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GENERAL INTRODUCTION & OUTLINE OF THE THESIS
approach could be the use of microRNAs (miRNAs).
miRNAs are small, non-coding RNA molecules of 18-22 nucleotides in length
that regulate gene expression at a post-transcriptional level by binding to target mRNAs, inducing degradation or translational repression. miRNAs are involved in essential pro- cesses in cells like homeostasis, growth, metabolism and inflammation. Also, miRNAs can be excreted by a variety of cells to exhibit their function in other cells or different parts of the body, via the blood stream. miRNAs are indispensable for normal brain develop- ment and functioning 115 and are linked to different processes in the pathogenesis of neurodegenerative disorders 116. The expression of several miRNAs was shown to change in both human epileptogenic brain and in experimental models of epilepsy, hereby indi- cating potential targets for treatment or valuable disease biomarkers 117, 118. Furthermore, it has been recently shown that modulating inflammatory pathways by administrating of a miRNA mimic molecule could prevent disease progression and reduce seizures in an experimental model of epilepsy, indicating that miRNAs related to neuroinflammation could have therapeutic potential in the treatment of epilepsy 119, 120.
Cell culture systems to study inflammatory pathways
In order to evaluate basic cellular mechanisms, in vitro cell culture systems can be used. Modulation of specific signaling pathways, and overexpression or knockdown of specific miRNAs in human cell cultures may be used to gain knowledge about general trends in astrocyte functioning and to give proof-of-concept information. Also, cell culture systems allow to specifically study functional effects of compounds prior to switching to pre-clinical experimental designs, and therefore minimizing animal use in epilepsy research. Despite the fact that astrocyte cultures never represent the complexity of the in vivo situation of an epileptogenic brain, it might offer advantages by studying direct effects of a modulation, without confounding variables that are present in other pre-clin- ical experimental models. Also, progress is made in improving the complexity of in vitro systems and hereby increasing the representation of the in vivo situation, like the use of 3D gel culture matrices and organoid cultures 121. Therefore, in vitro astrocyte cul- tures serve an excellent starting point for examining potential therapeutic treatments of inflammatory pathways in epilepsy.
Scope and outline of the thesis
In this thesis, we aimed to investigate the molecular mechanisms of pathology in TSC, in order to find potential targets and novel therapeutic strategies. We therefore examined both histological characteristics of TSC pathology and molecular pathways underlying the pathology, by investigating post-transcriptional regulation of inflammatory pathways.
In chapter 2, the aim was to define distinct histological patterns within tubers and to correlate these findings with clinical data. We semi-automatically quantified the expression of several cellular markers, including cell identity and mTOR activity, in brain material of TSC patients that underwent epilepsy surgery and based on this we proposed a new histopathological classification system for cortical tubers in TSC. Additionally, we aimed to evaluate possible functional modulations of inflammatory pathways using in vitro astrocyte cultures.
In chapter 3, we examined the complexity of the molecular signaling network in
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