Repeated loud noise can eventually contribute to deafness as it causes a permanent damage to the hair cells inside the cochlea. Although this phenomenon is irreparable in mammals, both birds and fish have the ability to restore hearing by reinstating the damaged hair cells. In a new research published in BMC Neuroscience, researchers from Western Kentucky University and the University of Louisville revealed that zebrafish accomplished this regeneration process with the aid of a growth hormone.
Researchers found distinct gene expression patterns while investigating which genes were switched on or off after acoustic trauma. Two days after injury, the inner ear cells were found to be rapidly multiplying in order to reinstate and restore the damaged hair cells. An alteration in the 839 gene regulation as well as many cellular pathways, similar to those involved in cancer, were associated with the repair process, which heightened the transcription of growth hormone by 64 times!
The gene MHC I ZE involved in immune response regulation is down-regulated. However, local inhibition of the immune response during injury repair is appropriate since the wound healing process might be interrupted by a strong inflammatory response to tissue damage. These levels were found to be restored after four days.
“Injecting growth hormone into zebrafish stimulated cell proliferation in their inner ears, especially cells of the utricle, a vestibular organ involved in balance. There are many homologs between zebrafish and human genes and we are beginning to work on the function of these genes within the ear. Understanding how fish are able to repair their hair cells may eventually help us to understand ear injury in people and provide treatments for hair cell loss,” commented Dr. Michael Smith.