Differential regulation of the glutamate transporters GLT-1 and GLAST by GSK3β

Jiménez, Esther; Núñez, Enrique; Ibáñez, Ignacio; Draffin, Jonathan E.; Zafra, Francisco; Giménez, Cecilio

doi:10.1016/j.neuint.2014.10.003

Cited by 20 publications

(7 citation statements)

References 71 publications

(77 reference statements)

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“…The physiological importance of the contrasting regulation of GLT‐1 and GLAST is unknown, although both transporters appear to respond distinctly to a variety of signaling pathways. For instance, polyunsaturated fatty acids and GSK3‐β activation inhibit the activity of GLAST while they potentiate that of GLT‐1 (Berry et al, ; Jimenez et al, ; Zerangue, Arriza, Amara, & Kavanaugh, ). Also PKA, PKC, and PI3K are each involved in the complex regulation of both transporters in distinct experimental systems.…”

Section: Discussionmentioning

confidence: 99%

Identification of novel regulatory partners of the glutamate transporter GLT‐1

Piniella

Martínez-Blanco

Ibáñez

et al. 2018

Glia

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We used proximity‐dependent biotin identification (BioID) to find proteins that potentially interact with the major glial glutamate transporter, GLT‐1, and we studied how these interactions might affect its activity. GTPase Rac1 was one protein identified, and interfering with its GTP/GDP cycle in mixed primary rat brain cultures affected both the clustering of GLT‐1 at the astrocytic processes and the transport kinetics, increasing its uptake activity at low micromolar glutamate concentrations in a manner that was dependent on the effector kinase PAK1 and the actin cytoskeleton. Interestingly, the same manipulations had a different effect on another glial glutamate transporter, GLAST, inhibiting its activity. Importantly, glutamate acts through metabotropic receptors to stimulate the activity of Rac1 in astrocytes, supporting the existence of cross‐talk between extracellular glutamate and the astrocytic form of the GLT‐1 regulated by Rac1. CDC42EP4/BORG4 (a CDC42 effector) was also identified in the BioID screen, and it is a protein that regulates the assembly of septins and actin fibers, influencing the organization of the cytoskeleton. We found that GLT‐1 interacts with septins, which reduces its lateral mobility at the cell surface. Finally, the G‐protein subunit GNB4 dampens the activity of GLT‐1, as revealed by its response to the activator peptide mSIRK, both in heterologous systems and in primary brain cultures. This effect occurs rapidly and thus, it is unlikely to depend on cytoskeletal dynamics. These novel interactions shed new light on the events controlling GLT‐1 activity, thereby helping us to better understand how glutamate homeostasis is maintained in the brain.

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Section: Discussionmentioning

confidence: 99%

Identification of novel regulatory partners of the glutamate transporter GLT‐1

Piniella

Martínez-Blanco

Ibáñez

et al. 2018

Glia

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“…The idea that a kinase can differentially regulate subtypes of transporters is not unprecedented. For example, glycogen synthase kinase 3b has been shown to differentially modulate GLAST and GLT-1, producing a down-regulation in GLAST but up-regulation in GLT-1 activity and cell-surface expression via phosphorylation of the transporters (Jimenez et al 2014). Future studies are required to determine how basal regulation of EAAT1 by CaMKII is coupled to EAAT2b function.…”

Section: Discussionmentioning

confidence: 99%

Constitutive regulation of the glutamate/aspartate transporter EAAT1 by Calcium‐Calmodulin‐Dependent Protein Kinase II

Chawla

Johnson

Zybura

et al. 2017

Journal of Neurochemistry

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Glutamate clearance by astrocytes is an essential part of normal excitatory neurotransmission. Failure to adapt or maintain low levels of glutamate in the central nervous system is associated with multiple acute and chronic neurodegenerative diseases. The primary excitatory amino acid transporters in human astrocytes are EAAT1 and EAAT2 (GLAST and GLT-1 respectively in rodents). While the inhibition of calcium/calmodulin-dependent kinase (CaMKII), a ubiquitously-expressed serine/threonine protein kinase, results in diminished glutamate uptake in cultured primary rodent astrocytes (Ashpole et al. 2013), the molecular mechanism underlying this regulation is unknown. Here, we use a heterologous expression model to explore CaMKII regulation of EAAT1 and EAAT2. In transiently transfected HEK293T cells, pharmacological inhibition of CaMKII (using KN-93 or tat-CN21) reduces [3H]-glutamate uptake in EAAT1 without altering EAAT2 mediated glutamate uptake. While overexpressing the Thr287Asp mutant to enhance autonomous CaMKII activity had no effect on either EAAT1 or EAAT2 mediated glutamate uptake, overexpressing a dominant-negative version of CaMKII (Asp136Asn) diminished EAAT1 glutamate uptake. SPOTS peptide arrays and recombinant GST-fusion proteins of the intracellular N- and C-termini of EAAT1 identified two potential phosphorylation sites at residues Thr26 and Thr37 in the N-terminus. Introducing an Ala (a non-phospho mimetic) at Thr37 diminished EAAT1-mediated glutamate uptake, suggesting that the phosphorylation state of this residue is important for constitutive EAAT1 function. Our study is the first to identify a glutamate transporter as a direct CaMKII substrate and suggests that CaMKII signaling is a critical driver of constitutive glutamate uptake by EAAT1.

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“…The authors suggest that this differential modulation may be particularly relevant in pathological conditions such as AD or ischemia in which glutamate transporters and GSK3β are involved (Jimenez et al . ). Recent evidence suggests that GSK3β regulation of GLT‐1 expression in the spinal dorsal horn plays a role with neuropathic pain (Weng et al .…”

Section: Transcription/translational Modulatorsmentioning

confidence: 97%

Current approaches to enhance glutamate transporter function and expression

Fontana

2015

Journal of Neurochemistry

131

120

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L-glutamate is the predominant excitatory neurotransmitter in the CNS and has a central role in a variety of brain functions. The termination of glutamate neurotransmission by excitatory amino acid transporters (EAATs) is essential to maintain glutamate concentration low in extracellular space and avoid excitotoxicity. EAAT2/GLT-1, being the most abundant subtype of glutamate transporter in the CNS, plays a key role in regulation of glutamate transmission. Dysfunction of EAAT2 has been correlated with various pathologies such as traumatic brain injury, stroke, amyotrophic lateral sclerosis, Alzheimer's disease, among others. Therefore, activators of the function or enhancers of the expression of EAAT2/GLT-1 could serve as a potential therapy for these conditions. Translational activators of EAAT2/GLT-1, such as ceftriaxone and LDN/OSU-0212320, have been described to have significant protective effects in animal models of amyotrophic lateral sclerosis and epilepsy. In addition, pharmacological activators of the activity of EAAT2/GLT-1 have been explored for decades and are currently emerging as promising tools for neuroprotection, having potential advantages over expression activators. This review describes the current status of the search for EAAT2/GLT-1 activators and addresses challenges and limitations that this approach might encounter.

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Differential regulation of the glutamate transporters GLT-1 and GLAST by GSK3β

Cited by 20 publications

References 71 publications

Identification of novel regulatory partners of the glutamate transporter GLT‐1

Identification of novel regulatory partners of the glutamate transporter GLT‐1

Constitutive regulation of the glutamate/aspartate transporter EAAT1 by Calcium‐Calmodulin‐Dependent Protein Kinase II

Current approaches to enhance glutamate transporter function and expression

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