Stem Cell Regeneration of Human Spiral Ganglion Neurons toward Hearing Restoration

Hearing loss is a major concern of military personnel, who are exposed to loud explosions and working environments that damage the cochlea, the small inner-ear organ that converts sound to neural impulses. For severe hearing losses, the cochlear implant (CI) is the preferred remedy. CI’s bring awareness of a person’s sound environment and speech perception. However, users struggle with hearing speech in noise, appreciating music, and understanding emotion and intonation of speech. Also, advances in CI performance have plateaued, indicating the need for new efforts. Fortunately, there are known problems that point to new “biohybrid” CI designs that combine bio-active components and proven CI technology. Damaged auditory nerve fibers (ANFs) -- which transmit information from cochlea to brain -- lack the axons that get close to CI electrodes. Lacking those intimate contacts, each CI electrode excites relatively large ANF groups, reducing the ability to transmit many channels of sound information and resulting in rather crude auditory perceptions. We want to advance CI performance by adding more neuronal channels to the damaged cochlea so that each CI electrode excites a smaller number of ANFs. That is, we want to close the gap between CI electrodes and surviving ANFs to increase the amount of detail transmitted to the brain. Thus, our long-term goal is a “biohybrid CI” that combines well-tested CI designs with newly transplanted ANFs derived from human stem cells (which we call “derived ANFs”). We have done the work to convert human pluripotent stem cells into derived ANFs and have transplanted derived ANFs into animal models. However, we seek to transplant the cells into the same cochlear compartment where CIs are placed (i.e., the scala tympani), so that they can extend new neural processes to the surviving ANFs, bridging the gaps and improving CI performance. Our short-term goals will be conducted within a 3-year plan and directed toward overcomin