Gene profiling of narrowband UVB-induced skin injury defines cellular and molecular innate immune responses

Acute ultraviolet B irradiation increases cholesterol and decreases Cyp7a1 expression in the liver of female mice

Recent studies have demonstrated that ultraviolet B (UVB) irradiation impacts both skin and hepatic functions. In this study, we investigated the effects of UVB irradiation on cholesterol metabolism in the liver. Hairless mice were exposed to UVB (1.6 J/cm2) irradiation. Dorsal skin and liver samples were collected 24 h after exposure. Total RNA was extracted from the skin and liver tissues, and used for DNA microarray analysis and real-time polymerase chain reaction (PCR). Hepatic mRNA expression of Cyp7a1 revealed a 4.4-fold decrease in the UVB (+) group compared to that in the UVB (-) group. No differences were observed in the expression of the other genes related to cholesterol metabolism. Additionally, the level of hepatic total cholesterol in the UVB (+) group was significantly higher than in the UVB (-) group. These findings suggest that acute UVB irradiation increases total cholesterol levels and decreases Cyp7a1 expression in the liver.

[Ultraviolet radiation in the pathogenesis of lupus erythematosus]

Photosensitivity represents an increased inflammatory reaction to sunlight, which can be observed particularly in the autoimmune disease lupus erythematosus. Cutaneous lupus erythematosus (CLE) can be provoked by ultraviolet (UV) radiation and can cause both acute, nonscarring and chronic, scarring skin changes. In systemic lupus erythematosus, on the other hand, provocation by UV radiation can lead to flare or progression of systemic involvement. The etiology of lupus erythematosus is multifactorial and includes genetic, epigenetic and immunologic mechanisms. In this review, we address the effect of UV radiation on healthy skin and photosensitive skin using the example of lupus erythematosus. We describe possible mechanisms of UV-triggered immune responses that could offer therapeutic approaches. Currently, photosensitivity can only be prevented by avoiding UV exposure itself. Therefore, it is important to better understand the underlying mechanisms in order to develop strategies to counteract the deleterious effects of photosensitivity.

The effect of phototherapy on Demodex density: a case-control study

BACKGROUND

Human Demodex mites, Demodex folliculorum and Demodex brevis, are microorganisms that reside in the pilosebaceous units, usually without causing symptoms. Phototherapy has been linked to demodicosis in previous studies. We aimed to determine whether there was an increase in the frequency of demodicosis and Demodex density after 20 phototherapy sessions.

METHODS

A case-control study was conducted with 32 participants who received narrowband ultraviolet B or ultraviolet A-1 therapy for various dermatological indications. Standardized skin surface biopsies were performed before and after phototherapy to assess Demodex density. The presence of Demodex-related skin conditions was assessed before phototherapy. A statistical analysis was performed to compare the Demodex densities and prevalence of demodicosis between the baseline and 20th session of phototherapy.

RESULTS

No significant change was observed in Demodex density after 20 sessions of phototherapy. The average Demodex density before treatment was 2.75 ± 4.48 (/cm2 ), and after treatment, it was 2.85 ± 4.81 (/cm2 ), indicating no significant difference (P = 0.879). The percentage of patients with demodicosis in at least one region of the face was 28.1% (9/32) before treatment, and after treatment, it was 31.3% (10/32), with no significant difference (P = 1.00).

CONCLUSIONS

Our findings contradict previous studies that suggested an increased Demodex density and demodicosis prevalence after phototherapy. The data from previous studies are open to debate due to their selected samples, designs, and interpretations regarding the phototherapy-immunosuppression-Demodex relationship. Larger-scale longitudinal studies conducted on a homogeneous sample are warranted to better understand the relationship between phototherapy and demodicosis.

Doxercalciferol alleviates UVB-induced HaCaT cell senescence and skin photoaging

Prolonged or excessive ultraviolet (UV) exposure can lead to premature skin aging. Doxercalciferol (Dox), an analog of vitamin D2, is chiefly used to treat endocrine diseases, cardiovascular diseases, kidney diseases, etc. To date, research on Dox in alleviating photoaging and UV-induced inflammation is scarce. In this research, we evaluated the function of Dox in ultraviolet radiation B (UVB)-induced photoaging and explored the potential mechanism in human keratinocytes (Hacat) and BALB/c mice. First, we established a stable UVB-induced photoaging cell model. Then, we found that the senescence β-galactosidase (SA-β-Gal) positive rate, senescence-related protein (p16), aging-related genes (p21 and p53), senescence-associated secretory phenotype (SASP), inflammatory driving factors (IL-1β and IL-6) and matrix metalloproteinases (MMPs) (MMP1 and MMP9) were upregulated in HaCaT cells after UVB irradiation. At the same time, the effect of UVB on the back skin of BALB/c mice showed a consistent trend. Dox effectively alleviated the aforementioned changes caused by UVB radiation. Mechanistically, we found that UVB activated mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways, and Dox inhibited UVB-activated NF-κB and MAPK. Furthermore, Dox inhibited UVB-induced skin photoaging and damage in mice. In summary, Dox has been improved to inhibit photoaging, which may help to develop therapies to delay skin photoaging.

Human skin CD141+ dendritic cells regulate cutaneous immunity via the neuropeptide urocortin 2

Skin immune homeostasis is a multi-faceted process where dermal dendritic cells (DDCs) are key in orchestrating responses to environmental stressors. We have previously identified CD141+CD14+ DDCs as a skin-resident immunoregulatory population that is vitamin-D3 (VitD3) inducible from monocyte-derived DCs (moDCs), termed CD141hi VitD3 moDCs. We demonstrate that CD141+ DDCs and CD141hi VitD3 moDCs share key immunological features including cell surface markers, reduced T cell stimulation, IL-10 production, and a common transcriptomic signature. Bioinformatic analysis identified the neuroactive ligand receptor pathway and the neuropeptide, urocortin 2 (UCN2), as a potential immunoregulatory candidate molecule. Incubation with VitD3 upregulated UCN2 in CD141+ DCs and UVB irradiation induced UCN2 in CD141+ DCs in healthy skin in vivo. Notably, CD141+ DDC generation of suppressive Tregs was dependent upon the UCN2 pathway as in vivo administration of UCN2 reversed skin inflammation in humanized mice. We propose the neuropeptide UCN2 as a novel skin DC-derived immunoregulatory mediator with a potential role in UVB and VitD3-dependent skin immune homeostasis.

Optimum fractionation of radiation to combine PD-1 blockade

The optimum fractionation of radiation to combine with immune checkpoint blockade is controversial. This study aimed to investigate the fractionated radiation to maximize immunity during combination therapy. To evaluate the abscopal effect, C57BL/6 hPD-1 knock-in mice bearing two syngeneic contralateral MC38 murine colon cancer tumors were treated with four distinct regimens of radiotherapy. Three fractions of 8 Gy were chosen as the optimal fractionation to combine with anti-PD-1 as the optimal fractionation for maximizing immunity. Anti-PD-1 administration enhanced both local and systemic antitumor immunity in a cytotoxic T cell-dependent manner. Meanwhile, the spleen exhibited decreased myeloid-derived suppressor cells (MDSCs) under combination treatment. Furthermore, RNA-sequencing revealed significantly increased tumor necrosis factor (TNF) receptors and cytokines associated with lymphocyte infiltration in the combining group. Here we demonstrate that the hypofractionation of 8 Gy × 3f was the optimum-fractionated dosage to maximize immunity, and the combination of anti-PD-1 showed promising results in boosting abscopal effect. Underlying mechanisms may include the activation of T cells and the reduction of MDSCs, which is achieved through the action of TNF and related cytokines. This study indicates a radioimmunotherapy dosage painting method that can be developed to overcome present limitations in tumor immunosuppression.

Induction of Endogenous Antimicrobial Peptides to Prevent or Treat Oral Infection and Inflammation

Antibiotics are often used to treat oral infections. Unfortunately, excessive antibiotic use can adversely alter oral microbiomes and promote the development of antibiotic-resistant microorganisms, which can be difficult to treat. An alternate approach could be to induce the local transcription and expression of endogenous oral antimicrobial peptides (AMPs). To assess the feasibility and benefits of this approach, we conducted literature searches to identify (i) the AMPs expressed in the oral cavity; (ii) the methods used to induce endogenous AMP expression; and (iii) the roles that expressed AMPs may have in regulating oral inflammation, immunity, healing, and pain. Search results identified human neutrophil peptides (HNP), human beta defensins (HBD), and cathelicidin AMP (CAMP) gene product LL-37 as prominent AMPs expressed by oral cells and tissues. HNP, HBD, and LL-37 expression can be induced by micronutrients (trace elements, elements, and vitamins), nutrients, macronutrients (mono-, di-, and polysaccharides, amino acids, pyropeptides, proteins, and fatty acids), proinflammatory agonists, thyroid hormones, and exposure to ultraviolet (UV) irradiation, red light, or near infrared radiation (NIR). Localized AMP expression can help reduce infection, inflammation, and pain and help oral tissues heal. The use of a specific inducer depends upon the overall objective. Inducing the expression of AMPs through beneficial foods would be suitable for long-term health protection. Additionally, the specialized metabolites or concentrated extracts that are utilized as dosage forms would maintain the oral and intestinal microbiome composition and control oral and intestinal infections. Inducing AMP expression using irradiation methodologies would be applicable to a specific oral treatment area in addition to controlling local infections while regulating inflammatory and healing processes.

The Potential Importance of CXCL1 in the Physiological State and in Noncancer Diseases of the Cardiovascular System, Respiratory System and Skin

In this paper, we present a literature review of the role of CXC motif chemokine ligand 1 (CXCL1) in physiology, and in selected major non-cancer diseases of the cardiovascular system, respiratory system and skin. CXCL1, a cytokine belonging to the CXC sub-family of chemokines with CXC motif chemokine receptor 2 (CXCR2) as its main receptor, causes the migration and infiltration of neutrophils to the sites of high expression. This implicates CXCL1 in many adverse conditions associated with inflammation and the accumulation of neutrophils. The aim of this study was to describe the significance of CXCL1 in selected diseases of the cardiovascular system (atherosclerosis, atrial fibrillation, chronic ischemic heart disease, hypertension, sepsis including sepsis-associated encephalopathy and sepsis-associated acute kidney injury), the respiratory system (asthma, chronic obstructive pulmonary disease (COPD), chronic rhinosinusitis, coronavirus disease 2019 (COVID-19), influenza, lung transplantation and ischemic-reperfusion injury and tuberculosis) and the skin (wound healing, psoriasis, sunburn and xeroderma pigmentosum). Additionally, the significance of CXCL1 is described in vascular physiology, such as the effects of CXCL1 on angiogenesis and arteriogenesis.

Antimicrobial Peptides and Biomarkers Induced by Ultraviolet Irradiation Have the Potential to Reduce Endodontic Inflammation and Facilitate Tissue Healing

Background: Ultraviolet (UV) irradiation can modulate host immune responses and this approach is a novel application for treating endodontic infections and inflammation in root canals. Methods: A dataset of UV-induced molecules was compiled from a literature search. A subset of this dataset was used to calculate expression log2 ratios of endodontic tissue molecules from HEPM cells and gingival fibroblasts after 255, 405, and 255/405 nm UV irradiation. Both datasets were analyzed using ingenuity pathway analysis (IPA, Qiagen, Germantown, MD, USA). Statistical significance was calculated using Fisher’s exact test and z-scores were calculated for IPA comparison analysis. Results: The dataset of 32 UV-induced molecules contained 9 antimicrobial peptides, 10 cytokines, 6 growth factors, 3 enzymes, 2 transmembrane receptors, and 2 transcription regulators. These molecules were in the IPA canonical pathway annotations for the wound healing signaling pathway (9/32, p = 3.22 × 10⁻¹¹) and communication between immune cells (6/32, p = 8.74 × 10⁻¹¹). In the IPA disease and function annotations, the 32 molecules were associated with an antimicrobial response, cell-to-cell signaling and interaction, cellular movement, hematological system development and function, immune cell trafficking, and inflammatory response. In IPA comparison analysis of the 13 molecules, the predicted activation or inhibition of pathways depended upon the cell type exposed, the wavelength of the UV irradiation used, and the time after exposure. Conclusions: UV irradiation activates and inhibits cellular pathways and immune functions. These results suggested that UV irradiation can activate innate and adaptive immune responses, which may supplement endodontic procedures to reduce infection, inflammation, and pain and assist tissues to heal.

Current concepts of photosensitivity in cutaneous lupus erythematosus

Cutaneous lupus erythematosus (CLE) represents a complex autoimmune disease with a broad phenotypic spectrum ranging from acute to chronic destructive cutaneous lesions. Patients with CLE exhibit high photosensitivity and ultraviolet (UV) irradiation can lead to systemic flares in systemic lupus erythematosus. However, the exact mechanisms how UV irradiation enhances cutaneous inflammation in lupus are not fully understood. Recently, new molecular mechanisms of UV-driven immune responses in CLE were identified, offering potential therapeutic approaches. Especially the induction of type I interferons, central cytokines in lupus pathogenesis which are released by various skin cells, have become the focus of current research. In this review, we describe current pathogenic concepts of photosensitivity in lupus erythematosus, including UV-driven activation of intracellular nucleic acid sensors, cellular cytokine production and immune cell activation. Furthermore, we discuss activated pathways contributing to enhanced apoptosis as well as intracellular translocation of autoantigens thereby promoting CLE upon UV light exposure.

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.

Transcriptome analysis of molecular response to UVC irradiation in zebrafish embryos

Ultraviolet (UV) rays can be both harmful and beneficial to humans. This study aimed to investigate the toxicity and safety of ultraviolet C (UVC) exposure in living organisms and the corresponding biodefense molecular mechanisms. Zebrafish embryos, at an early developmental stage (5-6 h post-fertilization), were irradiated with increasing UVC dosages using high-efficiency deep-ultraviolet light-emitting diodes (278 nm). Morphological phenotypes including survival rate, hatching rate, heart rate, and malformation rate were evaluated. Compared to un-irradiated controls, all zebrafish embryos exposed to 4.5 mJ/cm² UVC survived and showed no significant difference in hatching and heart rate. However, 7.5 mJ/cm² of UVC irradiation caused a significantly decreased survival rate (37.5%) and an increased malformation rate (81.8%). Therefore, 4.5 mJ/cm² was chosen as the limit dosage that the internal biodefense system of zebrafish embryos can protect against UVC radiation. Transcriptome analysis (RNA sequencing) performed on 3 min and 3 days post-irradiation embryos (4.5 mJ/cm²) revealed the molecular mechanisms underlying the response of zebrafish embryos to irradiation. The embryos quickly responded to UVC-induced stress by activating the p53 signaling pathway. In addition, after 3 days of recuperation, the embryos showed activation of signal transducer and activator of transcription (STAT) signaling pathway. To our knowledge, this is the first study to evaluate the toxicological effects and the molecular mechanism of biodefense in zebrafish embryos upon 278 nm UVC irradiation.

Programmed gene expression change in mouse skin after ultraviolet radiation damage

Ultraviolet (UV) radiation is a major cause of skin damage and carcinogenesis. Here, we systematically analyse the acute gene expression change in skin in vivo after UV exposure, aiming to establish the common C57BL/6 mouse strain as a convenient model for future pathological research and drug discovery. The back fur of C57BL/6 mice was depilated, and a mixed UV light source was used to irradiate the skin. Full-thickness skin samples were collected at 0, 0.5, 2, 6, 12 and 24 h. Total RNAs were extracted and subjected to RNA sequencing analysis. We found that the gene expression change in mouse skin is highly similar to previous reports in human skin. These include down-regulation of differentiation-related genes and extracellular matrix genes, and up-regulation of cytokine/chemokine genes. An early wave of activator protein 1 (AP-1) expression is induced, whereas activation of the p53 pathway is not significant. The impact of the AP-1 transcription factors and the antioxidant tea polyphenols is discussed. The analysis of acute gene expression change in skin after UV irradiation provides a starting point to investigate how the skin responds to genotoxic stress.

Keratinocyte death by ferroptosis initiates skin inflammation after UVB exposure

The ultraviolet B radiation (UVB) causes skin inflammation, which contributes to the causality and the exacerbation of a number of cutaneous diseases. However, the mechanism of UVB-driven inflammation in the skin remains poorly understood. We show that ferroptosis, a non-apoptotic programmed cell death pathway that is promoted by an excessive phospholipid peroxidation, is activated in the epidermal keratinocytes after their exposure to UVB. The susceptibility of the keratinocytes to UVB-induced ferroptosis depends on the extent of pro-ferroptosis death signal generation and the dysregulation of the glutathione system. Inhibition of ferroptosis prevents the release of HMGB1 from the human epidermal keratinocytes, and blocks necroinflammation in the UVB-irradiated mouse skin. We show that while apoptosis and pyroptosis are also detectable in the keratinocytes after UVB exposure, ferroptosis plays a significant role in initiating UVB-induced inflammation in the skin. Our results have important implications for the prevention and the treatment of a broad range of skin diseases which are fostered by UVB-induced inflammation.

Intense Pulsed Light Attenuates UV-Induced Hyperimmune Response and Pigmentation in Human Skin Cells

The skin of an organism is affected by various environmental factors and fights against aging stress via mechanical and biochemical responses. Photoaging induced by ultraviolet B (UVB) irradiation is common and is the most vital factor in the senescence phenotype of skin, and so, suppression of UVB stress-induced damage is critical. To lessen the UVB-induced hyperimmune response and hyperpigmentation, we investigated the ameliorative effects of intense pulsed light (IPL) treatment on the photoaged phenotype of skin cells. Normal human epidermal keratinocytes and human epidermal melanocytes were exposed to 20 mJ/cm² of UVB. After UVB irradiation, the cells were treated with green (525–530 nm) and yellow (585–592 nm) IPL at various time points prior to the harvest step. Subsequently, various signs of excessive immune response, including expression of proinflammatory and melanogenic genes and proteins, cellular oxidative stress level, and antioxidative enzyme activity, were examined. We found that IPL treatment reduced excessive cutaneous immune reactions by suppressing UVB-induced proinflammatory cytokine expression. IPL treatment prevented hyperpigmentation, and combined treatment with green and yellow IPL synergistically attenuated both processes. IPL treatment may exert protective effects against UVB injury in skin cells by attenuating inflammatory cytokine and melanogenic gene overexpression, possibly by reducing intracellular oxidative stress. IPL treatment also preserves antioxidative enzyme activity under UVB irradiation. This study suggests that IPL treatment is a useful strategy against photoaging, and provides evidence supporting clinical approaches with non-invasive light therapy.

A deep dive into UV-based phototherapy: Mechanisms of action and emerging molecular targets in inflammation and cancer

UV-based phototherapy (including psoralen plus UVA (PUVA), UVB and UVA1) has a long, successful history in the management of numerous cutaneous disorders. Photoresponsive diseases are etiologically diverse, but most involve disturbances in local (and occasionally systemic) inflammatory cells and/or abnormalities in keratinocytes that trigger inflammation. UV-based phototherapy works by regulating the inflammatory component and inducing apoptosis of pathogenic cells. This results in a fascinating and complex network of simultaneous events-immediate transcriptional changes in keratinocytes, immune cells, and pigment cells; the emergence of apoptotic bodies; and the trafficking of antigen-presenting cells in skin-that quickly transform the microenvironment of UV-exposed skin. Molecular elements in this system of UV recognition and response include chromophores, metabolic byproducts, innate immune receptors, neurotransmitters and mediators such as chemokines and cytokines, antimicrobial peptides, and platelet activating factor (PAF) and PAF-like molecules that simultaneously shape the immunomodulatory effects of UV and their interplay with the microbiota of the skin and beyond. Phototherapy's key effects-proapoptotic, immunomodulatory, antipruritic, antifibrotic, propigmentary, and pro-prebiotic-promote clinical improvement in various skin diseases such as psoriasis, atopic dermatitis (AD), graft-versus-host disease (GvHD), vitiligo, scleroderma, and cutaneous T-cell lymphoma (CTCL) as well as prevention of polymorphic light eruption (PLE). As understanding of phototherapy improves, new therapies (UV- and non-UV-based) are being developed that will modify regulatory T-cells (Treg), interact with (resident) memory T-cells and /or utilize agonists and antagonists as well as antibodies targeting soluble molecules such as cytokines and chemokines, transcription factors, and a variety of membrane-associated receptors.

Early transcriptional changes after UVB treatment in atopic dermatitis include inverse regulation of IL-36γ and IL-37

Phototherapy with narrow-band Ultraviolet B (nb-UVB) is a major therapeutic option in atopic dermatitis (AD), yet knowledge of the early molecular responses to this treatment is lacking. The objective of this study was to map the early transcriptional changes in AD skin in response to nb-UVB treatment. Adult patients (n = 16) with AD were included in the study and scored with validated scoring tools. AD skin was irradiated with local nb-UVB on day 0, 2 and 4. Skin biopsies were taken before and after treatment (day 0 and 7) and analysed for genome-wide modulation of transcription. When examining the early response after three local UVB treatments, gene expression analysis revealed 77 significantly modulated transcripts (30 down- and 47 upregulated). Among them were transcripts related to the inflammatory response, melanin synthesis, keratinization and epidermal structure. Interestingly, the pro-inflammatory cytokine IL-36γ was reduced after treatment, while the anti-inflammatory cytokine IL-37 increased after treatment with nb-UVB. There was also a modulation of several other mediators involved in inflammation, among them defensins and S100 proteins. This is the first study of early transcriptomic changes in AD skin in response to nb-UVB. We reveal robust modulation of a small group of inflammatory and anti-inflammatory targets, including the IL-1 family members IL36γ and IL-37, which is evident before any detectable changes in skin morphology or immune cell infiltrates. These findings provide important clues to the molecular mechanisms behind the treatment response and shed light on new potential treatment targets.

Proenkephalin+ regulatory T cells expanded by ultraviolet B exposure maintain skin homeostasis with a healing function

Regulatory T (Treg) cells, expressing CD25 (interleukin-2 receptor α chain) and Foxp3 transcription factor, maintain immunological self-tolerance and suppress various immune responses. Here we report a feature of skin Treg cells expanded by ultraviolet B (UVB) exposure. We found that skin Treg cells possessing a healing function are expanded by UVB exposure with the expression of an endogenous opioid precursor, proenkephalin (PENK). Upon UVB exposure, skin Treg cells were expanded with a unique TCR repertoire. Also, they highly expressed a distinctive set of genes enriched in "wound healing involved in inflammatory responses" and the "neuropeptide signaling pathway," as indicated by the high expression of Penk. We found that not only was PENK expression at the protein level detected in the UVB-expanded skin Treg (UVB-skin Treg) cells, but that a PENK-derived neuropeptide, methionine enkephalin (Met-ENK), from Treg cells promoted the outgrowth of epidermal keratinocytes in an ex vivo skin explant assay. Notably, UVB-skin Treg cells also promoted wound healing in an in vivo wound closure assay. In addition, UVB-skin Treg cells produced amphiregulin (AREG), which plays a key role in Treg-mediated tissue repair. Identification of a unique function of PENK⁺ UVB-skin Treg cells provides a mechanism for maintaining skin homeostasis.

UVB Irradiation Induced Cell Damage and Early Onset of Junbb Expression in Zebrafish

Ultraviolet B (UVB) radiation has drawn more attention over these past few decades since it causes severe DNA damage and induces inflammatory response. Serial gene profiling and high throughput data in UVB-associated phenomenon in human cultured cells or full rack of human skin have been investigated. However, results using different tissue models lead to ambiguity in UVB-induced pathways. In order to systematically understand the UVB-associated reactions, the zebrafish model was used, and whole organism gene profiling was performed to identify a novel biomarker which can be used to generate a new mechanistic approach for further screening on a UVB-related system biology. In this study, detailed morphological assays were performed to address biological response after receiving UVB irradiation at morphological, cellular, and molecular levels. Microarray screening and whole genome profiling revealed that there is an early onset expression of junbb in zebrafish embryos after UVB irradiation. Also, the identified novel biomarker junbb is more sensitive to UVB response than mmps which have been used in mouse models. Moreover, cellular and molecular response chronology after UVB irradiation in zebrafish provide a solid and fundamental mechanism for use in a UV radiation-associated study in the future.

UVB-dependent inhibition of lipin-1 protects against proinflammatory responses in human keratinocytes

Lipin-1 is an Mg²⁺-dependent phosphatidate phosphatase (PAP1) that catalyzes a critical step in the synthesis of glycerophospholipids and is also a cotranscriptional regulator. The role of lipin-1 in the regulation of inflammatory responses has been extensively studied in various cell types but not in skin cells. In the present study, the function of lipin-1 in UVB-induced proinflammatory responses was assessed in normal human epidermal keratinocytes (NHEKs). UVB radiation downregulated lipin-1 expression. Lipin-1 inhibition was mediated by UVB-dependent sterol-response element binding protein-1 (SREBP-1) inhibition. The UVB-dependent inhibition of lipin-1 and SREBP-1 was mediated by AMPK activation. UVB-induced activation of JNK was dependent on AMPK activation and mediated lipin-1 inhibition. Prevention of UVB-mediated lipin-1 repression by introducing a lipin-1 expression vector stimulated IL-6 and IL-8 production, suggesting that lipin-1 inhibition attenuates UVB-induced IL-6 and IL-8 production. The downregulation of lipin-1 ameliorated UVB-induced NF-ĸB phosphorylation, which might be attributed to the suppression of UVB-induced accumulation of free fatty acids (FFAs). Pharmacological inhibition of PAP1 with propranolol suppressed UVB-induced production of IL-6 and IL-8 in NHEKs and reconstituted human skin models. Taken together, lipin-1 is downregulated by exposure to UVB radiation, which confers protection against UVB-induced proinflammatory responses; therefore, the inhibition of lipin-1 is a potential strategy for photoaging.

Reduced production and activity of an enzyme in skin cells helps protect them from damage caused by exposure to ultra-violet light. Minjung Chae and colleagues at the Amorepacific Corporation in Yongin, South Korea, identified an anti-inflammatory effect caused by the reduction in expression of the enzyme lipin-1 when skin cells are exposed to UVB radiation. These ultra-violet rays are associated with aging and increased risk of skin cancer. Lipin-1 is involved in making glycerophospholipid molecules, which are key components of the membranes surrounding and inside cells. Identifying the enzyme’s significance for inflammation in skin cells extends previous similar findings with other cell types. The research also uncovered aspects of the molecular mechanisms mediating the skin cell response. Inhibiting lipin-1 activity might reduce the damage sunlight causes to skin.

Dose and time effects of solar-simulated ultraviolet radiation on the in vivo human skin transcriptome

Background

Terrestrial ultraviolet (UV) radiation causes erythema, oxidative stress, DNA mutations and skin cancer. Skin can adapt to these adverse effects by DNA repair, apoptosis, keratinization and tanning.

Objectives

To investigate the transcriptional response to fluorescent solar‐simulated radiation (FSSR) in sun‐sensitive human skin in vivo.

Methods

Seven healthy male volunteers were exposed to 0, 3 and 6 standard erythemal doses (SED). Skin biopsies were taken at 6 h and 24 h after exposure. Gene and microRNA expression were quantified with next generation sequencing. A set of candidate genes was validated by quantitative polymerase chain reaction (qPCR); and wavelength dependence was examined in other volunteers through microarrays.

Results

The number of differentially expressed genes increased with FSSR dose and decreased between 6 and 24 h. Six hours after 6 SED, 4071 genes were differentially expressed, but only 16 genes were affected at 24 h after 3 SED. Genes for apoptosis and keratinization were prominent at 6 h, whereas inflammation and immunoregulation genes were predominant at 24 h. Validation by qPCR confirmed the altered expression of nine genes detected under all conditions; genes related to DNA repair and apoptosis; immunity and inflammation; pigmentation; and vitamin D synthesis. In general, candidate genes also responded to UVA1 (340–400 nm) and/or UVB (300 nm), but with variations in wavelength dependence and peak expression time. Only four microRNAs were differentially expressed by FSSR.

Conclusions

The UV radiation doses of this acute study are readily achieved daily during holidays in the sun, suggesting that the skin transcriptional profile of ‘typical’ holiday makers is markedly deregulated.

What's already known about this topic?

The skin's transcriptional profile underpins its adverse (i.e. inflammation) and adaptive molecular, cellular and clinical responses (i.e. tanning, hyperkeratosis) to solar ultraviolet radiation.

Few studies have assessed microRNA and gene expression in vivo in humans, and there is a lack of information on dose, time and waveband effects.

What does this study add?

Acute doses of fluorescent solar‐simulated radiation (FSSR), of similar magnitude to those received daily in holiday situations, markedly altered the skin's transcriptional profiles.

The number of differentially expressed genes was FSSR‐dose‐dependent, reached a peak at 6 h and returned to baseline at 24 h.

The initial transcriptional response involved apoptosis and keratinization, followed by inflammation and immune modulation. In these conditions, microRNA expression was less affected than gene expression.

Linked Comment:Hart. Br J Dermatol 2020; 182:1328–1329.

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Disruption of the Sensory System Affects Sterile Cutaneous Inflammation In Vivo

Increasing evidence suggests that nerve fibers responding to noxious stimuli (nociceptors) modulate immunity in a variety of tissues, including the skin. Yet, the role of nociceptors in regulating sterile cutaneous inflammation remains unexplored. To address this question, we have developed a detailed description of the sterile inflammation caused by overexposure to UVB irradiation (i.e., sunburn) in the mouse plantar skin. Using this model, we observed that chemical depletion of nociceptor terminals did not alter the early phase of the inflammatory response to UVB, but it caused a significant increase in the number of dendritic cells and αβ⁺ T cells as well as enhanced extravasation during the later stages of inflammation. Finally, we showed that such regulation was driven by the nociceptive neuropeptide calcitonin gene-related peptide. In conclusion, we propose that nociceptors not only play a crucial role in inflammation through avoidance reflexes and behaviors, but can also regulate sterile cutaneous immunity in vivo.

The antimicrobial protein S100A12 identified as a potential autoantigen in a subgroup of atopic dermatitis patients

Background

Atopic dermatitis (AD) is a complex heterogeneous chronic inflammatory skin disease. Specific IgE antibodies against autoantigens have been observed in a subgroup of AD patients, however, little is known about IgG-auto-reactivity in AD. To investigate the presence of autoreactive IgG antibodies, we performed autoantibody profiling of IgG in patients with AD of different severities and in healthy controls (HC).

Methods

First, we performed an untargeted screening in plasma samples from 40 severe AD (sAD) patients and 40 HC towards 1152 protein fragments on planar antigen microarrays. Next, based on the findings and addition of more fragments, a targeted antigen suspension bead array was designed to profile a cohort of 50 sAD patients, 123 patients with moderate AD (mAD), and 84 HC against 148 protein fragments representing 96 unique proteins.

Results

Forty-nine percent of the AD patients showed increased IgG-reactivity to any of the four antigens representing keratin associated protein 17-1 (KRTAP17-1), heat shock protein family A (Hsp70) member 4 (HSPA4), S100 calcium binding proteins A12 (S100A12), and Z (S100Z). The reactivity was more frequent in the sAD patients (66%) than in those with mAD (41%), whereas only present in 25% of the HC. IgG-reactivity to S100A12, a protein including an antimicrobial peptide, was only observed in AD patients (13/173).

Conclusions

Autoantibody profiling of IgG-reactivity using microarray technology revealed an autoantibody-based subgroup in patients with AD. The four identified autoantigens and especially S100A12 could, if characterized further, increase the understanding of different pathogenic mechanisms behind AD and thereby enable better treatment.

Electronic supplementary material

The online version of this article (10.1186/s13601-019-0240-4) contains supplementary material, which is available to authorized users.

Dual Effects of Alpha-Hydroxy Acids on the Skin

AHAs are organic acids with one hydroxyl group attached to the alpha position of the acid. AHAs including glycolic acid, lactic acid, malic acid, tartaric acid, and citric acid are often used extensively in cosmetic formulations. AHAs have been used as superficial peeling agents as well as to ameliorate the appearance of keratoses and acne in dermatology. However, caution should be exercised in relation to certain adverse reactions among patients using products with AHAs, including swelling, burning, and pruritus. Whether AHAs enhance or decrease photo damage of the skin remains unclear, compelling us to ask the question, is AHA a friend or a foe of the skin? The aim of this manuscript is to review the various biological effects and mechanisms of AHAs on human keratinocytes and in an animal model. We conclude that whether AHA is a friend or foe of human skin depends on its concentration. These mechanisms of AHAs are currently well understood, aiding the development of novel approaches for the prevention of UV-induced skin damage.

Adipochemokines induced by ultraviolet irradiation contribute to impaired fat metabolism in subcutaneous fat cells

BACKGROUND

Adipose tissue is now appreciated as the pivotal regulator of metabolic and endocrine functions. Subcutaneous (SC) fat, in contrast to visceral fat, may protect against metabolic syndrome and systemic inflammation. We demonstrated that chronic as well as acute ultraviolet (UV) irradiation to the skin induces loss of underlying SC fat. UV-irradiated SC fat may produce chemokines or cytokines that modulate lipid homeostasis and secretion of adipokines.

OBJECTIVES

To elucidate UV-induced specific adipochemokines implicated in UV-induced modulation of SC fat.

METHODS

Primary cultured adipocytes were treated with conditioned medium from UV- or sham-irradiated skin cells. Young and older healthy participants provided SC fat from sun-exposed and sun-protected skin. Sun-protected skin from other participants was irradiated with UV. Differentially expressed adipochemokines were screened by cytokine array, and confirmed in vitro and in vivo. The functions of select adipochemokines involved in lipid metabolism were examined via short interfering RNA-mediated knockdown of cognate receptors.

RESULTS

Specific adipochemokines, including C-X-C motif chemokine (CXCL) family members such as CXCL5/ENA-78, and C-C motif chemokine (CCL) family members such as CCL20/MIP-3α and CCL5/RANTES, were greatly induced in SC fat by UV exposure. They could impair triglyceride synthesis via downregulation of lipogenic enzymes and sterol regulatory element-binding protein-1 through their respective cognate receptors, CXC chemokine receptor type (CXC-R)2, C-C chemokine receptor type (CCR)-6, and CCR-5. In addition, UV irradiation induced infiltration of adipose tissue macrophages responsible for the secretion of several chemokines into SC fat.

CONCLUSIONS

These UV-induced adipochemokines may be implicated in the reduction of lipogenesis in SC fat, leading to impairment of fat homeostasis and associated comorbidities such as obesity.

Unique profile of antimicrobial peptide expression in polymorphic light eruption lesions compared to healthy skin, atopic dermatitis, and psoriasis

Background

Polymorphic light eruption (PLE) has been attributed to type IV, most likely delayed‐type hypersensitivity response (adaptive immunity) but little is known on innate immunity, especially antimicrobial peptides (AMPs) in the disease. Abnormalities in AMP expression have been linked to pathological skin conditions such as atopic dermatitis (AD) and psoriasis.

Methods

Antimicrobial peptide profiling was carried out in PLE skin samples (n,12) compared with that of healthy (n,13), atopic (n,6), and psoriatic skin (n,6).

Results

Compared to healthy skin, we observed increased expression of psoriasin and RNAse7 (both mostly in stratum granulosum of the epidermis), HBD‐2 (in the cellular infiltrate of the dermis), and LL37 (mostly in and around blood vessels and glands) in PLE lesional skin, a similar expression profile as present in psoriatic skin and different to that of AD (with little or no expression of psoriasin, RNAse7, HBD‐2, and LL37). HBD‐3 was downregulated in PLE compared to its high expression in the epidermis and dermis of healthy skin, AD, and psoriasis.

Conclusion

The unique profile of differentially expressed AMPs in PLE implies a role in the pathophysiology of the disease, possibly directly or indirectly linked to the microbiome of the skin.

AhR mediates an anti-inflammatory feedback mechanism in human Langerhans cells involving FcεRI and IDO

BACKGROUND

Aryl hydrocarbon receptor (AhR), an important regulator of immune responses, is activated by UVB irradiation in the skin. Langerhans cells (LC) in the epidermis of patients with atopic dermatitis (AD) carry the high-affinity receptor for IgE, FcεRI, and are crucially involved in the pathogenesis of AD by inducing inflammatory responses and regulating tolerogenic processes.

OBJECTIVES

We investigated AhR and AhR repressor (AhRR) expression and functional consequences of AhR activation in human ex vivo skin cells and in in vitro-generated LC.

METHODS

Epidermal cells from healthy skin were analyzed for their expression of AhR and AhRR. LC generated from CD34⁺ hematopoietic stem cells (CD34LC) were treated with the UV photoproduct and AhR ligand 6-formylindolo[3,2-b]carbazole (FICZ). Cell surface receptors, transcription factors, and the tolerogenic tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) were analyzed using flow cytometry and quantitative PCR.

RESULTS

Epidermal LC and CD34LC express AhR and AhRR. AhR was also found in keratinocytes, which lack AhRR. AhR activation of LC by FICZ caused downregulation of FcεRI in CD34LC without affecting their maturation. AhR-mediated regulation of FcεRI did not involve any known transcription factors related to this receptor. Furthermore, we could show upregulation of IDO mediated by AhR engagement.

CONCLUSIONS

Our study shows that AhR activation by FICZ reduces FcεRI and upregulates IDO expression in LC. This AhR-mediated anti-inflammatory feedback mechanism may dampen the allergen-induced inflammation in AD.

Enhanced Inflammasome Activity in Systemic Lupus Erythematosus Is Mediated via Type I Interferon-Induced Up-Regulation of Interferon Regulatory Factor 1

OBJECTIVE

The inflammasome complex is a driver of organ damage in patients with systemic lupus erythematosus (SLE). Although type I interferons (IFNs) are well established as mediators of SLE pathogenesis, their role in inflammasome activation in SLE has not been assessed. The aim of this study was to examine type I IFNs as regulators of the inflammasome.

METHODS

SLE patients fulfilled ≥4 American College of Rheumatology criteria and were recruited from the University of Michigan Lupus Cohort. Primary monocytes were isolated from SLE patients or healthy controls by negative selection, treated with inflammasome activators in the presence or absence of IFNα, and IL-1β secretion was measured by enzyme-linked immunosorbent assay. Expression levels of IFN and inflammasome-related molecules were assessed by real-time polymerase chain reaction and Western blotting. IFN regulatory factor 1 (IRF-1) expression was specifically down-regulated by small interfering RNA (siRNA) transfection and a chemical inhibitor.

RESULTS

Monocytes from patients with SLE exhibited increased expression and enhanced activation of the inflammasome by ATP when compared with control monocytes. Expression of inflammasome and IFN-regulated genes was significantly correlated in monocytes from SLE patients but not in control monocytes. Inflammasome activity was increased after prolonged exposure to IFNα. Reduction of IRF-1 expression via siRNA blocked caspase 1 up-regulation after treatment with IFNα. Importantly, hyperactivity of the inflammasome in the monocytes of SLE patients was significantly reduced after knockdown or inhibition of IRF-1.

CONCLUSION

Prolonged type I IFN exposure, as seen in SLE patients, primes monocytes for robust inflammasome activation in an IRF-1-dependent manner. IRF-1 inhibition may serve as a novel target for treatment of SLE-associated inflammation and organ damage.

Topical application of glycolic acid suppresses the UVB induced IL-6, IL-8, MCP-1 and COX-2 inflammation by modulating NF-κB signaling pathway in keratinocytes and mice skin

BACKGROUND

Glycolic acid (GA), commonly present in fruits, has been used to treat dermatological diseases. Extensive exposure to solar ultraviolet B (UVB) irradiation plays a crucial role in the induction of skin inflammation. The development of photo prevention from natural materials represents an effective strategy for skin keratinocytes.

OBJECTIVE

The aim of this study was to investigate the molecular mechanisms underlying the glycolic acid (GA)-induced reduction of UVB-mediated inflammatory responses.

METHODS

We determined the effects of different concentrations of GA on the inflammatory response of human keratinocytes HaCaT cells and C57BL/6J mice dorsal skin. After GA was topically applied, HaCaT and mice skin were exposed to UVB irradiation.

RESULTS

GA reduced the production of UVB-induced nuclear factor kappa B (NF-κB)-dependent inflammatory mediators [interleukin (IL)-1β, IL-6, IL-8, cyclooxygenase (COX)-2, tumor necrosis factor-α, and monocyte chemoattractant protein (MCP-1)] at both mRNA and protein levels. GA inhibited the UVB-induced promoter activity of NF-κB in HaCaT cells. GA attenuated the elevation of senescence associated with β-galactosidase activity but did not affect the wound migration ability. The topical application of GA inhibited the genes expression of IL-1β, IL-6, IL-8, COX-2, and MCP-1 in UVB-exposed mouse skin. The mice to UVB irradiation after GA was topically applied for 9 consecutive days and reported that 1-1.5% of GA exerted anti-inflammatory effects on mouse skin.

CONCLUSION

We clarified the molecular mechanism of GA protection against UVB-induced inflammation by modulating NF-κB signaling pathways and determined the optimal concentration of GA in mice skin exposed to UVB irradiation.

S100A12 Induced in the Epidermis by Reduced Hydration Activates Dermal Fibroblasts and Causes Dermal Fibrosis

Disruption of the barrier function of skin increases transepidermal water loss and up-regulates inflammatory pathways in the epidermis. Consequently, sustained expression of proinflammatory cytokines from the epidermis is associated with dermal scarring. We found increased expression of S100A12 in the epidermis of human hypertrophic and keloid scar. Exposing a stratified keratinocyte culture to a reduced-hydration environment increased the expression and secretion of S100A12 by nearly 70%, which in turn activated dermal fibroblasts in vitro. Direct treatment of fibroblasts with conditioned medium collected from stratified keratinocyte culture under reduced-hydration conditions activated fibroblasts, shown by up-regulation of α-smooth muscle actin, pro-collagen 1, and F-actin expression. However, this fibroblast activation was not found when S100A12 was knocked down by RNA interference in keratinocytes. Pharmacological blockade of S100A12 receptors, RAGE, or TLR4 inhibited S100A12-induced fibroblast activation. Local delivery of S100A12 resulted in a marked hypertrophic scar formation in a validated rabbit hypertrophic scar model compared with saline control. Our findings indicate that S100A12 functions as a proinflammatory cytokine and suggest that S100A12 is a potential therapeutic target for dermal scarring.

The Skin Microbiome: Is It Affected by UV-induced Immune Suppression?

Human skin apart from functioning as a physical barricade to stop the entry of pathogens, also hosts innumerable commensal organisms. The skin cells and the immune system constantly interact with microbes, to maintain cutaneous homeostasis, despite the challenges offered by various environmental factors. A major environmental factor affecting the skin is ultraviolet radiation (UV-R) from sunlight. UV-R is well known to modulate the immune system, which can be both beneficial and deleterious. By targeting the cells and molecules within skin, UV-R can trigger the production and release of antimicrobial peptides, affect the innate immune system and ultimately suppress the adaptive cellular immune response. This can contribute to skin carcinogenesis and the promotion of infectious agents such as herpes simplex virus and possibly others. On the other hand, a UV-established immunosuppressive environment may protect against the induction of immunologically mediated skin diseases including some of photodermatoses such as polymorphic light eruption. In this article, we share our perspective about the possibility that UV-induced immune suppression may alter the landscape of the skin’s microbiome and its components. Alternatively, or in concert with this, direct UV-induced DNA and membrane damage to the microbiome may result in pathogen associated molecular patterns (PAMPs) that interfere with UV-induced immune suppression.

The S100 proteins in epidermis: Topology and function

BACKGROUND

S100 proteins are small calcium binding proteins encoded by genes located in the epidermal differentiation complex (EDC). Differently to other proteins encoded by EDC genes, which are indispensable for normal epidermal differentiation, the role of S100 proteins in the epidermis remains largely unknown.

SCOPE OF REVIEW

Particular S100 proteins differ in their distribution in epidermal layers, skin appendages, melanocytes and Langerhans cells. Taking into account that each epidermal component consists of specialized cells with well-defined functions, such differential distribution may be indicative of the function of a given S100 protein. We used this criterion together with the survey of the current experimental data pertinent to epidermis to provide a fairly comprehensive view on the possible function of individual S100 proteins in this tissue.

MAJOR CONCLUSIONS

S100 proteins are differently expressed and, despite extensive structural homology, perform diverse functions in the epidermis. Certain S100 proteins probably ensure constant epidermal renewal and support wound healing while others act in epidermal differentiation or have a protective role. As their expression is differently affected in various skin pathologies, particular S100 proteins could be valuable diagnostic markers.

GENERAL SIGNIFICANCE

S100 proteins seem to be important although not yet fully recognized epidermal constituents. Better understanding of their role in the epidermis might be helpful in designing therapies to various skin diseases.

The immunopathogenesis of psoriasis

Psoriasis vulgaris is a chronic inflammatory skin disease that results from the complex interplay between keratinocytes, dendritic cells, and T cells. Keratinocytes trigger innate and adaptive immune responses. Dermal myeloid dendritic cells regulate T cell activation and production of cytokines and chemokines that amplify inflammation. Most of the psoriatic T cells discretely produce interferon-γ, interleukin (IL)-17, and IL-22. The initiation phase of psoriasis involves Toll-like receptors, antimicrobial peptide LL37, and plasmacytoid dendritic cells. Keratinocytes are the main cutaneous cell type expressing IL-17 receptors and hence the immune circuit is amplified by keratinocytes upregulating mRNAs for a range of inflammatory products.

UV Radiation Induces the Epidermal Recruitment of Dendritic Cells that Compensate for the Depletion of Langerhans Cells in Human Skin

UVR causes skin injury and inflammation, resulting in impaired immune function and increased skin cancer risk. Langerhans cells (LCs), the immune sentinels of the epidermis, are depleted for several days following a single UVR exposure and can be reconstituted from circulating monocytes. However, the differentiation pathways leading to the recovery of a normal pool of LCs is still unclear. To study the dynamic changes in human skin with UV injury, we exposed a cohort of 29 healthy human volunteers to a clinically relevant dose of UVR and analyzed sequential epidermal biopsies for changes in leukocyte and dendritic cell (DC) subsets. UV-induced depletion of CD1a(high) LC was compensated by sequential appearance of various epidermal leukocytes. CD14(+) monocytes were recruited as early as D1 post exposure, followed by recruitment of two inflammatory DC subsets that may represent precursors of LCs. These CD1a(low) CD207(-) and the heretofore unknown CD1a(low) CD207(+) DCs appeared at day 1 and day 4 post UVR, respectively, and were endowed with T-cell-activating properties similar to those of LCs. We conclude that recruitment of monocytes and inflammatory DCs appear as a physiological response of the epidermis in order to repair UVR-induced LC depletion associated with immune suppression.

The consequences for human health of stratospheric ozone depletion in association with other environmental factors

Ozone depletion, climate and human health.

An endoplasmic reticulum stress-initiated sphingolipid metabolite, ceramide-1-phosphate, regulates epithelial innate immunity by stimulating β-defensin production

Antimicrobial peptides (AMP) are ubiquitous innate immune elements in epithelial tissues. We recently discovered that a signaling lipid, the ceramide metabolite sphingosine-1-phosphate (S1P), regulates production of a major AMP, cathelicidin antimicrobial peptide (CAMP), in response to a subtoxic level of endoplasmic reticulum (ER) stress that can be induced by external perturbants in keratinocytes. We hypothesized that an ER stress-initiated signal could also regulate production of another major class of AMPs: i.e., the human beta-defensins 2 (hBD2) and 3 (hBD3). Keratinocytes stimulated with a pharmacological ER stressor, thapsigargin (Tg), increased hBD2/hBD3 as well as CAMP mRNA expression. While inhibition of sphingosine-1-phosphate production did not alter hBD expression following ER stress, blockade of ceramide-1-phosphate (C1P) suppressed Tg-induced hBD2/hBD3 but not CAMP expression. Exogenous C1P also increased hBD2/hBD3 production, indicating that C1P stimulates hBD expression. We showed further that C1P-induced hBD2/hBD3 expression is regulated by a novel pathway in which C1P stimulates downstream hBD via a cPLA2a→15d-PGJ2→PPARα/PPARβ/δ→Src kinase→STAT1/STAT3 transcriptional mechanism. Finally, conditioned medium from C1P-stimulated keratinocytes showed antimicrobial activity against Staphylococcus aureus. In summary, our present and recent studies discovered two new regulatory mechanisms of key epidermal AMP, hBD2/hBD3 and CAMP. The C1P and S1P pathways both signal to enhance innate immunity in response to ER stress.

Immunology of psoriasis

The skin is the front line of defense against insult and injury and contains many epidermal and immune elements that comprise the skin-associated lymphoid tissue (SALT). The reaction of these components to injury allows an effective cutaneous response to restore homeostasis. Psoriasis vulgaris is the best-understood and most accessible human disease that is mediated by T cells and dendritic cells. Inflammatory myeloid dendritic cells release IL-23 and IL-12 to activate IL-17-producing T cells, Th1 cells, and Th22 cells to produce abundant psoriatic cytokines IL-17, IFN-γ, TNF, and IL-22. These cytokines mediate effects on keratinocytes to amplify psoriatic inflammation. Therapeutic studies with anticytokine antibodies have shown the importance of the key cytokines IL-23, TNF, and IL-17 in this process. We discuss the genetic background of psoriasis and its relationship to immune function, specifically genetic mutations, key PSORS loci, single nucleotide polymorphisms, and the skin transcriptome. The association between comorbidities and psoriasis is reviewed by correlating the skin transcriptome and serum proteins. Psoriasis-related cytokine-response pathways are considered in the context of the transcriptome of different mouse models. This approach offers a model for other inflammatory skin and autoimmune diseases.

Ultraviolet B irradiation induces skin accumulation of plasmacytoid dendritic cells: a possible role for chemerin

Photosensitivity represents a common feature for most forms of lupus erythematosus (LE) including cutaneous LE. Skin inflammatory infiltrates in response to ultraviolet (UV) exposure are closely involved in the development of skin lesions of LE patients. Skin-infiltrating plasmacytoid dendritic cells (pDCs), considered as a hallmark of cutaneous LE, contribute to its pathogenesis via the production of type I interferons (IFNs). Chemerin, a recently identified chemoattractant for pDCs through its functional receptor chemR23, was found to be elevated in skin lesions of LE patients. The aim of this study was to investigate the effect of UVB irradiation on skin pDC recruitment and chemerin expression. We found that UVB irradiation induced a rapid but transient influx of pDCs as well as a persistent infiltration of neutrophils and macrophages in the mouse skin. The mRNA expression levels of IRF-7, IFN-α and chemR23 were increased in UVB-irradiated skin. Furthermore, UVB irradiation up-regulated skin chemerin production and pDC accumulation in parallel, both of which reached their peaks simultaneously (24 h post-irradiation). Dermal fibroblasts seemed to be the major source of chemerin as evidenced by significantly increased chemerin secretion by UVB-irradiated dermal fibroblasts. More importantly, LE-prone MRL/lpr mouse exhibited greatly increased skin pDC accumulation and chemerin production in response to UVB irradiation, indicating their contributions to increased susceptibility of photosensitivity in the MRL/lpr mouse. Thus, our findings demonstrated that elevated chemerin expression positively correlates with pDC accumulation in UVB-irradiated skin, suggesting a role of chemerin in mediating skin recruitment of pDCs in response to UVB exposure.

UVB radiation generates sunburn pain and affects skin by activating epidermal TRPV4 ion channels and triggering endothelin-1 signaling

At our body surface, the epidermis absorbs UV radiation. UV overexposure leads to sunburn with tissue injury and pain. To understand how, we focus on TRPV4, a nonselective cation channel highly expressed in epithelial skin cells and known to function in sensory transduction, a property shared with other transient receptor potential channels. We show that following UVB exposure mice with induced Trpv4 deletions, specifically in keratinocytes, are less sensitive to noxious thermal and mechanical stimuli than control animals. Exploring the mechanism, we find that epidermal TRPV4 orchestrates UVB-evoked skin tissue damage and increased expression of the proalgesic/algogenic mediator endothelin-1. In culture, UVB causes a direct, TRPV4-dependent Ca(2+) response in keratinocytes. In mice, topical treatment with a TRPV4-selective inhibitor decreases UVB-evoked pain behavior, epidermal tissue damage, and endothelin-1 expression. In humans, sunburn enhances epidermal expression of TRPV4 and endothelin-1, underscoring the potential of keratinocyte-derived TRPV4 as a therapeutic target for UVB-induced sunburn, in particular pain.

Dendritic cells in the periphery control antigen-specific natural and induced regulatory T cells

Dendritic cells (DCs) are specialized antigen-presenting cells that regulate both immunity and tolerance. DCs in the periphery play a key role in expanding naturally occurring Foxp3⁺ CD25⁺ CD4⁺ regulatory T cells (Natural T-regs) and inducing Foxp3 expression (Induced T-regs) in Foxp3⁻ CD4⁺ T cells. DCs are phenotypically and functionally heterogeneous, and further classified into several subsets depending on distinct marker expression and their location. Recent findings indicate the presence of specialized DC subsets that act to expand Natural T-regs or induce Foxp3⁺ T-regs from Foxp3⁻ CD4⁺ T cells. For example, two major subsets of DCs in lymphoid organs act differentially in inducing Foxp3⁺ T-regs from Foxp3⁻ cells or expanding Natural T-regs with model-antigen delivery by anti-DC subset monoclonal antibodies in vivo. Furthermore, DCs expressing CD103 in the intestine induce Foxp3⁺ T-regs from Foxp3⁻ CD4⁺ T cells with endogenous TGF-β and retinoic acid. In addition, antigen-presenting DCs have a capacity to generate Foxp3⁺ T-regs in the oral cavity where many antigens and commensals exist, similar to intestine and skin. In skin and skin-draining lymph nodes, at least six DC subsets have been identified, suggesting a complex DC-T-reg network. Here, we will review the specific activity of DCs in expanding Natural T-regs and inducing Foxp3⁺ T-regs from Foxp3⁻ precursors, and further discuss the critical function of DCs in maintaining tolerance at various locations including skin and oral cavity.

TREM-1 as a potential therapeutic target in psoriasis

Our group recently described a population of antigen presenting cells that appear to be critical in psoriasis pathogenesis, termed inflammatory myeloid dendritic cells (CD11c⁺ BDCA1⁻). Triggering receptor expressed on myeloid cells type-1 (TREM-1) Signaling was a major canonical pathway in the published transcriptome of these cells. TREM-1 is a member of the immunoglobulin superfamily, active through the DAP12 signaling pathway, with an unknown ligand. Activation through TREM-1 induces inflammatory cytokines including IL-8, MCP/CCL2 and TNF. We now show that TREM-1 was expressed in the skin of healthy and psoriatic patients, and there was increased soluble TREM-1 in the circulation of psoriasis patients. In psoriasis lesions, TREM-1 was co-localized with dendritic cells as well as CD31⁺ endothelial cells. TREM-1 expression was reduced with successful NB-UVB, etanercept and anti-IL-17 treatments. An in vitro model of PGN-activated monocytes as inflammatory myeloid DCs was developed to study TREM-1 blockade, and treatment with a TREM-1 blocking chimera decreased allogeneic Th17 activation as well as IL-17 production. Furthermore, TREM-1 blockade of ex vivo psoriatic dendritic cells in an alloMLR also showed a decrease in IL-17. Together, these data suggest that the TREM-1 signaling pathway may be a previously unidentified therapeutic target to prevent the effects of inflammatory myeloid DCs in psoriasis.

TREM-1 as a potential therapeutic target in psoriasis

Our group recently described a population of antigen-presenting cells that appear to be critical in psoriasis pathogenesis, termed inflammatory myeloid dendritic cells (CD11c(+)/blood dendritic cell (DC) antigen 1(-)). Triggering receptor expressed on myeloid cells type-1 (TREM-1) signaling was a major canonical pathway in the published transcriptome of these cells. TREM-1 is a member of the Ig superfamily, active through the DAP12 signaling pathway, with an unknown ligand. Activation through TREM-1 induces inflammatory cytokines, including IL-8, MCP/CCL2, and tumor necrosis factor. We now show that TREM-1 was expressed in the skin of healthy and psoriatic patients, and there was increased soluble TREM-1 in the circulation of psoriasis patients. In psoriasis lesions, TREM-1 was colocalized with DCs, as well as CD31(+) endothelial cells. TREM-1 expression was reduced with successful narrow band UVB (NB-UVB), etanercept, and anti-IL-17 treatments. An in vitro model of peptidoglycan-activated monocytes as inflammatory myeloid DCs was developed to study TREM-1 blockade, and treatment with a TREM-1 blocking chimera decreased allogeneic T-helper type 17 cell activation, as well as IL-17 production. Furthermore, TREM-1 blockade of ex vivo psoriatic DCs in an allogeneic mixed leukocyte reaction also showed a decrease in IL-17. Together, these data suggest that the TREM-1 signaling pathway may be a previously unidentified therapeutic target to prevent the effects of inflammatory myeloid DCs in psoriasis.