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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. [ABSTRACT FROM AUTHOR]

Background: Atopic dermatitis (AD) is classified as extrinsic and intrinsic, representing approximately 80% and 20% of patients with the disease, respectively. Although sharing a similar clinical phenotype, only extrinsic AD is characterized by high serum IgE levels. Because most patients with AD exhibit high IgE levels, an “allergic”/IgE-mediated disease pathogenesis was hypothesized. However, current models associate AD with T-cell activation, particularly TH2/TH22 polarization, and epidermal barrier defects. Objective: We sought to define whether both variants share a common pathogenesis. Methods: We stratified 51 patients with severe AD into extrinsic AD (n = 42) and intrinsic AD (n = 9) groups (with similar mean disease activity/SCORAD scores) and analyzed the molecular and cellular skin pathology of lesional and nonlesional intrinsic AD and extrinsic AD by using gene expression (real-time PCR) and immunohistochemistry. Results: A significant correlation between IgE levels and SCORAD scores (r = 0.76, P < 10−5) was found only in patients with extrinsic AD. Marked infiltrates of T cells and dendritic cells and corresponding epidermal alterations (keratin 16, Mki67, and S100A7/A8/A9) defined lesional skin of patients with both variants. However, higher activation of all inflammatory axes (including TH2) was detected in patients with intrinsic AD, particularly TH17 and TH22 cytokines. Positive correlations between TH17-related molecules and SCORAD scores were only found in patients with intrinsic AD, whereas only patients with extrinsic AD showed positive correlations between SCORAD scores and TH2 cytokine (IL-4 and IL-5) levels and negative correlations with differentiation products (loricrin and periplakin). Conclusions: Although differences in TH17 and TH22 activation exist between patients with intrinsic AD and those with extrinsic AD, we identified common disease-defining features of T-cell activation, production of polarized cytokines, and keratinocyte responses to immune products. Our data indicate that a TH2 bias is not the sole cause of high IgE levels in patients with extrinsic AD, with important implications for similar therapeutic interventions. [Copyright &y& Elsevier]

Background: Atopic dermatitis (AD) is a common disease with an increasing prevalence. The primary pathogenesis of the disease is still elusive, resulting in the lack of specific treatments. AD is currently considered a biphasic disease, with TH2 predominating in acute disease and a switch to TH1 characterizing chronic disease. Elucidation of the molecular factors that participate in the onset of new lesions and maintenance of chronic disease is critical for the development of targeted therapeutics. Objectives: We sought to characterize the mechanisms underlying the onset and maintenance of AD. Methods: We investigated intrapersonal sets of transcriptomes from nonlesional skin and acute and chronic lesions of 10 patients with AD through genomic, molecular, and cellular profiling. Results: Our study associated the onset of acute lesions with a striking increase in a subset of terminal differentiation proteins, specifically the cytokine-modulated S100A7, S100A8, and S100A9. Acute disease was also associated with significant increases in gene expression levels of major TH22 and TH2 cytokines and smaller increases in IL-17 levels. A lesser induction of TH1-associated genes was detected in acute disease, although some were significantly upregulated in chronic disease. Further significant intensification of major TH22 and TH2 cytokines was observed between acute and chronic lesions. Conclusions: Our data identified increased S100A7, S100A8, and S100A9 gene expression with AD initiation and concomitant activation of TH2 and TH22 cytokines. Our findings support a model of progressive activation of TH2 and TH22 immune axes from the acute to chronic phases, expanding the prevailing view of pathogenesis with important therapeutic implications. [Copyright &y& Elsevier]

Hypocretin (orexin; Hcrt)-containing neurons of the hypothalamus are essential for the normal regulation of sleep and wake behaviors and have been implicated in feeding, anxiety, depression, and reward. The absence of these neurons causes narcolepsy in humans and model organisms. However, little is known about the molecular phenotype of these cells; previous attempts at comprehensive profiling had only limited sensitivity or were inaccurate. We generated a Hcrt translating ribosome affinity purification (bacTRAP) line for comprehensive translational profiling of all ribosome-bound transcripts in these neurons in vivo. From this profile, we identified >6000 transcripts detectably expressed above background and 188 transcripts that are highly enriched in these neurons, including all known markers of the cells. Blinded analysis of in situ hybridization databases suggests that 1/460% of these are expressed in a Hcrt marker-like pattern. Fifteen of these were confirmed with double labeling and microscopy, including the transcription factor Lhx9. Ablation of this gene results in a >30% loss specifically of Hcrt neurons, without a general disruption of hypothalamic development. Polysomnography and activity monitoring revealed a profound hypersomnolence in these mice. These data provide an in-depth and accurate profile of Hcrt neuron gene expression and suggest that Lhx9 may be important for specification or survival of a subset of these cells. [ABSTRACT FROM AUTHOR]

Background: Most epidemiological studies of hidradenitis suppurativa (HS) have described homogeneous patient populations., Objective: To characterize demographics, modifiable health behaviors, and comorbidities of HS patients within a diverse cohort., Methods: A retrospective cross-sectional study of 13,130 HS patients within a healthcare system was conducted., Results: A female sex bias of ∼3:1 in all racial/ethnic subgroups was observed. Black/African American (AA) patients had a lower age at HS diagnosis than White patients (37.1 years vs 39.4 years, P<0.001). A higher proportion of Black/AA females than White females with HS had BMI in the obese range (69.9% vs 56.5%; P=0.03). In contrast, fewer Black/African American males with HS had a BMI in the obese range compared to White males (51.4% vs. 61.0%; P<0.001). More Black/AA patients than White patients with HS had congestive heart failure (OR=2.10, CI=1.19-3.78; P<0.05), chronic pulmonary disease (OR=1.34; CI=1.02-1.78; P<0.05), diabetes with chronic complication (OR=1.73; CI=1.16-2.60; P<0.05), renal disease (OR=2.66; CI=1.67-4.34; P<0.05), and Charlson Comorbidity Index score ≥4 (OR=1.67; CI=1.09-2.58; P<0.05). Furthermore, male patients were more likely than female patients to have renal disease (OR=2.62; CI 1.66-4.14; P<0.05)., Limitations: A single-center study., Conclusion: Subgroups of HS patients had significant differences in demographics, risk factors, and comorbid conditions., (Copyright © 2024. Published by Elsevier Inc.)