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

Abstract

Neuroinflammation has been widely recognized as the primary pathophysiological mechanism underlying ischemic white matter lesions (IWML) in chronic cerebral hypoperfusion (CCH), with microglia serving as the principal effector cells. A2aR, an important adenosine receptor, exhibits a dual role in neuroinflammation by modulating both pro-inflammatory and anti-inflammatory responses, particularly through its regulation of microglial polarization. This study aimed to investigate the specific functions and mechanisms of A2aR in neuroinflammation. The findings revealed that A2aR initially exerted a pro-inflammatory role in the CCH model, transitioning to an anti-inflammatory role in later stages by regulating the phenotypic transformation of microglia. Further analyses using CoIP-MS, in situ proximity ligation assay, Alphafold protein structure prediction, [³⁵S]GTPγS Binding Assay and Nano-Bit technology demonstrated that A2aR formed heteromers with mGluR5 during the early stage of CCH under high glutamate conditions, promoting the polarization of microglia towards a pro-inflammatory phenotype. In contrast, during later stages characterized by low glutamate levels, A2aR predominantly existed as a monomer, facilitating microglial polarization towards an anti-inflammatory phenotype. Our findings indicate that elevated glutamate levels drive the formation of A2aR-mGluR5 heteromers, contributing to neuroinflammation by promoting pro-inflammatory 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.Significance Statement Neuroinflammation of white matter is widely recognized as the primary pathophysiological mechanism associated with vascular dementia (VaD) in middle-aged and elderly individuals.A2aR, a crucial adenosine receptor, exhibits a dual role in neuroinflammation by modulating both proinflammatory and anti-inflammatory responses, particularly in relation to microglia polarization. The objective of this study is to investigate the specific functions and mechanisms of A2aR in neuroinflammation. The results indicate that elevated glutamate levels facilitate the formation of A2aR-mGluR5 heteromers, thereby promoting the polarization of microglia towards a pro-inflammatory phenotype, which contributes to neuroinflammation in CCH white matter. Conversely, under conditions of low glutamate, A2aR predominantly exists in monomeric form, which favors the polarization of microglia towards an anti-inflammatory phenotype, thereby exerting a protective effect.