Researchers have managed for the first time to differentiate human inner ear cells in a laboratory from somatic progenitors and to investigate their origin. This will make it possible to develop new treatment methods for hearing impairment in the future. The study was published in the journal Nature Communications.
About 5% of the world population suffers from hearing impairment. The disabling hearing loss has far-reaching implications for those concerned and society as a whole. Hearing loss in adults alone ranks among the five largest disease burdens in Europe and generates enormous socioeconomic costs.
The hearing ability can be improved with hearing aids or cochlear implants, but to this day there is no causal treatment for hearing impairments.
Human Hair Cells
For the first time, they managed to imitate the development of human hair cells, which are responsible for sound reception in the inner ear, in-vitro (in the laboratory). As a result, in the future, it will be possible to try out new pharmacological treatment directly on human cells.
Sensory Cells In The Inner Ear
Our ability to hear depends on the coordinated activity of two specialized types of sensory cells in the inner ear, more precisely in the cochlea. The so-called hair cells function as sound receptors by responding to vibrations which are caused by sounds. The hair cells release chemical messengers who in turn stimulate the so-called spiral ganglion cells.
These cells form the auditory nerve, which passes the information on to the brain, where it is perceived as sound. These cell types are organized in a complex mosaic. This enables us to perceive different sound intensities and frequencies with unprecedented speed and accuracy.
Spiral Ganglion Cells
Hair cells and spiral ganglion cells from very early during fetal development, roughly in the 10th to 11th week of pregnancy, when they reach their definitive number. Loud noises, infections, aging processes or also exposure through toxins afflict the sensory cells from then on.
Because the cells cannot be replaced, their loss leads to a permanent hearing impairment. They have developed a methodology to isolate these progenitors from the human fetal cochlea and ultimately optimize the conditions for in-vitro generation of functional hair cells in the laboratory.
For this purpose, the researchers used three-dimensional cultures, also known as organoids. The results of the now published study constitute a unique template for future research projects in the field, in order to develop new strategies to combat neurosensory hearing loss.
Because the results would provide a blueprint for the generation of cochlear hair cells from other more abundant sources of cells such as pluripotent stem cells. This will pave the way for tests which are based on a patient's own cell types and enable more individualized treatment.