Approach that inspires DREADD could create new way to treat Parkinson’s disease

4093259323_32082865d7

Dopamine producing brain nerve cells, made from embryonic stem cells

Imagine having a treatment for Parkinson’s that acts like a light switch, enabling you to turn it on or off depending on your needs. Well, that’s what researchers at the University of Wisconsin-Madison have come up with. And if it works, it might help change the way we treat many other diseases.

For years researchers have been trying to come up with a way of replacing the dopamine-producing brain nerve cells, or neurons, that are attacked and destroyed by Parkinson’s. Those cells regulate movement and as they are destroyed they diminish a person’s ability to control their body, their movement and even their emotions.

Attempts to transplant dopamine-producing cells into the brains of people with Parkinson’s disease have met with mixed results. In some cases the transplanted cells have worked. In many cases the cells don’t make enough dopamine to control movement. In about 10 percent of cases the cells make too much dopamine, causing uncontrolled movements called graft-induced dyskinesia.

But now the researchers at UW Madison have found a new approach that might change that. Using the gene-editing tool CRISPR (you can read about that here) they reprogrammed embryonic stem cells to become two different types of neurons containing a kind of genetic switch called a DREADD, which stands for designer receptor exclusively activated by designer drug. When they gave mice the designer drug they created to activate DREADD, one group of cells boosted production of dopamine, the other group shut down its dopamine production.

In a news release about the study, which is published in the journal Cell Stem Cell, lead author Su-Chun Zhang says this kind of control is essential in developing safe, effective therapies:

“If we are going to use cell therapy, we need to know what the transplanted cell will do. If its activity is not right, we may want to activate it, or we may need to slow or stop it.”

Zhang says the cells developed using this approach have another big advantage:

“We can turn them on or off, up or down, using a designer drug that can only act on cells that express the designer receptor. The drug does not affect any host cell because they don’t have that specialized receptor. It’s a very clean system.”

Tests in mice showed that the cells, and the designer drug, worked as the researchers hoped they would with some cells producing more dopamine, and others halting production.

It’s an encouraging start but a lot more work needs to be done to make sure the the genetically engineered stem cells, and the designer drug, are safe and that they can get the cells to go to the part of the brain that needs increased dopamine production.

As Zhang says, having a method of remotely controlling the action of transplanted cells, one that is reversible, could create a whole new way of treating diseases.

“This is the first proof of principle, using Parkinson’s disease as the model, but it may apply to many other diseases, and not just neurological diseases.”

An inside look reveals the adult brain prunes its own branches

Did you know that when you’re born, your brain contains around 100 billion nerve cells? This is impressive considering that these nerve cells, also called neurons, are already connected to each other through an intricate, complex neural network that is essential for brain function.

Here’s how the brain does it. During development, neural stem cells produce neurons that navigate their way through the brain. Once at their destination, neurons set up shop and send out long extensions called axons and branched extensions called dendrites that allow them to form what are called synaptic connections through which they can communicate through electrical and chemical signals.

Studies of early brain development revealed that neurons in the developing brain go on overdrive and make more synaptic connections than they need. Between birth and early adulthood, the brain carefully prunes away weak or unnecessary connections, and by your mid-twenties, your brain has eliminated almost half of the synaptic connections you started out with as a baby.

This synaptic pruning process allows the brain to fine-tune its neural network and strengthen the connections between neurons that are important for brain function. It’s similar to how a gardener prunes away excess branches on fruit trees so that the resulting branches can produce healthier and better tasting fruit.

The brain can make new neurons

It was thought that by adulthood, this process of pruning excess connections between neurons was over. However, a new study from the Salk Institute offers visual proof that synaptic pruning occurs during adulthood similarly to how it does during development. The work was published today in the journal Nature Neuroscience, and it was funded in part by CIRM.

Rusty Gage, Salk Institute.

Rusty Gage, Salk Institute.

The study was led by senior author and Salk Professor Rusty Gage. Gage is well known for his earlier work on adult neurogenesis. In the late 90’s, he discovered that the adult brain can in fact make new neurons, a notion that overturned the central dogma that the brain doesn’t contain stem cells and that we’re born with all the neurons we will ever have.

There are two main areas of the adult brain that harbor neural stem cells that can generate new neurons. One area is called the dentate gyrus, which is located in the memory forming area of the brain called the hippocampus. Gage and his team were curious to know whether the new neurons generated from stem cells in the dentate gyrus also experienced the same synaptic overgrowth and pruning that the neurons in the developing brain did.

Pruning the Adult Brain

They developed a special microscope technique that allowed them to visually image the development of new neurons from stem cells in the dentate gyrus of the mouse brain. Every day, they would image the growing neurons and monitor how many dendritic branches they sent out.

Newly generated neurons (green) send out branched dendritic extensions to make connections with other neurons. (Image credit: Salk Institute)

Newly generated neurons (green) send out branched dendritic extensions to make connections with other neurons. (Image credit: Salk Institute)

After observing the neurons for a few weeks, they were amazed to discover that these new neurons behaved similarly to neurons in the developing brain. They sent out dozens of dendritic branches and formed synaptic connections with other neurons, some of which were eventually pruned away over time.

This phenomenon was observed more readily when they made the mice exercise, which stimulated the stem cells in the dentate gyrus to divide and produce more neurons. These exercise-induced neurons robustly sent out dendritic branches only to have them pruned back later.

First author on the paper, Tiago Gonçalves commented on their observations:

“What was really surprising was that the cells that initially grew faster and became bigger were pruned back so that, in the end, they resembled all the other cells.”

Rusty Gage was also surprised by their findings but explained that developing neurons, no matter if they are in the developing or adult brain, have evolved this process in order to establish the best connections.

“We were surprised by the extent of the pruning we saw. The results suggest that there is significant biological pressure to maintain or retain the dendrite tree of these neurons.”

A diagram showing how the adult brain prunes back the dendritic branches of newly developing neurons over time. (Image credit: Salk Institute).

A diagram showing how the adult brain prunes back the dendritic branches of newly developing neurons over time. (Image credit: Salk Institute).

Potential new insights into brain disorders

This study is important because it increases our understanding of how neurons develop in the adult brain. Such knowledge can help scientists gain a better understanding of what goes wrong in brain disorders such as autism, schizophrenia, and epilepsy, where defects in how neurons form synaptic connections or how these connections are pruned are to blame.

Gonçalves also mentioned that this study raises another important question related to the regenerative medicine applications of stem cells for neurological disease.

“This also has big repercussions for regenerative medicine. Could we replace cells in this area of the brain with new stem cells and would they develop in the same way? We don’t know yet.”


Related Links:

Unlocking the brain’s secrets: scientists find over 100 unique mutations in brain cells

Your brain is made up of approximately 100 billion neurons. These are the cells that process information and pass along electrical and chemical signals to their other neuron buddies throughout the body to coordinate thoughts, movement, and many other functions. It’s no small task to create the intricate neuronal network that is the backbone of the central nervous system. If any of these neurons or a group of neurons acquire genetic mutations that alter their function, a lot can go wrong.

The genetic makeup of neurons is particularly interesting because it appears that each neuron has its own unique genome. That means 100 billion different genomes in a single cell type in the brain. Scientists suggest that this “individuality” could explain why monozygotic, or identical, twins have different personalities and susceptibilities to neurological disorders or mental illnesses and why humans develop brain diseases or cancer over time.

To understand what a genome of a cell looks like, you need to sequence its genetic material, or the DNA, that’s housed in a cell’s nucleus. Sequencing the genome of an individual cell is hard to do accurately with our current technology, so scientists have developed clever alternatives to get a front-row view into the workings of neuronal genomes.

Cloning mouse neurons reveals 100+ unique genetic mutations

One such method was published recently in the journal Neuron by a CIRM-funded team from The Scripps Research Institute (TSRI). Led by senior author and Associate Professor at TSRI, Kristen Baldwin, the team took on the challenge of cloning individual mouse neurons to unlock the secrets of neuronal genomes. (For those who aren’t familiar with the term, cloning is a process that produces new cells or organisms that harbor identical genetic information from the originating cell.)

What they found from their cloning experiment was surprising: each neuron they sequenced had an average of more than 100 unique genetic mutations, and these mutations tended to appear in genes that were heavily used by neurons, something that is uncommon in cell types of other organs that tend to protect their frequently used genes. Their findings could help unravel the mystery behind some of the causes for diseases like Alzheimer’s and autism.

In a TSRI news release, Kristen Baldwin explained:

Kristen Baldwin

Kristen Baldwin

“Neuronal genomes have remained a mystery for a long time. The findings in this study and the extensive validation of genome sequencing-based mutation discovery that this method permits, open the door to additional studies of brain mutations in aging and disease, which may help us understand or treat cognitive decline in aging, neurodegeneration and neurodevelopmental diseases such as autism.”

Making mice with neuronal genomes

To clone individual neurons, the team took the nucleus of a single neuron and transplanted it into a mouse egg cell that lacked its own nucleus. The egg developed and matured all while copying and passing on the genetic information of the original mouse neuron. The team generated cloned embryonic stem cell lines from these eggs and were able to expand the stem cell lines to generate millions of stem cells that contained the same genetic material.

TSRI Research Assistant Alberto Rodriguez uses a tiny straw-like micropipette to pick up red fluorescent neurons and transfer their genomes into an egg.

TSRI scientists extract the nuclei of neurons and transfer their genomes into an egg. (Image courtesy of TSRI)

They made several different cloned stem cell lines representing different neuronal genomes and sequenced these lines to identify unique genetic mutations. They also were able to generate cloned stem cell lines from the neurons of older mice, and thus were able to track the accumulation of genetic mutations over time. Even more impressive, they made living mice that contained the cloned genomes of individual neurons in all of their cells, proving that neuronal genomes are compatible with development.

The team did report that not all neurons could be developed into cloned stem cell lines for reasons that they couldn’t fully explain, but they decided to focus on studying the cloned stem cell lines that were successful.

What does this mean for humans?

Baldwin explained that what was most surprising about their study was “that every neuron we looked at was unique – carrying more than 100 DNA changes or mutations that were not present in other cells.”

The next steps for their research are to explore why this diversity among neuronal genomes exists and how this could contribute to neurological disease in humans.

Co-first authors Jennifer Hazen and Gregory Faust.

Co-first authors Jennifer Hazen and Gregory Faust.

Co-first author Jennifer Hazen explains, “We need to know more about mutations in the brain and how they might impact cell function.”

Also mentioned in the news release, the team plans “to study neuronal genomes of very old mice and those with neurological diseases. They hope this work will lead to new insights and therapeutic strategies for treating brain aging and neurologic diseases caused by neuronal mutations.”


Related Links:

Bringing down the gatekeeper for a stem cell-based Parkinson’s cure

Feng-dopamine-HI

University of Buffalo researchers converted these dopamine neurons directly from human skin cells. Image shows a protein found only in neurons (red) and an enzyme that synthesizes dopamine (green). Cell DNA is labeled in blue.

On the surface, a stem cell-based cure for Parkinson’s disease seems pretty straight-forward. This age-related neurodegenerative disorder, which leads to progressively worsening tremors, slowness of movement and muscle rigidity, is caused by the death of a specific type of nerve cell, or neuron, that produces the chemical dopamine in a specific region of the brain. So it would seem that simply transplanting stem cell-derived dopamine-producing neurons (DA neurons) in the brains of Parkinson’s patients to replace the lost cells would restore dopamine levels and alleviate Parkinson’s symptoms.

Easier said than done
Well, it hasn’t turned out to be that easy. After initial promising results using fetal brain stem cell transplants in the 80’s and 90’s, larger clinical trials showed no significant benefit and even led to a worsening of symptoms in some patients. One potential issue with those early trials could have been variable cell composition of the fetal cell-based therapy. On top of that, the availability of fetal tissue is limited and the quantities of transplantable cells obtained from these samples are very low.

More recently, researchers have been busy at generating more pure populations of DA neurons from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs). Great progress has been made so far, but the field is still hampered by not being able to make enough DA neurons from hESCs and iPSCs in a timely manner.

Cutting out the pluripotent “middle man”
This week a research team at the University of Buffalo reported in Nature Communications about a much more efficient method for producing DA neurons. It’s a finding that could provide a strong push towards stem cell-based therapy development for Parkinson’s disease.

The team bypassed the need to start with hESCs or iPSCs and instead converted skin cells directly into DA neurons. A thorough analysis of the cells confirmed that they were functional and matched that characteristics of the specific dopamine neurons that are lost in Parkinson’s.

This direct reprogramming of skin cells into DA neurons as well as other cells is a technique pioneered by several independent researchers including some of our own grantees. This method is thought to have a few advantages over the specialization of immature hESCs or iPSCs into tissue-specific cells. Not only is the direct reprogramming process faster it also doesn’t require cell division so there’s less concern about the introduction of DNA mutations and the potential of tumor formation. Another plus for direct reprogramming is the possibility of inducing the direct conversion of one cell type into another inside the body rather than relying on the manipulation of hESCs and iPSCs in the lab. Still, despite these advantages the efficiency of direct reprogramming is still very low. That’s where the University of Buffalo team comes into the picture.

Bringing down the gatekeeper
The researchers led by physiology and biophysics professor Jian Feng, made a few key modifications to increase the efficiency of the current skin cell to DA neuron direct reprogramming methods. They first reduced the level of a protein call p53. This protein has several nicknames like “guardian of our genes” and “tumor suppressor” because it plays critical roles in controlling cell division and DNA repair and, in turn, helps keep a clamp on cell growth.

Reducing the presence of p53 during the direct reprogramming process led to a much more efficient conversion of skin cells to DA neurons. And because the conversion from a skin cell to a neuron happens quickly – just a couple days – timing the introduction of cell nutrients specific to neurons had to be carefully watched. Together, these tweaks improved upon previous studies as Feng mentioned in a University of Buffalo press release:

“The best previous method could take two weeks to produce 5 percent dopamine neurons. With ours, we got 60 percent dopamine neurons in ten days.”

blogDec09_Jian_Feng_7020_web

Jian Feng, PhD, professor of physiology and biophysics, Jacobs School of Medicine and Biomedical Sciences, University of Buffalo

IMHO (In my humble opinion)
I imagine there’s a lot more work ahead to get this method of deriving DA neurons from skin ready for the clinic. This reprogramming technique relied on the introduction of neuron-specific genes into the skin cells using a deactivated virus as the means of delivery. Even though the virus is inactive, its viral DNA randomly inserts into the cells’ chromosomes which can turn on genes that cause cancer. Therefore, a non-viral version of this method would need to be developed for clinical use.

Also, as mentioned earlier, since p53 inhibits tumors by suppressing uncontrolled cell division, it would be important to make sure that a reduction of p53 didn’t lead to any long-term negative consequences, like the transplantation of potentially cancerous cells into the patient.

Still, this dramatic increase in efficiency for making functional DA neurons and the identification of p53 as a key control point for direct reprogramming are very exciting developments for a disease field that is committed to finding cures for its patients.

Related links:

From the Stem Cellar archives: blogs about direct reprogramming
Video: CIRM Grantee Marius Wernig discusses direct reprogramming
Video: Thirty second elevator pitch describing direct reprogramming

CIRM Scholar Spotlight: Berkeley’s Maroof Adil on stem cell transplants for Parkinson’s disease

Maroof Adil, CIRM Scholar

Maroof Adil, CIRM Scholar

Stem cell therapy has a lot of potential for Parkinson’s patients and the scientists that study it. One of our very own CIRM scholars, Maroof Adil, is making it his mission to develop stem cell based therapies to treat brain degenerating diseases like Parkinson’s.

Maroof got his undergraduate degrees from MIT in both Chemical Engineering and Biology, and a PhD in Chemical Engineering from the University of Minnesota. As a graduate student, he dived into the world of cancer research and explored ways of delivering cancer-killing genes specifically to cancer cells in the body while leaving healthy tissues in the body unharmed.

While he enjoyed his time spent on cancer research, he realized his main interest was to apply his skills in chemical engineering and materials science to understand biological problems. This brought him to his current position as a postdoc at UC Berkeley in the Schaffer lab.

Maroof is doing some pretty cutting edge research to develop 3D biomaterials that will vastly improve the transplantation and survival of stem cell derived neurons (nerve cells) in the brain. Check out our exclusive interview with this talented scientist below!


Q: What are you working on and why?

MA: I have always been excited about finding engineering solutions to medically relevant problems. I decided to do a postdoc at UC Berkeley in David Schaffer’s lab because I wanted to combine chemical and materials engineering skills from my graduate research with stem cell technologies to solve biological problems. One of the exciting parts of Dave’s lab, and a reason why I joined, is that he is working on translational stem cell-based regenerative therapies for central nervous system diseases such as Parkinson’s and Huntington’s.

My current research is motivated by the need to find better therapies for these neurodegenerative diseases. While stem cell-based regenerative medicine is an up-and-coming field, there are still a lot of challenges that need to be addressed before stem cells can be successfully used in the clinic. There are three main challenges that are most relevant to my research. First, we need to improve the efficiency of stem cell differentiation, i.e. how well we can convert these stem cells to the mature, functional neurons that we need to treat neurodegenerative diseases. Second, after implanting these cells into the body, we need to increase their survival efficiency. This is because one of the main issues with stem cell-based transplants right now is that after implantation, most of these cells die. Given these first two challenges, we need to generate a lot of cells in order to effectively treat degenerative diseases. The third challenge is to make good quality, functional, transplantable cells in a large-scale fashion.

So given my chemical and materials engineering background, I wanted to see if we could use biologically inspired materials (biomaterials) to address some of these issues with stem cell differentiation and transplantation. In brief, we are developing functionalized biomaterials, differentiating stem cells within these biomaterials into neurons, characterizing the quality of these neurons, and testing the function of these stem cell-derived neurons in animal models of disease.

A major focus of our lab is to develop 3D biomaterials to increase the efficiency of large-scale production of clinical-grade stem cells [and the mature cells that are derived from them]. Our preliminary results suggest that we can get higher numbers of better quality neurons when we differentiate and grow them in 3D biomaterials compared to when they are traditionally grown on a flat, 2D tissue culture surface. Presently, I’m trying to verify that our 3D method works in the lab. If it does, this technology could help us save a lot of time and resources in generating the type of cells we need for effective cell replacement therapies.

Stem cells growing as clusters in 3D[1]Neurons generated in 3D platforms 1[1]

Stem cell derived neurons grown in 3D cultures (left) and generated on 3D biomaterials (right). Images courtesy of Maroof Adil.

Q: Your research sounds fascinating but complicated. How are you doing it?

MA: It’s certainly a multidisciplinary project, and constantly requires us to draw ideas from diverse fields including polymer chemistry, developmental biology and chemical engineering. I am very grateful to be part of a resourceful lab, to my mentors, and to have amazing, motivated people working with me. UC Berkeley provides a highly collaborative work environment. So for some of the follow-up work that further characterizes the quality of these stem cells and their mature cell derivatives, we are collaborating with other labs at UC Berkeley and at UCSF.

Q: Are you interested in applying this work to other brain diseases?

MA: Certainly. Although we are primarily working on generating stem cell-derived dopaminergic neurons, which are the major cell type that die in Parkinson’s patients, I’m also interested in applying similar biomaterials to derive other types of neurons, for instance medium spiny neurons for Huntington’s disease.

The advantage of some of the materials we are working with is their modular nature. That is, we can tune their properties so that they are useful for other applications.

Q: In your opinion what is the future of stem cells in your field? Will they bring cures?

MA: I am very hopeful given what I’m seeing right now in the scientific literature, and in clinical trials for stem cell-based therapies in general. Right now, there are several trials that are testing the benefit and safety of stem cell-based transplants in different diseases. However, right now there are no clinical trials applying stem cell-derived neurons to treat brain diseases. But I think there’s certainly a lot of promise. There are challenges that we need to address in this field, and some of these I outlined earlier. Researchers are working on finding solutions to these problems, and I think that if we find them, the chances of successfully finding cures will be higher.

Q: Tell us about your experience as a CIRM Scholar.

MA: I started as a CIRM scholar in 2014. It was really great to have a source of funding that lined up with what I was interested in, which was doing translational work in regenerative medicine.

I first began working with stem cells when I started my postdoc career, but I didn’t really have a background in this area. So being new to the stem cell field, I felt that CIRM provided the support structure that I needed. And I’m not just referring to funding. CIRM brings scientists with different scientific backgrounds together in one place, where we can learn from one another, and initiate fruitful collaborations. Being a CIRM scholar makes me feel like I’m part of a bigger community, with other scientists conducting very different, but related stem cell research.

Also, I am a big fan of the CIRM blog. I am able to learn about patients and about other researcher’s backgrounds. It helps you realize that patients and researchers are part of the same field. And I like that concept of bringing the field closer: patients towards researchers and researchers towards patients. I think that is useful to boost motivation for researchers, and to give patients a better idea of what we do.

Through CIRM, we’ve had a chance to go out into the local community and present some of our research. For example, the past two years I’ve talked to local high school students during Stem Cell Awareness Week, and that was a really great experience.  I’ve presented to other professionals before, but never to those as young as high school students.  To me, it was quite exciting to realize that these kids are very much interested in the type of work we are doing, and to feel like I was able to influence them to potentially pursue science as a career.

Q: What are your career goals?

MA: I definitely want to stay in science and solve medically relevant problems. It could be nice to be faculty at a research university and in a position to pursue my own independent ideas at the interface of biomaterials and stem cell based therapies. An industry position working towards regenerative medicine or other biologically relevant applications is also an exciting possibility. At this point, being in science is my priority.

Q: What’s your favorite thing about being a scientist?

MA: The excitement you get when your experiments work out, and the joy of making new discoveries. I also like the thrill of designing experiments that may advance the field, and the feeling that what you’re doing day-to-day is contributing to a body of knowledge that others may find useful. I find it especially rewarding to be a scientist in the medical field, working on translational projects closely related to finding cures for diseases.

Could We Reverse Alzheimer’s Disease with Stem Cells?

What if you could give people whose memories have been stolen the ability to remember again? I’m talking about curing a population of more than 5 million Americans living with Alzheimer’s disease (AD) – not a small task. Unfortunately, this number is predicted to more than triple by 2050, and with it so will healthcare costs and other burdens to society. The situation is dire enough that president Barack Obama signed a law last year that increased the amount of money to fund AD research, education, outreach, and caregiver support.

This weekend, a story was picked up in the news that brings hope for AD research. South China Morning Post covered a scientific study that claims it can reverse memory loss in mice with Alzheimer’s using a cell-based therapy. The study was published in Stem Cell Reports in mid October by a group of Chinese scientists.

Although the study is still in its early stages and the results are preliminary, what I like about it is its simplicity and logic. The authors decided to generate a type of nerve cell that is typically lost (or dysfunctional) in the brains of AD patients and some mouse models of AD. It’s called a basal forebrain cholinergic neuron, and it lives in an area near the bottom of our brains that’s responsible for processing certain functions such as learning and attention. The scientists proposed that they would replace these lost nerve cells in AD mice with healthy nerve cells derived from stem cells in hopes of restoring memory function.

How they did it

The authors first devised methods to make these specific nerve cells from both mouse and human embryonic stem cells in a dish. They were successful in making nerve cells that expressed the correct markers for cholinergic neurons and functioned properly, meaning they could send the correct electrical signals to other nerve cells.

The next step was to test the functionality of the nerve cells in mouse models of AD. Instead of transplanting adult nerve cells into the brain (which don’t survive very well), the authors transplanted progenitor cells, which developmentally, are more specialized than stem cells and eventually become adult nerve cells.

Untitled

Brain section from an Alzheimer’s mouse that received a transplant of progenitor cells (green) into the basal forebrain. (Yue et al., 2015)

When the mouse progenitor cells were transplanted into the basal forebrain of AD mice, most of them survived and matured into adult cholinergic nerve cells that were able to function in tandem with the original mouse nerve cells. When they transplanted human progenitor cells into the same area, a majority of the transplanted human cells did not survive (likely due to the mouse immune system rejecting them), however, the ones that did were able to turn into functioning cholinergic neurons.

Then came the final question, could the mouse and human progenitors improve the memory of these forgetful mice? The scientists compared the memories of AD mice that had received mouse or human cholinergic progenitor cells to AD mice that received no treatment and to healthy normal mice. The groups were put through a memory test where they were trained to find a hidden platform in a circular pool of water. Untreated AD mice had trouble finding the platform and couldn’t remember where it was in subsequent trials. However, the AD mice that received either mouse or human progenitor cell transplants six to eight weeks before were able to find the platform more quickly and remember where it was in multiple trials. This suggested that the transplanted nerve cells improved their ability to learn tasks and recall memories.

The water maze tests a mouse's ability to learn and recall where the hidden platform is. (Image adapted from Credit2M BioTech)

The water maze tests a mouse’s ability to learn and recall where the hidden platform is. (Image adapted from Credit2M BioTech)

Hold on: Primates before humans

So it seems from this study that replacing cholinergic nerve cells in the basal forebrain area of the brain is a potential approach to reversing memory loss in Alzheimer’s disease. However, the study’s senior author, Naihe Jing, cautioned everyone to not get ahead of themselves.

Dr. Naihe Jing, Shanghai Institutes of Biological Science

Dr. Naihe Jing

Mice are still very different from humans, so the results on mice do not guarantee the same success on human patients. Our next step is to test the method on primates. It will probably be a long time before clinical trials can be carried out on human volunteers.

 

But he also explained that his group is thoroughly testing the safety of their embryonic stem cell based therapy.

We used human embryonic stem cells because this method will eventually be used on humans. If the human neurons can get a footing and grow in the brain of a mouse, the chance is high the effect will be even better on a human host. The biggest concern of this development is safety. We were afraid that the transplanted cells would mutate to other types of neurons or even cause brain tumours. We have been improving the technology and making close observation of the mice for more than seven years. So far no mutation or cancerous development has been detected.

So while we might not have a cell therapy to treat Alzheimer’s in the near future, we can be comforted by the fact that groups like this one are taking all the precautions to develop safe and effective treatments.


Related Links:

Skipping a Step: Turning Brain Cells Directly into Neurons

It was once commonly believed that “what you see is what you get” with the human brain. As in, the brains cells that you are born with are the only ones you’ll have for the rest of your life because they can’t regenerate.

The discovery of brain stem cells in the late 90s disproved this notion and established that the brain can replace old cells and repair damage after injury. The brain’s regenerative capacity is limited, however. Consequently, patients suffering from neurodegenerative diseases like Alzheimer’s and Parkinson’s can’t rely on their brain stem cells to repopulate all of the sick and dying neurons in their brains.

This is where cellular reprogramming technology could come to the rescue. Induced pluripotent stem cells (iPSCs) generated from patient skin cells by cellular reprogramming can be turned into many types of brain cells to study diseases in a petri dish, as well as to test drugs and develop stem cell therapies. Eventually, the hope is to transplant iPSC-derived brain cells back into patient brains to treat or cure degenerative diseases.

Making neurons directly from other brain cells

Another form of cellular reprogramming, offers a more direct approach to generating populations of healthy brain cells. Using a similar technique to iPSCs, scientists can use specific factors to directly reprogram skin cells or other brain cells into neurons without making them go through the pluripotent stem cell state. By skipping a step in the reprogramming process, researchers save time, money, and energy – and it could result in safer cells.

The group used small molecules to directly reprogram human astrocytes into neurons that could be transplanted into mice. (Zhang et al., 2015)

The group used small molecules to directly reprogram human astrocytes into neurons that could be transplanted into mice. (Zhang et al., 2015)

While direct reprogramming of skin and non-neuronal brain cells into neurons has been published before, a study in Cell Stem Cell by a group at Penn State University last week described a new-and-improved method to make properly functioning neurons from brain astrocytes. Astrocytes are a type of glial cell that are abundant in the brain. They provide neurons with support, nutrients, and aid following injury.

Led by senior author Gong Chen, the group bathed human astrocytes in a cocktail of small molecules that turned the astrocytes into neurons in less than 10 days. These neurons survived in a dish for more than 5 months and were able to send electrical signals to each other (a sign that they were functional). Even more exciting was that the directly reprogrammed neurons survived and functioned properly when they were transplanted into the brains of mice.

When they studied the biological mechanism behind their direct reprogramming method, they found that the small molecule cocktail turned off the activity of astrocyte-specific genes in the astrocytes and turned on neuron-specific genes to convert them into neurons.

Human astrocytes (left) were directly reprogrammed into neurons (right). (Zhang et al., 2015)

Human astrocytes (left) were directly reprogrammed into neurons (right). (Zhang et al., 2015)

This discovery is great news for the reprogramming field as using small molecule reprogramming instead of the commonly used transcription-factor based reprogramming (which involves using viruses that can damage or alter the genome) is a more attractive method with broader applications­ for making neurons that can be transplanted into humans.

Direct reprogramming makes new neurons in the brain

But wait, there’s more! An article from TheScientist reported that multiple groups at the Society for Neuroscience (SFN) conference  in Chicago presented results on directly converting glial cells into neurons in mouse brains rather than in a dish.

One group from the Johannes Gutenberg University used two transcription factors, proteins that control which genes are turned on or off in the human genome, to directly reprogram mouse astrocytes into neurons. By producing more of Sox2 and Ascl1 in the cortex of the mouse brain than would normally be found there, they were able to turn 15% of the glial cells in that area into neurons.

The function of these directly reprogrammed neurons remains to be determined, but the lead scientist, Sophie Peron, told TheScientist:

“That’s the next step. Now that we have a system to get these cells converted we are currently studying their connectivity, functionality, and precise characteristics.”

Two other groups also reported similar findings when they worked with a type of glial cell called reactive astrocytes. These cells are specifically activated during injury to jumpstart the healing process. The first group from the University of Texas Southwestern used the factor Sox2 to directly reprogram reactive astrocytes into neurons in mice, while the group from Penn State University – mentioned earlier in this blog – did the same thing, but using a different factor, NeuroD1.

The Penn State group went further to test their direct reprogramming method in a mouse model of stroke and found that NeuroD1-reprogrammed neurons reduced cell death and tissue scarring after stroke.

Lead scientist Yuchen Chen said:

“These findings suggest that direct reprogramming of glial cells into functional neurons may provide a completely new approach for brain repair after stroke. Our next step is to analyze whether the glia-neuron conversion technology can facilitate functional recovery in stroke animals.”


Related Links:

Brain Stem Cells in a Dish to the Rescue

braindish

Image credit: CureCDKL5.org

The best way to impress your friends at the next party you attend might be to casually mention that scientists can grow miniature brain models in a dish using human stem cells. Sure, that might scare away some people, but when you explain how these tiny brain models can be used to study many different neurological diseases and could help identify new therapies to treat these diseases, your social status could sky rocket.

Recently, a group at UC San Diego used human stem cells to model a rare neurological disorder and identified a drug molecule that might be able to fix it. This work was funded in part by CIRM, and it was published today in the journal Molecular Psychiatry.

The disorder is called MECP2 duplication syndrome. It’s caused by a duplication of the MECP2 gene located in the X chromosome, and is genetically inherited as an X-linked disorder, meaning the disease is much more common in males. Having extra copies of this gene causes a number of unfortunate symptoms including reduced muscle tone (hypotonia), intellectual disabilities, impaired speech, seizures, and developmental delays, to name a few. So far, treatments for this disorder only help ease the symptoms and do not cure the disease.

The group from UCSD decided to model this disease using induced pluripotent stem cells (iPSCs) derived from patients with MECP2 duplication syndrome. iPSCs can form any cell type in the body, and the group used this to their advantage by coaxing the iPSCs into the specific type of nerve cell affected by the disorder. Their hard work was rewarded when they observed that the diseased nerve cells acted differently than normal nerve cells without the disease.

In fact, the diseased nerve cells generated more connections with other nearby nerve cells, and this altered their ability to talk to each other and perform their normal functions. The senior author Alysson Muotri described the difference as an “over-synchronization of the neuronal networks”, meaning that they were more active and tended to fire their signals in unison.

After establishing a relevant nerve cell model of MECP2 duplication disorder, the group tested out a library of drug molecules and identified a new drug candidate that was able to rescue the diseased nerve cells from their “over-synchronized” activity.

The senior author Alysson Muotri commented on the study in a press release:

Alysson Muotri (Photo by David Ahntholz)  

This work is encouraging for several reasons. First, this compound had never before been considered a therapeutic alternative for neurological disorders. Second, the speed in which we were able to do this. With mouse models, this work would likely have taken years and results would not necessarily be useful for humans.

 

The press release goes on to describe how Muotri and his team plan to push their preclinical studies using human stem-cell based models forward in hopes of entering clinical trials in the near future.


 

Related Links:

Building a Bridge to Therapies: Stem Cell-Derived Neurons Restore Feeling to Injured Limbs

It’s been a great week for spinal cord injury-related stem cell research – and it’s only Tuesday. In case you missed it, Asterias Biotherapeutics announced yesterday that they had treated their first clinical trial participant with an embryonic stem cell-based therapy for complete spinal cord injury. “Complete” refers to injuries that cause a total loss of feeling and movement below the site of injury.

Transplant human neurons (red) provide a bridge for the mice nerve fibers (green) to enter the spinal cord (spc). Image credit Hoeber et al. Scientific Reports

Transplanted human neurons (red) provide a bridge for the mice nerve fibers (green) to enter the spinal cord surface (spc). Image credit: Hoeber et al. Scientific Reports 5:10666

In another study also reported yesterday in Nature’s Scientific Reports, researchers at Uppsala University in Sweden made significant progress toward understanding and treating a related but different sort of injury that disrupts nerve signals coming into and out of the spinal cord. These so-called avulsion injuries are frequently seen after traffic, particularly motorcycle, accidents and lead to paralysis, loss of sensation, and chronic pain in the affected limbs. Although the ruptured nerve fibers from the limbs have the ability to extend back toward the spinal cord, inflammation from the site of injury makes the spinal cord impenetrable and blocks any restoration of normal sensory function.

To explore the potential of overcoming this spinal cord barrier, the research team transplanted human embryonic stem cell-derived neurons into mice mimicking human avulsion injury. Five months after the transplant, growth of nerve fibers into the spinal cord was seen. But these nerve fibers that had reconnected with the spinal cord were host animal cells and not the transplanted human stem cell-derived neurons. It turns out the human neuron fibers provide a physical bridge permitting the mouse nerve fibers to extend into the spinal cord. The human neurons also encourage this regrowth by releasing proteins that reduce the scar left by the injury and promote nerve fiber growth. The reconnected nerve fibers is an exciting result but did it have any impact on the animals? The answer is yes. Using standard behavior tests the team found that injured mice with the transplanted neurons had more sensitivity to touch stimulation and greater grip strength compared to untreated injured mice.

Because stem cells have the ability for unlimited growth, any future therapy based on these findings must shown that the transplant doesn’t lead to excessive cell growth. In an encouraging sign, no tumor formation or extreme growth of human neurons in the animals were observed.

Mutation Morphs Mitochondria in Models of Parkinson’s Disease, CIRM-Funded Study Finds

There is no singular cause of Parkinson’s disease, but many—making this disease so difficult to understand and, as a result, treat. But now, researchers at the Buck Institute for Research on Aging have tracked down precisely how a genetic change, or mutation, can lead to a common form of the disease. The results, published last week in the journal Stem Cell Reports, point to new and improved strategies at tackling the underlying processes that lead to Parkinson’s.

Mitochondria from iPSC-derived neurons. On the left is a neuron derived from a healthy individual, while the image on the right shows a neuron derived from someone with the Park2 mutation, the most common mutation in Parkinson's disease (Credit: Akos Gerencser)

Mitochondria from iPSC-derived neurons. On the left is a neuron derived from a healthy individual, while the image on the right shows a neuron derived from someone with the Park2 mutation, the most common mutation in Parkinson’s disease (Credit: Akos Gerencser)

The debilitating symptoms of Parkinson’s—most notably stiffness and tremors that progress over time, making it difficult for patients to walk, write or perform other simple tasks—can in large part be linked to the death of neurons that secrete the hormone dopamine. Studies involving fruit flies in the lab had identified mitochondria, cellular ‘workhorses’ that churn out energy, as a key factor in neuronal death. But this hypothesis had not been tested using human cells.

Now, scientists at the Buck Institute have replicated the process in human cells, with the help of stem cells derived from patients suffering from Parkinson’s, a technique called induced pluripotent stem cell technology, or iPSC technology. These newly developed neurons exactly mimic the disease at the cellular level. This so-called ‘disease in a dish’ is one of the most promising applications of stem cell technology.

“If we can find existing drugs or develop new ones that prevent damage to the mitochondria we would have a potential treatment for PD,” said Dr. Xianmin Zeng, the study’s senior author, in a press release.

And by using this technology, the Buck Institute team confirmed that the same process that occurred in fruit fly cells also occurred in human cells. Specifically, the team found that a particular mutation in these cells, called Park2, altered both the structure and function of mitochondria inside each cell, setting off a chain reaction that leads to the neurons’ inability to produce dopamine and, ultimately, the death of the neuron itself.

This study, which was funded in part by a grant from CIRM, could be critical in the search for a cure for a disease that, as of yet, has none. Current treatment regimens aimed at slowing or reducing symptoms have had some success, but most begin to fail overtime—or come with significant negative side effects. The hope, says Zeng, is that iPSC technology can be the key to fast-tracking promising drugs that can actually target the disease’s underlying causes, and not just their overt symptoms. Hear more from Dr. Xianmin Zeng as she answers your questions about Parkinson’s disease and stem cell research: