Atypical chemokine receptor 3 regulates synaptic removal in disease astrocytes

Astrocytes participate in the clearance of obsolete or unwanted neuronal synapses. However, the molecular machinery involved in synapse recognition remains unclear, particularly in pathological conditions. Here, we investigated the phagocytic process of astrocytes through individual gene silencing using a druggable gene library. Our study demonstrates that the Atypical chemokine receptor 3 (Ackr3) is a major player of astrocyte-mediated synapse engulfment. Mechanistically, we showed that Ackr3 recognizes phosphatidylethanolamine (PE)-bound C-X-C motif chemokine 12 (CXCL12) at synaptic terminals, thus serving as a novel marker of synaptic dysfunction. Notably, both ACKR3 and CXCL12 are upregulated in post-mortem brains of Alzheimer's disease (AD) patients, and AD mouse models. Genetic downregulation of Ackr3 in AD mice significantly reduces astrocyte-mediated synaptic elimination and rescues pathological phenotypes, including synapse loss and cognitive impairment. Overall, this work unveils a novel, possibly targetable mechanism of astrocyte-mediated synaptic engulfment implicated in neurodegenerative disease.