Histamine up-regulates astrocytic glutamate transporter 1 and protects neurons against ischemic injury.

Astrocytic glutamate transporter 1 (GLT-1) is responsible for the majority of extracellular glutamate clearance and is essential for preventing excitotoxicity in the brain. Up-regulation of GLT-1 shows benefit effect on ischemia-induced neuronal damage. In present study, we examined the effect of histamine, a neurotransmitter or neuromodulator, on GLT-1 expression and function. In acute hippocampal slices, histamine selectively increased GLT-1 expression independent of neuronal activities. Similar up-regulation of GLT-1 was also observed after histamine treatment in pure cultured astrocytes, which was abolished by H1 receptor antagonist or PKC inhibitor. Cell surface biotinylation and whole-cell patch recordings of glutamate transporter current confirmed the up-regulation of functional GLT-1 following histamine exposure. Histamine treatment decreased the extracellular glutamate content and alleviated neuronal cell death induced by exogenous glutamate challenge. Moreover, we found a significant neuroprotective effect of histamine in brain slices after oxygen-glucose deprivation (OGD). In addition, histidine, the precursor of histamine, also showed neuroprotection against ischemic injury, which was accompanied by reversion of declined expression of GLT-1 in adult rats subjected to middle cerebral artery occlusion (MCAO). These neuroprotective effects of histamine/histidine were blocked by GLT-1 specific inhibitor dihydrokainate or H1 receptor antagonist. In summary, our results suggest that histamine up-regulates GLT-1 expression and function via astrocytic H1 receptors, thus resulting in neuroprotection against excitotoxicity and ischemic injury.

Fang Q ，Hu WW ，Wang XF ，Yang Y ，Lou GD ，Jin MM ，Yan HJ ，Zeng WZ ，Shen Y ，Zhang SH ，Xu TL ，Chen Z ... -  《-》

Pharmacological evaluation of glutamate transporter 1 (GLT-1) mediated neuroprotection following cerebral ischemia/reperfusion injury.

Recently glutamate transporters have emerged as a potential therapeutic target in a wide range of acute and chronic neurological disorders, owing to their novel mode of action. The modulation of GLT-1, a major glutamate transporter has been shown to exert neuroprotection in various models of ischemic injury and motoneuron degeneration. Therefore, an attempt was made to explore its neuroprotective potential in cerebral ischemia/reperfusion injury using ceftriaxone, a GLT-1 modulator. Pre-treatment with ceftriaxone (100mg/kg. i.v) for five days resulted in a significant reduction (P<0.01) in neurological deficit as well as cerebral infarct volume after 1h of ischemia followed by 24h of reperfusion injury. It also caused a significant (P<0.05) upregulation of GLT-1 mRNA, protein and glutamine synthetase (GS) activity. Furthermore, inhibition of ceftriaxone-mediated increased glutamine synthetase activity by dihydrokainate (DHK), a GLT-1 specific inhibitor, confirms the specific effect of ceftriaxone on GLT-1 activity. In addition, ceftriaxone also induced a significant (P<0.01) increase in [(3)H]-glutamate uptake, mediated by GLT-1 in glial enriched preparation, as evidenced by use of DHK and DL-threo-beta-benzyloxyaspartate (DL-TBOA). Thus, the present study provides overwhelming evidence that modulation of GLT-1 protein expression and activity confers neuroprotection in cerebral ischemia/reperfusion injury.

Verma R ，Mishra V ，Sasmal D ，Raghubir R ... -  《-》

Selective blockade of astrocytic glutamate transporter GLT-1 with dihydrokainate prevents neuronal death during ouabain treatment of astrocyte/neuron cocultures.

Glutamate (Glu) is a major excitatory neurotransmitter of the mammalian central nervous system and under normal conditions plays an important role in information processing in the brain. Therefore, extracellular Glu is subject to strong homeostasis. Astrocytes in the brain have been considered to be mainly responsible for the clearance of extracellular Glu. In this study, using mixed neuron/astrocyte cultures, we investigated whether astrocytic Glu transporter GLT-1 is crucial to the survival of neurons under various conditions. Treatment of the mixed cultures with a low concentration of Glu did not produce significant death of neurons. However, cotreatment with dihydrokainate (DHK), a specific blocker of GLT-1, resulted in significant neuronal death that was suppressed by an antagonist of N-methyl-D-aspartate (NMDA) receptors. These results suggested that astrocytic GLT-1 participated in the clearance of extracellular Glu and protected neurons from NMDA receptor-mediated toxicity. When the cultures were treated with ouabain, an inhibitor of Na(+)/K(+)-ATPase, a low concentration of Glu resulted in massive neuronal death that was also suppressed by cotreatment with an antagonist of NMDA receptors. In this case, however, cotreatment with DHK significantly protected neurons from death, suggesting that GLT-1 was responsible for the death of neurons. The present study provides evidence suggesting that astrocytes use their Glu transporter GLT-1 to protect neurons from Glu toxicity, but, ironically, also use GLT-1 to kill neurons through Glu toxicity depending on their status.

Kawahara K ，Hosoya R ，Sato H ，Tanaka M ，Nakajima T ，Iwabuchi S ... -  《GLIA》

High extracellular glutamate modulates expression of glutamate transporters and glutamine synthetase in cultured astrocytes.

Lehmann C ，Bette S ，Engele J 《-》

Harmine mediated neuroprotection via evaluation of glutamate transporter 1 in a rat model of global cerebral ischemia.

Global cerebral ischemia (GCI) causes energy deficiency results in excessive release of glutamate from neurons. Astrocytic glutamate transporters play a predominant role in keeping extracellular glutamate concentrations below excitotoxic levels. Glutamate transporter 1 (GLT-1) may account for more than 90% of glutamate uptake in adult forebrain. Preclinical findings implicate that Harmine present neuroprotection effects in a rat model of amyotrophic lateral sclerosis disease, and the beneficial effects were specifically due to up-regulation of GLT-1. However, no experiments have explored the potential of Harmine to provide neuroprotection in the setting of GCI. The current study was designed to determine whether Harmine could attenuate cerebral infarction as well as improve neuronal survival after GCI. Furthermore, to test whether the mechanisms were associated with up-regulating of GLT-1, we used a GLT-1 specific inhibitor dihydrokainate (DHK) and analysis the expression of GLT-1 mRNA and protein in cortex of brain. We also examined whether Harmine treatment affected astrocytes activation via immunofluorescence. Our results showed that post-GCI administration of Harmine could attenuate cerebral infarct volume and decrease neurons death. It also caused significantly elevation of GLT-1 mRNA and protein and remarkably attenuation of astrocyte activation. We provide novel clues in understanding the mechanisms of which Harmine exerts its neuroprotective activity in neurological disorders.

Sun P ，Zhang S ，Li Y ，Wang L ... -  《-》