Abstract
Infection with Toxoplasma gondii (T. gondii) protozoan can lead to toxoplasmosis and has high seroprevalence in the human population. T. gondii can cross the Blood-retinal barrier, leading to ocular toxoplasmosis (OT), which can severely impair vision. Our group demonstrated microcirculatory alterations and reduced angiogenesis in mouse brains after acquired T. gondii infection, suggesting that such alterations may also occur in OT. This work aims to analyze the effects of acquired T. gondii in vivo infection on the retina and its vasculature. For the acquired OT model, C57BL/6 mice were intragastrically inoculated with two ME49 strain cysts and analyzed 10, 20, and 30 days post-infection (dpi). Clinical parameters, parasitic load, cytokine profiles, retinal vasculature, endothelial activation, vascular function, and glial activation were assessed. Infected mice exhibited significant weight loss and reduced chow consumption. Tachyzoites were detected by RT-qPCR at 10 dpi, while bradyzoites’ signal appeared at 20 and 30 dpi. Infected mice had elevated serum pro-inflammatory cytokines TNF-α, IFN-γ, and IL-6 at 10 dpi, transitioning to increased IL-4 and IL-10 at 20 dpi, returning to basal levels at 30 dpi. Retinal blood flow and functional capillary density were increased, while structural changes in the vasculature, such as vessel length and area, varied over time. Collagen IV expression increased at 20 and 30 dpi, indicating vascular remodeling. Angiogenic markers VEGFR1 and Notch1 expression were consistently downregulated, and Delta-like4 expression decreased at 20 and 30 dpi. Endothelium-leukocyte interaction, as assessed by rolling and adherent leukocytes, was increased in infected retinal venules. Retinal endothelial function was impaired, with reduced vasodilation response to acetylcholine and alterations in tight junction markers ZO-1, claudin5 and occludin. Increased glial activation was observed, with elevated GFAP immunoreactivity and expression at 20 and 30 dpi. CX3CR1 expression was elevated at all times studied, indicative of microglial activation, accompanied with Arg1 and iNOS upregulation and STAT3 phosphorylation, corroborating neuroinflammatory responses. T. gondii infection in mice induces systemic and retinal inflammation, leading to significant changes in the retinal vasculature and impaired endothelial function. These findings contribute to a better understanding of OT pathophysiology, enabling the design of future therapeutic strategies.