title: Astrocytic Toll-like receptor 3 is associated with ischemic preconditioning-induced protection against brain ischemia in rodents.
abstract: BACKGROUND
  Cerebral ischemic preconditioning (IPC) protects brain against ischemic injury. Activation of Toll-like receptor 3 (TLR3) signaling can induce neuroprotective mediators, but whether astrocytic TLR3 signaling is involved in IPC-induced ischemic tolerance is not known.
  
  
  METHODS
  IPC was modeled in mice with three brief episodes of bilateral carotid occlusion. In vitro, IPC was modeled in astrocytes by 1-h oxygen-glucose deprivation (OGD). Injury and components of the TLR3 signaling pathway were measured after a subsequent protracted ischemic event. A neutralizing antibody against TLR3 was used to evaluate the role of TLR3 signaling in ischemic tolerance.
  
  
  RESULTS
  IPC in vivo reduced brain damage from permanent middle cerebral artery occlusion in mice and increased expression of TLR3 in cortical astrocytes. IPC also reduced damage in isolated astrocytes after 12-h OGD. In astrocytes, IPC or 12-h OGD alone increased TLR3 expression, and 12-h OGD alone increased expression of phosphorylated NFκB (pNFκB). However, IPC or 12-h OGD alone did not alter the expression of Toll/interleukin receptor domain-containing adaptor-inducing IFNβ (TRIF) or phosphorylated interferon regulatory factor 3 (pIRF3). Exposure to IPC before OGD increased TRIF and pIRF3 expression but decreased pNFκB expression. Analysis of cytokines showed that 12-h OGD alone increased IFNβ and IL-6 secretion; 12-h OGD preceded by IPC further increased IFNβ secretion but decreased IL-6 secretion. Preconditioning with TLR3 ligand Poly I:C increased pIRF3 expression and protected astrocytes against ischemic injury; however, cells treated with a neutralizing antibody against TLR3 lacked the IPC- and Poly I:C-induced ischemic protection and augmentation of IFNβ.
  
  
  CONCLUSIONS
  The results suggest that IPC-induced ischemic tolerance is mediated by astrocytic TLR3 signaling. This reprogramming of TLR3 signaling by IPC in astrocytes may play an important role in suppression of the post-ischemic inflammatory response and thereby protect against ischemic damage. The mechanism may be via activation of the TLR3/TRIF/IRF3 signaling pathway.
authors.affiliation: Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People's Republic of China; Medical Department of Neurology, The Second Hospital of Nanchang, Nanchang, Jiangxi, People's Republic of China.
authors.forename: Lin-na
authors.initials: LN
authors.lastname: Pan
authors.affiliation: Department of Emergency Internal Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People's Republic of China; Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhu
authors.affiliation: Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People's Republic of China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People's Republic of China; The Key Laboratory of Drug Target Research and Pharmacodynamic Evaluation, Hubei Province, Wuhan, Hubei, People's Republic of China.
authors.forename: Xu-lin
authors.initials: XL
authors.lastname: Xu
authors.affiliation: Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People's Republic of China; The Key Laboratory of Drug Target Research and Pharmacodynamic Evaluation, Hubei Province, Wuhan, Hubei, People's Republic of China.
authors.forename: Lian-jun
authors.initials: LJ
authors.lastname: Guo
authors.affiliation: Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People's Republic of China; The Key Laboratory of Drug Target Research and Pharmacodynamic Evaluation, Hubei Province, Wuhan, Hubei, People's Republic of China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Lu
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D001921:Brain / Q000473:pathology; D002545:Brain Ischemia / Q000150:complications / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism / Q000473:pathology; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005947:Glucose / Q000172:deficiency; D020244:Infarction, Middle Cerebral Artery / Q000473:pathology; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D016899:Interferon-beta / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D019194:Ischemic Preconditioning; D008297:Male; D051379:Mice; D010100:Oxygen; D010766:Phosphorylation; D011070:Poly I-C / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D051196:Toll-Like Receptor 3 / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000378:metabolism
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D005904:Glial Fibrillary Acidic Protein; D050838:Interferon Regulatory Factor-3; D015850:Interleukin-6; D051196:Toll-Like Receptor 3; D051996:Transcription Factor RelA; D016899:Interferon-beta; D005947:Glucose; D011070:Poly I-C; D010100:Oxygen