The Expression of GLAST and GLT1 in a Transient Cerebral Ischemia Mongolian Gerbil Model

Chemically Functionalized Single-Walled Carbon Nanotubes Prevent the Reduction in Plasmalemmal Glutamate Transporter EAAT1 Expression in, and Increase the Release of Selected Cytokines from, Stretch-Injured Astrocytes in Vitro

We tested the effects of water-soluble single-walled carbon nanotubes, chemically functionalized with polyethylene glycol (SWCNT-PEG), on primary mouse astrocytes exposed to a severe in vitro simulated traumatic brain injury (TBI). The application of SWCNT-PEG in the culture media of injured astrocytes did not affect cell damage levels, when compared to those obtained from injured, functionalization agent (PEG)-treated cells. Furthermore, SWCNT-PEG did not change the levels of oxidatively damaged proteins in astrocytes. However, this nanomaterial prevented the reduction in plasmalemmal glutamate transporter EAAT1 expression caused by the injury, rendering the level of EAAT1 on par with that of control, uninjured PEG-treated astrocytes; in parallel, there was no significant change in the levels of GFAP. Additionally, SWCNT-PEG increased the release of selected cytokines that are generally considered to be involved in recovery processes following injuries. As a loss of EAATs has been implicated as a culprit in the suffering of human patients from TBI, the application of SWCNT-PEG could have valuable effects at the injury site, by preventing the loss of astrocytic EAAT1 and consequently allowing for a much-needed uptake of glutamate from the extracellular space, the accumulation of which leads to unwanted excitotoxicity. Additional potential therapeutic benefits could be reaped from the fact that SWCNT-PEG stimulated the release of selected cytokines from injured astrocytes, which would promote recovery after injury and thus counteract the excess of proinflammatory cytokines present in TBI.

Amburana cearensis seed extract stimulates astrocyte glutamate homeostatic mechanisms in hippocampal brain slices and protects oligodendrocytes against ischemia

BACKGROUND

Stroke is a leading cause of death and disability worldwide. A major factor in brain damage following ischemia is excitotoxicity caused by elevated levels of the neurotransmitter glutamate. In the brain, glutamate homeostasis is a primary function of astrocytes. Amburana cearensis has long been used in folk medicine and seed extract obtained with dichloromethane (EDAC) have previously been shown to exhibit cytoprotective activity in vitro. The aim of the present study was to analyse the activity of EDAC in hippocampal brain slices.

METHODS

We prepared a dichloromethane extract (EDAC) from A. cearensis seeds and characterized the chemical constituents by 1H and 13C-NMR. Hippocampal slices from P6-8 or P90 Wistar rats were used for cell viability assay or glutamate uptake test. Hippocampal slices from P10-12 transgenic mice SOX10-EGFP and GFAP-EGFP and immunofluorescence for GS, GLAST and GLT1 were used to study oligodendrocytes and astrocytes.

RESULTS

Astrocytes play a critical role in glutamate homeostasis and we provide immunohistochemical evidence that in excitotoxicity EDAC increased expression of glutamate transporters and glutamine synthetase, which is essential for detoxifying glutamate. Next, we directly examined astrocytes using transgenic mice in which glial fibrillary acidic protein (GFAP) drives expression of enhanced green fluorescence protein (EGFP) and show that glutamate excitotoxicity caused a decrease in GFAP-EGFP and that EDAC protected against this loss. This was examined further in the oxygen-glucose deprivation (OGD) model of ischemia, where EDAC caused an increase in astrocytic process branching, resulting in an increase in GFAP-EGFP. Using SOX10-EGFP reporter mice, we show that the acute response of oligodendrocytes to OGD in hippocampal slices is a marked loss of their processes and EDAC protected oligodendrocytes against this damage.

CONCLUSION

This study provides evidence that EDAC is cytoprotective against ischemia and glutamate excitotoxicity by modulating astrocyte responses and stimulating their glutamate homeostatic mechanisms.

Neuronal glutamate transporters are associated with cognitive impairment in obstructive sleep apnea patients without dementia

Increasing evidence supports a link between obstructive sleep apnea (OSA) and cognition, and the mechanism is complex and still not well understood. We analyzed the relationship between the glutamate transporters and cognitive impairment in OSA. For this study 317 subjects without dementia, including 64 healthy controls (HCs), 140 OSA patients with mild cognitive impairment (MCI) and 113 OSA patients without cognitive impairment were assessed. All participants who completed polysomnography, cognition and white matter hyperintensity (WMH) volume were used. Plasma neuron-derived exosomes (NDEs) excitatory amino acid transporter 2 (EAAT2) and vesicular glutamate transporter 1 (VGLUT1) proteins were measured by ELISA kits. After 1 year of continuous positive airway pressure (CPAP) treatment, we analyzed plasma NDEs EAAT2 level and cognition changes. Plasma NDEs EAAT2 level was significantly higher in OSA patients than in HCs. Higher plasma NDEs EAAT2 level were significantly associated with cognitive impairment than normal cognition in OSA patients. Plasma NDEs EAAT2 level was inversely associated with the total Montreal Cognitive Assessment (MoCA) scores, visuo-executive function, naming, attention, language, abstraction, delayed recall and orientation. One year after CPAP treatment, plasma NDEs EAAT2 level (P = 0.019) was significantly lower, while MoCA scores (P = 0.013) were significantly increased compared with baseline. Upregulation of neuronal glutamate transporters at baseline may reflect a self-compensatory mechanism to prevent further neuronal damage, while plasma NDEs EAAT2 level was decreased after one year of CPAP therapy, which may be due to the loss of astrocytes and neurons.