Madrid
Updated:05/04/2022 20:27h
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Hearing loss due to aging, noise and certain ototoxic drugs, for cancer and some antibiotics, is irreversible because until now it has not been possible to reprogram the hair cells with the necessary characteristics.
Now, scientists at Northwestern Medicine University in Chicago (USA), led by Spanish researcher Jaime García-Añoveros, have discovered a single master gene that programs ear hair cells to become the cell types needed , external or internal, thus overcoming a major obstacle that had prevented the development of these cells to restore hearing. The study has been published in Nature.
“Our finding provides us with the first clear cellular switch to make one type versus the other,” says lead study author Jaime García-Añoveros, a professor at Northwestern University Feinberg School of Medicine.
“This discovery will provide a previously unavailable tool for manufacturing inner or outer hair cells. We have overcome a major hurdle.”
García-Añoveros defines it as a «cellular dichotomy that is essential for hearing». The internal ones are the cells that, when activated by sound, send the information to the brain, while the external ones, an acquisition in the evolution of mammals, “amplify the sound”. These cells, explains the Spanish researcher, “literally move, dance, with respect to sound and when they move, they make the ear vibrate more and increase the stimulation received by the internal ones.”
This, he points out, allows us to hear sounds of very low intensity and the correct frequencies, higher or lower, and to distinguish, extract much more information from the sounds. “This is important for language, for music, for everything.”
Currently, scientists can generate an artificial hair cell, but cannot differentiate between them as internal or external, a factor that is important since they provide different functions essential to producing hearing. That is, he points out, “they are not used to generate hearing.”
The discovery then means an important step towards the development of these specific cells.
The death of the outer hair cells of the cochlea is the most common cause of deafness and hearing loss. The cells develop into the embryo and do not reproduce. The outer hair cells expand and contract in response to pressure from sound waves and amplify sound for the inner hair cells. The inner cells transmit those vibrations to the neurons to create the sounds we hear.
“It’s like a dance,” adds García-Añoveros, describing the coordinated movement of the inner and outer cells. “The external ones bend down and jump and raise the internal ones towards the interior of the ear” and adds “The ear is a precious organ. There is no other organ in a mammal in which the cells are arranged with such micron precision. If not, the audition does not take place.”
The master genetic switch that scientists discovered that programs ear hair cells is TBX2. When the gene is expressed, the cell becomes an inner hair cell. When the gene is blocked, the cell becomes an outer hair cell.
The ability to produce one of these cells will require a cocktail of genes, García Añoveros said. The ATOH1 and GF1 genes are required to create a cochlear hair cell from a non-hair cell. TBX2 would then be turned on or off to produce the required inner or outer cell.
The goal would be to reprogram the supporting cells, which sit between the hair cells and provide structural support, to become outer or inner hair cells.
This ability of cells to convert is something that was unprecedented in a cell so formed that it will never divide, the researcher points out.
In conclusion, the Spanish researcher points out, “now we can find out how to specifically manufacture inner or outer hair cells and identify why the latter are more likely to die and cause deafness.”
¿And for when a therapy for deafness? García Añoveros affirms that «with technological advances there is something, especially in biology, that is very difficult to predict. How close are you to the useful end product? Because sometimes the organism fixes itself.
In any case, believe in the next decade we can discover many of these things because for the first time we have the tools to do it for all the problems.
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