The present and future of regenerative medicine

One of the great pleasures of my job is getting to meet the high school students who take part in our SPARK or Summer Internship to Accelerate Regenerative Medicine Knowledge program. It’s a summer internship for high school students where they get to spend a couple of months working in a world class stem cell and gene therapy research facility. The students, many of whom go into the program knowing very little about stem cells, blossom and produce work that is quite extraordinary.

One such student is Tan Ieng Huang, who came to the US from China for high school. During her internship at U.C. San Francisco she got to work in the lab of Dr. Arnold Kriegstein. He is the Founding Director of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at the University of California, San Francisco. Not only did she work in his lab, she took the time to do an interview with him about his work and his thoughts on the field.

It’s a fascinating interview and shows the creativity of our SPARK students. You will be seeing many other examples of that creativity in the coming weeks. But for now, enjoy the interview with someone who is a huge presence in the field today, by someone who may well be a huge presence in the not too distant future.

‘a tête-à-tête with Prof. Arnold Kriegstein’

The Kriegstein lab team: Photo courtesy UCSF

Prof. Arnold Kriegstein is the Founding Director of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at the University of California, San Francisco. Prof. Kriegstein is also the Co-Founder and Scientific Advisor of Neurona Therapeutics which seeks to provide effective and safe cell therapies for chronic brain disorder. A Clinician by training, Prof. Kriegstein has been fascinated by the intricate workings of the human brain. His laboratory focuses on understanding the transcriptional and signaling networks active during brain development, the diversity of neuronal cell types, and their fate potential. For a long time, he has been interested in harnessing this potential for translational and therapeutic intervention.

During my SEP internship I had the opportunity to work in the Kriegstein lab. I was in complete awe. I am fascinated by the brain. During the course of two months, I interacted with Prof. Kriegstein regularly, in lab meetings and found his ideas deeply insightful. Here’s presenting some excerpts from some of our discussions, so that it reaches many more people seeking inspiration!

Tan Ieng Huang (TH): Can you share a little bit about your career journey as a scientist?

Prof. Arnold Kriegstein (AK): I wanted to be a doctor when I was very young, but in high school I started having some hands-on research experience. I just loved working in the lab. From then on, I was thinking of combining those interests and an MD/PhD turned out to be an ideal course for me. That was how I started, and then I became interested in the nervous system. Also, when I was in high school, I spent some time one summer at Rockefeller University working on a project that involved operant conditioning in rodents and I was fascinated by behavior and the role of the brain in learning and memory. That happened early on, and turned into an interest in cortical development and with time, that became my career.

TH: What was your inspiration growing up, what made you take up medicine as a career?

AK: That is a little hard to say, I have an identical twin brother. He and I used to always share activities, do things together. And early on we actually became eagle scouts, sort of a boy scout activity in a way. In order to become an eagle scout without having to go through prior steps, we applied to a special program that the scouts had, which allowed us to shadow physicians in a local hospital. I remember doing that at a very young age. It was a bit ironic, because one of the evenings, they showed us films of eye surgery, and my brother actually fainted when they made an incision in the eye. The reason it makes me laugh now is because my brother became an eye surgeon many years later. But I remember our early experience, we both became very fascinated by medicine and medical research.

Tan Ieng and Dr. Arnold Kriegstein at UCSF

TH: What inspired you to start the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research Institute?

AK: My interest in brain development over the years became focused on earlier stages of development and eventually Neurogenesis, you know, how neurons are actually generated during early stages of in utero brain development. In the course of doing that we discovered that the radial glial cells, which have been thought for decades to simply guide neurons as they migrate, turned out to actually be the neural stem cells, they were making the neurons and also guiding them toward the cortex. So, they were really these master cells that had huge importance and are now referred to as neural stem cells. But at that time, it was really before the stem cell field took off. But because we studied neurogenesis, because I made some contributions to understanding how the brain develops from those precursors or progenitor cells, when the field of stem cells developed, it was very simple for me to identify as someone who studied neural stem cells. I became a neural stem cell scientist. I started a neural stem cell program at Columbia University when I was a Professor there and raised 15 million dollars to seed the program and hired new scientists. It was shortly after that I was approached to join UCSF as the founder of a new stem cell program. And it was much broader than the nervous system; it was a program that covered all the different tissues and organ systems.

TH: Can you tell us a little bit about how stem cell research is contributing to the treatment of diseases? How far along are we in terms of treatments?

AK: It’s taken decades, but things are really starting to reach the clinic now. The original work was basic discovery done in research laboratories, now things are moving towards the clinic. It’s a really very exciting time. Initially the promise of stem cell science was called Regenerative medicine, the idea of replacing injured or worn-out tissues or structures with new cells and new tissues, new organs, the form of regeneration was made possible by understanding that there are stem cells that can be tweaked to actually help make new cells and tissues. Very exciting process, but in fact the main progress so far hasn’t been replacing worn out tissues and injured cells, but rather understanding diseases using human based model of disease. That’s largely because of the advent of induced pluripotent stem cells, a way of using stem cells to make neurons or heart cells or liver cells in the laboratory, and study them both in normal conditions during development and in disease states. Those platforms which are relatively easy to make now and are pretty common all over the world allow us to study human cells rather than animal cells, and the hope is that by doing that we will be able to produce conventional drugs and treatments that work much better than ones we had in the past, because they will be tested in actual human cells rather than animal cells.

TH: That is a great progress and we have started using human models because even though there are similarities with animal models, there are still many species-specific differences, right?

AK: Absolutely, in fact, one of the big problems now in Big Pharma, you know the drug companies, is that they invest millions and sometimes hundreds of millions of dollars in research programs that are based on successes in treating mice, but patients don’t respond the same way. So the hope is that by starting with a treatment that works on human cells it might be more likely that the treatment will work on human patients.

TH: What are your thoughts on the current challenges and future of stem cell research?

AK: I think this is an absolute revolution in modern medicine, the advent of two things that are happening right now, first the use of induced pluripotent stem cells, the ability to make pluripotent cells from adult tissue or cells from an individual allows us to use models of diseases that I mentioned earlier from actual patients. That’s one major advance. And the other is gene editing, and the combination of gene editing and cell-based discovery science allows us to think of engineering cells in ways that can make them much more effective as a form of cell therapy and those cell therapies have enormous promise. Right now, they are being used to treat cancer, but in the future, they might be able to treat heart attack, dementia, neurodegenerative diseases, ALS, Parkinson’s disease, a huge list of disorders that are untreatable right now or incurable. They might be approached by the combination of cell-based models, cell therapies, and gene editing.

TH: I know there are still some challenges right now, like gene editing has some ethical issues because people don’t know if there can be side effects after the gene editing, what are your thoughts?

AK: You know, like many other technologies there are uncertainties, and there are some issues. Some of the problems are off-target effects, that is you try to make a change in one particular gene, and while doing that you might change other genes in unexpected ways and cause complications. But we are understanding that more and more now and can make much more precise gene editing changes in just individual genes without affecting unanticipated areas of the genome. And then there are also the problems of how to gene-edit cells in a safe way. There are certain viral factors that can be used to introduce the gene editing apparatus into a cell, and sometimes if you are doing that in a patient, you can also have unwanted side effects from the vectors that you are using, often they are modified viral vectors. So, things get complicated very quickly when you start trying to treat patients, but I think these are all tractable problems and I think in time they will all be solved. It will be a terrific, very promising future when it comes to treating patients who are currently untreatable.

TH: Do you have any advice for students who want to get into this field?

AK: Yes, I think it’s actually never been a better time and I am amazed by the technologies that are available now. Gene editing that I mentioned before but also single cell approaches, the use of single cell multiomics revealing gene expression in individual cells, the molecular understanding of how individual cells are formed, how they are shaped, how they change from one stage to another, how they can be forced into different fates. It allows you to envision true Regenerative medicine, improving health by healing or replacing injured or diseased tissues. I think this is becoming possible now, so it’s a very exciting time. Anyone who has an interest in stem cell biology or new ways of treating diseases, should think about getting into a laboratory or a clinical setting. I think this time is more exciting than it’s ever been.

TH: So excited to hear that, because in school we have limited access to the current knowledge, the state-of-art. I want to know what motivates you every day to do Research and contribute to this field?

AK: Well, you know that I have been an MD/PhD, as I mentioned before, in a way, there are two different reward systems at play. In terms of the PhD and the science, it’s the discovery part that is so exciting. Going in every day and thinking that you might learn something that no one has ever known before and have a new insight into a mechanism of how something happens, why it happens. Those kinds of new insights are terrifically satisfying, very exciting. On the MD side, the ability to help patients and improve peoples’ lives is a terrific motivator. I always wanted to do that, was very driven to become a Neurologist and treat both adult and pediatric patients with neurological problems. In the last decade or so, I’ve not been treating patients so much, and have focused on the lab, but we have been moving some of our discoveries from the laboratory into the clinic. We have just started a clinical trial, of a new cell-based therapy for epilepsy in Neurona Therapeutics, which is really exciting. I am hoping it will help the patients but it’s also a chance to actually see something that started out as a project in the laboratory become translated into a therapy for patients, so that’s an achievement that has really combined my two interests, basic science, and clinical medicine. It’s a little late in life but not too late, so I’m very excited about that.

Tan Ieng Huang, Kriegstein Lab, SEP Intern, CIRM Spark Program 2022

Stem Cell Roundup: watching brain cells in real time, building better heart cells, and the plot thickens on the adult neurogenesis debate

Here are the stem cell stories that caught our eye this week.

Watching brain cells in real time

This illustration depicts a new method that enables scientists to see an astrocyte (green) physically interacting with a neuronal synapse (red) in real time, and producing an optical signal (yellow). (Khakh Lab, UCLA Health)

Our stem cell photo of the week is brought to you by the Khakh lab at UCLA Health. The lab developed a new method that allows scientists to watch brain cells interact in real time. Using a technique called fluorescence resonance energy-transfer (FRET) microscopy, the team can visualize how astrocytes (key support cells in our central nervous system) and brain cells called neurons form connections in the mouse brain and how these connections are affected by diseases like Alzheimer’s and ALS.

Baljit Khakh, the study’s first author, explained the importance of their findings in a news release:

“This new tool makes possible experiments that we have been wanting to perform for many years. For example, we can now observe how brain damage alters the way that astrocytes interact with neurons and develop strategies to address these changes.”

The study was published this week in the journal Neuron.


Turn up the power: How to build a better heart cell (Todd Dubnicoff)

For years now, researchers have had the know-how to reprogram a donor’s skin cells into induced pluripotent stem cells (iPSCs) and then specialize them into heart muscle cells called cardiomyocytes. The intervening years have focused on optimizing this method to accurately model the biology of the adult human heart as a means to test drug toxicity and ultimately develop therapies for heart disease. Reporting this week in Nature, scientists at Columbia University report an important step toward those goals.

The muscle contractions of a beating heart occur through natural electrical impulses generated by pacemaker cells. In the case of lab-grown cardiomyocytes, introducing mechanical and electrical stimulation is required to reliably generate these cells. In the current study, the research team showed that the timing and amount of stimulation is a critical aspect to the procedure.

The iPS-derived cardiomyocytes have formed heart tissue that closely mimics human heart functionality at over four weeks of maturation. Credit: Gordana Vunjak-Novakovic/Columbia University.

The team tested three scenarios on iPSC-derived cardiomyocytes (iPSC-CMs): no electrical stimulation for 3 weeks, constant stimulation for 3 weeks, and finally, two weeks of increasingly higher stimulation followed by a week of constant stimulation. This third setup mimics the changes that occur in a baby’s heart just before and just after birth.

These scenarios were tested in 12 day-old and 28 day-old iPSC-CMs. The results show that only the 12 day-old cells subjected to the increasing amounts of stimulation gave rise to fully mature heart muscle cells. On top of that, it only took four weeks to make those cells. Seila Selimovic, Ph.D., an expert at the National Institutes of Health who was not involved in the study, explained the importance of these findings in a press release:

“The resulting engineered tissue is truly unprecedented in its similarity to functioning human tissue. The ability to develop mature cardiac tissue in such a short time is an important step in moving us closer to having reliable human tissue models for drug testing.”

Read more at: https://phys.org/news/2018-04-early-bioengineered-human-heart-cells.html#jCp


Yes we do, no we don’t. More confusion over growing new brain cells as we grow older (Kevin McCormack)

First we didn’t, then we did, then we didn’t again, now we do again. Or maybe we do again.

The debate over whether we are able to continue making new neurons as we get older took another twist this week. Scientists at Columbia University said their research shows we do make new neurons in our brain, even as we age.

This image shows what scientists say is a new neuron in the brain of an older human. A new study suggests that humans continue to make new neurons throughout their lives. (Columbia University Irving Medical Center)

In the study, published in the journal Cell Stem Cell, the researchers examined the brains of 28 deceased donors aged 14 to 79. They found similar numbers of precursor and immature neurons in all the brains, suggesting we continue to develop new brain cells as we age.

This contrasts with a UCSF study published just last month which came to the opposite conclusion, that there was no evidence we make new brain cells as we age.

In an interview in the LA Times, Dr. Maura Boldrini, the lead author on the new study, says they looked at a whole section of the brain rather than the thin tissues slices the UCSF team used:

“In science, the absence of evidence is not evidence of absence. If you can’t find something it doesn’t mean that it is not there 100%.”

Well, that resolves that debate. At least until the next study.

New Insights into Adult Neurogenesis

To be a successful scientist, you have to expect the unexpected. No biological process or disease mechanism is ever that simple when you peel off its outer layers. Overtime, results that prove a long-believed theory can be overturned by new results that suggest an alternate theory.

UCSF scientist Arturo Alvarez-Buylla is well versed with the concept of unexpected results. His lab’s research is focused on understanding adult neurogenesis – the process of creating new nerve cells (called neurons) from neural stem cells (NSCs).

For a long time, the field of adult neurogenesis has settled on the theory that brain stem cells divide asymmetrically to create two different types of cells: neurons and neural stem cells. In this way, brain stem cells populate the brain with new neurons and they also self-renew to maintain a constant stem cell supply throughout the adult animal’s life.

New Insights into Adult Neurogenesis

Last week, Alvarez-Buylla and his colleagues published new insights on adult neurogenesis in mice in the journal Cell Stem Cell. The study overturns the original theory of asymmetrical neural stem cell division and suggests that neural stem cells divide in a symmetrical fashion that could eventually deplete their stem cell population over the lifetime of the animal.

Arturo Alvarez-Buylla explained the study’s findings in an email interview with the Stem Cellar:

Arturo Alvarez-Bulla

“Our results are not what we expected. Our work shows that postnatal NSCs are not being constantly renewed by splitting them asymmetrically, with one cell remaining as a stem cell and the other as a differentiated cell. Instead, self-renewal and differentiation are decoupled and achieved by symmetric divisions.”

In brief, the study found that neural stem cells (called B1 cells) divide symmetrically in an area of the adult mouse brain called the ventricular-subventricular zone (V-SVZ). Between 70%-80% of those symmetric divisions produced neurons while only 20%-30% created new B1 stem cells. Alvarez-Buylla said that this process would result in the gradual depletion of B1 stem cells over time and seems to be carefully choreographed for the length of the lifespan of a mouse.

What does this mean?

I asked Alvarez-Buylla how his findings in mice will impact the field and whether he expects human adult neurogenesis to follow a similar process. He explained,

“The implications are quite wide, as it changes the way we think about neural stem cell retention and aging. The cells do not seem open ended with unlimited potential to be renewed, which results in a progressive decrease in NSC number and neurogenesis with time.  Understanding the mechanisms regulating proliferation of NSCs and their self-renewal also provides new insights into how the whole process of neurogenesis is choreographed over long periods by suggesting that differentiation (generation of neurons) is regulated separately from renewal.”

He further explained that mice generate new neurons in the V-SVZ brain region throughout their lifetime while humans only appear to generate new neurons during infancy in the equivalent region of the human brain called the SVZ. In humans, he said, it remains unclear where and how many neural stem cells are retained after birth.

I also asked him how these findings will impact the development of neural stem cell-based therapies for neurological or neurodegenerative diseases. Alvarez-Buylla shared interesting insights:

“Our data also indicate that upon a self-renewing division, sibling NSCs may not be equal to each other. While one NSC might stay quiescent [non-dividing] for an extended period of time, its sister cell might become activated earlier on and either undergo another round of self-renewal or differentiate. Thus, for cell-replacement therapies it will be important to understand which kind of neuron the NSC of interest can produce, and when. The use of NSCs for brain repair requires a detailed understanding of which NSC subset will be utilized for treatment and how to induce them to produce progeny. The study also suggests that factors that control NSC renewal may be separate from those that control generation of neurons.”

Scientists developing adult NSC-based therapies will definitely need to take note of Alvarez-Buylla’s findings as some NSC populations might be more successful therapeutically than others.

Neural Stem Cells in the Wild

I’ll conclude with a beautiful image that the study’s first author, Kirsten Obernier, shared with me. It’s shows the V-SVZ of the mouse brain and a neural stem cell in red making contact with a blood vessel in green and neurons in blue.

Image of the mouse brain with a neural stem cell in red. (Credit: Kirsten Obernier, UCSF)

Kirsten described the complex morphology of B1 NSCs in the mouse brain and their dynamic behavior, which Kirsten observed by taking a time lapsed video of NSCs dividing in the mouse V-SVZ. Obernier and Alvarez-Buylla hypothesize that these NSCs could be receiving signals from their surrounding environment that tell them whether to make neurons or to self-renew.

Clearly, further research is necessary to peel back the complex layers of adult neurogenesis. If NSC differentiation is regulated separately from self-renewal, their insights could shed new light on how conditions of unregulated self-renewal like brain tumors develop.

Avalanches of exciting new stem cell research at the Keystone Symposia near Lake Tahoe

From January 8th to 13th, nearly 300 scientists and trainees from around the world ascended the mountains near Lake Tahoe to attend the joint Keystone Symposia on Neurogenesis and Stem Cells at the Resort at Squaw Creek. With record-high snowfall in the area (almost five feet!), attendees had to stay inside to stay warm and dry, and even when we lost power on the third day on the mountain there was no shortage of great science to keep us entertained.

Boy did it snow at the Keystone Conference in Tahoe!

Boy did it snow at the Keystone Conference in Tahoe!

One of the great sessions at the meeting was a workshop chaired by CIRM’s Senior Science Officer, Dr. Kent Fitzgerald, called, “Bridging and Understanding of Basic Science to Enable/Predict Clinical Outcome.” This workshop featured updates from the scientists in charge of three labs currently conducting clinical trials funded and supported by CIRM.

Regenerating injured connections in the spinal cord with neural stem cells

Mark Tuszynski, UCSD

Mark Tuszynski, UCSD

The first was a stunning talk by Dr. Mark from UCSD who is investigating how neural stem cells can help outcomes for those with spinal cord injury. The spinal cord contains nerves that connect your brain to the rest of your body so you can sense and move around in your environment, but in cases of severe injury, these connections are cut and the signal is lost. The most severe of these injuries is a complete transection, which is when all connections have been cut at a given spot, meaning no signal can pass through, just like how no cars could get through if a section of the Golden Gate Bridge was missing. His lab works in animal models of complete spinal cord transections since it is the most challenging to repair.

As Dr. Tuszynski put it, “the adult central nervous system does not spontaneously regenerate [after injury], which is surprising given that it does have its own set of stem cells present throughout.” Their approach to tackle this problem is to put in new stem cells with special growth factors and supportive components to let this process occur.

Just as most patients wouldn’t be able to come in for treatment right away after injury, they don’t start their tests until two weeks after the injury. After that, they inject neural stem cells from either the mouse, rat, or human spinal cord at the injury site and then wait a bit to see if any new connections form. Their group has shown very dramatic increases in both the number of new connections that regenerate from the injury site and extend much further than previous efforts have shown. These connections conduct electrochemical messages as normal neurons do, and over a year later they see no functional decline or tumors forming, which is often a concern when transplanting stem cells that normally like to divide a lot.

While very exciting, he cautions, “this research shows a major opportunity in neural repair that deserves proper study and the best clinical chance to succeed”. He says it requires thorough testing in multiple animal models before going into humans to avoid a case where “a clinical trial fails, not because the biology is wrong, but because the methods need tweaking.”

Everyone needs support – even dying cells

The second great talk was by Dr. Clive Svendsen of Cedars-Sinai Regenerative Medicine Institute on how stem cells might help provide healthy support cells to rescue dying neurons in the brains of patients with neurodegenerative diseases like Amyotrophic Lateral Sclerosis (ALS) and Parkinson’s. Some ALS cases are hereditary and would be candidates for a treatment using gene editing techniques. However, around 90 percent of ALS cases are “sporadic” meaning there is no known genetic cause. Dr. Svendsen explained how in these cases, a stem cell-based approach to at least fix the cellular cause of the disease, would be the best option.

While neurons often capture all the attention in the brain, since they are the cells that actually send messages that underlie our thoughts and behaviors, the Svendsen lab spends a great deal of time thinking about another type of cell that they think will be a powerhouse in the clinic: astrocytes. Astrocytes are often labeled as the support cells of the brain as they are crucial for maintaining a balance of chemicals to keep neurons healthy and functioning. So Dr. Svendsen reasoned that perhaps astrocytes might unlock a new route to treating neurodegenerative diseases where neurons are unhealthy and losing function.

ALS is a devastating disease that starts with early muscle twitches and leads to complete paralysis and death usually within four years, due to the rapid degeneration of motor neurons that are important for movement all over the body. Svendsen’s team found that by getting astrocytes to secrete a special growth factor, called “GDNF”, they could improve the survival of the neurons that normally die in their model of ALS by five to six times.

After testing this out in several animal models, the first FDA-approved trial to test whether astrocytes from fetal tissue can slow spinal motor neuron loss will begin next month! They will be injecting the precursor cells that can make these GDNF-releasing astrocytes into one leg of ALS patients. That way they can compare leg function and track whether the cells and GDNF are enough to slow the disease progression.

Dr. Svendsen shared with us how long it takes to create and test a treatment that is committed to safety and success for its patients. He says,

Clive Svendsen has been on a 15-year quest to develop an ALS therapy

Clive Svendsen 

“We filed in March 2016, submitted the improvements Oct 2016, and we’re starting our first patient in Feb 2017. [One document is over] 4500 pages… to go to the clinic is a lot of work. Without CIRM’s funding and support we wouldn’t have been able to do this. This isn’t easy. But it is doable!”

 

Improving outcomes in long-term stroke patients in unknown ways

Gary Steinberg

Gary Steinberg

The last speaker for the workshop, Dr. Gary Steinberg, a neurosurgeon at Stanford who is looking to change the lives of patients with severe limitations after having a stroke. The deficits seen after a stroke are thought to be caused by the death of neurons around the area where the stroke occurred, such that whatever functions they were involved with is now impaired. Outcomes can vary for stroke patients depending on how long it takes for them to get to the emergency department, and some people think that there might be a sweet spot for when to start rehabilitative treatments — too late and you might never see dramatic recovery.

But Dr. Steinberg has some evidence that might make those people change their mind. He thinks, “these circuits are not irreversibly damaged. We thought they were but they aren’t… we just need to continue figuring out how to resurrect them.”

He showed stunning videos from his Phase 1/2a clinical trial of several patients who had suffered from a stroke years before walking into his clinic. He tested patients before treatment and showed us videos of their difficulty to perform very basic movements like touching their nose or raising their legs. After carefully injecting into the brain some stem cells taken from donors and then modified to boost their ability to repair damage, he saw a dramatic recovery in some patients as quickly as one day later. A patient who couldn’t lift her leg was holding it up for five whole seconds. She could also touch her arm to her nose, whereas before all she could do was wiggle her thumb. One year later she is even walking, albeit slowly.

He shared another case of a 39 year-old patient who suffered a stroke didn’t want to get married because she felt she’d be embarrassed walking down the aisle, not to mention she couldn’t move her arm. After Dr. Steinberg’s trial, she was able to raise her arm above her head and walk more smoothly, and now, four years later, she is married and recently gave birth to a boy.

But while these studies are incredibly promising, especially for any stroke victims, Dr. Steinberg himself still is not sure exactly how this stem cell treatment works, and the dramatic improvements are not always consistent. He will be continuing his clinical trial to try to better understand what is going on in the injured and recovering brain so he can deliver better care to more patients in the future.

The road to safe and effective therapies using stem cells is long but promising

These were just three of many excellent presentations at the conference, and while these talks involved moving science into human patients for clinical trials, the work described truly stands on the shoulders of all the other research shared at conferences, both present and past. In fact, the reason why scientists gather at conferences is to give one another feedback and to learn from each other to better their own work.

Some of the other exciting talks that are surely laying down the framework for future clinical trials involved research on modeling mini-brains in a dish (so-called cerebral organoids). Researchers like Jürgen Knoblich at the Institute of Molecular Biotechnology in Austria talked about the new ways we can engineer these mini-brains to be more consistent and representative of the real brain. We also heard from really fundamental biology studies trying to understand how one type of cell becomes one vs. another type using the model organism C. elegans (a microscopic, transparent worm) by Dr. Oliver Hobert of Columbia University. Dr. Austin Smith, from the University of Cambridge in the UK, shared the latest about the biology of pluripotent cells that can make any cell type, and Stanford’s Dr. Marius Wernig, one of the meeting’s organizers, told us more of what he’s learned about the road to reprogramming an ordinary skin cell directly into a neuron.

Stay up to date with the latest research on stem cells by continuing to follow this blog and if you’re reading this because you’re considering a stem cell treatment, make sure you find out what’s possible and learn about what to ask by checking out closerlookatstemcells.org.


Samantha Yammine

Samantha Yammine

Samantha Yammine is a science communicator and a PhD candidate in Dr. Derek van der Kooy’s lab at the University of Toronto. You can learn more about Sam and her research on her website.

Salk Scientists Unlock New Secrets of Autism Using Human Stem Cells

Autism is a complex neurodevelopmental disorder whose mental, physical, social and emotional symptoms are highly variable from person to person. Because individuals exhibit different combinations and severities of symptoms, the concept of autism spectrum disorder (ASD) is now used to define the range of conditions.

There are many hypotheses for why autism occurs in humans (which some estimates suggest now affects around 3.5 million people in the US). Some of the disorders are thought to be at the cellular level, where nerve cells do not develop normally and organize properly in the brain, and some are thought to be at the molecular level where the building blocks in cells don’t function properly. Scientists have found these clues by using tools such as studying human genetics and animal models, imaging the brains of ASD patients, and looking at the pathology of ASD brains to see what has gone wrong to cause the disease.

Unfortunately, these tools alone are not sufficient to recreate all aspects of ASD. This is where cellular models have stepped in to help. Scientists are now developing human stem cell derived models of ASD to create “autism in a dish” and are finding that the nerve cells in these models show characteristics of these disorders.

Stem cell models of autism and ASD

We’ve reported on some of these studies in previous blogs. A group from UCSD lead by CIRM grantee Alysson Muotri used induced pluripotent stem cells or iPS cells to model non-syndromic autism (where autism is the primary diagnosis). The work has been dubbed the “Tooth Fairy Project” – parents can send in their children’s recently lost baby teeth which contain cells that can be reprogrammed into iPS cells that can then be turned into brain cells that exhibit symptoms of autism. By studying iPS cells from individuals with non-syndromic autism, the team found a mutation in the TRPC6 gene that was linked to abnormal brain cell development and function and is also linked to Rett syndrome – a rare form of autism predominantly seen in females.

Another group from Yale generated “mini-brains” or organoids derived from the iPS cells of ASD patients. They specifically found that ASD mini-brains had an increased number of a type of nerve cell called inhibitory neurons and that blocking the production of a protein called FOXG1 returned these nerve cells back to their normal population count.

Last week, a group from the Salk Institute in collaboration with scientists at UC San Diego published findings about another stem cell model for ASD that offers new clues into the early neurodevelopmental defects seen in ASD patients.  This CIRM-funded study was led by senior author Rusty Gage and was published last week in the Nature journal Molecular Psychiatry.

Unlocking clues to autism using patient stem cells

Gage and his team were fascinated by the fact that as many as 30 percent of people with ASD experience excessive brain growth during early in development. The brains of these patients have more nerve cells than healthy individuals of the same age, and these extra nerve cells fail to organize properly and in some cases form too many nerve connections that impairs their overall function.

To understand what is going wrong in early stages of ASD, Gage generated iPS cells from ASD individuals who experienced abnormal brain growth at an early age (their brains had grown up to 23 percent faster when they were toddlers compared to normal toddlers). They closely studied how these ASD iPS cells developed into brain stem cells and then into nerve cells in a dish and compared their developmental progression to that of healthy iPS cells from normal individuals.

Neurons derived from people with ASD (bottom) form fewer inhibitory connections (red) compared to those derived from healthy individuals (top panel). (Salk Institute)

Neurons derived from people with ASD (bottom) form fewer inhibitory connections (red) compared to those derived from healthy individuals (top panel). (Salk Institute)

They quickly observed a problem with neurogenesis – a term used to describe how brain stem cells multiply and create new nerve cells in the brain. Brain stem cells derived from ASD iPS cells displayed more neurogenesis than normal brain stem cells, and thus were creating an excess amount of nerve cells. The scientists also found that the extra nerve cells failed to form as many synaptic connections with each other, an essential process that allows nerve cells to send signals and form a functional network of communication, and also behaved abnormally and overall had less activity compared to healthy neurons. Interestingly, they saw fewer inhibitory neuron connections in ASD neurons which is contrary to what the Yale study found.

The abnormal activity observed in ASD neurons was partially corrected when they treated the nerve cells with a drug called IGF-1, which is currently being tested in clinical trials as a possible treatment for autism. According to a Salk news release, “the group plans to use the patient cells to investigate the molecular mechanisms behind IGF-1’s effects, in particular probing for changes in gene expression with treatment.”

Will stem cells be the key to understanding autism?

It’s clear that human iPS cell models of ASD are valuable in helping tease apart some of the mechanisms behind this very complicated group of disorders. Gage’s opinion is that:

“This technology allows us to generate views of neuron development that have historically been intractable. We’re excited by the possibility of using stem cell methods to unravel the biology of autism and to possibly screen for new drug treatments for this debilitating disorder.”

However, to me it’s also clear that different autism stem cell models yield different results, but these differences are likely due to which populations the iPS cells are derived from. Creating more cell lines from different ASD subpopulations will surely answer more questions about the developmental differences and differences in brain function seen in adults.

Lastly, one of the co-authors on the study, Carolina Marchetto, made a great point in the Salk news release by acknowledging that their findings are based on studying cells in a dish, not actual patient’s brains. However, Marchetto believes that these cells are useful tools for studying autism:

“It never fails to amaze me when we can see similarities between the characteristics of the cells in the dish and the human disease.”

Rusty Gage and Carolina Marchetto. (Salk Institute)

Rusty Gage and Carolina Marchetto. (Salk Institute)


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