Altered mechanisms underlying the abnormal glutamate release in amyotrophic lateral sclerosis at a pre-symptomatic stage of the disease

Abstract

Abnormal Glu release occurs in the spinal cord of SOD1(G93A) mice, a transgenic animal model for human ALS. Here we studied the mechanisms underlying Glu release in spinal cord nerve terminals of SOD1(G93A) mice at a pre-symptomatic disease stage (30days) and found that the basal release of Glu was more elevated in SOD1(G93A) with respect to SOD1 mice, and that the surplus of release relies on synaptic vesicle exocytosis. Exposure to high KCl or ionomycin provoked Ca(2+)-dependent Glu release that was likewise augmented in SOD1(G93A) mice. Equally, the Ca(2+)-independent hypertonic sucrose-induced Glu release was abnormally elevated in SOD1(G93A) mice. Also in this case, the surplus of Glu release was exocytotic in nature. We could determine elevated cytosolic Ca(2+) levels, increased phosphorylation of Synapsin-I, which was causally related to the abnormal Glu release measured in spinal cord synaptosomes of pre-symptomatic SOD1(G93A) mice, and increased phosphorylation of glycogen synthase kinase-3 at the inhibitory sites, an event that favours SNARE protein assembly. Western blot experiments revealed an increased number of SNARE protein complexes at the nerve terminal membrane, with no changes of the three SNARE proteins and increased expression of synaptotagmin-1 and β-Actin, but not of an array of other release-related presynaptic proteins. These results indicate that the abnormal exocytotic Glu release in spinal cord of pre-symptomatic SOD1(G93A) mice is mainly based on the increased size of the readily releasable pool of vesicles and release facilitation, supported by plastic changes of specific presynaptic mechanisms.

MicroRNA expression analysis identifies a subset of downregulated miRNAs in ALS motor neuron progenitors

“…Moreover, SYT1 downregulation has been reported in nerve terminals from highly affected muscles, which seems to be associated with SMA mouse muscle vulnerability 60 . However, in the spinal cords of SOD1 mice, higher SYT1 expression was observed and was linked to the altered calcium concentrations and ALS-linked excitotoxicity 61 . Of note, we confirmed an upregulation of SYT1 transcript levels in our ALS-MN progenitors.…”

Drosophila Nrf2/Keap1 Mediated Redox Signaling Supports Synaptic Function and Longevity and Impacts on Circadian Activity

“…Data indicate that the abnormal excitotoxic glutamate release in the spinal cord of pre-symptomatic ALS mice is mainly based on the increased size of the readily releasable pool of vesicles and release facilitation, supported by plastic changes of specific presynaptic mechanisms (Bonifacino et al, 2016). As ALS is characterized by enhanced cytotoxic oxidative stress, one could speculate that these conditions favor non-physiological release of neurotransmitter.…”

Chronic mild stress induces anhedonic behavior and changes in glutamate release, BDNF trafficking and dendrite morphology only in stress vulnerable rats. The rapid restorative action of ketamine

“…Purification and superfusion of synaptic terminals (synaptosomes) were performed as previously reported (Bonanno et al, 2005; Bonifacino et al, 2016; Treccani et al, 2014). Synaptosomes were freshly prepared from homogenized HPC of 8–12 animals/group, by centrifugation on discontinuous Percoll gradients, and superfused with a standard physiological medium (140 mM NaCl, 3 mM KCl, 1.2 mM MgSO 4 , 1.2 mM CaCl 2 , 1.2 mM NaH 2 PO 4 , 5 mM NaHCO 3 , 10 mM glucose, 10 mM HEPES, pH 7.4).…”