Pepsin Digest of Wheat Gliadin Fraction Increases Production of IL-1β via TLR4/MyD88/TRIF/MAPK/NF-κB Signaling Pathway and an NLRP3 Inflammasome Activation

Abstract

Celiac disease (CD) is a gluten-responsive, chronic inflammatory enteropathy. IL-1 cytokine family members IL-1β and IL-18 have been associated with the inflammatory conditions in CD patients. However, the mechanisms of IL-1 molecule activation in CD have not yet been elucidated. We show in this study that peripheral blood mononuclear cells (PBMC) and monocytes from celiac patients responded to pepsin digest of wheat gliadin fraction (PDWGF) by a robust secretion of IL-1β and IL-1α and a slightly elevated production of IL-18. The analysis of the upstream mechanisms underlying PDWGF-induced IL-1β production in celiac PBMC show that PDWGF-induced de novo pro-IL-1β synthesis, followed by a caspase-1 dependent processing and the secretion of mature IL-1β. This was promoted by K+ efflux and oxidative stress, and was independent of P2X7 receptor signaling. The PDWGF-induced IL-1β release was dependent on Nod-like receptor family containing pyrin domain 3 (NLRP3) and apoptosis-associated speck like protein (ASC) as shown by stimulation of bone marrow derived dendritic cells (BMDC) from NLRP3−/− and ASC−/− knockout mice. Moreover, treatment of human PBMC as well as MyD88−/− and Toll-interleukin-1 receptor domain-containing adaptor-inducing interferon-β (TRIF)−/− BMDC illustrated that prior to the activation of caspase-1, the PDWGF-triggered signal constitutes the activation of the MyD88/TRIF/MAPK/NF-κB pathway. Moreover, our results indicate that the combined action of TLR2 and TLR4 may be required for optimal induction of IL-1β in response to PDWGF. Thus, innate immune pathways, such as TLR2/4/MyD88/TRIF/MAPK/NF-κB and an NLRP3 inflammasome activation are involved in wheat proteins signaling and may play an important role in the pathogenesis of CD.

Increased Expression of TLR4 and TLR7 but Not Prolactin mRNA by Peripheral Blood Monocytes in Active Celiac Disease

“…Regrettably, the study did not measure TLR expression levels in cells per se. Gliadin fragments have been reported to activate the innate immune system via TLR2 and TLR4 [18]; this activation could be responsible for upregulated TLR expression in wheat-consuming CD subjects. Alternatively, the increased expression of TLR2 and TLR4 in monocytes from rCD patients who have gluten in their diet may be a consequence of bacterial imbalance in the gut in CD patients [2].…”

Microbiome and Gluten

“…Additional innate immunity cytokines are overproduced in CD mucosa and supposed to amplify the inflammation and tissue-damaging response. These include IL-1 cytokine family members (IL-1β and IL-18), TNF-α and IL-6, some of which seem to be involved particularly in refractory CD cases unresponsive to a gluten-free diet (GFD) [17,18] . The increased secretion of these proinflammatory cytokines may involve the activation of innate immune signaling pathways by gluten peptides (e.g.…”

“…peptide P31-43) that involve the myeloid differentiation factor 88 (MyD88), a key adapter molecule of the TLR/IL-1R pathways, but without depending neither on TLR2 nor TLR4 [19] . Other studies have also suggested that signaling pathways downstream TLRs, including MyD88/TRIF/ MAPK/NF-κB, may be involved in the responses to some innate gluten peptides [17] . Interestingly, these pathways also respond to bacterial motifs that are recognized by TLRs expressed in epithelial and innate immune cells [8] .…”

Prolactin May Be Increased in Newly Diagnosed Celiac Children and Adolescents and Decreases after 6 Months of Gluten-Free Diet

“…Inflammatory cytokines, overall IL-1β, TNF-α, IL-6 and IL-13, released in sites of immune processes, also activate the hypothalamus-inducing release of pituitary PRL [15]. In CD patients, the production of these inflammatory cytokines is increased by the ingestion of gliadin with food [32,33,34,35,36,37,38]. PRL increases the production of interferon-γ by lymphocytes and induces the expression of IL-2 receptors on the surface of lymphocytes [14,39].…”