The vacuolar iron transporter mediates iron detoxification in Toxoplasma gondii

Abstract

Iron is essential to living cells, acting as a cofactor in a number of important enzymes in metabolism; however in the absence of correct storage iron forms dangerous oxygen radicals. In both yeast and plants, iron is stored in a membrane-bound vacuole through the action of a vacuolar iron transporter (VIT). This transporter is conserved in the apicomplexan family of obligate intracellular parasites, including in Toxoplasma gondii, a pathogen of medical and veterinary importance. Here, we assess the role of VIT, and iron storage, in T. gondii. We show that iron is restricted to a compartment in the parasite that does not overlap with zinc. By deleting VIT we find a slight growth defect in vitro, however the absence of VIT leads to hypersensitivity to iron, confirming its essential role in iron detoxification in the parasite. This hypersensitivity can be rescued by scavenging of oxygen radicals. In the absence of VIT, parasites store less iron and are at a growth disadvantage when moving into an iron-depleted environment. We show parasite VIT expression is regulated by iron levels at both the transcript and protein level, and by altering the distribution of VIT within the cell. In the absence of VIT, we find that T. gondii responds by altering expression of genes with a role in iron metabolism and by increasing the activity of the antioxidant protein catalase. We also show that iron detoxification has an important role both in parasite survival within macrophages and in virulence in a mouse model. Together, by demonstrating a critical role for VIT during iron detoxification in T. gondii, we reveal the importance of iron storage in the parasite and provide the first insight into the machinery involved.

Iron transport pathways in the human malaria parasitePlasmodium falciparumrevealed by RNA-sequencing

“…An increase in the number of fluorescent punctate structures during parasite development (Fig. 3B) was also observed for VIT in Toxoplasma gondii (90). PfVIT shares 47.0% identity with…”

“…S2), PfMRS3 is likely essential for asexual growth like PBANKA_041620 (E = 1 x 10 -69 , 71.4% identity, 25% coverage) in P. berghei (89). The orthologous mitochondrial iron transporter (TgMIT, TGME49_277090, E = 15 7 x 10 -19 , 26.0% identity, 28% coverage) also localized to the mitochondrion in T. gondii and was upregulated at the protein level upon iron overload due to a TgVIT knock out in the related apicomplexan parasite (90). In line with our structural analyses (Fig.…”

“…This may be explained by differences between species or variation in methodology such as fixation, permeabilization, and immunolabeling techniques as opposed to live-cell imaging (92)(93)(94). While not essential during asexual blood stages (64), a knockout of VIT resulted in reduced liver stage development in P. berghei (30) and increased sensitivity to high iron levels in both P. berghei (30) and T. gondii (90). Similarly, growth of the ΔVIT P. falciparum line was not affected under standard conditions, whereas the addition of hepcidin -which increases free intracellular iron levels (Fig.…”

In vivoCRISPR screens identify novel virulence genes among proteins of unassigned subcellular localization inToxoplasma

“…TGGT1_273905 localizes to the cytoplasm (22). Although some candidates (VIT and DDI1) were previously reported to be required for parasite virulence (16, 17), none of the other top hits are assessed regarding virulence so far.…”

Iron depletion has different consequences on the growth and survival ofToxoplasma gondiistrains

“…Maintaining a proper iron balance becomes especially vital in the context of T. gondii infection 10,11 as the parasites need to acquire iron, while the host cells may deprive them of this essential metal. Consequently, host-driven iron withdrawal has the potential to inhibit the growth of these pathogens and can be part of the interferon gamma-dependent response to T. gondii infection 12 .…”