title: Dexamethasone Regulates Cochlear Expression of Deafness-associated Proteins Myelin Protein Zero and Heat Shock Protein 70, as Revealed by iTRAQ Proteomics.
abstract: OBJECTIVE
  Using proteomics, we aimed to identify the proteins differentially regulated by dexamethasone in the mouse cochlea based on mass-spectrometry data.
  
  
  BACKGROUND
  Glucocorticoid therapy is widely used for many forms of sensorineural hearing loss; however, the molecular mechanism of its action in the cochlea remains poorly understood.
  
  
  METHODS
  Dexamethasone or control saline was intratympanically applied to the cochleae of mice. Twelve hours after application, proteins differentially regulated by dexamethasone in the cochlea were analyzed by isobaric Tag for Relative and Absolute Quantitation (iTRAQ)-mass spectrometry. Next, dexamethasone-dependent regulation of these proteins was verified in the cochleae of mice with noise-induced hearing loss (NIHL) and systemic administration of dexamethasone by western blotting. Immunolocalizations of these proteins were examined in cochleae with NIHL.
  
  
  RESULTS
  A total of 247 proteins with a greater than 95% confidence interval of protein identification were found, and 11 differentially expressed proteins by dexamethasone were identified by the iTRAQ-mass spectrometry. One protein, myelin protein zero (Mpz), was upregulated (1.870 ± 0.201-fold change, p < 0.01) at 6 hours post-systemic dexamethasone and noise exposure in a mouse model of NIHL. Heat shock protein 70 (Hsp70) was downregulated (0.511 ± 0.274-fold change, p < 0.05) at 12 hours post-systemic dexamethasone. Immunohistochemistry confirmed Mpz localization to the efferent and afferent processes of the spiral neurons, whereas Hsp70 showed a more ubiquitous expression pattern in the cochlea.
  
  
  CONCLUSIONS
  Both Mpz and Hsp70 have been reported to be closely associated with sensorineural hearing loss in humans. Dexamethasone significantly modulated the expression levels of these proteins in the cochleae of mice.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Maeda
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Fukushima
authors.forename: Shin
authors.initials: S
authors.lastname: Kariya
authors.forename: Yorihisa
authors.initials: Y
authors.lastname: Orita
authors.forename: Kazunori
authors.initials: K
authors.lastname: Nishizaki
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D003051:Cochlea / Q000187:drug effects / Q000378:metabolism*; D003638:Deafness / Q000188:drug therapy / Q000235:genetics*; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics*; D006317:Hearing Loss, Noise-Induced / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D006319:Hearing Loss, Sensorineural / Q000188:drug therapy / Q000235:genetics; D007274:Injections, Intraperitoneal; D051379:Mice; D008810:Mice, Inbred C57BL; D018993:Myelin P0 Protein / Q000096:biosynthesis* / Q000235:genetics*; D040901:Proteomics / Q000379:methods*; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism; D014432:Tympanic Membrane
chemical_list: D000893:Anti-Inflammatory Agents; D018840:HSP70 Heat-Shock Proteins; D018993:Myelin P0 Protein; D003907:Dexamethasone