Neutrophil Extracellular Traps Promote AIM2-Dependent Microglial Pyroptosis Following Stroke.

Neutrophils are among the earliest and most abundant immune cells infiltrating the brain following ischemic stroke, aggravating neuroinflammation through the formation of neutrophil extracellular traps (NETs). Pyroptosis, an inflammasome-mediated form of programmed cell death, occurs in post-stroke brain tissue and amplifies inflammation by releasing proinflammatory mediators, propagating the inflammatory cascade. However, the mechanistic link between NETs and pyroptosis remains unclear. This study demonstrated significantly elevated NET levels in arterial blood at the infarct site compared with venous or femoral arterial blood in stroke patients. A positive correlation was observed between the 24-h change in NIHSS score (NIHSS_baseline - NIHSS_24h) and the difference in arterial citrullinated histone 3 (CitH3)-DNA (NETs) levels between the infarct site and femoral artery (NETs_{infarct site} - NETs_{femoral artery}). In a murine stroke model, NETs were detected in the brain parenchyma. Pharmacological inhibition of NET formation with GSK484, a selective protein-arginine deiminase type 4 antagonist, suppressed NET production, reduced absent in melanoma 2 (AIM2) inflammasome expression, and improved neurological outcomes in mice following stroke. AIM2 knockdown in brain tissue achieved similar neuroprotective effects. In both BV2 cells and stroke-induced mice, NETs triggered AIM2-dependent pyroptosis. These findings suggest that neutrophils in peripheral blood infiltrate the brain parenchyma to generate NETs, activating the AIM2 inflammasome in microglia and exacerbating stroke-induced brain injury through pyroptosis. Targeting NET formation or AIM2 inflammasome activation represents a potential therapeutic strategy for attenuating post-stroke neuroinflammation and secondary neuronal damage.