The protective role of Lactobacillus rhamnosus GG postbiotic on the alteration of autophagy and inflammation pathways induced by gliadin in intestinal models

Celiac disease (CD) is an autoimmune enteropathy caused by an abnormal immune response to gliadin peptides in genetically predisposed individuals. For people with CD, the only available therapy thus far is the lifelong necessity for a gluten-free diet (GFD). Innovative therapies include probiotics and postbiotics as dietary supplements, both of which may benefit the host. Therefore, the present study aimed to investigate the possible beneficial effects of the postbiotic Lactobacillus rhamnosus GG (LGG) in preventing the effects induced by indigested gliadin peptides on the intestinal epithelium. In this study, these effects on the mTOR pathway, autophagic function, and inflammation have been evaluated. Furthermore, in this study, we stimulated the Caco-2 cells with the undigested gliadin peptide (P31-43) and with the crude gliadin peptic-tryptic peptides (PTG) and pretreated the samples with LGG postbiotics (ATCC 53103) (1 × 108). In this study, the effects induced by gliadin before and after pretreatment have also been investigated. The phosphorylation levels of mTOR, p70S6K, and p4EBP-1 were increased after treatment with PTG and P31-43, indicating that the intestinal epithelial cells responded to the gliadin peptides by activating the mTOR pathway. Moreover, in this study, an increase in the phosphorylation of NF-κβ was observed. Pretreatment with LGG postbiotic prevented both the activation of the mTOR pathway and the NF-κβ phosphorylation. In addition, P31-43 reduced LC3II staining, and the postbiotic treatment was able to prevent this reduction. Subsequently, to evaluate the inflammation in a more complex intestinal model, the intestinal organoids derived from celiac disease patient biopsies (GCD-CD) and controls (CTR) were cultured. Stimulation with peptide 31-43 in the CD intestinal organoids induced NF-κβ activation, and pretreatment with LGG postbiotic could prevent it. These data showed that the LGG postbiotic can prevent the P31-43-mediated increase in inflammation in both Caco-2 cells and in intestinal organoids derived from CD patients.

p31-43 Gliadin Peptide Forms Oligomers and Induces NLRP3 Inflammasome/Caspase 1- Dependent Mucosal Damage in Small Intestine

Celiac disease (CD) is a chronic enteropathy elicited by a Th1 response to gluten peptides in the small intestine of genetically susceptible individuals. However, it remains unclear what drives the induction of inflammatory responses of this kind against harmless antigens in food. In a recent work, we have shown that the p31-43 peptide (p31-43) from α-gliadin can induce an innate immune response in the intestine and that this may initiate pathological adaptive immunity. The receptors and mechanisms responsible for the induction of innate immunity by p31-43 are unknown and here we present evidence that this may reflect conformational changes in the peptide that allow it to activate the NLRP3 inflammasome. Administration of p31-43, but not scrambled or inverted peptides, to normal mice induced enteropathy in the proximal small intestine, associated with increased production of type I interferon and mature IL-1β. P31-43 showed a sequence-specific spontaneous ability to form structured oligomers and aggregates in vitro and induced activation of the ASC speck complex. In parallel, the enteropathy induced by p31-43 in vivo did not occur in the absence of NLRP3 or caspase 1 and was inhibited by administration of the caspase 1 inhibitor Ac-YVAD-cmk. Collectively, these findings show that p31-43 gliadin has an intrinsic propensity to form oligomers which trigger the NLRP3 inflammasome and that this pathway is required for intestinal inflammation and pathology when p31-43 is administered orally to mice. This innate activation of the inflammasome may have important implications in the initial stages of CD pathogenesis.

Mechanisms of innate immune activation by gluten peptide p31-43 in mice

Celiac disease (CD) is an immune-mediated enteropathy triggered by gluten in genetically susceptible individuals. Innate immunity contributes to the pathogenesis of CD, but the mechanisms remain poorly understood. Although previous in vitro work suggests that gliadin peptide p31-43 acts as an innate immune trigger, the underlying pathways are unclear and have not been explored in vivo. Here we show that intraluminal delivery of p31-43 induces morphological changes in the small intestinal mucosa of normal mice consistent with those seen in CD, including increased cell death and expression of inflammatory mediators. The effects of p31-43 were dependent on MyD88 and type I IFNs, but not Toll-like receptor 4 (TLR4), and were enhanced by coadministration of the TLR3 agonist polyinosinic:polycytidylic acid. Together, these results indicate that gliadin peptide p31-43 activates the innate immune pathways in vivo, such as IFN-dependent inflammation, relevant to CD. Our findings also suggest a common mechanism for the potential interaction between dietary gluten and viral infections in the pathogenesis of CD.