Category: Huntington’s Disease

Australian scientists have identified the behaviour of the mutant protein 'huntingtin' which leads to the fatal Huntington's disease providing potential targets to treat the disease, a University of Melbourne study reveals.

Huntington's disease is a genetic disease with no cure, characterized by a steady decline in motor control and the dysfunction and death of brain cells. The cause of the disease has long baffled scientists.

Symptoms tend to first appear when the person is in their thirties or forties. The most common symptom is jerky movements of the arms and legs. A person with Huntington's disease may also have difficulties with speech, swallowing and concentration.

Using state of the art technology, Dr Danny Hatters and his colleagues at the University of Melbourne's Department of Biochemistry and Molecular Biology at the Bio 21 Institute observed how human mutant 'huntingtin' proteins form into large clumps, which kills brain cells and leads to progressed Huntington's disease.

"Steps prior to the clustering of the mutated proteins were thought to damage cells, but these steps were not clearly detectable under a microscope," Dr Hatters says.

"Understanding this process and finding the right target to block the ultimate death of the brain cells has been extremely difficult to determine," he says.

The technology called analytical ultracentrifugation and the methodology the researchers developed enabled them to visualize this process in much greater detail.

"What we have shown and are the first to show, is that mutated huntingtin protein forms three different sized clusters in the damaged cells," he says.

"This discovery will help to develop a targeted treatment that shuts down the key processes causing the clusters to form and for the disease to progress."

While researchers previously thought that small clusters of the mutant protein kept accumulating over time until they overwhelmed and killed the brain cells, Dr Hatters' team found that these clusters were static, which means they form in a more unpredictable manner than previously thought.

The discovery reveals the clusters place a steady stress on cells over time rather than steadily building up over time to some critical "toxic" level as previously thought.

"Why it takes so long for the cells to die in human disease is not known — however it could be that cells eventually cannot compensate anymore from the process where toxicity is built up to form one cluster called oligomers," he says.

"The real key of our work is that we now have direct targets in the critical steps in the process of cell toxicity and death and to gauge any therapeutic effects of drugs on these targets. We can also measure how this alleviates cellular toxicity and brain cell death.'

"Importantly our research techniques could have application in assisting to find drug targets for other neurodegenerative diseases where toxic clusters of proteins play a role in the progression of the disease, such as for Parkinson's disease."

The research is published in the current issue of the Journal of Biological Chemistry.

— The prevalence of Huntington's disease (HD) is substantially underestimated in the UK, with significant implications for those affected, the healthcare system, and research.

New estimates of prevalence, and their implications, are discussed in a comment published in an upcoming Lancet, written by Professor Sir Michael Rawlins, who is the Chairman of the UK National Institute for Health and Clinical Excellence (NICE), but writes in his capacity as an Honorary Professor of the London School of Hygiene and Tropical Medicine, UK.

HD is a progressive neurodegenerative disorder, which affects muscle coordination and leads to cognitive decline and dementia. Symptoms typically become noticeable in the fourth decade of life. HD is the most common genetic cause of involuntary writhing movements (called chorea), and is more common in people of Western European decent than in those from Asia or Africa. The disease is caused by a dominant mutation of either of a person's two copies of the Huntingtin gene, which means any child of an affected parent has a 50% chance of inheriting the disease. In rare situations where both parents have an affected gene, or either parent has two affected copies, this risk is greatly increased.

Previous studies based on 15 locations in the UK produced an estimated prevalence of 6.7 cases per 100,000 population. However, Professor Rawlins points out that the Huntington's Disease Association (HDA)-a not-for-profit organisation that provides services for patients with the disease and their families in England and Wales-currently cares for 6702 people with symptoms. Professor Rawlins says: "Specialist neurologists have referred all of them, so their diagnoses can hardly be in doubt. From these numbers alone, the minimum prevalence in England and Wales must therefore be at least 12·4 per 100 000."

Since the HDA does not cover all areas of England and Wales, Professor Rawlins says even this 12·4 per 100 000 estimate must be an underestimate. He believes there are several factors underlying the difficulty in reaching a true estimate. First, until a genetic test (discovered by Nancy Wexler and colleagues) recently became available, the diagnosis was based entirely on clinical features. Second, and probably most importantly, those affected might try to hide the true nature of this familial trait, even from their own family doctor. Professor Rawlins says: "As well as having profound implications for the families with a member who has Huntington's disease, the stigma has negatively affected research, particularly studies that have sought to investigate epidemiology and, most especially, prevalence… Huntington's disease is the only genetic condition for which the insurance industry loads those at risk. The stigma-to the insurance industry's eternal shame-is not only societal but also actuarial."

Professor Rawlins says there are two reasons why reliable estimates are needed: "First, the UK National Health Service (NHS) needs to ensure that there are appropriate services available now-and in the future-to care for those living with the disease and for their families. Second, combining those individuals with symptomatic Huntington's disease with those at risk emphasises the importance of encouraging research that will ultimately lead to treatments that will arrest progression. Such treatments, even if only partly effective, would need to be started long before the appearance of symptomatic disease. By the time symptoms appear, there are already substantial neuropsychiatric changes, and prophylactic therapy in those at risk, and who carry the genetic abnormality, would be essential even though at present we do not know when treatment might best be started."

He concludes: "To promote greater understanding and awareness of Huntington's disease, an All Party Parliamentary Group is being formed, under the chairmanship of Lord Walton of Detchant. With the organisational skills of the former NBC news and war reporter Charles Sabine-who is not only himself at risk but who also carries the abnormal gene-this Group aims to eradicate stigma, promote research, and chivvy the NHS to provide the best possible care."

In a linked Art of Medicine feature, Alice Wexler, sister of Nancy mentioned above, discusses the history of prejudice against HD, and refers to various narratives which undoubtedly played a part in strengthening hostile perceptions of families with HD, within medicine as well as outside it. Wexler currently works at the UCLA Center for the Study of Women, Public Affairs, Los Angeles, USA. She says: "[Those narratives] helped legitimise the notion that certain classes of people were undesirable as citizens. They bolstered stereotypes of individuals with disabilities as aggressive, violent, criminal, and dangerous, while adding to the stigmas associated with alcoholism, mental illness, and cognitive impairment. They gave a rationale for doctors to endorse sterilisation or even celibacy for people at risk of Huntington's, and encouraged medical indifference toward the care of those with the disease."

She adds: "Prejudicial representations of Huntington's disease also encouraged flawed biomedical research, such as the 1951 study published in Science claiming (falsely) that those with the mutant Huntington's gene had vastly more children than their siblings without it. Only in the civil rights era of the 1960s and 1970s, with the repudiation of eugenics and the advent of the first lay associations of families affected by Huntington's disease in North America and in Europe, did research priorities and representations begin to change."

She concludes: "Medical histories matter. Whatever the truths of the 17th century, it is clear that some 20th-century scientists and clinicians created historical narratives that deepened the stigmatisation of people with Huntington's disease in their own time-and of other psychiatric and neurological conditions as well. Confronting the eugenic origins and harmful psychological and social legacies of these narratives cannot undo the past, but I believe it can help us change the conditions that perpetuate stigma and shame in the present."

A linked news item in The Lancet Neurology, written by freelance journalist Laura Spinney, discusses the prevalence figures in the context of whether or not HD would be a rare disease in various countries, and how this affects manufacture of possible treatments. She concludes: "In the European Union, a rare disease is defined as one that is life-threatening or chronically debilitating, with a prevalence of 50 or fewer cases per 100 000. Therefore, even if the revised prevalence of Huntington's disease in the UK is twice as high as that with which the UK government is currently working, the disease will continue to be defined as rare. Patients could now begin to see a difference, however, as the new All Party Parliamentary Group strives to ensure that they have access to the health care and political representation that is due to them."

An article published in The Journal of Biological Chemistry presents a novel pharmacological target that, in combination with a neurotrophic factor, could be used to improve the survival of striatal neurons, the principal nerve cells affected by the neurodegeneration observed in Huntington's disease.

The study was conducted by the researchers Silvia Ginés, a lecturer in the University of Barcelona; and Paola Paoletti, a doctoral student and Jordi Alberch professor with the Department of Cell Biology, Immunology and Neurosciences in the Faculty of Medicine in the UB.

Huntington's chorea is a progressive neurodegenerative disease caused by a genetic mutation of the gene encoding for the protein Huntingtin. The disease principally affects the basal ganglia, which regulate motor control and other important functions. One of the most widely studied potential therapeutic targets for the treatment of Huntington's disease is the brain-derived neurotrophic factor (BDNF), essential in the survival of striatal neurons and severely depleted in Huntington's sufferers. The researchers used an in vitro cell model to study whether the cells that express the mutated Huntingtin respond to administration of BDNF. "We concluded that treatment with BDNF is an effective therapeutic strategy for this disease, but that combined treatments are probably needed to modulate different aspects of the pathology," explains the UB researcher Silvia Ginés, who is also a researcher for the August Pi i Sunyer Biomedical Research Institute (IDIBAPS) and the Networked Biomedical Research Centre for Neurodegenerative Diseases (CIBERNED).

In order to act, the neurotrophic factor BDNF must bind to the catalytic receptor TrkB, levels of which are also reduced in Huntington's disease. The receptor is the key to activating signalling of the three pathways involved in the survival of the striatal neurons. The researchers reproduced the conditions of the disease and induced oxidative stress, which alters the metabolism of the nerve cells and affects their DNA. They found that under oxidative stress, two of the pathways function correctly when BDNF is administered but the third (MAPK/ERK1/2) does not. To improve the treatment response, the team used the activator PMA, a phorbol ester of which scientists are trying to find a suitable human analogue. The next step in the research, as Silvia Ginés explains, is to find "modulators of the third pathway (MAPK/ERK1/2) as a possible final treatment and possibly even to develop a strategy for modulating the receptor itself to increase the efficiency of the response."

Although the genetic mutation affects the whole body to some degree its principal impact is on the brain, where it causes severe degeneration of the striatal neurons as well as a lesser degree of generation in the cerebral cortex and the hippocampus. Huntington's patients cannot coordinate their movements and are affected by uncontrollable contractions known as chorea, making it difficult for them to lead a normal life. Researchers are also studying the molecular mechanisms contributing to the cognitive defects observed in the initial stages of the disease, which are known to cause alterations of executive memory, thus affecting the sufferer's ability to complete or organize simple everyday tasks.

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Journal Reference:

1. Silvia Gines, Paola Paoletti and Jordi Alberch. Impaired TrkB-mediated ERK1/2 Activation in Huntington Disease Knock-in Striatal Cells Involves Reduced p52/p46 Shc Expression. Journal of Biological Chemistry, 2010; DOI: 10.1074/jbc.M109.08420

 Activity of certain neurons in the brain can signal the initiation and termination of behavioural sequences we learn anew, scientists have discovered. Furthermore, they found that this brain activity is essential for learning and executing novel action sequences, many times compromised in patients suffering from disorders such as Parkinson's or Huntington's.

Rui Costa, Principal Investigator of the Champalimaud Neuroscience Programme at the Instituto Gulbenkian de Ciência (Portugal), and Xin Jin, of the National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health (USA), describe their work in the latest issue of the journal Nature.

Animal behaviour, including our own, is very complex and is many times seen as a sequence of particular actions or movements, each with a precise start and stop step. This is evident in a wide range of abilities, from escaping a predator to playing the piano. In all of them there is a first initial step and one that signals the end. In this latest work, the researchers explored the role of certain brain circuits located in the basal ganglia in this process. They looked at the striatum, its dopaminergic input (dopamine-producing neurons that project into the striatum) and its output to the substantia nigra, another area in the basal ganglia, and found that both play an essential role in the initiation and termination of newly learnt behavioural sequences.

Rui Costa and Xin Jin show that when mice are learning to perform a particular behavioural sequence there is a specific neuronal activity that emerges in those brain circuits and signals the initiation and termination steps. Interestingly these are the circuits that degenerate in patients suffering from Parkinson's and Huntington's diseases, who also display impairments both in sequence learning, and in the initiation and termination of voluntary movements. Furthermore, the researchers were able to genetically manipulate those circuits in mice, and showed that this leads to deficits in sequence learning by the mice — again, a feature shared with human patients affected with basal ganglia disorders.

Rui Costa explains the implications of these results: "For the execution of learned skills, like playing a piano or driving a car, it is essential to know when to start and stop each particular sequence of movements, and we found the neuronal circuits that are involved in the initiation and termination of action sequences that are learnt. This can be of particular relevance for patients suffering from Huntington's and Parkinson's disease, but also for people suffering from other disorders like compulsivity."

Xin Jun adds: "This start/stop activity appears during learning and disrupting it genetically severely impairs the learning of new action sequences. These findings may provide a possible insight into the mechanism underlying the sequence learning and execution impairments observed in Parkinson's and Huntington's patients who have lost basal ganglia neurons which may be important in generating initiation and termination activity in their brain."

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Journal Reference:

1. Xin Jin, Rui M. Costa. Start/stop signals emerge in nigrostriatal circuits during sequence learning. Nature, 2010; 466 (7305): 457 DOI: 10.1038/nature09263

They might not be known for their big brains, but fruit flies are helping to make scientists and doctors smarter about what causes Huntington's disease and how to treat it. New research, published in the journal Genetics describes a laboratory test that allows scientists to evaluate large numbers of fruit fly genes for a possible role in the formation of plaque-like protein aggregates within cells. Those genes often have counterparts in humans, which might then be manipulated to stop or slow the formation of plaque-like protein aggregates, the hallmark of Huntington's and several other neurodegenerative diseases.

"Aggregate formations are closely linked to aging and brain diseases," said Sheng Zhang, Ph.D, a researcher involved in the work from the Research Center for Neurodegenerative Diseases, the Brown Foundation Institute of Molecular Medicine, the University of Texas Health Science Center at Houston. "We hope our study will not only help to uncover how the formation of aggregates is regulated in a cell, but also help find good drug-development targets. Then, we can find ways to slow down plaque formations during aging and prevent and treat aggregates-related brain diseases, which are a pressing challenge to a modern society that is enjoying a longer life expectancy."

To make this advance, scientists examined every known gene in the fruit fly genome and identified a small group of genes (more than 70 percent of which have human counterparts) that likely play important roles in regulating the formation of plaque-like protein aggregates within cells. They then expressed the Huntington's disease protein in the fruit fly and found that it caused plaque-like protein aggregates in different fly tissues, including the brain and in cultured cells. The plaque-like protein aggregates were similar in appearance and biochemical properties to those found in tissues of people with Huntington's disease. The scientists employed two methods to survey a large number of genes: automated microscopy for imaging the plaque-like protein aggregates in the cells at a high-magnification level, and a computer-assisted method to quantify information on the aggregates in each tested sample. By integrating these methods, researchers were able to quickly examine all the approximately 14,000 fruit fly genes and identify the ones that are important for regulating the formation of aggregates by the mutant Huntington protein.

"The genetic overlap between humans and fruit flies continues to be a treasure trove for scientific discoveries," said Mark Johnston, Editor-in-Chief of Genetics "One hundred years ago, no one would have ever thought that research on a fly's brain could lead to medicines for human brains, but this research is a perfect example of this possibility."

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Journal Reference:

1. S. Zhang, R. Binari, R. Zhou, N. Perrimon. A Genomewide RNA Interference Screen for Modifiers of Aggregates Formation by Mutant Huntingtin in Drosophila. Genetics, 2010; 184 (4): 1165 DOI: 10.1534/genetics.109.112516

Huntington's disease (HD) is a cruel, hereditary condition that leads to severe physical and mental deterioration, psychiatric problems and eventually, death. Currently, there are no treatments to slow down or stop it. HD sufferers are born with the disease although they do not show symptoms until late in life.

In a new study published in The Journal of Neuroscience, Stephen Ferguson and Fabiola Ribeiro of Robarts Research Institute at The University of Western Ontario identified a protective pathway in the brain that may explain why HD symptoms take so long to appear. The findings could also lead to new treatments for HD.

The symptoms of Huntington's disease are caused by cell death in specific regions of the brain. Patients who have HD are born with a mutated version of the protein huntingtin (Htt), which is thought to cause these toxic effects. While researchers know HD results from this single, mutated protein, no one seems to know exactly what it does, why it does not cause symptoms until later in life, or why it kills a specific set of brain cells, even though Htt is found in every single cell in the human body.

Ferguson and Ribeiro used a genetically-modified mouse model of HD to look at the effects of mutated Htt on the brain. "We found there was some kind of compensation going on early in the life of these mice that was helping to protect them from the development of the disease," says Ferguson, director of the Molecular Brain Research Group at Robarts, and a professor in the Department of Physiology & Pharmacology at Western's Schulich School of Medicine and Dentistry. "As they age, they lose this compensation and the associated protective effects, which could explain the late onset of the disease."

Ferguson adds that metabotropic glutamate receptors (mGluRs), which are responsible for communication between brain cells, play an important role in these protective effects. By interacting with the mutant Htt protein, mGluRs change the way the brain signals in the early stages of HD in an attempt to offset the disease, and save the brain from cell death. As a result, mGluRs could offer a drug target for HD treatment.

Because HD is a dominant genetic disease, every child with an affected parent has a 50 per cent chance of inheriting the fatal condition. This research, funded by the Canadian Institutes of Health Research, sheds light on the onset of HD and the potential role of a mutant protein in patients, paving the way for the development of new drug therapies.

 An early stage clinical trial of the experimental drug dimebon (latrepirdine) in people with Huntington's disease appears to be safe and may improve cognition. That is the conclusion of a study published in the Archives of Neurology.

"This is the first clinical trial that has focused on what is perhaps the most disabling aspect of the disease," said University of Rochester Medical Center neurologist Karl Kieburtz, M.D., the lead author of the study. "While more investigation needs to be done, these results are encouraging and show, for the first time, a statistically significant benefit in terms of improved cognitive function in patients with Huntington's disease."

Huntington's disease is a progressive neurodegenerative disorder that impacts movement, behavior, cognition, and generally results in death within 20 years of the disease's onset. The disease steadily erodes a person's memory and their ability to think and learn. Over time, this cognitive impairment contributes to the loss of the ability to work and perform the activities of daily life. There are no treatments current available that effectively alter the course of the disease or improve cognition.

It is believed that mitochondria — the part of the cell that helps convert food to energy — plays a role in the development of Huntington's disease. Lampridine stabilizes and enhances mitochondrial function, a result that has been shown to improve behavioral, cognitive, and functional outcomes in Alzheimer's disease. Scientists speculate that this may have the same effect in patients with Huntington's disease.

The investigators studied the impact of the drug on 91 patients over a 90 day period. Half were given the drug and the other half a placebo. The patients were then evaluated using a cognitive tool called the Mini-Mental State Examination. This exam — which is used by clinicians to evaluate the stage and severity of dementia and Alzheimer's disease — consists of series of questions used to test an individual's orientation, memory, and ability to follow commands. The researchers found that the drug on average improved the scores of people taking the drug vs. those who received the placebo.

Dimebon is being developed by Medivation, Inc., a San Francisco-based pharmaceutical company which funded the study. The drug is also being testing in patients with Alzheimer's disease. In July of last year, Medivation and Pfizer, Inc. launched a Phase 3 clinical trial of the drug for Huntington's disease. The study, called the Horizon Trial, is being conducted in sites throughout North America, Australia, and Europe. Kieburtz is the principal investigator of the Horizon Trial.

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Journal Reference:

1. Karl Kieburtz; Michael P. McDermott; Tiffini S. Voss; Jody Corey-Bloom; Lisa M. Deuel; E. Ray Dorsey; Stewart Factor; Michael D. Geschwind; Karen Hodgeman; Elise Kayson; Sarah Noonberg; Michael Pourfar; Karen Rabinowitz; Bernard Ravina; Juan Sanchez-Ramos; Lynn Seely; Francis Walker; Andrew Feigin; and The Dimebon in Subjects With Huntington Disease (DIMOND) Investigators of the Huntington Study Group. A Randomized, Placebo-Controlled Trial of Latrepirdine in Huntington Disease. Arch Neurol, 2010; 67 (2): 154-160 [link]

Scientists at the Brain Research Centre and Centre for Molecular Medicine and Therapeutics have uncovered a key cellular mechanism that alters brain cell function in Huntington's disease, and identified a possible treatment for the disease.

The results of the study were recently published online and will appear in the January 28 edition of the journal Neuron.

Huntington's disease is an inherited degenerative brain disease that causes cognitive and motor impairment, and eventually death. One in 10,000 Canadians suffers from Huntington's disease.

The researchers found that, in mouse models, the genetic mutation that causes Huntington's disease results in an excessive number of NMDA receptors — special receptors found at the surface of brain cells — to accumulate and be active outside synapses, which are the connections between brain cells. In healthy conditions, there should be few NMDA receptors outside the synapse.

The researchers also found that the over-activation of the NMDA receptors outside the synapse leads to a reduction in brain cell survival signals and disruption in brain function.

"Previous work in cell cultures showed that NMDA receptors located within the synapse can have beneficial effects on brain cells, whereas NMDA receptors outside the synapse, called 'extra-synaptic NMDA receptors,' have a detrimental effect," says Dr. Lynn Raymond, a professor in the UBC Department of Psychiatry, a member of the Brain Research Centre at UBC Hospital, and co-director of the Huntington's Disease Medical Clinic.

"Our study shows an increase in the number of extrasynaptic NMDA receptors, shifting the balance between these opposing cellular mechanisms in animal models of early stages of Huntington's disease," Raymond says.

While further work still needs to be done to determine how the genetic mutation causes the excessive number and activity of NMDA receptors to localize outside the synapses, the researchers did find a way to mitigate damage and slow disease progression at early stages of the disease — using Memantine, a drug currently used to treat Alzheimer's disease.

"Memantine in low dose works by preferentially blocking the activity of NMDA receptors outside the synapse," says Dr. Michael Hayden, director of the Centre for Molecular Medicine and Therapeutics, professor in the UBC Department of Medical Genetics, and co-author on the study.

"It was previously shown to reverse deficits and damage in late stages of animal models of Huntington's disease, but we found it could improve learning and cell survival signaling even at early stages of the disease," says Hayden. "A small human clinical trial of Memantine for Huntington's disease has also recently shown positive effects. Larger, international clinical trials are now being planned."

"Memantine's beneficial effects appear to be dose-specific," Raymond adds. "Before it can be prescribed to treat Huntington's disease, we need to know how to determine appropriate dosing and whether it interferes with other essential cellular and brain functions."

This study was funded by the Canadian Institutes of Health Research, Cure Huntington Disease Initiative, Michael Smith Foundation for Health Research, Heart & Stroke Foundation of BC & Yukon, Huntington's Disease Society of America, and the Huntington Society of Canada.

Scientists at Duke University Medical Center have found some compounds that improve a cell's ability to properly "fold" proteins and could lead to promising drugs for degenerative nerve diseases, including Huntington's disease, Alzheimer's disease and Parkinson's disease.

Misfolded proteins in nerve cells (neurons) are a common factor in all of these diseases. The Duke team has identified many new chemicals that activate a master regulator to increase the supply of "protein chaperone" molecules that help fold proteins properly.

The scientists further explored one of the candidate molecules to activate the master regulator of chaperone gene expression, Heat Shock Factor 1 (HSF1), to learn whether it would work in model systems of Huntington's disease, a devastating neurodegenerative disease of protein misfolding.

They were able to show that the molecule stimulated protein chaperones in cells and in an animal system. The damage to early-state rat neurons was much lower in cells pre-treated with the HSF1 activator, and damage to the neurons of fruit flies that had a Huntington's-like disorder was also greatly reduced.

Previous studies suggested that elevating the abundance of protein chaperones is effective in treating cell and animal models of Huntington's and Parkinson's diseases. This work provides a new approach to address the root cause of these diseases — protein misfolding. Earlier attempts had used heat shock and other approaches that stress a nerve cell in order to produce more chaperone molecules, but at a cost of damaging the cell to save it.

"The advantage of our screen is that it identifies molecules that can elevate the levels of chaperones without inducing cellular stress and that don't inhibit a key protein chaperone called Hsp90 that is needed for cells to function normally," said senior author Dennis J. Thiele, Ph.D., Professor of Pharmacology and Cancer Biology. "We found a creative way to identify new molecules that can activate the body's natural protein folding machinery."

The research was published in the Jan. 19 online issue of PLoS Biology.

Lead author Daniel Neef, Ph.D., says they used genetically altered yeast to find compounds that might aid chaperone development. The scientists took yeast with a deleted HSF1 (master regulator) gene and inserted the related human HSF1 gene. These yeast, however, still weren't able to activate human HSF1 on their own, and in effect, died. They needed an additional molecule to make human HSF1 become active.

The team put these "humanized yeasts" into wells and started testing compounds that would provide the missing link. In several of the wells, if the compound worked, the yeast started multiplying. "Out of over 12,000 compounds tested from chemical libraries, about 50 compounds worked," Neef said. The team decided to explore one of these compounds (HSF1A) in further experiments.

"The humanized yeast-based screening results in our study provide a way to identify new classes of small molecules, small enough to penetrate the blood-brain barrier to work in neurons, in flies as well as in humans," Thiele said. "These small molecules may be effective therapies in neurodegenerative diseases caused by protein conformational disorders such as Huntington's, Alzheimer's and Parkinson's disease."

The scientists found that HSF1A could stimulate more protein chaperones and reduce the protein misfolding. They showed that adding a small amount of HSF1A to the developing rat neurons kept the proteins dissolved throughout the cell, rather than clumping visibly as speckled areas (as seen under microscopes).

"We enhanced the cells' viability by four or five times by pre-treating them with this molecule," Neef said. "Otherwise, the cells would have died."

They used fruit flies with Huntington's disease for experiments to prove that the principle would work in an animal. Adding HSF1A to the fly's food produced more chaperone molecules in their neurons. This suggests that the molecule could travel from the fly's stomach into its circulation and cross a barrier to the fly brain.

In the key experiment, the Huntington's disease flies received either their usual food or food plus HSF1A. Those with untreated food developed eyes with dying photoreceptor neurons and lacking the normal red color. Those that ate HSF1A went on to have normal-colored eyes, indicating a repair had taken place, just by eating food laced with the promising compound.

Michelle Turski, now with Stanford University, was a co-author of the study. The work was supported by grants from the National Institutes of Health.

Scientists have identified a key molecular switch that may drive the onset of Huntington's disease (HD), an incurable neurodegenerative disorder that leads to severe disruptions in muscle coordination and cognitive function. The research, published in the December 24 issue of the journal Neuron, enhances the understanding of HD pathogenesis and may direct new strategies for treating this devastating brain disease.

HD is caused by an abnormally lengthy repeating stretch of the amino acid glutamine within a large protein called huntingtin (htt). Huntingtin is thought to function as a kind of molecular scaffold that mediates many intricate cellular processes. "It's unclear how the mutant protein causes age-related and progressive loss of brain cells in patients with Huntington's disease," explains senior study author X. William Yang, M.D., Ph.D., of the Jane and Terry Semel Institute of Neuroscience and Human Behavior at David Geffen School of Medicine at UCLA. "Our study explored whether regions of the protein besides the polyglutamine mutation play a role in the development of the disorder."

Recent work has revealed that two specific amino acids in htt, serine 13 (S13) and serine 16 (S16), can be phosphorylated. Phosphorylation is a relatively common signaling mechanism that enables proteins to be regulated via attachment of phosphate groups to specific amino acids. To investigate the importance of phosphorylation to disease pathogenesis in a mouse model of HD, Dr. Yang and colleagues introduced mutations that elicited or prevented phosphorylation of full-length mutant htt (mhtt). Specifically, they replaced the S13 and S16 with phosphomimetic aspartate (SD) or phosphoresistant alanine (SA).

The researchers found that full-length mhtt induced motor and psychiatric-like behavioral deficits, mhtt aggregation, and selective neurodegeneration in the SA mice but that these pathological changes were absent in the SD mice. In addition, SD mutations had a dramatic impact on the process of mhtt protein aggregation while SA mutations did not. Taken together, the findings demonstrate that subtle molecular changes of only two amino acids in full-length mhtt dramatically reduced the pathogenic potential of the mutant protein.

"It is now crucial to understand how subtle modifications in this critical molecular switch can have such a profound impact on disease pathogenesis," said Yang. "It is also important to screen for drugs that can enhance or mimic the effects of phosphorylation which may help to detoxify the mutant huntingtin protein and prevent the onset of HD."

The researchers include Xiaofeng Gu, University of California, Los Angeles, Los Angeles, CA; Erin R. Greiner, University of California, Los Angeles, Los Angeles, CA; Rakesh Mishra, University of Pittsburgh School of Medicine, Pittsburgh, PA; Ravindra Kodali, University of Pittsburgh School of Medicine, Pittsburgh, PA; Alex Osmand, University of Tennessee Graduate School of Medicine, Knoxville, TN; Steven Finkbeiner, University of California, San Francisco, San Francisco, CA; Joan S. Steffan, University of California, Irvine, Irvine, CA; Leslie Michels Thompson, University of California, Irvine, Irvine, CA; Ronald Wetzel, University of Pittsburgh School of Medicine, Pittsburgh, PA; and X. William Yang, University of California, Los Angeles, Los Angeles, CA.