| 1. |
- Agholme, Lotta, et al.
(författare)
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Amyloid-β Secretion, Generation, and Lysosomal Sequestration in Response to Proteasome Inhibition : Involvement of Autophagy
- 2012
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Ingår i: Journal of Alzheimer's Disease. - : I O S Press. - 1387-2877 .- 1875-8908. ; 31:2, s. 343-358
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Tidskriftsartikel (refereegranskat)abstract
- The proteasome is important for degradation of worn out and misfolded proteins. Decreased proteasome activity has been implicated in Alzheimer's disease (AD). Proteasome inhibition induces autophagy, but it is still unknown whether autophagy is beneficial or deleterious to AD neurons, as the autophagosome has been suggested as a site of amyloid-β (Aβ) generation. In this study, we investigated the effect of proteasome inhibition on Aβ accumulation and secretion, as well as the processing of amyloid-β protein precursor (AβPP) in AβPPSwe transfected SH-SY5Y neuroblastoma cells. We show that proteasome inhibition resulted in autophagy-dependent accumulation of Aβ in lysosomes, and increased levels of intracellular and secreted Aβ. The enhanced levels of Aβ could not be explained by increased amounts of AβPP. Instead, reduced degradation of the C-terminal fragment of AβPP (C99) by the proteasome makes C99 available for γ-secretase cleavage, leading to Aβ generation. Inhibition of autophagy after proteasome inhibition led to reduced levels of intracellular, but not secreted Aβ, and tended to further increase the C99 to AβPP ratio, supporting involvement of the autophagosome in Aβ generation. Furthermore, proteasome inhibition caused a reduction in cellular viability, which was reverted by inhibition of autophagy. Dysfunction of the proteasome could cause lysosomal accumulation of Aβ, as well as increased generation and secretion of Aβ, which is partly facilitated by autophagy. As a decrease in cellular viability was also detected, it is possible that upregulation of autophagy is an unsuccessful rescue mechanism, which instead of being protective, contributes to AD pathogenesis.
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| 2. |
- Agholme, Lotta, et al.
(författare)
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An In Vitro Model for Neuroscience: Differentiation of SH-SY5Y Cells into Cells with Morphological and Biochemical Characteristics of Mature Neurons
- 2010
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Ingår i: Journal of Alzheimer's Disease. - : Ios Press. - 1387-2877 .- 1875-8908. ; 20:4, s. 1069-1082
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Tidskriftsartikel (refereegranskat)abstract
- Neuroscience, including research on Alzheimers disease, is hampered by the lack of suitable in vitro models to study the human nervous system. To counteract this, many attempts to differentiate cell lines into more neuron-like cells have been performed, resulting in partial expression of neuronal features. Furthermore, it has been reported that neuroblastoma cell lines lack mature isoforms of tau. Our aim was to develop an improved in vitro model, generating sustainable cells with morphology and biochemistry of human, mature neurons. To obtain cells with neuronal differentiation and function, we investigated the effect of combining three-dimensional culturing of SH-SY5Y cells in extracellular matrix (ECM) gel with several factors reported to have neuro-differentiating effects. This resulted in cells with apparent neuronal morphology with long, extensively branched neurites. Further investigation revealed expression of several neurospecific markers including synapse protein Sv2 and nuclear marker NeuN, as well as the presence of synapses and axonal vesicle transport. In addition, these cells expressed mature tau isoforms, and tau protein expression was significantly increased compared to undifferentiated cells, reaching levels found in adult human brain. In conclusion, we found that pre-treatment with retinoic acid followed by ECM gel culturing in combination with brain derived neurotrophic factor, neuregulin beta(1), nerve growth factor, and vitamin D-3 treatment generated sustainable cells with unambiguous resemblance to adult neurons. These cells also expresses adult splicing forms of tau with neuronal localization, making this cellular in vitro model useful in many areas of neuroscience research, particularly the Alzheimers disease field.
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| 3. |
- Agholme, Lotta, et al.
(författare)
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Proteasome Inhibition Induces Stress Kinase Dependent Transport Deficits – Implications for Alzheimer’s Disease
- 2014
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Ingår i: Molecular and Cellular Neuroscience. - : Elsevier. - 1044-7431 .- 1095-9327. ; 58, s. 29-39
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Tidskriftsartikel (refereegranskat)abstract
- Alzheimer’s disease (AD) is characterized by accumulation of two misfolded and aggregated proteins, β-amyloid and hyperphosphorylated tau. Both cellular systems responsible for clearance of misfolded and aggregated proteins, the lysosomal and the proteasomal, have been shown to be malfunctioning in the aged brain and more so in AD patients. This malfunction could be the cause of β-amyloid and tau accumulation, eventually aggregating in plaques and tangles. We have investigated how decreased proteasome activity affects AD related pathophysiological changes of microtubule transport and stability, as well as tau phosphorylation. To do this, we used our recently developed neuronal model where human SH-SY5Y cells obtain neuronal morphology and function through differentiation. We found that exposure to low doses of the proteasome inhibitor MG-115 caused disturbed neuritic transport, together with microtubule destabilization and tau phosphorylation. Furthermore, reduced proteasome activity activated several kinases implicated in AD pathology, including JNK, c-Jun and ERK 1/2. Restoration of the microtubule transport was achieved by inhibiting ERK 1/2 activation, and simultaneous inhibition of both ERK 1/2 and c-Jun reversed the proteasome inhibition-induced tau phosphorylation. Taken together, this study suggests that a decrease in proteasome activity can, through activation of c-Jun and ERK 1/2, result in several events contributing to AD pathology. Restoring proteasome function or inhibiting ERK 1/2 and c-Jun could therefore be used as novel treatments against AD.
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| 4. |
- Agholme, Lotta
(författare)
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The involvement of degradation pathways and neuron-to-neuron transmission in Alzheimer’s disease
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the vast majority of Alzheimer’s disease (AD) cases are of the sporadic type, mutations causing the familial form have been the focus of AD research for decades. The disease is pathologically characterised by β-amyloid (Aβ) and tau protein aggregates in neuritic plaques and neurofibrillary tangles. Furthermore, it is known that AD pathology spreads throughout the brain, most often along the same anatomical pattern. However, so far no cause for the sporadic form of the disease has been found. Accumulation of protein aggregates as well as decreased activity of the protein degradation systems, lysosomes and proteasomes, is found in diseased brains. This indicates that defective degradation contributes to sporadic AD.The aim of this thesis was to develop an improved neuronal model, and study the effects of decreased proteasome function on tau phosphorylation and axonal transport. In addition, the effects on Aβ accumulation and generation upon proteasome inhibition were investigated. Finally, the possibility that intracellularly accumulated Aβ oligomers could be transferred from one neuron to another was tested.Differentiation of human SH-SY5Y neuroblastoma cells in an extracellular matrix gel, using a set of neurotrophic factors, resulted in cells with neuronal phenotype, expressing neuron specific markers and all six adult isoforms of tau. Within this neuronal model, we found that reduced proteasome activity inhibited neuritic transport, and caused tau phosphorylation in a c-Jun and ERK 1/2 dependent manner. Using proteasome inhibition in APP overexpressing cells, we found an autophagy dependent intralysosomal Aβ accumulation, together with elevation of intra- and extracellular concentrations of Aβ. Autophagy inhibition protected the cells from the toxicity induced by decreased proteasome activity. Finally, we could, as the first group, show that Aβ can be directly transferred from one neuron to another through connected neurites. Furthermore, accumulation of Aβ in the endo-lysosomal compartment of receiving cells caused toxicity and neurodegeneration.We believe that cells not able to degrade accumulated Aβ, due to increased generation or reduced degradative capacity, instead tries to clear its content through transfer to connected neurons. If not properly degraded in the receiving cell, this can accelerate AD pathology and cause neuritic and neuronal degeneration spreading throughout the brain. Increasing the activity of the degradative systems, or inhibiting transmission of Aβ between neurons could therefore be novel treatments for AD.
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| 5. |
- Andin, Josefine, et al.
(författare)
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Environmental enrichment induces changes in the mRNA expression of rat EAAC1 and NMDA but not in AMPA
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Interaction with the environment has a key role in refining the neuronal circuitry required for normal brain function throughout life. Profound effects of enriched environment has been shown on neuronal strucrure and chemistry in experimental animals. Epidemiological studies imply that this is true also in man, thus cognitive stimulation has a protective effect on neurodegeneration, e.g. Alzheimer's disease. Glutamatergic corticocortical pathways are imperative for cognitive functions, such as memory and learning, and long term porenriation relies on the AMPA and NMDAglutamate rcceptors. The glutamate signalling is also dependent on a fine-runed transport system, in the hippocampus primarily by theglutamate transporter EAACl. In this study we show how environmental enrichment modulates these parts of the glutamarergic system using in siru hybridization. This work demonstrates for the first time that environmental enrichment modulates the mRNA expression of EAAC1 which is significantly decreased in hippocampal and cortical areas. We also provide further evidence about the upregulation of NMDA mRNA after environmental enrichement, and show it to have a regionally and hemisphere specific regulation. The current work also confirms that AMPA mRNA is nor per se changed by environmental enrichment in adult animals. Taken together, our results extend the knowledge of the glutamatergic system and its modulation by environmental enrichment and could contribute to the development of strategies aimed at limiting pathological changes associated with glutamatergic dysfunctions.
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| 6. |
- Andin, Josefine, 1979-, et al.
(författare)
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Influence of environmental enrichment on steady-state mRNA levels for EAAC1, AMPA1 and NMDA2A receptor subunits in rat hippocampus
- 2007
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993 .- 1872-6240. ; 1174:1, s. 18-27
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Tidskriftsartikel (refereegranskat)abstract
- Interaction with the environment has a key role in refining the neuronal circuitry required for normal brain function throughout life. Profound effects of enriched environment have been shown on neuronal structure and chemistry in experimental animals. Epidemiological studies imply that this is true also in man, thus cognitive stimulation has a protective effect on neurodegeneration, e.g., in Alzheimer's disease. Glutamatergic pathways are imperative for cognitive functions, such as memory, learning and long-term potentiation, and relies on the AMPA and NMDA glutamate receptors and the hippocampus, with its specific subregions, is an important anatomical substrate in this. The glutamate signalling is also dependent on a fine-tuned transport system, in the hippocampus primarily achieved by the glutamate transporter EAAC1. In this study we show how environmental enrichment modulates these parts of the glutamatergic system using quantitative in situ hybridisation. This work demonstrates for the first time that environmental enrichment modulates the mRNA expression of EAAC1 which is significantly and region specifically decreased in the hippocampus. We also provide evidence for regional and hemisphere-specific upregulation of NMDA mRNA in the hippocampus after environmental enrichment. The current work also shows that AMPA mRNA of the hippocampus is not per se changed by environmental enrichment in adult animals. Taken together, our results extend the knowledge of the glutamatergic system of specific regions of the hippocampus and its modulation by environmental enrichment and could contribute to the development of strategies aimed at limiting pathological changes associated with glutamatergic dysfunctions. © 2007.
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| 7. |
- Bjartmar, Lisa, 1966-, et al.
(författare)
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Long-term treatment with antidepressants, but not environmental stimulation, induces expression of NP2 mRNA in hippocampus and medial habenula
- 2010
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Ingår i: Brain Research. - : Elsevier. - 0006-8993 .- 1872-6240. ; 1328, s. 24-33
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Tidskriftsartikel (refereegranskat)abstract
- Neuronal Pentraxin 2 (NP2, Narp), known to mediate clustering of glutamatergic AMPA receptors at synapses, is involved in activity-dependent synaptogenesis and synaptic plasticity. In experimental settings, antidepressant treatment as well as a stimulating environment has a positive influence on cognition and hippocampal plasticity. This study demonstrates that NP2 mRNA is robustly expressed in the hippocampus and the medial habenula (MHb), both regions implicated in cognitive functions. Furthermore, NP2 mRNA expression is enhanced in the hippocampal subregions as well as in the MHb after long-term treatment with antidepressant drugs of various monoaminergic profiles, indicating a common mode of action of different antidepressant drugs. This effect occurs at the time frame where clinical response is normally achieved. In contrast, neither environmental enrichment nor deprivation has any influence on long-term NP2 mRNA expression. These findings support an involvement of NP2 in the pathway of antidepressant induced plasticity, but not EE induced plasticity; that NP2 might constitute a common link for the action of different types of antidepressant drugs and that the MHb could be a putative region for further studies of NP2.
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| 8. |
- Domert, Jakob, 1986-
(författare)
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Neuron-to-neuron propagation of neurodegenerative proteins; relation to degradative systems
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) and Parkinson’s disease (PD) are defined by neurodegeneration and accumulations of misfolded proteins that spread through the brain in a well characterized manner. In AD these accumulations consist mainly of β-amyloid (Aβ) and tau, while in PD, α-synuclein (α-syn) make up the characteristic lewy pathology. The general aim of this thesis was to investigate mechanisms associated with neurotoxic peptide activity by Aβ, tau and α-syn in relation to cellular degradation and transfer with a cell-to-cell transfer model system. We found that intercellular transfer of oligomeric Aβ occurs independently of isoform. However, the amount of transfer correlates with each isoforms ability to resist degradation or cellular clearance. The Aβ1-42 isoform showed particular resistance to clearance, which resulted in higher levels of cell-to-cell transfer of the isoform and lysosomal stress caused by accumulation. As Aβ accumulations can inhibit the proteasomal degradation we investigated how reduced proteasomal degradation affected neuron-like cells. We found increased levels of phosphorylated tau protein, disturbed microtubule stability and impaired neuritic transport after reduced proteasomal activity. These changes was partly linked to c-Jun and ERK 1/2 kinase activity. We could also show that α-syn transferred from cell-to-cell in our model system, with a higher degree of transfer for the larger oligomer and fibrillar species. Similar to Aβ, α-syn mainly colocalized with lysosomes, before and after transfer. Lastly, we have developed our cell-to-cell transfer system into a model suitable for high throughput screening (HTS). The type of cells have been upgraded from SH-SY5Y cells to induced pluripotent stem cells (iPSCs), with a differentiation profile more similar to mature neurons. The next step will be screening a small molecular library for substances with inhibitory effect on cell-to-cell transfer of Aβ peptides. The importance of the degradative systems in maintaining protein homeostasis and prevent toxic accumulations in general is well known. Our findings shows the importance of these systems for neurodegenerative diseases and also highlight the link between degradation and cell-to-cell transfer. To restore or enhance the degradative systems would be an interesting avenue to treat neurodegenerative diseases. Another way would be to inhibit the transfer of misfolded protein aggregates. By using the HTS model we developed, a candidate substance with good inhibitory effect on transfer can hopefully be found.
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| 9. |
- Domert, Jakob, et al.
(författare)
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Spreading of Amyloid-β Peptides via Neuritic Cell-to-cell Transfer Is Dependent on Insufficient Cellular Clearance
- 2014
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Ingår i: Neurobiology of Disease. - : Elsevier. - 0969-9961 .- 1095-953X. ; 65, s. 82-92
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Tidskriftsartikel (refereegranskat)abstract
- The spreading of pathology through neuronal pathways is likely to be the cause of the progressive cognitive loss observed in Alzheimer's disease (AD) and other neurodegenerative diseases. We have recently shown the propagation of AD pathology via cell-to-cell transfer of oligomeric amyloid beta (Aβ) residues 1-42 (oAβ1-42) using our donor-acceptor 3-D co-culture model. We now show that different Aβ-isoforms (fluorescently labeled 1-42, 3(pE)-40, 1-40 and 11-42 oligomers) can transfer from one cell to another. Thus, transfer is not restricted to a specific Aβ-isoform. Although different Aβ isoforms can transfer, differences in the capacity to clear and/or degrade these aggregated isoforms result in vast differences in the net amounts ending up in the receiving cells and the net remaining Aβ can cause seeding and pathology in the receiving cells. This insufficient clearance and/or degradation by cells creates sizable intracellular accumulations of the aggregation-prone Aβ1-42 isoform, which further promotes cell-to-cell transfer; thus, oAβ1-42 is a potentially toxic isoform. Furthermore, cell-to-cell transfer is shown to be an early event that is seemingly independent of later appearances of cellular toxicity. This phenomenon could explain how seeds for the AD pathology could pass on to new brain areas and gradually induce AD pathology, even before the first cell starts to deteriorate, and how cell-to-cell transfer can act together with the factors that influence cellular clearance and/or degradation in the development of AD.
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| 10. |
- Hallbeck, Martin, et al.
(författare)
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Neuron-to-Neuron Transmission of Neurodegenerative Pathology
- 2013
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Ingår i: The Neuroscientist. - : Sage Publications. - 1073-8584 .- 1089-4098. ; 19:6, s. 560-566
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Forskningsöversikt (refereegranskat)abstract
- One of the hallmarks of neurodegenerative dementia diseases is the progressive loss of mental functions and the ability to manage activities of daily life. This progression is caused by the spread of the disease to more and more brain areas via anatomical connections. The pathophysiological process responsible for this spread of disease has long been sought after. There has been an increased understanding that the driving force of these neurodegenerative diseases could be the small, soluble intraneuronal accumulations of neurodegenerative proteins rather than the large, extracellular accumulations. Recently we have shown that the mechanism of spread of Alzheimer's disease most likely depends on the neuron-to-neuron spread of such soluble intraneuronal accumulations of -amyloid through neuritic connections. Similar transmissions have been shown for several other neurodegenerative proteins but little is known about the cellular mechanisms and about any potential strategies that might stop this spread. Resolving these questions requires good cellular models. We have established a unique model of synaptic transmission between human neuronal-like cells, something that has previously been difficult to target. This opens the possibility of developing potential inhibitors of progression of these devastating diseases.
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