The Effects of Growth Hormone in the Inner Ear of Zebrafish (Danio rerio) during Hair Cell Regeneration
Although deafness is a universal problem, effective treatments have remained elusive. In order to develop potential treatments, an overall understanding of the cellular process of auditory hair cell regeneration, which occurs in fish but not mammals, must be established. A previous microarray analysis and qRT-PCR validation of noise-exposed zebrafish showed that growth hormone (GH) was significantly upregulated during the process of auditory hair cell regeneration. Thus, GH may play an important role during hair cell regeneration. However, cellular effects of exogenous GH in the zebrafish auditory hair cell regeneration have not been examined after noise exposure. To understand the effect of GH in hair cell regeneration, adult zebrafish were exposed to a 150 Hz pure tone at a source level of 179 dB re 1 μPa RMS for 36 hours. Afterward the fish were immediately injected intraperitoneally with carp recombinant GH (20 μg/gram of body mass) or buffer (0.1 M, pH 7.4 phosphate buffer) and then placed in a recovery tank. The effect of GH on apoptosis in fish inner ear end organs were examined using TUNEL-labeling. Cell proliferation was measured by BrdU incorporation assay. Hair cell regeneration was determined by phalloidin-labeling to allow visualization of hair cell stereociliary bundles. After GH injection, the numbers of TUNEL-labeled cells showed a significant decrease in all three inner ear end organs (saccule, lagena, utricle), suggesting GH may suppress hair cell death induced by acoustic trauma. Higher levels of cell proliferation were also observed in the ears of GH-injected fish, indicating that GH is capable of activating cell mitosis in the zebrafish auditory system. Following sound exposure, the GH-injected group exhibited greater numbers of saccular hair cell bundles compared to the buffer-injected group. These results indicate that GH promotes hair cell regeneration following acoustic damage. Future studies are needed to examine the potential therapeutic benefits of GH in the mammalian ear.
Zebra danio, regeneration (biology), sensory receptors regeneration, hair cells generation, Aquaculture and Fisheries, Cell Biology, Genetics
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