Twenty years ago today, a team of more than 30 scientists at 13 research hospitals and universities reported the first gene, superoxide dismutase 1 (SOD1), linked to ALS. The gene encodes an enzyme critical to detoxify free radicals that are created during breathing. 

Scientists now estimate that mutations in the SOD1 gene explain about 1 in 5 cases of the inherited form of the disease.  The landmark discovery led to the identification of key players in ALS. And, paved the way toward preclinical testing of potential treatments and the first genetic test for the disease.  Take a look back at these advances by exploring our timeline.  Click on the text to learn more.

Image credits: Mark Dumont, Nature Publishing Group, NIGMS, Rockefeller University Press and George Shuklin.

References

Rosen, D.R. et al. (1993) Mutations in Cu/Zn superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis. Nature 362(6415), 59-62.  Abstract  |  Full Text  (Subscription Required)

Bowling, A.C., Schulz, J.B., Brown, R.H. Jr and Beal, M.F.  (1993)  Superoxide dismutase activity, oxidative damage, and mitochondrial energy metabolism in familial and sporadic amyotrophic lateral sclerosis.  Journal of Neurochemistry 61(6), 2322-2325. Abstract  |  Full Text  (Subscription Required)

Gurney, M.E. et al. (1994) Motor neuron degeneration in mice that express a human Cu,Zn superoxide dismutase mutation.  Science 264(5166), 1772-1775. Abstract  |  Full Text  (Subscription Required)

Gurney, M.E., Cutting, F.B., Zhai, P., Doble, A., Taylor, C.P., Andrus, P.K. and Hall, E.D. (1996) Benefit of vitamin E, riluzole, and gabapentin in a transgenic model of familial amyotrophic lateral sclerosis. Annals of Neurology 39(2), 147-157. Abstract  |  Full Text  (Subscription Required)

Bruijn, L.I., Houseweart, M.K., Kato, S., Anderson, K.L., Anderson, S.D., Ohama, E., Reaume , A.G., Scott, R.W. and Cleveland, D.W. (1998) Aggregation and motor neuron toxicity of an ALS-linked SOD1 mutant independent from wild-type SOD1.  Science 281(5384), 1851-1854.nbsp; Abstract  |  Full Text  (Subscription Required)

Tobisawa, S., Hozumi, Y., Arawaka, S., Koyama, S., Wada, M., Nagai, M., Aoki, M., Itoyama, Y., Goto, K. and Kato T. (2003) Mutant SOD1 linked to familial amyotrophic lateral sclerosis, but not wild-type SOD1, induces ER stress in COS7 cells and transgenic mice. Biochemical and Biophysical Research Communications 303(2), 496-503.  Abstract  |  Full Text  (Subscription Required)

Clement, A.M. et al. (2003) Wild-type nonneuronal cells extend survival of SOD1 mutant motor neurons in ALS mice. Science 302(5642), 113-117.  Abstract  |  Full Text  (Subscription Required)

Turner, B.J., Atkin, J.D., Farg, M.A,. Zang, D.W., Rembach, A., Lopes, E.C., Patch, J.D., Hill, A.F. and Cheema SS. (2005) Impaired extracellular secretion of mutant superoxide dismutase 1 associates with neurotoxicity in familial amyotrophic lateral sclerosis.  Journal of Neuroscience 25(1), 108-117.  Abstract  |  Full Text  

Boillée, S., Yamanaka, K., Lobsiger, C.S., Copeland, N.G., Jenkins, N.A., Kassiotis, G., Kollias, G. and Cleveland, D.W. (2006) Onset and progression in inherited ALS determined by motor neurons and microglia. Science 312(5778), 1389-92. Abstract  |  Full Text  (Subscription Required)

Scott, S. et al. (2008) Design, power, and interpretation of studies in the standard murine model of ALS.  Amyotrophic Lateral Sclerosis 9(1), 4-15.  Abstract  |  Full Text  (Subscription Required)

Yamanaka, K., Chun, S.J., Boillee, S., Fujimori-Tonou, N., Yamashita, H., Gutmann, D.H., Takahashi, R., Misawa, H. and Cleveland, D.W. (2008) Astrocytes as determinants of disease progression in inherited amyotrophic lateral sclerosis. Nature Neuroscience 11(3), 251-253.  Abstract  |  Full Text

Münch, C., O'Brien, J. and Bertolotti, A. (2011) Prion-like propagation of mutant superoxide dismutase-1 misfolding in neuronal cells.  Proceedings of the National Academy of Sciences 108(9), 3548-3553.  Abstract  |  Full Text  

Igoudjil, A., Magrané, J., Fischer, L.R., Kim, H.J., Hervias, I., Dumont, M., Cortez, C., Glass, J.D., Starkov, A.A. and Manfredi, G. (2011)  In vivo pathogenic role of mutant SOD1 localized in the mitochondrial intermembrane space. Journal of Neuroscience 31(44), 15826-15837. Abstract  |  Full Text  

van Blitterswijk, M. et al. (2011) Anti-superoxide dismutase antibodies are associated with survival in patients with sporadic amyotrophic lateral sclerosis.Amyotrophic lateral sclerosis 12(6):430-438. Abstract  |  Full Text  

The discovery and development of ALS medicines is picking up steam. In 2012 alone, at least 15 emerging treatments are being put to the test in the clinic – including 7 at the phase II and phase III stage.

Stem-cell based strategies including Neuralstem and Brainstorm hope to protect the motor nerves from further destruction. Mitochondrial-targeted medicines including Biogen-Idec’s dexpramipexole hope to treat ALS by keeping the energy flowing in the motor nerves. Immune system modulating drugs including Novartis’ Gilenya and Neuraltus’ NP001 hope to slow ALS in its tracks by reducing neuroinflammation. And, potential muscle boosters including Cytokinetics’ tirasemtiv (CK-357) hope to keep muscles moving.

Experts gathered at the International Symposium on ALS/MND in Chicago this month to discuss emerging treatment strategies currently being tested in the clinic and the challenges evaluating them going forward.

NP001

Neuraltus Pharmaceutical’s NP001 appears to be safe and tolerable according to phase II results presented by California Pacific Medical Center’s Robert Miller MD.  Some signs of benefit were detected in ALS patients that took the highest dose (2 mg/kg).  These include “modest” hints of reduced progression.  136 people with ALS participated.

“Our primary endpoints were not a home run,” says Miller.  “They were a bunt or a base hit.  But they were in the right direction.”

A second look at the phase II results, inspired by observations from doctors and trial participants, indicated that the progression appeared to “level off” in a significantly increased subset of people on the highest NP001 dose (27%) compared to placebo (including historical controls) (11%) during the 6 month treatment period. The strategy, called a post-hoc analysis, has been used previously to evaluate certain emerging cancer medicines.

“We feel the results justify the further development of NP001,” says Miller.

A phase III clinical trial is planned. Enrollment is expected to begin sometime in the second half of 2013.

To learn more about NP001 and its potential to treat ALS, tune into our podcast NP001: A quiet riot for ALS? with Robert Miller MD.

 

The NeuRX Diaphragm Pacing System. Image: Synapse Biomedical.

NeuRX DPS

Diaphragm pacing might extend survival of some people with ALS according to a new study led by California Pacific Medical Center’s Jonathan Katz MD.  The study found that ALS patients implanted with the NeuRX DPS phrenic pacer appeared to live about 16 months (60%) longer vs. historical controls – after the initiation of noninvasive ventilation. 77 people with ALS participated. 

“The procedure may work,” says Katz. “But more studies need to be done.”

A key question is whether healthier people with ALS are in some way selected for diaphragm pacer implantation – patients who could live longer otherwise unassisted.  

“Until that’s excluded, we need to have a great deal of caution,” says Katz. “We need to study [the DPS] a lot more. We need randomized trials.”

A randomized controlled phase II clinical trial to further evaluate the potential benefits of the NeuRX DPS for people with ALS is now planned.  180 people with ALS are expected to participate.  Sites include California and New York.  Clinical trials are currently ongoing in England and France.

To learn more about the NeuRX DPS, check out DPS Sleep.

Neuralstem

Neural stem cell transplantation into the spinal cord appears to be safe according to initial phase I clinical trial results presented by Emory University’s Jonathan Glass MD.  Stem cells could be detected in the spinal cord of autopsied tissue of some trial participants suggesting that engraftment occurred.  No significant changes appeared to be detected in rates of functional decline (including ALS-FRS) according to a recently published phase I analysis. “There is no indication that the treatment accelerated disease progression,” says Glass.  15 people with ALS participated.

A phase II ALS clinical trial is now planned.  Neural stem cells at higher doses will be injected into the cervical (diaphragm-moving) region of the spinal cord. The clinical trial is likely to include ALS patients with measurable functional decline and not be placebo-controlled according to Glass.  “We are awaiting FDA approval to move forward,” says Glass.

To learn more about stem cell transplantation and ALS, read Neuralstem, surging immunosuppression?

Tirasemtiv

 

Power up? Tirasemtiv may increase the power generated from fast skeletal muscle according to SUNY Medicine's Jeremy Shefner MD. Courtesy of Nature Publishing Group. All Rights Reserved.

Cytokinetics’ potential muscle booster tirasemtiv (CK-357) appears to be safe and tolerated.  But riluzole dosages need to be reduced 50% due to the drug’s ability to block riluzole breakdown according to phase IIa clinical trial results presented by State University of New York Medical University’s Jeremy Shefner MD PhD. “The evidence thus far supports the further evaluation of tirasemtiv,” says Shefner.

A phase IIB 20-week randomized, double-blind placebo-controlled clinical trial is now recruiting.  400 people are expected to participate.  Sites include clinics in US and Canada.

To learn more about tirasemtiv, read CK-357, helping pALS live strong?

SOD1-RX

Isis Pharmaceutical’s potential misfolded superoxide dismutase 1 (SOD1)-lowering therapy appears to be safe and tolerable according to initial phase I double-blind placebo-controlled clinical trial results presented by Washington University’s Timothy Miller MD PhD.  Patients received at least one dose of SOD1-directed 'gapmer' over a 12 hr period intrathecally - directly into the spinal cord.  21 people with SOD1-linked fALS participated.  Key side effects include headaches, backpain and nausea – typical of lumbar puncture.  The antisense oligonucleotide is now being redesigned in hopes to optimize its SOD1-lowering abilities.  “It is hard to predict when the next trial will be,” says Miller.

To find out about potential SOD1-directed strategies to treat sporadic ALS, check out our watchlist: Antibodies for sALS.

***

Enrollment in clinical trials remains challenging according to Duke University School of Medicine’s Rick Bedlack MD PhD MS. But other key obstacles to push ALS medicines forward also emerged at ALS MND Chicago 2012.

Ceftriaxone

Potential neuroprotective antibiotic ceftriaxone reduced functional decline more than 30% according to phase II double-blind placebo-controlled study results presented by Massachusetts General Hospital’s Merit Cudkowicz MD MSc. The drug was subsequently withdrawn in August of 2012 due to insufficient efficacy at the phase III stage. 513 people with ALS participated.

The results raise key questions about enrollment, the number of people with ALS needed to participate and study duration – particularly to inform and empower phase II go/no go decisions.

Olesoxime

Powerbar? Scientists hope to create mitochondrial-directed ALS medicines to boost energy levels in the deteriorating motor nerves. Image: David Furness PhD, Wellcome Images.

Better clinical trial outcome measures may be needed to evaluate emerging ALS medicines according to olesoxime study investigator and Hôpital de la Pitié-Salpêtrière neurologist Timothée Lenglet MD. The putative mitochondrial protectant failed to significantly extend life of people with ALS according to final randomized double-blind placebo-controlled phase III results presented at ALS MND 2012.  512 people with ALS participated.

“It may be difficult to detect a significant survival advantage in an 18 month clinical trial,” says Lenglet.

Clinical trial outcome measures including survival were a key subject of debate later that evening at Biogen-Idec’s ALS clinical trial roundtable.

“We have not really done well using survival as an endpoint,” says Carolinas Medical Center’s Benjamin Brooks MD.

Montreal Neurological Institute’s Angela Genge MD FRCP agrees. “We need a new endpoint that says that there is an effect and that the effect is worthwhile.”

An emerging technique called joint rank analysis may enable clinicians to do just that according to Genge. The combined functional survival measure is currently being used to help clinicians evaluate Biogen-Idec’s emerging ALS medicine dexpramipexole at the phase III stage. The initial results are anticipated by the end of 2012.

***

In the meantime, clinicians are working hard to care for people with ALS. Soft foods and thickened fluids help people with ALS meet their nutritional needs. Noninvasive ventilation helps ALS patients breathe easier, sleep better and boosts survival. And, certain medicines might help control emotionality and reduce spasticity.

But physicians remain divided on whether to recommend exercise for people with ALS.  A growing group of neurologists suspect that workouts can improve the quality of life and might even help fight the disease.  But others remain skeptical according to new results presented at ALS/MND 2012.

 

Exercise does a body good? Researchers at the University of Lisbon are developing treadmilling-based exercise regimens for people with ALS. Image: LuluLemon Athletica, Flickr.

Aerobic and Resistance Exercise

Certain forms of exercise including swimming might be safe for people with ALS according to a retrospective analysis of 234 patients’ hospital records led by the Hospice of Special Care’s Jinsy Andrews MD. No significant decline in survival was detected in people with ALS who exercised. What’s more, patients that exercised tended to experience slower functional and respiratory decline.

But key obstacles remain. Nearly 1 out of 4 health professionals are reluctant to routinely recommend exercise to people with ALS due to concerns of fatigue, falls and increased muscle weakness according to a survey from University of Pennsylvania’s Michele Lewis DPT.  And, workouts must be tailored to each ALS patient according to Northwestern Memorial Hospital’s Margaret McGovern-Denk MS OTR/L - making the design of general clinical practice guidelines challenging.

A big part of the problem is that there is insufficient evidence to indicate which exercises are the best choice for people with ALS.  A clinical trial of certain forms of exercise including stationary cycling and weightlifting led by Johns Hopkins University School of Medicine neurologist Nicholas Maragakis MD is ongoing. 60 people with ALS are expected to participate.

To learn more about exercise and ALS MND, check out Stretching the Limits of ALS Care.

Mitochondria produce the energy needed to keep muscles healthy and moving. But in people with ALS, these power plants go out of service likely contributing to muscle atrophy and ultimately, paralysis.

Scientists are developing treatments to supe up mitochondria in hopes to keep the energy flowing in the muscles and connecting nerves. One of these emerging medicines, Knopp Biosciences’ dexpramipexole now licensed by Biogen Idec, is gathering steam as a potential ALS treatment strategy. Reporting phase II results last fall, neurologists found that the drug slowed disease progression about 30%.

Some researchers suspect however, that these mitochondrial-targeted medicines may need to do much more than boost energy production to grind ALS to a halt. Even operating at full steam, these power plants may be unable to provide enough energy to keep muscles working because they may not be in the right place to do their job. Scientists are now beginning to understand why these mitochondria might stray, suggesting new strategies to tackle the disease.

Traffic Tie-up

When Massachusetts General Hospital researchers reported the first altered gene, superoxide dismutase 1 (SOD1), linked to ALS in 1993, researchers scrambled to generate and characterize mice with these same mutations in hopes to discover the cause of the disease.

Reporting the first mouse model in 1994, scientists quickly put their finger on a potential contributor to the disease: a power outage in the motor nerves. Researchers, led by Northwestern University School of Medicine neuroscientist Mark Gurney MD, now at Michigan’s Tetra Discovery Partners, reported that the mitochondria swelled up in the motor neurons of SOD mice before showing any signs of ALS suggesting that malfunctions in these intracellular power plants might, in part, lead to the disease.

“But whether [defective] mitochondria were driving the pathology of ALS, that was a question mark,” explains Johns Hopkins University School of Medicine neuroscientist Lee Martin PhD.

In 2004, University of California San Diego researchers led by neuroscientist Don Cleveland PhD found that these misshapen mitochondria appeared at the nerve terminals at about the same time as the muscles became unplugged.

University of California San Diego neuroscientist Christine Vande Velde PhD, now at the University of Montreal, however suspected that more than the breakdown of these power plants could be contributing to ALS. She noticed that these swollen mitochondria accumulate at the neuromuscular junctions in these mice as the disease progressed suggesting that these power plants were unable to travel back towards the cell body to be refurbished or recycled. This so-called retrograde transport of mitochondria is critical to meet energy demands in power-guzzling regions of the motor nerves including the nerve terminals where electric signals are transmitted across the neuromuscular junction which ‘tell’ the muscles to move. If these signaling systems are on the fritz, this too could contribute to muscle weakness and paralysis.

To try and determine whether this impaired mitochondrial dynamics could also be contributing to ALS, Jordi Magrané  PhD and Giovanni Manfredi PhD at Weill Cornell Medical College in New York introduced a system in the late 2000s in which they could fluorescently tag these intracellular power plants in cultured ALS SOD1 mouse spinal cord motor neurons in laboratory dishes and watch them move live in real time under a microscope.

Reporting just last month, the team found that mitochondrial trafficking is indeed affected in the SOD1 mutant motor neurons of the spinal cord. The number of mitochondria that undergo fusion – critical to keep these intracellular power plants in working order – dropped over 50%. And, the movement of mitochondria slowed to a crawl. (Check out the video.) 

Incredibly, the Weill Cornell team found that newly generated power plants constructed in the cell body are already operating at reduced capacity and accumulate at the so-called distal end of the axon, near the nerve terminal. And, the number of mitochondria appear to be reduced at synapse-like structures. These defects appear to be specific to motor neurons. 

“This could be happening in ALS,” says Magrané. 

These findings come at the heels of a study from Vande Velde’s team last summer in which they discovered that mitochondria pile-up in the spinal cord in mutant SOD1 mice during the disease course. 

 

Special delivery.  Mitochondria are pushed down the axons of motor neurons by kinesins along train tracks made of microtubules. The energy these intracellular power plants generate fuels the delivery of electrical signals that ‘tell’ the muscles to move. Adapted from Tsai, M. et al. Molecular Biology of the Cell (2000) 11(6), 2161-2173.

Now, the Weill Cornell team is using the same tools to monitor these intracellular power plants in living ALS mice to determine whether mitochondrial dynamics is indeed defective and contributes to denervation. Looking ahead, the researchers hope to take a look at other mouse models of ALS to determine whether these multi-mitochondrial pile-ups generally contribute to the disease. 

Tracking down the culprit

What causes the transport and recycling machinery to fail in ALS? Researchers remain unsure. One possibility is that the SOD1 enzyme which accumulates during the course of the disease could jam up the works. Reporting last summer, Vande Velde’s team found that these misfolded proteins stick to the surfaces of mitochondria in the spinal cord of ALS mice. This could make these intracellular power plants more difficult to pick up by motor proteins, the neurons’ delivery vehicles, and therefore more difficult to transport.

But new findings from the labs of Hugo Bellen PhD at the Baylor College of Medicine in Texas and Michael Miller PhD at the University of Alabama at Birmingham suggest that there could be an even bigger problem. The systems that keep these power plants upon delivery fixed in position and in tip-top condition could also be out to lunch. 

Reporting last month, the Bellen-Miller team discovered that the putative hormone VAP-B produced by neurons fine-tunes the positions of mitochondria and regulates the energy production in muscles. A hormone that is lacking in all people with ALS tested including those with the sporadic form of the disease.

The Electric Slide

Scientists first stumbled upon a link between VAP-B and ALS in 2004 when geneticist Mayana Zatz PhD and colleagues at São Paulo University in Brazil reported that a mutation in the gene, also known as ALS8, triggered the disease. Reporting in 2008, the Bellen-Miller team discovered that VAP-B appears to be a hormone and that this mutation blocked its secretion. But why a drop in VAP-B levels resulted in ALS remained unclear. 

 

Power punch.  Muscles are packed with mitochondria (arrows) to generate the energy needed for contraction. Here, a section of skeletal muscle is shown. Image: NHBLI, NIH.

To try and get a better idea of why a lack of VAP-B could contribute to ALS, Bellen’s team at Baylor College of Medicine generated fruit flies unable to produce the hormone and watched them develop. The researchers found that very few of these flies survived but the few that did could barely move. Taking a closer look at their muscles, the Bellen team quickly identified the problem. Most of the mitochondria appeared to be broken down. Their muscles just simply did not have enough fuel. 

But, these studies were extremely difficult to do. Too few flies survived for more detailed analysis. So, the researchers turned to Miller’s team at the University of Alabama who were studying the loss of VAP-B in the roundworm. The researchers also noticed that the mitochondria appeared to be malfunctioning. But they also noticed something else. The mitochondria were displaced from the muscle fibers. And, by watching the worms crawl under the microscope, the researchers found out why: these intracellular power plants were not fixed into place. 

VAP-B, however, appears to do a lot more than make sure that mitochondria are next to muscle fibers ready to rock and roll. The hormone appears to regulate the maintenance (fusion) of these power plants and even the amount of fuel produced. Without VAP-B, the mitochondria in these worms’ muscles were operating at as low as 50% capacity. 

”The muscles suffer due to a lack of energy,” explains Bellen. “They produce lactic acid. If you do that chronically, your muscles start to waste.” 

Bellen suspects however, that the loss of this potentially critical hormone could be responsible for a lot more than muscle atrophy in people with ALS. Without mitochondria in the right places in the muscle, calcium that gets generated during movement can build up triggering twitching. And, the drop of a critical protein produced by muscles according to studies in fruit flies could lead to synaptic die-back.

Actin Up

 

Junction box.  Researchers discovered that VAP-B regulates signalling mechanisms which during development, help plug nerves into the right muscles. The team suspects that VAP-B helps enable the movement of these muscles (2) by stabilizing mitochondria (5) at the nerve terminal (1). Image: Wikimedia Commons.

Now, the researchers are looking to see whether a drop in VAP-B levels also results in reduced energy production in motor neurons and a loss of mitochondria from the nerve terminals.

VAP-B appears to be in the right place at the right time to control mitochondrial dynamics in the motor nerves.  The hormone binds to receptors that are also present on the surface of adult nerve cells including motor neurons.

Furthermore, VAP-B appears to be able to do the job.  The hormone controls the position of mitochondria in muscles according to the Bellen-Miller team's findings by regulating the length of the actin-based filaments that anchor them on muscle fibers.  The same kinds of cytoskeletal fibers that are also present at nerve terminals.

“Microtubules form the freeway along which the mitochondria travel to the synapse.   But once they reach the synapse,” explains Bellen,” they need to transfer to another transport system.”

And, that transport system could be controlled by VAP-B.  VAP-B based signaling machanisms could stabilize these intracellular power plants at the nerve terminals – ensuring our muscles have the ability to move.

Looking ahead, the Bellen-Milller team hopes to figure out what triggers the release of VAP-B.  By identifying these regulatory signals, researchers may be able to boost the production of the hormone in people with ALS and in so doing, slow down the disease.

But there may be no need to wait that long.  VAP-B, in its secreted form, might be able to be administered directly to help keep the energy flowing in people with ALS. 

“Maybe there is some therapeutic potential here,” says Miller. “But it is early days.”

References

Han, S.M, Tsuda, H., Yang, Y., Vibbert, J., Cottee, P., Lee, S.J., Winek, J., Haueter, C., Bellen, H.J., Miller, M.A. (2012) Secreted Vap8/als8 major sperm protein domains modulate mitochondrial localization and morphology via growth cone guidance receptors.  Developmental Cell 22, 1-15. Abstract | Full Text  (Subscription Required)

Magrane, J., Sahawneh, M.A., Przedborski, S., Estevez, A.G. and Manfredi, G. (2012) Mitochondrial dynamics and bioenergetics dysfunction is associated with synaptic alterations in mutant SOD1 motor neurons.  Journal of Neuroscience 32(1), 229-242.  Abstract | Full Text  (Subscription Required)

Cudkowicz, M., et al. (2011)  The effects of dexpramipexole (KNS-760704) in individuals with amyotrophic lateral sclerosis. Nature Medicine 17(12), 1652-1656.  Abstract |  Full Text (Subscription Required)

Vande Velde, C, Garcia, M.L., Yin, X., Trapp, B.D. and Cleveland, D.W. (2004)  The neuroprotective factor Wlds does not attenuate mutant SOD1-mediated motor neuron disease.  NeuroMolecular Medicine 5(3), 193-203. Abstract |  Full Text (Subscription Required)

Magrané, J., Hervias, I., Henning, M.S., Damiano, M., Kawamata, H., and Manfredi G. (2009) Mutant SOD1 in neuronal mitochondria causes toxicity and mitochondrial dynamics abnormalities.  Human Molecular Genetics 18(23), 4552-4564. Abstract |  Full Text

Vande Velde, C., McDonald, K.K., Boukhedimi, Y., McAlonis-Downes, M., Lobsiger, C.S., Bel Hadj, S., Zandona A., Julien, J.P., Shah, S.B. and Cleveland, D.W. (2011) Misfolded SOD1 associated with motor neuron mitochondria alters mitochondrial shape and distribution prior to clinical onset.  PLoS One 6(7), e22031. Abstract |  Full Text

Nishimura, A.L., Mitne-Neto, M., Silva, H.C., Oliveira, J.R., Vainzof, M. and Zatz, M. (2004)  A novel locus for late onset amyotrophic lateral sclerosis/motor neurone disease variant at 20q13.  Journal of Medical Genetics 41(4), 315-320. Abstract |  Full Text

Tsuda, H et al. (2008) The amyotrophic lateral sclerosis 8 protein VAPB is cleaved, secreted, and acts as a ligand for Eph receptors.  Cell 133(6), 963-977. Abstract |  Full Text

Goold, C.P. and Davis, G.W. (2007)  The BMP ligand Gbb gates the expression of synaptic homeostasis independent of synaptic growth control. Neuron 56(1), 109-123. Abstract |  Full Text

Ratnaparkhi, A., Lawless, G.M., Schweizer, F.E., Golshani, P. and Jackson, G.R. (2008) A Drosophila model of ALS: human ALS-associated mutation in VAP33A suggests a dominant negative mechanism. PLoS One 3(6), e2334. Abstract |  Full Text 

Energy drain. Mitochondria can swell up and ultimately rupture in people with ALS depleting energy reserves in motor neurons. Image: NIA, NIH.

With Biogen Idec’s dexpramipexole now in phase III clinical trials and the phase III results soon to be in for Trophos’ olesoxime, treatment strategies which keep degenerating motor neurons alive by targeting mitochondria are gathering steam. But researchers remain unsure whether or not these drugs target these intracellular power plants or even whether a power outage causes the disease.

Now, researchers from Weill Cornell Medical College put this theory to the test by generating mice that exclusively produce ALS-associated mutant superoxide dismutase 1 (mSOD1) in mitochondria and look for tell tale signs of the disease.  The researchers find that these mice develop muscle weakness and motor impairment but do not develop paralysis or die of respiratory failure.

“We observe a progressive decline in mitochondrial function,” says Giovanni Manfredi PhD, “but the disease is not as severe and not as lethal.”

These results suggest that a breakdown of these intracellular power plants in motor neurons contributes but is the not the sole cause of the disease.

The study is published this month in the Journal of Neuroscience.

Scientists first suspected in the 1990s that mitochondrial malfunction might be involved in ALS when they noticed, looking under the microscope, defects in the skeletal muscle of people with the disease.  Subsequent studies in mSOD1 mice indicated that these intracellular power plants were not working full steam.  But scientists remained unsure whether the failure of mitochondria caused ALS or whether their breakdown was simply a consequence of the disease.

“One of the difficult things that we have been struggling with is the exact role of mitochondria – that’s always been a problem,” says Johns Hopkins University School of Medicine neuroscientist Lee Martin PhD who was not involved in the study.

As early as 1994, however, neuroscientists discovered mitochondrial defects in mSOD1 mice before these animals developed symptoms suggesting that these intracellular power plants at least contributed to the disease.  In 2009, Lee Martin’s team found that bolstering mitochondria by blocking the so-called mitochondrial permeability transition pore (mPTP) significantly delayed the onset of the disease in mice.  And last July, University of Montreal researchers found that a mitochondrial pile up in motor neurons in these mice occurred before the onset of ALS which might interrupt trafficking of life’s essentials – possibly explaining why motor neurons ultimately die during the course of the disease.

Traffic jam. Mitochondria pileup in motor neurons in mice before ALS onset suggesting that defects in them may contribute to the disease.  Adapted from Vande Velde et al. (2011) PLoS One: e22031.

But although these power outages occurred in the right place and the right time, researchers still could not prove in these mice that mitochondrial breakdown triggered the disease. 

”The problem I think that we were facing is that SOD1 is present abundantly,” explains Manfredi, “so the relative role of mitochondrial localization of SOD1 relative to everything else everywhere else has been difficult to assess.”

Now, Manfredi’s team find that mice which produced mSOD1 only in the intracellular membrane space of mitochondria in certain tissues including skeletal muscle develop both defects in energy production and a 30% motor neuron loss suggesting that albeit weakly such power outages may drive at least some aspects of ALS.  But the team sees no signs of motor neurons unplugging from muscles suggesting that there may be other triggers that together result in the disease.

These findings come at the heels of two previous studies in 2009 that demonstrated mutant SOD1 produced exclusively in the mitochondria of cultured motor neurons made them more susceptible to destruction.

Now, the Weill Cornell team hopes to use these mice to ferret out why these intracellular power plants may fail in people with ALS.  And looking ahead, says Manfredi, these mice could be used to find better drugs to keep the power on in dying motor nerves to slow or stop the progression of the disease.

“I don’t think we are at the stage that we have good mitochondrial drugs,” says Manfredi.   “They target only certain aspects of mitochondrial function.” 

Furthermore, with the growing understanding that there is much more to the disease that simply a power outage, combinatorial treatment strategies for ALS may need to be developed.

“Realistically, I don’t think there is going to be a magic bullet for this disease,” says Martin.  “Targeting mitochondria is only one aspect and there are other aspects that need to be explored.”

References

Igoudjil, A., Magrané, J., Fischer, L.R., Kim, H.J., Hervias, I., Dumont, M., Cortez, C., Glass, J.D., Starkov, A.A., and Manfredi, G. (2011) In Vivo Pathogenic Role of Mutant SOD1 Localized in the Mitochondrial Intermembrane Space.  Journal of Neuroscience 31(44), 15826-15837. Abstract | Full Text (Subscription Required) 

Fischer L.R., Igoudjil, A., Magrané, J., Li, Y., Hansen, J.M., Manfredi, G. and Glass J.D. (2011) SOD1 targeted to the mitochondrial intermembrane space prevents motor neuropathy in the Sod1 knockout mouse.  Brain, 134(1), 196-209. Abstract | Full Text (Subscription Required) 

Vande Velde, C. et al. (2011).  Misfolded SOD1 associated with motor neuron mitochondria alters mitochondrial shape and distribution prior to clinical onset.  PLoS One 6(7), e22031. Abstract | Full Text

Cozzolino, M., Pesaresi, M.G., Amori, I., Crosio, C., Ferri, A., Nencini, M., and Carri, M.T. (2009). Oligomerization of mutant SOD1 in mitochondria of motorneuronal cellsdrives mitochondrial damage and cell toxicity. Antioxidants and Redox Signaling, 11, 1547-1558.  Abstract | Full Text

Magrané, J., Hervias, I., Henning, M.S., Damiano, M., Kawamata, H., and Manfredi G. (2009). Mutant SOD1 in neuronal mitochondria causes toxicity and mitochondrial dynamics abnormalities. Human Molecular Genetics, 18(23), 4552-4564.  Abstract | Full Text

Martin, L.J., Gertz, B., Pan, Y., Price, A.C., Molkentin, J.D., Chang, Q (2009). The mitochondrial permeability transition pore in motor neurons: involvement in the pathobiology of ALS mice.  Experimental Neurobiology, 218(2), 333-346.  Abstract | Full Text

Dal Canto M.C. and Gurney M.E. (1994) Development of central nervous system pathology in a murine transgenic model of human amyotrophic lateral sclerosis.  American Journal of Pathology, 145(6), 1271-1279.  Abstract | Full Text

Further Reading

Martin, L.J. (2010). The mitochondrial permeability transition pore: a molecular target for amyotrophic lateral sclerosis therapy. Biochimica Biophysica Acta, 1802(1), 186-197.  Abstract |Full Text

Antibodies against misfolded antioxidant enzyme superoxide dismutase 1 (SOD1) may help people with the sporadic form of ALS (sALS) live longer according to a new study published this month.  The study which included nearly 300 people with sALS found that participants that produced antibodies against a misfolded form of the enzyme lived nearly 2.5 years longer than those that did not.  These results suggest that immunization strategies directed against misfolded SOD1 may have the potential to slow the progression of the disease even in people without ALS-associated SOD1 mutations.

Superoxide Dismutase 1 (SOD1). Conformational changes in SOD1 may contribute to sALS according to recent results.  Mutations in SOD1 are associated with 15-20% of cases of familial ALS. Image: Emw, Wikimedia.

References

van Blitterswijk, M. et al. (2011) Anti-superoxide dismutase antibodies are associated with survival in patients with sporadic amyotrophic lateral sclerosis. Amyotrophic  Lateral  Sclerosis. doi 10.3109/17482968.2011.585163 Abstract | Full Text (Subscription Required)

Further Reading

Bosco, D.A. et al. (2010) Wild-type and mutant SOD1 share an aberrant conformation and a common pathogenic pathway in ALS. Nature Neuroscience, 13, 1396-1403. Abstract | Full Text (Subscription Required)

Soak up the SOD. Researchers discovered that cultured neurons build up SOD1 (red) upon taking up misfolded forms of the enzyme. Adapted from Münch et al. (2011).

The buildup of proteins in the brain and spinal cord is a hallmark of ALS.  But how these proteins accumulate within the cells of the central nervous system in people with ALS remains a mystery.

Now, researchers from the University of Cambridge in England report that familial ALS type 1-associated superoxide dismutase 1 (SOD1) can spread from neuron to neuron.  And once inside these neurons, these misfolded proteins can trigger the aggregation of the cells’ own copies of the enzyme.

These results suggest that ALS may be similar to prion diseases such as the brain disorder Creutzfeldt-Jakob disease.  And at the same time, these findings suggest new therapeutic strategies to reduce the buildup of proteins in people with the disease.

Reference

Münch, C., O'Brien, J. and Bertolotti, A. (2011) Prion-like propagation of mutant superoxide dismutase-1 misfolding in neuronal cells. Proceedings of the National Academy of Sciences 108(9), 3548-3553. Abstract | Full Text