Characterization of the zinc-sensitive metal-regulatory transcription factor 1 in hippocampal epileptic network formation using an animal model of Temporal Lobe Epilepsy

Abstract

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy. It usually occurs after a transient brain insult, including status epilepticus (SE), which triggers a latent period of epileptogenesis prior to the occurrence of spontaneous seizures. In an experimental animal model, the Metal-regulatory Transcription Factor 1 (Mtf1) mediates the Zn²⁺-induced upregulation of the T-type Ca²⁺ channel Cav3.2, leading to an increase in intrinsic excitability of hippocampal neurons. However, Mtf1 emerged relatively recently as a pathogenetically relevant factor involved in the development of TLE and still little is known about its involvement in the process of epileptogenesis. Therefore, in this study we aim to achieve novel insights about Mtf1 with regard to its spatio-temporal location and activation during epileptogenesis, and to identify new Mtf1-downstream targets. Here, we provide evidence that Mtf1 is activated immediately after SE, and that it regulates several genes associated with synaptic plasticity processes. A transcriptional unit was successfully developed which allowed the identification of Mtf1-expressing neurons in vivo and the monitoring of Mtf1 activation during epileptogenesis. Adeno-associated virus (rAAV) transfer of Mtf1 and a dominant-negative form of Mtf1 (dnMtf1) in hippocampal neurons resulted in an increase of cAMP responsive element binding protein 1 (Creb1) mRNA expression. The kinetics of Creb1 expression followed the expression levels of Mtf1 in the hippocampal subregions of pilocarpine-SE animals. Immunofluorescence of murine slices showed a stronger Creb1 protein expression in neurons containing nuclear-activated Mtf1. Data from resected hippocampi of pharmacoresistant patients affected by TLE associated with hippocampal sclerosis support the Zn²⁺-Mtf1-Creb1 pathway. Finally, RNA-sequencing from dissected murine hippocampi transduced with Mtf1 and dnMtf1 revealed the Immunoglobulin Heavy Constant Gamma 1 (<em>Ighg1</em>), Serotonin 5-HT-2A Receptor (<em>Htr2a</em>) and the Dopamine Receptor D2 (<em>Drd2</em>) as downstream target genes of Mtf1. This work uncovered a novel transcription factor regulated transcript module in the process of epileptogenesis and provides new prospects for preventing and treating TLE.