Macrophage Functions in Psoriasis: Lessons from Mouse Models

Psoriasis is a systemic autoimmune/autoinflammatory disease that can be well studied in established mouse models. Skin-resident macrophages are classified into epidermal Langerhans cells and dermal macrophages and are involved in innate immunity, orchestration of adaptive immunity, and maintenance of tissue homeostasis due to their ability to constantly shift their phenotype and adapt to the current microenvironment. Consequently, both macrophage populations play dual roles in psoriasis. In some circumstances, pro-inflammatory activated macrophages and Langerhans cells trigger psoriatic inflammation, while in other cases their anti-inflammatory stimulation results in amelioration of the disease. These features make macrophages interesting candidates for modern therapeutic strategies. Owing to the significant progress in knowledge, our review article summarizes current achievements and indicates future research directions to better understand the function of macrophages in psoriasis.

The Immunology of Psoriasis-Current Concepts in Pathogenesis

Psoriasis is one of the most common inflammatory skin diseases with a chronic, relapsing-remitting course. The last decades of intense research uncovered a pathological network of interactions between immune cells and other types of cells in the pathogenesis of psoriasis. Emerging evidence indicates that dendritic cells, TH17 cells, and keratinocytes constitute a pathogenic triad in psoriasis. Dendritic cells produce TNF-α and IL-23 to promote T cell differentiation toward TH17 cells that produce key psoriatic cytokines IL-17, IFN-γ, and IL-22. Their activity results in skin inflammation and activation and hyperproliferation of keratinocytes. In addition, other cells and signaling pathways are implicated in the pathogenesis of psoriasis, including TH9 cells, TH22 cells, CD8+ cytotoxic cells, neutrophils, γδ T cells, and cytokines and chemokines secreted by them. New insights from high-throughput analysis of lesional skin identified novel signaling pathways and cell populations involved in the pathogenesis. These studies not only expanded our knowledge about the mechanisms of immune response and the pathogenesis of psoriasis but also resulted in a revolution in the clinical management of patients with psoriasis. Thus, understanding the mechanisms of immune response in psoriatic inflammation is crucial for further studies, the development of novel therapeutic strategies, and the clinical management of psoriasis patients. The aim of the review was to comprehensively present the dysregulation of immune response in psoriasis with an emphasis on recent findings. Here, we described the role of immune cells, including T cells, B cells, dendritic cells, neutrophils, monocytes, mast cells, and innate lymphoid cells (ILCs), as well as non-immune cells, including keratinocytes, fibroblasts, endothelial cells, and platelets in the initiation, development, and progression of psoriasis.

3,3'-Diindolylmethane inhibits Th17 cell differentiation via impairing IRF-7-mediated plasmacytoid dendritic cell activation in imiquimod-induced psoriasis mice

Psoriasis is a paradigmatic condition characterised by a heightened autoimmune response and chronic inflammation. However, the exact nature and the pathological causes behind it are still unknown. Growing evidence suggest dysregulated cytokine network as a result of over-activated T cells and plasmacytoid dendritic cells (pDCs) as the critical drivers in the development of psoriasis. In the present study, we aimed to investigate the therapeutic efficacy of 3,3'-diindolylmethane (DIM) on pDC activation and Th17 cell development in imiquimod (IMQ)-induced psoriasis mice. Our in vitro research investigated the IRF-7 signalling in pDCs that explained the reduced expression of the transcription factor IRF-7 responsible for pDC activation as a result of DIM treatment. Concurrently, DIM treatment decreased the release of Th17 cell polarising cytokines (IFN-α, IL-23, and IL-6) by pDCs which validated a reduction in differentiated pathogenic Th17 cell population and associated cytokine IL-17A in IMQ-induced psoriatic mice. Thus, our recent findings provide therapeutic evidence in targeting the early potential contributors for psoriasis treatment by preventing IRF-7-mediated pDC activation and Th17 cell development in IMQ-induced psoriasis mice.

3D-QSAR pharmacophore modeling, virtual screening, molecular docking, MD simulations, in vitro and in vivo studies to identify potential anti-hyperplasia drugs

Psoriasis is a common immune-mediated skin condition characterized by aberrant keratinocytes and cell proliferation. The purpose of this study was to explore the FDA-approved drugs by 3D-QSAR pharmacophore model and evaluate their efficiency by in-silico, in vitro, and in vivo psoriasis animal model. A 3D-QSAR pharmacophore model was developed by utilizing HypoGen algorithm using the structural features of 48 diaryl derivatives with diverse molecular patterns. The model was validated by a test set of 27 compounds, by cost analysis method, and Fischer's randomization test. The correlation coefficient of the best model (Hypo2) was 0.9601 for the training set while it was 0.805 for the test set. The selected model was taken as a 3D query for the virtual screening of over 3000 FDA-approved drugs. Compounds mapped with the pharmacophore model were further screened through molecular docking. The hits that showed the best docking results were screened through in silico skin toxicity approach. Top five hits were selected for the MD simulation studies. Based on MD simulations results, the best two hit molecules, that is, ebastine (Ebs) and mebeverine (Mbv) were selected for in vitro and in vivo antioxidant studies performed in mice. TNF-α and COX pro-inflammatory mediators, biochemical assays, histopathological analyses, and immunohistochemistry observations confirmed the anti-inflammatory response of the selected drugs. Based on these findings, it appeared that Ebs can effectively treat psoriasis-like skin lesions and down-regulate inflammatory responses which was consistent with docking predictions and could potentially be employed for further research on inflammation-related skin illnesses such as psoriasis.

Inflammatory macrophages reprogram to immunosuppression by reducing mitochondrial translation

Acute inflammation can either resolve through immunosuppression or persist, leading to chronic inflammation. These transitions are driven by distinct molecular and metabolic reprogramming of immune cells. The anti-diabetic drug Metformin inhibits acute and chronic inflammation through mechanisms still not fully understood. Here, we report that the anti-inflammatory and reactive-oxygen-species-inhibiting effects of Metformin depend on the expression of the plasticity factor ZEB1 in macrophages. Using mice lacking Zeb1 in their myeloid cells and human patient samples, we show that ZEB1 plays a dual role, being essential in both initiating and resolving inflammation by inducing macrophages to transition into an immunosuppressed state. ZEB1 mediates these diverging effects in inflammation and immunosuppression by modulating mitochondrial content through activation of autophagy and inhibition of mitochondrial protein translation. During the transition from inflammation to immunosuppression, Metformin mimics the metabolic reprogramming of myeloid cells induced by ZEB1. Mechanistically, in immunosuppression, ZEB1 inhibits amino acid uptake, leading to downregulation of mTORC1 signalling and a decrease in mitochondrial translation in macrophages. These results identify ZEB1 as a driver of myeloid cell metabolic plasticity, suggesting that targeting its expression and function could serve as a strategy to modulate dysregulated inflammation and immunosuppression.

Forward genetics and functional analysis highlight Itga11 as a modulator of murine psoriasiform dermatitis

Psoriasis is a chronic inflammatory skin condition. Repeated epicutaneous application of Aldara® (imiquimod) cream results in psoriasiform dermatitis in mice. The Aldara®-induced psoriasiform dermatitis (AIPD) mouse model has been used to examine the pathogenesis of psoriasis. Here, we used a forward genetics approach in which we compared AIPD that developed in 13 different inbred mouse strains to identify genes and pathways that modulated disease severity. Among our primary results, we found that the severity of AIPD differed substantially between different strains of inbred mice and that these variations were associated with polymorphisms in Itga11. The Itga11 gene encodes the integrin α11 subunit that heterodimerizes with the integrin β1 subunit to form integrin α11β1. Less information is available about the function of ITGA11 in skin inflammation; however, a role in the regulation of cutaneous wound healing, specifically the development of dermal fibrosis, has been described. Experiments performed with Itga11 gene-deleted (Itga11-/- ) mice revealed that the integrin α11 subunit contributes substantially to the clinical phenotype as well as the histopathological and molecular findings associated with skin inflammation characteristic of AIPD. Although the skin transcriptomes of Itga11-/- and WT mice do not differ from one another under physiological conditions, distinct transcriptomes emerge in these strains in response to the induction of AIPD. Most of the differentially expressed genes contributed to extracellular matrix organization, immune system, and metabolism of lipids pathways. Consistent with these findings, we detected a reduced number of fibroblasts and inflammatory cells, including macrophages, T cells, and tissue-resident memory T cells in skin samples from Itga11-/- mice in response to AIPD induction. Collectively, our results reveal that Itga11 plays a critical role in promoting skin inflammation in AIPD and thus might be targeted for the development of novel therapeutics for psoriasiform skin conditions. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Keratinoctye-neuro-immune-units (KNICUs): collaborative impact on the initiation and maintenance of psoriasis

The skin is the outermost barrier that separates the human body from the external environment. In psoriasis, immune cells reside within or infiltrate the epidermis to form the epidermal (epithelial) immunological microenvironment (EIME) and engage in complex interactions with keratinocytes, nerves, and microbiota. The proposed hypothesis is that psoriasis is a chronic inflammatory disease mainly mediated by a specific inflammatory environment composed of keratinocyte-neuro-immune cell units (KNICUs). These KNICUs arise from the interaction between activated epidermal keratinocytes, nerves, immune cells, and the skin microbiota, forming a complex interaction framework. Multiple units gather to complete the circulatory and amplified loops, consequently serving as a group army to initiate and maintain psoriasis.

IL-33-mediated activation of mast cells is involved in the progression of imiquimod-induced psoriasis-like dermatitis

BACKGROUND

Psoriasis is a chronic inflammatory dermatosis with an unclear pathogenesis. Mast cells (MCs) can serve as a bridge between innate and adaptive immunity and are involved in the regulation of the inflammatory state and immune homeostasis in diseases. MCs constitutively express interleukin-33 receptor T1/ST2 (IL-33R). IL-33 is a potent MCs activator that is actively secreted by keratinocytes in psoriasis. However, the regulatory role of MCs in psoriasis remains uncertain. Therefore, we hypothesised that IL-33 could promote MC activation to regulate psoriasis development.

METHODS

We performed experiments on wild-type (WT) and MC-deficient (Kit Wsh/Wsh) mice, established psoriasis-like mouse models using imiquimod (IMQ), and performed RNA sequencing and transcriptomic analysis of skin lesions. Exogenous administration was performed using recombinant IL-33. Validation and evaluation were performed using PSI scoring, immunofluorescence, immunohistochemistry, and qPCR.

RESULTS

We observed an upregulation in the number and activation of MCs in patients with psoriasis and in IMQ-induced psoriasis-like dermatitis. Deficiency of MCs ameliorates IMQ-induced psoriatic dermatitis at an early stage. IL-33 is increased and co-localized with MCs in the dermis of psoriasis-like lesions using immunofluorescence. Compared to WT mice, IMQ-induced Kit^Wsh/Wsh mice demonstrated a delayed response to exogenous IL-33.

CONCLUSIONS

MCs are activated by IL-33 in the early stages of psoriasis and exacerbate psoriasis-associated skin inflammation. The regulation of MC homeostasis may be a potential therapeutic strategy for psoriasis. Video Abstract.

Human dental pulp stem cells ameliorate the imiquimod-induced psoriasis in mice

Psoriasis is an autoimmune disease, which has a significant impact on the quality of patient's life. And, there is still no cure for psoriasis. The human dental pulp stem cell (hDPSC) possesses the properties of immunoregulation. In this study, we aimed to determine the effect of hDPSC on the imiquimod (IMQ)-induced psoriasis in mice. The psoriasis model was established by topical application of IMQ cream in mice for 7 days. We found that subcutaneous injection of hDPSC could reduce the symptoms of skin lesions in IMQ-induced psoriasis and suppress the expression of keratin 16, S100A8, S100A9, which are associated with abnormal epidermal proliferation. Subepithelial inflammatory cytokines, CD4⁺ T lymphocytes and CD11c⁺ dendritic cells infiltrations were significantly inhibited in by hDPSC. The TNF-α, IFN-γ expressions in serum were decreased, and splenomegaly induced by IMQ was improved after hDPSC treatment. In summary, our study demonstrated that hDPSC could reduce the symptoms of skin lesions and suppress local and systemic immune responses of IMQ-induced psoriasis in mice, which might provide a new sight for the treatment of psoriasis.

Pathogenesis, multi-omics research, and clinical treatment of psoriasis

Psoriasis is a common inflammatory skin disease involving interactions between keratinocytes and immune cells that significantly affects the quality of life. It is characterized by hyperproliferation and abnormal differentiation of keratinocytes and excessive infiltration of immune cells in the dermis and epidermis. The immune mechanism underlying this disease has been elucidated in the past few years. Research shows that psoriasis is regulated by the complex interactions among immune cells, such as keratinocytes, dendritic cells, T lymphocytes, neutrophils, macrophages, natural killer cells, mast cells, and other immune cells. An increasing number of signaling pathways have been found to be involved in the pathogenesis of psoriasis, which has prompted the search for new treatment targets. In the past decades, studies on the pathogenesis of psoriasis have focused on the development of targeted and highly effective therapies. In this review, we have discussed the relationship between various types of immune cells and psoriasis and summarized the major signaling pathways involved in the pathogenesis of psoriasis, including the PI3K/AKT/mTOR, JAK-STAT, JNK, and WNT pathways. In addition, we have discussed the results of the latest omics research on psoriasis and the epigenetics of the disease, which provide insights regarding its pathogenesis and therapeutic prospects; we have also summarized its treatment strategies and observations of clinical trials. In this paper, the various aspects of psoriasis are described in detail, and the limitations of the current treatment methods are emphasized. It is necessary to improve and innovate treatment methods from the molecular level of pathogenesis, and further provide new ideas for the treatment and research of psoriasis.

Calcium/calmodulin-dependent protein kinase IV promotes imiquimod-induced psoriatic inflammation via macrophages and keratinocytes in mice

CaMK4 has an important function in autoimmune diseases, and the contribution of CaMK4 in psoriasis remains obscure. Here, we show that CaMK4 expression is significantly increased in psoriatic lesional skin from psoriasis patients compared to healthy human skin as well as inflamed skin from an imiquimod (IMQ)-induced mouse model of psoriasis compared to healthy mouse skin. Camk4-deficient (Camk4^−/−) mice treated with IMQ exhibit reduced severity of psoriasis compared to wild-type (WT) mice. There are more macrophages and fewer IL-17A⁺γδ TCR⁺ cells in the skin of IMQ-treated Camk4^−/− mice compared to IMQ-treated WT mice. CaMK4 inhibits IL-10 production by macrophages, thus allowing excessive psoriatic inflammation. Deletion of Camk4 in macrophages alleviates IMQ-induced psoriatic inflammation in mice. In keratinocytes, CaMK4 inhibits apoptosis as well as promotes cell proliferation and the expression of pro-inflammatory genes such as S100A8 and CAMP. Taken together, these data indicate that CaMK4 regulates IMQ-induced psoriasis by sustaining inflammation and provides a potential target for psoriasis treatment.

Calcium/calmodulin-dependent protein kinase IV (CaMK4) has been shown to be involved in autoimmunity but it is not clear how it functions in psoriasis. Here the authors show that CaMK4 is increased in psoriasis and promotes inflammatory responses in mouse models of psoriasis mediated through macrophages and keratinocytes.

Brevilin A Ameliorates Imiquimod-Induced Psoriasis-like Dermatitis and Reduces Th17 Differentiation in Psoriasis Patients

Psoriasis is a predominantly Th17 cell-driven chronic autoinflammatory skin disorder. Brevilin A, a natural sesquiterpene lactone extracted from Centipeda minima, has been used as a traditional oriental medicine for allergic diseases for centuries. However, the effects of brevilin A on psoriasis have yet to be established. In this study, we investigated brevilin A to elucidate its potential effects on T cell activities in psoriasis, in animal models and patients. An imiquimod (IMQ)-induced psoriasis-like dermatitis murine model was utilized. Experimental mice were administered different doses of brevilin A (5, 10, 20 mg/kg respectively) for a duration of 5 days. Cutaneous manifestations were measured daily. Under hematoxylin and eosin (H&E) stain and immunohistochemistry (IHC), acanthosis and proinflammatory cytokine expression in the dorsal skin of mice were detected. Enzyme-linked immunosorbent assay (ELISA) was used for the measurement of IL-17A levels in serum samples. Naïve CD4+ T cells, isolated from mice spleen and lymph nodes and from peripheral blood mononuclear cells (PBMCs) of psoriatic patients, were used to evaluate the effects of brevilin A on Th17 differentiation. In brevilin A-treated mice, brevilin A significantly reduced skin redness and scaling; acanthosis as well as IL-6, IL-17A, and ki-67 expressions were downregulated in the dorsal skin, and serum levels of IL-17A were lowered. Brevilin A also inhibited Th17 differentiation. In conclusion, brevilin A demonstrated significant capability in ameliorating skin inflammation in IMQ-induced psoriasis-like dermatitis and could modulate Th17 differentiation. Therefore, brevilin A is potentially pharmacologically effective in the treatment of psoriasis.

The Roles of Skin Langerhans Cells in Immune Tolerance and Cancer Immunity

Langerhans cells (LC) are a unique population of tissue-resident macrophages with dendritic cell (DC) functionality that form a network of cells across the epidermis of the skin. Their location at the skin barrier suggests an important role for LC as immune sentinels at the skin surface. The classification of LC as DC over the past few decades has driven the scientific community to extensively study how LC function as DC-like cells that prime T cell immunity. However, LC are a unique type of tissue-resident macrophages, and recent evidence also supports an immunoregulatory role of LC at steady state and during specific inflammatory conditions, highlighting the impact of cutaneous environment in shaping LC functionality. In this mini review, we discuss the recent literature on the immune tolerance function of LC in homeostasis and disease conditions, including malignant transformation and progression; as well as LC functional plasticity for adaption to microenvironmental cues and the potential connection between LC population heterogeneity and functional diversity. Future investigation into the molecular mechanisms that LC use to integrate different microenvironment cues and adapt immunological responses for controlling LC functional plasticity is needed for future breakthroughs in tumor immunology, vaccine development, and treatments for inflammatory skin diseases.

Dendritic Cells and Macrophages in the Pathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by scaly indurated erythema. This disease impairs patients’ quality of life enormously. Pathological findings demonstrate proliferation and abnormal differentiation of keratinocytes and massive infiltration of inflammatory immune cells. The pathogenesis of psoriasis is complicated. Among immune cells, dendritic cells play a pivotal role in the development of psoriasis in both the initiation and the maintenance phases. In addition, it has been indicated that macrophages contribute to the pathogenesis of psoriasis especially in the initiation phase, although studies on macrophages are limited. In this article, we review the roles of dendritic cells and macrophages in the pathogenesis of psoriasis.

Langerhans cells are an essential cellular intermediary in chronic dermatitis

SHARPIN regulates signaling from the tumor necrosis factor (TNF) superfamily and pattern-recognition receptors. An inactivating Sharpin mutation in mice causes TNF-mediated dermatitis. Blocking cell death prevents the phenotype, implicating TNFR1-induced cell death in causing the skin disease. However, the source of TNF that drives dermatitis is unknown. Immune cells are a potent source of TNF in vivo and feature prominently in the skin pathology; however, T cells, B cells, and eosinophils are dispensable for the skin phenotype. We use targeted in vivo cell ablation, immune profiling, and extensive imaging to identify immune populations driving dermatitis. We find that systemic depletion of Langerin⁺ cells significantly reduces disease severity. This is enhanced in mice that lack Langerhans cells (LCs) from soon after birth. Reconstitution of LC-depleted Sharpin mutant mice with TNF-deficient LCs prevents dermatitis, implicating LCs as a potential cellular source of pathogenic TNF and highlighting a T cell-independent role in driving skin inflammation.

Loss of epidermal Langerhans cells in psoriasiform lesions of de novo induced or worsened pre-existing psoriasis following uses of immune checkpoint inhibitors

Immune checkpoint inhibitors (ICI), including monoclonal antibodies to programmed death 1, programmed death ligand 1, and cytotoxic T lymphocyte-associated antigen 4, have provided great therapeutic benefits for cancer patients at advanced stages. However, the introduction of ICI frequently results in the development of immune-related adverse events (irAE) through activation of autoreactive T cells. Here, we present three cases of cancer patients with cutaneous irAE, including development of de novo psoriasis and exacerbation of pre-existing psoriasis. Interestingly, these patients shared an altered histological feature characterized by loss of epidermal CD1a⁺ cells, namely Langerhans cells (LC), in the psoriasiform lesions in contrast to "conventional psoriasis" exhibiting unchanged or activated LC. A possible underlying mechanism was that ICI-mediated hyperactivation of effector T cells contributed to aggravation or establishment of psoriasis phenotype, which might be associated with direct cytotoxicity or expulsion of LC from the epidermis.

Relationship between Immune Cells, Depression, Stress, and Psoriasis: Could the Use of Natural Products Be Helpful?

Psoriasis is one of the most widespread chronic inflammatory skin diseases, affecting about 2%-3% of the worldwide adult population. The pathogenesis of this disease is quite complex, but an interaction between genetic and environmental factors has been recognized with an essential modulation of inflammatory and immune responses in affected patients. Psoriatic plaques generally represent the clinical psoriatic feature resulting from an abnormal proliferation and differentiation of keratinocytes, which cause dermal hyperplasia, skin infiltration of immune cells, and increased capillarity. Some scientific pieces of evidence have reported that psychological stress may play a key role in psoriasis, and the disease itself may cause stress conditions in patients, thus reproducing a vicious cycle. The present review aims at examining immune cell involvement in psoriasis and the relationship of depression and stress in its pathogenesis and development. In addition, this review contains a focus on the possible use of natural products, thus pointing out their mechanism of action in order to counteract clinical and psychological symptoms.

Hydrogel-mediated topical delivery of steroids can effectively alleviate psoriasis via attenuating the autoimmune responses

Psoriasis is a systemic, relapsing, and chronic autoimmune inflammatory disease of the skin. Topical use of betamethasone, a glucocorticoid, in the form of creams is a common treatment for psoriasis. However, topical use of these creams is challenging due to the ineffective entrapment of steroids, burst release of the entrapped drugs, poor skin permeability, and high toxicity. Herein, we present the engineering of a betamethasone-loaded topical hydrogel (B-Gel) that can efficiently entrap steroids with high spreadability, and can also maintain the sustained release of drugs. We used an imiquimod (IMQ) induced ear psoriasis model, and demonstrated that topical application of B-Gel can mitigate the autoimmune inflammation reactions, and leads to a reduction in erythema, induration, scaling, and ear thickness. As interleukin 17 (IL-17) secreting T helper 17 (Th17) cells and γδ⁺ T cells are responsible for psoriasis, B-Gel treatment witnessed a reduction in the infiltration of leukocytes, CD4⁺ T cells, Th17 T cells, and dermal γδ⁺ T cells. We further demonstrated that B-Gel mediated reduction of IL-1β, IL-17, and K16 (marker for keratinocyte proliferation) is responsible for alleviation of psoriasis. Therefore, the non-greasy nature of the hydrogel with a cooling effect provides an alternative for topical application of steroids.

Enhanced Skin Delivery of Therapeutic Peptides Using Spicule-Based Topical Delivery Systems

This study reports two therapeutic peptides, insulin (INS, as a hydrophilic model peptide) and cyclosporine A (CysA, as a hydrophobic one), that can be administrated through a transdermal or dermal route by using spicule-based topical delivery systems in vitro and in vivo. We obtained a series of spicules with different shapes and sizes from five kinds of marine sponges and found a good correlation between the skin permeability enhancement induced by these spicules and their aspect ratio L/D. In the case of INS, Sponge Haliclona sp. spicules (SHS) dramatically increased the transdermal flux of INS (457.0 ± 32.3 ng/cm²/h) compared to its passive penetration (5.0 ± 2.2 ng/cm²/h) in vitro. Further, SHS treatment slowly and gradually reduced blood glucose to 13.1 ± 6.3% of the initial level in 8 h, while subcutaneous injection resulted in a rapid blood glucose reduction to 15.9 ± 1.4% of the initial level in 4 h, followed by a rise back to 75.1 ± 24.0% of the initial level in 8 h. In the case of CysA, SHS in combination with ethosomes (SpEt) significantly (p < 0.05) increased the accumulation of CysA in viable epidermis compared to other groups. Further, SpEt reduced the epidermis thickness by 41.5 ± 9.4% in 7 days, which was significantly more effective than all other groups. Spicule-based topical delivery systems offer promising strategies for delivering therapeutic peptides via a transdermal or dermal route.

Methodological shortcomings in the reports of the imiquimod psoriatic model

Psoriasis is a chronic inflammatory skin disease affecting about 2-3% of the worldwide population. More of the knowledge of psoriasis is due to the in vitro and in vivo models tried to reproduce the disease and to know the mechanisms of pathogenesis, as well as to develop new therapies. One of the more simple, cheap and more used models is the imiquimod model based on the application of imiquimod in the depilated skin of mice. Several studies describing the methodology employed to develop an animal disease model does not present all the details about the model more especially related to the use of one sex or another and other methodological aspects that are relevant for researchers and to consider the accuracy of the study. In this review, we have selected 100 papers published in the last five years using the imiquimod psoriatic model recording different data such as animal, strain, sex, dose of imiquimod, area of administration, housing information, anaesthesia/euthanasia information, number of animals per group and control details among others. Our results revealed several methodological shortcomings in the models of imiquimod to study psoriasis namely sex bias and discrepancies in dose applied or time of imiquimod application among others. As long as these discrepancies exist in animal methodologies, there will be a poor translation from animal studies to clinical applications in dermatology and in other areas.

Skin Barrier Dysregulation in Psoriasis

The skin barrier is broadly composed of two elements-a physical barrier mostly localised in the epidermis, and an immune barrier localised in both the dermis and epidermis. These two systems interact cooperatively to maintain skin homeostasis and overall human health. However, if dysregulated, several skin diseases may arise. Psoriasis is one of the most prevalent skin diseases associated with disrupted barrier function. It is characterised by the formation of psoriatic lesions, the aberrant differentiation and proliferation of keratinocytes, and excessive inflammation. In this review, we summarize recent discoveries in disease pathogenesis, including the contribution of keratinocytes, immune cells, genetic and environmental factors, and how they advance current and future treatments.

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.

Differential Psoriatic Effect of Imiquimod on Balb/c and Swiss Mice

Introduction The influence of animal strain on psoriasis model development by imiquimod (IMQ) has been studied in Balb/c and Swiss mice.

Materials and Methods Female mice of either strain were challenged with 5% IMQ (62.5 mg on back skin, 10 mg on right ear). They were observed for the severity of the disease using Psoriasis area severity index (PASI), splenomegaly, and histopathological alterations. To validate the model, well-established antipsoriatic drug clobetasol (0.05%, 120 mg on the back skin, 10 mg on the right ear) was used. Additionally, to study the strain-dependent response to IMQ associated with oxidative stress, various antioxidant factors like superoxide dismutase (SOD), catalase (CT), and glutathione (GSH) were measured. Antioxidant natural product curcumin (1%, 150 mg on back skin, 12.5 mg on right ear) was used to evaluate the alleviation of oxidative stress on distinct mice strain.

Results PASI score, body weight, and histopathology indicated the development of disease in both the strains, severity, and stability of which was dependent on the particular strain. Splenomegaly suggested the systemic effect, which was comparable in both the stains. IMQ and its involvement in redox status were confirmed by an alteration in the activity of SOD, CT, and levels of GSH.

Conclusion This study demonstrated that, in the IMQ-induced psoriasis model, the genetic background has some impact on the disease severity, stability, and redox imbalance.

Uptake and trafficking of different sized PLGA nanoparticles by dendritic cells in imiquimod-induced psoriasis-like mice model

Psoriasis is an autoimmune inflammatory disease, where dendritic cells (DCs) play an important role in its pathogenesis. In our previous work, we have demonstrated that topical delivery of curcumin-loaded poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) could treat Imiquimod (IMQ)-induced psoriasis-like mice. The objective of this study is to further elucidate biofate of PLGA NPs after intradermal delivery including DCs uptake, and their further trafficking in psoriasis-like mice model by using fluorescence probes. Two-sized DiO/DiI-loaded PLGA NPs of 50 ± 4.9 nm (S-NPs) and 226 ± 7.8 nm (L-NPs) were fabricated, respectively. In vitro cellular uptake results showed that NPs could be internalized into DCs with intact form, and DCs preferred to uptake larger NPs. Consistently, in vivo study showed that L-NPs were more captured by DCs and NPs were firstly transported to skin-draining lymph nodes (SDLN), then to spleens after 8 h injection, whereas more S-NPs were transported into SDLN and spleens. Moreover, FRET imaging showed more structurally intact L-NPs distributed in skins and lymph nodes. In conclusion, particle size can affect the uptake and trafficking of NPs by DCs in skin and lymphoid system, which needs to be considered in NPs tailing to treat inflammatory skin disease like psoriasis.

Application of imiquimod-induced murine psoriasis model in evaluating interleukin-17A antagonist

BACKGROUND

Interleukin-17A (IL17A) is a proinflammatory cytokine critically involved in autoimmune diseases, and monoclonal antibodies of IL17A have been approved for clinical treatment of psoriasis. However, a usable psoriatic animal model has been always required for preclinical evaluation of IL17A antagonists. Imiquimod (IMQ)-induced psoriasis model is widely used in fundamental research, but it's not able to accurately show anti-psoriatic effect of IL17A antagonists with conventional modelling condition.

RESULTS

On female C57BL/6 mice, with optimization on the usage of IMQ, positive control reagent and anti-mIL17A antibody, a 7-day model with proper testing window, acceptable disease severity as well as high repeatability was developed, and the efficacy of IL17A antagonist can be objectively evaluated by several qualitative and quantitative indices. Meanwhile, we validated the detailed involvement of IL17A signaling in disease progression, confirmed that the expression levels of IL17A and its related cytokines were induced by IMQ application, and its downstream cytokines can be inhibited by IL17A antagonist treatment. In further study, we revealed that IL17A was transient induced by IMQ and directly caused downstream signaling activation. This finding on the kinetical change of IL17A signaling will manifest the pharmacokinetics-pharmacodynamics investigation of IL17A antagonists.

CONCLUSIONS

Our work presents the application of a convenient psoriatic animal model in the research and development of IL17A antagonists, meanwhile providing extra evidence for understanding IL17A's role in the progression of IMQ-induced psoriasis model, which manifest the research and development of IL17A antagonists.

Developmental cell programs are co-opted in inflammatory skin disease

The skin confers biophysical and immunological protection through a complex cellular network established early in embryonic development. We profiled the transcriptomes of more than 500,000 single cells from developing human fetal skin, healthy adult skin, and adult skin with atopic dermatitis and psoriasis. We leveraged these datasets to compare cell states across development, homeostasis, and disease. Our analysis revealed an enrichment of innate immune cells in skin during the first trimester and clonal expansion of disease-associated lymphocytes in atopic dermatitis and psoriasis. We uncovered and validated in situ a reemergence of prenatal vascular endothelial cell and macrophage cellular programs in atopic dermatitis and psoriasis lesional skin. These data illustrate the dynamism of cutaneous immunity and provide opportunities for targeting pathological developmental programs in inflammatory skin diseases.

Bone morphogenetic protein signaling regulates skin inflammation via modulating dendritic cell function

BACKGROUND

Bone morphogenetic proteins (BMPs) are members of the TGF-β family that signal via the BMP receptor (BMPR) signaling cascade, distinct from canonical TGF-β signaling. BMP downstream signaling is strongly induced within epidermal keratinocytes in cutaneous psoriatic lesions, and BMP7 instructs monocytic cells to acquire characteristics of psoriasis-associated Langerhans dendritic cells (DCs). Regulatory T (Treg)-cell numbers strongly increase during psoriatic skin inflammation and were recently shown to limit psoriatic skin inflammation. However, the factors mediating Treg-cell accumulation in psoriatic skin currently remain unknown.

OBJECTIVE

We sought to investigate the role of BMP signaling in Treg-cell accumulation in psoriasis.

METHODS

The following methods were used: immunohistology of patients and healthy controls; ex vivo models of Treg-cell generation in the presence or absence of Langerhans cells; analysis of BMP versus canonical TGF-β signaling in DCs and Treg cells; and modeling of psoriatic skin inflammation in mice lacking the BMPR type 1a in CD11c⁺ cells.

RESULTS

We here demonstrated a positive correlation between Treg-cell numbers and epidermal BMP7 expression in cutaneous psoriatic lesions and show that unlike Treg cells from healthy skin, a portion of inflammation-associated Treg cells exhibit constitutive-active BMP signaling. We further found that BMPR signaling licenses inflammation-associated Langerhans cell/DC to gain an enhanced capacity to promote Treg cells via BMPR-mediated CD25 induction and that this effect is associated with reduced skin inflammation.

CONCLUSIONS

Psoriatic lesions are marked by constitutive high BMP7/BMPR signaling in keratinocytes, which instructs inflammatory DCs to gain enhanced Treg-cell-stimulatory activity. Locally secreted BMP7 can directly promote Treg-cell generation through the BMP signaling cascade.

4'-O-β-D-glucosyl-5-O-methylvisamminol ameliorates imiquimod-induced psoriasis-like dermatitis and inhibits inflammatory cytokines production by suppressing the NF-κB and MAPK signaling pathways

Psoriasis is a chronic inflammatory skin disorder in humans, and the inflammatory reaction plays an important role in development and onset of psoriasis. 4'-O-β-D-glucosyl-5-O-methylvisamminol (4GMV) is one of the major active chromones isolated from Saposhnikoviae divaricata (Turcz.) Schischk, which has been reported to exhibit excellent anti-inflammatory activities. However, the possible therapeutic effect on psoriasis and underlying mechanism has not been reported. Thus, the aim of this study was to investigate the protective effect of 4GMV on the imiquimod (IMQ)-induced psoriasis-like lesions in BALB/c mice and the anti-inflammatory effect on the lipopolysaccharide (LPS)-induced inflammation in RAW264.7 macrophages. The results demonstrated that 4GMV decreased IMQ-induced keratinocyte proliferation and inflammatory cell infiltration. Moreover, 4GMV treatment significantly inhibited the production of NO, PEG 2, and cytokines such as interleukin (IL)-1β, IL-6, interferon (IFN)-γ, and IL-22 in LPS-stimulated RAW264.7 macrophages. 4GMV also suppressed the LPS-upregulated protein expressions of iNOS and COX-2 in a dose-dependent manner. Furthermore, qRT-PCR analysis showed that 4GMV down-regulated the mRNA level of IL-1β and IL-6 expression. Further studies by western blot indicated that 4GMV inhibited the activation of upstream mediator NF-κB by suppressing the expression of TLR4 and the phosphorylation of IκBα and p65. The phosphorylation of JNK, p38, and ERK were also markedly reversed by 4GMV in LPS-treated RAW264.7 macrophages. Taken together, these results demonstrated that 4GMV showed a protective effect in IMQ-induced psoriasis-like mice and inhibited inflammation through the NF-κB and MAPK signaling pathways, indicating that 4GMV might be a potential therapeutic drug for psoriasis.

New Treatment Addressing the Pathogenesis of Psoriasis

Psoriasis is an immune cell-mediated inflammatory skin disease. The interleukin (IL)23/IL17 axis plays an important role in the development of psoriasis. The effectiveness of biologic treatments such as tumor necrosis factor (TNF)α inhibitors (infliximab, adalimumab, certolizumab pegol), IL23 inhibitors (ustekinumab, guselkumab, tildrakizumab, risankizumab), and IL17 inhibitors (secukinumab, ixekizumab, brodalumab) have verified these findings. Immune-related cells such as dendritic cells (DCs) and macrophages, in addition to Toll-like receptors and cytokines such as interferon (IFN)α, TNFα, IFNɤ, IL12, IL22, IL23, and IL17, are related to the pathogenesis of psoriasis. Here, we first review new insights regarding the pathogenesis of psoriasis, as it relates to DCs, Langerhans cells, macrophages, the signal transducer and activator of transcription 3 pathway, and aryl hydrocarbon receptor in cutaneous vascular endothelial cells. Based on these findings, we summarize currently available oral treatments and biologics. Furthermore, we describe a new treatment option including Janus kinase inhibitor, tyrosine kinase 2 inhibitor, modulator of sphingosine 1-phosphate receptor 1, and Rho-associated kinase 2 inhibitor.

The mechanisms of hydroxychloroquine in rheumatoid arthritis treatment: Inhibition of dendritic cell functions via Toll like receptor 9 signaling

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HCQ efficiently inhibited DC phenotypic and functional maturation stimulated by serum from RA patients.

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HCQ prevented progression of arthritis by inhibiting DC maturation and migration from peripheral blood to LNs.

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HCQ inhibited CpG ODN 1826-activated BMDC maturation and migration.

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The effect of HCQ on DCs was related to the block in TLR9 signaling.

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The development of arthritis was impaired in TLR9^−/− mice.

Hydroxychloroquine (HCQ) is one of the most commonly prescribed immune-suppressants in treating rheumatoid arthritis (RA). Our previous research showed that HCQ suppressed RA development by inhibiting T follicular helper (Tfh) cells directly. Dendritic cells (DCs) serve as the link between innate and acquired immunity. Whether HCQ suppressed Tfh cell through DCs was not clear. In current study, we found that HCQ efficiently inhibited CD86, chemokine (C-X-C motif) receptor 4 (CXCR4) expression and interferon-α (IFN-α) secretion of healthy donor derived purified DCs stimulated by RA patient serum. To mimic RA, collagen-induced arthritis (CIA) mouse model was used and treated with HCQ daily for fifty-four days prior to sacrifice. We found HCQ inhibited DC maturation and migration to lymph nodes (LNs), manifested as down-regulated expression of CD40, CD80, CD86, MHCII (I-A^q) on LN DCs. In addition, HCQ reduced the level of chemokine receptor 7 (CCR7) and L-selectin on peripheral blood DCs and diminished percentage of LN DCs. Of note, HCQ only inhibited CpG ODN 1826-induced IL-12 secretion by bone marrow DCs (BMDCs) stimulated by various toll like receptor (TLR) agonists. Mechanistically, HCQ down-regulated the expression of TLR9 not only in healthy donor PBMC-derived DCs stimulated by RA patient serum, but also in LN DCs of CIA mice and CpG-activated BMDCs. Furthermore, arthritis scores in TLR9^−/− mice were much lower than that in wild type mice with impaired maturity and migration capability of DCs. Collectively, activation of DCs contributes to the pathogenesis of RA and HCQ shows protective effects on RA by inhibition of DC activation via blocking TLR9.

The role of Langerhans cells in epidermal homeostasis and pathogenesis of psoriasis

The skin is the main barrier between the human body and the outside world, which not only plays the role of a physical barrier but also functions as the first line of defence of immunology. Langerhans cells (LCs), as dendritic cells (DC) that play an important role in the immune system, are mainly distributed in the epidermis. This review focuses on the role of these epidermal LCs in regulating skin threats (such as microorganisms, ultraviolet radiation and allergens), especially psoriasis. Since human and mouse skin DC subsets share common ontogenetic characteristics, we can further explore the role of LCs in psoriatic inflammation.

Advanced Characterization of Imiquimod-Induced Psoriasis-Like Mouse Model

Many autoimmune disorders such as psoriasis lead to the alteration of skin components which generally manifests as unwanted topical symptoms. One of the most widely approved psoriasis-like animal models is the imiquimod (IMQ)-induced mouse model. This representation mimics various aspects of the complex cutaneous pathology and could be appropriate for testing topical treatment options. We perform a thorough characterization of this model by assessing some parameters that are not fully described in the literature, namely a precise description of skin disruption. It was evaluated by transepidermal water loss measurements and analyses of epidermis swelling as a consequence of keratinocyte hyperproliferation. The extent of neo-angiogenesis and hypervascularity in dermis were highlighted by immunostaining. Moreover, we investigated systemic inflammation through cytokines levels, spleen swelling and germinal centers appearance in draining lymph nodes. The severity of all parameters was correlated to IMQ concentration in skin samples. This study outlines new parameters of interest useful to assess this model. We highlight the skin barrier disruption and report a systemic inflammatory reaction occurring at distance both in spleen and lymph nodes. These newly identified biological endpoints could be exploited to investigate the efficacy of therapeutic candidates for psoriasis and more extensively for several other skin inflammatory diseases.

A Novel Small-Molecule Inhibitor of Endosomal TLRs Reduces Inflammation and Alleviates Autoimmune Disease Symptoms in Murine Models

Toll-like receptors (TLRs) play a fundamental role in the inflammatory response against invading pathogens. However, the dysregulation of TLR-signaling pathways is implicated in several autoimmune/inflammatory diseases. Here, we show that a novel small molecule TLR-inhibitor (TAC5) and its derivatives TAC5-a, TAC5-c, TAC5-d, and TAC5-e predominantly antagonized poly(I:C) (TLR3)-, imiquimod (TLR7)-, TL8-506 (TLR8)-, and CpG-oligodeoxynucleotide (TLR9)-induced signaling pathways. TAC5 and TAC5-a significantly hindered the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), reduced the phosphorylation of mitogen-activated protein kinases, and inhibited the secretion of tumor necrosis factor-α (TNF-α) and interleukin-6. Besides, TAC5-a prevented the progression of psoriasis and systemic lupus erythematosus (SLE) in mice. Interestingly, TAC5 and TAC5-a did not affect Pam₃CSK₄ (TLR1/2)-, FSL-1 (TLR2/6)-, or lipopolysaccharide (TLR4)-induced TNF-α secretion, indicating their specificity towards endosomal TLRs (TLR3/7/8/9). Collectively, our data suggest that the TAC5 series of compounds are potential candidates for treating autoimmune diseases such as psoriasis or SLE.

Immune Modulation of Monocytes Dampens the IL-17+ γδ T Cell Response and Associated Psoriasis Pathology in Mice

Psoriasis is a chronic inflammatory autoimmune skin condition that affects millions of people worldwide. It is driven by IL-17-producing CD4 and γδ T cells and targeted by current anti-IL-17 or anti-IL-23 mAb therapies. These treatments are expensive, increase the risk of opportunistic infections, and do not specifically target the inflammatory cascade. Other cells, including inflammatory monocytes, have been shown to migrate to psoriatic plaques in both human disease and the imiquimod-induced mouse model and could thus constitute potential alternative therapeutic targets. In the mouse, immune modifying particles (IMPs) specifically target Ly6C^hi inflammatory monocytes migrating to the site of inflammation, sequestering them in the spleen. In this project, we determined whether IMPs could mitigate the development of imiquimod -induced psoriasis in mice. IMP treatment significantly reduced imiquimod-induced psoriasis severity, decreasing dermal infiltration of Ly6C^hi monocytes as well as early-stage monocyte-derived dermal macrophages. This was associated with reduced levels of hallmark cytokines IL-23 and IL-1β as well as associated IL-17-producing γδ T cells. Our work highlights the crucial importance of inflammatory monocytes in the development of this disease as well as a therapeutic potential for IMP in psoriasis.

Retinol and vitamin A metabolites accumulate through RBP4 and STRA6 changes in a psoriasis murine model

Background

Psoriasis is a common chronic inflammatory skin disease that features the abnormal proliferation of keratinocytes. This proliferation could partly result from disturbances in vitamin A metabolism. Changes in psoriasis patients of the levels of retinol-binding protein 4 (RBP4), a carrier of retinol (vitamin A); transmembrane protein stimulated by retinoic acid 6 (STRA6); and other retinol metabolic molecules have not yet been fully established. Therefore, we investigated vitamin A-related proteins in mice with imiquimod (IMQ)-induced psoriasis.

Methods

Thirty mice were divided into four study groups: two groups underwent IMQ application for 3 or 6 days (groups A and B, respectively), and two groups underwent Vaseline application for 3 or 6 days (groups C and D, respectively). Blood and skin samples from both lesional and non-lesional areas of the mice were analyzed using enzyme-linked immunosorbent assays, hematoxylin and eosin staining, immunochemistry, real-time reverse transcription polymerase chain reaction, and RNA sequencing.

Results

IMQ-treated mice developed erythema, scales, and skin thickening. Compared with the control groups, IMQ-treated groups had the following changes: 1) interleukin (IL)-17A, IL-23, and tumor necrosis factor (TNF)-α levels were raised significantly in both serum and lesional skin (all p < 0.001); 2) retinol levels in lesional skin increased slightly (p = 0.364), but no change was evident in serum retinol levels; 3) STRA6 was upregulated in both lesional skin (p = 0.021) and serum (p = 0.034); 4) RBP4 levels were elevated in serum (p = 0.042), but exhibited only an increasing trend (p = 0.273) in lesional skin; and 5) proteins and enzymes that mediate retinoic acid formation and transformation were upregulated in lesional skin.

Conclusions

As the demand for vitamin A in psoriatic mice increased, retinol underwent relocation from the circulation to target tissues. RBP4, STRA6, and the transformation from retinol to retinoic acid were upregulated, which may be part of the mechanism of psoriasis skin lesion formation. We propose that a positive feedback mechanism was formed that maintained the severity of psoriasis.

Spermidine Suppresses Inflammatory DC Function by Activating the FOXO3 Pathway and Counteracts Autoimmunity

Dendritic cells (DCs) function is intimately linked to microenvironment and metabolism. Type I interferons (IFNs) condition dendritic cells to respond to weak self-signals, leading to autoimmunity. However, the metabolic adaption in the process is unclear. Here, we identified spermidine as a critical metabolite impacting the metabolic fitness of DC. First, dynamic metabolome screening indicated that spermidine decreased during IFN priming and following TLR7 ligand stimulation, accompanied by metabolic change from oxidative phosphorylation to glycolysis. Second, spermidine supplement restrained the glycolysis and prevented the overactivation of IFN-α primed DC both in vivo and in vitro. Third, mechanism study uncovered that the activity of FOXO3 adapted to the metabolic change, mediating the anti-inflammatory effect of spermidine. More importantly, addition of spermidine in vivo greatly alleviated the development of psoriasis-like symptom in mice. Thus, our studies revealed metabolic changes boosting DC responses and identified spermidine as a potential therapeutic agent for autoimmune diseases.

BMP7 aberrantly induced in the psoriatic epidermis instructs inflammation-associated Langerhans cells

BACKGROUND

Epidermal hyperplasia represents a morphologic hallmark of psoriatic skin lesions. Langerhans cells (LCs) in the psoriatic epidermis engage with keratinocytes (KCs) in tight physical interactions; moreover, they induce T-cell-mediated immune responses critical to psoriasis.

OBJECTIVE

This study sought to improve the understanding of epidermal factors in psoriasis pathogenesis.

METHODS

BMP7-LCs versus TGF-β1-LCs were phenotypically characterized and their functional properties were analyzed using flow cytometry, cell kinetic studies, co-culture with CD4 T cells, and cytokine measurements. Furthermore, immunohistology of healthy and psoriatic skin was performed. Additionally, in vivo experiments with Jun^f/fJunB^f/fK5cre-ER^T mice were carried out to assess the role of bone morphogenetic protein (BMP) signaling in psoriatic skin inflammation.

RESULTS

This study identified a KC-derived signal (ie, BMP signaling) to promote epidermal changes in psoriasis. Whereas BMP7 is strictly confined to the basal KC layer in the healthy skin, it is expressed at high levels throughout the lesional psoriatic epidermis. BMP7 instructs precursor cells to differentiate into LCs that phenotypically resemble psoriatic LCs. These BMP7-LCs exhibit proliferative activity and increased sensitivity to bacterial stimulation. Moreover, aberrant high BMP signaling in the lesional epidermis is mediated by a KC intrinsic mechanism, as suggested from murine data and clinical outcome after topical antipsoriatic treatment in human patients.

CONCLUSIONS

These data indicate that available TGF-β family members within the lesional psoriatic epidermis preferentially signal through the canonical BMP signaling cascade to instruct inflammatory-type LCs and to promote psoriatic epidermal changes. Targeting BMP signaling might allow to therapeutically interfere with cutaneous psoriatic manifestations.

Dendritic cells: The driver of psoriasis

Psoriasis is a chronic skin inflammatory disorder, the immune mechanism of which has been profoundly elucidated in the past few years. The dominance of the interleukin (IL)-23/IL-17 axis is a significant breakthrough in the understanding of the pathogenesis of psoriasis, and treatment targeting IL-23 and IL-17 has successfully benefited patients with the disease. The skin contains a complex network of dendritic cells (DC) mainly composed of epidermal Langerhans cells, bone marrow-derived dermal conventional DC, plasmacytoid DC and inflammatory DC. As the prominent cellular source of α-interferon, tumor necrosis factor-α, IL-12 and IL-23, DC play a pivotal role in psoriasis. Thus, targeting pathogenic DC subsets is a valid strategy for alleviating and preventing psoriasis and other DC-derived diseases. In this review, we survey the known role of DC in this disease.

Nanoparticle-Coupled Topical Methotrexate Can Normalize Immune Responses and Induce Tissue Remodeling in Psoriasis

Methotrexate (MTX) is an antiproliferative drug used for treating inflammatory diseases, including psoriasis. Nevertheless, its use in localized therapy is hindered because of poor transdermal penetration. We show that MTX coupled with gold nanoparticles (GNPs) demonstrates superior antiinflammatory efficacy than MTX alone in an imiquimod-induced mouse model, significantly reducing γδ T cells, CD4⁺ T cells, and neutrophils. Furthermore, it was well tolerated upon systemic and topical administration. In an AGR129 human xenograft mouse model, two-week topical treatment with MTX-GNPs inhibited skin hyperplasia significantly better than topical calcipotriol-betamethasone and led to profound tissue remodeling, involving the upregulation of extracellular matrix reorganization and the downregulation of cornification and keratinization processes. The number of resident T cells in the grafts, as well as interleukin-17 production, drastically decreased upon MTX-GNP treatment. While both MTX and MTX-GNPs directly prevented the proliferation and induced apoptosis of T cells, the suppression of cytokine production was a shared mechanism of GNP and MTX-GNPs. In conclusion, MTX-GNPs influence immune and stromal components of the skin, leading to the potent inhibition of pathogenesis in preclinical psoriasis. MTX-GNPs surpass the efficacy of conventional MTX and standard of care, emerging as a non-steroidal, topical alternative for psoriasis treatment.

Datura Metel L. Ameliorates Imiquimod-Induced Psoriasis-Like Dermatitis and Inhibits Inflammatory Cytokines Production through TLR7/8-MyD88-NF-κB-NLRP3 Inflammasome Pathway

Background: Psoriasis is a chronic, immune-mediated inflammatory skin disease, and the inflammatory response plays an important role in its development and progression. Datura metel L. is a traditional Chinese medicine that exhibited a significant therapeutic effect on psoriasis in our previous study due to its remarkable anti-inflammatory effect. Meanwhile, the mechanism underlying its effects on psoriasis is still unclear. Methods: An imiquimod-induced psoriasis-like dermatitis mouse model was constructed to evaluate the protective effect of the effective part of Datura metel L. (EPD), which was verified by evaluations of the Psoriasis Area and Severity Index (PASI) score. Hematoxylin and eosin (H&E) staining, immunohistochemical examination, enzyme-linked immunosorbent assay (ELISA), and Western blot were used to measure the inflammatory cytokines and the protein expression associated with the Toll-like receptor 7– myeloid differentiation primary response gene 88–nuclear Factor-κB–nucleotide-binding oligomerization domain (Nod)-like receptor family pyrin domain-containing 3 (TLR7/8–MyD88–NF-κB–NLRP3) inflammasome pathway. Results: EPD significantly decreased the PASI, reduced epidermal thickness, and decreased the proliferation and differentiation of epidermal cells in psoriasis-like dermatitis C57BL/6 mice induced by imiquimod (IMQ). Furthermore, EPD reduced the infiltration of CD3+ cells to psoriatic lesions, as well as ameliorated the elevations of intercellular adhesion molecule 1 (ICAM-1) and inhibited the production of imiquimod-induced inflammatory cytokines, including IL-1β, IL-2, IL-6, IL-10, IL-12, IL-17, IL-22, IL-23, tumor necrosis factor-α (TNF-α), monocyte chemotactic protein 1 (MCP-1), and interferon-γ (IFN-γ). Besides, EPD decreased the imiquimod-induced expression levels of TLR7, TLR8, TRAF6, MyD88, p-IKKα, p-IKBα, p-NF-κB, NLRP3, apoptosis-associated speck-like protein contained a caspase recruitment domain (ASC), cysteinyl aspartate specific proteinase 1 (caspase-1), and IL-1β. Conclusion: This study demonstrated that EPD exhibited a protective effect on an imiquimod-induced psoriasis mice model by inhibiting the inflammatory response, which might be ascribed to the inhibition of the TLR7/8–MyD88–NF-κb–NLRP3 inflammasome pathway.

The role of Langerhans cells in pathologies of the skin

Langerhans cells (LCs) are epidermal immune cells of myeloid origin. Although these cells were primarily thought to play a defensive role in the skin, evidence now indicates a diverse range of LC-mediated effects including the relay of viral antigens in herpes simplex infection, recruitment of eosinophils in atopic dermatitis and promotion of a Th17 response in Candida infection. LCs may have a protective or suppressive function in pathologies of the skin, with differing functions being driven by the skin milieu. Understanding LC function will help guide the development of interventions that modulate these cells for therapeutic benefit.

A Subset of Type I Conventional Dendritic Cells Controls Cutaneous Bacterial Infections through VEGFα-Mediated Recruitment of Neutrophils

Skin conventional dendritic cells (cDCs) exist as two distinct subsets, cDC1s and cDC2s, which maintain the balance of immunity to pathogens and tolerance to self and microbiota. Here, we examined the roles of dermal cDC1s and cDC2s during bacterial infection, notably Propionibacterium acnes (P. acnes). cDC1s, but not cDC2s, regulated the magnitude of the immune response to P. acnes in the murine dermis by controlling neutrophil recruitment to the inflamed site and survival and function therein. Single-cell mRNA sequencing revealed that this regulation relied on secretion of the cytokine vascular endothelial growth factor α (VEGF-α) by a minor subset of activated EpCAM+CD59+Ly-6D+ cDC1s. Neutrophil recruitment by dermal cDC1s was also observed during S. aureus, bacillus Calmette-Guérin (BCG), or E. coli infection, as well as in a model of bacterial insult in human skin. Thus, skin cDC1s are essential regulators of the innate response in cutaneous immunity and have roles beyond classical antigen presentation.

Ghrelin protects against contact dermatitis and psoriasiform skin inflammation by antagonizing TNF-α/NF-κB signaling pathways

Contact dermatitis and psoriasis are skin disorders caused by immune dysregulation, yet much remains unknown about their underlying mechanisms. Ghrelin, a recently discovered novel peptide and potential endogenous anti-inflammatory factor expressed in the epidermis, is involved in skin repair and disease. In this study, we investigated the expression pattern and therapeutic effect of ghrelin in both contact dermatitis and psoriasis mouse models induced by oxazolone (OXA) and imiquimod (IMQ), respectively, and in TNF-α-stimulated RAW264.7 macrophages, NHEKs and skin fibroblasts. Ghrelin expression was reduced in both the OXA-induced contact dermatitis and IMQ-induced psoriasis mouse models. Furthermore, treatment with ghrelin attenuated skin inflammation in both the contact dermatitis and psoriasis mouse models. Mice administered PBS after OXA- or IMQ-induced model generation exhibited typical skin inflammation, whereas ghrelin treatment in these mouse models substantially decreased the dermatitis phenotype. In addition, exogenous ghrelin attenuated the inflammatory reaction induced by TNF-α in RAW264.7 cells. Moreover, ghrelin administration limited activation of NF-κB signaling. In summary, ghrelin may represent a potential molecular target for the prevention and treatment of inflammatory skin diseases, including contact dermatitis and psoriasis.

Disrupting the IL-36 and IL-23/IL-17 loop underlies the efficacy of calcipotriol and corticosteroid therapy for psoriasis

Psoriasis is one of the most common skin inflammatory diseases worldwide. The vitamin D3 analog calcipotriol has been used alone or in combination with corticosteroids in treating plaque psoriasis, but how it suppresses psoriatic inflammation has not been fully understood. Using an experimental mouse psoriasis model, we show that topical calcipotriol inhibited the pivotal IL-23/IL-17 axis and neutrophil infiltration in psoriatic skin, and interestingly, such effects were mediated through the vitamin D receptor (VDR) in keratinocytes (KCs). We further reveal that IL-36α and IL-36γ, which have recently emerged as key players in psoriasis pathogenesis, were effectively repressed by calcipotriol via direct VDR signaling in mouse KCs. Accordingly, calcipotriol treatment suppressed IL-36α/γ expression in lesional skin from patients with plaque psoriasis, which was accompanied by a reduced IL-23/IL-17 expression. In contrast, dexamethasone indirectly reduced IL-36α/γ expression in mouse psoriatic skin through immune cells. Furthermore, we demonstrate that calcipotriol and dexamethasone, in combination, synergistically suppressed the expression of IL-36α/γ, IL-23, and IL-17 in the established mouse psoriasis. Our findings indicate that the combination of calcipotriol and corticosteroid efficiently disrupts the IL-36 and IL-23/IL-17 positive feedback loop, thus revealing a mechanism underlying the superior efficacy of calcipotriol and corticosteroid combination therapy for psoriasis.

The potential utility of iron oxide nanoparticles for the treatment of skin inflammation in a mouse model of psoriasis

Several studies have demonstrated that immunosuppressive effects accompany systemic administration of some iron oxide nanoparticles (IONPs). In our earlier study, conducted using human peripheral blood mononuclear cells, we showed that therapeutic formulation of IONPs, Feraheme, approved for clinical use in the United States for the treatment of iron deficiency in chronic kidney disease, suppresses the function of activated T-cells in vitro via a mechanism involving mitochondrial damage. Here we report an in vivo study demonstrating that topical application of Feraheme prior to disease onset decreases the development of skin lesions in the mouse model of chemically induced psoriasis.

Brief Exposure of Skin to Near-Infrared Laser Modulates Mast Cell Function and Augments the Immune Response

The treatment of skin with a low-power continuous-wave (CW) near-infrared (NIR) laser prior to vaccination is an emerging strategy to augment the immune response to intradermal vaccine, potentially substituting for chemical adjuvant, which has been linked to adverse effects of vaccines. This approach proved to be low cost, simple, small, and readily translatable compared with the previously explored pulsed-wave medical lasers. However, little is known on the mode of laser-tissue interaction eliciting the adjuvant effect. In this study, we sought to identify the pathways leading to the immunological events by examining the alteration of responses resulting from genetic ablation of innate subsets including mast cells and specific dendritic cell populations in an established model of intradermal vaccination and analyzing functional changes of skin microcirculation upon the CW NIR laser treatment in mice. We found that a CW NIR laser transiently stimulates mast cells via generation of reactive oxygen species, establishes an immunostimulatory milieu in the exposed tissue, and provides migration cues for dermal CD103+ dendritic cells without inducing prolonged inflammation, ultimately augmenting the adaptive immune response. These results indicate that use of an NIR laser with distinct wavelength and power is a safe and effective tool to reproducibly modulate innate programs in skin. These mechanistic findings would accelerate the clinical translation of this technology and warrant further explorations into the broader application of NIR lasers to the treatment of immune-related skin diseases.