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ABSTRACT: ATM and p53, effectors of the DNA damage checkpoint, are generally considered pro-apoptotic in neurons. We show that DNA damage and checkpoint activation occurs in postmitotic neurons in animal models of tauopathy, neurodegenerative disorders that include Alzheimer's disease. Surprisingly, checkpoint attenuation potently increases neurodegeneration through aberrant cell cycle re-entry of postmitotic neurons. These data suggest an unexpected neuroprotective role for the DNA damage checkpoint in tauopathies.
Aging cell 12/2011; 11(2):360-2. · 7.55 Impact Factor
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Frank Soldner,
Josée Laganière,
Albert W Cheng,
Dirk Hockemeyer,
Qing Gao,
Raaji Alagappan, Vikram Khurana,
Lawrence I Golbe,
Richard H Myers,
Susan Lindquist,
Lei Zhang,
Dmitry Guschin,
Lauren K Fong,
B Joseph Vu,
Xiangdong Meng,
Fyodor D Urnov,
Edward J Rebar,
Philip D Gregory,
H Steve Zhang,
Rudolf Jaenisch
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ABSTRACT: Patient-specific induced pluripotent stem cells (iPSCs) derived from somatic cells provide a unique tool for the study of human disease, as well as a promising source for cell replacement therapies. One crucial limitation has been the inability to perform experiments under genetically defined conditions. This is particularly relevant for late age onset disorders in which in vitro phenotypes are predicted to be subtle and susceptible to significant effects of genetic background variations. By combining zinc finger nuclease (ZFN)-mediated genome editing and iPSC technology, we provide a generally applicable solution to this problem, generating sets of isogenic disease and control human pluripotent stem cells that differ exclusively at either of two susceptibility variants for Parkinson's disease by modifying the underlying point mutations in the α-synuclein gene. The robust capability to genetically correct disease-causing point mutations in patient-derived hiPSCs represents significant progress for basic biomedical research and an advance toward hiPSC-based cell replacement therapies.
Cell 07/2011; 146(2):318-31. · 32.40 Impact Factor
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ABSTRACT: Expansion of the lysosomal system, including cathepsin D upregulation, is an early and prominent finding in Alzheimer's disease brain. Cell culture studies, however, have provided differing perspectives on the lysosomal connection to Alzheimer's disease, including both protective and detrimental influences. We sought to clarify and molecularly define the connection in vivo in a genetically tractable model organism. Cathepsin D is upregulated with age in a Drosophila model of Alzheimer's disease and related tauopathies. Genetic analysis reveals that cathepsin D plays a neuroprotective role because genetic ablation of cathepsin D markedly potentiates tau-induced neurotoxicity. Further, generation of a C-terminally truncated form of tau found in Alzheimer's disease patients is significantly increased in the absence of cathepsin D. We show that truncated tau has markedly increased neurotoxicity, while solubility of truncated tau is decreased. Importantly, the toxicity of truncated tau is not affected by removal of cathepsin D, providing genetic evidence that modulation of neurotoxicity by cathepsin D is mediated through C-terminal cleavage of tau. We demonstrate that removing cathepsin D in adult postmitotic neurons leads to aberrant lysosomal expansion and caspase activation in vivo, suggesting a mechanism for C-terminal truncation of tau. We also demonstrate that both cathepsin D knockout mice and cathepsin D-deficient sheep show abnormal C-terminal truncation of tau and accompanying caspase activation. Thus, caspase cleavage of tau may be a molecular mechanism through which lysosomal dysfunction and neurodegeneration are causally linked in Alzheimer's disease.
PLoS Genetics 07/2010; 6(7):e1001026. · 8.69 Impact Factor
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ABSTRACT: In ageing populations, neurodegenerative diseases increase in prevalence, exacting an enormous toll on individuals and their communities. Multiple complementary experimental approaches are needed to elucidate the mechanisms underlying these complex diseases and to develop novel therapeutics. Here, we describe why the budding yeast Saccharomyces cerevisiae has a unique role in the neurodegeneration armamentarium. As the best-understood and most readily analysed eukaryotic organism, S. cerevisiae is delivering mechanistic insights into cell-autonomous mechanisms of neurodegeneration at an interactome-wide scale.
Nature Reviews Neuroscience 06/2010; 11(6):436-49. · 26.48 Impact Factor
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Vikram Khurana
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ABSTRACT: The fruit fly Drosophila melanogaster has emerged as a powerful system in which to model human disease. This review focuses on the utility of the fly to model tau-dependent neurodegeneration, a hallmark of Alzheimer's disease and related neurodegenerative disorders. I provide a detailed description of fly tauopathy models and summarize a number of studies that demonstrate their ability to recapitulate both primary features of tauopathy, including tau-induced neurodegeneration and phosphorylation, and secondary features, including oxidative stress, cell-cycle activation and changes in the actin cytoskeleton. Important genetic and biochemical insights are discussed, and future directions proposed.
Journal of Alzheimer's disease: JAD 01/2009; 15(4):541-53. · 3.74 Impact Factor
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ABSTRACT: Studies in cell-culture systems and in postmortem tissue from human disease have suggested a connection between cell-cycle activation and neurodegeneration. The fruit fly Drosophila melanogaster has recently emerged as a powerful model system in which to model neurodegenerative diseases. Here we review work in the fly that has begun to address some of the important questions regarding the relationship between cell-cycle activation and neurodegeneration in vivo, including recent data implicating cell-cycle activation as a downstream effector of tau-induced neurodegeneration. We suggest how powerful research tools in Drosophila might be utilized to approach fundamental questions that remain.
Biochimica et Biophysica Acta 05/2007; 1772(4):446-56. · 4.66 Impact Factor
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ABSTRACT: Hyperphosphorylated forms of the microtubule-associated protein (MAP) tau accumulate in Alzheimer's disease and related tauopathies and are thought to have an important role in neurodegeneration. However, the mechanisms through which phosphorylated tau induces neurodegeneration have remained elusive. Here, we show that tau-induced neurodegeneration is associated with accumulation of filamentous actin (F-actin) and the formation of actin-rich rods in Drosophila and mouse models of tauopathy. Importantly, modulating F-actin levels genetically leads to dramatic modification of tau-induced neurodegeneration. The ability of tau to interact with F-actin in vivo and in vitro provides a molecular mechanism for the observed phenotypes. Finally, we show that the Alzheimer's disease-linked human beta-amyloid protein (Abeta) synergistically enhances the ability of wild-type tau to promote alterations in the actin cytoskeleton and neurodegeneration. These findings raise the possibility that a direct interaction between tau and actin may be a critical mediator of tau-induced neurotoxicity in Alzheimer's disease and related disorders.
Nature Cell Biology 03/2007; 9(2):139-48. · 19.49 Impact Factor
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ABSTRACT: Prion diseases are CNS disorders that can occur in sporadic, infectious, and inherited forms. Although all forms of prion disease are associated with the accumulation of pathogenic conformers of the prion protein, collectively termed PrP(Sc), the mechanisms by which PrP(Sc) molecules form and cause neuronal degeneration are unknown. Using the bipartite galactosidase-4-upstream activating sequence expression system, we generated transgenic Drosophila melanogaster heterologously expressing either wild-type (WT) or mutant, disease-associated (P101L) mouse PrP molecules in cholinergic neurons. Transgenic flies expressing neuronal P101L PrP molecules exhibited severe locomotor dysfunction and premature death as larvae and adults. These striking clinical abnormalities were accompanied by age-dependent accumulation of misfolded PrP molecules, intracellular PrP aggregates, and neuronal vacuoles. In contrast, transgenic flies expressing comparable levels of WT PrP displayed no clinical, pathological, or biochemical abnormalities. These results indicate that transgenic Drosophila expressing neuronal P101L PrP specifically exhibit several hallmark features of human Gerstmann-Sträussler-Scheinker (GSS) syndrome. Because the rates of abnormal PrP accumulation and clinical progression are highly accelerated in Drosophila compared with the rates of these processes in rodents or humans, the P101L mutant may be used for future genetic and pharmacologic studies as a novel invertebrate model of GSS.
Journal of Neuroscience 12/2006; 26(48):12408-14. · 7.11 Impact Factor
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ABSTRACT: Previous studies have demonstrated reexpression of cell-cycle markers within postmitotic neurons in neurodegenerative tauopathies, including Alzheimer's disease (AD). However, the critical questions of whether cell-cycle activation is causal or epiphenomenal to tau-induced neurodegeneration and which signaling pathways mediate cell-cycle activation in tauopathy remain unresolved.
Cell-cycle activation accompanies wild-type and mutant tau-induced neurodegeneration in Drosophila, and genetically interfering with cell-cycle progression substantially reduces neurodegeneration. Our data support a role for cell-cycle activation downstream of tau phosphorylation, directly preceding apoptosis. We accordingly show that ectopic cell-cycle activation leads to apoptosis of postmitotic neurons in vivo. As in AD, TOR (target of rapamycin kinase) activity is increased in our model and is required for neurodegeneration. TOR activation enhances tau-induced neurodegeneration in a cell cycle-dependent manner and, when ectopically activated, drives cell-cycle activation and apoptosis in postmitotic neurons.
TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model, identifying TOR and the cell cycle as potential therapeutic targets in tauopathies and AD.
Current Biology 03/2006; 16(3):230-41. · 9.65 Impact Factor
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Nature Neuroscience 12/2005; 8(11):1422-4. · 15.53 Impact Factor
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ABSTRACT: Hyperphosphorylated forms of the microtubule-associated protein (MAP) tau accumulate in Alzheimer's disease and related tauopathies and are thought to have an important role in neurodegeneration. However, the mechanisms through which phosphorylated tau induces neurodegeneration have remained elusive. Here, we show that tau-induced neurodegeneration is associated with accumulation of filamentous actin (F-actin) and the formation of actin-rich rods in Drosophila and mouse models of tauopathy. Importantly, modulating F-actin levels genetically leads to dramatic modification of tau-induced neurodegeneration. The ability of tau to interact with F-actin in vivo and in vitro provides a molecular mechanism for the observed phenotypes. Finally, we show that the Alzheimer's disease-linked human β-amyloid protein (Aβ) synergistically enhances the ability of wild-type tau to promote alterations in the actin cytoskeleton and neurodegeneration. These findings raise the possibility that a direct interaction between tau and actin may be a critical mediator of tau-induced neurotoxicity in Alzheimer's disease and related disorders. Members of the MAP family bind and stabilize microtubules in a manner that is regulated by phosphorylation of the MAPs at serine and threonine residues 1,2 . In addition, increasing evidence suggests that tau and other MAPs can interact directly or indirectly with the actin cytoskeleton 3–8 . However, in vitro experiments using purified proteins that examined the ability of tau to interact with actin have yielded conflicting results, raising concerns regarding the in vivo relevance of this interaction 9–13 . Intriguingly, actin-rich paracrystalline inclusions (known as Hirano bodies) have been described in Alzheimer's disease and other tauopa-thies, including Pick's disease 14–17 , but despite their discovery over 30 years ago, their mechanism of formation and role in neurodegenerative diseases remain poorly understood. On the basis of these findings and studies in yeast, and mammalian cell culture models directly implicat-ing actin stabilization and aggregation in activating cell death 18–21 , we hypothesized that a direct interaction between abnormally hyperphos-phorylated tau and the actin cytoskeletal network mediates neuronal degeneration in Alzheimer's disease and related disorders. We tested this hypothesis in Drosophila, which has recently been established as a useful model system for studying human tauopathies 22–25 , as well as in a mouse model of tauopathy. In Drosophila, wild-type human tau exhibits toxicity, as do mutant forms of tau found in familial fronto-temporal dementia linked to chromosome 17 (FTDP–17) including the R406W, V337M and P301L mutants. The mutant forms of tau often show enhanced toxicity 22,23,26 . Similarly, although wild-type human tau can show substantial toxicity when expressed in transgenic mice 27,28 , many mouse models use trans-genic expression of FTDP–17-associated mutant human tau. Mutant forms of tau, such as P301L, which is expressed in the rTg4510 trans-genic strain used in this study 29,30 , produce striking neurotoxicity, even when expressed in the presence of endogenous mouse tau.
