Abstract WMP112: Neutrophil Extracellular Traps Occlude the Cerebrovasculature Causing Delayed Cerebral Ischemia After Subarachnoid Hemorrhage in Mice

Abstract

Neutrophils are reported to be critical mediators of to poor outcome after subarachnoid hemorrhage (SAH). Following ischemic stroke, neutrophils cause vascular occlusion via neutrophil extracellular traps (NETs). In this study, our hypothesis was that NETs cause vascular occlusion leading to delayed cerebral ischemia (DCI) and worse outcome after SAH. SAH mice (male and female, young and aged) were administered one of the following: a neutrophil depleting antibody, a PAD4 inhibitor (to prevent NETosis), DNAse-I (to degrade NETs), or a vehicle (control). Mice had neurological assessment daily until day 7 and then were euthanized to quantify the amount of brain vascular NETs. Various subcohorts of mice were used to assess neutrophil propensity to NETose, in vivo formation of NETs via intravital microscopy, and MRI assessment of cerebral perfusion and infarct development. We also examined if NETs were present after SAH in 128 humans by measuring NETs markers via ELISA at 1, 2, 4, 7, and 10 days post-SAH. In mice, SAH induced a pro-NETosis phenotype selectively in skull neutrophils and caused intravascular NETs to be present by day 1 which persisted until at least day 7. Neutrophil depletion reduced NETs, improved cerebral perfusion and neurological outcome, and attenuated the incidence of DCI. Similar findings were observed for PAD4 inhibition. However, degrading NETs only marginally improved outcomes. Aneurysmal SAH patients who developed DCI had elevated markers of NETs compared to non-DCI patients. In conclusion, after SAH, skull-derived neutrophils are primed for NETosis, and neutrophils and NETosis are therapeutic targets to reduce DCI by preventing vascular occlusion by NETs.