Following last year’s discovery that the toxic effect of the mutation that leads to ALS—in one inherited form of the disease—can spread beyond the limits of a cell, researchers Cleveland and Goldstein have asked a logical next question, “Which cells are damaged directly?”

This year they’re using a novel technique (it’s the equivalent of an off switch) that lets them selectively eliminate the mutation’s effects in groups of cells. This way the scientists hope to tell if the disease originates in motor neurons, astrocytes, muscle cells, or immune system cells called microglia. In addition, the technique lets them follow the onset and progression of the disease in model mice with a thoroughness that hasn’t previously existed. This work is ongoing.

And in a study involving chimeras—mice that are a mix of normal cells and those carrying the mutation—the researchers have determined the importance of a cell’s surroundings in developing the disease or staving it off. This year’s work has shown that injury to motor neurons doesn’t come without prior damage to neighboring cells that carry an SOD1 mutation.

Most important, they’ve found that being in the vicinity of healthy cells without the mutation significantly prolongs the life of motor neurons at risk. This discovery is especially important in devising a new approach to therapy—one in which injecting normal nervous system cells or, perhaps, stem cells could dilute the effect of the disease.

^back to top

VAL CULOTTA, Ph.D.
Johns Hopkins University
Copper/zinc Superoxide Dismutase
and Mitochondria

Researchers have noticed that ALS patients have flawed mitochondria, the cell sites most responsible for producing energy. Mitochondria are also key way-stations in the process of apoptosis, a series of self-destruct reactions built into cells. To clarify a possible role for mitochondria in ALS-caused death of motor neurons, Val Culotta has set up a model system in yeast cells, focusing on the enzyme SOD1 that’s nearly identical in humans and yeast. Mutant SOD1 is instrumental in causing an inherited form of ALS.

It was thought that SOD1 could only be found in the cytoplasm of cells, but Culotta has shown, in yeast, that the mutant form of the enzyme is also capable of entering mitochondria. Now Culotta has moved closer to her goal of devising a technique to control the entry of SOD1 into mitochondria. That will tell if those bodies are directly involved in the destructive process the mutant enzyme triggers. This year’s published work was devoted to mapping out the basic science of transport into mitochondria, a necessary first step.

^back to top

JEFFREY ELLIOTT, M.D.
University of Texas, Southwestern
Medical Center
Mutant SOD1 in ALS: Structure
and Function Analysis

Last year, Jeffrey Elliott laid groundwork for his Center studies to explain how mutant SOD1—an abnormal protein found in cells of people with an inherited form of ALS—brings about death of cells. He’s trying to determine what parts of mutant SOD1 influence its ability to clump into large aggregates, an effect many scientists have noticed. Knowing what controls aggregation would help his team determine if clumping is linked to motor neuron death.

This year, Elliott sampled various tissues in SOD1 mice and found, interestingly, that while all those he analyzed contained the mutant SOD1 protein, only certain tissues—spinal cord and, to a lesser extent, brain tissue—contained aggregates. These tissues are the same ones damaged in ALS.

Elliott hypothesizes that something distinctive exists in the way mutant SOD1 is handled in these two tissues. To test this, he’s created models of abnormal handling, creating cultures of human cells and of mouse spinal cords to which he’s added a drug that blocks cells’ normal way of clearing damaged proteins. The drug inhibits bodies called proteasomes that assist in a cell’s “housekeeping.” Results showed that no SOD1 aggregates form in cultures with inactive proteasomes.

More important, Elliott’s discovered aggregate formation is reversible—a major finding that suggests the nervous system can correct itself.

^back to top

JONATHAN D. GLASS, M.D.
Emory University
Novel Therapeutic Interventions
in Familial ALS Mice

Jonathan Glass has studied the process of nerve cell degeneration from a slightly different angle. Most studies focus on the body of the nerve cell, the nucleus-containing area. But Glass has signs that destruction begins, instead, in the axons that extend from the nerve cell body.

Recently, he’s been working with a spontaneous mutation, called Wlds, that appears to protect mouse models of nerve disease by preventing or slowing axon damage. His crosses between mice bearing Wlds and those with genes for progressive motor neuropathy, a neural disorder that resembles ALS, show a dramatic protection of neurons. Other crosses between mice bearing Wlds and the SOD1 mice that more closely model ALS show the Wlds gene to have a mild protective effect. But Glass believes the latter results would be better if Wlds activity were heightened. So he’s engineering more potently-expressing Wlds mice.

A second study focuses on calpains, destructive enzymes activated in nerve cells that experience increased calcium. This year, Glass introduced a calpain-inhibiting drug into mutant SOD1 mice with exciting results. The drug greatly inhibited axon destruction.

In a third investigation, Glass is working with the Icelandic firm, deCode genetics, to isolate genes associated with sporadic ALS. They’re collecting DNA samples nationwide, hoping to find specific sites, called markers, that are more common in ALS patients than people without the disease. It’s a first step to isolating a gene. This year, Glass set up the study’s infrastructure and is now receiving blood samples.

^back to top

AHMET HÖKE, M.D., Ph.D.
Johns Hopkins University
Regeneration in Short- and Long-Term Denervation

Ahmet Höke’s work looks ahead to the possible repair of ALS damage in the body once the disease is stopped. Specifically, he’s focused on how regenerating motor nerve fibers grow towards target muscle tissue and make connections after prolonged periods of inactivity. In the peripheral nervous system, motor axons can regenerate only if their separation from muscle tissue is short-lived. If that period is longer, nerves don’t connect well with target muscle.

This year, Höke’s team worked on a model system that involved cutting motor neurons away from muscle. By supplying the cut nerves with an engineered mouse neuronal stem cell line that expresses the motor neuron growth factor GDNF, the researchers were able to regenerate motor axons even after prolonged periods of denervation.

Using microarray techniques, Höke’s lab is also examining which genes—and which factors those genes tell cells to make—might be important for motor axon regeneration.

^back to top

JEAN-PIERRE JULIEN, Ph.D.
Laval University, Quebec
The Role of Microglia in ALS Pathogenesis

A new area of ALS research focuses on an idea that much of the damage to motor neurons may come from an abnormal turning-on of the immune system’s response to unusual proteins. Activating the body’s innate immunity may be just one more insult to nerve cells in the disease, pushing them over the edge.

Jean-Pierre Julien has been studying motor neuron behavior in an atmosphere of heightened inflammation. He’s found that periodically exposing mouse models of ALS (SOD1 mice) to a foreign protein found in bacteria—setting up inflammation— causes numbers of small debris-devouring cells called microglia to soar. The mice die far sooner. Normal mice respond differently and don’t die. Likewise, minocycline, a drug that damps down microglia, extends the life of mouse models. More proof of an immune role may come from transgenic mice lacking microglia, which Julien’s team has created. They’ll be bred this year with ALS mouse models. Finally, the team’s been looking at a molecule called Cdks—one that causes neuron death when its production is improperly turned on. They’ve found levels of Cdks significantly higher in ALS model mice than in normal animals. Because inflammation can turn on Cdks production, the finding’s yet another that points to likelihood of an immune system role in ALS and a possible target for therapy.

^back to top

VASSILIS KOLIATSOS, M.D.
Johns Hopkins University
Neural Stem Cell Therapies in Experimental Models of Motor Neuron Disease

Vassilis Koliatsos and his colleague Jun Yan are exploring possible use of neural stem cells to reconstruct damaged motor neuron circuits—those similar to injured circuits in ALS patients. Koliatsos approaches the work with years of experience in trophic factors, small proteins with a sustaining/supporting role for motor neurons. Yan is a stem cell expert from a top lab at the NIH, now teamed with Koliatsos. Their studies use human-derived spinal cord stem cells that are predisposed to forming nerve tissue.

Taking pains to eliminate possible immune rejection, they implant the cells in cultures of rat spinal cord, both normal cords and those treated to damage motor neurons. The result has been that the cells “take” superbly, migrating through the spinal cord to enter the motor nerve roots, where they make synapses. Once in place, the cells act as conduits for the migration of more cells along the damaged pathway. This spells good news for potential stem cell therapy, where bridging the span between degenerating spinal cord and denervated muscle has been a formidable problem.

^back to top

MAHENDRA RAO, M.D., Ph.D.
Gerontology Research Center,
National Institute on Aging
Generation of Conditionally Immortalized
Human Neural Lines

Earlier work by Packard Center researchers and others suggests that an excess of the neurotransmitter glutamate, toxic to motor neurons at high levels, is a major step toward the death of those cells in ALS patients. A number of studies point to a failure of motor neurons’ neighboring cells, the astrocytes, to absorb the excess glutamate properly. Astrocytes apparently lack sufficient numbers of the transporter molecules to carry glutamate out of harm’s way.

But the discovery of human stem cells with the potential of forming nervous system cells has suggested a therapeutic approach that Mahendra Rao is pursuing. Recently, Rao has developed ways to isolate glial precursor cells—those somewhere between undifferentiated stem cells and true astrocytes—and to purify them. Fortunately, the precursors express high levels of glutamate transporters—molecules that clear away excess glutamate. This coming year, Rao and his team will add the cells to spinal cord slices exposed to high glutamate levels to see if they’re protective.

In other studies, Rao has nudged human embryonic stem cells into becoming cultures of apparent motor neurons, with membrane markers typical of the nerve cells and a like appearance. These cells, too, will be tested in spinal cord models to see if they’re protective.

A major side-benefit of the “motor neuron” cultures lies in their ability to test drugs or other therapeutic approaches for ALS. And the large, stable cultures Rao’s produced of glial precursor cells offer a new way to study astrocytes’ behavior in disease and their use as possible therapy.

^back to top

CLARKE G. TANKERSLEY, Ph.D.
Johns Hopkins University
Reversing Respiratory Insufficiency
in SOD1 G93A Mice

Because the immediate cause of death in ALS stems from weakened diaphragm and other breathing muscles, several researchers with the Packard Center are looking for a quick therapeutic advance to rescue the motor nerves that direct the muscles. The scientists’ goal is to test a variety of gene therapy approaches, including addition of genes that deliver extra glutamate transporters or genes that deliver cell-sustaining trophic factors to motor neurons.

But monitoring the success of these approaches requires understanding of respiratory system changes that typically occur with ALS. To that end, Clarke Tankersley is studying SOD1 animal models of ALS, following the course of their disease. He’ll record breathing and metabolic rate in the animals at intervals under normal and high carbon dioxide or low oxygen-challenging situations. In the few months he’s been with the Packard Center, Tankersley has found that abnormal breathing begins early in the disease, between 10 and 14 weeks.

^back to top

PHILIP WONG, Ph.D.
Johns Hopkins University
Mouse Models and the Physiological
Roles of ALS2/alsin

Recently, scientists discovered the ALS2 gene—one associated with yet another form of inherited ALS. This disease, however, appears at a far earlier age and is slower than more common, sporadic ALS. And unlike other inherited forms of the disease, the causal gene is recessive. ALS2 codes for a rather long protein called alsin.

This year, Philip Wong was one of a handful or researchers worldwide to explore characteristics of ALS2, hoping especially to find why the disease that its mutated form causes—as in the more common, sporadic form of ALS—appears restricted to spinal cord and brain.

Wong has been the first to create a mouse model of disease with a mutated human ALS2 gene. Developing an antibody to alsin, Wong used it to discover that brain and spinal cord are especially enriched with the protein, even though it also exists in other tissues in the model mice.

Because Wong suspects that disease results from a mutation in ALS2 that renders alsin unable to function normally, he’s taken the idea a step farther, developing alsin-free mice to study. He’ll monitor the mice to see if absence of the protein causes ALS-like illness.

^back to top

NEXT: featured donors >>