title: Growth hormone promotes hair cell regeneration in the zebrafish (Danio rerio) inner ear following acoustic trauma.
abstract: BACKGROUND
  Previous microarray analysis showed that growth hormone (GH) was significantly upregulated following acoustic trauma in the zebrafish (Danio rerio) ear suggesting that GH may play an important role in the process of auditory hair cell regeneration. Our objective was to examine the effects of exogenous and endogenous GH on zebrafish inner ear epithelia following acoustic trauma.
  
  
  RESULTS
  We induced auditory hair cell damage by exposing zebrafish to acoustic overstimulation. Fish were then injected intraperitoneally with either carp GH or buffer, and placed in a recovery tank for either one or two days. Phalloidin-, bromodeoxyuridine (BrdU)-, and TUNEL-labeling were used to examine hair cell densities, cell proliferation, and apoptosis, respectively. Two days post-trauma, saccular hair cell densities in GH-treated fish were similar to that of baseline controls, whereas buffer-injected fish showed significantly reduced densities of hair cell bundles. Cell proliferation was greater and apoptosis reduced in the saccules, lagenae, and utricles of GH-treated fish one day following trauma compared to controls. Fluorescent in situ hybridization (FISH) was used to examine the localization of GH mRNA in the zebrafish ear. At one day post-trauma, GH mRNA expression appeared to be localized perinuclearly around erythrocytes in the blood vessels of the inner ear epithelia. In order to examine the effects of endogenous GH on the process of cell proliferation in the ear, a GH antagonist was injected into zebrafish immediately following acoustic trauma, resulting in significantly decreased cell proliferation one day post-trauma in all three zebrafish inner ear end organs.
  
  
  CONCLUSIONS
  Our results show that exogenous GH promotes post-trauma auditory hair cell regeneration in the zebrafish ear through stimulating proliferation and suppressing apoptosis, and that endogenous GH signals are present in the zebrafish ear during the process of auditory hair cell regeneration.
authors.affiliation: Department of Biology and Biotechnology Center, Western Kentucky University, Bowling Green, Kentucky, United States of America.
authors.forename: Huifang
authors.initials: H
authors.lastname: Sun
authors.forename: Chia-Hui
authors.initials: CH
authors.lastname: Lin
authors.forename: Michael E
authors.initials: ME
authors.lastname: Smith
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002452:Cell Count; D049109:Cell Proliferation / Q000187:drug effects; D013006:Growth Hormone / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000473:pathology* / Q000502:physiology*; D006317:Hearing Loss, Noise-Induced / Q000473:pathology* / Q000503:physiopathology*; D034443:RNA Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012038:Regeneration / Q000187:drug effects*; D012444:Saccule and Utricle / Q000187:drug effects / Q000503:physiopathology; D015027:Zebrafish
chemical_list: D012333:RNA, Messenger; D013006:Growth Hormone