Establishment of zebrafish as an animal model for Tauopathy research and drug screening

Tau protein is a tubulin-binding protein, which plays important roles in the formation and stability of the microtubule. Mutations in the tau gene are associated with familial forms of frontotemporal dementia with Parkinsonism linked to chromosome-17 (FTDP-17). Neurofibrillary tangles (NFTs) of Tau and extracellular plaques containing amyloid-β (Aβ) are found in the brain of Alzheimer’s disease (AD) patients. Transgenic models, including those of zebrafish, have been employed to elucidate the mechanisms by which Tau protein causes neurodegeneration. In this study, a transient expression system was established to express GFP fusion proteins of zebrafish and human Tau under the control of a neuron-specific HuC promoter. The expression of Tau-GFP was observed to cause high levels of neuronal death which could be directly traced in vivo. Multiple signaling factors, such as Bcl2-L1, Nrf2, and GDNF, were found to effectively protect neuronal cells expressing Tau-GFP from death. Treatment with compounds that induce anti-oxidative or neurotrophic effects also resulted in a similar neuronal protective effect and maintained human Tau-GFP protein in a phosphorylated state, as detected by antibodies pT212 and AT8. Therefore, we used this model to screen 400 herbal extracts and found 45 of them to be effective on reducing Tau-GFP-induced neuronal death. One of the effective herbal extracts is the Tripterygium wilfordii. HPLC analysis and functional assay demonstrated that epicatechin (EC) is the major compound of Tripterygium wilfordii stem extract to decrease the neurotoxicity induced by Tau-GFP. ARE (antioxidant response elements)-luciferase reporter gene assay is usually used to detect the activity of Nrf2. We used the assay to demonstrate that EC could increase the activity of Nrf2 in zebrafish. These data suggest that EC from the Tripterygium wilfordii stem extract could diminish Tau-GFP-induced neuronal death through the activation of Nrf2.