Genetically controlled upregulation of adenosine A(1) receptor expression enhances the survival of primary cortical neurons.

Adenosine has a key endogenous neuroprotective role in the brain, predominantly mediated by the adenosine A(1) receptor (A(1)R). This has been mainly explored using pharmacological tools and/or receptor knockout mice strains. It has long been suggested that the neuroprotective effects of A(1)R are increased following receptor upregulation, thus attenuating neuronal damage in pathological conditions. We have previously shown that the neuroprotective and neuromodulatory actions of the cytokines IL-6 and oncostatin M are mediated by induction of neuronal A(1)R expression. In order to investigate the direct effects of A(1)R upregulation in neurons, we have generated a tetracycline-regulated expression system with a bidirectional promoter, directing the simultaneous expression of the mouse A(1)R and GFP/mCherry reporter genes. In a first step, we tested the efficacy of the system in transiently transfected human embryonic kidney 293 cells. In addition, we confirmed the functional integrity of the expressed A(1)R by whole-cell patch clamp recordings. We demonstrated that A(1)R-transfected primary neurons show enhanced survival against N-methyl-D-aspartate-induced excitotoxicity. Pretreatment with an A(1)R-selective agonist additionally strongly decreased neuronal cell death, while an A(1)R antagonist completely abolished the neuroprotective effects of A(1)R upregulation. The presented data provide for the first time direct evidence that the upregulation of A(1)R enhances neuronal survival.