Salk Institute

Salk scientists discover new findings related to the age of organs

/ Yimy Villa / 1 Comment
Dr. Rafael Arrojo e Drigo (left) and Dr. Martin Hetzer (right) at the Salk Institute in San Diego

It has been a long held belief in the scientific community that nerve cells, or possibly the heart, are the oldest cells in the body. This is due to the fact that the brain and heart are the first organs that begin to develop in the womb. Nerve cells have an average lifespan of approximately 80 years without the need of generating new cells. It has been difficult to determine the approximate age of other organs such as the liver and pancreas in the body until now.

Dr. Rafael Arrojo e Drigo and Dr. Martin Hetzer, scientists at the Salk Institute, have discovered a population of cells that reside in the mouse brain, liver, and pancreas that have extremely long lifespans. In some cases, some of these cells were the same age as the animal they were found in. The scientists used a complex labeling and imaging procedure to determine cell age in a mouse model.

Furthermore, the scientists also found that the brain, liver, and pancreas in the mice contain a mixture of “old” and “young” cells, like a mosaic painting composed of small, different colored pieces. They called this phenomenon age mosaicism, referring to the population of identical cells that could only be distinguished by lifespan.

Their method could be applied to other types of tissue in the body, which could provide valuable information, such as the lifelong function of non-dividing cells and how cells lose control over the quality and integrity of important cell structures during aging. The answers to these questions play a key role in understanding ways to prevent the age-related degeneration of organs, such as the brain in Alzheimer’s Disease or the pancreas in Type II Diabetes.

In a press release, Dr. Hetzer is quoted as saying that,

“Determining the age of cells and subcellular structures in adult organisms will provide new insights into cell maintenance and repair mechanisms and the impact of cumulative changes during adulthood on health and development of disease. The ultimate goal is to utilize these mechanisms to prevent or delay age-related decline of organs with limited cell renewal such as the brain, pancreas and heart.”

The full results of the study were published in Cell Metabolism.

You can also see a youtube video below of Dr. Rafael Arrojo e Drigo and Dr. Martin Hetzer discussing their findings.

Stories that caught our eye: National Geographic takes a deep dive into iPS cells; Japanese researchers start iPS cell clinical trial for spinal cord injury; and do high fat diets increase your risk of colorectal cancer

/ Kevin McCormack / 1 Comment

Can cell therapy beat the most difficult diseases?

That’s the question posed in a headline in National Geographic. The answer; maybe, but it is going to take time and money.

The article focuses on the use of iPS cells, the man-made equivalent of embryonic stem cells that can be turned into any kind of cell or tissue in the body. The reporter interviews Kemal Malik, the member of the Board of Management for pharmaceutical giant Bayer who is responsible for innovation. When it comes to iPS cells, it’s clear Malik is a true believer in their potential.

“Because every cell in our bodies can be produced from a stem cell, the applicability of cell therapy is vast. iPSC technology has the potential to tackle some of the most challenging diseases on the planet.”

But he also acknowledges that the field faces some daunting challenges, including:

  • How to manufacture the cells on a large scale without sacrificing quality and purity
  • How do you create products that have a stable shelf life and can be stored until needed?
  • How do you handle immune reactions if you are giving these cells to patients?

Nonetheless, Malik remains confident we can overcome those challenges and realize the full potential of these cells.

“I believe human beings are on the cusp of the next big wave of pharmaceutical innovation. The use of living cells to make people better.”

As if to prove Malik right there was also news this week that researchers at Japan’s Keio University have been given permission to start a clinical trial using iPS cells to treat people with spinal cord injuries. This would be the first of its kind anywhere in the world.

Japan launches iPSC clinical trial for spinal cord injury

An article in Biospace says that the researchers plan to treat four patients who have suffered varying degrees of paralysis due to a spinal cord injury.  They will take cells from the patients and, using the iPS method, turn them into the kind of nerve cells found in the spinal cord, and then transplant two million of them back into the patient. The hope is that this will create new connections that restore movement and feeling in the individuals.

This trial is expected to start sometime this summer.

CIRM has already funded a first-of-its-kind clinical trial for spinal cord injury with Asterias Biotherapeutics. That clinical trial used embryonic stem cells turned into oligodendrocyte progenitor cells – which develop into cells that support and protect nerve cells in the central nervous system. We blogged about the encouraging results from that trial here.

High fat diet drives colorectal cancer

Finally today, researchers at Salk have uncovered a possible cause to the rise in colorectal cancer deaths among people under the age of 55; eating too much high fat food.

Our digestive system works hard to break down the foods we eat and one way it does that is by using bile acids. Those acids don’t just break down the food, however, they also break down the lining of our intestines. Fortunately, our gut has a steady supply of stem cells that can repair and replace that lining. Unfortunately, at least according to the team from Salk, mutations in these stem cells can lead to colorectal cancer.

The study, published in the journal Cell, shows that bile acids affect a protein called FXR that is responsible for ensuring that gut stem cells produce a steady supply of new lining for the gut wall. When someone eats a high fat diet it upsets the balance of bile acids, starting a cascade of events that help cancer develop and grow.

In a news release Annette Atkins, a co-author of the study, says there is a strong connection between bile acid and cancer growth:

“We knew that high-fat diets and bile acids were both risk factors for cancer, but we weren’t expecting to find they were both affecting FXR in intestinal stem cells.”

So next time you are thinking about having that double bacon cheese burger for lunch, you might go for the salad instead. Your gut will thank you. And it might just save your life.

Research Targeting Prostate Cancer Gets Almost $4 Million Support from CIRM

/ Kevin McCormack / Leave a comment

Prostate cancer

A program hoping to supercharge a patient’s own immune system cells to attack and kill a treatment resistant form of prostate cancer was today awarded $3.99 million by the governing Board of the California Institute for Regenerative Medicine (CIRM)

In the U.S., prostate cancer is the second most common cause of cancer deaths in men.  An estimated 170,000 new cases are diagnosed each year and over 29,000 deaths are estimated in 2018.  Early stage prostate cancer is usually managed by surgery, radiation and/or hormone therapy. However, for men diagnosed with castrate-resistant metastatic prostate cancer (CRPC) these treatments often fail to work and the disease eventually proves fatal.

Poseida Therapeutics will be funded by CIRM to develop genetically engineered chimeric antigen receptor T cells (CAR-T) to treat metastatic CRPC. In cancer, there is a breakdown in the natural ability of immune T-cells to survey the body and recognize, bind to and kill cancerous cells. Poseida is engineering T cells and T memory stem cells to express a chimeric antigen receptor that arms these cells to more efficiently target, bind to and destroy the cancer cell. Millions of these cells are then grown in the laboratory and then re-infused into the patient. The CAR-T memory stem cells have the potential to persist long-term and kill residual cancer calls.

“This is a promising approach to an incurable disease where patients have few options,” says Maria T. Millan, M.D., President and CEO of CIRM. “The use of chimeric antigen receptor engineered T cells has led to impressive results in blood malignancies and a natural extension of this promising approach is to tackle currently untreatable solid malignancies, such as castrate resistant metastatic prostate cancer. CIRM is pleased to partner on this program and to add it to its portfolio that involves CAR T memory stem cells.”

Poseida Therapeutics plans to use the funding to complete the late-stage testing needed to apply to the Food and Drug Administration for the go-ahead to start a clinical trial in people.

Quest Awards

The CIRM Board also voted to approve investing $10 million for eight projects under its Discovery Quest Program. The Quest program promotes the discovery of promising new stem cell-based technologies that will be ready to move to the next level, the translational category, within two years, with an ultimate goal of improving patient care.

Among those approved for funding are:

  • Eric Adler at UC San Diego is using genetically modified blood stem cells to treat Danon Disease, a rare and fatal condition that affects the heart
  • Li Gan at the Gladstone Institutes will use induced pluripotent stem cells to develop a therapy for a familial form of dementia
  • Saul Priceman at City of Hope will use CAR-T therapy to develop a treatment for recurrent ovarian cancer

Because the amount of funding for the recommended applications exceeded the money set aside, the Application Subcommittee voted to approve partial funding for two projects, DISC2-11192 and DISC2-11109 and to recommend, at the next full Board meeting in October, that the projects get the remainder of the funds needed to complete their research.

The successful applications are:

 

APPLICATION

  

TITLE

  

INSTITUTION

 CIRM COMMITTED FUNDING
DISC2-11131 Genetically Modified Hematopoietic Stem Cells for the

Treatment of Danon Disease

 

  

U.C San Diego

  

$1,393,200

 
DISC2-11157 Preclinical Development of An HSC-Engineered Off-

The-Shelf iNKT Cell Therapy for Cancer

 

  

U.C. Los Angeles

  

$1,404,000
DISC2-11036 Non-viral reprogramming of the endogenous TCRα

locus to direct stem memory T cells against shared

neoantigens in malignant gliomas

 

  

U.C. San Francisco

  

$900,000
DISC2-11175 Therapeutic immune tolerant human islet-like

organoids (HILOs) for Type 1 Diabetes

 

  

Salk Institute

  

$1,637,209
DISC2-11107 Chimeric Antigen Receptor-Engineered Stem/Memory

T Cells for the Treatment of Recurrent Ovarian Cancer

 

  

City of Hope

  

$1,381,104
DISC2-11165 Develop iPSC-derived microglia to treat progranulin-

deficient Frontotemporal Dementia

 

  

Gladstone Institutes

  

$1,553,923
DISC2-11192 Mesenchymal stem cell extracellular vesicles as

therapy for pulmonary fibrosis

 

  

U.C. San Diego

  

$865,282
DISC2-11109 Regenerative Thymic Tissues as Curative Cell

Therapy for Patients with 22q11 Deletion Syndrome

 

  

Stanford University

  

$865,282

 

 

Coming up with a stem cell FIX for a life-threatening blood disorder

/ Pallavi Penumetcha / 1 Comment

Hemophilia

A promising new treatment option for hemophiliacs is in the works at the Salk Institute for Biological Sciences. Patients with Hemophilia B experience uncontrolled, and sometimes life threatening, bleeding due to loss or improper function of Factor IX (FIX), a protein involved in blood clotting. There is no cure for the disease and patients rely on routine infusions of FIX to prevent excessive blood loss. As you can imagine, this treatment regimen is both time consuming and expensive, while also becoming less effective over time.

Salk researchers, partially funded by CIRM, aimed to develop a more long-term solution for this devastating disease by using the body’s own cells to fix the problem.

In the study, published in the journal Cell Reports, They harvested blood cells from hemophiliacs and turned them into iPSCs (induced pluripotent stem cells), which are able to turn into any cell type. Using gene editing, they repaired the iPSCs so they could produce FIX and then turned the iPSCs into liver cells, the cell type that naturally produces FIX in healthy individuals.

One step therapy

To test whether these FIX-producing liver cells were able to reduce excess blood loss, the scientists injected the repaired human cells into a hemophiliac mouse. The results were very encouraging; they saw a greater than two-fold increase in clotting efficiency in the mice, reaching about a quarter of normal activity. This is particularly promising because other studies showed that increasing FIX activity to this level in hemophiliac humans significantly reduces bleeding rates. On top of that they also observed that these cells were able to survive and produce FIX for up to a year in the mice.

In a news release Suvasini Ramaswamy, the first author of the paper, said this method could eliminate the need for multiple treatments, as well as avoiding the immunosuppressive therapy that would be required for a whole liver transplant.

“The appeal of a cell-based approach is that you minimize the number of treatments that a patient needs. Rather than constant injections, you can do this in one shot.”

While these results provide an exciting new avenue in hemophilia treatment, there is still much more work that needs to be done before this type of treatment can be used in humans. This approach, however, is particularly exciting because it provides an important proof of principle that combining stem cell reprogramming with genetic engineering can lead to life-changing breakthroughs for treating genetic diseases that are not currently curable.

 

 

Making beating heart cells from stem cells just got easier

/ Karen Ring / 2 Comments

Here’s a heartwarming story for the holidays. Scientists from the Salk Institute in La Jolla, California have figured out a simple, easy way to make beating heart cells from human stem cells that will aid research and therapy development for heart disease. Their study, which received funding support from CIRM, was published last week in the journal Genes & Development.

The Salk team discovered that making beating heart tissue from human stem cells is as simple as turning off a single gene called YAP. You might be wondering how the team settled on this gene and no, it doesn’t involve pulling a random gene name out of a hat.

In previous studies, the researchers found that two cell signaling pathways, Wnt and Activin, are crucial for the development of embryonic stem cells into specialized cells like cardiomyocytes (beating heart cells). This research led to the discovery of a third pathway, controlled by YAP, which sets up a road block for cell specialization and keeps stem cells in their undifferentiated state.

Only hESCs without YAP (right panel) make heart cells (green) in one step. Blue dye marks cell nuclei. (Salk Institute)

The team deleted YAP from these stem cells using CRISPR gene editing technology, and then treated the stem cells to the Activin signaling molecule. Without YAP, exposure to Activin prompted the stem cells to develop immediately into beating cardiomyocytes that you can see beating away in the Salk video below.

Dr. Kathy Jones, Salk professor and senior author on the study, explained why this discovery is important to the field in a news release:

“This discovery is really exciting because it means we can potentially create a reliable protocol for taking normal cells and moving them very efficiently from stem cells to heart cells. Researchers and commercial companies want to easily generate cardiomyocytes to study their capacity for repair in heart attacks and disease—this brings us one step closer to being able to do that.”

First author, Conchi Estarás, emphasized how their new method for making cardiomyocytes is attractive not only for its simplicity, but also for its cost-effectiveness in enabling large-scale manufacturing of these cells for treatment.

“Instead of requiring two steps to achieve specialization, removing YAP cut it to just one step. That would mean a huge savings for industry in terms of reagent materials and expense.”

Looking ahead, Jones and her team do not plan on deleting the YAP gene from stem cells because of the potential side effects cause by the loss of YAP’s other cellular functions. Instead, they will be using commercially available molecules that can temporarily inhibit the function of YAP in hopes that this less permanent action will still readily produce beating heart cells from stem cells.

Kathy Jones and Conchi Estarás. (Image courtesy of Salk Institute)

Scientists fix heart disease mutation in human embryos using CRISPR

/ Karen Ring / Leave a comment

Last week the scientific community was buzzing with the news that US scientists had genetically modified human embryos using CRISPR gene editing technology. While the story broke before the research was published, many journalists and news outlets weighed in on the study’s findings and the ethical implications they raise. We covered this initial burst of news in last week’s stem cell stories that caught our eye.

Shoukhrat Mitalipov (Leah Nash, New York Times)

After a week of suspense, the highly-anticipated study was published yesterday in the journal Nature. The work was led by senior author Dr. Shoukhrat Mitalipov from Oregon Health and Sciences University (and a member of CIRM’s Grants Working Group, the panel of experts who review applications to us for funding) in collaboration with scientists from the Salk Institute and Korea’s Institute for Basic Science.

In brief, the study revealed that the teams’ CRISPR technology could correct a genetic mutation that causes a disease called hypertrophic cardiomyopathy (HCM) in 72% of human embryos without causing off-target effects, which are unwanted genome modifications caused by CRISPR. These findings are a big improvement over previous studies by other groups that had issues with off-target effects and mosaicism, where CRISPR only correctly modifies mutations in some but not all cells in an embryo.

Newly fertilized eggs before gene editing, left, and embryos after gene editing and a few rounds of cell division. (Image from Shoukrat Mitalipov in New York Times)

Mitalipov spoke to STATnews about a particularly interesting discovery that he and the other scientists made in the Nature study,

“The main finding is that the CRISPR’d embryos did not accept the “repair DNA” that the scientists expected them to use as a replacement for the mutated gene deleted by CRISPR, which the embryos inherited from their father. Instead, the embryos used the mother’s version of the gene, called the homologue.”

Sharon Begley, the author of the STATnews article, argued that this discovery means that “designer babies” aren’t just around the corner.

“If embryos resist taking up synthetic DNA after CRISPR has deleted an unwanted gene, then “designer babies,” created by inserting a gene for a desirable trait into an embryo, will likely be more difficult than expected.”

Ed Yong from the Atlantic also took a similar stance towards Mitalipov’s study in his article titled “The Designer Baby Era is Not Upon Us”. He wrote,

“The bigger worry is that gene-editing could be used to make people stronger, smarter, or taller, paving the way for a new eugenics, and widening the already substantial gaps between the wealthy and poor. But many geneticists believe that such a future is fundamentally unlikely because complex traits like height and intelligence are the work of hundreds or thousands of genes, each of which have a tiny effect. The prospect of editing them all is implausible. And since genes are so thoroughly interconnected, it may be impossible to edit one particular trait without also affecting many others.”

Dr. Juan Carlos Izpisua Belmonte, who’s a corresponding author on the paper and a former CIRM grantee from the Salk Institute, commented on the impact that this research could have on human health in a Salk news release.

Co-authors Juan Carlos Izpisua Belmonte and Jun Wu. (Salk Institute)

“Thanks to advances in stem cell technologies and gene editing, we are finally starting to address disease-causing mutations that impact potentially millions of people. Gene editing is still in its infancy so even though this preliminary effort was found to be safe and effective, it is crucial that we continue to proceed with the utmost caution, paying the highest attention to ethical considerations.”

Pam Belluck from The New York Times also suggested that this research could have a significant impact on how we prevent disease in newborns.

“This research marks a major milestone and, while a long way from clinical use, it raises the prospect that gene editing may one day protect babies from a variety of hereditary conditions.”

So when will the dawn of CRISPR babies arrive? Ed Yong took a stab at answering this million dollar question with help from experts in the field.

“Not for a while. The technique would need to be refined, tested on non-human primates, and shown to be safe. “The safety studies would likely take 10 to 15 years before FDA or other regulators would even consider allowing clinical trials,” wrote bioethicist Hank Greely in a piece for Scientific American. “The Mitalipov research could mean that moment is 9 years and 10 months away instead of 10 years, but it is not close.” In the meantime, Mitalipov’s colleague Sanjiv Kaul says, “We’ll get the method to perfection so that when it’s possible to use it in a clinical trial, we can.”

New stem cell technique gives brain support cells a starring role

/ Kevin McCormack / 1 Comment

Gage et al

The Salk team. From left: Krishna Vadodaria, Lynne Moore, Carol Marchetto, Arianna Mei, Fred H. Gage, Callie Fredlender, Ruth Keithley, Ana Diniz Mendes. Photo courtesy Salk Institute

Astrocytes are some of the most common cells in the brain and central nervous system but they often get overlooked because they play a supporting role to the more glamorous neurons (even though they outnumber them around 50 to 1). But a new way of growing those astrocytes outside the brain could help pave the way for improved treatments for stroke, Alzheimer’s and other neurological problems.

Astrocytes – which get their name because of their star shape (Astron – Greek for “star” and “kyttaron” meaning cell) – have a number of key functions in the brain. They provide physical and metabolic support for neurons; they help supply energy and fuel to neurons; and they help with detoxification and injury repair, particularly in terms of reducing inflammation.

Studying these astrocytes in the lab has not been easy, however, because existing methods of producing them have been slow, cumbersome and not altogether effective at replicating their many functions.

Finding a better way

Now a team at the Salk Institute, led by CIRM-funded Professor Fred “Rusty” Gage, has developed a way of using stem cells to create astrocytes that is faster and more effective.

Their work is published in the journal Stem Cell Reports. In a news release, Gage says this is an important discovery:

“This work represents a big leap forward in our ability to model neurological disorders in a dish. Because inflammation is the common denominator in many brain disorders, better understanding astrocytes and their interactions with other cell types in the brain could provide important clues into what goes wrong in disease.”

Stylized microscopy image of an astrocyte (red) and neuron (green). (Salk Institute)

In a step by step process the Salk team used a series of chemicals, called growth factors, to help coax stem cells into becoming, first, generic brain cells, and ultimately astrocytes. These astrocytes not only behaved like the ones in our brain do, but they also have a particularly sensitive response to inflammation. This gives the team a powerful tool in helping develop new treatment to disorders of the brain.

But wait, there’s more!

As if that wasn’t enough, the researchers then used the same technique to create astrocytes from induced pluripotent stem cells (iPSCs) – adult cells, such as skin, that have been re-engineered to have the ability to turn into any other kind of cell in the body. Those man-made astrocytes also showed the same characteristics as natural ones do.

Krishna Vadodaria, one of the lead authors on the paper, says having these iPSC-created astrocytes gives them a completely new tool to help explore brain development and disease, and hopefully develop new treatments for those diseases.

“The exciting thing about using iPSCs is that if we get tissue samples from people with diseases like multiple sclerosis, Alzheimer’s or depression, we will be able to study how their astrocytes behave, and how they interact with neurons.”

Stem cell stories that caught our eye: developing the nervous system, aging stem cells and identical twins not so identical

/ Karen Ring / Leave a comment

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

New theory for how the nervous system develops.

There’s a new theory on the block for how the nervous system is formed thanks to a study published yesterday by UCLA stem cell scientists in the journal Neuron.

The theory centers around axons, thin extensions projecting from nerve cells that transmit electrical signals to other cells in the body. In the developing nervous system, nerve cells extend axons into the brain and spinal cord and into our muscles (a process called innervation). Axons are guided to their final destinations by different chemicals that tell axons when to grow, when to not grow, and where to go.

Previously, scientists believed that one of these important chemical signals, a protein called netrin 1, exerted its influence over long distances in a gradient-like fashion from a structure in the developing nervous system called the floor plate. You can think of it like a like a cell phone tower where the signal is strongest the closer you are to the tower but you can still get some signal even when you’re miles away.

The UCLA team, led by senior author and UCLA professor Dr. Samantha Butler, questioned this theory because they knew that neural progenitor cells, which are the precursors to nerve cells, produce netrin1 in the developing spinal cord. They believed that the netrin1 secreted from these progenitor cells also played a role in guiding axon growth in a localized manner.

To test their hypothesis, they studied neural progenitor cells in the developing spines of mouse embryos. When they eliminated netrin1 from the neural progenitor cells, the axons went haywire and there was no rhyme or reason to their growth patterns.

Left: axons (green, pink, blue) form organized patterns in the normal developing mouse spinal cord. Right: removing netrin1 results in highly disorganized axon growth. (UCLA Broad Stem Cell Research Center/Neuron)

A UCLA press release explained what the scientists discovered next,

“They found that neural progenitors organize axon growth by producing a pathway of netrin1 that directs axons only in their local environment and not over long distances. This pathway of netrin1 acts as a sticky surface that encourages axon growth in the directions that form a normal, functioning nervous system.”

Like how ants leave chemical trails for other ants in their colony to follow, neural progenitor cells leave trails of netrin1 in the spinal cord to direct where axons go. The UCLA team believes they can leverage this newfound knowledge about netrin1 to make more effective treatments for patients with nerve damage or severed nerves.

In future studies, the team will tease apart the finer details of how netrin1 impacts axon growth and how it can be potentially translated into the clinic as a new therapeutic for patients. And from the sounds of it, they already have an idea in mind:

“One promising approach is to implant artificial nerve channels into a person with a nerve injury to give regenerating axons a conduit to grow through. Coating such nerve channels with netrin1 could further encourage axon regrowth.”

Age could be written in our stem cells.

The Harvard Gazette is running an interesting series on how Harvard scientists are tackling issues of aging with research. This week, their story focused on stem cells and how they’re partly to blame for aging in humans.

Stem cells are well known for their regenerative properties. Adult stem cells can rejuvenate tissues and organs as we age and in response to damage or injury. However, like most house hold appliances, adult stem cells lose their regenerative abilities or effectiveness over time.

Dr. David Scadden, co-director of the Harvard Stem Cell Institute, explained,

“We do think that stem cells are a key player in at least some of the manifestations of age. The hypothesis is that stem cell function deteriorates with age, driving events we know occur with aging, like our limited ability to fully repair or regenerate healthy tissue following injury.”

Harvard scientists have evidence suggesting that certain tissues, such as nerve cells in the brain, age sooner than others, and they trigger other tissues to start the aging process in a domino-like effect. Instead of treating each tissue individually, the scientists believe that targeting these early-onset tissues and the stem cells within them is a better anti-aging strategy.

David Sadden, co-director of the Harvard Stem Cell Institute.
(Jon Chase/Harvard Staff Photographer)

Dr. Scadden is particularly interested in studying adult stem cell populations in aging tissues and has found that “instead of armies of similarly plastic stem cells, it appears there is diversity within populations, with different stem cells having different capabilities.”

If you lose the stem cell that’s the best at regenerating, that tissue might age more rapidly.  Dr. Scadden compares it to a game of chess, “If we’re graced and happen to have a queen and couple of bishops, we’re doing OK. But if we are left with pawns, we may lose resilience as we age.”

The Harvard Gazette piece also touches on a changing mindset around the potential of stem cells. When stem cell research took off two decades ago, scientists believed stem cells would grow replacement organs. But those days are still far off. In the immediate future, the potential of stem cells seems to be in disease modeling and drug screening.

“Much of stem cell medicine is ultimately going to be ‘medicine,’” Scadden said. “Even here, we thought stem cells would provide mostly replacement parts.  I think that’s clearly changed very dramatically. Now we think of them as contributing to our ability to make disease models for drug discovery.”

I encourage you to read the full feature as I only mentioned a few of the highlights. It’s a nice overview of the current state of aging research and how stem cells play an important role in understanding the biology of aging and in developing treatments for diseases of aging.

Identical twins not so identical (Todd Dubnicoff)

Ever since Takahashi and Yamanaka showed that adult cells could be reprogrammed into an embryonic stem cell-like state, researchers have been wrestling with a key question: exactly how alike are these induced pluripotent stem cells (iPSCs) to embryonic stem cells (ESCs)?

It’s an important question to settle because iPSCs have several advantages over ESCs. Unlike ESCs, iPSCs don’t require the destruction of an embryo so they’re mostly free from ethical concerns. And because they can be derived from a patient’s cells, if iPSC-derived cell therapies were given back to the same patient, they should be less likely to cause immune rejection. Despite these advantages, the fact that iPSCs are artificially generated by the forced activation of specific genes create lingering concerns that for treatments in humans, delivering iPSC-derived therapies may not be as safe as their ESC counterparts.

Careful comparisons of DNA between iPSCs and ESCs have shown that they are indeed differences in chemical tags found on specific spots on the cell’s DNA. These tags, called epigenetic (“epi”, meaning “in addition”) modifications can affect the activity of genes independent of the underlying genetic sequence. These variations in epigenetic tags also show up when you compare two different preparations, or cell lines, of iPSCs. So, it’s been difficult for researchers to tease out the source of these differences. Are these differences due to the small variations in DNA sequence that are naturally seen from one cell line to the other? Or is there some non-genetic reason for the differences in the iPSCs’ epigenetic modifications?

Marian and Vivian Brown, were San Francisco’s most famous identical twins. Photo: Christopher Michel

A recent CIRM-funded study by a Salk Institute team took a clever approach to tackle this question. They compared epigenetic modifications between iPSCs derived from three sets of identical twins. They still found several epigenetic variations between each set of twins. And since the twins have identical DNA sequences, the researchers could conclude that not all differences seen between iPSC cell lines are due to genetics. Athanasia Panopoulos, a co-first author on the Cell Stem Cell article, summed up the results in a press release:

“In the past, researchers had found lots of sites with variations in methylation status [specific term for the epigenetic tag], but it was hard to figure out which of those sites had variation due to genetics. Here, we could focus more specifically on the sites we know have nothing to do with genetics. The twins enabled us to ask questions we couldn’t ask before. You’re able to see what happens when you reprogram cells with identical genomes but divergent epigenomes, and figure out what is happening because of genetics, and what is happening due to other mechanisms.”

With these new insights in hand, the researchers will have a better handle on interpreting differences between individual iPSC cell lines as well as their differences with ESC cell lines. This knowledge will be important for understanding how these variations may affect the development of future iPSC-based cell therapies.

Stem Cell Stories That Caught Our Eye: Plasticity in the pancreas and two cool stem cell tools added to the research toolbox

/ Karen Ring / Leave a comment

There’s more plasticity in the pancreas than we thought. You’re taught a lot of things about the world when you’re young. As you get older, you realize that not everything you’re told holds true and it’s your own responsibility to determine fact from fiction. This evolution in understanding happens in science too. Scientists do research that leads them to believe that biological processes happen a certain way, only to sometimes find, a few years later, that things are different or not exactly what they had originally thought.

There’s a great example of this in a study published this week in Cell Metabolism about the pancreas. Scientists from UC Davis found that the pancreas, which secretes a hormone called insulin that helps regulate the levels of sugar in your blood, has more “plasticity” than was originally believed. In this case, plasticity refers to the ability of a tissue or organ to regenerate itself by replacing lost or damaged cells.

The long-standing belief in this field was that the insulin producing cells, called beta cells, are replenished when beta cells actively divide to create more copies of themselves. In patients with type 1 diabetes, these cells are specifically targeted and killed off by the immune system. As a result, the beta cell population is dramatically reduced, and patients have to go on life-long insulin treatment.

UC Davis researchers have identified another type of insulin-producing cell in the islets, which appears to be an immature beta cell shown in red. (UC Davis)

But it turns out there is another cell type in the pancreas that is capable of making beta cells and they look like a teenage, less mature version of beta cells. The UC Davis team identified these cells in mice and in samples of human pancreas tissue. These cells hangout at the edges of structures called islets, which are clusters of beta cells within the pancreas. Upon further inspection, the scientists found that these immature beta cells can secrete insulin but cannot detect blood glucose like mature beta cells. They also found their point of origin: the immature beta cells developed from another type of pancreatic cell called the alpha cell.

Diagram of immature beta cells from Cell Metabolism.

In coverage by EurekAlert, Dr Andrew Rakeman, the director of discovery research at the Juvenile Diabetes Research Foundation, commented on the importance of this study’s findings and how it could be translated into a new approach for treating type 1 diabetes patients:

“The concept of harnessing the plasticity in the islet to regenerate beta cells has emerged as an intriguing possibility in recent years. The work from Dr. Huising and his team is showing us not only the degree of plasticity in islet cells, but the paths these cells take when changing identity. Adding to that the observations that the same processes appear to be occurring in human islets raises the possibility that these mechanistic insights may be able to be turned into therapeutic approaches for treating diabetes.”

 

Say hello to iPSCORE, new and improved tools for stem cell research. Stem cells are powerful tools to model human disease and their power got a significant boost this week from a new study published in Stem Cell Reports, led by scientists at UC San Diego School of Medicine.

The team developed a collection of over 200 induced pluripotent stem cell (iPS cell) lines derived from people of diverse ethnic backgrounds. They call this stem cell tool kit “iPSCORE”, which stands for iPSC Collection for Omic Research (omics refers to a field of study in biology ending in -omics, such as genomics or proteomics). The goal of iPSCORE is to identify particular genetic variants (unique differences in DNA sequence between people’s genomes) that are associated with specific diseases and to understand why they cause disease at the molecular level.

In an interview with Phys.org, lead scientist on the study, Dr. Kelly Frazer, further explained the power of iPSCORE:

“The iPSCORE collection contains 75 lines from people of non-European ancestry, including East Asian, South Asian, African American, Mexican American, and Multiracial. It includes multigenerational families and monozygotic twins. This collection will enable us to study how genetic variation influences traits, both at a molecular and physiological level, in appropriate human cell types, such as heart muscle cells. It will help researchers investigate not only common but also rare, and even family-specific variations.”

This research is a great example of scientists identifying a limitation in stem cell research and expanding the stem cell tool kit to model diseases in a diverse human population.

A false color scanning electron micrograph of cultured human neuron from induced pluripotent stem cell. Credit: Mark Ellisman and Thomas Deerinck, UC San Diego.

Stem cells that can grow into ANY type of tissue. Embryonic stem cells can develop into any cell type in the body, earning them the classification of pluripotent. But there is one type of tissue that embryonic stem cells can’t make and it’s called extra-embryonic tissue. This tissue forms the supportive tissue like the placenta that allows an embryo to develop into a healthy baby in the womb.

Stem cells that can develop into both extra-embryonic and embryonic tissue are called totipotent, and they are extremely hard to isolate and study in the lab because scientists lack the methods to maintain them in their totipotent state. Having the ability to study these special stem cells will allow scientists to answer questions about early embryonic development and fertility issues in women.

Reporting this week in the journal Cell, scientists from the Salk Institute in San Diego and Peking University in China identified a cocktail of chemicals that can stabilize human stem cells in a totipotent state where they can give rise to either tissue type. They called these more primitive stem cells extended pluripotent stem cells or EPS cells.

Salk Professor Juan Carlos Izpisua Bemonte, co–senior author of the paper, explained the problem their study addressed and the solution it revealed in a Salk news release:

“During embryonic development, both the fertilized egg and its initial cells are considered totipotent, as they can give rise to all embryonic and extra-embryonic lineages. However, the capture of stem cells with such developmental potential in vitro has been a major challenge in stem cell biology. This is the first study reporting the derivation of a stable stem cell type that shows totipotent-like bi-developmental potential towards both embryonic and extra-embryonic lineages.”

Human EPS cells (green) can be detected in both the embryonic part (left) and extra-embryonic parts (placenta and yolk sac, right) of a mouse embryo. (Salk Institute)

Using this new method, the scientists discovered that human EPS stem cells were able to develop chimeric embryos with mouse stem cells more easily than regular embryonic stem cells. First author on the study, Jun Wu, explained why this ability is important:

“The superior chimeric competency of both human and mouse EPS cells is advantageous in applications such as the generation of transgenic animal models and the production of replacement organs. We are now testing to see whether human EPS cells are more efficient in chimeric contribution to pigs, whose organ size and physiology are closer to humans.”

The Salk team reported on advancements in generating interspecies chimeras earlier this year. In one study, they were able to grow rat organs – including the pancreas, heart and eyes – in a mouse. In another study, they grew human tissue in early-stage pig and cattle embryos with the goal of eventually developing ways to generate transplantable organs for humans. You can read more about their research in this Salk news release.

Rhythmic brain circuits built from stem cells

/ Todd Dubnicoff / Leave a comment

The TV commercial is nearly 20 years old but I remember it vividly: a couple is driving down a street when they suddenly realize the music on their tape deck is in sync with the repetitive activity on the street. From the guy casually dribbling a basketball to people walking along the sidewalk to the delivery people passing packages out of their truck, everything and everyone is moving rhythmically to the beat.

The ending tag line was, “Sometimes things just come together,” which is quite true. Many of our basic daily activities like breathing and walking just come together as a result of repetitive movement. It’s easy to take them for granted but those rhythmic patterns ultimately rely on very intricate, interconnected signals between nerve cells, also called neurons, in the brain and spinal cord.

Circuitoids: a neural network in a lab dish

A CIRM-funded study published yesterday in eLife by Salk Institute scientists reports on a method to mimic these repetitive signals in a lab dish using neurons grown from embryonic stem cells. This novel cell circuitry system gives the researchers a tool for gaining new insights into neurodegenerative diseases, like Parkinson’s and ALS, and may even provide a means to fix neurons damaged by injury or disease.

The researchers changed or specialized mouse embryonic stem cells into neurons that either stimulate nerve signals, called excitatory neurons, or neurons that block nerve signals, called inhibitory neurons. Growing these groups of cells together led to spontaneous rhythmic nerve signals. These clumps of cells containing about 50,000 neurons each were dubbed circuitoids by the team.

pfaff-circutoid-cropped

Confocal microscope immunofluorescent image of a spinal cord neural circuit made entirely from stem cells and termed a “circuitoid.” Credit: Salk Institute.

Making neural networks dance to a different beat

A video produced by the Salk Institute (see below), shows some fascinating microscopy visualizations of these circuitoids’ repetitive signals. In the video, team leader Samuel Pfaff explains that changing the ratio of excitatory vs inhibitory neurons had noticeable effects on the rhythm of the nerve impulses:

“What we were able to do is combine different ratios of cell types and study properties of the rhythmicity of the circuitoid. And that rhythmicity could be very tightly control depending on the cellular composition of the neural networks that we were forming. So we could regulate the speed [of the rhythmicity] which is kind of equivalent to how fast you’re walking.”

It’s possible that the actual neural networks in our brains have the flexibility to vary the ratio of the active excitatory to inhibitory neurons as a way to allow adjustments in the body’s repetitive movements. But the complexity of those networks in the human brain are staggering which is why these circuitoids could help:

Samuel Pfaff. (Salk Institute)

Samuel Pfaff. (Salk Institute)

“It’s still very difficult to contemplate how large groups of neurons with literally billions if not trillions of connections take information and process it,” says Pfaff in a press release. “But we think that developing this kind of simple circuitry in a dish will allow us to extract some of the principles of how real brain circuits operate. With that basic information maybe we can begin to understand how things go awry in disease.”