Date Published: October 11, 2018
Publisher: Public Library of Science
Author(s): Yana Shaulov, Chikako Shimokawa, Meirav Trebicz-Geffen, Shruti Nagaraja, Karen Methling, Michael Lalk, Lea Weiss-Cerem, Ayelet T. Lamm, Hajime Hisaeda, Serge Ankri, William A. Petri.
Amebiasis, a global intestinal parasitic disease, is due to Entamoeba histolytica. This parasite, which feeds on bacteria in the large intestine of its human host, can trigger a strong inflammatory response upon invasion of the colonic mucosa. Whereas information about the mechanisms which are used by the parasite to cope with oxidative and nitrosative stresses during infection is available, knowledge about the contribution of bacteria to these mechanisms is lacking. In a recent study, we demonstrated that enteropathogenic Escherichia coli O55 protects E. histolytica against oxidative stress. Resin-assisted capture (RAC) of oxidized (OX) proteins coupled to mass spectrometry (OX-RAC) was used to investigate the oxidation status of cysteine residues in proteins present in E. histolytica trophozoites incubated with live or heat-killed E. coli O55 and then exposed to H2O2-mediated oxidative stress. We found that the redox proteome of E. histolytica exposed to heat-killed E. coli O55 is enriched with proteins involved in redox homeostasis, lipid metabolism, small molecule metabolism, carbohydrate derivative metabolism, and organonitrogen compound biosynthesis. In contrast, we found that proteins associated with redox homeostasis were the only OX-proteins that were enriched in E. histolytica trophozoites which were incubated with live E. coli O55. These data indicate that E. coli has a profound impact on the redox proteome of E. histolytica. Unexpectedly, some E. coli proteins were also co-identified with E. histolytica proteins by OX-RAC. We demonstrated that one of these proteins, E. coli malate dehydrogenase (EcMDH) and its product, oxaloacetate, are key elements of E. coli-mediated resistance of E. histolytica to oxidative stress and that oxaloacetate helps the parasite survive in the large intestine. We also provide evidence that the protective effect of oxaloacetate against oxidative stress extends to Caenorhabditis elegans.
Entamoeba histolytica is a protozoan parasite, which inhabits the gastrointestinal tract, and an E. histolytica infection is a substantial health risk in almost all countries where the barrier between food and water and human feces is inadequate. The major clinical manifestations of an E. histolytica infection are amebic colitis, amebic liver abscess, and extraintestinal amebiasis. It is estimated that amebiasis accounted for 55500 deaths and 2.237 million disability-adjusted life years (the sum of years of life lost and years lived with disability) in 2010. This mortality rate makes an E. histolytica infection the second leading cause of death due to a parasitic infection. E. histolytica is a dimorphic organism whose life cycle has two stages: a trophozoite, a cell-invasive form which can be found in the human intestine, and a cyst, an infective form which is found in the external environment. The conversion between the two stages is usually reversible. Infection of the host occurs upon ingestion of water or food contaminated with cysts. After ingestion, the cysts pass through the stomach, excyst in the small intestine where they produce ameboid trophozoites, which then colonize the large intestine. In the colon, the trophozoites can either asymptomatically colonize the gut, re-encyst, and be expelled in the feces or cause invasive disease. Although the exact conditions, which trigger the onset of invasive disease, are still unknown, the interaction between the parasite’s virulence factors and the host’s response contribute to the development of disease.
In a previous report, we informed on the results of our redox proteomics analysis of oxidatively stressed E. histolytica trophozoites . In order to understand the mechanisms of survival of E. histolytica trophozoites that were incubated with E. coli prior to their exposure to H2O2, we did a redox proteomics analysis of the parasite which was exposed first to heat-killed or live E. coli and then exposed to H2O2. The proteins involved in redox homeostasis, mainly, thioredoxin (TRX) and protein disulfide isomerase (PDI) were identified as OX-proteins in oxidatively stressed E. histolytica trophozoites which were exposed to heat-killed or live E. coli. This result indicates that the presence of heat-killed or live E. coli has no detectable effect on the oxidation status of these proteins. In previous investigations, we reported that TRX and PDI are oxidized and nitrosylated when E. histolytica trophozoites are exposed to oxidative and nitrosative stress [22, 53]. PDIs are oxidoreductases and isomerases which are involved in the unfolded protein response. In the oxidation-reduction reaction to reduce peroxyredoxin or decompose H2O2 into H2O, TRX is the first substrate to be transformed by TRX reductase (TrxR). Since TRX is susceptible to oxidation and is reduced as part of its antioxidant activity[57, 58], these properties may be reasons why TRX is oxidized in the oxidatively stressed parasite after its exposure to heat-killed or live E.coli.