Gliadin-mediated proliferation and innate immune activation in celiac disease are due to alterations in vesicular trafficking

Oral administration of Bifidobacterium longum CECT 7347 modulates jejunal proteome in an in vivo gliadin-induced enteropathy animal model

Celiac disease is an immune-mediated disorder triggered by gluten proteins of wheat (gliadins) and other cereals. Gliadin-mediated effects on weanling animals, sensitized or not with interferon (IFN)-γ, were investigated. Also, the influence of the co-administration of Bifidobacterium longum CECT 7347 was studied together with changes in the proteome of jejunal sections, using 2DE and MALDITOF-TOF peptide fingerprinting. Findings were compared to results for control animal groups. In the principal component analysis (PCA) of proteome pattern, two components were extracted accounting for 79.8% of variability in the expression of the identified proteins. PCA analysis clearly discriminated between the proteome of animals fed gliadins alone and those fed gliadins and B. longum simultaneously. However, the proteome patterns from animals sensitized with IFN-γ and fed gliadins together with B. longum, or alone, could not be discriminated. Gliadin feeding caused inflammatory effects as well as changes in proteins involved in intracellular ionic homeostasis, lipid turnover, cell motility and redox regulation in intestinal sections. After feeding gliadins to animals sensitized with IFN-γ, changes were also detected in proteins involved in recruitment and function of inmunocompetent cells, trophic effect on the intestine and organization of myofibers reflecting the more marked gliadin-mediated injury in jejunal sections. The administration of the bacterial strain to rats fed gliadins seemed to ameliorate the inflammation caused by gliadin feeding alone, although, in sensitized animals the co-administration of B. longum had less marked effects, which was probably due to the more extensive intestinal mucosal damage. The proteome patterns in animals administered B. longum alone did not reveal any changes reflecting impairment of jejunal functions.

Are transglutaminase 2 inhibitors able to reduce gliadin-induced toxicity related to celiac disease? A proof-of-concept study

PURPOSE

Celiac disease is an autoimmune-mediated enteropathy characterized by adaptive and innate immune responses to dietary gluten in wheat, rye and barley in genetically susceptible individuals. Gluten-derived gliadin peptides are deamidated by transglutaminase 2 (TG2), leading to an immune response in the small-intestinal mucosa. TG2 inhibitors have therefore been suggested as putative drugs for celiac disease. In this proof-of-concept study we investigated whether two TG2 inhibitors, cell-impermeable R281 and cell-permeable R283, can prevent the toxic effects of gliadin in vitro and ex vivo.

METHODS

Intestinal epithelial Caco-2 cells were treated with peptic-tryptic-digested gliadin (PT-gliadin) with or without TG2 inhibitors and thereafter direct toxic effects (transepithelial resistance, cytoskeletal rearrangement, junction protein expression and phoshorylation of extracellular-signal-regulated kinase 1/2) were determined. In an organ culture of celiac-patient-derived small-intestinal biopsies we measured secretion of TG2-autoantibodies into the culture medium and the densities of CD25- and interleukin (IL) 15-positive cells, forkhead box P3 (FOXP3)-positive regulatory T cells (Tregs) and Ki-67-positive proliferating crypt cells.

RESULTS

Both TG2 inhibitors evinced protective effects against gliadin-induced detrimental effects in Caco-2 cells but the cell-impermeable R281 seemed slightly more potent. In addition, TG2 inhibitor R281 modified the gluten-induced increase in CD25- and IL15-positive cells, Tregs and crypt cell proliferation, but had no effect on antibody secretion in celiac-patient-derived biopsies.

CONCLUSIONS

Our results suggest that TG2 inhibitors are able to reduce certain gliadin-induced effects related to responses in vitro and ex vivo.

Early tissue transglutaminase-mediated response underlies K562(S)-cell gliadin-dependent agglutination

INTRODUCTION

[corrected] K562(S) agglutination has been used as a rapid and economic tool for the in vitro screening of the toxicity of cereal fractions and prolamins in celiac disease (CD). A strict correlation has been reported between the toxicity of cereals and cereal fractions for celiac patients and their ability to agglutinate K562(S) cells. Whether this specificity of K562(S)-cell agglutination is caused by the activation of the same pathogenic events triggered by toxic cereal fractions in CD intestine or simply represents a bystander event of gluten toxicity is, however, unknown.

METHODS

K562(S) cells were incubated in vitro with the peptic-tryptic digest of wheat gliadin.

RESULTS

The agglutination of K562(S) cells by wheat gliadin peptides is orchestrated by a cascade of very early events occurring at the K562(S)-cell surface similar to those occurring at the intestinal epithelial surface. They involve a rapid increase in intracellular calcium levels that activate tissue transglutaminase (TG2), leading to a rapid actin reorganization that is pivotal in driving cell agglutination. These specific effects of toxic cereals are phenocopied by the gliadin-derived peptide p31-43, which orchestrates the activation of innate response to gliadin in CD.

DISCUSSION

Our study provides the rationale for the extensive use of K562(S)-cell agglutination as a valuable tool for screening cereal toxicity.

In vitro models for gluten toxicity: relevance for celiac disease pathogenesis and development of novel treatment options

In genetically predisposed individuals, dietary gluten in wheat, rye and barley triggers celiac disease, a systemic autoimmune disorder hallmarked by an extensive small-bowel mucosal immune response. The current conception of celiac disease pathogenesis is that it involves components of both innate and adaptive immunity whose activation typically leads to small-bowel villous atrophy with crypt hyperplasia. Currently, the only effective treatment for celiac disease is a strict lifelong gluten-free diet excluding all wheat-, rye- and barley-containing food products. During the diet, the clinical symptoms improve and the small-bowel mucosal damage recovers, while re-introduction of gluten into the diet leads to re-appearance of the symptoms and deterioration of the small-bowel mucosal architecture. In view of the restricted nature of the diet, alternative treatment is warranted. Improved understanding of the molecular basis of celiac disease has enabled researchers to suggest other therapeutic approaches. Although there is no animal model reproducing all features of celiac disease, the use of in vitro approaches including a variety of cell lines and the celiac patient small-bowel mucosal biopsy organ culture has generated knowledge about pathogenesis of celiac disease. In these culture systems, gluten induces different effects that can be quantified, thus also enabling studies concerning the efficacy of candidate therapeutic compounds for celiac disease. This review describes the intestinal epithelial cell models, celiac patient T-cell lines and clones, as well as the small-bowel mucosal organ culture methods widely used in studies of celiac disease, and summarizes the major findings obtained with these systems.

Immunogenicity of two oat varieties, in relation to their safety for celiac patients

OBJECTIVE

Most of the recent studies suggest that oats are well tolerated by celiac disease (CD) patients. However, it is still possible that different oat cultivars may display different biological properties relevant for CD pathogenesis. We aimed to investigate biological and immunological properties of two oat varieties, Avena genziana and Avena potenza, in relation to their safety for CD patients.

MATERIAL AND METHODS

Phosphorylation of extracellular signal-regulated kinase (ERK) and trans-epithelial electrical resistance (TEER) were evaluated in CaCo-2 cells treated with peptic-tryptic (PT) digests from the two oats and from gliadin (PTG). With the same PT-digests, duodenal biopsies from 22 CD patients were treated in vitro for 24 h and density of CD25+ cells in lamina propria and of intraepithelial CD3+ T cells was measured, as well as crypt cell proliferation and epithelial expression of interleukin 15. Finally, interferon γ (IFN-γ) production was measured as evidence of gliadin-specific T-cell activation by PT-digests.

RESULTS

In contrast to PTG, oats PT-digests were not able to induce significant increase in ERK phosphorylation and decrease in TEER in CaCo-2 cells. In the organ culture system, oats PT-digests, unlike PTG, did not induce significant increase in crypt enterocyte proliferation, increase in interleukin 15 expression or in lamina propria CD25+ cells. Nevertheless Avena potenza increased intraepithelial T-cell density, while Avena genziana-induced IFN-γ production in 3/8 CD intestinal T cell lines.

CONCLUSIONS

Our data show that Avena genziana and Avena potenza do not display in vitro activities related to CD pathogenesis. Some T-cell reactivity could be below the threshold for clinical relevance.