• New Muscle-Generating Stem Cells Isolated From Human Tissue
• Two Anti-Fibrosis Drugs Show Promise in Mice With DMD
• Cyclosporine-Like Compound Prevents Cell Death in Mice With CMD
• What Does Blocking Myostatin Do?
• SMA Researchers Break New Ground
• Clinical Trials and Studies
  • Duchenne MD Gene Therapy Trial on Track
  • Santhera Testing Idebenone in DMD and Friedreich's Ataxia

New Muscle-Generating Stem Cells Isolated From Human Tissue

by Margaret Wahl

Researchers at several U.S. and Italian institutions say they’ve isolated from human skeletal muscle a new type of stem cell that they believe could be “ideal” for the treatment of muscular dystrophy.

MDA-supported Giulio Cossu at the San Raffaele Scientific Institute in Milan, Italy, and Paolo Bianco of the San Raffaele Biomedical Science Park in Rome, led the team, which published results online Feb. 11 in Nature Cell Biology.

The researchers have dubbed the newfound cells, which are located around small blood vessels in muscles, pericyte-derived.

In November, Cossu and colleagues announced they had isolated another blood-vessel-associated stem cell, in dogs, that can also give rise to muscle. They used these cells (mesoangioblasts) to successfully treat canine muscular dystrophy. They say the cells in this new set of experiments may be related to mesoangioblasts.

When pericyte-derived cells taken from healthy human muscle tissue were given to mice missing the dystrophin protein (the cause of human Duchenne muscular dystrophy [DMD]) and also lacking an immune system, they showed a very high rate of maturation into muscle fibers.

They also improved the ability of these mice to grip a rotating rod and stay on a treadmill.

The pericyte-derived cells demonstrated that they could cross blood vessel walls into muscle tissue when injected into an artery, an important requirement if cells are to be delivered through the bloodstream in humans.

The investigators also took pericyte-derived cells from children with DMD and injected the cells with miniaturized dystrophin genes before giving them to dystrophin-deficient mice. These mice showed a similar improvement in functional performance compared to untreated mice, as did the animals that received cells from people without muscular dystrophy.

In eventual treatment, using a patient’s own muscle cells, altered to make a needed protein such as dystrophin, is probably preferable to using cells from a donor.

The mice that were given human cells from healthy people and from children with DMD both made significant numbers of muscle fibers and produced significant amounts of human dystrophin.

Cossu says his group plans a clinical trial using these cells in boys with DMD.

Two Anti-Fibrosis Drugs Show Promise in Mice With DMD

Two drugs, losartan and pirfenidone, have shown promise in reducing fibrosis (scar formation) in mice that lack the muscle protein dystrophin and have a disease resembling Duchenne muscular dystrophy (DMD).

Both drugs target transforming growth factor beta (TGF-beta), a natural body compound that interferes with muscle fiber formation and promotes formation of scar tissue in response to injury, inflammation or disease.

Fibrosis, the result of excess deposition of connective tissue, is a major factor in muscle function impairment in human DMD.

Luc Gosselin, an MDA research grantee at the State University of New York at Buffalo, and colleagues, who published results of their work with pirfenidone in the February issue of Muscle & Nerve, found the drug was somewhat effective in reducing fibrosis in mice treated for four weeks, but they say more testing at higher doses is needed.

Pirfenidone is in development by Intermune of Brisbane, Calif., for the treatment of interstitial pulmonary fibrosis, a condition in which excess collagen interferes with lung function.

In a separate study, Ronald Cohn at Johns Hopkins University in Baltimore, and colleagues, who published their findings online Jan. 21 in Nature Medicine, had more success with losartan, which they tested in dystrophin-deficient, DMD-affected mice for six to nine months.

In the losartan-treated mice, the diaphragm muscles showed less scarring (fibrosis in 18 percent of the tissue, compared to 32 percent in untreated mice). The mice had significantly better front and back leg grip strength than did their untreated counterparts, showed less muscle fatigue when challenged, and had muscle fibers that looked more normal.

Losartan is approved to treat high blood pressure and is marketed by Merck of Whitehouse Station, N.J., under the brand names

Cyclosporine-Like Compound Prevents Cell Death in Mice With CMD

Abnormalities in mitochondria, the energy-producing units inside cells, appear to underlie the muscle degeneration seen in Ullrich congenital muscular dystrophy (CMD), a form of MD caused by a lack of the protein collagen 6.

A few years ago, scientists at the University of Padua and other Italian institutions found that mutant mice unable to produce collagen 6 showed mitochondrial defects that lead to cell death. Specifically, a channel in the inner membrane surrounding each mitochondrion opens inappropriately, triggering a cell suicide program.

Now these researchers, who published their results in the Jan. 16 issue of Proceedings of the National Academy of Sciences, have studied muscle cells from five patients with Ullrich CMD, and found similar defects in their mitochondria, with similar results.

The muscle cell defects were reversed when the drug cyclosporine, which keeps the mitochondrial channel closed, was added to their environment, leading the investigators to think about this as a potential therapy for Ullrich CMD.

However, since cyclosporine is also a potent immune system suppressant, they decided to try the efficacy of a related compound, Debio 025. This compound, like cyclosporine, stabilizes mitochondria by keeping their inner membranes intact, but it doesn’t have immunosuppressive effects.

Debio 025 was shown to be equally effective in preventing mitochondrial defects and death of muscle cells from Ullrich CMD patients.

The researchers say their findings suggest new perspectives for treatment of people with collagen 6 disorders.

SMA Researchers Break New Ground

Research progress in spinal muscular atrophy (SMA) has been considerable in recent months.

Some 95 percent of people with this disorder of the muscle-controlling nerve cells of the spinal cord (lower motor neurons) have mutations in both copies of a gene on chromosome 5 known as SMN1, which normally makes the protein SMN (survival of motor neurons). But all people with SMA have at least two copies of a neighboring gene called SMN2, which makes some of the same SMN protein as the SMN1 gene normally does but mostly makes a shortened version of SMN.

The more copies of the SMN2 gene a person has, the less severe the effects of SMN1 mutations generally are. The most severe form of SMA, generally fatal in early childhood, is called type 1. An intermediate severity form is called type 2, and the least severe, chronic form is type 3.

The majority of SMA treatment strategies are based on increasing output of full-length SMN protein molecules from SMN2 genes, which everyone with SMA has.

A rare form of SMA is related to defects in an X chromosome gene that hasn’t yet been identified. This form is similar to the chromosome 5 SMA type 1.

Phenylbutyrate Trial Disappointing

A trial of phenylbutyrate (PB), a compound that in laboratory studies has increased cellular production of SMN, has failed to benefit children with type 2 spinal muscular atrophy (SMA2), say researchers at 10 centers in Italy, who conducted the trial.

Eugenio Mercuri at Catholic University in Rome, and colleagues, studied 107 children with SMA2 who were between 2 and 12 years old, randomly assigning them to receive either PB or a placebo for 13 weeks. Neither participants nor investigators knew which children were getting PB and which the placebo until the study was completed. After 13 weeks, the PB-treated children and the placebo-treated children had similar motor function test scores, the researchers reported in the Jan. 2 issue of Neurology.

The lack of difference in the two groups may, they say, be related to the short study duration and the dosing schedule, which was seven days on/seven days off. They say an altered schedule and longer exposure to PB might produce different results.

“[These results] don’t diminish our enthusiasm for pursuing additional studies on phenylbutyrate for two reasons,” says Kathryn Swoboda at the University of Utah, who’s conducting a trial of PB in SMA in the United States.

“One, the treatment duration of 13 weeks in this study was extremely short, and I wouldn’t necessarily have expected any significant effect with treatment for that duration of time for a medication expected to work on motor neurons [nerve cells].

“Two, the regimen used for treatment in this study involved a dosing schedule in which, on alternate weeks, children weren’t taking any medication. We’re encouraged by the enthusiasm of the Italian SMA community in bringing this trial to rapid fruition.”

Trials of PB in children with types 1, 2 and 3 SMA, sponsored by the National Institutes of Health, are slated to begin this spring.

For updated information, see MDA's clinical trials section online.

HDAC Inhibitor Benefits Mice

An experimental compound called trichostatin (TSA) can increase the amount of SMN protein in mice with SMA and shows promise for the treatment of the human disease.

When U.S. and Italian scientists, including MDA-supported Livio Pellizzoni at Dulbecco Telethon Institute of Cell Biology in Rome, gave TSA to mice with SMA, they saw 1.5-fold to twofold increases in total SMN protein levels in the brain, spinal cord and liver. They also saw healthier muscle and nerve cells, as well as significant improvement in the motor function and survival in three-quarters of the mice. About one-quarter didn’t respond to the drug.

These improvements occurred even though the mice were very weak when they started TSA therapy. In their paper, published online Feb. 22 in the Journal of Clinical Investigation, the researchers say this response bodes well for treatment of humans, since SMA is rarely diagnosed before weakness becomes evident. However, they also say that earlier intervention might be even more effective.

TSA belongs to a family of chemical compounds called HDAC inhibitors, which cause cells to interpret genetic instructions as “open” and ready to be read, rather than “closed” and silent.

Theoretically, TSA increases the amount of time that SMN2 genes are open for production of SMN protein molecules. SMN2 genes, which all SMA patients have, normally lead to production of a very small amount of full-length SMN protein and can only partially compensate for the loss of SMN1 gene function that is SMA’s underlying cause.

The researchers say their results provide a strong basis for examining HDAC inhibitors in clinical trials in SMA. TSA itself hasn’t been approved for clinical use, they note, but it probably could be developed for that.

Other HDAC inhibitors are in clinical trials for other diseases, and one has been approved by the U.S. Food and Drug Administration for treatment of lymphoma.

“In the future,” said Pellizzoni, “the use of HDAC inhibitors, in combination with other types of compounds that stimulate the levels (or activity) of the SMN protein, might be an attractive treatment strategy for this disease.”

SMN1 vs. SMN2 Gene Instructions

Investigators at Columbia University in New York and the University of California-Berkeley report a significant addition to the understanding of the differences in protein output between the SMN1 and SMN2 genes.

Tsuyoshi Kashima at UC Berkeley, and colleagues, writing in the Feb. 27 issue of Proceedings of the National Academy of Sciences, describe how two differences — one they previously identified and one new one — combine to cause the SMN2 gene to leave a sequence called exon 7 out of the final instructions for the SMN protein. Complete instructions for the full-length protein are in the “rough draft” instructions.

The omission of exon 7 from the final genetic blueprint means that most of the protein produced from the SMN2 gene is shorter than that produced from the SMN1 gene.

“Our data has provided evidence that a second rare ... difference between SMN1 and SMN2 contributes to SMN2 exon 7 exclusion,” the researchers write.

The more information scientists have about why exon 7 is excluded from SMN2 instructions, the better equipped they’ll be to coax its inclusion and production of full-length SMN protein from this gene.

SMA Can Be X-Linked

MDA grantee Lisa Baumbach-Reardon at the University of Miami’s Miller School of Medicine, with colleagues in the United States, Spain and Germany, can now say with assurance that there is an X-linked form of SMA that resembles the most severe (type 1) chromosome 5 form. X-linked diseases generally affect only males, but females can be carriers.

In the January issue of Genetics in Medicine, the investigators describe eight families (one previously analyzed and the other seven new to this study) with an X-linked disease affecting only male infants and involving severe loss of muscle tone, as well as multiple contractures (frozen joints) and/or bone fractures. Death occurred within the first two years of life in 75 percent of cases.

The investigators note that an X-linked disease resembling severe infantile SMA was first described in 1938, but the disorder has been presumed rare. They say their new findings, coupled with the approximately 4 percent of SMA patients who don’t appear to have SMN1 mutations, may mean that X-linked SMA isn’t as rare as has been presumed.

They’ve determined that X-linked SMA, like its chromosome 5 counterpart, is primarily a disease involving loss of lower motor neurons. Finding another SMA gene, they say, “will provide major insights ... into the etiology [origin] and developmental timing of motor neuron loss,” with implications for all types of SMA.