. Furthermore, the interference of D-serine and the effects of its supplementation on these tissues, suggest that a decrease of D-serine could account for this hypofunction pointing out D-serine as a potential therapeutic target to reduce or even prevent the detriment of the peripheral tissue associated with aging.

Lipidomic and transcriptional analysis of the linoleoyl-omega-hydroxyceramide biosynthetic pathway in human psoriatic lesions

A complex assembly of lipids including fatty acids, cholesterol, and ceramides is vital to the integrity of the mammalian epidermal barrier. The formation of this barrier requires oxidation of the substrate fatty acid, linoleic acid (LA), which is initiated by the enzyme 12R-lipoxygenase (LOX). In the epidermis, unoxidized LA is primarily found in long-chain acylceramides termed esterified omega-hydroxy sphingosine (EOS)/phytosphingosine/hydroxysphingosine (collectively EOx). The precise structure and localization of LOX-oxidized EOx in the human epidermis is unknown, as is their regulation in diseases such as psoriasis, one of the most common inflammatory diseases affecting the skin. Here, using precursor LC/MS/MS, we characterized multiple intermediates of EOx, including 9-HODE, 9,10-epoxy-13-HOME, and 9,10,13-TriHOME, in healthy human epidermis likely to be formed via the epidermal LOX pathways. The top layers of the skin contained more LA, 9-HODE, and 9,10,13-TriHOME EOSs, whereas 9,10-epoxy-13-HOME EOS was more prevalent deeper in the stratum corneum. In psoriatic lesions, levels of native EOx and free HODEs and HOMEs were significantly elevated, whereas oxidized species were generally reduced. A transcriptional network analysis of human psoriatic lesions identified significantly elevated expression of the entire biosynthetic/metabolic pathway for oxygenated ceramides, suggesting a regulatory function for EOx lipids in reconstituting epidermal integrity. The role of these new lipids in progression or resolution of psoriasis is currently unknown. We also discovered the central coordinated role of the zinc finger protein transcription factor, ZIC1, in driving the phenotype of this disease. In summary, long-chain oxygenated ceramide metabolism is dysregulated at the lipidomic level in psoriasis, likely driven by the transcriptional differences also observed, and we identified ZIC1 as a potential regulatory target for future therapeutic interventions.

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.

Biomarkers of neonatal skin barrier adaptation reveal substantial differences compared to adult skin

BACKGROUND

The objective of this study was to measure skin characteristics in premature (PT), late preterm (LPT), and full-term (FT) neonates compared with adults at two times (T1, T2).

METHODS

Skin samples of 61 neonates and 34 adults were analyzed for protein biomarkers, natural moisturizing factor (NMF), and biophysical parameters. Infant groups were: <34 weeks (PT), 34-<37 weeks (LPT), and ≥37 weeks (FT).

RESULTS

Forty proteins were differentially expressed in FT infant skin, 38 in LPT infant skin, and 12 in PT infant skin compared with adult skin at T1. At T2, 40 proteins were differentially expressed in FT infants, 38 in LPT infants, and 54 in PT infants compared with adults. All proteins were increased at both times, except TMG3, S100A7, and PEBP1, and decreased in PTs at T1. The proteins are involved in filaggrin processing, protease inhibition/enzyme regulation, and antimicrobial function. Eight proteins were decreased in PT skin compared with FT skin at T1. LPT and FT proteins were generally comparable at both times. Total NMF was lower in infants than adults at T1, but higher in infants at T2.

CONCLUSIONS

Neonates respond to the physiological transitions at birth by upregulating processes that drive the production of lower pH of the skin and water-binding NMF components, prevent protease activity leading to desquamation, and increase the barrier antimicrobial properties.

IMPACT

Neonates respond to the transitions at birth by upregulating processes that drive the production of lower pH of the skin and NMF, prevent protease activity leading to desquamation, and increase the antimicrobial properties of the barrier. The neonatal epidermal barrier exhibits a markedly different array of protein biomarkers both shortly after birth and 2-3 months later, which are differentially expressed versus adults. The major biomarker-functional classes included filaggrin processing, protease inhibitor/enzyme regulators, antimicrobials, keratins, lipids, and cathepsins. The findings will guide improvement of infant skin care practices, particularly for the most premature infants with the ultimate goals mitigating nosocomial infection.

Corneocytes: Relationship between Structural and Biomechanical Properties

BACKGROUND

Skin is the interface between an organism and the external environment, and hence the stratum corneum (SC) is the first to withstand mechanical insults that, in certain conditions, may lead to integrity loss and the development of pressure ulcers. The SC comprises corneocytes, which are vital elements to its barrier function. These cells are differentiated dead keratinocytes, without organelles, composed of a cornified envelope and a keratin-filled interior, and connected by corneodesmosomes (CDs).

SUMMARY

The current review focusses on the relationship between the morphological, structural, and topographical features of corneocytes and their mechanical properties, to understand how they assist the SC in maintaining skin integrity and in responding to mechanical insults. Key Messages: Corneocytes create distinct regions in the SC: the inner SC is characterized by immature cells with a fragile cornified envelope and a uniform distribution of CDs; the upper SC has resilient cornified envelopes and a honeycomb distribution of CDs, with a greater surface area and a smaller thickness than cells from the inner layer. The literature indicates that this upward maturation process is one of the most important steps in the mechanical resistance and barrier function of the SC. The morphology of these cells is dependent on the body site: the surface area in non-exposed skin is about 1,000-1,200 μm2, while for exposed skin, for example, the cheek and forehead, is about 700-800 μm2. Corneocytes are stiff cells compared to other cellular types, for example, the Young's modulus of muscle and fibroblast cells is typically a few kPa, while that of corneocytes is reported to be about hundreds of MPa. Moreover, these skin cells have 2 distinct mechanical regions: the cornified envelope (100-250 MPa) and the keratin matrix (250-500 MPa).

Antioxidative and Skin Protective Effects of Canarium subulatum Methanol Extract on Keratinocytes

Canarium subulatum is a traditional medical herb used in South Asia. Recently, the anti-inflammatory effects of C. subulatum methanol extract (Cs-ME) have been reported; however, the effect of Cs-ME on skin physiology has not yet been elucidated. Therefore, in this study, we evaluated the protective effect of Cs-ME on UV-induced skin aging and cell death as well as the reinforcing effect on the skin barrier. According to viable cell counting and MTT assays, Cs-ME significantly reduced UV-evoked HaCaT cell death. Cs-ME blocked reactive oxygen species (ROS) generation in UV-irradiated HaCaT cells and showed radical scavenging activity against DPPH and ABTS. In addition, H2O2-induced cell death was inhibited by Cs-ME, indicating that Cs-ME protects cells from UV-derived cell death through the suppression of ROS. PCR analysis revealed that Cs-ME diminished the expression of aging-related HYAL-1 and MMP-1 genes in UV-treated HaCaT cells. Elevated HYAL-1 and MMP-1 mRNA expression in H2O2-stimulated HaCaT cells was also decreased by Cs-ME, suggesting that Cs-ME exerts antiaging activity via the inhibition of ROS. Expression of skin barrier components including filaggrin and hyaluronic acid synthase-1 was increased by Cs-ME and was modulated by ERK/p38-AP-1 signaling. Collectively, our data show that Cs-ME has cytoprotective and antiaging activity based on antioxidant properties. Furthermore, Cs-ME exerts skin barrier protective ability by regulating the AP-1 signaling pathway. Therefore, Cs-ME has the potential for use as an ingredient in cosmetics to protect the skin from UV irradiation, prevent photoaging, and strengthen the skin barrier.

Methylation of TGM-3 Promoter and Its Association with Oral Squamous Cell Carcinoma (OSCC)

Background:

Oral Squamous Cell Carcinoma (OSCC) is among the ten most common cancers worldwide. Hypermethylation of CpG sites in the promoter region and subsequent down-regulation of a tumor suppressor gene, TGM-3 has been proposed to be linked to different types of human cancers including OSCC. In this study, methylation status of CpG sites in the promoter region of TGM-3 has been evaluated in a cohort of patients with OSCC compared to normal controls.

Methods:

Forty fresh tissue samples were obtained from newly diagnosed OSCC patients and normal individuals referred to dentistry clinic for tooth extraction. DNA was extracted, bisulfite conversion was performed and it was subjected to PCR using bisulfite-sequencing PCR (BSP) primers. Prepared samples were sequenced on a DNA analyzer with both forward and reverse primers of the region of interest. The peak height values of cytosine and thymine were calculated and methylation levels for each CpG site within the DNA sequence was quantified.

Results:

Quantitative DNA methylation analyses in CpG islands revealed that it was significantly higher in OSCC patients compared to controls. DNA methylation at CpG1/CpG3/CpG5 (p=0.004–0.01) and CpG1/CpG3 (p=0.001–0.019) sites was associated with tumor stage and grade, respectively. Male OSCC patients had higher methylation rate at CpG3 (p=0.032), while smoker patients showed higher methylation rate at CpG6 (p=0.045).

Conclusion:

These results manifested the contribution of DNA methylation of TGM-3 in OSCC and its potential association with clinico-pathologic parameters in OSCC.

Anti-Inflammatory and Photoaging-Protective Effects of Olea europaea through Inhibition of AP-1 and NF-[Formula: see text] B Pathways

Olea europaea is a beneficial edible plant with a number of biological activities like anti-inflammatory, anti-oxidant, antithrombic, antihyperglycemic, and anti-ischemic activities. The mechanisms behind the antiphotoaging and anti-inflammatory effects of Olea europaea are not fully understood. To investigate how an ethanol extract of Olea europaea (Oe-EE) exerts these effects, we explored its activities in human keratinocytes and dermal fibroblasts. We assessed the anti-oxidant effects of Oe-EE via 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2[Formula: see text]-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assays and measured the expression levels of matrix metalloproteinases (MMPs), cyclooxygenase-2, interleukin (IL)-6, tumor necrosis factor (TNF)-[Formula: see text], and moisturizing factors. Antiphotoaging and anti-inflammatory mechanisms of Oe-EE were explored by assessing signaling molecule activation via immunoblotting. Oe-EE treatment decreased the mRNA expression level of MMPs, cyclooxygenase-2, IL-6, and TNF-[Formula: see text] and restored type I collagen, filaggrin, and sirtuin 1 expression in UVB-irradiated cells. Furthermore, Oe-EE inhibited the activities of several activator protein 1 regulatory enzymes, including extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK), and inhibited nuclear factor (NF)-[Formula: see text]B pathway signaling proteins. Therefore, our results indicate that Oe-EE has photoaging-protective and anti-inflammatory effects.

Acute skin barrier disruption alters the secretion of lamellar bodies via the multilayered expression of ABCA12

BACKGROUND

The skin barrier consists of multiple lipid-enriched layers, which are characterized by lamellar repeated structures within the intercellular space. Sodium lauryl sulfate is a well-known substance that can disrupt the skin barrier. The mechanisms underlying the barrier repair process, especially the influence of topical sodium lauryl sulfate treatment on lipid transport in the barrier recovery phase, remain unresolved.

OBJECTIVE

To understand the process of reconstruction of the intercellular lipid layer of the skin after acute barrier disruption by sodium lauryl sulfate treatment in vivo.

METHODS

Female hairless mice were treated with 3 % sodium lauryl sulfate. Transepidermal water loss measurement, histopathological analysis, and gene expression analysis were performed from 1 to 288 h after the topical application of sodium lauryl sulfate. Western blot analysis, immunofluorescence staining, and transmission electron microscopy analysis were performed to examine the expression level of ATP-binding cassette, sub-family A, member 12 (ABCA12), and the secretion level of lamellar bodies.

RESULTS

We observed rapid hyper-keratinization at the stratum corneum and the subsequent concurrent secretion of lamellar bodies into the intercellular space of the stratum corneum during the process of skin barrier recovery. ABCA12 expression associated with lipid transportation into lamellar bodies was transiently upregulated and observed in multiple layers in the upper epidermis, especially in the stratum granulosum.

CONCLUSION

The skin reacts appropriately to maintain its barrier function by first initiating hyper-keratinization and then increasing lamellar body secretion. Activation of ABCA12 is an essential factor for the recovery of skin barrier function.

Spotlight on the Granules (Grainyhead-Like Proteins) - From an Evolutionary Conserved Controller of Epithelial Trait to Pioneering the Chromatin Landscape

Among the transcription factors that are conserved across phylogeny, the grainyhead family holds vital roles in driving the epithelial cell fate. In Drosophila, the function of grainyhead (grh) gene is essential during developmental processes such as epithelial differentiation, tracheal tube formation, maintenance of wing and hair polarity, and epidermal barrier wound repair. Three main mammalian orthologs of grh: Grainyhead-like 1-3 (GRHL1, GRHL2, and GRHL3) are highly conserved in terms of their gene structures and functions. GRHL proteins are essentially associated with the development and maintenance of the epithelial phenotype across diverse physiological conditions such as epidermal differentiation and craniofacial development as well as pathological functions including hearing impairment and neural tube defects. More importantly, through direct chromatin binding and induction of epigenetic alterations, GRHL factors function as potent suppressors of oncogenic cellular dedifferentiation program - epithelial-mesenchymal transition and its associated tumor-promoting phenotypes such as tumor cell migration and invasion. On the contrary, GRHL factors also induce pro-tumorigenic effects such as increased migration and anchorage-independent growth in certain tumor types. Furthermore, investigations focusing on the epithelial-specific activation of grh and GRHL factors have revealed that these factors potentially act as a pioneer factor in establishing a cell-type/cell-state specific accessible chromatin landscape that is exclusive for epithelial gene transcription. In this review, we highlight the essential roles of grh and GRHL factors during embryogenesis and pathogenesis, with a special focus on its emerging pioneering function.

Indirubin inhibits Wnt/β-catenin signal pathway via promoter demethylation of WIF-1

Background

Psoriasis is a common inflammatory skin disease. Abnormal proliferation of keratinocytes is one of the psoriatic histopathological features. Indirubin has an essential effect on the proliferation and activation of keratinocytes; however, in psoriasis, the specific mechanism of action of indirubin on keratinocytes is unclear. In the present study, we revealed the effects of indirubin on DNA methyltransferase 1 (DNMT1), wnt inhibitory factor 1 (wif-1), and wnt/β-catenin signal pathway, in the meantime, we explored the effects of indirubin on proliferation, cell cycle and the apoptosis of HaCaT cells.

Methods

The expression of DNMT1, wif-1, Frizzled2, Frizzled5, and β-catenin in HaCaT cells treated with different concentrations of indirubin were detected by Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR). The expression levels of DNMT1 and wif-1 were observed after treated with different concentrations of indirubin by enzyme-linked immunosorbent assay (ELISA). The wif-1 promoter methylation status was detected by DNA methylation-specific PCR (MSP). The transcriptional activities of wif-1 and β-catenin were discovered by a luciferase reporter gene system. Cell viability was determined by Cell Counting Kit-8 (CCK8) method. The cell cycle was detected by flow cytometry. The apoptotic cells were surveyed by the apoptosis kit. The expression of Inolucrin, Loricrin, Filaggrin, Keratin 17, and transcriptional activation of transglutaminase 1(TGase1) were detected by Western blotting.

Results

Indirubin inhibited the expression of DNMT1 and the methylation of the wif-1 promoter. In the wnt signal pathway, indirubin restored the protein expression of wif-1 and inhibited expression of Frizzled2, Frizzled5, and β-catenin. Besides, indirubin inhibited the proliferation of HaCaT cells, induced apoptosis, and arrest cell cycle. We also reported that indirubin could down-regulate the expression of Involucrin, TGase 1, and keratin 17, but the expression of Filaggrin and Loricrin had no significant effect.

Conclusion

Our research showed that indirubin promoted the demethylation of wif-1 and suppressed the wnt/β-catenin signal pathway, thereby exerted an anti-proliferative effect. This study reveals the anti-proliferation mechanism of indirubin, which may provide an effective option for the treatment of proliferative diseases.

Role of Resveratrol in Regulating Cutaneous Functions

Protective role of the skin is against external insults and maintenance of electrolyte homeostasis of the body. Cutaneous dysfunction can account for the development of both cutaneous and systemic disorders. Thus, improvements in cutaneous functions can benefit a number of extracutaneous and cutaneous functions. Resveratrol, a natural ingredient, displays multiple benefits for various systems/organs, including the skin. The benefits of resveratrol for cutaneous functions include stimulation of keratinocyte differentiation and antimicrobial peptide expression, inhibition of keratinocyte proliferation and cutaneous inflammation, UV protection, anticancer, antiaging, and inhibition of melanogenesis. The mechanisms of action of resveratrol include activation of sirtuin 1 and nuclear factor erythroid 2-related factor 2, and inhibition of mitogen-activated protein kinase signaling. Evidence suggests that topical resveratrol could be a valuable alternative not only for daily skin care, but also for the prevention and treatment of various cutaneous disorders. This review summarizes the benefits of resveratrol for cutaneous functions.