Mitochondrial glutamine metabolism drives epileptogenesis in primary hippocampal neurons.

Abstract

All available anti-seizure medications aim at symptomatic control of epilepsy, but there is no strategy to stop the development of the disease. The main reason is the lack of understanding of the epileptogenic mechanisms. Closing this knowledge gap is an essential prerequisite for developing disease-modifying therapies that can prevent the onset of epilepsy. Using primary co-cultures of hippocampal neurons and glial cells derived from rat pups of either sex, we show that epileptiform paroxysmal depolarization shifts (PDS) induce neuronal glucose hypometabolism which is compensated for by increased glutaminolysis. Glutaminolysis not only provides sufficient ATP to support electrical activity, but also leads to decreased vesicular glutamate release, thereby promoting neuronal hypersynchrony. Moreover, prolonged promotion of PDS increased neuronal arborization and synaptic density, which in combination with spontaneous recovery of neuronal glucose metabolism led to seizure-like discharge activity. Since inhibition of glutaminolysis did not prevent the PDS-induced morphogenesis, but eliminated seizure-like activity, we propose that glutaminolysis is a causative process linking neuronal metabolism with electrical activity thereby driving epileptogenesis.Significance statement The available pharmacotherapy for epilepsy provides symptomatic control of seizures by interfering with ictogenesis. However, understanding the preceding epileptogenic processes would offer an opportunity to intervene in the development of the disease. The electrical activity and glucose metabolism of the brain regions corresponding to the epileptic foci are disturbed long before the first seizures occur. The significance of the altered neuronal activity and metabolism is not well understood. We present evidence that abnormal neuronal electrical activity called paroxysmal depolarization shifts increase neuronal arborization and lead to metabolic shifts making neurons transiently rely on glutamine. We show that the interplay of these processes induces glucose hypometabolism, hyper-synchronization, and ultimately leads to seizure-like discharge activity, thus replicating several key features of epilepsy.