Expression of a thioredoxin peroxidase in insulin-producing cells

The presence of thioredoxin peroxidase (TPx), also known as thiol specific antioxidant (TSA), was investigated in neonatal and adult rat islets, and in the beta-cell line HIT-T15. Western blotting of extracts from neonatal and adult pancreatic islets and from the tumoral cell line HIT-T15 revealed the presence of a 25 kDa protein that comigrated with purified yeast TPx. Endocrine pancreatic TPx accounted for approximately 0.01% of the total protein content. Treatment with H2O2 for 3 h increased the expression of TPx in HIT-T15 cells. The distribution of TPx throughout the islet cells was confirmed by immunocytochemistry. Since pancreatic beta-cells possess a weak antioxicant enzyme defense system, especially with regard to hydrogen peroxidase-decomposing enzymes, the presence of a TPx analog in islets suggests that this enzyme may play a role in protecting pancreatic cells against reactive oxygen species.