Scientists Create Inner-ear "Organoids" in Cell Cultures to Research Hearing Loss

By carefully fine-tuning cell culture conditions, Renjie Chai, Huawei Li, Wenyan Li and colleagues from the Fudan University Eye Ear Nose and Throat Hospital in Shanghai, China, have succeeded in growing stem cells—complete with some of the key structural components that help us hear—isolated from mouse cochleae. Details of their work were published in the January 10, 2023 edition of Stem Cell Reports and summarized by International Society of Stem Cell Research.

According to the World Health Organization, disabling hearing loss affects 1 in every 10 people and up to 25% of people over 60, and can have genetic and environmental causes such as infections and noise exposure. Sensorineural hearing loss, the most frequent form of hearing loss, is caused by damage to hair cells (HCs) inside the cochlea and spiral ganglion neurons (SGNs), both of which are essential for hearing. HCs receive sounds as mechanical vibrations which are then turned into electrical impulses transmitted to the brain via SGNs. Once damaged or lost, these transmitters do not grow back, thus requiring hearing aids or cochlear implants to compensate for hearing loss.

The cochlea is about the size of a pencil eraser and situated next to vital nerves in the head and neck, making study of them extremely difficult. Research into ways of regenerating cochlear cells has been limited by the lack of suitable lab-based models of cochlear physiology and function. The researchers addressed this by generating stem cell cochlear avatars in the lab.

By carefully fine-tuning cell culture conditions, they succeeded in growing stem cells isolated from mouse cochleae. The stem cells grew as 3D structures—so-called “organoids”—and were then directed into cochlear HCs by adjusting culture conditions. Significantly, mouse SGNs added to the cultures connected with the HCs and transmitted electrical signals, an important step towards modeling cochlear function in the dish.

According to the authors, this study has generated “cochlear organoids with functional synapses for the first time, which provides a platform for deciphering the mechanisms of sensorineural hearing loss,” opening up avenues for investigating new therapeutic approaches.