title: Targeting of aquaporin 4 into lipid rafts and its biological significance.
abstract: Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system and is considered to be caused by the binding of NMO-IgG to aquaporin 4 (AQP4) on astrocytes, which initiates complement-dependent cytotoxicity. AQP4 has two isoforms, i.e., M1 and M23. AQP4 is considered to form heterotetramers containing both isoforms in vivo. Most of the previous studies were performed using either one of the isoforms expressing cell lines. In this study, we generated a fluorescent epitope-tagged AQP4 M1 and M23 co-expressing astrocyte cell line and examined the subcellular targeting of AQP4. In this cell line, AQP4 was targeted mostly to membrane lipid rafts fraction evidenced by sucrose density gradient ultracentrifugation followed by Western blotting with anti-AQP4 antibody. Cholesterol depletion with methyl-β-cyclodextrin or simvastatin resulted in the dislocation (relocation) of AQP4 from lipid rafts to non-rafts fraction of the membrane and AQP4 was not internalized intracellularly. This change in the localization of AQP4 on membrane significantly reduced complement-dependent cytotoxic effects of NMO-IgG obtained from patients with NMO without affecting AQP4 orthogonal arrays. Thus, these data strongly suggest that the targeting of AQP4 in the lipid rafts is closely related to the pathogenic effects of NMO-IgG.
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan. Electronic address: kasakura@fujita-hu.ac.jp.
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Asakura
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Ueda
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Sayuri
authors.initials: S
authors.lastname: Shima
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Tomomasa
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Chika
authors.initials: C
authors.lastname: Hikichi
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Seiko
authors.initials: S
authors.lastname: Hirota
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Fukui
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Ito
authors.affiliation: Department of Neurology, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Mutoh
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D051401:Aquaporin 4 / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D015153:Blotting, Western; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D005904:Glial Fibrillary Acidic Protein; D006801:Humans; D007074:Immunoglobulin G / Q000633:toxicity; D007150:Immunohistochemistry; D007536:Isomerism; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009471:Neuromyelitis Optica / Q000276:immunology; D019821:Simvastatin / Q000494:pharmacology; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: C496030:AQP4 protein, human; D000924:Anticholesteremic Agents; D051401:Aquaporin 4; D005904:Glial Fibrillary Acidic Protein; D007074:Immunoglobulin G; D009419:Nerve Tissue Proteins; D047392:beta-Cyclodextrins; C528900:glial fibrillary astrocytic protein, mouse; C108732:methyl-beta-cyclodextrin; D019821:Simvastatin
keywords: Aquaporin 4; Lipid raft; Methyl-β-cyclodextrin; Neuromyelitis optica; Simvastatin