Disruption of Epidermal Growth Factor Receptor Signaling in RPE Cells Increases Resistance to Ocular Toxoplasmosis

The in vivo role of RPE cells in ocular toxoplasmosis is poorly understood. Toxoplasma gondii activates Epidermal growth factor receptor (EGFR) to avoid autophagic killing. We examined the in vivo role of RPE using mice with dominant negative (DN) EGFR in RPE. We examined whether EGFR blockade in RPE increased resistance to ocular toxoplasmosis, induced autophagy-dependent killing of T. gondii, and modulated retinal invasion by T. gondii.

We bred mice expressing tetracycline-repressible transactivator under the control of MART-1 (RPE promotor) with mice expressing the tetracycline operator upstream of DN EGFR. Mice were infected with T. gondii tissue cysts. Histopathology and T. gondii B1 gene expression (qPCR) were examined. Retinal invasion by T. gondii was examined after intravenous challenge with the parasite. RPE were infected with T. gondii tachyzoites followed by assessment of parasite load and expression of LC3 and LAMP-1 (immunofluorescence).

Mice with DN EGFR in RPE exhibited lower parasite load and histopathology that became evident at 4 weeks post infection. No difference in parasite load was noted during hematogenous invasion of the retina by T. gondii. RPE with DN EGFR exhibited spontaneous recruitment of LC3 and LAMP-1 around intracellular parasites and toxoplasmacidal activity that was dependent on the autophagy protein ULK-1 and lysosomal enzymes.

DN EGFR in the RPE increases resistance against ocular toxoplasmosis, an effect that would occur after retinal invasion by T. gondii. Protection is accompanied by autophagic killing of T. gondii in RPE. This report provides the first evidence that RPE can protect against ocular toxoplasmosis.