Metabolic Pathways That Control Skin Homeostasis and Inflammation

A Familial Novel Putative-Pathogenic Mutation Identified in Plaque-Psoriasis by a Multigene Panel Analysis

Psoriasis is a chronic multifactorial skin disorder with an immune basis. It is characterized by patches of skin that are usually red, flaky and crusty, and that often release silvery scales. The patches appear predominantly on the elbows, knees, scalp and lower back, although they may also appear on other body areas and severity may be variable. The majority of patients (about 90%) present small patches known as "plaque psoriasis". The roles of environmental triggers such as stress, mechanical trauma and streptococcal infections are well described in psoriasis onset, but much effort is still needed to unravel the genetic component. The principal aim of this study was to use a next-generation sequencing technologies-based approach together with a 96 customized multigene panel in the attempt to determine if there are germline alterations that can explain the onset of the disease, and thus to find associations between genotypes and phenotypes. To this aim, we analyzed a family in which the mother showed mild psoriasis, and her 31-year-old daughter had suffered from psoriasis for several years, whereas an unaffected sister served as a negative control. We found variants already associated directly to psoriasis in the TRAF3IP2 gene, and interestingly we found a missense variant in the NAT9 gene. The use of multigene panels in such a complex pathology such as psoriasis can be of great help in identifying new susceptibility genes, and in being able to make early diagnoses especially in families with affected subjects.

Metabolomics analysis reveals cytotoxic effects of ouabain towards psoriatic keratinocytes via impairment of glutathione metabolism

Ouabain is a cardiac glycoside long studied for treating heart diseases, but the attempts to evaluate its anti-psoriatic activity have not been reported. We aimed to explore the effects of ouabain on proliferation and metabolism towards psoriatic keratinocytes. In human HaCaT keratinocytes, ouabain potently decreased viability, promoted apoptosis and caused G2/M cycle arrest. Metabolomics analysis indicated that ouabain markedly impaired glutathione metabolism. The solute carrier family 7 member 11 (SLC7A11) is an amino acid transporter highly specific to cysteine, which is critical for glutathione synthesis. Ouabain downregulated SLC7A11, reduced cysteine uptake and subsequently inhibited glutathione synthesis, probably through inhibiting Akt/mTOR/beclin axis that regulate protein activity of SLC7A11. The impaired glutathione synthesis and oxidative stress caused by ouabain may contribute to its cytotoxicity towards psoriatic keratinocytes. Our results provide experimental evidence supporting further study of ouabain as a potential anti-psoriatic agent.

Bibliometric Study of Adaptogens in Dermatology: Pharmacophylogeny, Phytochemistry, and Pharmacological Mechanisms

Background

Adaptogens are a class of medicinal plants that can nonspecifically enhance human resistance. Most of the plant adaptogens have relevant applications in dermatology, but there are still few studies related to their particular action and co-operative mechanisms in topical skin application.

Methods

Plant adaptogens related articles and reviews that published between 1999 and 2022 were obtained from the Web of Science Core Collection database. Various bibliographic elements were collected, including the annual number of publications, countries/regions, and keywords. CiteSpace, a scientometric software, was used to conduct bibliometric analyses. Also, the patsnap global patent database was used to analyze the patent situation of plant adaptogens in the field of cosmetics up to 2021.

Results

We found that the effects of plant adaptogens on skin diseases mainly involve atopic dermatitis, acne, allergic contact dermatitis, psoriasis, eczema, and androgenetic alopecia, etc. And the effects on skin health mainly involve anti-aging and anti-photoaging, anti-bacterial and anti-fungal, anti-inflammatory, whitening, and anti-hair loss, etc. Also, based on the results of patent analysis, it is found that the effects of plant adaptogens on skin mainly focus on aging retardation. The dermatological effects of plant adaptogens are mainly from Fabaceae Lindl., Araliaceae Juss. and Lamiaceae Martinov., and their mainly efficacy phytochemical components are terpenoids, phenolic compounds and flavonoids.

Conclusion

The plant adaptogens can repair the skin barrier and maintain skin homeostasis by regulating the skin HPA-like axis, influencing the oxidative stress pathway to inhibit inflammation, and regulating the extracellular matrix (ECM) components to maintain a dynamic equilibrium, ultimately achieving the treatment of skin diseases and the maintenance of a healthy state.

Dual targeting of mTOR/IL-17A and autophagy by fisetin alleviates psoriasis-like skin inflammation

Psoriasis is a chronic autoimmune inflammatory skin disorder characterized by epidermal hyperplasia and aberrant immune response. In addition to aberrant cytokine production, psoriasis is associated with activation of the Akt/mTOR pathway. mTOR/S6K1 regulates T-lymphocyte activation and migration, keratinocytes proliferation and is upregulated in psoriatic lesions. Several drugs that target Th1/Th17 cytokines or their receptors have been approved for treating psoriasis in humans with variable results necessitating improved therapies. Fisetin, a natural dietary polyphenol with anti-oxidant and anti-proliferative properties, covalently binds mTOR/S6K1. The effects of fisetin on psoriasis and its underlying mechanisms have not been clearly defined. Here, we evaluated the immunomodulatory effects of fisetin on Th1/Th17-cytokine-activated adult human epidermal keratinocytes (HEKa) and anti-CD3/CD28-stimulated inflammatory CD4+ T cells and compared these activities with those of rapamycin (an mTOR inhibitor). Transcriptomic analysis of HEKa revealed 12,713 differentially expressed genes (DEGs) in the fisetin-treated group compared to 7,374 DEGs in the rapamycin-treated group, both individually compared to a cytokine treated group. Gene ontology analysis revealed enriched functional groups related to PI3K/Akt/mTOR signaling pathways, psoriasis, and epidermal development. Using in silico molecular modeling, we observed a high binding affinity of fisetin to IL-17A. In vitro, fisetin significantly inhibited mTOR activity, increased the expression of autophagy markers LC3A/B and Atg5 in HEKa cells and suppressed the secretion of IL-17A by activated CD4+ T lymphocytes or T lymphocytes co-cultured with HEKa. Topical administration of fisetin in an imiquimod (IMQ)-induced mouse psoriasis model exhibited a better effect than rapamycin in reducing psoriasis-like inflammation and Akt/mTOR phosphorylation and promoting keratinocyte differentiation and autophagy in mice skin lesions. Fisetin also significantly inhibited T-lymphocytes and F4/80+ macrophage infiltration into skin. We conclude that fisetin potently inhibits IL-17A and the Akt/mTOR pathway and promotes keratinocyte differentiation and autophagy to alleviate IMQ-induced psoriasis-like disease in mice. Altogether, our findings suggest fisetin as a potential treatment for psoriasis and possibly other inflammatory skin diseases.

A prediction model identifying glycolysis signature as therapeutic target for psoriasis

Background

The hyperproliferation featured with upregulated glycolysis is a hallmark of psoriasis. However, molecular difference of keratinocyte glycolysis amongst varied pathologic states in psoriasis remain elusive.

Objectives

To characterize glycolysis status of psoriatic skin and assess the potential of glycolysis score for therapeutic decision.

Methods

We analyzed 345414 cells collected from different cohorts of single-cell RNA seq database. A new method, Scissor, was used to integrate the phenotypes in GSE11903 to guide single-cell data analysis, allowing identification of responder subpopulations. AUCell algorithm was performed to evaluate the glycolysis status of single cell. Glycolysis signature was used for further ordering in trajectory analysis. The signature model was built with logistic regression analysis and validated using external datasets.

Results

Keratinocytes (KCs) expressing SLC2A1 and LDH1 were identified as a novel glycolysis-related subpopulation. Scissor⁺ cells and Scissor^- cells were defined as response and non-response phenotypes. In Scissor⁺ SLC2A1⁺ LDH1⁺ KCs, ATP synthesis pathway was activated, especially, the glycolysis pathway being intriguing. Based on the glycolysis signature, keratinocyte differentiation was decomposed into a three-phase trajectory of normal, non-lesional, and lesional psoriatic cells. The area under the curve (AUC) and Brier score (BS) were used to estimate the performance of the glycolysis signature in distinguishing response and non-response samples in GSE69967 (AUC =0.786, BS =17.7) and GSE85034 (AUC=0.849, BS=11.1). Furthermore, Decision Curve Analysis suggested that the glycolysis score was clinically practicable.

Conclusion

We demonstrated a novel glycolysis-related subpopulation of KCs, identified 12-glycolysis signature, and validated its promising predictive efficacy of treatment effectiveness.

Acute cytokine treatment stimulates glucose uptake and glycolysis in human keratinocytes

During inflammation, cellular glucose uptake and glycolysis are upregulated to meet an increased energy demand. For example, keratinocyte glycolysis is essential for progression of psoriasis. Therefore, understanding the regulation of glucose metabolism in keratinocytes is of importance. Here, we show that the pro-inflammatory cytokines IFNγ and TNF together rapidly induce glucose uptake, glycolysis, and glycolytic capacity in cultured keratinocytes. Furthermore, we found that acute IFNγ and TNF stimulation induces glucose transporter 4 (GLUT4) translocation to the plasma membrane and engages AMPK-dependent intracellular signaling. Together, these findings suggest acute cytokine-induced glucose metabolism in keratinocytes could contribute to inflammation in psoriatic disease, and that GLUT4 is involved in these processes.

Epidermal stratification requires retromer-mediated desmoglein-1 recycling

Sorting transmembrane cargo is essential for tissue development and homeostasis. However, mechanisms of intracellular trafficking in stratified epidermis are poorly understood. Here, we identify an interaction between the retromer endosomal trafficking component, VPS35, and the desmosomal cadherin, desmoglein-1 (Dsg1). Dsg1 is specifically expressed in stratified epidermis and, when properly localized on the plasma membrane of basal keratinocytes, promotes stratification. We show that the retromer drives Dsg1 recycling from the endo-lysosomal system to the plasma membrane to support human keratinocyte stratification. The retromer-enhancing chaperone, R55, promotes the membrane localization of Dsg1 and a trafficking-deficient mutant associated with a severe inflammatory skin disorder, enhancing its ability to promote stratification. In the absence of Dsg1, retromer association with and expression of the glucose transporter GLUT1 increases, exposing a potential link between Dsg1 deficiency and epidermal metabolism. Our work provides evidence for retromer function in epidermal regeneration, identifying it as a potential therapeutic target.

Research Advances on the Damage Mechanism of Skin Glycation and Related Inhibitors

Our skin is an organ with the largest contact area between the human body and the external environment. Skin aging is affected directly by both endogenous factors and exogenous factors (e.g., UV exposure). Skin saccharification, a non-enzymatic reaction between proteins, e.g., dermal collagen and naturally occurring reducing sugars, is one of the basic root causes of endogenous skin aging. During the reaction, a series of complicated glycation products produced at different reaction stages and pathways are usually collectively referred to as advanced glycation end products (AGEs). AGEs cause cellular dysfunction through the modification of intracellular molecules and accumulate in tissues with aging. AGEs are also associated with a variety of age-related diseases, such as diabetes, cardiovascular disease, renal failure (uremia), and Alzheimer's disease. AGEs accumulate in the skin with age and are amplified through exogenous factors, e.g., ultraviolet radiation, resulting in wrinkles, loss of elasticity, dull yellowing, and other skin problems. This article focuses on the damage mechanism of glucose and its glycation products on the skin by summarizing the biochemical characteristics, compositions, as well as processes of the production and elimination of AGEs. One of the important parts of this article would be to summarize the current AGEs inhibitors to gain insight into the anti-glycation mechanism of the skin and the development of promising natural products with anti-glycation effects.

Edible bird’s nest, an Asian health food supplement, possesses anti-inflammatory responses in restoring the symptoms of atopic dermatitis: An analysis of signaling cascades

Edible bird’s nest (EBN) is a Chinese delicacy possessing skin rejuvenating functions. To verify skin anti-inflammatory function of EBN, water extract and enzymatic digest of EBN, as well as the major sialic acid, N-acetyl neuraminic acid (NANA), were probed in TNF-α-treated HaCaT keratinocytes. The mRNA expressions of pro-inflammatory cytokines, e.g., IL-1β, IL-6, TNF-α, and an enzyme responsible for inflammatory response, i.e., Cox-2, as well as filaggrin and filaggrin-2, were markedly altered after treating with different preparations of EBN. The EBN-mediated responses could be accounted by its robust reduction of reactive oxygen species (ROS), NF-κB signaling and phosphorylation of p38 MAPK and JNK, as triggered by TNF-α-induced inflammation. The anti-inflammatory response of EBN was further supported in animal model. In 2,4-dinitrochlorobenzene (DNCB)-induced dermatitic mice, the effects on skin thickness, severity level of damage and scratching behavior, exerted by DNCB, were reversed after EBN treatments, in dose-dependent manners. In parallel, the levels of immune cells and pro-inflammatory cytokines in dermatitic skin were markedly reduced by treatment of EBN preparations. In general, NANA and enzymatic digest of EBN showed better anti-inflammatory responses in both models of in vitro and in vivo. These lines of evidence therefore suggest the possible application of EBN in treating atopic dermatitis.

Effects of ambient PM2.5 on development of psoriasiform inflammation through KRT17-dependent activation of AKT/mTOR/HIF-1α pathway

Exposure to fine particulate matter (PM2.5) has significant effects on human skin health, mainly disrupting skin homeostasis and accelerating aging. To date, the effects of PM2.5 on psoriasis (PSO) have not been elucidated. An ambient particulate matter exposed and well characterized imiquimod (IMQ)-induced psoriasis mouse model was established. Thirty male C57BL/6 mice aged 8 weeks were randomly divided into three groups: filtered air (FA) group (Control group), PSO+ FA group and PSO + PM2.5 group. A KRT17 knockdown (KRT17-KD) mouse model was simultaneously established by subcutaneously injecting KRT17-KD lentivirus. Forty male C57BL/6 mice were randomly divided into four groups: PSO + FA + KRT17-RNAi negative control lentivirus (KRT17-NC) group, PSO+ FA+ KRT17-KD group, PSO + PM2.5 + KRT17-NC group and PSO + PM2.5 + KRT17-KD group. PM2.5 exposure continued for 8 weeks. Psoriasis was induced by topically applying IMQ on the dorsal skin of the mice for 6 days during week 8. Morphometric and histological analyses were performed to investigate the changes in psoriatic lesions. Differentially expressed genes and enriched pathways were explored using bioinformatics analysis and showed that KRT17 gene and the vascular endothelial growth factor receptor signaling pathway were associated with psoriasis. HaCaT cells were stimulated with interleukin-17A and infected with KRT17-KD lentivirus to establish an in vitro KRT17 knockdown psoriasis cell model. Notably, PM2.5 exposure increased the expression of KRT17 protein and activated AKT/mTOR/HIF-1α signaling pathway in vivo. Moreover, specific agonist of AKT (740Y-P) reversed the decreased neovascularization induced by KRT17 knockdown through AKT/mTOR/HIF-1α signaling pathway in vitro. Consequently, PM2.5 exposure could promote the development and progression of psoriasis through KRT17-dependent activation of AKT/mTOR/HIF-1α signaling pathway.

The regulation of skin homeostasis, repair and the pathogenesis of skin diseases by spatiotemporal activation of epidermal mTOR signaling

The epidermis, the outmost layer of the skin, is a stratified squamous epithelium that protects the body from the external world. The epidermis and its appendages need constantly renew themselves and replace the damaged tissues caused by environmental assaults. The mechanistic target of rapamycin (mTOR) signaling is a central controller of cell growth and metabolism that plays a critical role in development, homeostasis and diseases. Recent findings suggest that mTOR signaling is activated in a spatiotemporal and context-dependent manner in the epidermis, coordinating diverse skin homeostatic processes. Dysregulation of mTOR signaling underlies the pathogenesis of skin diseases, including psoriasis and skin cancer. In this review, we discuss the role of epidermal mTOR signaling activity and function in skin, with a focus on skin barrier formation, hair regeneration, wound repair, as well as skin pathological disorders. We propose that fine-tuned control of mTOR signaling is essential for epidermal structural and functional integrity.

Therapeutic effects of myricetin on atopic dermatitis in vivo and in vitro

BACKGROUND

Myricetin (Myr) is a flavonoid compound that exist widely in many natural plants. Myr has been proven to have multiple biological functions, including immunomodulatory and anti-inflammatory effects.

PURPOSE

In this study, we investigated the therapeutic effect of Myr on calcipotriol (MC903) induced atopic dermatitis (AD) mouse model and tumor necrosis factor (TNF)-α/interferon (IFN)-γ stimulated human immortal keratinocyte line (HaCaT) in vivo and in vitro.

METHODS

MC903 was applied topically to the left ears of mice to establish AD mouse model. After the AD model established successfully, the cream base, dexamethasone (DEX) cream or Myr cream were applied on the lesions of mice for 8 days. Through measuring ear thickness and scoring dermatitis severity, we evaluated the therapeutic effect of Myr, the draining lymph nodes (DLNs) and ears of the mice were collected for mechanistic study. In addition, TNF-α and IFN-γ-activated HaCaT cells were used to investigate the underlying mechanism.

RESULTS

Our data demonstrated that Myr alleviated the symptoms of AD by exerting anti-inflammatory and anti-allergic functions in vivo. We found that Myr treatment suppressed ear swelling and IgE level in the serum, reduced the infiltration of mast cells in skin lesions, decreased expressions of thymus and activation regulated chemokine (TARC), IL-4, IFN-γ and thymic stromal lymphopoietin (TSLP) in ear lesions, increased the expressions of filaggrin (FLG). Furthermore, our experimental results demonstrated that Myr down-regulated the mRNA expressions of T-bet and GATA-3 in DLNs. In vitro, Myr treatment decreased MDC and TARC expressions in IFN-γ and TNF-α-induced HaCaT cells by blocking the NF-κB and STAT1 signal pathway.

CONCLUSION

The present study is the first to investigate the anti-atopic effects of Myr. Our findings suggested the therapeutic effects of Myr against MC903-induced AD-like skin lesions in mice. Therefore, Myr may be a potential therapeutic agent for AD.

Serine and arginine rich splicing factor 1 deficiency alters pathways involved in IL-17A expression and is implicated in human psoriasis

Serine and Arginine Rich Splicing Factor 1 (SRSF1) is a splicing factor that binds to exonic enhancers and stimulates splicing and is previously implicated with autoimmunity. Herein, we investigate the role of SRSF1 in regulating innate immune functions that are pertinent in the pathogenesis of auto-inflammatory diseases. Specifically, we show that conditional deletion of SRSF1 in mature lymphocytes resulted in higher expression of il-17a and il-17 f and an expansion of IL17A+ CD8 T cells. Mechanistically, the aberrant expression of IL-17A in SRSF1 cKO mice could not be attributed to alternative splicing of il-17a or il-17 f genes but possibly to defective CD11B+LY6C+ myeloid derived suppressor function in the spleen. Finally, meta-analysis of RNA-Seq collected from psoriasis patients demonstrate a clear correlation between SRSF1 and psoriasis that suggests a putative role of SRSF1 in IL-17A-induced psoriasis.

Role of mTOR Signaling Cascade in Epidermal Morphogenesis and Skin Barrier Formation

Simple Summary

The skin epidermis is a stratified multilayered epithelium that provides a life-sustaining protective and defensive barrier for our body. The barrier machinery is established and maintained through a tightly regulated keratinocyte differentiation program. Under normal conditions, the basal layer keratinocytes undergo active proliferation and migration upward, differentiating into the suprabasal layer cells. Perturbation of the epidermal differentiation program often results in skin barrier defects and inflammatory skin disorders. The protein kinase mechanistic target of rapamycin (mTOR) is the central hub of cell growth, metabolism and nutrient signaling. Over the past several years, we and others using transgenic mouse models have unraveled that mTOR signaling is critical for epidermal differentiation and barrier formation. On the other hand, there is increasing evidence that disturbed activation of mTOR signaling is significantly implicated in the development of various skin diseases. In this review, we focus on the formation of skin barrier and discuss the current understanding on how mTOR signaling networks, including upstream inputs, kinases and downstream effectors, regulate epidermal differentiation and skin barrier formation. We hope this review will help us better understand the metabolic signaling in the epidermis, which may open new vistas for epidermal barrier defect-associated disease therapy.

Abstract

The skin epidermis, with its capacity for lifelong self-renewal and rapid repairing response upon injury, must maintain an active status in metabolism. Mechanistic target of rapamycin (mTOR) signaling is a central controller of cellular growth and metabolism that coordinates diverse physiological and pathological processes in a variety of tissues and organs. Recent evidence with genetic mouse models highlights an essential role of the mTOR signaling network in epidermal morphogenesis and barrier formation. In this review, we focus on the recent advances in understanding how mTOR signaling networks, including upstream inputs, kinases and downstream effectors, regulate epidermal morphogenesis and skin barrier formation. Understanding the details of the metabolic signaling will be critical for the development of novel pharmacological approaches to promote skin barrier regeneration and to treat epidermal barrier defect-associated diseases.

Investigating the clinical implication of corneometer and mexameter readings towards objective, efficient evaluation of psoriasis vulgaris severity

In clinical settings, although Psoriasis Area and Severity Index (PASI) scoring system can provide a quick visual assessment of the severity of psoriasis vulgaris, there is still a strong demand for higher efficiency and accuracy in quantifying the inflammation status of psoriatic lesions. Currently, there are already commercial systems, such as the Courage + Khazaka Corneometer and Mexameter that measure skin capacitance and optical reflectance, for conveniently quantifying the status of skin barrier function and erythema of skin. Despite numerous comparisons of the Courage + Khazaka system with the PASI scoring system, they are rarely compared on parity with diffuse reflectance spectroscopy (DRS) based systems. In this study, we employed a custom-built DRS system shown to be able to determine the skin water-protein binding status and the hemoglobin concentration, and we performed cross-validation of the DRS measurement results with the readings derived from the Corneometer and Mexameter as well as a portion of the PASI scores. Our results revealed that the erythema readings from the Mexameter were a good representation of skin oxygenated hemoglobin but not the deoxygenated hemoglobin. On the other hand, the dermatologists recruited in this study were inclined to rate higher scores on the “erythema” category as skin’s deoxygenated hemoglobin level was higher. Thus, the Mexameter derived erythema readings may not be coherent with the PASI erythema scores. Further, the Corneometer derived skin capacitance readings were well correlated to the PASI “desquamation” and “thickness” scores, while the PASI “desquamation” evaluation was a dominating factor contributing to the DRS deduced water-protein binding status. We conclude that the DRS method could be a valuable addition to existing skin capacitance/reflectance measurement systems and the PASI scoring system toward achieving a more efficient and objective clinical psoriasis vulgaris severity evaluation.

Intervention Mechanism of Hunag-Lian Jie-Du Decoction on Canonical Wnt/β-Catenin Signaling Pathway in Psoriasis Mouse Model

Background

Psoriasis is a common chronic inflammatory skin disease with multifactor etiology, characterized by abnormal proliferation and differentiation of keratinocytes. Huang-Lian Jie-Du decoction (HLJDD) is a traditional Chinese medicine prescription with good clinical curative effect on psoriasis. However, its therapeutic mechanisms are still unclear.

Methods

The psoriasis model of SKH-1 nude mice was established by imiquimod-induced and HLJDD gavage was given. Hematoxylin and eosin staining were used to evaluate pathological morphologies, and immunohistochemistry was used to detect the expressions of Wnt1, β-catenin, and c-Myc in psoriasis mice. Western blot was used to examine the expressions of Frizzled-2, LRP5/6, GSK-3β, APC, Axin2, TCF4, LEF1, cyclin D1, TBX3, EPHB2, and NOTUM enzyme.

Results

In this study, HLJDD reduced skin erythema and lesions, decreased the thickness of epidermal and downregulated the expressions of Wnt1, β-catenin, and c-Myc. Western blot results showed that HLJDD reduced the expressions of Wnt receptors Frizzled-2 and LRP5/6, and Wnt downstream target genes TCF4, LEF1, cyclin D1, TBX3, and EPHB2, while upregulated destruction complex proteins GSK-3β, APC, and Axin2.

Conclusions

HLJDD can effectively treat psoriasis and inhibit the Wnt/β-catenin signaling pathway at multiple stages.

Effects of Adipose-Derived Stem Cells and Their Conditioned Medium in a Human Ex Vivo Wound Model

Adult stem cells have been extensively investigated for tissue repair therapies. Adipose-derived stem cells (ASCs) were shown to improve wound healing by promoting re-epithelialization and vascularization as well as modulating the inflammatory immune response. In this study, we used ex vivo human skin cultured in a six-well plate with trans-well inserts as a model for superficial wounds. Standardized wounds were created and treated with allogeneic ASCs, ASCs conditioned medium (ASC-CM), or cell culture medium (DMEM) supplemented with fetal calf serum (FCS). Skin viability (XTT test), histology (hematoxylin and eosin, H and E), β-catenin expression as well as inflammatory mediators and growth factors were monitored over 12 days of skin culture. We observed only a moderate time-dependent decrease in skin metabolic activity while skin morphology was preserved, and re-epithelialization occurred at the wound edges. An increase in β-catenin expression was observed in the newly formed epithelia, especially in the samples treated with ASC-CM. In general, increased growth factors and inflammatory mediators, e.g., hepatocytes growth factor (HGF), platelet-derived growth factor subunit AA (PDGF-AA), IL-1α, IL-7, TNF-α, and IL-10, were observed over the incubation time. Interestingly, different expression profiles were observed for the different treatments. Samples treated with ASC-CM significantly increased the levels of inflammatory cytokines and PDGF-AA with respect to control, whereas the treatment with ASCs in DMEM with 10% FCS resulted in significantly increased levels of fibroblast growth factor-basic (FGF-basic) and moderate increases of immunomodulatory cytokines. These results confirm that the wound microenvironment can influence the type of mediators secreted by ASCs and the mode as to how they improve the wound healing process. Comparative investigations with pre-activated ASCs will elucidate further aspects of the wound healing mechanism and improve the protocols of ACS application.

LncRNA AGXT2L1-2:2 facilitates keratinocytes proliferation and inhibits apoptosis by interacting with estrogen-related receptor alpha in psoriasis

Our previous studies have revealed that long noncoding RNA (lncRNA) AGXT2L1-2:2 was highly expressed in keratinocytes of psoriasis. However, the functions of lnc-AGXT2L1-2:2 in keratinocytes remain unknown. Meanwhile, co-expression network analysis indicated lnc-AGXT2L1-2:2 could interact with estrogen-related receptor alpha (ERRα). In this study, interleukin (IL)-17A could stimulate the production of lnc-AGXT2L1-2:2 in keratinocytes, thus establishing an in vitro cellular model of psoriasis. Lnc-AGXT2L1-2:2 was overexpressed using lentiviral-vector and ERRα was downregulated with small interfering RNA. Then the effects of lnc-AGXT2L1-2:2 and ERRα on viability, apoptosis, and cell cycle in IL-17A-stimulated keratinocytes were assessed by CCK-8, EdU assay, and flow cytometry. We found that lnc-AGXT2L1-2:2 and ERRα both resulted in higher proliferation ability, lower apoptosis rates, and reduction of G0/G1 phase proportion. Furthermore, lnc-AGXT2L1-2:2 could promote the expression of ERRα and siERRα antagonized the effects of lnc-AGXT2L1-2:2 on the phenotypes above in IL-17A-induced keratinocytes. In conclusion, lnc-AGXT2L1-2:2 was found to promote keratinocytes proliferation, inhibit cell apoptosis and the effects of lnc-AGXT2L1-2:2 on keratinocytes are dependent on ERRα.

Beneficial effects of Rocchetta® oligomineral water in HaCaT keratinocytes after ultraviolet-B irradiation

BACKGROUND

Several reports have previously suggested that oligomineral water may have a beneficial immunomodulatory role in skin physiology. However, molecular, and cellular mechanisms through which oligo-elements act in cutaneous trophism have not yet been fully clarified. Among the external stimuli that affect the skin, ultraviolet (UV) radiation, which is frequently encountered in everyday life, is a major environmental factor of skin damage. Keratinocytes are the major target of UV, and they play a key role in a first line of body defenses. Accumulating evidence suggests that UVB irradiation induces nuclear DNA damage, membrane destruction, resulting in apoptosis and skin inflammation. The aim of this study was to investigate the anti-inflammatory, antioxidant, antiapoptotic effects of Rocchetta® oligomineral (Co.Ge.Di. International SpA, Rome, Italy) water in UVB-irradiated immortalized human keratinocytes.

METHODS

HaCaT UVB-irradiated was cultured with increasing concentrations of Rocchetta® oligomineral water. To evaluate the anti-inflammatory properties gene expression of TNF, IL1β, IL6, COX2 and Caspase1 was performed. Moreover, the antiapoptotic effects were evaluated through gene expression of GADD45, Caspase3 and RIPK3. Finally, we evaluated the antioxidant activity of Rocchetta® oligomineral water by measuring total ROS/RNS and superoxide production as markers of oxidative stress after UVB irradiation.

RESULTS

Our findings have shown that Rocchetta® oligomineral water is well tolerated by the cells and displays anti-inflammatory, antioxidant and antiapoptotic proprieties when used prior keratinocyte UVB irradiation.

CONCLUSIONS

Our results highlight a possible protective role of Rocchetta oligomineral water in modulating the cutaneous inflammatory response to external triggers and injuries.

The Inflammatory Response in Human Keratinocytes Exposed to Cinnamaldehyde Is Regulated by Nrf2

Keratinocytes (KC) play a crucial role in epidermal barrier function, notably through their metabolic activity and the detection of danger signals. Chemical sensitizers are known to activate the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2), leading to cellular detoxification and suppressed proinflammatory cytokines such as IL-1β, a key cytokine in skin allergy. We investigated the role of Nrf2 in the control of the proinflammatory response in human KC following treatment with Cinnamaldehyde (CinA), a well-known skin sensitizer. We used the well-described human KC cell line KERTr exposed to CinA. Our results showed that 250 μM of CinA did not induce any Nrf2 accumulation but increased the expression of proinflammatory cytokines. In contrast, 100 μM of CinA induced a rapid accumulation of Nrf2, inhibited IL-1β transcription, and downregulated the zymosan-induced proinflammatory response. Moreover, Nrf2 knockdown KERTr cells (KERTr ko) showed an increase in proinflammatory cytokines. Since the inhibition of Nrf2 has been shown to alter cellular metabolism, we performed metabolomic and seahorse analyses. The results showed a decrease in mitochondrial metabolism following KERTr ko exposure to CinA 100 µM. In conclusion, the fate of Nrf2 controls proinflammatory cytokine production in KCs that could be linked to its capacity to preserve mitochondrial metabolism upon chemical sensitizer exposure.

Mechanism of Huoluo Xiaoling Dan in the Treatment of Psoriasis Based on Network Pharmacology and Molecular Docking

Objective

To explore the mechanism of the action of Huoluo Xiaoling Dan (HLXLD) in the treatment of psoriasis based on network pharmacology and molecular docking.

Methods

The main active components and targets of HLXLD were collected from CMSP, and the targets related to psoriasis were collected from GeneCards, OMIM, TTD, DisGeNET, and DrugBank. Drug disease target genes were obtained by Venny tools, drug-component-target networks were constructed and analyzed, and pathway enrichment analysis was performed. AutoDockTools is used to connect the core components and the target, and PyMOL software is used to visualize the results.

Results

126 active components (such as quercetin, luteolin, tanshinone IIA, dihydrotanshinlactone, and beta-sitosterol) and 238 targets of HLXLD were screened out. 1,293 targets of psoriasis were obtained, and 123 drug-disease targets were identified. Key targets included AKT1, TNF, IL6, TP53, VEGFA, JUN, CASP3, IL1B, STAT3, PTGS2, HIF1A, EGF, MYC, EGFR, MMP9, and PPARG. Enrichment analysis showed that 735 GO analysis and 85 KEGG pathways were mainly involved in biological processes such as response to the drug, inflammatory response, gene expression, and cell proliferation and apoptosis, as well as signal pathways such as cancer, TNF, HIF-1, and T cell receptor. Molecular docking showed that there was strong binding activity between the active ingredient and the target protein.

Conclusions

HLXLD could treat psoriasis through multicomponents, multitargets, and multipathways, which provides a new theoretical basis for further basic research and clinical application.

The relapse of psoriasis: what’s the veil of mystery?

Over the past decades, tremendous success in the treatment of psoriasis has been achieved using biologics, such as neutralizing antibodies against TNF/TNFR, IL-23, and IL-17A/IL-17RA. Although psoriatic skin lesions appear to resolve after treatment with these biologics, lesions often recur after therapy is discontinued or during therapy. Memory T cells residing in the skin have been considered as the major driver of psoriasis relapse. However, whether structural cells in the skin such as keratinocytes and fibroblasts are involved in the relapse of psoriasis is unknown. In this review, we outline the therapeutic rationale of biologics used in the treatment of psoriasis, summarize different clinical features of psoriasis relapse on the basis of preclinical and clinical data, and specifically discuss how memory T cells and structural cells in the skin are involved in psoriasis relapse. Finally, we discuss the future challenges in the basic or clinical research on psoriasis.

Predominant Role of mTOR Signaling in Skin Diseases with Therapeutic Potential

The serine/threonine kinase mechanistic target of rapamycin (mTOR) plays a pivotal role in the regulation of cell proliferation, survival, and motility in response to availability of energy and nutrients as well as mitogens. The mTOR signaling axis regulates important biological processes, including cellular growth, metabolism, and survival in many tissues. In the skin, dysregulation of PI3K/AKT/mTOR pathway may lead to severe pathological conditions characterized by uncontrolled proliferation and inflammation, including skin hyperproliferative as well as malignant diseases. Herein, we provide an update on the current knowledge regarding the pathogenic implication of the mTOR pathway in skin diseases with inflammatory features (such as psoriasis, atopic dermatitis, pemphigus, and acne) and malignant characteristics (such as cutaneous T cell lymphoma and melanoma) while we critically discuss current and future perspectives for therapeutic targeting of mTOR axis in clinical practice.

An intronic transposon insertion associates with a trans-species color polymorphism in Midas cichlid fishes

Polymorphisms have fascinated biologists for a long time, but their genetic underpinnings often remain elusive. Here, we aim to uncover the genetic basis of the gold/dark polymorphism that is eponymous of Midas cichlid fish (Amphilophus spp.) adaptive radiations in Nicaraguan crater lakes. While most Midas cichlids are of the melanic "dark morph", about 10% of individuals lose their melanic pigmentation during their ontogeny and transition into a conspicuous "gold morph". Using a new haplotype-resolved long-read assembly we discover an 8.2 kb, transposon-derived inverted repeat in an intron of an undescribed gene, which we term goldentouch in reference to the Greek myth of King Midas. The gene goldentouch is differentially expressed between morphs, presumably due to structural implications of inverted repeats in both DNA and/or RNA (cruciform and hairpin formation). The near-perfect association of the insertion with the phenotype across independent populations suggests that it likely underlies this trans-specific, stable polymorphism.

Role of Epithelium-Derived Cytokines in Atopic Dermatitis and Psoriasis: Evidence and Therapeutic Perspectives

Atopic dermatitis and psoriasis are two of the most common chronic skin conditions. Current target therapies represent viable and safe solutions for the most severe cases of these two dermatoses but, presently, several limitations exist in terms of efficacy and side effects. A new class of products, epithelium-derived cytokines (TSLP, IL-25, IL-33), show an increasing potential for use in target therapy for these patients, and demonstrate a direct link between a generalized inflammatory and oxidative stress status and the human skin. A review was conducted to better understand their role in the aforementioned conditions. Of these three molecules, TSLP led has been most often considered in studies regarding target therapies, and most of the results in the literature are related to this cytokine. These three cytokines share common stimuli and are linked to each other in both acute and chronic phases of these diseases, and have been challenged as target therapies or biomarkers of disease activity. The results lead to the conclusion that epithelium-derived cytokines could represent a therapeutic opportunity for these patients, especially in itch control. Furthermore, they might work better when paired together with currently available therapies or in combination with in-development treatments. Further studies are needed in order to verify the efficacy and safety of the biologic treatments currently under development.

Thalidomide Exerts Anti-Inflammatory Effects in Cutaneous Lupus by Inhibiting the IRF4/NF-ҡB and AMPK1/mTOR Pathways

Thalidomide is effective in patients with refractory cutaneous lupus erythematosus (CLE). However, the mechanism of action is not completely understood, and its use is limited by its potential, severe side-effects. Immune cell subset analysis in thalidomide’s CLE responder patients showed a reduction of circulating and tissue cytotoxic T-cells with an increase of iNKT cells and a shift towards a Th2 response. We conducted an RNA-sequencing study using CLE skin biopsies performing a Therapeutic Performance Mapping System (TMPS) analysis in order to generate a predictive model of its mechanism of action and to identify new potential therapeutic targets. Integrating RNA-seq data, public databases, and literature, TMPS analysis generated mathematical models which predicted that thalidomide acts via two CRBN-CRL4A- (CRL4CRBN) dependent pathways: IRF4/NF-ҡB and AMPK1/mTOR. Skin biopsies showed a significant reduction of IRF4 and mTOR in post-treatment samples by immunofluorescence. In vitro experiments confirmed the effect of thalidomide downregulating IRF4 in PBMCs and mTOR in keratinocytes, which converged in an NF-ҡB reduction that led to a resolution of the inflammatory lesion. These results emphasize the anti-inflammatory role of thalidomide in CLE treatment, providing novel molecular targets for the development of new therapies that could avoid thalidomide’s side effects while maintaining its efficacy.

An integrative multi-omic analysis reveals a major metabolic rewiring between baby foreskin keratinocytes and adult female abdominal keratinocytes

Even though its development starts early in utero, neonatal skin is still immature at birth relative to adult and undergoes a maturation process extending to the first years of life. It is now established that the stratum corneum is thinner and dryer and that skin contains less natural moisturizing factors and lipids in newborns compared to children and adults. Moreover, it has been shown that skin surface area expansion is not linear throughout life and is peaking perinatally, suggesting that baby skin has a higher epidermal cellular turnover. Despite growing resources showing differences between adult and infant skin physiology, molecular and metabolic specificities of baby skin are still poorly understood. To address this critical knowledge gap, we performed an integrative transcriptomic and metabolomic study comparing human primary foreskin and abdominal keratinocytes from male babies and female adults, respectively. Based on state-of-the-art integrative frameworks, our analyses revealed a major shift in the global energetic metabolism in baby foreskin keratinocytes compared to adult abdominal keratinocytes, highlighting increased amino acid metabolism and mitochondrial oxidative phosphorylation in baby cells to fuel the citric acid cycle, while showing glycolysis as the major cell energy source in adult cells.

First-in-class topical therapeutic omilancor ameliorates disease severity and inflammation through activation of LANCL2 pathway in psoriasis

Psoriasis (PsO) is a complex immune-mediated disease that afflicts 100 million people. Omilancor is a locally-acting, small molecule that selectively activates the Lanthionine Synthetase C-like 2 (LANCL2) pathway, resulting in immunoregulatory effects at the intersection of immunity and metabolism. Topical omilancor treatment in an imiquimod-induced mouse model of PsO ameliorates disease severity, epidermal hyperplasia and acanthosis. Further, pharmacological activation of LANCL2 results in significant downregulation of proinflammatory markers including local reduction of IL17, and infiltration of proinflammatory cell subsets. These therapeutic effects were further validated in an IL-23 PsO model. This model reported increased preservation of homeostatic skin structure, accompanied by a decreased infiltration of proinflammatory T cell subsets. In CD4+ T cells and Th17 cells, the LANCL2 pathway regulates proinflammatory cytokine production, proliferation and glucose metabolism. Metabolically, the loss of Lancl2 resulted in increased glycolytic rates, lactate production and upregulated enzymatic activity of hexokinase and lactate dehydrogenase (LDH). Inhibition of LDH activity abrogated the increased proliferation rate in Lancl2^-/- CD4+ T cells. Additionally, topical omilancor treatment decreased the metabolic upregulation in keratinocytes, keratinocyte hyperproliferation and expression of inflammatory markers. Omilancor is a promising topical, LANCL2-targeting therapeutic candidate for the treatment of PsO and other dermatology indications.

Therapeutic Development Based on the Immunopathogenic Mechanisms of Psoriasis

Psoriasis, a complex inflammatory autoimmune skin disorder that affects 2–3% of the global population, is thought to be genetically predetermined and induced by environmental and immunological factors. In the past decades, basic and clinical studies have significantly expanded knowledge on the molecular, cellular, and immunological mechanisms underlying the pathogenesis of psoriasis. Based on these pathogenic mechanisms, the current disease model emphasizes the role of aberrant Th1 and Th17 responses. Th1 and Th17 immune responses are regulated by a complex network of different cytokines, including TNF-α, IL-17, and IL-23; signal transduction pathways downstream to the cytokine receptors; and various activated transcription factors, including NF-κB, interferon regulatory factors (IRFs), and signal transducer and activator of transcriptions (STATs). The biologics developed to specifically target the cytokines have achieved a better efficacy and safety for the systemic management of psoriasis compared with traditional treatments. Nevertheless, the current therapeutics can only alleviate the symptoms; there is still no cure for psoriasis. Therefore, the development of more effective, safe, and affordable therapeutics for psoriasis is important. In this review, we discussed the current trend of therapeutic development for psoriasis based on the recent discoveries in the immune modulation of the inflammatory response in psoriasis.

PPARdelta in Affected Atopic Dermatitis and Psoriasis: A Possible Role in Metabolic Reprograming

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors expressed in the skin. Three PPAR isotypes, α (NRC1C1), β or δ (NRC1C2) and γ (NRC1C3), have been identified. After activation through ligand binding, PPARs heterodimerize with the 9-cis-retinoic acid receptor (RXR), another nuclear hormone receptor, to bind to specific PPAR-responsive elements in regulatory regions of target genes mainly involved in organogenesis, cell proliferation, cell differentiation, inflammation and metabolism of lipids or carbohydrates. Endogenous PPAR ligands are fatty acids and fatty acid metabolites. In past years, much emphasis has been given to PPARα and γ in skin diseases. PPARβ/δ is the least studied PPAR family member in the skin despite its key role in several important pathways regulating inflammation, keratinocyte proliferation and differentiation, metabolism and the oxidative stress response. This review focuses on the role of PPARβ/δ in keratinocytes and its involvement in psoriasis and atopic dermatitis. Moreover, the relevance of targeting PPARβ/δ to alleviate skin inflammation is discussed.

The Anti-Inflammatory Effect of Aptamin C on House Dust Mite Extract-Induced Inflammation in Keratinocytes via Regulation of IL-22 and GDNF Production

Atopic dermatitis (AD), a chronic inflammatory skin disease, is characterized by eczemous lesions on the skin that manifest as severe itching and last a long time. AD is thought to be a response to local allergens, including house dust mites (HDMs). Aptamin C is a modified form of vitamin C comprised of aptamers (DNA fragments) that bind specifically to vitamin C and inhibit its oxidation, thereby increasing its stability and antioxidant effects. It is already known that vitamin C shows an anti-inflammatory effect on skin inflammation. Oxidative stress is one of the major causes of inflammatory diseases, including HDM-induced skin inflammation, suggesting that the antioxidant activity of Aptamin C could regulate inflammatory responses to HDMs in the skin keratinocyte cell line HaCaT and primary skin keratinocytes. Aptamin C not only inhibited HDM-induced proliferation of both type of cells, but suppressed HDM-induced increases in interleukin (IL)-1α and IL-6 production by these cells. In addition, Aptamin C suppressed the production of IL-17 and IL-22 by T cells, which are closely associated with AD pathogenesis, as well as HDM-induced IL-22Rα expression. Aptamin C also reduced the production of thymus and activation-regulated chemokine (TARC) by suppressing the interaction between IL-22 and IL-22Rα, as well as reducing T cell migration. Although HDM treatment markedly increased the expression of glial cell line-derived neurotrophic factor (GDNF), which is associated with itching in AD skin lesions, this increase was reduced by Aptamin C treatment. Taken together, these results suggest that Aptamin C can effectively regulate inflammatory lesions, such as AD, by regulating the production of inflammatory cytokines and GDNF induced by HDM.

The role of Helianthus tuberosus powder in healing of full-thickness wounds in mice

Background and Aim

Recently, many medicinal plants have received considerable attention in the medical field because of their role in the wound healing potential. This study aimed to determine the effectiveness of H. tuberosus powder on the healing pathway of full-thickness cutaneous wounds in a mouse model.

Materials and Methods

H. tuberosus powder was prepared by a freeze-drying process using a lyophilizer and its active ingredients were evaluated by high-performance liquid chromatography (HPLC), while its antibacterial properties were evaluated by agar well diffusion assay. The percentage wound contraction was also assessed. Thirty mice were used, which were divided equally into two groups, a control group and a treated group. A full-thickness wound, 1 cm×1 cm in size, was established on the dorsal aspect of the thoracolumbar region, into which H. tuberosus powder was topically applied in the treated group. In contrast, the control group was left without any treatment. The animals were euthanized on days 7, 14, and 21 after wounding for histopathological study.

Results

The agar well diffusion method indicated the antibacterial activity of H. tuberosus, while the HPLC results indicated that the active ingredients of H. tuberosus powder mainly consisted of three major kinds of fatty acid. In addition, the macroscopic results of wound contraction rate and the histopathological outcomes of the healing process were significantly (p≤0.05) enhanced in the treated group compared with those in the control group.

Conclusion

H. tuberosus powder acts as an antibacterial agent with the ability to enhance the wound healing process.

Therapeutic wavelengths of ultraviolet B radiation activate apoptotic, circadian rhythm, redox signalling and key canonical pathways in psoriatic epidermis

Ultraviolet B radiation (UVB) exerts pleiotropic effects on human skin. DNA damage response and repair pathways are activated by UVB; if damage cannot be repaired, apoptosis ensues. Although cumulative UVB exposure predisposes to skin cancer, UVB phototherapy is widely used as an effective treatment for psoriasis. Previous studies defined the therapeutic action spectrum of UVB and showed that psoriasis is resistant to apoptosis. This study aimed to investigate early molecular responses within psoriasis plaques following irradiation with single equi-erythemogenic doses of clinically-effective (311 nm, narrow-band) compared to clinically-ineffective (290 nm) UVB. Forty-eight micro-dissected epidermal samples from 20 psoriatic patients were analyzed using microarrays. Our bioinformatic analysis compared gene expression between 311 nm irradiated, 290 nm irradiated and control psoriasis epidermis to specifically identify 311 nm UVB differentially expressed genes (DEGs) and their upstream regulatory pathways. Key DEGs and pathways were validated by immunohistochemical analysis. There was a dynamic induction and repression of 311 nm UVB DEGs between 6 h and 18 h, only a limited number of DEGs maintained their designated expression status between time-points. Key disease and function pathways included apoptosis, cell death, cell migration and leucocyte chemotaxis. DNA damage response pathways, NRF2-mediated oxidative stress response and P53 signalling were key nodes, interconnecting apoptosis and cell cycle arrest. Interferon signalling, dendritic cell maturation, granulocyte adhesion and atherosclerotic pathways were also differentially regulated. Consistent with these findings, top transcriptional regulators of 311 nm UVB DEGs related to: a) apoptosis, DNA damage response and cell cycle control; b) innate/acquired immune regulation and inflammation; c) hypoxia/redox response and angiogenesis; d) circadian rhythmicity; f) EGR/AP1 signalling and keratinocyte differentiation; and g) mitochondrial biogenesis. This research provides important insights into the molecular targets of 311 nm UVB, underscoring key roles for apoptosis and cell death. These and the other key pathways delineated may be central to the therapeutic effects of 311 nm in psoriasis.

Recent Updates on the Involvement of PI3K/AKT/mTOR Molecular Cascade in the Pathogenesis of Hyperproliferative Skin Disorders

PhosphoInositide-3 Kinase (PI3K) represents a family of different classes of kinases which control multiple biological processes in mammalian cells, such as cell growth, proliferation, and survival. Class IA PI3Ks, the main regulators of proliferative signals, consists of a catalytic subunit (α, β, δ) that binds p85 regulatory subunit and mediates activation of AKT and mammalian Target Of Rapamycin (mTOR) pathways and regulation of downstream effectors. Dysregulation of PI3K/AKT/mTOR pathway in skin contributes to several pathological conditions characterized by uncontrolled proliferation, including skin cancers, psoriasis, and atopic dermatitis (AD). Among cutaneous cancers, basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) display PI3K/AKT/mTOR signaling hyperactivation, implicated in hyperproliferation, and tumorigenesis, as well as in resistance to apoptosis. Upregulation of mTOR signaling proteins has also been reported in psoriasis, in association with enhanced proliferation, defective keratinocyte differentiation, senescence-like growth arrest, and resistance to apoptosis, accounting for major parts of the overall disease phenotypes. On the contrary, PI3K/AKT/mTOR role in AD is less characterized, even though recent evidence demonstrates the relevant function for mTOR pathway in the regulation of epidermal barrier formation and stratification. In this review, we provide the most recent updates on the role and function of PI3K/AKT/mTOR molecular axis in the pathogenesis of different hyperproliferative skin disorders, and highlights on the current status of preclinical and clinical studies on PI3K-targeted therapies.

Low Threshold for Cutaneous Allergen Sensitization but No Spontaneous Dermatitis or Atopy in FLG-Deficient Mice

Loss of FLG causes ichthyosis vulgaris. Reduced FLG expression compromises epidermal barrier function and is associated with atopic dermatitis, allergy, and asthma. The flaky tail mouse harbors two mutations that affect the skin barrier, Flg^ft, resulting in hypomorphic FLG expression, and Tmem79^ma, inactivating TMEM79. Mice defective only for TMEM79 featured dermatitis and systemic atopy, but also Flg^ft/ft BALB/c congenic mice developed eczema, high IgE, and spontaneous asthma, suggesting that FLG protects from atopy. In contrast, a targeted Flg-knockout mutation backcrossed to BALB/c did not result in dermatitis or atopy. To resolve this discrepancy, we generated FLG-deficient mice on pure BALB/c background by inactivating Flg in BALB/c embryos. These mice feature an ichthyosis phenotype, barrier defect, and facilitated percutaneous sensitization. However, they do not develop dermatitis or atopy. Whole-genome sequencing of the atopic Flg^ft BALB/c congenics revealed that they were homozygous for the atopy-causing Tmem79^matted mutation. In summary, we show that FLG deficiency does not cause atopy in mice, in line with lack of atopic disease in a fraction of patients with ichthyosis vulgaris carrying two Flg null alleles. However, the absence of FLG likely promotes and modulates dermatitis caused by other genetic barrier defects.

Keratinocyte-Polyamines and Dendritic Cells: A Bad Duet for Psoriasis

The role of keratinocyte metabolism in psoriasis is not fully elucidated. In this issue of Immunity, Lou et al. describe that interleukin-17 (IL-17) re-programs the urea cycle in keratinocytes increasing polyamines that stabilize RNA-Ag-complexes that upon cellular turnover activate dendritic cells, which amplify psoriasis inflammation.

Dissecting the complexity of γδ T-cell subsets in skin homeostasis, inflammation, and malignancy

γδ T cells are much less common than αβ T cells, accounting for 0.5% to 5% of all T lymphocytes in the peripheral blood and lymphoid tissues in mice and humans. However, they are the most abundant T-lymphocyte subset in some epithelial barriers such as mouse skin. γδ T cells are considered innate lymphocytes because of their non-MHC restricted antigen recognition, as well as because of their rapid response to cytokines, invading pathogens, and malignant cells. Exacerbated expansion and activation of γδ T cells in the skin is a common feature of acute and chronic skin inflammation such as psoriasis and contact or atopic dermatitis. Different γδ T-cell subsets showing differential developmental and functional features are found in mouse and human skin. This review discusses the state of the art of research and future perspectives about the role of the different subsets of γδ T-cells detected in the skin in steady-state, psoriasis, dermatitis, infection, and malignant skin diseases. Also, we highlight the differences between human and mouse γδ T cells in skin homeostasis and inflammation, as understanding the differential role of each subtype of skin γδ T cells will improve the discovery of new therapies.