Dopamine inhibits glutamate release evoked by alpha-Synuclein aggregates in microglial cells

R. RAISMAN- VOZARI1; R. CHEHÍN; S. HAMADAT; P. P. MICHEL; E. DEL BEL; F. GONZÁLEZ LIZARRAGA; L. ACUÑA; J. SEPULVEDA-DIAZ; J. ROCCA; M. DOS SANTOS PEREIRA

Congreso; Society for Neuroscience 2017; 2017

Microglial cells, the resident immune cells of the brain, play a key role in inflammatory-type processes that promote neurodegeneration in Parkinson?s disease (PD). The presence of α-synuclein aggregates (ASa) in PD brains may be a trigger for the microglial inflammatory response. Here, our aim was to characterize the impact of ASa on microglial cells, using glutamate release as a marker of the activation state of these cells. For that, we established cultures of microglial cells purified from post-natal mouse pup brains (Sepulveda-Diaz et al, Glia, 2016) and exposed them to ASa prepared as described before (González-Lizárraga et al, Sci Rep, 2017). Conditioned media were collected for glutamate quantification using an ELISA assay kit. Adherent cells were used for either assessment of reactive oxygen species or immunostaining procedures and cell lysates for western blot immunoassays. The modulatory effect of ASa on cystine transport was monitored through a measure of [14C]-L-Cystine accumulation. ASa robustly stimulated glutamate release in microglial cells through a mechanism requiring concomitant activation of TLR-2 and P2X7 receptors and downstream stimulation of PI3K-dependent signaling. The increase in glutamate release and the intensification of oxidative stress associated to it, were prevented by antioxidants, such as Trolox, a vitamin E analog and apocynin, a NADPH oxidase inhibitor. Sulfasalazine, a drug used to treat chronic inflammatory diseases such as rheumatoid arthritis, prevented the release of glutamate induced by ASa and the concomitant increase in cystine uptake. This suggested that glutamate release induced by ASa was the consequence of the activation of the cystine/glutamate antiporter system Xc-. Most interestingly, the neurotransmitter dopamine (DA) totally prevented the induction of glutamate release induced by ASa through an antioxidant effect that required inhibition of PI3K signaling. Altogether, present data suggest that ASa may participate in PD progression by promoting a toxic build-up of extracellular glutamate and low-level excitotoxic stress. The deficit in DA that characterizes PD may amplify this process in a vicious circle mechanism.