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Don W. Cleveland, Ph.D.
Larry Goldstein, Ph.D.
University of California at San Diego
Finding Which Cells Are Directly Damaged by Familial ALS-linked SOD1 Mutants
If you were going to use stem cells as a therapy for ALS, what would you need to find out?
Center researchers Cleveland and Goldstein are in their second year of work to reveal exactly where ALS starts in the body and what role different nervous system cells play in the disease. Knowing that is crucial to develop stem cell therapy or to design drugs.
The two scientists are using a novel technique (the equivalent of an off switch) that lets them selectively eliminate the SOD1 mutation’s effects in specific groups of cells. So they’ll get an idea if disease starts in motor neurons, astrocytes, muscle cells or immune system cells called microglia.
This year they showed that blocking the mutation in small groups of motor neurons—even if the other cells still have it—delays disease onset and extends the life of model mice. They’ve now turned to microglia and are looking to see if canceling the mutation there affects the disease.
In separate studies that included human tissues, Cleveland determined that early on in the disease, mitochondria, the motor neuron’s energy-producing organelles, become clogged with mutant protein. This unleashes a downward spiral of toxic reactions. Knowing this presents powerful targets for therapy.
Jonathan D. Glass, M.D.
Emory University
Exploring the Course of ALS in Motor Neurons
Jonathan Glass is clarifying decline in motor neurons—something long overdue in the field—using an ALS model mouse with an especially rapid course of the disease. Where possible, he’s added autopsy data from ALS patients. His studies show motor cell death begins well before symptoms appear. He’s also found that, as in some other neurological diseases, motor neurons first sicken distally, at the part farthest from the nucleus. “That means,” he says, “there’s hope of intervening early to save neurons before the point of no return.”
Douglas Kerr, M.D.,
Ph.D.
Johns Hopkins University
Axonal Growth of Stem Cell-Derived Motor Neurons
Center scientist Douglas Kerr has both lab culture and live animal studies to test the ability of stem cells to restore function to damaged spinal cords. This year he’s shown that mouse embryonic stem (ES) cells can grow into motor neurons in cell cultures with access to target muscle cells.
He’s also shown that ES cells can survive in spinal cords of mice with motor neuron injury. With special treatment, they can send their processes across the cord—as occurs in nature—and a bit beyond. Now using various growth-enhancing agents, Kerr’s testing ways to prod ES—derived motor neurons in animals to extend farther, to reach target muscles. Such studies will be key to minimizing ALS damage once the disease is blocked.
Kerr’s project was made possible by funding from MDA’s Wings Over Wall Street®.
Mahendra Rao, M.D., Ph.D.
Gerontology Research Center, National Institute on Aging
Characterizing Stem Cells for Potential Nervous System Replacement
Center researchers and others have produced motor neurons from stem cells. The potential for spinal cord repair, then, is real. Key drawbacks exist, however, before transplants become appropriate for therapy. For one thing, says scientist Mahendra Rao, it’s difficult to get them to grow to the proper places. Also, their life span is too short to be useful.
Help may come in doctoring a motor neuron’s immediate environment. Normally, neighboring cells—astrocytes—release agents that support and encourage growth of motor neurons. The cells also help clear away toxic chemicals. Rao recently showed, for example, that added astrocytes protect spinal cords in lab dishes from toxic agents that mimic ALS. And he’s now testing astrocytes in SOD1 mouse models.
But Rao believes astrocytes may also improve chances for stem cell-derived neurons. To that end, he’s produced nearly pure cultures of both rodent and human astrocytes, first from undeveloped fetal cells and now from embryonic stem cells. Doing that is no easy feat: It’s driven by painstaking studies of astrocyte basic science. Now, however, Rao and colleagues anticipate results of their latest experiments: Will astrocytes sustain and encourage stem cells to help ALS model mice?
Richard Huganir, Ph.D.
Johns Hopkins University
Molecular Mechanisms of AMPA Receptor-Mediated Toxicity
ALS patients often have high levels of the nerve transmitter glutamate in spinal fluid and various tissues. And for more than a decade, scientists have known that motor neurons’ slow decline in ALS comes, in part, from a glut of glutamate in the synaptic space between neurons.
Normally, glutamate docks with receptors on the motor neuron membrane—the start of a nerve message. But too much glutamate can overstimulate motor neurons. The resulting unnatural inflow of calcium ions through the receptors damages the cell.
Richard Huganir and his team hope to explain how one type of glutamate receptor—the AMPA receptor—operates. Specifically, they’re exploring the system neurons use to control what kind of receptor appears on membranes as well as how many of them settle there. The idea is that ALS patients may have flaws in the control system or in the receptors themselves. Such flaws may make motor neurons more vulnerable to glutamate damage.
Understanding the system would finely hone targets for drugs or other therapies.
Huganir’s project was supported by funding from MDA’s Wings Over Wall Street®.
Marie Filbin, Ph.D.
Hunter College of City University of New York
Strategies to Encourage Stem Cell-Derived Motor Neurons to Regenerate
Marie Filbin is part of the group of Center researchers who hope to step in, seamlessly, when a way to halt the progress of ALS is found. They’re focusing on steps to encourage regrowth of damaged or degenerated motor neurons. Specifically, Filbin has worked on overcoming effects of myelin, a natural inhibitor of motor cell growth in the spinal cord. Her group has discovered distinct chemical inhibitors tied to myelin, and they’re investigating drugs that block them.
But Filbin is also studying the body’s natural “override button” for inhibiting nerve growth. It involves the enzyme arginase I, key in the body’s synthesis of polyamines—molecules that can spark cell division. In this year’s Packard grant work, Filbin’s working to make embryonic stem (ES) cells do double repair duty. By infusing ES cells with extra genes for arginase, her team assumes those cells will have the potential to morph into motor neurons while they also overcome blocks to growth.
Alex Kolodkin, Ph.D.
Johns Hopkins University
Neuropilin and Class 3 Semaphorin Function in Motor Neurons
Semaphorins are proteins that help set axons of growing motor neurons on the road to their proper muscle targets. Secreted by muscle cells, they guide axons by first binding to protein receptors embedded in nerve cell membranes. Specifically, they attach to neuropilin proteins. Alex Kolodkin’s team has shown this semaphorin-neuropilin contact is necessary for nerves to reach muscle.
Mice given mutant genes for either protein, for example, were a no-go. Their nerve fibers looked frayed and overshot muscle targets.
Little is known about the entire process, however, and if nerve cell repair/regrowth is to become part of ALS therapy, understanding must grow. Already the team has found that specific combinations of neuropilins and semaphorins—different types exist—influence which neurons connect to which muscle groups in the body. More interesting, the scientists are using this knowledge to explore the possibility that defects in the two molecules’ interactions help initiate ALS.
In a twist on that, international work suggests a cellular growth factor called VEGF is somehow tied both to ALS susceptibility and to nerve protection. Because VEGF interacts with neuropilins, Kolodkin’s group is piecing together that relationship. It’s a key step before anyone looks at VEGF as a therapy.
Katrin Andreasson, M.D.
Johns Hopkins University
Function of Prostaglandin Receptors in ALS
Neurologist Kati Andreasson researches prostaglandins, a poorly understood class of molecules that underlies the effect of aspirin, for example, and some arthritis medicines. Recently, Andreasson has found that prostaglandins may have profound impact on the survival of motor neurons in the spinal cord. She has inklings that a little-known pathway of prostaglandin activity may be part of a natural neuroprotective system in the body.
In studying that pathway—it involves the prostaglandin EP2 receptor, one normally active in inflammation—Andreasson alternately activated or blocked the receptor in spinal cord models of ALS. Stimulating the receptor dramatically protected neurons. Now she’s moved to the live SOD1 mice that model ALS, to see if they’ll benefit as well.
Andreasson’s project is supported by MDA Wings Over Wall Street®. and Regency Homes’ MDA Golf Classic Fund.
Ronald Oppenheim, Ph.D.
Wake Forest University
Rescuing Motor Neurons from Apoptosis Via Bax Gene Deletion
When ALS does its damage, it trips a cell death program that’s hard-wired in motor neurons. All cells, in fact, have this program, named apoptosis. Neuroscientist Ron Oppenheim has singled out a particular step on that downward path, hoping to disrupt it.
The step involves the action of an apoptotic gene called Bax. Oppenheim’s found that turning off the Bax gene in immature mice lets their embryonic nerve cells resist the apoptosis that normally occurs at an early stage as part of a natural winnowing process. The down side, however, is that about half of the surviving nerve cells don’t connect to muscle targets.
To get around that, Oppenheim adds GDNF, a natural agent that helps the cells stay on target. This year, he turned to studies in SOD1 mouse models of ALS. He found that blocking their Bax gene did extend the animals’ lives.
Now he’s testing to see if added GDNF will both protect motor neurons and keep the mice alive longer.
Merit Cudkowicz, M.D.
Harvard University/Northeast ALS Alliance
Merit Cudkowicz isn’t a Packard Center scientist. She’s much involved with Center research, however, as an expert and advisor on running clinical trials of the therapies we discover. She’s a neurologist, an expert in neuromuscular disease and epidemiology.
Cudkowicz co-directs the Northeast ALS Consortium (NEALS), a group of 25 major U.S. academic medical institutions committed to finding safe, effective therapy for ALS through well-run clinical trials. A faculty member of Harvard Medical School, Cudkowicz knows the ins and outs of designing trials—how to see they’re accurate and well-run. She’s collaborated with the NIH and FDA as well as private industry to extend trials’ scope.
NEALS regularly ushers the Center’s potential therapies into large-scale clinical trials. This year’s no exception. Drug trials of Celebrex, design of projected trials for the beta lactam antibiotics—a result of recent massive drug screening—and design of potential gene therapy trials have all come under its umbrella. Says Center director Rothstein: “NEALS is the trustworthy final step in our bench-to-bedside research plan.”