Injecting Second Gene in Mice Enhances Dystrophin
Gene Therapy
In experiments with mice, MDA grantees at Stanford
(Calif.) University have achieved excellent production and distribution
of dystrophin, the muscle protein needed but missing in Duchenne
muscular dystrophy (DMD).
The scientists used a new technique in which genes
are injected into the muscles without being carried in a virus,
but with a second gene that coaxes the new genes to integrate into
an existing chromosome.
Thomas Rando, an MDA-supported molecular biologist and
associate professor, and Carmen Bertoni, an MDA-supported postdoctoral
student working with Rando, injected the leg muscles of DMD-affected
mice with dystrophin genes. They also injected genes for integrase,
a protein that causes genetic material to integrate into a chromosome
instead of remaining separate from the chromosomes in the cell nucleus.
The research team, whose results are in the Jan.
10 issue of Proceedings of the National Academy of Sciences, also
included investigators from Stanford’s Genetics Department and the
Veterans Affairs Palo Alto Health Care System.
The team found that the mouse muscles receiving
both dystrophin and integrase genes had more than eight times the
amount of dystrophin six months after injection than did mouse muscles
that received dystrophin genes alone.
Moreover, while the muscle fibers that received
dystrophin genes alone showed dystrophin production centered around
the injection site, fibers that got both proteins produced dystrophin
along the whole length of the fiber. That result is thought to give
the fiber much better protection against damage.
The muscle fibers that received the combined gene
transfer strategy were less permeable to an injected dye than dystrophin-damaged
fibers, also a sign of superior protection.
“The issue of the distribution of dystrophin from end
to end of the fiber is an important factor that really pertains to any
form of muscle gene delivery. You need to consider not just the amount
of the protein produced, but where it is,” Rando said.
Acknowledging that the possibility of using an integrating
gene is a “step forward for virus-free gene therapy,” Rando said
it also carries an inherent risk, because gene integration in other
situations has led to genetic mutations.
“The development of this technology will involve
producing more specific integrases with the hope of targeting integration
to one place. Knowing where the gene is, knowing it’s safe, and
getting high levels of protein production are the ultimate goals.”
New Myostatin Blocker Enlarges
Mouse Muscles
A new compound that blocks myostatin, a natural
inhibitor of muscle growth, has increased muscle mass in mice by up
to 60 percent in two weeks, a team of scientists announced in the Dec.
13 issue of Proceedings of the National Academy of Sciences. The tested
mice didn’t have muscular dystrophy.
Se-Jin Lee at Johns Hopkins University in Baltimore,
with colleagues from several academic institutions and biotechnology
companies, says the compound blocks myostatin by providing it with
a portion of a molecule that it normally sticks to.
Known as ACVR2B, the new compound provides
myostatin with a partial molecule that keeps it from interacting with
its normal molecular binding partner. Without this interaction, myostatin
can’t send its usual growth-inhibiting signals to muscle cells.
A previously developed myostatin blocker is now being
tested in clinical trials in people with certain adult forms of muscular
dystrophy. That compound, MYO-029, was developed by Wyeth Pharmaceuticals,
and is based on an antibody (immune system protein) that sticks to and
interferes with the myostatin protein.
Lee, a professor of molecular biology and genetics
at the Johns Hopkins Institute for Basic Biomedical Sciences, has
MDA funding for work on myostatin mechanisms. He says the new inhibitor
is very potent and leads to dramatic effects in the mice. These
effects were “larger and faster than we’ve seen with any other agent
and even larger than we expected.”
He cautions, however, that the effects of ACVR2B can
be attributed to its ability to block more than just myostatin signaling,
which may increase the potential for side effects.
Lee also notes that increasing muscle mass alone
isn’t necessarily the answer in muscular dystrophy.
“In general, I am quite optimistic that targeting
this pathway will turn out to be an effective way to increase muscle
growth,” he says. “But much more work will be required to determine
whether this will be a viable approach.”
Altered
Protein Related to Autoimmune Diseases
A slight variation in an immune system protein called PTPN22 may cause susceptibility to autoimmune diseases,
disorders in which the immune system mistakenly mounts an attack on
the body’s own tissues, a new study says. (Autoimmune neuromuscular
diseases include myasthenia gravis, Lambert-Eaton syndrome, polymyositis and dermatomyositis.)
In the protein, the substitution of the amino acid tryptophan where most people have arginine appears to disrupt some of
the fine-tuning needed for a safe and effective immune response, according
to findings in the December issue of Nature Genetics. The altered protein
results from a variation in the gene for PTPN22.
Torkel Vang, at the Burnham Institute in La Jolla,
Calif., and colleagues, say the altered PTPN22 may interfere with
the necessary dampening of an immune response normally performed
by regulatory immune system cells, or with the normal destruction
of self-reactive cells.
They suggest that a small molecule that blocks this
alteration could be developed and potentially be used as a treatment
for a variety of autoimmune diseases.
MMD2 Rarity Questioned
At a January meeting of the European Neuromuscular Centre,
professionals from the United States and five European countries learned
that type 2 myotonic dystrophy (MMD2) may be much more
common than previously believed, at least in some areas. In Central
Finland, the estimated prevalence is about one person in 10,000.
MMD2, which results from an expanded, repeated section
of DNA on chromosome 3, is similar to type 1, which results from
a similar DNA expansion on chromosome 19. But the type 2 form has
been considered a rare disease, while the type 1 form, which occurs
in about one in 7,500 births, is relatively common.
Unlike type 1, type 2 MMD doesn’t seem to affect
newborns, doesn’t cause serious cognitive problems and affects thigh
muscles early.
MDA hosts a chat for families with MMD every Wednesday
evening. See www.mda.org and select MDA Chat. Online
groups focused solely on MMD2 can be reached through http://health.dir.groups.yahoo.com/dir/Health___Wellness;
and enter ”myotonic dystrophy 2” in the search box.
Protein
Flaw Turns on Heart-Damaging
Genes in 2 Dystrophies |
MDA grantee Howard
Worman at Columbia University in New York, a leading physician-scientist
in the field of lamin proteins, recently announced that his
group has uncovered the molecular connections between at least
one lamin gene mutation and heart disease. Mutations of lamins
underlie Emery-Dreifuss muscular dystrophy (EDMD) and type 1B limb-girdle MD (LGMD1B).
The group’s findings were presented at
a December meeting of the American Society for Cell Biology
in San Francisco. It seems that type A lamins, which are
produced in almost all cells in the body, may, when flawed,
have specific deleterious effects on the heart.
The researchers analyzed cardiac muscle
tissue from mice carrying a lamin A gene mutation that
causes the chromosome 1 type of human EDMD, a disorder
in which heart disease is nearly universal.
Unlike normal mouse hearts, those with the
mutated lamin genes showed increased activity of genes for
other proteins, called MAP kinases, which have been
implicated in heart enlargement and heart failure. The investigators
also found changes in gene activity for three other components
that can contribute to cardiac muscle disease.
Worman said, “The finding that MAP kinases
are activated in the heart in this mouse model of Emery-Dreifuss
muscular dystrophy suggests that inhibitors of these enzymes
may be useful as treatments. This of course remains to
be tested in animal models and, if successful, possibly
in human subjects.” |
|
