Apicomplexan Parasite Interactions with Host Organelles: Recruitment, Lipid Scavenging, and Consequences

[摘要] Apicomplexa parasites are harmful pathogens of humans and animals. They invade mammalian cells wherein they reside within a parasitophorous vacuole (PV) that protects them from cytosolic destructive pathways but forms a physical barrier from host-derived nutrients. Among Apicomplexa, Toxoplasma gondii has proficiently evolved to recruit host organelles to its PV to facilitate nutrient uptake. Almost nothing is known about the intracellular development of Neospora caninum, a closely relative of Toxoplasma. We show that N. caninum is also able to attract host organelles (ER, Golgi, endosomes) to its PV from which it retrieves cholesterol and ceramides, revealing conserved strategies among these parasites to exploit nutrient-filled host organelles. We next explore the role of host lipid droplets (LD) as sources of neutral lipids for Toxoplasma. We demonstrate that host LD cluster around the PV, and infection leads to an increase, then decrease in host LD numbers, suggesting a manipulation of these structures by Toxoplasma. Indeed, Toxoplasma is able to scavenge lipids from host LD, in part through the interception of Rab vesicles associated with LD and the translocation of host LD into its PV.Ectopic addition of oleic acid (OA) up to 1 mM (non toxic concentration for mammalian cells) stimulates LD biogenesis. When exposed to 0.2 mM OA, Toxoplasma scavenges this fatty acid in excess, channels it to LD that accumulate in the cytoplasm, as a result of increased transcription of its enzymes generating neutral lipids. However, this condition slows down both parasite replication and egress. By comparison, 0.2 mM palmitic acid does not affect the parasite’s intracellular development. Interestingly, ultrastructural analyses of OA-loaded Toxoplasma reveal for the first time, the presence of coated pits at the plasma membrane and structures potentially involved in endocytosis. More dramatically, addition of 0.4 mM OA to the medium results in massive accumulation of lipid deposits in the PV and the parasite, leading to replication defects and death. This highlights the high sensitivity of Toxoplasma towards deleterious effects of accumulating fatty acids. Deciphering the lipotoxic response of the parasite would reveal new vulnerabilities amenable to controlling Toxoplasma infections.

[发布机构] Johns Hopkins University

[效力级别] Lipids

[关键词] Toxoplasma;Lipids;Biology