Up‐regulated GLT‐1 Resists Glutamate Toxicity and Attenuates Glutamate‐induced Calcium Loading in Cultured Neurocytes

Abstract

Glutamate transporter-1 (GLT-1) plays a dual role in glutamate transportation: both normally devotion to the clearance of glutamate and during some pathological conditions extruding glutamate to the extracellular space. Therefore, it is uncertain whether increased expression of GLT-1 will actually be helpful against glutamate excitotoxicity. In this study, GLT-1 up-regulation was induced by ceftriaxone, and L-glutamate was added to induce glutamate toxicity in primary cultured rat cortical cells. The results showed that up-regulated GLT-1 induced by 1 lM ceftriaxone for 2 days markedly increased cell viability, decreased apoptotic cell death and alleviated ultrastructural damage induced by 50 lM glutamate 15 min. as well as promoted L-[ 3 H]-glutamate uptake in cultured cells. GLT-1 up-regulation had no effect on the intracellular free calcium concentration ([Ca 2+ ] i ) in the resting situation, while relieved intracellular calcium overloading by reducing the elevation and promoting the recovery of [Ca 2+ ] i following stimulation of 50 lM glutamate for 2 min. Applying 100 lM dihydrokainic acid (GLT-1 antagonist) 30 sec. before glutamate eliminated the above effect of GLT-1 up-regulation on [Ca 2+ ] i . In conclusion, GLT-1 up-regulation induced by ceftriaxone plays a positive glutamate transporting role against glutamate toxicity in primary cultured rat cortical cells.Glutamate excitotoxicity causes neuronal death by means of over-stimulation of glutamate receptors, especially the N-methyl-D-aspartate (NMDA) receptor subtype which is largely permeable to calcium leading to intracellular calcium overloading [1]. The extracellular concentration of glutamate is mainly regulated by glutamate transporters situated in neurons and glial cells, which normally eliminate glutamate from the synaptic space and terminate glutamate action on the postsynaptic receptors [2,3]. However, in some pathological conditions (e.g. ischaemia and hypoxia), glutamate transporters were found to extrude glutamate to the extracellular space, operating in the opposite direction and contributing to neuronal damage [4].In the glutamate transporter family, glutamate transporter-1 (GLT-1) highly expresses in astrocytes [5] and accounts for 90% of all glutamate uptake in the brain [6]. Alterations in GLT-1 expression and activity can exert profound influence in neuroprotection and neuropathology. On the one hand, several recent studies suggest that up-regulating GLT-1 expression may be beneficial because of the simultaneously increased positive transporter function in pathological conditions. For example, upregulation of GLT-1 expression by some agents [7] (e.g. b-lactam compounds ceftriaxone and the group II mGluR agonist 4-aminopyrrolidine-2,4-dicarboxylate) increased glutamate intake and attenuated the Huntington's disease phenotype in the R6/2 mouse [8], alleviated motor neurone degeneration and delayed loss of neurons in an animal model of amyotrophic lateral sclerosis (ALS) [9], and played an anti-nociceptive role in a c...

mGluR5 protect astrocytes from ischemic damage in postnatal CNS white matter

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The Effect of GLT-1 Upregulation on Extracellular Glutamate Dynamics

“…By nature, iGluSnFR decay tau values are significantly slower than the actual uptake rate of glutamate, which is estimated to increase to 1 mM for 1-2 milliseconds following synaptic release (Bergles et al, 1999;Clements et al, 1992); nonetheless, iGluSnFR represents a sensitive means to detect relative changes in clearance rates under different experimental conditions, and can do so on a millisecond timescale. As summarized in Table 1, the bulk of studies that report enhanced glutamate uptake following ceftriaxone treatment quantified the uptake of exogenous radiolabeled glutamate over multiple minutes (Beller et al, 2011;Chotibut et al, 2014;Hu et al, 2015;Lee et al, 2008;Liu et al, 2013;Rothstein et al, 2005;Thöne-Reineke et al, 2008;Verma et al, 2010;Yang et al, 2011). In contrast, the studies that quantified glutamate uptake using iGluSnFR or (Hefendehl et al, 2016;Rothstein et al, 2005;Wilkie et al, 2020).…”

Metabotropic Glutamate Receptors Protect Oligodendrocytes from Acute Ischemia in the Mouse Optic Nerve

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