Scientists Grow Inner Ear Organs from Stem Cells

Using human stem cells, Scientists from the University of Indiana report having grown the organs of the human inner ear in an article published in Nature Biotechnology. Developed as a potential source of in vitro screening technology, the techniques holds promise as a future stem cell-based therapy. The researchers employed a 3-D cell culture method that allows cells to develop specific three dimensional shapes, a prerequisite for the ability to grow organs or other complex biological structures in vitro.

Human pluripotent stem cells can be induced to differentiate into the more specific cell types associated with tissues and organs. Pluripotent, and even multipotent stem cells can programmed to alter their genetic expression patterns to reflect those of the specific target cell/tissue type.

It should be noted from an ethical standpoint, there are two types of stem cells: embryonic and adult stem cells. For those concerned with the ethics of stem cell use, there is no ethical concern when utilizing adult stem cells. As the name implies, adult stem cells are harvested from adults, and then in general used in as therapy in those same adults from whom the cells were harvested. Ethical concerns arise from the use of embryonic stem cells, which are harvested from viable human embryos. This particular blog post is not a commentary on the ethics of embryonic stem cell research; I have previously offered my perspective on this topic.

Differentiation of stem cells, in general, is induced by providing a specific mixture of specific compounds, each of which must be provided in a specific ratio. In this case, the specific compounds utilized are molecules involved with cell signaling, communication among cells, and transcriptional regulation, turning expression of certain genes on or off; these compounds altered TGF, BMP, FGF, and WNT signaling to generate multiple structures related to inner ear function from a single stem-cell aggregate. These cellular aggregates develop into “inner ear organoids with sensory epithelia that are innervated by sensory neurons,” over a period of approximately two months.

Otic hair cells function as the the sensory receptors in the auditory system and the vestibular system of all vertebrates. Damage to these cells results in a permanent decrease in hearing sensitivity, as the inner ear hair cells are not capable of regeneration. It is further noteworthy that the researchers were able to demonstrate that the innervated sensory neurons exhibit electrophysiological properties comparable to those of adult sensory hair cells, increasing the likelihood that such a technique could one day function as the basis for a stem cell-based therapy that can at least partially reverse hearing loss via replacement of the sound-sensitive cells of the inner ear.