title: Zinc is released by cultured astrocytes as a gliotransmitter under hypoosmotic stress-loaded conditions and regulates microglial activity.
abstract: OBJECTIVE
  Astrocytes contribute to the maintenance of brain homeostasis via the release of gliotransmitters such as ATP and glutamate. Here we examined whether zinc was released from astrocytes under stress-loaded conditions, and was involved in the regulation of microglial activity as a gliotransmitter.
  
  
  METHODS
  Hypoosmotic stress was loaded to astrocytes using balanced salt solution prepared to 214-314 mOsmol/L, and then intra- and extra-cellular zinc levels were assessed using Newport Green DCF diacetate (NG) and ICP-MS, respectively. Microglial activation by the astrocytic supernatant was assessed by their morphological changes and poly(ADP-ribose) (PAR) polymer accumulation.
  
  
  RESULTS
  Exposure of astrocytes to hypoosmotic buffer, increased the extracellular ATP level in osmolarity-dependent manners, indicating a load of hypoosmotic stress. In hypoosmotic stress-loaded astrocytes, there were apparent increases in the intra- and extra-cellular zinc levels. Incubation of microglia in the astrocytic conditioned medium transformed them into the activated "amoeboid" form and induced PAR formation. Administration of an extracellular zinc chelator, CaEDTA, to the astrocytic conditioned medium almost completely prevented the microglial activation. Treatment of astrocytes with an intracellular zinc chelator, TPEN, suppressed the hypoosmotic stress-increased intracellular, but not the extracellular, zinc level, and the increase in the intracellular zinc level was blocked partially by a nitric oxide synthase inhibitor, but not by CaEDTA, indicating that the mechanisms underlying the increases in the intra- and extra-cellular zinc levels might be different.
  
  
  CONCLUSIONS
  These findings suggest that under hypoosmotic stress-loaded conditions, zinc is released from astrocytes and then plays a primary role in microglial activation as a gliotransmitter.
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Shohei
authors.initials: S
authors.lastname: Segawa
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishiura
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Furuta
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ohsato
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Misaki
authors.initials: M
authors.lastname: Tani
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Nishida
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan. Electronic address: nagasawa@mb.kyoto-phu.ac.jp.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Nagasawa
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D027682:Cation Transport Proteins / Q000378:metabolism; D002478:Cells, Cultured; D004492:Edetic Acid / Q000494:pharmacology; D005029:Ethylenediamines / Q000494:pharmacology; D051379:Mice; D017628:Microglia / Q000187:drug effects / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000502:physiology*; D009997:Osmotic Pressure / Q000187:drug effects / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D015032:Zinc / Q000502:physiology*
chemical_list: D027682:Cation Transport Proteins; D005029:Ethylenediamines; D018377:Neurotransmitter Agents; C485803:Slc30a1 protein, mouse; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D015032:Zinc; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine
keywords: Astrocyte; Gliotransmitter; Hypoosmotic stress; Zinc