Transglutaminase-mediated cross-linking is involved in the stabilization of extracellular matrix in human liver fibrosis.

BACKGROUND/AIMS: Lysyl oxidase-mediated cross-linking contributes to the stabilization of collagen in liver fibrosis. We have investigated transglutaminase-mediated cross-linking, to determine if it participates in the stabilization of extracellular matrix in human liver fibrosis.

METHODS

Transglutaminase activity was assessed in vitro by incorporation of biotinylated amine into liver proteins. The product of the transglutaminase-catalyzed cross-linking reaction, Nepsilon(gamma-glutamyl)lysine, and the extracellular proteins cross-linked by it, were localized by immunohistochemistry in fibrotic livers. The cross-linked complexes were extracted from liver tissue, immunopurified and characterized by Western blot.

RESULTS

Transglutaminase, detected by immunohistochemistry, Western blot and by enzymatic activity, was found in higher amounts in fibrotic than in normal liver. The Nepsilon(gamma-glutamyl)lysine cross-link, undetectable in normal liver, was present extracellularly in fibrotic liver, where it was co-distributed with osteonectin, mostly in inflammatory areas submitted to an intense remodeling. Cross-linking of osteonectin by transglutaminase was confirmed by Western blot. In parasitic fibrosis transglutaminase also originates from the parasite.

CONCLUSIONS

Transglutaminase-mediated cross-linking occurs in liver extracellular matrix during the early, inflammatory, stage of liver fibrosis, whereas cross-linking by pyridinoline occurs mostly later in the fibrotic process. This could lead to the development of new anti-fibrotic treatments targeted to a specific stage of fibrosis.