Keratinocyte-derived IL-1β induces PPARG downregulation and PPARD upregulation in human reconstructed epidermis following barrier impairment

New Insights into the Role of PPARγ in Skin Physiopathology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a transcription factor expressed in many tissues, including skin, where it is essential for maintaining skin barrier permeability, regulating cell proliferation/differentiation, and modulating antioxidant and inflammatory responses upon ligand binding. Therefore, PPARγ activation has important implications for skin homeostasis. Over the past 20 years, with increasing interest in the role of PPARs in skin physiopathology, considerable effort has been devoted to the development of PPARγ ligands as a therapeutic option for skin inflammatory disorders. In addition, PPARγ also regulates sebocyte differentiation and lipid production, making it a potential target for inflammatory sebaceous disorders such as acne. A large number of studies suggest that PPARγ also acts as a skin tumor suppressor in both melanoma and non-melanoma skin cancers, but its role in tumorigenesis remains controversial. In this review, we have summarized the current state of research into the role of PPARγ in skin health and disease and how this may provide a starting point for the development of more potent and selective PPARγ ligands with a low toxicity profile, thereby reducing unwanted side effects.

Nuclear receptors for epidermal lipid barrier: Advances in mechanisms and applications

The skin plays an essential role in preventing the entry of external environmental threats and the loss of internal substances, depending on the epidermal permeability barrier. Nuclear receptors (NRs), present in various tissues and organs including full-thickness skin, have been demonstrated to exert significant effects on the epidermal lipid barrier. Formation of the lipid lamellar membrane and the normal proliferation and differentiation of keratinocytes (KCs) are crucial for the development of the epidermal permeability barrier and is regulated by specific NRs such as PPAR, LXR, VDR, RAR/RXR, AHR, PXR and FXR. These receptors play a key role in regulating KC differentiation and the entire process of epidermal lipid synthesis, processing and secretion. Lipids derived from sebaceous glands are influenced by NRs as well and participate in regulation of the epidermal lipid barrier. Furthermore, intricate interplay exists between these receptors. Disturbance of barrier function leads to a range of diseases, including psoriasis, atopic dermatitis and acne. Targeting these NRs with agonists or antagonists modulate pathways involved in lipid synthesis and cell differentiation, suggesting potential therapeutic approaches for dermatosis associated with barrier damage. This review focuses on the regulatory role of NRs in the maintenance and processing of the epidermal lipid barrier through their effects on skin lipid synthesis and KC differentiation, providing novel insights for drug targets to facilitate precision medicine strategies.

Up-Regulated Expression of ICAM1, MT1A, PTGS2, LCE3D, PPARD, and GM-CSF2 Following Solar Skincare Protection and Repair Strategies in a 3-Dimensional Reconstructed Human Skin Model

Background

Clinical, optical and histological research confirms that solar skin damage continues to pose a threat to human skin health globally despite widespread sunscreen usage and sun awareness campaigns. Despite this, very few studies examine the critical changes in gene expression and DNA repair activity following recommended topical solar protection and repair strategies to ameliorate the harmful effects of ultraviolet, visible light and near-infrared radiation.

Purpose

To investigate alterations in gene expression following topical solar protection and solar repair strategies.

Methods

Using epidermal keratinocytes and dermal fibroblasts derived from a 3-dimensional reconstructed human skin model, gene expression was assessed via the Genemarkers Standard Skin Panel using 112 genes deploying two analytical techniques: DNA microarray and quantitative real-time PCR exploration. Tissues were inoculated with products then collected after 24 hours following application of solar protection formulations and 16 hours following solar repair formulations (The Essential Six, RATIONALE, Victoria, Australia).

Results

A DNA microarray revealed 67 genes that were significantly up-regulated or down-regulated following the treatment. The quantitative real-time PCR revealed that, in comparison to the control, the genes encoding Intercellular Adhesion Molecule 1 (ICAM1), Metallothionein 1A (MT1A), Prostaglandin-Endoperoxide Synthase 1 (PTGS2), Late Cornified Envelope 3D (LCE3D), Peroxisome Proliferator Activated Receptor (PPARD), and Granulocyte/Macrophage Colony Stimulating Factor 2 (GM-CSF2) have been up-regulated following usage of the solar protection regime, 1.87, 861.16, 4.34, 1.91, 1.06, and 3.6, respectively. ICAM1, MT1A, PTGS2, LCE3D, PPARD, and GM-CSF2 were up-regulated following use of the solar repair regime, 3.78, 2.98, 14.89, 5.09, 2.42, and 13.51, respectively.

Conclusion

This study demonstrates that a specific solar protection and repair regime upregulated genes involved in photoprotection and repair mechanisms in a 3-dimensional (3D) reconstructed human-like skin model.

In vitro and in vivo exploration of the anti-atopic dermatitis mechanism of action of Tibetan medicine Qi-Sai-Er-Sang-Dang-Song decoction

ETHNOPHARMACOLOGICAL RELEVANCE

Tibetan medicine Qi-Sai-Er-Sang-Dang-Song Decoction(QSD, ཆུ་སེར་སེང་ལྡེང་སུམ་ཐང་།)is a traditional Tibetan medical formulation with demonstrated clinical benefits in atopic dermatitis (AD). However, its potential mechanism and molecular targets remain to be elucidated.

AIM OF THE STUDY

This study aims to explore the activity and mechanism of QSD on AD in multiple dimensions by combining in vitro and in vivo experiments with network pharmacology.

MATERIALS AND METHODS

The AD effect of QSD was investigated by evaluating the levels of nitric oxide (NO) and interleukin-6 (IL-6) in the lipopolysaccharide (LPS) stimulated RAW264.7 cells. AD-like skin lesions in female BALB/c mice were induced by 2,4-dinitrochlorobenzene (DNCB). QSD or dexamethasone (positive control) were gavagely administered daily for 15 consecutive days. The body weight and skin lesion severity were recorded throughout the study. Enzyme-linked immunosorbent assay (ELISA) and Western blot (WB) analysis were used to illuminate the molecular targets associated with the anti-AD effects of QSD. Meanwhile, the ingredients of QSD in the blood were revealed and analyzed by Ultra performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) method. Network pharmacology was used to predict the targets and mechanism of active ingredient therapy for AD. In addition, the network pharmacology outcomes were further verified by molecular docking.

RESULT

After treatment with QSD, the levels of NO and IL-6 were decreased in the cell supernatant. Herein, QSD markedly decreased the eosinophil and mast cells infiltration in the dorsal skin of the 2,4-dinitrochlorobenzene. Moreover, QSD reconstructed the epidermal barrier by increasing the content of collagen fibers and changing the arrangement of DNCB-treated mice. QSD not only inhibited the levels of tumor necrosis factor-α (TNF-α) and interleukin-12 (IL-12) but also inhibited phosphorylation of p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) proteins in the dorsal skin. Four active ingredients were identified through UPLC-Q-TOF/MS, including (-)-epicatechin, kaempferol-7-O-glucoside, cassiaside, and questin. After the network pharmacological analysis, six core targets of QSD closely related to AD were obtained, including TNF-α, IL-6, Caspase-3 (CASP3), Epidermal growth factor (EGFR), Peroxisome proliferator-activated receptor gamma (PPARG), and Neurotrophic Receptor Tyrosine Kinase 1 (NTRK1). Meanwhile, through Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, the Mitogen-activated protein kinase (MAPK) signaling pathway occupies an important position in the QSD treatment of AD. The molecular docking results showed that the six core targets are stable in binding to the four active ingredients as indicated by the molecular docking results.

CONCLUSIONS

The anti-AD effect of QSD might be related to the reconstruction of the epidermal barrier and inhibition of inflammation, which regulated the MAPK pathway. Hence, it provided a promising idea for the study of Tibetan medicine prescriptions for the treatment of AD.

Emphasis on Adipocyte Transformation: Anti-Inflammatory Agents to Prevent the Development of Cancer-Associated Adipocytes

Of the various cell types in the tumor microenvironment (TME), adipocytes undergo a dynamic transformation when activated by neighboring cancer cells. Although these adipocytes, known as cancer-associated adipocytes (CAAs), have been reported to play a crucial role in tumor progression, the factors that mediate their transformation remain elusive. In this review, we discuss the hypothesis that inflammatory signals involving NF-ĸB activation can induce lipolysis and adipocyte dedifferentiation. This provides a mechanistic understanding of CAA formation and introduces the concept of preventing adipocyte transformation via anti-inflammatory agents. Indeed, epidemiological studies indicate a higher efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) in obese patients with cancer, suggesting that NSAIDs can modulate the TME. Inhibition of cyclooxygenase-2 (COX-2) and prostaglandin production leads to the suppression of inflammatory signals such as NF-ĸB. Thus, we suggest the use of NSAIDs in cancer patients with metabolic disorders to prevent the transformation of TME components. Moreover, throughout this review, we attempt to expand our knowledge of CAA transformation to improve the clinical feasibility of targeting CAAs.

Identification of Novel Hub Genes Associated with Psoriasis Using Integrated Bioinformatics Analysis

Psoriasis is a chronic, prolonged, and recurrent inflammatory skin disease and the current therapeutics can only alleviate the symptoms rather than cure it completely. Therefore, we aimed to identify the molecular signatures and specific biomarkers of psoriasis to provide novel clues for psoriasis and targeted therapy. In the present study, the Gene Expression Omnibus (GEO) database was used to retrieve three microarray datasets (GSE166388, GSE50790 and GSE42632) and to explore the differentially expressed genes (DEGs) in psoriasis using the Affy package in R software. The gene ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway enrichment were utilized to determine the common DEGs and their capabilities. The STRING database was used to develop DEG-encoded proteins and a protein-protein interaction network (PPI) and the Cytohubba plugin to classify hub genes. Using the NetworkAnalyst platform, we detected transcription factors (TFs), microRNAs and drug candidates interacting with hub genes. In addition, the expression levels of hub genes in HaCaT cells were detected by western blot. We screened the up- and downregulated DEGs from the transcriptome microarrays of corresponding psoriasis patients. Functional enrichment of DEGs in psoriasis was mainly associated with positive regulation of leukocyte cell-cell adhesion and T cell activation, cytokine binding, cytokine activity and the Wnt signaling pathway. Through further data processing, we obtained 57 intersecting genes in the three datasets and probed them in STRING to determine the interaction of their expressed proteins and we obtained the critical 10 hub genes in the Cytohubba plugin, including TOP2A, CDKN3, MCM10, PBK, HMMR, CEP55, ASPM, KIAA0101, ESC02, and IL-1β. Using these hub genes as targets, we obtained 35 TFs and 213 miRNAs that may regulate these genes and 33 potential therapeutic agents for psoriasis. Furthermore, the expression levels of TOP2A, MCM10, PBK, ASPM, KIAA0101 and IL-1β were observably increased in HaCaT cells. In conclusion, we identified potential biomarkers, risk factors and drugs for psoriasis.

Small, Cationic Antifungal Proteins from Filamentous Fungi Inhibit Candida albicans Growth in 3D Skin Infection Models

The emerging resistance of human-pathogenic fungi to antifungal drugs urges the development of alternative therapeutic strategies. The small, cationic antifungal proteins (AFPs) from filamentous ascomycetes represent promising candidates for next-generation antifungals. These bio-molecules need to be tested for tolerance in the host and efficacy against fungal pathogens before they can be safely applied in humans. Testing of the efficacy and possible adverse effects of new drug candidates in three-dimensional (3D) human-cell based models represents an advantageous alternative to animal experiments. In, this study, as a proof-of-principle, we demonstrate the usefulness of 3D skin infection models for screening new antifungal drug candidates for topical application. We established a cutaneous infection with the opportunistic human-pathogenic yeast Candida albicans in a commercially available 3D full-thickness (FT) skin model to test the curative potential of distinct AFPs from Penicillium chrysogenum (PAFopt, PAFB, and PAFC) and Neosartorya (Aspergillus) fischeri (NFAP2) in vitro. All tested AFPs were comparably well tolerated by the skin models. The infected 3D models exhibited reduced epidermal permeability barriers, allowing C. albicans to colonize the epidermal and dermal layers, and showed increased secretion of the pro-inflammatory cytokine IL-6 and the chemokine IL-8. AFP treatment diminished the fungal burden and penetration depth of C. albicans in the infected models. The epidermal permeability barrier was restored and the secretion of IL-8 was decreased following AFP treatment. In summary, our study proves that the tested AFPs exhibit antifungal potential against cutaneous C. albicans infection in a 3D FT skin model. IMPORTANCE Candida albicans represents one of the most prevalent opportunistic fungal pathogens, causing superficial skin and mucosal infections in humans with certain predisposing health conditions and life-threatening systemic infections in immunosuppressed patients. The emerging drug resistance of this human-pathogenic yeast and the limited number of antifungal drugs for prevention and treatment of infections urgently demands the identification of new antifungal compounds with novel mechanisms of action. Small, cationic antifungal proteins (AFPs) from filamentous fungi represent promising candidates for next-generation antifungals for topical application. These bio-molecules need to be tested for tolerance by the host and efficacy in pathogen clearance prior to being involved in clinical trials. In a proof-of-principle study, we provide evidence for the suitability of 3D human-cell based models as advantageous alternatives to animal experiments. We document the tolerance of specific AFPs and their curative efficacy against cutaneous C. albicans infection in a 3D skin model.

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.

Do epidermal keratinocytes have sensory and information processing systems?

It was long considered that the role of epidermal keratinocytes is solely to construct a water-impermeable protective membrane, the stratum corneum, at the uppermost layer of the skin. However, in the last two decades, it has been found that keratinocytes contain multiple sensory systems that detect environmental changes, including mechanical stimuli, sound, visible radiation, electric fields, magnetic fields, temperature and chemical stimuli, and also a variety of receptor molecules associated with olfactory or taste sensation. Moreover, neurotransmitters and their receptors that play crucial roles in the brain are functionally expressed in keratinocytes. Recent studies have demonstrated that excitation of keratinocytes can induce sensory perception in the brain. Here, we review the sensory and information processing capabilities of keratinocytes. We discuss the possibility that epidermal keratinocytes might represent the earliest stage in the development of the brain during the evolution of vertebrates.

Peroxisomal Fatty Acid Oxidation and Glycolysis Are Triggered in Mouse Models of Lesional Atopic Dermatitis

Alterations of the lipid profile of the stratum corneum have an important role in the pathogenesis of atopic dermatitis (AD) because they contribute to epidermal barrier impairment. However, they have not previously been envisioned as a cellular response to altered metabolic requirements in AD epidermis. In this study, we report that the lipid composition in the epidermis of flaky tail, that is, ft/ft mice mimics that of human lesional AD (ADL) epidermis, both showing a shift toward shorter lipid species. The amounts of C24 and C26 free fatty acids and C24 and C26 ceramides-oxidized exclusively in peroxisomes-were reduced in the epidermis of ft/ft mice despite increased lipid synthesis, similar to that seen in human ADL edpidermis. Increased ACOX1 protein and activity in granular keratinocytes of ft/ft epidermis, altered lipid profile in human epidermal equivalents overexpressing ACOX1, and increased ACOX1 immunostaining in skin biopsies from patients with ADL suggest that peroxisomal β-oxidation significantly contributes to lipid signature in ADL epidermis. Moreover, we show that increased anaerobic glycolysis in ft/ft mouse epidermis is essential for keratinocyte proliferation and adenosine triphosphate synthesis but does not contribute to local inflammation. Thus, this work evidenced a metabolic shift toward enhanced peroxisomal β-oxidation and anaerobic glycolysis in ADL epidermis.

Human skin equivalents: Impaired barrier function in relation to the lipid and protein properties of the stratum corneum

To advance drug development representative reliable skin models are indispensable. Animal skin as test model for human skin delivery is restricted as their properties greatly differ from human skin. In vitro 3D-human skin equivalents (HSEs) are valuable tools as they recapitulate important aspects of the human skin. However, HSEs still lack the full barrier functionality as observed in native human skin, resulting in suboptimal screening outcome. In this review we provide an overview of established in-house and commercially available HSEs and discuss in more detail to what extent their skin barrier biology is mimicked in vitro focusing on the lipid properties and cornified envelope. Further, we will illustrate how underlying factors, such as culture medium improvements and environmental factors affect the barrier lipids. Lastly, potential improvements in skin barrier function will be proposed aiming at a new generation of HSEs that may replace animal skin delivery studies fully.

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.