Huntingtin in health and disease

Phosphorylation of huntingtin by cyclin-dependent kinase 5 is induced by DNA damage and regulates wild-type and mutant huntingtin toxicity in neurons

Huntingtin is an antiapoptotic protein that becomes toxic when its polyglutamine stretch is expanded, resulting in Huntington's disease (HD). Protein context and posttranslational modifications regulate huntingtin toxicity. Identifying signaling pathways that act on huntingtin is, therefore, key to understanding huntingtin function in normal and pathological conditions. We show here that huntingtin is phosphorylated by the cyclin-dependent kinase 5 (Cdk5) at serines 1181 and 1201. Phosphorylation can be induced by DNA damage in vitro and in vivo. The state of huntingtin phosphorylation is a crucial regulator of neuronal cell death. Absence of phosphorylation of huntingtin at serines 1181 and 1201 confers toxic properties to wild-type huntingtin in a p53-dependent manner in striatal neurons and accelerates neuronal death induced by DNA damage. In contrast, phosphorylation at serines 1181 and 1201 protects against polyQ-induced toxicity. Finally, we show in late stages of HD a sustained DNA damage that is associated with a decrease in Cdk5/p35 levels. We propose that wild-type huntingtin is a component of the DNA damage response signal in neurons and that the Cdk5/DNA damage pathway is dysregulated in HD.

The corticostriatal pathway in Huntington's disease

The corticostriatal pathway provides most of the excitatory glutamatergic input into the striatum and it plays an important role in the development of the phenotype of Huntington's disease (HD). This review summarizes results obtained from genetic HD mouse models concerning various alterations in this pathway. Evidence indicates that dysfunctions of striatal circuits and cortical neurons that make up the corticostriatal pathway occur during the development of the HD phenotype, well before there is significant neuronal cell loss. Morphological changes in the striatum are probably primed initially by alterations in the intrinsic functional properties of striatal medium-sized spiny neurons. Some of these alterations, including increased sensitivity of N-methyl-D-aspartate receptors in subpopulations of neurons, might be constitutively present but ultimately require abnormalities in the corticostriatal inputs for the phenotype to be expressed. Dysfunctions of the corticostriatal pathway are complex and there are multiple changes as demonstrated by significant age-related transient and more chronic interactions with the disease state. There also is growing evidence for changes in cortical microcircuits that interact to induce dysfunctions of the corticostriatal pathway. The conclusions of this review emphasize, first, the general role of neuronal circuits in the expression of the HD phenotype and, second, that both cortical and striatal circuits must be included in attempts to establish a framework for more rational therapeutic strategies in HD. Finally, as changes in cortical and striatal circuitry are complex and in some cases biphasic, therapeutic interventions should be regionally specific and take into account the temporal progression of the phenotype.

Cloning, expression, purification, crystallization and preliminary crystallographic analysis of pseudo death-effector domain of HIPPI, a molecular partner of Huntingtin-interacting protein HIP-1

The formation of a heterodimer between Huntingtin-interacting protein-1 (HIP-1) and its novel partner HIPPI (HIP-1 protein interactor) through their pseudo death-effector domains (pDEDs) is a key step that recruits caspase-8 and initiates apoptosis. This could be one of the pathways by which apoptosis is increased in Huntington's disease (HD). A construct consisting of the pDED of HIPPI has been cloned and overexpressed as 6NH-tagged protein and purified by Ni-NTA affinity chromatography. Crystals of the pDED of HIPPI were grown in space group P4(1), with unit-cell parameters a = b = 77.42, c = 33.31 A and a calculated Matthews coefficient of 1.88 A3 Da(-1) (33% solvent content) with two molecules per asymmetric unit.

Iron: a new target for pharmacological intervention in neurodegenerative diseases

Iron (Fe) is an essential element that is imperative for the redox-driven processes of oxygen transport, electron transport, and DNA synthesis. However, in the absence of appropriate storage or chelation, excess-free Fe readily participates in the formation of toxic-free radicals, inducing oxidative stress and apoptosis. A growing body of evidence suggests that Fe may play some role in neurodegenerative diseases such as Huntington disease, Alzheimer's disease, Parkinson's disease, and particularly Friedreich's ataxia. This review examines the role of Fe in the pathology of these conditions and the potential use of Fe chelators as therapeutic agents for the treatment of neurodegenerative disorders. Consideration is given to the features that comprise a clinically successful Fe chelator, with focus on the development of ligands such as desferrioxamine, clioquinol, pyridoxal isonicotinoyl hydrazone, and other novel aroylhydrazones.

What Do We Tell the Children? Contrasting the Disclosure Choices of Two HD Families Regarding Risk Statusand Predictive Genetic Testing

Above all else, predictive genetic testing provides information. Gaining insight into the psychosocial effects of this information is a primary goal of genetic counseling. For individuals utilizing predictive genetic testing, the acquisition of genetic information requires choices regarding disclosure within the family. This study uses a phenomenological methodology to explore the contrasting choices of two sets of HD parents regarding the disclosure of genetic risk status to their children. Additionally, the children (now adults) discuss their lived experience growing up with contrasting disclosure dynamics, and their current views regarding the use of predictive genetic testing for themselves. The primary finding of this study is that all of the adult children now express preference for early disclosure of genetic risk and an open/supportive communication style regarding HD. This finding has value for clinicians working with HD families who must make decisions regarding disclosure issues related to predictive genetic testing.

Inhibition of calcineurin by FK506 protects against polyglutamine-huntingtin toxicity through an increase of huntingtin phosphorylation at S421

Huntington's disease (HD) is caused by an abnormal expanded polyglutamine (polyQ) repeat in the huntingtin protein. Insulin-like growth factor-1 acting through the prosurvival kinase Akt mediates the phosphorylation of huntingtin at S421 and inhibits the toxicity of polyQ-expanded huntingtin in cell culture, suggesting that compounds enhancing phosphorylation are of therapeutic interest. However, it is not clear whether phosphorylation of S421 is crucial in vivo. Using a rat model of HD based on lentiviral-mediated expression of a polyQ-huntingtin fragment in the striatum, we demonstrate here that phosphorylation of S421 is neuroprotective in vivo. We next demonstrate that calcineurin (CaN), a calcium/calmodulin-regulated Ser/Thr protein phosphatase, dephosphorylates S421 in vitro and in cells. Inhibition of calcineurin activity, either by overexpression of the dominant-interfering form of CaN or by treatment with the specific inhibitor FK506, favors the phosphorylation of S421, restores the alteration in huntingtin S421 phosphorylation in HD neuronal cells, and prevents polyQ-mediated cell death of striatal neurons. Finally, we show that administration of FK506 to mice increases huntingtin S421 phosphorylation in brain. Collectively, these data highlight the importance of CaN in the modulation of S421 phosphorylation and suggest the potential use of CaN inhibition as a therapeutic approach to treat HD.

Cystamine and cysteamine increase brain levels of BDNF in Huntington disease via HSJ1b and transglutaminase

There is no treatment for the neurodegenerative disorder Huntington disease (HD). Cystamine is a candidate drug; however, the mechanisms by which it operates remain unclear. We show here that cystamine increases levels of the heat shock DnaJ-containing protein 1b (HSJ1b) that are low in HD patients. HSJ1b inhibits polyQ-huntingtin-induced death of striatal neurons and neuronal dysfunction in Caenorhabditis elegans. This neuroprotective effect involves stimulation of the secretory pathway through formation of clathrin-coated vesicles containing brain-derived neurotrophic factor (BDNF). Cystamine increases BDNF secretion from the Golgi region that is blocked by reducing HSJ1b levels or by overexpressing transglutaminase. We demonstrate that cysteamine, the FDA-approved reduced form of cystamine, is neuroprotective in HD mice by increasing BDNF levels in brain. Finally, cysteamine increases serum levels of BDNF in mouse and primate models of HD. Therefore, cysteamine is a potential treatment for HD, and serum BDNF levels can be used as a biomarker for drug efficacy.

Moderación en la actividad médica preventiva y curativa. Cuatro ejemplos de necesidad de prevención cuaternaria en España

Medical activities have more positive than negative outcomes. Because this balance, medicine has a great social recognition. But with new technology and more aggressive diagnostic and therapeutic interventions, there is a decreasing gap in between benefits and harms. Risk increases because more interventions, and because placing patients in more technology environments. As a consecuence, patient safety decreases. Quantity becomes as important as quality, and the place of care is crucial for patient safety. Medical activities should be of <<low intensity and high quality>>, performed in the low level of care possible. Then, quaternary prevention (to avoid unnecessary use and risk of medical interventions) should be a continuous parallel clinical activity. I consider four examples of needed quaternary prevention, with Spanish data: 1) cardiovascular prevention (where there is an inverse use of resources, as patients who need more receive less); 2) use of new antidepressants (which has provoke an artificial epidemic of <<depression"); 3) use of antibiotics (frequently, unnecessary use), and 4) genetic diagnosis (with the example of screening of haemochromatosis, and a commentary about genetics and medicalisation).

Inhibition of metabotropic glutamate receptor signaling by the huntingtin-binding protein optineurin

Huntington disease is caused by a polyglutamine expansion in the huntingtin protein (Htt) and is associated with excitotoxic death of striatal neurons. Group I metabotropic glutamate receptors (mGluRs) that are coupled to inositol 1,4,5-triphosphate formation and the release of intracellular Ca(2+) stores play an important role in regulating neuronal function. We show here that mGluRs interact with the Htt-binding protein optineurin that is also linked to normal pressure open angled glaucoma and, when expressed in HEK 293 cells, optineurin functions to antagonize agonist-stimulated mGluR1a signaling. We find that Htt is co-precipitated with mGluR1a and that mutant Htt functions to facilitate optineurin-mediated attenuation of mGluR1a signaling. In striatal cell lines derived from Htt(Q111/Q111) mutant knock-in mice mGluR5-stimulated inositol phosphate formation is also severely impaired when compared with striatal cells derived from Htt(Q7/Q7) knock-in mice. In addition, we show that a missense single nucleotide polymorphism optineurin H486R variant previously identified to be associated with glaucoma is selectively impaired in mutant Htt binding. Although optineurin H486R retains the capacity to bind to mGluR1a, optineurin H486R-dependent attenuation of mGluR1a signaling is not enhanced by the expression of mutant Htt. Because G protein-coupled receptor kinase 2 (GRK2) protein expression is relatively low in striatal tissue, we propose that optineurin may substitute for GRK2 in the striatum to mediate mGluR desensitization. Taken together, these studies identify a novel mechanism for mGluR desensitization and an additional biochemical link between altered glutamate receptor signaling and Huntington disease.

Clioquinol down-regulates mutant huntingtin expression in vitro and mitigates pathology in a Huntington's disease mouse model

In investigating the role of metal ions in the pathogenesis of Huntington's disease, we examined the effects of clioquinol, a metal-binding compound currently in clinical trials for Alzheimer's disease treatment, on mutant huntingtin-expressing cells. We found that PC12 cells expressing polyglutamine-expanded huntingtin exon 1 accumulated less mutant protein and showed decreased cell death when treated with clioquinol. This effect was polyglutamine-length-specific and did not alter mRNA levels or protein degradation rates. Clioquinol treatment of transgenic Huntington's mice (R6/2) improved behavioral and pathologic phenotypes, including decreased huntingtin aggregate accumulation, decreased striatal atrophy, improved rotarod performance, reduction of weight loss, normalization of blood glucose and insulin levels, and extension of lifespan. Our results suggest that clioquinol is a candidate therapy for Huntington's disease and other polyglutamine-expansion diseases.

Characterization of cDNA encoding a human sperm membrane protein sharing homology with Huntington protein

In our earlier study, we have reported the identification and characterization of a 57-kDa sperm membrane protein from human spermatozoa. The protein was found to be localized on the acrosome in acrosome intact spermatozoa and shifted to equatorial region after acrosomal induction. Further, we demonstrated that it plays a critical role in sperm--egg binding and fusion. Since the protein was found to be either absent or poorly expressed on the spermatozoa from infertile men, we designated it as Fertility Associated Sperm Antigen (FASA). A human epididymal cDNA library in Lambda-ZAP vector was screened with a polyclonal antibody raised against FASA. A clone was obtained with an insert of approximately 1.9 kb cDNA. The sequence showed 99% homology with a part of the human chromosome 11. EST database showed that a portion of 1.9 kb gene has 87% homology to gene encoding Huntington disease protein (HDP). The mutated form of this protein is responsible for Huntington's disease (HD) and is found in the brain cells of HD patients.

Nature, nurture and neurology: gene-environment interactions in neurodegenerative disease. FEBS Anniversary Prize Lecture delivered on 27 June 2004 at the 29th FEBS Congress in Warsaw

Neurodegenerative disorders, such as Huntington's, Alzheimer's, and Parkinson's diseases, affect millions of people worldwide and currently there are few effective treatments and no cures for these diseases. Transgenic mice expressing human transgenes for huntingtin, amyloid precursor protein, and other genes associated with familial forms of neurodegenerative disease in humans provide remarkable tools for studying neurodegeneration because they mimic many of the pathological and behavioural features of the human conditions. One of the recurring themes revealed by these various transgenic models is that different diseases may share similar molecular and cellular mechanisms of pathogenesis. Cellular mechanisms known to be disrupted at early stages in multiple neurodegenerative disorders include gene expression, protein interactions (manifesting as pathological protein aggregation and disrupted signaling), synaptic function and plasticity. Recent work in mouse models of Huntington's disease has shown that enriching the environment of transgenic animals delays the onset and slows the progression of Huntington's disease-associated motor and cognitive symptoms. Environmental enrichment is known to induce various molecular and cellular changes in specific brain regions of wild-type animals, including altered gene expression profiles, enhanced neurogenesis and synaptic plasticity. The promising effects of environmental stimulation, demonstrated recently in models of neurodegenerative disease, suggest that therapy based on the principles of environmental enrichment might benefit disease sufferers and provide insight into possible mechanisms of neurodegeneration and subsequent identification of novel therapeutic targets. Here, we review the studies of environmental enrichment relevant to some major neurodegenerative diseases and discuss their research and clinical implications.

Functional Genomics meets neurodegenerative disorders

The transcriptomic and proteomic techniques presented in part I (Functional Genomics meets neurodegenerative disorders. Part I: transcriptomic and proteomic technology) of this back-to-back review have been applied to a range of neurodegenerative disorders, including Huntington's disease (HD), Prion diseases (PrD), Creutzfeldt-Jakob disease, amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), frontotemporal dementia (FTD) and Parkinson's disease (PD). Samples have been derived either from human brain and cerebrospinal fluid, tissue culture cells or brains and spinal cord of experimental animal models. With the availability of huge data sets it will firstly be a major challenge to extract meaningful information and secondly, not to obtain contradicting results when data are collected in parallel from the same source of biological specimen using different techniques. Reliability of the data highly depends on proper normalization and validation both of which are discussed together with an outlook on developments that can be anticipated in the future and are expected to fuel the field. The new insight undoubtedly will lead to a redefinition and subdivision of disease entities based on biochemical criteria rather than the clinical presentation. This will have important implications for treatment strategies.

Phosphorylation of Arfaptin 2 at Ser260 by Akt Inhibits PolyQ-huntingtin-induced Toxicity by Rescuing Proteasome Impairment

Huntington disease (HD) is caused by an abnormal expanded polyglutamine repeat in the huntingtin protein. Insulin-like growth factor-1 is of particular interest in HD because it strongly inhibits polyQ-huntingtin-induced neurotoxicity. This neuroprotective effect involves the phosphorylation of huntingtin at Ser(421) by the prosurvival kinase Akt (Humbert, S., Bryson, E. A., Cordelieres, F. P., Connors, N. C., Datta, S. R., Finkbeiner, S., Greenberg, M. E., and Saudou, F. (2002) Dev. Cell 2, 831-837). Here, we report that Akt inhibits polyQ-huntingtin-induced toxicity in the absence of phosphorylation of huntingtin at Ser(421), suggesting that Akt also acts on other downstream effector(s) to prevent neuronal death in HD. We show that this survival effect involves the ADP-ribosylation factor-interacting protein arfaptin 2, the levels of which are increased in HD patients. Akt phosphorylated arfaptin 2 at Ser(260). Lack of phosphorylation of arfaptin 2 at this site substantially modified its subcellular distribution and increased neuronal death and intranuclear inclusions caused by polyQ-huntingtin. In contrast, arfaptin 2 had a neuroprotective effect on striatal neurons when phosphorylated by Akt. This effect is mediated through the proteasome, as phosphorylated arfaptin 2 inhibited the blockade of the proteasome induced by polyQ-huntingtin. This study points out a new mechanism by which Akt promotes neuroprotection in HD, emphasizing the potential therapeutic interest of this pathway in the disease.

Sleeping Beauty-mediated down-regulation of huntingtin expression by RNA interference

Huntington disease (HD) is a devastating neurologic disorder that is characterized by abnormal expansion of a CAG nt repeat in the first exon of the huntingtin (htt) gene, producing a mutant protein with an elongated polyglutamine stretch. The presence of this mutant protein is correlated with the characteristic loss of striatal neurons and the clinical manifestation of HD. Currently there is no effective treatment for the associated cell death. The aim of this study was to evaluate an innovative strategy combining RNA interference (RNAi) and gene transfer via the nonviral Sleeping Beauty (SB) transposon system to down-regulate Htt expression. siRNA expression vectors were designed to target exons 1, 4, 6, and 62 of the human htt gene. Real-time RT-PCR and Western blot analysis were used to quantify Htt mRNA and protein levels, respectively, in human cell lines. The results indicated that selected siRNA constructs significantly decreased Htt mRNA and protein levels relative to controls. In addition, SB transposition of the siRNA constructs into the genome reduced long-term protein expression of Htt by approximately 90%. The combination of siRNA, the SB transposon, and an accurate transgenic mouse model may permit evaluation of this approach in preventing the pathogenesis associated with expression of mutant Htt.

Therapeutic gene silencing in neurological disorders, using interfering RNA

The development of interfering RNA (RNAi) from a naturally occurring phenomenon to a tool for mediating highly specific gene silencing provides an exciting prospect as a novel therapeutic strategy for a wide range of disorders. Although the efficacy of RNAi as a research tool for analysing gene function has been well demonstrated in several cell types, the therapeutic potential of RNAi-mediated gene silencing has only recently started to be investigated. Several neurodegenerative disorders provide particularly suitable candidates for RNAi based therapy; however, many hurdles preclude the success of therapeutic application. These include the challenge of delivering active RNAi molecules to the specific target cell populations where they are required and appropriate regulation of gene suppression, such as to maintain a long-lasting therapeutic effect. Furthermore, for safety reasons, off-target effects should be minimised. Here we review the advancement of RNAi technology for therapeutic application and highlight the potential of targeted gene silencing for the treatment of neurodegenerative diseases.

Juvenile onset Huntington disease resulting from a very large maternal expansion

We report a 5(1/2)-year-old girl with a maternal family history of Huntington disease (HD), who presented clinically with unbalanced gait, impaired speech, and increasing difficulty with fine motor control. Onset of symptoms began at the age of 3(1/2) years. The suspected diagnosis of juvenile HD, based upon her family history, was confirmed by DNA analysis. At age 7, the patient died secondary to complications of her underlying disorder. Juvenile-onset Huntington disease is uncommon, predominantly transmitted by fathers and is always associated with very large expansions of the CAG repeat. Interestingly, this patient inherited a large CAG size expansion from her mother, who herself had symptoms of HD at the age of 18. Molecular analysis revealed that the mother had 70 CAG repeats whereas our patient had approximately 130 CAG repeats. This is the largest reported CAG expansion from a maternal transmission that has been confirmed molecularly and it demonstrates that very large expansions can also occur through the maternal lineage.

Inactivation of Drosophila Apaf-1 related killer suppresses formation of polyglutamine aggregates and blocks polyglutamine pathogenesis

Huntington's disease (HD) is caused by expansion of a polyglutamine tract near the N-terminal of huntingtin. Mutant huntingtin forms aggregates in striatum and cortex, where extensive cell death occurs. We used a Drosophila polyglutamine peptide model to assess the role of specific cell death regulators in polyglutamine-induced cell death. Here, we report that polyglutamine-induced cell death was dramatically suppressed in flies lacking Dark, the fly homolog of human Apaf-1, a key regulator of apoptosis. Dark appeared to play a role in the accumulation of polyglutamine-containing aggregates. Suppression of cell death, caspase activation and aggregate formation were also observed when mutant huntingtin exon 1 was expressed in homozygous dark mutant animals. Expanded polyglutamine induced a marked increase in expression of Dark, and Dark was observed to colocalize with ubiquitinated protein aggregates. Apaf-1 also was found to colocalize with huntingtin-containing aggregates in a murine model and HD brain, suggesting a common role for Dark/Apaf-1 in polyglutamine pathogenesis in invertebrates, mice and man. These findings suggest that limiting Apaf-1 activity may alleviate both pathological protein aggregation and neuronal cell death in HD.

Hypertrophy of medial globus pallidus and substantia nigra reticulata in 6-hydroxydopamine-lesioned rats treated with L-DOPA: Implication for L-DOPA-induced dyskinesia in Parkinson's disease

The medial globus pallidus plays a crucial role in generation of L-DOPA-induced dyskinesia in patients with Parkinson's disease. The 6-hydroxydopamine-lesioned rat exhibiting behavioral sensitization to L-DOPA is one useful animal model for examining L-DOPA-induced dyskinesia. To determine neuropathological abnormality responsible for behavioral sensitization, the medial globus pallidus and the substantia nigra reticulata in 6-hydroxydopamine-lesioned rats treated with L-DOPA were examined. Intermittent L-DOPA treatment induced hypertrophy of the lesioned-side of medial globus pallidus and substantia nigra reticulata of 6-hydroxydopamine-lesioned rats with behavioral sensitization to L-DOPA. Additionally, coadministration of a 5-HT1A receptor agonist, 8-hydroxy-2(di-n-propylamino)tetralin with L-DOPA, alleviated the hypertrophy with improvement of the behavioral sensitization. These results suggest that hypertrophy of the medial globus pallidus and substantia nigra reticulata is associated with induction of behavioral sensitization to L-DOPA in 6-hydroxydopamine-lesioned rats. Therefore, neuropathological changes corresponding to hypertrophy might underlie L-DOPA-induced dyskinesia in patients with Parkinson's disease.

Transcriptional dysregulation in striatal projection- and interneurons in a mouse model of Huntington's disease: neuronal selectivity and potential neuroprotective role of HAP1

Transcriptional dysregulation has been described as a central mechanism in the pathogenesis of Huntington's disease (HD), in which medium spiny projection neurons (MSN) selectively degenerate whereas neuronal nitric-oxide-synthase-positive interneurons (nNOS-IN) survive. In order to begin to understand this differential vulnerability we compared mRNA levels of selected genes involved in N-methyl-D-aspartate (NMDA) glutamate receptor and calcium (Ca2+) signaling pathways in MSN and nNOS-IN from 12-week-old R6/2 mice, a transgenic mouse model of HD and wild-type littermates. We undertook a laser capture microdissection (LCM) study to examine the contribution of transcriptional dysregulation in candidate genes involved in these two signaling pathways in discrete populations of striatal neurons. The use of LCM in combination with quantitative real-time polymerase chain reaction (Q-PCR) allowed us to quantify the neuronal abundance of candidate mRNAs. We found different transcriptional alterations in R6/2 neurons for both MSN and nNOS-IN, indicating that global transcriptional dysregulation alone does not account for selective vulnerability. Further, we observed a striking enrichment of several mRNAs in the nNOS-IN population, including that for the NMDA receptor subunit NR2D, the postsynaptic density protein 95 (PSD-95) and the huntingtin-associated protein 1 (HAP1) as well as nitric-oxide-synthase (nNOS) mRNA itself. The higher expression levels of these molecules in nNOS-IN when compared with MSN together with an association of nNOS, NR2D and HAP1 in a protein complex with PSD-95 suggest that these proteins may be involved in protective pathways that contribute to the resistance of this interneuron population to neurodegeneration in HD.

Molecular pathways to neurodegeneration

The molecular bases underlying the pathogenesis of neurodegenerative diseases are gradually being disclosed. One problem that investigators face is distinguishing primary from secondary events. Rare, inherited mutations causing familial forms of these disorders have provided important insights into the molecular networks implicated in disease pathogenesis. Increasing evidence indicates that accumulation of aberrant or misfolded proteins, protofibril formation, ubiquitin-proteasome system dysfunction, excitotoxic insult, oxidative and nitrosative stress, mitochondrial injury, synaptic failure, altered metal homeostasis and failure of axonal and dendritic transport represent unifying events in many slowly progressive neurodegenerative disorders.

Metal-catalyzed disruption of membrane protein and lipid signaling in the pathogenesis of neurodegenerative disorders

Membrane lipid peroxidation and oxidative modification of various membrane and associated proteins (e.g., receptors, ion transporters and channels, and signal transduction and cytoskeletal proteins) occur in a range of neurodegenerative disorders. This membrane-associated oxidative stress (MAOS) is promoted by redox-active metals, most notably iron and copper. The mechanisms whereby different genetic and environmental factors initiate MAOS in specific neurological disorders are being elucidated. In Alzheimer's disease (AD), the amyloid beta-peptide generates reactive oxygen species and induces MAOS, resulting in disruption of cellular calcium homeostasis. In Parkinson's disease (PD), mitochondrial toxins and perturbed ubiquitin-dependent proteolysis may impair ATP production and increase oxyradical production and MAOS. The inheritance of polyglutamine-expanded huntingtin may promote neuronal degeneration in Huntington's disease (HD), in part, by increasing MAOS. Increased MAOS occurs in amyotrophic lateral sclerosis (ALS) as the result of genetic abnormalities (e.g., Cu/Zn-superoxide dismutase mutations) or exposure to environmental toxins. Levels of iron are increased in vulnerable neuronal populations in AD and PD, and dietary and pharmacological manipulations of iron and copper modify the course of the disease in mouse models of AD and PD in ways that suggest a role for these metals in disease pathogenesis. An increasing number of pharmacological and dietary interventions are being identified that can suppress MAOS and neuronal damage and improve functional outcome in animal models of AD, PD, HD, and ALS. Novel preventative and therapeutic approaches for neurodegenerative disorders are emerging from basic research on the molecular and cellular actions of metals and MAOS in neural cells.

Novel Chelators for Central Nervous System Disorders That Involve Alterations in the Metabolism of Iron and Other Metal Ions

Recent evidence suggests that iron (Fe) and other metals play a role in a number of neurodegenerative diseases including Friedreich's ataxia, Alzheimer's disease, Huntington's disease, and Parkinson's disease. In this review, the role of Fe and other metals in the pathology of these conditions is assessed and the potential of Fe chelators for treatment is discussed. Lipophilic chelators have been designed that may be capable of crossing the blood-brain barrier, a property lacking in desferrioxamine (DFO), a chelator in widespread clinical use. A far less commonly used chelator, clioquinol, has already shown activity in vivo in animal models and also in Alzheimer's disease patients. Considering that there is no effective treatment for many neurological diseases, the therapeutic use of lipophilic Fe chelators remains a potential strategy that requires investigation. In particular, we discuss the development of several series of aroylhydrazone chelators that could have high potential in the treatment of these diseases.

Reduction of Htt inclusion formation in strains of Saccharomyces cerevisiae deficient in certain DNA repair functions: a statistical analysis of phenotype

Saccharomyces cerevisiae has been used as a model system to examine the aggregation of the huntingtin protein (Htt), a well-established marker in the pathology of the triplet expansion disorder Huntington's disease (HD). Several genetic backgrounds, such as Deltahsp104, have proven to be refractory to inclusion formation through a process yet to be fully elucidated. These results have prompted a wide-ranging search for other mutant strains that exhibit a lower level of Htt aggregation. A novel assay system in which Htt is expressed as a fusion protein containing eGFP enables an analysis of aggregation and the factors that suppress it. We have examined several strains that are devoid of certain mismatch repair genes and find that some of these support a reduced level of inclusion body formation. We apply a detailed and stringent statistical analysis to the results obtained for all yeast strains that exhibit a definable phenotype. Such analyses should be useful and applicable to other in vivo analyses of related phenomena.

Target discovery

Target discovery, which involves the identification and early validation of disease-modifying targets, is an essential first step in the drug discovery pipeline. Indeed, the drive to determine protein function has been stimulated, both in industry and academia, by the completion of the human genome project. In this article, we critically examine the strategies and methodologies used for both the identification and validation of disease-relevant proteins. In particular, we will examine the likely impact of recent technological advances, including genomics, proteomics, small interfering RNA and mouse knockout models, and conclude by speculating on future trends.