Blockade of adenosine A2A receptors prevents interleukin-1β-induced exacerbation of neuronal toxicity through a p38 mitogen-activated protein kinase pathway.

BACKGROUND AND PURPOSE

Blockade of adenosine A(2A) receptors (A(2A)R) affords robust neuroprotection in a number of brain conditions, although the mechanisms are still unknown. A likely candidate mechanism for this neuroprotection is the control of neuroinflammation, which contributes to the amplification of neurodegeneration, mainly through the abnormal release of pro-inflammatory cytokines such as interleukin(IL)-1β. We investigated whether A(2A)R controls the signaling of IL-1β and its deleterious effects in cultured hippocampal neurons.

METHODS

Hippocampal neuronal cultures were treated with IL-1β and/or glutamate in the presence or absence of the selective A(2A)R antagonist, SCH58261 (50 nmol/l). The effect of SCH58261 on the IL-1β-induced phosphorylation of the mitogen-activated protein kinases (MAPKs) c-Jun N-terminal kinase (JNK) and p38 was evaluated by western blotting and immunocytochemistry. The effect of SCH58261 on glutamate-induced neurodegeneration in the presence or absence of IL-1β was evaluated by nucleic acid and by propidium iodide staining, and by lactate dehydrogenase assay. Finally, the effect of A(2A)R blockade on glutamate-induced intracellular calcium, in the presence or absence of IL-1β, was studied using single-cell calcium imaging.

RESULTS

IL-1β (10 to 100 ng/ml) enhanced both JNK and p38 phosphorylation, and these effects were prevented by the IL-1 type 1 receptor antagonist IL-1Ra (5 μg/ml), in accordance with the neuronal localization of IL-1 type 1 receptors, including pre-synaptically and post-synaptically. At 100 ng/ml, IL-1β failed to affect neuronal viability but exacerbated the neurotoxicity induced by treatment with 100 μmol/l glutamate for 25 minutes (evaluated after 24 hours). It is likely that this resulted from the ability of IL-1β to enhance glutamate-induced calcium entry and late calcium deregulation, both of which were unaffected by IL-1β alone. The selective A(2A)R antagonist, SCH58261 (50 nmol/l), prevented both the IL-1β-induced phosphorylation of JNK and p38, as well as the IL-1β-induced deregulation of calcium and the consequent enhanced neurotoxicity, whereas it had no effect on glutamate actions.

CONCLUSIONS

These results prompt the hypothesis that the neuroprotection afforded by A(2A)R blockade might result from this particular ability of A(2A)R to control IL-1β-induced exacerbation of excitotoxic neuronal damage, through the control of MAPK activation and late calcium deregulation.