Adenosine metabolism as an endogenous protective mechanism in response to upstream ischemic injury

Following ischemic stroke (IS), endogenous protective mechanisms are activated to mitigate brain injury. Adenosine (ADO), a key endogenous immunomodulator, is implicated in this response, yet the precise regulatory pathways linking upstream ischemic injury to ADO-mediated protection remain incompletely elucidated.

We integrated single-cell RNA sequencing (scRNA-seq) data (GSE174574) and bulk RNA-seq data (GSE140275) from IS models. After preprocessing and t-SNE-based clustering, we conducted analyses of cell communication and differential expression. Differentially expressed genes were intersected with ADO metabolism-related genes from the GeneCards database to identify candidate regulators. The roles of these candidates in modulating ADO metabolism, oxidative stress, and apoptosis were functionally validated in vitro using qRT-PCR, Western blot, ELISA, and gene silencing in BV2 cells.

Unsupervised clustering of scRNA-seq data identified 14 cell types, with microglia displaying extensive intercellular communication, particularly via the CCL and TNF signaling pathways. Cross-database analysis identified four candidate molecules: HMBS, UCP2, POR, and TNF. These were positively correlated with pro-ADO metabolic genes in middle cerebral artery occlusion (MCAO) models and were upregulated in LPS-stimulated BV2 cells, coinciding with increased inflammation, oxidative stress, and ADO levels. Silencing HMBS or POR reversed these effects. Exogenous ADO reduced oxidative stress and apoptosis in BV2 cells and promoted M2 microglia polarization.

Our findings suggest that ischemic injury upregulates specific molecules (HMBS, UCP2, POR, and TNF) potentially associated with ADO metabolism, which may, in turn, alleviate oxidative stress and apoptosis while favoring anti-inflammatory microglial polarization. This supports the hypothesis that enhanced adenosine metabolism represents a potential endogenous protective mechanism activated in response to upstream ischemic insult. HMBS or POR silencing upregulated adenosine deaminase/adenosine kinase (ADA/ADK) and downregulated SLC29A1/A2 in LPS-stimulated BV2 cells. The protective effects of ADO were abolished by A₂aR antagonist SCH 58261, confirming the functional link between HMBS/POR and ADO-mediated neuroprotection.