Astrocytic Adenosine A2A Receptors Control the Amyloid-β Peptide-Induced Decrease of Glutamate Uptake

Alzheimer's disease (AD) is characterized by a progressive cognitive impairment tightly correlated with the accumulation of amyloid-beta (A beta) peptides (mainly A beta(1-42)). There is a precocious disruption of glutamatergic synapses in AD, in line with an ability of A beta to decrease astrocytic glutamate uptake. Accumulating evidence indicates that caffeine prevents the burden of AD, likely through the antagonism of A(2A) receptors (A(2A)R) which attenuates A beta-induced memory impairment and synaptotoxicity. Since A(2A)R also modulate astrocytic glutamate uptake, we now tested if A(2A)R blockade could prevent the decrease of astrocytic glutamate uptake caused by A beta. In cultured astrocytes, A beta(1-42) (1 mu M for 24 hours) triggered an astrogliosis typified by an increased density of GFAP, which was mimicked by the A(2A)R agonist, CGS 26180 (30 nM), and prevented by the A(2A)R antagonist, SCH 58261 (100 nM). A beta(1-42) also decreased D-aspartate uptake by 28 +/- 4%, an effect abrogated upon genetic inactivation or pharmacological blockade of A(2A)R. In accordance with the long term control of glutamate transporter expression by A(2A)R, A beta(1-42) enhanced the expression and density of astrocytic A(2A)R and decreased GLAST and GLT-I expression in astrocytes from wild type, but not from A(2A)R knockout mice. This impact of A beta(1-42) on glutamate transporters and uptake, dependent on A(2A)R function, was also confirmed in an ex vivo astrocyte preparation (gliosomes) from rats intracerebroventricularly (icv) injected with A beta(1-42). These results provide the first demonstration for a direct key role of astrocytic A(2A)R in the ability of A beta-induced impairment of glutamate uptake, which may underlie glutamatergic synaptic dysfunction and excitotoxicity in AD.