Scientists have developed a way of using stem cells to create key structures of the inner ear in mice, publishing their findings in the journal Nature.
The Indiana University researchers found that by using a 3D cell-culture method, they were able to persuade stem cells to develop into inner ear sensory epithelium, which detects head movement, gravity and sound. The epithelium contains hair cells, supporting cells and neurons.
A 3D cell-culture method can more closely copy natural tissues and organs than cells grown two-dimensionally. In 3D cell culture, cells can attach to each other and form natural cell-to-cell attachments.
Karl R. Koeheler, one of the researchers in the study, explains:
"The three-dimensional culture allows the cells to self-organize into complex tissues using mechanical cues that are found during embryonic development."
"We were surprised to see that once stem cells are guided to become inner ear precursors and placed in 3D culture, these cells behave as if they knew not only how to become different cell types in the inner ear, but also how to self-organize into a pattern remarkably similar to the native inner ear."
He adds that their initial goal was to make inner ear precursors, cells from which other cells are formed, in the 3D culture method - but when they did testing, thousands of hair cells were found in the culture dish.
The researchers carried out electrophysiology testing, the study of the electrical properties of biological cells and tissues, which found that the hair cells generated from stem cells were fully functional and sensed motion and gravity.
They also discovered that neurons - nerve cells - which would transmit sound information from the inner ear to the brain, had developed during the cell culture and were connected to the hair cells.
There have been attempts to grow inner ear hair cells before in standard cell culture systems. However, the necessary cues to develop "hair bundles" are lacking in the flat 2D cell culture dish. The hair bundles are vitally important in detecting sound and enabling balance.
The researchers say that further research is needed to find out how inner ear cells involved in auditory sensing can be developed, and also how human inner ear cells can be created.
They add, however, that the work in this study provides a better understanding of the inner ear development process and could lead to the development of new drugs or cellular therapy to treat inner ear disorders.