Uptake and compartmentalization of fluorescent lipid analogs in larval Schistosoma mansoni

Recent studies have suggested that host lipids are both a requirement for the human parasite Schistosoma mansoni and may play a role in evasion of host immunity. To study lipid utilization by this organism we have followed the uptake of fluorescent fatty acid and phospholipid analogs in two parasite stages, cercariae and schistosomula. As determined by both morphological and biochemical methods, a fluorescent fatty acid analog labeled with bodipy was incorporated into both stages. In cercariae, diffuse fluorescence was present throughout the organism and discrete lipid droplets were observed in the tail and in the anterior structures. In contrast, fluorescence distribution in cercariae transformed to schistosomula was restricted to cytoplasmic lipid droplets throughout the organism. Biochemical analysis demonstrated that the fatty acid analog was biosynthetically incorporated primarily into neutral lipids but also somewhat into phospholipids. The percentage of free label decreased with time. Similar results were obtained when organisms were labeled directly in vitro or indirectly by labeling the intermediate snail host. Compared to the fatty acid analogs, localization of fluorescent phospholipid analogs by schistosomula was considerably different. Phosphatidylcholine labeled on short acyl chains with either bodipy or NBD localized primarily to a network of cells beneath the organism's surface. A longer chain bodipy-labeled phosphatidylcholine localized to the parasite surface, gut and acetabulum. These studies show specificity in the transport of lipid analogs by this important human parasite, elucidate the compartments within the organism in which specific lipids preferentially accumulate, and demonstrate stage-dependent differences in the utilization of exogenous lipids by this organism.