Impact of Sickle-Trait on Transcriptional Regulation in P. falciparum Parasites
Sickle-trait hemoglobin protects African children from severe-life threatening falciparum malaria, but the mechanisms of this protection are incompletely understood. Several lines of evidence support the notion that hemoglobin mutations disrupt the expression of parasite-derived proteins on the surface of the infected red blood cell (iRBC). These proteins on the iRBC surface mediate the pathogenicity of the parasite, and therefore identifying mechanisms by which their expression can be disrupted will offer new strategies to neutralize the parasite. In our preliminary experiments, sickle-trait dramatically alters the strong, periodic transcriptional program of P. falciparum as it matures within the RBC. More specifically, during early parasite maturation we observe consistent reductions in the expression of transcripts encoding parasite proteins that are essential for the organization and loading of Maurer's clefts, including MAHRP1 and 2, REX 1 and 2, and SBP1; these proteins are necessary for normal trafficking of other parasite proteins to the iRBC surface. Notably, sickle-trait did not reduce the expression of transcripts encoding either surface proteins (2013 including PfEMP1, KAHRP and other variant surface antigens 2013) or components of the parasite translocation machinery, suggesting that
sickle-trait specifically attenuates the efficient loading of protein transport machinery. In this project, we propose to systematically compare transcriptomes of Plasmodium falciparum parasites growing in normal and sickle-trait RBCs in order to identify parasite gene expression networks that are disrupted by sickle-trait. We hypothesize that sickle-trait will produce early, pervasive aberrations in the
expression of parasite transcripts encoding proteins necessary for the assembly of protein export machinery. To test this, we will first cultivate field and reference parasites in normal and sickle-trait RBCs, densely sample parasite transcriptomes during the asexual blood stage, and serially compute gene expression networks. Additionally, we will assay parasite transcriptomes collected from malarious Malian children and compare parasite gene expression in those with normal and sickle-trait RBCs. Through this project, we will directly identify upstream components of the parasite's protein export network that are inhibited by sickle-trait hemoglobin. Because sickle-trait serves as a model of attenuated parasite pathogenesis, these transcriptional profiles will be associated with clinical
protection from malaria. The identification of transcripts and proteins that are impacted by sickle-trait will offer fresh targets for future interventions to neutralize the parasite.