HUMAN GENETIC CODE ALMOST DECIPHERED

On April 6, biotechnology company Celera Genomics announced that it has identified all of the pieces of DNA that make up the human genome. The company predicted that it could assemble its collection of short pieces into a complete, ordered genome draft this month.

The finished genome, which will require several more years to complete, will provide the complete recipe for making a human being - a 3 billion-letter code consisting entirely of A's, G's, T's and C's (abbreviations for the chemicals that make up DNA). Sprinkled throughout these 3 billion letters are the 80,000 or so sequences, called genes, that code for proteins.

Researchers predict that identifying the order of all the letters in the human genome will allow us to find not just disease-causing genes, but the more subtle "risk factor" genes that increase the chances of developing disorders such as sporadic amyotrophic lateral sclerosis (ALS). Researchers also hope to be able to learn who'll be most likely to respond to medications.

In neuromuscular disease research, the most immediate benefit of the genome draft will likely be an increase in the speed at which the remaining unknown disease-causing gene defects are found.

Marcy Speer, an MDA-funded geneticist at Duke University Medical Center in Durham, N.C., is interested in identifying unknown genes involved in limb-girdle muscular dystrophy. Speer thinks that decoding the genome will be a significant step forward in speeding the rate of disease-gene identification.

"Once general locations for disease genes are known," she says, "the painstaking steps of characterizing the genes and DNA in the region of interest will already be performed, saving researchers lots of time."

STEM CELLS TAKE CENTER STAGE AT SYMPOSIUM

Building new muscle to replace that lost to a genetic disease will require the synthesis of many areas of scientific knowledge, including gene therapy, stem cell technology, immunology and tissue engineering. At the recent Pittsburgh Orthopaedic Tissue Engineering Symposium, co-sponsored by MDA, experts in these specialties met to discuss progress in renewing tissues such as muscle, cartilage, bone and tendons.

Stem Cells

The recent isolation of stem cells from both muscle and bone marrow that are capable of renewing muscle when transplanted from one mouse to another has stimulated a flood of studies aimed at determining the precise nature and capabilities of these cells.

MDA researcher Johnny Huard of the University of Pittsburgh described two categories of primitive cells found in muscle that could be identified as stem cells and myoblasts (immature muscle cells). Huard found that stem cells were much more efficient at incorporating into host muscle after transplantation than myoblasts. He suggested that transplanting stem cells directly into the muscle could work better than transplanting myoblasts, an idea that met with disappointment several years ago.

MDA researcher Louis Kunkel of Harvard Medical School in Boston reported that donor stem cells derived from muscle are more efficient at renewing muscle than those derived from bone marrow. He also found that exercise seems to cause enough muscle injury to lure donated stem cells out of the circulation and into the muscle.

Gene Therapy

Jeffrey Chamberlain

Many researchers think that harvesting stem cells from a person with a genetic disorder, correcting the gene defect with gene therapy and returning the cells to the body will ultimately be the best way to use stem cells to correct a genetic disorder. This avoids the potential problem of stem cells donated from another person triggering an immune response. With this in mind, several researchers presented work on gene therapy vectors, or carriers, to deliver the gene for dystrophin, the protein involved in Duchenne MD, to stem cells.

MDA grantee Jeffrey Chamberlain of the University of Michigan Medical School in Ann Arbor reported that his new "gutted" adenovirus (AV), which lacks all of the viral genes, is capable of delivering a gene that can make the human dystrophin protein for an extended amount of time in the muscles of mice that lack dystrophin. When gene therapy based on this vector was administered to relatively young mice, Chamberlain saw some improvement in muscle function, but the effect was still not great enough to treat humans. The approach was less effective in older mice.

Xiao Xiao of the University of Pittsburgh is developing a smaller version of the dystrophin gene that will fit in the safer adeno-associated virus (AAV). Xiao has been determining what parts of the gene are needed to retain function.

Bioartificial Muscles (BAMs)

Herman Vandenburgh of Brown University School of Medicine in Providence, R.I., presented his work on bioartificial muscles, or BAMs, consisting of functional muscle tissue grown in the lab.

Vandenburgh's BAMs are created from individual muscle cells that are cultured in special gel molds to take the shape of a small muscle. While the cells are growing, he applies force to the mold to simulate the normal environment of developing muscle inside the human body. The resulting muscle tissue can contract but tends to fatigue easily.

Although this type of artificial muscle may one day be used for structural muscle replacement, in the near future it may be transplanted in small quantities to secrete missing proteins.

Robert Dennis of the University of Michigan is also working to develop artificial muscle tissue. Dennis' muscles are grown around artificial tendons and develop into tiny primitive muscles, which he calls myooids. He's currently working to make the myooids develop into fully mature and functional muscles, with the goal of growing large amounts of muscle mass to replace that lost in patients.

Maintaining What You Have

MDA grantee H. Lee Sweeney of the University of Pennsylvania in Philadel-phia discussed the possibility of maintaining muscle mass with insulin-like growth factor-1, or IGF-1. This molecule seems to promote the regeneration of muscle tissue by stimulating the primitive muscle satellite cells to divide and incorporate into existing muscle cells.

When mice that lacked dystrophin were engineered to produce more IGF-1, the mice lost less muscle than those that didn't receive IGF-1.

PEOPLE WITH FSHD NEEDED FOR STUDY

MDA-supported researchers Denise Figlewicz and Rabi Tawil at the University of Rochester (N.Y.) are looking for people with facioscapulohumeral muscular dystrophy to participate in a research study of the genetic cause of FSHD. The study involves a one-time visit to the University of Rochester Medical Center to obtain a blood sample and a muscle biopsy sample.

Contact Lynn Cos at (716) 275-7680 or lynn_cos@urmc.rochester.edu.

CELL DEATH BLOCKED IN MICE WITH ALS

Robert Friedlander

MDA researchers have found that a compound that blocks enzymes involved in a specific type of cell death delays the onset of amyotrophic lateral sclerosis (ALS) by 20 days and increases life span by 22 percent in mice with the disorder. The results were announced in the April 14 issue of Science.

The muscle-controlling nerve cells (motor neurons) lost in ALS are thought to die through a deliberate mechanism called apoptosis, or programmed cell death. This cellular death mechanism depends on a series of enzymes known as caspases.

Now MDA-funded researchers Robert Friedlander of Brigham and Women's Hospital and Harvard School of Medicine in Boston and Serge Przedborski of Columbia University in New York have used a pharmacological caspase blocker called zVAD-fmk to keep the motor neurons of mice with ALS alive longer.

The drug appears to be at least as effective as creatine and coenzyme Q10, and more effective than the drug riluzole, in protecting mice against the effects of ALS.

Friedlander and Przedborski suggest that caspase inhibitors might someday be combined with other drugs that work through different mechanisms to achieve additive effects.

Unfortunately, zVAD-fmk may be too toxic to be useful in humans. But the finding has stimulated interest among drug manufacturers in developing safer caspase inhibitors.

PEOPLE WITH MD, BONE MARROW TRANSPLANTS NEEDED

MDA is interested in locating people with MD who've undergone bone marrow transplants for any reason and would be willing to share their experience with researchers.

If you're in this category, please contact:
Research Department
Muscular Dystrophy Association
3300 E. Sunrise Drive
Tucson, AZ 85718-3208
research@mdausa.org. 

GENE THERAPY FOR ALS?

Researchers at Johns Hopkins University in Baltimore and Thomas Jefferson University in Philadelphia are collaborating on a new idea - gene therapy for amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease). ALS is a disorder that strikes mostly middle-aged and older adults and causes the death of motor neurons, muscle-controlling nerve cells.

Enhancing Glutamate Transport Using Genes or Drugs In the brain and spinal cord, nerve cells send signals to other nerve cells via glutamate (yellow). Excess glutamate is then "sucked up" up by glutamate transporter molecules (green) that sit on the surface of nearby glial (supporting) cells. It's then recycled for later use.

Since the disorder is only rarely caused by a known gene, gene therapy may seem paradoxical. But, says Jeffrey Rothstein, who co-directs MDA's ALS Center at Johns Hopkins, this study seeks to use genes more as drug delivery systems than as replacements for faulty genes.

Researchers are working on inserting genes for EAAT2, a protein that whisks glutamate away from the fluid surrounding cells in the brain and spinal cord. This protein, a glutamate transporter, keeps the brain chemical from building to toxic levels. Research shows that excess glutamate around neurons may be a key factor in cell death in ALS.

Meanwhile, a group in Switzerland has slowed the progress of ALS in mice by inserting genes for Bcl-2 into their spinal cords. Bcl-2 is a protein that's shown promise in preventing the death of neurons. A group at Northwestern University in Chicago has used the gene for GDNF, another protein shown to protect neurons. This team put the gene into leg muscles of mice, where the protein made from the gene may have been "soaked up" by nerve endings near the muscle.

Rothstein remains committed to the pursuit of gene therapy for ALS, but says he'd rather use a drug, if possible, to get the same effect.

Gene therapy, he notes, especially of the central nervous system, is fraught with technical hurdles, and a drug would be much easier to get into the brain and spinal cord.