The ability to restore hearing by regenerating outer hair cells in the cochlea of the inner ear, sometimes referred to as biological solutions for hearing loss, has shown success in restoring hearing sensitivity in animal studies. New research, however, indicates that restoring hearing is more than regenerating lost or damaged outer hair cells. In a recent study, published in the journal Proceedings of the National Academy of Sciences (PNAS), a research team from Mass Eye and Ear in Boston found that to effectively amplify and tune incoming sound, each of the outer hair cells must be arranged as a specific branch of a Y-shaped building block. Moreover, these Y-shaped building blocks must replicated thousands of times within the cochlea to form a highly organized cellular architecture.
Motivated by previous studies in their lab, the researchers, Hamid Motallebzadeh, Joris Soons and Sunil Puria, created a detailed computer simulation of the cochlea and the tiny structures within it. Motallebzadeh and colleagues then tested how different arrangements and malformations of the Y-shaped structures affect hearing function. They found that the outer hair cells could only produce precise hearing sensitivity and frequency selectivity when arranged in their natural configuration with respect to the surrounding structures. When they altered the geometry and material properties of these structures, the cells’ ability to amplify and tune sound was compromised.
“Our work suggests that in order for humans to hear well, the outer hair cells in the cochlea not only need to be in good working order, but also need to be connected to other nearby cochlear structures in a very particular way. It had been assumed that, if we could just succeed in regenerating outer hair cells, it would be sufficient to restore hearing. But our work shows that the spatial organization of the restored cells must also be taken into account. We built our model to test whether rearranging the cells in the Y-shaped structures of the inner ear alters the ear’s ability to amplify sound. By altering these structures in the model, we see strong evidence that amplification and tuning in the cochlea depend heavily on the natural arrangement of these structures.”
–Sunil Puria, PhD, in comments to Medical Xpress
The study provides an important step toward understanding the functional implications of how the outer hair cells are arranged in the inner ear—with far-reaching implications for emerging new clinical therapies that aim to restore hearing by regenerating these cells, but not necessarily in a way that restores their critical position within the natural Y-shaped building blocks of the cochlea.
Additionally, the findings of this study suggest that computational models of outer hair cell structure be used to replicate and interpret experimental measurements, which could reduce the need for animal-based hair cell regeneration studies, and allow researchers to conduct well-controlled virtual experiments.
Source: Motallebzadeh el al., “Cochlear amplification and tuning depend on the cellular arrangement within the organ of Corti,” PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1720979115