Restoring Muscle Strength in Aging Muscle


Unfortunately, muscle tone and strength decrease as we age. You can work out at the gym all you want. Eventually the relentless march and deterioration of age catches up with even the most avid athlete. However, a Stanford University group believes that they might have discovered why this happens and new cell targets to help reverse it.

According to Helen Blau (the doyen of muscle research), over time, stem cells that help repair damaged muscle cells after injury are less able to do so. This explains why regaining strength and recovering from a muscle injury gets more difficult with age. Blau and her team published their results in the journal Nature Medicine.

Fortunately, Blau’s study also suggests a way to make older muscle stem cells function more like younger ones. The caveat is that research in mice often doesn’t translate to humans. Therefore more work is necessary in order to determine if this technique could ever be used in people.

“In the past, it’s been thought that muscle stem cells themselves don’t change with age, and that any loss of function is primarily due to external factors in the cells’ environment,” study senior author Helen Blau, director of Stanford’s Baxter Laboratory for Stem Cell Biology, said in a university news release.

“However, when we isolated stem cells from older mice, we found that they exhibit profound changes with age,” said Blau, a professor of microbiology and immunology at the university. “Two-thirds of the cells are dysfunctional when compared to those from younger mice, and the defect persists even when transplanted into young muscles.”

The research also revealed, however, that there is a defect specific to old muscle stem cells that can be corrected, which allowed scientists to rejuvenate these stem cells.

“Most exciting is that we also discovered a way to overcome the defect,” Blau said. “As a result, we have a new therapeutic target that could one day be used to help elderly human patients repair muscle damage.”

The muscle stem cells in 2-year-old mice are the equivalent of those found in 80-years-old humans. In the course of their study, Blau and her team found that many muscle stem cells from these mice had increased activity in a certain biological pathway (p38α and p38β mitogen-activated kinase pathways, for those who are interested) that inhibits the production of the stem cells.

Drugs that block this pathway in old stem cells, however, allowed the aged stem cells to make a larger number of new cells that could effectively repair muscle damage.

According to Blau: “In mice, we can take cells from an old animal, treat them for seven days — during which time their numbers expand as much as 60-fold — and then return them to injured muscles in old animals to facilitate their repair.”

Once the mice received their rejuvenated muscle stem cells, the researchers tested their muscle strength with assistance from co-author Scott Delp, a professor in the School of Engineering, who has developed a way to measure muscle strength in animals that underwent stem cell therapy for muscle injuries.

Study lead author Benjamin Cosgrove, a postdoctoral scholar at the university, said: “We were able to show that transplantation of the old, treated muscle stem cell population repaired the damage and restored strength to injured muscles of old mice. Two months after transplantation, these muscles exhibited forces equivalent to young, uninjured muscles. This was the most encouraging finding of all.”

The study’s authors said they plan to continue their research to determine if people could benefit from this technique.

“If we could isolate the stem cells from an elderly person, expose them in culture to the proper conditions to rejuvenate them and transfer them back into a site of muscle injury, we may be able to use the person’s own cells to aid recovery from trauma or to prevent localized muscle atrophy and weakness due to broken bones,” Blau said.

“This really opens a whole new avenue to enhance the repair of specific muscles in the elderly, especially after an injury,” she said. “Our data pave the way for such a stem cell therapy.”

Turning Muscle Stem Cells into Brown Fat


Michael Rudnicki’s laboratory at the Ottawa Hospital Research Institute has managed to convert stem cells from skeletal muscle into brown fat. Because brown fat burns calories, studies have shown that trimmer people tend to have more brown fat, Therefore, Rudnicki’s findings are being viewed as a potential treatment for obesity.

According to Rudnicki, “This discovery significantly advances our ability to harness this good fat in the battle against bad fat and all the associated health risks that come with being overweight and obese. Rudnicki is a senior scientist and director for the Regenerative Medicine Program and Sprott Center for Stem Cell Research at the Ottawa Hospital Research Institute.

Obesity is the fifth leading risk death, globally speaking, and an estimated 2.8 million people dying every year from the effects of being overweight or obese, according to the World Health Organization. The Public Health Agency of Canada estimates that 25% of Canadian adults are obese.

in 2007, Rudnicki and his research team demonstrated the existence of a stem cell population in skeletal muscle. In this new publication, Rudnicki and others show that these adult muscle stem cells not only have the ability to produce muscle fibers, but can also make brown fat.

An even more important aspect of this paper (Yin, et al., Cell Metabolism 17(2) 2013: 210), is that it shows how adult muscle stem cells become brown fat. The main switch is a regulatory molecule called microRNA-133 or miR-133. When miR-133 is present, the muscle stem cells produce muscle fibers, but when the intracellular concentration of miR-133 is reduced, the muscle stem cells form brown fat.

Graphic Abstract

Rudnicki’s research staff developed a molecule that could reduce the concentration of miR-133 in cells. This molecule an antisense oligonucleotide or ASO that is complementary to miR-133. When injected into mice, the ASO caused the mice to produce more brown fat and prevented obesity. Additionally, when injected into the hind leg muscle, the metabolism of the mouse increased, and this effect lasted for four months after the ASO injection.

Even though antisense oligonucleotides are being used in clinical trials, such trials with miR-133 ASOs are still years away.

Rudnicki noted that “we are very excited by this breakthrough.” He continued: “While we acknowledge that it’s a first step there are still many questions to be answered, such as: Will it help adults who are already obese to lose weight? How should it be administered? How long do the effects last? Are there any adverse effects we have not yet observed?”

Surely these questions will be addressed in good time, and Rudnicki’s lab is probably working on them as you read this entry.

Researchers from the University of Minnesota Use Genetically Corrected Stem Cells To Repair Muscles


University of Minnesota researchers from the Lillehei Heart Institute have combined genetic engineering techniques to repair mutations in abnormal muscle cells with cellular reprogramming to generate stem cells that can repair and regenerate muscle regeneration in a mouse model for Duchenne Muscular Dystrophy (DMD). This research is a proof-of-principle experiment that determines the feasibility of combining induced pluripotent stem cell technology and genetic engineering techniques that correct mutations to treat muscular dystrophy. Experimental strategies such as these could represent a major step forward in autologous cell-based therapies for DMD. Furthermore, it might pave the way for clinical trials to test this approach in reprogrammed human pluripotent cells from muscular dystrophy patients.

University of Minnesota researchers combined three groundbreaking technologies to achieve effective muscular dystrophy therapy in a mouse model of DMD. First, researchers reprogrammed skin cells into induced pluripotent stem cells (iPSCs). iPSCs are capable of differentiating into any of the mature cell types within an adult organism. In this case, the University of Minnesota researchers generated pluripotent cells from the skin of mice that carry mutations in two genes; the dystrophin and utrophin genes. Mice with mutations in both the dystrophin and utrophin genes develop a severe case of muscular dystrophy that resembles the type of disease observed in human DMD patients. This provided a model system platform that successfully mimicked what would theoretically occur in humans.

The second technology employed is a genetic correction tool developed at the University of Minnesota. In this case, they used a transposon, which is a segment of DNA that can jump from one location to another within the genome. The specific transposon used is the “Sleeping Beauty Transposon.” The use of this transposon allowed them to transport genes into cells in a convenient manner. The Lillehei Heart Institute researchers used the Sleeping Beauty transposon to deliver a gene called “micro-utrophin” into the iPSCs made from the DMD mice.

Sleeping Beauty Transposon

Human micro-utrophin can support muscle fiber strength and prevent muscle fiber injury throughout the body. However, there is one essential difference micro-utrophin and dystrophin: dystrophin is absent in muscular dystrophy patients, but if it is introduced into the bodies of DMD patients, their immune system will initiate a devastating immune response against it. However, in those same patients, utrophin is active and functional, which makes it essentially “invisible” to the immune system. This invisibility allows the micro-utrophin to replace dystrophin build and repair muscle fibers within the body.

Utrophin

The third technology utilized is a method to produce skeletal muscle stem cells from pluripotent cells. This procedure was developed in the laboratory of Rita Perlingeiro, who is also the principal investigator of this latest study.

Rita Perlingeiro Ph.D.
Rita Perlingeiro Ph.D.

Perlingeiro’s technology gives pluripotent cells a short pulse of a muscle stem cell protein called Pax3, which nudges the pluripotent cells to become skeletal muscle stem cells, which can then be exponentially expanded in culture. These Pax3-induced muscle stem cells were then transplanted back into the same strain of DMD mice from which the pluripotent stem cells were originally derived.

Pax3 and 7

When combined, these platforms created muscle-generating stem cells that would not be rejected by the body’s immune system. According to Perlingeiro, the transplanted cells performed very well in the dystrophic mice, and they generated functional muscle and responded to muscle fiber injury.

“We were pleased to find the newly formed myofibers expressed the markers of the correction, including utrophin,” said Perlingeiro, a Lillehei endowed scholar within the Lillehei Heart Institute and an associate professor in the University of Minnesota Medical School. “However, a very important question following transplantation is if these corrected cells would self-renew, and produce new muscle stem cells in addition to the new muscle fibers.”

By injuring the transplanted muscle and watching it repair itself, the researchers demonstrated that the transplanted muscle stem cells endowed the recipient mice with fully functional muscle cells. This latest project provides the proof-of-principle for the feasibility of combining induced pluripotent stem cell technology and genetic correction to treat muscular dystrophy.

“Utilizing corrected induced pluripotent stem cells to target this specific genetic disease proved effective in restoring function,” said Antonio Filareto, Ph.D., a postdoctoral fellow in Perlingeiro’s laboratory and the lead author on the study. “These are very exciting times for research on muscular dystrophy therapies.”

These studies pave the way for testing this approach in a clinical trial that would use reprogrammed human pluripotent cells from muscular dystrophy patients.

According to Perlingeiro, “Developing methods to genetically repair muscular dystrophy in human cells, and demonstrating efficacy of muscle derived from these cells are critical near-term milestones, both for the field and for our laboratory. Testing in animal models is essential to developing effective technologies, but we remained focused on bringing these technologies into use in human cells and setting the stage for trials in human patients.”

This research was published in Nature Communications.