Skin deep: Epithelial cell metabolism and chronic skin inflammation.

Skin inflammation is potentiated by coordinated epithelial and immune cell metabolism. In this issue of Immunity, Subudhi and Konieczny et al. delineate how HIF1α regulates epithelial cell glycolysis during psoriasis. In turn, lactate is a byproduct that augments type 17 γδ T cell responses to sustain inflammatory skin disease.

Metabolic coordination between skin epithelium and type 17 immunity sustains chronic skin inflammation.

Inflammatory epithelial diseases are spurred by the concomitant dysregulation of immune and epithelial cells. How these two dysregulated cellular compartments simultaneously sustain their heightened metabolic demands is unclear. Single-cell and spatial transcriptomics (ST), along with immunofluorescence, revealed that hypoxia-inducible factor 1α (HIF1α), downstream of IL-17 signaling, drove psoriatic epithelial remodeling. Blocking HIF1α in human psoriatic lesions ex vivo impaired glycolysis and phenocopied anti-IL-17 therapy. In a murine model of skin inflammation, epidermal-specific loss of HIF1α or its target gene, glucose transporter 1, ameliorated epidermal, immune, vascular, and neuronal pathology. Mechanistically, glycolysis autonomously fueled epithelial pathology and enhanced lactate production, which augmented the γδ T17 cell response. RORγt-driven genetic deletion or pharmacological inhibition of either lactate-producing enzymes or lactate transporters attenuated epithelial pathology and IL-17A expression in vivo. Our findings identify a metabolic hierarchy between epithelial and immune compartments and the consequent coordination of metabolic processes that sustain inflammatory disease.

Metabolic rewiring of macrophages by epidermal-derived lactate promotes sterile inflammation in the murine skin.

Dysregulated macrophage responses and changes in tissue metabolism are hallmarks of chronic inflammation in the skin. However, the metabolic cues that direct and support macrophage functions in the skin are poorly understood. Here, we show that during sterile skin inflammation, the epidermis and macrophages uniquely depend on glycolysis and the TCA cycle, respectively. This compartmentalisation is initiated by ROS-induced HIF-1α stabilization leading to enhanced glycolysis in the epidermis. The end-product of glycolysis, lactate, is then exported by epithelial cells and utilized by the dermal macrophages to induce their M2-like fates through NF-κB pathway activation. In addition, we show that psoriatic skin disorder is also driven by such lactate metabolite-mediated crosstalk between the epidermis and macrophages. Notably, small-molecule inhibitors of lactate transport in this setting attenuate sterile inflammation and psoriasis disease burden, and suppress M2-like fate acquisition in dermal macrophages. Our study identifies an essential role for the metabolite lactate in regulating macrophage responses to inflammation, which may be effectively targeted to treat inflammatory skin disorders such as psoriasis.

naRNA-LL37 composite DAMPs define sterile NETs as self-propagating drivers of inflammation.

Neutrophil extracellular traps (NETs) are a key antimicrobial feature of cellular innate immunity mediated by polymorphonuclear neutrophils (PMNs). NETs counteract microbes but are also linked to inflammation in atherosclerosis, arthritis, or psoriasis by unknown mechanisms. Here, we report that NET-associated RNA (naRNA) stimulates further NET formation in naive PMNs via a unique TLR8-NLRP3 inflammasome-dependent pathway. Keratinocytes respond to naRNA with expression of psoriasis-related genes (e.g., IL17, IL36) via atypical NOD2-RIPK signaling. In vivo, naRNA drives temporary skin inflammation, which is drastically ameliorated by genetic ablation of RNA sensing. Unexpectedly, the naRNA-LL37 'composite damage-associated molecular pattern (DAMP)' is pre-stored in resting neutrophil granules, defining sterile NETs as inflammatory webs that amplify neutrophil activation. However, the activity of the naRNA-LL37 DAMP is transient and hence supposedly self-limiting under physiological conditions. Collectively, upon dysregulated NET release like in psoriasis, naRNA sensing may represent both a potential cause of disease and a new intervention target.

IL-17A Orchestrates Reactive Oxygen Species/HIF1α-Mediated Metabolic Reprogramming in Psoriasis.

Immune cell-derived IL-17A is one of the key pathogenic cytokines in psoriasis, an immunometabolic disorder. Although IL-17A is an established regulator of cutaneous immune cell biology, its functional and metabolic effects on nonimmune cells of the skin, particularly keratinocytes, have not been comprehensively explored. Using multiomics profiling and systems biology-based approaches, we systematically uncover significant roles for IL-17A in the metabolic reprogramming of human primary keratinocytes (HPKs). High-throughput liquid chromatography-tandem mass spectrometry and nuclear magnetic resonance spectroscopy revealed IL-17A-dependent regulation of multiple HPK proteins and metabolites of carbohydrate and lipid metabolism. Systems-level MitoCore modeling using flux-balance analysis identified IL-17A-mediated increases in HPK glycolysis, glutaminolysis, and lipid uptake, which were validated using biochemical cell-based assays and stable isotope-resolved metabolomics. IL-17A treatment triggered downstream mitochondrial reactive oxygen species and HIF1α expression and resultant HPK proliferation, consistent with the observed elevation of these downstream effectors in the epidermis of patients with psoriasis. Pharmacological inhibition of HIF1α or reactive oxygen species reversed IL-17A-mediated glycolysis, glutaminolysis, lipid uptake, and HPK hyperproliferation. These results identify keratinocytes as important target cells of IL-17A and reveal its involvement in multiple downstream metabolic reprogramming pathways in human skin.

Treg cells require Izumo1R to regulate γδT cell-driven inflammation in the skin.

Izumo1R is a pseudo-folate receptor with an essential role in mediating tight oocyte/spermatozoa contacts during fertilization. Intriguingly, it is also expressed in CD4+ T lymphocytes, in particular Treg cells under the control of Foxp3. To understand Izumo1R function in Treg cells, we analyzed mice with Treg-specific Izumo1r deficiency (Iz1rTrKO). Treg differentiation and homeostasis were largely normal, with no overt autoimmunity and only marginal increases in PD1+ and CD44hi Treg phenotypes. pTreg differentiation was also unaffected. Iz1rTrKO mice proved uniquely susceptible to imiquimod-induced, γδT cell-dependent, skin disease, contrasting with normal responses to several inflammatory or tumor challenges, including other models of skin inflammation. Analysis of Iz1rTrKO skin revealed a subclinical inflammation that presaged IMQ-induced changes, with an imbalance of Rorγ+ γδT cells. Immunostaining of normal mouse skin revealed the expression of Izumo1, the ligand for Izumo1R, electively in dermal γδT cells. We propose that Izumo1R on Tregs enables tight contacts with γδT cells, thereby controlling a particular path of skin inflammation.

Deficiency in IL-17-committed Vγ4(+) γδ T cells in a spontaneous Sox13-mutant CD45.1(+) congenic mouse substrain provides protection from dermatitis.

Interleukin 17 (IL-17)-committed γδ T cells (γδT17 cells) participate in many immune responses, but their developmental requirements and subset specific functions remain poorly understood. Here we report that a commonly used CD45.1(+) congenic C57BL/6 mouse substrain is characterized by selective deficiency in Vγ4(+) γδT17 cells. This trait was due to a spontaneous mutation in the gene encoding the transcription factor Sox13 that caused an intrinsic defect in development of those cells in the neonatal thymus. The γδT17 cells migrated from skin to lymph nodes at low rates. In a model of psoriasis-like dermatitis, the Vγ4(+) γδT17 cell subset expanded considerably in lymph nodes and homed to inflamed skin. Sox13-mutant mice were protected from psoriasis-like skin changes, which identified a role for Sox13-dependent γδT17 cells in this inflammatory condition.

IL-21 promoting angiogenesis contributes to the development of psoriasis.

BACKGROUND: Elevated IL-21 expression which can effectively induce Th17 cell differentiation has been implicated in the pathogenesis of psoriasis, but its role in angiogenesis remains poorly understood. METHODS: PASI and PSI score assessment was applied to evaluate the severity of psoriatic lesions. The expression of IL-21, IL-21 receptor (IL-21R), CD31, VEGFA, MMP-9, and ICAM-1 in skin was determined by immunohistochemistry or quantitative real-time polymerase chain reaction. The serum level of IL-21 was measured by enzyme-linked immunosorbent assay (ELISA). Then, their correlation was analyzed statistically. Human umbilical vein endothelial cells (HUVECs) cocultured with conditional medium from normal human epidermal keratinocytes (NHEKs) were treated with IL-21 and/or M5 cocktail (mixture of IL-1α, IL-17A, IL-22, TNF-α, and oncostatin M). The migration and tube formation of HUVECs were detected, and the levels of VEGFA, MMP-9, and ICAM-1 in NHEKs were measured by Western blotting or ELISA. RESULTS: Increased IL-21 and IL-21R expression was observed in psoriatic sera or skin specimens, with IL-21R mainly locating in keratinocytes and IL-21 in immune cells. Pearson analysis showed significantly positive correlation between IL-21/IL-21R and erythema scores/microvessel density in psoriatic lesions. Moreover, the expression of proangiogenic genes, VEGFA, ICAM-1, and MMP-9 was upregulated in skins of psoriasis. Additionally, in M5 microenvironment, migration and tube formation could be magnified in HUVECs using IL-21 pre-treated NHEK medium. Mechanically, the co-stimulation of IL-21 and M5 to NEHKs increased the expression of ICAM-1. CONCLUSION: IL-21 could regulate keratinocytes to secrete ICAM-1, thereby promoting angiogenesis in psoriasis.

ANKRD22 promotes resolution of psoriasiform skin inflammation by antagonizing NIK-mediated IL-23 production.

Inflammation resolution is an essential process for preventing the development of chronic inflammatory diseases. However, the mechanisms that regulate inflammation resolution in psoriasis are not well understood. Here, we report that ANKRD22 is an endogenous negative orchestrator of psoriasiform inflammation because ANKRD22-deficient mice are more susceptible to IMQ-induced psoriasiform inflammation. Mechanistically, ANKRD22 deficiency leads to excessive activation of the TNFRII-NIK-mediated noncanonical NF-κB signaling pathway, resulting in the hyperproduction of IL-23 in DCs. This is due to ANKRD22 being a negative feedback regulator for NIK because it physically binds to and assists in the degradation of accumulated NIK. Clinically, ANKRD22 is negatively associated with IL-23A expression and psoriasis severity. Of greater significance, subcutaneous administration of an AAV carrying ANKRD22-overexpression vector effectively hastens the resolution of psoriasiform skin inflammation. Our findings suggest ANKRD22, an endogenous supervisor of NIK, is responsible for inflammation resolution in psoriasis, and may be explored in the context of psoriasis therapy.

Keratin 17 in psoriasis: Current understanding and future perspectives.

Keratin 17 (K17) is a multifaceted cytoskeletal protein that is not commonly expressed in the epidermis under normal physiological conditions. However, in psoriasis, K17 is overexpressed in the suprabasal layer of the epidermis and plays an important role in the pathogenesis of the disease. In this review, we have summarized our findings and those reported in other studies concerning the pathogenic functions of K17, as well as the mechanisms underlying the increase in K17 expression in psoriasis. K17 exerts both pro-proliferative and pro-inflammatory effects on keratinocytes. Moreover, K17 peptides trigger autoreactive T cells and promote psoriasis-related cytokine production. In turn, these cytokines modulate the expression, stability, and protein-protein interactions of K17 through transcriptional and translational regulation and post-translational modification of K17 in keratinocytes. Thus, a K17/T-cell/cytokine autoimmune loop is implicated in the pathogenesis of psoriasis, which is supported by the fact that therapies targeting K17 have achieved good outcomes in psoriasis-like mouse models. Future perspectives of K17 in psoriasis have also been discussed to provide potential directions for further studies.

The regulation of the PD-1/PD-L1 pathway in imiquimod-induced chronic psoriasis itch and itch sensitization in mouse.

PD-1/PD-L1 inhibitors have been demonstrated to induce itch in both humans and experimental animals. However, whether the PD-1/PD-L1 pathway is involved in the regulation of chronic psoriatic itch remains unclear. This study aimed to investigate the role of the PD-1/PD-L1 pathway in imiquimod-induced chronic psoriatic itch. The intradermal injection of PD-L1 in the nape of neck significantly alleviated chronic psoriatic itch in imiquimod-treated skin. Additionally, we observed that spontaneous scratching behavior induced by imiquimod disappeared on day 21. Still, intradermal injection of PD-1/PD-L1 inhibitors could induce more spontaneous scratching for over a month, indicating that imiquimod-treated skin remained in an itch sensitization state after the spontaneous scratching behavior disappeared. During this period, there was a significant increase in PD-1 receptor expression in both the imiquimod-treated skin and the spinal dorsal horn in mice, accompanied by significant activation of microglia in the spinal dorsal horn. These findings suggest the potential involvement of the peripheral and central PD-1/PD-L1 pathways in regulating chronic itch and itch sensitization induced by imiquimod.

Increased expression of complement C3c, iC3b, and cells containing CD11b or CD14 in experimentally induced psoriatic lesion.

Psoriasis is a chronic inflammatory skin disease with a characteristic isomorphic reaction, i.e. the Köbner reaction, induced by slight epidermal trauma. In this study, the tape-stripping technique was used to induce the development of Köbner reaction in 18 subjects with psoriasis. Eight subjects developed a positive reaction. To study the early cellular changes, skin biopsies were taken at the baseline and subsequent time points of 2 h, 1 d, 3 d, and 7 d for the immunostaining of complement C3c, iC3b, and cells expressing complement receptor 3 (CD11b/CD18; a receptor of iC3b) or CD14. The results show that the positive Köbner reaction is associated with rapid (2 h-1 d) and sustained (3-7 d) increase in the expression of epidermal C3c and iC3b and dermal C3c. In addition, there was a positive correlation between CD11b+ and CD14+ cells in baseline and 2 h-1 d biopsies with a subsequent increase in CD11b+ and CD14+ cells in 3-7 d biopsies in the Köbner-positive group. In the Köbner-negative group, only a transient increase in epidermal iC3b at 2 h-1 d, as well as rapid (2 h-1 d) and sustained increase (3-7 d) in dermal iC3b and CD14+ cells, was observed. In experiments with cultured monolayer keratinocytes, a slight cell damage already at 30 mJ/cm2 ultraviolet B irradiation led to increased expression of C3c, but not iC3b. Therefore, there are marked differences between Köbner groups in respect to the expression of C3c, iC3b, and cells expressing CD11b or CD14. Of note is the rapid and sustained increase in epidermal C3c and iC3b in the positive Köbner reaction.

LIGHT signaling through LTßR and HVEM in keratinocytes promotes psoriasis and atopic dermatitis-like skin inflammation.

Psoriasis (PS) and atopic dermatitis (AD) are common skin inflammatory diseases characterized by hyper-responsive keratinocytes. Although, some cytokines have been suggested to be specific for each disease, other cytokines might be central to both diseases. Here, we show that Tumor necrosis factor superfamily member 14 (TNFSF14), known as LIGHT, is required for experimental PS, similar to its requirement in experimental AD. Mice devoid of LIGHT, or deletion of either of its receptors, lymphotoxin ß receptor (LTßR) and herpesvirus entry mediator (HVEM), in keratinocytes, were protected from developing imiquimod-induced psoriatic features, including epidermal thickening and hyperplasia, and expression of PS-related genes. Correspondingly, in single cell RNA-seq analysis of PS patient biopsies, LTßR transcripts were found strongly expressed with HVEM in keratinocytes, and LIGHT was upregulated in T cells. Similar transcript expression profiles were also seen in AD biopsies, and LTßR deletion in keratinocytes also protected mice from allergen-induced AD features. Moreover, in vitro, LIGHT upregulated a broad spectrum of genes in human keratinocytes that are clinical features of both PS and AD skin lesions. Our data suggest that agents blocking LIGHT activity might be useful for therapeutic intervention in PS as well as in AD.

Differences in transcriptional changes in psoriasis and psoriatic arthritis skin with immunoglobulin gene enrichment in psoriatic arthritis.

OBJECTIVES: Approximately 20% of people with psoriasis develop PsA. Although genetic, clinical and environmental risk factors have been identified, it is not known why some people with psoriasis develop PsA. The skin disease is traditionally considered the same in both. This study compares transcriptional changes in psoriasis and PsA skin for the first time. METHODS: Skin biopsies were collected from healthy controls (HC), and uninvolved and lesional skin from patients with PsA. Bulk tissue sequencing was performed and analysed using the pipeline Searchlight 2.0. Transcriptional changes in PsA skin were compared with existing sequencing data from participants with psoriasis without PsA (GSE121212). Psoriasis and PsA datasets could not be directly compared as different analysis methods were used. Data from participants with PsA in the GSE121212 dataset were used for validation. RESULTS: Skin samples from 9 participants with PsA and 9 HC were sequenced, analysed and compared with available transcriptomic data for 16 participants with psoriasis compared with 16 HC. Uninvolved skin in psoriasis shared transcriptional changes with lesional skin in psoriasis, but uninvolved skin in PsA did not. Most transcriptional changes in psoriasis and PsA lesional skin were shared, but immunoglobulin genes were upregulated in PsA lesional skin specifically. The transcription factor POU2F1, which regulates immunoglobulin gene expression, was enriched in PsA lesional skin. This was confirmed in the validation cohort. CONCLUSIONS: Immunoglobulin genes are upregulated in PsA but not in psoriasis skin lesions. This may have implications for the spread from the cutaneous compartment to other tissues.

Increased tissue expression of IL-31 in patients with psoriasis.

Psoriasis is a chronic inflammatory skin disease, and its pathogenesis remains unclear. Although many studies have demonstrated the role of serum interleukin-31 (IL-31) in psoriasis, only one study has examined histopathological expression in lesional skin. This study aimed to investigate the expression of IL-31 in skin biopsy specimens of psoriasis patients compared to healthy subjects and identify its possible correlation to disease severity and itch intensity. Psoriasis patients and healthy volunteers were recruited. Four-millimeter punch biopsy was performed at the lesional skin of psoriasis patients and normal skin of healthy subjects. Expression of IL-31 was measured by immunohistochemistry. Baseline characteristics, disease activity, itch intensity, and related laboratory results were collected. Twenty-six biopsy specimens of psoriasis patients and 10 tissue samples of healthy subjects were evaluated. Epidermal and dermal psoriasis lesions had significantly higher IL-31 expression compared to the healthy skin (P < 0.001). However, there was no significant difference in lesional expression of IL-31 by disease severity or itch intensity. Increased IL-31 expression in the lesions of psoriasis patients suggests the involvement of IL-31 in the pathogenesis of psoriasis.

The opposite effect of tapinarof between IMQ and IL-23 induced psoriasis mouse models.

Tapinarof is an aryl hydrocarbon receptor (AHR) ligand which is used to treat plaque psoriasis in adults. However, the underlying mechanism is not yet fully understood. In this study, we applied two of the most studied psoriasis mouse models: topical application of imiquimod (IMQ) and subcutaneous injection of IL-23. Although both models successfully induced psoriasis-like lesions in mice, tapinarof had a completely opposite effect on the two models. Tapinarof decreased the expression of multiple essential cytokines involved in the pathological IL-23/IL-17/IL-22 axis and ameliorated IMQ-induced psoriatic dermatitis, inhibiting keratinocyte proliferation and abnormal differentiation. However, in the IL-23-injection-model, tapinarof instead aggravated the disease. Here, tapinarof increased epidermal thickness and differentiated epidermal dysplasia in mice. Our data suggest that tapinarof may have different effects on varied types of psoriasis.

Extracellular vesicles from keratinocytes and other skin-related cells in psoriasis: A review.

Psoriasis is a highly prevalent chronic inflammatory skin condition involving abnormal proliferation and differentiation of keratinocytes, together with substantial infiltration of immune cells. Extracellular vesicles (EVs), which are released spontaneously into the extracellular space by virtually all cell types, play a crucial role in cell-to-cell communication by delivering bioactive cargos such as mRNA nucleic acids and proteins to recipient cells. Numerous studies have highlighted the significant contributions of EVs to both the pathogenesis and treatment of psoriasis. This review provides a concise overview of skin-derived EVs and their involvement in the pathogenesis of psoriasis.

Serum miRNA profiling identified miRNAs associated with disease severity in psoriasis.

Psoriasis vulgaris is a chronic, autoimmune skin disease involving a complex interplay of epidermal keratinocytes, dermal fibroblast and infiltrating immune cells. Differential expressions of miRNAs are observed in psoriasis and the deregulated miRNAs are sometimes associated with disease severity. This study aims to identify miRNAs altered in the serum of psoriasis patients that are associated with the Psoriasis Area and Severity Index (PASI). In order to assess miRNA levels in the serum of psoriasis patients, we selected 24 differentially expressed miRNAs in the psoriatic skin are possibly derived from the skin and immune cells, as well as five miRNAs that are enriched in other tissues. We identified 16 miRNAs that exhibited significantly (p < 0.05) altered levels in the serum of psoriasis patients compared to healthy individuals. Among these, 13 miRNAs showed similar expression pattern in the serum of psoriasis patients as also observed in the psoriatic skin tissues. Ten miRNAs showed an accuracy of greater than 75% in classifying the psoriasis patients from healthy individuals. Further analysis of differential miRNA levels between the low PASI group and the high PASI group identified three miRNAs (miR-147b, miR-3614-5p, and miR-125a-5p) with significantly altered levels between the low severity and the high severity psoriasis patients. Our systematic investigation of skin and immune cell-derived miRNAs in the serum of psoriasis patients revealed alteration in miRNA levels to be associated with disease severity, which may help in monitoring the disease progression and therapeutic response.

The m6 A modification of Il17a in CD4+ T cells promotes inflammation in psoriasis.

Psoriasis is a chronic inflammatory skin disorder. The mechanism of psoriasis pathogenesis is not entirely clear. Here, we reported that the level of the N6-methyladenosine (m6 A) modification was increased in psoriatic CD4+ T cells compared with healthy controls. In the psoriasis mouse model, depletion of the RNA demethylase, Alkbh5, from CD4+ T cells promoted the psoriasis-like phenotype and inflammation. Intriguingly, this phenotype and inflammation were alleviated by the ablation of the m6 A methyltransferase Mettl3 in CD4+ T cells. Mechanistically, we found that the m6 A modification of IL17A mRNA increased the expression of IL-17A (an important pro-inflammatory factor in psoriasis) and promoted psoriasis. Thus, our study provided evidence that the m6 A modification of IL17A in CD4+ T cells regulates inflammation in psoriasis.

eIF4E plays the role of a pathogenic gene in psoriasis, and the inhibition of eIF4E phosphorylation ameliorates psoriasis-like skin damage.

Psoriasis is a complex inflammatory skin disease with uncertain pathogenesis. eIF4E (eukaryotic translation initiation factor 4E) and its phosphorylation state p-eIF4E are highly expressed in psoriatic tissues. However, the role eIF4E played in psoriasis is still unclear. To investigate the function of eIF4E and p-eIF4E in psoriasis and to figure out whether eFT-508 (Tomivosertib, eIF4E phosphorylation inhibitor) can relieve the disease severity and become a promising candidate for the psoriasis treatment. We first verified the expression of eIF4E and p-eIF4E in psoriasis patients' lesional skin. Then, we demonstrated the effect of eIF4E and p-eIF4E on the abnormal proliferation and inflammatory state of keratinocytes by using eIF4E-specific small interfering RNA (si-eIF4E) and eFT-508. In this study, all cell experiments were performed under the psoriasis-model condition. Moreover, the external application of eFT-508 on imiquimod (IMQ)-induced psoriasis mice was performed to explore its potential clinical value. Results showed that eIF4E and p-eIF4E were significantly overexpressed in skin lesions of psoriasis patients. Knocking down eIF4E or adding eFT-508 can relieve the abnormal proliferation and the excessive inflammatory state of keratinocytes by reducing the expression of cyclin D1, IL-1ß, CXCL10, IL23, Wnt 5a, NBS1 and p-AKT from mRNA or protein levels. Furthermore, these results were consistent with those obtained from the in vitro experiments. Then, we conclude that eIF4E plays the role of the pathogenic gene in psoriasis, and eFT-508 may be a promising candidate for anti-prosoriasis drugs.