The Detrimental Action of Adenosine on Glutamate-Induced Cytotoxicity in PC12 Cells Can Be Shifted towards a Neuroprotective Role through A1AR Positive Allosteric Modulation

Abstract

Glutamate cytotoxicity is implicated in neuronal death in different neurological disorders including stroke, traumatic brain injury, and neurodegenerative diseases. Adenosine is a nucleoside that plays an important role in modulating neuronal activity and its receptors have been identified as promising therapeutic targets for glutamate cytotoxicity. The purpose of this study is to elucidate the role of adenosine and its receptors on glutamate-induced injury in PC12 cells and to verify the protective effect of the novel A1 adenosine receptor positive allosteric modulator, TRR469. Flow cytometry experiments to detect apoptosis revealed that adenosine has a dual role in glutamate cytotoxicity, with A2A and A2B adenosine receptor (AR) activation exacerbating and A1 AR activation improving glutamate-induced cell injury. The overall effect of endogenous adenosine in PC12 cells resulted in a facilitating action on glutamate cytotoxicity, as demonstrated by the use of adenosine deaminase and selective antagonists. However, enhancing the action of endogenous adenosine on A1ARs by TRR469 completely abrogated glutamate-mediated cell death, caspase 3/7 activation, ROS production, and mitochondrial membrane potential loss. Our results indicate a novel potential therapeutic strategy against glutamate cytotoxicity based on the positive allosteric modulation of A1ARs.