Epidermal barrier: Adverse and beneficial changes induced by ultraviolet B irradiation depending on the exposure dose and time (Review)

Modes of type 2 immune response initiation

Type 2 immunity defends against macro-parasites and can cause allergic diseases. Our understanding of the mechanisms governing the initiation of type 2 immunity is limited, whereas we know more about type 1 immune responses. Type 2 immunity can be triggered by a wide array of inducers that do not share common features and via diverse pathways and mechanisms. To address the complexity of the type 2 initiation pathways, we suggest a framework that conceptualizes different modes of induction of type 2 immunity. We discuss categories of type 2 inducers and their immunogenicity, types of tissue perturbations that are caused by these inducers, sensing strategies for the initiation of Th2 immune responses, and categorization of the signals that are produced in response to type 2 challenges. We describe tissue-specific examples of functional disruption that could lead to type 2 inflammation and propose that different sensing strategies that operate at the tissue level converge on the initiation of type 2 immune responses.

Effect of a hyaluronic acid-based mesotherapeutic injectable on the gene expression of CLOCK and Klotho proteins, and environmentally induced oxidative stress in human skin cells

OBJECTIVE

Normal circadian rhythms are essential to the repair mechanisms of oxidative stress implicated in skin aging. Given reports that hyaluronic acid (HA) homeostasis exhibits a different profile in chronological skin aging, as compared to environmental or extrinsic aging, an improved understanding of the way HA interacts with its surroundings, and the impact of HA injectables in replacing lost HA and encouraging rejuvenation, is of key benefit to skin aging treatments. The objectives of these current studies were twofold. Firstly, to demonstrate the in vitro effects of two lightweight hyaluronic-based injectables on the expression of CLOCK protein in human skin fibroblasts, and their effects on Klotho protein expression as a marker for circadian rhythms in a combined human keratinocyte and Merkel cell model. Secondly, to ascertain whether these findings could be correlated with in vitro effects on various environmental oxidative stress aging markers (blue light, UVA/UVB, Urban Dust, and IR exposures).

METHODS

Oxidative stress studies were aimed to highlight possible protective effects through different challenge conditions in two models, ex vivo human skin explants and in vitro monolayer cultures of normal human dermal fibroblasts (NHDF). The protective effects of the test products were evaluated against an increase of cyclobutene pyrimidine dimers (CPDs) abundance within epidermal section of ex vivo skin explants after UVA/UVB radiation; effects of blue light on gene expression from NHDFs fibroblasts; effects of pollutants (Urban dust, UbD) on gene expression in NHDFs fibroblasts; and an increase of reactive oxygen species (ROS) production by NHDFs fibroblasts after infrared-A radiation. Gene expression was assayed and analyzed utilizing microfluidic TaqMan qPCR arrays. CLOCK expression was measured in young and senescing NHDFs by immunostaining, and Klotho and melatonin expression by immunostaining in Merkel cell-enriched normal adult human epidermal cell cultures.

RESULTS

In an aging culture of mixed keratinocyte and Merkel skin cells, activation of Klotho expression was induced by the application of both HA test products. Moreover, the HA products increase Klotho protein expression in both Merkel cells and keratinocytes. The observed positive effect of the tested products on melatonin receptors 1A and 1B expression in aging Merkel cell culture and keratinocytes is also interesting. HA-Y (developed for patients 25+ years old) stimulated melatonin receptors type 1B expression in aging cell cultures more strongly than HA-S (developed for patients 35-65 years old). In age (stressed) cells, a lower expression of Klotho protein and melatonin receptors 1A and 1B is apparent. The addition of HA-Y and HA-S stimulates their expression thus providing a "protective" effect. The blue light irradiation at 40 J/cm² performed in NHDF fibroblast cultures led to a modification of the expression of several genes, all involved in mechanisms known to be modulated in case of solar radiation stress.

CONCLUSIONS

Although these are preliminary findings, they are the first we know of that demonstrate HA facial injectables having a benefit and possibilities beyond the "physical filling" of the skin. As regards the beneficial effects against blue light-induced oxidative stress, and a return to cellular homeostasis, there is a need to conduct further and more precise investigations into HA-S. Furthermore, the benefit of these HA injectables (Novacutan®) in the modulation of oxidative stressed circadian rhythms widens their potential benefit.

NRF2 in dermatological disorders: Pharmacological activation for protection against cutaneous photodamage and photodermatosis

The skin barrier and its endogenous protective mechanisms cope daily with exogenous stressors, of which ultraviolet radiation (UVR) poses an imminent danger. Although the skin is able to reduce the potential damage, there is a need for comprehensive strategies for protection. This is particularly important when developing pharmacological approaches to protect against photocarcinogenesis. Activation of NRF2 has the potential to provide comprehensive and long-lasting protection due to the upregulation of numerous cytoprotective downstream effector proteins that can counteract the damaging effects of UVR. This is also applicable to photodermatosis conditions that exacerbate the damage caused by UVR. This review describes the alterations caused by UVR in normal skin and photosensitive disorders, and provides evidence to support the development of NRF2 activators as pharmacological treatments. Key natural and synthetic activators with photoprotective properties are summarized. Lastly, the gap in knowledge in research associated with photodermatosis conditions is highlighted.

Are TRPA1 and TRPV1 channel-mediated signalling cascades involved in UVB radiation-induced sunburn?

Burn injuries are underappreciated injuries associated with substantial morbidity and mortality. Overexposure to ultraviolet (UV) radiation has dramatic clinical effects in humans and is a significant public health concern. Although the mechanisms underlying UVB exposure are not fully understood, many studies have made substantial progress in the pathophysiology of sunburn in terms of its molecular aspects in the last few years. It is well established that the transient receptor potential ankyrin 1 (TRPA1), and vanilloid 1 (TRPV1) channels modulate the inflammatory, oxidative, and proliferative processes underlying UVB radiation exposure. However, it is still unknown which mechanisms underlying TRPV1/A1 channel activation are elicited in sunburn induced by UVB radiation. Therefore, in this review, we give an overview of the TRPV1/A1 channel-mediated signalling cascades that may be involved in the pathophysiology of sunburn induced by UVB radiation. These data will undoubtedly help to explain the various features of sunburn and contribute to the development of novel therapeutic approaches to better treat it.

An Electroluminodynamic Flexible Device for Highly Efficient Eradication of Drug-Resistant Bacteria

Photodynamic therapy (PDT) has attracted wide attention in antibacterial applications due to its advantages of spatial-temporal selectivity, noninvasiveness, and low incidence to develop drug resistance. To make it more convenient, universal, and manipulatable for clinical application, a conceptually antibacterial strategy, namely "electroluminodynamic therapy" (ELDT), is presented by nanoassembly of an electroluminescent (EL) material and a photosensitizer, which is capable of generating reactive oxygen species (ROS) in situ under an electric field, i.e., the fluorescence emitted by the EL molecules excites the photosensitizer to generate singlet oxygen (¹ O₂ ), for the oxidative damage of pathogens. Based on the scheme of ELDT, a flexible therapeutic device is fabricated through a hydrogel loading with ELDT nanoagents, followed by integration with a flexible battery, satisfying the requirements of being light and wearable for wound dressings. The ELDT-based flexible device presents potent ROS-induced killing efficacies against drug-resistant bacteria (>99.9%), so as to effectively inhibit the superficial infection and promote the wound healing. This research reveals a proof-of-concept ELDT strategy as a prospective alternative to PDT, which avoids the utilization of a physical light source, and achieves convenient and effective killing of drug-resistant bacteria through a hydrogel-based flexible therapeutic device.

Characterization of Permeability Barrier Dysfunction in a Murine Model of Cutaneous Field Cancerization Following Chronic UV-B Irradiation: Implications for the Pathogenesis of Skin Cancer

Simple Summary

In the present work, we developed an experimental preclinical model of skin with cutaneous field cancerization after chronic UV-B light exposure in an immunologically intact mouse model (SKH1 aged mice). We observed impairments in the transepidermal water loss, stratum corneum hydration, and surface pH. We also detected a marked hyperkeratotic hyperplasia of the epidermis, induction of keratinocyte hyperproliferation, incidental actinic keratosis, and in situ squamous cell carcinomas in the UV-B light-irradiated groups. In this context, the association between the permeability barrier impairment and keratinocyte hyperproliferation might be considered a new target in the management of skin with cutaneous field cancerization. As current therapeutic approaches to actinic keratosis and cutaneous field cancerization only focus on the direct antineoplastic, immunomodulatory, or photodynamic effects of approved topical drugs, this mouse model of skin with cutaneous field cancerization might be helpful for both the identification and screening of potentially new preventive strategies or treatments (e.g., skin barrier therapies).

Abstract

Chronic ultraviolet B (UV-B) irradiation is known to be one of the most important hazards acting on the skin and poses a risk of developing photoaging, skin with cutaneous field cancerization (CFC), actinic keratosis (AKs), and squamous cell carcinomas (SCCs). Most of the UV-B light is absorbed in the epidermis, affecting the outermost cell layers, the stratum corneum, and the stratum granulosum, which protects against this radiation and tries to maintain the permeability barrier. In the present work, we show an impairment in the transepidermal water loss, stratum corneum hydration, and surface pH after chronic UV-B light exposure in an immunologically intact mouse model (SKH1 aged mice) of skin with CFC. Macroscopic lesions of AKs and SCCs may develop synchronically or over time on the same cutaneous surface due to both the presence of subclinical AKs and in situ SCC, but also the accumulation of different mutations in keratinocytes. Focusing on skin with CFC, yet without the pathological criteria of AKs or SCC, the presence of p53 immunopositive patches (PIPs) within the epidermis is associated with these UV-B-induced mutations. Reactive epidermis to chronic UV-B exposure correlated with a marked hyperkeratotic hyperplasia, hypergranulosis, and induction of keratinocyte hyperproliferation, while expressing an upregulation of filaggrin, loricrin, and involucrin immunostaining. However, incidental AKs and in situ SCC might show neither hypergranulosis nor upregulation of differentiation markers in the upper epidermis. Despite the overexpression of filaggrin, loricrin, involucrin, lipid enzymes, and ATP-binding cassette subfamily A member 12 (ABCA12) after chronic UV-B irradiation, the permeability barrier, stratum corneum hydration, and surface pH were severely compromised in the skin with CFC. We interpret these results as an attempt to restore the permeability barrier homeostasis by the reactive epidermis, which fails due to ultrastructural losses in stratum corneum integrity, higher pH on skin surface, abundant mast cells in the dermis, and the common presence of incidental AKs and in situ SCC. As far as we know, this is the first time that the permeability barrier has been studied in the skin with CFC in a murine model of SCC induced after chronic UV-B irradiation at high doses. The impairment in the permeability barrier and the consequent keratinocyte hyperproliferation in the skin of CFC might play a role in the physiopathology of AKs and SCCs.

Ethanol Extract of Yak-Kong Fermented by Lactic Acid Bacteria from a Korean Infant Markedly Reduces Matrix Metallopreteinase-1 Expression Induced by Solar Ultraviolet Irradiation in Human Keratinocytes and a 3D Skin Model

Yak-Kong is a type of black soybean that is colloquially referred to as the "medicinal bean" and it elicits several beneficial effects that are relevant to human health, including attenuating the formation of skin wrinkles. It has previously been shown that soybean extracts elicit additional bioactivity that is fermented by lactic acid bacteria. In this study of lactic acid bacteria strains that were isolated from the stools of breast-feeding infants (<100 days old), we selected Bifidobacterium animalis subsp. Lactis LDTM 8102 (LDTM 8102) as the lead strain for the fermentation of Yak-Kong. We investigated the effects of LDTM 8102-fermented Yak-Kong on solar-ultraviolet irradiation (sUV)-induced wrinkle formation. In HaCaT cells, the ethanol extract of LDTM 8102-fermented Yak-Kong (EFY) effectively reduced sUV-induced matrix metalloproteinase-1 (MMP-1) secretion. The effect of EFY was superior to that of unfermented (UFY)- and Lactis KCTC 5854 (another Bifidobacterium animalis species)-fermented Yak-Kong. Additionally, EFY reduced sUV-induced MMP-1 mRNA expression and promoter activity, as well as the transactivation of AP-1 and phosphorylation of ERK1/2 and JNK1/2. Furthermore, EFY alleviated sUV-induced MMP-1 secretion, the destruction of the epidermis, and degradation of collagen in a three-dimensional (3D) skin culture model. EFY had a higher total polyphenol content and anti-oxidative activity than UFY. Twelve metabolites were significantly (≥2-fold) increased in Yak-Kong extract after fermentation by LDTM 8102. Among them, the metabolites of major isoflavones, such as 6,7,4'-trihydroxyisoflavone (THIF), exerted the reducing effect of MMP-1, which indicated that the isoflavone metabolites contributed to the effect of EFY on MMP-1 expression as active compounds. These findings suggest that EFY is a potent natural material that can potentially prevent sUV-induced wrinkle formation.

IgE Autoreactivity in Atopic Dermatitis: Paving the Road for Autoimmune Diseases?

Atopic dermatitis (AD) is a common skin disease affecting 20% of the population beginning usually before one year of age. It is associated with the emergence of allergen-specific IgE, but also with autoreactive IgE, whose function remain elusive. This review discusses current knowledge relevant to the mechanisms, which leads to the secretion of autoreactive IgE and to the potential function of these antibodies in AD. Multiple autoantigens have been described to elicit an IgE-dependent response in this context. This IgE autoimmunity starts in infancy and is associated with disease severity. Furthermore, the overall prevalence of autoreactive IgE to multiple auto-antigens is high in AD patients. IgE-antigen complexes can promote a facilitated antigen presentation, a skewing of the adaptive response toward type 2 immunity, and a chronic skin barrier dysfunction and inflammation in patients or AD models. In AD, skin barrier defects and the atopic immune environment facilitate allergen sensitization and the development of other IgE-mediated allergic diseases in a process called the atopic march. AD is also associated epidemiologically with several autoimmune diseases showing autoreactive IgE secretion. Thus, a potential outcome of IgE autoreactivity in AD could be the development of further autoimmune diseases.

Expression of functional TRPV1 receptor in primary culture of canine keratinocytes

The interest for the endovanilloid system and for transient receptor potential vanilloid 1 (TRPV1) is continuously increasing, due to their involvement in inflammation, nociception and pruritus. Even if TRPV1 enrolment was highlighted in both physiological and pathological conditions, some aspects remain unclear, mostly in veterinary medicine. This study aimed to verify the expression and functionality of TRPV1 in canine keratinocytes to investigate in vitro the role of TRPV1 in these cells that are involved in different cutaneous pathologies. Keratinocytes primary cultures were isolated from bioptical samples and cultivated. Binding assay (using ³ [H]-resiniferatoxin), displacement assay (in the presence of 1.2 nM ³ [H]-resiniferatoxin) and functional assays (in the presence of 1 μCi/⁴⁵ Ca²⁺ ) with vanilloid agonists and antagonists, specifically addressed to TRPV1 receptor, were performed. Binding assay demonstrated the presence of measurable concentrations of TRPV1 (B_max  = 1,240 ± 120 fmol/mg protein; K_d  = 0.01 ± 0.004 nM). Displacement assay highlighted the highest affinity for resiniferatoxin (RTX) and 5-iodo-resiniferatoxin (5-I-RTX), among agonists and antagonists, respectively. The same compounds results as the most potent in the functional assays. This study demonstrated the identification and the characterization of TRPV1 receptor in primary canine keratinocytes cultures. The results are promising for a clinical use, but further in vivo investigations are required.

S100A7 (psoriasin) inhibits human epidermal differentiation by enhanced IL-6 secretion through IκB/NF-κB signalling

Psoriasin (S100A7), a member of the S100 protein family, is a well-known antimicrobial peptide and a signalling molecule which regulates cellular function and is highly expressed in hyperproliferative skin conditions such as atopic dermatitis (AD) and psoriasis with disrupted skin barrier function. However, its role in epidermal differentiation remains unknown. We examined the effect of S100A7 on epidermal differentiation in normal human keratinocytes (NHKs) and on a reconstituted human epidermis model. When NHKs were exposed to disruptive stimuli such as Staphylococcus aureus, ultraviolet irradiation and retinoic acid, the secretion of S100A7 into the culture medium increased and the expression of epidermal differentiation markers decreased. Treatment of NHKs with S100A7 significantly inhibited epidermal differentiation by reducing the expression of keratin 1, keratin 10, involucrin and loricrin and by increasing the expression of abnormal differentiation markers (keratin 6 and keratin 16). We verified that the MyD88-IκB/NF-κB signal cascade was activated via RAGE after S100A7 treatment, resulting in the upregulation of interleukin-6. Finally, we confirmed that S100A7 is a negative regulator of epidermal differentiation using a reconstituted human epidermis model. This study suggests that S100A7-related signalling molecules could be potent targets for recovering skin barrier function in AD and psoriasis where S100A7 is accumulated excessively.