A Promoter Variant Within the Aryl Hydrocarbon Receptor Gene Is Associated with an Epithelial Barrier Defect in Smokers with Crohn's Disease

Predictive Potential of Biomarkers of Intestinal Barrier Function for Therapeutic Management with Teduglutide in Patients with Short Bowel Syndrome

INTRODUCTION

The human intestinal tract reacts to extensive resection with spontaneous intestinal adaptation. We analyzed whether gene expression analyses or intestinal permeability (IP) testing could provide biomarkers to describe regulation mechanisms in the intestinal barrier in short bowel syndrome (SBS) patients during adaptive response or treatment with the glucagon-like peptide-2 analog teduglutide.

METHODS

Relevant regions of the GLP-2 receptor gene were sequenced. Gene expression analyses and immunohistochemistry were performed from mucosal biopsies. IP was assessed using a carbohydrate oral ingestion test.

RESULTS

The study includes 59 SBS patients and 19 controls. Increases in gene expression with teduglutide were received for sucrase-isomaltase, sodium/glucose cotransporter 1, and calcium/calmodulin serine protein kinase. Mannitol recovery was decreased in SBS but elevated with teduglutide (Δ 40%), showed a positive correlation with remnant small bowel and an inverse correlation with parenteral support.

CONCLUSIONS

Biomarkers predicting clinical and functional features in human SBS are very limited. Altered specific gene expression was shown for genes involved in nutrient transport but not for genes controlling tight junctions. However, mannitol recovery proved useful in describing the absorptive capacity of the gut during adaptation and treatment with teduglutide.

Identification of Gene Expression Profiles Associated with an Increased Risk of Post-Operative Recurrence in Crohn's Disease

BACKGROUND AND AIMS

Ileocolonic resection is frequently needed in the course of Crohn's disease [CD] treatment and post-operative recurrence is extremely common. Our main objective was to analyse gene expression in the mucosa of CD patients at the time of surgery and at post-operative endoscopy, in order to identify predictors and mechanisms of early endoscopic recurrence.

METHODS

We conducted transcriptome analyses on ileal mucosa samples collected from inflamed sections of the surgical specimens [n = 200], from ileal resection margins [n = 149] and in the neo-terminal ileum 6 months after surgery [n = 122]; these were compared with non-inflammatory bowel disease controls [n = 25]. The primary endpoint was post-operative endoscopic recurrence at 6 months. We applied regression models to identify gene signatures predicting endoscopic recurrence.

RESULTS

Chronic inflammation was associated with strong expression of inflammatory genes [IL-6, IL-8, IL-1B] and decreased expression of genes involved in metabolic processes, but with a high inter-individual heterogeneity. Gene signatures associated with early endoscopic recurrence were mainly characterized by upregulation of TNFα, IFNγ, IL23A and IL17A. Pathway analyses showed that upregulation of mitochondrial dysfunction within the inflamed sections and JAK/STAT at the ileal margin were predictive of post-operative recurrence. A combined model integrating these top pathway signatures improved the prediction of endoscopic recurrence [area under the curve of 0.79]. STAT3 phosphorylation at the surgical ileal margin was associated with severe recurrence at 6 months.

CONCLUSION

We identified several biological pathways in surgical ileal mucosa specimens associated with an increased risk of disease recurrence. Integration of the JAK/STAT and mitochondrial dysfunction pathways in the clinical model improved the prediction of post-operative recurrence.

AHR gene expression and the polymorphism rs2066853 are associated with clinicopathological parameters in colorectal carcinoma

The relationship between red and processed meat and its risk towards colorectal carcinoma (CRC) is not fully explored in literature. Polycyclic aromatic hydrocarbons (PAHs) are pro-carcinogenic molecules that are ingested with meat cooked at high temperatures. The metabolic conversion of PAHs to carcinogenic diol epoxides is in part mediated by the aryl hydrocarbon receptor (AhR)-dependent induction of CYP1A1. This study aims to examine and expression profiles and polymorphisms of the AHR (aryl hydrocarbon receptor) gene which is involved in the metabolic conversion of PAHs in patients with CRC. Genetic analysis was done in matched cancer and non-neoplastic tissues from 79 patients diagnosed with CRCs. Low AHR mRNA expression was associated mucinous colorectal adenocarcinoma. Exon 10 of AHR showed that 27% of patients had the rs2066853 single nucleotide polymorphism resulting in an arginine to lysine change at codon 554. This variant was significantly associated with a lower likelihood of perineural invasion, presence of synchronous cancer, and multiple colorectal polyps. Furthermore, rs2066853 individuals were significantly more likely to be of more advanced age and have a more favourable tumour grade and pathological stage. These results imply the pathogenic roles of AHR in PAH-associated colorectal carcinogenesis.

Evolution of Hominin Detoxification: Neanderthal and Modern Human Ah Receptor Respond Similarly to TCDD

In studies of hominin adaptations to fire use, the role of the aryl hydrocarbon receptor (AHR) in the evolution of detoxification has been highlighted, including statements that the modern human AHR confers a significantly better capacity to deal with toxic smoke components than the Neanderthal AHR. To evaluate this, we compared the AHR-controlled induction of cytochrome P4501A1 (CYP1A1) mRNA in HeLa human cervix epithelial adenocarcinoma cells transfected with an Altai-Neanderthal or a modern human reference AHR expression construct, and exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We compared the complete AHR mRNA sequences including the untranslated regions (UTRs), maintaining the original codon usage. We observe no significant difference in CYP1A1 induction by TCDD between Neanderthal and modern human AHR, whereas a 150–1,000 times difference was previously reported in a study of the AHR coding region optimized for mammalian codon usage and expressed in rat cells. Our study exemplifies that expression in a homologous cellular background is of major importance to determine (ancient) protein activity. The Neanderthal and modern human dose–response curves almost coincide, except for a slightly higher extrapolated maximum for the Neanderthal AHR, possibly caused by a 5′-UTR G-variant known from modern humans (rs7796976). Our results are strongly at odds with a major role of the modern human AHR in the evolution of hominin detoxification of smoke components and consistent with our previous study based on 18 relevant genes in addition to AHR, which concluded that efficient detoxification alleles are more dominant in ancient hominins, chimpanzees, and gorillas than in modern humans.

Links Between Inflammatory Bowel Disease and Chronic Obstructive Pulmonary Disease

Inflammatory bowel disease (IBD) and chronic obstructive pulmonary disease (COPD) are chronic inflammatory diseases of the gastrointestinal and respiratory tracts, respectively. These mucosal tissues bear commonalities in embryology, structure and physiology. Inherent similarities in immune responses at the two sites, as well as overlapping environmental risk factors, help to explain the increase in prevalence of IBD amongst COPD patients. Over the past decade, a tremendous amount of research has been conducted to define the microbiological makeup of the intestine, known as the intestinal microbiota, and determine its contribution to health and disease. Intestinal microbial dysbiosis is now known to be associated with IBD where it impacts upon intestinal epithelial barrier integrity and leads to augmented immune responses and the perpetuation of chronic inflammation. While much less is known about the lung microbiota, like the intestine, it has its own distinct, diverse microflora, with dysbiosis being reported in respiratory disease settings such as COPD. Recent research has begun to delineate the interaction or crosstalk between the lung and the intestine and how this may influence, or be influenced by, the microbiota. It is now known that microbial products and metabolites can be transferred from the intestine to the lung via the bloodstream, providing a mechanism for communication. While recent studies indicate that intestinal microbiota can influence respiratory health, intestinal dysbiosis in COPD has not yet been described although it is anticipated since factors that lead to dysbiosis are similarly associated with COPD. This review will focus on the gut-lung axis in the context of IBD and COPD, highlighting the role of environmental and genetic factors and the impact of microbial dysbiosis on chronic inflammation in the intestinal tract and lung.

Epigenetic Regulations of AhR in the Aspect of Immunomodulation

Environmental factors contribute to autoimmune disease manifestation, and as regarded today, AhR has become an important factor in studies of immunomodulation. Besides immunological aspects, AhR also plays a role in pharmacological, toxicological and many other physiological processes such as adaptive metabolism. In recent years, epigenetic mechanisms have provided new insight into gene regulation and reveal a new contribution to autoimmune disease pathogenesis. DNA methylation, histone modifications, chromatin alterations, microRNA and consequently non-genetic changes in phenotypes connect with environmental factors. Increasing data reveals AhR cross-roads with the most significant in immunology pathways. Although study on epigenetic modulations in autoimmune diseases is still not well understood, therefore future research will help us understand their pathophysiology and help to find new therapeutic strategies. Present literature review sheds the light on the common ground between remodeling chromatin compounds and autoimmune antibodies used in diagnostics. In the proposed review we summarize recent findings that describe epigenetic factors which regulate AhR activity and impact diverse immunological responses and pathological changes.

Association of Crohn's Disease with Aryl Hydrocarbon Receptor Gene Polymorphisms in Patients from Southeast China

Aims The aryl hydrocarbon receptor (AhR) plays a pivotal role in regulating the innate and the acquired immune systems. The present study aimed to investigate the association of Crohn's disease (CD) with AhR polymorphisms in a cohort of patients from Southeast China. Methods An improved multiple ligase detection reaction technique was applied to examine the polymorphisms of rs2158041, rs2066853, and rs10249788 in 310 patients with CD and 573 controls. Results Compared to the controls, the variant allele (T) and genotype (CT+TT) of rs2158041 were less frequent in patients with CD (both p < 0.05). Similar conclusions were drawn from patients with ileal CD and with stricture CD as compared to the controls (all p < 0.0083). However, no significant differences were observed in allele and genotype frequencies of rs2066853 and rs10249788 between patients with CD and the controls (all p > 0.05). Although rs2158041 and rs10249788 were in complete linkage disequilibrium with rs2066853, respectively, only the frequency of haplotype (TG) formed by rs2158041 and rs2066853 was significantly lower in patients with CD than that in the controls (p < 0.05). Conclusions AhR (rs2158041) might be a susceptible locus for CD, especially for the two subtypes: ileal CD and stricture CD.

Gut Microbiota-Produced Tryptamine Activates an Epithelial G-Protein-Coupled Receptor to Increase Colonic Secretion

Tryptamine, a tryptophan-derived monoamine similar to 5-hydroxytryptamine (5-HT), is produced by gut bacteria and is abundant in human and rodent feces. However, the physiologic effect of tryptamine in the gastrointestinal (GI) tract remains unknown. Here, we show that the biological effects of tryptamine are mediated through the 5-HT₄ receptor (5-HT₄R), a G-protein-coupled receptor (GPCR) uniquely expressed in the colonic epithelium. Tryptamine increases both ionic flux across the colonic epithelium and fluid secretion in colonoids from germ-free (GF) and humanized (ex-GF colonized with human stool) mice, consistent with increased intestinal secretion. The secretory effect of tryptamine is dependent on 5-HT₄R activation and is blocked by 5-HT₄R antagonist and absent in 5-HT₄R^-/- mice. GF mice colonized by Bacteroides thetaiotaomicron engineered to produce tryptamine exhibit accelerated GI transit. Our study demonstrates an aspect of host physiology under control of a bacterial metabolite that can be exploited as a therapeutic modality. VIDEO ABSTRACT.

Aryl hydrocarbon receptor polymorphisms are associated with dry skin phenotypes in Chinese patients with atopic dermatitis

BACKGROUND

Epidermal barrier dysfunction is the initial event in the development of atopic dermatitis (AD). Recent studies have identified a crucial role for the aryl hydrocarbon receptor (AHR) in controlling the gene expression of filaggrin and other skin barrier proteins, suggesting an underlying association between AHR and AD pathogenesis.

AIM

To investigate the role of AHR gene polymorphisms in the susceptibility to AD and in AD-associated phenotypes.

METHODS

We enrolled 487 patients with AD, 210 patients with psoriasis and 226 healthy controls (HCs) from the Han Chinese population, and genotyped two AHR single-nucleotide polymorphisms (rs10249788 and rs2066853) by PCR and subsequent DNA sequencing.

RESULTS

The AHR rs10249788 and rs2066853 polymorphisms were found in both sets of patients (AD and psoriasis) and in HCs, but no significant differences were detected in genotype or allele frequencies between the three groups. However, patients with AD with the rs10249788 (CT/TT) or rs2066853 (AG + AA) genotype were more likely to have severe dry skin scores. In the stratification analysis, the AHR rs2066853 (AG + AA) and rs10249788 (CT + TT) genotypes could predict a higher risk of severe dry skin phenotypes in the male, early-onset and allergic rhinitis subgroups. Furthermore, the combined rs10249788 (CT + TT) and rs2066853 (AG + AA) genotypes led to a higher risk for severe dry skin in patients with AD.

CONCLUSION

AHR polymorphisms are not associated with the risk of AD; however, they may predict a dry skin phenotype in patients with AD.

The aryl hydrocarbon receptor in the crossroad of signalling networks with therapeutic value

The aryl hydrocarbon receptor (AhR) is well-known for its major contributions to the cellular responses against environmental toxins and carcinogens. Notably, AhR has also emerged as a key transcription factor controlling many physiological processes including cell proliferation and apoptosis, differentiation, adhesion and migration, pluripotency and stemness. These novel functions have broadened our understanding of the signalling pathways and molecular intermediates interacting with AhR under both homeostatic and pathological conditions. Recent discoveries link AhR with the function of essential organs such as liver, skin and gonads, and with complex organismal structures including the immune and cardiovascular systems. The identification of potential endogenous ligands able to regulate AhR activity, opens the possibility of designing ad hoc molecules with pharmacological and/or therapeutic value to treat human diseases in which AhR may have a causal role. Integration of experimental data from in vitro and in vivo studies with "omic" analyses of human patients affected with cancer, immune diseases, inflammation or neurological disorders will likely contribute to validate the clinical relevance of AhR and the possible benefits of modulating its activity by pharmacologically-driven strategies. In this review, we will highlight signalling pathways involved in human diseases that could be targetable by AhR modulators and discuss the feasibility of using such molecules in therapy. The pros and cons of AhR-aimed approaches will be also mentioned.