When people hear the term "stem cell research," many automatically think of the extraordinary advocacy efforts of the late Christopher Reeve and assume that modern scientific studies are focusing on using stem cells to repair damaged spinal cords. While much research is being conducted in this important area, stem cells also are being studied because they offer promise in the treatment of a variety of other diseases and disabilities, including hearing loss.
A review of recent research shows that scientists have been trying to develop a cell-based therapy for hearing loss for more than 20 years and that current research is being conducted all over the world. A small sampling of current research reveals exciting, diverse and innovative projects:
- Scientists at Oregon Health & Science University have been able to produce auditory (hearing) cells in the cochlea (inner ear) of mice by transferring a key gene into the cochlea as it was developing. The researchers believe their findings may be applicable to all mammals.
- In Italy, researchers also used mice to show that damaged cochlear tissue was regenerated and repaired when human umbilical cord cells were transplanted into a mouse cochlea. This project suggested that hearing damage caused by noise is more severe than damage caused by chemicals.
- At the University of California - Davis, scientists are studying whether hearing cells-which are called "hair cells" because of their appearance-might be replaced with stem cells from certain parts of the brain.
- At the Indiana School of Medicine, scientists are working to transform stem cells taken from adult bone marrow into cells with many of the characteristics of neurons found in the ear.
- In Greece, researchers are seeking a better understanding of the genetic components of hearing with a goal to regenerate hair cells in the cochlea.
- Genetic research at Purdue is finding that the lack of a key molecule leads to deafness, and studies at the University of Rochester Medical Center are showing that genes controlling cell death may cause age-related hearing loss.
- Scientists working on a project at the University of Sheffield were able to grow hair cells from stem cells extracted from the cochlea of a fetus.
- At Uppsala Universitet in Sweden, researchers have identified immature stem cells in the inner ears of humans and cultivated hearing nerves from stem cells and human tissue from donated cochleae. This project also is working on imaging techniques to view how auditory nerves develop.
Since there currently is no cure for hearing loss, the possibilities of cell-based therapies are exciting to imagine. However, remember that previous and existing studies have been conducted only on animals; in fact, it may be years before any of the research theories can be tested on people. Also, even in the face of recently relaxed guidelines for U.S. governmental funding of stem cell research due to President Obama's support and executive order, many ethical questions and dilemmas remain that may affect the course of future research.
While there is hope that research may lead to an eventual cure for hearing loss or a mechanism to repair it, nothing is on the immediate horizon. Our ability to hear remains a precious--and irreplaceable--gift.