The role of the GABAA receptor-stabilizing protein ubiquilin-1 in a mouse model of in vitro epilepsy
Loading...
Date issued
Authors
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
Reuse License
Abstract
For more than ten years following a traumatic brain injury (TBI), the risk of being diagnosed
with posttraumatic epilepsy (PTE) is substantially increased (104). PTEs constitute an
increasing socioeconomic and global public health concern and thus, a large proportion of
acquired epilepsies (97, 99). To this day, no effective and antiepileptogenic treatment strategy
has been implemented in clinical practice and therefore remains a challenging subject of
research (98). With the advent of newer techniques in epilepsy research, the deciphering of
the pathophysiology underlying posttraumatic epileptogenesis is steadily improving. The use
of animal models of epilepsy and TBI is of great significance for the discovery of biomarkers
or potential therapeutic interventions (56). For this purpose, specific molecular targets with an
altered expression during TBI-inflicted epileptogenesis prove promising for devising
antiepileptogenic treatment strategies (98). By using our established animal models of TBI and
in vitro epilepsy, we gained new insights into the regulation of the GABAA receptor-interacting
protein ubiquilin-1. Recent studies have demonstrated that ubiquilin-1 is strongly regulated in
epilepsy (64), ischemic brain injuries (121) as well as in neurodegenerative diseases, e.g.
Alzheimer’s and Huntington’s disease (118, 120). In the preliminary work for this study, a
quantitative approach of proteomic analysis on isolated GFP+ interneurons from the
contralateral hemisphere after unilateral TBI-induction was implemented to identify target
proteins implicated in posttraumatic brain injury mechanisms. The label-free quantification in
cortical GABAergic interneurons from CCI-treated GAD67-GFP mice revealed a significant
downregulation of ubiquilin-1 24 hours post-lesion. To investigate the common features
between this regulation post-TBI and epilepsy, we implemented an epilepsy model to study
the ubiquilin-1 expression in slices from the cortex and hippocampus. In the present study,
epileptiform activity was induced in vitro by application of the combination of kainic acid (KA,
500 nM) and the GABAA receptor antagonist picrotoxin (PTX, 50 μM). These
chemoconvulsives have already been established as a highly reliable in vitro model of epilepsy
by Ridler et al. (170). We monitored the highly repetitive occurrence of seizure-like events
(SLEs) with extracellular multielectrode array (MEA) recordings in the hippocampal CA1 region
of acute brain slices. Following the induction of epileptiform events, we quantified the
expression of our target ubiquilin-1 in hippocampal and cortical slices in a time window of up
to seven hours after seizure induction with Western blots. Here, we disclosed a reduction of
ubiquilin-1 expression at all time points of incubation in both the hippocampus and the cortex.
Next, we successfully performed a pharmacological rescue in order to recover the previously
diminished ubiquilin-1 levels by use of the non-selective monoamine oxidase inhibitor
nialamide (NM,10 μM). Our Western blot data raised the question of whether an upregulation
of ubiquilin-1 expression would alter the properties of in vitro epileptiform activity. Therefore,
we recorded dose-response relationships by applying increasing concentrations of PTX (0-100 - 82 -
μM). Interestingly, the application of NM during MEA recordings substantially alleviated
epileptiform activity with regard to the number of SLEs and the mean peak amplitudes. Our
observation indicates that aside from a restored ubiquilin-1 expression, the different
monoamine transmitter systems might contribute to this epileptostatic effect and have a great
potential for future investigations.