Celiac Disease Monocytes Induce a Barrier Defect in Intestinal Epithelial Cells

Role of tight junction proteins in shaping the immune milieu of malignancies

INTRODUCTION

Tight junctions (TJs) and their constituent proteins play pivotal roles in cellular physiology and anatomy by establishing functional boundaries within and between neighboring cells. While the involvement of TJ proteins, such as claudins, in cancer is extensively studied, studies highlighting their interaction with immune system are still meager. Studies indicate that alterations in cytokines and immune cell populations can affect TJ proteins, compromising TJ barrier function and exacerbating pro-inflammatory conditions, potentially leading to epithelial cell malignancy. Disrupted TJs in established tumors may foster a pro-tumor immune microenvironment, facilitating tumor progression, invasion, epithelial-to-mesenchymal transition and metastasis. Although previous literature contains many studies describing the involvement of TJs in pathogenesis of malignancies their role in modulating the immune microenvironment of tumors is just beginning to be unleashed.

AREAS COVERED

This article for the first time attempts to discern the importance of interaction between TJs and immune microenvironment in malignancies. To achieve the above aim a thorough search of databases like PubMed and Google Scholar was conducted to identify the recent and relevant articles on the topic.

EXPERT OPINION

Breaking the vicious cycle of dysbiosis/infections/chemical/carcinogen-induced inflammation-TJ remodeling-malignancy-TJ dysregulation-more inflammation can be used as a strategy to complement the effect of immunotherapies in various malignancies.

Intestinal permeability correlates with disease activity and DNA methylation changes in lupus patients

OBJECTIVE

Systemic lupus erythematosus (SLE or lupus) is a chronic autoimmune disease that can involve various organ systems. Several studies have suggested that increased intestinal permeability may play a role in the pathogenesis of lupus. The aim of this study was to elucidate the relationship between intestinal permeability, disease activity, and epigenetic changes in lupus patients.

METHODS

A total of 25 female lupus patients were included in this study. Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) scores were used as indicator of disease activity. Plasma zonulin levels were measured, using an ELISA, as a marker of intestinal permeability. Genome-wide DNA methylation patterns were assessed in neutrophils for 19 of the lupus patients using the Infinium MethylationEPIC array. Linear regression and Pearson's correlation were used to evaluate the correlation between zonulin concentrations and SLEDAI scores. The relationship between DNA methylation levels and zonulin concentrations was assessed using beta regression, linear regression, and Pearson's correlation, adjusting for age and race.

RESULTS

Intestinal permeability positively correlated with disease activity in lupus patients (p-value = 7.60 × 10-3, r = 0.53). DNA methylation levels in 926 CpG sites significantly correlated with intestinal permeability. The highest correlation was identified in LRIG1 (cg14159396, FDR-adjusted p-value = 1.35 × 10-12, adjusted r2 = 0.92), which plays a role in intestinal homeostasis. Gene Ontologies related to cell-cell adhesion were enriched among the genes that were hypomethylated with increased intestinal permeability in lupus.

CONCLUSION

Our data suggest a correlation between increased intestinal permeability and disease activity in lupus patients. Further, increased intestinal permeability might be associated with epigenetic changes that could play a role in the pathogenesis of lupus.

Isolation and cryopreservation of peripheral blood mononuclear cells

The study of peripheral blood mononuclear cells (PBMCs) in immune-mediated diseases, such as celiac disease (CD), is important to uncover pathogenesis, find new biomarkers and discover and evaluate new treatments. Many studies have been published about the use and value of PBMCs in CD such as those including enzyme-linked immunospot (ELISPOT) assays, flow cytometry, peptide-MHC tetramers, genetic and proteomic analyses, and in vitro and proliferation assays. We present here and easy and efficient method for isolation of PBMCs using density gradient centrifugation. We also describe a simple way to freeze PBMCs in order to preserve their number and viability and a thawing procedure leading to high rates of viability of the cryopreserved cells to be used in subsequent applications.

Role of Vitamin D in Celiac Disease and Inflammatory Bowel Diseases

Vitamin D (VD) is a pro-hormone that has long been known as a key regulator of calcium homeostasis and bone health in both children and adults. In recent years, studies have shown that VD may exert many extra-skeletal functions, mainly through a relevant modulation of the innate and adaptive immune system. This has suggested that VD could play a fundamental role in conditioning development, clinical course, and treatment of several autoimmune disorders, including celiac disease (CD) and inflammatory bowel diseases (IBDs). The main aim of this review is to evaluate the relationships between VD, CD, and IBDs. Literature analysis showed a potential impact of VD on CD and IBDs can be reasonably assumed based on the well-documented in vitro and in vivo VD activities on the gastrointestinal tract and the immune system. The evidence that VD can preserve intestinal mucosa from chemical and immunological damage and that VD modulation of the immune system functions can contrast the mechanisms that lead to the intestinal modifications characteristic of gastrointestinal autoimmune diseases has suggested that VD could play a role in controlling both the development and the course of CD and IBDs. Administration of VD in already diagnosed CD and IBD cases has not always significantly modified disease course. However, despite these relevant problems, most of the experts recommend monitoring of VD levels in patients with CD and IBDs and administration of supplements in patients with hypovitaminosis.

The modulation of macrophage subsets in celiac disease pathogenesis

BACKGROUND

So far, limited studies have focused on the role of Macrophages (MQs) in the development or progression of celiac disease (CD). Researchers believe that increasing knowledge about the function of MQs in inflammatory disorders plays a critical role in finding a new treatment for these kinds of diseases.

MAIN BODY

CD is a permanent autoimmune intestinal disorder triggered by gluten exposure in predisposed individuals. This disorder happens due to the loss of intestinal epithelial barrier integrity characterized by dysregulated innate and adaptive immune responses. MQs are known as key players of the innate immune system that link innate and adaptive immunity. MQs of human intestinal lamina propria participate in maintaining tissue homeostasis, and also intestinal inflammation development. Previous studies suggested that gliadin triggers a proinflammatory phenotype (M1 MQ) in human primary MQs. Moreover, M2-related immunosuppressive mediators are also present in CD. In fact, CD patients present an impaired transition from pro-inflammatory to anti-inflammatory responses due to inappropriate responses to gliadin peptides.

CONCLUSION

The M1/M2 MQs polarization balancing regulators can be considered novel therapeutic targets for celiac disease.

Oat β-glucan alleviates DSS-induced colitis via regulating gut microbiota metabolism in mice

Ulcerative colitis (UC) is one of the most prevalent inflammatory bowel diseases (IBD) worldwide, while oat β-glucan has been shown to suppress the progress of colitis in UC mice. However, the underlying mechanism of oat β-glucan in ameliorating colitis is unclear and the role of gut microbiota in the protective effect of oat β-glucan against colitis remains unknown. In the present study, we aim to investigate the effect of oat β-glucan on gut microbiota in colitis mice and explore the health effect related mechanism. Dextran sulfate sodium (DSS) was used to induce the colitis model in mice. The results showed that β-glucan treatment attenuated hematochezia, splenomegaly and colon shortening in colitis mice. Histological evaluation of H&E and TUNEL staining showed that β-glucan treatment suppressed DSS-induced colonic inflammatory infiltration and reduced cell apoptosis levels of colon tissues. mRNA expression levels of the pro-inflammatory factors were also significantly reduced in the β-glucan group. Moreover, β-glucan treatment increased the protein and mRNA expression levels of tight junction proteins. Analysis of gut microbiota community showed that β-glucan treatment modulated gut microbial composition and structure at the OTU level in colitis mice. Further analysis of gut microbial metabolism revealed that β-glucan treatment significantly increased acetate, propionate and butyrate concentrations, and affected microbial metabolome in colitis mice. Notably, the increased acetate and propionate concentrations could directly affect pro-inflammatory factor expression levels and tight junction protein levels. In contrast, the changes in metabolic profiles affected pro-inflammatory factor levels and thus affected tight junction protein levels. Overall, our study revealed that oat β-glucan ameliorated DSS-induced colitis in mice simultaneously through regulating gut-derived short-chain fatty acids (SCFAs) and microbial metabolic biomarkers. Our study demonstrated that oat β-glucan could be an effective nutritional intervention strategy towards targeting gut microbiota metabolism for ameliorating colitis.

Inulin ameliorates schizophrenia via modulation of the gut microbiota and anti-inflammation in mice

The microbiome-gut-brain (MGB) axis, which regulates neurological and cognitive functions, plays an essential role in schizophrenia (SCZ) progression. Dietary inulin could be a novel strategy for the treatment of SCZ due to its modulating effects on the gut microbiota. In this study, the effects of inulin on mice with SCZ were studied. As indicated by the behavioural tests, expression of neurotransmitters, inflammatory indicators, and brain morphology, inulin administration ameliorated aberrant behaviours (locomotor hypoactivity, anxiety disorders and depressive behaviours, and impaired learning and spatial recognition memory) and effectively reduced neuroinflammation and neuronal damage. In addition, inulin improved intestinal integrity and permeability, as indicated by the elevated expression of tight junction proteins (p < 0.05). The results of 16S rRNA sequencing and analysis showed that inulin increased the abundance of Lactobacillus and Bifidobacterium, which were negatively correlated with 5-hydroxytryptamine and inflammatory cytokines and positively correlated with brain-derived neurotrophic factor (BDNF). Inulin caused a reduction in Akkermansia that was positively correlated with inflammatory cytokines and negatively correlated with BDNF. These results suggested that dietary inulin modulated the gut microbiota and exerted anti-inflammatory effects in mice though the MGB axis, which further ameliorated SCZ. Therefore, the results of this study provide a potential explanation for inulin intervention in the treatment of SCZ.

The diverse roles of myeloid derived suppressor cells in mucosal immunity

The mucosal immune system plays a vital role in protecting the host from the external environment. Its major challenge is to balance immune responses against harmful and harmless agents and serve as a 'homeostatic gate keeper'. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of undifferentiated cells that are characterized by an immunoregulatory and immunosuppressive phenotype. Herein we postulate that MDSCs may be involved in shaping immune responses related to mucosal immunity, due to their immunomodulatory and tissue remodeling functions. Until recently, MDSCs were investigated mainly in cancerous diseases, where they induce and contribute to an immunosuppressive and inflammatory environment that favors tumor development. However, it is now becoming clear that MDSCs participate in non-cancerous conditions such as chronic infections, autoimmune diseases, pregnancy, aging processes and immune tolerance to commensal microbiota at mucosal sites. Since MDSCs are found in the periphery only in small numbers under normal conditions, their role is highlighted during pathologies characterized by acute or chronic inflammation, when they accumulate and become activated. In this review, we describe several aspects of the current knowledge characterizing MDSCs and their involvement in the regulation of the mucosal epithelial barrier, their crosstalk with commensal microbiota and pathogenic microorganisms, and their complex interactions with a variety of surrounding regulatory and effector immune cells. Finally, we discuss the beneficial and harmful outcomes of the MDSC regulatory functions in diseases affecting mucosal tissues. We wish to illuminate the pivotal role of MDSCs in mucosal immunity, the limitations in our understanding of all the players and the intricate challenges stemming from the complex interactions of MDSCs with their environment.

Systematic Prioritization of Candidate Genes in Disease Loci Identifies TRAFD1 as a Master Regulator of IFNγ Signaling in Celiac Disease

Celiac disease (CeD) is a complex T cell-mediated enteropathy induced by gluten. Although genome-wide association studies have identified numerous genomic regions associated with CeD, it is difficult to accurately pinpoint which genes in these loci are most likely to cause CeD. We used four different in silico approaches-Mendelian randomization inverse variance weighting, COLOC, LD overlap, and DEPICT-to integrate information gathered from a large transcriptomics dataset. This identified 118 prioritized genes across 50 CeD-associated regions. Co-expression and pathway analysis of these genes indicated an association with adaptive and innate cytokine signaling and T cell activation pathways. Fifty-one of these genes are targets of known drug compounds or likely druggable genes, suggesting that our methods can be used to pinpoint potential therapeutic targets. In addition, we detected 172 gene combinations that were affected by our CeD-prioritized genes in trans. Notably, 41 of these trans-mediated genes appear to be under control of one master regulator, TRAF-type zinc finger domain containing 1 (TRAFD1), and were found to be involved in interferon (IFN)γ signaling and MHC I antigen processing/presentation. Finally, we performed in vitro experiments in a human monocytic cell line that validated the role of TRAFD1 as an immune regulator acting in trans. Our strategy confirmed the role of adaptive immunity in CeD and revealed a genetic link between CeD and IFNγ signaling as well as with MHC I antigen processing, both major players of immune activation and CeD pathogenesis.

Pro-Inflammatory Effect of Gliadins and Glutenins Extracted from Different Wheat Cultivars on an In Vitro 3D Intestinal Epithelium Model

There is a need to assess the relationship between improved rheological properties and the immunogenic potential of wheat proteins. The present study aimed to investigate the in vitro effects of total protein extracts from three modern and two landrace Triticum aestivum commercial flour mixes, with significant differences in gluten strength (GS), on cell lines. Cytotoxicity and innate immune responses induced by wheat proteins were investigated using Caco-2 monocultures, two dimensional (2D) Caco-2/U937 co-cultures, and three dimensional (3D) co-cultures simulating the intestinal mucosa with Caco-2 epithelial cells situated above an extra-cellular matrix containing U937 monocytes and L929 fibroblasts. Modern wheat proteins, with increased GS, significantly reduced Caco-2 cell proliferation and vitality in monoculture and 2D co-cultures than landrace proteins. Modern wheat proteins also augmented Caco-2 monolayer disruption and tight junction protein, occludin, redistribution in 3D co-cultures. Release of interleukin-8 into the cell medium and increased U937 monocyte migration in both 2D and 3D co-cultures were similarly apparent. Immuno-activation of migrating U937 cells was evidenced from cluster of differentiation 14 (CD14) staining and CD11b-related differentiation into macrophages. The modern wheat proteins, with gluten polymorphism relatedness and increased GS, were shown to be more cytotoxic and immunogenic than the landrace wheat proteins.

Special Issue on "The Tight Junction and Its Proteins: More than Just a Barrier"

For a long time, the tight junction (TJ) was known to form and regulate the paracellular barrier between epithelia and endothelial cell sheets. Starting shortly after the discovery of the proteins forming the TJ—mainly, the two families of claudins and TAMPs—several other functions have been discovered, a striking one being the surprising finding that some claudins form paracellular channels for small ions and/or water. This Special Issue covers numerous dedicated topics including pathogens affecting the TJ barrier, TJ regulation via immune cells, the TJ as a therapeutic target, TJ and cell polarity, the function of and regulation by proteins of the tricellular TJ, the TJ as a regulator of cellular processes, organ- and tissue-specific functions, TJs as sensors and reactors to environmental conditions, and last, but not least, TJ proteins and cancer. It is not surprising that due to this diversity of topics and functions, the still-young field of TJ research is growing fast. This Editorial gives an introduction to all 43 papers of the Special Issue in a structured topical order.

Iron Absorption in Celiac Disease and Nutraceutical Effect of 7-Hydroxymatairesinol. Mini-Review

Anemia is the main extra-gastrointestinal symptom in inflammatory bowel diseases (IBDs). Interleukin-6 (IL-6) and other cytokines are secreted and act in the microenvironment of the small intestine mucous membrane of IBD patients. Iron is essential for multiple cell functions and its homeostasis is regulated by the hepcidin–ferroportin axis. Hepcidin (HEPC) is mainly produced by the liver in response to iron needs but is also an acute phase protein. During inflammation, hepcidin is upregulated by IL-6 and is responsible for iron compartmentalization within cells, in turn causing anemia of inflammation. Tissues other than liver can produce hepcidin in response to inflammatory stimuli, in order to decrease iron efflux at a local level, then acting in an autocrine–paracrine manner. In IBDs and, in particular, in celiac disease (CeD), IL-6 might trigger the expression, upregulation and secretion of hepcidin in the small intestine, reducing iron efflux and exacerbating defective iron absorption. 7-Hydroxymatairesinol (7-HMR) belongs to the family of lignans, polyphenolic compounds produced by plants, and has nutraceutical antioxidant, anti-inflammatory and estrogenic properties. In this mini-review we revise the role of inflammation in IBDs and in particular in CeD, focusing our attention on the close link among inflammation, anemia and iron metabolism. We also briefly describe the anti-inflammatory and estrogenic activity of 7-HMR contained in foods that are often consumed by CeD patients. Finally, considering that HEPC expression is regulated by iron needs, inflammation and estrogens, we explored the hypothesis that 7-HMR consumption could ameliorate anemia in CeD using Caco-2 cells as bowel model. Further studies are needed to verify the regulation pathway through which 7-HMR may interfere with the local production of HEPC in bowel.

Possible Role of Vitamin D in Celiac Disease Onset

Beside skeletal system maintenance and protection, possible extra-calcium roles of vitamin D have been recently described. In particular, studies have investigated possible roles of vitamin D as a key modulator of inflammation and immune mechanisms and of the intestinal mucosa barrier. In this regard, vitamin D has been considered as a factor that affects different conditions such as immune-mediated diseases. The new emerging role of vitamin D and its involvement in immune modulation has led it to be considered as a possible key factor involved in celiac disease (CD) onset. CD is a chronic immune-mediated enteropathy of the small intestine that is triggered by dietary gluten protein exposure in individuals who are genetically predisposed. However, along with gluten, other environmental factors are also involved in CD onset. The renewed interest in a molecule that offers great possibilities for new roles has led to an increase in studies, although there remains a lack of studies aimed at contextualizing the role of vitamin D on CD. This review aims to define the possible role of vitamin D in CD onset as it is presently understood, taking into account potential links among vitamin D, the immune system and CD.