Irreversible hearing loss can be age-related, congenital, or acquired during childhood and is due to the inability of the cochlear sensory epithelium to replace hair cells. Transplantation of progenitor cells capable of differentiating into hair cells could be potentially therapeutic, but a reliable source for these progenitors in not known. In the October 27 PNAS, Huawei Li and colleagues from Harvard Medical School show that cochlear hair cells can be generated by stepwise differentiation of embryonic stem (ES) cells (PNAS, DOI:10.1073/pnas.2334503100, October 27, 2003).

Li et al. developed a cell culture protocol that enabled them to create inner ear progenitors from murine embryonic stem (ES) cells. They showed that the resulting progenitors expressed a broad set of marker genes that define the developing sensory patches. These progenitors could integrate into the developing inner ear at sites of epithelial injury, and when situated in cochlear or vestibular sensory epithelia in vivo, the integrated cells started expressing hair cell markers and displayed hair bundles.

"These studies complement the recent discovery of adult inner ear stem cells and could be the foundation of assessing the ultimate therapeutic potential of ES cell–derived inner ear progenitors in cell replacement therapy to functionally restore hearing in deaf patients," conclude the authors.