Deciphering the role of nuclear Tau and the Influence of ABeta oligomers. in neurons under physiological and stress conditions. – EPITAUDNA

- The functionality of Tau was studied in cellular models (wild type and KOTau primary neuronal cultures) and in vivo in animal models (wild type and KOTau mice).
- The DNA-binding regions of Tau were determined par Nuclear Magnetic Resonnance (RMN) in collaboration with Isabelle Landrieu (Villeneuve d’Ascq), the DNA sequences bound by Tau were determined using Chromatin ImmunoPrecipitaion (Chip) coupled or not to arrays designed for studying promoter regions.
- The nuclear localization of Tau was analyzed by biochemical technics (cellular fractionnation, confocale microscopy).
- mRNA expression was analyzed by bRT-qPCR.
- DNA integrity was analyzed by Comet assay and TUNEL assay.

In this study we characterized :
- The regions of Tau involved in Tau-DNA binding,
- The capacity of Tau to bind to specific sequences of genomic DNA in neurons
- The capacity of Tau to modulate transcription of genes associated either with DNA repair, neuronal functions altered during neurodegeneratives diseases, or pericentromeric DNA sequences transcribed in long non-coding RNAs.
- The regulatory role of Tau on the establishment of epigenetic mechanisms (post-translational modifications of histones).
The results obtained during this study will have a major impact in the understanding of the function of nuclear Tau. They clearly highlight a role for Tau in the transcription regulation of genes associated to neurodegenerative diseases like Alzheimer’s disease. Furthermore, they show a role for Tau on the regulation of long non-coding RNAs and the establishment of epigenetic marks modulating transcription.
The data obtained during this project constitute innovating results either submitted or in preparation for publication.
In future work, it will be imperative to assess if these important new nuclear functions of Tau are altered in vulnerable neurons during the physiopathology of Alzheimer’s disease, and notably, to evaluate the effect of Abeta peptide upon the nuclear functions of Tau.

The project EPITAUDNA is a basic research project coordinated by Marie-Christine Galas with Eliette Bonnefoy (CNRS, Paris) as a partner. The project began in January 2011 and lasted 36 months. ANR gave 370880 euros corresponding to the overall cost of the project.

- The role of Tau in the protection of DNA and RNA was observed in vivo in the mouse brain under physiological conditions and hyperthermic stress.
publication
- Violet M., L. Delattre, Tardivel M., A. Sultan, A. Chauderlier, Caillierez R, S Talahari, Nesslany F., B. Lefebvre, E. Bonnefoy, Condensation L., Galas MC. A major role for Tau in neuronal DNA and RNA in vivo protection under physiological and hyperthermic conditions. Submitted
- Landrieu et al (in preparation).
- Mansuroglu et al (in preparation).
- Mokrani et al (in preparation)..

Alzheimer disease (AD) is the only neurodegenerative disease where both Abeta and Tau pathologies are associated. Until today, the mechanisms underlying the interplay between Abeta and Tau pathologies remain unresolved. To decipher these mechanisms remains an essential point to understand the etiopathology of AD. Tau is mainly known as microtubule-associated protein. A recent study performed in collaboration between our two teams highlighted a new function of Tau as an essential nuclear key player in the neuronal early stress response. In this work, we reported that oxidative and heat stress (HS) induced a reversible accumulation of dephosphorylated Tau in nuclei of neurons. Further, we demonstrated that dephosphorylated nuclear Tau was able to bind DNA and preserve neuronal DNA integrity under stress condition. Contrary to HS, cold stress increased Tau phosphorylation, prevented nuclear Tau accumulation and induced DNA damage. Abeta oligomers are now known to be the actors of Abeta toxicity. Abeta toxicity has been demonstrated to be mediated by Tau but the mechanisms underlying this relationship remain poorly understood. Altogether, hyperphosphorylation of Tau induced by Abeta might likely prevent nuclear Tau accumulation and impair the DNA protective role of Tau in stress condition. Given the capacity of Tau to form protein-DNA complexes, we cannot exclude that nuclear Tau could affect gene expression in neurons either by directly binding to regulatory DNA sequences and/or through regulation of the epigenetics of neurons. Therefore prevention of nuclear Tau accumulation mediated by Abeta oligomers could also impair Tau-regulated gene expression in stress condition and contribute to the etiopathology of AD. The double aim of the present project is to further explore the role of nuclear Tau respect to gene expression regulation and specific epigenetic modifications in the differentiated neurons under physiological and stress conditions and to analyze the influence of Abeta oligomers on these mechanisms. The specific goals are the following : 1) Analyze the binding capacity of nuclear Tau to endogenous neuronal DNA under physiological and heat stress conditions. Using ChIP assays, we will first focus on the capacity of Tau to interact with some specific loci, such as those DNA sequences that are present on the nuclear compartments where Tau has been observed in neuroblastoma and non-neuronal cells. Secondly, using ChIP-on-chip technique, we will analyze the capacity of Tau to interact with DNA genome-wide with a special emphasis on promoter regions. Finally, we will try to determine the regions of Tau protein necessary to form protein-DNA complexes, using adenoviral vectors encoding either wild type or mutated forms of Tau. 2) Analyze the capacity of Tau to regulate gene expression. We will analyze the capacity of Tau to regulate gene expression respect to some specific loci (centromeric and pericentromeric sequences and rDNA genes). and we will analyze the effect of Tau genome-wide on the expression of mRNAs as well as on non-coding microRNAs using the corresponding microarrays. 3) Investigate the capacity of Tau to affect epigenetic mechanisms, mainly histone modifications. We will specially focus on the rate and distribution of diverse histone modifications (acetylation, methylation) marks associated to either gene silencing or transcriptional activation modifications. We will also analyze the effect of Tau on the expression and distribution of factors and cofactors regulating these histone modifications in neurons 4) Challenge the effect of Abeta oligomers on stress-induced nuclear Tau accumulation, Tau-DNA complex formation and nuclear Tau function. We will test if Abeta oligomers-induced Tau hyperphosphorylation impairs the ability of Tau to accumulate into the nuclei of neurons under stress condition. The capacity of Tau to bind DNA, regulate gene expression and modulate epigenetic mechanisms will also be evaluated.