Expression of Cytosolic Peroxiredoxins in Plasmodium berghei Ookinetes Is Regulated by Environmental Factors in the Mosquito Bloodmeal

Abstract

The Plasmodium ookinete develops over several hours in the bloodmeal of its mosquito vector where it is exposed to exogenous stresses, including cytotoxic reactive oxygen species (ROS). How the parasite adapts to these challenging conditions is not well understood. We have systematically investigated the expression of three cytosolic antioxidant proteins, thioredoxin-1 (Trx-1), peroxiredoxin-1 (TPx-1), and 1-Cys peroxiredoxin (1-Cys Prx), in developing ookinetes of the rodent parasite Plasmodium berghei under various growth conditions. Transcriptional profiling showed that tpx-1 and 1-cys prx but not trx-1 are more strongly upregulated in ookinetes developing in the mosquito bloodmeal when compared to ookinetes growing under culture conditions. Confocal immunofluorescence imaging revealed comparable expression patterns on the corresponding proteins. 1-Cys Prx in particular exhibited strong expression in mosquito-derived ookinetes but was not detectable in cultured ookinetes. Furthermore, ookinetes growing in culture upregulated tpx-1 and 1-cys prx when challenged with exogenous ROS in a dose-dependent fashion. This suggests that environmental factors in the mosquito bloodmeal induce upregulation of cytosolic antioxidant proteins in Plasmodium ookinetes. We found that in a parasite line lacking TPx-1 (TPx-1KO), expression of 1-Cys Prx occurred significantly earlier in mosquito-derived TPx-1KO ookinetes when compared to wild type (WT) ookinetes. The protein was also readily detectable in cultured TPx-1KO ookinetes, indicating that 1-Cys Prx at least in part compensates for the loss of TPx-1 in vivo. We hypothesize that this dynamic expression of the cytosolic peroxiredoxins reflects the capacity of the developing Plasmodium ookinete to rapidly adapt to the changing conditions in the mosquito bloodmeal. This would significantly increase its chances of survival, maturation and subsequent escape. Our results also emphasize that environmental conditions must be taken into account when investigating Plasmodium-mosquito interactions.

Protein S-nitrosylation in Plasmodium falciparum

“…The active site cysteines were demonstrated to be responsible for the denitrosylating activity of PfTrx1, consistent with the denitrosylation mechanism of Trx in higher eukaryotic organisms (57). Considering the fact that PfTrx1 is generally located in the parasites' cytosol and ubiquitously expressed in asexual and sexual stages of P. falciparum and also in parasite ookinetes (25,52), denitrosylation mediated by PfTrx1 may represent an important defense mechanism against nitrosative stress throughout the life cycle of Plasmodium parasites.…”

A Knockout Screen of ApiAP2 Genes Reveals Networks of Interacting Transcriptional Regulators Controlling the Plasmodium Life Cycle

“…Neither the gliding speed of ap2-o4 ookinetes nor the shape of their trajectories in matrigel motility assays (Moon et al., 2009) differed from wild-type (Figures S3A and S3B), raising the possibility that their developmental defect is due to either a block at the point of midgut traversal, as has been observed with mutants in secreted traversal proteins (e.g., Dessens et al., 2001), or to reduced survival of ap2-o4 ookinetes under in vivo conditions in the blood meal, where oxidative stress is high (Turturice et al., 2013) and availability of nutrients presumably reduced compared with optimized culture conditions (Sturm et al., 2015). None of the four ookinete stage mutants produced sporozoites in mosquito salivary glands; neither could they be transmitted back to mice by mosquito bite (Data S1).…”

Oxidative stress generated during monensin treatment contributes to altered Toxoplasma gondii mitochondrial function

“…To normalize our results across conditions, we employ a transgenic parasite line (RHΔpLuc) that expresses the luciferase enzyme 49 whose activity can be used to control for parasite numbers. In brief, intracellular parasites were vehicle or drug treated for 30 minutes with monensin or paraquat, a quaternary ammonium bipyridyl herbicide that has been shown to generate reactive oxygen species in the related parasite Plasmodium falciparum 50 and thus serves as a positive control. After treatment, parasites were manually released and filtered away from host cell debris.…”