Gliadin-Mediated Proliferation and Innate Immune Activation in Celiac Disease Are Due to Alterations in Vesicular Trafficking

Abstract

Background and ObjectivesDamage to intestinal mucosa in celiac disease (CD) is mediated both by inflammation due to adaptive and innate immune responses, with IL-15 as a major mediator of the innate immune response, and by proliferation of crypt enterocytes as an early alteration of CD mucosa causing crypts hyperplasia. We have previously shown that gliadin peptide P31-43 induces proliferation of cell lines and celiac enterocytes by delaying degradation of the active epidermal growth factor receptor (EGFR) due to delayed maturation of endocytic vesicles. IL-15 is increased in the intestine of patients affected by CD and has pleiotropic activity that ultimately results in immunoregulatory cross-talk between cells belonging to the innate and adaptive branches of the immune response. Aims of this study were to investigate the role of P31-43 in the induction of cellular proliferation and innate immune activation.Methods/Principal FindingsCell proliferation was evaluated by bromodeoxyuridine (BrdU) incorporation both in CaCo-2 cells and in biopsies from active CD cases and controls. We used real-time PCR to evaluate IL-15 mRNA levels and FACS as well as ELISA and Western Blot (WB) analysis to measure protein levels and distribution in CaCo-2 cells.Gliadin and P31-43 induce a proliferation of both CaCo-2 cells and CD crypt enterocytes that is dependent on both EGFR and IL-15 activity. In CaCo-2 cells, P31-43 increased IL-15 levels on the cell surface by altering intracellular trafficking. The increased IL-15 protein was bound to IL15 receptor (IL-15R) alpha, did not require new protein synthesis and functioned as a growth factor.ConclusionIn this study, we have shown that P31-43 induces both increase of the trans-presented IL-15/IL5R alpha complex on cell surfaces by altering the trafficking of the vesicular compartments as well as proliferation of crypt enterocytes with consequent remodelling of CD mucosa due to a cooperation of IL-15 and EGFR.

Biochemical modifications of gliadins induced by microbial transglutaminase on wheat flour

“…This can result in target cell killing thus contributing to the disappearance of the villi in CD. Subsequent studies showed that p31-43 altered the trafficking of vesicular compartments in the intestinal Caco-2 cell line leading to overexpression of IL-15/IL5R alpha complex and delaying the degradation of the active epidermal growth factor receptor (EGFR) that induces cell proliferation of cell lines and, possibly, crypts hyperplasia in CD [35]. More recently, gliadin peptide p31-43 was reported to induce tTGase activation in Caco-2 cells, an event mediated by the release of Ca 2+ ions from intracellular stores [24].…”

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

“…This leads to prolonged epidermal growth factor receptor inactivation, overexpression of transpresented interleukin (IL) 15/IL15 receptor-α complex as well as increased reactive oxygen species generation, and TG2 activation (16,(30)(31)(32). Such a complex cascade of intracellular events following gliadin exposure likely derails intracellular control systems thus disrupting Ca 2+ homeostasis by still unknown mechanisms.…”

Transglutaminase 2 and Transglutaminase 2 Autoantibodies in Celiac Disease: a Review

“…2). This upregulation has been attributed to a specific subset of toxic gliadin peptides which includes for instance the peptide p31-43 [139]. IL-15 induces a simultaneous upregulation of MICA expression in epithelial cells [140] and the activating NKG2D receptor in intraepithelial lymphocytes [141].…”