A method to grow inner ear tissue from human stem cells has been developed by researchers at Indiana University School of Medicine. The work could lead to new platforms to model disease and new therapies for the treatment of hearing and balance disorders.
Eri Hashino, PhD, Ruth C. Holton Professor of Otolaryngology at IU School of Medicine, explains:
“The inner ear is only one of few organs with which biopsy is not performed and because of this, human inner ear tissues are scarce for research purposes. Dish-grown human inner ear tissues offer unprecedented opportunities to develop and test new therapies for various inner ear disorders."
3D Cell Culture
The research was led by Karl R. Koehler, PhD, assistant professor in the Department of Otolaryngology and Head and Neck Surgery at IU School of Medicine, and Dr. Hashino in collaboration with Jeffrey Holt, PhD, professor of otology and laryngology at Harvard Medical School and Boston Children’s Hospital.
The research builds on the team’s previous work with a technique called three-dimensional culture, which involves incubating stem cells in a floating ball-shaped aggregate, unlike traditional cell culture in which cells grow in a flat layer on the surface of a culture dish. This allows for more complex interactions between cells, and creates an environment that is closer to what occurs in the body during development, Dr. Koehler said.
By culturing human stem cells and treating them with specific signaling molecules, the investigators were able to guide cells through key processes involved in the development of the human inner ear. This resulted in what the scientists have termed inner ear organoids, or three-dimensional structures containing sensory cells and supporting cells found in the inner ear.
“This is essentially a recipe for how to make human inner ears from stem cells. After tweaking our recipe for about a year, we were shocked to discover that we could make multiple inner ear organoids in each pea-sized cell aggregate,"
said Dr. Koehler, lead author of the study and whose research lab works on modeling human development.
Inner Ear Organoids
The researchers used CRISPR gene editing technology to engineer stem cells that produced fluorescently labeled inner ear sensory cells. Targeting the labeled cells for analysis, they revealed that their organoids contained a population of sensory cells that have the same functional signature as cells that detect gravity and motion in the human inner ear.
“We also found neurons, like those that transmit signals from the ear to the brain, forming connections with sensory cells,” Dr. Koehler said. “This is an exciting feature of these organoids because both cell types are critcal for proper hearing and balance."
Dr. Hashino said these findings are
“a real game changer, because up until now, potential drugs or therapies have been tested on animal cells, which often behave differently from human cells."
The researchers are currently using the human inner ear organoids to study how genes known to cause deafness interrupt normal development of the inner ear and plan to start the first-ever drug screening using human inner ear organoids.
Karl R Koehler, Jing Nie, Emma Longworth-Mills, Xiao-Ping Liu, Jiyoon Lee, Jeffrey R Holt, Eri Hashino Generation of inner ear organoids containing functional hair cells from human pluripotent stem cells Nature Biotechnology, 2017; DOI: 10.1038/nbt.3840
Image: Human inner ear organoid with sensory hair cells (cyan) and sensory neurons (yellow). An antibody for the protein CTBP2 reveals cell nuclei as well as synapses between hair cells and neurons (magenta). Credit: Karl Koehler