title: Apelin-13 Protects against Ischemic Blood-Brain Barrier Damage through the Effects of Aquaporin-4.
abstract: Apelin-13 has been found to have protective effects on many neurological diseases, including cerebral ischemia. However, whether Apelin-13 acts on blood-brain barrier (BBB) disruption following cerebral ischemia is largely unknown. Aquaporin-4 (AQP4) has a close link with BBB due to the high concentration in astrocyte foot processes and regulation of astrocytes function. Here, we aimed to test Apelin-13's effects on ischemic BBB injury and examine whether the effects were dependent on AQP4.
  
  
  
  We detected the expression of AQP4 induced by Apelin-13 injection at 1, 3, and 7 days after middle cerebral artery occlusion. Meanwhile, we examined the effects of Apelin-13 on neurological function, infarct volume, and BBB disruption owing to cerebral ischemia in wild type mice, and tested whether such effects were AQP4 dependent by using AQP4 knock-out mice. Furthermore, we assessed the possible signal transduction pathways activated by Apelin-13 to regulate AQP4 expression via astrocyte cultures.
  
  
  
  It was found that Apelin-13 highly increased AQP4 expression as well as reduced neurological scores and infarct volume. Importantly, Apelin-13 played a role of BBB protection in both types of mice by reducing BBB permeability, increased vascular endothelial growth factor, upregulated endothelial nitric oxide synthase, and downregulated inducible NOS. In morphology, we demonstrated Apelin-13 suppressed tight junction opening and endothelial cell swelling via electron microscopy detection. Meanwhile, Apelin-13 also alleviated apoptosis of astrocytes and promoted angiogenesis. Interestingly, effects of AQP4 on neurological function and infarct volume varied with time course, while AQP4 elicited protective effects on BBB at all time points. Statistical analysis of 2-way analysis of variance with replication indicated that AQP4 was required for these effects. In addition, Apelin-13 upregulated phosphorylation of extracellular signal-regulated kinase (ERK) and Akt as well as AQP4 protein in cultured astrocytes. The latter was inhibited by ERK and phosphatidylinositol 3'-kinase (PI3K) inhibitors.
  
  
  
  Our data suggest that Apelin-13 protects BBB from disruption after cerebral ischemia both morphologically and functionally, which is highly associated with the increased levels of AQP4, possibly through the activation of ERK and PI3K/Akt pathways. This study provides double targets to protection of ischemic BBB damage, which can present new insights to drugs development.
authors.affiliation: Department of Neurology, Huashan Hospital, State Key Laboratory of Medical Neurobiology, Shanghai, China.
authors.forename: Heling
authors.initials: H
authors.lastname: Chu
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Yang
authors.forename: Chuyi
authors.initials: C
authors.lastname: Huang
authors.forename: Zidan
authors.initials: Z
authors.lastname: Gao
authors.forename: Yuping
authors.initials: Y
authors.lastname: Tang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Dong
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051401:Aquaporin 4 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D001812:Blood-Brain Barrier / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology / Q000648:ultrastructure; D002199:Capillary Permeability / Q000187:drug effects*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020244:Infarction, Middle Cerebral Artery / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D008297:Male; D018345:Mice, Knockout; D018919:Neovascularization, Physiologic / Q000187:drug effects; D018696:Neuroprotective Agents / Q000494:pharmacology*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D019108:Tight Junctions / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D013997:Time Factors; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: C496031:Aqp4 protein, mouse; D051401:Aquaporin 4; D036341:Intercellular Signaling Peptides and Proteins; D018696:Neuroprotective Agents; D042461:Vascular Endothelial Growth Factor A; C495199:apelin-13 peptide; C467480:vascular endothelial growth factor A, mouse; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases
keywords: Apelin-13; Aquapoin-4; Blood-brain barrier; Cerebral ischemia