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.

DMD_KhanAcademy

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.

The Five Types of Stem Cells

When I give an “Intro to Stem Cells” presentation to, say, high school students or to a local Rotary Club, I begin by explaining that there are three main types of stem cells: (1) embryonic stem cells (ESCs) (2) adult stem cells and (3) induced pluripotent stem cells (iPSCs). Well, like most things in science, it’s actually not that simple.

To delve a little deeper into the details of characterizing stem cells, I recommend checking out a video animation produced by BioInformant, a stem cell market research company. The video is introduced in a blog, “Do you know the 5 types of stem cells?” by Cade Hildreth, BioInformant’s founder and president.

Stem-Cell-Types

Image credit: BioInformant

Hildreth’s list categorizes stem cells by the extent of each type’s shape-shifting abilities. So while we sometimes place ESCs and iPSCs in different buckets because the methods for obtaining them are very different, in this list, they both belong to the pluripotent stem cell type. Pluri (“many”) – potent (“potential”) refers to the ability of both stem cell types to specialize into all of the cell types in the body. They can’t, though, make the cells of the placenta and other extra-embryonic cells too. Those ultimate blank-slate stem cells are called toti (“total”) – potent (“potential”).

When it comes to describing adult stem cells in my talks, I often lump blood stem cells together with muscle stem cells because they are stem cells that are present within us throughout life. But based on their ability to mature into specialized cells, these two stem cell types fall into two different categories in Hildreth’s list:  blood stem cells which can specialize into closely related cell types – the various cell types found in the blood – are considered “oligopotent” while muscle stem cells are “unipotent” because the can only mature into one type of cell, a muscle cell.

For more details on the five types of stem cells based on their potential to specialize, head over to the BioInformant blog. And scroll to the very bottom for the video animation which can also viewed on FaceBook.

Stem Cell Roundup: Artificial Embryos to Study Miscarriage and ALS Insight – Muscle Repair Cells Go Rogue

Stem Cell Image of the Week: Artificial embryos for studying miscarriage (Adonica Shaw)

etxembryos

Mouse embryos artificially generated by combining three types of stem cells.
Image: University of Cambridge.

This week’s stem cell image of the week comes from a team of researchers from The University of Cambridge who published research in Nature Cell Biology earlier this week indicating they’d achieved a breakthrough in stem cell research that resulted in the generation of a key developmental step that’d never before been achieved when trying to generate an artificial embryo.

To create the artificial embryo, the scientists combined mouse embryonic stem cells with two other types of stem cells that are present in the very earliest stages of embryo development. The reseachers grew the three stem cell types into a dish and coaxed them into simulating a process called gastrulation – one of the very first events that happens during a creature’s development in which the early embryo begins reorganizing into more and more complex multilayer organ structures.

In an interview with The Next Web (TNW), Professor Magdalena Zernicka-Goetz, who led the research team, says:

”Our artificial embryos underwent the most important event in life in the culture dish. They are now extremely close to real embryos. To develop further, they would have to implant into the body of the mother or an artificial placenta.”

The goal of this research isn’t to create mice on demand. Its purpose is to gain insights into early life development. And that could lead to a giant leap in our understanding of what happens during the period in a woman’s pregnancy where the risk of miscarriage is highest.

According to professor Zernicka-Goetz,

magda3

Magdalena Zernicka-Goetz, PhD

“We can also now try to apply this to the equivalent human stem cell types and so study the very earliest events in human embryo development without actually having to use natural human embryos.The early stages of embryo development are when a large proportion of pregnancies are lost and yet it is a stage that we know very little about. Now we have a way of simulating embryonic development in the culture dish, so it should be possible to understand exactly what is going on during this remarkable period in an embryo’s life, and why sometimes this process fails.”

Muscle repair cells go rogue – a possible drug target for ALS?
Call it a case of a good cell gone bad. This week researchers at Sanford Burnham Prebys Medical Discovery Institute, report in Nature Cell Biology that fibro-adipogenic progenitors (FAPs) – cells that are critical in coordinating the repair of torn muscles – can turn rogue, causing muscles to wither and scar. This “Dr. Jekyl and Mr. Hype” discovery may lead to novel treatments for a number of incurable disorders like amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA) and spinal cord injury.

drjekyllmrhy

Senior author Pier Lorenzo Puri, M.D. (right) and co-first author Luca Madaro, Ph.D. Credit: Fondazione Santa Lucia IRCCS

When muscle is strained, whether due to an acute injury or even weight-lighting, a consistent order of events occurs within the muscle. FAB cells enter the muscle tissue after immune cells called macrophages come in and gobble up dead tissue but before muscle stem cells are stimulated to regenerate the lost muscle. However, to the researchers’ surprise, something entirely different happens in the case of neuromuscular disorders like ALS where nerve signal connections to the muscles degenerate.

Once nerves are no longer attached to muscle and stop sending movement signals from the brain, the macrophages don’t infiltrate the muscle and instead the FAPs pile up in the muscle and never leave. And as a result, muscle stem cells are never activated. In ALS patients, this cellular train crash leads to progressive loss of muscle control to move the limbs and ultimately even to breathe.

The promising news from these findings, which were funded in part by CIRM, is that the team identified of an out-of-whack cell signaling pathway that is responsible for the breakdown in the rogue function of the FAP cells. The researchers hope further studies of this pathway’s role in muscle degeneration may lead to novel therapies and disease-screening technologies for ALS and other motor neuron diseases.

A scalable, clinic-friendly recipe for converting skin cells to muscle cells

Way back in 1987, about two decades before Shinya Yamanaka would go on to identify four proteins that can reprogram skin cells into induced pluripotent stem cells (iPSCs), Harold Weintraub’s lab identified the first “master control” protein, MyoD, which can directly convert a skin cell into a muscle cell. Though MyoD opened up new approaches for teasing out the molecular mechanisms of a cell’s identity, it did not produce therapeutic paths for replacing muscle damaged by disease and injury.

That’s because MyoD-generated muscle cells are not amenable to a clinical setting. For a cell therapy to be viable, you need to manufacture large amounts of your product to treat many people. But these MyoD cells do not grow well enough to be effective to serve as a cell replacement therapy. Generating iPSC-derived muscle cells provides the potential of overcoming this limitation but the capacity of the embryonic stem cell-like iPSC for unlimited growth carries a risk of forming tumors after the transplanting iPSC-derived cell therapies into the muscle.

169572_web

This image shows iMPCs stained for markers of muscle stem, progenitor and differentiated cells. iMPCs recapitulate muscle differentiation in a dish. Credit: Ori Bar-Nur and Mattia Gerli

A recent study in Stem Cell Reports, by Konrad Hochedlinger’s lab at Massachusetts General Hospital and the Harvard Stem Cell Institute, may provide a work around. The team came up with a recipe that calls for the temporary activation of MyoD in mouse skin cells, along with the addition of three molecules that boost cell reprogramming. The result? Cells they dubbed induced myogenic progenitor cells, or iMPCs, that can make self-sustaining copies of themselves and can be scaled up for manufacturing purposes. On top of that, they show that these iMPCs carry the hallmarks of muscle stem cells and generate muscle fibers when transplanted into mice with leg injuries without signs of tumor formation.

A lot of work still remains to be done, like confirming that these iMPCs truly have the same characteristics as muscle stem cells. But if everything pans out, the potential applications for people suffering from various muscle disorders and injuries is very exciting, as co-first author Mattia FM Gerli, PhD points out in a press release:

in7czFjH_400x400

Mattia FM Gerli, PhD

“Patient-specific iMPCs could be used for personalized medicine by treating patients with their own genetically matched cells. If disease-causing mutations are known, as is the case in many muscular dystrophies, one could in principle repair the mutation in iMPCs prior to transplantation of the corrected cells back into the patient.”

Researchers find connection between aging muscles and mutations in stem cells

It’s a humbling fact of life that our muscles decline as we age which is why you didn’t see any 50-year-olds competing for Olympic Gold in figure skating at the 2018 Winter Games.

You can blame your muscle stem cells for this. Also called satellite cells, these adult stem cells lie mostly dormant in muscle tissue until, in response to exercise or injury, they begin to divide, specialize and replenish damaged muscle cells. But, this restorative function declines over time diminishing the ability of aging muscle stem cells to grow new muscle, and in turn, leading to a gradual deterioration in strength and agility.

muscle stem cell

Muscle stem cell (pink with green outline) sits along a muscle fiber. Image: Michael Rudnicki/OIRM

While this connection between aging muscle and stem cells has been well-known, the underlying reasons are less well understood. However, a recent Nature Communications study by researchers at the Karolinska Institute in Sweden makes an important inroad: muscle stem cells from healthy, older individuals have a surprising number of genetic mutations compared to their younger counterparts.

To carry out the comparison, the researchers isolated muscle stem cells from muscle biopsies taken from groups of young (21-24 yrs) and more senior (68-75 yrs) healthy adults. Single cell DNA sequencing (which creates a genetic blueprint for individual cells) showed that the older stem cells had accumulated 2 to 3 times more mutations in genes that are active in the muscle stem cells. This higher “burden” of mutations also appeared to impair cell function: in the older group, those stem cells with higher numbers of mutations had a lower capacity to divide and specialize into certain types of muscle cells. The younger stem cells did not show this behavior suggesting they are better protected from these mutations, as team lead, Professor Maria Eriksson, explained in a press release:

maria_eriksson_webb_sir

Maria Eriksson. Photo: Ulf Sirborn

“We can demonstrate that this protection diminishes the older you become, indicating an impairment in the cell’s capacity to repair their DNA. And this is something we should be able to influence with new drugs.”

 

 

In addition to possible drug interventions, Dr. Eriksson is also interested in evaluating the role of exercise to counteract the effects of these mutations:

“We aim to discover whether it is possible to individually influence the burden of mutations. Our results may be beneficial for the development of exercise programs, particularly those designed for an aging population.”

Stem Cell Stories that Caught Our Eye: GPS for Skin & Different Therapies for Aging vs. Injured Muscles?

Skin stem cells specialize into new skin by sensing neighborhood crowding
When embarking on a road trip, the GPS technology inside our smartphones helps us know where we are and how to get where we’re going. The stem cells buried in the deepest layers of our skin don’t have a GPS and yet, they do just fine determining their location, finding their correct destination and becoming the appropriate type of skin cell. And as a single organ, all the skin covering your body maintains the right density and just the right balance of skin stem cells versus mature skin cells as we grow from a newborn into adult.

crowdinginth

Skin cells growing in a petri dish (green: cytoskeleton, red: cell-cell junction protein).
Credit: MPI for Biology of Aging

This easily overlooked but amazing feat is accomplished as skin cells are continually born and die about every 30 days over your lifetime. How does this happen? It’s an important question to answer considering the skin is our first line of defense against germs, toxins and other harmful substances.

This week, researchers at the Max Planck Institute for Biology of Aging in Cologne, Germany reported a new insight into this poorly understood topic. The team showed that it all comes down to the skin cells sensing the level of crowding in their local environment. As skin stem cells divide, it puts the squeeze on neighboring stem cells. This physical change in tension on these cells “next door” triggers signals that cause them to move upward toward the skin surface and to begin maturing into skin cells.

Lead author Yekaterina Miroshnikova explained in a press release the beauty of this mechanism:

“The fact that cells sense what their neighbors are doing and do the exact opposite provides a very efficient and simple way to maintain tissue size, architecture and function.”

The research was picked up by Phys.Org on Tuesday and was published in Nature Cell Biology.

Stem cells respond differently to aging vs. injured muscle
From aging skin, we now move on to our aging and injured muscles, two topics I know oh too well as a late-to-the-game runner. Researchers at the Sanford Burnham Prebys Medical Discovery Institute (SBP) in La Jolla report a surprising discovery that muscle stem cells respond differently to aging versus injury. This important new insight could help guide future therapeutic strategies for repairing muscle injuries or disorders.

muscle stem cell

Muscle stem cell (pink with green outline) sits along a muscle fiber.
Image: Michael Rudnicki/OIRM

Muscle stem cells, also called satellite cells, make a small, dormant population of cells in muscle tissue that springs to life when muscle is in need of repair. It turns out that these stem cells are not identical clones of each other but instead are a diverse pool of cells.  To understand how the assortment of muscle stem cells might respond differently to the normal wear and tear of aging, versus damage due to injury or disease, the research team used a technology that tracks the fate of individual muscle stem cells within living mice.

The analysis showed a clear but unexpected result. In aging muscle, the muscle stem cells maintained their diversity but their ability to divide and grow declined. However, the opposite result was observed in injured muscle: the muscle stem cell diversity became limited but the capacity to divide was not affected. In a press release, team leader Alessandra Sacco explains the implications of these findings for therapy development:

sacco

Alessandra Sacco, PhD

“This study has shown clear-cut differences in the dynamics of muscle stem cell pools during the aging process compared to a sudden injury. This means that there probably isn’t a ‘one size fits all’ approach to prevent the decline of muscle stem cells. Therapeutic strategies to maintain muscle mass and strength in seniors will most likely need to differ from those for patients with degenerative diseases.”

This report was picked up yesterday by Eureka Alert and published in Cell Stem Cell.

The life of a sleeping muscle stem cell is very busy

For biological processes, knowing when to slow down is as important as knowing when to step on the accelerator. Take for example muscle stem cells. In a healthy state, these cells mostly lay quiet and rarely divide but upon injury, they bolt into action by dividing and specializing into new muscle cells to help repair damaged muscle tissue. Once that mission is accomplished, the small pool of muscle stem cells is replenished through self-renewal before going back into a dormant, or quiescent, state.

muscle stem cell

Muscle stem cell (pink with green outline) sits along a muscle fiber. Image: Michael Rudnicki/OIRM

“Dormant” may not be the best way to describe it because a lot of activity is going on within the cells to maintain its sleepy state. And a better understanding of the processes at play in a dormant state could reveal insights about treating aging or diseased muscles which often suffer from a depletion of muscle stem cells. One way to analyze cellular activity is by examining RNA transcripts which are created when a gene is turned “on”. These transcripts are the messenger molecules that provide a gene’s instructions for making a particular protein.

By observing something, you change it
In order to carry out the RNA transcript analyses in animal studies, researchers must isolate and purify the stem cells from muscle tissue. The worry here is that all of the necessary poking of prodding of the cells during the isolation method will alter the RNA transcripts leading to a misinterpretation of what is actually happening in the native muscle tissue. To overcome this challenge, Dr. Thomas Rando and his team at Stanford University applied a recently developed technique that allowed them to tag and track the RNA transcripts within living mice.

The CIRM-funded study reported today in Cell Reports found that there are indeed significant differences in results when comparing the standard in vitro lab method to the newer in vivo method. As science writer Krista Conger summarized in a Stanford Medical School press release, those differences led to some unexpected results that hadn’t been observed previously:

“The researchers were particularly surprised to learn that many of the RNAs made by the muscle stem cells in vivo are either degraded before they are made into proteins, or they are made into proteins that are then rapidly destroyed — a seemingly shocking waste of energy for cells that spend most of their lives just cooling their heels along the muscle fiber.”

It takes a lot of energy to stay ready
Dr. Rando thinks that these curious observations do not point to an inefficient use of a cell’s resources but instead, “it’s possible that this is one way the cells stay ready to undergo a rapid transformation, either by blocking degradation of RNA or proteins or by swiftly initiating translation of already existing RNA transcripts.”

The new method provides Rando’s team a whole new perceptive on understanding what’s happening behind the scenes during a muscle stem cell’s “dormant” state. And Rando thinks the technique has applications well beyond this study:

Rando

Thomas Rando

“It’s so important to know what we are and are not modeling about the state of these cells in vivo. This study will have a big impact on how researchers in the field think about understanding the characteristics of stem cells as they exist in their native state in the tissue.”

 

 

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.”

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.”