Advanced gene therapy may prevent severe loss of muscle mass in elderly people

Reviewed by Emily Henderson, B.Sc.Feb 24 2022

Researchers at NTNU have managed to restore muscle function in older mice with muscle loss using advanced gene therapy. The hope is that this method might eventually be used on humans to prevent severe loss of muscle mass.

Many millions of elderly people worldwide suffer from sarcopenia, a disease that is characterized by muscle wasting. A large proportion become so frail that they can no longer exercise."

Jose Bianco Moreira, Researcher, NTNU

"Gene therapy is the most effective method to be able to give these people the same health benefits you normally get with physical exercise," says Moreira, who has been involved in the new research. He is part of the Cardiac Exercise Research Group (CERG).

In the darkest and least understood part of our genetic material, the researchers found an absolutely crucial RNA strand.

Then they used gene therapy to trigger the genes to create more of this muscle-building RNA strand.

The experiment had impressive effects in both mice and roundworms, as well as in experiments with precursors to human muscle cells.

Gene therapy with CRISPR

The research article, which was published in one of the journals of the world-leading Science family, was a collaborative project between CERG and researchers in Switzerland and Denmark.

In the study, the researchers used the Nobel Prize-winning gene editing method CRISPR-Cas9. This method involves supplying the body with an enzyme (Cas9) that finds its way to specific genes and introduces a change into them, thus editing the gene itself.

"The potential of CRISPR is virtually limitless. We can treat disease conditions once, and then patients don't have to take a pill every day," says Moreira.

Hunting for health gains in dark DNA

The main challenge of the method is to determine which gene needs to be changed to obtain the desired health effect.

"If we can isolate the crucial genes and mechanisms, we'll be able to start developing more effective medicines that simulate the effect of exercise. A lot of the molecular mechanisms that provide the training effect might be hidden in the dark part of our genetic material," says Martin Wohlwend.

Wohlwend is the main author of the study, and the article is part of the doctoral degree he recently completed at NTNU.

Our DNA contains the recipe for making all the proteins our cells need. The first step in protein production involves copying a sequence of DNA into RNA. This is called transcription. This RNA strand is a messenger that gives cells information about how to make a protein.

But 99 per cent of our DNA makes RNA strands that don't encode any protein sequences. Wohlwend refers to this part of the genetic material as "dark DNA".

"RNA strands from dark DNA could have important health effects. But there's still a lot we don't know about this part of our genetic material," he says.

Discovered important exercise gene

Strength training can cause our genes to increase the production of RNA strands that help the body maintain or gain more muscle mass. One of the most important of these RNA strands is called CYTOR.

"We discovered CYTOR in the dark genetic material in skeletal muscle cells. Of all the gene transcripts that changed level after strength training, CYTOR was the one that showed the greatest increase," says Wohlwend.

The research team then searched their way to the part of ​​the DNA strand that is responsible for producing CYTOR. It turned out that people with a specific variant of this gene produce more CYTOR than people who have other variants of the same gene.

Older people who have the "good gene variant" are also able to go faster and longer on a walking test than other older people.

"We also noticed that CYTOR levels drop as we get older. Overall, all of these findings gave us really good clues so we could move forward with more thorough studies of the CYTOR gene and how it affects age-related muscle loss," says Wohlwend.

Stimulates growth of fast-twitch muscle cells

Your average 80-year-old has lost over 30 per cent of the muscle mass they had as a young adult. Without exercising to counteract the loss of muscle mass, humans already start to lose muscle around age 30.

The body has two basic types of muscle fibers: the slow-twitch (type I) muscle fibers needed for endurance activities, and the fast-twitch (type II) muscle fibers used for short bursts of strength. As we age, we primarily lose type II muscle mass.

"Our experiments show that CYTOR contributes to increased development of precisely the type II muscle fibers," says Wohlwend.

Increased levels counteracted muscle loss

The next step for the researchers was to take a closer look at what happens when gene therapy is used to increase CYTOR levels.

Using the CRISPR-Cas9 method, the researchers increased CYTOR production in live animals and in precursors to muscle cells from older humans. The results are very promising.

"In human cells, CYTOR production increased as a result of gene therapy. We also observed that the therapy stimulated the cells to promote the development of fast-twitch type II muscle," Wohlwend says.

Experiments with mice confirmed that gene therapy not only provides a theoretical effect at the cellular level, but can actually provide improved muscle function.

Gene therapy, which increased CYTOR production in the calf muscles of aging mice, gave the mice increased muscle mass, better grip strength in their hind legs and greater running capacity.

When the researchers reduced CYTOR production in young mice, however, the mice developed weaker muscles and more inflammation and cell death in the muscles.

"The CYTOR gene seems to be absolutely crucial in order to maintain normal muscle function," the NTNU researcher said.

Basis for new treatment of the elderly

Finally, the researchers cloned human CYTOR into the roundworm Caenorhabditis elegans. The goal was to take a closer look at how human CYTOR affects muscle function and health in a living organism that ages rapidly.

This roundworm is a favorite research model among researchers in the field of aging because it only lives for a few weeks. It does not have its own gene with the same function as CYTOR.

"We observed that human CYTOR delayed the aging process of the worms in many ways. The worms gained stronger, more functional muscles and moved faster than worms that didn't receive the same treatment. They also lived longer," says Wohlwend.

Of course it will take a while until editing the genes of humans in the same way as in these animal experiments becomes common practice. But researchers are now working to develop gene therapy that is based on RNA.

"All in all, our findings may have laid the groundwork for new treatment methods for muscle loss in the elderly," says Moreira.