151
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van Groen T, Miettinen P, Kadish I. Axonal tract tracing for delineating interacting brain regions: implications for Alzheimer's disease-associated memory. FUTURE NEUROLOGY 2014; 9:89-98. [PMID: 24678267 DOI: 10.2217/fnl.13.67] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We are studying the projections from the entorhinal cortex to the hippocampal formation in the mouse. The dentate gyrus is innervated by the lateral entorhinal cortex (lateral perforant path) and medial entorhinal cortex (medial perforant path). The entorhinal cortex also projects to hippocampal areas CA3 and CA1, and to the subiculum. In young transgenic Alzheimer's disease mouse models (before amyloid-β pathology), the connections are not different from normal mice. In Alzheimer's disease mice with pathology, two changes occur: first, dystrophic axon endings appear near amyloid-β plaques, and second, there are sparse aberrant axon terminations not in the appropriate area or lamina of the hippocampus. Furthermore, MRI-diffusion tensor imaging analysis indicates a decrease in the quality of the white matter tracts connecting the hippocampus to the brain; in other words, the fimbria/fornix and perforant path. Similar changes in white matter integrity have been found in Alzheimer's disease patients and could potentially be used as early indicators of disease onset.
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Affiliation(s)
- Thomas van Groen
- Department of Cell, Developmental & Integrative Biology, University of Alabama at Birmingham, 1900 University Boulevard, THT 912, Birmingam, AL 35294-0006, USA
| | - Pasi Miettinen
- Department of Neuroscience, University of Eastern Finland, FIN 70211, Kuopio, Finland
| | - Inga Kadish
- Department of Cell, Developmental & Integrative Biology, University of Alabama at Birmingham, 1900 University Boulevard, THT 912, Birmingam, AL 35294-0006, USA
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152
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Mohamed NV, Herrou T, Plouffe V, Piperno N, Leclerc N. Spreading of tau pathology in Alzheimer's disease by cell-to-cell transmission. Eur J Neurosci 2013; 37:1939-48. [PMID: 23773063 DOI: 10.1111/ejn.12229] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2013] [Revised: 03/20/2013] [Accepted: 03/22/2013] [Indexed: 11/28/2022]
Abstract
It is well documented that neurofibrillary tangles composed of aggregated tau protein propagate in a predictable pattern in Alzheimer's disease (AD). The mechanisms underlying the propagation of tau pathology are still poorly understood. Recent studies have provided solid data demonstrating that in several neurodegenerative diseases including AD, the spreading of misfolded protein aggregates in the brain would result from prion-like cell-to-cell transmission. Consistent with this new concept, recent studies have reported that human tau can be released in the extracellular space by an active process of secretion, and can be endocytosed both in vitro and in vivo. Most importantly, it was reported that the spreading of tau pathology was observed along synaptically connected circuits in a transgenic mouse model where human tau overexpression was restricted in the entorhinal cortex. This indicates that secretion of tau by presynaptic neurons and its uptake by postsynaptic neurons could be the sequential events leading to the propagation of tau pathology in the brain.
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Affiliation(s)
- Nguyen-Vi Mohamed
- Département de pathologie et biologie cellulaire, Université de Montréal, Montréal, QC, Canada
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153
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Mehta AK, Rosen RF, Childers WS, Gehman JD, Walker LC, Lynn DG. Context dependence of protein misfolding and structural strains in neurodegenerative diseases. Biopolymers 2013; 100:722-30. [PMID: 23893572 PMCID: PMC3979318 DOI: 10.1002/bip.22283] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2013] [Revised: 04/19/2013] [Accepted: 05/07/2013] [Indexed: 01/28/2023]
Abstract
Vast arrays of structural forms are accessible to simple amyloid peptides and environmental conditions can direct assembly into single phases. These insights are now being applied to the aggregation of the Aβ peptide of Alzheimer's disease and the identification of causative phases. We extend use of the imaging agent Pittsburgh compound B to discriminate among Aβ phases and begin to define conditions of relevance to the disease state. Also, we specifically highlight the development of methods for defining the structures of these more complex phases.
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Affiliation(s)
- Anil K. Mehta
- Departments of Chemistry and Biology, Alzheimer’s Disease Research Center, Emory University, Atlanta, Georgia 30322, USA
| | - Rebecca F. Rosen
- Yerkes National Primate Research Center, Center for Neurodegenerative Disease, Emory University, Atlanta, Georgia 30322, USA
| | - W. Seth Childers
- Departments of Chemistry and Biology, Alzheimer’s Disease Research Center, Emory University, Atlanta, Georgia 30322, USA
| | - John D. Gehman
- School of Chemistry, Bio21 Institute, University of Melbourne, Melbourne, Vic. 3010, Australia
| | - Lary C. Walker
- Yerkes National Primate Research Center, Center for Neurodegenerative Disease, Emory University, Atlanta, Georgia 30322, USA
- Department of Neurology, Emory University, Atlanta, Georgia 30322, USA
| | - David G. Lynn
- Departments of Chemistry and Biology, Alzheimer’s Disease Research Center, Emory University, Atlanta, Georgia 30322, USA
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154
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Propagation of tau pathology in Alzheimer's disease: identification of novel therapeutic targets. ALZHEIMERS RESEARCH & THERAPY 2013; 5:49. [PMID: 24152385 PMCID: PMC3978816 DOI: 10.1186/alzrt214] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Accumulation and aggregation of the microtubule-associated protein tau are a pathological hallmark of neurodegenerative disorders such as Alzheimer’s disease (AD). In AD, tau becomes abnormally phosphorylated and forms inclusions throughout the brain, starting in the entorhinal cortex and progressively affecting additional brain regions as the disease progresses. Formation of these inclusions is thought to lead to synapse loss and cell death. Tau is also found in the cerebrospinal fluid (CSF), and elevated levels are a biomarker for AD. Until recently, it was thought that the presence of tau in the CSF was due to the passive release of aggregated tau from dead or dying tangle-bearing neurons. However, accumulating evidence from different AD model systems suggests that tau is actively secreted and transferred between synaptically connected neurons. Transgenic mouse lines with localized expression of aggregating human tau in the entorhinal cortex have demonstrated that, as these animals age, tau becomes mislocalized from axons to cell bodies and dendrites and that human tau-positive aggregates form first in the entorhinal cortex and later in downstream projection targets. Numerous in vitro and in vivo studies have provided insight into the mechanisms by which tau may be released and internalized by neurons and have started to provide insight into how tau pathology may spread in AD. In this review, we discuss the evidence for regulated tau release and its specific uptake by neurons. Furthermore, we identify possible therapeutic targets for preventing the propagation of tau pathology, as inhibition of tau transfer may restrict development of tau tangles in a small subset of neurons affected in early stages of AD and therefore prevent widespread neuron loss and cognitive dysfunction associated with later stages of the disease.
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155
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Abstract
The initial preclinical phase of Alzheimer disease (AD), which has no symptoms, is followed by a phase whereby cognitive impairment, but no functional impairment is present (mild cognitive impairment), after which comes the third phase of dementia. Diagnosis of AD has primarily been one of exclusion of all other causes of reversible and irreversible dementia. Overlapping clinical presentations of diseases causing neurodegeneration, however, create challenges for accurate diagnosis. Algorithms are provided for the most current guidelines. Use of clinical magnetic resonance and PET imaging modalities increase the specificity of diagnosis, and several new promising experimental approaches are being developed.
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Affiliation(s)
- Robert M Cohen
- Neuroscience Program, Graduate Division of Biological and Medical Sciences, Department of Psychiatry and Behavioral Neuroscience, Emory University, 101 Woodruff Circle, Suite WMB4003, Atlanta, GA 30322, USA.
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156
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Sigurdsson EM. Tau immunotherapy and imaging. NEURODEGENER DIS 2013; 13:103-6. [PMID: 24029727 DOI: 10.1159/000354491] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 07/18/2013] [Indexed: 01/05/2023] Open
Abstract
Disappointing findings from recent phase III trials on amyloid-β (Aβ) immunotherapy for Alzheimer's disease (AD) have shifted the focus of such treatments to the tau protein. As tau pathology correlates better with the degree of dementia than Aβ plaque burden, it is a more attractive target once cognitive impairments are evident, while Aβ therapies may be better suited for the presymptomatic phase of the disease. Over 12 years ago, we initiated a tau immunotherapy program, seeking to alleviate the functional impairments associated with tau lesions in tauopathies. We have reported that various active and passive tau immunizations diminish tau pathology and improve function, including cognition, in different mouse models. Both extra- and intracellular pathways are likely involved. The antibodies may block the spread of tau pathology via microglial phagocytosis of the antibody-tau complex and facilitate lysosomal tau clearance in neurons after endosomal uptake. We have observed such antibody internalization following intracarotid injection in mice and in various culture models. These include brain slices and primary neurons from tangle mice as well as human neuroblastoma cell lines. Antibody targeting of different intracellular protein aggregates, including α-synuclein, Aβ and superoxide dismutase has been reported by others. Now, several laboratories have confirmed and extended our findings using various active and passive tau immunizations in different models, thereby clearly establishing the feasibility of this approach for clinical trials. We are also working on imaging approaches to monitor tau pathology, its consequences and the efficacy of treatments. Dire need exists for such diagnostic methods for tauopathies. Overall, therapies and diagnostic tools targeting tau pathology have a great potential for AD and other tauopathies.
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Affiliation(s)
- Einar M Sigurdsson
- Department of Neuroscience and Physiology, New York University School of Medicine, New York, N.Y., USA
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157
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Sepulcre J, Sabuncu MR, Becker A, Sperling R, Johnson KA. In vivo characterization of the early states of the amyloid-beta network. ACTA ACUST UNITED AC 2013; 136:2239-52. [PMID: 23801740 DOI: 10.1093/brain/awt146] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Alzheimer's disease is a neurodegenerative disease that is associated with the abnormal accumulation of amyloid-β. Much is known about regional brain atrophy in Alzheimer's disease, yet our knowledge about the network nature of Alzheimer's disease-associated amyloid-β accumulation is limited. We use stepwise connectivity analysis of Pittsburgh Compound B positron emission tomography images to reveal the network properties of amyloid-β deposits in normal elderly subjects and clinical patients with Alzheimer's disease. We found that amyloid-β accumulation in the medial temporal lobe is associated with accumulation in cortical regions such as orbitofrontal, lateral temporal and precuneus/posterior cingulate cortices in Alzheimer's disease. In normal subjects, there was a predominant association between amyloid-β deposits in the hippocampus and the midline prefrontal/orbitofrontal regions, even in those with very low amyloid-β burden. Moreover, the orbitofrontal cortex, amygdala nucleus and hippocampus exhibit hub properties in the amyloid-β network that may be critical to understanding the putative spreading mechanisms of Alzheimer's disease pathology in early stages.
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Affiliation(s)
- Jorge Sepulcre
- Division of Nuclear Medicine and Molecular Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
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158
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Abstract
Alzheimer's disease (AD) is a major cause of morbidity in the elderly. AD affects aver 5 million persons in the United States, but because it increases in incidence in the elderly, and the "graying" population, AD is projected to increase in prevalence by many-fold over the coming decades. AD causes progressive mental impairment, resulting in the inability of persons to care for themselves. As a consequence, AD results in enormous costs to society due to both lost productivity, and required care. Thus, improved management and treatment is essential. In this review we will briefly review current understanding of the disease, including roles of beta-amyloid and tau proteins. We will then discuss current therapies in use, including the evidence for treatments with supplements, established drugs, and investigational therapeutic strategies, recently completed and ongoing.
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159
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Gerson JE, Kayed R. Formation and propagation of tau oligomeric seeds. Front Neurol 2013; 4:93. [PMID: 23882255 PMCID: PMC3713404 DOI: 10.3389/fneur.2013.00093] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Accepted: 07/01/2013] [Indexed: 12/14/2022] Open
Abstract
Tau misfolding and aggregation leads to the formation of neurofibrillary tangles (NFTs), which have long been considered one of the main pathological hallmarks for numerous neurodegenerative diseases known as tauopathies, including Alzheimer’s Disease (AD) and Parkinson’s Disease (PD). However, recent studies completed both in vitro and in vivo suggest that intermediate forms of tau, known as tau oligomers, between the monomeric form and NFTs are the true toxic species in disease and the best targets for anti-tau therapies. However, the exact mechanism by which the spread of pathology occurs is unknown. Evidence suggests that tau oligomers may act as templates for the misfolding of native tau, thereby seeding the spread of the toxic forms of the protein. Recently, researchers have reported the ability of tau oligomers to enter and exit cells, propagating from disease-affected regions to unaffected areas. While the mechanism by which the spreading of misfolded tau occurs has yet to be elucidated, there are a few different models which have been proposed, including cell membrane stress and pore-formation, endocytosis and exocytosis, and non-traditional secretion of protein not enclosed by a membrane. Coming to an understanding of how toxic tau species seed and spread through the brain will be crucial to finding effective treatments for neurodegenerative tauopathies.
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Affiliation(s)
- Julia E Gerson
- George P. and Cynthia Woods Mitchell Center for Neurodegenerative Diseases, University of Texas Medical Branch , Galveston, TX , USA ; Department of Neurology, University of Texas Medical Branch , Galveston, TX , USA ; Department of Neuroscience and Cell Biology, University of Texas Medical Branch , Galveston, TX , USA
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160
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Affiliation(s)
- Maiken Nedergaard
- School of Medicine and Dentistry, University of Rochester Medical Center, Rochester, NY 14642, USA.
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