Profiling the expression dynamics of virulence-associated genes in clinical Plasmodium falciparum isolates
Final Report Abstract
Malaria caused by P. falciparum remains one of the major global health problems and is a leading cause of death, particularly affecting children under the age of five. In general, malaria parasites infect and replicate inside erythrocytes, and this blood phase is responsible for clinical symptoms of the disease. Central for the development of malaria pathogenesis are parasite proteins exported to the red blood cell surface enable the infected erythrocytes to adhere to the vascular endothelium. The binding causes disturbances of the microcirculation in the brain and other organs and can result in life-threatening organ failure. The major exported variant surface antigen, the PfEMP1 protein family, has diversified to encompass variants that can bind different and multiple endothelial receptors and expanded to include a high number of different sequence variants conferring same phenotypes. However, severe malaria is also a complication of non-immune travelers and adults from regions with unstable transmission. Disease symptomatology varies according to patient age, although the factors that drive age-related differences are largely unknown. In the first part of the study, we exploit deep RNA-seq analysis of parasites isolated from 32 adult non-immune travelers to globally map transcription profiles in a multidimensional approach and explored and correlated the immunological history as well as the clinical manifestations of the patients. We tailored this investigation on PfEMP1, the major pathogenicity factor of the parasite. Analysis at the multi-, single- and sub-domain levels showed that severe malaria was associated with expression of A-type PfEMP1 or those containing the endothelial protein C receptor (EPCR)-binding CIDRα1 domain, whereas CD36-binding PfEMP1 was linked to nonsevere malaria outcomes. Nevertheless, the vast majority of transcripts in parasites from all group of adult patients encode PfEMP1 with CD36-binding properties, which is in clear contrast to severe childhood malaria. These findings were supported by an orthogonal analysis using DBLα expressed sequence tags to predict the encoding PfEMP1 domain composition. In the second part of this study, we provided deeper insights into P. falciparum strategies to maintain long-lasting, chronic infections. Samples from a unique controlled human malaria infection study were used to characterize gene expression changes during the course of infection in parasites from infected volunteers naturally exposed to malaria since birth. For the first time a shift in the dominant var gene variant could be observed in vivo, which occurred in parallel to an increasing expression of the interstrain conserved variant var2csa supporting the hypothesis that var2csa may act as a switching intermediate. Overall, the study provides the so far deepest and most comprehensive analysis of PfEMP1 expression in patients with different immunological and clinical outcomes. It is the first time that a cohort of firsttime malaria infected adults was analyzed in relation to infection time, PfEMP1 expression and disease outcome providing a hint that parasites with more pathogenic PfEMP1 variants are more common in patients with a naïve immune status and/or adverse inflammatory host responses to first infections favors growth of EPCR-binding parasites. Moreover, our longitudinal in vivo data provide a first glimpse on the strategy P. falciparum is using to escape from arising immune response during an acute infection.
Publications
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(2019): Controlled human malaria infection with Plasmodium falciparum demonstrates impact of naturally acquired immunity on virulence gene expression. PLoS Pathogens, 15(7): e1007906
Bachmann A, Bruske E, Krumkamp R, Turner L, Wichers JS, Petter M, Held J, Duffy MF, Sim BKL, Hoffman SL, Kremsner PG, Lell B, Lavstsen T, Frank M, Mordmüller B, Tannich E
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(2019): Dissecting the gene expression, localization, membrane topology, and function of the Plasmodium falciparum STEVOR protein family. mBio, 10(4): e01500-19
Wichers JS, Scholz JAM, Strauss J, Witt S, Lill A, Ehnhold LI, Neupert N, Liffner B, Lühken R, Petter M, Lorenzen S, Wilson DW, Löw C, Lavazec C, Bruchhaus I, Tannich E, Gilberger TW, Bachmann A
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(2020): Adhesion between P. falciparum infected erythrocytes and human endothelial receptors follows alternative binding dynamics under flow and febrile conditions. Scientific Reports, 10(1): 4548
Lubiana P, Bouws P, Roth LK, Dörpinghaus M, Rehn T, Brehmer J, Wichers JS, Bachmann A, Höhn K, Roeder T, Thye T, Gutsmann T, Burmester T, Bruchhaus I, Metwally NG
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(2020): Structural insights into PfARO and characterization of its interaction with PfAIP. Journal of Molecular Biology, 432(4): 878-896
Geiger M, Brown C, Wichers JS, Strauss J, Lill A, Thuenauer R, Liffner B, Wilcke L, Lemcke S, Heincke D, Pazicky S, Bachmann A, Löw C, Wilson DW, Filarsky M, Burda PC, Zhang K, Junop M, Gilberger TW
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(2021). Identification of novel inner membrane complex and apical annuli proteins of the malaria parasite Plasmodium falciparum. Cell Microbiol. 2021 Sep;23(9):e13341
Wichers JS, Wunderlich J, Heincke D, Pazicky S, Strauss J, Schmitt M, Kimmel J, Wilcke L, Scharf S, von Thien H, Burda PB, Spielmann T, Löw C, Filarsky M, Bachmann A, Gilberger, TW
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(2021): Common virulence gene expression in adult first-time infected malaria patients and severe cases. Elife. 2021 Apr 28;10:e69040
Wichers JS, Tonkin-Hill G, Thye T, Krumkamp R, Kreuels B, Strauss J, von Thien H, Scholz JAM, Hansson HH, Jensen RW, Turner L, Lorenz F-R, Schöllhorn A, Bruchhaus I, Tannich E, Fendel R, Otto TD, Lavstsen T, Gilberger T-W, Duffy MF, Bachmann A
