The Plasmodium parasite has a complex life cycle alternating between the mosquito vector and vertebrate host. When a mosquito bites, the parasite makes it way to the liver, where it invades a liver cell and asexually replicates to produce thousands of parasites. Invasion of RBCs then marks the pathogenic blood stage where parasites can rapidly asexually replicate and also produce mosquito-infective sexual stage progeny. As human RBCs are largely devoid of protein trafficking machinery the malaria parasite must set this up from scratch to survive and propagate, dedicating nearly 10 % of its genes to this effort. This allows the parasite to change the nature of the RBC making it rigid and sticky, and ultimately altering how they flow within the bloodstream. While this is good for the parasite, it can cause cerebral malaria that leads to coma and death.
Identifying key players in malaria-induced RBC remodelling
The PfPHIST project was designed to investigate how the parasite remodels human RBCs during the blood life cycle stage. Undertaken with the support of the Marie Skłodowska-Curie (MSC) programme, it took place in Taco Kooij’s lab at the Radboud Universtiy Medical Centre, the Netherlands and focused on proteins the malaria parasite uses to alter human RBCs. “We were particularly interested in the mechanism underlying rigidity changes in the RBC membrane as it enables parasites to escape the bloodstream circulation,” explains MSC research fellow Nick Proellochs. Accumulating evidence indicates that the parasite exports a large number of proteins into the RBC to carry out the remodelling process. These changes in membrane rigidity also appear to be required for the parasite’s sexual development and transmission to the mosquito. PfPHIST research focused on the role of the Plasmodium helical interspersed subtelomeric PHIST family of proteins. For this purpose, the MCS fellow undertook genetic manipulation of selected parasite genes to obtain mutant parasites for analysis.
Technological developments aid future malaria research
The researchers developed a new fluorescence-based gene knockout strategy that allowed them to easily select parasites lacking the target protein. At the same time, they were able to track the entire life cycle of these fluorescent parasites from blood to mosquito to the liver. To measure the changes of the malaria-infected RBCs, the scientific team developed a new microfluidics-based technique in collaboration with Wilhelm Huck at Radboud University. This enabled them to record normal and infected RBCs travelling through microscopic channels and analyse their properties. Researchers found that a certain gene, previously thought to play a role in the blood stage of the Plasmodium life cycle, is implicated in parasite development within the mosquito. This clearly indicated that the parasite’s ability to modify membranes could be important in other life-cycle stages. “Our findings strongly suggest that we should look further in the Plasmodium life cycle to unveil the functional role of these exported proteins,” emphasises Proellochs. Albeit short in duration, PfPHIST helped unravel the remodelling role of the PHIST family of parasite proteins as well as their implication in malaria spread. Project findings pave the way towards elucidation of the mechanism of parasite spread and shape the future development of antimalarial strategies.
Pf PHIST, RBC, malaria, Plasmodium, mosquito, membrane, malaria parasite, PHIST proteins, red blood cell