Food or foe: Interaction of myxozoans with red blood cells

Myxozoan parasites are relatives of free-living jellyfish and are best known for the diseases they can cause in wild fish and aquaculture. Some species are categorized as emerging pathogens whose expansion or disease severity is linked to climate change. Despite the obvious need, there is no legalized treatment or vaccine for myxozoans. Solutions are delayed due to quirks in the biological and molecular characteristics of myxozoans and a lack of knowledge of host exploitation and specific gene/protein function. We have established Sphaerospora molnari, a myxozoan parasite of carp, as our laboratory model. The species proliferates in the blood and our preliminary data strongly indicate that S. molnari is a blood-feeding parasite. Independent of the site of proliferation, anemia is a common manifestation in early infections with several pathogenic myxozoans. We thus hypothesize that myxozoans use red blood cells as an essential host energy source. Hemoglobinolysis requires the activation of proteolytic enzymes, and we suspect that the inactivation of these enzymes would lead to highly detrimental effects on parasite development or to a switch to alternative host resources. We hypothesize that myxozoans show varying degrees of host hemoglobin dependency and have the need to detoxify heme, an essential, but at high concentration toxic component. Our preliminary data also show that red blood cells in fish can respond to and partially resist parasite exploitation as they express different immune factors and receptors. We will use transcriptomics, proteomics and biochemical activity profiling to characterize the hemoglobinolytic cascade of proteases in S. molnari. Comparative analysis will show whether hemoglobin is a universal host protein source and to what extent the heme biosynthesis pathway is reduced in the main myxozoan lineages. We will recombinantly produce and biochemically characterize the hemoglobinolytic protease SmolCathL2, determine its interaction partners, and localize it intracellularly using immunofluorescence and immunogold techniques. In a second step, we will determine the effects of SmolCathL2 deprivation using CrisprCAS9 mutants. Finally, we will compare the transcriptomic signatures of erythrocytes exposed to SmolCathL2-activated and - inactivated S. molnari. The project will provide original knowledge on hematophagy of myxozoans as well as red blood cell host-parasite interactions and will considerably advance our understanding of host exploitation and mutual adaptation, using a synthesis of modern approaches and innovative methods, previously not applied in this field.