Ampelopsin (AMP) preserves glutamate homeostasis between astrocyte and neuron against cerebral ischemia injury

Abstract

The glutamate-glutamine(Glu-Gln) cycle between astrocytes and neurons is an essential component in balancing extracellular Glu levels during excitatory neurotoxicity. Glutamine synthetase (GS) and glutaminase (GLS) are the key mediators in keeping Glu balance. Ampelopsin (AMP) has an inhibitory effect on peripheral GLS. It is uncertain whether this effect of AMP could produce neuroprotective effects and affect glutamate balance. The middle cerebral artery occlusion/ reperfusion (MCAO/R) model was constructed to investigate the effect of AMP and CB-839 on glutamate-induced ischemic injury in vivo. The protein expression of GLS, GS, glutamate transporter-1 (GLT-1), and N-methyl-D-aspartate receptor (NMDAR) was detected, and the distribution of GLS and GS in brain astrocytes and neurons was analyzed by immunofluorescence staining. Glu is the active molecule that mediates the upstream and downstream excitotoxic responses. The levels of Glu and Gln in the Glu-Gln metabolic cycle were also assayed. Our studies demonstrated that either AMP or CB-839 showed neuroprotective effects on MCAO/R mice through alleviating cerebral infarction area, relieving brain edema and neurological deficit function. They also reduced the necrosis of nerve tissue, rescued the damage of neurons and Nissl bodies undergoing ischemia. In addition, both AMP and CB-839 enhanced GS-mediated conversion of Glu to Gln on astrocytes by increasing ischemic brain GS activity and reducing Glu accumulation via facilitating GLT-1 expression and promoting Glu uptake. On neurons, the GLS-mediated hydrolysis of Gln to Glu is hindered by AMP and CB-839 through reducing the expression of GLS, which results in elevated Gln content and downregulated Glu levels in cerebral ischemia. At the same time, the expression of NMDAR was decreased to prevent the excitatory neurotoxicity caused by Glu's excessive activation. AMP exhibited neuroprotection in mice subjected transient focal cerebral ischemia via its ability to promote the dynamic balance of the glutamate concentration.