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

Raising awareness about mental health

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World Mental Health Day is observed on 10 October every year. It’s a time to try and raise awareness about mental health issues and the impact they have not just on the individual but their family, their community and all of us. The theme for World Mental Health Day 2021 is ‘mental health in an unequal world.’

Dr. Le Ondra Clark Harvey: Photo courtesy CCCBHA

To highlight the issues raised on World Mental Health Day we talked to one of CIRM’s newest Board member, Dr. Le Ondra Clark Harvey. She’s a psychologist and the CEO of the California Council of Community Behavioral Health Agencies (CCCBHA) a statewide advocacy organization representing mental health and substance use disorder non-profit agencies that collectively serve over 750 thousand Californians annually.

What made you want to be on the CIRM Board?

I was recommended to apply for the CIRM Board by a member of CCCBHA, the organization I am privileged to lead and serve. I saw the position as an opportunity to shed light on cognitive disorders that many do not readily think of when they think about stem cell research. The appointment also has personal meaning to me as I have a grandfather who is a cancer survivor and  who has an Alzheimer’s diagnosis.  Breast cancer has also affected women in my family, including myself, and I know that the research that CIRM funds can assist with finding a cure and providing accessible treatment options for all Californians. 

A lot of people might not think that stem cells would have a role in addressing mental health issues, what role do you think they can play?

You are correct, most people do not immediately think of stem cell therapies as a remedy to brain health disorders. However, there are many cognitive disorders and symptoms that can be mitigated, and hopefully someday ameliorated, as a result of stem cell therapies. For example, autism and other developmental disabilities, dementia, Alzheimer’s, Tourette’s and tardive dyskinesia.  

What are the biggest challenges we face in addressing mental health issues in this country?

Stigma remains a significant barrier that impacts the ability to provide – particularly among racially and ethnically diverse communities. In my own practice, I’ve seen how stigma can prevent individuals from entering into care even when access issues have been mitigated. Public awareness campaigns, and culturally specific advocacy efforts and practices must be integrated into treatment models in order to provide individuals with the specific care they need. 

Do you think that the widespread media attention paid to Naomi Osaka and Simone Biles has helped raise awareness about mental health and perhaps also reduced some of the stigma surrounding it?

Yes, I do. Also, the pandemic has opened many individuals eyes, and engendered a sense of empathy, about the prevalence and impact that isolation and loneliness can have on a person. 

Lack of diversity impacts research into Alzheimer’s and dementia

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A National Institutes of Allergy and Infectious Diseases clinical trial admissions coordinator collects information from a volunteer to create a medical record. Credit: NIAID

Alzheimer’s research has been in the news a lot lately, and not for the right reasons. The controversial decision by the Food and Drug Administration (FDA) to approve the drug Aduhelm left many people wondering how, when, or even if it should be used on people battling Alzheimer’s disease. Now a new study is raising questions about many of the clinical trials used to test medications like Aduhelm.

The research, published in the journal Jama Neurology, looked at 302 studies on dementia published in 2018 and 2019. Most of these studies were carried out in North America or Europe, and almost 90 percent of those studied were white.

In an accompanying editorial in the journal, Dr. Cerise Elliott, PhD, of the National Institute on Aging (NIA) in Bethesda, Maryland, and co-authors wrote that this limited the value of the studies: “This, combined with the fact that only 22% of the studies they analyzed even reported on race and ethnicity, and of those, a median 89% of participants were white, reflects the fact that recruitment for research participation is challenging; however, it is unacceptable that studies continue to fail to report participant demographics and that publishers allow such omissions.”

That bias is made all the more glaring by the fact that recent data from the Centers for Disease Control and Prevention shows that among people 65 and older, the Black community has the highest prevalence of Alzheimer’s disease and related dementias (13.8%), followed by Latinx (12.2%), non-Hispanic white (10.3%), American Indian and Alaskan Native (9.1%), and Asian and Pacific Islander (8.4%) populations.

The researchers admitted that the limited sample size – more than 40 percent of the studies they looked at included fewer than 50 patients – could have impacted their findings. Even so this clearly suggests there is a huge divide between the people at greatest risk of developing Alzheimer’s, or some other form of dementia, and the people being studied.

In the editorial, Elliott and his colleagues wrote that without a more diverse and balanced patient population this kind of research: “will continue to underrepresent people most affected by the disease and perpetuate systems that exclude important valuable knowledge about the disease.”


There are more details on this in Medpage Today.

An editorial in the New England Journal of Medicine highlights how this kind of bias is all too common in medical research.

“For years, the Journal has published studies that simply do not include enough participants from the racial and ethnic groups that are disproportionately affected by the illnesses being studied to support any conclusions about their treatment. In the United States, for example, Black Americans have high rates of hypertension and chronic kidney disease, Hispanic Americans have the highest prevalence of nonalcoholic fatty liver disease, Native Americans are disproportionately likely to have metabolic syndrome, and Asian Americans are at particular risk for hepatitis B infection and subsequent cirrhosis, but these groups are frequently underrepresented in clinical trials and cohort studies.”

“For too long, we have tolerated conditions that actively exclude groups from critical resources in health care delivery, research, and education. This exclusion has tragic consequences and undermines confidence in the institutions and the people who are conducting biomedical research. And clinicians cannot know how to optimally prevent and treat disease in members of communities that have not been studied.”

The encouraging news is that, finally, people are recognizing the problem and trying to come up with ways to correct it. The not so encouraging is that it took a pandemic to get us to pay attention.

At CIRM we are committed to being part of the solution. We are now requiring everyone who applies to us for funding to have a written plan on Diversity, Equity and Inclusion, laying out how their work will reflect the diversity of California. We know this will be challenging for all of us. But the alternative, doing nothing, is no longer acceptable.

Paving the way for a treatment for dementia

What happens in a stroke

When someone has a stroke, the blood flow to the brain is blocked. This kills some nerve cells and injures others. The damaged nerve cells are unable to communicate with other cells, which often results in people having impaired speech or movement.

While ischemic and hemorrhagic strokes affect large blood vessels and usually produce recognizable symptoms there’s another kind of stroke that is virtually silent. A ‘white’ stroke occurs in blood vessels so tiny that the impact may not be noticed. But over time that damage can accumulate and lead to a form of dementia and even speed up the progression of Alzheimer’s disease.

Now Dr. Tom Carmichael and his team at the David Geffen School of Medicine at UCLA have developed a potential treatment for this, using stem cells that may help repair the damage caused by a white stroke. This was part of a CIRM-funded study (DISC2-12169 – $250,000).

Instead of trying to directly repair the damaged neurons, the brain nerve cells affected by a stroke, they are creating support cells called astrocytes, to help stimulate the body’s own repair mechanisms.

In a news release, Dr. Irene Llorente, the study’s first author, says these astrocytes play an important role in the brain.

“These cells accomplish many tasks in repairing the brain. We wanted to replace the cells that we knew were lost, but along the way, we learned that these astrocytes also help in other ways.”

The researchers took skin tissue and, using the iPSC method (which enables researchers to turn cells into any other kind of cell in the body) turned it into astrocytes. They then boosted the ability of these astrocytes to produce chemical signals that can stimulate healing among the cells damaged by the stroke.

These astrocytes were then not only able to help repair some of the damaged neurons, enabling them to once again communicate with other neurons, but they also helped another kind of brain cell called oligodendrocyte progenitor cells or OPCs. These cells help make a protective sheath around axons, which transmit electrical signals between brain cells. The new astrocytes stimulated the OPCs into repairing the protective sheath around the axons.

Mice who had these astrocytes implanted in them showed improved memory and motor skills within four months of the treatment.  

And now the team have taken this approach one step further. They have developed a method of growing these astrocytes in large amounts, at very high quality, in a relatively short time. The importance of that is it means they can produce the number of cells needed to treat a person.

“We can produce the astrocytes in 35 days,” Llorente says. “This process allows rapid, efficient, reliable and clinically viable production of our therapeutic product.”

The next step is to chat with the Food and Drug Administration (FDA) to see what else they’ll need to do to show they are ready for a clinical trial.

The study is published in the journal Stem Cell Research.

Scientists use stem cell ‘mini-brains’ to better understand signs of frontotemporal dementia

Dementia is a general term that describes a set of diseases that impair the ability to remember, think, or make decisions that interfere with doing everyday activities. According to the World Health Organization (WHO), around 50 million people worldwide have dementia with nearly 10 million new cases every year. Although it primarily affects older people it is not a normal part of aging. As our population ages its critical to better understand why this occurs.

Frontotemporal dementia is a rare form of dementia where people start to show signs between the ages of 40 and 60. It affects the front and side (temporal) areas of the brain, hence the name. It leads to behavior changes and difficulty with speaking and thinking. This form of the disease is caused by a genetic mutation called tau, which is known to be associated with Alzheimer’s disease and other dementias.

A CIRM supported study using induced pluripotent stem cells (iPSCs) led by Kathryn Bowles, Ph.D. and conducted by a team of researchers at Mount Sinai were able to recreate much of the damage seen in a widely studied form of the frontotemporal dementia by growing special types of ‘mini-brains’, also known as cerebral organoids.

iPSCs are a kind of stem cell that can be created from skin or blood cells through reprogramming and have the ability to turn into virtually any other kind of cell. The team used iPSCs to create thousands of tiny, 3D ‘mini-brains’, which mimic the early growth and development of the brain.

The researchers examined the growth and development of these ‘mini-brains’ using stem cells derived from three patients, all of whom carried a mutation in tau. They then compared their results with those observed in “normal” mini-brains which were derived from patient stem cells in which the disease-causing mutation was genetically corrected.

After six months, signs of neurodegeneration were seen in the patient ‘mini-brains’. The patient-derived ‘mini-brains’ had fewer excitatory neurons compared to the “normal” ones which demonstrates that the tau mutation was sufficient to cause higher levels of cell death of this specific class of neurons. Additionally, the patient-derived ‘mini-brains’ also had higher levels of harmful versions of tau protein and elevated levels of inflammation.

In a news release from Mount Sinai, Dr. Bowles elaborated on the results of this study.

“Our results suggest that the V337M mutant tau sets off a vicious cycle in the brain that puts excitatory neurons under great stress. It hastens the production of new proteins needed for maturation but prevents disposal of the proteins that are being replaced.”

The full results of this study were published in Cell.

CIRM funded stem cell therapy could one day help stroke and dementia patients

Image Description: Microscope images showing brain tissue that has been damaged by white matter stroke (left) and then repaired by the new glial cell therapy (right). Myelin (seen in red), is a substance that protects the connections between neurons and is lost due to white matter stroke. As seen at right, the glial cell therapy (green) restores lost myelin and improves connections in the brain. | Credit: UCLA Broad Stem Cell Research Center/Science Translational Medicine

Dementia is a general term that describes problems with memory, attention, communication, and physical coordination. One of the major causes of dementia is white matter strokes, which occurs when multiple strokes (i.e. a lack of blood supply to the brain) gradually damages the connecting areas of the brain (i.e. white matter).

Currently, there are no therapies capable of stopping the progression of white matter strokes or enhancing the brain’s limited ability to repair itself after they occur.

However, a CIRM-funded study ($2.09 million) conducted by S. Thomas Carmichael, M.D., Ph.D. and his team at UCLA showed that a one-time injection of an experimental stem cell therapy can repair brain damage and improve memory function in mice with conditions that mimic human strokes and dementia.

The therapy consists of glial cells, which are a special type of cell present in the central nervous system that surround and protect neurons. The glial cells are derived from induced pluripotent stem cells (iPSCS), stem cells that are derived from skin or blood cells through the process of reprogramming and have the ability to become virtually any type of cell.

Dr. Carmichael and his team injected the newly developed glial cells into the brains of mice that had damage similar to humans in the early to middle stages of dementia. The team found that the cell therapy traveled to the damaged areas of the brain and secreted chemicals that stimulated the brain’s own stem cells to start repairing the damage. This not only limited the progression of damage, but also enhanced the formation of new neural connections and increased the production of myelin, a fatty substance that covers and protects neurons.

In a press release from UCLA, Francesca Bosetti, Ph.D., Pharm.D., Program Director at the National Institute of Neurological Disorders and Strokes, was optimistic about what these findings could mean for patients with strokes or dementia.

“These preliminary results suggest that glial cell-based therapies may one day help combat the white matter damage that many stroke and vascular dementia patients suffer every year.”

Another interesting finding from this study is that even if the injected cells were eliminated a few months after they had been transplanted, the mice’s recovery was unaffected. The researchers believe that this indicates that the therapy primarily serves as a way to stimulate the brain’s own repair process.

In the same press release, Dr. Carmichael elaborates on this concept.

“Because the cell therapy is not directly repairing the brain, you don’t need to rely on the transplanted cells to persist in order for the treatment to be successful.”

The team is now conducting the additional studies necessary to apply to the Food and Drug Administration (FDA) for permission to test the therapy in a clinical trial in humans. If the therapy is shown to be safe and effective through clinical trials in humans, the team envisions that it could be used at hospitals as a one-time treatment for people with early signs of white matter stroke.

The full results of this study were published in Science Translational Medicine.

Peering inside the brain: how stem cells could help turn skin into therapies for dementia

To truly understand a disease you need to be able to see how it works, how it causes our body to act in ways that it shouldn’t. In cancer, for example, you can take cells from a tumor and observe them under a microscope to see what is going on. But with diseases of the brain it’s much harder. You can’t just open someone’s skull to grab some cells to study. However, now we have new tools that enable us to skip the skull-opening bit, and examine brain cells in people with diseases like dementia, to see what’s going wrong, and maybe even to get some ideas on how to make it right.

AF_neuronTHMito(2)_webThe latest example of this comes from researchers in Belgium who have developed a new strategy for treating patients with an inherited form of dementia. They used the induced pluripotent stem cell (iPSC) method, taking take skin cells from patients with frontotemporal dementia, and turning them into neurons, the kind of brain cell damaged by the disease. They were then able to study those neurons for clues as to what was happening inside the brain.

The study is reported in the journal Stem Cell Reports, and in an accompanying news release the senior author, Catherine Verfaillie, says this approach allows them to study problems in the brain in ways that weren’t possible before.

“iPSC models can now be used to better understand dementia, and in particular frontotemporal dementia, and might lead to the development of drugs that can curtail or slow down the degeneration of cortical neurons.”

The researchers identified problems with a particular signaling pathway in the brain, Wnt, which plays an important role in the development of neurons. In patients with frontotemporal dementia, the neurons weren’t able to mature into cortical neurons, which play a key role in enabling thought, perception and voluntary movement. However, by genetically correcting that problem they were able to restore the ability of the neurons to turn into cortical neurons.

Philip Van Damme, a lead researcher on the project, says this may open up possible ways to treat the problem.

“Our findings suggest that signaling events required for neurodevelopment may also play major roles in neurodegeneration. Targeting such pathways, as for instance the Wnt pathway presented in this study, may result in the creation of novel therapeutic approaches for frontotemporal dementia.”

What was Old is New Again: Scientists Transplant Brain Cells into Aged Mice and Reverse Memory Loss

Alzheimer’s disease starts with small, almost imperceptible steps. And then it builds. Sometimes slowly over a period of decades, other times more quickly—in just a matter of years. But no matter the speed of progression, the end outcome is always the same.

Transplanted cells (shown in green) in the hippocampus, 3 months after transplantation.  Cell nuclei are labeled in blue.  [Credit: Leslie Tong and Yadong Huang/Gladstone Institutes]

Transplanted cells (shown in green) in the hippocampus, 3 months after transplantation. Cell nuclei are labeled in blue. [Credit: Leslie Tong and Yadong Huang/Gladstone Institutes]

The sixth leading cause of death in the United State, Alzheimer’s develops as brain cells, or neurons, are destroyed over time. The hippocampus, the brain’s memory center, is the hardest hit, which is why memory loss is the single most common—and most devastating—symptom of the disease.

As a result, scientists have looked to the field of regenerative medicine to replace the vital cells lost to Alzheimer’s. And now, researchers at the Gladstone Institutes in San Francisco have made an important step towards that goal.

Reporting in the latest issue of the Journal of Neuroscience, researchers in the laboratory of Dr. Yadong Huang have successful transplanted early-stage brain cells, called “neuron progenitor cells,” into aged mice that have been modified to mimic Alzheimer’s symptoms. And after doing so, what they saw was extraordinary.

Not only did the cells survive the transplantation—a feat in and of itself—they began to grow and integrate into the molecular circuitry of the brain. And that’s when they noticed changes to the animals’ behavior.

These mice, whose age corresponded to humans in late-stage adulthood, were living with physical signs of memory loss. But after the cell transplants, the team saw signs that memory and learning were restored.

Leslie Tong, a graduate student at Gladstone and the University of California, San Francisco and the paper’s first author, elaborated on the importance of these findings in a news release:

“Working with older animals can be challenging from a technical standpoint, and it was amazing that the cells not only survived but affected activity and behavior.”

For a brain to function normally, there should be a balance between two types of neurons: ‘excitatory’ neurons, that act as the brain’s gas pedal, and ‘inhibitory’ neurons that serve as the brake. If this balance between these two cell types gets thrown out of whack, normal function is disrupted—and cells, especially the inhibitory neurons, degrade and die. Combined with other factors, such as genetic risk and the buildup of toxic proteins—this imbalance plays a key role in the dysfunction that eventually leads to Alzheimer’s.

The success of this treatment not only reveals the importance of maintaining this balance in memory and learning, but is also proof of concept that if neurons are lost—they can in principle be replaced.

Huang is particularly excited about the therapeutic potential of these findings. As he stated in the same news release:

“The fact that we see a functional integration of these cells into the hippocampal circuitry and a…rescue of learning and memory deficits in an aged model of Alzheimer’s disease is very exciting.”

This study, which was supported in part by CIRM, points towards several possible therapeutic strategies that could one day help human brains ravaged by Alzheimer’s regrow the cells they’ve lost—and repair the damage to learning and memory that today remains irreparable. According to Huang:

“This study tells us that if there is any way we can enhance inhibitory neuron function in the hippocampus, like through the development of small molecule compounds, it may be beneficial for Alzheimer’s disease patients.”