title: Regulation of mitochondrial uncoupling proteins in mouse inner ear ganglion cells in response to systemic kanamycin challenge.
abstract: Mitochondrial uncoupling proteins are a proton transporter family involved in regulation mitochondrial superoxide and ATP production. Uncoupling proteins are expressed by rat spiral ganglion and vestibular ganglion cells [Hear Res 196 (2004) 39]. This study tests the hypothesis that uncoupling protein expression is up-regulated in response to the reactive oxygen species challenge imposed by kanamycin and antioxidant (2,3-dihydroxybenzoate) treatment in mice. In control C57BL/6, CBA/J and BALB/c mice, mRNA for uncoupling protein 1, uncoupling protein 2, uncoupling protein 3, Slc25a27 (uncoupling protein 4) and Slc25a14 (uncoupling protein 5/BMCP1) was expressed in the spiral and vestibular ganglia. After kanamycin-treatment (700 mg/kg twice daily for 14 days s.c.), uncoupling protein 2 and uncoupling protein 3 mRNA expression increased significantly in spiral and vestibular ganglia and kidney, but was unaffected in cerebral cortex. Significant Slc25a27 (uncoupling protein 4) mRNA up-regulation was also observed in spiral and vestibular ganglia, but not in kidney or cerebral cortex. These effects were blocked by simultaneous administration of kanamycin and 2,3-dihydroxybenzoate (300 mg/kg twice daily for 14 days s.c.). Western immunoblotting and immunohistochemistry confirmed the uncoupling protein 2 and uncoupling protein 3 up-regulation in inner ear. Finally, 2,3-dihydroxybenzoate treatment alone produced an upregulation of uncoupling protein 1 mRNA in the spiral ganglion, vestibular ganglion and cerebral cortex, but not the kidney. Uncoupling protein 2 and uncoupling protein 3 upregulation in the kidney and inner ear ganglia likely reflects their general role as a feedback pathway to reduce mitochondrial superoxide generation. Slc25a27 (uncoupling protein 4) upregulation in the inner ear ganglia, by contrast, is likely to be a secondary response to kanamycin-induced hair cell death. We propose that increased uncoupling protein 2, uncoupling protein 3 and Slc25a27 expression has several neuroprotective effects via reduction in mitochondrial superoxide generation and local thermogenesis, including: (1) reducing mean ROS load to prevent apoptosis, (2) increasing signal-to-noise characteristics of intracellular ROS signaling pathways (e.g. lipoxygenases, growth factor and transcription factors), (3) heat-related alteration of enzyme kinetics and (4) promotion of cell depolarization (activation of heat-gated ion channels).
authors.affiliation: Department of Otolaryngology, University of Pittsburgh School of Medicine, 107 Eye and Ear Institute, Pittsburgh, PA 15213, USA.
authors.forename: T
authors.initials: T
authors.lastname: Kitahara
authors.forename: H S
authors.initials: HS
authors.lastname: Li-Korotky
authors.forename: C D
authors.initials: CD
authors.lastname: Balaban
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015152:Blotting, Northern; D015153:Blotting, Western / Q000379:methods; D002352:Carrier Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D007758:Ear, Inner; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D007150:Immunohistochemistry / Q000379:methods; D007473:Ion Channels; D007612:Kanamycin / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D024101:Mitochondrial Proteins; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013136:Spiral Ganglion / Q000166:cytology*; D000071256:Uncoupling Protein 1; D014725:Vestibular Nerve / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; C000604372:Ucp1 protein, mouse; C000604373:Ucp1 protein, rat; D000071256:Uncoupling Protein 1; D007612:Kanamycin