Hair Cell Regeneration as a Therapy for Deafness

In addition to the below post on gene therapy, keep a watch out for a review paper on the topic (by yours truly) that was just accepted into Hearing Research.

Deafness and hearing impairment are serious medical concerns in America, with nearly 30 million Americans affected to some degree. This is such a widespread problem in our society due to the combined effects of loud noises, aging, and heredity. Hearing loss happens when cochlear hair cells are lost (for a primer on the cochlea and hair cells, go here). Mammals, including humans, are unable to re-grow hair cells although birds and a few other species can. This is one reason I am so fascinated by birds---you can deafen them repeatedly, and within 2 weeks, they regenerate hair cells and their hearing is restored! If people could also do this, no one would ever suffer from deafness ever again. This aim, the regeneration of hair cells in humans, is the focus of my lab and my thesis. (continued......)

In order to sum up a very large body of research stemming from our lab, I'm going to talk about a Nature Medicine paper from 2005 which was the realization of a lot of our theories.

The idea goes like this: a certain gene, called Atoh1, is solely expressed in hair cells during their development and differentiation. It is necessary and sufficient for hair cell development, and in Atoh1-knockout mice, no hair cells are seen. This convinced us that Atoh1 was an excellent candidate for viral over-expression, possibly resulting in new hair cells in the deaf ear.

Viral over-expression refers to the ability to insert a gene of interest into an inactivated virus. The virus is no longer harmful, and no longer replicates its DNA when it infects a cell. Instead it replicated the gene of interest, forcing the cell to express that protein. Our lab used a type of virus called an adenovirus, and inserted Atoh1 under the control of the promiscuous human-CMV promoter. The next step was to inject the modified virus into the fluids of the deaf inner ear, and observe whether hair cells regenerated as a result.

To deafen an animal, we use a combination of the antibiotic kanamycin and the diuretic ethacrynic acid. These two drugs, when administered in close succession, result in the death of all hair cells in the cochlea. Five days following the deafening procedure, we administered a very small volume of the modified virus into the scala media, the area where the hair cells lie. Then, we waited. During the interim, we tested the animals' hearing thresholds ever few weeks with Auditory Brainstem Response (ABR) measurement. With this technique, we can measure the activity in the brain while an animal is perceiving a sound of a controlled intensity. In this way, we can "step down" in the decibel level of the presented sound, and when the ABR gets no response, we can infer that that is the level of the animal's hearing threshold.

Here is a scanning electron micrograph of a normal hair cell region (called the organ of Corti):
i-bf445d4db0ee3ce369877475682a4edf-normal corti sem.bmp

And here is what the same region looks like after all the hair cells are eliminated (deafened):

It is immediately obvious that the ordered structure of the previous picture has completely changed. The "V" shaped structures are the "hairs" of the hair cells. These are called stereocilia, and they project into the fluid space to receive vibrations when sound waves pass through.

So, what were the results of our study? Not only did we find a significant amount of regenerated hair cells in the virus-treated ears, but their hearing was significantly improved as well. As a control on all animals, only the left cochlea received the virus, the right cochlea received nothing. There was a large difference in hearing between the left and right ears of the guinea pigs (left was better). I will explain the figure below in some detail:

i-d6f30d310b320fd9a69b273f0b9fccab-fig 2.gif

A-C: SEMs of virus-treated organ of Corti 2 months post treatment. Many hair cells have regenerated and the organization is in rows, like normal. Some hair cells are ectopic. These are three representative levels of recovery with A being the best and C being the worst. Even C has a significant level of regeneration.
D. This is an organ of Corti which was deafened and received no treatment (a right ear). There are no hair cells.
E. This cochlea received a sham virus surgery. Instead of Atoh1, there was no gene insert in the virus. No regeneration was seen.
F. This is a higher magnification of an inner hair cell.
G. This is a higher magnification of an outer hair cell.

It is clear that there is an increase in hair cells after Atoh1 virus therapy, and no hair cell regeneration in controls. In addition we also observed some improvements in ABR thresholds 2 months after the virus therapy (below). In the figure below, A represents a "hearing waveform" of the treated ear corresponding to a threshold of about 60 decibels, while on the right, B represents a "deaf waveform" of the control ear, with no response even at 105 decibels.

i-8c6759adf8fcf3926ee712199a49b1a0-fig 5 ab.GIF

We concluded that virally-mediated overexpression of Atoh1 in the deaf ear resulted in numerous hair cells as well as hearing improvement after 2 months. This therapy is still in its infancy and very far away from being developed for humans

Reference: Izumikawa et al. 2005. Auditory hair cell replacement and hearing improvement by Atoh1 gene therapy in deaf mammals. Nature Medicine. 11, 3, pg 271-276.


More like this

Lets play a game. Think of a human disease.  Any disease.  Viral, bacterial, genetic, acquired, anything. Im pretty sure that no matter what disease you just thought of, there is a scientist, somewhere, trying to use a virus to cure/treat that disease. As I was doing my rounds on PubMed, looking…
Hat tip to Abel Pharmboy for this fascinating story! A recent US government study has found that: a) Black adults hear better than white adults b) Women hear better than men c) Average hearing thresholds are the same in the US as they were 35 years ago (despite the much-maligned iPod and Walkman…
Many of my SciBlings have been doing posts on "basic concepts" in their fields of expertise. As I am studying hair cell regeneration as a therapy for hearing impairment, I thought I might do a 'basic concepts post' on what hearing is, how humans hear, and why we lose it sometimes. The most…
If you read the 'About' page, or anything about me, you probably noticed that I work on hair cell regeneration in the cochlea. But, perhaps, some readers are not familiar with the machinations of the inner ear. So, I'll make a quick post with some relavent info to help in understanding future…

Have you guys published any patchclamp data from these regenerated hair cells? Be interested to see how well the mechanosensory apparatus has redeveloped (can you resolve tiplinks on those EM images?).

Cool stuff.

Haven't done that yet, Rev, but a post-doc in our lab is working on it. Can patch-clamp be done in guinea pig cochlear cultures? Close ups of the tip links seem to reveal disorganized stereocilia in some and neat and ordered/linked ones in others. We're not sure why that is yet. The kinocilium also has some problems regenerating, which may contribute to only the partial restoration in hearing that we saw.

Hmmm... might be difficult. I recall some guys recently isolating human hair cells (from tumor op tissue), but mentioning that the microcilia disappear during culture. Not sure if that happens across the board. I think most patch studies have been done on the intact epithelium (Holt et al 1997?).

Hi Shelley;

Most interesting but I've noticed like so many of these "press announcements" over the years from the Universities, the media have a feeding frenzy then the whole topic of corti hair regeneration slides back into oblivion until the next Phd Candidate takes up the reins and the cycle continues. I've not seen you make any new posts since almost a year ago. Does this mean that you too have moved on to other things?
Anyway, everyone keeps saying we're years from human trials. But why? They've been saying this the past 20 years already.
Hope you do keep us updated and are not just another flash in the pan.

A deaf Scarlet Macaw lover in Cape Town, South Africa.

If you are aware that retinoic acid can actually regenerate damaged inner ear hair cells.See:
Also, I have been giving methylcobalamine to sensorineural loss patients with remarkable improvements in patient advised cochlear implant have actually started recovering hearing.
Congrats, however on your fine work.
Professor and Head,
Division of otolaryngology
AJ Medical college,Mangalore

By Dr.Devan.P.P. (not verified) on 15 Sep 2008 #permalink

Yow, very cool! I just bounced over here due to a reference by GrrlScientist. How long have you been mentioning the hair-cell stuff in your bioblurb? I'm not a regular reader here, but even so, I'm surprised that I hadn't noticed it before.

Iam very interesting with your research shelley
I have son who suffer profound hearing loss both of his ear.He is 2 years old.The doctor recomended to cochlear implant. Is it possible that my son'hair cell can able to grow again. What do you think? thanks for your response

Thank you for this information on cochlear hair cell regeneration.I have had severe tinnitus for 20 years due to a very bad ear infection. The infection wiped out all the hair cells on my cochlea. I have insomnia which limits my sleep time from two to three hours a night. The loud ringing in my ears has made my life miserable. Please let me know if there is any place in the USA that I can volunteer as a testing patient for this gene therapy for cochlear hair cell regeneration. Thank You- Joel Anderson

By Joel Anderson (not verified) on 20 Feb 2009 #permalink

omg! congrats. i am a year 10 student (i'm 14-15) at hamilton girls high, all the way over in tiny New Zealand, i bumped into this site by accident while searching for pictures of pens (for a tec project) this weird for me because i sooo want to be a neuroscientist (cept i wana work on death e.g why do people that have died and come back to life, go on about being in heaven?)my whole family is really into science, and unless you hit a great gag, there's no money in it ( or in engineering, for that matter)p.s have you considered using near infra red, might solve a few problems (search full spectrum on internet);]

Very noble occupation.
I wish you the best of luck in this undertaking.

Hi there. My daughter is profoundly deaf having been implanted on right side at the age of 2 years. She is now 7. She wears a hearing aid on the left - of which she gets nothing out of. My hubby and I are at a rather difference of opinion about whether to implant the other ear, or wait for hair cell regeneration. What would you advise. WE live in the UK and this sort of thing doesn't seem to strike the news too ofen. I am just eager to hear when test subjects are likely to be used for trials. Could you possibly fill me in?
Kind regards,
Natalie Callaghan

By Natalie Callaghan (not verified) on 25 Nov 2009 #permalink

Your work are simple awesome... hope to see any update soon i'd glad that u tried very hard to get the way to solve the problem every person who are suffering regarding hearing impairment.

I am a singer, teacher of voice & also completing Certificate IV in Kinesiology.
Thank you for your fascinating research. Apppreciate the commitment it takes, many thanks to you & your part of the matrix!

I've always sensed that being able to "reawaken" the uniformity of the cochlea is possible and wonder at the implications for those who experience tinnitus. My understanding of tinnitus is that the cilia representing particular frequencies are constantly in a state of "hyper-alert" or "on" particularly the high end frequencies.

Given that this organ is developed in the human foetus early in pregnancy (in my daughter it was noticed at 16 weeks) the unborn child is learning via its nervous system & its auditory system about its environment from a very early stage. If a constant stress is present (as in a mother & therefore environment) it would make sense that certain frequencies corresponding with the stress response would gradually develop a ridigity ie always "on" or hyper-alert.

I realise that, as a scientist, you're working with the minutae of body mechanics. I'm fascinated with the quantum perspective, which seems to be implicated in the minutae in any event! What is your intuition on the issue of tinnitus?

Many thanks again,

By Kelesi Woodhouse (not verified) on 09 Jan 2010 #permalink

Hi Shelley, Kelesi again. A further thought/occurrence...

I just sliced a raw, small cucumber longitudinally in quarters. Perhaps you call them pickles? Anyway I was quite struck by the similarity of appearance with your electron micrograph pic of normal (cochlear) hair cell. Consider the idea of like treating like...

I have also experienced chronic intestitial cystitis & found that it was greatly helped by going on an alkaline diet, & raw cucumber has a highly alkalizing effect. When I'm feeling stressed internally & externally !! I find it "soothing" & remediating to eat such foods. It actually has a calming effect, curiously, as well as a sense of more energy & well being.

This is more connected with the question of tinnitus, but perhaps there is also a link in the healing aspects of hearing as well?

Just a thought.
Kind regards

By Kelesi Woodhouse (not verified) on 09 Jan 2010 #permalink

mt.clemens ,mi. woke up on nov.1st. 09 deaf in the right ear. tried ear specialist and had two shots of steroids. can hear very little to this day and have constant buzzing in my ear. doctor called it an inner ear virus like herpes that killed the hairs. been trying to find some help and have been very dissapointed. i would hope that if it can be done on animals it can be done for humans. would love to find out

By susan darling (not verified) on 17 Jul 2010 #permalink

Congrats on getting the paper accepted!!!

If people could also do this, no one would ever suffer from deafness ever again

and not to be picky, but there are other types of hearing loss that have nothing to do with loss of hair cells. and i know you know that. but as a fellow hearing researcher who doesn't work on hair cells i felt the need to comment. your work is still crazy awesome. :)

Yep, you are absolutely right Jen! There can be nerve damage, infections, etc. What I meant to say was "hair cell-related hearing loss."

I'll volunteer for experimentation. Use me.

Every now and then the popular press runs a story about this research - interesting to discover the blog of someone actually doing it.

I'm one of the people your research may help. I've no hearing on the right, a 90 db loss on the left. It's a progressive sensioneural loss, but I'm not certain whether that means hair cell restoration would make a difference (How do I find out?)

I had some hearing on the right before age four and the left held out long enough for me to acquire normal speech, use the phone, enjoy the radio, watch TV, etc.

Nowadays, my speech remains clear, but I perceive incoming speech as babble - and that's with a full-power BTE hearing aid. Without the hearing aid, I can't even hear my own voice. TV, radio, phone - forget it, even with the hearing aid.

I could probably get a CI, but installing a CI destroys the original cochlea and once that's done, there's no turning back. The current CIs are terrible at rendering music, and I want to hear Elton John banging out Bennie and the Jets at full throttle again.

I know your research is still in early stages, and may not even be the answer for me, but know that I and others are very interested in your work and progress.

hey, just stumbled across this post... i will have to read your paper now. anyway, random question - do you know if the ectopic hair cells are innervated? has anyone looked at that? my lab studies HC regeneration also - mostly in fish, but in a few other models as well - but i haven't heard of any studies that looked specifically at innervation of regenerated hair cells.

hey, just stumbled across this post... i will have to read your paper now. anyway, random question - do you know if the ectopic hair cells are innervated? has anyone looked at that? my lab studies HC regeneration and toxicity also - mostly in fish, but in a few other models as well - but i haven't heard of any studies that looked specifically at innervation of regenerated hair cells.

kevin - there are studies being done on music appreciation in CI patients. of course the earlier implants are getting pretty horrible reviews, but as they are able to cram more electrodes into the implant, improving the resolution of the sound, music rendering should improve. though i wonder, could you get an implant in the "bad" ear, and leave the "good" ear alone? that way you could turn it off when you felt like rocking out......?

Kevin, Just wanted to let you know that i have just had a cochlear implant and am enjoying listening to music again. It's good enough for me to appreciate 'new' music i.e melodies and tunes that i had not heard before and I can recognize them again. Prior to the implant my hearing had got to the stage where I couldn't really distinguish between the instruments or the singer and I even had trouble identifying music that i knew! As Kat says, you could always have the implant in your 'bad' ear - that still leaves you with one ear left for future developments! I look forward to spending the rest of my life exploring music - i have so much to catch up on! I'm sure your memory of music will stand you in good stead - I was never a real music fan, but i am now!
By the way, i can also listen to the radio again (fantastic) and use the telephone again, including a mobile.I still wear a BTE in my other ear but I can easily manage on just the implant alone.

By Jan Hinsley (not verified) on 12 May 2007 #permalink

My daughter is deaf, so you can guess how thrilled I am about this information. How long before humans can benefit from this therapy? Can I volunteer my daughter for candidacy in a test program?

Doug: This is only in the research phase, quite far from human therapy at the moment.

By Doug Bailey (not verified) on 06 Sep 2007 #permalink

Thank you Shelley. Thank you UofM. I'm always thankful to learn of new research that is pushing the limits of science in the efforts to help millions. As the father of a son born deaf, I dream one day for him to be able to hear me play guitar. He is a beautiful person and I love him greatly - exactly how he is; but it breaks my heart when he wishes he could hear. Some day I believe that wish will come true. Be proud Shelley knowing every lost hour of sleep is another hour closer to aiding his and many others dreams.

Ken, thank you for that beautiful sentiment. I hope one day to make your dreams come true.

Yow, very cool! I just bounced over here due to a reference by GrrlScientist. How long have you been mentioning the hair-cell stuff in your bioblurb? I'm not a regular reader here, but even so, I'm surprised that I hadn't noticed it before.

By David Harmon (not verified) on 13 Oct 2007 #permalink

Does this you can also correct for hearing loss where older men gradually lose the ability to hear higher pitched sounds making it harder or impossible for them to hear womens and children's voices? If so you might save more than just people's hearing but might also be able to help out a lot of marriages. You are super dope, keep up the good work on your blog and offline.

hello, i accidently bumped into this site. im still finding it hard to believe what i just read. Well, im completely deaf in my right ear and wear a hearing aid in the other. The problem with this ear is.....well, from what i was told, is that, my hair cells are all tangled and therefore, sounds does not travel well. So for u to say u can degenerate and regenerate hairs is exciting and of course risky. just like as one says, once u degenerate the hair, there is no turning back., but im willing to take the risk. so, if u discover that it will work on humans, pleaaaase let me know. im dying to hear better.

By jamal dejong (not verified) on 19 Jan 2008 #permalink

Good work.I have been interested in transdifferentiation.My uncle Dr.B.V.Shenoi has done some pioneering have been able to stimulate cells morphologically resembling endothelium to transdifferentiate to epithelial cell types.The factor8 which is a marker for endothelium is carried to the epithelium.My uncle passed away recently.The work has also been published as a monograph.Would it be of some interest to you?Kindly refer also to nature network where I have dealt with in more detail.Jagesh

By Dr.M.Jagesh Kamath (not verified) on 23 Feb 2008 #permalink

Hello, my name is andreas I am from Austria.
I have TTus after small arms fire and a high rate from hearing loss.
Congratulations to your work!
When does it works for patients?

Any updates? Any other groups you could work with to push this forward. So many of use have different degrees of deafness that might be helped by this. Is there a telethon or fundraiseing/ awareness raising group?