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In Alzheimer's disease, Aβ deposits are considered the initial cardinal events that induce tauopathy secondarily. However, the relationship between Aβ amyloidosis and tauopathy has not been determined in detail. We produced double transgenic mice, 2×TgTau(+/-) APP(+/-) , by mating Tg2576 mice that exhibit Aβ amyloidosis and TgTauP301L mice that show tauopathy, and statistically analyzed the effect of Aβ accumulation on tauopathy. There was no significant difference in theprogression of Aβ accumulation among 2×TgTau(+/-) APP(+/-) and 1×TgTau(-/-) APP(+/-) , and tau accumulation among 2×TgTau(+/-) APP(+/-) and 1×Tg Tau(+/-) APP(-/-) . The appearance rates of phosphorylated tau developing in neurons and processes were significantly accelerated in 2×TgTau(+/-) APP(+/-) mice compared with those in 1×TgTau(+/-) APP(-/-) mice at 23 months of age. Accumulation of phosphorylated and confomationally altered tau and GSK3β in neuronal processes was accelerated in the white matter in 2×TgTau(+/-) APP(+/-) . The level of phosphorylated tau in the sarkosyl-insoluble fraction was increased in 2×TgTau(+/-) APP(+/-) brains compared with that in 1×TgTau(+/-) APP(-/-) brains. Thus, Aβ amyloid partially enhances tauopathy through accumulation of insoluble, phosphorylated, and conformationally changed tau in neuronal cytoplasm and processes in the late stage.

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TgTauP301L mice that overexpress the mutant human tauP301L present in FTDP-17 reproduce neurofibrillary tangles (NFTs), neuronal cell losses, memory disturbance, and substantial phenotypic variation. To demonstrate factors responsible for NFT formation and neuronal cell losses, sets of TgTauP301L for comparison with or without NFTs and neuronal cell losses were studied with oligonucleotide microarrays. Gene expressions were altered in biological pathways, including oxidative stress, apoptosis, mitochondrial fatty acid betaoxidation, inflammatory response pathway, and complement and coagulation cascade pathways. Among 24 altered genes, increased levels of apolipoprotein D (ApoD) and neuronal PAS domain protein 4 (Npas4) and decreased levels of doublecortin (DCX) and potassium channel, voltage-gated, shaker-related subfamily, β member 1 (Kcnab1) were found in the TgTauP301L with NFTs and neuronal cell losses, Alzheimer's brains, and tauopathy brains. Thus, many biological pathways and novel molecules are associated with NFT formation and neuronal cell losses in tauopathy brains.

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