Lipid storage and trafficking mechanisms in Plasmodium falciparum

Abstract

Plasmodium falciparum, the causative agent of the most severe form of human malaria, undergoes dramatic metabolic shifts across its complex life cycle. Lipid metabolism is critical for membrane biogenesis, energy storage, and developmental transitions. Despite increasing recognition of lipid droplet (LD) biology in other eukaryotes, how P. falciparum stores and regulates neutral lipids (NLs) remains poorly understood. This thesis investigates the formation, composition, and dynamics of neutral lipid storage compartments across blood-stage development. Progressive accumulation of triacylglycerol (TAG)-rich LDs from ring to schizont stage was demonstrated in the asexual stages. Using Nile Red spectral imaging, three-dimensional focused ion beam scanning electron microscopy (3D FIB-SEM) ultrastructural analysis, and metabolic inhibitor assays were used to demonstrate that LD formation and turnover are essential for schizogony, supporting their crucial role in membrane biosynthesis and prevention of lipotoxicity. A bioinformatic analysis identified candidate LD associated proteins in P. falciparum, including conserved lipid synthesis enzymes such as P. falciparum diacylglycerol acyltransferase (PfDGAT), acyl-CoA:cholesterol acyltransferase (PfACAT), and phospholipase (PfPL), as well as potential stage-specific regulators such as lysophospholipase 1 (PfLPL1) and ATP-binding cassette transporter G2 (PfABCG2). Analyses of transcriptomic data revealed distinct expression patterns: the TAG synthesis enzyme PfDGAT is enriched in asexual stages and male gametocytes, while the putative cholesteryl ester (CE) synthesis enzyme PfACAT is enriched in female gametocytes, reflecting stage and sex-specific lipid metabolic strategies. In gametocytes, classical LD structures were not observed. Instead, a female-specific, neutral lipid-rich compartment - termed femLB - was ultrastructurally characterised in this thesis, revealing a densely packed membrane compartment with co-localisation of the ABC transporter PfABCG2. Altogether, this work demonstrates that P. falciparum employs distinct, stage- and sex-specific strategies for neutral lipid storage: TAG-rich LDs are accumulated in asexual stages to support rapid proliferation while female gametocytes store neutral lipids in particular membrane compartments in female gametocytes. These findings provide new insights into the structural and molecular diversity of lipid storage in malaria parasites and lay the foundation for future studies exploring lipid metabolism as a potential target for stage-specific or transmission-blocking antimalarial strategies.