Neuroprotection afforded by adenosine A2A receptor blockade is modulated by corticotrophin-releasing factor (CRF) in glutamate injured cortical neurons

In situations of hypoxia, glutamate excitotoxicity induces neuronal death. The release of extracellular adenosine is also triggered and is accompanied by an increase of the stress mediator, corticotrophin-releasing factor (CRF). Adenosine A2A receptors contribute to glutamate excitoxicity and their blockade is effective in stress-induced neuronal deficits, but the involvement of CRF on this effect was never explored. We now evaluated the interaction between A2A and CRF receptors (CRFR) function, upon glutamate insult. Primary rat cortical neuronal cultures (9 days in vitro) expressing both CRF1R and CRF2R were challenged with glutamate (201000 mu M, 24 h). CRF1R was found to co-localize with neuronal markers and CRF2R to be present in both neuronal and glial cells. The effects of the CRF and A2A receptors ligands on cell viability were measured using propidium iodide and Syto-13 fluorescence staining. Glutamate decreased cell viability in a concentration-dependent manner. Urocortin (10 pM), an agonist of CRF receptors, increased cell survival in the presence of glutamate. This neuroprotective effect was abolished by blocking either CRF1R or CRF2R with antalarmin (10 nM) or anti-Sauvagine-30 (10 nM), respectively. The blockade of A2A receptors with a selective antagonist SCH 58261 (50 nM) improved cell viability against the glutamate insult. This effect was dependent on CRF2R, but not on CRF1R activation. Overall, these data show a protective role of CRF in cortical neurons, against glutamate-induced death. The neuroprotection achieved by A2A receptors blockade requires CRF2R activation. This interaction between the adenosine and CRF receptors can explain the beneficial effects of using A2A receptor antagonists against stress-induced noxious effects.