Abstract
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.
Highlights
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
We wished to determine whether the analogs were localized preferentially within the parasite, to correlate such localization with chemical structure of the lipid analogs, and to determine whether alterations in the distribution or transport of the fatty acid analog occur during transformation from cercaria to schistosomulum of this important human parasite
In vitro labeling of cercariae and schistosomula with fatty acid analogs Bodipy-C12was readily incorporated by cercariae and schistosomula in vitro and labeling was time, concentration, and temperature dependent
Summary
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. Biochemically and morphologically [8] during these two Bodipy-C 12 short-term labeling experiments, worms were important stages in the parasite's life cycle and during the incubated at 37OC for 15 min to 2 h in 1 ml of RPMI contransformation process itself. The goals of these studies taining 40 nM, 100 nM, 200 nM, 400 nM, 1 p M , and 2 were to follow uptake of fatty acids and phospholipids by p M Bodipy-C 1 2 (final concentrations). To determine the tem for examining lipid transport in a multicellular organism. temperature dependence of lipid uptake, parallel experiments for lipid analogs were carried out at 0°C and 37°C
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