Stem cell scientists take to the lab to make cochlear implants an option for more people who have disabling hearing loss
Little Courtney Kellogg was a stubborn 3-year-old. Or so that’s what people thought when she wouldn’t follow her mother’s directions or come when she was called.
But an audiologist confirmed that Kellogg wasn’t being difficult—she had severe, progressive hearing loss. She could hear some low sound frequencies (like drumming) but had trouble with higher frequencies (like voices).
As a young child, Kellogg heard well enough to get by. As an older child, she resisted the idea of getting cochlear implants, even though she knew that without them she would eventually lose her ability to hear. Eventually, she relented, receiving one implant at age 15 and another at 23—with excellent results.
“I hear much better with both implants,” says Kellogg, who is now 27. “Conversations, daily life—everything. Honestly, I can’t even remember my life before I got my implants.”
Cochlear implants have made hearing possible for many among the approximately 5 percent of people worldwide who experience disabling hearing loss. About 100,000 people in the United States today have them.
“It’s probably the most successful neurobiological implant that we have because it changes people’s lives so much,” says Peter Santi, Ph.D., a hearing researcher in the University of Minnesota Medical School’s Department of Otolaryngology, especially for young children who can develop language because of it.
And yet the device doesn’t work for everyone. A successful implant requires the recipient to have enough specialized inner-ear nerve cells for the device to stimulate. That action allows sound-like signals to be transmitted to the brain. Many people have too few of these nerve cells. And when these cells die, they’re gone forever, Santi says.
Unless, that is, Santi and his colleagues at the U’s Stem Cell Institute find a way to regenerate them.
“Regenerating these neurons could allow people who would not be candidates for implants to become candidates,” says postdoctoral fellow Aleta Steevens, Ph.D. “It also could improve efficacy for people who have the implant—make it function better.”
Right place, right time
Stem cell scientists around the world have tried, unsuccessfully, to regenerate these specialized inner-ear nerve cells, called spiral ganglion neurons. But the U of M team is taking a different approach, called blastocyst complementation, says Medical School neuroscientist Walter Low, Ph.D.
The induced pluripotent stem cells the U team is growing go through the complete genetic programming process that allows them to integrate into the inner ear properly, Low says.
“The way we are doing it, these cells have been exposed to all of the inductive cues that a stem cell would normally be exposed to during the course of development,” he says. “So they are at the right place at the right time, and they become what they should be.”
This is no easy task. Different cells in the ear are responsible for detecting different sound frequencies. That’s why the U scientists’ technique aims to allow the environment to guide how and where the nerve cells develop.
So far, they like what they see. In a mouse model, the stem cells they’ve created are incorporating into the auditory neurons—exactly where they’re supposed to go.
Next up? Proving that the new cells are functional.
A new movement
Low envisions that, one day, a person who gets a cochlear implant could also get an infusion of these specialized cells to help the device function better. Those stem cells could be made from the recipient’s own skin cells, he says, and provide a “younger and healthier” supplement to the person’s sparse inner-ear nerve cell population.
The U team’s technique has implications for other disease areas, as well, Low says. Research on any neurologic disorder in which a specific type of neural cell is lost—vision loss, spinal cord injury, and Parkinson’s disease, for example—stands to benefit from what this group learns about repairing the nervous system.
The project so far has been funded entirely by gifts from Bridget Sperl and John McCormick, who have an adult daughter with hearing loss.
From another angle
University of Minnesota researchers are also leading another effort to restore hearing by developing a new implantable device and surgical procedure. The technique would involve implanting electrodes directly into the auditory nerve, providing access to the hearing pathway and potentially improving activation of the auditory pathway to the brain. Learn more about the project, which recently received a $9.7 million grant from the National Institutes of Health.
“We’re really building all of this up from the philanthropic donation from their family,” Steevens says. “It’s really incredible that, from this one family, this is hopefully starting a new movement.”
Now Courtney Kellogg is part of the movement, too. A Ph.D. candidate at the University of Rochester in New York who is studying how the inner ear develops, Kellogg—along with her lab mates—will collaborate with the Minnesota team on the project.
“I’m a big believer in access to health care and technology,” Kellogg says, whether people choose to use the technologies or not. “For me, it was one of the best adult decisions that I have made.”
Find out how you can support this research by contacting Nathan Brown of the University of Minnesota Foundation at firstname.lastname@example.org or 651-403-2515.