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The formation of small aggregates contributes to the neurotoxic effects of tau 45-230. Neurochem Int 2022; 152:105252. [PMID: 34856321 PMCID: PMC8712401 DOI: 10.1016/j.neuint.2021.105252] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 11/08/2021] [Accepted: 11/28/2021] [Indexed: 01/03/2023]
Abstract
Intracellular deposits of hyperphosphorylated tau are commonly detected in tauopathies. Furthermore, these aggregates seem to play an important role in the pathobiology of these diseases. In the present study, we determined whether the recently identified neurotoxic tau45-230 fragment also formed aggregates in neurodegenerative disorders. The presence of such aggregates was examined in brain samples obtained from Alzheimer's disease (AD) subjects by means of Western blot analysis performed under non-denaturing conditions. Our results showed that a mixture of tau45-230 oligomers of different sizes was easily detectable in brain samples obtained from AD subjects. Our data also suggested that tau45-230 oligomers could be internalized by cultured hippocampal neurons, mainly through a clathrin-mediated mechanism, triggering their degeneration. In addition, in vitro aggregation studies showed that tau45-230 modulated full-length tau aggregation thereby inducing the formation of smaller, and potentially more toxic, aggregates of this microtubule-associated protein. Together, these data identified alternative mechanisms underlying the toxic effects of tau45-230.
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Limorenko G, Lashuel HA. Revisiting the grammar of Tau aggregation and pathology formation: how new insights from brain pathology are shaping how we study and target Tauopathies. Chem Soc Rev 2021; 51:513-565. [PMID: 34889934 DOI: 10.1039/d1cs00127b] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Converging evidence continues to point towards Tau aggregation and pathology formation as central events in the pathogenesis of Alzheimer's disease and other Tauopathies. Despite significant advances in understanding the morphological and structural properties of Tau fibrils, many fundamental questions remain about what causes Tau to aggregate in the first place. The exact roles of cofactors, Tau post-translational modifications, and Tau interactome in regulating Tau aggregation, pathology formation, and toxicity remain unknown. Recent studies have put the spotlight on the wide gap between the complexity of Tau structures, aggregation, and pathology formation in the brain and the simplicity of experimental approaches used for modeling these processes in research laboratories. Embracing and deconstructing this complexity is an essential first step to understanding the role of Tau in health and disease. To help deconstruct this complexity and understand its implication for the development of effective Tau targeting diagnostics and therapies, we firstly review how our understanding of Tau aggregation and pathology formation has evolved over the past few decades. Secondly, we present an analysis of new findings and insights from recent studies illustrating the biochemical, structural, and functional heterogeneity of Tau aggregates. Thirdly, we discuss the importance of adopting new experimental approaches that embrace the complexity of Tau aggregation and pathology as an important first step towards developing mechanism- and structure-based therapies that account for the pathological and clinical heterogeneity of Alzheimer's disease and Tauopathies. We believe that this is essential to develop effective diagnostics and therapies to treat these devastating diseases.
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Affiliation(s)
- Galina Limorenko
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, École Polytechnique Federal de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
| | - Hilal A Lashuel
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, École Polytechnique Federal de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
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Haj-Yahya M, Lashuel HA. Protein Semisynthesis Provides Access to Tau Disease-Associated Post-translational Modifications (PTMs) and Paves the Way to Deciphering the Tau PTM Code in Health and Diseased States. J Am Chem Soc 2018; 140:6611-6621. [DOI: 10.1021/jacs.8b02668] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Mahmood Haj-Yahya
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Hilal A. Lashuel
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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4
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Vintilescu CR, Afreen S, Rubino AE, Ferreira A. The Neurotoxic TAU 45-230 Fragment Accumulates in Upper and Lower Motor Neurons in Amyotrophic Lateral Sclerosis Subjects. Mol Med 2016; 22:477-486. [PMID: 27496042 PMCID: PMC5072411 DOI: 10.2119/molmed.2016.00095] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Accepted: 07/23/2016] [Indexed: 12/12/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a progressive and lethal neurodegenerative disease characterized by the loss of upper and lower motor neurons leading to muscle paralysis in affected individuals. Numerous mechanisms have been implicated in the death of these neurons. However, the pathobiology of this disease has not been completely elucidated. In the present study, we investigated to what extent tau cleavage and the generation of the neurotoxic tau45-230 fragment is associated with ALS. Quantitative Western blot analysis indicated that high levels of tau45-230 accumulated in lumbar and cervical spinal cord specimens obtained from ALS subjects. This neurotoxic tau fragment was also detected in ALS upper motor neurons located in the precentral gyrus. Our results also showed that tau45-230 aggregates were present in the spinal cord of ALS patients. On the other hand, this neurotoxic fragment was not generated in a mouse model of a familial form of this disease. Together, these results suggest a potential role for this neurotoxic tau fragment in the mechanisms leading to the degeneration of motor neurons in the context of sporadic ALS.
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Affiliation(s)
- Claudia R Vintilescu
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, IL 60611
| | - Sana Afreen
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, IL 60611
| | - Ashlee E Rubino
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, IL 60611
| | - Adriana Ferreira
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, IL 60611
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5
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Patterson KR, Remmers C, Fu Y, Brooker S, Kanaan NM, Vana L, Ward S, Reyes JF, Philibert K, Glucksman MJ, Binder LI. Characterization of prefibrillar Tau oligomers in vitro and in Alzheimer disease. J Biol Chem 2011; 286:23063-76. [PMID: 21550980 DOI: 10.1074/jbc.m111.237974] [Citation(s) in RCA: 243] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Neurofibrillary tangles, composed of insoluble aggregates of the microtubule-associated protein Tau, are a pathological hallmark of Alzheimer disease (AD) and other tauopathies. However, recent evidence indicates that neuronal dysfunction precedes the formation of these insoluble fibrillar deposits, suggesting that earlier prefibrillar Tau aggregates may be neurotoxic. To determine the composition of these aggregates, we have employed a photochemical cross-linking technique to examine intermolecular interactions of full-length Tau in vitro. Using this method, we demonstrate that dimerization is an early event in the Tau aggregation process and that these dimers self-associate to form larger oligomeric aggregates. Moreover, using these stabilized Tau aggregates as immunogens, we generated a monoclonal antibody that selectively recognizes Tau dimers and higher order oligomeric aggregates but shows little reactivity to Tau filaments in vitro. Immunostaining indicates that these dimers/oligomers are markedly elevated in AD, appearing in early pathological inclusions such as neuropil threads and pretangle neurons as well as colocalizing with other early markers of Tau pathogenesis. Taken as a whole, the work presented herein demonstrates the existence of alternative Tau aggregates that precede formation of fibrillar Tau pathologies and raises the possibility that these hierarchical oligomeric forms of Tau may contribute to neurodegeneration.
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Affiliation(s)
- Kristina R Patterson
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
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6
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Effect of phosphorylation on interaction of human tau protein with 14-3-3ζ. Biochem Biophys Res Commun 2009; 379:990-4. [DOI: 10.1016/j.bbrc.2008.12.164] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2008] [Accepted: 12/30/2008] [Indexed: 11/19/2022]
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Iliev AI, Ganesan S, Bunt G, Wouters FS. Removal of pattern-breaking sequences in microtubule binding repeats produces instantaneous tau aggregation and toxicity. J Biol Chem 2006; 281:37195-204. [PMID: 17008320 DOI: 10.1074/jbc.m604863200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aggregated and highly phosphorylated tau protein is a pathological hallmark of Alzheimer's disease (AD) and other tauopathies. We identified motifs of alternating polar and apolar amino acids within the microtubule-binding repeats of tau which were interrupted by small breaking stretches. Minimal mutation of these breaking sequences yielded a unique instantly aggregating tau mutant containing longer stretches of polar/apolar amino acids without losing its microtubule-binding capacity. These modifications produced rapid aggregation and cytotoxicity with accompanying occurrence of pathologic tau phosphoepitopes (AT8, AT180, AT270, AT100, Ser(422), and PHF-1) and conformational epitopes (MC-1 and Alz50) in cells. Similar to pathological tau in the pretangle state, toxicity appeared to occur early without the requirement for extensive fibril formation. Thus, our mutant protein provides a novel platform for the investigation of the molecular mechanisms for toxicity and cellular behavior of pathologically aggregated tau proteins and the identification of its interaction partners.
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Affiliation(s)
- Asparouh Iliev Iliev
- Cell Biophysics Group, European Neuroscience Institute-Göttingen, Waldweg 33, 37073 Göttingen, Germany.
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8
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Abstract
The signaling pathways that mediate neurodegeneration are complex and involve a balance between phosphorylation and dephosphorylation of signaling and structural proteins. We have shown previously that 17beta-estradiol and its analogs are potent neuroprotectants. The purpose of this study was to delineate the role of protein phosphatases (PPs) in estrogen neuroprotection against oxidative stress and excitotoxicity. HT-22 cells, C6-glioma cells, and primary rat cortical neurons were exposed to the nonspecific serine/threonine protein phosphatase inhibitors okadaic acid and calyculin A at various concentrations in the presence or absence of 17beta-estradiol and/or glutamate. Okadaic acid and calyculin A caused a dose-dependent decrease in cell viability in HT-22, C6-glioma, and primary rat cortical neurons. 17beta-Estradiol did not show protection against neurotoxic concentrations of either okadaic acid or calyculin A in these cells. In the absence of these serine/threonine protein phosphatase inhibitors, 17beta-estradiol attenuated glutamate toxicity. However, in the presence of effective concentrations of these protein phosphatase inhibitors, 17beta-estradiol protection against glutamate toxicity was lost. Furthermore, glutamate treatment in HT-22 cells and primary rat cortical neurons caused a 50% decrease in levels of PP1, PP2A, and PP2B protein, whereas coadministration of 17beta-estradiol with glutamate prevented the decrease in PP1, PP2A, and PP2B levels. These results suggest that 17beta-estradiol may protect cells against glutamate-induced oxidative stress and excitotoxicity by activating a combination of protein phosphatases.
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Affiliation(s)
- Kun Don Yi
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, Texas 76107, USA
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9
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Walton JR. Aluminum in hippocampal neurons from humans with Alzheimer's disease. Neurotoxicology 2006; 27:385-94. [PMID: 16458972 DOI: 10.1016/j.neuro.2005.11.007] [Citation(s) in RCA: 191] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2005] [Revised: 10/28/2005] [Accepted: 11/07/2005] [Indexed: 11/29/2022]
Abstract
Using a staining technique developed in 2004, we examined hippocampal tissue from autopsy-confirmed cases of Alzheimer's disease (AD) and controls. The stain disclosed aluminum in cells and subcellular structure. All pyramidal neurons in these aged specimens appeared to exhibit at least some degree of aluminum staining. Many displayed visible aluminum only in their nucleolus. At the other extreme were neurons that stained for aluminum throughout their nucleus and cytoplasm. The remainder exhibited intermediate degrees of staining. On the basis of their aluminum staining patterns, all pyramidal neurons could be classified into stages that indicated two distinct neuropathological processes, either (1) progressive increase of nuclear aluminum (often accompanied by granulovacuolar degeneration with granules that stain for aluminum) or (2) formation of neurofibrillary tangles (NFTs) in regions of aluminum-rich cytoplasm, especially in AD brain tissue. In the latter process, intraneuronal NFTs appeared to displace nuclei and then enucleate the affected neurons during the course of their transformation into extracellular NFTs. Given that the NFTs we observed in human neurons always developed in conjunction with cytoplasmic aluminum, we hypothesize that aluminum plays an important role in their formation and should therefore be reconsidered as a causative factor for AD.
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Affiliation(s)
- J R Walton
- Australian Institute for Biomedical Research, Sydney, NSW 2204, Australia.
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10
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Bouras C, Riederer BM, Kövari E, Hof PR, Giannakopoulos P. Humoral immunity in brain aging and Alzheimer's disease. ACTA ACUST UNITED AC 2005; 48:477-87. [PMID: 15914253 DOI: 10.1016/j.brainresrev.2004.09.009] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 08/11/2004] [Accepted: 09/08/2004] [Indexed: 01/18/2023]
Abstract
Although the contribution of inflammatory processes in the etiology of late-onset Alzheimer's disease (AD) has been suspected for years, most studies were confined to the analysis of cell-mediated immunological reactions thought to represent an epiphenomenon of AD lesion development. Based on the traditional view of the "immunological privilege" of the brain, which excludes a direct access of human immunoglobulins (Ig) to the central nervous system under normal conditions, little attention has been paid to a possible role of humoral immunity in AD pathogenesis. In the first part of this review, we summarize evidences for a blood-brain barrier (BBB) dysfunction in this disorder and critically comment on earlier observations supporting the presence of anti-brain autoantibodies and immunoglobulins (Ig) in AD brains. Current concepts regarding the Ig turnover in the central nervous system and the mechanisms of glial and neuronal Fc receptors activation are also discussed. In the second part, we present new ex vivo and in vitro data suggesting that human immunoglobulins can interact with tau protein and alter both the dynamics and structural organization of microtubules. Subsequent experiments needed to test this new working hypothesis are addressed at the end of the review.
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Affiliation(s)
- Constantin Bouras
- Department of Psychiatry, University Hospitals of Geneva, 1225 Geneva, Switzerland.
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11
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Gold M. Tau therapeutics for Alzheimer's disease: the promise and the challenges. J Mol Neurosci 2002; 19:331-4. [PMID: 12540060 DOI: 10.1385/jmn:19:3:329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The pathological diagnosis of Alzheimer's disease (AD) depends on the presence of plaques consisting of the beta-amyloid peptide as well as neurofibrillary tangles consisting of paired helical filaments (PHFs) of the tau (tau) protein. The role of each type of pathology in the pathogenesis and progression of AD remains unclear. Previous hypotheses suggested that these two processes were independent, whereas more recent data suggest that there may be a bidirectional interaction between these two pathological processes. The identification of the neurotoxic effects of beta-amyloid and the discovery of mutations responsible for early-onset Alzheimer's disease (EOAD) and their linkage to beta-amyloid overproduction, has made the amyloid hypothesis of AD the predominant influence for therapeutic targets. Several approaches have emerged from preclinical testing and have entered early phases of clinical developments. The recent identification of tau mutations and their linkage to progressive neurodegenerative disorders provides a counterbalancing influence on the search for therapeutic targets for AD. Therapeutic approaches that are targeted to either beta-amyloid or tau share certain features at the level of pharmacology and will face many of the same challenges as they progress through drug development paradigms. The aim of this article is to provide a brief overview of some of the commonalities and the challenges faced by tau-related therapeutic strategies. The issues discussed in this article are not exhaustively dealt with in either scope or detail.
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Affiliation(s)
- Michael Gold
- Global Clinical Research and Development, CNS/Analgesia, Johnson & Johnson Pharmaceutical Research and Development, Titusville, NJ 08560, USA.
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12
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Utton MA, Gibb GM, Burdett ID, Anderton BH, Vandecandelaere A. Functional differences of tau isoforms containing 3 or 4 C-terminal repeat regions and the influence of oxidative stress. J Biol Chem 2001; 276:34288-97. [PMID: 11438517 DOI: 10.1074/jbc.m011384200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We report functional differences between tau isoforms with 3 or 4 C-terminal repeats and a difference in susceptibility to oxidative conditions, with respect to the regulation of microtubule dynamics in vitro and tau-microtubule binding in cultured cells. In the presence of dithiothreitol in vitro, a 3-repeat tau isoform promotes microtubule nucleation, reduces the tubulin critical concentration for microtubule assembly, and suppresses dynamic instability. Under non-reducing conditions, threshold concentrations of 3-repeat tau and tubulin exist below which this isoform still promotes microtubule nucleation and assembly but fails to reduce the tubulin critical concentration or suppress dynamic instability; above these threshold concentrations, amorphous aggregates of 3-repeat tau and tubulin can be produced at the expense of microtubule formation. A 4-repeat tau isoform is less sensitive to the oxidative potential of the environment, behaving under oxidative conditions similarly to the 3-repeat isoform under reducing conditions. Under conditions of oxidative stress, in Chinese hamster ovary cells stably expressing either 3- or 4-repeat tau, 3-repeat tau disassociates from microtubules more readily than the 4-repeat isoform, and tau-containing high molecular weight aggregates are preferentially observed in lysates from the Chinese hamster ovary cells expressing 3-repeat tau, indicating greater susceptibility of 3-repeat tau to oxidative conditions, compared with 4-repeat tau in vivo.
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Affiliation(s)
- M A Utton
- Department of Neuroscience, Institute of Psychiatry, King's College London, De Crespigny Park, London SE5 8AF, United Kingdom.
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13
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Lesort M, Tucholski J, Miller ML, Johnson GV. Tissue transglutaminase: a possible role in neurodegenerative diseases. Prog Neurobiol 2000; 61:439-63. [PMID: 10748319 DOI: 10.1016/s0301-0082(99)00052-0] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Tissue transglutaminase is a multifunctional protein that is likely to play a role in numerous processes in the nervous system. Tissue transglutaminase posttranslationally modifies proteins by transamidation of specific polypeptide bound glutamines. This action results in the formation of protein crosslinks or the incorporation of polyamines into substrate proteins, modifications that likely have significant effects on neural function. Tissue transglutaminase is a unique member of the transglutaminase family as in addition to catalyzing the calcium-dependent transamidation reaction, it also binds and hydrolyzes ATP and Guanosine 5'-triphosphate and may play a role in signal transduction. Tissue transglutaminase is a highly regulated and inducible enzyme that is developmentally regulated in the nervous system. In vitro, numerous substrates of tissue transglutaminase have been identified, and several of these proteins have been shown to be in situ substrates as well. Several specific roles for tissue transglutaminase have been described and there is evidence that tissue transglutaminase may also play a role in apoptosis. Recent findings have provided evidence that dysregulation of tissue transglutaminase may contribute to the pathology of several neurodegenerative conditions including Alzheimer's disease and Huntington's disease. In both of these diseases tissue transglutaminase and transglutaminase activity are elevated compared to age-matched controls. Further, immunohistochemical studies have demonstrated that there is an increase in tissue transglutaminase reactivity in affected neurons in both Alzheimer's and Huntington's disease. Although intriguing, many issues remain to be addressed to definitively establish a role for tissue transglutaminase in these neurodegenerative diseases.
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Affiliation(s)
- M Lesort
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 Seventh Avenue S., SC1061, Birmingham 35294-0017, USA
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14
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Norlund MA, Lee JM, Zainelli GM, Muma NA. Elevated transglutaminase-induced bonds in PHF tau in Alzheimer's disease. Brain Res 1999; 851:154-63. [PMID: 10642839 DOI: 10.1016/s0006-8993(99)02179-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Transglutaminase-induced epsilon-(gamma-glutamyl)lysine bonds covalently cross-link and polymerize peptides into insoluble high molecular weight protein aggregates resistant to degradation and proteolytic digestion. We investigated the hypothesis that excessive deposition of epsilon-(gamma-glutamyl)lysine bonds is a neuropathological mechanism which induces the polymerization of tau protein into stable aggregates leading to the formation of paired helical filaments (PHFs) which deposit into neurofibrillary tangles in Alzheimer's disease (AD) brain. We demonstrate a significant (45%) elevation in epsilon-(gamma-glutamyl)lysine cross-links in AD cortex as compared to control cortex. In vivo, PHF tau, and high and medium molecular weight neurofilament proteins have significantly greater cross-linking by epsilon-(gamma-glutamyl)lysine bonds in AD brains as compared to controls. The cross-linking of PHF tau occurs both intra-molecularly and inter-molecularly. The inter-molecular cross-linking of tau could account for the formation of high molecular weight tau polymers. These results suggest that transglutaminase-induced cross-linking of tau protein could play a role in the formation and stabilization of neurofibrillary tangles. Inhibition of transglutaminase-induced cross-linking may therefore, provide a novel strategy for the treatment of AD.
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Affiliation(s)
- M A Norlund
- Department of Pharmacology, Loyola University Medical Center, Maywood IL 60153, USA
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15
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Gärtner U, Janke C, Holzer M, Vanmechelen E, Arendt T. Postmortem changes in the phosphorylation state of tau-protein in the rat brain. Neurobiol Aging 1998; 19:535-43. [PMID: 10192212 DOI: 10.1016/s0197-4580(98)00094-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The phosphorylation state of tau-protein is crucial for the regulation of neuronal microtubule organization. Functional conclusions on tau-protein require an accurate assessment of phosphorylated sites. Therefore, the in vivo distribution and postmortem preservation of some phospho-epitopes on tau-protein were examined in the rat brain under different fixation and preparation conditions. Detection of tau-protein with a phosphorylation-independent antiserum revealed both axonal and somatodendritic localizations, which were not influenced by a postmortem interval of 30 min. The phospho-epitopes recognized by 12E8, AT8, and PHF-1 were mainly localized in the somatodendritic compartment. The binding sites of AT8 and PHF-1 were rapidly dephosphorylated postmortem, whereas the Tau-1 epitope was unmasked in the somatodendritic region. The axonally located phospho-epitope of AT270 and the nuclear epitope of AT100 were still detectable after a postmortem interval of 30 min. Postmortem dephosphorylation and inhibition of this process by PP1 and/or PP2A was further demonstrated on Western blot. In conclusion, rapid processing of tau-protein is essential for the correct assessment of investigations on phospho-isoforms.
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Affiliation(s)
- U Gärtner
- Paul Flechsig Institute of Brain Research, Department of Neuroanatomy, University of Leipzig, Germany
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16
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Paudel HK. Phosphorylation by neuronal cdc2-like protein kinase promotes dimerization of Tau protein in vitro. J Biol Chem 1997; 272:28328-34. [PMID: 9353289 DOI: 10.1074/jbc.272.45.28328] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In Alzheimer's disease, the microtubule-associated protein tau forms paired helical filaments (PHFs) that are the major structural component of neurofibrillary tangles. Although tau isolated from PHFs (PHF-tau) is abnormally phosphorylated, the role of this abnormal phosphorylation in PHF assembly is not known. Previously, neuronal cdc2-like protein kinase (NCLK) was shown to phosphorylate tau on sites that are abnormally phosphorylated in PHF-tau (Paudel, H. K., Lew, J., Ali, Z., and Wang, J. H. (1993) J. Biol. Chem. 268, 23512-23518). In this study, phosphorylation by NCLK was found to promote dimerization of recombinant human tau (R-tau) and brain tau (B-tau) purified from brain extract. Chemical cross-linking by disuccinimidyl suberate (DSS), a homobifunctional chemical cross-linker that specifically cross-linked R-tau dimers, and a Superose 12 gel filtration chromatography revealed that R-tau preparations contain mixtures of monomeric and dimeric R-tau species. When the structure of NCLK-phosphorylated R-tau was studied by a similar approach, DSS preferentially cross-linked the phosphorylated R-tau over the nonphosphorylated R-tau, and the phosphorylated R-tau eluted as a dimeric species from the gel filtration column. Phosphorylated R-tau became resistant to DSS upon dephosphorylation and was recovered as a monomeric species from the gel filtration column. In the presence of a low concentration of dithiothreitol (1.65 microM), R-tau formed disulfide cross-linked R-tau dimers. When compared, phosphorylated R-tau formed more disulfide cross-linked dimers than the nonphosphorylated R-tau. B-tau also was specifically cross-linked to dimers by DSS. When B-tau and NCLK-phosphorylated B-tau were treated with DSS, phosphorylated B-tau was preferentially cross-linked over nonphosphorylated counterpart. Taken together, these results suggest that phosphorylation by NCLK promotes dimerization and formation of disulfide cross-linked tau dimers, which is suggested to be the key step leading to PHF assembly (Schweers, O., Mandelkow, E.-M., Biernat, J., and Mandelkow, E. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 8463-8467).
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Affiliation(s)
- H K Paudel
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital and Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, H3T 1E2, Canada.
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17
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Hoffmann R, Dawson NF, Wade JD, Otvös L. Oxidized and phosphorylated synthetic peptides corresponding to the second and third tubulin-binding repeats of the tau protein reveal structural features of paired helical filament assembly. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 1997; 50:132-42. [PMID: 9273897 DOI: 10.1111/j.1399-3011.1997.tb01178.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The microtubule-associated protein tau of normal brains is attached to tubulin through its 18-amino-acid repeat units. In the paired helical filaments (PHF) of Alzheimer's disease, however, tau is oligomerized in an abnormally hyperphosphorylated from (PHF-tau). tau contains two cysteine residues in repeat units 2 and 3, but only the R3-R3 homodimer is present in PHF-tau. A serine residue two amino acids downstream of the R3 cysteine is a major phosphate acceptor site for protein kinase C. In the work repeated here, we used synthetic peptides corresponding to R2, R3 and phosphorylated R3 to determine the binding of the tau repeat peptides to a peptide fragment corresponding to the C-terminal domain of beta-tubulin and to study the kinetics of homo- and heterodimer formation. Additionally, we studied two major biochemical properties of the peptides that distinguish between normal tau and PHF-tau: conformation and metabolic stability. All R2 and R3 peptides bound specifically to the tubulin peptide regardless of the state of phosphorylation or dimerization. The reverse-turn conformation of the tau repeat peptides in the presence of the tubulin peptide remained unaffected. Phosphorylation slightly loosened the turn structure of the monomeric and dimeric peptides, and did not univocally affect the serum stability of the peptides or the ability of the peptides to form dimers. The isolated R2 and R3 units formed homodimers approximately in the same rate. When the two peptides were mixed, however, the R2-R3 heterodimer was formed preferentially over the homodimers. The dimers were generally more stable in human serum than the monomers. Our results with the synthetic peptide fragments of tau indicate that neither oxidation nor phosphorylation of the repeat units is able to generate extended structure such as that found in PHF-tau. Additionally, phosphorylation of Ser324 does not appear to modulate the kinetics of oligomerization of tau, and in general biochemistry terms, does not affect disulfide bridge formation nearby. In agreement with studies at the full-protein level, the formation of homodimers of the peptides, a model of the self-association of tau, is not preferred. If the dimers are formed, however, their clearance is considerably slower than that of the monomers, explaining the remarkable protease resistance of PHF-tau in the affected brains.
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Affiliation(s)
- R Hoffmann
- Wistar Institute, Philadelphia, Pennsylvania 19104, USA
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18
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Billingsley ML, Kincaid RL. Regulated phosphorylation and dephosphorylation of tau protein: effects on microtubule interaction, intracellular trafficking and neurodegeneration. Biochem J 1997; 323 ( Pt 3):577-91. [PMID: 9169588 PMCID: PMC1218358 DOI: 10.1042/bj3230577] [Citation(s) in RCA: 318] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
This review attempts to summarize what is known about tau phosphorylation in the context of both normal cellular function and dysfunction. However, conceptions of tau function continue to evolve, and it is likely that the regulation of tau distribution and metabolism is complex. The roles of microtubule-associated kinases and phosphatases have yet to be fully described, but may afford insight into how tau phosphorylation at the distal end of the axon regulates cytoskeletal-membrane interactions. Finally, lipid and glycosaminoglycan modification of tau structure affords yet more complexity for regulation and aggregation. Continued work will help to determine what is causal and what is coincidental in Alzheimer's disease, and may lead to identification of therapeutic targets for halting the progression of paired helical filament formation.
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Affiliation(s)
- M L Billingsley
- Department of Pharmacology, Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
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Johnson GV, Cox TM, Lockhart JP, Zinnerman MD, Miller ML, Powers RE. Transglutaminase activity is increased in Alzheimer's disease brain. Brain Res 1997; 751:323-9. [PMID: 9099822 DOI: 10.1016/s0006-8993(96)01431-x] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Transglutaminase is a calcium-activated enzyme that crosslinks substrate proteins into insoluble, often filamentous aggregates resistant to proteases. Because the neurofibrillary tangles in Alzheimer's disease have similar characteristics, and because tau protein, the major component of these tangles is an excellent substrate of transglutaminase in vitro, transglutaminase activity and levels were measured in control and Alzheimer's disease brain. Frozen prefrontal cortex and cerebellum samples from Alzheimer's disease and control cases matched for age and postmortem interval were used in the analyses. Total transglutaminase activity was significantly higher in the Alzheimer's disease prefrontal cortex compared to control. In addition the levels of tissue transglutaminase, as determined by quantitative immunoblotting, were elevated approximately 3-fold in Alzheimer's disease prefrontal cortex compared to control. To our knowledge, this is the first demonstration that transglutaminase is increased in Alzheimer's disease brain. There were no significant differences in transglutaminase activity or levels in the cerebellum between control and Alzheimer's disease cases. Because the elevation of transglutaminase in the Alzheimer's disease samples occurred in the prefrontal cortex, where neurofibrillary pathology is usually abundant, and not in the cerebellum, which is usually spared in Alzheimer's disease, it can be suggested that transglutaminase could be a contributing factor in neurofibrillary tangle formation.
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Affiliation(s)
- G V Johnson
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 35294-0017, USA.
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Guttmann RP, Elce JS, Bell PD, Isbell JC, Johnson GV. Oxidation inhibits substrate proteolysis by calpain I but not autolysis. J Biol Chem 1997; 272:2005-12. [PMID: 8999893 DOI: 10.1074/jbc.272.3.2005] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
In this study, the effects of oxidation on calpain I autolysis and calpain-mediated proteolysis were examined. Calpain I was incubated with increasing concentrations of free calcium in the presence or absence of oxidant, and autolytic conversion of both the 80- and 30-kDa subunits was measured by immunoblotting utilizing monoclonal antibodies which recognize both autolyzed and non-autolyzed forms of each subunit, respectively. Autolytic conversion of the 80-kDa subunit of calpain I was not detected until free calcium concentration was greater than 40 microM, whereas autolysis of the 30-kDa subunit did not occur until the free calcium concentration was greater than 100 microM. In addition, autolytic conversion of either the 80- or 30-kDa subunit was not inhibited by the presence of oxidant. Calpain I activity was measured using the fluorescent peptide N-succinyl-L-leucyl-L-leucyl-L-valyl-L-tyrosine-7-amido-4- methylcoumarin or the microtubule-associated protein tau as substrate. Calpain I was found to have proteolytic activity at free calcium concentrations below that required for autolysis. Calpain I activity was strongly inhibited by oxidant at all calcium concentrations studied, suggesting that proteolytic activity of both the non-autolyzed 80-kDa and autolyzed 76-kDa forms was susceptible to oxidation. Interestingly, whereas oxidation did not inhibit autolytic conversion, the presence of high substrate concentrations did result in a significant reduction of autolysis without altering calpain proteolytic activity. Calpain I activity that had been inhibited by the presence of oxidant was recovered immediately by addition of the reducing agent dithiothreitol.
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Affiliation(s)
- R P Guttmann
- Department of Psychiatry, University of Alabama at Birmingham, Birmingham, Alabama 35294-0017, USA
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21
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Litersky JM, Johnson GV, Jakes R, Goedert M, Lee M, Seubert P. Tau protein is phosphorylated by cyclic AMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase II within its microtubule-binding domains at Ser-262 and Ser-356. Biochem J 1996; 316 ( Pt 2):655-60. [PMID: 8687413 PMCID: PMC1217397 DOI: 10.1042/bj3160655] [Citation(s) in RCA: 108] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Phosphorylation of tau protein at Ser-262 has been shown to diminish its ability to bind to taxol-stabilized microtubules. The paired helical filaments (PHFs) found in Alzheimer's disease brain are composed of PHF-tau, which is hyperphosphorylated at multiple sites including Ser-262. However, protein kinase(s) able to phosphorylate this site are still under investigation. In this study, the ability of cyclic AMP-dependent protein kinase (cAMP-PK) and calcium/calmodulin-dependent protein kinase II (CaMKII) to phosphorylate tau at Ser-262, as well as Ser-356, is demonstrated by use of a monoclonal antibody (12E8) which has been shown to recognize tau when these sites are phosphorylated. Cleavage of cAMP-PK-phosphorylated tau at cysteine residues by 2-nitro-5-thiocyanobenzoic acid, which cuts the protein into essentially two fragments and separates Ser-262 from Ser-356, revealed that cAMP-PK phosphorylates both Ser-262 and Ser-356. In addition, phosphorylation with cAMP-PK or CaMKII of recombinant tau in which Ser-262, Ser-356 or both had been mutated to alanines, clearly demonstrated that cAMP-PK and CaMKII were able to phosphorylate both sites. Mitogen-activated protein kinase or protein kinase C did not phosphorylate tau at Ser-262 and/or Ser-356. Finally, evidence is presented that phosphorylation of both these sites occurs in cultured nerve cells under certain conditions, indicating their potential physiological relevance.
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Affiliation(s)
- J M Litersky
- Department of Psychiatry, University of Alabama at Birmingham 35294-0017, USA
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Smith MA, Sayre LM, Monnier VM, Perry G. Oxidative posttranslational modifications in Alzheimer disease. A possible pathogenic role in the formation of senile plaques and neurofibrillary tangles. MOLECULAR AND CHEMICAL NEUROPATHOLOGY 1996; 28:41-8. [PMID: 8871940 DOI: 10.1007/bf02815203] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The distinctive pathological lesions of Alzheimer disease (AD), senile plaques, and neurofibrillary tangles comprise aggregates of insoluble fibrillar protein. We and other investigators recently demonstrated that several mechanisms related to oxidative stress and free-radical reactions could play a crucial role in the pathogenesis of AD and, specifically, in the formation of senile plaques and neurofibrillary tangles (NFT).
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Affiliation(s)
- M A Smith
- Department of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA
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Schweers O, Mandelkow EM, Biernat J, Mandelkow E. Oxidation of cysteine-322 in the repeat domain of microtubule-associated protein tau controls the in vitro assembly of paired helical filaments. Proc Natl Acad Sci U S A 1995; 92:8463-7. [PMID: 7667312 PMCID: PMC41177 DOI: 10.1073/pnas.92.18.8463] [Citation(s) in RCA: 283] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
One of the hallmarks of Alzheimer disease is the pathological aggregation of tau protein into paired helical filaments (PHFs) and neurofibrillary tangles. Here we describe the in vitro assembly of recombinant tau protein and constructs derived from it into PHFs. Though whole tau assembled poorly, constructs containing three internal repeats (corresponding to the fetal tau isoform) formed PHFs reproducibly. This ability depended on intermolecular disulfide bridges formed by the single Cys-322. Blocking the SH group, mutating Cys for Ala, or keeping tau in a reducing environment all inhibited assembly. With constructs derived from four-repeat tau (having the additional repeat no. 2 and a second Cys-291), PHF assembly was blocked because Cys-291 and Cys-322 interact within the molecule. PHF assembly was enabled again by mutating Cys-291 for Ala. The synthetic PHFs bound the dye thioflavin S used in Alzheimer disease diagnostics. The data imply that the redox potential in the neuron is crucial for PHF assembly, independently or in addition to pathological phosphorylation reactions.
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Affiliation(s)
- O Schweers
- Max-Planck Unit for Structural Molecular Biology, c/o Deutsches Elektronen Synchroton, Hamburg, Germany
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Johnson GV, Greenwood JA. Understanding the hyperphosphorylation of tau in Alzheimer's disease: Importance of examining site-specific phosphorylation in non-disease systems. Neurobiol Aging 1995. [DOI: 10.1016/0197-4580(95)00028-d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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