Attenuation of Tau Hyperphosphorylation by Chronic Toxoplasma gondii Infection in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) peptide accumulation and tau protein-mediated neurodegeneration, and neuroinflammation is increasingly recognized as a major process associated with tau pathology. Chronic Toxoplasma gondii infection reduces amyloid accumulation in AD models through immune modulation, but its stage-specific associations with tau-related pathology remain unclear. Here, we investigated how chronic T. gondii infection is associated with tau-related molecular and neuropathological changes in the 5XFAD AD mouse model. At 40 weeks post-infection, we profiled transcriptomic changes and evaluated Aβ-associated (21 genes), Aβ/tau-shared (22 genes), and tau-associated (21 genes) pathological programs together with p-tau immunoreactivity in brain sections. Chronic infection was associated with selective modulation of molecular networks linked to neuroimmune signalling and tau-related pathways rather than broad suppression of AD-related gene expression. Among tau-related pathological stages, the neuroinflammation-related amplification module linking Aβ and tau exhibited the most prominent transcriptomic change in T. gondii-infected AD mice, whereas upstream kinase-related initiation pathways and downstream toxin conversion or accumulation-related processes changed relatively minimally. These transcriptomic changes were accompanied by a marked reduction in phosphorylated tau load at the tissue level. Collectively, these findings suggest that chronic T. gondii infection is associated with selective modulation of tau-related pathogenic programs and reduced p-tau burden in the 5XFAD brain.