Biochemical characterization and role of the proteasome in the oxidative stress response of adult Schistosoma mansoni worms

The trematode Schistosoma mansoni, an important parasite of humans, is the principle agent of the disease schistosomiasis. In the human host, one of the most important stress factors of this parasite is the oxidative stress generated by both the metabolism of the worm and the immune system of the host. The proteasomal system is responsible for protein homeostasis during oxidative stress. The 26S proteasome is a multicatalytic protease formed by two compartments, a 20S core and regulatory particle 19S, and controls the degradation of intracellular proteins, hence regulating many cellular processes. In the present report, we describe the biochemical characterization and role of the 20S proteasome in the response of adult S. mansoni worms exposed to hydrogen peroxide. Characterization of the response to the oxidative stress included the evaluation of viability, egg production, mortality, tegument integrity, and both expression and activity of proteasome. We observed decreases in viability, egg production as well as 100 % mortality at the higher concentrations of hydrogen peroxide tested. The main changes observed in the tegument of adult worms were peeling as well as the appearance of bubbles and a decrease of spines on the tubercles. Furthermore, there were increases in 26S activity to the same extent as 20S proteasome activity, although there was increase of 20S proteasome content, suggesting that degradation of protein oxidized in adult worms is due to the 20S proteasome. It was demonstrated that adult S. mansoni worms are sensitive to oxidative stress, and that a variety of processes in this parasite are altered under this condition. The work contributes to a better understanding of the mechanisms employed by S. mansoni to survive under oxidative stress.