Regulatory cells in the skin: Pathophysiologic role and potential targets for anti-inflammatory therapies

Inflammatory Memory in Epidermal Stem Cells - A New Strategy for Recurrent Inflammatory Skin Diseases

The ability of the skin to "remember" has been a potential mechanism for studying recurrent skin diseases. While it has been thought that the ability to retain past encounters is the prerogative of immune cells, it has recently been discovered that skin tissue stem cells can also take on this task. Epithelial stem cells undergoing inflammation retain their "memory" through epigenetic reprogramming and exhibit rapid epithelialization and epidermal proliferation upon secondary stimulation. This is a non-specific memory modality independent of conventional immune memory, in which histone modifications (acetylation and methylation) and specific transcription factors (AP-1 and STAT3) are involved in the establishment of inflammatory memories, and AIM2/Caspase-1/IL-1β mainly performs the rapid effects of memory. This finding is intriguing for addressing recurrent inflammatory skin diseases, which may explain the fixed-site recurrence of inflammatory skin diseases and develop new therapeutic strategies in the future. However, more research is still needed to decipher the mysteries of memory.

RBPJ Knockdown Promotes M2 Macrophage Polarization Through Mitochondrial ROS-mediated Notch1-Jagged1-Hes1 Signaling Pathway in Uveitis

Uveitis is an autoimmune eye disease that can be involved in the entire body and is one of the leading causes of blindness. Therefore, comprehending the mechanisms underlying the development and regulation of ocular immune responses in uveitis is crucial for designing effective therapeutic interventions. In this study, we investigated how RBPJ regulates macrophage polarization in uveitis. We demonstrated that targeted RBPJ knockdown (RBPJKD) promotes M2 macrophage polarization and ameliorates uveitis through the mtROS-mediated Notch1-Jagged1-Hes1 signaling pathway. Real-time quantitative (Q-PCR) analysis revealed that the Notch1-Jagged1-Hes1 signaling pathway was active in the eye tissues of experimental autoimmune uveitis (EAU) rats. Immunofluorescence double staining confirmed enhanced signaling primarily occurring in macrophages, establishing a correlation between the Notch1 signaling pathway and macrophages. Transmission electron microscopy evaluated the morphological and functional changes of mitochondria in each group's eye tissues. It demonstrated significant swelling and disorganization in the EAU group, which were effectively restored upon RBPJ knockdown intervention. Finally, by employing an antioxidant N-acetyl-L-cysteine (NAC) to eliminate mtROS in vivo, we observed a decrease in the M2 macrophage polarization level, which prevented the cytoprotective effect conferred by RBPJKD. These findings underscore the relevance of the Notch signaling pathway to the immune system while highlighting the potential role of mtROS as a therapeutic target for inflammation and other related diseases.

SPRR1B is Related to the Immune Microenvironment and Can Be Used as a Biomarker for the Diagnosis of Psoriasis

Background

Psoriasis, a chronic inflammatory disorder with an unknown cause, significantly impacts the physical and psychological well-being of patients. However, current biomarkers related to psoriasis lack clinical specificity, sensitivity, and predictive ability.

Methods

In this study, we collected skin lesion tissues from 20 psoriasis patients and 20 normal skin samples. Additionally, we obtained four datasets from the GEO database, which included human psoriasis and healthy specimens. We utilized SVM-RFE analysis and the LASSO regression model to identify potential biomarkers. Furthermore, we examined the composition of immune cell types in psoriasis and their correlation with specific genes.

Results

Our investigation revealed 57 differentially expressed genes (DEGs), and we identified significantly enriched pathways through KEGG pathway analysis. The results of machine learning and WGCNA suggested that LCE3D and SPRR1B could potentially be used as marker genes for diagnosing psoriasis. RT-PCR and immunohistochemical detection confirmed the abnormally high expression of the SPRR1B gene in psoriasis. Analysis of immune cell infiltration revealed a strong positive correlation between SPRR1B and Macrophages M0 and T cells follicular helper, while showing the strongest negative correlation with resting Mast cells. In addition, we found that silencing SPRR1B in IFN-γ-treated HaCat cells could significantly reduce the increase in IL-17, IL-22, KRT6, and KRT16 caused by IFN-γ.

Conclusion

These findings suggest that SPRR1B may have a significant role in the pathogenesis of psoriasis and could be employed as a novel immunomarker for its development.

The Involvement of Cysteine-X-Cysteine Motif Chemokine Receptors in Skin Homeostasis and the Pathogenesis of Allergic Contact Dermatitis and Psoriasis

Members of the C-X-C motif chemokine receptor (CXCR) superfamily play central roles in initiating the innate immune response in mammalian cells by orchestrating selective cell migration and immune cell activation. With its multilayered structure, the skin, which is the largest organ in the body, performs a crucial defense function, protecting the human body from harmful environmental threats and pathogens. CXCRs contribute to primary immunological defense; these receptors are differentially expressed by different types of skin cells and act as key players in initiating downstream innate immune responses. While the initiation of inflammatory responses by CXCRs is essential for pathogen elimination and tissue healing, overactivation of these receptors can enhance T-cell-mediated autoimmune responses, resulting in excessive inflammation and the development of several skin disorders, including psoriasis, atopic dermatitis, allergic contact dermatitis, vitiligo, autoimmune diseases, and skin cancers. In summary, CXCRs serve as critical links that connect innate immunity and adaptive immunity. In this article, we present the current knowledge about the functions of CXCRs in the homeostasis function of the skin and their contributions to the pathogenesis of allergic contact dermatitis and psoriasis. Furthermore, we will examine the research progress and efficacy of therapeutic approaches that target CXCRs.

The elucidation of structure-activity and structure-permeation relationships for the cutaneous delivery of phytosterols to attenuate psoriasiform inflammation

Phytosterols have been reported to exert anti-inflammatory activity. This study aimed to investigate the capacity of campesterol, β-sitosterol, and stigmasterol on the mitigation of psoriasiform inflammation. We also tried to establish structure-activity and structure-permeation relationships for these plant sterols. To support this study, we first approached the in silico data of the physicochemical properties and the molecular docking of phytosterols with stratum corneum (SC) lipids. The anti-inflammatory activity of the phytosterols was explored in the activated keratinocytes and macrophages. Using the activated keratinocyte model, a significant inhibition of IL-6 and CXCL8 overexpression by phytosterols was detected. A comparable inhibition level was found for the three phytosterols tested. The macrophage-based study showed that the anti-IL-6 and anti-CXCL8 activities of campesterol were greater than those of the other compounds, which indicated that a phytosterol structure without a double bond on C₂₂ and with methyl moiety on C₂₄ was more effective. The conditioned medium of phytosterol-treated macrophages decreased STAT3 phosphorylation in the keratinocytes, suggesting the inhibition of keratinocyte hyperproliferation. β-sitosterol was the penetrant with the highest pig skin absorption (0.33 nmol/mg), followed by campesterol (0.21 nmol/mg) and stigmasterol (0.16 nmol/mg). The therapeutic index (TI) is a parameter measured by multiplying the cytokine/chemokine suppression percentage with skin absorption for anticipating the anti-inflammatory activity after topical delivery. β-sitosterol is a potential candidate for treating psoriatic inflammation due to having the greatest TI value. In this study, β-sitosterol attenuated epidermal hyperplasia and immune cell infiltration in the psoriasis-like mouse model. The psoriasiform epidermis thickness could be reduced from 92.4 to 63.8 μm by the topical use of β-sitosterol, with a downregulation of IL-6, TNF-α, and CXCL1. The skin tolerance study manifested that the reference drug betamethasone but not β-sitosterol could generate barrier dysfunction. β-sitosterol possessed anti-inflammatory activity and facile skin transport, showing the potential for development as an anti-psoriatic agent.

GBP5 exacerbates rosacea-like skin inflammation by skewing macrophage polarization towards M1 phenotype through the NF-κB signalling pathway

BACKGROUND

Rosacea is a chronic inflammatory skin disease with increased macrophage infiltration. However, the molecular mechanism remains unclear.

OBJECTIVES

To determine the significance of macrophage infiltration, and the correlation between Guanylate-binding protein 5 (GBP5) and polarization of macrophages in rosacea-like inflammation.

METHODS

Here we tested the hypothesis that Guanylate-binding protein 5 (GBP5) aggravates rosacea-like skin inflammation by promoting the polarization of the M1 macrophages through the NF-κB signalling pathway. We depleted macrophage by injecting clodronate-containing liposomes. We next explored the association between GBP5 and macrophage in rosacea tissue through transcriptome analysis and immunofluorescence analysis. We evaluated the severity of rosacea-like skin inflammation when BALB/c mice were injected with GBP5 siRNA intradermally daily for three consecutive days. At last, to study the causality of knocking down GBP5-blunted M1 macrophage polarization, THP-1 cell was treated with GBP5 siRNA.

RESULTS

Macrophage depletion ameliorated rosacea-like skin inflammation in mice, implying the important role of macrophages in rosacea. Based on the transcriptome analysis, Guanylate-binding protein 5 (GBP5) was identified as hub gene that was associated with macrophage infiltration in rosacea. Next, we found that GBP5 expression was significantly upregulated in rosacea tissues and positively correlated with macrophage infiltration, the immunofluorescence analysis revealed the co-localization between GBP5 and macrophages. In vivo, silencing of GBP5 attenuated rosacea-like skin inflammation in the LL-37-induced mouse model and suppressed the expression of M1 signature genes such as IL-6, iNOS and TNF-a. In vitro, knocking down GBP5 significantly blunted the polarization of the M1 macrophages partly by repressing the activation of the NF-κB signalling pathways.

CONCLUSIONS

Together, our study revealed the important role of macrophages in rosacea and identified GBP5 as a key regulator of rosacea by inducing M1 macrophage polarization via NF-κB signalling pathways.

Pathogenesis-oriented therapy of psoriasis using biologics

INTRODUCTION

Psoriasis is currently regarded an immune-mediated inflammatory disease. The central pathogenic axis comprises interleukin-23, TH17-lymphocytes differentiating under its influence, and interleukin-17A as a key effector cytokine of these T-lymphocytes. All of these can selectively be targeted using biological therapies, thus potentially increasing efficacy and reducing adverse events when compared to conventional systemic therapeutics.

AREAS COVERED

We review the current concept of psoriasis as an immune-mediated inflammatory disease, assessing the evidence for a role of elements of the innate and adaptive immune system. We then correlate the pharmacological effects of biologics in psoriasis in light of the known physiologic as well as pathophysiological role of the respective targets. This is done on the basis of an extensive literature search of publications since 2018 which describe the role of the above-mentioned elements in health and disease or the effects of blocking these as an attempt to treat psoriasis.

EXPERT OPINION

Biologics targeting the above-mentioned central pathogenic axis provide a particularly effective and safe way to treat psoriasis. Given the impact of comorbidities on therapeutic decision-making, and the efficacy of some biologics also on certain comorbidities, these drugs represent a first step toward personalized medicine in the management of psoriasis.

Cytokine-Mediated Crosstalk Between Keratinocytes and T Cells in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by barrier dysfunction, dysregulated immune response, and dysbiosis with increased Staphylococcus aureus colonization. Infiltration of various T helper cell subsets into lesional skin and subsequent cytokine release are a hallmark of AD. Release of cytokines by both T cells and keratinocytes plays a key role in skin inflammation and drives many AD features. This review aims to discuss cytokine-mediated crosstalk between T cells and keratinocytes in AD pathogenesis and the potential impact of virulence factors produced by Staphylococcus aureus on these interactions.

Activity of nuclear factor κB in lymphocyte populations of children with psoriasis

Alterations in intracellular signaling pathways affecting immune cell activation, proliferation and differentiation of keratinocytes in psoriasis could explain the complex pathogenesis of the disease. NF-κB is one of the intracellular signaling pathways, which is involved in regulation of numerous pro-inflammatory genes, and affects the synthesis of pro-inflammatory cytokines directly involved in the development of psoriasis. The study was aimed to assess the number of cells with NF-κB translocation in lymphocyte populations of children with psoriasis depending in the disease severity and therapy. A total of 130 children with psoriasis vulgaris were examined. The comparison group included 30 healthy children. The study was conducted using the imaging flow cytometry Amnis ImageStreamX system. It was found that there were significant differences in the number of cells with NF-κB translocation in the lymphocyte populations of both children with psoriasis and comparison group. Children with psoriasis had a higher number of cells with NF-κB translocation in the populations of T helper cells, Tact, Treg, and Th17 compared to healthy children (p < 0.05). The number of cells with NF-κB translocation in children with psoriasis correlated with the disease severity PASI (Rmul = 0.32) and BSA (Rmul = 0.31) scores, as well as with the disease duration (p < 0.05). NF-κB determination could be considered an additional criterion for the disease severity assessment in children with psoriasis. The differences in the degree of reduction of the number of cells with NF-κB translocation 24 h after administration of biologics (adalimumab, etanercept, ustekinumab) have been shown. Studying NF-κB in cell populations offers the prospect of understanding pathogenetic mechanisms of inflammation and developing new therapeutic methods for psoriasis.

Azithromycin pretreatment exacerbates atopic dermatitis in trimellitic anhydride-induced model mice accompanied by correlated changes in the gut microbiota and serum cytokines

Atopic dermatitis (AD) is a common inflammatory skin disease. This study aims to investigate the effect of azithromycin (AZI) pretreatment, a common macrolide-type antibiotic, on the trimellitic anhydride (TMA) induced AD-like symptoms in mice. AZI (25 mg/kg, once daily, 5 days) was administered intragastrically before the 10-day TMA challenge. AD-like symptoms were assessed by ear thickening, scratching behavior, and pathological or immunofluorescence staining; Cytokines in the skin tissue and serum were measured by cytometric bead array; and the compositions of gut microbiota were assessed by 16S rRNA gene sequencing. AZI pretreatment accelerated the development of ear thickening and enhanced the severity of developed AD-like symptoms. AZI pretreatment promoted the infiltrations of neutrophil-like cells, T cells, and mast cells in ear skin. AZI pretreatment elevated the levels of IL-4, IL-6, and IL-17A in the ear skin of AD model mice, but it increased serum TNF-α and IL-6. AZI-pretreatment increased four gut bacterial genera (Bacteroides, Candidatus_Saccharibacteria_unclassified, Acetatifactor, Firmicutes_unclassified) but depleted three short-chain fatty acids producing gut bacterial genera (Alistipes, Clostridiales_unclassified, Butyricicoccus). AD-associated symptoms were positively associated with skin IL-4 and IL-17A, serum TNF-α, and IL-6, and Acetatifactor, but they negatively correlated to the three decreased gut bacterial genera (Alistipes, Clostridiales_unclassified, Butyricicoccus). Thus, our results demonstrate that AZI exposure deteriorates TMA-induced AD-like symptoms in mice, which is related to the imbalances of gut microbiota and skin/serum cytokines.

The histopathological landscape of the major psoriasiform dermatoses

Psoriasiform dermatoses represent a wide spectrum of inflammatory conditions, with several major forms represented by psoriasis, as the prototype of this category, followed by pustular psoriasis, Reiter's syndrome, pityriasis rubra pilaris, lichen simplex chronicus and large-plaques parapsoriasis. They create a diagnostic challenge, both clinical and histopathological, because of their complexity and frequent overlapping of the microscopical features. The characteristic histopathological features of psoriasiform reaction comprise extensive hyperkeratosis, with horizontally confluent but vertically intermittent parakeratosis, which alternate with orthokeratosis, thin granular layer, with relative frequent mitoses, uniform elongated and fused rete ridges, edematous superficial papillary dermis, with dilated capillaries, perivascular lymphocytic infiltrate, Munro's microabscesses, and spongiform pustules of Kogoj. Our paper aims to review the histopathology of major form of psoriasiform dermatoses and to emphasize the characteristic microscopical differences between them, for a better approach of the diagnosis as an important key for clinical and therapeutical management. Using the clinicopathological correlations, a thoroughly evaluation of the microscopical features and compartments distribution or special stainings and techniques, the range of differential diagnosis can be decreased and a more accurate diagnostic can be usually achieved. The insights into the pathogenic mechanisms can lead to new therapeutic opportunities targeted to the specific type of inflammatory lesion.

Cudraxanthone D Ameliorates Psoriasis-like Skin Inflammation in an Imiquimod-Induced Mouse Model via Inhibiting the Inflammatory Signaling Pathways

Psoriasis is a chronic inflammatory skin disease accompanied by excessive keratinocyte proliferation. Corticosteroids, vitamin D3 analogs, and calcineurin inhibitors, which are used to treat psoriasis, have diverse adverse effects, whereas natural products are popular due to their high efficiency and relatively low toxicity. The roots of the Cudrania tricuspidata (C. tricuspidata) are known to have diverse pharmacological effects, among which the anti-inflammatory effect is reported as a potential therapeutic agent in skin cells. Nevertheless, its effectiveness against skin diseases, especially psoriasis, is not fully elucidated. Here, we investigated the effect of cudraxanthone D (CD), extracted from the roots the C. tricuspidata Bureau, on psoriasis using an imiquimod (IMQ)-induced mouse model and the tumor necrosis factor (TNF)-α/interferon (IFN)-γ-activated keratinocytes. IMQ was topically applied to the back skin of C57BL/6 mice for seven consecutive days, and the mice were orally administered with CD. This resulted in reduced psoriatic characteristics, such as the skin thickness and Psoriasis Area Severity Index score, and the infiltration of neutrophils in IMQ-induced skin. CD inhibited the serum levels of TNF-α, immunoglobulin G2a, and myeloperoxidase, and the expression of Th1/Th17 cells in splenocytes. In TNF-α/IFN-γ-activated keratinocytes, CD reduced the expressions of CCL17, IL-1β, IL-6, and IL-8 by inhibiting the phosphorylation of STAT1 and the nuclear translocation of NF-kB. Taken together, these results suggest that CD could be a potential drug candidate for the treatment of psoriasis.

Psoriasiform Inflammation Is Associated with Mitochondrial Fission/GDAP1L1 Signaling in Macrophages

While psoriasis is known as a T cell- and dendritic cell-driven skin inflammation disease, macrophages are also reported to play some roles in its development. However, the signaling pathway of activated macrophages contributing to psoriasis is not entirely understood. Thus, we aimed to explore the possible mechanisms of how macrophages initiate and sustain psoriasis. The differentiated THP1 cells, stimulated by imiquimod (IMQ), were utilized as the activated macrophage model. IMQ was also employed to produce psoriasis-like lesions in mice. A transcriptomic assay of macrophages revealed that the expressions of pro-inflammatory mediators and GDAP1L1 were largely increased after an IMQ intervention. The depletion of GDAP1L1 by short hairpin (sh)RNA could inhibit cytokine release by macrophages. GDAP1L1 modulated cytokine production by activating the phosphorylation of mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-κB pathways. Besides GDAP1L1, another mitochondrial fission factor, Drp1, translocated from the cytosol to mitochondria after IMQ stimulation, followed by the mitochondrial fragmentation according to the immunofluorescence imaging. Clodronate liposomes were injected into the mice to deplete native macrophages for examining the latter’s capacity on IMQ-induced inflammation. The THP1 cells, with or without GDAP1L1 silencing, were then transplanted into the mice to monitor the deposition of macrophages. We found a significant THP1 accumulation in the skin and lymph nodes. The silencing of GDAP1L1 in IMQ-treated animals reduced the psoriasiform severity score from 8 to 2. After depleting GDAP1L1, the THP1 recruitment in the lymph nodes was decreased by 3-fold. The skin histology showed that the GDAP1L1-mediated macrophage activation induced neutrophil chemotaxis and keratinocyte hyperproliferation. Thus, mitochondrial fission can be a target for fighting against psoriatic inflammation.

Anti-Inflammatory Effects of Compounds from Cudrania tricuspidata in HaCaT Human Keratinocytes

The root bark of Cudrania tricuspidata has been reported to have anti-sclerotic, anti-inflammatory, antioxidant, neuroprotective, hepatoprotective, and cytotoxic activities. In the present study, the effect of 16 compounds from C. tricuspidata on tumor necrosis factor-α+interferon-γ-treated HaCaT cells were investigated. Among these 16 compounds, 11 decreased IL-6 production and 15 decreased IL-8 production. The six most effective compounds, namely, steppogenin (2), cudraflavone C (6), macluraxanthone B (12), 1,6,7-trihydroxy-2-(1,1-dimethyl-2-propenyl)-3- methoxyxanthone (13), cudraflavanone B (4), and cudratricusxanthone L (14), were selected for further experiments. These six compounds decreased the expression levels of chemokines, such as regulated on activation, normal T cell expressed and secreted (RANTES) and thymus and activation-regulated chemokine (TARC), and downregulated the protein expression levels of intercellular adhesion molecule-1. Compounds 2, 6, 12, 4, and 14 inhibited nuclear factor-kappa B p65 translocation to the nucleus; however, compound 13 showed no significant effects. In addition, extracellular signal regulatory kinase-1/2 phosphorylation was only inhibited by compound 14, whereas p38 phosphorylation was inhibited by compounds 13 and 4. Taken together, the compounds from C. tricuspidata showed potential to be further developed as therapeutic agents to suppress inflammation in skin cells.

2,4-Dimethoxy-6-Methylbenzene-1,3-diol, a Benzenoid From Antrodia cinnamomea, Mitigates Psoriasiform Inflammation by Suppressing MAPK/NF-κB Phosphorylation and GDAP1L1/Drp1 Translocation

Antrodia cinnamomea exhibits anti-inflammatory, antioxidant, and immunomodulatory activities. We aimed to explore the antipsoriatic potential of 2,4-dimethoxy-6-methylbenzene-1,3-diol (DMD) derived from A. cinnamomea. The macrophages activated by imiquimod (IMQ) were used as the cell model for examining the anti-inflammatory effect of DMD in vitro. A significantly high inhibition of IL-23 and IL-6 by DMD was observed in THP-1 macrophages and bone marrow-derived mouse macrophages. The conditioned medium of DMD-treated macrophages could reduce neutrophil migration and keratinocyte overproliferation. DMD could downregulate cytokine/chemokine by suppressing the phosphorylation of mitogen-activated protein kinases (MAPKs) and NF-κB. We also observed inhibition of GDAP1L1/Drp1 translocation from the cytoplasm to mitochondria by DMD intervention. Thus, mitochondrial fission could be a novel target for treating psoriatic inflammation. A psoriasiform mouse model treated by IMQ showed reduced scaling, erythema, and skin thickening after topical application of DMD. Compared to the IMQ stimulation only, the active compound decreased epidermal thickness by about 2-fold. DMD diminished the number of infiltrating macrophages and neutrophils and their related cytokine/chemokine production in the lesional skin. Immunostaining of the IMQ-treated skin demonstrated the inhibition of GDAP1LI and phosphorylated Drp1 by DMD. The present study provides insight regarding the potential use of DMD as an effective treatment modality for psoriatic inflammation.

Gardenia Jasminoides Ameliorates Antibiotic-Associated Aggravation of DNCB-Induced Atopic Dermatitis by Restoring the Intestinal Microbiome Profile

The intestinal microbiome is considered one of the key regulators of health. Accordingly, the severity of atopic dermatitis (AD) is mediated by the skin and intestinal microbiome environment. In this study, while evaluating the aggravation in AD symptoms by the antibiotics cocktail (ABX)-induced depletion of the intestinal microbiome, we sought to verify the effect of Gardenia jasminoides (GJ), a medicinal herb used for inflammatory diseases, on AD regarding its role on the intestinal microbiome. To verify the aggravation in AD symptoms induced by the depletion of the intestinal microbiome, we established a novel mouse model by administrating an ABX to create a microbiome-free environment in the intestine, and then applied 2,4-dinitrochlorobenzene (DNCB) to induce an AD-like skin inflammatory response. While ABX treatment aggravated AD-like symptoms, the 2-week administration of GJ improved these pathological changes. DNCB application upregulated immune cell count and serum cytokine expression, which were alleviated by GJ. Moreover, pathological alterations by antibiotics and DNCB, including histological damage of the intestine and the intestinal expression of IL-17, were recovered in GJ-treated mice. The beneficial effect of GJ was due to the restoration of the intestinal microbiome composition. Overall, we suggest GJ as a potential therapeutic agent for AD due to its regulation of the intestinal microbiome.

Immune responses and therapeutic options in psoriasis

Psoriasis is a chronic inflammatory disease of the skin that affects about 2-3% of the population and greatly impairs the quality of life of affected individuals. Psoriatic skin is characterized by excessive proliferation and aberrant differentiation of keratinocytes, as well as redness caused by increased dilation of the dermal blood vessels and infiltration of immune cells. Although the pathogenesis of psoriasis has not yet been completely elucidated, it is generally believed to arise from a complex interplay between hyperproliferating keratinocytes and infiltrating, activated immune cells. So far, the exact triggers that elicit this disease are still enigmatic, yet, it is clear that genetic predisposition significantly contributes to the development of psoriasis. In this review, we summarize current knowledge of important cellular and molecular mechanisms driving the initiation and amplification stages of psoriasis development, with a particular focus on cytokines and emerging evidence illustrating keratinocyte-intrinsic defects as key drivers of inflammation. We also discuss mouse models that have contributed to a better understanding of psoriasis pathogenesis and the preclinical development of novel therapeutics, including monoclonal antibodies against specific cytokines or cytokine receptors that have revolutionized the treatment of psoriasis. Future perspectives that may have the potential to push basic research and open up new avenues for therapeutic intervention are provided.

Spontaneously Resolved Atopic Dermatitis Shows Melanocyte and Immune Cell Activation Distinct From Healthy Control Skin

Atopic dermatitis (AD) typically starts in infancy or early childhood, showing spontaneous remission in a subset of patients, while others develop lifelong disease. Despite an increased understanding of AD, factors guiding its natural course are only insufficiently elucidated. We thus performed suction blistering in skin of adult patients with stable, spontaneous remission from previous moderate-to-severe AD during childhood. Samples were compared to healthy controls without personal or familial history of atopy, and to chronic, active AD lesions. Skin cells and tissue fluid obtained were used for single-cell RNA sequencing and proteomic multiplex assays, respectively. We found overall cell composition and proteomic profiles of spontaneously healed AD to be comparable to healthy control skin, without upregulation of typical AD activity markers (e.g., IL13, S100As, and KRT16). Among all cell types in spontaneously healed AD, melanocytes harbored the largest numbers of differentially expressed genes in comparison to healthy controls, with upregulation of potentially anti-inflammatory markers such as PLA2G7. Conventional T-cells also showed increases in regulatory markers, and a general skewing toward a more Th1-like phenotype. By contrast, gene expression of regulatory T-cells and keratinocytes was essentially indistinguishable from healthy skin. Melanocytes and conventional T-cells might thus contribute a specific regulatory milieu in spontaneously healed AD skin.

Profiles of Innate Immune Cell Infiltration and Related Core Genes in Psoriasis

Psoriasis is an inflammatory skin disease with substantial morbidity. Numerous patients with psoriasis experience recurrence after therapy. The underlying mechanism about psoriasis is still not fully understood. Some evidences suggest that innate immunity may play an unexpected and important role in active severe psoriasis. In this work, the deconvolution algorithm CIBERSORT was conducted to identify the infiltration of innate immune cells and related core genes in psoriatic plaque. Datasets from the Gene Expression Omnibus, including skin samples from 405 psoriasis patients and 91 healthy donors, were downloaded for analysis. Considerable differences of the innate immune cell composition were uncovered between psoriatic plaque and control skin. Results revealed that γδ T cells, resting NK cells, M0 macrophages, M1 macrophages, activated dendritic cells, and neutrophils were significantly increased in psoriatic skin, while resting mast cells and active NK cells were significantly decreased. Moreover, the proportion of M0 macrophages or resting mast cells was found to be associated with disease severity. Spearman correlation analysis suggests that RORC and S100A12 genes were related to disease severity, while genes including S100A12, CLEC4C, IL-19, AIM2, IL-17F, and PPARGC1A were correlated with biologic treatment response. In conclusion, this work displays innate immune status in psoriatic skin and provides novel clues for clinical decisions and mechanism study.

More than skin deep: using polymers to facilitate topical delivery of nitric oxide

Skin, the largest organ in the human body, provides several important functions, including providing protection from mechanical impacts, micro-organisms, radiation and chemicals; regulation of body temperature; the sensations of touch and temperature; and the synthesis of several substances including vitamin D, melanin, and keratin. Common dermatological disorders (CDDs) include inflammatory or immune-mediated skin diseases, skin infection, skin cancer, and wounds. In the treatment of skin disorders, topical administration has advantages over other routes of administration, and polymers are widely used as vehicles to facilitate the delivery of topical therapeutic agents, serving as matrices to keep therapeutic agents in contact with the skin. Nitric oxide (NO), a cellular signalling molecule, has attracted significant interest in treating a broad spectrum of diseases, including various skin disorders. However, there are a number of challenges in effectively delivering NO. It must be delivered in a controlled manner at sufficient concentrations to be efficacious and the delivery system must be stable during storage. The use of polymer-based systems to deliver NO topically can be an effective strategy to overcome these challenges. There are three main approaches for incorporating NO with polymers in topical delivery systems: (i) physical incorporation of NO donors into polymer bases; (ii) covalent attachment of NO donors to polymers; and (iii) encapsulation of NO donors in polymer-based particles. The latter two approaches provide the greatest control over NO release and have been used by numerous researchers in treating CDDs, including chronic wounds and skin cancer.

Guselkumab: the First Selective IL-23 Inhibitor for Active Psoriatic Arthritis in Adults

INTRODUCTION

Guselkumab is a subcutaneously administered human monoclonal antibody, selectively blocking IL-23 through binding to its p19 subunit. It was initially approved for the treatment of patients with moderate-to-severe plaque-psoriasis who are candidates for systemic therapy or phototherapy. Pubmed and Embase databases were searched for publications, using the following search terms: psoriasis, psoriatic arthritis, guselkumab, risankizumab, tildrakizumab, p19, interleukin 23, guidelines, treatment recommendations, DISCOVER, ECLIPSE, and VOYAGE.

AREAS COVERED

Accumulating evidence suggests that the IL-23/Th17 pathway is important in the pathogenesis of both psoriasis and psoriatic arthritis. Following a successful development program in psoriasis, guselkumab was evaluated for its efficacy and safety in psoriatic arthritis in a comprehensive clinical trial program, comprising one phase-2 study and two phase-3 studies (DISCOVER-1 and -2). Complementary data on pharmacokinetics and safety exist from pre-clinical experiments and pooled analyses from two long-term studies in psoriasis (VOYAGE-1 and -2). Based on the DISCOVER-1 and -2 data, guselkumab was approved by the FDA for the treatment of active psoriatic arthritis in 2020.

EXPERT OPINION

Guselkumab is the first selective IL-23 inhibitor approved to treat adults with active psoriatic arthritis, broadening therapeutic options in the field through a novel mode of action.

Extracellular vesicles in Inflammatory Skin Disorders: from Pathophysiology to Treatment

Extracellular vesicles (EVs), naturally secreted by almost all known cell types into extracellular space, can transfer their bioactive cargos of nucleic acids and proteins to recipient cells, mediating cell-cell communication. Thus, they participate in many pathogenic processes including immune regulation, cell proliferation and differentiation, cell death, angiogenesis, among others. Cumulative evidence has shown the important regulatory effects of EVs on the initiation and progression of inflammation, autoimmunity, and cancer. In dermatology, recent studies indicate that EVs play key immunomodulatory roles in inflammatory skin disorders, including psoriasis, atopic dermatitis, lichen planus, bullous pemphigoid, systemic lupus erythematosus, and wound healing. Importantly, EVs can be used as biomarkers of pathophysiological states and/or therapeutic agents, both as carriers of drugs or even as a drug by themselves. In this review, we will summarize current research advances of EVs from different cells and their implications in inflammatory skin disorders, and further discuss their future applications, updated techniques, and challenges in clinical translational medicine.

Guselkumab in patients with active psoriatic arthritis who were biologic-naive or had previously received TNFα inhibitor treatment (DISCOVER-1): a double-blind, randomised, placebo-controlled phase 3 trial

BACKGROUND

Many patients with psoriatic arthritis have an inadequate response to tumor necrosis factor (TNF) inhibitors. Guselkumab, a specific inhibitor of interleukin-23 (IL-23) via IL-23 p19 subunit binding, significantly improved psoriatic arthritis signs and symptoms with an acceptable safety profile in a phase 2 trial.

METHODS

This multicentre, double-blind, randomised, placebo-controlled, phase 3 trial was done at 86 sites in 13 countries across Asia, Australasia, Europe, and North America and enrolled adults with active psoriatic arthritis (at least three swollen and three tender joints; and C-reactive protein ≥0·3 mg/dL) despite standard therapies. Eligibility criteria included inadequate response to or intolerance of standard treatment, including at least 4 months of apremilast, at least 3 months of non-biologic disease-modifying antirheumatic drugs (DMARDs), or at least 4 weeks of non-steroidal anti-inflammatory drugs for psoriatic arthritis. About 30% of study participants could have previously received one or two TNF inhibitors. Patients were randomly assigned (1:1:1, computer-generated permuted blocks; stratified by baseline DMARD and previous TNF inhibitor use) to subcutaneous guselkumab 100 mg every 4 weeks; guselkumab 100 mg at weeks 0, 4, then every 8 weeks; or matching placebo. The primary endpoint was American College of Rheumatology 20% improvement (ACR20) at week 24 in all patients per assigned treatment group using non-responder imputation. Safety was assessed in all patients per treatment received. This trial is registered at ClinicalTrials.gov, NCT03162796 (active, not recruiting).

FINDINGS

From Aug 28, 2017, to Aug 17, 2018, we screened 624 patients, of whom 381 were randomly assigned and treated with guselkumab every 4 weeks (n=128), guselkumab every 8 weeks (n=127), or placebo (n=126). 362 patients continued study treatment up to week 24. The primary endpoint was met: ACR20 at week 24 was achieved by significantly greater proportions of patients in the guselkumab every 4 weeks group (76 [59%] of 128 [95% CI 50-68]) and every 8 weeks group (66 [52%] of 127 [43-61]) than in the placebo group (28 [22%] of 126 [15-30]), with percentage differences versus placebo of 37% (95% CI 26-48) for the every 4 weeks group and 30% (19-41) for the every 8 weeks group (both p<0·0001). Serious adverse events up to week 24 occurred in no patients receiving guselkumab every 4 weeks, four (3%) patients receiving guselkumab every 8 weeks, and five (4%) patients receiving placebo. Up to week 24, one patient in the placebo group died from cardiac failure and two had serious infections; no guselkumab-treated patient died or had serious infections.

INTERPRETATION

Guselkumab demonstrated a favourable benefit-risk profile and might be an effective treatment option for patients with active psoriatic arthritis.

FUNDING

Janssen Research and Development.

CD200-CD200R1 signalling attenuates imiquimod-induced psoriatic inflammation by inhibiting the activation of skin inflammatory macrophages

Psoriasis is an autoimmune skin disease caused by interactions between keratinocytes and immune cells, such as macrophages. CD200 is expressed on the surface of various cell types, and its receptor, CD200R1, belongs to a family of immunosuppressive receptors that are mainly expressed on myeloid cells. CD200/CD200R1 signalling is associated with the prevention of autoimmune diseases; however, the role of CD200/CD200R1 signalling in the pathogenesis of psoriasis remains unknown. In this study, we detected in vivo effect of the CD200 protein on psoriasis and in vitro effects of CD200 on macrophages and keratinocytes co-cultured with macrophages were also evaluated. Our data showed that the expression of CD200 and CD200R1 was decreased and the expression of macrophage-related pro-inflammatory factors (IL-6, IL-1β, TNF-α) was increased in IMQ-induced psoriasis-like skin of mice. After subcutaneous injection of CD200, the symptoms were alleviated, local expression of CD200R1 was markedly induced, infiltrated CD68⁺ cells were significantly reduced and the expression levels of IL-6, IL-1β, and TNF-α were strongly downregulated. In in vitro experiments, CD200 suppressed the migration of macrophages, induced CD200R1 expression on the surface of macrophages, and decreased the levels of pro-inflammatory factors. Western blot (WB) data showed that the CD200-CD200R1 reaction controlled the activation of inflammatory macrophages by inhibiting the NF-κB signalling pathway. These results demonstrate that CD200-CD200R1 signalling can reduce IMQ-induced psoriasis-like skin inflammation by inhibiting the activation of macrophages.

Autoreactive T-Lymphocytes in Inflammatory Skin Diseases

The presence of one or several autoantigen(s) and a response by the adaptive immune system are the key criteria to classify a pathology as an autoimmune disease. The list of entities fulfilling this criterion is currently growing in the light of recent advancements in the pathogenetic understanding of a number of important dermatoses. The role of autoreactive T-lymphocytes differs amongst these pathologies. While they are directly involved as effector cells attacking and sometimes killing their respective target in some diseases (e.g., vitiligo), they provide help to B-lymphocytes, which in turn produce the pathogenic autoreactive antibodies in others (pemphigus and pemphigoid). Atopic dermatits is a chimera in this regard, as there is evidence for both functions. Psoriasis is an example for an entity where autoantigens were finally identified, suggesting that at least a subgroup of patients should be classified as suffering from a true autoimmune rather than autoinflammatory condition. Identification of resident memory T-lymphocytes (T_RM) helped to understand why certain diseases relapse at the same site after seemingly effective therapy. Therefore, the in-depth characterization of autoreactive T-lyphocytes goes way beyond an academic exercise and opens the door toward improved therapies yielding durable responses. T_RM are particularly suitable targets in this regard, and the clinical efficacy of some established and emerging therapeutic strategies such as the inhibition of Janus Kinase 3 or interleukin 15 may rely on their capacity to prevent T_RM differentiation and maintenance. Research in this field brings us closer to the ultimate goal in the management of autoimmunity at large, namely resetting the immune system in order to restore the state of tolerance.