title: Neuronal production of lipocalin-2 as a help-me signal for glial activation.
abstract: OBJECTIVE
  We explored the hypothesis that injured neurons release lipocalin-2 as a help me signal.
  
  
  METHODS
  In vivo lipocalin-2 responses were assessed in rat focal cerebral ischemia and human stroke brain samples using a combination of ELISA and immunostaining. In vitro, microglia and astrocytes were exposed to lipocalin-2, and various markers and assays of glial activation were quantified. Functional relevance of neuron-to-glia lipocalin-2 signaling was examined by transferring conditioned media from lipocalin-2-activated microglia and astrocytes onto neurons to see whether activated glia could protect neurons against oxygen-glucose deprivation and promote neuroplasticity.
  
  
  RESULTS
  In human stroke samples and rat cerebral ischemia, neuronal expression of lipocalin-2 was significantly increased. In primary cell cultures, exposing microglia and astrocytes to lipocalin-2 resulted in glial activation. In microglia, lipocalin-2 converted resting ramified shapes into a long-rod morphology with reduced branching, increased interleukin-10 release, and enhanced phagocytosis. In astrocytes, lipocalin-2 upregulated glial fibrillary acid protein, brain-derived neurotropic factor, and thrombospondin-1. Conditioned media from lipocalin-2-treated astrocytes upregulated synaptotagmin, and conditioned media from lipocalin-2-treated microglia upregulated synaptophysin and post-synaptic density 95 (PSD95) and protected neurons against oxygen-glucose deprivation.
  
  
  CONCLUSIONS
  These findings provide proof of concept that lipocalin-2 is released by injured neurons as a help me distress signal that activates microglia and astrocytes into potentially prorecovery phenotypes.
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.). Lo@helix.mgh.harvard.edu xing.changhong@mgh.harvard.edu.
authors.forename: Changhong
authors.initials: C
authors.lastname: Xing
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Xiaoshu
authors.initials: X
authors.lastname: Wang
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Chongjie
authors.initials: C
authors.lastname: Cheng
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Joan
authors.initials: J
authors.lastname: Montaner
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Emiri
authors.initials: E
authors.lastname: Mandeville
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Wendy
authors.initials: W
authors.lastname: Leung
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Klaus
authors.initials: K
authors.lastname: van Leyen
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Josephine
authors.initials: J
authors.lastname: Lok
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.).
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Wang
authors.affiliation: From the Departments of Radiology, Neurology, and Pediatrics, Massachusetts General Hospital, Harvard Medical School, Charlestown (C.X., Xiaoshu Wang, C.C., E.M., W.L., K.v.L., J.L., Xiaoying Wang, E.H.L.); Department of Neurosurgery, First Affiliated Hospital, Chongqing Medical University, Chongqing, China (Xiaoshu Wang, C.C.); and Neurovascular Research Laboratory, Vall d'Hebron University Hospital Research Institute, Barcelona, Spain (J.M.). Lo@helix.mgh.harvard.edu xing.changhong@mgh.harvard.edu.
authors.forename: Eng H
authors.initials: EH
authors.lastname: Lo
mesh_terms: D000209:Acute-Phase Proteins / Q000378:metabolism*; D000368:Aged; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D002545:Brain Ischemia / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D000071068:Lipocalin-2; D054834:Lipocalins / Q000378:metabolism*; D008297:Male; D017628:Microglia / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000378:metabolism*; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D016037:Single-Blind Method; D020521:Stroke / Q000378:metabolism*
chemical_list: D000209:Acute-Phase Proteins; D015415:Biomarkers; C489506:LCN2 protein, human; C097278:Lcn2 protein, rat; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins
keywords: astrocytes; lipocalins; microglia; neurons