Abstract WP359: Targeting Annexin A5 prevents microglia-mediated synaptic elimination in stroke

Blackground: Neuroinflammation is critical for functional prognosis after stroke. Previously, microglia have been proven to change their function from harmful inflammation to nerve repair. However, activated microglia still produce inflammatory mediators and phagocytose the stressed neurons. Inhibiting specific phagocytic pathways in microglia can prevent delayed neuronal loss in the chronic phase of stroke. Neuron-microglia interactions underlie this process but the detailed mechanisms remain unclear. Therefore, we reveal a critical role of microglia-mediated selective phagocytosis and find a translational target in the chronic phase of stroke. Method: A model mouse with middle cerebral artery occlusion (MCAO) is employed to determine the involvement of microglia in phagocytosis at excitatory synapses. Using spatial transcriptomics to visualize the transcriptional landscape in the brain of MCAO mouse and identify gene expression profiles. Drug consumption of microglia and C1q gene knockout mice were used to determine the role of microglia-derived C1q. Whole-cell patch clamp recording of mouse neuronal function. Binding assays experiments and PLA confirmed that C1q binds to exposed phosphatidylserine (EPS). Annexin A5 was injected into the mice to block EPS. Serum Annexin A5 levels were measured by ELISA in patients participating in a multicenter clinical trial, and the long-term prognosis of patients was evaluated. Results: We used spatial transcriptomics to identify increased activity and gene expression of phagocytosis related pathways in the ischemic hemispheric, and C1q was identified as a key regulator of this process. We found that pharmacological depletion of microglia inhibited C1q activation and the elimination excitatory synapses. Binding assays experiments and PLA demonstrated that C1q can mediate excitatory synaptic excursions through the binding of PS to microglia.Blocking these PS-C1q interactions via Annexin A5 injections effectively inhibits synaptic elimination, improving long-term recovery. Finally, we found that serum Annexin A5 levels were elevated in stroke patients and were associated with good prognosis in patients. Conclusion: In a proof-of-concept analysis, increased plasma Annexin V were associated with early neurological improvement in stroke patients with salvageable penumbra. These findings indicate that Annexin A5 inhibition of the C1q-PS interaction may constitute a critical therapeutic target during the stroke repair phase.