Therapeutic opportunities in polyglutamine disease

The impact of ATP-binding cassette transporters in the diseased brain: Context matters

ATP-binding cassette (ABC) transporters facilitate the movement of diverse molecules across cellular membranes, including those within the CNS. While most extensively studied in microvascular endothelial cells forming the blood-brain barrier (BBB), other CNS cell types also express these transporters. Importantly, disruptions in the CNS microenvironment during disease can alter transporter expression and function. Through this comprehensive review, we explore the modulation of ABC transporters in various brain pathologies and the context-dependent consequences of these changes. For instance, downregulation of ABCB1 may exacerbate amyloid beta plaque deposition in Alzheimer's disease and facilitate neurotoxic compound entry in Parkinson's disease. Upregulation may worsen neuroinflammation by aiding chemokine-mediated CD8 T cell influx into multiple sclerosis lesions. Overall, ABC transporters at the BBB hinder drug entry, presenting challenges for effective pharmacotherapy. Understanding the context-dependent changes in ABC transporter expression and function is crucial for elucidating the etiology and developing treatments for brain diseases.

Research advances in Zein-based nano-delivery systems

Zein is the main vegetable protein from maize. In recent years, Zein has been widely used in pharmaceutical, agriculture, food, environmental protection, and other fields because it has excellent biocompatibility and biosafety. However, there is still a lack of systematic review and research on Zein-based nano-delivery systems. This paper systematically reviews preparation and modification methods of Zein-based nano-delivery systems, based on the basic properties of Zein. It discusses the preparation of Zein nanoparticles and the influencing factors in detail, as well as analyzing the advantages and disadvantages of different preparation methods and summarizing modification methods of Zein nanoparticles. This study provides a new idea for the research of Zein-based nano-delivery system and promotes its application.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Chemical biology of non-canonical structures of nucleic acids for therapeutic applications

DNA forms not only the canonical duplex structure but also non-canonical structures. Most potential sequences that induce the formation of non-canonical structures are present in disease-related genes. Interestingly, biological reactions are inhibited or dysregulated by non-canonical structure formation in disease-related genes. To control biological reactions, methods for inducing the formation of non-canonical structures have been developed using small molecules and oligonucleotides. In this feature article, we review biological reactions such as replication, transcription, and reverse transcription controlled by non-canonical DNA structures formed by disease-related genes. Furthermore, we discuss recent studies aimed at developing methods for regulating these biological reactions using drugs targeting the DNA structure.

Osmolytes: A Possible Therapeutic Molecule for Ameliorating the Neurodegeneration Caused by Protein Misfolding and Aggregation

Most of the neurological disorders in the brain are caused by the abnormal buildup of misfolded or aggregated proteins. Osmolytes are low molecular weight organic molecules usually built up in tissues at a quite high amount during stress or any pathological condition. These molecules help in providing stability to the aggregated proteins and protect these proteins from misfolding. Alzheimer’s disease (AD) is the uttermost universal neurological disorder that can be described by the deposition of neurofibrillary tangles, aggregated/misfolded protein produced by the amyloid β-protein (Aβ). Osmolytes provide stability to the folded, functional form of a protein and alter the folding balance away from aggregation and/or degradation of the protein. Moreover, they are identified as chemical chaperones. Brain osmolytes enhance the pace of Aβ aggregation, combine with the nearby water molecules more promptly, and avert the aggregation/misfolding of proteins by providing stability to them. Therefore, osmolytes can be employed as therapeutic targets and may assist in potential drug design for many neurodegenerative and other diseases.

Glutamine Codon Usage and polyQ Evolution in Primates Depend on the Q Stretch Length

Amino acid usage in a proteome depends mostly on its taxonomy, as it does the codon usage in transcriptomes. Here, we explore the level of variation in the codon usage of a specific amino acid, glutamine, in relation to the number of consecutive glutamine residues. We show that CAG triplets are consistently more abundant in short glutamine homorepeats (polyQ, four to eight residues) than in shorter glutamine stretches (one to three residues), leading to the evolutionary growth of the repeat region in a CAG-dependent manner. The length of orthologous polyQ regions is mostly stable in primates, particularly the short ones. Interestingly, given a short polyQ the CAG usage is higher in unstable-in-length orthologous polyQ regions. This indicates that CAG triplets produce the necessary instability for a glutamine stretch to grow. Proteins related to polyQ-associated diseases behave in a more extreme way, with longer glutamine stretches in human and evolutionarily closer nonhuman primates, and an overall higher CAG usage. In the light of our results, we suggest an evolutionary model to explain the glutamine codon usage in polyQ regions.

Childhood-onset (Juvenile) Huntington's disease: A rare case report

Huntington's disease (HD) is a rare dominantly inherited neurodegenerative disorder characterized clinically by a combination of abnormal involuntary (choreic) movements, neuropsychiatric manifestations, and dementia. It is caused by an unstable CAG repeat expansion in the gene IT15 which encodes a Huntingtin protein. We present a case of a 9 year old boy who had developmental regression starting from the age of 8 years of age along with resistant seizures and signs of cerebellar involvement with absence of chorea and is on anticonvulsants, baclofen, and tetrabenzine. As is expected in a case of childhood-onset HD, our patient is rapidly deteriorating and is currently in the terminal phase of his illness along with resistant convulsions.

Molecular chaperone dysfunction in neurodegenerative diseases and effects of curcumin

The intra- and extracellular accumulation of misfolded and aggregated amyloid proteins is a common feature in several neurodegenerative diseases, which is thought to play a major role in disease severity and progression. The principal machineries maintaining proteostasis are the ubiquitin proteasomal and lysosomal autophagy systems, where heat shock proteins play a crucial role. Many protein aggregates are degraded by the lysosomes, depending on aggregate size, peptide sequence, and degree of misfolding, while others are selectively tagged for removal by heat shock proteins and degraded by either the proteasome or phagosomes. These systems are compromised in different neurodegenerative diseases. Therefore, developing novel targets and classes of therapeutic drugs, which can reduce aggregates and maintain proteostasis in the brains of neurodegenerative models, is vital. Natural products that can modulate heat shock proteins/proteosomal pathway are considered promising for treating neurodegenerative diseases. Here we discuss the current knowledge on the role of HSPs in protein misfolding diseases and knowledge gained from animal models of Alzheimer's disease, tauopathies, and Huntington's diseases. Further, we discuss the emerging treatment regimens for these diseases using natural products, like curcumin, which can augment expression or function of heat shock proteins in the cell.

Association of heat-shock proteins in various neurodegenerative disorders: is it a master key to open the therapeutic door?

A number of acute and chronic neurodegenerative disorders are caused due to misfolding and aggregation of many intra- and extracellular proteins. Protein misfolding and aggregation processes in cells are strongly regulated by cellular molecular chaperones known as heat-shock proteins (Hsps) that include Hsp60, Hsp70, Hsp40, and Hsp90. Recent studies have shown the evidences that Hsps are colocalized in protein aggregates in Alzheimer's disease (AD), Parkinson's disease (PD), Polyglutamine disease (PGD), Prion disease, and other neurodegenerative disorders. This fact indicates that Hsps might have attempted to prevent aggregate formation in cells and thus to suppress disease conditions. Experimental findings have already established in many cases that selective overexpression of Hsps like Hsp70 and Hsp40 prevented the disease progression in various animal models and cellular models. However, recently, various Hsp modulators like geldanamycin, 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin, and celastrol have shown to up-regulate the expression level of Hsp70 and Hsp40, which in turn triggers the solubilization of diseased protein aggregates. Hsps are, therefore, if appropriately selected, an attractive choice for therapeutic targeting in various kinds of neurodegeneration and hence are expected to have strong potential as therapeutic agents in suppressing or curing AD, PD, PGD, and other devastative neurodegenerative disorders. In the present review, we report the experimental findings that describe the implication of Hsps in the development of neurodegeneration and explore the possibility of how Hsps can be used directly or as a target by other agents to prevent various neurodegeneration through preventing aggregation process and thus reducing the toxicity of the oligomers based on the previous reports.

Concentration and temperature dependences of polyglutamine aggregation by multiscale coarse-graining molecular dynamics simulations

The solvent-free multiscale coarse-graining model of polyglutamine was employed to study polyglutamine aggregation at different concentrations and temperatures by means of molecular dynamics simulation. The heterogeneity order parameter (HOP) was used to quantify the polyglutamine aggregation. Our simulation results demonstrate that polyglutamine aggregation is sensitive to concentration and temperature changes. In equilibrium states, polyglutamine molecules fluctuate between aggregating tightly and distributing uniformly. The degree of aggregation monotonically increases with decreasing temperature, but the fluctuation of HOP reaches its maximum at an intermediate temperature. With increasing concentration, the distribution of polyglutamines first changes from more uniform to more nonuniform and then changes back to be more uniform, and the HOP has the widest distribution at the turning point. Simulations with different system sizes indicate that the finite-size effect is trivial and do not change the conclusions drawn for the polyglutamine system. In addition, the composition of the potential energies has been analyzed to confirm that the nonbonded interactions dominate the aggregation of polyglutamines. These results can be thermodynamically understood by considering the competition between the system entropy and molecular interactions, and a statistical model based on HOP has been developed to explain the microscopic mechanism of polyglutamine aggregation.

Probing the role of structural features of mouse PrP in yeast by expression as Sup35-PrP fusions

The yeast Saccharomyces cerevisiae is a tractable model organism in which both to explore the molecular mechanisms underlying the generation of disease-associated protein misfolding and to map the cellular responses to potentially toxic misfolded proteins. Specific targets have included proteins which in certain disease states form amyloids and lead to neurodegeneration. Such studies are greatly facilitated by the extensive 'toolbox' available to the yeast researcher that provides a range of cell engineering options. Consequently, a number of assays at the cell and molecular level have been set up to report on specific protein misfolding events associated with endogenous or heterologous proteins. One major target is the mammalian prion protein PrP because we know little about what specific sequence and/or structural feature(s) of PrP are important for its conversion to the infectious prion form, PrP (Sc) . Here, using a study of the expression in yeast of fusion proteins comprising the yeast prion protein Sup35 fused to various regions of mouse PrP protein, we show how PrP sequences can direct the formation of non-transmissible amyloids and focus in particular on the role of the mouse octarepeat region. Through this study we illustrate the benefits and limitations of yeast-based models for protein misfolding disorders.

Dysregulation of upstream binding factor-1 acetylation at K352 is linked to impaired ribosomal DNA transcription in Huntington's disease

Huntington's disease (HD) is an autosomal-dominant neurological disorder caused by expanded CAG repeats in the Huntingtin (Htt) gene, but it is not known how this mutation causes neurodegeneration. Herein, we found that dysfunction of upstream binding factor-1 (UBF-1) is linked to reduced ribosomal DNA (rDNA) transcription in HD. We identified that UBF1 acetylation at Lys (K) 352 by CREB binding protein (CBP) is crucial for the transcriptional activity of rDNA. UBF1 mutation (K352A, K352Q, and K352R) decreased rDNA transcriptional activity. Moreover, both CBP-dHAT mutant and knockdown of CBP by siRNA reduced acetylation of UBF1 and resulted in the decreased transcription of rDNA into rRNA. ChIP analysis showed a significant reduction of UBF1 occupancy in the promoter of rDNA in STHdh(Q111) cell line model of HD. These results demonstrate that abnormal activity of UBF1 and its acetylation by CBP are linked to impaired rDNA transcription in HD. This novel mechanism suggests that modulation of UBF-mediated rDNA synthesis by CBP may be a therapeutic target for improving neuronal rDNA transcription in HD.

Molecular dynamics simulations of polyglutamine aggregation using solvent-free multiscale coarse-grained models

The multiscale coarse-graining (MS-CG) method is used to construct solvent-free CG models for polyglutamine peptides having various repeat lengths. Because the resulting CG models have fewer degrees of freedom than a corresponding all-atom simulations, they make it possible to study the self-assembly of polyglutamines at high concentrations for the first time by allowing for better equilibration and statistical sampling that is well beyond the range achievable by all-atom models. Molecular dynamics (MD) simulations performed with these models show that polyglutamine monomers with repeat lengths < or = 28 fluctuate between their folded and unfolded states. Monomers with 32 or more residues are stable and form alpha-helix solid structures. The degree of monomer compactness increases with chain length in both cases. CG MD simulations of equilibrium polyglutamine aggregates show that even at high concentrations, the system statistically fluctuates between heterogeneous and homogeneous configurations, rather than simply aggregates. The degree of aggregation and fluctuation increases with concentration and chain length. All of these phenomena are consistent with the experimental observations and may be explained by a mechanism that the collective nonbonded interactions between polyglutamine molecules in water solution are only weakly attractive. Finally, this work demonstrates that computer simulation of polypeptides self-assembly and aggregation, which is presently beyond the reach of all-atom MD simulations, is attainable using solvent-free MS-CG models.

The pathogenic mechanisms of polyglutamine diseases and current therapeutic strategies

Expansion of CAG trinucleotide repeat within the coding region of several genes results in the production of proteins with expanded polyglutamine (PolyQ) stretch. The expression of these pathogenic proteins leads to PolyQ diseases, such as Huntington's disease or several types of spinocerebellar ataxias. This family of neurodegenerative disorders is characterized by constant progression of the symptoms and molecularly, by the accumulation of mutant proteins inside neurons causing their dysfunction and eventually death. So far, no effective therapy actually preventing the physical and/or mental decline has been developed. Experimental therapeutic strategies either target the levels or processing of mutant proteins in an attempt to prevent cellular deterioration, or they are aimed at the downstream pathologic effects to reverse or ameliorate the caused damages. Certain pathomechanistic aspects of PolyQ disorders are discussed here. Relevance of disease models and recent knowledge of therapeutic possibilities is reviewed and updated.

Antisense RNA sequences modulating the ataxin-1 message: molecular model of gene therapy for spinocerebellar ataxia type 1, a dominant-acting unstable trinucleotide repeat disease

Spinocerebellar ataxia type 1 (SCA1) is a dominant inherited disease caused by expanded trinucleotide repeats resulting in an increased polyglutamine tract in the gene product. As a potential therapeutic approach for SCA1, we tested antisense RNAs targeting two regions of the ataxin-1 message. Single-stranded regions around the translational initiation site and the intron 8 splice donor site of the ataxin-1 message were identified by computer-assisted RNA secondary structure prediction. Plasmids were generated to contain a 254-bp antisense sequence spanning the translation initiation site (pLasBDini) or a 317-bp sequence spanning the intron 8 splice donor site (pLasBDei) of the ataxin-1 message. These plasmids were transfected into Chinese hamster ovary cells engineered to express either expanded or unexpanded ataxin-1 message and protein. Reduced levels of mutant ataxin-1 message (82 CAG repeats), wild-type ataxin-1 message (30 CAG repeats), and ataxin-1 protein were observed by Northern and Western blot analyses in pLasBDini-transfected clones. pLasBDei-transfected 293 cells exhibited a shift in ataxin-1 message to a size several kilobases longer than that of the natural message. Reverse transcriptase/polymerase chain reaction assays demonstrated the retention of message spanning the intron 8 splice acceptor and the inability to amplify sequences between exons 8 and 9, implying that normal splicing of intron 8 had been interrupted. We conclude that antisense RNAs were effective in reducing or modifying ataxin-1 messages in transfected cells, and may be an effective genetic strategy for therapy of SCA1 and similar dominant-acting neurological disorders.

Neurosteroids as modulators of neurogenesis and neuronal survival

Neurons and glia in the central nervous system express the necessary enzymes for the synthesis of neurosteroids that are produced in concentrations high enough to exert paracrine effects. Synthesis of brain neurosteroids declines with age, during stressful conditions (including major depression, chronic psychological stress), and in chronic inflammatory and neurodegenerative diseases. Recent reports associate the decrease of brain neurosteroids to neuronal dysfunction and degeneration. This review summarizes the recent findings on how the most studied neurosteroids (dehydroepiandrosterone, pregnenolone and their sulphate esters, progesterone and allopregnanolone) affect neuronal survival, neurite outgrowth and neurogenesis; furthermore, this review discusses potential applications of these neurosteroids in the therapeutic management of neurodegenerative conditions, including that of age-related brain atrophy.

Chromatin and nuclear architecture in the nervous system

Neurons are arguably the most varied cell type both morphologically and functionally. Their fate during differentiation and development and the activity of mature neurons are significantly determined and regulated by chromatin. The nucleus is compartmentalized and the arrangement of these compartments, termed the nuclear architecture, distinguishes one cell type from another and dictates many nuclear processes. Nuclear architecture determines the arrangement of chromosomes, the positioning of genes within chromosomes, the distribution of nuclear bodies and the interplay between these different factors. Importantly, chromatin regulation has been shown to be the basis for a variety of central nervous system processes including grooming and nursing, depression and stress, and drug abuse, among others. Here we review the regulation and function of nuclear architecture and chromatin structure in the context of the nervous system and discuss the potential use of histone deacetylase inhibitors as chromatin-directed therapy for nervous system disorders.

Hsp27 decreases inclusion body formation from mutated GTP-cyclohydrolase I protein

GTP cyclohydrolase I (GCH), an oligomeric protein composed of 10 identical subunits, is required for the synthesis of neurotransmitters; mutations in GCH are associated with dopa-responsive dystonia (DRD) and hyperphenylalaninemia. Mutated GCH proteins are unstable and prone to dominant-negative effect. We show herein that expression of the GCH mutant GCH-201E or the splicing variant GCH-II caused intracellular inclusion bodies. When Hsp27 was expressed together with the GCH mutants, Hsp27 expression decreased the formation of inclusion bodies by GCH (as assessed by immunofluorescence) and decreased the amount of insoluble GCH mutant proteins (as assessed by Western blot). Transfection of pcDNA-Hsp27-S3D, a phosphorylation-mimicry Hsp27 mutant, was more effective at the mutated GCH proteins than transfection with pcDNA-Hsp27, but okadaic acid, a phosphatase inhibitor, enhanced the effect of pcDNA-Hsp27. Hsp27-S3D also abolished the dominant-negative action of GCH-II. The mutated GCH proteins interacted with the wild-type GCH protein; the inclusion bodies were positive for lysosomal marker LAMP1, soluble in 2% SDS, and were not ubiquitinated. Phophorlyated Hsp27 also decreased the inclusion body formation by the huntingtin polyglutamines. Therefore, diseases involving mutated oligomeric proteins would be manageable by chaperone therapies.

A systematic review of the treatment studies in Huntington's disease since 1990

Huntington's disease (HD) is an autosomal dominant, inherited, neuropsychiatric disease that gives rise to progressive motor, cognitive and behavioural symptoms. Current drug therapy has no effect on the progression of disability, and the need for any pharmacological treatment should be carefully considered. Hyperkinesias and psychiatric symptoms may respond well to pharmacotherapy, but neuropsychological deficits and dementia remain untreatable. Pharmacological intervention in the treatment of the movement disorder of HD is aimed at restoring the balance of neurotransmitters in the basal ganglia. A surprising amount of current drug therapy of HD in clinical practice is based on studies published before 1990. The authors conducted a systematic review of pharmacological therapy in HD using the available papers that were published between 1990 and 2006.

Normal huntingtin function: an alternative approach to Huntington's disease

Several neurological diseases are characterized by the altered activity of one or a few ubiquitously expressed cell proteins, but it is not known how these normal proteins turn into harmful executors of selective neuronal cell death. We selected huntingtin in Huntington's disease to explore this question because the dominant inheritance pattern of the disease seems to exclude the possibility that the wild-type protein has a role in the natural history of this condition. However, even in this extreme case, there is considerable evidence that normal huntingtin is important for neuronal function and that the activity of some of its downstream effectors, such as brain-derived neurotrophic factor, is reduced in Huntington's disease.

Evidence for polyproline II helical structure in short polyglutamine tracts

Nine neurodegenerative diseases, including Huntington's disease, are associated with the aggregation of proteins containing expanded polyglutamine sequences. The end result of polyglutamine aggregation is a beta-sheet-rich deposit. There exists evidence that an important intermediate in the aggregation process involves intramolecular beta-hairpin structures. However, little is known about the starting state, monomeric polyglutamine. Most experimental studies of monomeric polyglutamine have concluded that the backbone is completely disordered. However, such studies are hampered by the inherent tendency for polyglutamine to aggregate. A recent computational study suggested that the glutamine residues in polyglutamine tracts have a significant propensity to adopt the left-handed polyproline II (P(II)) helical conformation. In this work, we use NMR spectroscopy to demonstrate that glutamine residues possess a high propensity to adopt the P(II) conformation. We present circular dichroism spectra that indicate the presence of significant amounts of P(II) helical structure in short glutamine tracts. These data demonstrate that the propensity to adopt the P(II) structure is retained for glutamine repeats of up to at least 15 residues. Although other structures, such as alpha-helices and beta-sheets, become possible at greater lengths, our data indicate that glutamine residues in monomeric polyglutamine have a significant propensity to adopt the P(II) structure, although not necessarily in long contiguous helical stretches. We note that we have no evidence to suggest that the observed P(II) helical structure is a precursor to polyglutamine aggregation. Nonetheless, increased understanding of monomeric polyglutamine structures will aid our understanding of the aggregation process.

Cystamine and cysteamine prevent 3-NP-induced mitochondrial depolarization of Huntington's disease knock-in striatal cells

Abstract Cystamine significantly improved motor deficits and extended survival in mouse models of Huntington's disease (HD); however, the precise mechanism(s) by which cystamine and the related compound cysteamine are beneficial remain to be elucidated. Using clonal striatal cell lines from wild-type (STHdhQ7/HdhQ7) and mutant huntingtin knock-in (STHdhQ111/HdhQ111) mice, we have tested the hypothesis that cystamine and cysteamine could be beneficial by preventing the depolarization of mitochondria in cell cultures. Treatment with 3-nitroproprionic acid (3-NP), a mitochondrial complex II inhibitor, induces mitochondrial depolarization and cell death of mutant HD striatal cells but not of wild-type cells. The 3-NP-mediated decrease in the mitochondrial membrane potential was attenuated by 50 microm cystamine and completely inhibited by 250 microm cystamine. Similar results were obtained using cysteamine (50-500 microm). In addition, both cystamine and cysteamine significantly attenuated the 3-NP-induced cell death. Treatment of mutant HD striatal cells with 3-NP resulted in a robust decrease in the cellular and mitochondrial levels of glutathione (GSH) compared with cells exposed to the vehicle alone. Pre-treatment of the cells with cystamine and cysteamine completely prevented the 3-NP-mediated decrease in cellular and mitochondrial GSH levels. Incubation with L-buthionine (S,R) sulfoximine (BSO) 250 microm in combination with cystamine (250 microm) or cysteamine (250 microm) prior to being treated with 3-NP completely prevented the beneficial effects of cystamine and cysteamine on the 3-NP-mediated mitochondrial depolarization. These results demonstrate that cystamine and cysteamine prevent the 3-NP-induced mitochondrial depolarization of HD striatal cell cultures.

Huntingtin and Mutant SOD1 Form Aggregate Structures with Distinct Molecular Properties in Human Cells

Expression of many proteins associated with neurodegenerative disease results in the appearance of misfolded species that readily adopt alternate folded states. In vivo, these appear as punctated subcellular structures typically referred to as aggregates or inclusion bodies. Whereas groupings of these distinct proteins into a common morphological class have been useful conceptually, there is some suggestion that aggregates are not homogeneous and can exhibit a range of biological properties. In this study, we use dynamic imaging analysis of living cells to compare the aggregation and growth properties of mutant huntingtin with polyglutamine expansions or mutant SOD1 (G85R/G93A) to examine the formation of aggregate structures and interactions with other cellular proteins. Using a dual conditional expression system for sequential expression of fluorescence-tagged proteins, we show that mutant huntingtin forms multiple intracellular cytoplasmic and nuclear structures composed of a dense core inaccessible to nascent polypeptides surrounded by a surface that stably sequesters certain transcription factors and interacts transiently with molecular chaperones. In contrast, mutant SOD1 (G85R/G93A) forms a distinct aggregate structure that is porous, through which nascent proteins diffuse. These results reveal that protein aggregates do not correspond to a single common class of subcellular structures, and rather that there may be a wide range of aggregate structures, perhaps each corresponding to the specific disease-associated protein with distinct consequences on the biochemical state of the cell.

Compounds blocking mutant huntingtin toxicity identified using a Huntington's disease neuronal cell model

Neuronal cell death in HD is believed to be largely a dominant cell-autonomous effect of the mutant huntingtin protein. We previously developed an inducible PC12 cell model which expresses an N-terminal huntingtin fragment with an expanded poly Q repeat (N63-148Q) under the control of the tet-off system. In order to evaluate the ability of compounds to protect against mutant huntingtin toxicity in our model, we measured LDH released by dead cells into the medium. We have now screened the library of 1040 compounds from the NINDS Custom Collection as part of a National Institute of Neurological Disorders and Stroke (NINDS) collaborative project. Each positive compound was tested at 3-8 concentrations. Five compounds significantly attenuated mutant huntingtin (htt)-induced LDH release without affecting the expression level of huntingtin and independent of effect on aggregates. We also tested a broad spectrum caspase inhibitor Z-VAD-fmk and previously proposed candidate compounds. This cell model can provide a method to screen potential therapeutic compounds for treating Huntington's disease.

Neurodegenerative disorders: Parkinson's disease and Huntington's disease

Parkinson's disease and Huntington's disease are both model diseases. Parkinson's disease is the most common of several akinetic-rigid syndromes and Huntington's disease is only one of an ever growing number of trinucleotide repeat disorders. Molecular genetic studies and subsequent molecular biological studies have provided fascinating new insights into the pathogenesis of both disorders and there is now real hope for disease modifying treatment in the not too distant future for patients with Parkinson's disease or Huntington's disease.

Beyond the signal sequence: protein routing in health and disease

Receptors, hormones, enzymes, ion channels, and structural components of the cell are created by the act of protein synthesis. Synthesis alone is insufficient for proper function, of course; for a cell to operate effectively, its components must be correctly compartmentalized. The mechanism by which proteins maintain the fidelity of localization warrants attention in light of the large number of different molecules that must be routed to distinct subcellular loci, the potential for error, and resultant disease. This review summarizes diseases known to have etiologies based on defective protein folding or failure of the cell's quality control apparatus and presents approaches for therapeutic intervention.

A novel therapeutic strategy for polyglutamine diseases by stabilizing aggregation-prone proteins with small molecules

Polyglutamine diseases, such as Huntington disease (HD) and spinocerebellar ataxia 1 and 3, are autosomal dominant neurodegenerative disorders. They are caused by CAG trinucleotide repeat expansions that are translated into abnormally long polyglutamine tracts. One of the pathological hallmarks in polyglutamine diseases is the formation of intranuclear inclusions of polyglutamine-containing proteins in the brain. Although causal relationships between polyglutamine aggregation and cellular toxicity are much debated, inhibition of the polyglutamine-mediated protein aggregation may provide treatment options for polyglutamine diseases. However, the extreme insolubility of expanded polyglutamines makes it difficult to prepare polyglutamine-containing proteins on a large scale and to search for aggregation inhibitors by in vitro high-throughput screening. To overcome this we developed a novel in vitro model system for polyglutamine diseases using myoglobin as a host protein. We searched for small molecules that inhibit polyglutamine-mediated aggregation by in vitro screening with a mutant myoglobin containing a 35 polyglutamine repeat. The screening assay revealed that disaccharides have a potential to inhibit polyglutamine-induced protein aggregation and to increase survival in a cellular model of HD. Oral administration of trehalose, the most effective disaccharide in vitro, decreased polyglutamine aggregates in the cerebrum and liver, improved motor dysfunction and extended life span in a transgenic mouse model of HD. In vitro experiments suggest that the beneficial effects of trehalose result from its ability to bind and stabilize polyglutamine-containing proteins. The lack of toxicity and high solubility, coupled with its efficacy upon oral administration, make trehalose promising as a therapeutic drug or lead compound for the treatment of polyglutamine diseases. The stabilization of aggregation-prone proteins with small molecules is an attractive strategy because it can block the initial stage of the disease cascade. In addition, this therapeutic approach could be applied not only to polyglutamine diseases but also to a wide variety of misfolding-induced diseases.

Development of novel therapies for Huntington's disease: hope and challenge

Huntington's disease (HD) is an autosomal dominant neurological disease. It is a fatal neurological disorder affecting 5-10 out of 10,000 people. While there are intensive research efforts focusing on uncovering molecular mechanisms of the pathogenesis of HD, a number of studies have begun to look for effective therapies for HD. There is a large body of encouraging news on novel therapeutic developments. The present paper reviews drugs used for symptomatic treatment of HD and experimental therapies targeting HD molecular pathology.

Celastrols as inducers of the heat shock response and cytoprotection

Alterations in protein folding and the regulation of conformational states have become increasingly important to the functionality of key molecules in signaling, cell growth, and cell death. Molecular chaperones, because of their properties in protein quality control, afford conformational flexibility to proteins and serve to integrate stress-signaling events that influence aging and a range of diseases including cancer, cystic fibrosis, amyloidoses, and neurodegenerative diseases. We describe here characteristics of celastrol, a quinone methide triterpene and an active component from Chinese herbal medicine identified in a screen of bioactive small molecules that activates the human heat shock response. From a structure/function examination, the celastrol structure is remarkably specific and activates heat shock transcription factor 1 (HSF1) with kinetics similar to those of heat stress, as determined by the induction of HSF1 DNA binding, hyperphosphorylation of HSF1, and expression of chaperone genes. Celastrol can activate heat shock gene transcription synergistically with other stresses and exhibits cytoprotection against subsequent exposures to other forms of lethal cell stress. These results suggest that celastrols exhibit promise as a new class of pharmacologically active regulators of the heat shock response.

A cell-based screen for drugs to treat Huntington's disease

We have developed a medium-throughput cell-based assay to screen drugs for Huntington's disease (HD). The assay measures the ability of drugs to protect cultured neuronal (PC12) cells from death caused by an expanded polyglutamine (poly Q) form of huntingtin exon 1. Using this assay, we have blindly screened a library of 1040 compounds compiled by the NINDS: the NIH Custom Collection (NCC). Each compound was tested at five concentrations for its ability to protect cells against huntingtin-induced cell death as well as for its toxicity. Of the compounds tested, 18 prevented cell death completely, and 51 partially. Some of these also exhibited toxicity at higher doses. The majority of drugs (81%) were ineffective. Caspase inhibitors and cannabinoids showed reproducible protection in our assay. We believe these compounds, and others in our hit list, are appealing candidates for further investigation. Additionally, this assay is amenable to scaling up to screen additional compounds for treating Huntington's disease.

Trehalose alleviates polyglutamine-mediated pathology in a mouse model of Huntington disease

Inhibition of polyglutamine-induced protein aggregation could provide treatment options for polyglutamine diseases such as Huntington disease. Here we showed through in vitro screening studies that various disaccharides can inhibit polyglutamine-mediated protein aggregation. We also found that various disaccharides reduced polyglutamine aggregates and increased survival in a cellular model of Huntington disease. Oral administration of trehalose, the most effective of these disaccharides, decreased polyglutamine aggregates in cerebrum and liver, improved motor dysfunction and extended lifespan in a transgenic mouse model of Huntington disease. We suggest that these beneficial effects are the result of trehalose binding to expanded polyglutamines and stabilizing the partially unfolded polyglutamine-containing protein. Lack of toxicity and high solubility, coupled with efficacy upon oral administration, make trehalose promising as a therapeutic drug or lead compound for the treatment of polyglutamine diseases. The saccharide-polyglutamine interaction identified here thus provides a new therapeutic strategy for polyglutamine diseases.

Neuropathogenic Forms of Huntingtin and Androgen Receptor Inhibit Fast Axonal Transport

Huntington's and Kennedy's disease are autosomal dominant neurodegenerative diseases caused by pathogenic expansion of polyglutamine tracts. Expansion of glutamine repeats must in some way confer a gain of pathological function that disrupts an essential cellular process and leads to loss of affected neurons. Association of huntingtin with vesicular structures raised the possibility that axonal transport might be altered. Here we show that polypeptides containing expanded polyglutamine tracts, but not normal N-terminal huntingtin or androgen receptor, directly inhibit both fast axonal transport in isolated axoplasm and elongation of neuritic processes in intact cells. Effects were greater with truncated polypeptides and occurred without detectable morphological aggregates.

Experimental therapeutics in Huntington's disease: are models useful for therapeutic trials?

PURPOSE OF REVIEW

Research conducted over the past 10 years has uncovered molecular mechanisms that are likely to be important in the early stages of Huntington's disease pathogenesis. This review summarizes the resources and strategies that are in place in order to exploit these new findings and use them to develop novel Huntington's disease therapeutics. The role that disease models will play in this process is discussed.

RECENT FINDINGS

A wide variety of models of Huntington's disease have been developed including yeast, Caenorhabditis elegans, Drosophila melanogaster and mouse. These can be developed as screening assays for the identification of chemical compounds that show beneficial effects against a specific phenotype and for the cross validation of potential therapeutics. The first compounds arising through this drug development pipeline have been reported. Similarly, the preclinical screening of compounds in mouse models is being developed in a coordinated manner.

SUMMARY

Our understanding of the molecular basis of Huntington's disease is increasing at an exponential rate. Over the next few years an increasing number of potential therapeutic compounds will have been identified. It will only be possible to take a small number of these through to phase III clinical trials. The challenge will be to use the in-vivo models of Huntington's disease to best predict which of these compounds should be pursued in the clinic, to avoid depleting the patient population willing to enter into trials, and demoralizing them by conducting repeated unsuccessful trials.

Formation of Hirano bodies induced by expression of an actin cross-linking protein with a gain-of-function mutation

Hirano bodies are paracrystalline actin filament-containing structures reported to be associated with a variety of neurodegenerative diseases. However, the biological function of Hirano bodies remains poorly understood, since nearly all prior studies of these structures were done with postmortem samples of tissue. In the present study, we generated a full-length form of a Dictyostelium 34-kDa actin cross-linking protein with point mutations in the first putative EF hand, termed 34-kDa DeltaEF1. The 34-kDa DeltaEF1 protein binds calcium normally but has activated actin binding that is unregulated by calcium. The expression of the 34-kDa DeltaEF1 protein in Dictyostelium induces the formation of Hirano bodies, as assessed by both fluorescence microscopy and transmission electron microscopy. Dictyostelium cells bearing Hirano bodies grow normally, indicating that Hirano bodies are not associated with cell death and are not deleterious to cell growth. Moreover, the expression of the 34-kDa DeltaEF1 protein rescues the phenotypes of cells lacking the 34-kDa protein and cells lacking both the 34-kDa protein and alpha-actinin. Finally, the expression of the 34-kDa DeltaEF1 protein also initiates the formation of Hirano bodies in cultured mouse fibroblasts. These results show that the failure to regulate the activity and/or affinity of an actin cross-linking protein can provide a signal for the formation of Hirano bodies. More generally, the formation of Hirano bodies is a cellular response to or a consequence of aberrant function of the actin cytoskeleton.

A cell-based assay for aggregation inhibitors as therapeutics of polyglutamine-repeat disease and validation in Drosophila

The formation of polyglutamine-containing aggregates and inclusions are hallmarks of pathogenesis in Huntington's disease that can be recapitulated in model systems. Although the contribution of inclusions to pathogenesis is unclear, cell-based assays can be used to screen for chemical compounds that affect aggregation and may provide therapeutic benefit. We have developed inducible PC12 cell-culture models to screen for loss of visible aggregates. To test the validity of this approach, compounds that inhibit aggregation in the PC12 cell-based screen were tested in a Drosophila model of polyglutamine-repeat disease. The disruption of aggregation in PC12 cells strongly correlates with suppression of neuronal degeneration in Drosophila. Thus, the engineered PC12 cells coupled with the Drosophila model provide a rapid and effective method to screen and validate compounds.

Are Huntington's and polyglutamine-based ataxias proteasome storage diseases?

To date, 10 neurological diseases, including Huntington's and several ataxias, are caused by a lengthening of glutamine (Q) tracts in various proteins. Even though the Q expansions arise in unrelated proteins, the diseases share three striking features: (1) 35 contiguous glutamines constitutes the pathological threshold for 9 of the 10 diseases; (2) the Q-expanded proteins are expressed in many tissues, yet pathology is largely restricted to neurons; and (3) the Q-expanded proteins or fragments thereof form nuclear inclusions that also contain ubiquitin, proteasomes and chaperones. Our studies of the proteasome activator REGgamma suggest a possible explanation for these shared properties. REGgamma is highly expressed in brain, located in the nucleus and actually suppresses the proteasome active sites principally responsible for cleaving glutamine-MCA bonds. These observations coupled with reports that peptides longer than 35 residues, the polyQ pathology threshold, are unable to diffuse out of the proteasome suggest the following hypothesis. Proteins containing long glutamine tracts are efficiently pumped into REGgamma-capped 26S proteasomes, but REGgamma suppression of cleavage after glutamine produces polyQ fragments too long to diffuse out of the 20S proteolytic core thereby inactivating the 26S proteasome. In effect, we hypothesize that the polyQ pathologies may be proteasomal storage diseases analogous to disorders of lysosome catabolism.

Targeting aggregation in the development of therapeutics for the treatment of Huntington's disease and other polyglutamine repeat diseases

Huntington's disease (HD) is one of a number of familial polyglutamine (polyQ) repeat diseases. These neurodegenerative disorders are caused by expression of otherwise unrelated proteins that contain an expansion of a polyQ tract, rendering them toxic to specific subsets of vulnerable neurons. These expanded repeats have an inherent propensity to aggregate; insoluble neuronal nuclear and cytoplasmic polyQ aggregates or inclusions are hallmarks of the disorders [1,2]. In HD, inclusions in diseased brains often precede onset of symptoms, and have been proposed to be involved in pathogenicity [3-5]. Various strategies to block the process of aggregation have been developed in an effort to create drugs that decrease neurotoxicity. A discussion of the effect of antibodies, caspase inhibitors, chemical inhibitors, heat-shock proteins, suppressor peptides and transglutaminase inhibitors upon aggregation and disease is presented.

Histone deacetylase inhibitors prevent oxidative neuronal death independent of expanded polyglutamine repeats via an Sp1-dependent pathway

Oxidative stress is believed to be an important mediator of neurodegeneration. However, the transcriptional pathways induced in neurons by oxidative stress that activate protective gene responses have yet to be fully delineated. We report that the transcription factor Sp1 is acetylated in response to oxidative stress in neurons. Histone deacetylase (HDAC) inhibitors augment Sp1 acetylation, Sp1 DNA binding, and Sp1-dependent gene expression and confer resistance to oxidative stress-induced death in vitro and in vivo. Sp1 activation is necessary for the protective effects of HDAC inhibitors. Together, these results demonstrate that HDAC inhibitors inhibit oxidative death independent of polyglutamine expansions by activating an Sp1-dependent adaptive response.

Chaperones and aging: role in neurodegeneration and in other civilizational diseases

Chaperones are highly conserved proteins responsible for the preservation and repair of the correct conformation of cellular macromolecules, such as proteins, RNAs, etc. Environmental stress leads to chaperone (heat-shock protein, stress protein) induction reflecting the protective role of chaperones as a key factor for cell survival and in repairing cellular damage after stress. The present review summarizes our current knowledge about the chaperone-deficiency in the aging process, as well as the possible involvement of chaperones in neurodegenerative diseases, such as in Alzheimer's, Parkinson's, Huntington- and prion-related diseases. We also summarize a recent theory implying chaperones as "buffers" of variations in the human genome, which role probably increased during the last 200 years of successful medical practice minimizing natural selection. Chaperone-buffered, silent mutations may be activated during the aging process, which leads to the phenotypic exposure of previously hidden features and might contribute to the onset of polygenic diseases, such as atherosclerosis, cancer, diabetes and several neurodegenerative diseases.

The spinocerebellar ataxias: order emerges from chaos

In the past decade, the genetic etiologies accounting for most cases of adult-onset dominant cerebellar ataxia have been discovered. This group of disorders, generally referred to as the spinocerebellar ataxias (SCAs), can now be classified by a simple genetic nosology, essentially a sequential list in which each new SCA is given a number. However, recent advances in the elucidation of SCA pathogenesis provide the opportunity to subclassify the disorders into three discrete groups based on pathogenesis: 1) the polyglutamine disorders, SCAs 1, 2, 3, 7, and 17, which result from proteins with toxic stretches of polyglutamine; 2) the channelopathies, SCA6 and episodic ataxia types 1 and 2 (EA1 and EA2), which result from disruption of calcium or potassium channel function; and 3) the gene expression disorders, SCAs 8, 10, and 12, which result from repeat expansions outside of coding regions that may quantitatively alter gene expression. SCAs 4, 5, 9, 11, 13-16, 19, 21, and 22 are of unknown etiology, and may or may not fit into one of these three groups. At present, most diagnostic and therapeutic strategies apply equally to all of the SCAs. Therapy specific for individual diseases or types of diseases is a realistic goal in the foreseeable future.

Transforming growth factor-beta1-modulated cerebral gene expression

Transforming growth factor-beta1 (TGF-beta1) plays a central role in the response of the brain to different types of injury. Increased TGF-beta1 has been found in the central nervous system of patients with acute or chronic disorders such as stroke or Alzheimer disease. To further define the molecular targets of TGF-beta1 in cerebral tissues, a selection of high-density cDNA arrays was used to characterize the mRNA expression profile of 7,000 genes in transgenic mice overexpressing TGF-beta1 from astrocytes as compared with the wild-type line. Selected findings were further evaluated by reverse transcription-polymerase chain reactions from independent transgenic and wild-type mice. Furthermore, the expression pattern of seven selected genes such as Delta-1, CRADD, PRSC-1, PAI-1, Apo-1/Fas, CTS-B, and TbetaR-II were confirmed in either cultured cortical neurons or astrocytes following TGF-beta1 treatment. The authors' observations enlarge the repertoire of known TGF-beta1-modulated genes and their possible involvement in neurodegenerative processes.

Amino acid sequence requirements of peptides that inhibit polyglutamine-protein aggregation and cell death

Proteins with expanded polyglutamine domains cause eight inherited neurodegenerative diseases including Huntington's disease. In a previous paper, we identified peptides that inhibit polyglutamine protein aggregation and cell death and now describe the amino acid sequence requirements necessary for these activities. The original 11 amino acid polyglutamine (Q) Binding Peptide 1(QBP1; SNWKWWPGIFD) can be shortened to 8 amino acids (WKWWPGIF) without loss of ability to inhibit polyglutamine aggregation. Three determinants are responsible for inhibition: a tryptophan-rich motif (WKWW), a spacer amino acid and the tripeptide GIF. GIF can be replaced by a repeat of the tryptophan-rich motif, but the spacer remains necessary. We also demonstrate concordance between peptide activity in the in vitro assay and a cellular assay of polyglutamine aggregation and cell death. Polyglutamine binding peptides targeted for intracellular delivery by fusion to TAT retain the ability to inhibit polyglutamine aggregation and cell death in transfected COS 7 cells.