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by Monica Coenraads

[Italian translation]
[Spanish translation]
[Press Release]

Faced with the complex problem of discovering the elusive function of the Rett protein, RSRT set out to conduct an experiment of our own. We shook the conventional practice of laboratories working in isolation and instead convened three scientists to work collaboratively: the MECP2 Consortium. We gave them the necessary financial resources and provided infrastructure including in-person meetings. The results surprised us all.

Adrian Bird

Adrian Bird

Michael Greenberg

Michael Greenberg

Gail Mandel

Gail Mandel

The MECP2 Consortium was launched in 2011 with a $1 million lead gift by Tony and Kathy Schoener.
RSRT has committed an additional $3.4 million of funding to the Consortium.
We are extremely grateful to the Schoeners for their second $1 million pledge to support this effort.

The Consortium quickly reported significant advancements. The Mandel and Bird labs showed, for the first time, a dramatic reversal of symptoms in fully symptomatic Rett mice using gene therapy techniques that could be utilized in people.

The “Rett mouse” moving around received healthy Mecp2 via gene therapy. The immobile mouse did not receive treatment. The video was taken four weeks after treatment.

The Bird lab discovered that the function of the Rett protein, MeCP2, depends on its ability to recruit a novel binding partner, NCoR/SMRT to DNA. Disrupt that ability and the symptoms of Rett ensue.

The Greenberg lab built on the work of the Bird lab and discovered that adding a phosphate group to MeCP2 alters its ability to interact with NCoR/SMRT and affects the expression of downstream genes.

While the clinical implications of the gene therapy experiments are obvious some may think “so what?” when it comes to the NCoR experiments.

I suspect that in the mind of many Rett parents the best evidence of research progress is clinical trials. However, this is often not the best measure of progress.

Thomas Südhof, recent Nobel Laureate, recently commented  “I strongly feel that attempts to bypass a basic understanding of disease and just to get to therapies immediately are a misguided and extremely expensive mistake. The fact is that for many of the diseases we are working on, we just don’t have an understanding at all of the pathogenesis. There really is not much to translate. So NIH and many disease foundations are pouring money into clinical trials based on the most feeble hypotheses.”

So I will argue that investing in a better understanding of MECP2 – a primary goal of this Consortium – is money well spent, as it will add to our current arsenal of strategic approaches to combat Rett.

A repurposed drug may partially treat some of the symptoms, but to achieve the kind of dramatic improvement that most parents and I ache for will likely require attacking the problem at its very root.

As Rett parents will attest to the symptoms of the disorder are numerous and devastating. Whatever MECP2 is doing, it’s acting globally on many systems in the body. A repurposed drug may partially treat some of the symptoms but to achieve the kind of dramatic improvement that most parents and I ache for will likely require attacking the problem at its very root.

There are multiple ways to achieve this end goal: gene and/or protein therapy, activating the silent MECP2, modifier genes. These are all areas in which RSRT is financially and intellectually engaged with.

In parallel, however, it is imperative to understand what MECP2 does. RSRT has therefore committed an additional $3.4 million of funding to the MECP2 Consortium. We are extremely grateful to Tony and Kathy Schoener for their second $1 million pledge to support this important project.

I recently discussed the experiences of the past few years and what lies ahead with the Consortium members.

Greenberg: Research in neuroscience is undergoing a revolution. We now have the technologies in hand to solve some of the most difficult neurobiological questions. However, progress towards answering these hard questions requires scientists working together. A single lab working alone doesn’t have the expertise or the resources to make significant progress when the scientific problem is particularly challenging.

The MECP2 Consortium is a model for something much bigger: how neuroscience overall needs to operate so that we can find therapies and cures for disease.

The MECP2 Consortium is a model for something much bigger: how neuroscience overall needs to operate so that we can find therapies and cures for disease.   We are scientists in different parts of the world, working together, sharing their results long before publication, and brainstorming openly on a regular basis.  The different perspectives of the three labs allow for a wonderful exchange of ideas to advance the science. I believe this is what the Consortium is all about.  We have ignored the typical barriers of geography and have brought together scientists from Edinburgh, Portland, and Boston on a regular basis.  The results have been stunning.  There has been much more rapid progress than would have been made by the individual labs.

Consortium meeting in Boston in November of 2013.

Consortium meeting in Boston in November of 2013.

Bird: I agree. An over arching goal of the Consortium is to understand the way the MECP2 protein works at the molecular level.  We are at last starting to make real progress on this and will be testing some of the new ideas in cellular and animal models.  Our ultimate aim is to use this new knowledge to provide rational approaches to therapy.

Mandel:  Front and center is always our goal to find a therapy for Rett. This guides our experiments and keeps us focused. The fact that financial support comes from families who have a child with Rett and their networks makes us work harder.

Coenraads: In your opinion what are the elements that have made this consortium “work”?

Greenberg:  Trust and openness, a willingness on the part of all three Principal Investigators to talk through any potential problems immediately as they come up.  A willingness to check egos at the door so that we can work together for something that is more important than our individual advancement. Importantly the participants, Mandel, Bird, Greenberg and Coenraads like and trust each other.

consortium4Bird: We all have different backgrounds and interests, but we share a commitment to understanding Rett Syndrome.  We compliment each other surprisingly well.

Mandel:  The regular meetings and exchanges and the quality of the scientists involved have been key factors as well as the availability of sufficient funding for each of us to follow our scientific noses.

Coenraads:  Fortunately science is not linear. There are technologies available now that weren’t available when the Consortium started. How does this impact your Rett research?

Greenberg:  There are a lot of new technologies available – in particular Cre lines that will allow us to study the effect of MeCP2 loss in a relatively homogeneous population of neurons, CRISPR and Talen technology that will facilitate gene correction, and genomic technologies that are providing a new understanding of the role of methylation in the control of neuronal gene expression.  Also, better equipment, such as microscopy will help.

Bird:  The technologies for genetic modification have existed for a decade, but the advent of CRISPR has made this facile.  Being able to edit genetic mistakes in patients is no longer a science fiction dream, but has become a real possibility.  Exploring this option will be an important focus for the Consortium.

Coenraads:  Harrison Gabel from Mike’s lab recently shared with me in an email:  Our group meetings are essential to critically assessing our work. Each lab group has its own “world view,” and having that view shaken up every six months is very constructive.

So I look forward to lots more critical assessments and worldviews getting shaken as together we get to the bottom of what MeCP2 does.


* Due to the success of the MECP2 Consortium, and its positive gene therapy findings, RSRT has just announced funding for a second consortium: the MECP2 Gene Therapy Consortium. Read more about this newly formed second collaboration.

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by Monica Coenraads

[Italian translation]
[Spanish translation]
[Press release]

The videos below are perhaps the most well-known in the Rett community. If you love a child with Rett then chances are you’ve watched them obsessively.

This work published in 2007 by Adrian Bird, declared to the world that Rett is reversible, but did not tell us how this could be done in people.

Fast-forward six years and the video below from the RSRT-funded labs of Gail Mandel and Adrian Bird may have given us an answer: gene therapy.

The mouse moving around was given gene therapy treatment and received healthy Mecp2 gene. The immobile mouse did not receive treatment. The video was taken four weeks after treatment.

So how do we make the giant leap from recovered mice to recovered children?

To move us towards this goal, RSRT has launched their second collaborative group – the MECP2 Gene Therapy Consortium. This new group comes after the success of RSRT’s MECP2 Consortium, established in 2011, that led to the initial encouraging gene therapy findings. With a budget of $1.5 million the members of this international gene therapy collaboration are charged with tackling the necessary experiments to get us to clinical trials as quickly as possible.

I recently caught up with the investigators to discuss this novel collaboration:

Brian Kaspar (Nationwide Children’s Hospital)
Currently working on gene therapy clinical trial for Spinal Muscular Atrophy

Stuart Cobb (University of Glasgow)
Neurophysiology lab and co-author on 2007 reversal paper with Adrian Bird

Steven Gray (UNC Chapel Hill)
Currently working on gene therapy clinical trial for Giant Axonal Neuropathy

Gail Mandel (OHSU)
Member of MECP2 Consortium and author of gene therapy paper published this summer

Brain KasparNationwide Children's Hospital

Brain Kaspar

Stuart CobbUniversity of Glasgow

Stuart Cobb

Steven GrayUNC Chapel Hill

Steven Gray

Gail MandelOHSU

Gail Mandel



Coenraads:  Let’s jump right in. Why Rett? Why now? 

Cobb: While there have been major advances in understanding the molecular actions of the MeCP2 protein, it is still difficult to conceive of a small ‘traditional’ drug molecule being able to mimic its function. While traditional drug approaches will likely be restricted to correcting specific aspects of what goes wrong in Rett it is conceivable that gene therapy can correct the cause of Rett at its very source and thus provide a profound recovery of function.

While traditional drug approaches will likely be restricted to correcting specific aspects of what goes wrong in Rett it is conceivable that gene therapy can correct the cause of Rett at its very source and thus provide a profound recovery of function. – Stuart Cobb

Mandel:  It has been known for some time now that when MeCP2 is expressed genetically in cells throughout an MeCP2-deficient mouse, major Rett symptoms are reversible in mice.  Two of the big outstanding questions then are: 1) Will this be true for humans and 2) Can we add MeCP2 back to patients and also achieve reversal?  The first question is currently still an open question, although upcoming experiments using human neurons and astrocytes derived from iPSCs and xenografts (transplanting human cells into mice) may provide some important clues. The second question is challenging because currently there are no reliable ways to introduce MeCP2 throughout the brain, although recent studies in mice, funded through RSRT consortiums, suggest that AAV9-mediated transduction (delivery via a virus) might have potential. Therefore, two advancing technologies, iPSCs and AAV9 viruses, are converging to compel us to jump right in now.

Kaspar: A major advantage in Rett is that the genetic target is defined for us: MeCP2.  Another advantage is that it’s not neurodegenerative – neurons don’t die.  And importantly, we know that restoring the proper level of MeCP2, even later in life, at least in a mouse, results in dramatic improvements.

Why now? Because the gene therapy field now has an arsenal of powerful new tools.  We have at our disposal a tool kit that can express genes for long periods of time and that can target many cell types efficiently throughout the entire nervous system. Our challenge will be to utilize our toolkit to hit the precise cells at the right expression levels.  I’m certain we can accomplish this goal.

Gray: That said, the devil is in the details.  We have to get MeCP2 broadly distributed throughout the whole brain, which is something that has been done in animals but not yet in humans.  Just as important, we have to be very careful to get the level of MeCP2 correct – too little may not work well enough and too much could cause a different spectrum of disease.

Coenraads: What have we learned thus far regarding gene therapy for Rett?

We’ve learned that a single one-time administration of a gene therapeutic can have a clinically meaningful result in the workhorse rodent model of this disease, even when delivered later in life. The results have been quite promising, and now multiple laboratories have similar promising results, it’s not just an isolated manuscript happening in one laboratory. – Brian Kaspar

Kaspar: We’ve learned that a single one-time administration of a gene therapeutic can have a clinically meaningful result in the workhorse rodent model of this disease, even when delivered later in life.  The results have been quite promising, and now multiple laboratories have similar promising results, it’s not just an isolated manuscript happening in one laboratory.  Using similar approaches, multiple groups have encouraging results.  That’s good for science and that’s good for Rett patients.

Steve Gray (far right) and Stuart Cobb (second from the right) at an RSRT science meeting in late 2012.

Steve Gray (far right) and Stuart Cobb (second from the right) at an RSRT science meeting in late 2012.

Cobb:  The studies have also shown that the level of MeCP2 protein produced by the gene therapy is not producing any obvious defects in its own right and it therefore seems possible to deliver protein within limits that are tolerable to cells.

We have also learned that it is not necessary to ‘hit’ all cells with the virus, this is never going to be achievable in practice anyway. Fortunately, a substantial therapeutic impact may be achieved by delivering the gene to a subset of cells. Of course the absolute number of cells, the types of cells and location in the brain is likely to be very significant. These are important issues that will be investigated by the MECP2 Gene Therapy Consortium.

Gray: Finally, the studies tell us that we have to be very careful how we target the MeCP2 gene, to make sure too much isn’t delivered to a particular organ, such as the liver.

Coenraads: Have you ever worked in collaboration with multiple labs?  What do you think are the advantages?  Could there be disadvantages?

Mandel: I have been fortunate enough to be part of a productive collaboration funded by RSRT to work on how MeCP2 functions normally, and in mutants, and to do, with Kaspar’s group and Adrian Bird, the initial pilot proof of principle for gene therapy for Rett, using AAV9 vectors.

Gray:  Most of my work is done in collaboration with other labs, and I’m very comfortable doing research that way.  I have a small and fairly specialized lab.  We aren’t experts at everything, and it is much more efficient to collaborate with someone that has expertise than try to develop it on your own.  This speeds things up and raises the quality of the work.  The keys to making it work are that everyone has to be fully committed, and there has to be a level of trust across the members of the consortium.  Trust that you can share data openly, and trust that the work is being carried out to the highest standards.  If one investigator isn’t doing their part or does sloppy science then things can fall apart.

Stuart Cobb (right) with David Katz.

Stuart Cobb (right) with David Katz.

Cobb:  I have enjoyed a number of successful bilateral collaborations in the past but the formation of the four-lab Consortium is going to be a new venture for me. Clearly there will be big advantages in terms of pooling complementary expertise to make swift progress. However, there will also be challenges, one being the necessity to maintain very good communication within the Consortium to coordinate our efforts and work together efficiently.

Kaspar:  My laboratory is engaged in a number of collaborations and they are a major reason we have been successful.  Our international collaborations have given us access to patient samples as well as opened the door to new ideas and interactions that just couldn’t be accomplished sitting in isolation. Collaborations bring everyone’s experience and expertise to the table and allow the participants to rapidly answer difficult questions. We don’t always have to reach consensus but the right team will be open to sharing ideas and comfortable with hearing criticism as well as be aligned on goals and focused on the patients.

Coenraads: What are the strengths your lab brings to the table?

Steve Gray in his lab at UNC Chapel Hill

Steve Gray in his lab at UNC Chapel Hill

Gray:  We are part of one of the best gene therapy centers in the world, with a vector core facility that makes hundreds of research preps and several clinical preps each year.  My lab in particular has, as its primary goal, a mission to develop nervous system gene therapy platforms.  We’ve made enormous strides using existing vectors to their full potential, and also leading the way to develop newer and better vectors.  Also, our experience bringing our Giant Axonal Neuropathy project to clinical trial gave us experience on the process of moving a biological from the bench to the bedside. 

Cobb:  My own lab brings expertise in the neurobiology side in terms of accurately mapping out Rett syndrome-like features in mice and within the brain and being able to assess in detail the ability for gene therapy to improve aspects of the disorder.

Mandel:  I am a basic science lab and I have strengths in applying state of the art molecular tools to questions related to gene therapy.  My lab also has much expertise in histology of the brain.

Kaspar: We have successfully navigated two programs from bench research to human clinical trials.  We have flexibility to focus on complex basic biology questions, while keeping in mind our goal to advance therapies towards human clinical trials.

Coenraads:  Gene therapy has had a rocky road. How do you view the field at the moment?

Kaspar:  Expectations and promises were far too high in the early days of gene therapy. I think transformative therapies go through this track of failing and then triumphing. One simply has to look at the field of organ transplantation as an example. I think gene therapy will triumph, but we still have much to learn and pay attention to. There is a great deal of excitement and hope in the field today.  We have to be good custodians of this technology with laser focus on safety and design of human clinical trials.

Gray:  There are a lot of good things happening in the field right now with patients seeing major improvements in their lives as a result of gene therapy.  The first gene therapy product received full regulatory approval last year in Europe.  Biotechnology companies are taking an interest in gene therapy.  Frankly, it is a good time to be in the field.

Modern, safer, approaches to gene therapy are developing very rapidly and it is one of the most vibrant fields in the genetics and molecular medicine arena at the moment. – Stuart Cobb

Mandel: I think that there is a large and growing momentum now for gene therapy because of the huge advances in molecular biology and viral technologies.

Coenraads: I find that the gene therapy area is polarizing – people love it or hate it – have you encountered a similar response?

Cobb:  Yes, I have indeed encountered such contrasting views. Even within the community of Rett clinicians, I have had views of gene therapy being ‘the obvious route to follow’ versus others expressing great skepticism. Interestingly, the view within industry has been more accepting, perhaps due to the massive shift towards biologicals (alternatives to classical small molecule drugs) that has occurred in recent years.

Kaspar:  Typically those that are not fans of this technology focus on past failures. With any transformative findings there will be disbelievers.   I’m reminded by a quote from Alexander von Humboldt:  There are three stages of scientific discovery: first people deny it is true; then they deny it is important; finally they credit the wrong person.

Gray:  I can’t blame some people for hating it.  Gene therapy promised a lot early on, before the technology was very developed.  Expectations should have been tempered somewhat while the science was worked out, but instead the field moved too fast and people got hurt.  That said, I don’t think you should turn your back on a potentially revolutionary medical technology because of mistakes made over a decade ago when the field was in its infancy.  If you take a fresh look at the things happening today, there is a lot of real and well-founded optimism.

Gail Mandel at a recent RSRT meeting.

Gail Mandel at a
recent RSRT meeting.

Mandel:  As in any area of science, there are proponents and detractors.  There are technical issues with gene therapy, such as scaling and side effects that need to be addressed before more people will lose some skepticism, although some skepticism is quite healthy and pushes us to be as rigorous as possible.



Coenraads: Dr. Kaspar, tell us a bit about your experience bringing the Spinal Muscular Atrophy project to clinical trial.   How long did it take from mouse experiments to trial? How much money was invested from your lab?

Brian Kaspar (middle) at an RSRT workshop.

Brian Kaspar (middle) at an RSRT workshop.

Kaspar:  Our SMA program is quite exciting. We discovered the unique capacity for AAV9 to cross the blood brain barrier in 2009, in 2010 we were in progress to have the longest living SMA mouse in the world. We further tested safety and navigated the regulatory process including the NIH Recombinant Advisory Committee, the Food and Drug Administration and our institutional review board.  Late in 2013 we were granted approval from the FDA and we will be injecting our first patients in a Phase 1/2 clinical trial early this year.  It was a hectic 3-year process that cost $4 million and counting.  We are excited and hopeful to help children with SMA type 1.

Coenraads:  Dr. Gray, you are developing a gene therapy treatment for a disease called Giant Axonal Neuropathy.  Can you tell us about your experience with that project? How far from clinical trials are you?   How long did it take from mouse experiments to trial? How much money did it cost?

Gray:  My GAN project has been life changing.  This was the project that made the connection for me to patients and changed the way I think about research.  Before then it was just about getting a good paper, or a grant, or doing the right things to advance my career.  Now it is about making a real difference in the lives of people I’ve come to know and love.  We’re on track to treat the first patient in the first half of 2014. We developed the treatment about 3 ½ years after starting the project, which included testing the treatment in the laboratory and developing an approach that should translate to humans.  It’s taken another two years to start the trial. Our preclinical supporting studies were approximately $1.5 million.  The FDA-required safety studies were another $0.75 million.  We are budgeting another $1.5 million for the clinical trial. Most of these funds were provided by a small grass-roots foundation called Hannah’s Hope Fund.

Coenraads:  I’m delighted that you have all agreed to collaborate. I look forward to our bi-monthly phone calls and in-person meetings twice a year.  Parents all over the world will be waiting anxiously to hear about your progress. As you know, there is a lot at stake.

We are starting the New Year with the wonderful news that Professor Adrian Bird has been Knighted for his services to science.  For anyone following Rett research Prof. Bird needs no introduction. His list of contributions to the Rett field are numerous starting with the discovery of the MeCP2 protein in the early 1990’s to the development of the first animal  model in 2001 to the unexpected discovery that Rett symptoms are reversible.  We congratulate Sir Adrian Bird and wish him the best for 2014 – may the discoveries continue!

AdrianBird

Professor Adrian Bird

Prof Bird with fellow trustees Heidi Epstein,
Monica Coenraads and Marci Valner

To profoundly impact a disorder with as many varied and debilitating symptoms as Rett Syndrome, it is likely that intervention must be directed toward the very root of the problem. There are several ways to do this: activate the silent back-up copy of the Rett gene; target modifier genes; explore gene therapy.

Today, we announce a study funded through the MECP2 Consortium suggesting that gene therapy may indeed provide a feasible approach to treat Rett Syndrome.

The work was led by Gail Mandel at Oregon Health and Sciences University in collaboration with Adrian Bird of the University of Edinburgh and Brian Kaspar of Nationwide Children’s Hospital.

Gail Mandel with lab members Dan Lioy and Saurabh Garg

Gail Mandel with lab members
Dan Lioy and Saurabh Garg

Adrian Bird and post-doc Hélène Cheval

Adrian Bird and post-doc
Hélène Cheval

In the past sixty days, four key papers have been published detailing research advances supported financially and intellectually by RSRT. Three of those papers are funded through the MECP2 Consortium, a unique alliance launched by RSRT in 2011 among three leading labs: Bird, Greenberg (Harvard) and Mandel. If you are a donor to RSRT, the accelerated research these projects represent is the result of your money at work.

We wish to express our gratitude to all of our generous supporters and the parent organizations that make this progress possible. Special thanks to our funding partners, the Rett Syndrome Research Trust UK and the Rett Syndrome Research & Treatment Foundation.

Below are some resources to help you understand today’s announcement.

Press Release [Spanish Translation] [German Translation]


Video interview with Dr. Mandel & lab members

adrian-bird

Adrian Bird (left) and Matt Lyst
University of Edinburgh

michael-greenberg

Michael Greenberg (right) and Dan Ebert
Harvard Medical School

It stands to reason that in our battle to cure Rett Syndrome it would be of great benefit to understand the function of the “Rett protein”, MeCP2. Towards this end RSRT launched the MECP2 Consortium in 2011, a unique $1.8 MM collaboration between three distinguished scientists, Adrian Bird, Michael Greenberg, Gail Mandel.  On June 16th the first two publications from this collaborative effort are published in Nature Neuroscience and Nature. Together these papers provide further clarification of the elusive function of the MeCP2 protein and how mutations within it contribute to Rett.

We thank Kathy and Tony Schoener whose visionary $1 MM gift made the Consortium possible. We thank all of our donors and parent organizations worldwide who support us, in particular our funding partners Rett Syndrome Research Trust UK and the Rett Syndrome Research & Treatment Foundation.

We are providing a variety of resources to help you understand the progress being reported today.

Press release

Animation of Nature Neuroscience Paper (courtesy of Jeff Canavan)

Chinese Translation

Interview with Matt Lyst, post-doc in Bird lab

Interview with Michael Greenberg and Dan Ebert,
post-doc in Greenberg lab

Rett Syndrome Research Trust Website

Adrian Bird and colleagues recently published  their latest paper on MeCP2 in the journal Human Molecular Genetics. The series of experiments described in the paper were designed to explore what happens when the MeCP2 protein is removed from mice of various ages, including in a fully adult mouse. This work was funded in part by RSRT with generous support from RSRT UK, Rett Syndrome Research & Treatment Foundation (Israel) and other organizations who financially support our research effort.

Below are excerpts from a conversation with joint first authors Hélène Cheval and Jacky Guy.

Jacky Guy (far right), Hélène Cheval (2nd from right) with Adrian Bird and other lab members. University of Edinburgh, Scotland

MC  Dr. Cheval, you trained as a neuroscientist. What attracted you to the Bird lab, which is very biochemistry-based, and where you are the sole neuroscientist?

HC  My previous lab, run by Serge Laroche,  was a pure neuroscience lab focused on learning and memory. However, I was actually doing biochemistry and I was very much interested in how to get from molecule to behavior, and I was also quite interested in chromatin.  I had read the Bird lab reversal paper of 2007 and thought it was one of the most exciting papers I had ever seen. Upon receiving my PhD I applied for a post-doc position, convinced that it would be a great experience for me but also thinking that perhaps the lab would benefit from having someone with a neuroscience background.  I joined the lab in 2009.

MC  Dr. Guy, you co-authored your first paper on Rett Syndrome in 2001. That was the paper that described the MeCP2 knockout mouse model made in the lab, one that is now used in hundreds of labs around the world.

JG  I joined the lab in 1997. My first project was to make the conditional mouse models of Mecp2, meaning mice where the protein can be removed at will.  At that stage we didn’t yet know about the link between MECP2 and Rett Syndrome.  That came about as I was working on the project. It was a very exciting time.

MC  It’s unusual for people to stay in a lab so long. This gives you an amazing depth of uninterrupted knowledge about the field.

JG  I took a rather unconventional path. I’m very happy to do bench work and being able to work in the same field has been wonderful.

MC  Dr. Guy, perhaps you can start us off. What are the key questions you were trying to answer with this series of experiments?

Jacky Guy

JG  This was actually an experiment we had been wanting to do for a long time.  We have always been interested in defining when MeCP2 is important.  Rett had been thought of as a neurodevelopmental disease. Since we were completely new to Rett, we thought maybe it’s not neurodevelopmental. So we set out to remove the protein at different ages and see what happens.  Removing the protein is not quite as simple as reactivating the gene, which we had already done in the reversal experiment. When you reactivate the gene it makes protein right away. In this experiment, however, when you deactivate the gene you have to wait for the protein to decay away. We found it takes about two weeks for the amount of MeCP2 protein to fall by half.

HC  Jacky’s reversal experiment suggested that MeCP2 is implicated in adulthood. But many papers were still describing Rett as a neurodevelopmental disease.  We also wanted to confirm a hypothesis that we all shared in the lab that MeCP2 is required throughout life.

MC  That is a hypothesis that was also put forth in Huda Zoghbi’s 2011 Science paper. She showed that removing Mecp2 in adult mice aged 9 weeks and older caused Rett symptoms. Do you think that her paper and your new data have definitively put to rest the notion that Rett is neurodevelopmental?

HC  To my mind it’s clear that it’s not merely neurodevelopmental.

JG  I think “merely” is the key word here. The phenotypes we analyze in mice are those that are quite easy to see; for example, lifespan, breathing, gait. There might be more subtle things that we are not observing, or that are not affected by knocking out the protein in adulthood.  And we are not analyzing cognitive aspects. So we can’t completely rule out the possibility that there could be some things that are indeed of a neurodevelopmental origin that we are not seeing in these experiments.

JG  Mecp2 can be deleted by treating the mouse with tamoxifen in the same way the protein was reactivated in the reversal paper.  In this paper we picked three different time points to turn off the gene: three weeks (which is when mice are weaned and begin to live independently) eleven weeks and twenty weeks.   In all three scenarios the tamoxifen was able to delete Mecp2 in about 80% of the cells.

What you might expect is that at whatever age you delete the gene, there will be a certain amount of time for the protein to disappear and then the effects of not having the protein will appear.

In fact, what we found is that the time it took for symptoms to appear varied with the age at which we inactivated the gene.  It took longer for the symptoms to appear when we deactivated Mecp2 at 3 weeks.  When we removed MeCP2 in older mice, the symptoms appeared more rapidly.  So it seems that younger mice are able to live symptom-free without MeCP2 for a longer period of time. There is a certain period when the need for MeCP2 becomes more important in mice. This is the first critical time period that we talk about in the paper; it happens around eleven weeks.

Drs. Cheval and Guy with Prof. Bird and other lab members

As we followed the mice treated at all three time periods, eventually they all started to die at about the same age, approximately thirty-nine weeks, regardless of when MeCP2 was removed. We concluded that this time period centered around thirty-nine weeks represented a second critical period for MeCP2 requirement. This is a time in a mouse that roughly coincides with middle age in humans. We think that maybe MeCP2 is playing a role in maintaining the brain as it ages.

Interestingly, this time frame of thirty-nine weeks is when female mice that are MeCP2-deficient in about 50% of their cells from conception begin to show symptoms. The male mice which have zero MeCP2 can’t make it past the first critical time period of eleven weeks. When you delete MeCP2 in 80% of the cells, the male mice show symptoms at 11 weeks and die at 39 weeks. So having about 20% normally expressing cells allows you to survive the first critical period but not the second.

MC  I’ve heard clinicians say that women with Rett in their 30s and 40s and beyond look older than they are. I wonder if this has anything to do with your hypothesis that MeCP2 may play a role in aging. Of course we don’t know if the premature aging is primary or secondary.  It may have to do with the effects of dealing with a chronic illness for many years.

JC  We are quite interested to learn about  a potential late deterioration in women with Rett but there is very little published on the subject.

MC  There are two potentially critically relevant points made in your paper. One is the fact that the half-life of the MeCP2 protein is two weeks. That could be relevant and encouraging for a protein replacement approach.

JG  We certainly had this in mind when we were doing the experiment.  The half-life of MeCP2 is longer than we expected. And could in fact bode well for protein replacement therapy. One caveat, ours was a bulk brain experiment. It could very well be that if you looked regionally in the brain or by cell type you might find varying results.

MC  The other potentially clinically relevant information comes from comparing the severity of symptoms seen in the mice in this study versus the adult knockout done in the Zoghbi lab and correlating symptoms to amount of MeCP2 protein. Your experiments yielded 3% more protein and resulted in less severely affected animals. Can you elaborate?

HC   That such a small difference in protein could have such a significant impact on survival is unexpected and indeed may be relevant for therapeutic interventions. We may not need to get the protein back to wildtype levels to have an effect. It may be possible that even small increases may be helpful.

MC  Congratulations to you both on this publication. The Bird lab has made numerous seminal contributions to the Rett field. The Rett parent community doesn’t typically have a chance to glimpse the researchers behind the experiments, doing the day-to-day work, so I’m delighted to provide an opportunity for our readers to get to know you a bit.  I look forward to the next publication. Best wishes for your ongoing work.

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hotos courtesy of Kevin Coloton