title: Glymphatic distribution of CSF-derived apoE into brain is isoform specific and suppressed during sleep deprivation.
abstract: Apolipoprotein E (apoE) is a major carrier of cholesterol and essential for synaptic plasticity. In brain, it's expressed by many cells but highly expressed by the choroid plexus and the predominant apolipoprotein in cerebrospinal fluid (CSF). The role of apoE in the CSF is unclear. Recently, the glymphatic system was described as a clearance system whereby CSF and ISF (interstitial fluid) is exchanged via the peri-arterial space and convective flow of ISF clearance is mediated by aquaporin 4 (AQP4), a water channel. We reasoned that this system also serves to distribute essential molecules in CSF into brain. The aim was to establish whether apoE in CSF, secreted by the choroid plexus, is distributed into brain, and whether this distribution pattern was altered by sleep deprivation.
  
  
  
  We used fluorescently labeled lipidated apoE isoforms, lenti-apoE3 delivered to the choroid plexus, immunohistochemistry to map apoE brain distribution, immunolabeled cells and proteins in brain, Western blot analysis and ELISA to determine apoE levels and radiolabeled molecules to quantify CSF inflow into brain and brain clearance in mice. Data were statistically analyzed using ANOVA or Student's t- test.
  
  
  
  We show that the glymphatic fluid transporting system contributes to the delivery of choroid plexus/CSF-derived human apoE to neurons. CSF-delivered human apoE entered brain via the perivascular space of penetrating arteries and flows radially around arteries, but not veins, in an isoform specific manner (apoE2 > apoE3 > apoE4). Flow of apoE around arteries was facilitated by AQP4, a characteristic feature of the glymphatic system. ApoE3, delivered by lentivirus to the choroid plexus and ependymal layer but not to the parenchymal cells, was present in the CSF, penetrating arteries and neurons. The inflow of CSF, which contains apoE, into brain and its clearance from the interstitium were severely suppressed by sleep deprivation compared to the sleep state.
  
  
  
  Thus, choroid plexus/CSF provides an additional source of apoE and the glymphatic fluid transporting system delivers it to brain via the periarterial space. By implication, failure in this essential physiological role of the glymphatic fluid flow and ISF clearance may also contribute to apoE isoform-specific disorders in the long term.
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Thiyagaragan M
authors.initials: TM
authors.lastname: Achariyar
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.|Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang, China.
authors.forename: Baoman
authors.initials: B
authors.lastname: Li
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Weiguo
authors.initials: W
authors.lastname: Peng
authors.affiliation: Department of Neurology, Hope Center for Neurological Disorders, and the Charles F. and Joanne Knight Alzheimer's Disease Research Center, Washington University School of Medicine, St Louis, MO, 63110, USA.
authors.forename: Philip B
authors.initials: PB
authors.lastname: Verghese
authors.affiliation: Department of Neurology, Hope Center for Neurological Disorders, and the Charles F. and Joanne Knight Alzheimer's Disease Research Center, Washington University School of Medicine, St Louis, MO, 63110, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Evan
authors.initials: E
authors.lastname: McConnell
authors.affiliation: Center for Translational Neuromedicine, Division of Cell and Gene Therapy, University of Rochester Medical Center, Rochester, NY, 14642, USA.
authors.forename: Abdellatif
authors.initials: A
authors.lastname: Benraiss
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Tristan
authors.initials: T
authors.lastname: Kasper
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Song
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Takano
authors.affiliation: Department of Neurology, Hope Center for Neurological Disorders, and the Charles F. and Joanne Knight Alzheimer's Disease Research Center, Washington University School of Medicine, St Louis, MO, 63110, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Holtzman
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA.
authors.forename: Maiken
authors.initials: M
authors.lastname: Nedergaard
authors.affiliation: Center for Translational Neuromedicine, Division of Glial Disease and Therapeutics, Department of Neurosurgery, University of Rochester Medical Center, University of Rochester, Rochester, NY, 14642, USA. Rashid_Deane@urmc.rochester.edu.
authors.forename: Rashid
authors.initials: R
authors.lastname: Deane
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism*; D000818:Animals; D001057:Apolipoproteins E / Q000134:cerebrospinal fluid / Q000378:metabolism*; D051401:Aquaporin 4 / Q000378:metabolism; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D008297:Male; D051379:Mice; D009474:Neurons / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D012892:Sleep Deprivation / Q000134:cerebrospinal fluid / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001057:Apolipoproteins E; C496031:Aqp4 protein, mouse; D051401:Aquaporin 4; D020033:Protein Isoforms
keywords: AQP4; Alzheimer’s disease; Brain clearance; Glymphatic pathways; Lymphatic system; Sleep/wake