RAR-Related Orphan Receptor Gamma T (RoRγt)-Related Cytokines Play a Role in Neutrophil Infiltration of the Central Nervous System After Subarachnoid Hemorrhage
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How inflammatory cells are recruited into the central nervous system is a topic of interest in a number of neurological injuries. In aneurysmal subarachnoid hemorrhage (SAH), neutrophil accumulation in the central nervous system 3 days after the hemorrhage is a critical step in the development of delayed cerebral injury (DCI). The mechanism by which neutrophils enter the central nervous system is still unclear.
Methods and Results
To identify human effectors of neutrophil recruitment, cerebrospinal fluid (CSF) samples were taken from a small, selected sample of SAH patients with external ventricular drainage devices (10 patients). Among a battery of CSF cytokines tested 3 days after SAH, five cytokines were associated with poor 90-day outcome (modified Rankin Score 3–6). A parallel study in a mouse model of mild SAH showed elevation in three cytokines in the CNS compared to sham. IL-17 and IL-2 were increased in both patients and the mouse model. IL-17 was investigated further because of its known role in neutrophil recruitment. Inhibition of RAR-Related Orphan Receptor Gamma T, the master transcription factor of IL-17, with the inverse agonist GSK805 suppressed neutrophils entry into the CNS after SAH compared to control. Using an IL-17 reporter mouse, we investigated the source of IL-17 and found that myeloid cells were a common IL-17-producing cell type in the meninges after SAH, suggesting an autocrine role for neutrophil recruitment.
Taken together, IL-17 appears to be in important factor in the recruitment of neutrophils into the meninges after SAH and could be an important target for therapies to ameliorate DCI.
KeywordsSubarachnoid hemorrhage Neuroinflammation Neutrophils IL-17 Delayed cerebral injury
Bovine serum albumin
Central nervous system
Dulbecco’s modified Eagle medium
Delayed cerebral injury
External ventricular drain
Green fluorescent protein
Modified Rankin Scale
RAR-related orphan receptor gamma t
Tumor necrosis factor
APC and WTG conceived the mouse experiments, synthesized data and wrote the manuscript, VS and JD collected samples, analyzed human data samples and revised the manuscript, JAG collected human samples, supervised human outcome data and revised manuscript, LR developed techniques, performed mouse experiments, and revised the manuscript, JJP conceived of experiments, supervised the entire project, reviewed and revised the manuscript.
Source of support
This work was funded by The Aneurysm and AVM Foundation (JJP and JAG), NIH 1RO1NS0749971 and K08 NS 051350 (JJP).
Conflict of interest
No author reports conflicts of interest for this work.
Ethical approval/informed consent
Human subject study was approved by the Cleveland Clinic Institutional Review Board and was conducted over parts of 2013 and 2014. All patients were consented for participation. All animal experiments were done with the approval of the University of Virginia Animal Care and Use Committee.
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