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 vesicle-bound GAPDH/3-PGK at the expense of their substrates. The GAPDH inhibitor iodoacetate suppressed GAPDH/3-PGK-dependent, but not exogenous ATP-dependent, [(3)H]glutamate uptake into isolated synaptic vesicles. It also decreased vesicular [(3)H]glutamate content in the nerve ending preparation synaptosome; this decrease was reflected in reduction of depolarization-induced [(3)H]glutamate release. In contrast, oligomycin, a mitochondrial ATP synthase inhibitor, had minimal effect on any of these parameters. ADP at concentrations above 0.1 mm inhibited vesicular glutamate and dissipated membrane potential. This suggests that the coupled GAPDH/3-PGK system, which converts ADP to ATP, ensures maximal glutamate accumulation into presynaptic vesicles. Together, these observations provide insight into the essential nature of glycolysis in sustaining normal synaptic transmission.
Highlights
Glucose is the major source of brain energy and is essential for maintaining normal brain and neuronal function
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
We show that the glycolytic intermediate 1,3BPG 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
Summary
3-PG, 3-phosphoglycerate; t-ACPD, trans-1-aminocyclopentane-1,3-dicarboxylic acid; 4-AP, 4-aminopyridine; 1,3-BPG, 1,3-bisphosphoglycerate; DHAP, dihydroxyacetone phosphate; FCCP, carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone; GAP, glyceraldehyde-3-phosphate; GAPDH, glyceraldehyde-3phosphate dehydrogenase; 3-PGK, 3-phosphoglycerate kinase; PGM, monophosphoglycerate mutase; ACSF, artificial cerebrospinal fluid. GAPDH and Vesicular Glu Accumulation insight into the essential nature of glycolysis in normal synaptic transmission
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