Cerebral malaria (CM) is the leading cause of death in children infected with Plasmodium falciparum. Approximately 20% of children admitted to hospital with CM will die. Breakdown of the blood brain barrier (BBB) is a key feature of CM. Although the mechanisms behind this are not fully understood, it is clear that the barrier can be disrupted by two mechanisms: apoptosis of endothelial cells and opening of the tight junctions. The Plasmodium berghei ANKA mouse model of cerebral malaria (experimental cerebral malaria, ECM) shares many features of human CM and has demonstrated a critical role for T cells in the development of this condition. Previous work has suggested that cytotoxic T cells accumulate in the brain in response to inflammation induced by sequestered Plasmodium infected red blood cells (iRBCs). Eph receptors are the largest family of receptor tyrosine kinases. Here we propose that EphA2 is a critical molecule that facilitates endothelial cell apoptosis by targeting ephrin A ligand-expressing T cell adhesion. This, along with binding of soluble ephrin A ligands, initiates signaling pathways that induce opening of the tight junctions between endothelial cells. The long-term goal of this project is to develop an adjunct therapy for CM based on blocking the EphA2 molecule. Using the P. berghei ANKA model the objective of this proposal is to determine the mechanism by which EphA2 leads to breakdown of the BBB during ECM. Analysis of the expression of ephrin A ligands on PBMCs from children in Cameroon who have uncomplicated or cerebral malaria will determine whether ephrin A ligand expression (soluble and on peripheral T cells) is correlated with the development of CM. The central hypothesis of this proposal is that EphA2 is upregulated on brain endothelial cells upon inflammation and mediates adhesion of ephrin A ligand T cells which in turn facilitates degranulation and endothelial apoptosis. EphA2-mediated signaling pathways will be initiated by binding of T cell-bound and soluble ephrin A ligands and this will mediate opening of tight junctions in the BBB. Our preliminary data shows that EphA2-/- mice have an intact BBB and are resistant to death during ECM. We also show that there is modulation of EphA2 and ephrin A ligands on brain endothelial cells and T cells, respectively. The rationale for this research is that EphA2 could be a novel target for the development of an adjunctive therapy against CM. The central hypothesis will be tested by pursuing the following three specific aims: 1) Test the hypothesis that ligation of EphA2 expressed on brain endothelial cells induces opening of the endothelial junctions during CM 2) Test the hypothesis that EphA2 targets CD8+T cell degranulation and brain endothelial cell apoptosis in CM and 3) Demonstrate that ephrin A ligand expression in the circulation (soluble and cell surface bound) is elevated in P. falciparum-infected children with symptoms of CM. The approach is innovative because a role for Eph receptors in cerebral malaria has never been proposed. This research is significant because identification of new targets for adjunct therapies for use in malaria are urgently needed.
The proposed research is relevant to public health because EphA2 is a completely novel target for an adjunc- tive therapy to limit breakdown of the blood brain barrier - a key event in cerebral malaria. This in turn has the potential to save the lives of >0.5 million children with life-threatening symptoms of this condition every year. Thus, the proposed research is relevant to the part of the NIH's mission that pertains to developing fundamen- tal knowledge that will help to reduce the burdens of human disease and disability.
