Adenosine binds predominantly to adenosine receptor A1 subtype in astrocytes and mediates an immunosuppressive effect.

The four kinds of adenosine receptor subtypes (ARs), named as ARA1, ARA2A, ARA2B and ARA3, have multiple biological functions. ARs are differently distributed across the body and have distinguished ability of binding adenosine. We try to figure out how these ARs were expressed in astrocytes and which one has the first priority of utilizing adenosine. Firstly, mRNA expressions and membrane localization of all ARs were evaluated by qPCR and western blot. After the membrane localization of all ARs in astrocytes was being confirmed their individual adenosine binding ability was determined by radio-active ligand binding assay respectively. It was revealed that ARA1 had much superior adenosine binding ability than other AR subtypes. Functional study demonstrated that ARA1 potentially mediated an immune suppressive effect in astrocytes. The activation of ARA1 signaling lead to decreased IL-12 and IL-23 production, and decreased chemokine production, including CCL2, CXCL8 and IP-10. When interacted with CD4 cells ARA1 agonist pre-treated astrocytes showed hindered ability of stimulating CD4 cells to secret IL-17 and IFN-γ and inducing CD4 cells' chemo taxi. Finally, in vivo experiment confirmed that local administration of ARA1agonist ameliorated EAE in wild type B6 recipients, but not Ara1-/- recipients. As a conclusion, this paper suggested that adenosine receptor A1 subtype predominantly binds adenosine in astrocytes and mediates an immunosuppressive effect.