Glutamate receptor | EPFL Graph Search

Glutamate receptors are synaptic and non synaptic receptors located primarily on the membranes of neuronal and glial cells. Glutamate (the conjugate base of glutamic acid) is abundant in the human body, but particularly in the nervous system and especially prominent in the human brain where it is the body's most prominent neurotransmitter, the brain's main excitatory neurotransmitter, and also the precursor for GABA, the brain's main inhibitory neurotransmitter. Glutamate receptors are responsible for the glutamate-mediated postsynaptic excitation of neural cells, and are important for neural communication, memory formation, learning, and regulation. Glutamate receptors are implicated in a number of neurological conditions. Their central role in excitotoxicity and prevalence in the central nervous system has been linked or speculated to be linked to many neurodegenerative diseases, and several other conditions have been further linked to glutamate receptor

Regulation of the protein complex NEEP21 - GRIP - GluR2 implicated in AMPAR trafficking through endosomal compartments

Karina Kulangara

It is important for neurotransmission to control the number of receptors at synapses. The synaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type of glutamate receptors (AMPARs) control the strength of excitatory transmission. These receptors are mobile and cycle between internal endosomal compartments and the plasma membrane. We have identified previously a protein complex between the endosomal protein NEEP21, the AMPAR subunit GluR2 and the scaffold protein GRIP necessary for correct GluR2 recycling. Here we elucidate the regulation underlying the complex formation and dissociation necessary for the trafficking through endosomal compartments. We show that a 85 kDa protein kinase, which is associated with NEEP21, phosphorylates GRIP on serine 917. Protein kinase C is activated by glutamate receptor stimulation, and leads to the activation of the NEEP21-associated kinase. The phosphorylation of GRIP leads to a reduced binding between GRIP and NEEP21, and GRIP and GluR2. Serine 917 is implicated in AMPAR cycling, since a wildtype carboxyterminal GRIP fragment expressed in hippocampal neurons interferes with GluR2 surface expression. On the contrary, a S917D mutant fragment does not interfere with GluR2 surface expression. The regulation of the formation and dissociation of the protein complex between NEEP21, GluR2 and GRIP1 may suggest a sorting mechanism between the recycling and degradation pathways for the AMPAR subunit GluR2. This is especially important in the light of the discovery of a form of plasticity which implicates GluR2-lacking AMPAR, and the fact that insertion of GluR2-lacking AMPAR are implicated in a number of neurological diseases like ALS or ischemia. Our results identify an important regulatory mechanism in the trafficking of AMPAR subunits between internal compartments and the plasma membrane.

EPFL2006

Lentiviral Transgenesis as a Tool to Study the Role of Uncoupling Protein Isoforms in the Nervous System

Hélène Danielle Perreten Lambert

A tight coupling exists between synaptic activity and glucose utilization by astrocytes. Metabolic cooperation between neurons and astrocytes mediates this coupling. During synaptic activation, glutamate that is released in the synaptic cleft as a neurotransmitter by neurons is rapidly cleared by an active uptake into astrocytes. One glutamate is co-transported with three Na+. Intracellular astrocytic Na+ homeostasis is re-established by the Na+/K+-ATPase which requires ATP provided mainly by glycolysis. The resulting lactate is released in extracellular space and contributes to the energetic balance of activated neurons. This coupling between astrocytes and neurons is known as the astrocyte-neuron lactate shuttle hypothesis (ANLSH). The role of mitochondria in this coupling remains to be determined and more specifically the role of uncoupling proteins (UCP) which have been recently identified in neural tissues. UCPs belong to a family of mitochondrial carriers which are present in the inner mitochondrial membrane. There are five isoforms named UCP1 to UCP5. The well-known characterized is UCP1, also named thermogenin, which is present in the brown adipose tissue (BAT) of the small rodents and is responsible of non-shivering thermogenesis. It dissipates the proton gradient across the inner mitochondrial membrane, thereby producing heat instead of ATP. UCP2 is ubiquitous and is implicated in protection against excessive reactive oxygen (ROS) production. The expression of UCP3 is restricted to skeletal muscle where it is linked to fatty acid metabolism. The role of the brain isoforms UCP4 and UCP5 is still poorly understood. Initially, we set out to evaluate their function in energy metabolism of astrocytes and neurons. We used the lentiviral strategy to overexpress or silence the UCPs isoforms in primary cultures of astrocytes and neurons. We found that only UCP4 and UCP5 had an uncoupling activity in brain cells. Indeed, we observed a reduced mitochondrial potential and a reduced ATP/ADP ratio in astrocytes as well as in neurons overexpressing UCP4 or UCP5. UCP4 reduced the oxidative pathway of astrocytes without modifying the basal glucose metabolism and without having a lethal effect on the cell. Oxygen consumption rate (OCR) of brain cells ovexpressing UCPs was reduced. Moreover, UCP4 increased lactate release by astrocytes, suggesting an implication in the astrocyte-neuron coupling. We also brought evidence that both UCP4 and UCP5 partially protect brain cells from oxidative damage. All these results were confirmed by experiments on UCPs silencing. In a second step, we used a co-culture model to study the impact of astrocytic uncoupling protein on neuronal survival and we demonstrated that the presence of uncoupling protein in astrocytes prevents neuronal death after glutamate excitotoxicity. Taken together, all these results support an important role of uncoupling proteins in the regulation of astrocytic energy production, thus promoting local export of lactate which can be used by neurons.

EPFL2011

Elevated NMDA receptor levels and enhanced postsynaptic long-term potentiation induced by prenatal exposure to valproic acid

Henry Markram, Tania Rinaldi

Valproic acid (VPA) is a powerful teratogen causing birth defects in humans, including autism spectrum disorder (ASD), if exposure occurs during the first trimester of embryogenesis. Learning and memory alterations are common symptoms of ASD, but underlying molecular and synaptic alterations remain unknown. We therefore studied plasticity-related mechanisms in the neocortex of 2-week-old rats prenatally exposed to VPA and tested for changes in glutamate-mediated transmission and plasticity in the neocortex. We found a selective overexpression of NR2A and NR2B subunits of NMDA receptors, as well as the commonly linked kinase calcium/calmodulin-dependent protein kinase II. Synaptic plasticity experiments between pairs of pyramidal neurons revealed an augmented postsynaptic form of long-term potentiation. These results indicate that VPA significantly enhances NMDA receptor-mediated transmission and causes increased plasticity in the neocortex. Enhanced plasticity introduces a surprising perspective to the potential molecular and synaptic mechanisms involved in children prenatally exposed to VPA.

2007