This article presents reports on research in: Duchenne MD, Becker MD, facioscapulohumeral MD, limb-girdle MD types 2A and 2B, Myioshi myopathy, nemaline myopathy, polymyositis, dermatomyositis, inclusion-body myositis, slow-channel myasthenic syndrome, myasthenia gravis, Lambert-Eaton syndrome and spinal muscular atrophy.
MDA grantee Tejvir S. Khurana at the University of Pennsylvania and colleagues say they’ve found support for their hypothesis that low levels of oxygen (hypoxia) not only result from impaired respiratory muscle function in Duchenne muscular dystrophy (DMD), but that a lack of sufficient oxygen also causes further damage to the respiratory and other muscles. If this hypothesis proves to be true, Khurana says, weakened respiratory muscles would cause hypoxia, which would cause more muscle weakness, setting up a vicious cycle.
His research group is conducting experiments in mice, worms and flies that lack the dystrophin protein and therefore have a DMD-like disease.
Khurana, with German medical student Gabriel Willmann, recently conducted some of the experiments on Mount McKinley (Denali) in Alaska, which is about 20,000 feet above sea level and provides a very low-oxygen environment. The environment, while potentially dangerous for the researchers, allowed them to accurately mimic the effects of impaired respiration seen in DMD, Khurana says. (MDA didn’t fund the Mount McKinley expedition.)
Next, the investigators want to try to stabilize a protein called hypoxia-inducible factor (HIF), which can help an organism compensate for hypoxia but which is normally degraded quickly. HIF’s actions include coaxing the formation of new blood vessels, increasing production of red blood cells and changing metabolism. Khurana says he hopes stabilizing HIF might provide a new treatment for MD-induced hypoxia.
Having dystrophin, the muscle protein missing in Duchenne muscular dystrophy (DMD), in only 50 percent of the cells of the heart appears adequate to prevent the cardiac dysfunction associated with this disease in mice, say researchers at the University of Missouri-Columbia.
They say the research has important implications for DMD therapies, including cell and gene transfer strategies now being explored, in that it suggests that not every cell in the heart has to have dystrophin for the heart to function. (Although not the subject of this investigation, other research studies have found that it’s likewise not necessary for every skeletal muscle fiber to produce dystrophin for adequate muscle function in the limbs and trunk to occur.)
The research team, coordinated by MDA-supported Dongsheng Duan, an associate professor in the Department of Molecular Microbiology and Immunology at the University of Missouri-Columbia, studied aged (21-month-old) mice that were female carriers of DMD.
Like human carriers, these female mouse carriers of DMD had a mutation in the dystrophin gene on one of their two X chromosomes and a fully functional dystrophin gene on their other X chromosome. This genetic background generally leads to dystrophin production in about 50 percent of the cardiac muscle cells. (In humans, dystrophin production in carriers can be less than 50 percent, sometimes resulting in DMD symptoms.)
The investigators note that about 10 percent of human female carriers of DMD or Becker muscular dystrophy (BMD), which also results from dystrophin deficiency, develop severe heart disease. However, studies have shown that the majority of carriers experience no cardiac problems even at age 55.
“Taken together, we have demonstrated a complete prevention of cardiomyopathy [cardiac muscle abnormality] through 50 percent ... dystrophin expression in old carrier mice,” the researchers say in a paper published online Oct. 25 in Circulation Research. “Because 100 percent correction is not feasible in gene and/or cell therapy, our results have provided a strong theoretical basis for the clinical usefulness of these novel treatments.”
New findings show that the effects of slow-channel myasthenic syndrome (SCS), a genetic disorder in which a muscle-fiber channel remains open too long after receiving a chemical signal from a nerve fiber, can be partially alleviated in mice by blocking a potentially destructive enzyme called calpain.
Christopher Gomez at the University of Chicago coordinated a group of researchers who published these findings in the October issue of the Journal of Clinical Investigation.
The group, which included MDA grantee Melissa Spencer at the University of California at Los Angeles, tested the effects of calpastatin, a calpain-blocking protein, on mice with genetically caused slow-channel myasthenic syndrome by genetically engineering these mice to overproduce calpastatin.
The disease-affected mice with the extra capastatin showed more normal nerve-to-muscle signaling and better strength than did untreated mice, but they weren’t cured of the disease, leading the researchers to suspect that there are additional enzymes, known as caspases, involved in slow-channel syndrome.
“Our findings showing inhibition of calpain with overexpressed CS [calpastatin] demonstrate that calpain can be effectively inhibited while caspase 3 appears unaffected,” the investigators write. “These studies demonstrate that the calpain and caspase ... systems play predominant roles in the pathogenesis [cause] of the slow-channel syndrome. Therapies designed to chronically reduce excessive calpain and caspase activities may be useful in the treatment of the SCS and related ... disorders.”
A new type of molecular profiling may hold clues to muscle degeneration in general and to variations in muscle degeneration among different diseases, says a multinational team of researchers that included MDA grantee Alan Beggs at Children’s Hospital and Harvard Medical School in Boston.
Lou Kunkel, also at Children’s Hospital and Harvard Medical School, and a member of MDA’s Scientific Advisory Committee, coordinated the multinational research team, which published its findings in the Oct. 23 issue of Proceedings of the National Academy of Sciences.
In their paper, the investigators describe how so-called microRNA signatures provide the basis for a new set of potential targets for therapy in several muscle diseases.
MicroRNAs are a recently identified class of very small molecules that regulate gene activity by inactivating genetic information (RNA) that would otherwise lead to the production of proteins.
They can change the way basic processes, including cell death, cell proliferation, tissue development and the immune response take place.
The investigators analyzed 88 muscle samples representing 10 different muscle diseases, including Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), facioscapulohumeral muscular dystrophy (FSHD), types 2A and 2B limb-girdle muscular dystrophies (LGMD2A, LGMD2B), Miyoshi myopathy, nemaline myopathy, polymyositis (PM), dermatomyositis (DM) and inclusion-body myositis (IBM).
Each of the muscle diseases studied proved to have a unique microRNA signature that’s presumably a result of the underlying genetic defect (such as a dystrophin mutation in DMD or BMD) for each disease.
Measuring levels of 18 of the micro-RNA molecules allowed researchers to accurately tell disease-affected muscle tissue from normal muscle tissue and to distinguish among the various muscle diseases.
Although each disease showed its own profile, several diseases showed levels of microRNAs involved in regulating inflammation and the immune response that were different from those seen in the normal muscle samples.
The investigators say that their findings “raise the opportunity for therapeutic intervention at the miRNA [microRNA] level in preventing specific physiological pathways underlying [a] disease.”
Support for the idea that autoimmunity (a mistaken attack by the immune system on the body’s own tissues) is part of the disease process in nonfamilial inclusion-body myositis (IBM) was recently demonstrated in studies from the laboratory of Marinos Dalakas at the U.S. National Institutes of Health in Bethesda, Md.
Some experts have argued that IBM is primarily an inflammatory, autoimmune disease, while others have argued that it is primarily degenerative in nature. There is evidence for both processes, though which is primary remains debatable.
Dalakas and colleagues, who published their results in the Oct. 23 issue of Neurology, studied muscle and blood cells from 12 people with nonfamilial (“sporadic”) IBM and compared the two kinds of cells with each other and with blood cells from unaffected people.
They found that certain proteins on the surfaces of the immune system’s T-cells were different in muscle compared to blood in people with IBM, with the muscle T-cells showing a narrower range of specific surface proteins than the blood cells. Both kinds of cells showed less variation in their surface-protein patterns than did blood T-cells from people without the disease.
The surface proteins the researchers analyzed are those that make up the T-cell receptors, the parts of the cells that participate directly in an immune response.
The results, the investigators say, suggest that the T-cells in IBM are specifically reacting against the patients’ muscle fibers, and that after they enter the fibers from the bloodstream, they begin to specialize in this anti-muscle reaction.
The T-cells that are still in the bloodstream don’t have the same degree of anti-muscle specification, even in the IBM patients, and the T-cells from the unaffected samples don’t show any such specification.
When the researchers compared T-cells in muscle biopsy samples taken from people with IBM a year after the initial samples were examined, they found the degree of specificity of the surface proteins was essentially unchanged.
They say their findings support the view that muscle-fiber proteins are a stimulus for an undesired, chronic response by the immune system in this disease.
They say further probing of the response should help clarify the relationship between inflammation and degeneration in IBM and offer means of “better customizing therapeutic strategies.”
Genetically altering immature muscle cells so that they lack a protein known as myoD significantly improves their ability to survive after they’re injected into mouse muscles, researchers have found.
They say the findings, published Oct. 16 in Proceedings of the National Academy of Sciences USA, could have implications for muscle-cell transplantation therapies in patients (see “Moving Away from the Blasts of the Past”).
MDA grantee Atsushi Asakura at the University of Minnesota Medical School in Minneapolis coordinated the research team, which also included MDA grantee Michael Rudnicki at Ottawa Health Research Institute in Canada.
MyoD is considered a “master transcription factor” that plays an essential role in muscle-cell maturation. When muscle satellite cells, a type of immature muscle cell that participates in repair and regeneration of muscle fibers, were taken from mice lacking myoD and injected into the leg muscles of other mice, they survived much better than did myoD-containing satellite cells.
The investigators say suppressing myoD production in immature muscle cells used for transplantation in humans might be beneficial, because the cells would likely still mature (differentiate) into muscle but at a slower than normal rate, allowing them to survive the critical week or two following injection when most transplanted cells die.
A study published in the Oct. 16 issue of Proceedings of the National Academy of Sciences USA describes in greater detail than previously demonstrated how the protein myocardin acts as a switch to determine whether a cell will become skeletal muscle, the kind that controls the trunk and limbs, or smooth muscle, the kind that makes the bladder, gastrointestinal tract and uterus contract. (In most muscular dystrophies, the problem is primarily in the skeletal muscles.)
Eric Olson at the University of Texas Southwestern Medical Center in Dallas and Joseph Miano at the University of Rochester (N.Y.) led a team that has shed new light on how myocardin turns down the genes that cause a cell to become skeletal muscle and activates those that cause it to become smooth muscle.
The description of a previously unrecognized role for myocardin in repressing the skeletal muscle maturation program has “important implications for understanding the molecular underpinnings” that determine which kind of muscle cell a stem cell will become, the investigators say.
Understanding the forces involved in ensuring that stem cells become the kind of muscle that’s needed will be helpful for development of cell-based therapies for muscle disease. (See “Moving Away from the Blasts of the Past.”)
A class of compounds known as histone deacetylase (HDAC) inhibitors, which cause genetic instructions to be interpreted by cells as “open” (ready to be followed as recipes for proteins), can apparently cause an increase in numbers and activity levels of so-called T-regulatory cells, natural quieters of an immune response.
Inducing immunologic tolerance to transplanted cells or proteins from one person to another or quieting an unwanted immune response to one’s own cells and proteins (the root cause of so-called autoimmune diseases) are usually accomplished with drugs that suppress the immune system, sometimes with serious side effects.
But in recent years, it’s become clear that the body has its own mechanisms to control a potentially damaging immune-system response and that some of these can be harnessed by biomedicine to increase the acceptance of transplanted tissues (for instance, in muscle-cell transplantation) and treat autoimmune disease.
Wayne Hancock at Children’s Hospital of Philadelphia and the University of Pennsylvania, coordinated a team of researchers who offer evidence supporting this strategy in an Oct. 7 online publication in Nature Medicine.
Through mouse experiments, the authors show that an HDAC inhibitor such as trichostatin could be beneficial in inflammatory bowel disease and possibly other autoimmune diseases. (Myositis, myasthenia gravis and Lambert-Eaton syndrome are autoimmune neuromuscular diseases.)
Other experiments in mice, they say, show that treatment with an HDAC inhibitor and the immunosuppressant rapamycin (which spares the T-regulatory cells) might be an attractive strategy for transplant recipients. (Cell and gene transfer strategies to treat genetic neuromuscular diseases pose some of the same immunologic obstacles as do organ transplant procedures.)
The authors say their studies “show important new mechanisms by which HDAC inhibitors can modulate inflammatory and immune responses in vivo [in living organisms] through their effects on naturally occurring T-regulatory cells” and that the findings “constitute an important, previously uncharacterized and therapeutically relevant mechanism of action.”
Some 50 representatives of the Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) communities in Europe, North America, Australia and Japan convened in Montpellier, France, Nov. 7 through 9, to address the need to identify patients with specific gene mutations who may be eligible to participate in forthcoming clinical trials. MDA Medical and Science Editor Margaret Wahl represented MDA.
A major goal of the meeting was to assess obstacles to collecting information about patients in various countries and combining it into a global database under the auspices of TREAT-NMD (Translational Research in Europe — Assessment and Treatment of Neuromuscular Diseases).
Representatives of four spinal muscular atrophy (SMA) advocacy groups — MDA, Fight SMA, Families of SMA and the SMA Foundation — met in Bethesda, Md., Sept. 28 and 29 to hear presentations from the National Institute of Neurological Disorders and Stroke (part of the National Institutes of Health, or NIH) and from biotechnology companies and others interested in drug development for SMA.
Sharon Hesterlee, MDA’s vice president of translational research, represented the Association.
The Patient Advisory Group of the International Coordinating Committee for SMA Clinical Trials, under the auspices of NIH, organized the meeting.
Among the presenters were NIH, Tikvah Therapeutics, deCODE Genetics, Paratek Pharmaceuticals, Trophos, MethylGene and PTC Therapeutics.
Most of the drug development research is aimed at increasing production of SMN, the protein needed but deficient in SMA, either by changing the way cells process instructions from a gene known as SMN2, or by increasing the stability of the protein made from the SMN2 gene.
Several candidate compounds were discussed. Among them were analogs (chemical relatives) of indoprofen; sodium phenylbutyrate; quinazoline analogs; tetracycline analogs; TRO19622; and histone deacetylase (HDAC) inhibitors.
Also discussed were the establishment of standardized end points (measurements of strength and other aspects of the disease) and the development of a large, unified network of institutions for the conduct of SMA clinical trials.
The Patient Advocacy Group also released SMA standard of care guidelines in September. (See Research Updates, Quest, November-December 2007.)
This group and the International Coordinating Committee encourage all SMA-affected families to join the International SMA Patient Registry. For details contact Connie Garland at Indiana University at 317) 274-5745 or email@example.com.