Walk, Block, and Turn!

By Maggie Niu

April 27 is International Noise Awareness Day (INAD), a day dedicated to encouraging people to “do something about bothersome noise where they work, live, and play.”

Every day in our environment we experience sound, whether it’s pleasant, like music, or bothersome, like sirens. Unpleasant or unwanted noisy environments can be dreadful; not only can noise increase our stress level and inhibit us from carrying out daily tasks, but also in the long run overexposure to noise can damage our hearing. This is known as noise-induced hearing loss (NIHL). All too often, we become immune to the constant hum of traffic (about 85 decibels, or dB) and noisy subway stations (95 dB). The Safe and Sound safe listening levels chart, on the left, details the effects of various decibel levels on our ears.

There are two causes of NIHL. One is impulse noise, a one-time exposure to a loud sound such as an explosion. This can cause temporary and/or permanent hearing loss. The other cause of NIHL is continuous exposure to loud noise. This type of hearing loss happens gradually over time.

NIHL affects our inner-ear hair cells (the cells that help us hear) as well as the auditory or hearing nerve. Not only can this type of hearing loss be permanent, it can also lead to tinnitus. Tinnitus is hearing a constant ringing, buzzing, or roaring without an external sound source. It can be in one or both ears and often occurs with hearing loss.

Now the question is: How do we protect ourselves from NIHL? It can be as easy as remembering to Walk, Block, and Turn! Walk away from loud sounds. Block noise by wearing earplugs or other hearing protective devices. Turn the volume down on stereos and personal music devices. If you work in a noisy environment, take proper measures to protect your ears by wearing ear plugs or ear muffs. Being able to hear is important for daily interactions and often taken for granted until it's too late.

To learn more about Hearing Health Foundation's Safe and Sound program, please email development@hhf.org.

Unraveling Genes Critical for Inner Ear Development

By Albert Edge, Ph.D., and Alain Dabdoub, Ph.D

The goal of the Hearing Restoration Project (HRP) is to determine how to regenerate inner ear sensory cells in humans to eventually restore hearing for millions of people worldwide. These sensory cells, called hair cells, in the cochlea detect and turn sound waves into electrical impulses that are sent to the brain. Once hair cells are damaged or die, hearing is impaired, but in most species, hair cells spontaneously regrow and hearing is restored. The HRP is aiming to enable this ability in humans. 

All cells develop through a chain of events triggered by chemical signals (proteins) from outside the cell. The signals kick off responses inside the cell that can change the cell’s ability to proliferate (grow and divide) and differentiate (take on specialized functions).

The Wnt signaling pathway, a sequence of events triggered by the Wnt protein, helps guide inner ear cell development, including the proliferation of cells that differentiate into the hair cells and supporting cells necessary for hearing and balance. But in mice and other mammals, inner ear cell proliferation does not continue past newborn stages.

Underscoring their importance in evolutionary terms, Wnt signals occur across species, from fruit flies to humans—the “W” in Wnt refers to “wingless”—and Wnt signaling is guided by dozens of genes. Albert Edge, Ph.D., Alain Dabdoub, Ph.D., and colleagues performed a comprehensive screen of 84 Wnt signaling-related genes and identified 72 that are expressed (turned on) during mouse inner ear development and maturation. Their results appeared in the journal PLoS One this February.

The Wnt signaling network has three primary pathways. Two are known to be integral to the formation of the mammalian inner ear, including the determination of a cell’s “fate,” or what type of cell it ultimately turns into. This is particularly significant because the inner ear’s sensory epithelium tissue is a highly organized structure with specific numbers and types of cells in an exact order. The precise arrangement and number of hair cells and supporting cells is essential for optimal hearing.

The relationship between the Wnt-related genes, the timing of their expression, and the various signaling pathways that act on inner ear cells is extremely complex. For instance, the composition of components inside a cell in addition to the cell’s context (which tissue the cell is in, and the tissue’s stage of development) will influence which pathway Wnt signaling will take. It is known that inhibiting the action of Wnt signaling causes hair cells to fail to differentiate.

The new research complements previous chicken inner ear studies of Wnt-related genes as well as a recent single-cell analysis of the newborn sensory epithelium in mice (conducted by HRP scientist Stefan Heller, Ph.D., and colleagues). Comprehensively detailing these 72 Wnt-related genes in the mouse cochlea across four developmental and postnatal time periods provides a deeper understanding of a critical component of hair cell development, bringing the HRP closer to identifying genes for their potential in hair cell regeneration.

Your Support Is Needed!

Hair cell regeneration is a plausible goal for eventual treatment of hearing and balance disorders.

The question is not if we will regenerate hair cells in humans, but when.  

However, we need your support to continue this vital research and find a cure!

Please make your gift today.  

Are Hair Cell Regeneration Genes Blocked?

By Yishane Lee

On March 8, 2016, Hearing Health Foundation hosted a live-video research briefing, as part of an ongoing effort to provide regular updates on our research programs and progress. Through these briefings, our goal is for our attendees to learn new information and achieve a greater understanding of hearing loss, prevention, and to o develop effective therapies for hearing loss and tinnitus.

Peter Barr-Gillespie, Ph.D., the scientific director of the Hearing Restoration Project (HRP), began the webinar with announcing the newest HRP consortium member, Ronna Hertzano, M.D., Ph.D., from the University of Maryland. Ronna is a clinician as well as a research scientist, a rare combination and an asset for the HRP. She also developed a bioinformatics platform, gEAR, that the HRP is using to efficiently compare large, complex genetic datasets between species.

Dr. Barr-Gillespie went on to outline a year in the life of the HRP—how the investigators collaborate, discuss, and develop research projects. He then provided an overview of a currently funded project focused on examining whether genes can be manipulated to overcome a block to hair cell regeneration in mammals, including humans. The advancements in technologies, such as CRISPR gene modification, provides the HRP with the ability to study hair cell regeneration in different species and at a level of detail and manipulation unheard of before.

We invite you to watch the video with captioning, or read the presentation with summary notes. We are excited to share this discussion of the HRP’s progress to date and our plans for 2016 and beyond.

Your Support Is Needed!

Hair cell regeneration is a plausible goal for eventual treatment of hearing and balance disorders.

The question is not if we will regenerate hair cells in humans, but when.  

However, we need your support to continue this vital research and find a cure!

Please make your gift today.

Scientists restore hearing in noise-deafened mice

By the University of Michigan Health System

Scientists have restored the hearing of mice partly deafened by noise, using advanced tools to boost the production of a key protein in their ears.

This microscope image of tissue from deep inside a normal mouse ear shows how ribbon synapses (red) form the connections between the hair cells of the inner ear (blue) and the tips of nerve cells (green) that connect to the brain.

Credit: Corfas lab - University of Michigan

By demonstrating the importance of the protein, called NT3, in maintaining communication between the ears and brain, these new findings pave the way for research in humans that could improve treatment of hearing loss caused by noise exposure and normal aging.

In a new paper in the online journal eLife, the team from the University of Michigan Medical School's Kresge Hearing Research Institute and Harvard University report the results of their work to understand NT3's role in the inner ear, and the impact of increased NT3 production on hearing after a noise exposure.

Their work also illustrates the key role of cells that have traditionally been seen as the "supporting actors" of the ear-brain connection. Called supporting cells, they form a physical base for the hearing system's "stars": the hair cells in the ear that interact directly with the nerves that carry sound signals to the brain. This new research identifies the critical role of these supporting cells along with the NT3 molecules that they produce.

NT3 is crucial to the body's ability to form and maintain connections between hair cells and nerve cells, the researchers demonstrate. This special type of connection, called a ribbon synapse, allows extra-rapid communication of signals that travel back and forth across tiny gaps between the two types of cells.

"It has become apparent that hearing loss due to damaged ribbon synapses is a very common and challenging problem, whether it's due to noise or normal aging," says Gabriel Corfas, Ph.D., who led the team and directs the U-M institute. "We began this work 15 years ago to answer very basic questions about the inner ear, and now we have been able to restore hearing after partial deafening with noise, a common problem for people. It's very exciting."

Using a special genetic technique, the researchers made it possible for some mice to produce additional NT3 in cells of specific areas of the inner ear after they were exposed to noise loud enough to reduce hearing. Mice with extra NT3 regained their ability to hear much better than the control mice.

Now, says Corfas, his team will explore the role of NT3 in human ears, and seek drugs that might boost NT3 action or production. While the use of such drugs in humans could be several years away, the new discovery gives them a specific target to pursue.

Corfas, a professor and associate chair in the U-M Department of Otolaryngology, worked on the research with first author Guoqiang Wan, Ph.D., Maria E. Gómez-Casati, Ph.D., and others in his former institution, Harvard. Some of the authors now work with Corfas in his new U-M lab. They set out to find out how ribbon synapses -- which are found only in the ear and eye -- form, and what molecules are important to their formation and maintenance.

Anyone who has experienced problems making out the voice of the person next to them in a crowded room has felt the effects of reduced ribbon synapses. So has anyone who has experienced temporary reduction in hearing after going to a loud concert. The damage caused by noise -- over a lifetime or just one evening -- reduces the ability of hair cells to talk to the brain via ribbon synapse connections with nerve cells.

Targeted genetics made discovery possible

After determining that inner ear supporting cells supply NT3, the team turned to a technique called conditional gene recombination to see what would happen if they boosted NT3 production by the supporting cells. The approach allows scientists to activate genes in specific cells, by giving a dose of a drug that triggers the cell to "read" extra copies of a gene that had been inserted into them. For this research, the scientists activated the extra NT3 genes only into the inner ear's supporting cells.

The genes didn't turn on until the scientists wanted them to -- either before or after they exposed the mice to loud noises. The scientists turned on the NT3 genes by giving a dose of the drug tamoxifen, which triggered the supporting cells to make more of the protein. Before and after this step, they tested the mice's hearing using an approach called auditory brainstem response or ABR -- the same test used on humans.

The result: the mice with extra NT3 regained their hearing over a period of two weeks, and were able to hear much better than mice without the extra NT3 production. The scientists also did the same with another nerve cell growth factor, or neurotrophin, called BDNF, but did not see the same effect on hearing.

Next steps

Now that NT3's role in making and maintaining ribbon synapses has become clear, Corfas says the next challenge is to study it in human ears, and to look for drugs that can work like NT3 does. Corfas has some drug candidates in mind, and hopes to partner with industry to look for others.

Boosting NT3 production through gene therapy in humans could also be an option, he says, but a drug-based approach would be simpler and could be administered as long as it takes to restore hearing.

Corfas notes that the mice in the study were not completely deafened, so it's not yet known if boosting NT3 activity could restore hearing that has been entirely lost. He also notes that the research may have implications for other diseases in which nerve cell connections are lost -- called neurodegenerative diseases. "This brings supporting cells into the spotlight, and starts to show how much they contribute to plasticity, development and maintenance of neural connections," he says.

In addition to Corfas, Wan and Gómez-Casati, who now works in Argentina, the research was performed by Angelica R. Gigliello, and M. Charles Liberman, Ph.D. director of the Eaton-Peabody Laboratories of the Massachusetts Eye and Ear Infirmary. The research was supported by the National Institute on Deafness and Other Communication Disorders (DC004820, DC005209) and by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (HD18655), both part of the National Institutes of Health, and by the Hearing Health Foundation.

The above post is reprinted from materials provided by University of Michigan Health System. 

  We need your help in funding the exciting work of hearing and balance scientists. 

To donate today to Hearing Health Foundation and support groundbreaking research, visit hhf.org/name-a-grant.

Unlocking the Potential for Hair Cell Regeneration

By Laura Friedman

On November 5, 2015, Hearing Health Foundation hosted its second live-video research briefing as part of our effort to provide regular updates on our research programs and progress. Through these briefings, our goal is for our attendees to obtain new information and understanding about hearing loss, prevention and research toward a cure.

Dr. Andy Groves, Hearing Restoration Project consortium member, presented recent research advances and new discoveries, the use of new technology, and our future plans to prevent and cure hearing loss and tinnitus. The HRP was founded in 2011 and is the first and only international research consortium focused on investigating hair cell regeneration as a cure for hearing loss and tinnitus. The overarching principle of the consortium is collaboration: open sharing of data and ideas. The HRP consortium consists of 13 of the top investigators in the audiological space, as well as a scientific director, Dr. Barr-Gillespie.

We wanted to share with you highlights from the presentation, which is available to watch with live captioning or to read with notes summarizing each slide.

Your Support Is Needed!

Hair cell regeneration is a plausible goal for eventual treatment of hearing and balance disorders. 

The question is not if we will regenerate hair cells in humans, but when.  

However, we need your support to continue this vital research and find a cure! Please make your gift today. 

Handicapable

By Kate Yandell

Dominic Pisano hadn’t even arrived on campus to start his freshman year at Johns Hopkins University when he got his first email from biomedical engineer Tilak Ratnanather. He had heard Pisano was deaf and wanted to meet with him. Ratnanather, who has been deaf since birth, showed up for the meeting accompanied by a second deaf student who would later become a doctor. “He was, like: ‘Here’s my deaf army,’” Pisano recalls.

Soon, Pisano, a soccer enthusiast from Ohio, was interpreting magnetic resonance imaging (MRI) in Ratnanather’s department. When Pisano decided he wanted to go to medical school, Ratnanather was ready to introduce him to his wide network of friends in the otolaryngology department at Hopkins. Pisano assisted in MRI research at Hopkins for a year before attending Tufts University School of Medicine in Boston.

“I’ll be honest with you, if it weren’t for Tilak I probably wouldn’t have gone to medical school,” says Pisano, now a resident in anesthesiology at Tufts Medical Center. “I probably wouldn’t have done biomedical engineering research. Most importantly, I probably wouldn’t have the kind of network I have.”

Photo: Tilak Ratnanather

Courtesy Johns Hopkins School of Medicine

It was this kind of service that won Ratnanather the Presidential Award for Excellence in Science, Mathematics, and Engineering Mentoring this past March. Over the years, Ratnanather has lobbied for better resources for deaf attendees at conferences, organized annual dinners for deaf researchers, helped award scholarships to hearing-impaired students through the Alexander Graham Bell Association for the Deaf and Hard of Hearing (AG Bell), and mentored more than a dozen hearing-impaired students.

“He’s by nature the most gregarious and extroverted individual,” says Howard Francis, a professor of otolaryngology at Hopkins who has known Ratnanather for 23 years. “He has a sense of mission and is committed to making it possible for others to achieve what he has achieved.”

“A lot of people have a hard time understanding him [due to his deafness-related difficulties with speech],” says Pisano, “but despite that, they still enjoy his company, and they want to be connected with him.”

Ratnanather was born in 1963 in Sri Lanka with profound hearing loss of unknown origin. His family moved to London when he was 18 months old, and he grew up wearing hearing aids and attending the Mary Hare School for Deaf Children.

Ratnanather’s parents, a pediatrician and a computer systems programmer, had high hopes for their son. “My father and I would talk about mathematics and would go through some problems at home,” he says. “I had an aptitude, and then, of course, I would go to the science museum and learn about famous mathematicians.” Ratnanather enrolled at University College London, where he met mathematician Keith Stewartson, who immediately made the young undergrad comfortable about his hearing loss and the assistive technologies he needed to use in the classroom. “I knew he would make my life easy,” says Ratnanather. “I didn’t have to worry about my deafness.”

Tragically, Stewartson died suddenly at the end of Ratnanather’s first year at university. But the young student forged ahead, and after doing some reading about Stewartson’s research on fluid dynamics, Ratnanather went on to study the subject in graduate school at the University of Oxford, receiving his D.Phil. in mathematics in 1989.

Up until that point, Ratnanather had only had occasional opportunities to learn about an area near to his heart: hearing research. This changed after he attended a research symposium at the 1990 AG Bell Convention in Washington, D.C. Fascinated by the work of William Brownell, Ratnanather approached the Johns Hopkins researcher after Brownell had given a talk about outer hair cell electromotility—the process by which these sensory cells shorten or lengthen in response to electrical impulses.

When outer hair cells change shape, they transmit mechanical force to the cochlea, amplifying the ear’s sensitivity to soft sounds at specific frequencies. Forces transmitted through pressurized fluids in outer hair cells make electromotility possible, explains Brownell, who is now at Baylor College of Medicine in Houston. He needed someone who could model the dynamics of fluid within these tiny spaces. “Tilak had the computational tools to begin to study this,” Brownell says.

Ratnanather began a postdoc in Brownell’s lab in 1991. During his postdoc, he realized he could bestow upon students the confidence his mentors fostered in him. The Internet helped him reach out to other deaf people through newsgroups. Lina Reiss, who had severe hearing loss by age 2, first met Ratnanather when she was an undergraduate at Princeton University and he replied to an online post in which she introduced herself to one of these newsgroups.

The daughter of two Ph.D.s, Reiss had always known that she wanted to go into the sciences. But she was not sure what career would be possible with her hearing loss. “I didn’t have any role models of what it was like to be a deaf faculty member,” she recalls. “Until I met [Tilak and some of his deaf friends], I couldn’t imagine becoming a professor.”

Ratnanather helped get Reiss a summer internship in the hearing-research lab of a colleague at Johns Hopkins, where she studied how neurons in the brain stem encode and process sound. Enthralled with the research, she went on to do her Ph.D. in biomedical engineering in the same lab. She is now an assistant professor at Oregon Health & Science University in Portland researching how hearing loss, hearing aids, and cochlear implants influence the way people perceive sound.

Ratnanather now primarily does brain-mapping research focused on understanding how brain structures are altered in people with diseases such as schizophrenia, Alzheimer’s, and bipolar disorder. But hearing science continues to influence his work. He has published several recent studies on fluid dynamics and hair cell function and has upcoming papers on imaging the auditory regions of the brain in deaf adults and babies.

And, spurred partly by his own cochlear implant surgery in 2012, Ratnanather has created an app for adults learning how to hear following the surgery. Called Speech Banana, the app is named after the banana-shaped region in an audiogram that contains human speech.

More than just providing professional connections, Ratnanather has influenced how his former students navigate the world. Being deaf can make it scary to think outside the box or challenge opinions, Pisano says.  Ratnanather encourages his mentees to keep an open mind and engage with others—hearing and nonhearing alike. “That helped shape my mentality about life in general today,” Pisano says.

Reprinted with permission. "Handicapable" originally appeared in the October 2015 issue of The Scientist, a special issue devoted to hearing research. The article can be accessed online here. See also The Scientist’s Facebook page, where this article generated many comments.

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Hearing Health Foundation is thrilled that Tilak Ratnanather, D.Phil., received this outstanding honor and recognition from the White House for his mentoring efforts. Ratnanather was a recipient of an Emerging Research Grant (ERG) in 1993, and has continued to champion HHF and its mission to prevent and cure hearing loss and tinnitus.

Dominic Pisano, M.D., who is quoted in this article, served on HHF’s inaugural National Junior Board (now known as HHF’s New York Council) in 2012. He has written about his decision to get a cochlear implant (CI) on our website and the tips and tricks he used to succeed in medical school in our magazine, and he appeared in an HHF public service announcement.

Also quoted in the article, Lina Reiss, Ph.D., was an ERG recipient in 2012 and 2013, and went on to win funding from the National Institute on Deafness and Other Communication and Disorders. She cowrote a piece about hybrid CIs and the way they make use of residual hearing ability. HHF congratulates all for their achievements!

Best Supporting Actors - In Your Ears?

By the University of Michigan Health System

This microscopic view of cells deep within the ear of a newborn mouse show in red and blue the supporting cells that surround the hair cells (green) that send sound signals to the brain. New research shows that the supporting cells can regenerate if damaged in the first days of life, allowing hearing to develop normally. This gives new clues for potential ways to restore hearing.

Credit: Guoqiang Wan, Univ. of Michigan

There’s a cast of characters deep inside your ears -- many kinds of tiny cells working together to allow you to hear. The lead actors, called hair cells, play the crucial role in carrying sound signals to the brain.

But new research shows that when it comes to restoring lost hearing ability, the spotlight may fall on some of the ear’s supporting actors – and their understudies.

In a new paper published online first by the Proceedings of the National Academy of Sciences, researchers from the University of Michigan Medical School, St. Jude Children’s Research Hospital and colleagues report the results of in-depth studies of these cells, fittingly called supporting cells.  

The research shows that damage to the supporting cells in the mature mouse results in the loss of hair cells and profound deafness. But the big surprise of this study was that if supporting cells are lost in the newborn mouse, the ear rapidly regenerates new supporting cells – resulting in complete preservation of hearing. This remarkable regeneration resulted from cells from an adjacent structure moving in and transforming into full-fledged supporting cells. 

It was as if a supporting actor couldn’t perform, and his young understudy stepped in suddenly to carry on the performance and support the lead actor -- with award-winning results.

The finding not only shows that deafness can result from loss of supporting cells -- it reveals a previously unknown ability to regenerate supporting cells that’s present only for a few days after birth in the mice.

If scientists can determine what’s going on inside these cells, they might be able to harness it to find new approaches to regenerating auditory cells and restoring hearing in humans of all ages.

Senior author and U-M Kresge Hearing Research Institute director Gabriel Corfas, Ph.D., says the research shows that supporting cells play a more critical role in hearing than they get credit for.

In fact, he says, efforts to restore hearing by making new hair cells out of supporting cells may fail, unless researchers also work to replace the supporting cells. “We had known that losing hair cells results in deafness, and there has been an effort to find a way to regenerated these specialized cells. One idea has been to induce supporting cells to become hair cells. Now we discover that losing supporting cells kills hair cells as well,” he explains.

“And now, we’ve found that there’s an intrinsic regenerative potential in the very early days of life that we could harness as we work to cure deafness,” continues Corfas, who is a professor in the U-M Department of Otolaryngology. “This is relevant to many forms of inherited and congenital deafness, and hearing loss due to age and noise exposure. If we can identify the molecules that are responsible for this regeneration, we may be able to turn back the clock inside these ears and regenerate lost cells.”

In the study, the “understudy” supporting cells found in a structure called the greater epithelial ridge transformed into full-fledged supporting cells after the researchers destroyed the mice’s own supporting cells with a precisely targeted toxin that didn’t affect hair cells. The new cells differentiated into the kinds that had been lost, called inner border cells and inner phalangeal cells.

“Hair cell loss can be a consequence of supporting cell dysfunctional or loss, suggesting that in many cases deafness could be primarily a supporting cell disease,” says Corfas. “Understanding the mechanisms that underlie these processes should help in the development of regenerative medicine strategies to treat deafness and vestibular disorders.”

Making sure that the inner ear has enough supporting cells, which themselves can transform into hair cells, will be a critical upstream step of any regenerative medicine approaches, he says.

Corfas and his colleagues continue to study the phenomenon, and hope to find drugs that can trigger the same regenerative powers that they saw in the newborn mice.

The research was a partnership between Corfas’ team at U-M and that of Jian Zuo, Ph.D., of St. Jude, and the two share senior authorship. Marcia M. Mellado Lagarde, Ph.D. of St. Jude and Guoqiang Wan, Ph.D., of U-M are co-first authors. Additional authors are LingLi Zhang of St. Jude, Corfas’ former colleagues at Harvard University Angelica R. Gigliello and John J. McInnis; and Yingxin Zhang and Dwight Bergles, both of Johns Hopkins University.

The research was funded by a Sir Henry Wellcome Fellowship, a Hearing Health Foundation Emerging Research Grant, the Boston Children’s Hospital Otolaryngology Foundation, National Institutes of Health grants DC004820, HD18655, DC006471, and CA21765; Office of Naval Research Grants N000140911014, N000141210191, and N000141210775, and by the American Lebanese Syrian Associated Charities of St. Jude Children’s Research Hospital.

The above post is reprinted from materials provided by University of Michigan Health System. 

  We need your help in funding the exciting work of hearing and balance scientists. 

To donate today to Hearing Health Foundation and support groundbreaking research, visit hhf.org/name-a-grant.

Hearing: It Takes Two

By Teresa Nicolson

A major challenge in hearing research is to understand how structures known as ‘hair bundles’ are formed in the cochlea. Hair bundles have a crucial role in the detection of sound and the conversion of mechanical signals (that is, sound waves) into electrical signals. The cochlea contains two types of hair cells – inner and outer – and a hair bundle protrudes from the top of every hair cell. Each hair bundle consists of a collection of smaller hair-like structures called stereocilia that line up in rows within the bundle to form a structure that resembles a staircase (Figure 1). The stereocilia are filled with filaments made of the protein actin.

Figure 1: The roles of the two isoforms of myosin 15 (MYO15) in hair bundles.

Left: Schematic depiction showing the three rows of stereocilia in a normal hair bundle, with the first row (dark green) being the shortest and the third row (pale purple) being the tallest. This difference in height results in a characteristic staircase-like structure. The stereocilia in the first two rows mediate the process of mechanotransduction, and the large isoform of myosin 15 localizes to the tips of these stereocilia; the small isoform is found primarily in the taller stereocilia in the third row. Right: When both isoforms are defective or absent, the stereocilia in the third row do not reach their normal height (top). If the N-terminal extension in the large isoform is absent in mice, hair bundles form normally but some of the stereocilia in the first two rows degenerate in older animals (bottom). The large isoform of myosin 15 has a large extension (shown in orange) at its N-terminus.

Through studies of deaf patients, geneticists have made remarkable progress in identifying genes that are required for hearing (see hereditaryhearingloss.org). Many of the corresponding proteins are important for the function of hair cells and more than a dozen of them have roles in the hair bundle; these proteins include several myosin motor proteins that differ from the conventional myosin motors that are found in muscle cells. Hair cells actually produce two versions (or isoforms) of one of these unconventional myosin motors, myosin 15 (Wang et al., 1998; Liang et al., 1999). One of these isoforms has a large (134kD) extension at its N-terminus, but the role played by this extension in hair cells has long been a mystery.

A clue to the importance of the extension is provided by the fact that mutations in the gene (exon 2) that encodes the additional amino acids in the extension cause deafness in humans (Nal et al., 2007). To explore the role of this extension Jonathan Bird and co-workers – including Qing Fang as first author – have compared mice in which the myosin 15 proteins have the extension (isoform 1) and mice in which they do not (isoform 2; Fang et al., 2015).

Previously our knowledge about the function of myosin 15 was based on studies of mice with a mutant shaker2 gene: this mutation leads to defective hair cells in both the cochlea and the vestibular system, which is the part of the ear that controls balance. (The name shaker was coined to describe the unsteady movements seen in these mice). The shaker2 mutation effects both isoforms of myosin 15 and prevents the stereocilia growing beyond a certain height (Probst et al., 1998). The staircase-like structure seen in normal hair bundles is not seen in the shaker2 mice.

Experiments with an antibody that recognizes both isoforms suggest that myosin 15 is located at the tips of the stereocilia (Belyantseva et al., 2003). The shaker2 phenotype suggests that myosin 15 promotes the growth of stereocilia, presumably by working as an actual motor that interacts with actin filaments (Bird et al., 2014). However, the details of how this happens are not fully understood, although it might depend on proteins that are transported to the growing tip by myosin 15 (Belyantseva et al., 2005; Zampini et al., 2011).

The large isoform of myosin 15 (green) localizes predominately at the tips of short stereocilia (magenta), but not tall stererocilia, in inner hair cells in the cochlea of mice

To examine the role played by the large extension in isoform 1, Fang, Bird and colleagues – who are based at the University of Michigan, the National Institute on Deafness and Other Communication Disorders, and the University of Kentucky – generated an antibody that is specific to this isoform and used it to investigate the effects of deleting the exon 2 gene (Fang et al., 2015). Surprisingly, they found that isoform 1 is restricted to the first two rows of stereocilia in inner hair cells (Figure 1). In outer hair cells, on the other hand, isoform 1 is also found at the tall stereocilia in the third row. As for isoform 2, it is mainly present in the third row in inner hair cells.

Finding the two isoforms in different locations came as a surprise, but it could help to explain why deletion of the N-terminus and shaker2 mutations lead to different phenotypes. Shaker2 mutations affect both isoforms and lead to short hair bundles. Deletion of the N-terminus does not affect the length of stereocilia: rather, the hair bundles develop normally at first, but the first two rows of stereocilia then wither away. This suggests that the large isoform is important for the maintenance of a subset of the stereocilia: in particular, it maintains the stereocilia are involved in converting sound energy into an electrical signal in the inner part of the cochlea.

This conversion process, which is called mechanotransduction, is largely present in both the shaker2 mutants and in the mice in which the N-terminus has been deleted, albeit with some subtle differences. This phenotype suggests that myosin 15 is not directly involved in mechanotransduction: however, it seems that the large isoform of myosin 15 can recognize and accumulate at sites where this process takes place. The localization pattern of myosin 15 observed in the outer hair cells reinforces the idea that some form of membrane tension is required for accumulation of the large isoform.

A similar result was found with another protein (called sans) that is required for growth of stereocilia: deleting sans after hair bundles had fully formed caused the first two rows of stereocilia to shrink over time (Caberlotto et al., 2011). Sans interacts with the mechanotransduction machinery in hair cells (Lefèvre et al., 2008), and the loss of sans has a more dramatic effect on mechanotransduction than the loss of myosin 15. Nevertheless, these two cases suggest that it is possible to uncouple the different roles of various proteins in development and in the subsequent maintenance of mechanically-sensitive stereocilia in hair bundles. It will be interesting to see whether other short bundle mutants may have a similar phenotype, if given the chance.

Paper Acknowledgements

We thank Dennis Drayna, Lisa Cunningham, Katie Kindt and Melanie Barzik for critical reading; and Stacey Cole, Elizabeth Wilson, Joe Duda, Karin Halsey, Lisa Kabara, Jennifer Benson, Stephanie Edelmann, Anastasiia Nelina and Ron Petralia for expert technical assistance. This research was supported by funds from the NIDCD intramural research program DC000039-18 and DC000048-18 (JEB, IAB, TBF), NIDCD extramural funds R01 DC05053 (SAC, GIF, QF, MM, and AAI), R01 DC008861 (AAI, GIF), P30 DC05188 (DFD), the Hearing Health Foundation (MM) and a University of Michigan Barbour Scholarship and James V. Neel Fellowship (QF). We thank the University of Michigan Transgenic Animal Model Core and grants that support them (P30 CA46592), and the animal care staff at each institution.

This post originally appeared on eLife Science on October 6, 2015 in reference to the scientific publication, "The 133-kDa N-terminal domain enables myosin 15 to maintain mechanotransducing stereocilia and is essential for hearing." For the article's references and citations, please click here. 

Distilling the Data

By Michael Lovett, Ph.D.

The burgeoning field of bioinformatics allows the Hearing Restoration Project to analyze and compare large genomics datasets and identify the best genes for more testing. This sophisticated data analysis will help speed the way toward a cure for hearing loss and tinnitus.

Since its launch in 2011, the Hearing Restoration Project (HRP) is focused on identifying new therapies that will restore inner ear hair cell function, and hence hearing. Within the consortium, smaller research groups engage in separate projects over the course of the year, to move the science along more quickly.

Over the past decade my group, and the group led by my collaborator Mark Warchol, Ph.D., have worked to identify genes that are potential targets for drug development or for gene therapies to cure hearing loss. Our approach has been to determine the exact mechanisms that some vertebrates—in our case, birds—use to regenerate their hair cells and thus spontaneously restore their hearing. We have been comparing this genetic “tool kit” with the mechanisms that mammals normally use to make hair cells.

Unlike birds, mammals cannot regenerate adult hair cells when they are damaged, which is a leading cause of human hearing and balance disorders. Our working hypothesis is that birds have regeneration mechanisms that mammals are missing—or that mammals have developed a repressive mechanism that prevents hair cell regeneration.

In either case, our strategy has been to get a detailed picture of what transpires during hair cell regeneration in birds by using cutting-edge technologies developed during the Human Genome Project (the international research collaboration whose goal was the complete mapping of all the nuclear DNA in humans). These next-generation (NextGen) DNA sequencing methods have allowed us to accurately measure changes in every single gene as chick sensory hair cells regenerate.

The good news is that this gives us, for the first time, an exquisitely detailed and accurate description of all of the genes that are potential players in the process. The bad news is that this is an enormous amount of information; thousands of genes change over the course of seven days of regeneration.

Some of these will be the crucially important—and possibly game-changing—genes that we want to explore in potential therapies, but most will be downstream effects of those upstream formative events. The challenge is to correctly identify the important causative needles in the haystack of later consequences.

We already know some important genetic players, but we are still far from understanding the genetic wiring of hair cell development or regeneration. For example, after decades of basic research, we know that certain signaling pathways, such as those termed Notch and Wnt, are important in specifying how hair cells develop. These chemical signaling pathways are made of multiple protein molecules, each of which is encoded by a single gene.

However, the Notch and Wnt pathways together comprise fewer than 100 genes and, despite being intensively studied for years, we do not completely understand every nuance of how they fit together.

It also may seem surprising that—more than a decade after the completion of the Human Genome Project and projects sequencing mouse, chick, and many other species’ genomic DNA—we still do not know the exact functions of many of the roughly 20,000 genes, mostly shared, that are found in each organism. This is partly because teasing out all of their interactions and biochemical properties is a painstaking process, and some of the genes exert subtly different effects in different organs. It is also because the genetic wiring diagram in different cells is a lot more complicated than a simple set of “on/off” switches.

All of this sounds a bit dire. Fortunately, we do have some tools for filtering the data deluge into groups of genes that are more likely to be top candidates. The first is to extract all of the information on “known” pathways, such as the Notch and Wnt mentioned earlier. That is relatively trivial and can be accomplished by someone reasonably well versed in Microsoft Excel.

That leaves us with the vast “unknown” world. Analyzing this requires computational, mathematical, and statistical methods that are collectively called bioinformatics. This burgeoning field has been in existence for a couple of decades and covers the computational analysis of very large datasets in all its forms. For example, we routinely use well-established bioinformatic methods to assemble and identify all of the gene sequences from our NextGen DNA sequence reads. These tasks would take many years if done by hand, but a matter of hours by computational methods.

In the case of our hair cell regeneration data, our major bioinformatic task is to identify the best genes for further experimental testing. One method is to computationally search the vast biological literature to see if any of them can be connected into new networks or pathways. There are now numerous software tools for conducting these types of searches. However, this really is not very helpful when searching through several thousand genes at once. The data must be filtered another way to be more useful.

We have used statistical pattern matching tools called self-organizing maps to analyze all of our data across every time point of hair cell regeneration. In this way we can detect genes that show similar patterns of changes and then drill down deeper into whether these genes are connected. This has provided us with an interesting “hit list” of genes that have strong supporting evidence of being good candidates for follow-up.

An additional approach is to compare our chick data to other datasets that the HRP consortium is collecting. The logic here is that we expect key genetic components to be shared across species. For example, we now know a great deal about what genes are used in zebrafish hair cell regeneration and the genes that specify mouse hair cells during normal development. We can conduct computational comparisons across these big datasets to identify what is similar and what is different. Again, this has yielded a small and interesting collection of genes that is being experimentally tested. 

Our final strategy has been to extract classes of genes that act as important switches in development. These transcription factors control other genetic circuits. We have identified all of these that change during chick hair cell regeneration. As a consortium the HRP now has a collection of about 200 very good candidate genes for follow-up. However, software and high-speed computation are not going to do it all for us. We still need biologists to ask and answer the important questions and to direct the correct bioinformatics comparisons.

Hair cell regeneration is a plausible goal for the treatment of hearing and balance disorders. The question is not if we will regenerate hair cells in humans, but when. Your financial support will help to ensure we can continue this vital research and find a cure in our lifetime! Please help us accelerate the pace of hearing and balance research and donate today. Your HELP is OUR hope!

If you have any questions about this research or our progress toward a cure for hearing loss and tinnitus, please contact Hearing Health Foundation at info@hhf.org.

Michael Lovett, Ph.D., is a professor at the National Lung & Heart Institute in London and the chair in systems biology at Imperial College London.

Orchestrating Hair Cell Regeneration

By the Stowers Institute for Medical Research

The older we get, the less likely we are to hear well, as our inner ear sensory hair cells succumb to age or injury. Intriguingly, humans are one-upped by fish here. Similar hair cells in a fish sensory system that dots their bodies and forms the lateral line, by which they discern water movement, are readily regenerated if damage or death occurs.

A neuromast sensory structure (green) of the zebrafish lateral line, which helps the fish detect water movement, is shown among surrounding cells (cell nuclei in red).

Credit: Piotrowski Lab, Stowers Institute for Medical Research

A new study in the July 16 online and August 10 print issue of Developmental Cell, from Stowers Institute for Medical Research Associate Investigator Tatjana Piotrowski, Ph.D., zeros in on an important component of this secret weapon in fish: the support cells that surround centrally-located hair cells in each garlic-shaped sensory organ, or neuromast. “We’ve known for some time that fish hair cells regenerate from support cells,” Piotrowski explains, “but it hasn’t been clear if all support cells are capable of this feat, or if subpopulations exist, each with different fates.”

While mammals also have support cells, they unfortunately do not respond to hair cell death in the same way. So understanding how zebrafish support cells respond to hair cell loss may provide insight into how mammalian support cells might be coaxed into regenerating hair cells as well. Zebrafish are particularly amenable to studies of regeneration because transparent embryos and larvae render developmental processes visible and experimentally accessible.

Piotrowski and her team treated zebrafish larvae with the antibiotic neomycin, which kills hair cells, then monitored support cell proliferation in regenerating neuromasts for three days using time-lapse movies. “These single cell lineage analyses were tremendously time-consuming but very informative,” Piotrowski notes. The study’s lead author, Andrés Romero-Carvajal, Ph.D., previously a predoctoral researcher at the Stowers Institute, carefully kept track of every individual support cell’s location and behavior across different time-lapse frames.

The researchers determined that approximately half of the dividing support cells differentiated into hair cells, while the rest self-renewed. Self-renewal is an equally important fate, Piotrowski points out, because it ensures maintenance of a reserve force that, if necessary, can spring into regenerative action. The researchers also observed that lineage fate of support cells hinged on where they were located in the neuromast, as self-renewing cells were found clustered at opposite poles while differentiating cells were distributed in a random, circular pattern close to the center. 

Such distinct support cell locations were “strongly indicative of differences in gene expression”, Piotrowski says, so the team turned its attention to exploring some of the genes and signaling pathways involved. A study of gene expression patterns showed that members of the Notch and Wnt pathways were expressed in different parts of the neuromast, specifically the Notch members in the center and the Wnt members at the poles. To determine if and how these two pathways regulate each other, the researchers used an inhibitor to turn off Notch signaling in neuromasts. This halt in Notch activity mimics the halt known to occur immediately after neomycin-induced hair cell death. After inhibitor treatment, they saw transient upregulation of Wnt ligands in the neuromast center, along with support cell proliferation. The majority of the proliferating cells became hair cells.

“We found that Notch directly suppresses differentiation (of support cells into hair cells), and indirectly inhibits proliferation by keeping Wnt in check,” Piotrowski explains. “Previously, others thought perhaps it was Wnt that had to be downregulated, to initiate regeneration. However, our data support the loss of Notch signaling as a more likely trigger.” Essentially, the process of restoring injured or dead hair cells in neuromasts is jump-started by the transient suppression of Notch, while its eventual reactivation restores the balance, ensuring that not all support cells answer the call to regenerate through proliferation and differentiation.

Piotrowski’s research is partially supported by the Hearing Health Foundation through its Hearing Restoration Project (HRP), which emphasizes collaborations across multiple institutions to develop new therapies for hearing loss. By continuing to illuminate the intricacies of hair cell regeneration in zebrafish, she and her team are providing other HRP scientists with candidate genes and molecular pathways to probe in other models such as chicken and mice, with the goal of providing insight that could someday make human inner ear hair cells readily replaceable.

The study was also funded by the Stowers Institute and the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health (award RC1DC010631). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Other Institute contributors include Joaquín Navajas Acedo; Linjia Jiang, Ph.D.; Agnė Kozlovskaja-Gumbrienė; Richard Alexander; and Hua Li, Ph.D.

Lay summary of findings

Hair cells in sensory structures called neuromasts, which form the sensory system fish use to orient themselves in water, are similar to mammalian inner ear hair cells responsible for our sense of hearing. Unlike the latter, however, they are constantly replaced after damage or death. In the current issue of Developmental Cell, Stowers Associate Investigator Tatjana Piotrowski, Ph.D., and members of her lab closely examine, in zebrafish, the support cells from which hair cells regenerate. By tracking individual support cells during neuromast regeneration, first author Andrés Romero-Carvajal, Ph.D., shows that approximately half become hair cells, while the rest self-renew as support cells. These lineage decisions are coordinated by interactions between the Notch and Wnt signaling pathways and are location-specific, as differentiation into hair cells occurs toward the center of neuromasts and self-renewal occurs at opposite poles of the structures. Piotrowski hopes her lab’s findings in zebrafish may be extrapolated to mammals someday, to help provide basic insight needed to progress towards the ultimate goal of regenerating human inner ear hair cells.

About the Stowers Institute for Medical Research

The Stowers Institute for Medical Research is a non-profit, basic biomedical research organization dedicated to improving human health by studying the fundamental processes of life. Jim Stowers, founder of American Century Investments, and his wife, Virginia, opened the Institute in 2000. Since then, the Institute has spent over one billion dollars in pursuit of its mission.

Currently, the Institute is home to almost 550 researchers and support personnel; over 20 independent research programs; and more than a dozen technology-development and core facilities.

The above post is reprinted, with permission, from materials provided by Stowers Institute for Medical Research.

Your financial support will help to ensure we can continue this vital research and find a cure in our lifetime! Please help us accelerate the pace of hearing and balance research and donate today. Your HELP is OUR hope!

If you have any questions about this research or our progress toward a cure for hearing loss and tinnitus, please contact Hearing Health Foundation at info@hhf.org.