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

Potential Role of IL-37 in Atopic Dermatitis

Interleukin 37 (IL-37) is a recently discovered member of the IL-1 cytokine family that appears to have anti-inflammatory and immunosuppressive effects in various diseases. IL-37 acts as a dual-function cytokine, exerting its effect extracellularly by forming a complex with the receptors IL-18 α (IL-18Rα) and IL-1R8 and transmitting anti-inflammatory signals, as well as intracellularly by interacting with Smad3, entering the nucleus, and inhibiting the transcription of pro-inflammatory genes. Consequently, IL-37 is linked to IL-18, which plays a role in the pathogenesis of atopic dermatitis (AD), consistent with our studies. Some isoforms of IL-37 are expressed by keratinocytes, monocytes, and other skin immune cells. IL-37 has been found to modulate the skewed T helper 2 (Th2) inflammation that is fundamental to the pathogenesis of AD. This review provides an up-to-date summary of the function of IL-37 in modulating the immune system and analyses its potential role in the pathogenesis of AD. Moreover, it speculates on IL-37's hypothetical value as a therapeutic target in the treatment of AD.

Regulatory Mechanism of the IL-33-IL-37 Axis via Aryl Hydrocarbon Receptor in Atopic Dermatitis and Psoriasis

Interleukin (IL)-33 and IL-37 have been identified as novel cytokines involved in various inflammatory diseases. However, their specific roles remain largely unknown. Recent studies have shown that IL-33, which triggers inflammation, and IL-37, which suppresses it, cooperatively regulate the balance between inflammation and anti-inflammation. IL-33 and IL-37 are also deeply involved in the pathogenesis of inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis. Furthermore, a signaling pathway by which aryl hydrocarbon receptor (AHR), a receptor for dioxins, regulates the expression of IL-33 and IL-37 has been revealed. Here, we outline recent findings on the mechanisms regulating IL-33 and IL-37 expression in AD and psoriasis. IL-33 expression is partially dependent on mitogen-activated protein kinase (MAPK) activation, and IL-37 has a role in suppressing MAPK in human keratinocytes. Furthermore, IL-33 downregulates skin barrier function proteins including filaggrin and loricrin, thereby downregulating the expression of IL-37, which colocalizes with these proteins. This leads to an imbalance of the IL-33-IL-37 axis, involving increased IL-33 and decreased IL-37, which may be associated with the pathogenesis of AD and psoriasis. Therefore, AHR-mediated regulation of the IL-33-IL-37 axis may lead to new therapeutic strategies for the treatment of AD and psoriasis.

Oleic acid-induced interleukin-36γ: A possible link between facial skin redness and sebum

BACKGROUND

Redness of the facial skin is an important cosmetic concern. Although qualitative and quantitative modifications of sebum on the skin surface are major pathogenic factors of chronic inflammatory skin conditions, the relationship between skin redness, sebum, and mild inflammation on the cheeks of healthy subjects remains elusive.

AIMS

We aimed to explore the correlation between cheek redness and sebum and inflammatory cytokines in the stratum corneum (SC) of healthy subjects. We also examined the effects of representative sebum lipids on the gene expression of inflammatory cytokines in cultured keratinocytes.

PATIENTS/METHODS

This study included 198 healthy participants. Skin sebum was analyzed using flow injection analysis, and skin redness was assessed using a spectrophotometer. Inflammatory cytokines in tape-stripped SC were measured using enzyme-linked immunosorbent assay.

RESULTS

Cheek redness parameters positively correlated with the amount of skin sebum and the proportion of monounsaturated free fatty acids (C16:1 and C18:1) in the sebum. They also positively correlated with the interleukin (IL)-36γ/IL-37 ratio in the SC. Among the representative sebum lipids examined, oleic acid (C18:1, cis-9) dose- and time-dependently regulated the mRNA expression of IL-36γ and IL-37 in cultured keratinocytes, and this effect was attenuated by the N-methyl-D-aspartate (NMDA)-type glutamate receptor antagonist, MK801.

CONCLUSIONS

Skin surface sebum may be related to cheek redness in healthy subjects, and oleic acid-induced IL-36γ through NMDA-type glutamate receptors may be a link between them. Our study provides a possible skincare strategy for mitigating unfavorable increase in skin redness by targeting the facial skin sebum, particularly oleic acid.

IL-33 and IL-37: A Possible Axis in Skin and Allergic Diseases

Interleukin (IL)-37 and IL-33 are among the latest cytokines identified, playing a role in several inflammatory conditions, spanning from systemic conditions to tumors to localized diseases. As newly discovered interleukins, their role is still scarcely understood, but their potential role as therapeutic targets or disease activity markers suggests the need to reorganize the current data for a better interpretation. The aim of this review is to collect and organize data produced by several studies to create a complete picture. The research was conducted on the PubMed database, and the resulting articles were sorted by title, abstract, English language, and content. Several studies have been assessed, mostly related to atopic dermatitis and immunologic pathways. Collective data demonstrates a pro-inflammatory role of IL-33 and an anti-inflammatory one for IL-37, possibly related to each other in an IL-33/IL-37 axis. Although further studies are needed to assess the safety and plausibility of targeting these two interleukins for patients affected by skin conditions, the early results indicate that both IL-33 and IL-37 represent markers of disease activity.

Natural Compounds Tapinarof and Galactomyces Ferment Filtrate Downregulate IL-33 Expression via the AHR/IL-37 Axis in Human Keratinocytes

Interleukin (IL)-37 suppresses systemic and local inflammation. It is expressed in the epidermis, the external layer of the skin, and is decreased in inflammatory skin diseases including atopic dermatitis (AD) and psoriasis. Therefore, an agent applied topically on the skin that can increase IL-37 could be promising for treating AD and psoriasis; however, the mechanism regulating IL-37 remains largely unknown. Given that IL-37 expression is induced in differentiated keratinocytes, a major component of the epidermis, and that activation of aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, promotes keratinocyte differentiation, we hypothesized that AHR might be involved in the IL-37 expression in human keratinocytes. We analyzed normal epidermal human keratinocytes (NHEKs) treated with tapinarof and Galactomyces ferment filtrate (GFF), which are potent AHR modulators. We found that tapinarof and GFF upregulated IL-37 in NHEKs, which was canceled by the knockdown of AHR using siRNA transfection, indicating that AHR mediates IL-37 expression in NHEKs. Furthermore, we found that the knockdown of IL-37 resulted in the upregulation of IL-33, an alarmin cytokine with crucial roles in the pathogenesis of AD and psoriasis. These findings suggest that IL-37 negatively regulates IL-33 expression in NHEKs. Finally, we examined whether tapinarof and GFF treatment modulates IL-33 expression in NHEKs. Such treatment inhibited IL-33 expression, which was partially reversed by the knockdown of either AHR or IL-37. Taken together, our findings provide the first evidence that tapinarof and GFF could have potential to prevent IL-33-overexpressing disorders such as AD and psoriasis via the AHR/IL-37 axis.

Quantification of Immunohistochemically Stained Cells in Skin Biopsies

Immunohistochemical quantification of inflammatory cells in skin biopsies is a valuable tool for diagnosing skin diseases and assessing treatment response. The quantification of individual cells in biopsies is time-consuming, tedious, and difficult. In this study, we presented and compared two methods for the quantification of CD8⁺ T cells in skin biopsies from patients with psoriasis using both commercial software (Adobe Photoshop) and open-source software (Qupath). In addition, we provided a detailed, step-by-step description of both methods. The methods are scalable by replacing the CD8 antibody with other antibodies to target different cells. Moreover, we investigated the correlation between quantifying CD8⁺ cells normalized to area or epidermal length and cell classifications, compared cell classifications in QuPath with threshold classifications in Photoshop, and analyzed the impact of data normalization to epidermal length or area on inflammatory cell densities in skin biopsies from patients with psoriasis. We found a satisfactory correlation between normalizing data to epidermal length and area for psoriasis skin. However, when non-lesional and lesional skin samples were compared, a significant underestimation of inflammatory cell density was found when data were normalized to area instead of epidermal length. Finally, Bland–Altman plots comparing Qupath and Photoshop to quantify inflammatory cell density demonstrated a good agreement between the two methods.

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.

Intravenous immunoglobulin-induced severe vesicular eczematous eruption successfully treated with narrow band-ultraviolet B therapy

Intravenous immunoglobulins (IVIg) are increasingly being used to treat a wide spectrum of dermatological and neurological autoimmune diseases. Although the administration of IVIg does not usually result in severe adverse reactions, side effects of IVIg reportedly occur in 6-13% of patients. Most reported cases were not severe, and IVIg is considered a relatively safe drug. Some reports described a vesicular eczematous eruption caused by IVIg that was cured by applying topical steroid ointments or systemic steroids. Herein, we present, to the best of our knowledge, the first case of severe vesicular eczematous eruption all over the body induced by IVIg that was unresponsive to topical steroid ointment and was subsequently treated with narrow band-ultraviolet B (NB-UVB) therapy successfully. NB-UVB was started at a dose of 400 mJ/cm² once a week, and swift improvement was observed. The skin rash disappeared in the first 2 months, and the pathogenesis of IVIg-induced eczematous eruption remains unelucidated. No change in eosinophils and complement levels were observed in our case. Given the increase in the widespread use of IVIg, we have shown that NB-UVB therapy is a candidate choice for the treatment of IVIg-induced severe vesicular eczematous eruption.

Shifts in the Skin Microbiota after UVB Treatment in Adult Atopic Dermatitis

BACKGROUND

The pathophysiology in atopic dermatitis (AD) is not fully understood, but immune dysfunction, skin barrier defects, and alterations of the skin microbiota are thought to play important roles. AD skin is frequently colonized with Staphylococcus aureus (S. aureus) and microbial diversity on lesional skin (LS) is reduced compared to on healthy skin. Treatment with narrow-band ultraviolet B (nb-UVB) leads to clinical improvement of the eczema and reduced abundance of S. aureus. However, in-depth knowledge of the temporal dynamics of the skin microbiota in AD in response to nb-UVB treatment is lacking and could provide important clues to decipher whether the microbial changes are primary drivers of the disease, or secondary to the inflammatory process.

OBJECTIVES

To map the temporal shifts in the microbiota of the skin, nose, and throat in adult AD patients after nb-UVB treatment.

METHODS

Skin swabs were taken from lesional AD skin (n = 16) before and after 3 treatments of nb-UVB, and after 6-8 weeks of full-body treatment. We also obtained samples from non-lesional skin (NLS) and from the nose and throat. All samples were characterized by 16S rRNA gene sequencing.

RESULTS

We observed shifts towards higher diversity in the microbiota of lesional AD skin after 6-8 weeks of treatment, while the microbiota of NLS and of the nose/throat remained unchanged. After only 3 treatments with nb-UVB, there were no significant changes in the microbiota.

CONCLUSION

Nb-UVB induces changes in the skin microbiota towards higher diversity, but the microbiota of the nose and throat are not altered.

IL-1 Family Antagonists in Mouse and Human Skin Inflammation

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.