Growth factor-like activity of gliadin, an alimentary protein: implications for coeliac disease

Abstract

Background: Gliadins, a family of wheat proteins, are central to the pathogenesis of celiac disease (CD). In addition to 'immunogenic' effects, gliadin directly affects cultured cells and intestine preparations, and produces damage in vivo, via a separate 'toxic' peptide, such as A-gliadin p31-43 (P31-43). Aims: Understanding the molecular mechanisms underlying direct non T-cell mediated effects of gliadin peptides, and assessing their potential role in promoting CD.Method: Gliadin effects were tested on a number of cell lines and on cultured mucosa samples by evaluating cytoskeleton rearrangements, endocytosis, proliferation and apoptosis. Standard biochemical methods were used to assess prolonged epidermal growth factor receptor (EGFR) activation. Results: Crude gliadin peptic-tryptic peptides (PTG], or P31-43 alone, fully reproduce the effects of epidermal growth factor (EGF] on actin cytosketon, cell cycle and cell proliferation of various cell lines. Inhibitor studies demonstrate the role of EGFR in the early response to gliadin exposure, pointing to activation of the EGFR pathway. Peptide P31-43 is not similar to any EGFR ligand, but can delay inactivation of the EGFR interfering with its endocytosis. Gliadin-induced delay of EGFR endocytosis in cultured intestinal biopsies, together with S-phase entry of epithelial intestinal cells, confirm a role for EGFR activation in CD. Conclusion: The ability of gliadin peptides to delay EGFR inactivation through interference with the endocytic pathway suggests a model where gliadin fragments amplify the effects of trace amounts of EGF, and possibly of other growth factors, by prolonging receptor activation. The results, using cultures of coeliac intestinal biopsies, highlight the role of the EGF pathway in establishing and maintaining the typical atrophic and proliferative alterations of the small intestine in CD.

Identification of human zonulin, a physiological modulator of tight junctions, as prehaptoglobin-2

“…It has recently been reported that gliadin, a glycoprotein present in wheat and several other cereals and identified as the environmental trigger responsible for the autoimmune damage of the small intestine typical of CD (15), fully reproduces the effects of EGF on the actin cytoskeleton (16), effects that are very similar to those previously reported for zonulin (7,10,16). Furthermore, structural analysis revealed that the pre-HP2 ␤-chain includes an EGF motif that contains 6 spatially conserved cysteine residues that form 3 intramolecular disulfide bonds (Fig.…”

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.…”

Gliadin Induces an Increase in Intestinal Permeability and Zonulin Release by Binding to the Chemokine Receptor CXCR3

“…Intestinal epithelial cell lines, IEC6 (rat, passage 36-46) and CaCo-2 (human, passage [30][31][32][33][34][35][36][37][38][39][40], were grown on Lab-Tek I chamber slides and stained for CXCR3 as described above. To localize CXCR3 expression in intestinal tissues, 4-µm sections were prepared, and laser capture microdissection (mouse tissue) or immunohistochemistry (human tissue) were performed as previously described.…”