Category: Huntington’s Disease

— A major leap forward in understanding Huntington's disease may give patients hope for a cure.

Laboratory tests on skin cells and post-mortem brain tissue of Huntington's disease patients determined that an overactive protein triggers a chain reaction that causes brain nerve cells to die. Toning down the activity of that protein, known as DRP1, prevented the chain reaction and kept those cells alive, according to the research team led by University of Central Florida Professor Ella Bossy-Wetzel.

Huntington's is an inherited, incurable neurodegenerative disease affecting 35,000 people annually. The disease gradually kills nerve cells in the brain, stripping away a person's physical abilities and causing hallucinations, antisocial behavior and paranoia.

People diagnosed with the disease usually die 15 to 20 years from the onset of symptoms, and there is an increased rate of suicide among those struggling with the disease.

"The next step will be to test the DRP1 function in animals and patients to see whether the protein also protects the brain," Bossy-Wetzel said. "This could be done before the onset of disease in patients who have the mutant Huntington gene, but have no neurological symptoms. The hope is that we might be able to delay the onset of disease by improving the energy metabolism of the brain."

The research findings were published online in the journal Nature Medicine, and they will be featured in the cover story of the March edition.

Until now, little has been known about how Huntington's works. Scientists knew that people with the mutant Huntington gene develop the disease. They also knew that a cell's powerhouse- mitochondria, which turn food into energy — was somehow involved. But until Bossy-Wetzel's team completed its work, little else was known.

"Mitochondria require balanced cycles of division and fusion to maintain their ability to produce energy," Bossy-Wetzel said. "The protein DRP1 is needed for mitochondrial division. We found that in Huntington's disease, DRP1 becomes overactive and causes too much mitochondrial division without balancing fusion."

That production error causes the brain's nerve cells to die. The UCF team toned down the activity of DRP1, which restored a normal balance of mitochondrial division and fusion and improved the energy metabolism and survival of neurons.

Other scientists in the field say the discovery is an important step toward eventually finding a cure.

"It is an outstanding piece of work, which further implicates mitochondrial dysfunction in the pathogenesis of Huntington's disease," said Flint Beal, a professor of neurology and neuroscience at the Weill Medical College of Cornell University who specializes in the disease and is a practicing physician. "It opens new therapeutic targets for therapies aimed at disease modification."

Bossy-Wetzel joined UCF in 2007. She trained at the Cold Spring Harbor Laboratory; the University of California, San Francisco; the Pasteur Institute of Paris, France. Prior to joining UCF, Bossy-Wetzel was an assistant professor at the Burnham Institute for Medical Research in La Jolla, Calif. She has received numerous prestigious awards and her publications have received more than 8,900 citations. She serves on grant review boards for the National Institutes of Health, the National Science Foundation the Swiss National Funds, and the American Heart Association (AHA).

Others who contributed to the study and appear as authors in the Nature Medicine article are UCF doctoral students Wenjun Song, Jin Chen, Alejandra Petrilli and Yue Zhou; postdoctoral fellow Geraldine Liot; and Research Professor Blaise Bossy from the UCF Burnett School of Biomedical Sciences, College of Medicine.

Other collaborators include Eva Klinglmayr and Robert Schwarzenbacher, University of Salzburg, Austria; Patrick Poquiz, Jonathan Tjiong, Mark Ellisman and Guy Perkins, University of California San Diego; Eliezer Masliah, University of San Diego; Mahmoud Pouladi and Michael Hayden, University of British Columbia, Canada; and Isabelle Rouiller, McGill University, Canada.

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Journal Reference:

1. Wenjun Song, Jin Chen, Alejandra Petrilli, Geraldine Liot, Eva Klinglmayr, Yue Zhou, Patrick Poquiz, Jonathan Tjong, Mahmoud A Pouladi, Michael R Hayden, Eliezer Masliah, Mark Ellisman, Isabelle Rouiller, Robert Schwarzenbacher, Blaise Bossy, Guy Perkins, Ella Bossy-Wetzel. Mutant huntingtin binds the mitochondrial fission GTPase dynamin-related protein-1 and increases its enzymatic activity. Nature Medicine, 2011; DOI: 10.1038/nm.2313

 One bad apple is all it takes to spoil the barrel. And one misfolded protein may be all that's necessary to corrupt other proteins, forming large aggregations linked to several incurable neurodegenerative diseases such as Huntington's, Parkinson's and Alzheimer's.

Stanford biology Professor Ron Kopito has shown that the mutant, misfolded protein responsible for Huntington's disease can move from cell to cell, recruiting normal proteins and forming aggregations in each cell it visits.

Knowing that this protein spends part of its time outside cells "opens up the possibility for therapeutics," he said. Kopito studies how such misfolded proteins get across a cell's membrane and into its cytoplasm, where they can interact with normal proteins. He is also investigating how these proteins move between neuronal cells.

The ability of these proteins to move from one cell to another could explain the way Huntington's disease spreads through the brain after starting in a specific region. Similar mechanisms may be involved in the progress of Parkinson's and Alzheimer's through the brain.

Kopito discussed his research on Feb. 18 at the annual meeting of the American Association for the Advancement of Science in Washington, D.C.

Not all bad

Not all misfolded proteins are bad. The dogma used to be that all our proteins formed neat, well-folded structures, packed together in complexes with a large number of other proteins, Kopito said. But over the past 20 years, researchers have found that as much as 30 percent of our proteins never fold into stable structures. And even ordered proteins appear to have some disordered parts.

Disordered proteins are important for normal cellular functions. Unlike regular proteins, they only interact with one partner at a time. But they are much more dynamic, capable of several quick interactions with many different proteins. This makes them ideal for a lot of the standard communication that happens within a cell for its normal functioning, Kopito said.

But if some of our proteins are always disordered, how do our cells tell which proteins need to be properly folded, and which don't? "It's a big mystery," said Kopito, and one that he's studying. This question has implications for how people develop neurodegenerative diseases, all of which appear to be age-related.

Huntington's disease is caused by a specific mutated protein. But the body makes this mutant protein all your life, so why do you get the disease in later adulthood? Kopito said it's because the body's protective mechanisms stop doing their job as we get older. He said his lab hopes to determine what these mechanisms are.

A bad influence

But it's clear what happens when these mechanisms stop working — misfolded proteins start recruiting normal versions of the same protein and form large aggregations. The presence of these aggregations in neurons has been closely linked with several neurodegenerative diseases.

Kopito found that the mutant protein associated with Huntington's disease can leave one cell and enter another one, stirring up trouble in each new cell as it progresses down the line. The spread of the misfolded protein may explain how Huntington's progresses through the brain.

This disease, like Parkinson's and Alzheimer's, starts in one area of the brain and spreads to the rest of it. This is also similar to the spread of prions, the self-replicating proteins implicated in mad cow disease and, in humans, Creutzfeldt-Jakob disease. As the misfolded protein reaches more parts of the brain, it could be responsible for the progressive worsening of these diseases.

Now that we know that these misfolded proteins spend part of their time outside of cells, traveling from one cell to another, new drugs could target them there, Kopito said. This could help prevent or at least block the progression of these diseases.

Kopito is currently working to figure out how misfolded proteins get past cell membranes into cells in the first place. It is only once in the cell's cytoplasm that these proteins can recruit others. So these studies could help find ways to keep these mischief-makers away from the normal proteins.

He is also collaborating with biology professor Liqun Luo to track these proteins between cells in the well-mapped fruit fly nervous system. In the future, Kopito said he hopes to link his cell biology work to disease pathology in order to understand the role misfolded proteins play in human disease.

Protein aggregation underlies several neurodegenerative diseases such as Alzheimer's, Huntington's chorea or Parkinson's. Scientists at the Max Planck Institute of Biochemistry (MPIB) in Martinsried near Munich, Germany, now discovered a fundamental mechanism which explains how toxic protein aggregation occurs and why it leads to a widespread impairment of essential cellular functions.

"Not all proteins are affected by aggregation," says Heidi Olzscha, PhD student at the MPIB. "Especially those proteins are susceptible, which possess specific structural characteristics and are involved in important biological processes."

The results are published in the journal Cell (Jan. 7, 2011).

To fulfill their different functions, proteins have to acquire the correct three-dimensional structure. In other words, polypeptides have to fold first. Molecular chaperones, a diverse group of conserved proteins, have specialized to assist other proteins during their folding. If the chaperones fail, misfolding and aggregation of the newly synthesized and pre-existing proteins might occur. In the worst case, this results then in neurodegenerative diseases, such as Alzheimer's, Huntington's chorea or Parkinson's. Alzheimer's disease, for example, develops because the A-beta and tau proteins aggregate, which leads to neuronal dysfunction and cell death. According to Alzheimer Forschung Initiative e. V., approximately 1.2 million people suffer from this disease only in Germany. The risk to fall ill grows with increasing age.

Scientists in the Department of Cellular Biochemistry at the Max Planck Institute of Biochemistry, headed by F.-Ulrich Hartl, now established a novel experimental model aimed at elucidating cellular protein misfolding and discovered why the misfolding and aggregation are deleterious for cells. They prepared several artificial aggregating proteins without any biological function and introduced them into cells. These model proteins clumped together, coaggregating many natural proteins and, in that way, disturbing their function. By means of quantitative proteomics, the researchers discovered that the affected proteins share certain structural characteristics which predispose them for the co-aggregation: They are large in size, less hydrophobic and show a significant increase of disorder in their structure.

"These are proteins that have not only many, but also very important functions in the cell," explains Martin Vabulas. "For instance, they are responsible for the stability of the cytoskeleton, the organization of the chromatin in nucleus, the transcription of DNA to RNA or the synthesis of proteins. Simultaneous disturbance of several of these essential processes is most probably the reason of the cellular break-down. As a consequence, protein misfolding diseases develop."

Molecular chaperones could possibly prevent this dire scenario. They are able to shield the aggregates, so that the aggregates cannot get in touch with other proteins anymore. The scientists hope that their new insights might help to develop novel therapeutic strategies in the battle against neurodegenerative diseases, especially at the earlier stages, before the irreversible collapse of cellular protein network sets in.

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Journal Reference:

1. Heidi Olzscha, Sonya M. Schermann, Andreas C. Woerner, Stefan Pinkert, Michael H. Hecht, Gian G. Tartaglia, Michele Vendruscolo, Manajit Hayer-Hartl, F. Ulrich Hartl, R. Martin Vabulas. Amyloid-like Aggregates Sequester Numerous Metastable Proteins with Essential Cellular Functions. Cell, 2011; 144 (1): 67 DOI: 10.1016/j.cell.2010.11.050

Investigators at Southern Methodist University and The University of Texas at Dallas have discovered a family of small molecules that shows promise in protecting brain cells against nerve-degenerative diseases such as Parkinson's, Alzheimer's and Huntington's, which afflict millions.

Dallas-based startup EncephRx, Inc. was granted the worldwide license to the jointly owned compounds. A biotechnology and therapeutics company, EncephRx will develop drug therapies based on the new class of compounds as a pharmaceutical for preventing nerve-cell damage, delaying onset of degenerative nerve disease and improving symptoms.

Treatments currently in use don't stop or reverse degenerative nerve diseases, but instead only alleviate symptoms, sometimes with severe side effects. If proved effective and nontoxic in humans, EncephRx's small-molecule pharmaceuticals would be the first therapeutic tools able to stop affected brain cells from dying.

"Our compounds protect against neurodegeneration in mice," said synthetic organic chemist Edward R. Biehl, the SMU Department of Chemistry professor who led development of the compounds at SMU. "Given successful development of the compounds into drug therapies, they would serve as an effective treatment for patients with degenerative brain diseases."

EncephRx initially will focus its development and testing efforts toward Huntington's disease and potentially will have medications ready for human trials in two years, said Aaron Heifetz, CEO at EncephRx.

Biehl developed the compounds in collaboration with UT Dallas biology professor Santosh R. D'Mello, whose laboratory has been studying the process of neurodegeneration for several years.

"Additional research needs to be done, but these compounds have the potential for stopping or slowing the relentless loss of brain cells in diseases such as Alzheimer's and Parkinson's," said D'Mello, professor of molecular and cell biology at UT Dallas, with a joint appointment in the School of Brain and Behavioral Science. "The protective effect that they display in tissue culture and animal models of neurodegenerative disease provides strong evidence of their promise as drugs to treat neurodegenerative disorders."

Millions are suffering, particularly the elderly

Parkinson's, Huntington's and Alzheimer's are disorders of the central nervous system marked by abnormal and excessive loss of neurons in a part of the mid-brain, say the researchers.

The diseases steadily erode motor skills, including speech and the ability to walk, cause tremors, slowed movement, stooped posture, memory loss and mood and behavior problems.

The risk of developing a degenerative nerve disease increases with age. These diseases affect more than 5 million Americans.

Novel compounds effectively proved protective in initial studies

One member of a class of heterocyclic organic compounds, the synthetic chemicals developed and tested by SMU and UT Dallas scientists, was shown to be highly protective of neurons in tissue culture models and effective against neurodegeneration in animal models.

The most promising lead compound, designated HSB-13, was tested in Huntington's disease animal models. It not only reduced degeneration in a part of the forebrain but also improved behavioral performance while proving nontoxic. The compound also was efficacious in a commonly used fly model of Alzheimer's disease.

"These preliminary tests demonstrated that the compound was an extremely potent neuroprotective agent," Biehl said.

The findings were published in the article "Identification of novel 1,4-benzoxazine compounds that are protective in tissue culture and in vivo models of neurodegeneration," which appeared in the Journal of Neuroscience Research. The National Institutes of Health and the Defense Advanced Research Projects Agency funded the project.

The SMU and UT Dallas researchers developed and tested more than 100 compounds for neuroprotective efficacy and toxicity over the course of four years before making the discovery in 2007.

Fisetin, a naturally occurring compound found in strawberries and other fruits and vegetables, slows the onset of motor problems and delays death in three models of Huntington's disease, according to researchers at the Salk Institute for Biological Studies. The study, published in the online edition of Human Molecular Genetics, sets the stage for further investigations into fisetin's neuroprotective properties in Huntington's and other neurodegenerative conditions.

Huntington's disease (HD) is an inherited disorder that destroys neurons in certain parts of the brain and slowly erodes victims' ability to walk, talk and reason. It is caused by a kind of genetic stutter, which leads to the expansion of a trinucleotide repeat in the huntingtin protein. When the length of the repeated section reaches a certain threshold, the bearer will develop Huntington's disease. In fact, the longer the repeat, the earlier symptoms develop and the greater their severity.

One of the intracellular signaling cascades affected by mutant huntingtin is the so-called Ras/ERK pathway. It is activated by growth factors and is particularly important in brain development, learning, memory and cognition.

In earlier studies, Pamela Maher, Ph.D., a senior staff scientist in the Salk Cellular Neurobiology Laboratory, had found that fisetin exerted its neuroprotective and memory-enhancing effects through the activation of the Ras/ERK signaling pathway. "Because Ras/ERK is known to be less active in HD, we thought fisetin might prove useful in the condition," Maher says.

Maher and her team began their study by looking at a nerve cell line that could be made to express a mutant form of the huntingtin protein. Without treatment, about 50 percent of these cells will die within a few days. Adding fisetin, however, prevented cell death and appeared to achieve it by activating the Ras-ERK cascade.

The researchers then turned their attention to Drosophila. In collaboration with J. Lawrence Marsh, Ph.D., a professor of developmental and cell biology at the University of California, Irvine, Maher tested fisetin in fruit flies overexpressing mutant huntingtin in neurons in the brain. The affected flies don't live as long as normal flies and also have defective eye development. When they were fed fisetin, however, the HD flies maintained their life span and had fewer eye defects.

Finally, Maher and her team tested fisetin's effects in a mouse model of HD. HD mice develop motor defects early on and have much shorter life spans than normal control animals. When Maher and her team fed them fisetin, the onset of the motor defects was delayed, and their life span was extended by about 30 percent.

"Fisetin was not able to reverse or stop the progress of the disease," Maher notes, "but the treated mice retained better motor function for longer, and they lived longer."

Fisetin, which also has anti-inflammatory properties and maintains levels of glutathione, a major cellular antioxidant that plays a key role in protecting against different types of stress in cells, has not yet been tested in humans. But Maher's findings suggest that the compound may be able to slow down the progression of Huntington's disease in humans and improve the quality of life for those who have it. While she cautions that it won't necessarily be effective for people already in the advanced stages of the disease, for those in the early stages or who are presymptomatic, fisetin might help.

Furthermore, once their safety and efficacy are proved in humans, the advent of substances like fisetin might prompt more people to be tested for the mutation. "Cells are damaged and dying before there are overt symptoms," Maher says. "If patients know they have the mutation, then they could potentially start treatment before they start showing symptoms, which might be more effective than waiting for the symptoms to appear, as many do now."

Maher's lab has developed a variety of fisetin derivatives that are more potent in cell-based assays than the fisetin used in the study, and she plans further tests to see which combination is most effective in HD and other neurodegenerative disorders.

In the meantime, does she recommend eating a lot of strawberries to gain fisetin's benefits?

"It probably couldn't hurt," she says.

In addition to Maher and Marsh, Richard Dargusch of the Salk Institute and Laszlo Bodai, Paul Gerard and Judy Purcell of the University of California, Irvine, contributed to the study.

This work was supported in part by the National Institutes of Health.

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Journal Reference:

1. Pamela Maher, Richard Dargusch, Laszlo Bodai, Paul E. Gerard, Judith M. Purcell, and J. Lawrence Marsh. ERK activation by the polyphenols fisetin and resveratrol provides neuroprotection in multiple models of Huntington's disease. Hum. Mol. Genet., October 15, 2010 DOI: 10.1093/hmg/ddq460

A team of American scientists claim that a new method of testing for neurological diseases could provide doctors with a rapid and non-invasively method of diagnosing degenerative disorders. The research, published in The journal of Comparative Neurology, reveals that Magnetic Resonance Spectroscopy (MRS) can distinguish between different disorders in patients, allowing earlier diagnosis.

The diagnosis of neurological degenerative disorders such as Huntington's disease remains a difficult clinical task and while tests such as Magnetic Resonance Imaging (MRI) can reveal loss of brain tissue, until now no diagnostic testing methods could help distinguish between Alzheimer's disease, Huntington's disease, or Parkinson's disease reliably.

"We discovered that MRS can reliably identify brain pathology in Huntington disease model mice by measuring 17 different brain metabolites at the same time," said project leader Dr. Jason B. Nikas from the University of Minnesota. "This technology, if expanded to humans and applied to a range of neurological disorders, could potentially provide diagnostic information to distinguish different causes of dementia and other forms of neurological illness, rapidly and non-invasively, with current generation MR scanners."

MRI and MRS both work by applying a magnetic field to a biological tissue, and then perturbing it with a radio-frequency (RF) signal, certain types of atoms in the tissue will give a response that can be detected externally.

MRI is based upon the response of hydrogen atoms in water molecules in the tissue, however MRS can quantify the amounts of complex biological molecules in tissue.

Nikas and colleagues measured the amounts of 17 different biochemical substances in the brains of mice and found that the Huntington mutation 'R6/2' caused a signature change in the levels of these substances. This allowed the team to successfully identify which mice had the mutation, 100% of the time, by non-invasive MRS.

This method has enormous implications both for neuroscience and for clinical neurology. For patients with clinical syndromes that are difficult to diagnose, such as the cause of a dementing illness, MRS might be able to identify signature "MR fingerprints" of specific diseases, leading to rapid, non-invasive diagnosis.

"Scanning animals non-invasively by MRS could be useful in the monitoring of various interventions in mice with genetic disorders," concluded Nikas. "However, it could be even more valuable for identifying human subjects who were asymptomatic, but showed the MRS signature of a particular disease, which they might develop years later; moreover, it could be very valuable in assessing disease progression and/or the efficacy of an applied medical treatment."

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Journal Reference:

1. Jason B. Nikas, C. Dirk Keene, Walter C. Low. Comparison of analytical mathematical approaches for identifying key nuclear magnetic resonance spectroscopy biomarkers in the diagnosis and assessment of clinical change of diseases. The Journal of Comparative Neurology, 2010; DOI: 10.1002/cne.22365

New research finds that a protein that is often mutated in Huntington's disease (HD) plays an unexpected role in the process of neurogenesis. The research, published in the August 12 issue of the journal Neuron, provides new insight into HD pathology and has even broader implications for human health and disease.

HD is an inherited neurodegenerative disease that causes uncontrolled movements, emotional disturbances, and severe mental deterioration. Previous research has demonstrated that abnormal huntingtin protein (htt) is associated with HD pathology. "Given the predominant neurological signs and striking neuronal death in HD, most studies on htt function have focused on adult neurons," explains senior study author, Dr. Sandrine Humbert from the Institut Curie in Orsay, France. "However, although htt is not restricted to differentiated neurons and is found at high levels in dividing cells, no studies have investigated a possible role for htt during cell division."

Cell division, known as mitosis, is the process where a single cell divides into two new but identical daughter cells. It is a complex and highly regulated sequence of events that occurs in a series of well-defined stages. One key step of mitosis involves the assembly and orientation of a structure called the "mitotic spindle." During mitosis, the proteins dynein and dynactin must interact with the spindle. Because htt is known to facilitate dynein/dynactin activity, Dr. Humbert's group investigated whether htt played a functional role during mitosis.

The researchers discovered that htt was specifically localized to the mitotic spindle during mitosis in mouse neurons and that htt was required for recruitment of dynein/dynactin to the spindle. Importantly, interference with htt led to misorientation of the spindle in both mice and flies. The researchers went on to show that htt was critical for both mitosis and cell fate determination. "Our findings demonstrate a previously unknown function for htt protein and open new lines of investigation for elucidating the pathogenic mechanisms in HD," concludes Dr. Humbert. "Our work also identifies htt as a crucial part of spindle orientation and neurogenesis."

The researchers include Juliette D. Godin, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Kelly Colombo, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Maria Molina-Calavita, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Guy Keryer, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Diana Zala, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Benedicte C. Charrin, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Paula Dietrich, University of Tennessee Health Science Center, Memphis, TN; Marie-Laure Volvert, University of Liege, Liege, Belgium; Francois Guillemot, National Institute for Medical Research, London, UK; Ioannis Dragatsis, University of Tennessee Health Science Center, Memphis, TN; Yohanns Bellaiche, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France, CNRS UMR 3215, INSERM U934, Paris University, Paris, France; Frederic Saudou, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France; Laurent Nguyen, University of Liege, Liege, Belgium; and Sandrine Humbert, Institut Curie, CNRS UMR 3306, INSERM U1005, Orsay, France.

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Journal Reference:

1. Juliette D. Godin, Kelly Colombo, Maria Molina-Calavita, Guy Keryer, Diana Zala, Bénédicte C. Charrin, Paula Dietrich, Marie-Laure Volvert, François Guillemot, Ioannis Dragatsis, Yohanns Bellaiche, Frédéric Saudou, Laurent Nguyen, Sandrine Humbert. Huntingtin Is Required for Mitotic Spindle Orientation and Mammalian Neurogenesis. Neuron, Volume 67, Issue 3, 392-406, 12 August 2010 DOI: 10.1016/j.neuron.2010.06.027

 In neurodegenerative diseases, clumps of insoluble proteins appear in patients' brains. These aggregates contain proteins that are unique to each disease, such as amyloid beta in Alzheimer's disease, but they are intertwined with small amounts of many other insoluble proteins that are normally present in a soluble form in healthy young individuals. For years, these other proteins were thought to be accidental inclusions in the aggregates, much as a sea turtle might be caught in a net of fish.

Now, in a surprising new finding, researchers at the University of California, San Francisco, report that many of the proteins present as minor components of disease aggregates actually clump together as a normal part of aging in healthy individuals.

The discovery, in the C. elegans roundworm, refutes a widespread belief that the presence of insoluble proteins is unique to degenerative disease and that the main proteins traditionally associated with each disease (like amyloid beta in Alzheimer's disease) are the only ones that could have an impact.

The research showed that a variety of common soluble proteins, such as those responsible for growth, can become insoluble and form aggregates in animals as they age. Moreover, the research demonstrated that gene manipulations that extend C. elegans lifespan prevent these common proteins from clumping.

The findings appear in the August 11, 2010 issue of the journal PLoS Biology.

"If you take people with Alzheimer's and look at their aggregates, there are many other proteins in the clump that no one has paid much attention to," said UCSF biochemist Cynthia Kenyon, PhD, director of the Larry L. Hillblom Center for the Biology of Aging at UCSF and senior author of the paper. "It turns out that about half of these proteins are aggregating proteins that become insoluble as a normal part of aging."

The team found that, in the presence of proteins specific to Huntington's disease, these other insoluble proteins actually sped up the course of the disease, indicating that they could be fundamental to its progression.

The findings indicate that widespread protein insolubility and aggregation is an inherent part of aging and that it may influence both lifespan and neurodegenerative disease, Kenyon said.

The presence of insoluble protein aggregates has long been recognized as a hallmark of such neurodegenerative diseases as Alzheimer's, Huntington's and amyotrophic lateral sclerosis (ALS). The team, led by first author Della C. David, PhD, a postdoctoral scholar in the UCSF Department of Biochemistry and Biophysics, asked a simple question that had never been addressed: Do normal proteins form insoluble clumps when normal, healthy individuals age?

They identified roughly 700 proteins in a C. elegans worm that become insoluble as the animal ages. These insoluble proteins are highly over-represented in the aggregates found in human neurodegeneration, the researchers wrote in their paper. They found that many of the proteins that became insoluble were already known to accelerate the aging process and to influence the aggregation of the major disease proteins. Yet even in the healthy aging worms, these proteins had a propensity for clumping and forming hard, rocklike structures.

The team found that this aggregation was significantly delayed or even halted by reducing insulin and IGF-1 hormone activity, whose reduction is known to extend animal lifespan and to delay the progression of Huntington's and Alzheimer's disease in animal models of neurodegenerative diseases.

While there are indisputable differences between worms and men, the roundworm C. elegans (Caenorhabditis elegans) often has led the way in advancing our understanding of human biology, notably in such areas as the mechanism of cell death, insulin pathways, the genes involved in cancer, and aging.

Some of those advances have originated in Kenyon's lab, including the discovery that blocking the activity of a single gene in C. elegans doubled the animal's lifespan. The gene, known as daf-2, encodes a receptor for insulin as well as for IGF-1. The same or related hormone pathways have since been shown to affect lifespan in fruit flies and mice, and are thought to influence lifespan in humans.

Co-authors on the paper include Michael P. Cary, also in the UCSF Department of Biochemistry and Biophysics; Noah Ollikainen, in the UCSF Graduate Program in Biological and Medical Informatics; and Jonathan C. Trinidad and Alma L. Burlingame, both with the Mass Spectrometry Facility in the UCSF Department of Pharmaceutical Chemistry.

The research was supported by fellowships from the Swiss National Foundation and the Larry L. Hillblom Foundation. The work was further supported by the UCSF Program for Breakthrough Biomedical Research and the National Institutes of Health. The authors have declared that no competing interests exist.

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Journal Reference:

1. David DC, Ollikainen N, Trinidad JC, Cary MP, Burlingame AL, et al. Widespread Protein Aggregation as an Inherent Part of Aging in C. elegans. PLoS Biology, 2010; 8 (8): e1000450 DOI: 10.1371/journal.pbio.1000450

Although their genetic underpinnings differ, Alzheimer's disease, Parkinson's disease and Huntington's disease are all characterized by the untimely death of brain cells. What triggers cell death in the brain?

According to a new study published by researchers at Sanford-Burnham Medical Research Institute (Sanford-Burnham) in the July 30 issue of Molecular Cell, the answer in some cases is the untimely transfer of a gaseous molecule (known as nitric oxide, or NO) from one protein to another.

"We and other researchers have shown that NO and related molecules can contribute to either nerve cell death or nerve cell survival. However, these new findings reveal that NO can actually jump from one protein to another in molecular pathways that lead to cellular suicide," explained Stuart A. Lipton, M.D., Ph.D., senior author of the study and director of the Del E. Web Center for Neuroscience, Aging and Stem Cell Research at Sanford-Burnham. "Now that we have this molecular clue to the cause of nerve cell death in Parkinson's, Alzheimer's, and Huntington's diseases, we can figure out how to use it to better diagnose and treat these diseases." Dr. Lipton is also a Harvard-trained neurologist who sees many of these patients in his own clinical practice.

In this study, Dr. Lipton and his colleagues, led by Tomohiro Nakamura, Ph.D., found that NO-like molecules are transferred from caspases, proteins that normally initiate cell death, to XIAP, a protein that normally inhibits cell death. In other words, caspases pass NO to XIAP like a 'hot potato.' This process occurs by a chemical reaction known as transnitrosylation. When XIAP is left holding NO, the result is a double whammy for brain cells, since cells are programmed to self-destruct when either XIAP has NO attached to it or when caspases don't. Hence, both brain cell-destroying events occur at the same time. The researchers then found that XIAP holding the NO 'hot potato' was much more common in brains of human patients with neurodegenerative diseases than in normal brains, solidifying their suspicion that this protein modification leads to cell damage.

To calculate which protein is more likely to end up with the NO 'hot potato,' caspases or XIAP, the researchers created a new version of the Nernst equation — a 19th century mathematical equation taught in every general chemistry class. This power of prediction might allow doctors to diagnose neurodegenerative disorders like Parkinson's or Alzheimer's disease earlier.

"We are currently analyzing cerebrospinal fluid and brain tissue from Parkinson's, Alzheimer's and other patients to determine if we can use the NO-tagged proteins as biomarkers for the disease," Dr. Lipton said.

In order to develop therapies to treat Parkinson's, Alzheimer's and Huntington's diseases based on their new findings, Dr. Lipton's laboratory is also applying the robotic technology in Sanford-Burnham's Conrad Prebys Center for Chemical Genomics to screen thousands of chemicals for potential drugs that prevent the aberrant or excessive transfer of NO from one protein to another, and thus to prevent nerve cell injury and death.

This study was supported by grants from the National Institutes of Health (NIH) and the San Diego chapter of the American Parkinson's Disease Association.

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Journal Reference:

1. Nakamura T, Wang L, Wong CCL, Scott FL, Eckelman BP, Han X, Tzitzilonis C, Meng F, Gu Z, Holland EA, Clemente AJ, Okamoto S, Salvesen GS, Riek R, Yates JR 3rd, Lipton SA. Transnitrosylation of XIAP regulates caspase-dependent neuronal cell death. Molecular Cell, July 30, 2010

Scientists at the Buck Institute for Age Research have discovered that a particular family of enzymes are involved in the breakdown of proteins that modify the production of toxic fragments that lead to the pathology of Huntington's disease. These enzymes, matrix metalloproteinases (MMPs), provide new targets for drug therapies for the disease — targets that have already been shown to respond to cancer drugs currently in clinical development.

Results of the research, from the laboratories of Buck faculty members Lisa Ellerby, Ph.D. and Robert Hughes, Ph.D., appear as the cover story in the July 29, 2010 edition of Neuron.

Huntington's disease (HD) is an incurable progressive neurodegenerative genetic disorder which affects motor coordination and leads to cognitive decline and dementia. Symptoms usually begin to occur in middle age; patients are often totally incapacitated prior to death. The worldwide prevalence of HD is 5-10 cases per 100,000 people; the rate of occurrence is highest in peoples of Western European descent.

The disease stems from a mutation in the huntingtin gene, located on human chromosome four. The mutation causes abnormalities in the huntingtin protein (mutantHtt, or mHtt). The pathology of HD is accelerated when mHtt is cut into smaller, highly toxic fragments via various molecular activities. Dr. Ellerby said to date, scientific queries into how those fragments are cut have focused primarily on caspases, a family of intracellular proteins that mediate cell death, and calpains, enzymes regulated by the concentration of calcium ions. The Buck Institute study involved proteases, various enzymes that catalyze the breakdown of proteins in reaction to water. Dr. Ellerby said this research marks the first time all of the 514 different types of proteases found in humans were individually screened in cell culture to see how they affect mHtt proteolysis. Buck Institute researchers identified 11 proteases that, when inhibited, reduced the accumulation of toxic fragments associated with HD.

Four of the proteases belong to a family called matrix metalloproteinases (MMP), a class of enzymes already involved in drug development, Dr. Ellerby said. "We've found a target that has known drugs for cancer treatment that could possibly have significance for HD," added Dr. Ellerby. "MMPs are also involved in stroke, inflammation and many neurological processes; we expect a lot of scientific attention to now be focused on this important class of proteases," she said.

Results involving MMPs were verified in mouse models of HD, Dr. Ellerby said. In collaborative studies with Dr. Juan Botas at Baylor College of Medicine in Houston, researchers found that homologs of MMPs suppressed HD-induced neuronal dysfunction in fruit flies. "The next step in this research will be to test some of the MMP inhibitor drugs as a potential treatment in HD mouse models," said Dr. Ellerby. "We'll also be crossing mice that no longer have particular MMPs with those who have HD to see what effect that has on offspring," she said.

Other contributors to the work: Other Buck Institute researchers involved in the study include John P. Miller, Jennifer Holcomb, Juliette Gafni, Ningzhe Zhang, Cameron Torcassi and Robert E. Hughes. Juan Botas, Ismael Al-Ramahi, Maria de Haro, Eugene Kim and Mario Sanhueza from the Department of Molecular and Human Genetics at Baylor College of Medicine in Houston, TX also contributed to the work, along with Seung Kwak of the CHDI Foundation in Princeton, NJ. The work was supported by grants from the National Institutes of Health and the CHDI Foundation.

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Journal Reference:

1. John P. Miller, Jennifer Holcomb, Ismael Al-Ramahi, Maria de Haro, Juliette Gafni, Ningzhe Zhang, Eugene Kim, Mario Sanhueza, Cameron Torcassi, Seung Kwak, Juan Botas, Robert E. Hughes, Lisa M. Ellerby. Matrix Metalloproteinases Are Modifiers of Huntingtin Proteolysis and Toxicity in Huntington's Disease. Neuron, 2010; DOI: 10.1016/j.neuron.2010.06.021