Posts tagged SOD1
Articles and news from the latest research reports.
(Image caption: In the top image, cells from a mouse model of amyotrophic lateral sclerosis caused normal healthy brain cells (green) to die. But when scientists blocked an enzyme in the cells from the mouse model, more of the normal cells and their branches survived (bottom))
Digoxin, a medication used in the treatment of heart failure, may be adaptable for the treatment of amyotrophic lateral sclerosis (ALS), a progressive, paralyzing disease, suggests new research at Washington University School of Medicine in St. Louis.
ALS, also known as Lou Gehrig’s disease, destroys the nerve cells that control muscles. This leads to loss of mobility, difficulty breathing and swallowing and eventually death. Riluzole, the sole medication approved to treat the disease, has only marginal benefits in patients.
But in a new study conducted in cell cultures and in mice, scientists showed that when they reduced the activity of an enzyme or limited cells’ ability to make copies of the enzyme, the disease’s destruction of nerve cells stopped. The enzyme maintains the proper balance of sodium and potassium in cells.
“We blocked the enzyme with digoxin,” said senior author Azad Bonni, MD, PhD. “This had a very strong effect, preventing the death of nerve cells that are normally killed in a cell culture model of ALS.”
The findings appear online Oct. 26 in Nature Neuroscience.
The results stemmed from Bonni’s studies of brain cells’ stress responses in a mouse model of ALS. The mice have a mutated version of a gene that causes an inherited form of the disease and develop many of the same symptoms seen in humans with ALS, including paralysis and death.
Efforts to monitor the activity of a stress response protein in the mice unexpectedly led the scientists to another protein: sodium-potassium ATPase. This enzyme ejects charged sodium particles from cells and takes in charged potassium particles, allowing cells to maintain an electrical charge across their outer membranes.
Maintenance of this charge is essential for the normal function of cells. The particular sodium-potassium ATPase highlighted by Bonni’s studies is found in nervous system cells called astrocytes. In the ALS mice, levels of the enzyme are higher than normal in astrocytes.
Bonni’s group found that the increase in sodium-potassium ATPase led the astrocytes to release harmful factors called inflammatory cytokines, which may kill motor neurons.
Recent studies have suggested that astrocytes may be crucial contributors to neurodegenerative disorders such as ALS, and Alzheimer’s, Huntington’s and Parkinson’s diseases. For example, placing astrocytes from ALS mice in culture dishes with healthy motor neurons causes the neurons to degenerate and die.
“Even though the neurons are normal, there’s something going on in the astrocytes that is harming the neurons,” said Bonni, the Edison Professor of Neurobiology and head of the Department of Anatomy and Neurobiology.
How this happens isn’t clear, but Bonni’s results suggest the sodium-potassium ATPase plays a key role. When he conducted the same experiment but blocked the enzyme in ALS astrocytes using digoxin, the normal motor nerve cells survived. Digoxin blocks the ability of sodium-potassium ATPase to eject sodium and bring in potassium.
In mice with the mutation for inherited ALS, those with only one copy of the gene for sodium-potassium ATPase survived an average of 20 days longer than those with two copies of the gene. When one copy of the gene is gone, cells make less of the enzyme.
“The mice with only one copy of the sodium-potassium ATPase gene live longer and are more mobile,” Bonni said. “They’re not normal, but they can walk around and have more motor neurons in their spinal cords.”
Many important questions remain about whether and how inhibitors of the sodium-potassium ATPase enzyme might be used to slow progressive paralysis in ALS, but Bonni said the findings offer an exciting starting point for further studies.
Scientists Link ALS Progression to Increased Protein Instability
A new study by scientists from The Scripps Research Institute (TSRI), Lawrence Berkeley National Laboratory (Berkeley Lab) and other institutions suggests a cause of amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease.
“Our work supports a common theme whereby loss of protein stability leads to disease,” said John A. Tainer, professor of structural biology at TSRI and senior scientist at Berkeley Lab, who shared senior authorship of the new research with TSRI Professor Elizabeth Getzoff.
Getzoff, Tainer and their colleagues, who focused on the effects of mutations to a gene coding for a protein called superoxide dismutase (SOD), report their findings this week in the online Early Edition of the Proceedings of the National Academy of Sciences. The study provides evidence that those proteins linked to more severe forms of the disease are less stable structurally and more prone to form clusters or aggregates.
“The suggestion here is that strategies for stabilizing SOD proteins could be useful in treating or preventing SOD-linked ALS,” said Getzoff.
Striking in the Prime of Life
ALS is notorious for its ability to strike down people in the prime of life. It first leapt into public consciousness when it afflicted baseball star Lou Gehrig, who succumbed to the disease in 1941 at the age of only 38. Recently, the ALS Association’s Ice Bucket Challenge has enhanced public awareness of the disease.
ALS kills by destroying muscle-controlling neurons, ultimately including those that control breathing. At any one time, about 10,000 Americans are living with the disease, according to new data from the Centers for Disease Control and Prevention, but it is almost always lethal within several years of the onset of symptoms.
SOD1 mutations, the most studied factors in ALS, are found in about a quarter of hereditary ALS cases and seven percent of ordinary “sporadic” ALS cases. SOD-linked ALS has nearly 200 variants, each associated with a distinct SOD1 mutation. Scientists still don’t agree, though, on just how the dozens of different SOD1 mutations all lead to the same disease.
One feature that SOD1-linked forms of ALS do have in common is the appearance of SOD clusters or aggregates in affected motor neurons and their support cells. Aggregates of SOD with other proteins are also found in affected cells, even in ALS cases that are not linked to SOD1 mutations.
In 2003, based on their and others’ studies of mutant SOD proteins, Tainer, Getzoff and their colleagues proposed the “framework destabilization” hypothesis. In this view, ALS-linked mutant SOD1 genes all code for structurally unstable forms of the SOD protein. Inevitably some of these unstable SOD proteins lose their normal folding enough to expose sticky elements that are normally kept hidden, and they begin to aggregate with one another, faster than neuronal cleanup systems can keep up—and that accumulating SOD aggregation somehow triggers disease.
Faster Clumping, Worse Disease
In the new study, the Tainer and Getzoff laboratories and their collaborators used advanced biophysical methods to probe how different SOD1 gene mutations in a particular genetic ALS “hotspot” affect SOD protein stability.
To start, they examined how the aggregation dynamics of the best-studied mutant form of SOD, known as SOD G93A, differed from that of non-mutant, “wild-type” SOD. To do this, they developed a method for gradually inducing SOD aggregation, which was measured with an innovative structural imaging system called SAXS (small-angle X-ray scattering) at Berkeley Lab’s SIBYLS beamline.
“We could detect differences between the two proteins even before we accelerated the aggregation process,” said David S. Shin, a research scientist in Tainer’s laboratories at Berkeley Lab and TSRI who continues structural work on SOD at Berkeley.
The G93A SOD aggregated more quickly than wild-type SOD, but more slowly than an SOD mutant called A4V that is associated with a more rapidly progressing form of ALS.
Subsequent experiments with G93A and five other G93 mutants (in which the amino acid glycine at position 93 on the protein is replaced with a different amino acid) revealed that the mutants formed long, rod-shaped aggregates, compared to the compact folded structure of wild-type SOD. The mutant SOD proteins that more quickly formed longer aggregates were again those that corresponded to more rapidly progressing forms of ALS.
What could explain these SOD mutants’ diminished stability? Further tests focused on the role of a copper ion that is normally incorporated within the SOD structure and helps stabilize the protein. Using two other techniques, electron-spin resonance (ESR) spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS), the researchers found that the G93-mutant SODs seemed normal in their ability to take up copper ions, but had a reduced ability to retain copper under mildly stressing conditions—and this ability was lower for the SOD mutants associated with more severe ALS.
“There were indications that the mutant SODs are more flexible than wild-type SOD, and we think that explains their relative inability to retain the copper ions,” said Ashley J. Pratt, the first author of the study, who was a student in the Getzoff laboratory and postdoctoral fellow with Tainer at Berkeley Lab.
Toward New Therapies
In short, the G93-mutant SODs appear to have looser, floppier structures that are more likely to drop their copper ions—and thus are more likely to misfold and stick together in aggregates.
Along with other researchers in the field, Getzoff and Tainer suspect that deviant interactions of mutant SOD trigger inflammation and disrupt ordinary protein trafficking and disposal systems, stressing and ultimately killing affected neurons.
“Because mutant SODs get bent out of shape more easily,” said Getzoff, “they don’t hold and release their protein partners properly. By defining these defective partnerships, we can provide new targets for the development of drugs to treat ALS.”
The researchers also plan to confirm the relationship between structural stability and ALS severity in other SOD mutants.
“If our hypothesis is correct,” said Shin, “future therapies to treat SOD-linked ALS need not be tailored to each individual mutation—they should be applicable to all of them.”
Findings point toward one of first therapies for Lou Gehrig’s disease
Researchers have determined that a copper compound known for decades may form the basis for a therapy for amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease.
In a new study just published in the Journal of Neuroscience, scientists from Australia, the United States (Oregon), and the United Kingdom showed in laboratory animal tests that oral intake of this compound significantly extended the lifespan and improved the locomotor function of transgenic mice that are genetically engineered to develop this debilitating and terminal disease.
In humans, no therapy for ALS has ever been discovered that could extend lifespan more than a few additional months. Researchers in the Linus Pauling Institute at Oregon State University say this approach has the potential to change that, and may have value against Parkinson’s disease as well.
“We believe that with further improvements, and following necessary human clinical trials for safety and efficacy, this could provide a valuable new therapy for ALS and perhaps Parkinson’s disease,” said Joseph Beckman, a distinguished professor of biochemistry and biophysics in the OSU College of Science.
“I’m very optimistic,” said Beckman, who received the 2012 Discovery Award from the OHSU Medical Research Foundation as the leading medical researcher in Oregon.
ALS was first identified as a progressive and fatal neurodegenerative disease in the late 1800s and gained international recognition in 1939 when it was diagnosed in American baseball legend Lou Gehrig. It’s known to be caused by motor neurons in the spinal cord deteriorating and dying, and has been traced to mutations in copper, zinc superoxide dismutase, or SOD1. Ordinarily, superoxide dismutase is an antioxidant whose proper function is essential to life.
When SOD1 is lacking its metal co-factors, it “unfolds” and becomes toxic, leading to the death of motor neurons. The metals copper and zinc are important in stabilizing this protein, and can help it remain folded more than 200 years.
“The damage from ALS is happening primarily in the spinal cord and that’s also one of the most difficult places in the body to absorb copper,” Beckman said. “Copper itself is necessary but can be toxic, so its levels are tightly controlled in the body. The therapy we’re working toward delivers copper selectively into the cells in the spinal cord that actually need it. Otherwise, the compound keeps copper inert.”
“This is a safe way to deliver a micronutrient like copper exactly where it is needed,” Beckman said.
By restoring a proper balance of copper into the brain and spinal cord, scientists believe they are stabilizing the superoxide dismutase in its mature form, while improving the function of mitochondria. This has already extended the lifespan of affected mice by 26 percent, and with continued research the scientists hope to achieve even more extension.
The compound that does this is called copper (ATSM), has been studied for use in some cancer treatments, and is relatively inexpensive to produce.
“In this case, the result was just the opposite of what one might have expected,” said Blaine Roberts, lead author on the study and a research fellow at the University of Melbourne, who received his doctorate at OSU working with Beckman.
“The treatment increased the amount of mutant SOD, and by accepted dogma this means the animals should get worse,” he said. “But in this case, they got a lot better. This is because we’re making a targeted delivery of copper just to the cells that need it.
“This study opens up a previously neglected avenue for new disease therapies, for ALS and other neurodegenerative disease,” Roberts said.
(Source: oregonstate.edu)
New hope for treating ALS
Patient stem cells help identify common problem, leading to clinical trials
Harvard stem cell scientists have discovered that a recently approved medication for epilepsy might be a meaningful treatment for amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, a uniformly fatal neurodegenerative disorder. The researchers are now collaborating with Massachusetts General Hospital (MGH) to design an initial clinical trial testing the safety of the treatment in ALS patients.
The investigators all caution that a great deal of work needs to be done to assure the safety and efficacy of the treatment in ALS patients before physicians should start offering it.
The work, laid out in two related advance online publications in April by Cell Stem Cell and Cell Reports, is the long-term fruit of studies by Harvard Stem Cell Institute (HSCI) principal faculty member Kevin Eggan, who in a 2008 Science paper first raised the possibility of using ALS patient-derived stem cells to better understand the disease and identify therapeutic targets for new drugs.