The role of diurnal fluctuations in excitatory amino acid carrier 1 levels in post-ischemic hippocampal Zn 2+ accumulation

Exp Neurol. 2021 Feb;336:113538. doi: 10.1016/j.expneurol.2020.113538. Epub 2020 Nov 27.

Abstract

Accumulating evidence indicates time-of-day variations in ischemic neuronal injury. Under ischemic conditions, Zn2+ is massively released from hippocampal glutamatergic neurons, and intracellular Zn2+ accumulation results in neuron death. Notably, excitatory amino acid carrier 1 (EAAC1), known as a cysteine transporter, is involved in Zn2+ homeostasis, and its expressions exhibit a diurnal fluctuation. This study aimed to investigate whether time of day of an ischemic insult affects Zn2+ accumulation and neuronal injury and determine whether altered Zn2+ accumulation is modulated by EAAC1 diurnal fluctuation in the hippocampus in a mouse model of ischemic stroke. Mice subjected to transient global ischemia for 40 min at Zeitgeber time 18 (ZT18) (23:00) exhibited reduced Zn2+ accumulation and neuronal death in the hilar region of the hippocampus compared to those at ZT4 (09:00). The EAAC1 protein expression in the hippocampus was increased at ZT18 relative to ZT4. Intracerebroventricular injection of a non-selective excitatory amino acid transporter inhibitor, DL-threo-β-benzyloxyaspartate, or a selective EAAC1 inhibitor, L-aspartic acid β-hydroxamate, increased ischemia-induced Zn2+ accumulation and neuronal death in the hilus at ZT18. These findings suggest that ischemia-induced Zn2+ accumulation displays circadian fluctuations through diurnal variations in EAAC1 expressions and affects susceptibility to ischemic neuronal injury in the hippocampal hilar region.

Keywords: Circadian rhythm; Excitatory amino acid carrier 1; Ischemia; Zinc.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain Ischemia / metabolism*
  • Cell Death
  • Circadian Rhythm / physiology*
  • Excitatory Amino Acid Transporter 3 / antagonists & inhibitors
  • Excitatory Amino Acid Transporter 3 / metabolism*
  • Glutathione / metabolism
  • Hippocampus / metabolism*
  • Injections, Intraventricular
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Nerve Degeneration / pathology
  • Neurons / pathology
  • Zinc / metabolism*

Substances

  • Excitatory Amino Acid Transporter 3
  • Slc1a1 protein, mouse
  • Glutathione
  • Zinc