Investigating the Role of Cellular Signaling in Liver-Stage Malaria Infection

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DESCRIPTION (provided by applicant): Malaria presents a severe health burden, particularly in the developing world yet no vaccine is currently available. The parasites enter the human host through the bite of the female Anopheles mosquito and first infect liver hepatocytes, before moving to the blood infection that causes all disease. During liver stage development, parasites protect their home in the host hepatocyte by preventing programmed cell death (apoptosis) of the infected cell. Genetically attenuated parasite (GAP) strains that induce sterile immunity in mice have been developed, and it was shown for one of these strains that it cannot control host cell apoptosis. The mechanism of the inhibition of apoptosis by wildtype parasites, however, has not been elucidated. I will first fully delineate the apoptotic phenotype of hepatocytes infected with wildtype parasites and GAPs using a variety of phenotypic assays. Next, I plan to monitor a number of candidate signaling proteins in hepatocytes in response to both wildtype and GAP infections. This will allow us to identify candidate genes that are differentially activated in response to pro-apoptotic attenuated parasites and anti-apoptotic wildtype parasites. Finally, I propose to further investigate candidate genes that are differentially regulated using a cell culture model, as well as immunization and challenge experiments in mice. This study will lead to the discovery of hepatocyte proteins critical to modulating the inhibition of apoptosis by wildtype parasites. Since infected apoptotic cells are a better stimulus for the immune system than surviving cells, inhibiting these host proteins may cause the induction of apoptosis by wildtype parasites and might also enhance immunity induced by live-attenuated vaccines. Altering the hepatocyte response to infection could convert a wildtype, disease promoting parasite into one that promotes protective immunity and might thus inform new intervention strategies at the early stage of malaria infection. PUBLIC HEALTH RELEVANCE: Malaria presents a major public health burden, particularly in the developing world. The liver stage of malaria is an attractive target for intervention since live-attenuated vaccines that arrest at this stage prevent further infection. This application seeks to investigate the mechanism and role of host cell programmed cell death in wildtype infection and infection with live-attenuated vaccine strains.