Mechanism of Ceftriaxone Induction of Excitatory Amino Acid Transporter-2 Expression and Glutamate Uptake in Primary Human Astrocytes

Abstract

Glutamate is an essential neurotransmitter regulating brain functions. Excitatory amino acid transporter (EAAT)-2 is one of the major glutamate transporters primarily expressed in astroglial cells. Dysfunction of EAAT2 is implicated in acute and chronic neurological disorders, including stroke/ischemia, temporal lobe epilepsy, amyotrophic lateral sclerosis, Alzheimer disease, human immunodeficiency virus 1-associated dementia, and growth of malignant gliomas. Ceftriaxone, one of the ␤-lactam antibiotics, is a stimulator of EAAT2 expression with neuroprotective effects in both in vitro and in vivo models based in part on its ability to inhibit neuronal cell death by glutamate excitotoxicity. Based on this consideration and its lack of toxicity, ceftriaxone has potential to manipulate glutamate transmission and ameliorate neurotoxicity. We investigated the mechanism by which ceftriaxone enhances EAAT2 expression in primary human fetal astrocytes (PHFA). Ceftriaxone elevated EAAT2 transcription in PHFA through the nuclear factor-B (NF-B) signaling pathway. The antibiotic promoted nuclear translocation of p65 and activation of NF-B. The specific NF-B binding site at the ؊272 position of the EAAT2 promoter was responsible for ceftriaxone-mediated EAAT2 induction. In addition, ceftriaxone increased glutamate uptake, a primary function of EAAT2, and EAAT2 small interference RNA completely inhibited ceftriaxone-induced glutamate uptake activity in PHFA. Taken together, our data indicate that ceftriaxone is a potent modulator of glutamate transport in PHFA through NF-Bmediated EAAT2 promoter activation. These findings suggest a mechanism for ceftriaxone modulation of glutamate transport and for its potential effects on ameliorating specific neurodegenerative diseases through modulation of extracellular glutamate.Glutamate plays a central role in brain physiology and pathology (1). It is the major mediator of excitatory signal transduction in the mammalian central nervous system and is implicated in most aspects of normal brain function, including cognition, memory, and learning (2). Glutamate exerts its signaling role by acting on glutamate receptors located on the surface of target cells. Accordingly, it is the glutamate concentration in the surrounding extracellular fluid that determines the extent of receptor stimulation. It is clinically relevant that the extracellular glutamate concentration is maintained at a low level, because excessive activation of glutamate receptors is harmful and glutamate is a potent neurotoxin at high concentration (2). The brain contains large quantities of glutamate, but only a small fraction of this glutamate is normally present in the extracellular fluid. Glutamate is constantly being released from cells and is continually being removed from the extracellular fluid (3). Glutamate transporters, also known as excitatory amino acid transporters, regulate this removal of glutamate from the extracellular fluid (3). Five excitatory amino acid transporter (EAAT) 4 cDNAs have been identified an...

The mGluR2/3 Agonist LY379268 Blocks the Effects of GLT-1 Upregulation on Prepulse Inhibition of the Startle Reflex in Adult Rats

“…Rothstein et al (2005) showed that CEF robustly stimulates GLT-1 expression, but not that of the other glutamate transporters, through increased GLT-1 gene transcription. This finding has been replicated in different laboratories (eg, Chu et al, 2007;Ouyang et al, 2007;Lee et al, 2008), including ours Omrani et al, 2009). We also showed that CEF increases GLT-1a expression in forebrain regions that regulate PPI of the startle .…”

Targeting Astrocytes for Stroke Therapy

“…However, because CFX induces the expression of the transcription factors NF-B and Nrf2, CFX may protect against cell death through multiple mechanisms. 66,67 In contrast to its administration before stroke, administration of CFX 30 minutes after the onset of ischemia did not significantly reduce stroke volume. 65 This lack of protection is not surprising, given that glutamate excitotoxicity is such an early event after onset of ischemia.…”

Glutamate Transporters and the Excitotoxic Path to Motor Neuron Degeneration in Amyotrophic Lateral Sclerosis

“…Ceftriaxone increases EAAT2 transcription in astrocytes through the nuclear factor-kB (NF-kB) signaling pathway by promoting nuclear translocation of p65 and activation of NF-kB (84). The mechanism of action of GPI-1046 is still not clear and must be investigated more in detail, although the initial indication suggests that immunophilins are involved in this upregulation (52).…”