Up to 30% of patients surviving aneurysmal subarachnoid hemorrhage (aSAH) develop delayed cerebral ischemia and neurological deficits 4-10 days post-SAH which are leading causes of morbidity and mortality. Recent clinical studies indicate that the cause of delayed ischemia and neurological deficits is multifactorial, and includes microthrombi and inflammation. Intravascular microthrombi after aSAH in humans peak 1-2 week post- SAH, mirroring delayed neurological deficit onset, and are significantly higher in the brains of aSAH patients who had delayed deficits vs aSAH patients who did not have delayed deficits. SAH triggers an inflammatory response which has been linked to delayed neurological decline in aSAH patients. Inflammation-induced neutrophil extracellular traps (NETs, extracellular web-like chromatin scaffolds which mediate inflammation and thrombosis) has been reported in aSAH patients, but have not been studied in the context of delayed deficits post-SAH. Our preliminary data in humans and mice suggest that microthrombi and NETs contribute to the development of delayed ischemia and deficits after SAH. So, our central hypothesis is that microthrombi and NETs are causative factors (via lower brain perfusion, small infarcts, and inflammation) for the development of delayed deficits after SAH. This will be the first proposal designed to specifically study delayed neurological deficits using a mouse model of SAH to investigate the potential contributing factors of delayed deficits.
Specific Aim 1 : Interrogate the role of microthrombi in delayed functional deficits after SAH in mice. Our hypothesis is that microthrombi formation causes a sustained reduction in brain tissue perfusion leading to delayed infarction and delayed functional deficits. To test our hypothesis, we will use prototypic inhibitors of platelet activation to attenuate microthrombi in wild-type and platelet-fluorescent mice subjected to SAH. Various imaging modalities will be used to assess brain perfusion, microthrombi formation, and infarction. Functional performance will be tested daily for 6 days post-SAH.
This aim will identify if platelet-inhibition/microthrombi have a substantial influence on delayed SAH injury, including delayed infarction and delayed functional deficits.
Specific Aim 2 : Investigate the contribution of neutrophil extracellular traps to delayed functional deficits after SAH in mice. Our hypothesis is that NETs contribute to vessel occlusion leading to delayed infarction and deficits. To test this, we will use SAH mice depleted of peripheral neutrophils (with a Ly6G antibody), or treated with Cl-amidine (to prevent NETs) or DNase-I (to lyse NETs). Several imaging modalities will be used to assess brain perfusion, NET formation, infarction, and infiltrating immune cells. Neurobehavior will be tested for 6 days.
This aim will determine the role of neutrophil extracellular traps in delayed ischemia and deficits post- SAH. The long-term goals are to determine if microthrombi and/or NETs are key contributors to the development of delayed deficits, and to identify potential therapeutic targets to prevent delayed ischemia and deficits after SAH.
Up to 30% of patients surviving subarachnoid hemorrhage develop delayed functional deficits 4-10 days post- SAH which is a major clinical concern. Microthrombi, infarction, and inflammation may be contributing factors and this proposal is designed to investigate which of these factors are crucial for delayed deficits. This research will also determine if microthrombi and/or inflammation are causes of delayed deficits and identify potential therapeutic targets delayed functional deficits after subarachnoid hemorrhage.