Hypothalamic involvement in Huntington's disease: an in vivo PET study

Neuroimaging to Facilitate Clinical Trials in Huntington's Disease: Current Opinion from the EHDN Imaging Working Group

 Neuroimaging is increasingly being included in clinical trials of Huntington's disease (HD) for a wide range of purposes from participant selection and safety monitoring, through to demonstration of disease modification. Selection of the appropriate modality and associated analysis tools requires careful consideration. On behalf of the EHDN Imaging Working Group, we present current opinion on the utility and future prospects for inclusion of neuroimaging in HD trials. Covering the key imaging modalities of structural-, functional- and diffusion- MRI, perfusion imaging, positron emission tomography, magnetic resonance spectroscopy, and magnetoencephalography, we address how neuroimaging can be used in HD trials to: 1) Aid patient selection, enrichment, stratification, and safety monitoring; 2) Demonstrate biodistribution, target engagement, and pharmacodynamics; 3) Provide evidence for disease modification; and 4) Understand brain re-organization following therapy. We also present the challenges of translating research methodology into clinical trial settings, including equipment requirements and cost, standardization of acquisition and analysis, patient burden and invasiveness, and interpretation of results. We conclude, that with appropriate consideration of modality, study design and analysis, imaging has huge potential to facilitate effective clinical trials in HD.

Inflammation and Huntington's disease - a neglected therapeutic target?

INTRODUCTION

Huntington's Disease (HD) is a genetic neurodegenerative disease for which there is currently no disease-modifying treatment. One of several underlying mechanisms proposed to be involved in HD pathogenesis is inflammation; there is now accumulating evidence that the immune system may play an integral role in disease pathology and progression. As such, modulation of the immune system could be a potential therapeutic target for HD.

AREAS COVERED

To date, the number of trials targeting immune aspects of HD has been limited. However, targeting it, may have great advantages over other therapeutic areas, given that many drugs already exist that have actions in this system coupled to the fact that inflammation can be measured both peripherally and, to some extent, centrally using CSF and PET imaging. In this review, we look at evidence that the immune system and the newly emerging area of the microbiome are altered in HD patients, and then present and discuss clinical trials that have targeted different parts of the immune system.

EXPERT OPINION

We then conclude by discussing how this field might develop going forward, focusing on the role of imaging and other biomarkers to monitor central immune activation and response to novel treatments in HD.

Increased microglia activation in late non-central nervous system cancer survivors links to chronic systemic symptomatology

Prolonged inflammatory expression within the central nervous system (CNS) is recognized by the brain as a molecular signal of "sickness", that has knock-on effects to the blood-brain barrier, brain-spinal barrier, blood-cerebrospinal fluid barrier, neuro-axonal structures, neurotransmitter activity, synaptic plasticity, neuroendocrine function, and resultant systemic symptomatology. It is concurred that the inflammatory process associated with cancer and cancer treatments underline systemic symptoms present in a large portion of survivors, although this concept is largely theoretical from disparate and indirect evidence and/or clinical anecdotal reports. We conducted a proof-of-concept study to link for the first time late non-CNS cancer survivors presenting chronic systemic symptoms and the presence of centralized inflammation, or neuroinflammation, using TSPO-binding PET tracer [11 C]-PBR28 to visualize microglial activation. We compared PBR28 SUVR in 10 non-CNS cancer survivors and 10 matched healthy controls. Our data revealed (1) microglial activation was significantly higher in caudate, temporal, and occipital regions in late non-central nervous system/CNS cancer survivors compared to healthy controls; (2) increased neuroinflammation in cancer survivors was not accompanied by significant differences in plasma cytokine markers of peripheral inflammation; (3) increased neuroinflammation was not accompanied by reduced fractional anisotropy, suggesting intact white matter microstructural integrity, a marker of neurovascular fiber tract organization; and (4) the presentation of chronic systemic symptoms in cancer survivors was significantly connected with microglial activation. We present the first data empirically supporting the concept of a peripheral-to-centralized inflammatory response in non-CNS cancer survivors, specifically those previously afflicted with head and neck cancer. Following resolution of the initial peripheral inflammation from the cancer/its treatments, in some cases damage/toxification to the central nervous system occurs, ensuing chronic systemic symptoms.

Mechanisms linking neurological disorders with reproductive endocrine dysfunction: Insights from epilepsy research

Gonadal hormone actions in the brain can both worsen and alleviate symptoms of neurological disorders. Although neurological conditions and reproductive endocrine function are seemingly disparate, compelling evidence indicates that reciprocal interactions exist between certain disorders and hypothalamic-pituitary-gonadal (HPG) axis irregularities. Epilepsy is a neurological disorder that shows significant reproductive endocrine dysfunction (RED) in clinical populations. Seizures, particularly those arising from temporal lobe structures, can drive HPG axis alterations, and hormones produced in the HPG axis can reciprocally modulate seizure activity. Despite this relationship, mechanistic links between seizures and RED, and vice versa, are still largely unknown. Here, we review clinical evidence alongside recent investigations in preclinical animal models into the contributions of seizures to HPG axis malfunction, describe the effects of HPG axis hormonal feedback on seizure activity, and discuss how epilepsy research can offer insight into mechanisms linking neurological disorders to HPG axis dysfunction, an understudied area of neuroendocrinology.

From Pathogenesis to Therapeutics: A Review of 150 Years of Huntington's Disease Research

Huntington's disease (HD) is a debilitating neurodegenerative genetic disorder caused by an expanded polyglutamine-coding (CAG) trinucleotide repeat in the huntingtin (HTT) gene. HD behaves as a highly penetrant dominant disorder likely acting through a toxic gain of function by the mutant huntingtin protein. Widespread cellular degeneration of the medium spiny neurons of the caudate nucleus and putamen are responsible for the onset of symptomology that encompasses motor, cognitive, and behavioural abnormalities. Over the past 150 years of HD research since George Huntington published his description, a plethora of pathogenic mechanisms have been proposed with key themes including excitotoxicity, dopaminergic imbalance, mitochondrial dysfunction, metabolic defects, disruption of proteostasis, transcriptional dysregulation, and neuroinflammation. Despite the identification and characterisation of the causative gene and mutation and significant advances in our understanding of the cellular pathology in recent years, a disease-modifying intervention has not yet been clinically approved. This review includes an overview of Huntington's disease, from its genetic aetiology to clinical presentation and its pathogenic manifestation. An updated view of molecular mechanisms and the latest therapeutic developments will also be discussed.

Excessive response to provocation rather than disinhibition mediates irritable behaviour in Huntington's disease

Background

Irritable and impulsive behaviour are common in Huntington's disease (HD: an autosomal dominant disorder causing degeneration in cortico-striatal networks). However, the cognitive mechanisms underlying these symptoms remain unclear, and previous research has not determined if common mechanisms underpin both symptoms. Here we used established and novel tasks to probe different aspects of irritable and impulsive behaviour to determine the neural mechanisms involved.

Methods

We recruited a cohort of 53 gene positive HD participants and 26 controls from non-affected family members and local volunteers. We used established questionnaire measures of irritability in HD (Snaith Irritability Scale, Problem Behaviours Assessment) and impulsivity [Urgency, Premeditation Perseverance, Sensation-seeking, Positive urgency scale (UPPSP), Barratt Impulsivity Scale], in addition to cognitive tasks of provocation, motor inhibition, delay discounting and decision making under uncertainty. We used generalised linear models to determine differences between cases and controls, and associations with irritability in the HD group.

Results

We found differences between cases and controls on the negative urgency subscale of the UPPSP, which was associated with irritability in HD. The frustrative non-reward provocation task also showed differences between cases and controls, in addition to predicting irritability in HD. The stop signal reaction time task showed case-control differences but was not associated with irritability in HD. None of the other measures showed group differences or predicted irritability in HD after correcting for confounding variables.

Discussion

Irritability in HD is mediated by excessive response to provocation, rather than a failure of motor inhibition.

Clinical Spectrum and Trajectory of Innovative Therapeutic Interventions for Insomnia: A Perspective

Increasing incidences of insomnia in adults, as well as the aging population, have been reported for their negative impact on the quality of life. Insomnia episodes may be associated with neurocognitive, musculoskeletal, cardiovascular, gastrointestinal, renal, hepatic, and metabolic disorders. Epidemiological evidence also revealed the association of insomnia with oncologic and asthmatic complications, which has been indicated as bidirectional. Two therapeutic approaches including cognitive behavioral therapy (CBT) and drugs-based therapies are being practiced for a long time. However, the adverse events associated with drugs limit their wide and long-term application. Further, Traditional Chinese medicine, acupressure, and pulsed magnetic field therapy may also provide therapeutic relief. Notably, the recently introduced cryotherapy has been demonstrated as a potential candidate for insomnia which could reduce pain, by suppressing oxidative stress and inflammation. It seems that the synergistic therapeutic approach of cryotherapy and the above-mentioned approaches might offer promising prospects to further improve efficacy and safety. Considering these facts, this perspective presents a comprehensive summary of recent advances in pathological aetiologies of insomnia including COVID-19, and its therapeutic management with a greater emphasis on cryotherapy.

Microarray profiling of hypothalamic gene expression changes in Huntington’s disease mouse models

Structural changes and neuropathology in the hypothalamus have been suggested to contribute to the non-motor manifestations of Huntington’s disease (HD), a neurodegenerative disorder caused by an expanded cytosine-adenine-guanine (CAG) repeat in the huntingtin (HTT) gene. In this study, we investigated whether hypothalamic HTT expression causes transcriptional changes. Hypothalamic RNA was isolated from two different HD mouse models and their littermate controls; BACHD mice with ubiquitous expression of full-length mutant HTT (mHTT) and wild-type mice with targeted hypothalamic overexpression of either wild-type HTT (wtHTT) or mHTT fragments. The mHTT and wtHTT groups showed the highest number of differentially expressed genes compared to the BACHD mouse model. Gene Set Enrichment Analysis (GSEA) with leading-edge analysis showed that suppressed sterol- and cholesterol metabolism were shared between hypothalamic wtHTT and mHTT overexpression. Most distinctive for mHTT overexpression was the suppression of neuroendocrine networks, in which qRT-PCR validation confirmed significant downregulation of neuropeptides with roles in feeding behavior; hypocretin neuropeptide precursor (Hcrt), tachykinin receptor 3 (Tacr3), cocaine and amphetamine-regulated transcript (Cart) and catecholamine-related biological processes; dopa decarboxylase (Ddc), histidine decarboxylase (Hdc), tyrosine hydroxylase (Th), and vasoactive intestinal peptide (Vip). In BACHD mice, few hypothalamic genes were differentially expressed compared to age-matched WT controls. However, GSEA indicated an enrichment of inflammatory- and gonadotropin-related processes at 10 months. In conclusion, we show that both wtHTT and mHTT overexpression change hypothalamic transcriptome profile, specifically mHTT, altering neuroendocrine circuits. In contrast, the ubiquitous expression of full-length mHTT in the BACHD hypothalamus moderately affects the transcriptomic profile.

Inflammasome activation and assembly in Huntington's disease

Huntington's disease (HD) is a rare neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. Inflammasomes are multiprotein complexes capable of sensing pathogen-associated and damage-associated molecular patterns, triggering innate immune pathways. Activation of inflammasomes results in a pro-inflammatory cascade involving, among other molecules, caspases and interleukins. NLRP3 (nucleotide-binding domain, leucine-rich-repeat containing family, pyrin domain-containing 3) is the most studied inflammasome complex, and its activation results in caspase-1 mediated cleavage of the pro-interleukins IL-1β and IL-18 into their mature forms, also inducing a gasdermin D mediated form of pro-inflammatory cell death, i.e. pyroptosis. Accumulating evidence has implicated NLRP3 inflammasome complex in neurodegenerative diseases. The evidence in HD is still scant and mostly derived from pre-clinical studies. This review aims to present the available evidence on NLRP3 inflammasome activation in HD and to discuss whether targeting this innate immune system complex might be a promising therapeutic strategy to alleviate its symptoms.

Oxytocin in Huntington’s disease and the spectrum of amyotrophic lateral sclerosis-frontotemporal dementia

Neurodegenerative disorders (NDDs) such as Huntington’s disease (HD) and the spectrum of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by progressive loss of selectively vulnerable populations of neurons. Although often associated with motor impairments, these NDDs share several commonalities in early symptoms and signs that extend beyond motor dysfunction. These include impairments in social cognition and psychiatric symptoms. Oxytocin (OXT) is a neuropeptide known to play a pivotal role in the regulation of social cognition as well as in emotional behaviors such as anxiety and depression. Here, we present an overview of key results implicating OXT in the pathology of HD, ALS and FTD and seek to identify commonalities across these NDDs. OXT is produced in the hypothalamus, a region in the brain that during the past decade has been shown to be affected in HD, ALS, and FTD. Several studies using human post-mortem neuropathological analyses, measurements of cerebrospinal fluid, experimental treatments with OXT as well as genetic animal models have collectively implicated an important role of central OXT in the development of altered social cognition and psychiatric features across these diseases. Understanding central OXT signaling may unveil the underlying mechanisms of early signs of the social cognitive impairment and the psychiatric features in NDDs. It is therefore possible that OXT might have potential therapeutic value for early disease intervention and better symptomatic treatment in NDDs.

IKKβ signaling mediates metabolic changes in the hypothalamus of a Huntington disease mouse model

Huntington disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Metabolic changes are associated with HD progression, but underlying mechanisms are not fully known. As the IKKβ/NF-κB pathway is an essential regulator of metabolism, we investigated the involvement of IKKβ, the upstream activator of NF-κB in hypothalamus-specific HD metabolic changes. We expressed amyloidogenic N-terminal fragments of mutant HTT (mHTT) in the hypothalamus of mice with brain-specific ablation of IKKβ (Nestin/IKKβ^lox/lox) and control mice (IKKβ^lox/lox). We assessed effects on body weight, metabolic hormones, and hypothalamic neuropathology. Hypothalamic expression of mHTT led to an obese phenotype only in female mice. CNS-specific inactivation of IKKβ prohibited weight gain in females, which was independent of neuroprotection and microglial activation. Our study suggests that mHTT in the hypothalamus causes metabolic imbalance in a sex-specific fashion, and central inhibition of the IKKβ pathway attenuates the obese phenotype.

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Mutant huntingtin in the hypothalamus causes sex-specific metabolic imbalance

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CNS-specific inactivation of the IKKβ pathway prevents the obese phenotype

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IKKβ inactivation leads to an increased number of mutant huntingtin inclusions

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IKKβ inactivation does not prevent orexin or A13 TH neuron loss

Effects of mutant huntingtin inactivation on Huntington disease-related behaviours in the BACHD mouse model

AIMS

Huntington disease (HD) is a fatal neurodegenerative disorder with no disease-modifying treatments approved so far. Ongoing clinical trials are attempting to reduce huntingtin (HTT) expression in the central nervous system (CNS) using different strategies. Yet, the distribution and timing of HTT-lowering therapies required for a beneficial clinical effect is less clear. Here, we investigated whether HD-related behaviours could be prevented by inactivating mutant HTT at different disease stages and to varying degrees in an experimental model.

METHODS

We generated mutant BACHD mice with either a widespread or circuit-specific inactivation of mutant HTT by using Cre recombinase (Cre) under the nestin promoter or the adenosine A2A receptor promoter respectively. We also simulated a clinical gene therapy scenario with allele-specific HTT targeting by injections of recombinant adeno-associated viral (rAAV) vectors expressing Cre into the striatum of adult BACHD mice. All mice were assessed using behavioural tests to investigate motor, metabolic and psychiatric outcome measures at 4-6 months of age.

RESULTS

While motor deficits, body weight changes, anxiety and depressive-like behaviours are present in BACHD mice, early widespread CNS inactivation during development significantly improves rotarod performance, body weight changes and depressive-like behaviour. However, conditional circuit-wide mutant HTT deletion from the indirect striatal pathway during development and focal striatal-specific deletion in adulthood failed to rescue any of the HD-related behaviours.

CONCLUSIONS

Our results indicate that widespread targeting and the timing of interventions aimed at reducing mutant HTT are important factors to consider when developing disease-modifying therapies for HD.

Microglia Activation in Basal Ganglia Is a Late Event in Huntington Disease Pathophysiology

OBJECTIVE

To define the role played by microglia in different stages of Huntington disease (HD), we used the TSPO radioligand [11C]-ER176 and PET to evaluate microglial activation in relation to neurodegeneration and in relation to the clinical features seen at premanifest and manifest stages of the disease.

METHODS

This is a cross-sectional study in which 18 subjects (6 controls, 6 premanifest, and 6 manifest HD gene carriers) underwent a [11C]-ER176 PET scan and an MRI for anatomic localization. Segmentation of regions of interest (ROIs) was performed, and group differences in [11C]-ER176 binding (used to evaluate the extent of microglial activation) were assessed by the standardized uptake value ratio (SUVR). Microglial activation was correlated with ROIs volumes, disease burden, and the scores obtained in the clinical scales. As an exploratory aim, we evaluated the dynamic functions of microglia in vitro, by using induced microglia-like (iMG) cells from peripheral blood monocytes.

RESULTS

Individuals with manifest HD present higher [11C]-ER176 SUVR in both globi pallidi and putamina in comparison with controls. No differences were observed when we compared premanifest HD with controls or with manifest HD. We also found a significant correlation between increased microglial activation and cumulative disease burden, and with reduced volumes. iMG from controls, premanifest HD, and manifest HD patients showed similar phagocytic capacity.

CONCLUSIONS

Altogether, our data demonstrate that microglial activation is involved in HD pathophysiology and is associated with disease progression.

Hair and salivary cortisol and their relationship with lifestyle, mood and cognitive outcomes in premanifest Huntington's disease

Salivary cortisol dysrhythmias have been reported in some, but not all studies assessing hypothalamic-pituitary-adrenal (HPA) axis function in Huntington's disease (HD). These differences are presumed to be due to environmental influences on temporal salivary cortisol measurement. Further exploration of HPA-axis function using a more stable and longer-term measure, such as hair cortisol, is needed to confirm earlier findings. This study aimed to evaluate hair and salivary cortisol concentrations and their associations with clinical and lifestyle outcomes in individuals with premanifest HD (n = 26) compared to healthy controls (n = 14). Participants provided saliva and hair samples and data were collected on clinical disease outcomes, mood, cognition, physical activity, cognitive reserve, sleep quality and social network size to investigate relationships between clinical and lifestyle outcomes and cortisol concentrations. Hair and salivary cortisol concentrations did not significantly differ between the premanifest HD and control groups. No significant associations were observed between hair or salivary cortisol concentrations and cognitive, mood or lifestyle outcomes. However, hair cortisol concentrations were significantly associated with disease outcomes in individuals with premanifest HD. Significant associations between hair cortisol concentrations and measures of disease burden and onset may suggest a potential disease marker and should be explored longitudinally in a larger sample of individuals with HD.

Carbon-11: Radiochemistry and Target-Based PET Molecular Imaging Applications in Oncology, Cardiology, and Neurology

The positron emission tomography (PET) molecular imaging technique has gained its universal value as a remarkable tool for medical diagnosis and biomedical research. Carbon-11 is one of the promising radiotracers that can report target-specific information related to its pharmacology and physiology to understand the disease status. Currently, many of the available carbon-11 (t_1/2 = 20.4 min) PET radiotracers are heterocyclic derivatives that have been synthesized using carbon-11 inserted different functional groups obtained from primary and secondary carbon-11 precursors. A spectrum of carbon-11 PET radiotracers has been developed against many of the upregulated and emerging targets for the diagnosis, prognosis, prediction, and therapy in the fields of oncology, cardiology, and neurology. This review focuses on the carbon-11 radiochemistry and various target-specific PET molecular imaging agents used in tumor, heart, brain, and neuroinflammatory disease imaging along with its associated pathology.

Quantification of Huntington's Disease Related Markers in the R6/2 Mouse Model

Huntington’s disease (HD) is caused by an expansion of CAG triplets in the huntingtin gene, leading to severe neuropathological changes that result in a devasting and lethal phenotype. Neurodegeneration in HD begins in the striatum and spreads to other brain regions such as cortex and hippocampus, causing motor and cognitive dysfunctions. To understand the signaling pathways involved in HD, animal models that mimic the human pathology are used. The R6/2 mouse as model of HD was already shown to present major neuropathological changes in the caudate putamen and other brain regions, but recently established biomarkers in HD patients were yet not analyzed in these mice. We therefore performed an in-depth analysis of R6/2 mice to establish new and highly translational readouts focusing on Ctip2 as biological marker for motor system-related neurons and translocator protein (TSPO) as a promising readout for early neuroinflammation. Our results validate already shown pathologies like mutant huntingtin aggregates, ubiquitination, and brain atrophy, but also provide evidence for decreased tyrosine hydroxylase and Ctip2 levels as indicators of a disturbed motor system, while vesicular acetyl choline transporter levels as marker for the cholinergic system barely change. Additionally, increased astrocytosis and activated microglia were observed by GFAP, Iba1 and TSPO labeling, illustrating, that TSPO is a more sensitive marker for early neuroinflammation compared to GFAP and Iba1. Our results thus demonstrate a high sensitivity and translational value of Ctip2 and TSPO as new marker for the preclinical evaluation of new compounds in the R6/2 mouse model of HD.

Hypothalamic pathology in Huntington disease

Huntington's disease (HD), an autosomal dominant hereditary disorder associated with the accumulation of mutant huntingtin, is classically associated with cognitive decline and motor symptoms, notably chorea. However, growing evidence suggests that nonmotor symptoms are equally prevalent and debilitating. Some of these symptoms may be linked to hypothalamic pathology, demonstrated by findings in HD animal models and HD patients showing specific changes in hypothalamic neuropeptidergic populations and their associated functions. At least some of these alterations are likely due to local mutant huntingtin expression and toxicity, while others are likely caused by disturbed hypothalamic circuitry. Common problems include circadian rhythm disorders, including desynchronization of daily hormone excretion patterns, which could be targeted by novel therapeutic interventions, such as timed circadian interventions with light therapy or melatonin. However, translation of these findings from bench-to-bedside is hampered by differences in murine HD models and HD patients, including mutant huntingtin trinucleotide repeat length, which is highly heterogeneous across the various models. In this chapter, we summarize the current knowledge regarding hypothalamic alterations in HD patients and animal models, and the potential for these findings to be translated into clinical practice and management.

Retina and melanopsin neurons

Melanopsin retinal ganglion cells (mRGCs) are the third class of retinal photoreceptors with unique anatomical, electrophysiological, and biological features. There are different mRGC subtypes with differential projections to the brain. These cells contribute to many nonimage-forming functions of the eye, the most relevant being the photoentrainment of circadian rhythms through the projections to the suprachiasmatic nucleus of the hypothalamus. Other relevant biological functions include the regulation of the pupillary light reflex, mood, alertness, and sleep, as well as a possible role in formed vision. The relevance of the mRGC-related pathways in the brain is highlighted by the role that the dysfunction and/or loss of these cells may play in affecting circadian rhythms and sleep in many neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease and in aging. Moreover, the occurrence of circadian dysfunction is a known risk factor for dementia. In this chapter, the anatomy, physiology, and functions of these cells as well as their resistance to neurodegeneration in mitochondrial optic neuropathies or their predilection to be lost in other neurodegenerative disorders will be discussed.

The sleep and circadian problems of Huntington's disease: when, why and their importance

Introduction

Mounting evidence supports the existence of an important feedforward cycle between sleep and neurodegeneration, wherein neurodegenerative diseases cause sleep and circadian abnormalities, which in turn exacerbate and accelerate neurodegeneration. If so, sleep therapies bear important potential to slow progression in these diseases.

Findings

This cycle is challenging to study, as its bidirectional nature renders cause difficult to disentangle from effect. Likewise, well-controlled intervention studies are often impractical in the setting of established neurodegenerative disease. It is this that makes understanding sleep and circadian abnormalities in Huntington’s disease (HD) important: as a monogenic fully penetrant neurodegenerative condition presenting in midlife, it provides a rare opportunity to study sleep and circadian abnormalities longitudinally, prior to and throughout disease manifestation, and in the absence of confounds rendered by age and comorbidities. It also provides potential to trial sleep therapies at a preclinical or early disease stage. Moreover, its monogenic nature facilitates the development of transgenic animal models through which to run parallel pre-clinical studies. HD, therefore, provides a key model condition through which to gain new insights into the sleep-neurodegeneration interface.

Conclusions

Here, we begin by summarising contemporary knowledge of sleep abnormalities in HD, and consider how well these parallel those of Alzheimer’s and Parkinson’s as more common neurodegenerative conditions. We then discuss what is currently known of the sleep-neurodegeneration cyclical relationship in HD. We conclude by outlining key directions of current and future investigation by which to advance the sleep-neurodegeneration field via studies in HD.

The Therapeutic Potential of Neuronal K-Cl Co-Transporter KCC2 in Huntington's Disease and Its Comorbidities

Intracellular chloride levels in the brain are regulated primarily through the opposing effects of two cation-chloride co-transporters (CCCs), namely K+-Cl- co-transporter-2 (KCC2) and Na+-K+-Cl- co-transporter-1 (NKCC1). These CCCs are differentially expressed throughout the course of development, thereby determining the excitatory-to-inhibitory γ-aminobutyric acid (GABA) switch. GABAergic excitation (depolarisation) is important in controlling the healthy development of the nervous system; as the brain matures, GABAergic inhibition (hyperpolarisation) prevails. This developmental switch in excitability is important, as uncontrolled regulation of neuronal excitability can have implications for health. Huntington's disease (HD) is an example of a genetic disorder whereby the expression levels of KCC2 are abnormal due to mutant protein interactions. Although HD is primarily considered a motor disease, many other clinical manifestations exist; these often present in advance of any movement abnormalities. Cognitive change, in addition to sleep disorders, is prevalent in the HD population; the effect of uncontrolled KCC2 function on cognition and sleep has also been explored. Several mechanisms by which KCC2 expression is reduced have been proposed recently, thereby suggesting extensive investigation of KCC2 as a possible therapeutic target for the development of pharmacological compounds that can effectively treat HD co-morbidities. Hence, this review summarizes the role of KCC2 in the healthy and HD brain, and highlights recent advances that attest to KCC2 as a strong research and therapeutic target candidate.

Imbalance of the oxytocin-vasopressin system contributes to the neuropsychiatric phenotype in the BACHD mouse model of Huntington disease

Neuropsychiatric disturbances with altered social cognition, depression and anxiety are among the most debilitating early features in the fatal neurodegenerative disorder Huntington disease (HD) which is caused by an expanded CAG repeat in the huntingtin gene. The underlying neurobiological mechanisms are not known. Neuropathological analyses of postmortem human HD hypothalamic tissue have demonstrated loss of the neuropeptides oxytocin and vasopressin. The dynamic interplay between these neuropeptides is crucial for modulating emotional and social behavior but its role in HD is unclear. In the present study, we have investigated the effect of expressing the mutant huntingtin gene on the development of behavioral changes using the transgenic BACHD mouse model at different ages. We show for the first time that BACHD mice exhibit deficits in social behavior with parallel aberrations in the balance of the oxytocin-vasopressin system. Importantly, our data also show that restoration of the interplay within the system with an acute dose of intranasal oxytocin immediately prior to behavioral testing can rescue the depressive-like phenotype but not anxiety-like behavior in this transgenic model. These findings demonstrate that imbalances in the oxytocin-vasopressin interplay contribute to the neuropsychiatric component of HD and suggest that interventions aimed at restoring the blunted levels of oxytocin may confer therapeutic benefits for this disease.

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.

Deterioration of neuroregenerative plasticity in association with testicular atrophy and dysregulation of the hypothalamic-pituitary-gonadal (HPG) axis in Huntington's disease: A putative role of the huntingtin gene in steroidogenesis

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder mainly affecting the structure and functions of the striatum, cerebral cortex and hippocampus leading to movement disorders, cognitive dysfunctions and emotional disturbances. The onset of HD has been linked to a pathogenic CAG repeat expansion in the huntingtin (HTT) gene that encodes for the polyglutamine (polyQ) stretches in the huntingtin (Htt) protein. Notably, the neuropathogenic events of the mutant HTT gene appear to be primed during adulthood and magnified along the ageing process. While the normal Htt protein is vital for the neuronal differentiation and neuroprotection, experimental HD models and postmortem human HD brains have been characterized by neurodegeneration and defects in neuroregenerative plasticity in the basal ganglia and limbic system including the hippocampus. Besides gonadal dysfunctions, reduced androgen levels and abnormal hypothalamic-pituitary-gonadal (HPG) axis have increasingly been evident in HD. Recently, ageing-related changes in levels of steroid sex hormones have been proposed to play a detrimental effect on the regulation of hippocampal neurogenesis in the adult brain. Considering its adult-onset nature, a potential relationship between dysregulation in the synthesis of sex steroid hormones and the pathogenesis of the mutant HTT gene appears to be an important clinical issue in HD. While the hippocampus and testis are the major sites of steroidogenesis, the presence of Htt in both areas is conclusively evident. Hence, the expression of the normal HTT gene may take part in the steroidogenic events in aforementioned organs in the physiological state, whereas the mutant HTT gene may cause defects in steroidogenesis in HD. Therefore, this review article comprehends the potential relationship between the gonadal dysfunctions and abnormal hippocampal plasticity in HD and represents a hypothesis for the putative role of the HTT gene in the regulation of steroidogenesis in gonads and in the brain.

Extending the Phenotypic Spectrum of Huntington Disease: Hypothermia

Huntington disease (HD) is an autosomal dominant progressive neurodegenerative disorder associated with expanded CAG repeat size in the huntingtin gene and usually presenting with movement disorder, psychiatric symptoms, and cognitive decline. Sleep problems, weight loss, and cachexia are also common. Here, we report a patient presenting with hypothermia in late-stage HD. Although thermoregulatory defects were documented in animal models, this is the first report describing HD with hypothermia in humans.

Neuroendocrine Disturbances in Neurodegenerative Disorders: A Scoping Review

BACKGROUND

Neurodegenerative diseases cause progressive irreversible neuronal loss that has broad downstream effects. The neuroendocrine system regulates homeostasis of circuits that control critical functions such as the stress response, metabolism, reproduction, fluid balance, and glucose control. These systems are frequently disrupted in neurodegenerative disorders yet often overlooked in clinical practice.

OBJECTIVE

This review aims to gather the available data regarding these disturbances in Alzheimer's disease, Parkinson's disease, frontotemporal dementia, amyotrophic lateral sclerosis, and Huntington's disease and also to demonstrate the volume of literature in these individual arenas.

METHODS

Using the scoping review framework, a literature search was performed in PubMed to identify relevant articles published within the past 30 years (January 1988 to November 2018). The search criteria produced a total of 2022 articles, 328 of which were identified as relevant to this review.

RESULTS

Several major themes emerged from this review. These neuroendocrine disturbances may be a precursor to the illness, a part of the primary pathophysiology, or a direct consequence of the disease or independent of it. They have the potential to further understanding of the disease, exacerbate the underlying pathology, or provide therapeutic benefit.

CONCLUSIONS

By synthesizing the data from a systems' perspective, we aim to broaden how clinicians think about these illnesses and provide care.

Multidisciplinary rehabilitation reduces hypothalamic grey matter volume loss in individuals with preclinical Huntington's disease: A nine-month pilot study

BACKGROUND

Hypothalamic pathology is a well-documented feature of Huntington's disease (HD) and is believed to contribute to circadian rhythm and habitual sleep disturbances. Currently, no therapies exist to combat hypothalamic changes, nor circadian rhythm and habitual sleep disturbances in HD.

OBJECTIVE

To evaluate the effects of multidisciplinary rehabilitation on hypothalamic volume, brain-derived neurotrophic factor (BDNF), circadian rhythm and habitual sleep in individuals with preclinical HD.

METHODS

Eighteen individuals with HD (ten premanifest and eight prodromal) undertook a nine-month multidisciplinary rehabilitation intervention (intervention group), which included exercise, cognitive and dual task training and social events, and were compared to a community sample of eleven individuals with premanifest HD receiving no intervention (control group). Hypothalamic volume, serum BDNF, salivary cortisol and melatonin concentrations, subjective sleep quality, daytime somnolence, habitual sleep-wake patterns, stress and anxiety and depression symptomatology were evaluated.

RESULTS

Hypothalamus grey matter volume loss was significantly attenuated in the intervention group compared to the control group after controlling for age, gender, Unified Huntington's Disease Rating Scale-Total Motor Score and number of cytosine-adenine-guanine repeats. Serum BDNF levels were maintained in the intervention group, but decreased in the control group following the study period. Both groups exhibited decreases in cortisol and melatonin concentrations. No changes were observed in sleep or mood outcomes.

CONCLUSIONS

This exploratory study provides evidence that multidisciplinary rehabilitation can reduce hypothalamic volume loss and maintain peripheral BDNF levels in individuals with preclinical HD but may not impact on circadian rhythm. Larger, randomised controlled trials are required to confirm these findings.

Morphological MRI investigations of the hypothalamus in 232 individuals with Parkinson's disease

BACKGROUND

The pathophysiology of the hypothalamic involvement in Parkinson's disease (PD) is not well understood. The objective of this study was the quantification of hypothalamic volumes in vivo in PD.

METHODS

High-resolution T₁ -weighted magnetic resonance imaging (MRI) data from 232 individuals with PD and 130 healthy non-PD individuals were used for quantification of the hypothalamic volumes.

RESULTS

The hypothalamus in PD was not atrophied, as indicated by volumetric analyses in the prospectively collected subcohort (30 PD, V = 921 ± 78 mm³ vs 30 non-PD, V = 917 ± 67 mm³ ; P = 0.850) and validated in a large cohort (202 PD, V = 925 ± 88 mm³ vs 100 non-PD, V = 932 ± 114 mm³ ; P = 0.602).

CONCLUSIONS

Hypothalamic involvement in PD as shown by a large body of histopathological evidence does not appear to be detectable by MRI-based volumetric quantification. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The Panomics Approach in Neurodegenerative Disorders

BACKGROUND

The molecular genetic technologies revolutionized the diagnostics of many disorders. Thanks to the new molecular techniques and the rapid improvement of the information technologies the number of mendelien inherited disorders has increased rapidly in the last five years. The omics era brought radical changes in the understanding of complex disorders and the underlying pathomechanisms. However, in most complex disorders the genome wide association studies could not clarify the genetic background even for disorders where a very strong heritability had been observed.

OBJECTIVE

In this paper the changing concept of the neurodegenerative disorders is discussed. The traditional classification of these disorders was purely based on clinical symptoms and morphological signs in the last century. Identifying the signature lesions of various neurodegenerative disorders may reveal a common pathological pathway in these disorders. New neuroimaging methods provided additional tools to assess pathological pathways in vivo already in the early stages of the diseases. Visualizing in vivo amyloid deposits and neuroinflammation improved our understanding of their role in various neurodegenerative disorders. Genetics may be the most precise way to identify the background of these disorders. However, there is only limited number of cases where true association can be proved between the disorder and the genetic mutations. Most of the neurodegenerative disorders seem to be multifactorial and cannot be traced back to one single cause.

CONCLUSION

In conclusion, shifting from a classification based on symptomatology only to a modern multidisciplinary approach, based on the constantly evolving panomics findings, would improve our understanding of neurodegenerative diseases and could be the basis of novel therapeutic research.

Sleep Disorders in Huntington's Disease

Huntington's chorea (Huntington's disease, HD) is a genetic disorder caused by autosomal dominant mutation, leading to progressive neurodegenerative changes in the central nervous system. Involuntary movements such as chorea occur typically in HD patients, accompanied by progressive cognitive and psychiatric disturbances. Other common symptoms of HD are circadian and sleep abnormalities, which are observed from the earliest stages of the disease or even before the occurrence of clinical symptoms. The most common sleep problems reported by HD patients include insomnia, difficulties in falling asleep, frequent nocturnal awakenings, and excessive daytime sleepiness. Also, specific changes in sleep architecture have been identified in HD. In this paper, we review studies on sleep and circadian rhythm disorders in HD. We outline findings concerning sleep patterns and disturbances of circadian rhythms in HD patients, as well as the role of psychiatric disorders and motor disorders in HD patients' sleep problems. We also discuss problems related to the different methods of diagnosing sleep disorders in HD. Furthermore, the adverse effects of medication used for the treatment of core HD symptoms as one of the sources of sleep disturbances in HD are emphasized. In conclusion, the diversity and complexity of the determinants of sleep and circadian rhythm disorders in HD are highlighted. Finally, the relevance of effective treatment to improve patients' functioning and quality of life as well as the potential relief of their cognitive and emotional symptoms is addressed.

Neuroinflammation in Huntington's Disease: New Insights with 11C-PBR28 PET/MRI

Huntington's disease is a devastating neurodegenerative genetic disorder that causes progressive motor dysfunction, emotional disturbances, and cognitive impairment. Unfortunately, there is no treatment to cure or slow the progression of the disease. Neuroinflammation is one hallmark of Huntington's disease, and modulation of neuroinflammation has been suggested as a potential target for therapeutic intervention. The relationship between neuroinflammation markers and the disease pathology is still poorly understood. To improve our understanding of neuroinflammation in Huntington's disease, we measured translocator protein (TSPO) expression using ¹¹C-PBR28 and simultaneous PET/MRI. Standardized-uptake-value ratios, normalized by whole brain uptake, were calculated for data acquired 60-90 min after radiotracer administration. We identified distinct patterns of regional neuroinflammation (as defined by TSPO overexpression relative to a control group) in the basal ganglia of Huntington's disease patients. These patterns were observed at the individual level in all patients, with region of interest analysis confirming significant differences between patients and the control group in the putamen and the pallidum. Additionally, we observed further distinct regional and subregional signatures, which may provide insights into phenotypical variability. For example, in certain Huntington's disease patients, we observed in vivo elevation of the level of TSPO binding in subnuclei in the thalamus and brainstem that have been previously associated with visual function, motor function, and motor coordination. Our main result is an objective score, based solely on ¹¹C-PBR28 measurements, that correlates well with measurements of brain atrophy. We conclude that PET/MR imaging using ¹¹C-PBR28 provides a high signal-to-background ratio and has the potential to be used to assess Huntington's disease progression. Our results suggest ¹¹C-PBR28 might prove useful in clinical trials evaluating therapies targeting neuroinflammation.

Molecular Imaging in Huntington's Disease

Huntington's disease (HD) is a rare monogenic neurodegenerative disorder caused by a trinucleotide CAG repeat expansion in the huntingtin gene resulting in the formation of intranuclear inclusions of mutated huntingtin. The accumulation of mutated huntingtin leads to loss of GABAergic medium spiny neurons (MSNs); subsequently resulting in the development of chorea, cognitive dysfunction and psychiatric symptoms. Premanifest HD gene expansion carriers, provide a unique cohort to examine very early molecular changes, occurring before the development of overt symptoms, to elucidate disease pathophysiology and identify reliable biomarkers of HD progression. Positron emission tomography (PET) is a non-invasive molecular imaging technique allowing the evaluation of specific molecular targets in vivo. Selective PET radioligands provide invaluable tools to investigate the role of the dopaminergic system, brain metabolism, microglial activation, phosphodiesterase 10A, and cannabinoid, GABA, adenosine and opioid receptors in HD. PET has been employed to monitor disease progression aiming to identify a reliable biomarker to predict phenoconversion from premanifest to manifest HD.

Hybrid PET-MRI Applications in Movement Disorders

Even before the success of combined positron emission tomography and computed tomography (PET/CT), the neuroimaging community was conceiving the idea to integrate the positron emission tomography (PET), with very high molecular quantitative data but low spatial resolution, and magnetic resonance imaging (MRI), with high spatial resolution. Several technical limitations have delayed the use of a hybrid scanner in neuroimaging studies, including the full integration of the PET detector ring within the MRI system, the optimization of data acquisition, and the implementation of reliable methods for PET attenuation, motion correction, and joint image reconstruction. To be valid and useful in clinical and research settings, this instrument should be able to simultaneously acquire PET and MRI, and generate quantitative parametric PET images comparable to PET-CT. While post hoc co-registration of combined PET and MRI data acquired separately became the most reliable technique for the generation of "fused" PET-MRI images, only hybrid PET-MRI approach allows merging these measurements naturally and correlating them in a temporal manner. Furthermore, hybrid PET-MRI represents the most accurate tool to investigate in vivo the interplay between molecular and functional aspects of brain pathophysiology. Hybrid PET-MRI technology is still in the early stages in the movement disorders field, due to the limited availability of scanners with integrated optimized methodological models. This technology is ideally suited to investigate interactions between resting-state functional/arterial spin labeling MRI and [¹⁸F]FDG PET glucose metabolism in the evaluation of the brain "hubs" particularly vulnerable to neurodegeneration, areas with a high degree of connectivity and associated with an efficient synaptic neurotransmission. In Parkinson's disease, hybrid PET-MRI is also the ideal instrument to deeper explore the relationship between resting-state functional MRI and dopamine release at [¹¹C]raclopride PET challenge, in the identification of early drug-naïve Parkinson's disease patients at higher risk of motor complications and in the evaluation of the efficacy of novel neuroprotective treatment able to restore at the same time the altered resting state and the release of dopamine. In this chapter, we discuss the key methodological aspects of hybrid PET-MRI; the evidence in movement disorders of the key resting-state functional and perfusion MRI; [¹⁸F]FDG PET and [¹¹C]raclopride PET challenge studies; the potential advantages of using hybrid PET-MRI to investigate the pathophysiology of movement disorders and neurodegenerative diseases. Future directions of hybrid PET-MRI will be discussed alongside with up-to-date technological innovations on hybrid systems.

Neuroimaging of Sleep Disturbances in Movement Disorders

Sleep dysfunction is recognized as a distinct clinical manifestation in movement disorders, often reported early on in the disease course. Excessive daytime sleepiness, rapid eye movement sleep behavior disorder and restless leg syndrome, amidst several others, are common sleep disturbances that often result in significant morbidity. In this article, we review the spectrum of sleep abnormalities across atypical Parkinsonian disorders including multiple system atrophy (MSA), progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS), as well as Parkinson's disease (PD) and Huntington's disease (HD). We also explore the current concepts on the neurobiological underpinnings of sleep disorders, including the role of dopaminergic and non-dopaminergic pathways, by evaluating the molecular, structural and functional neuroimaging evidence based on several novel techniques including magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Based on the current state of research, we suggest that neuroimaging is an invaluable tool for assessing structural and functional correlates of sleep disturbances, harboring the ability to shed light on the sleep problems attached to the limited treatment options available today. As our understanding of the pathophysiology of sleep and wake disruption heightens, novel therapeutic approaches are certain to transpire.

SIRT1 is increased in affected brain regions and hypothalamic metabolic pathways are altered in Huntington disease

AIMS

Metabolic dysfunction is involved in modulating the disease process in Huntington disease (HD) but the underlying mechanisms are not known. The aim of this study was to investigate if the metabolic regulators sirtuins are affected in HD.

METHODS

Quantitative real-time polymerase chain reactions were used to assess levels of SIRT1-3 and downstream targets in post mortem brain tissue from HD patients and control cases as well as after selective hypothalamic expression of mutant huntingtin (HTT) using recombinant adeno-associated viral vectors in mice.

RESULTS

We show that mRNA levels of the metabolic regulator SIRT1 are increased in the striatum and the cerebral cortex but not in the less affected cerebellum in post mortem HD brains. Levels of SIRT2 are only increased in the striatum and SIRT3 is not affected in HD. Interestingly, mRNA levels of SIRT1 are selectively increased in the lateral hypothalamic area (LHA) and ventromedial hypothalamus (VMH) in HD. Further analyses of the LHA and VMH confirmed pathological changes in these regions including effects on SIRT1 downstream targets and reduced mRNA levels of orexin (hypocretin), prodynorphin and melanin-concentrating hormone (MCH) in the LHA and of brain-derived neurotrophic factor (BDNF) in the VMH. Analyses after selective hypothalamic expression of mutant HTT suggest that effects on BDNF, orexin, dynorphin and MCH are early and direct, whereas changes in SIRT1 require more widespread expression of mutant HTT.

CONCLUSIONS

We show that SIRT1 expression is increased in HD-affected brain regions and that metabolic pathways are altered in the HD hypothalamus.

TSPO-PET imaging using [18F]PBR06 is a potential translatable biomarker for treatment response in Huntington's disease: preclinical evidence with the p75NTR ligand LM11A-31

Huntington's disease (HD) is an inherited neurodegenerative disorder that has no cure. HD therapeutic development would benefit from a non-invasive translatable biomarker to track disease progression and treatment response. A potential biomarker is using positron emission tomography (PET) imaging with a translocator protein 18 kDa (TSPO) radiotracer to detect microglial activation, a key contributor to HD pathogenesis. The ability of TSPO-PET to identify microglial activation in HD mouse models, essential for a translatable biomarker, or therapeutic efficacy in HD patients or mice is unknown. Thus, this study assessed the feasibility of utilizing PET imaging with the TSPO tracer, [18F]PBR06, to detect activated microglia in two HD mouse models and to monitor response to treatment with LM11A-31, a p75NTR ligand known to reduce neuroinflammation in HD mice. [18F]PBR06-PET detected microglial activation in striatum, cortex and hippocampus of vehicle-treated R6/2 mice at a late disease stage and, notably, also in early and mid-stage symptomatic BACHD mice. After oral administration of LM11A-31 to R6/2 and BACHD mice, [18F]PBR06-PET discerned the reductive effects of LM11A-31 on neuroinflammation in both HD mouse models. [18F]PBR06-PET signal had a spatial distribution similar to ex vivo brain autoradiography and correlated with microglial activation markers: increased IBA-1 and TSPO immunostaining/blotting and striatal levels of cytokines IL-6 and TNFα. These results suggest that [18F]PBR06-PET is a useful surrogate marker of therapeutic efficacy in HD mice with high potential as a translatable biomarker for preclinical and clinical HD trials.

Investigating the relationships between hypothalamic volume and measures of circadian rhythm and habitual sleep in premanifest Huntington's disease

Objective

Pathological changes within the hypothalamus have been proposed to mediate circadian rhythm and habitual sleep disturbances in individuals with Huntington's disease (HD). However, investigations examining the relationships between hypothalamic volume and circadian rhythm and habitual sleep in individuals with HD are sparse. This study aimed to comprehensively evaluate the relationships between hypothalamic pathology and circadian rhythm and habitual sleep disturbances in individuals with premanifest HD.

Methods

Thirty-two individuals with premanifest HD and twenty-nine healthy age- and gender-matched controls participated in this dual-site, cross-sectional study. Magnetic resonance imaging scans were performed to evaluate hypothalamic volume. Circadian rhythm and habitual sleep were assessed via measurement of morning and evening cortisol and melatonin levels, wrist-worn actigraphy, the Consensus Sleep Diary and sleep questionnaires. Information on mood, physical activity levels and body composition were also collected.

Results

Compared to healthy controls, individuals with premanifest HD displayed significantly reduced grey matter volume in the hypothalamus, decreased habitual sleep efficiency and increased awakenings; however, no alterations in morning cortisol or evening melatonin release were noted in individuals with premanifest HD. While differences in the associations between hypothalamic volume and cortisol and melatonin output existed in individuals with premanifest HD compared to healthy controls, no consistent associations were observed between hypothalamic volume and circadian rhythm or habitual sleep outcomes.

Conclusion

While significant differences in associations between hypothalamic volume and cortisol and melatonin existed between individuals with premanifest HD and healthy controls, no differences in circadian markers were observed between the groups. This suggests that circadian regulation is maintained despite hypothalamic pathology, perhaps via neural compensation. Longitudinal studies are required to further understand the relationships between the hypothalamus and circadian rhythm and habitual sleep disturbances in HD as the disease course lengthens.

Clinical utility of FDG-PET in amyotrophic lateral sclerosis and Huntington's disease

AIM

To evaluate the incremental value of FDG-PET over clinical tests in: (i) diagnosis of amyotrophic lateral sclerosis (ALS); (ii) picking early signs of neurodegeneration in patients with a genetic risk of Huntington's disease (HD); and detecting metabolic changes related to cognitive impairment in (iii) ALS and (iv) HD patients.

METHODS

Four comprehensive literature searches were conducted using the PICO model to extract evidence from relevant studies. An expert panel then voted using the Delphi method on these four diagnostic scenarios.

RESULTS

The availability of evidence was good for FDG-PET utility to support the diagnosis of ALS, poor for identifying presymptomatic subjects carrying HD mutation who will convert to HD, and lacking for identifying cognitive-related metabolic changes in both ALS and HD. After the Delphi consensual procedure, the panel did not support the clinical use of FDG-PET for any of the four scenarios.

CONCLUSION

Relative to other neurodegenerative diseases, the clinical use of FDG-PET in ALS and HD is still in its infancy. Once validated by disease-control studies, FDG-PET might represent a potentially useful biomarker for ALS diagnosis. FDG-PET is presently not justified as a routine investigation to predict conversion to HD, nor to detect evidence of brain dysfunction justifying cognitive decline in ALS and HD.

Neurocardiovascular pathology in pre-manifest and early-stage Huntington's disease

BACKGROUND AND PURPOSE

Cardiovascular events are a major cause of early death in the Huntington's disease (HD) population. Dysautonomia as well as deterioration of circadian rhythms can be detected early in the disease progression and can have profound effects on cardiac health. The aim of the present study was to determine if patients with HD and pre-manifest mutation carriers present a higher risk of cardiovascular disease than non-mutation-carrying controls.

METHODS

This was a prospective, cross-sectional, multicentre study of 38 HD mutation carriers (23 pre-manifest and 15 early-stage patients) compared with 38 age- and gender-matched healthy controls. Clinical and epidemiological variables, including the main haematological vascular risk factors, were recorded. Ambulatory blood-pressure monitoring and carotid intima-media thickness (CIMT) measurement were performed to assess autonomic function and as target-organ damage markers.

RESULTS

Most (63.2%) patients with HD (86.7% and 47.8%, respectively, of the early-stage and pre-manifest patients) were non-dippers compared with 23.7% of controls (P = 0.001). CIMT values were in the 75^th percentile in 46.7% and 43.5%, respectively, of the early-stage and pre-manifest patients, whereas none of the controls presented pathological values (P = 0.001 and P = 0.006, respectively). Nocturnal non-dipping was significantly associated with CIMT values in patients (P = 0.002) but not in controls.

CONCLUSIONS

These results suggest that higher cardiovascular risks and target-organ damage are present even in pre-manifest patients. Although larger studies are needed to confirm these findings, clinicians should consider these results in the cardiovascular management of patients with HD.

Striatal molecular alterations in HD gene carriers: a systematic review and meta-analysis of PET studies

BACKGROUND

Over the past years, positron emission tomography (PET) imaging studies have investigated striatal molecular changes in premanifest and manifest Huntington's disease (HD) gene expansion carriers (HDGECs), but they have yielded inconsistent results.

OBJECTIVE

To systematically examine the evidence of striatal molecular alterations in manifest and premanifest HDGECs as measured by PET imaging studies.

METHODS

MEDLINE, ISI Web of Science, Cochrane Library and Scopus databases were searched for articles published until 7 June 2017 that included PET studies in manifest and premanifest HDGECs. Meta-analyses were conducted with random effect models, and heterogeneity was addressed with I² index, controlling for publication bias and quality of study. The primary outcome was the standardised mean difference (SMD) of PET uptakes in the whole striatum, caudate and putamen in manifest and premanifest HDGECs compared with healthy controls (HCs).

RESULTS

Twenty-four out of 63 PET studies in premanifest (n=158) and manifest (n=191) HDGECs and HCs (n=333) were included in the meta-analysis. Premanifest and manifest HDGECs showed significant decreases in dopamine D₂ receptors in caudate (SMD=-1.233, 95% CI -1.753 to -0.713, p<0.0001; SMD=-5.792, 95% CI -7.695 to -3.890, p<0.0001) and putamen (SMD=-1.479, 95% CI -1.965 to -0.992, p<0.0001; SMD=-5.053, 95% CI -6.558 to -3.549, p<0.0001), in glucose metabolism in caudate (SMD=-0.758, 95% CI -1.139 to -0.376, p<0.0001; SMD=-3.738, 95% CI -4.880 to -2.597, p<0.0001) and putamen (SMD=-2.462, 95% CI -4.208 to -0.717, p=0.006; SMD=-1.650, 95% CI -2.842 to -0.458, p<0.001) and in striatal PDE10A binding (SMD=-1.663, 95% CI -2.603 to -0.723, p=0.001; SMD=-2.445, 95% CI -3.371 to -1.519, p<0.001).

CONCLUSIONS

PET imaging has the potential to detect striatal molecular changes even at the early premanifest stage of HD, which are relevant to the neuropathological mechanisms underlying the development of the disease.

Hypothalamic Alterations in Neurodegenerative Diseases and Their Relation to Abnormal Energy Metabolism

Neurodegenerative diseases (NDDs) are disorders characterized by progressive deterioration of brain structure and function. Selective neuronal populations are affected leading to symptoms which are prominently motor in amyotrophic lateral sclerosis (ALS) or Huntington’s disease (HD), or cognitive in Alzheimer’s disease (AD) and fronto-temporal dementia (FTD). Besides the common existence of neuronal loss, NDDs are also associated with metabolic changes such as weight gain, weight loss, loss of fat mass, as well as with altered feeding behavior. Importantly, preclinical research as well as clinical studies have demonstrated that altered energy homeostasis influences disease progression in ALS, AD and HD, suggesting that identification of the pathways leading to perturbed energy balance might provide valuable therapeutic targets Signals from both the periphery and central inputs are integrated in the hypothalamus, a major hub for the control of energy balance. Recent research identified major hypothalamic changes in multiple NDDs. Here, we review these hypothalamic alterations and seek to identify commonalities and differences in hypothalamic involvement between the different NDDs. These hypothalamic defects could be key in the development of perturbations in energy homeostasis in NDDs and further understanding of the underlying mechanisms might open up new avenues to not only treat weight loss but also to ameliorate overall neurological symptoms.

Cognitive dysfunction in Huntington's disease: mechanisms and therapeutic strategies beyond BDNF

One of the main focuses in Huntington's disease (HD) research, as well as in most neurodegenerative diseases, is the development of new therapeutic strategies, as currently there is no treatment to delay or prevent the progression of the disease. Neuronal dysfunction and neuronal death in HD are caused by a combination of interrelated pathogenic processes that lead to motor, cognitive and psychiatric symptoms. Understanding how mutant huntingtin impacts on a plethora of cellular functions could help to identify new molecular targets. Although HD has been classically classified as a neurodegenerative disease affecting voluntary movement, lately cognitive dysfunction is receiving increased attention as it is very invalidating for patients. Thus, an ambitious goal in HD research is to find altered molecular mechanisms that contribute to cognitive decline. In this review, we have focused on those findings related to corticostriatal and hippocampal cognitive dysfunction in HD, as well as on the underlying molecular mechanisms, which constitute potential therapeutic targets. These include alterations in synaptic plasticity, transcriptional machinery and neurotrophic and neurotransmitter signaling.

Thermoregulatory disorders in Huntington disease

Huntington disease (HD) is a paradigmatic autosomal-dominant adult-onset neurodegenerative disease. Since the identification of an abnormal expansion of a trinucleotide repeat tract in the huntingtin gene as the underlying genetic defect, a broad range of transgenic animal models of the disease has become available and these have helped to unravel the relevant molecular pathways in unprecedented detail. Of note, some of the most informative of these models develop thermoregulatory defects such as hypothermia, problems with adaptive thermogenesis, and an altered circadian temperature rhythm. Both central, e.g., in the hypothalamus and peripheral, i.e., the brown adipose tissue and skeletal muscle, problems contribute to the phenotype. Importantly, these structures and pathways are also affected in human HD. Yet, currently the evidence for bona fide thermodysregulation in human HD patients remains anecdotal. This may be due to a lack of reliable tools for monitoring body temperature in an outpatient setting. Regardless, study of the temperature phenotype has contributed to the identification of unexpected molecular targets, such as the PGC-1α pathway.

Circadian rhythm and autonomic dysfunction in presymptomatic and early Huntington's disease

INTRODUCTION

Sleep and circadian rhythm disturbances are common in patients with neurodegenerative diseases such as Huntington's disease (HD). The aim of this study was to evaluate variability in circadian blood pressure (BP) to determine the association between abnormal circadian BP and sleep quality in patients with HD.

METHODS

Cross-sectional, multicenter study of 38 HD mutation carriers (23 premanifest and 15 early stage patients) who were compared to 38 age- and sex-matched controls. BP was evaluated by ambulatory blood pressure monitoring (ABPM). Based on the percentage decrease in nocturnal BP, subjects were classified as either dippers (≥10%) or non-dippers (<10%). Sleep quality and daytime sleepiness were measured, respectively, using the Pittsburgh Sleep Quality Index (PSQI) and the Epworth Daytime Sleepiness Scale (ESS) and the scores on these indices were correlated with the ABPM findings.

RESULTS

Sixty-three percent HD mutation carriers were non-dippers (86.7% of the symptomatic and 47.8% of the premanifest patients) versus 23.7% of controls (p = 0.001). In the HD group, sleep quality was significantly more impaired (PSQI>5) (p = 0.016) with more excessive daytime sleepiness (ESS>9) (p = 0.001) than in the control group. Nocturnal non-dipping was associated with worse sleep quality in patients (p = 0.011) but not in controls.

CONCLUSION

These results show that patients with HD present early disturbances in the circadian rhythm of BP and that this altered nocturnal BP is associated with poor sleep quality. These findings suggest the potential role of subtle hypothalamic dysfunction in this population.

Functional neuroimaging and chorea: a systematic review

Chorea is a hyperkinetic movement disorder consisting of involuntary irregular, flowing movements of the trunk, neck or face. Although Huntington’s disease is the most common cause of chorea in adults, chorea can also result from many other neurodegenerative, metabolic, and autoimmune conditions. While the pathophysiology of these different conditions is quite variable, recent advances in functional imaging have enabled the development of new methods for analysis of brain activity and neuronal dysfunction. In this paper we review the growing body of functional imaging data that has been performed in chorea syndromes and identify particular trends, which can be used to better understand the underlying network changes within the basal ganglia. While it can be challenging to identify whether changes are primary, secondary, or compensatory, identification of these trends can ultimately be useful in diagnostic testing and treatment in many of the conditions that cause chorea.

Beneficial effects of Panax ginseng for the treatment and prevention of neurodegenerative diseases: past findings and future directions

In recent years, several therapeutic drugs have been rationally designed and synthesized based on the novel knowledge gained from investigating the actions of biologically active chemicals derived from foods, plants, and medicinal herbs. One of the major advantages of these naturalistic chemicals is their ability to interact with multiple targets in the body resulting in a combined beneficial effect. Ginseng is a perennial herb (Araliaceae family), a species within the genus Panax, and a highly valued and popular medicinal plant. Evidence for the medicinal and health benefits of Panax ginseng and its components in preventing neurodegeneration has increased significantly in the past decade. The beneficial effects of P. ginseng on neurodegenerative diseases have been attributed primarily to the antioxidative and immunomodulatory activities of its ginsenoside components. Mechanistic studies on the neuroprotective effects of ginsenosides revealed that they act not only as antioxidants but also as modulators of intracellular neuronal signaling and metabolism, cell survival/death genes, and mitochondrial function. The goal of the present paper is to provide a brief review of recent knowledge and developments concerning the beneficial effects as well as the mechanism of action of P. ginseng and its components in the treatment and prevention of neurodegenerative diseases.