pH-dependent entry of chikungunya virus into Aedes albopictus cells.

BACKGROUND: The chikungunya virus (CHIKV) recently caused explosive outbreaks in Indian Ocean islands and India. During these episodes, the virus was mainly spread to humans through the bite of the mosquito Aedes albopictus. Concomitantly to the description of symptoms of an unexpected severity in infants and elderly patients, a viral genome microevolution has been highlighted, in particular consisting in the acquisition of an A226V mutation in the gene encoding envelope glycoprotein E1, which was later found to confer an increased fitness for A. albopictus. We previously decrypted the entry pathway used by CHIKV to infect human epithelial cells and showed that these mechanisms are modulated by the E1-A226V mutation. In this report we investigated the conditions for CHIKV entry into mosquito cells and we assessed the consequence of E1 gene mutation on these parameters. PRINCIPAL
FINDINGS: Our main findings indicate that CHIKV infection of A. albopictus cell lines is sensitive to Bafilomycin A1 and chloroquine and to membrane cholesterol depletion. The E1-226V mutated LR-OPY1 isolate collected during the 2005 outbreak in La Réunion replicated more efficiently than the 37997 African reference strain in C6/36 cells. Moreover, the LR-OPY1 strain displayed greater membrane cholesterol dependence and was more sensitive to inhibition of endosomal pH acidification. Finally, using electron microscopy, we imaged CHIKV entry into C6/36 cells.
CONCLUSIONS: Our data support that CHIKV is endocyted into A. albopictus cells and requires membrane cholesterol as well as a low-pH environment for entry. These features are modulated in some extent by the A226V mutation in the E1 gene of the LR-OPY1 isolate. Altogether, our data provide information regarding the pathways used by CHIKV to infect A. albopictus cells.