Stem Cell Roundup: Lab-grown meat, stem cell vaccines for cancer and a free kidney atlas for all

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

Cool Stem Cell Photo: Kidneys in the spotlight

At an early stage, a nephron forming in the human kidney generates an S-shaped structure. Green cells will generate the kidneys’ filtering device, and blue and red cells are responsible for distinct nephron activities. (Image/Stacy Moroz and Tracy Tran, Andrew McMahon Lab, USC Stem Cell)

I had to take a second look at this picture when I first saw it. I honestly thought it was someone’s scientific interpretation of Vincent van Gogh’s Starry Night. What this picture actually represents is a nephron. Your kidney has over a million nephrons packed inside it. These tiny structures filter our blood and remove waste products by producing urine.

Scientists at USC Stem Cell are studying kidney development in animals and humans in hopes of gaining new insights that could lead to improved stem cell-based technologies that more accurately model human kidneys (by coincidence, we blogged about another human kidney study on Tuesday). Yesterday, these scientists published a series of articles in the Journal of American Society of Nephrology that outlines a new, open-source kidney atlas they created. The atlas contains a catalog of high resolution images of different structures representing the developing human kidney.

CIRM-funded researcher Andrew McMahon summed it up nicely in a USC news release:

“Our research bridges a critical gap between animal models and human applications. The data we collected and analyzed creates a knowledge-base that will accelerate stem cell-based technologies to produce mini-kidneys that accurately represent human kidneys for biomedical screening and replacement therapies.”

And here’s a cool video of a developing kidney kindly provided by the authors of this study.

Video Caption: Kidney development begins with a population of “progenitor cells” (green), which are similar to stem cells. Some progenitor cells (red) stream out and aggregate into a ball, the renal vesicle (gold). As each renal vesicle grows, it radically morphs into a series of shapes — can you spot the two S-shaped bodies (green-orange-pink structures)? – and finally forms a nephron. Each human kidney contains one million mature nephrons, which form an expansive tubular network (white) that filters the blood, ensuring a constant environment for all of our body’s functions. (Video courtesy of Nils Lindstorm, Andy McMahon, Seth Ruffins and the Microscopy Core Facility at the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at the Keck School of Medicine of USC)


Lab-grown hamburgers coming to a McDonald’s near you…

“Lab-grown meat is coming, whether you like it or not” sure makes a splashy headline! This week, Wired magazine featured two Bay Area startup companies, Just For All and Finless Foods, dedicated to making meat-in-a-dish in hopes of one day reducing our dependence on livestock. The methods behind their products aren’t exactly known. Just For All is engineering “clean meat” from cells. On the menu currently are cultured chorizo, nuggets, and foie gras. I bet you already guessed what Finless Foods specialty is. The company is isolating stem-like muscle progenitor cells from fish meat in hopes of identifying a cell that will robustly create the cell types found in fish meat.

Just’s tacos made with lab-grown chorizo. (Wired)

I find the Wired article particularly interesting because of the questions and issues Wired author Matt Simon raises. Are clean meat companies really more environmentally sustainable than raising livestock? Currently, there isn’t enough data to prove this is the case, he argues. And what about the feasibility of convincing populations that depend on raising livestock for a living to go “clean”? And what about flavor and texture? Will people be willing to eat a hamburger that doesn’t taste and ooze in just the right way?

As clean meat technologies continue to advance and become more affordable, I’ll be interested to see what impact they will have on our eating habits in the future.


Induced pluripotent stem cells could be the next cancer vaccine

Our last story is about a new Cell Stem Cell study that suggests induced pluripotent stem cells (iPSCs) could be developed into a vaccine against cancer. CIRM-funded scientist Joseph Wu and his team at Stanford University School of Medicine found that injecting iPSCs into mice that were transplanted with breast cancer cells reduced the formation of tumors.

The team dug deeper and discovered that iPSCs shared similarities with cancer cells with respect to the panel of genes they express and the types of proteins they carry on their cell surface. This wasn’t surprising to them as both cells represent an immature development stage. Because of these similarities, injecting iPSCs primed the mouse’s immune system to recognize and reject similar cells like cancer cells.

The team will next test their approach on human cancer cells in the lab. Joseph Wu commented on the potential future of iPSC-based vaccines for cancer in a Stanford news release:

“Although much research remains to be done, the concept itself is pretty simple. We would take your blood, make iPS cells and then inject the cells to prevent future cancers. I’m very excited about the future possibilities.”

 

Seeing is believing. Proof a CIRM-funded therapy is making a difference

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Thelma, participant in the CAMELLIA clinical trial

You have almost certainly never heard of Thelma, or met her, or know anything about her. She’s a lady living in England who, if it wasn’t for a CIRM-funded therapy, might not be living at all. She’s proof that what we do, is helping people.

Thelma is featured in a video about a treatment for acute myeloid leukemia, one of the most severe forms of blood cancer. Thelma took part in a clinical trial, called CAMELLIA, at Oxford Cancer Centre in Oxford, UK. The clinical trial uses a therapy that blocks a protein called CD47 that is found on the surface of cancer cells, including cancer stem cells which can evade traditional therapies. The video was shot to thank the charity Bloodwise for raising the funds to pay for the trial.

Prof. Paresh Vyas of Oxford University, who was part of the clinical trial team that treated Thelma, says patients with this condition face long odds.

“Patients with acute myeloid leukemia have the most aggressive blood cancer. We really haven’t had good treatments for this condition for the last 40 years.”

While this video was shot in England, featuring English nurses and doctors and patients, the therapy itself was developed here in California, first at Stanford University under the guidance of Irv Weissman and, more recently, at Forty Seven Inc. That company is now about to test their approach in a CIRM-funded clinical trial here in the US.

This is an example of how CIRM doesn’t just fund research, we invest in it. We help support it at every stage, from the earliest research through to clinical trials. Without our early support this work may not have made it this far.

The Forty Seven Inc. therapy uses the patient’s own immune system to help fight back against cancer stem cells. It’s looking very promising. But you don’t have to take our word for it. Take Thelma’s.

A Tribute to Stem Cells on Valentine’s Day

In case you forgot, today is Valentine’s Day. Whether you love, hate, or could care less about this day, you do have one thing in common with our other readers – you’re a fan of stem cells. (If you’re not, then why are you reading this blog??)

As a tribute to how awesome and important stem cell research is, I offer you a special Valentine’s Day-themed interview with the authors of the CIRM Stem Cellar blog.


What’s your favorite type of stem cell and why? 

Kevin: Embryonic stem cells. Without that one cell none of this work, none of us when you come to think of it, would be possible. Whenever I give talks to the public one of the first things I talk about when explaining what stem cells are and how they work is the cartoon from Piraro, the one featuring the snowmen who look up at snowflakes and say “oh look, stem cells”. For me that captures the power and beauty of these cells. Without them the snowmen/women would not exist. With them all is possible.

Karen: Neural stem cells (NSCs) for the win! First off, they created my brain, so I am truly in their debt. Second, NSCs and I have an intimate relationship. I spent eight years of my life (PhD and postdoc) researching these stem cells in the lab on an epic quest to understand what causes Alzheimer’s and Huntington’s disease. As you can see from the subject matter of my latest blogs (here, here, here), I am pretty stoked to write about NSCs any chance I get.

Microscopic image of a mini brain organoid, showing layered neural tissue and different groups of neural stem cells (in blue, red and magenta) giving rise to neurons (green). Image: Novitch laboratory/UCLA

Todd: Induced pluripotent stem cells (iPSCs) rule! They’re my favorite because they allow researchers to study poorly understood human diseases in a way that just wasn’t possible before iPSCs came on the scene in the late 2000’s. For instance, it’s neither practical nor ethical to study autism by taking cell samples out of the brains of affected children. But with iPSC technology, you can recover cells from an autistic child’s baby teeth after they fall out and grow them into nerve cells in the lab to more directly study the cellular causes of the disorder. I also like the fact that iPSCs are the ultimate in personalized medicine in that you could make a stem cell-based therapy from a person’s own cells.


What do you love most about your job at CIRM?

Kevin: That’s hard to say, it’s like asking which is your favorite child? I love getting to work with the team here at CIRM. It’s such an incredible group of individuals who are fiercely committed to this work, but who are also ridiculously smart and funny. It makes for a great work place and one I enjoy coming into every day.

I also love working with patient advocates. Their courage, compassion and commitment to the work that we do at CIRM is inspirational. If ever I think I am having a bad day I simply have to think about what these extraordinary people go through every day and it puts my day in perspective. They are the reason we do this work. They are the reason this work has value and purpose.

Karen: You know how some people have a hard time choosing what flavor of ice cream to get? I have the same issue with science. I enjoyed my time doing stem cell experiments in the lab but at the same time, I was frustrated that my research and communications was so narrowly focused. I joined CIRM because I love educating patients and the public about all types of stem cell research. I also am a self-professed multitasker and love that my job is to find new ways to connect with different audiences through social media, blogging, and whatever I can think of!

I guess if I really had to choose a favorite, it would be managing the SPARK high school educational program. Each year, I get to work with 60 high school students who spend their summers doing stem cell research in labs across California. They are extremely motivated and it’s easy to see by watching their journeys on instagram how these students will be the next generation of talented stem cell scientists.

Todd: My interests have always zig-zagged between the worlds of science and art. I love that my job allows me to embrace both equally. I could be writing a blog about stem cell-derived mini-intestines one moment, then in the next moment I’m editing video footage from an interview with a patient.

Speaking of patients, they’re the other reason I love my job. As a graduate student I worked in a fruit fly lab so it probably doesn’t surprise you that I had virtually no interactions with patients. But as a member of the science communications team at CIRM, I’ve been fortunate to hear firsthand from the patients and their caregivers who show so much courage in the face of their disease. It makes the work we do here all the more motivating.

CIRM communications team: Todd Dubnicoff, Kevin McCormack, Maria Bonneville, Karen Ring


Please share a poem inspired by your love for stem cell research

 Kevin: I’m from Ireland so obviously I wrote a limerick.

There was a young scientist at CIRM

Whose research made some people squirm

He took lots of cells

Fed them proteins and gels

Until they were grown to full-term

 Karen: I wrote a haiku because that was the only type of poem I received a good grade for in elementary school.

Pluripotency

One stem cell to rule them all

Many paths to choose

Todd: Limerick-shimerick, Kevin. Only true poets haiku!

Shape-shifting stem cell

Hero for those who suffer

Repairing lost hope


One year ago…

In a stem cell first, functioning human kidney structures grown in living animals

One of the ultimate quests in the stem cell field – growing organs to repair diseased or damaged ones – took a significant step forward this week. In a first, researchers at the University of Manchester, in the U.K., showed that human embryonic stem cell-derived kidney tissue forms into functional kidney structures, capable of filtering blood and producing urine, when implanted under the skin of mice.

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Cross-section of human stem cell-derived kidney tissue grown in mouse. When injected in blood, dextran (green) was taken up by the kidney structure, proving it’s functional. (Credit University of Manchester/ Stem Cell Reports)

When a person has end-stage kidney disease, their body can no longer filter out waste products and extra fluid from the blood which leads to serious health complications, even death. Blood filtration therapy, called dialysis, can substitute for a kidney but the average life expectancy is only about 10 years for patients receiving dialysis. Kidney transplants are another answer for treating kidney disease, but organ availability is in limited supply. About 2.2 million people die worldwide from a lack of access to these treatment options. So other therapeutic approaches to help end-stage kidney disease sufferers are sorely needed.

The current study, published in Stem Cell Reports, used human embryonic stem cells to grow kidney tissue in the lab. While the lab-grown tissues showed hallmarks of kidney structures, they were unable to fully develop into mature kidney structures in a culture dish. So the scientists tried implanting the human kidney tissue under the skin of mice and left it there for 12 weeks. The team showed that kidney structures, called glomeruli, which play a key role in filtering the blood, formed over that time and had become vascularized, or connected with the animal’s blood supply. The team further showed those structures were functional by injecting a fluorescently tagged substance called dextran. Tracing the fate of the dextran in the blood showed that it had been filtered and taken up by tubular structures in the kidney tissue which indicates urine production had begun.

Professor Sue Kimber, one of the leaders of the study, summed up the significance and current limitations of these results in a press release:

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Sue Kimber

“We have proved beyond any doubt these structures function as kidney cells by filtering blood and producing urine – though we can’t yet say what percentage of function exists. What is particularly exciting is that the structures are made of human cells which developed an excellent capillary blood supply, becoming linked to the vasculature of the mouse.

Though this structure was formed from several hundred glomeruli, and humans have about a million in their kidneys – this is clearly a major advance. It constitutes a proof of principle- but much work is yet to be done.”

To be sure, curing a person suffering from end-stage kidney disease with a stem cell-grown kidney is some ways off. But, on the nearer horizon, this advance will provide a means to study the human kidney in a living animal, a powerful tool for uncovering insights into kidney disease and new therapeutic approaches.

California gets first royalty check from Stem Cell Agency investments

COH image

CIRM recently shared in a little piece of history. The first royalty check, based on CIRM’s investment in stem cell research, was sent to the California State Treasurer’s office from City of Hope. It’s the first of what we hope will be many such checks, helping repay, not just the investment the state made in the field, but also the trust the voters of California showed when they created CIRM.

The check, for $190,345.87, was for a grant we gave City of Hope back in 2012 to develop a therapy for glioblastoma, one of the deadliest forms of brain cancer. That has led to two clinical trials and a number of offshoot inventions that were subsequently licensed to a company called Mustang Bio.

Christine Brown, who is now the principal investigator on the project, is quoted in a front page article in the San Francisco Chronicle, on the significance of the check for California:

“This is an initial payment for the recognition of the potential of this therapy. If it’s ultimately approved by the FDA as a commercial product, this could be a continued revenue source.”

In the same article, John Zaia, Director of the City of Hope Alpha Stem Cell Clinic, says this also reflects the unique nature of CIRM:

“I think this illustrates that a state agency can actually fund research in the private community and get a return on its investment. It’s something that’s not done in general by other funding agencies such as the National Institutes of Health, and this is a proof of concept that it can work.”

Maria Millan, CIRM’s President & CEO, says the amount of the payment is not the most significant part of this milestone – after all CIRM has invested more than $2.5 billion in stem cell research since 2004. She says the fact that we are starting to see a return on the investment is important and reflects some of the many benefits CIRM brings to the state.

“It’s a part of the entire picture of the return to California. In terms of what it means to the health of Californians, and access to these transformative treatments, as well as the fact that we are growing an industry.”

 

Stem Cell Roundup: New infertility tools, helping the 3 blind mice hear and cow ESCs

Cool Stem Cell Image of the Week

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Human egg grown from immature cells in ovarian tissue. (credit: David Albertini)

This week’s Cool Stem Cell Image of the Week comes to us from the lab of reproductive biologist Evelyn Telfer at the University of Edinburgh. Telfer and her team successfully grew human eggs cells from immature ovarian tissue.

This technology could revolutionize the way doctors approach infertility. For instance, when girls and young women undergo chemotherapy for cancer, their eggs are often damaged. By preserving a small piece of ovarian tissue before the cancer treatments, this method could be used to generate eggs later in life for in vitro fertilization. Much more work is necessary to figure out if these eggs are healthy and safe to use to help infertile women.

The study was recently published in Molecular Human Reproduction and was picked up this Science writer Kelly Servick.

Forget 3 blind mice, iPS cells could help 3 deaf mice hear again (Kevin McCormack)
For years scientists have been trying to use stem cells to restore hearing to people who are deaf or hearing impaired. Now a group of researchers in Japan may have found a way.

The team used human iPS cells to create inner ear cells, the kind damaged in one of the most common forms of hereditary deafness. They then transplanted them into the inner ears of mice developing in the womb that are suffering from a congenital form of hearing loss. The cells appeared to engraft and produce a protein, Connexin 30, known to be critical in hearing development.

The research, published in the journal Scientific Reports, could be an important step towards developing a therapy for congenital hearing loss in people.

UC Davis team isolates cow embryonic stem cells for the first time

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An early stage cow embryo. Inner cell mass (red) is source of embryonic stem cells. (Credit: Pablo Ross/UC Davis) 

Although human embryonic stem cells (ESCs) were isolated way back in ’98, researchers haven’t had similar luck with embryonic stem cells from cows. Until this week, that is.  A UC Davis team just published a report in PNAS showing that they not only can isolate cow ESCs but their method works almost 100% of the time.

 

Genetic engineering of these cow stem cells could have huge implications for the cattle industry. Senior author Pablo Ross mentioned in a press release how this breakthrough could help speed up the process of generating superior cows that produce more milk, release less methane and are more resistant to disease:

“In two and a half years, you could have a cow that would have taken you about 25 years to achieve. It will be like the cow of the future. It’s why we’re so excited about this.”

These cow ESCs may also lead to better models of human disease. Because of their small size, rat and mouse models are not always a good representation of how potential therapies or drugs will affect humans. Creating stem cell models from larger animals may provide a better representation.

Stanford Scientist Sergiu Pasca Receives Prestigious Vilcek Prize for Stem Cell Research on Neuropsychiatric Disorders

Sergiu Pasca, Stanford University

Last month, we blogged about Stanford neuroscientist Sergiu Pasca and his interesting research using stem cells to model the human brain in 3D. This month we bring you an exciting update about Dr. Pasca and his work.

On February 1st, Pasca was awarded one of the 2018 Vilcek Prizes for Creative Promise in Biomedical Science. The Vilcek Foundation is a non-profit organization dedicated to raising awareness of the important contributions made by immigrants to American arts and sciences.

Pasca was born in Romania and got his medical degree there before moving to the US to pursue research at Stanford University in 2009. He is now an assistant professor of psychiatry and behavioral sciences at Stanford and has dedicated his lab’s research to understanding human brain development and neuropsychiatric disorders using 3D brain organoid cultures derived from pluripotent stem cells.

The Vilcek Foundation produced a fascinating video (below) featuring Pasca’s life journey and his current CIRM-funded research on Timothy Syndrome – a rare form of autism. In the video, Pasca describes how his lab’s insights into this rare psychiatric disorder will hopefully shed light on other neurological diseases. He shares his hope that his research will yield something that translates to the clinic.

The Vilcek Prize for Creative Promise in Biomedical Science comes with a $50,000 cash award. Pasca along with the other prize winners will be honored at a gala event in New York City in April 2018.

You can read more about Pasca’s prize winning research on the Vilcek website and in past CIRM blogs below.


Related Links:

Novel approach to slowing deadly brain cancer stem cells may lead to new treatments

Glioblastoma, a form of brain cancer, is one of the most dreaded cancer diagnoses. Standard radiation and chemotherapy treatments for glioblastoma almost always prove ineffective because of the cancer’s ability to grow back. With their unlimited potential to self-renew, cancer stem cells within the brain tumor are thought to be responsible for its aggressive reoccurrence. Not surprisingly, researchers looking to develop more effective therapies are focused on trying to better understand the biology of these cancer stem cells in order to exploit their vulnerabilities.

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MRI image of high grade glioma brain tumor (white mass on left). Image: Wikipedia

This week, the Dartmouth-Hitchcock Medical Center reports that a research team led by Damian A. Almiron Bonnin has identified a cell signal that the brain cancer stem cells rely on to resist standard treatments and to regrow. They also showed that drugs which interrupt this signal reduced tumor growth in animal studies.

Because if its aggressive growth, the cells within the glioblastoma eventually become starved for oxygen or, in scientific lingo, they become hypoxic. The presence of hypoxia in brain tumors is actually predictive of a poor prognosis in affected patients. A protein called hypoxia-inducible factor (HIF) becomes activated in these low oxygen conditions and helps the cancer stem cells to survive and continue to grow. The research team found that HIF carries out this function by triggering a cascade of cell activity that leads to the secretion of a protein called VEGF out into the microenvironment of the tumor. As secreted VEGF spreads through the tumor, it stimulates new blood vessel growth which is key to the tumor’s survival by nourishing the tumor with oxygen and nutrients.

Adding drugs that block a cell’s ability to release proteins, led to a reduction in glioblastoma tumor growth both in petri dishes and in animal studies. With these results, published in Oncogene, Dr. Almiron Bonnin’s team is performing the necessary preclinical studies that could lead to testing this novel strategy in patients. He summed this effort in a press release:

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Damian Almiron Bonnin

“Being able to target the cancer stem cells within these tumors, like we did here, could potentially improve response to current chemotherapies and prevent recurrences, which would translate into an increase in patient survival rates.”

 

Creating a platform to help transplanted stem cells survive after a heart attack

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Developing new tools to repair damaged hearts

Repairing, even reversing, the damage caused by a heart attack is the Holy Grail of stem cell researchers. For years the Grail seemed out of reach because the cells that researchers transplanted into heart attack patients didn’t stick around long enough to do much good. Now researchers at Stanford may have found a way around that problem.

In a heart attack, a blockage cuts off the oxygen supply to muscle cells. Like any part of our body starved off oxygen the muscle cells start to die, and as they do the body responds by creating a layer of scars, effectively walling off the dead tissue from the surviving healthy tissue.  But that scar tissue makes it harder for the heart to effectively and efficiently pump blood around the body. That reduced blood flow has a big impact on a person’s ability to return to a normal life.

In the past, efforts to transplant stem cells into the heart had limited success. Researchers tried pairing the cells with factors called peptides to help boost their odds of surviving. That worked a little better but most of the peptides were also short-lived and weren’t able to make a big difference in the ability of transplanted cells to stick around long enough to help the heart heal.

Slow and steady approach

Now, in a CIRM-funded study published in the journal Nature Biomedical Engineering, a team at Stanford – led by Dr. Joseph Wu – believe they have managed to create a new way of delivering these cells, one that combines them with a slow-release delivery mechanism to increase their chances of success.

The team began by working with a subset of bone marrow cells that had been shown in previous studies to have what are called “pro-survival factors.” Then, working in mice, they identified three peptides that lived longer than other peptides. That was step one.

Step two involved creating a matrix, a kind of supporting scaffold, that would enable the researchers to link the three peptides and combine them with a delivery system they hoped would produce a slow release of pro-survival factors.

Step three was seeing if it worked. Using fluorescent markers, they were able to show, in laboratory tests, that unlinked peptides were rapidly released over two or three days. However, the linked peptides had a much slower release, lasting more than 15 days.

Out of the lab and into animals

While these petri dish experiments looked promising the big question was could this approach work in an animal model and, ultimately, in people. So, the team focused on cardiac progenitor cells (CPCs) which have shown potential to help repair damaged hearts, but which also have a low survival rate when transplanted into hearts that have experienced a heart attack.

The team delivered CPCs to the hearts of mice and found the cells without the pro-survival matrix didn’t last long – 80 percent of the cells were gone four days after they were injected, 90 percent were gone by day ten. In contrast the cells on the peptide-infused matrix were found in large numbers up to eight weeks after injection. And the cells didn’t just survive, they also engrafted and activated the heart’s own survival pathways.

Impact on heart

The team then tested to see if the treatment was helping improve heart function. They did echocardiograms and magnetic resonance imaging up to 8 weeks after the transplant surgery and found that the mice treated with the matrix combination had a statistically improved left ventricular function compared to the other mice.

Jayakumar Rajadas, one of the authors on the paper told CIRM that, because the matrix was partly made out of collagen, a substance the FDA has already approved for use in people, this could help in applying for approval to test it in people in the future:

“This paper is the first comprehensive report to demonstrate an FDA-compliant biomaterial to improve stem cell engraftment in the ischemic heart. Importantly, the biomaterial is collagen-based and can be readily tested in humans once regulatory approval is obtained.”

 

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.