Interaction networks of intracellular pathogens and their host cells are complex and predicted to be adaptive in promoting pathogen survival. During malaria parasite intrahepatocytic liver stage infection, parasites protect their host hepatocyte by preventing its death and fully exploit the host cell resources for growth and replication. The host hepatocyte molecular signaling landscape that undergirds successful liver stage replication has not been elucidated, yet it is highly medically relevant. We will use wild-type and attenuated parasite strains that arrest at different points after hepatocyte infection as a tool to investigat the differences between how healthy, wild-type parasites manipulate their host cell and how attenuated parasites, which are cleared from the liver shortly after arrest, are unable to do so. I this proposal, we propose experiments that fully delineate the pro- apoptotic milieu that the parasite can evade, and what intrinsic and extrinsic perturbations lead to the demise of even a wild-type parasite. Next, we will expand upon our already intriguing molecular dataset by extensively interrogating signaling proteins in hepatocytes in response to both wild-type and attenuated parasites using protein lysate microarrays, an approach that allows us to monitor hundreds of protein and post-translational modification levels using lysates derived from ~10,000 liver stage-infected hepatocytes. We propose monitoring hepatocyte signals not only in response to rodent malaria infection, but also in response to the most deadly human malaria parasite, Plasmodium falciparum, using infected hepatocytes from a mouse with a humanized liver. In preliminary studies, we have recently correlated the down-regulation of the tumor suppressor gene p53 with successful Plasmodium liver stage infection, and have demonstrated that artificially increasing p53 levels can eliminate liver stage parasites. We plan to further elucidate the mechanism behind the parasite's dependence on low host p53 for survival. Finally, we investigate the role that BH3-domain containing proteins in the mitochondria of hepatocytes play in malaria parasite liver-stage infection and ask if they are targeted by the parasite to prevent host cell apoptosis. The proposed studies will lead to a more comprehensive understanding of the hepatocyte signaling landscape critical to modulating the host response to Plasmodium liver stage parasite infection, including unparalleled understanding of parasites that infect humans and that impact human health. Accomplishing our aims opens the possibility of altering the hepatocyte signaling landscape with small-molecules that could prevent a wild-type parasite from progressing to symptomatic erythrocyte infection. Such a host-based approach for prophylaxis is novel and will circumvent the massive problem of continuously developing resistance to standard antimalarial drugs. This approach is further fostered by the fact that many hepatocyte proteins are already targets of known therapeutic inhibitors. Perturbations of hepatocyte signaling by a complex intracellular pathogen might also reveal new intrinsic features of the signaling system within hepatocytes.
The complex web of signals that arise from malaria parasite development within a host hepatocyte is highly medically relevant, as malaria kills more than one million people annually. This proposal seeks to investigate the molecular signals by which the hepatocyte and intracellular pathogen interact over the course of the parasite's liver stage development.
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|Kaushansky, A; Metzger, P G; Douglass, A N et al. (2013) Malaria parasite liver stages render host hepatocytes susceptible to mitochondria-initiated apoptosis. Cell Death Dis 4:e762|