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Proteasome Inhibition Induces Stress Kinase Dependent Transport Deficits – Implications for Alzheimer’s Disease
Linköping University, Department of Clinical and Experimental Medicine, Division of Neuroscience. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Local Health Care Services in East Östergötland, Department of Geriatric Medicine in Norrköping.
Linköping University, Department of Clinical and Experimental Medicine, Division of Neuroscience. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Division of Neuroscience. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Division of Neuroscience. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Local Health Care Services in Central Östergötland, Department of Geriatric Medicine in Linköping.
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2014 (English)In: Molecular and Cellular Neuroscience, ISSN 0890-8508, E-ISSN 1095-9327, Vol. 58, 29-39 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier , 2014. Vol. 58, 29-39 p.
National Category
Clinical Medicine
Identifiers
URN: urn:nbn:se:liu:diva-81339DOI: 10.1016/j.mcn.2013.11.001ISI: 000331853600004OAI: oai:DiVA.org:liu-81339DiVA: diva2:551720
Available from: 2012-09-12 Created: 2012-09-12 Last updated: 2017-02-23Bibliographically approved
In thesis
1. The involvement of degradation pathways and neuron-to-neuron transmission in Alzheimer’s disease
Open this publication in new window or tab >>The involvement of degradation pathways and neuron-to-neuron transmission in Alzheimer’s disease
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 69 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1317
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-81341 (URN)978-91-7519-848-4 (ISBN)
Public defence
2012-10-05, Nils-Holger salen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2012-09-12 Created: 2012-09-12 Last updated: 2012-09-12Bibliographically approved
2. Neuron-to-neuron propagation of neurodegenerative proteins; relation to degradative systems
Open this publication in new window or tab >>Neuron-to-neuron propagation of neurodegenerative proteins; relation to degradative systems
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. 63 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1535
Keyword
Cell-to-cell transfer, beta-amyloid, Alzheimer's disease, degradation, proteasome, alpha-synuclein, Parkinson's disease, high throughput screening model
National Category
Cell and Molecular Biology Neurosciences
Identifiers
urn:nbn:se:liu:diva-134667 (URN)10.3384/diss.diva-134667 (DOI)9789176857014 (ISBN)
Public defence
2017-03-23, Linden, Campus US, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2017-02-27 Created: 2017-02-23 Last updated: 2017-02-27Bibliographically approved

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Agholme, LottaNath, SangeetaDomert, JakobMarcusson, JanKågedal, KatarinaHallbeck, Martin
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Division of NeuroscienceFaculty of Health SciencesDepartment of Geriatric Medicine in NorrköpingDepartment of Geriatric Medicine in LinköpingDivision of Cell BiologyDepartment of Clinical Pathology and Clinical Genetics
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