title: Stimulation of transient receptor potential vanilloid 4 channel suppresses abnormal activation of microglia induced by lipopolysaccharide.
abstract: Microglia are intrinsic immune cells in the brain. In response to neurodegenerative events, excessively activated microglia change their shapes and release various cytokines leading to the pathogenesis of central nervous system (CNS) disease. Because the intracellular mechanisms of this process are still unclear, we have evaluated the functional roles of transient receptor potential vanilloid 4 (TRPV4) channel expressed in the microglia. Robust microglial activation after an injection of lipopolysaccharide (LPS) into the mouse cerebral ventricle was suppressed by concurrent administration of a selective TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4α-PDD). When the mechanism was further investigated using cultured rat microglia intrinsically expressing functional TRPV4, release of tumor necrosis factor-α (TNF-α) and expression of galectin-3 were both increased by LPS. These increases were significantly suppressed by cotreatment with 4α-PDD, and the inhibitory effects of 4α-PDD were abolished by knockdown of TRPV4 or TRPV4 antagonists. The amplitude of voltage-dependent K(+) current, which is augmented during microglial activation, was also suppressed by 4α-PDD treatment. Opening of TRPV4 channels with 4α-PDD induced membrane depolarization mainly by increasing Na(+) influx. In addition, mimicking depolarization with a high-K(+) solution suppressed LPS-induced TNF-α release and galectin-3 upregulation. Both depolarizing treatments with 4α-PDD and high-K(+) solution decreased store-operated Ca(2+) influx caused by thapsigargin. These results suggest that depolarization in response to opening of the TRPV4 channel attenuates the driving force for extracellular Ca(2+) and suppresses microglial activation.
authors.affiliation: Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Konno
authors.forename: Hisashi
authors.initials: H
authors.lastname: Shirakawa
authors.forename: Shota
authors.initials: S
authors.lastname: Iida
authors.forename: Shinya
authors.initials: S
authors.lastname: Sakimoto
authors.forename: Ikkei
authors.initials: I
authors.lastname: Matsutani
authors.forename: Takahito
authors.initials: T
authors.lastname: Miyake
authors.forename: Keiko
authors.initials: K
authors.lastname: Kageyama
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Koji
authors.initials: K
authors.lastname: Shibasaki
authors.forename: Shuji
authors.initials: S
authors.lastname: Kaneko
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D015536:Down-Regulation / Q000276:immunology*; D007276:Injections, Intraventricular; D008070:Lipopolysaccharides / Q000008:administration & dosage* / Q000037:antagonists & inhibitors*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D010704:Phorbols / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D050916:TRPV Cation Channels / Q000819:agonists / Q000096:biosynthesis* / Q000502:physiology; D015854:Up-Regulation / Q000276:immunology*
chemical_list: C517592:4alpha-phorbol 12,13-didecanone; D008070:Lipopolysaccharides; D010704:Phorbols; D050916:TRPV Cation Channels; C486577:Trpv4 protein, rat