Dissecting the molecular interaction between hepatocytes and Plasmodium liver parasites

Dissertation presented to obtain the Ph.D degree in Biology

Malaria is one of the world´s leading causes of death, responsible for over 700,000 deaths per year, the majority of which are African children under 5 years of age. Malaria disease is caused by the transmission of an Apicomplexa parasite, Plasmodium, through the bit of a female Anopheles mosquito, and transmitted parasites quickly reach the mammalian host liver, where the first round of replication begins. Plasmodium sporozoites, once inside the liver, must invade and survive within hepatocytes until the first replicative stage within the mammalian host is accomplished. Upon migration through various cells, sporozoites are able to actively enter hepatocytes, forming a Parasitophorous Vacuole Membrane (PVM) around itself. Once this intracellular niche is established, parasite replication and growth is initiated. Dramatic morphological as well as gene expression modifications occur at this stage, and the parasite achieves one of the highest replication rates known within eukaryotic species (Sinnis and Sim, 1997). Although the Plasmodium life-cycle has been extensively characterized, relatively little is known about sporozoite interaction with host organelles, vesicles and proteins. To address this issue, Plasmodium interactions with the host cell endomembranes was analyzed at various stages of liver infection using indirect immunofluorescence. Plasmodium parasites were seen closely associated with host endoplasmic reticulum (ER) and the Golgi apparatus. Surprisingly, late endosomes/lysosomes, observed with the membrane markers Rab7a, CD63 and LAMP1, aggregated around the parasite. No interaction with host peroxisomes, early and recycling endosomes was observed.(...)

Financial support was provided by Fundação para a Ciência e Tecnologia. Portugal, through the Ph.D. fellowship grant SFRH/BD/27705/2006.