Gut microbiota and atopic dermatitis: a two-sample Mendelian randomization study

Genetic landscape of atopic dermatitis

PURPOSE OF REVIEW

This review summarizes recent advances in identifying genetic risk factors for atopic dermatitis and how these genetic associations are being used to explore the causal relationships between atopic dermatitis and potential risk factors and downstream outcomes.

RECENT FINDINGS

A recent large-scale GWAS meta-analysis has identified 91 genetic loci associated with atopic dermatitis. Rare variant studies have also identified new gain-of-function or loss-of-function variants implicated in atopic dermatitis, particularly for FLG and STAT6/JAK1. Finally, there has been a surge in utilizing genetic association data to investigate the causal relationships between atopic dermatitis and other traits. Mendelian randomization studies have found that various metabolites and gut microbiota are causal for atopic dermatitis and have causally implicate atopic dermatitis in the development of alopecia areata, diabetes, vascular dementia and some cancers.

SUMMARY

The past year has seen a huge increase in the genes implicated for atopic dermatitis and in the use of genetics to explore causal relationships. The latter requires caution in implementation and interpretation, but is a promising area of research. In the coming years, increasing the ethnic diversity of atopic dermatitis genetic studies would be very welcome and the translation of current genetic findings into new drugs will be an exciting area of development.

IL-17A inhibitors alleviate Psoriasis with concomitant restoration of intestinal/skin microbiota homeostasis and altered microbiota function

Background

Disturbed gut microbiota and associated metabolic dysfunction exist in Psoriasis. Despite the growing use of interleukin-17 inhibitor (anti-IL17) therapy, the effect of anti-IL17 on gut/skin microbiota function is not fully understood in patients with Psoriasis.

Objective

Therefore, we explored whether Psoriasis is associated with alterations in selected gut/skin microbiota in a study cohort, and a longitudinal cohort study to reveal the effects of IL-17A inhibitor treatment on gut microbiota in Psoriasis.

Methods

In a case-control study, 14 patients with Psoriasis and 10 age, sex and body mass index-matched Healthy Controls were recruited. Longitudinal mapping of the gut microbiome was performed using 16S rRNA gene sequencing. Mouse models were used to further study and validate the interrelationship between the skin microbiome and the gut microbiome in Psoriasis. PICRUST2 was applied to predict the function of the bacterial community.

Results

In Psoriasis patients, gut microbiota dysbiosis was present with increased heterogeneity: decreased Bacteroidota and increased Firmicutes as well as Actinobacteriota predominating in Psoriasis. Escherichia-Shigella enrichment was associated with reduction in serum levels of total bile acid and markers in Apoptotic pathways. After IL-17A inhibitor treatment in Psoriasis patients, longitudinal studies observed a trend toward a normal distribution of the gut microbiome and modulation of apoptosis-related metabolic pathways. Results from a mouse model showed dysregulation of the skin microbiota in Psoriasis characterized by Staphylococcus colonization.

Conclusion

The psoriatic gut/skin microbiota exhibits loss of community stability and pathogen enrichment. IL-17A inhibitors restore microbiota homeostasis and metabolic pathways, reduce pro-inflammatory cytokine expression, and alleviate symptoms in patients with Psoriasis.

The Role of the Gut Microbiome and Microbial Dysbiosis in Common Skin Diseases

Dermatoses are an increasingly common problem, particularly in developed countries. The causes of this phenomenon include genetic factors and environmental elements. More and more scientific reports suggest that the gut microbiome, more specifically its dysbiosis, also plays an important role in the induction and progression of diseases, including dermatological diseases. The gut microbiome is recognised as the largest endocrine organ, and has a key function in maintaining human homeostasis. In this review, the authors will take a close look at the link between the gut-skin axis and the pathogenesis of dermatoses such as atopic dermatitis, psoriasis, alopecia areata, and acne. The authors will also focus on the role of probiotics in remodelling the microbiome and the alleviation of dermatoses.

Gastrointestinal Comorbidities Associated with Atopic Dermatitis-A Narrative Review

The current understanding of atopic dermatitis (AD) seems to be extending beyond a skin-confined condition frequently associated with allergic comorbidities, as in a number of epidemiological studies, the prevalence rate of a range of illnesses has been determined to be greater in patients with AD, or inversely. In most cases, the reasons for this are vague. A subset of these conditions are gastrointestinal disorders, including food sensitization (FS) and food allergy (FA), eosinophilic esophagitis (EoE) (it is of mixed background, both IgE-dependent and independent), food protein-induced enterocolitis syndrome (FPIES) (it exemplifies an IgE-independent food allergy), Crohn's disease (CD), colitis ulcerosa (CU), celiac disease, irritable bowel syndrome (IBS), and gastroesophageal reflux disease (GERD). In this review, we performed a comprehensive search of the literature using the PubMed database. We addressed the epidemiology of the increased co-occurrence of these diseases with AD and discussed potential causes for this subject. Multiple gastroenterological comorbidities appear to be more common in patients with AD, according to our review. The mechanisms that underlie this phenomenon are largely unknown, highlighting the need for further study in this field.

Causal associations between gut microbiota and regional cortical structure: a Mendelian randomization study

Introduction

Observational studies have reported associations between gut microbiota composition and central nervous system diseases. However, the potential causal relationships and underlying mechanisms remain unclear. Here, we applied Mendelian randomization (MR) to investigate the causal effects of gut microbiota on cortical surface area (SA) and thickness (TH) in the brain.

Methods

We used genome-wide association study summary statistics of gut microbiota abundance in 18,340 individuals from the MiBioGen Consortium to identify genetic instruments for 196 gut microbial taxa. We then analyzed data from 56,761 individuals from the ENIGMA Consortium to examine associations of genetically predicted gut microbiota with alterations in cortical SA and TH globally and across 34 functional brain regions. Inverse-variance weighted analysis was used as the primary MR method, with MR Egger regression, MR-PRESSO, Cochran's Q test, and leave-one-out analysis to assess heterogeneity and pleiotropy.

Results

At the functional region level, genetically predicted higher abundance of class Mollicutes was associated with greater SA of the medial orbitofrontal cortex (β = 8.39 mm2, 95% CI: 3.08-13.70 mm2, p = 0.002), as was higher abundance of phylum Tenericutes (β = 8.39 mm2, 95% CI: 3.08-13.70 mm2, p = 0.002). Additionally, higher abundance of phylum Tenericutes was associated with greater SA of the lateral orbitofrontal cortex (β = 10.51 mm2, 95% CI: 3.24-17.79 mm2, p = 0.0046). No evidence of heterogeneity or pleiotropy was detected.

Conclusion

Specific gut microbiota may causally influence cortical structure in brain regions involved in neuropsychiatric disorders. The findings provide evidence for a gut-brain axis influencing cortical development, particularly in the orbitofrontal cortex during adolescence.