A functional SNP associated with atopic dermatitis controls cell type-specific methylation of the VSTM1 gene locus

Understanding Atopic Dermatitis in Asian and European Population Cohorts Using Complementary Omics Techniques

Atopic dermatitis is highly heterogeneous with respect to pathogenesis, clinical manifestations, and treatment response. There is evidence that ancestry and skin type each contribute to this heterogeneity, indicating the need to improve understanding of disease mechanisms in diverse populations. Methods to integrate multiomics studies have been well-described, but this review focuses on the importance and the strategies needed to integrate data across different ancestral groups, focusing, because of data availability, on Asian and European populations. Skin scientists and clinicians will each benefit from an understanding of how the multiple complimentary layers of omics data may inform future clinical management, from insight into disease pathogenesis and treatment targets.

Deciphering epigenetic regulations in the inflammatory pathways of atopic dermatitis

Atopic dermatitis, commonly referred to as atopic eczema, is a persistent inflammatory skin disorder that predominantly manifests in children but may endure into adulthood. Its clinical management poses challenges due to the absence of a definitive cure, and its prevalence varies across ethnicities, genders, and geographic locations. The epigenetic landscape of AD includes changes in DNA methylation, changes in histone acetylation and methylation, and regulation by non-coding RNAs. These changes affect inflammatory and immune mechanisms, and research has identified AD-specific variations in DNA methylation, particularly in the affected epidermis. Histone modifications, including acetylation, have been associated with the disruption of skin barrier function in AD, suggesting the potential therapeutic benefit of histone deacetylase inhibitors such as belinostat. Furthermore, non-coding RNAs, particularly microRNAs and long non-coding RNAs (lncRNAs), have been implicated in modulating various cellular processes central to AD pathogenesis. Therapeutic implications in AD include the potential use of DNA methylation inhibitors and histone deacetylase inhibitors to correct aberrant methylation patterns and modulate gene expression related to immune responses and skin barrier functions. Additionally, the emerging role of lncRNAs suggests the possibility of using small interfering RNAs or antisense oligonucleotides to inhibit lncRNAs and adjust their regulatory impact on gene expression. In conclusion, the importance of epigenetic elements in AD is becoming increasingly clear as studies highlight the contribution of DNA methylation, histone modifications and, control by non-coding RNAs to the onset and progression of the disease. Understanding these epigenetic changes provides valuable insights for developing targeted therapeutic strategies.

Identification of rat Vstm1 with conservative anti-inflammatory effect between rat and human homologs

Human VSTM1 (also known as SIRL1) is an inhibitory immune checkpoint receptor involved in leukocyte activation. Identification of the homologous genes in other species, such as mice and rats, will undoubtedly contribute to functional studies and clinical applications. Here, we successfully cloned the Vstm1 gene in rats, as supported by high-throughput sequencing data. However, Vstm1 is degenerated to a pseudogene in the mouse genome. Rat Vstm1 mRNA contains a complete open reading frame (ORF) of 630 nucleotides encoding 209 amino acids. Rat Vstm1 is highly expressed in bone marrow, especially in granulocytes. The expression levels of Vstm1 gradually increase with the development of granulocytes in bone marrow but are downregulated in response to inflammatory stimuli. Rat VSTM1 does not have an immunoreceptor tyrosine-based inhibitory motif (ITIM), however, it shows a conservative function of inflammatory inhibition with human VSTM1, and both are anti-correlated with many inflammatory cytokines, such as IL-1α and TNF-α. In bone marrow-derived macrophages (BMDMs), either rat or human VSTM1 suppressed the secretion of inflammatory cytokines in response to LPS stimulation. Further analysis in lung cancer microenvironment revealed that VSTM1 is mainly expressed in myeloid cells, anti-correlated with inflammatory cytokines and associated with tumor development and metastasis.

Toward Precision Medicine in Atopic Dermatitis Using Molecular-Based Approaches

Atopic dermatitis is the most common chronic inflammatory skin disorder, affecting up to 20% of children and 10% of adults in developed countries. The pathophysiology of atopic dermatitis is complex and involves a strong genetic predisposition and T-cell driven inflammation. Although our understanding of the pathology and drivers of this disease has improved in recent years, there are still knowledge gaps in the immune pathways involved. Therefore, advances in new omics technologies in atopic dermatitis will play a key role in understanding the pathogenesis of this burden disease and could develop preventive strategies and personalized treatment strategies. In this review, we discuss the latest developments in genetics, transcriptomics, epigenomics, proteomics, and metagenomics and understand how integrating multiple omics datasets will identify potential biomarkers and uncover nets of associations between several molecular levels.

Toward Precision Medicine in Atopic Dermatitis Using Molecular-Based Approaches

Atopic dermatitis is the most common chronic inflammatory skin disorder, affecting up to 20% of children and 10% of adults in developed countries. The pathophysiology of atopic dermatitis is complex and involves a strong genetic predisposition and T-cell driven inflammation. Although our understanding of the pathology and drivers of this disease has improved in recent years, there are still knowledge gaps in the immune pathways involved. Therefore, advances in new omics technologies in atopic dermatitis will play a key role in understanding the pathogenesis of this burden disease and could develop preventive strategies and personalized treatment strategies. In this review, we discuss the latest developments in genetics, transcriptomics, epigenomics, proteomics, and metagenomics and understand how integrating multiple omics datasets will identify potential biomarkers and uncover nets of associations between several molecular levels.

Lipidomics and Metabolomics in Infant Atopic Dermatitis: What's the Correlation with Early Nutrition?

To date, the complex picture of atopic dermatitis (AD) has not yet been fully clarified, despite the important prevalence of this disease in the pediatric population (20%) and the possibility of persistence into adulthood, with important implications for the quality of life of those affected, as well as significant social and financial costs. The most recent scientific evidence suggests a new interpretation of AD, highlighting the important role of the environment, particularly that of nutrition in the early stages of development. In fact, the new indications seem to point out the harmful effect of elimination diets, except in rare cases, the uselessness of chrono-insertions during complementary feeding and some benefits, albeit weak, of breastfeeding in those at greater risk. In this context, metabolomics and lipidomics can be necessary for a more in-depth knowledge of the complex metabolic network underlying this pathology. In fact, an alteration of the metabolic contents in children with AD has been highlighted, especially in correlation to the intestinal microbiota. While preliminary lipidomic studies showed the usefulness of a more in-depth knowledge of the alterations of the skin barrier to improve the development of baby skin care products. Therefore, investigating the response of different allergic phenotypes could be useful for better patient management and understanding, thus providing an early intervention on dysbiosis necessary to regulate the immune response from the earliest stages of development.

Intrinsic Effects of Exposome in Atopic Dermatitis: Genomics, Epigenomics and Regulatory Layers

Atopic dermatitis (AD) or atopic eczema is an increasingly manifested inflammatory skin disorder of complex etiology which is modulated by both extrinsic and intrinsic factors. The exposome includes a person's lifetime exposures and their effects. We recently reviewed the extrinsic exposome's environmental risk factors that contribute to AD. The periods of pregnancy, infancy, and teenage years are recognized as crucial stages in the formation of AD, where the exposome leads to enduring impacts on the immune system. However, research is now focusing on the interactions between intrinsic pathways that are modulated by the extrinsic exposome, including genetic variation, epigenetic modifications, and signals, such as diet, stress, and microbiome interactions. As a result, immune dysregulation, barrier dysfunction, hormonal fluctuations, and skin microbiome dysbiosis are important factors contributing to AD development, and their in-depth understanding is crucial not only for AD treatment but also for similar inflammatory disorders.

Inferring cell-type-specific causal gene regulatory networks during human neurogenesis

BACKGROUND

Genetic variation influences both chromatin accessibility, assessed in chromatin accessibility quantitative trait loci (caQTL) studies, and gene expression, assessed in expression QTL (eQTL) studies. Genetic variants can impact either nearby genes (cis-eQTLs) or distal genes (trans-eQTLs). Colocalization between caQTL and eQTL, or cis- and trans-eQTLs suggests that they share causal variants. However, pairwise colocalization between these molecular QTLs does not guarantee a causal relationship. Mediation analysis can be applied to assess the evidence supporting causality versus independence between molecular QTLs. Given that the function of QTLs can be cell-type-specific, we performed mediation analyses to find epigenetic and distal regulatory causal pathways for genes within two major cell types of the developing human cortex, progenitors and neurons.

RESULTS

We find that the expression of 168 and 38 genes is mediated by chromatin accessibility in progenitors and neurons, respectively. We also find that the expression of 11 and 12 downstream genes is mediated by upstream genes in progenitors and neurons. Moreover, we discover that a genetic locus associated with inter-individual differences in brain structure shows evidence for mediation of SLC26A7 through chromatin accessibility, identifying molecular mechanisms of a common variant association to a brain trait.

CONCLUSIONS

In this study, we identify cell-type-specific causal gene regulatory networks whereby the impacts of variants on gene expression were mediated by chromatin accessibility or distal gene expression. Identification of these causal paths will enable identifying and prioritizing actionable regulatory targets perturbing these key processes during neurodevelopment.

Soluble Signal Inhibitory Receptor on Leukocytes-1 Is Released from Activated Neutrophils by Proteinase 3 Cleavage

Signal inhibitory receptor on leukocytes-1 (SIRL-1) is an immune inhibitory receptor expressed on human granulocytes and monocytes that dampens antimicrobial functions. We previously showed that sputum neutrophils from infants with severe respiratory syncytial virus (RSV) bronchiolitis have decreased SIRL-1 surface expression compared with blood neutrophils and that SIRL-1 surface expression is rapidly lost from in vitro activated neutrophils. This led us to hypothesize that activated neutrophils lose SIRL-1 by ectodomain shedding. Here, we developed an ELISA and measured the concentration of soluble SIRL-1 (sSIRL-1) in patients with RSV bronchiolitis and hospitalized patients with COVID-19, which are both characterized by neutrophilic inflammation. In line with our hypothesis, sSIRL-1 concentration was increased in sputum compared with plasma of patients with RSV bronchiolitis and in serum of hospitalized patients with COVID-19 compared with control serum. In addition, we show that in vitro activated neutrophils release sSIRL-1 by proteolytic cleavage and that this diminishes the ability to inhibit neutrophilic reactive oxygen species production via SIRL-1. Finally, we found that SIRL-1 shedding is prevented by proteinase 3 inhibition and by extracellular adherence protein from Staphylococcus aureus. Notably, we recently showed that SIRL-1 is activated by PSMα3 from S. aureus, suggesting that S. aureus may counteract SIRL-1 shedding to benefit from preserved inhibitory function of SIRL-1. In conclusion, we report that SIRL-1 is released from activated neutrophils by proteinase 3 cleavage and that endogenous sSIRL-1 protein is present in vivo.

VSTM1-v2 does not drive human Th17 cell differentiation: A replication study

Signal inhibitory receptor on leukocytes-1 (SIRL-1) is an immune inhibitory receptor expressed on human myeloid cells. We previously showed that dendritic cell (DC)-driven Th17 cell differentiation of human naive CD4+ T cells requires presence of neutrophils, which is inhibited by SIRL-1 ligation. VSTM1-v2 is a soluble isoform of SIRL-1, which was previously proposed to function as a Th17 polarizing cytokine. Here, we investigated the effect of VSTM1-v2 on DC-driven Th17 cell development. Neutrophils induced DC-driven Th17 cell differentiation, which was not enhanced by VSTM1-v2. Similarly, we found no effect of VSTM1-v2 on cytokine-driven Th17 cell development. Thus, our results do not support a role for VSTM1-v2 in Th17 cell differentiation.

Signal inhibitory receptor on leukocytes-1 regulates the formation of the neutrophil extracellular trap in rheumatoid arthritis

BACKGROUND

Neutrophil extracellular trap (NET) has been demonstrated to play important roles in the pathogenesis and progression of rheumatoid arthritis (RA). Emerging evidence indicates that ligation of signal inhibitory receptor on leukocytes-1 (SIRL-1) can dampen Fc receptor-induced reactive oxygen species (ROS) production in primary human neutrophils by reducing extracellular signal-regulated kinase (ERK) activation. The current study aimed to determine the regulatory effects of SIRL-1 on the NET formation and ROS production by comparing RA patients and healthy controls (HC).

METHODS

Multiple assays were employed to detect the expression level of SIRL-1, including immunohistochemical staining, quantitative reverse transcription polymerase chain reaction (RT-PCR) and flow cytometry. Peripheral blood neutrophils from both HC and RA patients were freshly isolated. The NET formation was assessed spontaneously before and after exposure to serum samples from HC and RA patients, respectively. The quantification of NET formation was determined by fluorescence microscopy and Spectra Max M5 fluorescent plate reader. The ROS production was examined by flow cytometry.

RESULTS

The expression level of SIRL-1 in peripheral blood neutrophils was decreased in RA, comparing to HC. The RA-originated neutrophils showed higher levels of ROS production and NET formation. Ligation of SIRL-1 to neutrophils suppressed ROS production and NET formation. Stimulation of neutrophils with severe anti-cyclic citrullinated peptides (CCP) induced NET formation, which could be inhibited by application of SIRL-1 ligation.

CONCLUSION

The current study identified SIRL-1 differentially expressed in neutrophils between RA and HC. Ligation of SIRL-1 inhibited ROS production and NET formation. Downregulation of SIRL-1 showed correlation with upregulation of NET formation in RA. These findings showed the regulation of SIRL-1 on NET formation and provided a potential therapeutic target for RA.

Multiple datasets to explore the molecular mechanism of sepsis

Background

This study aimed to identify potential biomarkers, by means of bioinformatics, affecting the occurrence and development of septic shock.

Methods

Download GSE131761 septic shock data set from NCBI geo database, including 33 control samples and 81 septic shock samples. GSE131761 and sequencing data were used to identify and analyze differentially expressed genes in septic shock patients and normal subjects. In addition, with sequencing data as training set and GSE131761 as validation set, a diagnostic model was established by lasso regression to identify key genes. ROC curve verified the stability of the model. Finally, immune infiltration analysis, enrichment analysis, transcriptional regulation analysis and correlation analysis of key genes were carried out to understand the potential molecular mechanism of key genes affecting septic shock.

Results

A total of 292 differential genes were screened out from the self-test data, 294 differential genes were screened out by GSE131761, Lasso regression was performed on the intersection genes of the two, a diagnostic model was constructed, and 5 genes were identified as biomarkers of septic shock. These 5 genes were SIGLEC10, VSTM1, GYPB, OPTN, and GIMAP7. The five key genes were strongly correlated with immune cells, and the ROC results showed that the five genes had good predictive performance on the occurrence and development of diseases. In addition, the key genes were strongly correlated with immune regulatory genes.

Conclusion

In this study, a series of algorithms were used to identify five key genes that are associated with septic shock, which may become potential candidate targets for septic shock diagnosis and treatment.

Trial registration

Approval number:2019XE0149-1.

Disease-associated genetic variants in the regulatory regions of human genes: mechanisms of action on transcription and genomic resources for dissecting these mechanisms

Whole genome and whole exome sequencing technologies play a very important role in the studies of the genetic aspects of the pathogenesis of various diseases. The ample use of genome-wide and exome-wide association study methodology (GWAS and EWAS) made it possible to identify a large number of genetic variants associated with diseases. This information is accumulated in the databases like GWAS central, GWAS catalog, OMIM, ClinVar, etc. Most of the variants identified by the GWAS technique are located in the noncoding regions of the human genome. According to the ENCODE project, the fraction of regions in the human genome potentially involved in transcriptional control is many times greater than the fraction of coding regions. Thus, genetic variation in noncoding regions of the genome can increase the susceptibility to diseases by disrupting various regulatory elements (promoters, enhancers, silencers, insulator regions, etc.). However, identification of the mechanisms of influence of pathogenic genetic variants on the diseases risk is difficult due to a wide variety of regulatory elements. The present review focuses on the molecular genetic mechanisms by which pathogenic genetic variants affect gene expression. At the same time, attention is concentrated on the transcriptional level of regulation as an initial step in the expression of any gene. A triggering event mediating the effect of a pathogenic genetic variant on the level of gene expression can be, for example, a change in the functional activity of transcription factor binding sites (TFBSs) or DNA methylation change, which, in turn, affects the functional activity of promoters or enhancers. Dissecting the regulatory roles of polymorphic loci have been impossible without close integration of modern experimental approaches with computer analysis of a growing wealth of genetic and biological data obtained using omics technologies. The review provides a brief description of a number of the most well-known public genomic information resources containing data obtained using omics technologies, including (1) resources that accumulate data on the chromatin states and the regions of transcription factor binding derived from ChIP-seq experiments; (2) resources containing data on genomic loci, for which allele-specific transcription factor binding was revealed based on ChIP-seq technology; (3) resources containing in silico predicted data on the potential impact of genetic variants on the transcription factor binding sites

Signal inhibitory receptor on leukocytes-1 recognizes bacterial and endogenous amphipathic α-helical peptides

Signal inhibitory receptor on leukocytes-1 (SIRL-1) is a negative regulator of myeloid cell function and dampens antimicrobial responses. We here show that different species of the genus Staphylococcus secrete SIRL-1-engaging factors. By screening a library of single-gene transposon mutants in Staphylococcus aureus, we identified these factors as phenol-soluble modulins (PSMs). PSMs are amphipathic α-helical peptides involved in multiple aspects of staphylococcal virulence and physiology. They are cytotoxic and activate the chemotactic formyl peptide receptor 2 (FPR2) on immune cells. Human cathelicidin LL-37 is also an amphipathic α-helical peptide with antimicrobial and chemotactic activities, structurally and functionally similar to α-type PSMs. We demonstrate that α-type PSMs from multiple staphylococcal species as well as human cathelicidin LL-37 activate SIRL-1, suggesting that SIRL-1 recognizes α-helical peptides with an amphipathic arrangement of hydrophobicity, although we were not able to show direct binding to SIRL-1. Upon rational peptide design, we identified artificial peptides in which the capacity to ligate SIRL-1 is segregated from cytotoxic and FPR2-activating properties, allowing specific engagement of SIRL-1. In conclusion, we propose staphylococcal PSMs and human LL-37 as a potential new class of natural ligands for SIRL-1.

Current understanding of epigenetics in atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin disorder affecting up to 20% of the paediatric population worldwide. AD patients commonly exhibit dry skin and pruritus and are at a higher risk for developing asthma as well as allergic rhinitis. Filaggrin loss‐of‐function variants are the most widely replicated genetic risk factor among >40 genes associated with AD susceptibility. The prevalence of AD has tripled in the past 30 years in industrial countries around the world. This urgent public health issue has prompted the field to more thoroughly investigate the mechanisms that underlie AD pathogenesis amidst environmental exposures. Epigenetics is the study of heritable, yet reversible, modifications to the genome that affect gene expression. The past decade has seen an emergence of exciting studies identifying a role for epigenetic regulation associated with AD and at the interface of environmental factors. Such epigenetic studies have been empowered by sequencing technologies and human genome variation and epigenome maps. miRNAs that post‐transcriptionally modify gene expression and circRNAs have also been discovered to be associated with AD. Here, we review our current understanding of epigenetics associated with atopic dermatitis. We discuss studies identifying distinct DNA methylation changes in keratinocytes and T cells, eQTLs as DNA methylation switches that impact gene expression, and histone modification changes associated with AD‐related microbial dysbiosis. We further highlight the need for integrative and collaborative analyses to elucidate the impact of these epigenetic findings as potential drivers for AD pathogenesis and the translation of this new knowledge to develop newer targeted treatments.

Genetic Variants in Transcription Factor Binding Sites in Humans: Triggered by Natural Selection and Triggers of Diseases

Variants of transcription factor binding sites (TFBSs) constitute an important part of the human genome. Current evidence demonstrates close links between nucleotides within TFBSs and gene expression. There are multiple pathways through which genomic sequences located in TFBSs regulate gene expression, and recent genome-wide association studies have shown the biological significance of TFBS variation in human phenotypes. However, numerous challenges remain in the study of TFBS polymorphisms. This article aims to cover the current state of understanding as regards the genomic features of TFBSs and TFBS variants; the mechanisms through which TFBS variants regulate gene expression; the approaches to studying the effects of nucleotide changes that create or disrupt TFBSs; the challenges faced in studies of TFBS sequence variations; the effects of natural selection on collections of TFBSs; in addition to the insights gained from the study of TFBS alleles related to gout, its associated comorbidities (increased body mass index, chronic kidney disease, diabetes, dyslipidemia, coronary artery disease, ischemic heart disease, hypertension, hyperuricemia, osteoporosis, and prostate cancer), and the treatment responses of patients.

Leveraging functional annotation to identify genes associated with complex diseases

To increase statistical power to identify genes associated with complex traits, a number of transcriptome-wide association study (TWAS) methods have been proposed using gene expression as a mediating trait linking genetic variations and diseases. These methods first predict expression levels based on inferred expression quantitative trait loci (eQTLs) and then identify expression-mediated genetic effects on diseases by associating phenotypes with predicted expression levels. The success of these methods critically depends on the identification of eQTLs, which may not be functional in the corresponding tissue, due to linkage disequilibrium (LD) and the correlation of gene expression between tissues. Here, we introduce a new method called T-GEN (Transcriptome-mediated identification of disease-associated Genes with Epigenetic aNnotation) to identify disease-associated genes leveraging epigenetic information. Through prioritizing SNPs with tissue-specific epigenetic annotation, T-GEN can better identify SNPs that are both statistically predictive and biologically functional. We found that a significantly higher percentage (an increase of 18.7% to 47.2%) of eQTLs identified by T-GEN are inferred to be functional by ChromHMM and more are deleterious based on their Combined Annotation Dependent Depletion (CADD) scores. Applying T-GEN to 207 complex traits, we were able to identify more trait-associated genes (ranging from 7.7% to 102%) than those from existing methods. Among the identified genes associated with these traits, T-GEN can better identify genes with high (>0.99) pLI scores compared to other methods. When T-GEN was applied to late-onset Alzheimer's disease, we identified 96 genes located at 15 loci, including two novel loci not implicated in previous GWAS. We further replicated 50 genes in an independent GWAS, including one of the two novel loci.

Epigenetic alterations in skin homing CD4+CLA+ T cells of atopic dermatitis patients

T cells expressing the cutaneous lymphocyte antigen (CLA) mediate pathogenic inflammation in atopic dermatitis (AD). The molecular alterations contributing to their dysregulation remain unclear. With the aim to elucidate putative altered pathways in AD we profiled DNA methylation levels and miRNA expression in sorted T cell populations (CD4⁺, CD4⁺CD45RA⁺ naïve, CD4⁺CLA⁺, and CD8⁺) from adult AD patients and healthy controls (HC). Skin homing CD4⁺CLA⁺ T cells from AD patients showed significant differences in DNA methylation in 40 genes compared to HC (p < 0.05). Reduced DNA methylation levels in the upstream region of the interleukin-13 gene (IL13) in CD4⁺CLA⁺ T cells from AD patients correlated with increased IL13 mRNA expression in these cells. Sixteen miRNAs showed differential expression in CD4⁺CLA⁺ T cells from AD patients targeting genes in 202 biological processes (p < 0.05). An integrated network analysis of miRNAs and CpG sites identified two communities of strongly interconnected regulatory elements with strong antagonistic behaviours that recapitulated the differences between AD patients and HC. Functional analysis of the genes linked to these communities revealed their association with key cytokine signaling pathways, MAP kinase signaling and protein ubiquitination. Our findings support that epigenetic mechanisms play a role in the pathogenesis of AD by affecting inflammatory signaling molecules in skin homing CD4⁺CLA⁺ T cells and uncover putative molecules participating in AD pathways.

SNPs in Sites for DNA Methylation, Transcription Factor Binding, and miRNA Targets Leading to Allele-Specific Gene Expression and Contributing to Complex Disease Risk: A Systematic Review

INTRODUCTION

The complex genetic diversity among human populations results from an assortment of factors acting at various sequential levels, including mutations, population migrations, genetic drift, and selection. Although there are a plethora of DNA sequence variations identified through genome-wide association studies (GWAS), the challenge remains to explain the mechanisms underlying interindividual phenotypic disparity accounting for disease susceptibility. Single nucleotide polymorphisms (SNPs) present in the sites for DNA methylation, transcription factor (TF) binding, or miRNA targets can alter the gene expression. The systematic review aimed to evaluate the complex crosstalk among SNPs, miRNAs, DNA methylation, and TFs for complex multifactorial disease risk.

METHODS

PubMed and Scopus databases were used from inception until May 15, 2019. Initially, screening of articles involved studies assessing the interaction of SNPs with TFs, DNA methylation, or miRNAs resulting in allele-specific gene expression in complex multifactorial diseases. We also included the studies which provided experimental validation of the interaction of SNPs with each of these factors. The results from various studies on multifactorial diseases were assessed.

RESULTS

A total of 11 articles for SNPs interacting with DNA methylation, 30 articles for SNPs interacting with TFs, and 11 articles for SNPs in miRNA binding sites were selected. The interactions of SNPs with epigenetic factors were found to be implicated in different types of cancers, autoimmune diseases, cardiovascular diseases, diabetes, and asthma.

CONCLUSION

The systematic review provides evidence for the interplay between genetic and epigenetic risk factors through allele-specific gene expression in various complex multifactorial diseases.

Signal Inhibitory Receptor on Leukocytes-1 is highly expressed on lung monocytes, but absent on mononuclear phagocytes in skin and colon

Signal Inhibitory Receptor on Leukocytes-1 (SIRL-1) is expressed on human blood monocytes and granulocytes and inhibits myeloid effector functions. On monocytes, but not granulocytes, SIRL-1 expression is low or absent in individuals with the single nucleotide polymorphism (SNP) rs612529C. The expression of SIRL-1 in tissue and the influence of rs612529 hereon is currently unknown. Here, we used flow cytometry to determine SIRL-1 expression on immune cells in human blood and three barrier tissues; skin, colon and lung. SIRL-1 was expressed by virtually all neutrophils and eosinophils in these tissues. In contrast, SIRL-1 was not expressed by monocyte-derived cells in skin and colon, whereas it was highly expressed by lung classical monocytes. Lung monocytes from individuals with a rs612529C allele had decreased SIRL-1 expression, consistent with the genotype association in blood. Within the different monocyte subsets in blood and lung, SIRL-1 expression was highest in classical monocytes and lowest in nonclassical monocytes. SIRL-1 was not expressed by dendritic cells in blood and barrier tissues. Together, these results indicate that SIRL-1 is differentially expressed on phagocyte subsets in blood and barrier tissues, and that its expression on monocytes is genotype- and tissue-specific. Immune regulation of monocytes by SIRL-1 may be of particular importance in the lung.

A genome-wide analysis of DNA methylation identifies a novel association signal for Lp(a) concentrations in the LPA promoter

Lipoprotein(a) [Lp(a)] is a major cardiovascular risk factor, which is largely genetically determined by one major gene locus, the LPA gene. Many aspects of the transcriptional regulation of LPA are poorly understood and the role of epigenetics has not been addressed yet. Therefore, we conducted an epigenome-wide analysis of DNA methylation on Lp(a) levels in two population-based studies (total n = 2208). We identified a CpG site in the LPA promoter which was significantly associated with Lp(a) concentrations. Surprisingly, the identified CpG site was found to overlap the SNP rs76735376. We genotyped this SNP de-novo in three studies (total n = 7512). The minor allele of rs76735376 (1.1% minor allele frequency) was associated with increased Lp(a) values (p = 1.01e-59) and explained 3.5% of the variation of Lp(a). Statistical mediation analysis showed that the effect on Lp(a) is rather originating from the base change itself and is not mediated by DNA methylation levels. This finding is supported by eQTL data from 208 liver tissue samples from the GTEx project, which shows a significant association of the rs76735376 minor allele with increased LPA expression. To evaluate, whether the association signal at rs76735376 may actually be derived from a stronger eQTL signal in LD with this SNP, eQTL association results of all correlated SNPs (r2≥0.1) were integrated with genetic association results. This analysis pinpointed to rs10455872 as the potential trigger of the effect of rs76735376. Furthermore, both SNPs coincide with short apo(a) isoforms. Adjusting for both, rs10455872 and the apo(a) isoforms diminished the effect size of rs76735376 to 5.38 mg/dL (p = 0.0463). This indicates that the effect of rs76735376 can be explained by both an independent effect of the SNP and a strong correlation with rs10455872 and apo(a) isoforms.

Genetics and Epigenetics of Atopic Dermatitis: An Updated Systematic Review

BACKGROUND

Atopic dermatitis is a common inflammatory skin disorder that affects up to 15-20% of the population and is characterized by recurrent eczematous lesions with intense itching. As a heterogeneous disease, multiple factors have been suggested to explain the nature of atopic dermatitis (AD), and its high prevalence makes it necessary to periodically compile and update the new information available. In this systematic review, the focus is set at the genetic and epigenetic studies carried out in the last years.

METHODS

A systematic literature review was conducted in three scientific publication databases (PubMed, Cochrane Library, and Scopus). The search was restricted to publications indexed from July 2016 to December 2019, and keywords related to atopic dermatitis genetics and epigenetics were used.

RESULTS

A total of 73 original papers met the inclusion criteria established, including 9 epigenetic studies. A total of 62 genes and 5 intergenic regions were described as associated with AD.

CONCLUSION

Filaggrin (FLG) polymorphisms are confirmed as key genetic determinants for AD development, but also epigenetic regulation and other genes with functions mainly related to the immune system and extracellular matrix, reinforcing the notion of skin homeostasis breakage in AD.

Resistin expression in human monocytes is controlled by two linked promoter SNPs mediating NFKB p50/p50 binding and C-methylation

Resistin is a key cytokine associated with metabolic and inflammatory diseases. Especially in East Asian populations, the expression levels are strongly influenced by genetic polymorphisms. Mechanisms and functional implications of this genetic control are still unknown. By employing reporter assays, EMSA, inhibition studies, bisulphite sequencing, ChIP-Seq and gene-editing we show that the p50/p50 homodimer known to act as repressor for a number of pro-inflammatory genes plays a central role in the genetic regulation of resistin in monocytes along with promoter methylation. In the common RETN haplotype p50/p50 constitutively dampens the expression by binding to the promoter. In an Asian haplotype variant however this interaction is disrupted by the A allele of rs3219175. The SNP is in very close linkage to rs34861192, a CpG SNP, located 280 bp upstream which provides an allele-specific C-methylation site. rs34861192 is located in a 100 bp region found to be methylated in the common but not in the Asian haplotype, resulting in the latter having a higher basal expression, which also associates with elevated histone acetylation (H3K27ac). Genotype associations within cohort data of 200 East Asian individuals revealed significant associations between this haplotype and the plasma levels of factors such as TGF-b, S100B, sRAGE and IL-8 as well as with myeloid DC counts. Thus, the common RETN haplotype is tightly regulated by the epigenetic mechanism linked to p50/p50-binding. This control is lost in the Asian haplotype, which may have evolved to balance the antagonistic RETN effects on pathogen protection vs. metabolic and inflammatory disease induction.

Crosstalk of Genetic Variants, Allele-Specific DNA Methylation, and Environmental Factors for Complex Disease Risk

Over the past decades, genome-wide association studies (GWAS) have identified thousands of phenotype-associated DNA sequence variants for potential explanations of inter-individual phenotypic differences and disease susceptibility. However, it remains a challenge for translating the associations into causative mechanisms for complex diseases, partially due to the involved variants in the noncoding regions and the inconvenience of functional studies in human population samples. So far, accumulating evidence has suggested a complex crosstalk among genetic variants, allele-specific binding of transcription factors (ABTF), and allele-specific DNA methylation patterns (ASM), as well as environmental factors for disease risk. This review aims to summarize the current studies regarding the interactions of the aforementioned factors with a focus on epigenetic insights. We present two scenarios of single nucleotide polymorphisms (SNPs) in coding regions and non-coding regions for disease risk, via potentially impacting epigenetic patterns. While a SNP in a coding region may confer disease risk via altering protein functions, a SNP in non-coding region may cause diseases, via SNP-altering ABTF, ASM, and allele-specific gene expression (ASE). The allelic increases or decreases of gene expression are key for disease risk during development. Such ASE can be achieved via either a "SNP-introduced ABTF to ASM" or a "SNP-introduced ASM to ABTF." Together with our additional in-depth review on insulator CTCF, we are convinced to propose a working model that the small effect of a SNP acts through altered ABTF and/or ASM, for ASE and eventual disease outcome (named as a "SNP intensifier" model). In summary, the significance of complex crosstalk among genetic factors, epigenetic patterns, and environmental factors requires further investigations for disease susceptibility.

Convergence of evidence from a methylome-wide CpG-SNP association study and GWAS of major depressive disorder

DNA methylation is an epigenetic modification that provides stability and diversity to the cellular phenotype. It is influenced by both genetic sequence variation and environmental factors, and can therefore potentially account for variation of heritable phenotypes and disorders. Therefore, methylome-wide association studies (MWAS) are promising complements to genome-wide association studies (GWAS) of genetic variants. Of particular interest are methylation sites (CpGs) that are created or destroyed by the alleles of single-nucleotide polymorphisms (SNPs), as these so-called CpG-SNPs may show variation in methylation levels on top of what can be explained by the sequence variation. Using sequencing-based data from 1132 major depressive disorder (MDD) cases and controls, we performed a MWAS of 970,414 common CpG-SNPs. The analysis identified 27 suggestively significant (P < 1.00 × 10^-5) CpG-SNPs associations. Furthermore, the MWAS results were over-represented (odds ratios ranging 1.36-5.00; P ranging 4.9 × 10^-3-8.1 × 10^-2) among findings from three recent GWAS for MDD-related phenotypes. Overlapping loci included, e.g., ROBO2, ASIC2, and DCC. As the CpG-SNP analysis accounts for the number of alleles that creates CpGs, the methylation differences could not be explained by differences in allele frequencies. Thus, the results show that the MWAS and GWASs provide independent lines of evidence for the involvement of these loci in MDD. In conclusion, our methylation study of MDD contributes novel information about loci of relevance that complements previous findings and generates new hypothesis about MDD etiology, such as that the functional effects of genetic association may be partly mediated and/or enhanced by the methylation status in these loci.