The In Vitro Effects of Enzymatic Digested Gliadin on the Functionality of the Autophagy Process

Gliadin, the alcohol-soluble protein fraction of wheat, contains the factor toxic for celiac disease (CD), and its toxicity is not reduced by digestion with gastro-pancreatic enzymes. Importantly, it is proved that an innate immunity to gliadin plays a key role in the development of CD. The immune response induces epithelial stress and reprograms intraepithelial lymphocytes into natural killer (NK)-like cells, leading to enterocyte apoptosis and an increase in epithelium permeability. In this contribution, we have reported that in Caco-2 cells the administration of enzymatically digested gliadin (PT-gliadin) reduced significantly the expression of the autophagy-related marker LC3-II. Furthermore, electron and fluorescent microscope analysis suggested a compromised functionality of the autophagosome apparatus. The rescue of the dysregulated autophagy process, along with a reduction of PT-gliadin toxicity, was obtained with a starvation induction protocol and by 3-methyladenine administration, while rapamycin, a well-known autophagy inducer, did not produce a significant improvement in the clearance of extra- and intra-cellular fluorescent PT-gliadin amount. Altogether, our results highlighted the possible contribution of the autophagy process in the degradation and in the reduction of extra-cellular release of gliadin peptides and suggest novel molecular targets to counteract gliadin-induced toxicity in CD.

A structural and immunological basis for the role of human leukocyte antigen DQ8 in celiac disease

The risk of celiac disease is strongly associated with human leukocyte antigen (HLA) DQ2 and to a lesser extent with HLA DQ8. Although the pathogenesis of HLA-DQ2-mediated celiac disease is established, the underlying basis for HLA-DQ8-mediated celiac disease remains unclear. We showed that T helper 1 (Th1) responses in HLA-DQ8-associated celiac pathology were indeed HLA DQ8 restricted and that multiple, mostly deamidated peptides derived from protease-sensitive sites of gliadin were recognized. This pattern of reactivity contrasted with the more absolute deamidation dependence and relative protease resistance of the dominant gliadin peptide in DQ2-mediated disease. We provided a structural basis for the selection of HLA-DQ8-restricted, deamidated gliadin peptides. The data established that the molecular mechanisms underlying HLA-DQ8-mediated celiac disease differed markedly from the HLA-DQ2-mediated form of the disease. Accordingly, nondietary therapeutic interventions in celiac disease might need to be tailored to the genotype of the individual.

Gliadin characterization by SANS and gliadin nanoparticle growth modelization

Nanosized colloidal carriers can ensure a controlled and targeted therapeutic substances delivery. The original contribution of this work was to use biopolymers of vegetable source, which are an interesting alternative to synthetic polymers. The aim of this study was to prepare submicronic particles from wheat proteins: Gliadins extracted from gluten. The carrier preparation was based on the desolvatation of the macromolecules by a couple solvent/non-solvent of the proteins. In a first step, it was of interest to elucidate the gliadin macromolecular conformation in order to understand the mechanism of nanoparticle formation. The experimental work was based on SANS experiments. Because the size of the colloidal particle suspension is an important parameter to monitor, the modelization of the particle growth was thoroughly studied. Furthermore, it was observed that the determination of the solubility parameters of the proteins allowed optimization of the size of the particles. From those previous experimental results it can be concluded that there is a correlation between the protein conformation in the solvent and the size of the nanoparticles (NP).

Microheterogeneity and microrheology of wheat gliadin suspensions studied by multiple-particle tracking

By monitoring the thermally driven displacements of imbedded polystyrene microspheres via video fluorescence microscopy, we quantified the microstructural and micromechanical heterogeneities of wheat gliadin suspensions. We found that the degree of heterogeneity of the suspensions, as measured by the width and skewness of the microspheres' mean squared displacement (MSD) distribution, increased dramatically over a narrow range of gliadin concentrations. The ensemble-averaged MSD of a 250 mg/mL gliadin suspension exhibited a power-law behavior scaling linearly with time, a behavior similar to that observed for a homogeneous aqueous glycerol solution. However, the MSD distribution was wider and more asymmetric than for glycerol. With increasing concentration of gliadin, the ensemble-averaged MSD rapidly displayed a plateau at small time scales, the MSD distribution became wider and more asymmetric, and the local viscoelastic moduli extracted from multiple-particle-tracking measurements showed an increasingly wide range.

Molecular images of cereal proteins by STM

Scanning tunnelling microscopy (STM) has been used to study a seed storage protein of wheat known as gamma-gliadin. The protein was deposited onto highly oriented pyrolytic graphite (HOPG) from solutions of trifluoroethanol (TFE) and 1% acetic acid. Samples were dried down and then scanned in air. Transmission electron microscopy (TEM) was also used to visualise the distribution of protein on the substrate. Small-angle X-ray scattering (SAXS) was used to compare the molecular size and shape obtained with those from the STM images.