71 for Proposition 71

Proposition 71 is the state ballot initiative that created California’s Stem Cell Agency. This month, the Agency reached another milestone when the 71st clinical trial was initiated in the CIRM Alpha Stem Cell Clinics (ASCC) Network. The ASCC Network deploys specialized teams of doctors, nurses and laboratory technicians to conduct stem cell clinical trials at leading California Medical Centers.

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These teams work with academic and industry partners to support patient-centered for over 40 distinct diseases including:

  • Amyotrophic Lateral Sclerosis (ALS)
  • Brain Injury & Stroke
  • Cancer at Multiple Sites
  • Diabetes Type 1
  • Eye Disease / Blindness Heart Failure
  • HIV / AIDS
  • Kidney Failure
  • Severe Combined Immunodeficiency (SCID)
  • Sickle Cell Anemia
  • Spinal Cord Injury

These clinical trials have treated over 400 patients and counting. The Alpha Stem Cell Clinics are part of CIRM’s Strategic Infrastructure. The Strategic Infrastructure program which was developed to support the growth of stem cell / regenerative medicine in California. A comprehensive update of CIRM’s Infrastructure Program was provided to our Board, the ICOC.

CIRM’s infrastructure catalyzes stem cell / regenerative medicine by providing resources to all qualified researchers and organizations requiring specialized expertise. For example, the Alpha Clinics Network is supporting clinical trials from around the world.

Many of these trials are sponsored by commercial companies that have no CIRM funding. To date, the ASCC Network has over $27 million in contracts with outside sponsors. These contracts serve to leverage CIRMs investment and provide the Network’s medical centers with a diverse portfolio of clinical trials to address patients’’ unmet medical needs.

Alpha Clinics – Key Performance Metrics

  • 70+ Clinical Trials
  • 400+ Patients Treated
  • 40+ Disease Indications
  • Over $27 million in contracts with commercial sponsors

The CIRM Alpha Stem Cell Clinics and broader Infrastructure Programs are supporting stem cell research and regenerative medicine at every level, from laboratory research to product manufacturing to delivery to patients. This infrastructure has emerged to make California the world leader in regenerative medicine. It all started because California’s residents supported a ballot measure and today we have 71 clinical trials for 71.

 

 

Stories that caught our eye: Is a Texas law opening up access to stem cell treatments working? Another CIRM-funded company gets good news from the FDA.

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Texas Capitol. (Shutterstock)

In 2017 Texas passed a sweeping new law, HB 810, which allowed medical clinics to provide “investigational stem cell treatments to patients with certain severe chronic diseases or terminal illnesses.” Those in favor of the law argued that patients battling life-threatening or life-changing diseases should have the right to try stem cell therapies that were involved in a clinical trial.

Now a new study, published in the journal Stem Cells and Development, looks at the impact of the law. The report says that despite some recent amendments t there are still some concerns about the law including:

  • It allows treatment only if the patient has a “severe, chronic” illness but doesn’t define what that means
  • It doesn’t have clearly defined procedures on tracking and reporting procedures so it’s hard to know how many patients might be treated and what the outcomes are
  • There is no Food and Drug Administration (FDA) oversight of the patients being treated
  • Because the treatments are unproven there are fears this will “open up the state to unsavory and predatory practices by individuals preying on vulnerable patients”

The researchers conclude:

“While HB 810 opens up access to patients, it also increases significant risks for their safety and financial cost for something that might have no positive impact on their disease. Truly understanding the impact of stem cell based interventions (SCBI) requires scientific rigor, and accurate outcome data reporting must be pursued to ensure the safety and efficacy behind such procedures. This information must be readily available so that patients can make informed decisions before electing to pursue such treatments. The creation of the SCBI registry could allow for some level of scientific rigor, provide a centralized data source, and offer the potential for better informed patient choices, and might be the best option for the state to help protect patients.”

Another CIRM-funded company gets RMAT designation

Poseida

When Congress approved the 21st Century Cures Act a few years ago one of the new programs it created was the Regenerative Medicine Advanced Therapy (RMAT) designation. This was given to therapies that are designed to treat a serious or life-threatening condition, where early clinical stage trials show the approach is safe and appears to be effective.

Getting an RMAT designation is a big deal. It means the company or researchers are able to apply for an expedited review by the FDA and could get approval for wider use.

This week Poseida Therapeutics was granted RMAT designation by the Food and drug Administration (FDA) for P-BCMA-101, its CAR-T therapy for relapsed/refractory multiple myeloma. This is currently in a Phase 1 clinical trial that CIRM is funding

In this trial Poseida’s technology takes an immunotherapy approach that uses the patient’s own engineered immune system T cells to seek and destroy cancerous myeloma cells.

In a news release Eric Ostertag, Poseida’s CEO, welcomed the news:

“Initial Phase 1 data presented at the CAR-TCR Summit earlier this year included encouraging response rates and safety data, including meaningful responses in a heavily pretreated population. We expect to have an additional data update by the end of the year and look forward to working closely with the FDA to expedite development of P-BCMA-101.”

This means that five CIRM-funded companies have now been granted RMAT designations:

Deep dive into muscle repair yields new strategies to combat Duchenne muscular dystrophy

Researchers at the Sanford Burnham Prebys Medical Discovery Institute (SBP) reported new findings this week that may lead to novel therapeutic strategies for people suffering from Duchenne muscular dystrophy (DMD). DMD, a muscle-wasting disease that affects 1 in 7250 males aged 5 to 24 years in the United States, is caused by a genetic mutation leading to the lack of a protein called dystrophin. Without dystrophin, muscle cells become fragile and are easily damaged. Instead of self-repair, the muscles are replaced by scar tissue, a process called fibrosis that leads to muscle degeneration and wasting.

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Dystrophin, a protein that maintains the structural integrity of muscle fibers, is missing in people with DMD. Image credit: Khan Academy

Boys with DMD first show signs of muscle weakness between ages 3-5 and often stop walking by the time they’re teenagers. Eventually the muscles critical for breathing and heart function stop working. Average life expectancy is 26 and there is no cure.

The SBP scientists are aiming to treat DMD by boosting muscle repair in affected individuals. But to do that, they sought to better understand how muscle regeneration works in the first place. In the current study, they focused their efforts on so-called fibro/adipogenic precursor (FAP) cells which, in response to acute injury, appear to play a role in stimulating muscle stem cells to divide and replace damaged muscle in healthy individuals. But FAPs are also implicated in the muscle wasting and scarring that’s seen in DMD.

By examining the gene activity of single FAP cells from mouse models of acute injury and DMD, the researchers identified a sub-population of FAP cells (sub-FAPs). Further study of these sub-FAPs showed that during early stages of muscle regeneration, these cells promote muscle stem cell activation but then at later stages, sub-FAPs – identified by a cell surface protein called Vcam1 – stimulate fibrosis. It turns out that during healthy acute muscle injury, the sub-FAPs with cell-surface Vcam1 protein are readily eaten up and removed by immune cells thereby avoiding muscle fibrosis. But in the DMD mouse model, removal of these sub-FAPs is impaired and instead collagen deposits and muscle fibrosis occur which are hallmarks of the progressive degeneration seen in DMD.

Barbora Malecova, Ph.D., a first author of the study, explained the implications of these results in a press release:

“This study elucidates the cellular and molecular pathogenesis of muscular dystrophy. These results indicate that removing or modulating the activity of Vcam1-positive sub-FAPs, which promote fibrosis, could be an effective treatment for DMD.”

The lab, led by Pier Lorenzo Puri, M.D., next will explore the possibility of finding drugs that target the Vcam1 sub-FAPs which in turn could help prevent fibrosis in DMD.

The study, funded in part by CIRM, appears in Nature Communications. CIRM is also funding a Phase 2 clinical trial testing a stem cell-based therapy that aims to improve the life-threatening heart muscle degeneration that occurs in DMD patients.

New CIRM Alpha Stem Cell Clinic offers HOPE for boys with deadly disease

UC Davis Institute for Regenerative Cures

For people battling Duchenne Muscular Dystrophy (DMD), a rare and fatal genetic disorder that slowly destroys muscles, hope has often been in short supply. There is no cure and treatments are limited. But now a new clinical trial at the site of one of the newest CIRM Alpha Stem Cell Clinic Network members could change that.

The HOPE-2 clinical trial has treated its first patient at UC Davis Medical Center, inaugurating the institution’s Alpha Stem Cell Clinic. The clinic is part of a CIRM-created network of top California medical centers that specialize in delivering stem cell clinical trials to patients. The key to the Network’s success is the ability to accelerate the delivery of treatments to patients through partnerships with patients, medical providers and clinical trial sponsors.

UC Davis is one of five medical centers that now make up the network (the others are UC San Francisco, UCLA/UC Irvine, UC San Diego and City of Hope).

Jan NoltaIn a news release, Jan Nolta, the director of the UC Davis Institute for Regenerative Cures, says the UC Davis Alpha Clinic is well equipped to move promising therapies out of the lab and into clinical trials and people.

“We have the full range of resource experts in regenerative medicine, from the cellular to the clinical trials level. We’re also excited about the prospect of being able to link with other Alpha Stem Cell Clinics around the state to help speed the process of testing and refining treatments so we can get therapies to patients in need.”

The news of this first patient is a cause for double celebration at CIRM. The trial is run by Capricor and CIRM funded the first phase of this work. You can read the story of Caleb Sizemore, who took part in that trial or watch this video of him talking about his fight.

When the CIRM Board approved funding for the UC Davis Alpha Clinic in October of 2017, Abla Creasey, CIRM’s Vice President for Therapeutics and Strategic Infrastructure, said:

“The Alpha Clinics are a one-of-a-kind network that gives patients access to the highest quality stem cell trials for a breadth of diseases including cancer, diabetes, heart disease and spinal cord injury. Expanding our network will allow more patients to participate in stem cell trials and will advance the development of stem cell treatments that could help or possibly cure patients.”

The UC Davis Alpha Clinic provides a one-stop shop for delivering stem cell therapies, gene therapies and immunotherapies, as well as conducting follow-up visits. It’s this type of CIRM-funded infrastructure that helps steer potential clinical trial participants away from illegitimate, unproven and potentially harmful fee-for-service stem cell treatments.

The DMD trial is the first of what we are confident will be many high-quality trials at the Clinic, bringing promising stem cell therapies to patients with unmet medical needs.

 

UCLA scientists on track to develop a stem cell replacement therapy for Duchenne Muscular Dystrophy

Muscle cells generated by April Pyle’s Lab at UCLA.

Last year, we wrote about a CIRM-funded team at UCLA that’s on a mission to develop a stem cell treatment for patients with Duchenne muscular dystrophy (DMD). Today, we bring you an exciting update on this research just in time for the holidays (Merry Christmas and Happy Hanukkah and Kwanza to our readers!).

DMD is a deadly muscle wasting disease that primarily affects young boys and young men. The UCLA team is trying to generate better methods for making skeletal muscle cells from pluripotent stem cells to regenerate the muscle tissue that is lost in patients with the condition. DMD is caused by genetic mutations in the dystrophin gene, which codes for a protein that is essential for skeletal muscle function. Without dystrophin protein, skeletal muscles become weak and waste away.

In their previous study, the UCLA team used CRISPR gene editing technology to remove dystrophin mutations in induced pluripotent stem cells (iPSCs) made from the skin cells of DMD patients. These corrected iPSCs were then matured into skeletal muscle cells that were transplanted into mice. The transplanted muscle cells successfully produced dystrophin protein – proving for the first time that DMD mutations can be corrected using human iPSCs.

A Step Forward

The team has advanced their research a step forward and published a method for making skeletal muscle cells, from DMD patient iPSCs, that look and function like real skeletal muscle tissue. Their findings, which were published today in the journal Nature Cell Biology, address a longstanding problem in the field: not being able to make stem cell-derived muscle cells that are mature enough to model DMD or to be used for cell replacement therapies.

Dr. April Pyle, senior author on the study and Associate Professor at the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA explained in a news release:

April Pyle, UCLA.

“We have found that just because a skeletal muscle cell produced in the lab expresses muscle markers, doesn’t mean it is fully functional. For a stem cell therapy for Duchenne to move forward, we must have a better understanding of the cells we are generating from human pluripotent stem cells compared to the muscle stem cells found naturally in the human body and during the development process.”

By comparing the proteins expressed on the cell surface of human fetal and adult muscle cells, the team identified two proteins, ERBB3 and NGFR, that represented a regenerative population of skeletal muscle cells. They used these two markers to isolate these regenerative muscle cells, but found that the muscle fibers they created in a lab dish were smaller than those found in human muscle.

First author, Michael Hicks, discovered that using a drug to block a human developmental signaling pathway called TGF Beta pushed these ERBB3/NGFR cells past this intermediate stage and allowed them to mature into functional skeletal muscle cells similar to those found in human muscle.

Putting It All Together

In their final experiments, the team combined the new stem cell techniques developed in the current study with their previous work using CRISPR gene editing technology. First, they removed the dystrophin mutations in DMD patient iPSCs using CRISPR. Then, they coaxed the iPSCs into skeletal muscle cells in a dish and isolated the regenerative cells that expressed ERBB3 and NGFR. Mice that lacked the dystrophin protein were then transplanted with these cells and were simultaneously given an injection of a TGF Beta blocking drug.

The results were exciting. The transplanted cells were able to produce human dystrophin and restore the expression of this protein in the Duchenne mice.

Skeletal muscle cells isolated using the ERBB3 and NGFR surface markers (right) restore human dystrophin (green) after transplantation significantly greater than previous methods (left). (Image courtesy of UCLA)

Dr. Pyle concluded,

“The results were exactly what we’d hoped. This is the first study to demonstrate that functional muscle cells can be created in a laboratory and restore dystrophin in animal models of Duchenne using the human development process as a guide.”

In the long term, the UCLA team hopes to translate this research into a patient-specific stem cell therapy for DMD patients. In the meantime, the team will use funding from a recent CIRM Quest award to make skeletal muscle cells that can regenerate long-term in response to chronic injury in hopes of developing a more permanent treatment for DMD.

The UCLA study discussed in this blog received funding from Discovery stage CIRM awards, which you can read more about here and here.

Stem Cell Stories That Caught our Eye: Stem Cell Therapies for Stroke and Duchenne Muscular Dystrophy Patients

With the Thanksgiving holiday behind us, we’re back to the grind at CIRM. Here are two exciting CIRM-funded stem cell stories that happened while you were away.

Stanford Scientists Are Treating Stroke Patients with Stem Cells

Smithsonian Magazine featured the work of a CIRM-funded scientist in their December Magazine issue. The article, “A Neurosurgeon’s Remarkable Plan to Treat Stroke Victims with Stem Cells”, features Dr. Gary Steinberg, who is the Chair of Neurosurgery at Stanford Medical Center and the founder of the Stanford Stroke Center.

Gary Steinberg (Photo by Jonathan Sprague)

The brain and its 100 billion cells need blood, which carries oxygen and nutrients, to function. When that blood supply is cut off, brain cells start to die and patients experience a stroke. Stroke can happen in one of two ways: either by blood clots that block the arteries and blood vessels that send blood to the brain or by blood vessels that burst within the brain itself. Symptoms experienced by stroke victims vary based on the severity of the stroke, but often patients report experiencing numbness or paralysis in their limbs or face, difficulty walking, talking and understanding.

Steinberg and his team at Stanford are developing a stem cell treatment to help stroke patients. Steinberg believes that not all brain cells die during a stroke, but rather some brain cells become “dormant” and stop functioning instead. By transplanting stem cells derived from donated bone marrow into the brains of stroke patients, Steinberg thinks he can wake up these dormant cells much like how the prince wakens Sleeping Beauty from her century of enchanted sleep.

Basically, the transplanted cells act like a defibrillator for the dormant cells in the stroke-damaged area of the brain. Steinberg thinks that the transplanted cells secrete proteins that signal dormant brain cells to wake up and start functioning normally again, and that they also trigger a “helpful immune response” that prompts the brain to repair itself.

Sonia has seen first hand how a stroke can rob you of even your most basic abilities.

Steinberg tested this stem cell treatment in a small clinical trial back in 2013. 18 patients were treated and many of them showed improvements in their symptoms. The Smithsonian piece mentions a particular patient who had a remarkable response to the treatment. Sonia Olea Coontz, at age 32, suffered a stroke that robbed her of most of her speech and her ability to use her right arm and leg. After receiving Steinberg’s stem cell treatment, Sonia rapidly improved and was able to raise her arm above her head and gained most of her speech back. You can read more about her experience in our Stories of Hope.

In collaboration with a company called SanBio, Steinberg’s team is now testing this stem cell therapy in 156 stroke patients in a CIRM-funded phase 2 clinical trial. The trial will help answer the question of whether this treatment is safe and also effective in a larger group of patients.

The Smithsonian article, which I highly recommend reading, shared Steinberg’s future aspirations to pursue stem cell therapies for traumatic brain and spinal cord injuries as well as neurodegenerative diseases like Alzheimer’s, Parkinson’s and ALS.

 

Capricor Approved to Launch New Clinical Trial for Duchenne Muscular Dystrophy

On Wednesday, Capricor Therapeutics achieved an exciting milestone for its leading candidate CAP-1002 – a stem cell-based therapy developed to treat boys and young men with a muscle-wasting disease called Duchenne muscular dystrophy (DMD).

The Los Angeles-based company announced that it received approval from the US Food and Drug Administration (FDA) for their investigational new drug (IND) application to launch a new clinical trial called HOPE II that’s testing repeated doses of CAP-1002 cells in DMD patients. The cells are derived from donated heart tissue and are believed to release regenerative factors that strengthen heart and other muscle function in DMD patients.

Capricor is currently conducting a Phase 2 trial, called HOPE-1, that’s testing a single dose of CAP-1002 cells in 24 DMD patients. CIRM is funding this trial and you can learn more about it on our clinical dashboard website and watch a video interview we did with a young man who participated in the trial.

Earlier this year, the company shared encouraging, positive results from the HOPE-1 trial suggesting that the therapy was improving some heart function and upper limb movement six months after treatment and was well-tolerated in patients. The goal of the new trial will be to determine whether giving patients repeated doses of the cell therapy over time will extend the benefits in upper limb movement in DMD patients.

In a news release, Capricor President and CEO Dr. Linda Marbán shared her company’s excitement for the launch of their new trial and what this treatment could mean for DMD patients,

Linda Marban, CEO of Capricor Therapeutics

“The FDA’s clearance of this IND upon its initial submission is a significant step forward in our development of CAP-1002. While there are many clinical initiatives in Duchenne muscular dystrophy, this is one of the very few to focus on non-ambulant patients. These boys and young men are looking to maintain what function they have in their arms and hands and, based on our previous study, we think CAP-1002 may be able to do exactly that.”

Giving thanks to Caleb and all of our stem cell pioneers [Video]

For our last blog before the Thanksgiving holiday, we give thanks to the patients and their caregivers who are forging a path toward a new era of regenerative medicine therapies through their participation in CIRM-funded clinical trials.

Some of our trials are in the early stages which means they are mainly focused on safety. Participants go into these trials knowing that the cell therapy dose they receive will probably be too low to get any benefit for themselves. And in later trials, some patients will receive a placebo, or blank therapy, for comparison purposes. Even if a patient gets an effective dose, it may not work for them. So the decision to enroll in an experimental clinical trial is often a selfless act. Yet final approval of a therapy by the U.S. Food and Drug Administration (and other regulatory agencies around the world) depends on these brave souls and for that we are truly grateful.

So, with this Thanksgiving Day spirit in mind, we leave you with our latest video featuring Caleb Sizemore, a charming young man who epitomizes the courage of our clinical trial pioneers. At just 7 years old, Caleb was diagnosed with Duchenne Muscular Dystrophy (DMD), a degenerative muscle disease which makes it difficult for him to walk and climb stairs, has led to dangerous scarring of his heart muscle and carries a shortened life expectancy with most DMD patients not living past their 20s or 30s.

In a sit-down interview with us and in clips from his June 2017 presentation to the CIRM governing Board, Caleb talked about the impact of DMD on his life and his experience enrolling in Capricor Therapeutics’ CIRM-funded clinical trial. The trial is testing a stem cell therapy designed to repair the heart scarring that occurs with DMD. By the end of the three-minute video, I can assure you that you’ll be as captivated as we were by Caleb’s delightful, sincere and full-of-faith personality.

Using heart stem cells to help boys battling a deadly disorder

 

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Caleb Sizemore, a young man with DMD, speaks to the CIRM Board about his treatment in the Capricor clinical trial.

It’s hard to imagine how missing just one tiny protein can have such a devastating impact on a person. But with Duchenne Muscular Dystrophy (DMD) the lack of a single protein called dystrophin has deadly consequences. Now a new study is offering hope we may be able to help people with this rare genetic disorder.

DMD is a muscle wasting condition that steadily destroys the muscles in the arms and legs, heart and respiratory system. It affects mostly boys and it starts early in life, sometimes as young as 3 years old, and never lets up. By early teens many boys are unable to walk and are in a wheelchair. Their heart and breathing are also affected. In the past most people with DMD didn’t survive their teens. Now it’s more common for them to live into their 20’s and 30’s, but not much beyond that.

Results from a clinical trial being run by Capricor Therapeutics – and funded by CIRM – suggest we may be able to halt, and even reverse, some of the impacts of DMD.

Capricor has developed a therapy called CAP-1002 using cells derived from heart stem cells, called cardiospheres. Boys and young men with DMD who were treated with CAP-1002 experienced what Capricor calls “significant and sustained improvements in cardiac structure and function, as well as skeletal muscle function.”

In a news release Dr. Ronald Victor, a researcher at Cedars-Sinai Heart Institute and the lead investigator for the trial, said they followed these patients for 12 months after treatment and the results are encouraging:

“Because Duchenne muscular dystrophy is a devastating, muscle-wasting disease that causes physical debilitation and eventually heart failure, the improvements in heart and skeletal muscle in those treated with a single dose of CAP-1002 are very promising and show that a subsequent trial is warranted. These early results provide hope for the Duchenne community, which is in urgent need of a major therapeutic breakthrough.”

According to the 12-month results:

  • 89 percent of patients treated with CAP-1002 showed sustained or improved muscle function compared to untreated patients
  • The CAP-1002 group had improved heart muscle function compared to the untreated group
  • The CAP-1002 group had reduced scarring on their heart compared to the untreated group.

Now, these results are still very early stage and there’s a danger in reading too much into them. However, the fact that they are sustained over one year is a promising sign. Also, none of the treated patients experienced any serious side effects from the therapy.

The team at Capricor now plans to go back to the US Food and Drug Administration (FDA) to get clearance to launch an even larger study in 2018.

For a condition like DMD, that has no cure and where treatments can simply slow down the progression of the disorder, this is a hopeful start.

Caleb Sizemore is one of the people treated in this trial. You can read his story and listen to him describing the impact of the treatment on his life.

CIRM-Funded Clinical Trials Targeting the Heart, Pancreas, and Kidneys

This blog is part of our Month of CIRM series, which features our Agency’s progress towards achieving our mission to accelerate stem cell treatments to patients with unmet medical needs.

This week, we’re highlighting CIRM-funded clinical trials to address the growing interest in our rapidly expanding clinical portfolio. Today we are featuring trials in our organ systems portfolio, specifically focusing on diseases of the heart/vasculature system, the pancreas and the kidneys.

CIRM has funded a total of nine trials targeting these disease areas, and eight of these trials are currently active. Check out the infographic below for a list of our currently active trials.

For more details about all CIRM-funded clinical trials, visit our clinical trials page and read our clinical trials brochure which provides brief overviews of each trial.

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.”