Trypanosoma cruzi is a blood and tissue parasite that affects millions of individuals causing significant human morbidity and mortality. Basic understanding of the role of the critical surface molecules that participate in the first step of T. cruzi infection may provide novel targets for therapy. Our long-range goal is to understand the molecular mechanisms that allow T. cruzi to infect mammalian cells and cause disease, so that specific molecular intervention strategies can be developed against T. cruzi infection. The objective of this application is to identify which host cell receptors mediate T. cruzi binding to mammalian cells, when receptor-mediated signaling pathways contribute to infection. The hypothesis of this application is that T. cruzi gp83, a ligand molecule that the parasite uses to attach to mammalian cells, binds to the lectin-like oxidized low-density lipoprotein receptor (LOX-1) of mammalian host cells to mediate trypanosome attachment, thereby activating signaling events leading to initial infection and pathogenesis. We have formulated this hypothesis based on strong preliminary results, showing that interruption of LOX-1 gene by gene trapping or silencing LOX-1 gene by RNAi inhibits T. cruzi binding to cells and infection, whereas over-expression of LOX-1 in cells causes over-attachment of trypanosomes to cells and increased infection. Supporting also this hypothesis are our findings showing that gp83 specifically binds to LOX-1 and that we have identified critical regions on gp83 and LOX-1 that interact with each other to apparently mediate T. cruzi attachment leading to parasite entry. We will test our central hypothesis by pursuing the following specific aims: (1) to determine the structural-function relationships of the LOX-1-gp83 interaction;(2) to determine the LOX-1- dependent signaling pathways that mediate trypanosome gp83-dependent infection;and (3) to determine the in vivo role of the LOX-1 gene in the process of T. cruzi infection and pathogenesis using a novel LOX-1 knock out mouse model and a novel transgenic mouse model over-expressing LOX-1. Mutations, deletions and substitutions in critical regions of LOX-1 and gp83 will be performed to identify the motifs in each interacting molecule involved in T. cruzi binding to cells. Computational modeling of the trypanosome gp83 and the interacting peptide loop from the extracellular domain of LOX-1 will be determined. The mechanism underlying the novel gp83-LOX-1 signal transduction pathway leading to regulation of laminin ?-1 expression and infection will be elucidated using LOX-1(-/-) cells and LOX(+/+) cells. We will use our novel mouse models that over-express LOX-1 or that are null for LOX-1 expression to provide definitive in vivo tools to understand the other complementary mechanisms that contribute to trypanosome infection (in the LOX-1 null animals) and the mechanisms by which LOX-1 mediates infection (in the over-expressing animals).