Microglia modulate gliotransmission through the regulation of VAMP2 proteins in astrocytes.

Vesicular release is one of the release mechanisms of various signaling molecules. In neurons, the molecular machinery involved in vesicular release has been designed through evolution to trigger fast and synchronous release of neurotransmitters. Similar machinery with a slower kinetic and a slightly different molecular assembly allows astrocytes to release various transmitters such as adenosine triphosphate (ATP), glutamate, and D-serine. Astrocytes are important modulators of neurotransmission through gliotransmitter release. We recently demonstrated that microglia, another type of glia, release ATP to modulate synaptic transmission using astrocytes as intermediate. We now report that microglia regulate astrocytic gliotransmission through the regulation of SNARE proteins in astrocytes. Indeed, we found that gliotransmission triggered by P2Y1 agonist is impaired in slices from transgenic mice devoid of microglia. Using total internal reflection fluorescence imaging, we found that the vesicular release of gliotransmitter by astrocytes was different in cultures lacking microglia compared to vesicular release in astrocytes cocultured with microglia. Quantification of the kinetic of vesicular release indicates that the overall release appears to be faster in pure astrocyte cultures with more vesicles close to the membrane when compared to astrocytes cocultured with microglia. Finally, biochemical investigation of SNARE protein expression indicates an upregulation of VAMP2 in absence of microglia. Altogether, these results indicate that microglia seems to be involved in the regulation of an astrocytic phenotype compatible with proper gliotransmission. The mechanisms described in this study could be of importance for central nervous system diseases where microglia are activated.

Levetiracetam treatment influences blood-brain barrier failure associated with angiogenesis and inflammatory responses in the acute phase of epileptogenesis in post-status epilepticus mice.

Our previous study showed that treatment with levetiracetam (LEV) after status epilepticus (SE) termination by diazepam might prevent the development of spontaneous recurrent seizures via the inhibition of neurotoxicity induced by brain edema events. In the present study, we determined the possible molecular and cellular mechanisms of LEV treatment after termination of SE. To assess the effect of LEV against the brain alterations after SE, we focused on blood-brain barrier (BBB) dysfunction associated with angiogenesis and brain inflammation. The consecutive treatment of LEV inhibited the temporarily increased BBB leakage in the hippocampus two days after SE. At the same time point, the LEV treatment significantly inhibited the increase in the number of CD31-positive endothelial immature cells and in the expression of angiogenic factors. These findings suggested that the increase in neovascularization led to an increase in BBB permeability by SE-induced BBB failure, and these brain alterations were prevented by LEV treatment. Furthermore, in the acute phase of the latent period, pro-inflammatory responses for epileptogenic targets in microglia and astrocytes of the hippocampus activated, and these upregulations of pro-inflammatory-related molecules were inhibited by LEV treatment. These findings suggest that LEV is likely involved in neuroprotection via anti-angiogenesis and anti-inflammatory activities against BBB dysfunction in the acute phase of epileptogenesis after SE.