Tauopathies are characterized by the intraneuronal inclusions of hyperphosphorylated tau in human brain. Tau is a microtubule-associated protein, which stabilizes the microtubules cytoskeleton and regulates the dynamic of tubulin assembly. Recent studies have demonstrated that mutations in certain sites of Tau that associated with autosomal dominant tauopathy FTDP-17 (frontotemporal dementia with parkinsonism linked to chromosome 17) can lead to hyperphosphorylated tau aggregates in the neurons. While Tau protein phosphorylation is the major focus of tauopathies studies, several reports found that Tau-induced cytotoxicity could be uncoupled with its phosphorylation state. Here, we have employed a well-characterized Drosophila model of tauopathy to investigate whether the toxicity of tau is due to the cleavage by Caspases. Overexpression of human tau in fly recapitulates the features of tauopathies, and the phenotype could be suppressed by RNA interference (RNAi)-mediated knockdown of selected Drosophila Caspases. Surprisingly, we observe that under the condition of the equivalent expression of wild type tau and tau with mutation of a Caspase cleavage site (TauD421A), the eye phenotype is strikingly mild in TauD421A as compared to the Tauwt, suggesting that the processing of tau by caspase is crucial for the tau-mediated cytotoxicity. Our data provide an important insight into tauopathies and help to understand the molecular mechanism of tau-related neurodegeneration.

[1] Cleveland, D.W., Hwo, S.Y., Kirschner, M.W., 1977. Purification of tau, a microtubule-associated protein that induces assembly of microtubules from purified tubulin. J. Mol. Biol. 116, 207–225.
[2] Weingarten, M.D., Lockwood, A.H., Hwo, S.Y., Kirschner, M.W., 1975. A protein factor essential for microtubule assembly. Proc. Natl. Acad. Sci. U. S. A. 72, 1858–1862.
[3] Andreadis, A., Brown, W.M., Kosik, K.S., 1992. Structure and novel exons of the human tau gene. Biochemistry 31, 10626–10633.
[4] Buee, L., Bussiere, T., Buee-Scherrer, V., Delacourte, A., Hof, P.R., 2000. Tau protein isoforms, phosphorylation and role in neurodegenerative disorders. Brain Res. Brain Res. Rev. 33, 95–130.
[5] Drechsel DN, Hyman AA, Cobb MH, Kirschner MW. 1992. Modulation of the dynamic instability of tubulin assembly by
the microtubule-associated protein tau. Mol. Biol. Cell 3(10):1141–54
[6] Bramblett GT, Goedert M, Jakes R, Merrick SE, Trojanowski JQ, Lee VM-Y. 1993. Abnormal tau phosphorylation at Ser396 in Alzheimer’s disease recapitulates development and contributes to reduced microtubule binding. Neuron 10(6):1089–99
[7] Biernat J, Gustke N, Drewes G, Mandelkow EM, Mandelkow E. 1993. Phosphorylation of Ser262 strongly reduces binding of tau to microtubules: distinction between PHF-like immunoreactivity and microtubule binding. Neuron 11(1):153–63
[8] Foster NL, Wilhelmsen K, Sima AA, Jones MZ, D’Amato CJ, et al. 1997. Frontotemporal dementia and parkinsonism linked to chromosome 17: a consensus conference. Ann. Neurol. 41(6):706–15
[9] Hutton M, Lendon CL, Rizzu P, Baker M, Froelich S, et al. 1998. Association of missense and 5′ -splice-site mutations in tau with the inherited dementia FTDP-17. Nature 393(6686):702–5
[10] Poorkaj P, Bird TD, Wijsman E, Nemens E, Garruto RM, et al. 1998. Tau is a candidate gene for chromosome 17 frontotemporal dementia. Ann. Neurol. 43(6):815–25
[11] Spillantini MG, Bird TD, Ghetti B. 1998a. Frontotemporal dementia and parkinsonism linked to chromosome 17: a new group of tauopathies. Brain Pathol. 8(2):387–402
[12] A.A.F. Sima, R. Defendini, C. Keohane, C. D’Amato, N.L. Foster, P.
Parchi, M. Gambetti, T. Lynch, K.C. Wilhelmsen, The neuropathol-
ogy of chromosome 17-linked dementia, Ann. Neurol. 39 (1996)
734 – 743.
[13] Basurto-Islas, G., Luna-Munoz, J., Guillozet-Bongaarts, A.L., Binder, L.I., Mena, R., Garcia-Sierra, F., 2008. Accumulation of aspartic acid 421- and glutamic acid 391-cleaved tau in neurofibrillary tangles correlates with progression in Alzheimer disease.J. Neuropathol. Exp. Neurol. 67, 470–483.
[13] Mondragon-Rodriguez, S., Basurto-Islas, G., Santa-Maria, I., Mena, R., Binder, L.I., Avila, J., Smith, M.A., Perry, G., Garcia-Sierra, F., 2008. Cleavage and conformational changes of tau protein follow phosphorylation during Alzheimer’s disease. Int. J. Exp. Pathol. 89, 81–90.
[14] Horowitz, P.M., Patterson, K.R., Guillozet-Bongaarts, A.L., Reynolds, M.R., Carroll, C.A., Weintraub, S.T., Bennett, D.A., Cryns, V.L., Berry, R.W., Binder, L.I., 2004. Early N-terminal changes and caspase-6 cleavage of tau in Alzheimer’s disease. J. Neurosci. 24, 7895–7902.
[14] Saito, M., Chakraborty, G., Mao, R.F., Paik, S.M., Vadasz, C., 2010. Tau phosphorylation and cleavage in ethanol-induced neurodegeneration in the developing mouse brain. Neurochem. Res. 35, 651–659.
[15] Alix de Calignon, Leora M. Fox, Rose Pitstick, George A. Carlson, Brian J. Bacskai, Tara L. Spires-Jones & Bradley T. Hyman,2010. Caspase activation precedes and leads to tangles Nature. 464, 1201-1204.
[16] Guillozet-Bongaarts, A.L., Cahill, M.E., Cryns, V.L., Reynolds, M.R., Berry, R.W., Binder, L.I., 2006. Pseudophosphorylation of tau at serine 422 inhibits caspase cleavage: in vitro evidence and implications for tangle formation in vivo. J. Neurochem. 97, 1005–1014.
[17] Park, S.Y., Ferreira, A., 2005. The generation of a 17 kDa neurotoxic fragment: an alternative mechanism by which tau mediates beta-amyloid-induced neurodegeneration. J. Neurosci. 25, 5365–5375.
[18] Helene Doerflinger, Richard Benton, Joshua M. Shulman and Daniel St Johnston. The role of PAR-1 in regulating the polarised microtubule cytoskeleton in the Drosophila follicular epithelium Development 130, 3965-3975.
[19] Soon Ji Yoo , Jun R. Huh, Israel Muro, Hong Yu, Lijuan Wang, Susan L. Wang, R. M. Renny Feldman, Rollie J. Clem, H.-Arno J. Muller & Bruce A. Hay. Hid, Rpr and Grim negatively regulate DIAP1 levels through distinct mechanisms. Nature Cell Biology 4, 416 - 424 (2002)
[20] Vikram Khurana, Yiran Lu, Michelle L. Steinhilb, Sean Oldham, Joshua M. Shulman, and Mel B. Feany. TOR-Mediated Cell-Cycle Activation Causes Neurodegeneration in a Drosophila Tauopathy Model Current Biology 16, 230–241 (2006).
[21] Michelle L. Steinhilb, Dora Dias-Santagata, Erin E. Mulkearns
Joshua M. Shulman, Jacek Biernat, Eva-Maria Mandelkow, Mel B. Feany. S/P and T/P Phosphorylation Is Critical for Tau Neurotoxicity in Drosophila Journal of Neuroscience Research 85:1271–1278 (2007).
[22]Chang HY., Ready DF. Rescue of photoreceptor degeneration in rhodopsin-null Drosophila mutants by activated Rac1. Science 290(5498):1978-80
[23]Sang TK., Ready DF. eyes closed, a Drosophila p47 homolog, is essential for photoreceptor morphogenesis. Development 129(1):143-54.
[24]Jackson GR, Wiedau-Pazos M, Sang TK, Wagle N, Brown CA, Massachi S, Geschwind DH. Human Wild-Type Tau Interacts with wingless Pathway Components and Produces Neurofibrillary Pathology in Drosophila. Neuron. 2002 May 16;34(4):509-19.
[25] Dawson HN, Ferreira A, Eyster MV, Ghoshal N, Binder LI, Vitek MP. Inhibition of neuronal maturation in primary hippocampal neurons from tau deficient mice. J Cell Sci. 2001 Mar;114(Pt 6):1179-87.
[26] Gordon P, Hingula L, Krasny ML, Swienckowski JL, Pokrywka NJ, Raley-Susman KM. The invertebrate microtubule-associated protein PTL-1 functions in mechanosensation and development in Caenorhabditis elegans. Dev Genes Evol. 2008 Oct;218(10):541-51. Epub 2008 Sep 19.
[27] Doerflinger H, Benton R, Shulman JM, St Johnston D. The role of PAR-1 in regulating the polarised microtubule cytoskeleton in the Drosophila follicular epithelium. Development. 2003 Sep;130(17):3965-75.
[28] Talmat-Amar Y, Arribat Y, Redt-Clouet C, Feuillette S, Bouge AL, Lecourtois M, Parmentier ML. Important neuronal toxicity of microtubule-bound Tau in vivo in Drosophila. Hum Mol Genet. 2011 Jun 24.
[29]Chatterjee S, Sang TK, Lawless GM, Jackson GR. Dissociation of tau toxicity and phosphorylation: role of GSK-3beta, MARK and Cdk5 in a Drosophila model. Hum Mol Genet. 2009 Jan 1;18(1):164-77.