IL-17A-mediated copper accumulation participates in chronic neuropathic pain-induced cognitive impairment by enhancing microglial synaptic pruning

Chronic neuropathic pain is frequently accompanied by cognitive impairment, which seriously influence the quality of the patient's life. The stability of synapse is the basis for maintaining neural circuits. And overactive microglia can prune normal synapses through phagocytosis, leading to cognitive impairment. This study aims to investigate the role of microglial synaptic pruning in chronic neuropathic pain-induced cognitive impairment, and explore the mechanisms of microglial activation through Interleukin-17A (IL-17A) activation and copper accumulation. We found that chronic neuropathic pain resulted in cognitive impairment, and microglial activation, abnormal microglial synaptic pruning, synaptic loss in hippocampus. Depleting microglia ameliorated the activations of microglial and complement pathways, and rescued synaptic loss and cognitive impairment. The copper was accumulated in hippocampus, and copper chelator tetrathiomolybdate (TTM) inhibited microglial and complement activations and rescued synaptic loss and cognitive impairment. Further research found that suppressing mitochondrial oxidative stress response inhibited copper accumulation-induced microglial activation. Finally, IL-17A was found to be increased in serum and hippocampus. IL-17A neutralization antibody (anti-IL-17A Abs) alleviated copper accumulation by inhibiting six transmembrane epithelial antigens of prostate 4 (STEAP4) / copper transporter 1 (CTR1), and inhibited microglial and complement activation, interrupting abnormal synaptic elimination and ameliorating cognitive impairment. Our results suggest that IL-17A can induce copper accumulation in microglia through STEAP4/CTR1, the latter promotes complement-mediated microglia synaptic pruning, reducing synapse number, and ultimately resulting in cognitive impairment. These provide a new potential therapeutic target for the treatment of chronic neuropathic pain-induced cognitive impairment.