Expression and enzymatic activity of small intestinal tissue transglutaminase in celiac disease

The molecular and functional properties of small intestinal tissue transglutaminase are largely unknown despite growing interest because of its role in celiac disease (CD). In this study, we aimed to evaluate tissue transglutaminase expression and enzymatic activity in bioptic fragments obtained from the duodenum of untreated individuals with CD and from control subjects.

Analysis of tissue transglutaminase mRNA expression was performed by reverse transcription-polymerase chain reaction (RT-PCR). The presence of the enzyme in bioptic fragments as well as in homogenates from CD patients and controls was revealed by immunohistochemistry and Western blot, respectively, using the antitissue transglutaminase CUB 7402 clone. To evaluate in situ transglutaminase activity, sections of bioptic fragments were incubated in the presence of 5 mmol/L CaCl(2) with 5-(biotinamido)pentylamine or, alternatively, with a biotinylated glutamine-containing hexapeptide (TVQQEL) and the biotinylated 31-43 A-gliadin-derived peptide.

Tissue transglutaminase mRNA levels were 1.0-fold higher (p < 0.05) in CD patients than in controls. Immunohistochemistry and in situ demonstration of enzymatic activity in celiac mucosa clearly showed an increased expression of active tissue transglutaminase in the extracellular matrix of the subepithelial region and in the enterocytes. Staining of the biotinylated 31-43 A-gliadin peptide in the same area of tissue transglutaminase suggested the presence of lysine-donor substrates in intestinal mucosa.

Tissue transglutaminase is more expressed and active in defined areas of the small intestinal mucosa from patients with CD. The presence in the celiac mucosa of proteins able to act as amine-donor substrates suggests that tissue transglutaminase-mediated post-translational modification of proteins cross-linked with gliadin peptides may represent a pathogenic mechanism of CD.