Neurotrophic Factors Protect Cortical Synaptic Terminals Against Amyloid- and Oxidative Stress-induced Impairment of Glucose Transport, Glutamate Transport and Mitochondrial Function

Abstract

Previous studies have shown that several different neurotrophic factors can prevent death of cortical and hippocampal neurons induced by excitotoxic and oxidative insults in cell culture and in vivo. Because neuronal degeneration may be initiated by alterations occurring in synaptic compartments in disorders ranging from Alzheimer's disease to stroke, we tested the hypothesis that neurotrophic factors can exert direct protective actions at the level of the synapse. We now report that a nine amino acid bioactive fragment of activity-dependent neurotrophic factor (ADNF-9) enhances basal glucose and glutamate transport, and attenuates oxidative impairment of glucose and glutamate transport induced by amyloid β-peptide and Fe²⁺, in neocortical synaptosomes. Preservation of transporter function required only short-term (1–2 h) pretreatments. Basic fibroblast growth factor (bFGF) was also effective in suppressing oxidative impairment of synaptic transporter functions, while nerve growth factor (NGF) was less effective. Additional analyses showed that ADNF-9, bFGF and NGF suppress oxidative stress and mitochondrial dysfunction induced by amyloid β-peptide and Fe²⁺ in synaptosomes. Our data suggest that ADNF-9 can act locally in synaptic compartments to suppress oxidative stress and preserve function of glucose and glutamate transporters. Such synapto-protective actions suggest roles for activity-dependent trophic signaling in preventing degeneration of neuronal circuits, and indicate possible therapeutic applications of agents that stimulate local synaptic (transcription-independent) neurotrophic factor signaling pathways.