Early changes in Huntington's disease patient brains involve alterations in cytoskeletal and synaptic elements

Mild cognitive impairment in Huntington's disease: challenges and outlooks

Although Huntington's disease (HD) has classically been viewed as an autosomal-dominant inherited neurodegenerative motor disorder, cognitive and/or behavioral changes are predominant and often an early manifestation of disease. About 40% of individuals in the presymptomatic period of HD meet the criteria for mild cognitive impairment, later progressing to dementia. The heterogenous spectrum of cognitive decline is characterized by deficits across multiple domains, particularly executive dysfunctions, but the underlying pathogenic mechanisms are still poorly understood. Investigating the pathophysiology of cognitive changes may give insight into important and early neurodegenerative events. Multimodal imaging revealed circuit-wide gray and white matter degenerative processes in several key brain regions, affecting prefronto-striatal/cortico-basal ganglia circuits and many other functional brain networks. Studies in transgenic animal models indicated early synaptic dysfunction, deficient neurotrophic transport and other molecular changes contributing to neuronal death. Synaptopathy within the cerebral cortex, striatum and hippocampus may be particularly important in mediating cognitive and neuropsychiatric manifestations of HD, although many other neuronal systems are involved. The interaction of mutant huntingtin protein (mHTT) with tau and its implication for cognitive impairment in HD is a matter of discussion. Further neuroimaging and neuropathological studies are warranted to better elucidate early pathophysiological mechanisms and to develop validated biomarkers to detect patients' cognitive status during the early stages of the condition significantly to implement effective preventing or management strategies.

Coherent light scattering from cellular dynamics in living tissues

This review examines the biological physics of intracellular transport probed by the coherent optics of dynamic light scattering from optically thick living tissues. Cells and their constituents are in constant motion, composed of a broad range of speeds spanning many orders of magnitude that reflect the wide array of functions and mechanisms that maintain cellular health. From the organelle scale of tens of nanometers and upward in size, the motion inside living tissue is actively driven rather than thermal, propelled by the hydrolysis of bioenergetic molecules and the forces of molecular motors. Active transport can mimic the random walks of thermal Brownian motion, but mean-squared displacements are far from thermal equilibrium and can display anomalous diffusion through Lévy or fractional Brownian walks. Despite the average isotropic three-dimensional environment of cells and tissues, active cellular or intracellular transport of single light-scattering objects is often pseudo-one-dimensional, for instance as organelle displacement persists along cytoskeletal tracks or as membranes displace along the normal to cell surfaces, albeit isotropically oriented in three dimensions. Coherent light scattering is a natural tool to characterize such tissue dynamics because persistent directed transport induces Doppler shifts in the scattered light. The many frequency-shifted partial waves from the complex and dynamic media interfere to produce dynamic speckle that reveals tissue-scale processes through speckle contrast imaging and fluctuation spectroscopy. Low-coherence interferometry, dynamic optical coherence tomography, diffusing-wave spectroscopy, diffuse-correlation spectroscopy, differential dynamic microscopy and digital holography offer coherent detection methods that shed light on intracellular processes. In health-care applications, altered states of cellular health and disease display altered cellular motions that imprint on the statistical fluctuations of the scattered light. For instance, the efficacy of medical therapeutics can be monitored by measuring the changes they induce in the Doppler spectra of livingex vivocancer biopsies.

Detection of proteomic alterations at different stages in a Huntington's disease mouse model via matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging

Huntington's disease (HD) is a progressive and irreversible neurodegenerative disease leading to the inability to carry out daily activities and for which no cure exists. The underlying mechanisms of the disease have not been fully elucidated yet. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) allows the spatial information of proteins to be obtained upon the tissue sections without homogenisation. In this study, we aimed to examine proteomic alterations in the brain tissue of an HD mouse model with MALDI-MSI coupled to LC-MS/MS system. We used 3-, 6- and 12-month-old YAC128 mice representing pre-stage, mild stage and pathological stage of the HD and their non-transgenic littermates, respectively. The intensity levels of 89 proteins were found to be significantly different in YAC128 in comparison to their control mice in the pre-stage, 83 proteins in the mild stage, and 82 proteins in the pathological stage. Among them, Tau, EF2, HSP70, and NogoA proteins were validated with western blot analysis. In conclusion, the results of this study have provided remarkable new information about the spatial proteomic alterations in the HD mouse model, and we suggest that MALDI-MSI is an excellent technique for identifying such regional proteomic changes and could offer new perspectives in examining complex diseases.

Neuroprotectant Effects of Hibiscetin in 3-Nitropropionic Acid-Induced Huntington's Disease via Subsiding Oxidative Stress and Modulating Monoamine Neurotransmitters in Rats Brain

BACKGROUND

Previously reported data suggest that hibiscetin, isolated from roselle, contains delphinidin-3-sambubioside and cyanidin-3-sambubioside including anthocyanidins and has a broad range of physiological effects. In this study, we aim to analyze the effect of hibiscetin neuroprotective ability in rats against 3-nitropropionic acid (3-NPA)-induced Huntington's disease (HD).

METHODS

To investigate possible toxicities in animals, oral acute toxicity studies of hibiscetin were undertaken, and results revealed the safety of hibiscetin in animals with a maximum tolerated dose. Wistar rats were divided into four groups (n = 6); (group-1) treated with normal saline, (group-2) hibiscetin (10 mg/kg) only, (group-3) 3-NPA only, and (group-4) 3-NPA +10 mg/kg hibiscetin. The efficacy of hibiscetin 10 mg/kg was studied with the administration of 3-NPA doses for the induction of experimentally induced HD symptoms in rats. The mean body weight (MBW) was recorded at end of the study on day 22 to evaluate any change in mean body weight. Several biochemical parameters were assessed to support oxidative stress (GSH, SOD, CAT, LPO, GR, and GPx), alteration in neurotransmitters (DOPAC, HVA, 5-HIAA, norepinephrine, serotonin, GABA, and dopamine), alterations in BDNF and cleaved caspase (caspase 3) activity. Additionally, inflammatory markers, i.e., tumor necrosis factor alpha (TNF-α), interleukins beta (IL-1β), and myeloperoxidase (MPO) were evaluated.

RESULTS

The hibiscetin-treated group exhibits a substantial restoration of MBW than the 3-NPA control group. Furthermore, 3-NPA caused a substantial alteration in biochemical, neurotransmitter monoamines, and neuroinflammatory parameters which were restored successfully by hibiscetin.

CONCLUSION

The current study linked the possible role of hibiscetin by offering neuroprotection in experimental animal models.

Tubulin Cytoskeleton in Neurodegenerative Diseases–not Only Primary Tubulinopathies

Neurodegenerative diseases represent a large group of disorders characterized by gradual loss of neurons and functions of the central nervous systems. Their course is usually severe, leading to high morbidity and subsequent inability of patients to independent functioning. Vast majority of neurodegenerative diseases is currently untreatable, and only some symptomatic drugs are available which efficacy is usually very limited. To develop novel therapies for this group of diseases, it is crucial to understand their pathogenesis and to recognize factors which can influence the disease course. One of cellular structures which dysfunction appears to be relatively poorly understood in the light of neurodegenerative diseases is tubulin cytoskeleton. On the other hand, its changes, both structural and functional, can considerably influence cell physiology, leading to pathological processes occurring also in neurons. In this review, we summarize and discuss dysfunctions of tubulin cytoskeleton in various neurodegenerative diseases different than primary tubulinopathies (caused by mutations in genes encoding the components of the tubulin cytoskeleton), especially Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, prion diseases, and neuronopathic mucopolysaccharidoses. It is also proposed that correction of these disorders might attenuate the progress of specific diseases, thus, finding newly recognized molecular targets for potential drugs might become possible.

Glutamatergic Synapse Dysfunction in Drosophila Neuromuscular Junctions Can Be Rescued by Proteostasis Modulation

Glutamate is the major excitatory neurotransmitter in the nervous system, and the Drosophila glutamatergic neuromuscular junctions (NMJs) offer a tractable platform to understand excitatory synapse biology both in health and disease. Synaptopathies are neurodegenerative diseases that are associated with synaptic dysfunction and often display compromised proteostasis. One such rare, progressive neurodegenerative condition, Spinocerebellar Ataxia Type 3 (SCA3) or Machado-Joseph Disease (MJD), is characterized by cerebellar ataxia, Parkinsonism, and degeneration of motor neuron synapses. While the polyQ repeat mutant protein ataxin-3 is implicated in MJD, it is unclear how it leads to impaired synaptic function. In this study, we indicated that a Drosophila model of MJD recapitulates characteristics of neurodegenerative disorders marked by motor neuron dysfunction. Expression of 78 polyQ repeats of mutant ataxin-3 protein in Drosophila motor neurons resulted in behavioral defects, such as impaired locomotion in both larval and adult stages. Furthermore, defects in eclosion and lifespan were observed in adult flies. Detailed characterization of larval glutamatergic neuromuscular junctions (NMJs) revealed defects in morphological features along with compromised NMJ functioning. Autophagy, one of the key proteostasis pathways, is known to be impaired in the case of several synaptopathies. Our study reveals that overexpression of the autophagy-related protein Atg8a rescued behavioral defects. Thus, we present a model for glutamatergic synapse dysfunction that recapitulates synaptic and behavioral deficits and show that it is an amenable system for carrying out genetic and chemical biology screens to identify potential therapeutic targets for synaptopathies.

Huntington's disease mouse models: unraveling the pathology caused by CAG repeat expansion

Huntington's disease (HD) is a neurodegenerative disease that results in motor and cognitive dysfunction, leading to early death. HD is caused by an expansion of CAG repeats in the huntingtin gene (HTT). Here, we review the mouse models of HD. They have been used extensively to better understand the molecular and cellular basis of disease pathogenesis as well as to provide non-human subjects to test the efficacy of potential therapeutics. The first and best-studied in vivo rodent model of HD is the R6/2 mouse, in which a transgene containing the promoter and exon 1 fragment of human HTT with 150 CAG repeats was inserted into the mouse genome. R6/2 mice express rapid, robust behavioral pathologies and display a number of degenerative abnormalities in neuronal populations most vulnerable in HD. The first conditional full-length mutant huntingtin (mHTT) mouse model of HD was the bacterial artificial chromosome (BAC) transgenic mouse model of HD (BACHD), which expresses human full-length mHTT with a mixture of 97 CAG-CAA repeats under the control of endogenous HTT regulatory machinery. It has been useful in identifying the role of mHTT in specific neuronal populations in degenerative processes. In the knock-in (KI) model of HD, the expanded human CAG repeats and human exon 1 are inserted into the mouse Htt locus, so a chimera of the full-length mouse protein with the N-terminal human portion is expressed. Many of aspects of the pathology and behavioral deficits in the KI model better mimic disease characteristics found in HD patients than other models. Accordingly, some have proposed that these mice may be preferable models of the disease over others. Indeed, as our understanding of HD advances, so will the design of animal models to test and develop HD therapies.

Synaptic Damage and Its Clinical Correlates in People With Early Huntington Disease: A PET Study

BACKGROUND AND OBJECTIVES

Synaptic damage has been proposed to play a major role in the pathophysiology of Huntington's disease (HD), but in vivo evidence in humans is lacking. We performed a PET imaging study to assess synaptic damage and its clinical correlates in early HD in vivo. METHODS: In this cross-sectional study, premanifest and early manifest (Shoulson-Fahn stage 1 and 2) HD mutation carriers and age- and gender-matched healthy controls underwent clinical assessment of motor and non-motor manifestations and time-of-flight PET with ¹¹C-UCB-J, a radioligand targeting the ubiquitous presynaptic terminal marker SV2A. We also performed ¹⁸F-FDG PET in all subjects, as regional cerebral glucose consumption is thought to largely reflect synaptic activity. Volumes of interest were delineated based on individual 3D T1 MRI. Standardized uptake value ratio (SUVR)-1 images were calculated for ¹¹C-UCB-J with the centrum semiovale as reference region. ¹⁸F-FDG PET activity was normalized to the pons. All PET data were corrected for partial volume effects. Volume of interest- and voxel-based analyses were performed. Correlations between clinical scores and ¹¹C-UCB-J PET data were calculated.

RESULTS

18 HD mutation carriers (51.4 ± 11.6 years; 6 female; 7 premanifest, 11 early manifest) and 15 healthy controls (52.3 ± 3.5 years; 4 female) were included. In the HD group, significant loss of SV2A binding was found in putamen, caudate, pallidum, cerebellum, parietal, temporal and frontal cortex, whereas reduced ¹⁸F-FDG uptake was restricted to caudate and putamen. In the premanifest subgroup, ¹¹C-UCB-J and ¹⁸F-FDG PET showed significant reductions in putamen and caudate only. In the total HD group, SV2A loss in the putamen correlated with motor impairment.

DISCUSSION

Our data reveal loss of presynaptic terminal integrity in early HD, which begins in the striatum in the premanifest phase, spreads extensively to extrastriatal regions in the early manifest phase, and correlates with motor impairment. ¹¹C-UCB-J PET is more sensitive than ¹⁸F-FDG PET for detection of extrastriatal changes in early HD.

CLASSIFICATION OF EVIDENCE

This study provides class III evidence that ¹¹C-UCB-J PET accurately identifies HD from normal controls.

Synaptic vesicle glycoprotein 2A is affected in the CNS of Huntington's Disease mice and post-mortem human HD brain

Synaptic dysfunction is a primary mechanism underlying Huntington's Disease (HD) progression. This study investigated changes in synaptic vesicle glycoprotein 2A (SV2A) density by means of ¹¹C-UCB-J microPET imaging in the central nervous system (CNS) of HD mice. METHODS: Dynamic ¹¹C-UCB-J microPET imaging was performed at clinically relevant disease stages (at 3, 7, 10, and 16 months, M) in the heterozygous knock-in Q175DN mouse model of HD and WT littermates (n = 16-18/genotype and time point). Cerebral ¹¹C-UCB-J analyses were performed to assess genotypic differences during pre-symptomatic (3M) and symptomatic (7-16M) disease stages. ¹¹C-UCB-J binding in the spinal cord was quantified at 16M. 3H-UCB-J autoradiography and SV2A immunofluorescence were performed post-mortem in mouse and human brain tissue. RESULTS: ¹¹C-UCB-J binding was declined in symptomatic heterozygous mice compared to WT littermates in parallel with disease progression (7M: p<0.01, 16M: p<0.0001). Specific ¹¹C-UCB-J binding was detectable in the spinal cord, with symptomatic heterozygous mice displaying a significant reduction (p<0.0001). 3H-UCB-J autoradiography and SV2A immunofluorescence corroborated the in vivo measurements demonstrating lowered SV2A in heterozygous mice (p<0.05). Finally, preliminary analysis of SV2A in post-mortem human brain suggested lower SV2A in HD gene carrier compared to nondemented control. CONCLUSION: ¹¹C-UCB-J PET detects SV2A deficits during symptomatic disease in heterozygous mice in both brain and spinal cord, offering a novel marker of synaptic integrity widely distributed in CNS. Upon clinical application, ¹¹C-UCB-J PET imaging yields promise for SV2A measurement in patients with HD during disease progression and following disease-modifying therapeutic strategies.

Transcriptional Dysregulation in Huntington's Disease: The Role in Pathogenesis and Potency for Pharmacological Targeting

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by a mutation in the gene that encodes a critical cell regulatory protein, huntingtin (Htt). The expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats causes improper folding of functional proteins and is an initial trigger of pathological changes in the brain. Recent research has indicated that the functional dysregulation of many transcription factors underlies the neurodegenerative processes that accompany HD. These disturbances are caused not only by the loss of wild-type Htt (WT Htt) function but also by the occurrence of abnormalities that result from the action of mutant Htt (mHtt). In this review, we aim to describe the role of transcription factors that are currently thought to be strongly associated with HD pathogenesis, namely, RE1-silencing transcription factor, also known as neuron-restrictive silencer factor (REST/NRSF), forkhead box proteins (FOXPs), peroxisome proliferator-activated receptor gamma coactivator-1a (PGC1α), heat shock transcription factor 1 (HSF1), and nuclear factor κ light-chain-enhancer of activated B cells (NF- κB). We also take into account the role of these factors in the phenotype of HD as well as potential pharmacological interventions targeting the analyzed proteins. Furthermore, we considered whether molecular manipulation resulting in changes in transcription factor function may have clinical potency for treating HD.

Taming the Huntington's Disease Proteome: What Have We Learned?

Mass spectrometry (MS) is a physical technique used to identify specific chemicals and molecules by precise analysis of their mass and charge; this technology has been adapted for biological sciences applications. Investigators have used MS to identify differential expressions of proteins in Huntington’s disease (HD), to discover Huntingtin (HTT) interacting proteins and to analyze HTT proteoforms. Using systems biology and computational approaches, data from MS screens have been leveraged to find differentially expressed pathways. This review summarizes the data from most of the MS studies done in the HD field in the last 20 years and compares it to the protein data reported before the use of MS technology. The MS results validate early findings in the field such as differential expression of PDE10a and DARPP-32 and identify new changes. We offer a perspective on the MS approach in HD, particularly for identification of disease pathways, the challenges in interpreting data across different studies, and its application to protein studies moving forward.

Do Changes in Synaptic Autophagy Underlie the Cognitive Impairments in Huntington's Disease?

Although Huntington's disease (HD) is classically considered from the perspective of the motor syndrome, the cognitive changes in HD are prominent and often an early manifestation of disease. As such, investigating the underlying pathophysiology of cognitive changes may give insight into important and early neurodegenerative events. In this review, we first discuss evidence from both HD patients and animal models that cognitive changes correlate with early pathological changes at the synapse, an observation that is similarly made in other neurodegenerative conditions that primarily affect cognition. We then describe how autophagy plays a critical role supporting synaptic maintenance in the healthy brain, and how autophagy dysfunction in HD may thereby lead to impaired synaptic maintenance and thus early manifestations of disease.

Gene Expression Changes in a Model Neuron Cell Line Exposed to Autoantibodies from Patients with Traumatic Brain Injury and/or Type 2 Diabetes

Traumatic brain injury and adult type 2 diabetes mellitus are each associated with the late occurrence of accelerated cognitive decline and Parkinson’s disease through unknown mechanisms. Previously, we reported increased circulating agonist autoantibodies targeting the 5-hydroxytryptamine 2A receptor in plasma from subsets of Parkinson’s disease, dementia, and diabetic patients suffering with microvascular complications. Here, we use a model neuron, mouse neuroblastoma (N2A) cell line, to test messenger RNA expression changes following brief exposure to traumatic brain injury and/or type 2 diabetes mellitus plasma harboring agonist 5-hydroxytryptamine 2A receptor autoantibodies. We now report involvement of the mitochondrial dysfunction pathway and Parkinson’s disease pathways in autoantibody-induced gene expression changes occurring in neuroblastoma cells. Functional gene categories upregulated significantly included cell death, cytoskeleton-microtubule function, actin polymerization or depolymerization, regulation of cell oxidative stress, mitochondrial function, immune function, protein metabolism, and vesicle function. Gene categories significantly downregulated included microtubule function, cell adhesion, neurotransmitter release, dopamine metabolism synaptic plasticity, maintenance of neuronal differentiation, mitochondrial function, and cell signaling. Taken together, these results suggest that agonist 5-hydroxytryptamine receptor autoantibodies (which increase in Parkinson’s disease and other forms of neurodegeneration) mediate a coordinating program of gene expression changes in a model neuron which predispose to neuro-apoptosis and are linked to human neurodegenerative diseases pathways.

D1R- and D2R-Medium-Sized Spiny Neurons Diversity: Insights Into Striatal Vulnerability to Huntington's Disease Mutation

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by an aberrant expansion of the CAG tract within the exon 1 of the HD gene, HTT. HD progressively impairs motor and cognitive capabilities, leading to a total loss of autonomy and ultimate death. Currently, no cure or effective treatment is available to halt the disease. Although the HTT gene is ubiquitously expressed, the striatum appears to be the most susceptible district to the HD mutation with Medium-sized Spiny Neurons (MSNs) (D1R and D2R) representing 95% of the striatal neuronal population. Why are striatal MSNs so vulnerable to the HD mutation? Particularly, why do D1R- and D2R-MSNs display different susceptibility to HD? Here, we highlight significant differences between D1R- and D2R-MSNs subpopulations, such as morphology, electrophysiology, transcriptomic, functionality, and localization in the striatum. We discuss possible reasons for their selective degeneration in the context of HD. Our review suggests that a better understanding of cell type-specific gene expression dysregulation within the striatum might reveal new paths to therapeutic intervention or prevention to ameliorate HD patients' life expectancy.

A Progressive Loss of phosphoSer138-Profilin Aligns with Symptomatic Course in the R6/2 Mouse Model of Huntington's Disease: Possible Sex-Dependent Signaling

The R6/2 transgenic mouse model of Huntington’s disease (HD) carries several copies of exon1 of the huntingtin gene that contains a highly pathogenic 120 CAG-repeat expansion. We used kinome analysis to screen for kinase activity patterns in neural tissues from wildtype (WT) and R6/2 mice at a pre-symptomatic (e.g., embryonic) and symptomatic (e.g., between 3 and 10 weeks postnatal) time points. We identified changes in several signaling cascades, for example, the Akt/FoxO3/CDK2, mTOR/ULK1, and RAF/MEK/CREB pathways. We also identified the Rho-Rac GTPase cascade that contributes to cytoskeleton organization through modulation of the actin-binding proteins, cofilin and profilin. Immunoblotting revealed higher levels of phosphoSer138-profilin in embryonic R6/2 mouse samples (cf. WT mice) that diminish progressively and significantly over the postnatal, symptomatic course of the disease. We detected sex- and genotype-dependent patterns in the phosphorylation of actin-regulators such a ROCK2, PAK, LIMK1, cofilin, and SSH1L, yet none of these aligned consistently with the changing levels of phosphoSer138-profilin. This could be reflecting an imbalance in the sequential influences these regulators are known to exert on actin signaling. The translational potential of these observations was inferred from preliminary observations of changes in LIMK-cofilin signaling and loss of neurite integrity in neural stem cells derived from an HD patient (versus a healthy control). Our observations suggest that a pre-symptomatic, neurodevelopmental onset of change in the phosphorylation of Ser138-profilin, potentially downstream of distinct signaling changes in male and female mice, could be contributing to cytoskeletal phenotypes in the R6/2 mouse model of HD pathology.

RE-PERG in early-onset Alzheimer's disease: A double-blind, electrophysiological pilot study

PURPOSE

To evaluate the ability of re-test pattern electroretinogram (RE-PERG), a non-invasive and fast steady-state PERG, to detect inner retinal bioelectric function anomalies in patients with early-onset Alzheimer's disease (AD).

METHODS

The study population consisted of 17 patients with AD-related mild cognitive impairment (MCI), 16 patients with vascular dementia (VD)-related MCI, both assessed using the neuropsychological Mini-Mental State Examination (MMSE) and by structural magnetic resonance imaging, and 19 healthy, age-matched normal controls (NC). All participants were visually asymptomatic, had normal or near-normal general cognitive functioning and no or minimal impairments in daily life activities. Visual field (VF) test, optical coherence tomography (OCT) and RE-PERG, sampled in five consecutive blocks of 130 events, were performed.

RESULTS

There was no statistically significant difference among the three groups with respect to age, VF parameters (mean and pattern standard deviations) and OCT parameters (ganglion cell complex thickness and retinal nerve fiber layer thickness). The mean amplitude in the RE-PERG was significantly lower, but only weakly in the AD group than in NC (p = 0.1) whereas the intrinsic variability of the 2nd harmonic phase was significantly higher in the AD group than in either the VD or NC group (p<0.001).

CONCLUSIONS

RE-PERG is altered in early-stage AD, showing a reduced amplitude with high intrinsic phase variability. It also allows the discrimination of AD from VD. A high intrinsic variability in the PERG signal, determined using RE-PERG, may thus be a new promising test for neurodegenerative diseases.

Epigenomic Remodeling in Huntington's Disease-Master or Servant?

In light of our aging population, neurodegenerative disorders are becoming a tremendous challenge, that modern societies have to face. They represent incurable, progressive conditions with diverse and complex pathological features, followed by catastrophic occurrences of massive neuronal loss at the later stages of the diseases. Some of these disorders, like Huntington’s disease (HD), rely on defined genetic factors. HD, as an incurable, fatal hereditary neurodegenerative disorder characterized by its mid-life onset, is caused by the expansion of CAG trinucleotide repeats coding for glutamine (Q) in exon 1 of the huntingtin gene. Apart from the genetic defect, environmental factors are thought to influence the risk, onset and progression of HD. As epigenetic mechanisms are known to readily respond to environmental stimuli, they are proposed to play a key role in HD pathogenesis. Indeed, dynamic epigenomic remodeling is observed in HD patients and in brains of HD animal models. Epigenetic signatures, such as DNA methylation, histone variants and modifications, are known to influence gene expression and to orchestrate various aspects of neuronal physiology. Hence, deciphering their implication in HD pathogenesis might open up new paths for novel therapeutic concepts, which are discussed in this review.

The Role of Hypothalamic Pathology for Non-Motor Features of Huntington's Disease

 Huntington’s disease (HD) is a fatal genetic neurodegenerative disorder. It has mainly been considered a movement disorder with cognitive symptoms and these features have been associated with pathology of the striatum and cerebral cortex. Importantly, individuals with the mutant huntingtin gene suffer from a spectrum of non-motor features often decades before the motor disorder manifests. These symptoms and signs include a range of psychiatric symptoms, sleep problems and metabolic changes with weight loss particularly in later stages. A higher body mass index at diagnosis is associated with slower disease progression. The common psychiatric symptom of apathy progresses with the disease. The fact that non-motor features are present early in the disease and that they show an association to disease progression suggest that unravelling the underlying neurobiological mechanisms may uncover novel targets for early disease intervention and better symptomatic treatment. The hypothalamus and the limbic system are important brain regions that regulate emotion, social cognition, sleep and metabolism. A number of studies using neuroimaging, postmortem human tissue and genetic manipulation in animal models of the disease has collectively shown that the hypothalamus and the limbic system are affected in HD. These findings include the loss of neuropeptide-expressing neurons such as orexin (hypocretin), oxytocin, vasopressin, somatostatin and VIP, and increased levels of SIRT1 in distinct nuclei of the hypothalamus. This review provides a summary of the results obtained so far and highlights the potential importance of these changes for the understanding of non-motor features in HD.

Structural and functional features of medium spiny neurons in the BACHDΔN17 mouse model of Huntington's Disease

In the BACHD mouse model of Huntington’s disease (HD), deletion of the N17 domain of the Huntingtin gene (BACHDΔN17, Q97) has been reported to lead to nuclear accumulation of mHTT and exacerbation of motor deficits, neuroinflammation and striatal atrophy (Gu et al., 2015). Here we characterized the effect of N17 deletion on dorsolateral striatal medium spiny neurons (MSNs) in BACHDΔN17 (Q97) and BACWTΔN17 (Q31) mice by comparing them to MSNs in wildtype (WT) mice. Mice were characterized on a series of motor tasks and subsequently whole cell patch clamp recordings with simultaneous biocytin filling of MSNs in in vitro striatal slices from these mice were used to comprehensively assess their physiological and morphological features. Key findings include that: Q97 mice exhibit impaired gait and righting reflexes but normal tail suspension reflexes and normal coats while Q31 mice do not differ from WT; intrinsic membrane and action potential properties are altered -but differentially so- in MSNs from Q97 and from Q31 mice; excitatory and inhibitory synaptic currents exhibit higher amplitudes in Q31 but not Q97 MSNs, while excitatory synaptic currents occur at lower frequency in Q97 than in WT and Q31 MSNs; there is a reduced total dendritic length in Q31 -but not Q97- MSNs compared to WT, while spine density and number did not differ in MSNs in the three groups. The findings that Q31 MSNs differed from Q97 and WT neurons with regard to some physiological features and structurally suggest a novel role of the N17 domain in the function of WT Htt. The motor phenotype seen in Q97 mice was less robust than that reported in an earlier study (Gu et al., 2015), and the alterations to MSN physiological properties were largely consistent with changes reported previously in a number of other mouse models of HD. Together this study indicates that N17 plays a role in the modulation of the properties of MSNs in both mHtt and WT-Htt mice, but does not markedly exacerbate HD-like pathogenesis in the BACHD model.

Longitudinal atrophy characterization of cortical and subcortical gray matter in Huntington's disease patients

Huntington's disease (HD) is an inherited neurodegenerative disease with clinical manifestations that involve motor, cognitive and psychiatric deficits. Cross-sectional magnetic resonance imaging (MRI) studies have described the main cortical and subcortical macrostructural atrophy of HD. However, longitudinal studies characterizing progressive atrophy are lacking. This study aimed to describe the cortical and subcortical gray matter atrophy using complementary volumetric and surface-based MRI analyses in a cohort of seventeen early HD patients in a cross-sectional and longitudinal analysis and to correlate the longitudinal volumetric atrophy with the functional decline using several clinical measures. A group of seventeen healthy individuals was included as controls. After obtaining structural MRIs, volumetric analyses were performed in 36 cortical and 7 subcortical regions of interest per hemisphere and surface-based analyses were performed in the whole cortex, caudate, putamen and thalamus. Cross-sectional cortical surface-based and volumetric analyses showed significant decreases in frontoparietal and temporo-occipital cortices, while subcortical volumetric analysis showed significant decreases in all subcortical structures except the hippocampus. The longitudinal surface-based analysis showed widespread cortical thinning with volumetric decreases in the superior frontal lobe, while a subcortical volumetric decrease occurred in the caudate, putamen and thalamus with shape deformation on the anterior, medial and dorsal side. Functional capacity and motor status decline correlated with caudate progressive atrophy, while cognitive decline correlated with left superior frontal and right paracentral progressive atrophy. These results provide new insights into progressive volumetric and surface-based morphometric atrophy of gray matter in HD.

From the Cover: Proteome Profile of Different Rat Brain Regions After Sarin Intoxication

Sarin is an organophosphorus (OP) chemical warfare agent which irreversibly inhibits acetylcholinesterase. Acute toxicity after sarin exposure is because of hyper activation of the nicotinic and muscarinic receptor. Survivors of sarin exposure often develop long-term neuropathology referred as OP ester-induced chronic neurotoxicity. However, the exact mechanism of chronic neurotoxicity is yet unknown. We studied proteomic changes in rat brain regions after 0.5 LD50 dose of sarin and investigated some milestone changes associated with long-term CNS injury. We used two-dimensional gel electrophoresis/mass spectrometry approach to identify early proteomic changes and traced expression of selected proteins for longer time points. This study shows changes in chaperone function, endoplasmic reticulum stress, and defect in cytoskeleton functions at earlier stages. Predictive interaction analysis demonstrated putative role of Parkinson's disease-related proteins after sarin exposure. Our results clearly indicated neurodegenerative changes which started after 2.5 h and showed prominence after 3-month postexposure. The study also unmasks changes in proteins related to movement and cognitive function. The markers for astrocytosis (GFAP) and neurodegenerative changes (alpha-synuclein and amyloid precursor protein) exhibited altered expression in brain. This is the first proteomic study among survivors of sarin exposure in animal model. Some of the early changes, including those involved in neurodegeneration, movement, and cognitive function, defects in chaperone function and cytoskeleton, were shown to persist for a longer period. The study provides a preliminary framework for further validation of major mechanisms of sarin toxicity is suggested here and opens new avenues for elucidation of therapeutic intervention.

Dose-Dependent Lowering of Mutant Huntingtin Using Antisense Oligonucleotides in Huntington Disease Patients

On December 11 of 2017, Ionis Pharmaceuticals published a press release announcing dose-dependent reductions of mutant huntingtin protein in their HTTRx Phase 1/2a study in Huntington disease (HD) patients. The results from this Ionis trial have gained much attention from the patient community and the oligonucleotide therapeutics field, since it is the first trial targeting the cause of HD, namely the mutant huntingtin protein, using antisense oligonucleotides (ASOs). The press release also states that the primary endpoints of the study (safety and tolerability) were met, but does not contain data. This news follows the approval of another therapeutic ASO nusinersen (trade name Spinraza) for a neurological disease, spinal muscular atrophy, by the U.S. Food and Drug Administration and European Medicines Agency, in 2016 and 2017, respectively. Combined, this offers hope for the development of the HTTRx therapy for HD patients.

Axonal degeneration induced by glutamate-excitotoxicity is mediated by necroptosis

Neuronal excitotoxicity induced by glutamate leads to cell death and functional impairment in a variety of central nervous system pathologies. Glutamate-mediated excitotoxicity triggers neuronal apoptosis in the cell soma as well as degeneration of axons and dendrites by a process associated to calcium increase and mitochondrial dysfunction. Importantly, degeneration of axons initiated by diverse stimuli, including excitotoxicity, has been proposed as an important pathological event leading to functional impairment in neurodegenerative conditions. Here we demonstrate that excitotoxicity-induced axonal degeneration proceeds by a mechanism dependent on the necroptotic kinases RIPK1, RIPK3 and the necroptotic mediator MLKL. Inhibition of RIPK1, RIPK3 or MLKL prevent key steps in the axonal degeneration cascade including mitochondrial depolarization, the opening of the permeability transition pore and calcium dysregulation in the axon. Interestingly, the same excitotoxic stimuli lead to apoptosis in the cell soma, demonstrating the co-activation of two independent degenerative mechanisms in different compartments of the same cell. The identification of necroptosis as a key mechanism of axonal degeneration after excitotoxicity is an important initial step to develop novel therapeutic strategies for nervous system disorders.

Cholinergic interneurons in the Q140 knockin mouse model of Huntington's disease: Reductions in dendritic branching and thalamostriatal input

We have previously found that thalamostriatal axodendritic terminals are reduced as early as 1 month of age in heterozygous Q140 HD mice (Deng et al. [] Neurobiol Dis 60:89-107). Because cholinergic interneurons are a major target of thalamic axodendritic terminals, we examined the VGLUT2-immunolabeled thalamic input to striatal cholinergic interneurons in heterozygous Q140 males at 1 and 4 months of age, using choline acetyltransferase (ChAT) immunolabeling to identify cholinergic interneurons. Although blinded neuron counts showed that ChAT⁺ perikarya were in normal abundance in Q140 mice, size measurements indicated that they were significantly smaller. Sholl analysis further revealed the dendrites of Q140 ChAT⁺ interneurons were significantly fewer and shorter. Consistent with the light microscopic data, ultrastructural analysis showed that the number of ChAT⁺ dendritic profiles per unit area of striatum was significantly decreased in Q140 striata, as was the abundance of VGLUT2⁺ axodendritic terminals making synaptic contact with ChAT⁺ dendrites per unit area of striatum. The density of thalamic terminals along individual cholinergic dendrites was, however, largely unaltered, indicating that the reduction in the areal striatal density of axodendritic thalamic terminals on cholinergic neurons was due to their dendritic territory loss. These results show that the abundance of thalamic input to individual striatal cholinergic interneurons is reduced early in the life span of Q140 mice, raising the possibility that this may occur in human HD as well. Because cholinergic interneurons differentially affect striatal direct vs. indirect pathway spiny projection neurons, their reduced thalamic excitatory drive may contribute to early abnormalities in movement in HD. J. Comp. Neurol. 524:3518-3529, 2016. © 2016 Wiley Periodicals, Inc.

Identification of chemicals that mimic transcriptional changes associated with autism, brain aging and neurodegeneration

Environmental factors, including pesticides, have been linked to autism and neurodegeneration risk using retrospective epidemiological studies. Here we sought to prospectively identify chemicals that share transcriptomic signatures with neurological disorders, by exposing mouse cortical neuron-enriched cultures to hundreds of chemicals commonly found in the environment and on food. We find that rotenone, a pesticide associated with Parkinson's disease risk, and certain fungicides, including pyraclostrobin, trifloxystrobin, famoxadone and fenamidone, produce transcriptional changes in vitro that are similar to those seen in brain samples from humans with autism, advanced age and neurodegeneration (Alzheimer's disease and Huntington's disease). These chemicals stimulate free radical production and disrupt microtubules in neurons, effects that can be reduced by pretreating with a microtubule stabilizer, an antioxidant, or with sulforaphane. Our study provides an approach to prospectively identify environmental chemicals that transcriptionally mimic autism and other brain disorders.

This study presents gene expression responses of cultured brain cells to hundreds of chemicals found in the environment and in food. The authors identified chemicals that induce transcriptomic profiles that overlap those seen in human brains affected with autism, aging, and neurodegeneration.

Allosteric activation of M4 muscarinic receptors improve behavioral and physiological alterations in early symptomatic YAC128 mice

Mutations that lead to Huntington's disease (HD) result in increased transmission at glutamatergic corticostriatal synapses at early presymptomatic stages that have been postulated to set the stage for pathological changes and symptoms that are observed at later ages. Based on this, pharmacological interventions that reverse excessive corticostriatal transmission may provide a novel approach for reducing early physiological changes and motor symptoms observed in HD. We report that activation of the M4 subtype of muscarinic acetylcholine receptor reduces transmission at corticostriatal synapses and that this effect is dramatically enhanced in presymptomatic YAC128 HD and BACHD relative to wild-type mice. Furthermore, chronic administration of a novel highly selective M4 positive allosteric modulator (PAM) beginning at presymptomatic ages improves motor and synaptic deficits in 5-mo-old YAC128 mice. These data raise the exciting possibility that selective M4 PAMs could provide a therapeutic strategy for the treatment of HD.

The Potential Regulatory Mechanisms of miR-196a in Huntington's Disease through Bioinformatic Analyses

High throughput screening is a powerful tool to identify the potential candidate molecules involved during disease progression. However, analysis of complicated data is one of the most challenging steps on the way to obtaining useful results from this approach. Previously, we showed that a specific miRNA, miR-196a, could ameliorate the pathological phenotypes of Huntington’s disease (HD) in different models, and performed high throughput screening by using the striatum of transgenic mice. In this study, we further tried to identify the potential regulatory mechanisms using different bioinformatic tools, including Database for Annotation, Visualization and Integrated Discovery (DAVID), Molecular Signatures Database (MSigDB), TargetScan and MetaCore. The results showed that miR-196a dominantly altered “ABC transporters”, “RIG-I-like receptor signaling pathway”, immune system”, “adaptive immune system”,“tissue remodeling and wound repair” and “cytoskeleton remodeling”. In addition, miR-196a also changed the expression of several well-defined pathways of HD, such as apoptosis and cell adhesion. Since these analyses showed the regulatory pathways are highly related to the modification of the cytoskeleton, we further confirmed that miR-196a could enhance the neurite outgrowth in neuroblastoma cells, suggesting miR-196a might provide beneficial functions through the alteration of cytoskeleton structures. Since impairment of the cytoskeleton has been reported in several neuronal diseases, this study will provide not only the potential working mechanisms of miR-196a but also insights for therapeutic strategies for use with different neuronal diseases.

Analysis of YFP(J16)-R6/2 reporter mice and postmortem brains reveals early pathology and increased vulnerability of callosal axons in Huntington's disease

Cumulative evidence indicates that the onset and severity of Huntington's disease (HD) symptoms correlate with connectivity deficits involving specific neuronal populations within cortical and basal ganglia circuits. Brain imaging studies and pathological reports further associated these deficits with alterations in cerebral white matter structure and axonal pathology. However, whether axonopathy represents an early pathogenic event or an epiphenomenon in HD remains unknown, nor is clear the identity of specific neuronal populations affected. To directly evaluate early axonal abnormalities in the context of HD in vivo, we bred transgenic YFP(J16) with R6/2 mice, a widely used HD model. Diffusion tensor imaging and fluorescence microscopy studies revealed a marked degeneration of callosal axons long before the onset of motor symptoms. Accordingly, a significant fraction of YFP-positive cortical neurons in YFP(J16) mice cortex were identified as callosal projection neurons. Callosal axon pathology progressively worsened with age and was influenced by polyglutamine tract length in mutant huntingtin (mhtt). Degenerating axons were dissociated from microscopically visible mhtt aggregates and did not result from loss of cortical neurons. Interestingly, other axonal populations were mildly or not affected, suggesting differential vulnerability to mhtt toxicity. Validating these results, increased vulnerability of callosal axons was documented in the brains of HD patients. Observations here provide a structural basis for the alterations in cerebral white matter structure widely reported in HD patients. Collectively, our data demonstrate a dying-back pattern of degeneration for cortical projection neurons affected in HD, suggesting that axons represent an early and potentially critical target for mhtt toxicity.

Complexin2 modulates working memory-related neural activity in patients with schizophrenia

The specific contribution of risk or candidate gene variants to the complex phenotype of schizophrenia is largely unknown. Studying the effects of such variants on brain function can provide insight into disease-associated mechanisms on a neural systems level. Previous studies found common variants in the complexin2 (CPLX2) gene to be highly associated with cognitive dysfunction in schizophrenia patients. Similarly, cognitive functioning was found to be impaired in Cplx2 gene-deficient mice if they were subjected to maternal deprivation or mild brain trauma during puberty. Here, we aimed to study seven common CPLX2 single-nucleotide polymorphisms (SNPs) and their neurogenetic risk mechanisms by investigating their relationship to a schizophrenia-related functional neuroimaging intermediate phenotype. We examined functional MRI and genotype data collected from 104 patients with DSM-IV-diagnosed schizophrenia and 122 healthy controls who participated in the Mind Clinical Imaging Consortium study of schizophrenia. Seven SNPs distributed over the whole CPLX2 gene were tested for association with working memory-elicited neural activity in a frontoparietal neural network. Three CPLX2 SNPs were significantly associated with increased neural activity in the dorsolateral prefrontal cortex and intraparietal sulcus in the schizophrenia sample, but showed no association in healthy controls. Since increased working memory-related neural activity in individuals with or at risk for schizophrenia has been interpreted as 'neural inefficiency,' these findings suggest that certain variants of CPLX2 may contribute to impaired brain function in schizophrenia, possibly combined with other deleterious genetic variants, adverse environmental events, or developmental insults.

Biological wires, communication systems, and implications for disease

Microtubules, actin, and collagen are macromolecular structures that compose a large percentage of the proteins in the human body, helping form and maintain both intracellular and extracellular structure. They are biological wires and are structurally connected through various other proteins. Microtubules (MTs) have been theorized to be involved in classical and quantum information processing, and evidence continues to suggest possible semiconduction through MTs. The previous Dendritic Cytoskeleton Information Processing Model has hypothesized how MTs and actin form a communication network in neurons. Here, we review information transfer possibilities involving MTs, actin, and collagen, and the evidence of an organism-wide high-speed communication network that may regulate morphogenesis and cellular proliferation. The direct and indirect evidence in support of this hypothesis, and implications for chronic diseases such as cancer and neurodegenerative diseases are discussed.

Differential loss of thalamostriatal and corticostriatal input to striatal projection neuron types prior to overt motor symptoms in the Q140 knock-in mouse model of Huntington's disease

Motor slowing and forebrain white matter loss have been reported in premanifest Huntington's disease (HD) prior to substantial striatal neuron loss. These findings raise the possibility that early motor defects in HD may be related to loss of excitatory input to striatum. In a prior study, we showed that in the heterozygous Q140 knock-in mouse model of HD that loss of thalamostriatal axospinous terminals is evident by 4 months, and loss of corticostriatal axospinous terminals is evident at 12 months, before striatal projection neuron pathology. In the present study, we specifically characterized the loss of thalamostriatal and corticostriatal terminals on direct (dSPN) and indirect (iSPN) pathway striatal projection neurons, using immunolabeling to identify thalamostriatal (VGLUT2+) and corticostriatal (VGLUT1+) axospinous terminals, and D1 receptor immunolabeling to distinguish dSPN (D1+) and iSPN (D1-) synaptic targets. We found that the loss of corticostriatal terminals at 12 months of age was preferential for D1+ spines, and especially involved smaller terminals, presumptively of the intratelencephalically projecting (IT) type. By contrast, indirect pathway D1- spines showed little loss of axospinous terminals at the same age. Thalamostriatal terminal loss was comparable for D1+ and D1- spines at both 4 and 12 months. Regression analysis showed that the loss of VGLUT1+ terminals on D1+ spines was correlated with a slight decline in open field motor parameters at 12 months. Our overall results raise the possibility that differential thalamic and cortical input loss to SPNs is an early event in human HD, with cortical loss to dSPNs in particular contributing to premanifest motor slowing.

Progressive axonal transport and synaptic protein changes correlate with behavioral and neuropathological abnormalities in the heterozygous Q175 KI mouse model of Huntington's disease

A long-term goal of modeling Huntington's disease (HD) is to recapitulate the cardinal features of the disease in mice that express both mutant and wild-type (WT) huntingtin (Htt), as HD commonly manifests as a heterozygous condition in humans, and loss of WT Htt is associated with loss-of-function. In a new heterozygous Q175 knock-in (KI) mouse model, we performed an extensive evaluation of motor and cognitive functional deficits, neuropathological and biochemical changes and levels of proteins involved in synaptic function, the cytoskeleton and axonal transport, at 1-16 months of age. Motor deficits were apparent at 6 months of age in Q175 KI mice and at that time, postmortem striatal gamma-aminobutyric acid (GABA) levels were elevated and mutant Htt inclusions were present throughout the brain. From 6 months of age, levels of proteins associated with synaptic function, including SNAP-25, Rab3A and PSD-95, and with axonal transport and microtubules, including KIF3A, dynein and dynactin, were altered in the striatum, motor cortex, prefrontal cortex and hippocampus of Q175 KI mice, compared with WT levels. At 12-16 months of age, Q175 KI mice displayed motor and cognitive deficits, which were paralleled at postmortem by striatal atrophy, cortical thinning, degeneration of medium spiny neurons, dense mutant Htt inclusion formation, decreased striatal dopamine levels and loss of striatal brain-derived neurotrophic factor (BDNF). Data from this study indicate that the heterozygous Q175 KI mouse represents a realistic model for HD and also provides new insights into the specific and progressive synaptic, cytoskeletal and axonal transport protein abnormalities that may accompany the disease.

Live cell imaging and biophotonic methods reveal two types of mutant huntingtin inclusions

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disorder that can be characterized by the presence of protein inclusions containing mutant huntingtin within a subset of neurons in the brain. Since their discovery, the relevance of inclusions to disease pathology has been controversial. We show using super-resolution fluorescence imaging and Förster resonance energy transfer (FRET) in live cells, that mutant huntingtin fragments can form two morphologically and conformationally distinct inclusion types. Using fluorescence recovery after photobleaching (FRAP), we demonstrate that the two huntingtin inclusion types have unique dynamic properties. The ability to form one or the other type of inclusion can be influenced by the phosphorylation state of serine residues at amino acid positions 13 and 16 within the huntingtin protein. We can define two types of inclusions: fibrillar, which are tightly packed, do not exchange protein with the soluble phase, and result from phospho-modification at serines 13 and 16 of the N17 domain, and globular, which are loosely packed, can readily exchange with the soluble phase, and are not phosphorylated in N17. We hypothesize that the protective effect of N17 phosphorylation or phospho-mimicry seen in animal models, at the level of protein inclusions with elevated huntingtin levels, is to induce a conformation of the huntingtin amino-terminus that causes fragments to form tightly packed inclusions that do not exit the insoluble phase, and hence exert less toxicity. The identification of these sub-types of huntingtin inclusions could allow for drug discovery to promote protective inclusions of mutant huntingtin protein in HD.

Screening and identification of dynamin-1 interacting proteins in rat brain synaptosomes

Dynamin-1 is a multi-domain GTPase that is crucial for the fission stage of synaptic vesicle recycling and vesicle trafficking. In this study, we constructed prokaryotic expression plasmids for the four functional domains of dynamin-1, which are pGEX-4T-2-PH, pGEX-4T-2-PRD, pGEX-4T-2-GED and pGEX-4T-2-GTPase. Glutathione S-transferase pull-down, co-immunoprecipitation (co-IP), and liquid chromatography/mass spectrometry were used to screen and identify dynamin-1 interacting proteins in rat brain synaptosomes. We identified a set of 63 candidate protein interactions, including 36 proteins interacting with dynamin-1 C-terminal proline-rich domain (PRD), 14 with pleckstrin-homology domain (PH), 7 with GTPase effector domain (GED) and 6 with GTPase domain, consisting of synaptic vesicle-associated proteins, cytoskeletal proteins, metabolic enzymes and other proteins. We selected three previously unreported dynamin-1 interacting proteins to verify their interaction with dynamin-1 under native conditions. Using co-IP, we found that Rab GDP-dissociation inhibitor (Rab GDI) and chloride channel 3 (ClC-3) do interact with dynamin-1, but not with TUC-4b (the TOAD-64/Ulip/CRMP (TUC) family member). Those novel interactions detected in our study offer valuable insight into the protein-protein interacting network that could enhance our understanding of dynamin-1 mediated synaptic vesicle recycling.

Loss of corticostriatal and thalamostriatal synaptic terminals precedes striatal projection neuron pathology in heterozygous Q140 Huntington's disease mice

Motor slowing, forebrain white matter loss, and striatal shrinkage have been reported in premanifest Huntington's disease (HD) prior to overt striatal neuron loss. We carried out detailed LM and EM studies in a genetically precise HD mimic, heterozygous Q140 HD knock-in mice, to examine the possibility that loss of corticostriatal and thalamostriatal terminals prior to striatal neuron loss underlies these premanifest HD abnormalities. In our studies, we used VGLUT1 and VGLUT2 immunolabeling to detect corticostriatal and thalamostriatal (respectively) terminals in dorsolateral (motor) striatum over the first year of life, prior to striatal projection neuron pathology. VGLUT1+ axospinous corticostriatal terminals represented about 55% of all excitatory terminals in striatum, and VGLUT2+ axospinous thalamostriatal terminals represented about 35%, with VGLUT1+ and VGLUT2+ axodendritic terminals accounting for the remainder. In Q140 mice, a significant 40% shortfall in VGLUT2+ axodendritic thalamostriatal terminals and a 20% shortfall in axospinous thalamostriatal terminals were already observed at 1 month of age, but VGLUT1+ terminals were normal in abundance. The 20% deficiency in VGLUT2+ thalamostriatal axospinous terminals persisted at 4 and 12 months in Q140 mice, and an additional 30% loss of VGLUT1+ corticostriatal terminals was observed at 12 months. The early and persistent deficiency in thalamostriatal axospinous terminals in Q140 mice may reflect a development defect, and the impoverishment of this excitatory drive to striatum may help explain early motor defects in Q140 mice and in premanifest HD. The loss of corticostriatal terminals at 1 year in Q140 mice is consistent with prior evidence from other mouse models of corticostriatal disconnection early during progression, and can explain both the measurable bradykinesia and striatal white matter loss in late premanifest HD.

Syndapin--a membrane remodelling and endocytic F-BAR protein

Syndapin [also called PACSIN (protein kinase C and casein kinase II interacting protein)] is an Fes-CIP4 homology Bin-amphiphysin-Rvs161/167 (F-BAR) and Src-homology 3 domain-containing protein. Three genes give rise to three main isoforms in mammalian cells. They each function in different endocytic and vesicle trafficking pathways and provide critical links between the cytoskeletal network in different cellular processes, such as neuronal morphogenesis and cell migration. The membrane remodelling activity of syndapin via its F-BAR domain and its interaction partners, such as dynamin and neural Wiskott-Aldrich syndrome protein binding to its Src-homology 3 domain, are important with respect to its function. Its various partner proteins provide insights into its mechanism of action, as well as its differential roles in these cellular processes. Signalling pathways leading to the regulation of syndapin function by phosphorylation are now contributing to our understanding of the broader functions of this family of proteins.

Silver nanoparticles (AgNPs) cause degeneration of cytoskeleton and disrupt synaptic machinery of cultured cortical neurons

BACKGROUND

Silver nanoparticles (AgNPs), owing to their effective antimicrobial properties, are being widely used in a broad range of applications. These include, but are not limited to, antibacterial materials, the textile industry, cosmetics, coatings of various household appliances and medical devices. Despite their extensive use, little is known about AgNP safety and toxicity vis-à-vis human and animal health. Recent studies have drawn attention towards potential neurotoxic effects of AgNPs, however, the primary cellular and molecular targets of AgNP action/s remain to be defined.

RESULTS

Here we examine the effects of ultra fine scales (20 nm) of AgNPs at various concentrations (1, 5, 10 and 50 μg/ml) on primary rat cortical cell cultures. We found that AgNPs (at 1-50 μg/ml) not only inhibited neurite outgrowth and reduced cell viability of premature neurons and glial cells, but also induced degeneration of neuronal processes of mature neurons. Our immunocytochemistry and confocal microscopy studies further demonstrated that AgNPs induced the loss of cytoskeleton components such as the β-tubulin and filamentous actin (F-actin). AgNPs also dramatically reduced the number of synaptic clusters of the presynaptic vesicle protein synaptophysin, and the postsynaptic receptor density protein PSD-95. Finally, AgNP exposure also resulted in mitochondria dysfunction in rat cortical cells.

CONCLUSIONS

Taken together, our data show that AgNPs induce toxicity in neurons, which involves degradation of cytoskeleton components, perturbations of pre- and postsynaptic proteins, and mitochondrial dysfunction leading to cell death. Our study clearly demonstrates the potential detrimental effects of AgNPs on neuronal development and physiological functions and warns against its prolific usage.

Mechanisms underlying synaptic vulnerability and degeneration in neurodegenerative disease

Recent developments in our understanding of events underlying neurodegeneration across the central and peripheral nervous systems have highlighted the critical role that synapses play in the initiation and progression of neuronal loss. With the development of increasingly accurate and versatile animal models of neurodegenerative disease it has become apparent that disruption of synaptic form and function occurs comparatively early, preceding the onset of degenerative changes in the neuronal cell body. Yet, despite our increasing awareness of the importance of synapses in neurodegeneration, the mechanisms governing the particular susceptibility of distal neuronal processes are only now becoming clear. In this review we bring together recent developments in our understanding of cellular and molecular mechanisms regulating synaptic vulnerability. We have placed a particular focus on three major areas of research that have gained significant interest over the last few years: (i) the contribution of synaptic mitochondria to neurodegeneration; (ii) the contribution of pathways that modulate synaptic function; and (iii) regulation of synaptic degeneration by local posttranslational modifications such as ubiquitination. We suggest that targeting these organelles and pathways may be a productive way to develop synaptoprotective strategies applicable to a range of neurodegenerative conditions.

BDNF-based synaptic repair as a disease-modifying strategy for neurodegenerative diseases

Increasing evidence suggests that synaptic dysfunction is a key pathophysiological hallmark in neurodegenerative disorders, including Alzheimer's disease. Understanding the role of brain-derived neurotrophic factor (BDNF) in synaptic plasticity and synaptogenesis, the impact of the BDNF Val66Met polymorphism in Alzheimer's disease-relevant endophenotypes - including episodic memory and hippocampal volume - and the technological progress in measuring synaptic changes in humans all pave the way for a 'synaptic repair' therapy for neurodegenerative diseases that targets pathophysiology rather than pathogenesis. This article reviews the key issues in translating BDNF biology into synaptic repair therapies.

Modeling Huntington's disease with induced pluripotent stem cells

Huntington's disease (HD) causes severe motor dysfunction, behavioral abnormalities, cognitive impairment and death. Investigations into its molecular pathology have primarily relied on murine tissues; however, the recent discovery of induced pluripotent stem cells (iPSCs) has opened new possibilities to model neurodegenerative disease using cells derived directly from patients, and therefore may provide a human-cell-based platform for unique insights into the pathogenesis of HD. Here, we will examine the practical implementation of iPSCs to study HD, such as approaches to differentiate embryonic stem cells (ESCs) or iPSCs into medium spiny neurons, the cell type most susceptible in HD. We will explore the HD-related phenotypes identified in iPSCs and ESCs and review how brain development and neurogenesis may actually be altered early, before the onset of HD symptoms, which could inform the search for drugs that delay disease onset. Finally, we will speculate on the exciting possibility that ESCs or iPSCs might be used as therapeutics to restore or replace dying neurons in HD brains.

Huntington's disease and cell therapies: past, present, and future

Huntington's disease (HD) is an inherited neurodegenerative disease that is characterized by movement abnormalities, cognitive impairment, and abnormal behavior as well as sleep and weight problems. It is an autosomal dominant disorder caused by a mutation in the huntingtin gene on the short arm of chromosome 4, which results in the progressive degeneration of the basal ganglia (caudate, putamen, and globus pallidus), cerebral cortex, brainstem, thalamus, and hypothalamus. This chapter considers four avenues of research: (a) the restoration of neurogenesis as an endogenous cell therapy in HD, (b) fetal tissue transplantation, (c) stem cell transplantation, and finally (d) the use of endogenous trophic factors such as brain derived neurotrophic factor.

Striatal neuronal loss correlates with clinical motor impairment in Huntington's disease

Huntington's disease (HD) is characterized clinically by chorea, motor impairment, psychiatric manifestations, and dementia. Atrophy of the striatum is the neuropathological hallmark of HD, and previous studies have suggested that striatal atrophy correlates more closely with motor impairment than with chorea. Motor impairment, as measured by motor impairment score, correlates with functional disability in HD patients, but chorea does not. In this study, we investigated the relation between neuronal loss and these motor features. We conducted neuropathological and stereologic assessments of neurons in putamen and subthalamic nuclei in HD patients and age-matched controls. In putamen, we estimated the total number and volume of medium spiny neurons labeled with dopamine- and cAMP-regulated phosphoprotein 32 kDa (DARPP-32). In subthalamic nuclei, we estimated the total number of neurons on hematoxylin & eosin/luxol fast blue stains. In putamen of HD, immunohistochemistry showed DARPP-32 neuronal atrophy with extensive disruption of neurites and neuropil; stereologic studies found significant decreases in both the number and size of DARPP-32 neurons; we also detected a significant reduction of overall putamen volume in HD patients, compared to controls. In subthalamic nuclei, there was a mild, but significant, neuronal loss in the HD group. The loss of neurons in putamen and subthalamic nuclei as well as putaminal atrophy were significantly correlated with severity of motor impairment, but not with chorea. Our findings suggest that neuronal loss and atrophy in striatum and neuronal loss in subthalamic nuclei contribute specifically to the motor impairment of HD, but not to chorea.

Replacement of huntingtin exon 1 by trans-splicing

Huntington's disease (HD) is an autosomal-dominant neurodegenerative disorder caused by polyglutamine expansion in the amino-terminus of huntingtin (HTT). HD offers unique opportunities for promising RNA-based therapeutic approaches aimed at reducing mutant HTT expression, since the HD mutation is considered to be a "gain-of-function" mutation. Allele-specific strategies that preserve expression from the wild-type allele and reduce the levels of mutant protein would be of particular interest. Here, we have conducted proof-of-concept studies to demonstrate that spliceosome-mediated trans-splicing is a viable molecular strategy to specifically repair the HTT allele. We employed a dual plasmid transfection system consisting of a pre-mRNA trans-splicing module (PTM) containing HTT exon 1 and a HTT minigene to demonstrate that HTT exon 1 can be replaced in trans. We detected the presence of the trans-spliced RNA in which PTM exon 1 was correctly joined to minigene exons 2 and 3. Furthermore, exon 1 from the PTM was trans-spliced to the endogenous HTT pre-mRNA in cultured cells as well as disease-relevant models, including HD patient fibroblasts and primary neurons from a previously described HD mouse model. These results suggest that the repeat expansion of HTT can be repaired successfully not only in the context of synthetic minigenes but also within the context of HD neurons. Therefore, pre-mRNA trans-splicing may be a promising approach for the treatment of HD and other dominant genetic disorders.