Abstract
Trypanosoma cruzi, the protozoan that causes Chagas disease, has a complex life cycle involving several morphologically and biochemically distinct stages that establish intricate interactions with various insect and mammalian hosts. It has also a heterogeneous population structure comprising strains with distinct properties such as virulence, sensitivity to drugs, antigenic profile and tissue tropism. We present a comparative transcriptome analysis of two cloned T. cruzi strains that display contrasting virulence phenotypes in animal models of infection: CL Brener is a virulent clone and CL-14 is a clone that is neither infective nor pathogenic in in vivo models of infection. Gene expression analysis of trypomastigotes and intracellular amastigotes harvested at 60 and 96 hours post-infection (hpi) of human fibroblasts revealed large differences that reflect the parasite’s adaptation to distinct environments during the infection of mammalian cells, including changes in energy sources, oxidative stress responses, cell cycle control and cell surface components. While extensive transcriptome remodeling was observed when trypomastigotes of both strains were compared to 60 hpi amastigotes, differences in gene expression were much less pronounced when 96 hpi amastigotes and trypomastigotes of CL Brener were compared. In contrast, the differentiation of the avirulent CL-14 from 96 hpi amastigotes to extracellular trypomastigotes was associated with considerable changes in gene expression, particularly in gene families encoding surface proteins such as trans-sialidases, mucins and the mucin associated surface proteins (MASPs). Thus, our comparative transcriptome analysis indicates that the avirulent phenotype of CL-14 may be due, at least in part, to a reduced or delayed expression of genes encoding surface proteins that are associated with the transition of amastigotes to trypomastigotes, an essential step in the establishment of the infection in the mammalian host. Confirming the role of members of the trans-sialidase family of surface proteins for parasite differentiation, transfected CL-14 constitutively expressing a trans-sialidase gene displayed faster kinetics of trypomastigote release in the supernatant of infected cells compared to wild type CL-14.
Highlights
Trypanosoma cruzi is the etiological agent of Chagas disease, a disease affecting at least 8 million people throughout Latin America and for which there are only two drugs available, both with poor efficacy and harmful side effects
Using homology searches to four protein domains known to be present in RNA binding proteins (PUF (Pumilio), zinc finger, RNA recognition motif (RRM) and Alba domains), we identified a total of 253 T. cruzi sequences representing 147 genes, which are shown in S6 Table
Our in vivo infection assays confirmed previous studies, which have shown that, in contrast to an infection with the CL Brener clone, no patent parasitemia can be detected in immune competent animals that were inoculated with trypomastigotes from the attenuated CL-14 clone
Summary
Trypanosoma cruzi is the etiological agent of Chagas disease, a disease affecting at least 8 million people throughout Latin America and for which there are only two drugs available, both with poor efficacy and harmful side effects (http://www.who.int/mediacentre/factsheets/fs340/ en/). After reaching the bloodstream through skin cuts or through the mucosa, trypomastigotes invade different cell types in the mammalian host. They differentiate into replicative non-flagellated amastigotes, which undergo several rounds of division before differentiating again into trypomastigotes and bursting out of the host cell. Bloodstream trypomastigotes, ingested by the vector during a blood meal, differentiate into epimastigotes and replicate in the insect midgut [1]. Such a complex life cycle, involving several morphologically and biochemically distinct parasite forms and very different host environments, requires complex regulatory mechanisms to direct gene expression and the adaptive strategies that allow parasites to thrive within distinct hosts
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