DNA methylation-based subclassification of psoriasis in the Chinese Han population

The critical importance of epigenetics in autoimmune-related skin diseases

Autoimmune-related skin diseases are a group of disorders with diverse etiology and pathophysiology involved in autoimmunity. Genetics and environmental factors may contribute to the development of these autoimmune disorders. Although the etiology and pathogenesis of these disorders are poorly understood, environmental variables that induce aberrant epigenetic regulations may provide some insights. Epigenetics is the study of heritable mechanisms that regulate gene expression without changing DNA sequences. The most important epigenetic mechanisms are DNA methylation, histone modification, and noncoding RNAs. In this review, we discuss the most recent findings regarding the function of epigenetic mechanisms in autoimmune-related skin disorders, including systemic lupus erythematosus, bullous skin diseases, psoriasis, and systemic sclerosis. These findings will expand our understanding and highlight the possible clinical applications of precision epigenetics approaches.

The Role of T Helper 22 Cells in Dermatological Disorders

T helper 22 (Th22) cells are a newly identified subset of CD4+ T cells that secrete the effector cytokine interleukin 22 (IL-22) upon specific antigen stimulation, barely with IFN-γ or IL-17. Increasing studies have demonstrated that Th22 cells and IL-22 play essential roles in skin barrier defense and skin disease pathogenesis since the IL-22 receptor is widely expressed in the skin, especially in keratinocytes. Herein, we reviewed the characterization, differentiation, and biological activities of Th22 cells and elucidated their roles in skin health and disease. We mainly focused on the intricate crosstalk between Th22 cells and keratinocytes and provided potential therapeutic strategies targeting the Th22/IL-22 signaling pathway.

Copy Number Variation Analysis of IL22 and LCE3C in Different Subtypes of Psoriasis in a Chinese Han Population

BACKGROUND Psoriasis is a chronic, immune-mediated and hyperproliferative skin disease with both genetic and environmental components. Copy number variations (CNV) of IL22 and LCE3C-LCE3B deletion have been confirmed to be predisposed to psoriasis vulgaris (PsV) in several ethnic groups. However, it remains to be clarified whether CNVs of IL22 and LCE3C are associated with different subtypes of psoriasis (psoriatic arthritis, PsA; erythrodermic psoriasis, EP; and generalized pustular psoriasis, GPP). MATERIAL AND METHODS We enrolled 897 Han Chinese individuals, including 478 patients and 419 healthy controls, and detected CNVs of IL22 and LCE3C using the comparative CT method by real-time PCR, and Pearson's χ² test was used to evaluated the copy number difference among subtypes. RESULTS CNVs of IL22 were significantly higher in PsV than in healthy controls (P<0.001). CNV of LCE3C in PsV, PsA, and GPP groups were significantly lower compared to healthy controls. When linked with clinical parameters, mild psoriasis carried less IL22 copy numbers than that in severe psoriasis (P=0.043). Neither IL22 or LCE3C CNVs were associated with age of onset. CONCLUSIONS CNVs of LCE3C and IL22 might differentially contribute to subtypes of psoriasis. These findings suggest complex and diverse genetic variations in and among different clinical subtypes of psoriasis.

Skin Barrier Dysregulation in Psoriasis

The skin barrier is broadly composed of two elements-a physical barrier mostly localised in the epidermis, and an immune barrier localised in both the dermis and epidermis. These two systems interact cooperatively to maintain skin homeostasis and overall human health. However, if dysregulated, several skin diseases may arise. Psoriasis is one of the most prevalent skin diseases associated with disrupted barrier function. It is characterised by the formation of psoriatic lesions, the aberrant differentiation and proliferation of keratinocytes, and excessive inflammation. In this review, we summarize recent discoveries in disease pathogenesis, including the contribution of keratinocytes, immune cells, genetic and environmental factors, and how they advance current and future treatments.

Anti-tumor necrosis factor drug responses and skin-blood DNA methylation age: Relationships in moderate-to-severe psoriasis

Studies have examined the utility of DNA methylation as a biomarker of psoriasis treatment responses, but investigations of treatment responses with Skin-Blood DNA methylation age (SkinBloodAge)-a methylation-based measure of health designed using skin tissues-are lacking. Using a HumanMethylation450 BeadChip blood DNA methylation data set from 70 white patients who presented with moderate-to-severe plaque psoriasis and were treated with anti-tumor necrosis factor (TNF) agents in Madrid, Spain, we examined the cross-sectional relationships of SkinBloodAge with anti-TNF treatment responses. Partial responders had a 7.2-year higher mean SkinBloodAge than excellent responders (P = .03). In linear regression models adjusted for chronological age, sex and anti-TNF agents - on average - partial responders had a 2.65-year higher SkinBloodAge than excellent responders (95%CI: 0.44, 4.86, P = .02). This relationship was attenuated in a sensitivity analysis adjusting for white blood cells including known T-cell mediators of psoriasis pathophysiology (β = 1.91-years, 95%CI: -0.50, 4.32, P = .12). Overall, our study suggests that partial responders to anti-TNF therapy have higher SkinBloodAges when compared to excellent responders. Although these findings still need to be confirmed more broadly, they further suggest that SkinBloodAge may be a useful treatment response biomarker that can be incorporated with other blood tests before anti-TNF therapy initiation in moderate-to-severe psoriasis patients.

Epigenetics of Psoriasis

Psoriasis is a chronic and recurrent inflammatory skin disease, involving the rapid proliferation and abnormal differentiation of keratinocytes and activation of T cells. It is generally accepted that the central pathogenesis of psoriasis is a T cell-dominant immune disorder affected by multiple factors including genetic susceptibility, environmental factors, innate and adaptive immune responses, etc. However, the exact etiology is largely unknown. In recent years, epigenetic involvements, such as the DNA methylation, chromatin modifications, and noncoding RNA regulation are reported to be critical for the pathogenesis of psoriasis. However, the interplay between these factors has only recently been started to be unraveled. Notably, inhibitors of enzymes that work in epigenetic modifications, such as DNA methyltransferases and histone deacetylases, are beginning to appear in the clinical setting to restore normal epigenetic patterns (Generali et al. in J Autoimmun 83:51-61, 2017), providing novel therapeutic potential as novel treatment targets for psoriasis. Indeed, medications previously used to treat autoimmune diseases have later been discovered to exert their action via epigenetic mechanisms. Herein, we review the findings on epigenetics associated with psoriasis, and discuss future perspectives in this field.

DNA methylation age is not affected in psoriatic skin tissue

Background

Psoriasis (Ps) is a common chronic inflammatory skin disease. The keratinocytes of psoriatic skin defy normal apoptosis and exhibit active cell proliferation. Aberrant DNA methylation (DNAm) has been suggested relevant through regulating the expression of Ps susceptibility genes. However, it is unclear whether the biological age inferred from DNA methylome is affected.

Results

To address the above issue, we applied a recently developed methylation clock model to our Chinese Han population dataset, which includes DNAm data of 114 involved psoriatic skin tissues (PP) and 41 uninvolved psoriatic skin tissues (PN) from Ps patients, and 62 normal skin tissues (NN) from health controls. We first confirmed the applicability of the clock in PN and NN. We then showed that PP samples have largely unchanged DNAm age, and that no association was observed between available clinical features and DNAm age acceleration. Examination of genome-wide CpGs yielded age-associated CpGs with concordant age-association coefficients among the three groups, which was also supported by an external dataset. We also interestingly observed two clock CpGs differentially methylated between PP and PN.

Conclusions

Overall, our results suggest no significant alteration in DNAm age in PN and PP. Therefore, the increase in keratinocyte proliferation and alteration in DNAm caused by Ps may not affect the biological age of psoriatic skin tissue.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0584-y) contains supplementary material, which is available to authorized users.