How mRNA and CRISPR-Cas9 could treat muscle atrophy


Researchers use mRNA to introduce the gene editor CRISPR-Cas9 into human muscle stem cells. These cells fused into multinucleated myotubes following mRNA-mediated CRISPR-Cas9 gene editing. A myosin heavy chain is seen in green and the nuclei in blue. Photo: Spuler Lab

A team of researchers from Experimental and Clinical Research Center (ECRC) has introduced the gene editor CRISPR-Cas9 into human muscle stem cells for the first time using messenger RNA (mRNA), potentially discovering a method suitable for therapeutic applications. 

The researchers are aiming to discover if this tool can repair mutations that lead to muscle atrophy in humans, and they are one step closer after finding that the method worked in mice suffering from the condition. But the method had a catch, ECRC researcher Helena Escobar says.  

“We introduced the genetic instructions for the gene editor into the stem cells using plasmids – which are circular, double-stranded DNA molecules derived from bacteria.” But plasmids could unintentionally integrate into the genome of human cells, which is also double stranded, and then lead to undesirable effects that are difficult to assess. “That made this method unsuitable for treating patients,” Escobar says.   

Getting mRNA Into Stem Cells

So the team set out to find a better alternative. They found it in the form of mRNA, a single-stranded RNA molecule that recently gained acclaim as a key component of two Covid-19 vaccines. 

To get the mRNA into the stem cells, the researchers used a process called electroporation, which temporarily makes cell membranes more permeable to larger molecules. “With the help of mRNA containing the genetic information for a green fluorescent dye, we first demonstrated that the mRNA molecules entered almost all the stem cells,” explains Christian Stadelmann, a doctoral student at ECRC.  

In the next step, the team used a deliberately altered molecule on the surface of human muscle stem cells to show that the method can be used to correct gene defects in a targeted manner.   

Paving the Way for a Clinical Trial 

Finally, the team tried out a tool similar to the CRISPR-Cas9 gene editor that does not cut the DNA, but only tweaks it at one spot with accuracy. In petri dish experiments, Stadelmann and his team were able to show that the corrected muscle stem cells are just as capable as healthy cells of fusing with each other and forming young muscle fibers. 

Their latest paper, which is appearing in the journal Molecular Therapy Nucleic Acids, paves the way for a clinical trial for patients with hereditary muscle atrophy. The team expects to enroll five to seven patients toward the end of the year. 

“Of course we cannot expect miracles,” says Simone Spuler, head of the Myology Lab at ECRC. “Sufferers who are in wheelchairs won’t just get up and start walking after the therapy. But for many patients, it is already a big step forward when a small muscle that is important for grasping or swallowing functions better again.” 

Read the source article here.

Friends, Romans, countrymen, lend me your ears – we have a podcast for you.

It seems like everyone, including my dog Freddie, has a podcast these days. So now we do too.

According to the website there are some two million podcasts in the world. Make that two million and one. That’s because CIRM is launching its own podcast and doing it with one of the biggest names in biotech.

Our podcast is called – with a nod to The Who – “Talking ’bout (Re)Generation” and the first episode features our President & CEO Dr. Maria Millan interviewing Dr. Derrick Rossi, the co-founder of Moderna. Moderna, as I am sure you know, is the maker of one of the most effective vaccines against COVID.

In the interview Dr. Rossi talks about his early days as a postdoc at Stanford – supported by CIRM – and the career arc that led him to help create the company behind the vaccine, and what his plans are for the future. It’s a fun, chatty, lively interview; one you can listen to in the car, at home or wherever you listen to your podcasts.

We want the podcast to be fun for your ear holes and interesting and engaging for your brain. We’re going to be talking to scientists and researchers, doctors and nurses, patients and patient advocates and anyone else we think has something worth listening to.

We have other episodes planned and will share those with you in the near future. In the meantime, if you have any ideas or individuals you think would make a good subject for a podcast let us know, we are always happy to hear from you.

In the meantime, enjoy the show.

How a CIRM scholar helped create a life-saving COVID vaccine

Dr. Derrick Rossi might be the most famous man whose name you don’t recognize. Dr. Rossi is the co-founder of Moderna. Yes, that Moderna. The COVID-19 vaccine Moderna. The vaccine that in clinical trials proved to be around 95 percent effective against the coronavirus.

Dr. Rossi also has another claim to fame. He is a former CIRM scholar. He did some of his early research, with our support, in the lab of Stanford’s Dr. Irv Weissman.

So how do you go from a lowly post doc doing research in what, at the time, was considered a rather obscure scientific field, to creating a company that has become the focus of the hopes of millions of people around the world?  Well, join us on Wednesday, January 27th at 9am (PST) to find out.

CIRM’s President and CEO, Dr. Maria Millan, will hold a live conversation with Dr. Rossi and we want you to be part of it. You can join us to listen in, and even post questions for Dr. Rossi to answer. Think of the name dropping credentials you’ll get when say to your friends; “Well, I asked Dr. Rossi about that and he told me…..”

Being part of the conversation is as simple as clicking on this link:

After registering, you will receive a confirmation email containing information about joining the webinar.

We look forward to seeing you there.

Filling the Holes in our Understanding of Stem Cell Fate

How does a single-celled human embryo transform into a human body with intricate organ systems containing trillions of specialized cells? Step into any college lecture discussing this question and I bet “transcription factors” is a phrase you’ll often hear.

Transcription factors are DNA-binding proteins that act as cell fate control switches during development. For cells destined to become, say muscle tissue, transcription factors bind DNA and help activate muscle-specific genes or keep non-muscle-specific genes silent. And so it goes for all other cell types as they form inside the growing embryo.

But file this blog entry under “Hold up a moment” because in research published today in Stem Cell Reports, CIRM-funded scientists at U.C. San Diego (UCSD) pinpoint another cellular process that appears equally as important as transcription factors in cell fate decisions. The process they studied is called nonsense-mediated mRNA decay (NMD). To go into details about NMD we need to first delve a bit more into transcription factors.

A bit of molecular biology 101
When a gene is said to be activated, or “turned on”, that’s just shorthand for describing the process of transcription in which a stretch of DNA corresponding to a gene is “read” by cell machinery and transcribed into messenger RNA (mRNA). The mRNA is then translated into a string of amino acids which forms a particular protein. By binding to the DNA in the vicinity of a gene, the transcription factors provide a physical platform for the transcribing machinery to form the mRNA. Frequent transcribing leads to more mRNA and more protein.


Transcription and translation: turning genes on to produce proteins (image:


The nonsense mRNA decay (NMD) pathway (Wikipedia)

The NMD pathway regulates transcription from the opposite end of the process by promoting the degradation of mRNAs. It was once thought to only be involved in getting rid of mRNAs that contain transcribing errors but more recent studies have shown that NMD has roles in normal cell functions. For instance, the UCSD team had shown that neural stem cells contain high levels of NMD which must be reduced to allow those stem cells to specialize into neurons. In the current paper, the team sought to better understand these underlying mechanisms that enable the NMD pathway to regulate development.

To accomplish this goal, NMD function was examined during the very early stages of human development using human embryonic stem cells (hESC). All adult tissues are derived from the three germ layers that form during embryogenesis: endoderm (which gives rise to lung and gut), mesoderm (which gives rise to muscle, bone, blood) and ectoderm (which gives rise to skin and neurons). When the researchers grew the hESCs under conditions that favored endoderm formation, they observed dramatically reduced levels of NMD activity. But growing hESC toward mesoderm and ectoderm fates, led to increased levels of NMD. So these very early forks in the road of cell fate decisions led to diverging levels of NMD.

NMD activities: cell fate bystander or participant?
But does this change in NMD activity play a direct role during the specialization of hESCs? To answer this question, the team focused on the manipulating NMD activity as hESCs formed into endoderm. Instead of the natural decrease in NMD proteins during endodermal formation, NMD levels were artificially maintained at high levels. Sure enough, this hampered the ability of the hESCs to take on properties of endodermal cells and instead they kept hallmarks of stem cells. Approaching this analysis from the opposite angle, NMD factors were removed from the hESCs under conditions that should block endoderm formation. In support of the previous experiment, this artificial drop in NMD activity led to the initiation of endodermal differentiation.

Further experiments determined that NMD activity specifically inhibits TGF-b, a protein that signals cells toward an endoderm fate. Conversely, the team’s results also suggest that NMD stimulates BMP which is an important signal for a mesoderm fate. So just like transcription factors, the activity of NMD modulates the balance of other proteins which ultimately direct the fate of a cell’s identity. In fact, the TGF- b and BMP pathways themselves stimulate the actions of transcription factors so there’s likely some cooperation going with these factors and NMD. We reached out to UCSD professor Miles Wilkinson, the principal investigator for this study, to get his team’s reaction to their results:

“Most of what we know about human embryonic stem cell fate revolves around the role of factors that regulate RNA synthesis – transcription factors.  In our study, we examined the other side of the coin – the role of factors required for a selective RNA decay pathway.  We were surprised to find that not only did the NMD RNA decay pathway influence embryonic cell differentiation, but it is critical for cell fate decisions through its effect on signaling pathways.  Thus, we envisage that RNA decay pathways and transcriptional pathways converge on signaling pathways to control embryonic stem cell fate.”


And a better understanding of how embryonic stem cell fate is controlled could help optimize stem cell-based therapies for a given tissue or organ. Whatever the case, it shouldn’t be long before future college students in a developmental biology class will hear “NMD” in the same breath as “transcription factors”.