Modelling mitochondrial epilepsy in vitro :conceptualisation, mechanisms, and therapeutic implications

Abstract

Up to a third of patients with mitochondrial disease exhibit epilepsy which is difficult to control with existing pharmacotherapies. Anti-epileptic drug development in this field has stalled due to a paucity of pre-clinical models. To address this, I developed a novel in vitro model of mitochondrial epilepsy. The main features of the model are respiratory chain complex I and IV inhibition as well as astrocytic aconitase inhibition using pharmacological agents. In this way, I observed epileptiform discharges in rodent and murine hippocampal brain slices. Using immunohistochemical techniques, I confirmed findings from human neuropathological studies in that epileptic slices showed a selective loss of GABAergic interneurons, sparing of pyramidal neurons, and profound astrogliosis. To demonstrate the models clinical relevancy, I illustrated the model’s predictive validity by observing that epileptic activity was unaffected by various antiepileptic drugs. These studies did reveal that there was an involvement of AMPA and GABAA receptors in the generation of the epileptiform discharges. Further experiments also implicated the astroglial glutamate-glutamine cycle in the process of epileptogenesis. Using metabolic tracing experiments, glutamine was observed to be depleted during the epileptic state. Glutamine supplementation sustained the synthesis of GABA in the epileptic tissue, presumably to restore metabolic homeostasis. Finally, aerobic respiration was inhibited alongside the upregulation of anaerobic glycolysis during the epileptic state. To dissect the role of glutamine in the modulation of mitochondrial respiration, I isolated neuronal and astrocytic populations and performed measurements of metabolic flux during the induction of seizure activity. Glutamine was able to rescue partial mitochondrial respiratory chain inhibition selectively in the astrocytes. Overall, I have developed an in vitro model of mitochondrial epilepsy and showed the interaction between astrocytes and neurons is prerequisite for seizure generation. Several pharmacological targets have emerged from these studies which may provide future novel therapeutic targets for this condition.