SNAP25 is a pre‐synaptic target for the depressant action of reactive oxygen species on transmitter release

Abstract

Reactive oxygen species (ROS) participate in various physiological and pathological processes in the nervous system, but the specific pathways that mediate ROS signalling remain largely unknown. Using electrophysiological techniques and biochemical evaluation of isolated fusion proteins, we explored the sensitivity to standard oxidative stress of the entire synapse, the pre-synaptic machinery and essential fusion proteins underlying transmitter exocytosis. Oxidative stress induced by H 2 O 2 plus Fe 2+ inhibited both evoked and spontaneous quantal release from frog or mouse motor nerve endings, while it left post-synaptic sensitivity unchanged. The depressant effect of H 2 O 2 on acetylcholine release was pertussis toxin-insensitive, ruling out G-protein cascades. Experiments with ionomycin, a Ca 2+ ionophore, revealed that ROS directly impaired the function of releasing machinery. In line with this, SNAP25, one of three essential fusion proteins, showed a selectively high sensitivity to the oxidative signals. Several ROS scavengers enhanced evoked synaptic transmission, consistent with tonic inhibition by endogenous ROS. Our data suggest that ROS-induced impairment of releasing machinery is mediated by SNAP25, which appears to be a pre-synaptic ROS sensor. This mechanism of ROS signalling could have widespread implications in the nervous system and might contribute to the pathogenesis of neurodegenerative diseases.

Nox enzymes, ROS, and chronic disease: An example of antagonistic pleiotropy

“…In guinea pig striatal slices, H 2 O 2 production was Ca 2+ -dependent and modulated neurotransmitter release, revealing a signaling role for ROS in synaptic transmission [154]. A possible target is the fusion protein SNAP25, which may function as a presynaptic ROS sensor [155].…”

Axonal Degeneration in Motor Neuron Disease

“…This phenomenon was recently linked to increased Cdk5 kinase activity that occurs in response to oxidative stress [86] . In addition, free radicals have been shown to inhibit synaptic vesicle release, through interference with SNARE assembly at motor nerve terminals [87] . Experimental inhibition of vesicle release by a similar mechanism, using botulinum toxin, has been shown to cause synapse withdrawal and even cell death in CNS neurons [88] .…”

Dietary (n-3) Fatty Acids and Brain Development1

“…This process requires formation of a tight ternary complex between the vesicular (v) SNARE, termed synaptobrevin (or VAMP, vesicle-associated membrane protein), and 2 membrane target (t)-SNARE, known as syntaxin and SNAP-25 on the cytosolic surface of the plasma membrane (46). Interestingly, recent studies have shown that reactive oxygen species impair acetylcholine release, independent of G-protein cascades, through presynaptic functioning of SNAP-25 as a reactive oxygen species sensor (47). Possibly, this may provide a link between the role of DHA in protection against oxidative stress (24) and in altering neurotransmission (23), including acetylcholine (48).…”