ALS Research News (A monthly summary of significant articles about ALS research)
Roberta Friedman, Ph.D., ALSA Research Department Information Coordinator
While this summary is not exhaustive, it does include some of the most recent advances. If you would like certain news items featured, please contact the Research Department at researchgrants@alsa-national.org.
Genome Wide Chip Study Suggests Gene Variants in ALS
In a report in the New England Journal of Medicine, researchers at TGen and collaborators found variations in at least ten genes that may be linked to sporadic ALS, using blood samples from more than 220 ALS patients at the Methodist Neurological Institute in Houston. Confirmation was with the samples stored in the ALS patient DNA repository at Coriell collected as part of a joint collaboration with The ALS Association, The National Institutes of Neurological Disorders and Stroke and MDA. The researchers collaborating with Dietrich Stephan, Ph.D., noted that “no single, overwhelming genetic association underlying sporadic ALS” could be identified, but the suggestion of ten or so “candidate susceptibility loci in this and other studies is an essential first step” to document the network of complex environmental factors and what are likely to be numerous genetic variations that interact with lifetime exposures to produce ALS. This follows the publication of a similar effort to identify genes associated with sporadic ALS. More Info.
Microarray Study in Mice Rounds up Usual Suspects
A carefully executed and confirmed analysis of the genes that are actively making their proteins, or that are tuned down, in motor neurons during the disease process in the mouse model of ALS found changes in pathways already implicated, according to results published by Pamela Shaw, M.D. and colleagues at the University of Sheffield, in the Journal of Neuroscience. Genes with changes in their readout activities include those involved in the regulation of cell division, inflammation, and mitochondria function, as well as in metabolism of fats and sugars.
SOD1 Mutant Motor Neurons More Sensitive to Prompts for Programmed Cell Loss
Joseph Beckman, Ph.D., and colleagues at the University of Oregon report that motor neurons are more vulnerable when they make large amounts of the mutant protein linked to some inherited forms of ALS (copper-zinc superoxide dismutase: SOD1). The signal molecule called nerve growth factor helps prune motor neurons through the process that is a normal part of nervous system development. But nerve growth factor may be abnormally producing cell death in ALS. The increased susceptibility of SOD1 mutant motor neurons to this programmed cell death occurred through a decrease in another molecule called nuclear factor erythroid 2-related factor 2 (Nrf2). It also involved lowered production of the enzymes involved in making a protective molecule, glutathione. Normal motor neurons became more sensitive to programmed cell death if they were starved for glutathione. Raising antioxidant defenses by activating Nrf2 prevented cell loss. The report in the Journal of Neuroscience suggests leads towards therapeutic strategy.
Mutant SOD1 Increases Reactive Oxygen in Mitochondria
Nerve cells growing in the lab make more than usual amounts of reactive oxygen in their mitochondria if they have the mutant SOD1 protein, report investigators who had previously shown that toxicity of mutant SOD1 can be prevented by increasing another of the superoxide dismutase enzymes, SOD2. The elevated reactive oxygen levels in mitochondria were significantly diminished by increased production of SOD2. The findings, concluded the team at the University of Iowa headed by Shawn Flanagan, Ph.D., implicate mitochondrial-produced free radicals in the disease.
Mutant SOD1 Interrupts Message for Protective VEGF
Researchers working with Peter King, M.D. at the University of Alabama, Birmingham, observed that SOD1 mutant mice make less of the message for construction of the helper protein, vascular endothelial growth factor (VEGF) early in the course of the disease. Using glial cells living in lab dishes, expressing mutant SOD1, the investigators showed that the messenger RNA molecule for VEGF is destabilized. They also found, as reported in the Journal of Neuroscience, that the mutant SOD1 seems to become attached to elements that aid in making the VEGF protein. By altering the so-called ribonucleoprotein complex that directs production of VEGF, the SOD1 mutant protein may critically reduce the level of this protective growth factor and accelerate the damage in ALS.
ALS Patient Tissue Shows Changes in Protein Handling Machinery
As published in Brain, Manuel Portero-Otin, M.D., Ph.D., University of Lleida, and collaborators at various research institutes in Spain report that ALS patients show evidence that the function of the cell structure called the endoplasmic reticulum is impaired in the disease. This is suggested in studies in tissue from sporadic ALS patients, and has been suggested for the inherited form of the disease by animal models. The investigators analyzed the spinal cord tissue from patients who had died with the disease, as well as frontal lobe of the brain, and found chemical changes in components that are involved in the protein manufacture and disposal governed by this cell structure. They concluded that changes in fatty acid composition, mitochondrial function, and proteasome activity indicate altered function of the cell’s protein handling capacity in sporadic ALS
Chemical Bond Critical in Mutant SOD1 Toxicity
Japanese investigators working with Gen Sobue, M.D., Ph.D., at Nagoya University found a particular place in the mutant SOD1 molecule that may be responsible for the abnormal formation of clumps within neurons. Toxicity of the mutant protein is reduced when the protein is protected at this so called disulfide bond site, as published in the Journal of Biological Chemistry. This supports previously published findings.
Net Charge May Produce Mutant SOD1 Effects
The toxicity of the many different mutations to the SOD1 protein may result from changing the net negative charge of the molecule, Swedish researchers show in a report in the Journal of Biological Chemistry. Analysis of 100 ALS-associated mutations in SOD1 found a decrease the proteins' net negative charge. This charge is normally -6. Because biological molecules maintain a net negative charge to keep them dissolved in the inside of the cell, the findings support the idea that abnormal clumping of protein (aggregation) is an initiating event in the disease process of ALS. The strength of the preferential reduction of repulsive charge is higher in SOD1-associated ALS than in other inherited protein disorders, concluded the researchers, a team at Stockholm University led by Mikael Oliveberg, Ph.D.
SOD1 Mutant Protein: Particular Portion in Mouse Cord
Teams working with Oliveberg and Stephan Marklund at the University of Umea reported in the Proceedings of the National Academy of Sciences that only a particular portion of the mutant SOD1 protein may be involved in the disease process in ALS, and that proportion might differ with different mutations to this protein. Using mice that made one of four known mutant SOD1 proteins, the investigators pulled out a particular portion using a chemical separation process, hydrophobic interaction chromatography. This method was intended to find the relative amounts of disease causing, improperly folded SOD1 in tissues in the mice. The method trapped most of the mutant protein with the G85R and G127X mutations but only minute amounts of the overall amount of the D90A and G93A mutants. The mutant proteins trapped by the chemical method were present in relatively large amounts in the spinal cord of the transgenic mice. And, these levels were high from birth until death and are comparable to the amounts of SOD1 that become sequestered in aggregates as the animals die of the disease. The mutant SOD1 pulled out by the chromatography lacked metal ions and apparently carried abnormal chemical bonds (rather than the proper disulfide links present in normal SOD1). Over a hundred different mutations to SOD1 cause ALS. This finding suggests a common way these diverse protein changes could produce cell toxicity.
TDP-43 Protein in ALS, Frontotemporal Dementia Also in Parkinson’s
John Trojanowski, M.D., Ph.D., and colleagues at the University of Pennsylvania, Philadelphia, reported that the protein, TDP-43, newly linked with ALS and the cognitive change (frontotemporal dementia, FTD) that can accompany it, is present in some patients with another neurological disorder, Parkinson’s disease. Parkinson’s is marked by another abnormal protein deposit, called Lewy bodies. Apparently TDP-43 co-exists with other markers of disease in nerve cells. Researchers are still trying to learn more about the role of TDP-43 and how it relates to ALS and other diseases of the brain and spinal cord. The findings were published in Acta Neuropathologica. More Info.
Trojanowski and colleagues also showed that TDP-43 is present in the disease that appears on the island of Guam and in fact distinguishes the affected Chamorro patients better than the earlier described deposits of the protein, tau. This report appeared in Acta Neuropathologica. More Info
Tau Mutated Mice Show Motor Defects and Parkinsonism
Researchers at Duke University in Durham, North Carolina, published in the Journal of Neuroscience on the features of mice that have an engineered mutation that is also present in people with neurodegenerative diseases. The mutation to the protein called tau can produce frontotemporal dementia. The engineering resulted in a tau protein that is selectively edited to produce an altered version (alternatively spliced from its genetic instructions). Mice with this change showed motor and behavioral changes and damaged astrocytes, the glial support cells of the nervous system, and evidence of increased cell loss through programmed cell death (apoptosis). The team works with Michael Vitek, Ph.D.
Brain Imaging Confirms FTD, ALS, Continuum
French researchers working with Eric Guedj, M.D., at Marseille Hospital and Vincent Meininger, M.D., Ph.D., published in Neurology imaging studies of patients with ALS or FTD or both, demonstrating a loss of blood flow to the frontal regions of the brain in both disorders.
VEGF Ratio in Body Fluid May Indicate ALS
The ratio of VEGF to another protein, both measured in the fluid surrounding the spinal cord (cerebrospinal fluid, or CSF) might be able to indicate the presence of ALS, according to a report by Japanese investigators published in Neurological Research. Koji Abe, M.D., Ph.D., at Okayama University led the team.
Nortriptyline Identified in Drug Screen May Act via Mitochondria
Nortriptyline, a drug once used to treat depression, was first pinpointed as a possible therapy for neurodegeneration in a collaborative effort to screen existing drugs for helpful action in lab models of ALS and Huntington’s disease (the NIH 1040 screening effort). This included tests in isolated mitochondria, which power cell reactions. Nortriptyline was able to stop mitochondrial leaks. The new findings are that nortriptyline significantly delayed disease onset and extended the lifespan of ALS mice, which add to evidence that mitochondria are affected early in the disease. The published data in the European Journal of Neuroscience were reported by a team working with Robert Friedlander, M.D., at Brigham and Women's Hospital, Harvard Medical School. Another drug picked up by the screening effort, ceftriaxone, is already in clinical trials for ALS. Further testing would have to confirm this finding before any patient testing would be warranted (see following item).
Guidelines Discussed for Mutant SOD1 Mouse Model
A report from a European meeting of drug company researchers and ALS investigators in 2006, published in Amyotrophic Lateral Sclerosis (Albert Ludolph, M.D., University of Ulm, Germany, and others), focused on the methods that should reliably produce therapeutic leads from the model. The consortium suggested that attention needs to go towards gender, genetic background, and copy number of the SOD1 transgene. Researchers should compare treatment effect prior to symptoms, to when the mice are already paralyzed. Appropriate endpoints are motor performance and survival. A dose response should be established in the rodent prior to testing in patients. Studies should be blinded. New models of the disease will help in drug development and these models are under construction: the zebrafish, and a mutation in dynactin in mice.
Orla Hardiman, M.D., and colleagues at Beaumont Hospital in Dublin published online in the Journal of Neurology, Neurosurgery, and Psychiatry that the incidence of ALS in Ireland did not change for two compared, recent time periods. In the mid 1990s, and from 2002 to 2004, incidence remained at about 2 per 100,000. Prevalence also did not change and remained at about 6 per 100,000 for the two different times measured. This stable rate agrees with recently reported incidence of the disease in Rochester, Minnesota, where investigators reported stable incidence of 1.7 per 100,000, from 1925 to 1998. The Irish investigators suggested that feeding aid (direct to the stomach nutrition also known as PEG feeding) did not help survival with ALS in their country, but that the effect of breathing aid (noninvasive ventilation or NIPPV) could not be ascertained as this was not yet widespread in Ireland at the times of data collection.
AIDS Dementia Protein Acts on Pathway Implicated in ALS
Stuart A. Lipton, M.D., Ph.D. and colleagues at the Burnham Institute for Medical Research published online in the journal Cell Stem Cell on the effect of a protein associated with AIDS. Called HIV/gp120, this viral protein plays a key role in AIDS dementia. The researchers observed a significant decrease in the number of proliferating stem cells in the brains of HIV/gp120-mice, a model for AIDS dementia that mimics several features of the disease, when compared with similar tissue from normal mice. Cells exposed to HIV/gp120 got stuck in the resting phase of cell division. An enzyme called p38 mitogen-activated protein kinase known to disrupt the cell cycle now appears to be the mechanism underlying decreased stem cell proliferation in the brain with HIV/AIDS. When the scientists neutralized this pathway, they restored stem cell proliferation. Drugs to counter this pathway are being tested for other diseases. The pathway is also under investigation in research funded by The ALS Association.
Biopsy of Unaffected Muscle Might Confirm Diagnosis of ALS
Dutch investigators at Nijmegen Medical Centre working with Machiel Zwarts, M.D., Ph.D., reported in the Journal of Neurological Sciences that signs of denervation in as yet apparently unaffected muscle could be found using muscle fiber conduction velocity. After a mean follow-up of 16 months, nine patients developed probable or definite ALS according to the El Escorial criteria. Knowing that these patients now had ALS, the sensitivity of their abnormal muscle measurement for developing ALS was 89%. Muscle biopsy confirmed that the abnormal readings were due to denervation. The technique might be able to provide faster, more definitive diagnosis of ALS, the researchers suggested.
Dynein could be the Motor Protein Key to ALS Damage
Moving required cellular supplies along the long fiber of nerve cells is an exquisite balance between the actions of motor molecules that govern motion towards the targeted cell and back towards the supplying cell body, as demonstrated by findings reported in Brain Research by University of Massachusetts investigators. A key to ALS may be the activities of the molecule dynein that helps move materials back to the cell body. By boosting one of the dynein molecule’s components, the investigators produced the type of accumulation of nerve fiber proteins that marks ALS damage. These neurofilaments piled up within the nerve fiber. The accumulation was followed by retraction of nerve endings from their target cells, the hallmark early event of ALS. The team is headed by Thomas Shea, Ph.D.
Korean Embryonic Stem Cells Came from Egg Alone
Researchers working with George Daley, M.D., Ph.D., at Children's Hospital Boston and the Harvard Stem Cell Institute found that the stem cells created by the Korean investigation that has since been retracted from publication were products of parthenogenesis, that is, they formed solely from an egg cell without fertilization by sperm—not from nuclear transfer, as originally claimed. Their report was published online in Cell Stem Cell.
CORRECTION: In the July 07 issue of the monthly news, it was stated that a technique to deliver RNA silencing molecules across the blood brain barrier targeted mutant SOD1 expression. The gene silencing molecule was directed at the wild type (normal) SOD1 gene. Corrected text follows.
SOD1 RNA Therapeutic Ferried into Brain
Harvard researchers published in Nature on a method to get into brain the relatively large molecules that can silence the genetic instructions for mutant SOD1. Protein from the rabies virus is able to carry therapeutic RNA silencing molecules across the blood brain barrier that usually excludes such large entities. They used an RNA silencing molecule targeted to the SOD1 protein to demonstrate their technique. Silencing RNA is a therapeutic approach considered for some inherited ALS, as the production of the mutant protein responsible for the disease can be decreased. This new approach should add to the ability to reach the affected tissues, the brain and spinal cord, with RNA silencing therapeutics. The team, including researchers from the University of Iowa and in Korea, was led by Manjunath N. Swamy, M.D.
