Effects of amyloid-beta on homeostatic network plasticity in human iPSC-derived neuronal networks

Alzheimer’s disease (AD) is a progressive, neurodegenerative disorder and it is the most common cause of dementia in elderly. The disease is characterized by memory loss, mood swings, and communication problems. This uniquely human disease has been investigated in various mouse models mimicking d...

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Bibliographic Details
Main Author: Tanriöver, Gaye
Contributors: Nieweg, Katja (Jun Prof.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2017
Pharmazie
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Summary:Alzheimer’s disease (AD) is a progressive, neurodegenerative disorder and it is the most common cause of dementia in elderly. The disease is characterized by memory loss, mood swings, and communication problems. This uniquely human disease has been investigated in various mouse models mimicking different pathological hallmarks of AD, which supplied valuable insight into disease mechanisms; however, clinical trials based on these models failed and current treatments are unsatisfactory. To overcome the limitations of animal models of AD, the emerging induced pluripotent stem cell (iPSC) technology promises great potential. It offers the possibility to investigate underlying disease mechanisms, screen for drug targets and validate therapeutic effects in disease-relevant cell types of human origin on a patient-specific background. Current iPSC studies to model AD have been addressing the questions of the pathological hallmarks such as an increase in amyloid beta (Aß) and hyperphosphorylated tau. However, to investigate the AD-related phenomenon of neuronal hyperactivity, mature human neuronal cultures with spontaneously active networks are necessary, and their generation remains a challenge. In this study, to achieve spontaneously firing mature neuronal networks, human iPS cells were differentiated into neurons and were supported with endogenously differentiated human astrocytes or primary cortical astrocytes (PCA) isolated from rat brains. Neuronal activity was recorded by using multi electrode array (MEA) to detect single spikes and network bursts. Calcium imaging of spontaneously firing networks was performed to monitor synchronously active neurons in cultures. To trigger hyperactivity-induced homeostatic plasticity in human networks, iPSC-derived cultures were treated with 4-Aminopyridine (4AP), a non-selective inhibitor of voltage-gated K+ channels. It increased the network activity only in mature (burst firing) cultures. This induced hyperactivity further led to activation of homeostatic plasticity dependent mechanisms to reduce the firing rate. Single spike analysis suggested Na+ channel removal from the axonal membrane as one of these compensatory mechanisms. Moreover, repressor element-1 silencing transcription factor (REST) was identified as a key player in this process. To study AD-related impairments in the established model, cell-derived and synthetic Aß oligomers were prepared and characterized by semi-native western blot. Synthetic Aß oligomers were surprisingly stable when added to neuronal cultures and caused no cell death and no change in spontaneous network activity. However, upon 4AP treatment, Aß-treated networks showed impaired homeostatic plasticity and were not able to reduce the firing rate appropriately. According to the analysis of spike properties, the plasticity-associated reduction of axonal Na+ channels was also impaired. In Aß-treated cultures, nuclear REST expression was diminished at basal levels and after triggering homeostatic plasticity by 4AP. Thus, AD-related hyperactivity may be caused by dysfunctional homeostatic plasticity in a REST-dependent manner. Taken together, the results of this study provided the first hint on a previously unknown impairment of homeostatic plasticity mechanisms in AD and identified REST as a target which might contribute to the hyperactivity phenomenon at early stages of AD. This knowledge of plasticity impairment might expand our understanding of disease development and REST manipulation might be a new target for potential therapeutic strategies.
Physical Description:164 Pages
DOI:https://doi.org/10.17192/z2018.0043