Production of H₂O₂ in the endoplasmic reticulum promotes in vivo disulfide bond formation.

Aims: Oxidative protein folding in the luminal compartment of endoplasmic reticulum (ER) is thought to be accompanied by the generation of H2O2, as side-product of disulfide bond formation. We aimed to examine the role of H2O2 produced in the lumen, which on one hand can lead to redox imbalance and hence can contribute to ER stress caused by overproduction of secretory proteins; on the other hand, as an excellent electron acceptor, H2O2 might serve as an additional pro-oxidant in physiological oxidative folding. Results: Stimulation of H2O2 production in the hepatic ER resulted in a decrease in microsomal GSH and protein-thiol contents and in a redox shift of certain luminal oxidoreductases in mice. The oxidative effect, accompanied by moderate signs of ER stress and reversible dilation of ER cisternae, was prevented by concomitant reducing treatment. The imbalance also affected the redox state of pyridine nucleotides in the ER. Antibody producing cells artificially engineered with powerful luminal H2O2 eliminating system showed diminished secretion of mature antibody polymers, while incomplete antibody monomers/dimers were accumulated and/or secreted. Innovation: Evidence are provided by using in vivo models that hydrogen peroxide can promote disulfide bond formation in the ER. Conclusion: The results indicate that local H2O2 production promotes, while quenching of H2O2 impairs disulfide formation. The contribution of H2O2 to disulfide bond formation previously observed in vitro can be also shown in cellular and in vivo systems. Antioxid. Redox Signal. 16, 1088-1099.