Lipid transfer from insect fat body to lipophorin: comparison between a mosquito triacylglycerol-rich lipophorin and a sphinx moth diacylglycerol-rich lipophorin.

Two insect lipoproteins, triacylglycerol-rich Aedes aegypti lipophorin and diacylglycerol-rich Manduca sexta lipophorin, were compared in their ability to load neutral lipid from fat body. When fat body of M. sexta was incubated in vitro with [3H]oleic acid, all radiolabeled fatty acids were esterified, predominantly to triacylglycerol. In A. aegypti fat body, however, half of the label remained as free fatty acids. When A. aegypti fat body was radiolabeled with [3H]glycerol, most of the radiolabel was incorporated in triacylglycerol. When either A. aegypti or M. sexta lipophorin was incubated with A. aegypti fat body, labeled with [3H]oleic acid, both lipophorins incorporated mainly radiolabeled free fatty acids, while almost no radiolabeled glycerides were transferred. When the same experiment was performed with A. aegypti fat body, radiolabeled with [3H]glycerol, very little transfer of radiolabeled glycerides was detected. In contrast, when either M. sexta or A. aegypti lipophorin was incubated with M. sexta fat body, both lipophorins incorporated neutral lipids, predominantly diacyglycerol. A. aegypti lipophorin incorporated half the amount of radiolabeled lipid, compared to M. sexta lipophorin. Lipophorins from both species were treated with triacylglycerol lipase of the yeast Candida cylindracea. Although this lipase readily delipidated M. sexta HDLp, it was not able to remove triacylglycerol from A. aegypti HDLp. The data presented suggest that, under the conditions used, lipid transfer from fat body to lipophorin in A. aegypti is not as efficient as in M. sexta.