The Dual Role of A2aR in Neuroinflammation: Modulating Microglial Polarization in White Matter Lesions

Neuroinflammation has been widely recognized as the primary pathophysiological mechanism underlying ischemic white matter lesions (IWML) in chronic cerebral hypoperfusion (CCH). Adenosine A2A receptor (A2aR), an important adenosine receptor, exhibits a dual role in neuroinflammation by modulating both proinflammatory and anti-inflammatory responses. This study aimed to investigate the specific functions and mechanisms of A2aR in neuroinflammation. The findings revealed that A2aR initially exerted a proinflammatory role in the CCH model, transitioning to an anti-inflammatory role in later stages by regulating the phenotypic transformation of microglia. Further analyses using coimmunoprecipitation couple with mass spectrometry, in situ proximity ligation assay, AlphaFold protein structure prediction, [³⁵S]GTPγS binding assay, and NanoBiT technology demonstrated that A2aR formed heteromers with mGluR5 during the early stage of CCH under high glutamate conditions, promoting the polarization of microglia toward a proinflammatory phenotype. In contrast, during later stages characterized by low glutamate levels, A2aR predominantly existed as a monomer, facilitating microglial polarization toward an anti-inflammatory phenotype. Our findings indicate that elevated glutamate levels drive the formation of A2aR-mGluR5 heteromers, contributing to neuroinflammation by promoting proinflammatory microglial polarization in CCH white matter. Conversely, under low glutamate conditions, A2aR primarily functions in its monomeric form, favoring an anti-inflammatory microglial phenotype and exerting a protective effect. This study elucidates the mechanism by which A2aR mediates microglial phenotypic transformation and participates in neuroinflammation under CCH. It also identifies A2aR as a potential therapeutic target for the treatment of IWML.