Sphingomyelinase treatment on human erythrocytes: influence on Membrane lipid rafts and malaria parasite invasion

Abstract

The erythrocyte membrane, the entry site of the malaria parasite, has lipid micro domains referred to as the lipid rafts, which are enriched in sphingomyelin and cholesterol. Evidences have demonstrated the importance of cholesterol in structure and functions of the lipid rafts and malaria parasite invasion into erythrocytes, while that of sphingomyelinase is poorly understood. In this study, we examined the influence of sphingomyelinase treatment on erythrocyte lipid rafts and malaria parasite invasion into erythrocytes. Sphingomyelin was decreased by about 65% after sphingomyelinase treatment, and sphingomyelin, cholesterol and flotillin-1, a lipid raft marker protein, were absent from lipid raft fractions. The treatment also significantly reduced the association of Gs a in lipid raft fractions, suggesting that Gs a -mediated signal transduction was impaired. More importantly, malaria parasite invasion was prevented by this treatment. Our study illustrates that sphingomyelin, like cholesterol, is essential for the structure and functions of the lipid rafts in the erythrocyte membrane and malaria parasite invasion. Mark-release-recapture (MRR) experiments were conducted with emerging Anopheles gambiae s.l. and Anophelesfunestus Giles at Jaribuni and Mtepeni in Kilifi, along the Kenyan Coast. Of 739 and 1246 Anopheles released at Jaribuni and Mtepeni, 24.6 and 4.33% were recaptured, respectively. The daily survival probability was 0.96 for An. funestus and 0.95 for An. gambiae in Jaribuni and 0.83 and 0.95, respectively, in Mtepeni. The maximum flight distance recorded was 661 m. The high survival probability of An. gambiae and An. funestus estimated accounts for the continuous transmission of malaria along the Kenyan coast. This study also shows that the release of young, emergent female Anopheles improves the recapture rates and may be a better approach to MRR studies.