muscle fibers

How mRNA and CRISPR-Cas9 could treat muscle atrophy

/ Esteban Cortez / 1 Comment

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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.

Study shows that exercise rejuvenates muscle stem cells of old mice

/ Yimy Villa / 3 Comments
Dr. Thomas Rando, Stanford University

While we’re all at home and practicing social distancing during this global pandemic, it has become a challenge to get in daily exercise. Aside from outward physical appearance, what other benefits does exercise hold? Dr. Thomas Rando and his team at Stanford University explored this question in more detail in a CIRM supported animal study.

The Stanford research team found that exercise played a key role in restoring the youthful properties in the muscle stem cells of old mice. Muscle stem cells play an important role in tissue regeneration. They are usually on standby alongside muscle fibers in a resting state known as quiescence until called upon to repair damage.

For this study, the researchers wanted to see if voluntary exercise had an effect on the muscle stem cells in mice. Older mice that were 20 months old, the equivalent of 60-70 human years, were given an exercise wheel where they were allowed to run at will. Younger mice that were 3-4 months old, the equivalent of 20-30 human years, were also given an exercise wheel and allowed to run at will. A separate group of younger and older mice were given a wheel that didn’t rotate to compare them with the groups of mice that exercised.

They found that the older animals that had exercised regularly were significantly better at repairing muscle damage compared to their counterparts that did not exercise. However, this exercise benefit was not observed between the younger group of mice.

The researchers also transplanted the muscle stem cells from the older mice that had exercised into younger mice that had not exercised. They found that the muscle stem cells from the older mice contributed more to the repair process than did those from the non-exercising mice.

What was also surprising is that injecting blood from an old mouse that had exercised into an old mouse that hadn’t created a similar benefit in the muscle stem cells. This finding suggests that exercise simulates the production of some factors that then circulate in the blood and enhance the function of older stem cells.

Lastly, the researchers were ably to identify a molecular pathway that activates the resting muscle stem cells in response to damage.

In a press release, Dr. Rando discusses how this discovery could potentially lead to the development of a drug that could rejuvenate muscle stem cells.

“If we could develop a drug that mimics this effect, we may be able to experience the benefit without having to do months of exercise.”

The full results of this study were published in Nature Metabolism.