An unexpected link: immune cells send muscle injury signal to activate stem cell regeneration

We’ve written many blogs over the years about research focused on muscle stem cell function . Those stories describe how satellite cells, another name for muscle stem cells, lay dormant but jump into action to grow new muscle cells in response to injury and damage. And when satellite function breaks down with aging as well as with diseases like muscular dystrophy, the satellite cells drop in number and/or lose their capacity to divide, leading to muscle degeneration.

Illustration of satellite cells within muscle fibers. Image source: APSU Biology

One thing those research studies don’t focus on is the cellular and molecular signals that cause the satellite cells to say, “Hey! We need to start dividing and regenerating!” A Stanford research team examining this aspect of satellite cell function reports this week in Nature Communications that immune cells play an unexpected role in satellite cell activation. This study, funded in part by CIRM, provides a fundamental understanding of muscle regeneration and repair that could aid the development of novel treatments for muscle disorders.

ADAMTS1: a muscle injury signal?
To reach this conclusion, the research team drew upon previous studies that indicated a gene called Adamts1 was turned on more strongly in the activated satellite cells compared to the dormant satellite cells. The ADAMTS1 protein is a secreted protein so the researchers figured it’s possible it could act as a muscle injury signal that activates satellites cells. When ADAMTS1 was applied to mouse muscle fibers in a petri dish, satellite cells were indeed activated.

Next, the team examined ADAMTS1 in a mouse model of muscle injury and found the protein clearly increased within one day after muscle injury. This timing corresponds to when satellite cells drop out of there dormant state after muscle injury and begin dividing and specializing into new muscle cells. But follow up tests showed the satellite cells were not the source of ADAMTS1. Instead, a white blood cell called a macrophage appeared to be responsible for producing the protein at the site of injury. Macrophages, which literally means “big eaters”, patrol our organs and will travel to sites of injury and infection to keep them clean and healthy by gobbling up dead cells, bacteria and viruses. They also secrete various proteins to alert the rest of the immune system to join the fight against infection.

Immune cell’s double duty after muscle injury: cleaning up the mess and signaling muscle regeneration
To confirm the macrophages’ additional role as the transmitter of this ADAMTS1 muscle injury signal, the researchers generated transgenic mice whose macrophages produce abnormally high levels of ADAMTS1. The activation of satellite cells in these mice was much higher than in normal mice lacking this boost of ADAMTS1 production. And four months after birth, the increased activation led to larger muscles in the transgenic mice. In terms of muscle regeneration, one-month old transgenic mice recovered from muscle injury faster than normal mice. Stanford professor Brian Feldman, MD, PhD, the senior author of the study, described his team’s initial reaction to their findings in an interview with Scope, Stanford Medicine’s blog:

“While, in retrospect, it might make intuitive sense that the same cells that are sent into a site of injury to clean up the mess also carry the tools and signals needed to rebuild what was destroyed, it was not at all obvious how, or if, these two processes were biologically coupled. Our data show a direct link in which the clean-up crew releases a signal to launch the rebuild. This was a surprise.”

Further experiments showed that ADAMTS1 works by chopping up a protein called NOTCH that lies on the surface of satellite cells. NOTCH provides signals to the satellite cell to stay in a dormant state. So, when ADAMTS1 degrades NOTCH, the dormancy state of the satellite cells is lifted and they begin to divide and transform into muscle cells.

A pathway to novel muscle disorder therapies?
One gotcha with the ADAMTS1 injury signal is that too much activation can lead to a depletion of satellite cells. In fact, after 8 months, muscle regeneration actually weakened in the transgenic mice that were designed to persistently produce the protein. Still, this novel role of macrophages in stimulating muscle regeneration via the secreted ADAMTS1 protein opens a door for the Stanford team to explore new therapeutic approaches to treating muscle disorders:

“We are excited to learn that a single purified protein, that functions outside the cell, is sufficient to signal to muscle stem cells and stimulate them to differentiate into muscle,” says Dr. Feldman. “The simplicity of that type of signal in general and the extracellular nature of the mechanism in particular, make the pathway highly tractable to manipulation to support efforts to develop therapies that improve health.”

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Stem Cell Stories That Caught our Eye: Duchenne muscular dystrophy and short telomeres, motor neurons from skin, and students today, stem cell scientists tomorrow

Short telomeres associated with Duchenne Muscular Dystrophy.

Duchenne Muscular Dystrophy (DMD) is a severe muscle wasting disease that typically affects young men. There is no cure for DMD and the average life expectancy is 26. These are troubling facts that scientists at the University of Pennsylvania are hoping to change with their recent findings in Stem Cell Reports.

Muscle stem cells with telomeres shown in red. (Credit: Penn Medicine)

The team discovered that the muscle stem cells in DMD patients have shortened telomeres, which are the protective caps on the ends of chromosomes that prevent the loss of precious genetic information during cell division. Each time a cell divides, a small section of telomere is lost. This typically isn’t a problem because telomeres are long enough to protect cells through many divisions.

But it turns out this is not the case for the telomeres in the muscle stem cells of DMD patients. Because DMD patients have weak muscles, they experience constant muscle damage and their muscle stem cells have to divide more frequently (basically non-stop) to repair and replace muscle tissue. This is bad news for the telomeres in their muscle stem cells. Foteini Mourkioti, senior author on the study, explained in a news release,

“We found that in boys with DMD, the telomeres are so short that the muscle stem cells are probably exhausted. Due to the DMD, their muscle stem cells are constantly repairing themselves, which means the telomeres are getting shorter at an accelerated rate, much earlier in life. Future therapies that prevent telomere loss and keep muscle stem cells viable might be able to slow the progress of disease and boost muscle regeneration in the patients.”

With these new insights, Mourkioti and his team believe that targeting muscle stem cells before their telomeres become too short is a good path to pursue for developing new treatments for DMD.

“We are now looking for signaling pathways that affect telomere length in muscle stem cells, so that in principle we can develop drugs to block those pathways and maintain telomere length.”

Making Motor Neurons from Skin.

Skin cells and brain cells are like apples and oranges, they look completely different and have different functions. However, in the past decade, researchers have developed methods to transform skin cells into neurons to study neurodegenerative disorders and develop new strategies to treat brain diseases.

Scientists at Washington University School of Medicine in St. Louis published new findings on this topic yesterday in the journal Cell Stem Cell. In a nut shell, the team discovered that a specific combination of microRNAs (molecules involved in regulating what genes are turned on and off) and transcription factors (proteins that also regulate gene expression) can turn human skin cells into motor neurons, which are the brain cells that degenerate in neurodegenerative diseases like ALS, also known as Lou Gehrig’s disease.

Human motor neurons made from skin. (Credit: Daniel Abernathy)

This magical cocktail of factors told the skin cells to turn off genes that make them skin and turn on genes that transformed them into motor neurons. The scientists used skin cells from healthy individuals but will soon use their method to make motor neurons from patients with ALS and other motor neuron diseases. They are also interested in generating neurons from older patients who are more advanced in their disease. Andrew Yoo, senior author on the study, explained in a news release,

“In this study, we only used skin cells from healthy adults ranging in age from early 20s to late 60s. Our research revealed how small RNA molecules can work with other cell signals called transcription factors to generate specific types of neurons, in this case motor neurons. In the future, we would like to study skin cells from patients with disorders of motor neurons. Our conversion process should model late-onset aspects of the disease using neurons derived from patients with the condition.”

This research will make it easier for other scientists to grow human motor neurons in the lab to model brain diseases and potentially develop new treatments. However, this is still early stage research and more work should be done to determine whether these transformed motor neurons are the “real deal”. A similar conclusion was shared by Julia Evangelou Strait, the author of the Washington University School of Medicine news release,

“The converted motor neurons compared favorably to normal mouse motor neurons, in terms of the genes that are turned on and off and how they function. But the scientists can’t be certain these cells are perfect matches for native human motor neurons since it’s difficult to obtain samples of cultured motor neurons from adult individuals. Future work studying neuron samples donated from patients after death is required to determine how precisely these cells mimic native human motor neurons.”

Students Today, Scientists Tomorrow.

What did you want to be when you were growing up? For Benjamin Nittayo, a senior at Cal State University Los Angeles, it was being a scientist researching a cure for acute myeloid leukemia (AML), a form of blood cancer that took his father’s life. Nittayo is making his dream into a reality by participating in a summer research internship through the Eugene and Ruth Roberts Summer Student Academy at the City of Hope in Duarte California.

Nittayo has spent the past two summers doing cancer research with scientists at the Beckman Research Institute at City of Hope and hopes to get a PhD in immunology to pursue his dream of curing AML. He explained in a City of Hope news release,

“I want to carry his memory on through my work. Being in this summer student program helped me do that. It influenced the kind of research I want to get into as a scientist and it connected me to my dad. I want to continue the research I was able to start here so other people won’t have to go through what I went through. I don’t wish that on anybody.”

The Roberts Academy also hosts high school students who are interested in getting their first experience working in a lab. Some of these students are part of CIRM’s high school educational program Summer Program to Accelerate Regenerative Medicine Knowledge or SPARK. The goal of SPARK is to train the next generation of stem cell scientists in California by giving them hands-on training in stem cell research at leading institutes in the state.

This year, the City of Hope hosted the Annual SPARK meeting where students from the seven different SPARK programs presented their summer research and learned about advances in stem cell therapies from City of Hope scientists.

Ashley Anderson, a student at Mira Costa High School in Manhattan Beach, had the honor of giving the City of Hope SPARK student talk. She shared her work on Canavan’s disease, a progressive genetic disorder that damages the brain’s nerve cells during infancy and can cause problems with movement and muscle weakness.

Under the guidance of her mentor Yanhong Shi, Ph.D., who is a Professor of Developmental and Stem Cell Biology at City of Hope, Ashley used induced pluripotent stem cells (iPSCs) from patients with Canavan’s to generate different types of brain cells affected by the disease. Ashley helped develop a protocol to make large quantities of neural progenitor cells from these iPSCs which the lab hopes to eventually use in clinical trials to treat Canavan patients.

Ashley has always been intrigued by science, but thanks to SPARK and the Roberts Academy, she was finally able to gain actual experience doing science.

“I was looking for an internship in biosciences where I could apply my interest in science more hands-on. Science is more than reading a textbook, you need to practice it. That’s what SPARK has done for me. Being at City of Hope and being a part of SPARK was amazing. I learned so much from Dr. Shi. It’s great to physically be in a lab and make things happen.”

You can read more about Ashley’s research and those of other City of Hope SPARK students here. You can also find out more about the educational programs we fund on our website and on our blog (here and here).

Have scientists discovered a natural way to boost muscle regeneration?

Painkillers like ibuprofen and aspirin are often a part of an athlete’s post-exercise regimen after intense workouts. Sore muscles, aches and stiffness can be more manageable by taking these drugs – collectively called non-steroidal anti-inflammatory drugs, or NSAIDS – to reduce inflammation and pain. But research suggests that the anti-inflammatory effects of these painkillers might cause more harm than good by preventing muscle repair and regeneration after injury or exercise.

A new study out of Stanford Medicine supports these findings and proposes that a component of the inflammatory process is necessary to promote muscle regeneration. Their study was funded in part by a CIRM grant and was published this week in the Proceedings of the National Academy of Sciences.

Muscle stem cells are scattered throughout skeletal muscle tissue and remain inactive until they are stimulated to divide. When muscles are damaged or injured, an inflammatory response involving a cascade of immune cells, molecules and growth factors activates these stem cells, prompting them to regenerate muscle tissue.

Andrew Ho, Helen Blau and Adelaida Palla led a study that found drugs like aspirin and ibuprofen can inhibit the ability of muscle tissue to repair itself in mice. (Image credit: Scott Reiff)

The Stanford team discovered that a molecule called Prostaglandin E2 or PGE2 is released during the inflammatory response and stimulates muscle repair by directly targeting the EP4 receptor on the surface of muscle stem cells. The interaction between PGE2 and EP4 causes muscle stem cells to divide and robustly regenerate muscle tissue.

Senior author on the study, Dr. Helen Blau, explained her team’s interest in PGE2-mediated muscle repair in a news release,

“Traditionally, inflammation has been considered a natural, but sometimes harmful, response to injury. But we wondered whether there might be a component in the pro-inflammatory signaling cascade that also stimulated muscle repair. We found that a single exposure to prostaglandin E2 has a profound effect on the proliferation of muscle stem cells in living animals. We postulated that we could enhance muscle regeneration by simply augmenting this natural physiological process in existing stem cells already located along the muscle fiber.”

Further studies in mice revealed that injury increased PGE2 levels in muscle tissue and increased expression of the EP4 receptor on muscle stem cells. This gave the authors the idea that treating mice with a pulse of PGE2 could stimulate their muscle stem cells to regenerate muscle tissue.

Their hunch turned out to be right. Co-first author Dr. Adelaida Palla explained,

“When we gave mice a single shot of PGE2 directly to the muscle, it robustly affected muscle regeneration and even increased strength. Conversely, if we inhibited the ability of the muscle stem cells to respond to naturally produced PGE2 by blocking the expression of EP4 or by giving them a single dose of a nonsteroidal anti-inflammatory drug to suppress PGE2 production, the acquisition of strength was impeded.”

Their research not only adds more evidence against the using NSAID painkillers like ibuprofen and aspirin to treat sore muscles, but also suggests that PGE2 could be a natural therapeutic strategy to boost muscle regeneration.

This cross-section of regenerated muscle shows muscle stem cells (red) in their niche along the muscle fibers (green). (Photo courtesy of Blau lab)

PGE2 is already approved by the US Food and Drug Administration (FDA) to induce labor in pregnant women, and Dr. Blau hopes that further research in her lab will pave the way for repurposing PGE2 to treat muscle injury and other conditions.

“Our goal has always been to find regulators of human muscle stem cells that can be useful in regenerative medicine. It might be possible to repurpose this already FDA-approved drug for use in muscle. This could be a novel way to target existing stem cells in their native environment to help people with muscle injury or trauma, or even to combat natural aging.”

Stem cell stories that caught our eye: update on Capricor’s heart attack trial; lithium on the brain; and how stem cells do math

Capricor ALLSTARToday our partners Capricor Therapeutics announced that its stem cell therapy for patients who have experienced a large heart attack is unlikely to meet one of its key goals, namely reducing the scar size in the heart 12 months after treatment.

The news came after analyzing results from patients at the halfway point of the trial, six months after their treatment in the Phase 2 ALLSTAR clinical trial which CIRM was funding. They found that there was no significant difference in the reduction in scarring on the heart for patients treated with donor heart-derived stem cells, compared to patients given a placebo.

Obviously this is disappointing news for everyone involved, but we know that not all clinical trials are going to be successful. CIRM supported this research because it clearly addressed an unmet medical need and because an earlier Phase 1 study had showed promise in helping prevent decline in heart function after a heart attack.

Yet even with this failure to repeat that promise in this trial,  we learned valuable lessons.

In a news release, Dr. Tim Henry, Director of the Division of Interventional Technologies in the Heart Institute at Cedars-Sinai Medical Center and a Co-Principal Investigator on the trial said:

“We are encouraged to see reductions in left ventricular volume measures in the CAP-1002 treated patients, an important indicator of reverse remodeling of the heart. These findings support the biological activity of CAP-1002.”

Capricor still has a clinical trial using CAP-1002 to treat boys and young men developing heart failure due to Duchenne Muscular Dystrophy (DMD).

Lithium gives up its mood stabilizing secrets

As far back as the late 1800s, doctors have recognized that lithium can help people with mood disorders. For decades, this inexpensive drug has been an effective first line of treatment for bipolar disorder, a condition that causes extreme mood swings. And yet, scientists have never had a good handle on how it works. That is, until this week.

evan snyder

Evan Snyder

Reporting in the Proceedings of the National Academy of Sciences (PNAS), a research team at Sanford Burnham Prebys Medical Discovery Institute have identified the molecular basis of the lithium’s benefit to bipolar patients.  Team lead Dr. Evan Snyder explained in a press release why his group’s discovery is so important for patients:

“Lithium has been used to treat bipolar disorder for generations, but up until now our lack of knowledge about why the therapy does or does not work for a particular patient led to unnecessary dosing and delayed finding an effective treatment. Further, its side effects are intolerable for many patients, limiting its use and creating an urgent need for more targeted drugs with minimal risks.”

The study, funded in part by CIRM, attempted to understand lithium’s beneficial effects by comparing cells from patient who respond to those who don’t (only about a third of patients are responders). Induced pluripotent stem cells (iPSCs) were generated from both groups of patients and then the cells were specialized into nerve cells that play a role in bipolar disorder. The team took an unbiased approach by looking for differences in proteins between the two sets of cells.

The team zeroed in on a protein called CRMP2 that was much less functional in the cells from the lithium-responsive patients. When lithium was added to these cells the disruption in CRMP2’s activity was fixed. Now that the team has identified the molecular location of lithium’s effects, they can now search for new drugs that do the same thing more effectively and with fewer side effects.

The stem cell: a biological calculator?

math

Can stem cells do math?

Stem cells are pretty amazing critters but can they do math? The answer appears to be yes according to a fascinating study published this week in PNAS Proceedings of the National Academy of Sciences.

Stem cells, like all cells, process information from the outside through different receptors that stick out from the cells’ outer membranes like a satellite TV dish. Protein growth factors bind those receptors which trigger a domino effect of protein activity inside the cell, called cell signaling, that transfers the initial receptor signal from one protein to another. Ultimately that cascade leads to the accumulation of specific proteins in the nucleus where they either turn on or off specific genes.

Intuition would tell you that the amount of gene activity in response to the cell signaling should correspond to the amount of protein that gets into the nucleus. And that’s been the prevailing view of scientists. But the current study by a Caltech research team debunks this idea. Using real-time video microscopy filming, the team captured cell signaling in individual cells; in this case they used an immature muscle cell called a myoblast.

goentoro20170508

Behavior of cells over time after they have received a Tgf-beta signal. The brightness of the nuclei (circled in red) indicates how much Smad protein is present. This brightness varies from cell to cell, but the ratio of brightness after the signal to before the signal is about the same. Image: Goentoro lab, CalTech.

To their surprise the same amount of growth factor given to different myoblasts cells led to the accumulation of very different amounts of a protein called Smad3 in the cells’ nuclei, as much as a 40-fold difference across the cells. But after some number crunching, they discovered that dividing the amount of Smad3 after growth factor stimulation by the Smad3 amount before growth stimulation was similar in all the cells.

As team lead Dr. Lea Goentoro mentions in a press release, this result has some very important implications for studying human disease:

“Prior to this work, researchers trying to characterize the properties of a tumor might take a slice from it and measure the total amount of Smad in cells. Our results show that to understand these cells one must instead measure the change in Smad over time.”

Could revving up stem cells help senior citizens heal as fast as high school seniors?

All physicians, especially surgeons, sport medicine doctors, and military medical corps share a similar wish: to able to speed up the healing process for their patients’ incisions and injuries. Data published this week in Cell Reports may one day fulfill that wish. The study – reported by a Stanford University research team – pinpoints a single protein that revs up stem cells in the body, enabling them to repair tissue at a quicker rate.

Screen Shot 2017-04-19 at 5.37.38 PM

Muscle fibers (dark areas surrounding by green circles) are larger in mice injected with HGFA protein (right panel) compared to untreated mice (left panel), an indication of faster healing after muscle injury.
(Image: Cell Reports 19 (3) p. 479-486, fig 3C)

Most of the time, adult stem cells in the body keep to themselves and rarely divide. This calmness helps preserve this important, small pool of cells and avoids unnecessary mutations that may happen whenever DNA is copied during cell division.

To respond to injury, stem cells must be primed by dividing one time, which is a very slow process and can take several days. Once in this “alert” state, the stem cells are poised to start dividing much faster and help repair damaged tissue. The Stanford team, led by Dr. Thomas Rando, aimed to track down the signals that are responsible for this priming process with the hope of developing drugs that could help jump-start the healing process.

Super healing serum: it’s not just in video games
The team collected blood serum from mice two days after the animals had been subjected to a muscle injury (the mice were placed under anesthesia during the procedure and given pain medication afterwards). When that “injured” blood was injected into a different set of mice, their muscle stem cells became primed much faster than mice injected with “uninjured” blood.

“Clearly, blood from the injured animal contains a factor that alerts the stem cells,” said Rando in a press release. “We wanted to know, what is it in the blood that is doing this?”

 

A deeper examination of the priming process zeroed in on a muscle stem cell signal that is turned on by a protein in the blood called hepatocyte growth factor (HGF). So, it seemed likely that HGF was the protein that they had been looking for. But, to their surprise, there were no differences in the amount of HGF found in blood from injured and uninjured mice.

HGFA: the holy grail of healing?
It turns out, though, that HGF must first be chopped in two by an enzyme called HGFA to become active. When the team went back and examined the injured and uninjured blood, they found that it was HGFA which showed a difference: it was more active in the injured blood.

To show that HGFA was directly involved in stimulating tissue repair, the team injected mice with the enzyme two days before the muscle injury procedure. Twenty days post injury, the mice injected with HGFA had regenerated larger muscle fibers compared to untreated mice. Even more telling, nine days after the HGFA treatment, the mice had better recovery in terms of their wheel running activity compared to untreated mice.

To mimic tissue repair after a surgery incision, the team also looked at the impact of HGFA on skin wound healing. Like the muscle injury results, injecting animals with HGFA two days before creating a skin injury led to better wound healing compared to untreated mice. Even the hair that had been shaved at the surgical site grew back faster. First author Dr. Joseph Rodgers, now at USC, summed up the clinical implications of these results :

“Our research shows that by priming the body before an injury you can speed the process of tissue repair and recovery, similar to how a vaccine prepares the body to fight infection. We believe this could be a therapeutic approach to improve recovery in situations where injuries can be anticipated, such as surgery, combat or sports.”

Could we help senior citizens heal as fast as high school seniors?
Another application for this therapeutic approach may be for the elderly. Lots of things slow down when you get older including your body’s ability to heal itself. This observation sparks an intriguing question for Rando:

“Stem cell activity diminishes with advancing age, and older people heal more slowly and less effectively than younger people. Might it be possible to restore youthful healing by activating this [HGFA] pathway? We’d love to find out.”

I bet a lot of people would love for you to find out, too.

Meat the future of stem cells. And I do mean “meat”.

'...And just a pince of stem cells.'

Over the years there have been a lot of interesting, odd ball, even a few really rather crazy stories about stem cell research that have made the news. So in honor of Halloween, we thought we’d look back at a few of them to remind ourselves that not all science is worthy of pursuit.

Celebrity meat:

meat

Back in 2014 a company called BiteLabs claimed it was going to make  “fine artisanal salami from meat that has been lab-grown from celebrity tissue samples.” You read that right. They were going to make salami from famous people.

Here’s how they described the process. First they would take a small sample of stem cells from the celebrity, the kind of cell that is used to grow and repair damaged muscles. Then they would grow those cells in the lab, increasing their number to millions of muscle cells. Those are then ground up, mixed with regular salami and some spices, fats and oils until you had the desired consistency and texture.

Then they were stuffed into casings, and dried, aged and cured until you end up with celebrity salami.

Not surprisingly it attracted a lot of attention. The Twitterverse was filled with images of celebrities people wanted to “eat” – Jennifer Lawrence, ‘a new kind of Hunger Games’. It was also filled with headlines from magazines like Cosmopolitan asking “Is this the weirdest food of all time”.

Turns out it was more of a joke, or at least a fun way to get people discussing bioethics and pushing the boundaries – or maybe it was the buttons – of tech and society.

Meet the most expensive meat in the world

If that was meant to be a joke then some researchers at Maastricht University in the Netherlands didn’t get it. Because the next year they actually produced a burger that was made out of stem cells.

They took some bovine – aka ‘cow’ – stem cells, grew them in the lab (this took three months so definitely not a “fast food”), then mixed them with salt, breadcrumbs and egg and cooked them in a little butter and sunflower oil.

People who tried it described it as “tough” and “not that juicy”. Harder to stomach than the burger itself was the price tag, more than $300,000.

A mammoth task

woollymammoth

It’s not just meat that is attracting the attention of stem cell researchers. More recently a team of Korean and Russian scientists decided it might be fun to try and use stem cells to “grow” a mammoth. You know, the giant, woolly, elephant-like creatures that went extinct thousands of years ago – except for occasional starring roles in the Ice Age animated movies.

They were going to take some DNA from the remnants of a mammoth found in the frozen tundra in Siberia, decode its genome, then create a functioning cell nucleus and transplant that into an elephant’s embryo. Easy right? What could possible go wrong (for some suggestions see Jurassic Park/World).

Maybe if that doesn’t work out they could just grow the cells into meat and market them. Mammoth burgers. Sounds yummy doesn’t it.

Happy Halloween.

 

Scientists find new stem cell target for regenerating aging muscles

Young Arnold (wiki)

Young Arnold (wiki)

Today I’m going to use our former governor Arnold Schwarzenegger as an example of what happens to our muscles when we age.

One of Arnold’s many talents when he was younger was being a professional bodybuilder. As you can see in this photo, Arnold worked hard to generate an impressive amount of muscle that landed him lead roles in movies Conan the Barbarian and The Terminator.

Older Arnold

Older Arnold

If you look at pictures of Arnold now (who is now 68), while still being an impressively large human being, it’s obvious that much of his muscular bulk has diminished. That’s because as humans age, so do their muscles.

Muscles shrink with age

As muscles age, they slowly lose mass and shrink (a condition called sarcopenia) because of a number of reasons – one of them being their inability to regenerate new muscle tissue efficiently. The adult stem cells responsible for muscle regeneration are called satellite cells. When muscles are injured, satellite cells are activated to divide and generate new muscle fibers that can repair injury and also improve muscle function.

However, satellite cells become less efficient at doing their job over time because of environmental and internal reasons, and scientists are looking for new targets that can restore and promote the regenerative abilities of muscle stem cells for human therapeutic applications.

A study published earlier this week in Nature Medicine, identified a potential new target that could boost muscle stem cell regeneration and improved muscle function in a mouse model of Duchenne muscular dystrophy.

β1-integrin is important for muscle regeneration

Scientists from the Carnegie Institute of Washington found that β1-integrin is important for maintaining the homeostasis (or balance) of the muscle stem cell environment. If β1-integrin is doing its job properly, muscle stem cells are able to go about their regular routine of being dormant, activating in response to injury, dividing to create new muscle tissue, and then going back to sleep.

When the scientists studied the function of β1-integrin in the muscles of aged mice, they found that the integrin wasn’t functioning properly. Without β1-integrin, mouse satellite cells spontaneously turned into muscle tissue and were unable to maintain their regenerative capacity following muscle injury.

Upon further inspection, they found that β1-integrin interacts with a growth factor called fibroblast growth factor 2 (Fgf2) and this relationship was essential for promoting muscle regeneration following injury. When β1-integrin function deteriorates as in the muscles of aged mice, the mice lose sensitivity to the regenerative capacity of Fgf2.

Restoring muscle function in mice with muscular dystrophy

By using an antibody to artificially activate β1-integrin function in the muscles of aged mice, they were able to restore Fgf2 responsiveness and boosted muscle regeneration after injury. When a similar technique was used in mice with Duchenne muscular dystrophy, they observed muscle regeneration and improved muscle function.

Muscle loss seen in muscular dystrophy mice (left). Treatment with beta1 intern boosts muscle regeneration in the same mice (right). (Nature Medicine)

Muscle loss seen in muscular dystrophy mice (left). Treatment with B1-integrin boosts muscle regeneration in the same mice (right). (Nature Medicine)

The authors believe that β1-integrin acts as a sensor of the muscle stem cell environment that it maintains a balance between a dormant and a regenerative stem cell state. They conclude in their publication:

“β1-integrin senses the SC [satellite cell] niche to maintain responsiveness to Fgf2, and this integrin represents a potential therapeutic target for pathological conditions of the muscle in which the stem cell niche is compromised.”

Co-author on the study Dr. Chen-Ming Fan also spoke to the clinical relevance of their findings in a piece by GenBio:

“Inefficient muscular healing in the elderly is a significant clinical problem and therapeutic approaches are much needed, especially given the aging population. Finding a way to target muscle stem cells could greatly improve muscle renewal in older individuals.”

Does this mean anyone can be a body builder?

So does this study mean that one day we can prevent muscle loss in the elderly and all be body builders like Arnold? I highly doubt that. It’s important to remember these are preclinical studies done in mouse models and much work needs to be done to test whether β1-integrin is an appropriate therapeutic target in humans.

However, I do think this study sheds new light on the inner workings of the muscle stem cell environment. Finding out more clues about how to promote the health and regenerative function of this environment will bring the field closer to generating new treatments for patients suffering from muscle wasting diseases like muscular dystrophy.

Stem cell stories that caught our eye: growing muscle, new blood vessels and pacemakers and Tommy John surgery

Here are some stem cell stories that caught our eye this past week. Some are groundbreaking science, others are of personal interest to us, and still others are just fun.

Better way to grow muscle.  The specialized stem cells responsible for repairing muscle, the satellite cells, have always been difficult to grow in large quantities in the lab. They have a strong natural hankering to mature into muscle. Researchers have not been able to keep them in their stem cell state in the lab and that prevents creating enough of them for effective therapies for diseases like muscular dystrophy.

new muscle Kodaira

New muscle fibers in green grown in mice from satellite stem cells

A team at the National Institute of Neuroscience in Kodaira, Japan, published what seems to be a simple solution to the problem. In a press release from the publisher of the Journal of Neuromuscular Diseases posted by Science Daily they reported that adding just one protein to satellite cells allowed them to grow indefinitely in the lab and expand to the point they could provide a meaningful transplant that resulted in muscle repair in mice.

 “This research enables us to get one step closer to the optimal culture conditions for muscle stem cells,” said Shin’ichi Takeda from the institute.

The protein they used, leukemia inhibitory factor, and its downstream impacts on other genes is now the subject of their ongoing research.

 

Regenerating heart vessels. A CIRM funded team at Sanford Burnham Prebys Medical Discovery Institute (SBP) in San Diego and at Stanford University have shown that repressing a single gene can encourage the formation of new blood vessels in the heart. Creating those new conduits for oxygen after a heart attack could reduce damage to the heart muscle and prevent development of heart failure.

Building new blood vessels requires coordination of several growth factors and clinical trials evaluating individual factors have resulted in failure. The SBP team found that a single gene repressed all those needed factors and blocking it could let them do their job and create new blood vessels.

Mark Mercola

Mark Mercola

“We found that a protein called RBPJ serves as the master controller of genes that regulate blood vessel growth in the adult heart,” said senior author Mark Mercola, a professor at SBP and at Stanford, in an institute press release. “RBPJ acts as a brake on the formation of new blood vessels. Our findings suggest that drugs designed to block RBPJ may promote new blood supplies and improve heart attack outcomes.”

 The authors also suggested that RBPJ itself might be beneficial in cancer if it can inhibit the new blood vessels tumors need to thrive.

 

Bionic patch as pacemaker.  Chemists at Harvard have designed nanoscale electronic scaffolds that can be seeded with heart cells and are able to conduct current to detect irregular heart rhythms and potentially send out electrical signals to correct them.

 “Rather than simply implanting an engineered patch built on a passive scaffold, our works suggests it will be possible to surgically implant an innervated patch that would now be able to monitor and subtly adjust its performance,” said Charles Lieber the senior author in a university press release posted by Phys.Org. The research was published in Nature Nanotechnology

 With its electronics built into the patch that is integrated into the heart, Lieber suggested the bionic patch could detect heart rhythm problems sooner than traditional pace makers. Another use for the patch he suggested could be to screen potential drugs.

 

Alternate to Tommy John in pictures. Sports fans generally have a vague idea of what Tommy John surgery is. First performed on baseball pitcher Tommy John of the LA Dodgers in 1974, the surgery replaces a torn elbow tendon with one from another part of the body.  A number of baseball players in the past couple years have made headlines because they sought out an alternative to this invasive procedure using stem cells.

The players sometimes improve, but with their high-priced team doctors also demanding extensive physical therapy and other interventions, we don’t really know how much of the improvement is due to the stem cells.  I am not aware of controlled clinical trials looking at the alternative therapy.

LA Angels Andrew HeaneyBut given how much it is in the news, I thought it would be good to share this excellent info-graphic from the LA Times explaining exactly what happens with the stem cell version of the Tommy John procedure. The Times posted the graphic yesterday, and then today, papers around the country ran stories that the most recent famous recipient of the cells, Los Angeles Angels lefthander Andrew Heaney, was going to have the old-fashioned surgery today because the stem cell treatment did not work in this case.

There may be some individuals, likely those with only partial tears who might benefit from this stem cell procedure that uses a type of stem cell that is not likely to replace tendons, but can release factors that summons the body’s natural healing apparatus to do a better job.  But until more formal clinical trials are conducted, it will be hard for     doctors to know who would and would not benefit.

Helping stem cells sleep can boost their power to heal

Mouse muscle

Mighty mouse muscle cells

We are often told that sleep is one of the most important elements of a healthy lifestyle, that it helps in the healing and repair of our heart and blood vessels – among other things.

It turns out that sleep, or something very similar, is equally important for stem cells, helping them retain their power or potency, which is a measure of their effectiveness and efficiency in generating the mature adult cells that are needed to repair damage. Now researchers from Stanford, with a little help from CIRM, have found a way to help stem cells get the necessary rest before kicking in to action. This could pave the way for a whole new approach to treating a variety of genetic disorders such as muscular dystrophy.

Inside out

One problem that has slowed down the development of stem cell therapies has been the inability to manipulate stem cells outside of the body, without reducing their potency. In the body these cells can remain quiescent or dormant for years until called in to action to repair an injury. That’s because they are found in a specialized environment or niche, one that has very particular physical, chemical and biological properties. However, once the stem cells are removed from that niche and placed in a dish in the lab they become active and start proliferating and changing into other kinds of cells.

You might think that’s good, because we want those stem cells to change and mature, but in this case we don’t, at least not yet. We want them to wait till we return them to the body to do their magic. Changing too soon means they have less power to do that.

Researchers at Stanford may have found a way to stop that happening, by creating an environment in the lab that more closely resembles that in the body, so the stem cells remain dormant longer.

As senior author, Thomas Rando, said in a Stanford news release, they have found a way to keep the stem cells dormant longer:

Dr. Thomas Rando, Stanford

Dr. Thomas Rando, Stanford

“Normally these stem cells like to cuddle right up against their native muscle fibers. When we disrupt that interaction, the cells are activated and begin to divide and become less stemlike. But now we’ve designed an artificial substrate that, to the cells, looks, smells and feels like a real muscle fiber. When we also bathe these fibers in the appropriate factors, we find that the stem cells maintain high-potency and regenerative capacity.”

Creating an artificial home

When mouse muscle stem cells (MuSCs) are removed from the mouse they lose their potency after just two days. So the Stanford team set out to identify what elements in the mouse niche helped the cells remain dormant. They identified the molecular signature of the quiescent MuSCs and used that to help screen different compounds to see which ones could help keep those cells dormant, even after they were removed from the mouse and collected in a lab dish.

They whittled down the number of potential compounds involved in this process from 50 to 10, and then tested these in different combinations until they found a formulation that kept the stem cells quiescent for at least 2 days outside of the mouse.

But that was just the start. Next they experimented with different kinds of engineered muscle fibers, to simulate the physical environment inside the mouse niche. After testing various materials, they found that the one with the greatest elasticity was the most effective and used that to create a kind of scaffold for the stem cells.

The big test

The artificial niche they created clearly worked in helping keep the MuSCs in a dormant state outside of the mouse. But would they work when transplanted back into the mouse? To answer this question they tested these stem cells to see if they retained their ability to self-renew and to change into other kinds of cells in the mouse. The good news is they did, and were far more effective at both than MuSCs that had not been stored in the artificial niche.

So, great news for mice but what about people, would this same approach work with human muscle stem cells (hMuSCs)? They next tested this approach using hMuSCs and found that the hMuSCs cultured on the artificial niche were more effective at both self-renewal and retaining their potency than hMuSCs kept in more conventional conditions, at least in the lab.

In the study, published in the journal Nature Biotechnology, the researchers say this finding could help overcome some of the challenges that have slowed down the development of effective therapies:

“Research on MuSCs, hematopoietic stem cells and neural stem cells has shown that very small numbers of quiescent stem cells, even single cells, can replace vast amounts of tissue; culture systems that that maintain stem cell quiescence may allow these findings to be translated to clinical practice. In addition, the possibility of culturing hMuSCs for longer time periods without loss of potency in order to correct mutations associated with genetic disorders, such as muscular dystrophy, followed by transplantation of the corrected cells to replace the pathogenic tissue may enable improved stem cell therapeutics for muscle disorders.”

Stem cell stories that caught our eye: sexual identity of organs, upping the game of muscle stem cells, mini guts produce insulin

Here are some stem cell stories that caught our eye this past week. Some are groundbreaking science, others are of personal interest to us, and still others are just fun.

A new sexual identity crisis—in our organs. With the transition from Mr. to Ms. Jenner and other transsexual news this year, it seems inevitable that a research paper would come out suggesting we may all have some mosaic sexual identity. A team in the U.K. found that the stem cells that develop our organs can have varying sexual identities and that can impact the function of the organ.

The organ in question in this case, intestines in fruit flies, is smaller in males than in females. By turning on and off certain genes the researchers at the Medical Research Council’s Clinical Science Centre found that making stem cells in the gut more masculine reduced their ability to multiply and produced smaller intestines. They also found that female intestines were more prone to tumors, just as many diseases are more common in one sex than the other.

In an interview with Medical News Today, Bruno Hudry, the first author on the paper, which is published in Nature, talked about the likelihood that we all have some adult cells in us with genes of the opposite sex.

 “This study shows that there is a wider spectrum than just two sexes. You can be chromosomally, hormonally or phenotypically female but still having some specific adult stem cells (here the stem cells of the intestine) acting like male. So it is hard to say if someone is “really” male or female. Some people are simply a mosaic of male and female cells within a phenotypically ‘male’ or ‘female’ body.”

Hurdry speculated that if the results are duplicated in humans it could provide a window into other sex-linked differences in diseases and could be a matching factor added to the standard protocol for blood and organ donations.

 

Reprogramming stomach to produce insulin.  The stem cells in our gut show an efficiency not seen in most of our organs. They produce a new lining for our stomach and intestine every few days. On the opposite end of the spectrum, the insulin-producing cells in our pancreas rank poorly in self renewal. So, what if you could get some of those vigorous gut stem cells to make insulin producing beta cells? Turns out you can and they can produce enough insulin to allow a diabetic mouse to survive.

mini stomach

A mini-gut with insulin-producing cells (red) and stem cells (green).

A team at the Harvard Stem Cell Institute manipulated three genes known to be associated with beta cell development and tested the ability of many different tissues—from tail to snout—to produce beta cells. A portion of the stomach near the intestine, which naturally produces other hormones, easily reprogrammed into insulin producing cells. More important, if the first batch of those cells was destroyed by the team, the remaining stem cells in the tissue quickly regenerated more beta cells. Since a misbehaving immune system causes type 1 diabetes, this renewal ability could be key to preventing a return of the disease after a transplant of these cells.

In the lab the researchers pushed the tissue from the pylorous region of the stomach to self-organize into mini-stomachs along with the three genetic factors that drive beta cell production.  When transplanted under the skin of mice that had previously had their beta cells destroyed, the mice survived. The genetic manipulations used in this research could not be used in people, but the team is working on a system that could.

 “What is potentially really great about this approach is that one can biopsy from an individual person, grow the cells in vitro and reprogram them to beta cells, and then transplant them to create a patient-specific therapy,” said Qiao Zhou, the senior author. “That’s what we’re working on now. We’re very excited.”

Medicalxpress ran a story about the work published in Cell Stem Cell.

 

muscle stem cells

Muscle stem cells generate new muscle (green) in a mouse.

Better way to build muscle.  Stem cells behave differently depending on what environment they find themselves in, but they are not passive about their environment. They can actively change it. A CIRM-funded team at Sanford Burnham Prebys Medical Discovery Institute (SBP) found that fetal muscle stem cells and adult muscle stem cells make very different changes in the micro-environment around them.

Fetal muscle stem cells become very good at generating large quantities of new muscle, while the adult stem cells take the role of maintaining themselves for emergencies. As a result, when major repair is needed like in muscular dystrophies and aging, they easily get overwhelmed. So the SBP team looked for ways to make the adult stem cells behave more like their fetal predecessors.

 “We found that fetal MuSCs remodel their microenvironment by secreting specific proteins, and then examined whether that same microenvironment can encourage adult MuSCs to more efficiently generate new muscle. It does, which means that how adult MuSCs normally support muscle growth is not an intrinsic characteristic, but can be changed,” said Matthew Tierney, first author of the study in an institute press release distributed by Newswise.

The results point to paths for developing therapies for a number of muscle wasting conditions.