PROJECT SUMMARY Toxoplasma gondii is an obligate intracellular parasite and causative infectious agent of ocular toxoplasmosis (OT). This chronic, recurrent infection is the top cause of infectious retinitis worldwide and can lead to blindness in one eye in 25% of patients. Current treatment does not positively influence visual outcomes. T. gondii resides in a parasitophorous vacuole and induces mechanisms that block autophagosome-lysosome formation from targeting the parasite in infected cells. After parasite invasion, T. gondii activates the host cell signaling molecule, Src, which drives prolonged autophosphorylation of the EGFR and activates the downstream autophagy inhibitor, Akt. Activated Akt persistently avoids autophagic targeting and survival within the cell. Previously, EGFR inhibition was shown to induce autophagic killing of T. gondii in approximately half of the cells and is partially protective against OT. This partial protection may be a result of partial Akt inhibition and the restricted expression of EGFR. Thus, Src is likely a better target because it appears to activate Akt independently of EGFR and is broadly and highly expressed in neural tissue and the retina. This project seeks to understand the host signaling mechanism utilized by T. gondii in cells lacking EGFR that prevent autophagy-mediated targeting of the parasite, to understand the molecular events triggered by Src inhibition that are responsible for selective targeting of T. gondii by autophagy, and to determine whether Src inhibition protects against OT. Our preliminary studies demonstrate that knockdown of Src induces parasite killing in cells lacking EGFR through an autophagy-mediated mechanism. Additionally, Src inhibition induces autophagic targeting that appears dependent on the activation of a protein kinase. Therefore, the central hypothesis of this proposal is that, even in the absence of EGFR, Src inhibition kills T. gondii due to protein kinase-dependent selective targeting by autophagosomes, and Src inhibition controls OT. Experiments proposed in Aim 1 will investigate the role of Src in preventing the autophagic killing of T. gondii in the absence of EGFR in vitro. Experiments proposed in Aim 2 will explore the role of protein kinase activation in selective parasite targeting by autophagosomes after Src inhibition. Aim 3 will explore the effects of Src inhibition on pre-established OT in vivo. Together these data will define mechanisms in which T. gondii inhibits autophagic targeting, explain how autophagy selectively targets the parasite and may be applied to improved treatment for OT.