Characterization of oxysterol-binding protein and sterol carrier protein-2 in the yellow fever mosquito, Aedes aegypti

Sterol transporters in the sterol acquisition and redistribution in vertebrates and insects are reviewed in Chapter I mainly focusing on their function in model organisms Drosophila melanogaster and Aedes aegypti. In Chapter II, the oxysterol-binding protein (OSBP) and related proteins (ORPs) genes with their splicing variants were cloned in A. aegypti. The temporal and spatial transcription patterns of members of the AeOSBP gene family through developmental stages and the gonotrophic cycle were profiled. AeORP1 transcription was head tissue-specific, whereas AeOSBP and AeORP9 expressions were induced by a blood meal. Overexpression of AeORPs facilitated [3H]-cholesterol uptake in A. aegypti cultured Aag2 cells. Additionally we investigated if sterol carrier protein-2 (SCP-2) is a critical host factor for dengue virus (DENV) propagation in the mosquito host cells (Chapter III), since it is known that cellular cholesterol plays an important role in the life cycle of DENV. Treatment with an SCP-2 specific inhibitor or expression knockdown of SCP-2 drastically reduced the virus replication in cultured cells. The intracellular cholesterol distribution was altered by SCP-2 inhibitor treatment, suggesting that SCP-2 mediated cholesterol trafficking pathway is important for viral RNA replication in the mosquito host. Finally, we compared the function of SCP-2 in viral replication in both mosquito host cells and human host cells. Our results suggested that SCP-2 may be critical for mosquito vector competence.