Regulation of Glutamate Transporter Type 1 by TSA and the Antiepileptic Mechanism of TSA

Abstract

Epilepsy (EP) is a neurological disorder characterized by abnormal, sudden neuronal discharges. Seizures increase extracellular glutamate levels, causing excitotoxic damage. Glutamate transporter type 1 (GLT-1) and its human homologue excitatory amino acid transporter-2 (EAAT2) clear 95% of extracellular glutamate. Studies on neurodegenerative diseases suggest that trichostatin A (TSA), a broad-spectrum histone deacetylase (HDAC) inhibitor, can increase GLT-1/EAAT2 transcription. However, the precise mechanism by which TSA modulates GLT-1/EAAT2 levels remains unclear. This research demonstrated that TSA increases GLT-1/EAAT2 expression through histone acetylation, exerting substantial antiepileptic effects. Our results identify a promising therapeutic strategy for EP involving the modulation of glutamate transporters to mitigate seizures. Future research should explore the specific mechanisms underlying the effects of TSA and its potential clinical applications. Acute and chronic EP models were induced using kainic acid (KA) to assess the effects of TSA on the seizure threshold and frequency. Electrophysiological recordings of the hippocampus were used to evaluate the impact of TSA on neuronal excitability. RNA-Seq was used to analyse changes in glutamate transporter-related gene expression. Western blot analysis and qRT‒PCR were used to assess the influence of TSA on HDAC expression. To validate the role of GLT-1/EAAT2 in the antiepileptic effects of TSA, the impact of the GLT-1/EAAT2 inhibitor dihydrokainic acid (DHK) on the effects of TSA was assessed. Glutamate release was measured, and microdialysis was used to determine the glutamate content in the cerebrospinal fluid. Finally, metabolomics analysis was used to explore changes in amino acid levels in the hippocampus following TSA treatment to further confirm the antiepileptic potential of TSA. TSA effectively inhibited seizures in both acute and chronic models. It reduced the amplitude of excitatory postsynaptic currents (PSCs) and the frequency of spontaneous excitatory PSCs in the hippocampus without affecting inhibitory PSCs. Transcriptome analysis was used to identify glutamate transmission-related targets and revealed significant upregulation of the GLT-1 and EAAT2 genes in the hippocampus, which was confirmed by qRT‒PCR and Western blotting. Acetylation-induced upregulation of GLT-1/EAAT2 was observed, and inhibition of these transporters by DHK reduced the seizure-mitigating effects of TSA, underscoring the role of GLT-1/EAAT2 in clearing glutamate and its contribution to the observed antiepileptic effects of TSA. Our findings highlight the crucial role of GLT-1/EAAT2 in mediating the impact of TSA on glutamatergic transmission and seizure activity. These insights pave the way for the development of novel therapeutic approaches for EP involving the modulation of glutamate transporters.