HDAC6 mutations rescue human tau-induced microtubule defects in Drosophila

Abstract

Neurons from the brains of Alzheimer's disease (AD) and related tauopathy patients contain neurofibrillary tangles composed of hyperphosphorylated tau protein. Tau normally stabilizes microtubules (MTs); however, tau hyperphosphorylation leads to loss of this function with consequent MT destabilization and neuronal dysfunction. Accordingly, MT-stabilizing drugs such as paclitaxel and epothilone D have been shown as possible therapies for AD and related tauopathies. However, MT-stabilizing drugs have common side effects such as neuropathy and neutropenia. To find previously undescribed suppressors of tau-induced MT defects, we established a Drosophila model ectopically expressing human tau in muscle cells, which allow for clear visualization of the MT network. Overexpressed tau was hyperphosphorylated and resulted in decreased MT density and greater fragmentation, consistent with previous reports in AD patients and mouse models. From a genetic screen, we found that a histone deacetylase 6 (HDAC6) null mutation rescued tau-induced MT defects in both muscles and neurons. Genetic and pharmacological inhibition of the tubulin-specific deacetylase activity of HDAC6 indicates that the rescue effect may be mediated by increased MT acetylation. These findings reveal HDAC6 as a unique potential drug target for AD and related tauopathies.disease model | genetic study T au is a neuronal microtubule-associated protein (MAP) that binds to and stabilizes microtubules (MTs). However, in Alzheimer's disease (AD), frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), and other tauopathies, tau is hyperphosphorylated and aggregated into straight or paired helical filaments (PHFs) in the cell bodies and neurites of central neurons (1). In vitro biochemical studies demonstrated that hyperphosphorylated tau does not bind to MTs and thus does not promote MT stability (2, 3). Furthermore, mutations in tau lead to FTDP-17, and some of these mutations have been reported to reduce MT-tau binding affinity (4, 5), underscoring the importance of loss of normal MT-stabilizing function of tau in the pathogenesis of neurodegenerative tauopathies.MTs are disrupted in the brains of patients and animal models of tauopathies. For example, MT density was reduced in both hippocampal neurons of transgenic mice expressing V337M mutant human tau and the spinal ventral root axons of transgenic mice expressing the smallest isoform of human tau (6, 7). Furthermore, administration of the MT-stabilizing agents paclitaxel and epothilone D to human tau-expressing mice results in improved MT density and axonal integrity (8), as well as enhanced cognitive performance (9, 10). However, paclitaxel has poor blood-brain barrier (BBB) permeability and thus is unsuitable for clinical treatment of brain diseases. Epothilone D is BBB-permeable; however, as a general MT stabilizer and genotoxic agent, it may have side effects such as neuropathy and neutropenia.In this study, we aimed to find new strategies for mitigating tau toxicity by identifying...

Microtubule-severing protein Katanin regulates neuromuscular junction development and dendritic elaboration in Drosophila

“…Histone deacetylase 6 (HDAC6) antagonizes Katanin 60 in regulating synaptic growth A previous study on cultured mammalian cells reported that acetylated MTs are favored for severing by katanin (Sudo and Baas, 2010 Xiong et al, 2013). We confirmed the effects of HDAC6 on the MT acetylation by western analysis (Fig.…”

“…The spastin-null mutant spastin 5.75 was from N. Sherwood (Sherwood et al, 2004) and a UAS-spastin line was from K. Broadie (Trotta et al, 2004). The HDAC6 null mutant (HDAC6 KO ) and the UAS-HDAC6 line were from R. Jiao (Du et al, 2010), and two UAS lines expressing mutant HDAC6 with mutation H237A or H664A in the two deacetylase domains were described previously (Xiong et al, 2013). An RNAi line of Katanin 60 (v38369) was obtained from the Vienna Drosophila RNAi Center.…”

“…To define further the effects of HDAC6 on the severing ability of Katanin, we analyzed genetic interactions between Katanin 60 and HDAC6 by quantifying the intensities of perinuclear MT staining and the length of MT fibers in larval muscle cells, which are large and allow clear visualization of MT networks (Jin et al, 2009;Xiong et al, 2013;Yao et al, 2011). Katanin 60 17A mutant muscle cells had an unevenly distributed MT network and a significantly increased perinuclear MT intensity compared with wild-type cells (P<0.01; Fig.…”

“…To investigate whether the tubulin deacetylase activity of HDAC6 was responsible for the protection of MTs from severing by Katanin 60, we tested genetic interactions when Katanin 60 and wild-type or mutated HDAC6 disrupting the deacetylase activities were co-overexpressed. The effect on MT severing was examined for two HDAC6 mutants with mutations in either of the two deacetylase domains (DD), H237A in DD1 and H664A in DD2 [the latter disrupts the tubulin deacetylase activity specifically (Xiong et al, 2013)]. We found that co-overexpression of the H237A mutant rescued the MT defects caused by Katanin 60 overexpression as well as wild-type HDAC6, whereas the H664A mutant, expressed at similar levels as the H237A mutant (Xiong et al, 2013), did not (supplementary material MTs have been shown to regulate the formation of dendritic spines, the postsynaptic structures of excitatory synapses in the mammalian brain (Penzes et al, 2009;Jaworski et al, 2009) and synapse growth at Drosophila NMJ terminals (Conde and Cáceres, 2009;Jin et al, 2009;Nahm et al, 2013;Wang et al, 2007;Yao et al, 2011;Zhang et al, 2001).…”

<i>In Vivo</i> Screening of Traditional Medicinal Plants for Neuroprotective Activity against Aβ42 Cytotoxicity by Using <i>Drosophila</i> Models of Alzheimer’s Disease

“…8,15,16) Moreover, as Drosophila AD models show various and easily-quantifiable phenotypes, such as eye degeneration, developmental defects, shortened lifespan, locomotor defects, increased oxidative stress sensitivity, and learning and memory defects, they have been employed for finding genetic modifiers of AD-associated genes. [17][18][19][20][21][22][23] In addition, Drosophila AD models have been used to search and evaluate possible candidate drugs for AD.8) Recently, usage of Drosophila models has been extended to test the efficacy of traditional medicines, and successfully played a role in the analysis of their action mechanism at the molecular level.8) Our laboratory study revealed that SuHeXiang Wan, a traditional prescription, is neuroprotective against the cytotoxicity of Aβ42 by using Drosophila AD models. 24,25) …”