The research community has in recent years demonstrated the ability to grow fully or near fully functional organ tissue of many types from stem cells, and the research presented here adds a new type to the list. Tissue engineering of this sort is at present limited in size to very small tissue sections, called organoids, because researchers have yet to establish a reliable solution for integrating blood vessel networks into tissue built from the starting point of a few cells. Still, it is important work, as the recipes for various tissue types, all quite different in their details, are a necessary foundation for the next stage of organ engineering. That is expected to start up after blood vessel networks can be created efficiently and cheaply. The creation of organoids is also very useful for research here and now; a lot more can be done for a given amount of funding with organoids than with animal models.
Researchers at have successfully developed a method to grow inner ear tissue from human stem cells - a finding that could lead to new platforms to model disease and new therapies for the treatment of hearing and balance disorders. "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."
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. By culturing human stem cells in this manner 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." 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. This is an exciting feature of these organoids because both cell types are critical for proper hearing and balance."