Late cornified envelope (LCE) proteins: distinct expression patterns of LCE2 and LCE3 members suggest nonredundant roles in human epidermis and other epithelia

Challenges in Psoriasis Research: A Systematic Review of Preclinical Models

INTRODUCTION

Psoriasis is a chronic inflammatory skin disease with variable clinical presentation, multifactorial etiology and an immunogenetic basis. Several studies demonstrate that it results from a dysregulated interaction between skin keratinocytes, immune cells, and the environment that leads to a persistent inflammatory process modulated by cytokines and T cells. The development of new treatment options requires increased understanding of pathogenesis. However, the successful implementation of effective drugs requires well-characterized and highly available preclinical models that allow researchers to quickly and reproducibly determine their safety and efficacy.

METHODS

A systematic search on PubMed and Scopus databases was performed and assessed to find appropriate articles about psoriasis models applying the key words previously defined. The PRISMA guidelines were employed.

RESULTS

A total of 45 original articles were selected that met the selection criteria. Among these, there are articles on in vivo, in vitro, and ex vivo models, with the in vitro model being the majority due to its ease of use. Within animal models, the most widely used in recent years are chemically induced models using a compound known as imiquimod. However, the rest of the animal models used throughout the disease's research were also discussed. On the other hand, in vitro models were divided into two and three dimensions. The latter were the most used due to their similarity to human skin. Lastly, the ex vivo models were discussed, although they were the least used due to their difficulty in obtaining them.

CONCLUSIONS

Therefore, this review summarizes the current preclinical models (in vivo, in vitro, and ex vivo), discussing how to develop them, their advantages, limitations, and applications. There are many challenges to improve the development of the different models. However, research in these in vitro model studies could reduce the use of animals. This is favored with the use of future technologies such as 3D bioprinting or organ-on-a-chip technologies.

Skin barrier-inflammatory pathway is a driver of the psoriasis-atopic dermatitis transition

As chronic inflammatory conditions driven by immune dysregulation are influenced by genetics and environment factors, psoriasis and atopic dermatitis (AD) have traditionally been considered to be distinct diseases characterized by different T cell responses. Psoriasis, associated with type 17 helper T (Th17)-mediated inflammation, presents as well-defined scaly plaques with minimal pruritus. AD, primarily linked to Th2-mediated inflammation, presents with poorly defined erythema, dry skin, and intense itching. However, psoriasis and AD may overlap or transition into one another spontaneously, independent of biological agent usage. Emerging evidence suggests that defects in skin barrier-related molecules interact with the polarization of T cells, which forms a skin barrier-inflammatory loop with them. This loop contributes to the chronicity of the primary disease or the transition between psoriasis and AD. This review aimed to elucidate the mechanisms underlying skin barrier defects in driving the overlap between psoriasis and AD. In this review, the importance of repairing the skin barrier was underscored, and the significance of tailoring biologic treatments based on individual immune status instead of solely adhering to the treatment guidelines for AD or psoriasis was emphasized.

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.

Pervasive incomplete lineage sorting illuminates speciation and selection in primates

Incomplete lineage sorting (ILS) causes the phylogeny of some parts of the genome to differ from the species tree. In this work, we investigate the frequencies and determinants of ILS in 29 major ancestral nodes across the entire primate phylogeny. We find up to 64% of the genome affected by ILS at individual nodes. We exploit ILS to reconstruct speciation times and ancestral population sizes. Estimated speciation times are much more recent than genomic divergence times and are in good agreement with the fossil record. We show extensive variation of ILS along the genome, mainly driven by recombination but also by the distance to genes, highlighting a major impact of selection on variation along the genome. In many nodes, ILS is reduced more on the X chromosome compared with autosomes than expected under neutrality, which suggests higher impacts of natural selection on the X chromosome. Finally, we show an excess of ILS in genes with immune functions and a deficit of ILS in housekeeping genes. The extensive ILS in primates discovered in this study provides insights into the speciation times, ancestral population sizes, and patterns of natural selection that shape primate evolution.

CYSRT1: an antimicrobial epidermal protein that can interact with late cornified envelope (LCE) proteins

Late cornified envelope (LCE) proteins are small cationic epidermal proteins with antimicrobial properties, and the combined deletion of LCE3B and LCE3C genes is a risk factor for psoriasis that affects skin microbiome composition. In a yeast two-hybrid screen we identified cysteine-rich tail 1 protein (CYSRT1) as an interacting partner of members of all LCE groups except LCE6. These interactions were confirmed in a mammalian cell system by co-immunoprecipitation. CYSRT1 is a protein of unknown function that is specifically expressed in cutaneous and oral epithelia and spatially colocalizes with LCE proteins in the upper layers of the suprabasal epidermis. Constitutive CYSRT1 expression is present in fully differentiated epidermis and can be further induced in vivo by disruption of the skin barrier upon stratum corneum removal. Transcriptional regulation correlates to keratinocyte terminal differentiation but not to skin bacteria exposure. Similar to LCEs, CYSRT1 was found to have antibacterial activity against Pseudomonas aeruginosa. Comparative gene sequence analysis and protein amino acid alignment indicates that CYSRT1 is highly conserved among vertebrates and has putative antimicrobial activity. To summarize, we identified CYSRT1 in the outer skin layer, where it colocalizes with LCE proteins and contributes to the constitutive epidermal antimicrobial host defense repertoire.

Inhibition of dipeptidyl-peptidase 4 induces upregulation of the late cornified envelope cluster in keratinocytes

Dipeptidyl-peptidase 4 (DPP4) is a multifunctional type II transmembrane glycoprotein that is expressed on various cell surfaces. While DPP4 inhibitors have a therapeutic role in the treatment of diabetes mellitus, they are an independent risk factor in the development of bullous pemphigoid. Contrarily, there are reports of improvement in psoriasis with DPP4 inhibition. We investigated the effect of DPP4 inhibition on primary human keratinocytes to determine whether DPP4 modulates keratinocyte inflammatory signaling and keratinocyte homeostasis. We performed RNA sequencing of primary adult human keratinocytes treated with DPP4 inhibitor, identifying 424 differentially expressed genes. Gene ontology analysis revealed significant enrichment of epidermal differentiation and cornified envelope genes. Using three-dimensional organotypic cultures and a pan-late cornified envelope 2 (LCE2) antibody, we demonstrate a dose dependent relationship between DPP4 inhibition and increased expression of LCE2 during epidermal development. The late cornified envelope gene clusters are expressed at the late stages of epithelial development, responding to stimuli such as calcium and ultraviolet light. While its biologic function is not fully understood, mutations in LCE3B/LCE3C confer a 40% increased risk in the development of plaque psoriasis. While we did not identify significant modulation of keratinocyte inflammatory markers, DPP4 inhibition increased expression of the late cornified envelope may offer a potential alternative therapeutic mechanism in psoriasis.

Antimicrobial late cornified envelope (LCE) proteins: the psoriasis risk factor LCE3B/C-del affects microbiota composition

Late cornified envelope (LCE) proteins are predominantly expressed in the skin and other cornified epithelia. Based on sequence similarity, this eighteen-member homologous gene family has been subdivided into six groups. The LCE3 proteins have been the focus of dermatological research, as the combined deletion of LCE3B and LCE3C genes (LCE3B/C-del) is a risk factor for psoriasis. We previously reported that LCE3B/C-del increases expression of the LCE3A gene and that LCE3 proteins exert antibacterial activity. In the current study we analyzed the antimicrobial properties of other family members and the role of LCE3B/C-del in modulation of microbiota composition of the skin and oral cavity. Differences in killing efficiency and specificity between the LCE proteins and their target microbes were found, and the amino acid content, rather than the order, of the well-conserved central domain of the LCE3A protein was found responsible for its antibacterial activity. In vivo, LCE3B/C-del correlated with a higher beta-diversity in the skin and oral microbiota. From these results we conclude that all LCE proteins possess antimicrobial activity. Tissue-specific and genotype-dependent antimicrobial protein profiles impact skin and oral microbiota composition, which could direct towards LCE3B/C-del associated dysbiosis and a possible role for microbiota in the pathophysiology of psoriasis.

Identifying Novel Psoriatic Disease Drug Targets Using a Genetics-Based Priority Index Pipeline

BACKGROUND

Despite numerous genome-wide association studies conducted in psoriasis and psoriatic arthritis, only a small fraction of the identified genes has been therapeutically targeted.

OBJECTIVE

We sought to identify and analyze potential therapeutic targets for psoriasis and psoriatic arthritis (PsA) using the priority index (Pi), a genetics-dependent drug target prioritization approach.

METHODS

Significant genetic variants from GWAS for psoriasis, PsA, and combined psoriatic disease were annotated and run through the Pi pipeline. Potential drug targets were identified based on genomic predictors, annotation predictors, pathway enrichment, and pathway crosstalk.

RESULTS

Several gene targets were identified for psoriasis and PsA that demonstrated biological associations to their respective diseases. Some are currently being explored as potential therapeutic targets (i.e. ICAM1, NF-kB, REV3L, ADRA1B for psoriasis; CCL11 for PsA); others have not yet been investigated (i.e. LNPEP, LCE3 for psoriasis; UBLCP1 for PsA). Additionally, many nodal points of potential intervention were identified as promising therapeutic targets. Of these, some are currently being studied such as TYK2 for psoriasis, and others have yet to be explored (i.e. PPP2CA, YAP1, PI3K, AKT, FOXO1, RELA, CSF2, IFNGR1, IFNGR2 for psoriasis; GNAQ, PLCB1, GNAI2 for PsA).

CONCLUSION

Through Pi, we identified data-driven candidate therapeutic gene targets and pathways for psoriasis and PsA. Given the sparse PsA specific genetic studies and PsA specific drug targets, this analysis could prove to be particularly valuable in the pipeline for novel psoriatic therapies.

Combining Understanding of Immunological Mechanisms and Genetic Variants Toward Development of Personalized Medicine for Psoriasis Patients

Psoriasis is multifactorial disease with complex genetic predisposition. Recent advances in genetics and genomics analyses have provided many insights into the relationship between specific genetic predisposition and the immunopathological mechanisms driving psoriasis manifestation. Novel approaches which utilize array-based genotyping technologies such as genome-wide association studies and bioinformatics tools for transcriptomics analysis have identified single nucleotide polymorphisms, genes and pathways that are associated with psoriasis. The discovery of these psoriasis-associated susceptibility loci, autoimmune targets and altered signaling pathways have provided opportunities to bridge the gap of knowledge from sequence to consequence, allowing new therapeutic strategies for the treatment of psoriasis to be developed. Here, we discuss recent advances in the field by highlighting how immune functions associated with psoriasis susceptibility loci may contribute to disease pathogenesis in different populations. Understanding the genetic variations in psoriasis and how these may influence the immunological pathways to cause disease will contribute to the efforts in developing novel and targeted personalized therapies for psoriasis patients.

Bioactive Dietary VDR Ligands Regulate Genes Encoding Biomarkers of Skin Repair That Are Associated with Risk for Psoriasis

Treatment with 1,25-dihydroxyvitamin D₃ (1,25D) improves psoriasis symptoms, possibly by inducing the expression of late cornified envelope (LCE)3 genes involved in skin repair. In psoriasis patients, the majority of whom harbor genomic deletion of LCE3B and LCE3C (LCE3C_LCE3B-del), we propose that certain dietary analogues of 1,25D activate the expression of residual LCE3A/LCE3D/LCE3E genes to compensate for the loss of LCE3B/LCE3C in the deletant genotype. Herein, human keratinocytes (HEKn) homozygous for LCE3C_LCE3B-del were treated with docosahexaenoic acid (DHA) and curcumin, two low-affinity, nutrient ligands for the vitamin D receptor (VDR). DHA and curcumin induce the expression of LCE3A/LCE3D/LCE3E mRNAs at concentrations corresponding to their affinity for VDR. Moreover, immunohistochemical quantitation revealed that the treatment of keratinocytes with DHA or curcumin stimulates LCE3 protein expression, while simultaneously opposing the tumor necrosis factor-alpha (TNFα)-signaled phosphorylation of mitogen activated protein (MAP) kinases, p38 and Jun amino-terminal kinase (JNK), thereby overcoming inflammation biomarkers elicited by TNFα challenge. Finally, DHA and curcumin modulate two transcription factors relevant to psoriatic inflammation, the activator protein-1 factor Jun B and the nuclear receptor NR4A2/NURR1, that is implicated as a mediator of VDR ligand-triggered gene control. These findings provide insights into the mechanism(s) whereby dietary VDR ligands alter inflammatory and barrier functions relevant to skin repair, and may provide a molecular basis for improved treatments for mild/moderate psoriasis.

Psoriasis-Associated Late Cornified Envelope (LCE) Proteins Have Antibacterial Activity

Terminally differentiating epidermal keratinocytes express a large number of structural and antimicrobial proteins that are involved in the physical barrier function of the stratum corneum and provide innate cutaneous host defense. Late cornified envelope (LCE) genes, located in the epidermal differentiation complex on chromosome 1, encode a family of 18 proteins of unknown function, whose expression is largely restricted to epidermis. Deletion of two members, LCE3B and LCE3C (LCE3B/C-del), is a widely-replicated psoriasis risk factor that interacts with the major psoriasis-psoriasis risk gene HLA-C*06. Here we performed quantitative trait locus analysis, utilizing RNA-seq data from human skin and found that LCE3B/C-del was associated with a markedly increased expression of LCE3A, a gene directly adjacent to LCE3B/C-del. We confirmed these findings in a 3-dimensional skin model using primary keratinocytes from LCE3B/C-del genotyped donors. Functional analysis revealed that LCE3 proteins, and LCE3A in particular, have defensin-like antimicrobial activity against a variety of bacterial taxa at low micromolar concentrations. No genotype-dependent effect was observed for the inside-out or outside-in physical skin barrier function. Our findings identify an unknown biological function for LCE3 proteins and suggest a role in epidermal host defense and LCE3B/C-del-mediated psoriasis risk.

Repeated short climatic change affects the epidermal differentiation program and leads to matrix remodeling in a human organotypic skin model

Human skin is subject to frequent changes in ambient temperature and humidity and needs to cope with these environmental modifications. To decipher the molecular response of human skin to repeated climatic change, a versatile model of skin equivalent subject to “hot–wet” (40°C, 80% relative humidity [RH]) or “cold–dry” (10°C, 40% RH) climatic stress repeated daily was used. To obtain an exhaustive view of the molecular mechanisms elicited by climatic change, large-scale gene expression DNA microarray analysis was performed and modulated function was determined by bioinformatic annotation. This analysis revealed several functions, including epidermal differentiation and extracellular matrix, impacted by repeated variations in climatic conditions. Some of these molecular changes were confirmed by histological examination and protein expression. Both treatments (hot–wet and cold–dry) reduced the expression of genes encoding collagens, laminin, and proteoglycans, suggesting a profound remodeling of the extracellular matrix. Strong induction of the entire family of late cornified envelope genes after cold–dry exposure, confirmed at protein level, was also observed. These changes correlated with an increase in epidermal differentiation markers such as corneodesmosin and a thickening of the stratum corneum, indicating possible implementation of defense mechanisms against dehydration. This study for the first time reveals the complex pattern of molecular response allowing adaption of human skin to repeated change in its climatic environment.