Psoriatic keratinocytes prime neutrophils for an overproduction of superoxide anions

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.

Neutrophil-to-lymphocyte ratio and platelet-to-lymphocyte ratio in psoriasis: a systematic review and meta-analysis

Psoriasis is a chronic, inflammatory skin disorder characterized by well-demarcated erythematous lesions with surface scaling. The disease is underpinned by a dysregulated immune response with a shift in the balance of neutrophils, lymphocytes and platelets. We sought to evaluate the novel systemic inflammatory markers, neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR), as psoriatic indicators. Pubmed, Web of Science and Scopus were systematically searched for relevant studies. Twenty-four studies consisting of a total of 2,275 psoriatic patients (1,301 males and 974 females) and 2,334 healthy controls (1,401 males and 933 females) were identified for inclusion in the quantitative analysis. The NLR and PLR were found to be significantly increased in psoriatic patients [standardized mean difference (SMD) = 0.68, 95% CI 0.56-0.80, p < 0.01, and SMD = 0.37, 95% CI 0.14-0.60, p < 0.01, respectively]. However, no association between the NLR and PLR with psoriasis severity was detected (p = 0.93, and p = 0.83, respectively). In conclusion, the NLR and PLR are simple and cost-effective markers of psoriatic presence, but their value as severity markers requires further study.

Targeting anti-inflammatory immunonanocarriers to human and murine neutrophils via the Ly6 antigen for psoriasiform dermatitis alleviation

Psoriasis is a refractory and difficult-to-treat skin disorder. The neutrophil-targeting approach represents a promising option for psoriasis therapy. This study developed and examined NIMP-R14-conjugated immunonanoparticles for specific targeting to neutrophils associated with psoriasiform dermatitis. In the process, roflumilast (RFL), as a phosphodiesterase (PDE) 4 inhibitor, was encapsulated in the nanocarriers to assess the anti-inflammatory capability against primary neutrophil activation and murine psoriasiform lesion. The average size and surface charge of the immunonanocarriers were 305 ± 36 nm and -18 ± 6 mV, respectively. The monovalent antibody-conjugated nanoparticles offered precise uptake by both human and mouse neutrophils but failed to exhibit this effect in monocytes and lymphocytes. The intracellular RFL concentration of the immunonanocarriers was five-fold superior to that of the passive counterparts. The immunonanocarriers specifically recognized the neutrophils through the Ly6 antigen with no apparent cytotoxicity. The antibody-conjugated nanoparticles mitigated superoxide anion production and migration of the activated human neutrophils. The in vivo biodistribution in the psoriasiform mice, found using an in vivo imaging system (IVIS) and liquid chromatography (LC)-mass-mass analysis, showed that the antibody conjugation increased the nanoparticle residence in systemic circulation after intravenous administration. On the other hand, most of the nanoparticles were accumulated in the lesional skin after subcutaneous injection. The actively-targeted nanocarriers were better than the free RFL and unfunctionalized nanoparticles in suppressing psoriasiform inflammation. The immunonanocarriers reduced neutrophil recruitment and epidermal hyperplasia in the plaque. Intravenous and subcutaneous treatments with the immunonanocarriers significantly reduced the overexpressed cytokines and chemokines in the inflamed skin, demonstrating that the nanosystems could both systematically and locally alleviate inflammation. The results indicated that the NIMP-R14-conjugated RFL-loaded nanoparticles have potential as an anti-autoimmune disease delivery system for neutrophil targeting.

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.

Gene Profiling of a 3D Psoriatic Skin Model Enriched in T Cells: Downregulation of PTPRM Promotes Keratinocyte Proliferation through Excessive ERK1/2 Signaling

Psoriasis is a complex, immune-mediated skin disease involving a wide range of epithelial and immune cells. The underlying mechanisms that govern the epidermal defects and immunological dysfunction observed in this condition remain largely unknown. In recent years, the emergence of new, more sophisticated models has allowed the evolution of our knowledge of the pathogenesis of psoriasis. The development of psoriatic skin biomaterials that more closely mimic native psoriatic skin provides advanced preclinical models that will prove relevant in predicting clinical outcomes. In this study, we used a tissue-engineered, two-layered (dermis and epidermis) human skin substitute enriched in T cells as a biomaterial to study both the cellular and molecular mechanisms involved in psoriasis’ pathogenesis. Gene profiling on microarrays revealed significant changes in the profile of genes expressed by the psoriatic skin substitutes compared with the healthy ones. Two genes, namely, PTPRM and NELL2, whose products influence the ERK1/2 signaling pathway have been identified as being deregulated in psoriatic substitutes. Deregulation of these genes supports excessive activation of the ERK1/2 pathway in psoriatic skin substitutes. Most importantly, electrophoresis mobility shift assays provided evidence that the DNA-binding properties of two downstream nuclear targets of ERK1/2, both the NF-κB and Sp1 transcription factors, are increased under psoriatic conditions. Moreover, the results obtained with the inhibition of RSK, a downstream effector of ERK1/2, supported the therapeutic potential of inhibiting this signaling pathway for psoriasis treatment. In conclusion, this two-layered human psoriatic skin substitute enriched in T cells may prove particularly useful in deciphering the mechanistic details of psoriatic pathogenesis and provide a relevant biomaterial for the study of potential therapeutic targets.

Oxidative Stress Induced by High Salt Diet—Possible Implications for Development and Clinical Manifestation of Cutaneous Inflammation and Endothelial Dysfunction in Psoriasis vulgaris

Although oxidative stress is recognized as an important effector mechanism of the immune system, uncontrolled formation of reactive oxygen and nitrogen species promotes excessive tissue damage and leads to disease development. In view of this, increased dietary salt intake has been found to damage redox systems in the vessel wall, resulting in endothelial dysfunction associated with NO uncoupling, inflammation, vascular wall remodeling and, eventually, atherosclerosis. Several studies have reported increased systemic oxidative stress accompanied by reduced antioxidant capacity following a high salt diet. In addition, vigorous ionic effects on the immune mechanisms, such as (trans)differentiation of T lymphocytes are emerging, which together with the evidence of NaCl accumulation in certain tissues warrants a re-examination of the data derived from in vitro research, in which the ionic influence was excluded. Psoriasis vulgaris (PV), as a primarily Th17-driven inflammatory skin disease with proven inflammation-induced accumulation of sodium chloride in the skin, merits our interest in the role of oxidative stress in the pathogenesis of PV, as well as in the possible beneficial effects that could be achieved through modulation of dietary salt intake and antioxidant supplementation.

Enhanced Migratory Ability of Neutrophils Toward Epidermis Contributes to the Development of Psoriasis via Crosstalk With Keratinocytes by Releasing IL-17A

Microabscess of neutrophils in epidermis is one of the histological hallmarks of psoriasis. The axis of neutrophil–keratinocyte has been thought to play a critical role in the pathogenesis of psoriasis. However, the features and mechanism of interaction between the two cell types remain largely unknown. Herein, we found that blood neutrophils were increased in psoriasis patients, positively correlated with disease severity and highly expressed CD66b, but not CD11b and CD62L compared to healthy controls. Keratinocytes expressed high levels of psoriasis-related inflammatory mediators by direct and indirect interaction with neutrophils isolated from psoriasis patients and healthy controls. The capacity of neutrophils in provoking keratinocytes inflammatory response was comparable between the two groups and is dependent on IL-17A produced by itself. Neutrophils isolated from psoriasis patients displayed more transcriptome changes related to integrin and increased migration capacity toward keratinocytes with high CD11b expression on cell surface. Of interest, neutrophils were more susceptible to keratinocyte stimulation than to fibroblasts and human umbilical vein endothelial cells (HUVECs) in terms of CD11b expression and the production of ROS and NETs. In conclusion, neutrophils from psoriasis patients gain a strong capacity of IL-17A production and integrins expression that possibly facilitates their abilities to promote production of psoriasis-related inflammatory mediators and migration, a phenomenon likely induced by their interaction with keratinocytes but not with fibroblasts. These findings provide a proof-of-concept that development of new drugs targeting migration of neutrophils could be a more specific and safe solution to treat psoriasis.

Pinocembrin Reduces Keratinocyte Activation and Ameliorates Imiquimod-Induced Psoriasis-like Dermatitis in BALB/c Mice through the Heme Oxygenase-1/Signal Transducer and Activator of Transcription 3 Pathway

Psoriasis is an autoimmune disease characterized by chronic skin inflammation and excessive keratinocyte proliferation. The itchy, scaly, and erythematous lesions present on psoriatic skin negatively affect patients' quality of life. Pinocembrin is a flavonoid present in propolis, fruits, and vegetables. It exerts neuroprotective effects and was used for treating ischemic stroke in a human clinical trial. However, the effects of pinocembrin on psoriasis have never been examined. In this study, we evaluated the effects of pinocembrin on human HaCaT keratinocytes and BALB/c mice with imiquimod- (IMQ-) induced psoriatic dermatitis. In interferon-γ- (IFN-γ-) activated HaCaT cells, pinocembrin reduced the expression of inflammatory cytokines, namely, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and keratinocyte proliferation markers, namely, keratin (K)16, K17, and Ki-67. The mechanism underlying these inhibitory effects involved the regulation of the heme oxygenase- (HO-) 1/signal transducer and activator of transcription (STAT) 3 pathway. In the IMQ-induced psoriatic dermatitis mouse model, the topical application of pinocembrin significantly ameliorated the Skin Psoriasis Area and Severity Index score, epidermal thickness, inflammation, hyperplasia, hyperkeratosis, and cluster of differentiation (CD) 4⁺ T-cell infiltration. Expression of the inflammatory cytokines and keratinocyte proliferation markers in dorsal skin was significantly decreased in the pinocembrin-treated group. Meanwhile, in lesional skin, the expression of HO-1 was upregulated, but that of phospho-STAT3 (pSTAT3) was downregulated. Collectively, our results indicated the therapeutic potential of pinocembrin. Additional studies are warranted to evaluate its clinical benefits in patients with psoriasis.

Imperatorin Alleviates Psoriasiform Dermatitis by Blocking Neutrophil Respiratory Burst, Adhesion, and Chemotaxis Through Selective Phosphodiesterase 4 Inhibition

Aim: Neutrophil infiltration and increased oxidative stress are involved in the pathogenesis and severity of psoriasis. Although the therapy of psoriasis remains elusive, targeting treatment to reduce oxidative stress is considered a potential option. Our study demonstrates the anti-inflammatory effects of a natural furocoumarin, imperatorin, on activated human neutrophils and psoriasiform dermatitis in mice. Results: Imperatorin inhibited superoxide anion generation, neutrophil adhesion, and migration in N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLF)-stimulated human neutrophils. Further studies showed that imperatorin induced a decrease in cAMP-specific phosphodiesterase (PDE) activity, and increased intracellular cAMP levels and protein kinase A (PKA) activity in human neutrophils. The enzyme activities of PDE4 subtypes, but not PDE3 and PDE7, were inhibited by imperatorin. Furthermore, imperatorin inhibited the phosphorylation of protein kinase B (Akt), extracellular regulated kinase (ERK), and c-Jun N-terminal kinase (JNK), as well as Ca²⁺ mobilization in fMLF-stimulated neutrophils. These suppressive effects of imperatorin on cell responses and signaling were reversed by PKA inhibitor, suggesting that cAMP/PKA is involved in the anti-inflammatory effects of imperatorin. In vivo studies of imiquimod- and interleukin-23-induced mouse psoriasiform dermatitis demonstrated that imperatorin alleviated skin desquamation, epidermal thickening, keratinocyte hyperproliferation, and neutrophil infiltration. Innovation and Conclusion: Our results demonstrate that imperatorin inhibits human neutrophil respiratory burst, adhesion, and migration through the elevation of cAMP/PKA to inhibit Akt, ERK, JNK, and Ca²⁺ mobilization. Imperatorin is a natural inhibitor of PDE4A/B/C and may serve as a lead for developing new therapeutics to treat neutrophilic psoriasis. Antioxid. Redox Signal. 35, 885-903.

Neutrophils as Drivers of Immune Dysregulation in Autoimmune Diseases with Skin Manifestations

Dysregulation in the phenotype and function of neutrophils may play important roles in the initiation and perpetuation of autoimmune responses, including conditions affecting the skin. Neutrophils can have local and systemic effects on innate and adaptive immune cells as well as on resident cells in the skin, including keratinocytes (KCs). Aberrant formation/clearance of neutrophil extracellular traps (NETs) in systemic autoimmunity and chronic inflammatory diseases have been associated with the externalization of modified autoantigens in peripheral blood and tissues. NETs can impact the function of many cells, including macrophages, lymphocytes, dendritic cells, fibroblasts, and KCs. Emerging evidence has unveiled the pathogenic key roles of neutrophils in systemic lupus erythematosus, idiopathic inflammatory myopathies, psoriasis, hidradenitis suppurativa, and other chronic inflammatory conditions. As such, neutrophil-targeting strategies represent promising therapeutic options for these diseases.

Natural Xanthones and Skin Inflammatory Diseases: Multitargeting Mechanisms of Action and Potential Application

The pathogenesis of skin inflammatory diseases such as atopic dermatitis, acne, psoriasis, and skin cancers generally involve the generation of oxidative stress and chronic inflammation. Exposure of the skin to external aggressors such as ultraviolet (UV) radiation and xenobiotics induces the generation of reactive oxygen species (ROS) which subsequently activates immune responses and causes immunological aberrations. Hence, antioxidant and anti-inflammatory agents were considered to be potential compounds to treat skin inflammatory diseases. A prime example of such compounds is xanthone (xanthene-9-one), a class of natural compounds that possess a wide range of biological activities including antioxidant, anti-inflammatory, antimicrobial, cytotoxic, and chemotherapeutic effects. Many studies reported various mechanisms of action by xanthones for the treatment of skin inflammatory diseases. These mechanisms of action commonly involve the modulation of various pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor α (TNF-α), as well as anti-inflammatory cytokines such as IL-10. Other mechanisms of action include the regulation of NF-κB and MAPK signaling pathways, besides immune cell recruitment via modulation of chemokines, activation, and infiltration. Moreover, disease-specific activity contributed by xanthones, such as antibacterial action against Propionibacterium acnes and Staphylococcus epidermidis for acne treatment, and numerous cytotoxic mechanisms involving pro-apoptotic and anti-metastatic effects for skin cancer treatment have been extensively elucidated. Furthermore, xanthones have been reported to modulate pathways responsible for mediating oxidative stress and inflammation such as PPAR, nuclear factor erythroid 2-related factor and prostaglandin cascades. These pathways were also implicated in skin inflammatory diseases. Xanthones including the prenylated α-mangostin (2) and γ-mangostin (3), glucosylated mangiferin (4) and the caged xanthone gambogic acid (8) are potential lead compounds to be further developed into pharmaceutical agents for the treatment of skin inflammatory diseases. Future studies on the structure-activity relationships, molecular mechanisms, and applications of xanthones for the treatment of skin inflammatory diseases are thus highly recommended.

Role of Neutrophils in Psoriasis

Psoriasis is a common inflammatory disease that can involve the skin, joints, or both. The abnormalities of innate immunity play crucial roles in the pathogenesis of psoriasis. Neutrophils are the most abundant leukocytes in the circulation. Emerging evidences have demonstrated that neutrophils may play a role in autoimmune diseases. The neutrophil-to-lymphocyte ratio (NLR), the activity of neutrophils, and the number of NETotic cells were significantly higher in psoriasis patients compared to healthy controls. The number of low-density granulocytes (LDGs) in the blood of psoriasis patients was significantly higher than those in the control blood. Furthermore, neutrophils may play important roles in the cardiovascular risk in psoriasis. However, the exact role of neutrophils in psoriasis remains unclear. In this review, we highlight the role of neutrophils in the pathogenesis of psoriasis.

Platelet Dysfunction and Its Role in the Pathogenesis of Psoriasis

BACKGROUND

Psoriasis is an immune-mediated inflammatory skin disease in conjunction with the systemic inflammatory process. It appears to be related to increased risks of cardiovascular disease events, especially in severe cases. The hemostatic balance is disrupted due to the prothrombotic bias in psoriasis, which might be mainly preserved by platelet hyperactivity. Platelets are also immune cells that initiate and regulate immune and inflammatory processes, except as the principal mediator of hemostasis and thrombosis, and platelet dysfunction is deeply involved in the pathogenesis of psoriasis.

SUMMARY

The aim of this study is to perform a review that expounds abnormal platelet function in psoriasis and explains the important role of platelets in the pathogenic mechanism of psoriasis in order to provide new targets for comprehensive medical treatment.

Neutrophils in Psoriasis

Neutrophils are the most abundant innate immune cells. The pathogenic roles of neutrophils are related to chronic inflammation and autoimmune diseases. Psoriasis is a chronic systemic inflammatory disease affecting ~2–3% of the world population. The abundant presence of neutrophils in the psoriatic skin lesions serves as a typical histopathologic hallmark of psoriasis. Recent reports indicated that oxidative stress, granular components, and neutrophil extracellular traps from psoriatic neutrophils are related to the initial and maintenance phases of psoriasis. This review provides an overview on the recent (up to 2019) advances in understanding the role of neutrophils in the pathophysiology of psoriasis, including the effects of respiratory burst, degranulation, and neutrophil extracellular trap formation on psoriatic immunity and the clinical relationships.

Sensory nerves mediate spontaneous behaviors in addition to inflammation in a murine model of psoriasis

Psoriasis is characterized by keratinocyte hyperproliferation, erythema, as well as a form of pruritus, involving cutaneous discomfort. There is evidence from both clinical and murine models of psoriasis that chemical or surgical depletion of small-diameter sensory nerves/nociceptors benefits the condition, but the mechanisms are unclear. Hence, we aimed to understand the involvement of sensory nerve mediators with a murine model of psoriasis and associated spontaneous behaviors, indicative of cutaneous discomfort. We have established an Aldara model of psoriasis in mice and chemically depleted the small-diameter nociceptors in a selective manner. The spontaneous behaviors, in addition to the erythema and skin pathology, were markedly improved. Attenuated inflammation was associated with reduced dermal macrophage influx and production of reactive oxygen/nitrogen species (peroxynitrite and protein nitrosylation). Subsequently, this directly influenced observed behavioral responses. However, the blockade of common sensory neurogenic mechanisms for transient receptor potential (TRP)V1, TRPA1, and neuropeptides (substance P and calcitonin gene-related peptide) using genetic and pharmacological approaches inhibited the behaviors but not the inflammation. Thus, a critical role of the established sensory TRP-neuropeptide pathway in influencing cutaneous discomfort is revealed, indicating the therapeutic potential of agents that block that pathway. The ongoing inflammation is mediated by a distinct sensory pathway involving macrophage activation.-Kodji, X., Arkless, K. L., Kee, Z., Cleary, S. J., Aubdool, A. A., Evans, E., Caton, P., Pitchford, S. C., Brain, S. D. Sensory nerves mediate spontaneous behaviors in addition to inflammation in a murine model of psoriasis.

Neutrophils and redox stress in the pathogenesis of autoimmune disease

Polymorphonuclear leukocytes, or neutrophils, are specialist phagocytic cells of the innate immune system. Their primary role is host defence against micro-organisms, which they kill via phagocytosis, followed by release of reactive oxygen species (ROS) and proteolytic enzymes within the phagosome. ROS are generated via the action of the NADPH oxidase (also known as NOX2), in a process termed the 'Respiratory Burst'. This process consumes large amounts of oxygen, which is converted into the highly-reactive superoxide radical O₂^- and H₂O₂. Subsequent activation of myeloperoxidase (MPO) generates secondary oxidants and chloroamines that are highly microbiocidal in nature, which together with proteases such as elastase and gelatinase provide a toxic intra-phagosomal environment able to kill a broad range of micro-organisms. However, under certain circumstances such as during an auto-immune response, neutrophils can be triggered to release ROS and proteases extracellularly causing damage to host tissues, modification of host proteins, lipids and DNA and dysregulation of oxidative homeostasis. This review describes the range of ROS species produced by human neutrophils with a focus on the implications of neutrophil redox products in autoimmune inflammation.

Contribution of myeloperoxidase and inducible nitric oxide synthase to pathogenesis of psoriasis

INTRODUCTION

Histological changes of psoriasis include invasion of neutrophils into the epidermis and formation of Munro abscesses in the epidermis. Neutrophils are the predominant white blood cells in circulation when stimulated; they discharge the abundant myeloperoxidase (MPO) enzyme that uses hydrogen peroxide to oxidize chloride for killing ingested bacteria.

AIM

To investigate the contribution of neutrophils to the pathogenesis of psoriasis at the blood and tissue levels through inducible nitric oxide synthase (iNOS) and MPO.

MATERIAL AND METHODS

A total of 50 adult patients with a chronic plaque form of psoriasis and 25 healthy controls were enrolled to this study. Serum MPO and iNOS levels were measured using ELISA method. Two biopsy specimens were taken in each patient from the center of the lesion and uninvolved skin. Immunohistochemistry was performed for MPO and iNOS on both normal and psoriasis vulgaris biopsies.

RESULTS

While a significant difference between serum myeloperoxidase levels were detected, a similar statistical difference between participants in the serum iNOS levels was not found. In immunohistochemistry, intensely stained leukocytes with MPO and intensely staining with iNOS in psoriatic skin was observed.

CONCLUSIONS

Neutrophils in psoriasis lesions are actively producing MPO and this indirectly triggers the synthesis of iNOS. Targeting of MPO or synthesis of MPO in the lesion area may contribute to development of a new treatment option.

Aquaporin-3-mediated hydrogen peroxide transport is required for NF-κB signalling in keratinocytes and development of psoriasis

Aquaporin 3 (AQP3), a water/glycerol channel protein, has been found to transport hydrogen peroxide (H2O2). Here, we show that H2O2, imported via AQP3, is involved in nuclear factor-κB (NF-κB) signalling in keratinocytes and in the pathogenesis of psoriasis. IL-23-mediated induction of psoriasis is reduced in AQP3 knockout mice (AQP3(-/-)), and is accompanied by impaired NF-κB activation and intracellular H2O2 accumulation. In primary keratinocyte cultures, cellular import of H2O2 produced by membrane NADPH oxidase 2 (Nox2) in response to TNF-α is facilitated by AQP3 and required for NF-κB activation by regulation of protein phosphatase 2A. As AQP3 associates with Nox2, we propose that this interplay constitutes H2O2-mediated signalling in response to TNF-α stimulation. Collectively, these data indicate that AQP3-facilitated H2O2 transport is required for NF-κB activation in keratinocytes in the development of psoriasis.

Cellular dissection of psoriasis for transcriptome analyses and the post-GWAS era

Background

Genome-scale studies of psoriasis have been used to identify genes of potential relevance to disease mechanisms. For many identified genes, however, the cell type mediating disease activity is uncertain, which has limited our ability to design gene functional studies based on genomic findings.

Methods

We identified differentially expressed genes (DEGs) with altered expression in psoriasis lesions (n = 216 patients), as well as candidate genes near susceptibility loci from psoriasis GWAS studies. These gene sets were characterized based upon their expression across 10 cell types present in psoriasis lesions. Susceptibility-associated variation at intergenic (non-coding) loci was evaluated to identify sites of allele-specific transcription factor binding.

Results

Half of DEGs showed highest expression in skin cells, although the dominant cell type differed between psoriasis-increased DEGs (keratinocytes, 35%) and psoriasis-decreased DEGs (fibroblasts, 33%). In contrast, psoriasis GWAS candidates tended to have highest expression in immune cells (71%), with a significant fraction showing maximal expression in neutrophils (24%, P < 0.001). By identifying candidate cell types for genes near susceptibility loci, we could identify and prioritize SNPs at which susceptibility variants are predicted to influence transcription factor binding. This led to the identification of potentially causal (non-coding) SNPs for which susceptibility variants influence binding of AP-1, NF-κB, IRF1, STAT3 and STAT4.

Conclusions

These findings underscore the role of innate immunity in psoriasis and highlight neutrophils as a cell type linked with pathogenetic mechanisms. Assignment of candidate cell types to genes emerging from GWAS studies provides a first step towards functional analysis, and we have proposed an approach for generating hypotheses to explain GWAS hits at intergenic loci.