Glycolysis and Glutamate Accumulation into Synaptic Vesicles

Abstract

Glucose is the major source of brain energy and is essential for maintaining normal brain and neuronal function. Hypoglycemia causes impaired synaptic transmission. This occurs even before significant reduction in global cellular ATP concentration, and relationships among glycolysis, ATP supply, and synaptic transmission are not well understood. We demonstrate that the glycolytic enzymes glyceraldehyde phosphate dehydrogenase (GAPDH) and 3-phosphoglycerate kinase (3-PGK) are enriched in synaptic vesicles, forming a functional complex, and that synaptic vesicles are capable of accumulating the excitatory neurotransmitter glutamate by harnessing ATP produced by vesiclebound GAPDH/3-PGK at the expense of their substrates. The GAPDH inhibitor iodoacetate suppressed GAPDH/ 3-PGK-dependent, but not exogenous ATP-dependent, Glycolysis plays a vital role in maintaining normal brain function. Glucose is known to serve as the major substrate for cerebral energy under normal conditions (1). Recent evidence suggests a direct correlation between glucose utilization and cognitive function (2). Reduction of glucose levels results in pathophysiological states and abnormal electrophysiological activity; however, this occurs long before significant alteration in tissue ATP levels is detected (3-7). Substitution of pyruvate for glucose does not support normal evoked neuronal activity, although tissue ATP level returns to normal (8 -10). Abnormal synaptic transmission caused by hypoglycemia occurs in part if not entirely by a presynaptic mechanism (7,11,12). Fleck et al. (7) have shown that substantial reduction of extracellular glucose results in a decrease in stimulus-evoked Glu release, with no changes in ATP levels. These studies together suggest that glycolysis or glycolytic intermediate(s) are necessary for normal synaptic transmission independent of global cellular ATP levels.In an attempt to reveal the underlying mechanism of hypoglycemia-induced aberrant synaptic transmission, we previously explored the possibility that glycolytic intermediates could modify proteins localized in the nerve ending (13,14). 3-Phosphoglycerate (3-PG) 1 was demonstrated to stimulate phosphorylation of 155-and 72-kDa proteins. The latter was identified as glucose-1,6-bisphosphate synthetase, and 1,3-bisphosphoglycerate (1,3-BPG) was found to serve as the direct substrate for phosphorylation of this enzyme, by donating 1-phosphate. Both of these phosphorylated proteins are enriched in the synaptosomal (nerve ending preparation) as well as cell body soluble fractions, but the significance of these modifications in synaptic transmission remains unclear.In this paper, we show that the glycolytic intermediate 1,3-BPG forms an acyl-enzyme intermediate with vesicle-bound glyceraldehyde phosphate dehydrogenase (GAPDH), that vesicle-bound GAPDH exists in a complex with 3-phosphoglycerate kinase (3-PGK), and that activation of vesicle-associated GAPDH and 3-PGK is sufficient to support vesicular uptake of Glu. Glutamate is now recognized as the major ex...

A Preferential Role for Glycolysis in Preventing the Anoxic Depolarization of Rat Hippocampal Area CA1 Pyramidal Cells

“…It has been suggested (Raffin et al, 1992;Rosenthal and Sick, 1992) that the plasma membrane Na ϩ /K ϩ -ATPase is preferentially fueled by ATP produced from glycolysis (although it is unclear why mitochondrially produced ATP cannot diffuse to plasma membrane Na ϩ pumps, and an increase in glycolytic rate via the Pasteur effect might explain why mitochondrial block has relatively little effect). Consistent with a metabolic compartmentation within cells in which glycolysis powers ion pumping, glycolytic enzymes have been detected in synaptic locations where energy use on ion pumping is high (Wu et al, 1997;Ikemoto et al, 2003). This could explain why fueling glycolysis with glucose while blocking mitochondria prevents an AD; glycolytic ATP might allow the Na ϩ /K ϩ -ATPase to function sufficiently to maintain transmembrane ion gradients.…”

The Muscle-specific Calmodulin-dependent Protein Kinase Assembles with the Glycolytic Enzyme Complex at the Sarcoplasmic Reticulum and Modulates the Activity of Glyceraldehyde-3-phosphate Dehydrogenase in a Ca2+/Calmodulin-dependent Manner

“…Thus, these studies point to a previously unrecognized role for the multifunctional CaMKII in regulating membrane ATP through targeting and activation of glycolytic enzymes such as GAPDH in response to the calcium signal. Although, PGK and GAPDH normally exist in a complex and at the SR membrane (20,39,(41)(42)(43), we were unable to detect this in our assay conditions, because this association is fragile and disrupted in 0.1 M KCl (44).…”

“…A role for GAPDH together with 3-phosphoglycerate kinase (PGK) has been previously established in the production of ATP from GAP, NAD ϩ , P i , and ADP at the level of the SR membrane (19,20,39,40). In addition, a recent study demonstrated that synaptic vesicles were capable of generating local ATP via the membrane-associated GAPDH system, which could support the accumulation of the excitatory neurotransmitter glutamate even during significantly reduced global cellular ATP concentrations (41). It is notable that synaptic vesicles contain a CaMKII␤ isoform (42), which we found to associate with GAPDH but to a much less degree when compared with the muscle-specific isoform of the kinase.…”

“…A model of CaMKII␤ M assembly with the glycolytic enzyme complex at the SR. CaMKII␤ M is targeted to SR membrane by ␣-KAP (11). CaMKII␤ M binds GAPDH, which further assembles with aldolase (47) and 3-phosphoglycerate kinase (PGK) (41)(42)(43). Calcium release from RyR activates phosphorylase b kinase, which mobilizes glycogen to glucose by glycogen phosphorylase and glycogen debranching enzymes (36,37).…”

Malaria Plasmodium agent induces alteration in the head proteome of their Anopheles mosquito host

“…Four metabolic enzymes were up-regulated in the MI group suggesting an increased energy metabolism in the head of sporozoite-infected mosquitoes. A modification of metabolic enzyme activity could modify the production of ATP and consequently be detrimental to normal brain and neuronal function [34][35][36]. In the CNS of vertebrates, ATP is not only the energy source but can also act directly as a neuromodulator at purinergic synapses and as a factor with the potential to regulate: (i) neural development and plasticity; (ii) proliferation and apoptosis of glial and brain capillary endothelial cells; and (iii) the response of the nervous system to disease processes [37,38].…”