Optogenetic activation of intracellular adenosine A(2A) receptor signaling in hippocampus is sufficient to trigger CREB phosphorylation and impair memory

Human and animal studies have converged to suggest that caffeine consumption prevents memory deficits in aging and Alzheimer’s disease through the antagonism of adenosine A(2A) receptors (A(2A)R). To test if A(2A)R activation in hippocampus is actually sufficient to impair memory function and to begin elucidating the intracellular pathways operated by A(2A)R, we have developed a chimeric rhodopsin-A(2A)R protein (optoA(2A)R), which retains the extracellular and transmembrane domains of rhodopsin (conferring light responsiveness and eliminating adenosine binding pockets) fused to the intracellular loop of A(2A)R to confer specific A(2A)R signaling. The specificity of the optoA(2A)R signaling was confirmed by light-induced selective enhancement of cAMP and phospho-MAPK (but not cGMP) levels in HEK293 cells, which was abolished by a point mutation at the C-terminal of A(2A)R. Supporting its physiological relevance, optoA(2A)R activation and the A(2A)R agonist CGS21680 produced similar activation of cAMP and phospho-MAPK signaling in HEK293 cells, of pMAPK in nucleus accumbens, of c-Fos/pCREB in hippocampus and similarly enhanced long-term potentiation in hippocampus. Remarkably, optoA(2A)R activation triggered a preferential phospho-CREB signaling in hippocampus and impaired spatial memory performance while optoA(2A)R activation in the nucleus accumbens triggered MAPK signaling and modulated locomotor activity. This shows that the recruitment of intracellular A(2A)R signaling in hippocampus is sufficient to trigger memory dysfunction. Furthermore, the demonstration that the biased A(2A)R signaling and functions depend on intracellular A(2A)R loops, prompts the possibility of targeting the intracellular A(2A)R interacting partners to selectively control different neuropsychiatric behaviors.