Mitigation of murine focal cerebral ischemia by the hypocretin/orexin system is associated with reduced inflammation.
OBJECTIVE
Brain ischemia causes immediate and delayed cell death that is exacerbated by inflammation. Recent studies show that hypocretin-1/orexin-A (Hcrt-1) reduces ischemic brain injury, and Hcrt-positive neurons modulate infection-induced inflammation. Here, we tested the hypothesis that Hcrt plays a protective role against ischemia by modulating inflammation.


METHODS
Orexin/ataxin-3 (AT) mice, a transgenic strain in which Hcrt-producing neurons degenerate in early adulthood, and wild-type mice were subjected to transient middle cerebral artery occlusion (MCAO). Infarct volume, neurological score, and spontaneous home cage activity were assessed. Inflammation was measured using immunohistochemistry, ELISA, and assessment of cytokine mRNA levels.


RESULTS
Infarct volumes 24 and 48 hours after MCAO were significantly larger, neurological score was worse, and spontaneous activity decreased in AT compared with wild-type mice. Macrophage/microglial infiltration and myeloperoxidase-positive cells were higher in AT compared with wild-type mice. Pre-MCAO intracerebroventricular injection of Hcrt-1 significantly reduced infarct volume and macrophage/microglial infiltration in both genotypes and improved neurological score in AT mice. Post-MCAO treatment decreased infarct size in both wild-type and AT mice, but had no effect on neurological score in either genotype. Microglia express the Hcrt-1 receptor after MCAO. Tumor necrosis factor-α production by lipopolysaccharide-stimulated microglial BV2 cells was significantly reduced by Hcrt-1 pretreatment. Sham AT mice exhibit increased brain tumor necrosis factor-α and interleukin-6 mRNA, suggesting chronic inflammation.


CONCLUSIONS
Loss of Hcrt neurons in AT mice resulted in worsened stroke outcomes, which were reversed by administration of exogenous Hcrt-1. The mechanism underlying Hcrt-mediated neuroprotection includes attenuation of inflammatory responses after ischemic insult.
AfaSci Research Laboratories, Redwood City, CA 94063, USA.
Xiaoxing
X
Xiong
Robin E
RE
White
Lijun
L
Xu
Liya
L
Yang
Xiaoyun
X
Sun
Bende
B
Zou
Conrado
C
Pascual
Takeshi
T
Sakurai
Rona G
RG
Giffard
Xinmin Simon
XS
Xie
D000818:Animals; D002545:Brain Ischemia / Q000473:pathology / Q000503:physiopathology* / Q000517:prevention & control*; D002465:Cell Movement; D004660:Encephalitis / Q000473:pathology / Q000503:physiopathology* / Q000517:prevention & control*; D020244:Infarction, Middle Cerebral Artery / Q000150:complications; D007276:Injections, Intraventricular; D015850:Interleukin-6 / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology* / Q000627:therapeutic use*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000378:metabolism / Q000473:pathology; D023421:Models, Animal; D009479:Neuropeptides / Q000235:genetics / Q000502:physiology* / Q000627:therapeutic use*; D064446:Orexin Receptors; D000068797:Orexins; D012333:RNA, Messenger / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D018013:Receptors, Neuropeptide / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D015850:Interleukin-6; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D014409:Tumor Necrosis Factor-alpha