title: Activation of mitochondrial transient receptor potential vanilloid 1 channel contributes to microglial migration.
abstract: Microglia, the resident immune cells in the brain, survey the environment of the healthy brain. Microglial migration is essential for many physiological and pathophysiological processes. Although microglia express some members of the transient receptor potential (TRP) channel family, there is little knowledge regarding the physiological roles of TRP channels in microglia. Here, we explored the role of TRP vanilloid 1 (TRPV1), a channel opened by capsaicin, heat, protons, and endovanilloids, in microglia. We found that application of capsaicin induced concentration-dependent migration in microglia derived from wild-type mice but not in those derived from TRPV1 knockout (TRPV1-KO) mice. Capsaicin-induced microglial migration was significantly inhibited by co-application of the TRPV1 blocker SB366791 and the Ca(2+) chelator BAPTA-AM. Using RT-PCR and immunocytochemistry, we validated that TRPV1 was expressed in microglia. Electrophysiological recording, intracellular Ca(2+) imaging, and immunocytochemistry indicated that TRPV1 was localized primarily in intracellular organelles. Treatment with capsaicin induced an increase in intramitochondrial Ca(2+) concentrations and mitochondrial depolarization. Furthermore, microglia derived from TRPV1-KO mice showed delayed Ca(2+) efflux compared with microglia derived from wild-type mice. Capsaicin-induced microglial migration was inhibited by membrane-permeable antioxidants and MAPK inhibitors, suggesting that mitochondrial TRPV1 activation induced Ca(2+) -dependent production of ROS followed by MAPK activation, which correlated with an augmented migration of microglia. Moreover, a mixture of three endovanilloids augmented microglial migration via TRPV1 activation. Together, these results indicate that mitochondrial TRPV1 plays an important role in inducing microglial migration. Activation of TRPV1 triggers an increase in intramitochondrial Ca(2+) concentration and following depolarization of mitochondria, which results in mtROS production, MAPK activation, and enhancement of chemotactic activity in microglia.
authors.affiliation: Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Takahito
authors.initials: T
authors.lastname: Miyake
authors.affiliation: Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Shirakawa
authors.affiliation: Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.|Department of Clinical Pharmacology and Therapeutics, Kyoto University Hospital, Kyoto, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nakagawa
authors.affiliation: Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Shuji
authors.initials: S
authors.lastname: Kaneko
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002211:Capsaicin / Q000494:pharmacology; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D017628:Microglia / Q000502:physiology* / Q000648:ultrastructure; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009599:Nitroprusside / Q000378:metabolism; D018689:Sensory System Agents / Q000494:pharmacology; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D015850:Interleukin-6; D018689:Sensory System Agents; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D009599:Nitroprusside; D048670:MAP Kinase Kinase 4; D002211:Capsaicin
keywords: Ca2+ signaling; TRPV1; cell movement; microglia; mitochondria