Toxoplasma gondii alters NMDAR signaling and induces signs of Alzheimer’s disease in wild-type, C57BL/6 mice

Abstract Background Alzheimer’s disease (AD) is a progressive neurodegenerative disease associated with cognitive decline and complete loss of basic functions. The ubiquitous apicomplexan parasite Toxoplasma gondii (T. gondii) infects up to one third of the world’s population and is implicated in AD. Methods We infected C57BL/6 wild-type male and female mice with 10 T. gondii ME49 cysts and assessed whether infection led to behavioral and anatomical effects using immunohistochemistry, immunofluorescence, Western blotting, cell culture assays, as well as an array of mouse behavior tests. Results We show that T. gondii infection induced two major hallmarks of AD in the brains of C57BL/6 male and female mice: beta-amyloid (Aβ) immunoreactivity and hyperphosphorylated Tau. Infected mice showed significant neuronal death, loss of N-methyl-d-aspartate receptor (NMDAR) expression, and loss of olfactory sensory neurons. T. gondii infection also caused anxiety-like behavior, altered recognition of social novelty, altered spatial memory, and reduced olfactory sensitivity. This last finding was exclusive to male mice, as infected females showed intact olfactory sensitivity. Conclusions These results demonstrate that T. gondii can induce advanced signs of AD in wild-type mice and that it may induce AD in some individuals with underlying health problems

Additional file 2: of Toxoplasma gondii alters NMDAR signaling and induces signs of Alzheimer’s disease in wild-type, C57BL/6 mice

Figure S2. T. gondii induces Aβ immunoreactivity. A. Representative × 20 magnification images from control brains and brains from mice orally infected with 10 ME49 cysts for 30 (top) and 60 days (bottom). The inset shows a close-up image at × 63 magnification. Tissue sections were fixed and stained with an anti-T. gondii antibody BAG1 (red) and counterstained with DAPI (blue). A comparable brain section from the same animal was stained with a mouse anti-beta amyloid antibody (green) and counterstained with DAPI (blue). Scale bar: 50 μm. B. Representative × 20 magnification images from control brains and brains from mice orally infected with 10 ME49 cysts for 60 days. Tissue sections from the same animals used in A were fixed and stained with a human anti-beta amyloid antibody, 6E10 (green) and an anti-T. gondii antibody BAG1 (red) and counterstained with DAPI (blue). A separate set of sections from T. gondii-infected brains were stained with isotype controls (mouse IgG and Rabbit IgG) to control for the specificity of the 6E10 and BAG-1 antibodies, respectively. A different set of sections from T. gondii-infected brains were stained for fluorescent secondary antibodies (anti-mouse 488 and Texas-Red anti-rabbit) to control for their specificity. Scale bar: 50 μm. (JPEG 303 kb

Additional file 1: of Toxoplasma gondii alters NMDAR signaling and induces signs of Alzheimer’s disease in wild-type, C57BL/6 mice

Figure S1. Specificity of the 6E10 and BAG-1 antibodies. Representative × 20 magnification images from control brains and brains from mice orally infected with 10 ME49 cysts for 60 days. Brains were collected after perfusion with ice-cold PBS. Control and infected brains were fixed and stained with a human anti-beta amyloid antibody, 6E10 (green) and an anti-T. gondii antibody BAG1 (red) and counterstained with DAPI (blue). A separate set of sections from T. gondii-infected brains were stained with isotype controls (mouse IgG and Rabbit IgG) to control for the specificity of the 6E10 and BAG-1 antibodies, respectively. A different set of sections from T. gondii-infected brains were stained for fluorescent secondary antibodies (anti-mouse 488 and Texas-Red anti-rabbit) to control for their specificity. Scale bar: 50 μm. (JPEG 114 kb

Additional file 5: Figure S4. of Non-alcoholic fatty liver disease induces signs of Alzheimer’s disease (AD) in wild-type mice and accelerates pathological signs of AD in an AD model

Positive pixel count of oil O-red staining in the liver of WT and APP-Tg mice fed with SD or HFD for 1 year. Fixed liver sections were stained with oil O-red and positive pixels (red) were counted using Zen Software. **indicates p < 0.01. (two-way ANOVA with Bonferroni post-test, n = 2)

Additional file 2: Figure S1. of Non-alcoholic fatty liver disease induces signs of Alzheimer’s disease (AD) in wild-type mice and accelerates pathological signs of AD in an AD model

Brain sections from SD and HFD-fed WT mice at 2 months stained with Thioflavin S (Green). Sections were counter-stained with DAPI to visualize nuclei. Scale bar = 200 μm