Neutrophil extracellular traps delivering lactylated S100a9 aggravate neuronal cuproptosis by regulating Ttr/Commd1/Atp7b axis after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability and mortality, with secondary injury mechanisms involving neuronal death and neuroinflammation, for which effective treatments remain limited. Neutrophil extracellular traps (NETs) are implicated in post-TBI neuropathology. Cuproptosis, a copper-dependent cell death pathway characterized by mitochondrial oxidative stress, dysfunction, and disrupted dynamics, has recently been implicated in neurological disorders. This study aims to investigate whether NETs exacerbate secondary brain injury by promoting neuronal cuproptosis after TBI and to elucidate the underlying molecular mechanism. We observed elevated NET levels in brain tissues from both TBI patients and mice, which correlated with poor prognosis. Single-cell RNA sequencing revealed a significant upregulation of transthyretin (Ttr) in neurons post-TBI. Mechanistically, NETs deliver lactylated S100a9 (S100a9K26la), a glycolysis-dependent lactylated protein, to neurons. S100a9K26la translocates to the nucleus and promotes Ttr transcription. Increased neuronal Ttr protein then competes with ATPase copper transporting β (Atp7b) for binding to copper metabolism MURR1 domain-containing 1 (Commd1) at the W123 residue. This competition disrupts the Commd1-Atp7b interaction, impairing copper efflux and leading to intracellular copper accumulation, mitochondrial oxidative stress, aggregation of DLAT, loss of Fe-S cluster proteins, and ultimately neuronal cuproptosis. Neuron−specific Ttr conditional knockout ameliorated neuronal death, neuroinflammation, blood-brain barrier (BBB) disruption, and neurological deficits in a TBI model. Conversely, inhibition of cuproptosis with the copper chelator tetrathiomolybdate (TTM) yielded similar protective effects. In summary, our findings elucidate a novel pathway wherein NETs, via delivery of S100a9K26la, drive neuronal Ttr overexpression. Ttr disrupts copper homeostasis by interfering with the Commd1-Atp7b axis, ultimately triggering neuronal cuproptosis and exacerbating secondary injury after TBI. This study identifies NETosis and the Ttr/Commd1/Atp7b axis as potential therapeutic targets for mitigating TBI-induced damage.