Jennifer Stone

Uncovering a Signaling Molecule That Modulates Avian Hair Cell Regeneration

By Rebecca M. Lewis, Au.D., Ph.D., and Jennifer Stone, Ph.D.

Mammals including humans cannot regenerate hair cells, but other species such as birds and fish readily regenerate hair cells after damage to restore auditory function. The gene ATOH1 produces a protein that pushes supporting cells—cells that neighbor hair cells—to either directly convert into a hair cell or to divide and form a new hair cell. However, ATOH1 expression (when the gene is turned on) does not guarantee that hair cells develop in birds or mammals, which suggests that there are factors that prevent supporting cells from changing into hair cells. Identifying these factors in birds may help us better understand the lack of hair cell regeneration in mammals.

This schematic depicts our current ideas for how BMP4 regulates ATOH1 expression and therefore hair cell regeneration in the avian hearing organ. It shows (from left) typical hair cells, hair cell damage, and hair cell regeneration. Typical hair cells secrete BMP4. When hair cells die, BMP4 signaling is reduced, which allows ATOH1 to be expressed in supporting cells and pushes supporting cells to turn into hair cells. The newly regenerated hair cells secrete BMP4, suppressing ATOH1 in supporting cells and restoring the normal condition.

This schematic depicts our current ideas for how BMP4 regulates ATOH1 expression and therefore hair cell regeneration in the avian hearing organ. It shows (from left) typical hair cells, hair cell damage, and hair cell regeneration. Typical hair cells secrete BMP4. When hair cells die, BMP4 signaling is reduced, which allows ATOH1 to be expressed in supporting cells and pushes supporting cells to turn into hair cells. The newly regenerated hair cells secrete BMP4, suppressing ATOH1 in supporting cells and restoring the normal condition.

We examined the avian auditory system to characterize a potential inhibitor to ATOH1 during hair cell regeneration: bone morphogenetic protein 4 (BMP4). Bone morphogenetic proteins are secreted signaling molecules that regulate cellular processes in many regions of the body, including the nervous system. We found that BMP4 localizes to hair cells of the mature avian hearing organ and disappears when hair cells die or sustain damage. From this, we hypothesized that BMP4 may prevent ATOH1 expression in supporting cells and loss of BMP4 when hair cells die may enable ATOH1 to be expressed in supporting cells, driving them to convert into hair cells.

When we exposed avian auditory organs to BMP4 after selectively killing hair cells, this prevented ATOH1 expression and hair cell regeneration. When we antagonized BMP4 using an inhibitor, we found a generally opposite result: an increase in the number of regenerated hair cells.

We conclude that BMP4 is a potent inhibitor of ATOH1 and therefore suppresses hair cell regeneration. We recommend that BMP4 be explored further in studies of mammalian hair cell regeneration.

Published in Hearing Research on May 2, 2018, this study detailing BMP4’s negative effect on ATOH1 expands our knowledge of signaling molecules that suppress hair cell regeneration in birds and may also modulate hair cell regeneration in humans.

Rebecca M. Lewis, Au.D., Ph.D., is a clinical audiologist and auditory neuroscientist at Massachusetts Eye and Ear/Harvard Medical School in Boston. HRP researcher Jennifer Stone, Ph.D., is the director of research in the department of otolaryngology–head and neck surgery at the Virginia Merrill Bloedel Hearing Research Center at the University of Washington.

Empower the Hearing Restoration Project's life-changing research. If you are able, please make a contribution today.

 
 
Print Friendly and PDF

Women’s History Through the Lens of HHF

By C. Adrean Mejia

Before Women’s History Month concludes, Hearing Health Foundation (HHF) would like to highlight the accomplishments of women in science, technology, engineering, and mathematics (STEM), including those who have been instrumental to our own progress toward preventing, treating, and curing hearing loss and related conditions.

Historically, STEM has been majority male, but the growing inclusion of women in the industry is closing the gender gap. In fact, LinkedIn reports the percentage of women entering STEM roles in the last four decades is greater than that of any other professional sector. In 1978, the STEM workforce was only 10% female, while today about a third of this field is comprised of women.

Emerging Research Grants (ERG) recipient Dr. Wafaa Kaf administers a hearing screening. Credit: Missouri State University.

Emerging Research Grants (ERG) recipient Dr. Wafaa Kaf administers a hearing screening. Credit: Missouri State University.

As individuals and as an organization that values inclusiveness, we all at HHF applaud the trend of growing opportunity for women in scientific professions, while remaining equally grateful to the male researchers and Board members who offer their commitment, support, and expertise. Our founder was a woman; 60 years ago, Mrs. Collette Ramsey Baker began a quest to find better treatments and cures for hearing and balance conditions which is championed by all today.

We would like to acknowledge the outstanding women on HHF’s Board of Directors, whose altruism and intelligence have furthered hearing research and HHF’s growth. Our Board Chair, Elizabeth Keithley, Ph.D., who has been an auditory researcher for more than 30 years, began her association with HHF as a grant reviewer. Dr. Keithley has conducted and published a number of studies related to the mechanisms of inflammation and aging on the inner ear.

From left: HHF Board Chair Elizabeth Keithley, Ph.D., and Board member Judy Dubno, Ph.D.

From left: HHF Board Chair Elizabeth Keithley, Ph.D., and Board member Judy Dubno, Ph.D.

Board member Judy Dubno, Ph.D., professor at the Medical University of South Carolina, is considered one of the most important otolaryngology researchers in the nation. Her work has focused on auditory perception, hearing loss, and speech recognition. Dr. Dubno was also a contributor to the report that successfully urged the FDA to create a category of over-the-counter hearing aids to make hearing loss treatment more accessible to American adults.

Also serving on the Board is Ruth Anne Eatock, Ph.D., of the University of Chicago, who studies sensory signaling by hair cells and neurons in the inner ear. She was recently published in The Journal of Neuroscience for her investigation of inner ear sensory cells in rodents.

HHF is also thankful for the three female scientists who are part of our Hearing Restoration Project (HRP) consortium working to permanently cure hearing loss: Ronna Hertzano, M.D., Ph.D., Tatjana Piotrowski, Ph.D., and Jennifer S. Stone, Ph.D. Their labs at the University of Maryland, Stowers Institute for Medical Research, and the University of Washington, respectively, have uncovered valuable insights related to a biological cure for hearing loss.

Our Emerging Research Grants (ERG) program has empowered many brilliant, female researchers, including those recently published: Wafaa Kaf, Ph.D., researching new techniques to diagnose Ménière's disease; Michelle Hastings, Ph.D., investigating early genetic intervention for Usher syndrome; Elizabeth McCullagh, Ph.D., examining the connection between sound localization difficulties and Fragile X Syndrome; and Samira Anderson, Au.D., Ph.D., working to improve hearing aid fit to enhance usage.

Finally, we are fortunate to have Nadine Dehgan serving as our CEO. Ms. Dehgan plays a crucial role in our growth and programming efficiency, and her leadership experience and passion for how hearing science can better people’s lives has made her a strong fit to drive HHF forward.

HHF deeply values the work of all individuals who bring us closer to a world without hearing loss and tinnitus. For Women’s History Month, we’re honored to call special attention to the women who have been part of these life-changing efforts in the spirit of Mrs. Ramsey Baker, whose determination and selflessness still inspires us today.

Print Friendly and PDF

New Method Enables Systematic Study of Hair Cell Loss and Regeneration in Chickens

By Carol Stoll

Most forms of hearing loss are permanent because damage to inner ear sensory hair cells is irreversible in mammals, including humans. Mammalian vestibular hair cells have the potential to regenerate albeit at a low rate, but the hair cells of the adult mammalian cochlea are not regenerated. Birds, however, have a robust regenerative response to hair cell damage and are able to restore structure and function in inner ear organs. Consequently, the study of the molecular mechanisms that trigger the onset of avian hair cell regeneration in the balance organs as well as in the cochlea is important and may lead to therapies for hearing loss in humans.

This image shows the undamaged and damaged utricle, an inner ear balance organ, in a chicken. HRP researchers have devised a new method to study the precise timing of hair cell regeneration in chickens using a single surgical application of an ototoxic drug. Photo by Amanda Janesick, Ph.D.

This image shows the undamaged and damaged utricle, an inner ear balance organ, in a chicken. HRP researchers have devised a new method to study the precise timing of hair cell regeneration in chickens using a single surgical application of an ototoxic drug. Photo by Amanda Janesick, Ph.D.

Past experiments that investigate these regeneration mechanisms in living chickens required multiple injections of a drug to induce hair cell loss, making it difficult to determine the exact timing of the regeneration response. A collaboration of two Hearing Restoration Project researchers, Stefan Heller, Ph.D. and Jennifer Stone, Ph.D., and two talented postdoctoral fellows from their laboratories was recently published in Journal of the Association for Research in Otolaryngology identifying a potential solution to this problem. They developed an experimental framework that uses a single ototoxic drug application, enabling them to study the precise onset and timing of hair cell regeneration in vivo.

Heller, Stone, and colleagues performed their experiments on a total of 75 chickens. At seven days of age, the chickens were anesthetized and underwent surgery to eliminate hair cells in the inner ear organs. During the surgery, streptomycin (an ototoxic antibiotic) was delivered to the chicken’s inner ear. At various time points after the surgery, two sensory organs—the utricle, a vestibular organ; and the basilar papilla, the hearing organ—were dissected, labeled for various cellular markers, and analyzed under a microscope. Hair cells and their surrounding supporting cells were counted and observed for damage. EdU, a marker of cell division, was administered to the chickens to determine whether or not new hair cells were generated by cell division. These techniques enabled the researchers to quantitatively characterize the regenerative response of the utricle after damage.

The results of the study demonstrate that surgical application of a single streptomycin dose is a feasible approach to elicit hair cell loss and regeneration in the chicken utricle and basilar papilla. Just hours after streptomycin delivery, hair cell numbers significantly declined and DNA replication was activated. The team was then able to record specific events of the regeneration process, which get initiated around 12 hours after streptomycin-induced hair cell loss, and continue over the course of several days.

Supporting cells produce new hair cells either by converting into a hair cell (direct transdifferentiation), or by dividing, usually asymmetrically, into a supporting cell and a hair cell.  Throughout this regenerative response, supporting cell numbers and density in the utricle remain relatively constant, suggesting that there is a mechanism that responds to specific levels of damage and coordinates the individual events of the regeneration process.

The study establishes a framework for the refined study of the two modes of hair cell regeneration in the chicken utricle. The next steps of the work will focus on understanding the exact timing and mechanism of coordination of the regeneration response. With only a single application of streptomycin necessary to induce near-complete hair cell loss in hearing and balance organs, the new animal model allows for study of the entire process including initiation, realization, and termination. The fundamental understanding of the avian regenerative mechanisms may lead to future development of therapies for loss of hearing and balance in humans.

Empower the Hearing Restoration Project's life-changing research. If you are able, please make a contribution today.

 
 
Print Friendly and PDF