Anopheles gambiae lipophorin: characterization and role in lipid transport to developing oocyte.

Lipid transport in arthropods is achieved by highly specialized lipoproteins, which resemble those described in vertebrate blood. Here, we describe purification and characterization of the lipid-apolipoprotein complex, lipophorin (Lp), in the malaria vector mosquito Anopheles gambiae. We also describe the Lp-mediated lipid transfer to developing eggs and the distribution of the imported lipid in developing embryos. The density of the Lp complex was 1.135 g/ml with an apparent molecular weight of 630 kDa. It is composed of two major polypeptides, apoLp I (260 kDa) and apoLp II (74 kDa) and composed of 50% protein, 48% lipid and 2% carbohydrate (w/w). Hydrocarbon, cholesterol, phosphatidyl choline, phosphatidyl ethanolamine, cholesteryl ester and diacylglyceride were the major Lp-associated lipids. Using fluorescently tagged lipids, we observed patterns that suggest that in live developing oocytes, the Lp was taken up by a receptor-mediated endocytic process. Such process was blocked at low temperature and in the presence of excess unlabeled Lp, but not by bovine serum albumin. Imported Lp was segregated in the spherical yolk bodies (mean size 1.8 microm) and distributed evenly in the cortex of the oocyte. In embryonic larvae, before hatching, a portion of the fatty acid in vesicles was found evenly distributed along the body, whereas portion of phospholipids was accumulated in the intestine.

Lysophosphatidylcholine acts as an anti-hemostatic molecule in the saliva of the blood-sucking bug Rhodnius prolixus.

Blood-sucking arthropods possess a variety of anti-hemostatic factors in their salivary glands to maintain blood fluidity during feeding. In this work we demonstrate the anti-hemostatic properties of lysophosphatidylcholine (lysoPC) isolated from the salivary glands of Rhodnius prolixus. First, we examined salivary glands of fourth and fifth instar nymphs for their phospholipid composition. The lumen displayed an accumulation of its phospholipid content, mainly phosphatidylcholine and lysoPC, with a 6-fold increase for the latter. To determine the presence of phospholipids in the saliva, fourth instar nymphs were fed with a32P-enriched blood meal. After 28 days their saliva was collected and subjected to lipid extraction, thin-layer chromatography, and autoradiography. The results showed the presence in the saliva of the same phospholipids present in the lumen. We then examined possible biological roles of these phospholipids when compared with other known effects of lysoPC. The luminal lipid extract and purified lysoPC from the lumen and saliva were tested for inhibition of washed rabbit platelets' aggregation induced by alpha-thrombin and platelet-activating factor. Both the luminal lipid extract and salivary lysoPC showed an increasing inhibition of aggregation, which correlated with the response of the platelets to standard lysoPC (up to 13 microg/ml). Next, salivary lysoPC was incubated with porcine arterial endothelial cells for 24 h. After incubation, culture medium was assayed for nitric oxide and showed increased nitric oxide production, similar to control cells exposed to standard lysoPC (up to 20 microg/ml). Together these data demonstrate the presence of lysoPC in the saliva of Rhodnius prolixus and its potential anti-hemostatic activities.