Reduced Levels of Proteasome Products in a Mouse Striatal Cell Model of Huntington’s Disease

Huntington’s disease is the result of a long polyglutamine tract in the gene encoding huntingtin protein, which in turn causes a large number of cellular changes and ultimately results in neurodegeneration of striatal neurons. Although many theories have been proposed, the precise mechanism by which the polyglutamine expansion causes cellular changes is not certain. Some evidence supports the hypothesis that the long polyglutamine tract inhibits the proteasome, a multiprotein complex involved in protein degradation. However, other studies report normal proteasome function in cells expressing long polyglutamine tracts. The controversy may be due to the methods used to examine proteasome activity in each of the previous studies. In the present study, we measured proteasome function by examining levels of endogenous peptides that are products of proteasome cleavage. Peptide levels were compared among mouse striatal cell lines expressing either 7 glutamines (STHdh ^Q7/Q7) or 111 glutamines in the huntingtin protein, either heterozygous (STHdh ^Q7/Q111) or homozygous (STHdh ^Q111/Q111). Both of the cell lines expressing huntingtin with 111 glutamines showed a large reduction in nearly all of the peptides detected in the cells, relative to levels of these peptides in cells homozygous for 7 glutamines. Treatment of STHdh ^Q7/Q7 cells with proteasome inhibitors epoxomicin or bortezomib also caused a large reduction in most of these peptides, suggesting that they are products of proteasome-mediated cleavage of cellular proteins. Taken together, these results support the hypothesis that proteasome function is impaired by the expression of huntingtin protein containing long polyglutamine tracts.     

Cardiac Dysfunction in the BACHD Mouse Model of Huntington’s Disease

While Huntington’s disease (HD) is classified as a neurological disorder, HD patients exhibit a high incidence of cardiovascular events leading to heart failure and death. In this study, we sought to better understand the cardiovascular phenotype of HD using the BACHD mouse model. The age-related decline in cardiovascular function was assessed by echocardiograms, electrocardiograms, histological and microarray analysis. We found that structural and functional differences between WT and BACHD hearts start at 3 months of age and continue throughout life. The aged BACHD mice develop cardiac fibrosis and ultimately apoptosis. The BACHD mice exhibited adaptive physiological changes to chronic isoproterenol treatment; however, the medication exacerbated fibrotic lesions in the heart. Gene expression analysis indicated a strong tilt toward apoptosis in the young mutant heart as well as changes in genes involved in cellular metabolism and proliferation. With age, the number of genes with altered expression increased with the large changes occurring in the cardiovascular disease, cellular metabolism, and cellular transport clusters. The BACHD model of HD exhibits a number of changes in cardiovascular function that start early in the disease progress and may provide an explanation for the higher cardiovascular risk in HD.     

Development of Hippocampus-Associated Cognitive Dysfunction in Huntington’s Disease Mouse Model

Journal of Evolutionary Biochemistry and Physiology - Huntington’s disease is a hereditary, incurable, neurodegenerative disease characterized by movement disorders—progressive choreic...     

A Novel Pharmacological Protective Role for Safranal in an Animal Model of Huntington’s Disease

Neurochemical Research - Huntington’s disease (HD) is a progressive, neurodegenerative and inherited disease and recent years have witnessed the understanding of the cellular and molecular...     

The Role of Mutant RNA in the Pathogenesis of Huntington’s Disease and Other Polyglutamine Diseases

Molecular Biology - Polyglutamine diseases are rare, inherited neurodegenerative pathologies that arise as a result of expansion of trinucleotide CAG repeats in the coding segment of certain genes....     

Inhibition of BACE1 Activity by a DNA Aptamer in an Alzheimer’s Disease Cell Model

An initial step in amyloid-β (Aβ) production includes amyloid precursor protein (APP) cleavage via β-Site amyloid precursor protein cleaving enzyme 1 (BACE1). Increased levels of brain Aβ have been implicated in the pathogenesis of Alzheimer’s disease (AD). Thus, β-secretase represents a primary target for inhibitor drug development in AD. In this study, aptamers were obtained from combinatorial oligonucleotide libraries using a technology referred to as systematic evolution of ligands by exponential enrichment (SELEX). A purified human BACE1 extracellular domain was used as a target to conduct an in vitro selection process using SELEX. Two DNA aptamers were capable of binding to BACE1 with high affinity and good specificity, with Kd values in the nanomolar range. We subsequently confirmed that one aptamer, A1, exhibited a distinct inhibitory effect on BACE1 activity in an AD cell model. We detected the effects of M17-APPsw cells that stably expressed Swedish mutant APP after aptamer A1 treatment. Aβ40 and Aβ42 concentrations secreted by M17-APPsw cells decreased intracellularly and in culture media. Furthermore, Western blot analysis indicated that sAPPβ expression significantly decreased in the A1 treated versus control groups. These findings support the preliminary feasibility of an aptamer evolved from a SELEX strategy to function as a potential BACE1 inhibitor. To our knowledge, this is the first study to acquire a DNA aptamer that exhibited binding specificity to BACE1 and inhibited its activity.     

Olfactory Deficits in an Alpha-Synuclein Fly Model of Parkinson’s Disease

Parkinson’s disease (PD) is the most common motor neurodegenerative disorder. Olfactory dysfunction is a prevalent feature of PD. It often precedes motor symptoms by several years and is used in assisting PD diagnosis. However, the cellular and molecular bases of olfactory dysfunction in PD are not known. The fruit fly Drosophila melanogaster, expressing human alpha-synuclein protein or its mutant, A30P, captures several hallmarks of PD and has been successfully used to model PD in numerous studies. First, we report olfactory deficits in fly expressing A30P (A30P), showing deficits in two out of three olfactory modalities, tested – olfactory acuity and odor discrimination. The remaining third modality is odor identification/naming. Second, oxidative stress is an important environmental risk factor of PD. We show that oxidative stress exacerbated the two affected olfactory modalities in younger A30P flies. Third, different olfactory receptor neurons are activated differentially by different odors in flies. In a separate experiment, we show that the odor discrimination deficit in A30P flies is general and not restricted to a specific class of chemical structure. Lastly, by restricting A30P expression to dopamine, serotonin or olfactory receptor neurons, we show that A30P expression in dopamine neurons is necessary for development of both acuity and discrimination deficits, while serotonin and olfactory receptor neurons appeared not involved. Our data demonstrate olfactory deficits in a synuclein fly PD model for exploring olfactory pathology and physiology, and for monitoring PD progression and treatment.     

Modeling Pathogenesis of Huntington��s Disease with Inducible Neuroprogenitor Cells

Huntington's disease (HD) is caused by an abnormal expansion of CAG trinucleotide repeats encoding polyglutamine (polyQ) in the first exon of the huntingtin (htt) gene. Despite considerable efforts, the pathogenesis of HD remains largely unclear due to a paucity of models that can reliably reproduce the pathological characteristics of HD. Here, we report a neuronal cell model of HD using the previously established tetracycline regulated rat neuroprogenitor cell line, HC2S2. Stable expression of enhanced green fluorescence protein tagged htt exon 1 (referred to as 28Q and 74Q, respectively) in the HC2S2 cells did not affect rapid neuronal differentiation. However, compared to the cells expressing wild type htt, the cell line expressing mutant htt showed an increase in time-dependent cell death and neuritic degeneration, and displayed increased vulnerability to oxidative stress. Increased protein aggregation during the process of neuronal aging or when the cells were exposed to oxidative stress reagents was detected in the cell line expressing 74Q but not in its counterpart. These results suggest that the neuroprogenitor cell lines mimic the major neuropathological characteristics of HD and may provide a useful tool for studying the neuropathogenesis of HD and for high throughput screening of therapeutic compounds.     

Visualization of Altered Hippocampal Connectivity in an Animal Model of Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by cognitive decline and neurodegeneration in the hippocampus. Despite the pathological importance of the hippocampal degeneration in AD, little topographical evidence exists of impaired hippocampal connectivity in patients with AD. To investigate the anatomical connections of the hippocampus, we injected the neurotracer 1,1′-dioctadecyl-3,3,3′3,3′-tetramethyl-indocarbocyanine perchlorate (DiI) into the hippocampi of 5XFAD mice, which were used as an animal model of AD. In wild-type controls, DiI-containing cells were found in the entorhinal cortex, medial septum, locus coeruleus, dorsal raphe, substantia nigra pars compacta, and olfactory bulb. Hippocampal inputs were decreased in multiple brain regions in the 5XFAD mice compared to wild-type littermate mice. These results are the first to reveal alterations at the cellular level in hippocampal connectivity in the brains of 5XFAD mice. These results suggest that anatomical mapping of hippocampal connectivity will elucidate new pathogenic mechanisms and therapeutic targets for AD treatment.     

Counterfactual Thinking Deficit in Huntington’s Disease

Background and Objective

Counterfactual thinking (CFT) refers to the generation of mental simulations of alternatives to past events, actions and outcomes. CFT is a pervasive cognitive feature in every-day life and is closely related to decision-making, planning and problem-solving – all of which are cognitive processes linked to unimpaired frontal lobe functioning. Huntington’s Disease (HD) is a neurodegenerative disorder characterised by motor, behavioral and cognitive dysfunctions. Because an impairment in frontal and executive functions has been described in HD, we hypothesised that HD patients may have a CFT impairment.

Methods

Tests of spontaneous counterfactual thoughts and counterfactual-derived inferences were administered to 24 symptomatic HD patients and 24 age- and sex-matched healthy subjects.

Results

Our results show a significant impairment in the spontaneous generation of CFT and low performance on the Counterfactual Inference Test (CIT) in HD patients. Low performance on the spontaneous CFT test significantly correlates with impaired attention abilities, verbal fluency and frontal lobe efficiency, as measured by Trail Making Test – Part A, Phonemic Verbal Fluency Test and FAB.

Conclusions

Spontaneous CFT and the use of this type of reasoning are impaired in HD patients. This deficit may be related to frontal lobe dysfunction, which is a hallmark of HD. Because CFT has a pervasive role in patients’ daily lives regarding their planning, decision making and problem solving skills, cognitive rehabilitation may improve HD patients’ ability to analyse current behaviors and future actions.     

DNA Repair Mechanisms in Huntington’s Disease

The human genome is under continuous attack by a plethora of harmful agents. Without the development of several dedicated DNA repair pathways, the genome would have been destroyed and cell death, inevitable. However, while DNA repair enzymes generally maintain the integrity of the whole genome by properly repairing mutagenic and cytotoxic intermediates, there are cases in which the DNA repair machinery is implicated in causing disease rather than protecting against it. One case is the instability of gene-specific trinucleotides, the causative mutations of numerous disorders including Huntington’s disease. The DNA repair proteins induce mutations that are different from the genome-wide mutations that arise in the absence of repair enzymes; they occur at definite loci, they occur in specific tissues during development, and they are age-dependent. These latter characteristics make pluripotent stem cells a suitable model system for triplet repeat expansion disorders. Pluripotent stem cells can be kept in culture for a prolonged period of time and can easily be differentiated into any tissue, e.g., cells along the neural lineage. Here, we review the role of DNA repair proteins in the process of triplet repeat instability in Huntington’s disease and also the potential use of pluripotent stem cells to investigate neurodegenerative disorders.     

Metabonomic Characterization of the 3-Nitropropionic Acid Rat Model of Huntington’s Disease

3-Nitropropionic acid (3-NP)-induced neurotoxicity can be used as a model for the genetic neurodegenerative disorder Huntington’s disease (HD). A metabolic profiling strategy was adopted to explore the biochemical consequences of 3-NP administered to rats in specific brain regions. ¹H NMR spectroscopy was used to characterize the metabolite composition of several brain regions following 3-NP-intoxication. Dose-dependent increases in succinate levels were observed in all neuroanatomical regions, resulting from the 3-NP-induced inhibition of succinate dehydrogenase. Global decreases in taurine and GABA were observed in the majority of brain regions, whereas altered lipid profiles were observed only in the globus pallidus and dorsal striatum. Depleted phosphatidylcholine and elevated glycerol levels, which are indicative of apoptosis, were also observed in the frontal cortex of the 3-NP model. Many of the metabolic anomalies are consistent with those reported in HD. The 3-NP-induced model of HD provides a means of monitoring potential mechanisms of pathology and therapeutic response for drug interventions, which can be efficiently assessed using metabolic profiling strategies.     

A Metabolic Study of Huntington’s Disease

Background

Huntington’s disease patients have a number of peripheral manifestations suggestive of metabolic and endocrine abnormalities. We, therefore, investigated a number of metabolic factors in a 24-hour study of Huntington’s disease gene carriers (premanifest and moderate stage II/III) and controls.

Methods

Control (n = 15), premanifest (n = 14) and stage II/III (n = 13) participants were studied with blood sampling over a 24-hour period. A battery of clinical tests including neurological rating and function scales were performed. Visceral and subcutaneous adipose distribution was measured using magnetic resonance imaging. We quantified fasting baseline concentrations of glucose, insulin, cholesterol, triglycerides, lipoprotein (a), fatty acids, amino acids, lactate and osteokines. Leptin and ghrelin were quantified in fasting samples and after a standardised meal. We assessed glucose, insulin, growth hormone and cortisol concentrations during a prolonged oral glucose tolerance test.

Results

We found no highly significant differences in carbohydrate, protein or lipid metabolism markers between healthy controls, premanifest and stage II/III Huntington’s disease subjects. For some markers (osteoprotegerin, tyrosine, lysine, phenylalanine and arginine) there is a suggestion (p values between 0.02 and 0.05) that levels are higher in patients with premanifest HD, but not moderate HD. However, given the large number of statistical tests performed interpretation of these findings must be cautious.

Conclusions

Contrary to previous studies that showed altered levels of metabolic markers in patients with Huntington’s disease, our study did not demonstrate convincing evidence of abnormalities in any of the markers examined. Our analyses were restricted to Huntington’s disease patients not taking neuroleptics, anti-depressants or other medication affecting metabolic pathways. Even with the modest sample sizes studied, the lack of highly significant results, despite many being tested, suggests that the majority of these markers do not differ markedly by disease status.     

Suppression of Somatic Expansion Delays the Onset of Pathophysiology in a Mouse Model of Huntington’s Disease

Huntington’s Disease (HD) is caused by inheritance of a single disease-length allele harboring an expanded CAG repeat, which continues to expand in somatic tissues with age. The inherited disease allele expresses a toxic protein, and whether further somatic expansion adds to toxicity is unknown. We have created an HD mouse model that resolves the effects of the inherited and somatic expansions. We show here that suppressing somatic expansion substantially delays the onset of disease in littermates that inherit the same disease-length allele. Furthermore, a pharmacological inhibitor, XJB-5-131, inhibits the lengthening of the repeat tracks, and correlates with rescue of motor decline in these animals. The results provide evidence that pharmacological approaches to offset disease progression are possible.