Pepsin Digest of Wheat Gliadin Fraction Increases Production of IL-1 beta via TLR4/MyD88/TRIF/MAPK/NF-kappa B Signaling Pathway and an NLRP3 Inflammasome Activation
Abstract
Celiac disease (CD) is a gluten-responsive, chronic inflammatory enteropathy. IL-1 cytokine family members IL-1 beta 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-1 beta and IL-1 alpha and a slightly elevated production of IL-18.
The analysis of the upstream mechanisms underlying PDWGF-induced IL-1 beta production in celiac PBMC show that PDWGF-induced de novo pro-IL-1 beta synthesis, followed by a caspase-1 dependent processing and the secretion of mature IL-1 beta. This was promoted by K+ efflux and oxidative stress, and was independent of P2X7 receptor signaling.
The PDWGF-induced IL-1 beta 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-beta (TRIF)(-/-) BMDC illustrated that prior to the activation of caspase-1, the PDWGF-triggered signal constitutes the activation of the MyD88/TRIF/MAPK/NF-kappa B pathway.
Moreover, our results indicate that the combined action of TLR2 and TLR4 may be required for optimal induction of IL-1 beta in response to PDWGF. Thus, innate immune pathways, such as TLR2/4/MyD88/TRIF/MAPK/NF-kB and an NLRP3 inflammasome activation are involved in wheat proteins signaling and may play an important role in the pathogenesis of CD.