The metabolic profile of early Huntington's disease- a combined human and transgenic mouse study

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.

Mitochondrial dysfunction in chromaffin cells from the R6/1 mouse model of Huntington's disease: Impact on exocytosis and calcium current regulation

From a pathogenic perspective, Huntington's disease (HD) is being considered as a synaptopathy. As such, alterations in brain neurotransmitter release occur. As the activity of the sympathoadrenal axis is centrally controlled, deficits in the exocytotic release of catecholamine release may also occur. In fact, in chromaffin cells (CCs) of the adrenal medulla of the R6/1 model of HD, decrease of secretion and altered kinetics of the exocytotic fusion pore have been reported. Those alterations could be linked to mitochondrial deficits occurring in peripheral CCs, similar to those described in brain mitochondria. Here we have inquired about alterations in mitochondrial structure and function and their impact on exocytosis and calcium channel currents (I_Ca). We have monitored various parameters linked to those events, in wild type (WT) and the R6/1 mouse model of HD at a pre-disease stage (2 months age, 2 m), and when motor deficits are present (7 months age, 7 m). In isolated CCs from 7 m and in the adrenal medulla of R6/1 mice, we found the following alterations (with respect 7 m WT mice): (i) augmented fragmented mitochondria and oxidative stress with increased oxidized glutathione; (ii) decreased basal and maximal respiration; (iii) diminution of ATP cell levels; (iv) mitochondrial depolarization; (v) drastic decrease of catecholamine release with poorer potentiation by protonophore FCCP; (vi) decreased I_Ca inhibition by FCCP; and (vii) lesser potentiation by BayK8644 of I_Ca and smaller prolongation of current deactivation. Of note was the fact several of these alterations were already manifested in CCs from 2 m R6/1 mice at pre-disease stages. Based on those results, a plausible hypothesis can be raised in the sense that altered mitochondrial function seems to be an early primary event in HD pathogenesis. This is in line with an increasing number of mitochondrial, metabolic, and inflammatory alterations being recently reported in various HD peripheral tissues.

The updated development of blood-based biomarkers for Huntington's disease

Huntington's disease is a progressive neurodegenerative disease caused by mutation of the huntingtin (HTT) gene. The identification of mutation carriers before symptom onset provides an opportunity to intervene in the early stage of the disease course. Optimal biomarkers are of great value to reflect neuropathological and clinical progression and are sensitive to potential disease-modifying treatments. Blood-based biomarkers have the merits of minimal invasiveness, low cost, easy accessibility and safety. In this review, we summarized the updated development of blood-based biomarkers for HD from six aspects, including neuronal injuries, oxidative stress, endocrine functions, immune reactions, metabolism and differentially expressed miRNAs. The blood-based biomarkers presented and discussed in this review were close to clinical applicability and might facilitate clinical design as surrogate endpoints. Exploration and validation of robust blood-based biomarkers require further standard and systemic study design in the future.

The Mammalian Circadian Time-Keeping System

Our physiology and behavior follow precise daily programs that adapt us to the alternating opportunities and challenges of day and night. Under experimental isolation, these rhythms persist with a period of approximately one day (circadian), demonstrating their control by an internal autonomous clock. Circadian time is created at the cellular level by a transcriptional/translational feedback loop (TTFL) in which the protein products of the Period and Cryptochrome genes inhibit their own transcription. Because the accumulation of protein is slow and delayed, the system oscillates spontaneously with a period of ∼24 hours. This cell-autonomous TTFL controls cycles of gene expression in all major tissues and these cycles underpin our daily metabolic programs. In turn, our innumerable cellular clocks are coordinated by a central pacemaker, the suprachiasmatic nucleus (SCN) of the hypothalamus. When isolated in slice culture, the SCN TTFL and its dependent cycles of neural activity persist indefinitely, operating as "a clock in a dish". In vivo, SCN time is synchronized to solar time by direct innervation from specialized retinal photoreceptors. In turn, the precise circadian cycle of action potential firing signals SCN-generated time to hypothalamic and brain stem targets, which co-ordinate downstream autonomic, endocrine, and behavioral (feeding) cues to synchronize and sustain the distributed cellular clock network. Circadian time therefore pervades every level of biological organization, from molecules to society. Understanding its mechanisms offers important opportunities to mitigate the consequences of circadian disruption, so prevalent in modern societies, that arise from shiftwork, aging, and neurodegenerative diseases, not least Huntington's disease.

Altered Adipocyte Cell Size Distribution Prior to Weight Loss in the R6/2 Model of Huntington's Disease

BACKGROUND

Metabolic alterations contribute to disease onset and prognosis of Huntington's disease (HD). Weight loss in the R6/2 mouse model of HD is a consistent feature, with onset in mid-to-late stage of disease.

OBJECTIVE

In the present study, we aimed to investigate molecular and functional changes in white adipose tissue (WAT) that occur at weight loss in R6/2 mice. We further elaborated on the effect of leptin-deficiency and early obesity in R6/2 mice.

METHODS

We performed analyses at 12 weeks of age; a time point that coincides with the start of weight loss in our R6/2 mouse colony. Gonadal (visceral) and inguinal (subcutaneous) WAT depot weights were monitored, as well as adipocyte size distribution. Response to isoprenaline-stimulated glycerol release and insulin-stimulated glucose uptake in adipocytes from gonadal WAT was assessed.

RESULTS

In R6/2 mice, WAT depot weights were comparable to wildtype (WT) mice, and the response to insulin and isoprenaline in gonadal adipocytes was unaltered. Leptin-deficient R6/2 mice exhibited distinct changes compared to leptin-deficient WT mice. At 12 weeks, female leptin-deficient R6/2 mice had reduced body weight accompanied by an increased proportion of smaller adipocytes, while in contrast; male mice displayed a shift towards larger adipocyte sizes without a significant body weight reduction at this timepoint.

CONCLUSIONS

We here show that there are early sex-specific changes in adipocyte cell size distribution in WAT of R6/2 mice and leptin-deficient R6/2 mice.

Hypothalamic expression of huntingtin causes distinct metabolic changes in Huntington's disease mice

Objective

In Huntington's disease (HD), the disease-causing huntingtin (HTT) protein is ubiquitously expressed and causes both central and peripheral pathology. In clinical HD, a higher body mass index has been associated with slower disease progression, indicating the role of metabolic changes in disease pathogenesis. Underlying mechanisms of metabolic changes in HD remain poorly understood, but recent studies suggest the involvement of hypothalamic dysfunction. The present study aimed to investigate whether modulation of hypothalamic HTT levels would affect metabolic phenotype and disease features in HD using mouse models.

Methods

We used the R6/2 and BACHD mouse models that express different lengths of mutant HTT to develop lean- and obese phenotypes, respectively. We utilized adeno-associated viral vectors to overexpress either mutant or wild-type HTT in the hypothalamus of R6/2, BACHD, and their wild-type littermates. The metabolic phenotype was assessed by body weight measurements over time and body composition analysis using dual-energy x-ray absorptiometry at the endpoint. R6/2 mice were further characterized using behavioral analyses, including rotarod, nesting-, and hindlimb clasping tests during early- and late-time points of disease progression. Finally, gene expression analysis was performed in R6/2 mice and wild-type littermates in order to assess transcriptional changes in the hypothalamus and adipose tissue.

Results

Hypothalamic overexpression of mutant HTT induced significant gender-affected body weight gain in all models, including wild-type mice. In R6/2 females, early weight gain shifted to weight loss during the corresponding late stage of disease despite increased fat accumulation. Body weight changes were accompanied by behavioral alterations. During the period of early weight gain, R6/2 mice displayed a comparable locomotor capacity to wild-type mice. When assessing behavior just prior to weight loss onset in R6/2 mice, decreased locomotor performance was observed in R6/2 females with hypothalamic overexpression of mutant HTT. Transcriptional downregulation of beta-3 adrenergic receptor (B3AR), adipose triglyceride lipase (ATGL), and peroxisome proliferator-activated receptor-gamma (PPARγ) in gonadal white adipose tissue was accompanied by distinct alterations in hypothalamic gene expression profiles in R6/2 females after mutant HTT overexpression. No significant effect on metabolic phenotype in R6/2 was seen in response to wild-type HTT overexpression.

Conclusions

Taken together, our findings provide further support for the role of HTT in metabolic control via hypothalamic neurocircuits. Understanding the specific central neurocircuits and their peripheral link underlying metabolic imbalance in HD may open up avenues for novel therapeutic interventions.

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Overexpression of hypothalamic huntingtin affects weight in Huntington's disease mice.

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Hypothalamic huntingtin expression results in gene expression changes in white fat and the hypothalamus.

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Hypothalamic huntingtin cannot prevent late-stage weight loss in R6/2 mice.

New Avenues for the Treatment of Huntington's Disease

Huntington’s disease (HD) is a neurodegenerative disorder caused by a CAG expansion in the HD gene. The disease is characterized by neurodegeneration, particularly in the striatum and cortex. The first symptoms usually appear in mid-life and include cognitive deficits and motor disturbances that progress over time. Despite being a genetic disorder with a known cause, several mechanisms are thought to contribute to neurodegeneration in HD, and numerous pre-clinical and clinical studies have been conducted and are currently underway to test the efficacy of therapeutic approaches targeting some of these mechanisms with varying degrees of success. Although current clinical trials may lead to the identification or refinement of treatments that are likely to improve the quality of life of those living with HD, major efforts continue to be invested at the pre-clinical level, with numerous studies testing novel approaches that show promise as disease-modifying strategies. This review offers a detailed overview of the currently approved treatment options for HD and the clinical trials for this neurodegenerative disorder that are underway and concludes by discussing potential disease-modifying treatments that have shown promise in pre-clinical studies, including increasing neurotropic support, modulating autophagy, epigenetic and genetic manipulations, and the use of nanocarriers and stem cells.

The relationship between non-motor features and weight-loss in the premanifest stage of Huntington's disease

Weight-loss is an integral part of Huntington's disease (HD) that can start before the onset of motor symptoms. Investigating the underlying pathological processes may help in the understanding of this devastating disease as well as contribute to its management. However, the complex behavior and associations of multiple biological factors is impractical to be interpreted by the conventional statistics or human experts. For the first time, we combine a clinical dataset, expert knowledge and machine intelligence to model the multi-dimensional associations between the potentially relevant factors and weight-loss activity in HD, specifically at the premanifest stage. The HD dataset is standardized and transformed into required knowledge base with the help of clinical HD experts, which is then processed by the class rule mining and self-organising maps to identify the significant associations. Statistical results and experts' report indicate a strong association between severe weight-loss in HD at the premanifest stage and measures of certain cognitive, psychiatric functional ability factors. These results suggest that the mechanism underlying weight-loss in HD is, at least partly related to dysfunction of certain areas of the brain, a finding that may have not been apparent otherwise. These associations will aid the understanding of the pathophysiology of the disease and its progression and may in turn help in HD treatment trials.

The absence of the aryl hydrocarbon receptor in the R6/1 transgenic mouse model of Huntington's disease improves the neurological phenotype

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an abnormal CAG repeat expansion in the huntingtin gene coding for a protein with an elongated polyglutamine sequence. HD patients present choreiform movements, which are caused by the loss of neurons in the striatum and cerebral cortex. Previous reports indicate that the absence of the aryl hydrocarbon receptor (AhR) protects mice from excitotoxic insults and increases the transcription of neurotrophic factors. Based on these data, we evaluated the effects of the lack of the AhR on a mice model of HD, generating a double transgenic mouse, expressing human mutated huntingtin (R6/1 mice) and knockout for the AhR. Our results show that the body weight of 30-week-old double transgenic mice is similar to that of R6/1 mice; however, feet clasping, an indicative of neuronal damage in the R6/1 animals, was not observed. In addition, motor coordination and ambulatory behavior in double transgenic mice did not deteriorate over time as occur in the R6/1 mice. Moreover, the anxiety behavior of double transgenic mice was similar to wild type mice. Interestingly, astrogliosis is also reduced in the double transgenic mice. The present data demonstrate that the complete loss of the AhR reduces the motor and behavioral deterioration observed in R6/1 mice, suggesting that the pharmacological modulation of the AhR could be a therapeutic target in HD.

Brown Adipose Tissue: A Metabolic Regulator in a Hypothalamic Cross Talk?

Since the discovery of functionally competent, energy-consuming brown adipose tissue (BAT) in adult humans, much effort has been devoted to exploring this tissue as a means for increasing energy expenditure to counteract obesity. However, despite promising effects on metabolic rate and insulin sensitivity, no convincing evidence for weight-loss effects of cold-activated human BAT exists to date. Indeed, increasing energy expenditure would naturally induce compensatory feedback mechanisms to defend body weight. Interestingly, BAT is regulated by multiple interactions with the hypothalamus from regions overlapping with centers for feeding behavior and metabolic control. Therefore, in the further exploration of BAT as a potential source of novel drug targets, we discuss the hypothalamic orchestration of BAT activity and the relatively unexplored BAT feedback mechanisms on neuronal regulation. With a holistic view on hypothalamic-BAT interactions, we aim to raise ideas and provide a new perspective on this circuit and highlight its clinical relevance.

A Mobile Application for Smart Computer-Aided Self-Administered Testing of Cognition, Speech, and Motor Impairment

We present a model for digital neural impairment screening and self-assessment, which can evaluate cognitive and motor deficits for patients with symptoms of central nervous system (CNS) disorders, such as mild cognitive impairment (MCI), Parkinson's disease (PD), Huntington's disease (HD), or dementia. The data was collected with an Android mobile application that can track cognitive, hand tremor, energy expenditure, and speech features of subjects. We extracted 238 features as the model inputs using 16 tasks, 12 of them were based on a self-administered cognitive testing (SAGE) methodology and others used finger tapping and voice features acquired from the sensors of a smart mobile device (smartphone or tablet). Fifteen subjects were involved in the investigation: 7 patients with neurological disorders (1 with Parkinson's disease, 3 with Huntington's disease, 1 with early dementia, 1 with cerebral palsy, 1 post-stroke) and 8 healthy subjects. The finger tapping, SAGE, energy expenditure, and speech analysis features were used for neural impairment evaluations. The best results were achieved using a fusion of 13 classifiers for combined finger tapping and SAGE features (96.12% accuracy), and using bidirectional long short-term memory (BiLSTM) (94.29% accuracy) for speech analysis features.

Developmental Trajectory of Height, Weight, and BMI in Children and Adolescents at Risk for Huntington's Disease: Effect of mHTT on Growth

BACKGROUND

The gene (Huntingtin or HTT) causing Huntington's disease (HD) is vital for development and is expressed throughout the brain and body lifelong. The mutant form (mHTT) may influence growth and development.

OBJECTIVE

To determine the impact of mHTT on human measures of growth, including height, weight, and body mass index (BMI), between child and adolescent carriers of mHTT and control peers.

METHODS

Children ages 6-18 years of age (n = 186) at risk for HD were enrolled in the KidsHD study. For research purposes only, genetic testing was performed to classify participants as Gene-Expanded (GE = 78) or as Gene Non-Expanded (GNE = 108). Outcome measures included height, weight, and body mass index (BMI). Mixed models were used to determine if non-linear age trends differed between groups for BMI, height, and weight.

RESULTS

Differences were seen in the trajectory of BMI in which the GE group reached a plateau in late adolescence with no further increase, compared with a nearly linear increase in the GNE group. There was a significant sex interaction pattern where GE males were taller than GNE males in adolescence, in the presence of similar weight. In contrast, GE females weighed significantly less than their GNE counterparts in adolescence, in the presence of similar height.

CONCLUSION

Measures of growth are abnormal in child and adolescent carriers of mHTT, decades before HD onset. Although further studies are needed for replication, the current findings suggest that developmental aberrations may be systemic and a vital part of disease pathology.

A Critical Evaluation of Wet Biomarkers for Huntington's Disease: Current Status and Ways Forward

There is an unmet clinical need for objective biomarkers to monitor disease progression and treatment response in Huntington's disease (HD). The aim of this review is, therefore, to provide practical advice for biomarker discovery and to summarise studies on biofluid markers for HD. A PubMed search was performed to review literature with regard to candidate saliva, urine, blood and cerebrospinal fluid biomarkers for HD. Information has been organised into tables to allow a pragmatic approach to the discussion of the evidence and generation of practical recommendations for future studies. Many of the markers published converge on metabolic and inflammatory pathways, although changes in other analytes representing antioxidant and growth factor pathways have also been found. The most promising markers reflect neuronal and glial degeneration, particularly neurofilament light chain. International collaboration to standardise assays and study protocols, as well as to recruit sufficiently large cohorts, will facilitate future biomarker discovery and development.

Leptin deficiency reverses high metabolic state and weight loss without affecting central pathology in the R6/2 mouse model of Huntington's disease

Body weight has been shown to be a predictor of clinical progression in Huntington's disease (HD). Alongside widespread neuronal pathology, both HD patients and the R6/2 mouse model of HD exhibit weight loss and increased energy expenditure, providing a rationale for targeting whole-body energy metabolism in HD. Leptin-deficient mice display low energy expenditure and increased body weight. We therefore hypothesized that normalizing energy metabolism in R6/2 mice, utilizing leptin- deficiency, would lead to a slower disease progression in the R6/2 mouse. In this study, we show that R6/2 mice on a leptin-deficient genetic background display increased body weight and increased fat mass compared to R6/2 mice, as well as wild type littermates. The increased body weight was accompanied by low energy expenditure, illustrated by a reduction in respiratory exchange rate. Leptin-deficient R6/2 mice had large white adipocytes with white adipocyte gene expression characteristics, in contrast to white adipose tissue in R6/2 mice, where white adipose tissue showed signs of browning. Leptin-deficient R6/2 mice did not exhibit improved neuropathological measures. Our results indicate that lowering energy metabolism in HD, by increasing fat mass and reducing respiratory exchange rate, is not sufficient to affect neuropathology. Further studies targeting energy metabolism in HD are warranted.

Peripheral Expression of Mutant Huntingtin is a Critical Determinant of Weight Loss and Metabolic Disturbances in Huntington's Disease

Deteriorating weight loss in patients with Huntington’s disease (HD) is a complicated peripheral manifestation and the cause remains poorly understood. Studies suggest that body weight strongly influences the clinical progression rate of HD and thereby offers a valuable target for therapeutic interventions. Mutant huntingtin (mHTT) is ubiquitously expressed and could induce toxicity by directly acting in the peripheral tissues. We investigated the effects of selective expression of mHTT exon1 in fat body (FB; functionally equivalent to human adipose tissue and liver) using transgenic Drosophila. We find that FB-autonomous expression of mHTT exon1 is intrinsically toxic and causes chronic weight loss in the flies despite progressive hyperphagia, and early adult death. Moreover, flies exhibit loss of intracellular lipid stores, and decline in the systemic levels of lipids and carbohydrates which aggravates over time, representing metabolic defects. At the cellular level, besides impairment, cell death also occurs with the formation of mHTT aggregates in the FB. These findings indicate that FB-autonomous expression of mHTT alone is sufficient to cause metabolic abnormalities and emaciation in vivo without any neurodegenerative cues.

Ghrelin-mediated improvements in the metabolic phenotype in the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a heritable neurodegenerative disorder, characterised by metabolic disturbances, along with cognitive and psychiatric impairments. Targeting metabolic HD dysfunction via the maintenance of body weight and fat mass and restoration of peripheral energy metabolism can improve the progression of neurological symptoms. In this respect, we focused on the therapeutic potential of the orexigenic peptide hormone ghrelin, which plays an important role in promoting a positive energy balance. In the present study, we found a significant disruption of circadian metabolic regulation in a R6/2 mouse HD model in the late stage of disease. Daily circadian rhythms of activity, energy expenditure, respiratory exchange ratio and feeding were strongly attenuated in R6/2 mice. During the rest phase, R6/2 mice had a higher total activity, elevated energy expenditure and excessive water consumption compared to control mice. We also found that, in the late stage of disease, R6/2 mice had ghrelin axis deficiency as a result of low circulating ghrelin levels, in addition to down-regulation of the ghrelin receptor and several key signalling molecules in the hypothalamus, as well as a reduced responsiveness to exogenous peripheral ghrelin. We demonstrated that, in pre-symptomatic mice, responsiveness to ghrelin is preserved. Chronic ghrelin treatment efficiently increased lean body mass and decreased the energy expenditure and fat utilisation of R6/2 mice in the early stage of disease. In addition, ghrelin treatment was also effective in the normalisation of drinking behaviour and the rest activity of these mice. Ghrelin treatment could provide a novel therapeutic possibility for delaying disease progression; however, deficiency in ghrelin receptor expression could limit its therapeutic potential in the late stage of disease.

Alterations in the tyrosine and phenylalanine pathways revealed by biochemical profiling in cerebrospinal fluid of Huntington's disease subjects

Huntington’s disease (HD) is a severe neurological disease leading to psychiatric symptoms, motor impairment and cognitive decline. The disease is caused by a CAG expansion in the huntingtin (HTT) gene, but how this translates into the clinical phenotype of HD remains elusive. Using liquid chromatography mass spectrometry, we analyzed the metabolome of cerebrospinal fluid (CSF) from premanifest and manifest HD subjects as well as control subjects. Inter-group differences revealed that the tyrosine metabolism, including tyrosine, thyroxine, L-DOPA and dopamine, was significantly altered in manifest compared with premanifest HD. These metabolites demonstrated moderate to strong associations to measures of disease severity and symptoms. Thyroxine and dopamine also correlated with the five year risk of onset in premanifest HD subjects. The phenylalanine and the purine metabolisms were also significantly altered, but associated less to disease severity. Decreased levels of lumichrome were commonly found in mutated HTT carriers and the levels correlated with the five year risk of disease onset in premanifest carriers. These biochemical findings demonstrates that the CSF metabolome can be used to characterize molecular pathogenesis occurring in HD, which may be essential for future development of novel HD therapies.

Non-motor symptoms in Huntington's disease: a comparative study with Parkinson's disease

BACKGROUND/AIMS

The presence of non-motor symptoms in Huntington's disease (HD) has not been systematically assessed so far. Our objective was to know their prevalence and to compare it with a cohort of patients with Parkinson's disease (PD).

MATERIALS AND METHODS

Participants were consecutively recruited from our outpatient clinic. They were assessed through the motor part of the Unified Huntington's Disease Rating Scale, the motor part of the Unified Parkinson's Disease Rating Scale, the total functional capacity scale and the PD non-motor symptoms questionnaire.

RESULTS

We enrolled 123 participants: 53 HD, 45 PD and 25 healthy controls (HC). Non-motor symptoms were significantly more prevalent in HD patients than in HC. The most frequent non-motor symptoms in HD, involving more than 50% of patients, were attentional deficits, apathy, dysphagia, memory complaints, depression falls, insomnia and urinary urgency. The total score of non-motor symptoms correlated with disease duration, total functional capacity and disease stage. HD scored significantly higher than PD in 11 items (dysphagia, constipation, bowel incontinence, faecal tenesmus, weight loss, memory, apathy, attention, falls, nightmares, delusions) and in four domains (cognitive, hallucinations and delusions, digestive and cardiovascular). PD did not score significantly higher than HD in any domain.

CONCLUSIONS

HD patients have a high prevalence of non-motor symptoms, which is even higher than in PD, and correlates with disease progression.

Adipogenic Differentiation of Bone Marrow-Derived Mesenchymal Stem Cells in Pig Transgenic Model Expressing Human Mutant Huntingtin

BACKGROUND

Although the highest expression of mutant huntingtin (mtHtt) was observed in the brain, its negative effects were also apparent in other tissues. Specifically, mtHtt impairs metabolic homeostasis and causes transcriptional dysregulation in adipose tissue. Adipogenic differentiation can be induced by the activation of two transcription factors: CCAAT/enhancer-binding protein alpha (CEBPα) and peroxisome proliferator-activated receptor gamma (PPARγ). These same transcription factors were found to be compromised in some tissues of Huntington's disease (HD) mouse models and in lymphocytes of HD patients.

OBJECTIVE

This study investigated the adipogenic potential of mesenchymal stem cells (MSCs) derived from transgenic Huntington's disease (TgHD) minipigs expressing human mtHtt (1-548aa) containing 124 glutamines. Two differentiation conditions were used, employing PPARγ agonist rosiglitazone or indomethacin.

METHODS

Bone marrow MSCs were isolated from TgHD and WT minipig siblings and compared by their cluster of differentiation using flow cytometry. Their adipogenic potential in vitro was analyzed using quantitative immunofluorescence and western blot analysis of transcription factors and adipogenic markers.

RESULTS

Flow cytometry analysis did not reveal any significant difference between WT and TgHD MSCs. Nevertheless, following differentiation into adipocytes, the expression of CEBPα nuclear, PPARγ and adipogenic marker FABP4/AP2 were significantly lower in TgHD cells compared to WT cells. In addition, we proved both rosiglitazone and indomethacin to be efficient for adipogenic differentiation of porcine MSCs, with rosiglitazone showing a better adipogenic profile.

CONCLUSIONS

We demonstrated a negative influence of mtHtt on adipogenic differentiation of porcine MSCs in vitro associated with compromised expression of adipogenic transcription factors.

Customized Dietary Intervention Avoids Unintentional Weight Loss and Modulates Circulating miRNAs Footprint in Huntington's Disease

SCOPE

Huntington's disease (HD) is a rare progressive neurodegenerative disorder of genetic origin, with no definitive treatment. Unintentional weight loss (UWL) is a clinical feature of symptomatic HD subjects. To prevent UWL, a customized HD diet is designed and its impact on plasma miRNA HD footprint and neurological parameters is examined.

METHODS AND RESULTS

Eleven participants are included, BMI ≤ 18 kg m^-2 or UWL of 5% in 6 months or 10% in a year. Diet design is based on nutritional surveys and interviews of participants and caregivers and on published literature review. Twelve-month dietary intervention, with follow-up every 3 months, induces high diet adherence, which manages to curb UWL in all participants (73% gained weight). Noticeable increases in fat mass and leptin levels are obtained. The results also show significant decrease in the expression of 19 miRNAs, which are previously reported to be upregulated in HD-patients versus healthy controls: revealing hsa-miR-338-3p, hsa-miR-128-3p, hsa-miR-23a-3p, and hsa-miR-24-3p as potential HD-biomarkers. The diminished expression of hsa-miR-100-5p reflects the general maintenance of the functional status. Cognitive status is improved in six of 11 participants, while only three present better motor-score values.

CONCLUSION

A customized HD-diet prevents UWL and modified miRNAs HD-footprint. The normalization of miRNA values suggests its potentially use as HD-biomarkers.

Normalizing glucocorticoid levels attenuates metabolic and neuropathological symptoms in the R6/2 mouse model of huntington's disease

Huntington's disease (HD) is a fatal genetic neurological disorder caused by a mutation in the human Huntingtin (HTT) gene. This mutation confers a toxic gain of function of the encoded mutant huntingtin (mHTT) protein, leading to widespread neuropathology including the formation of mHTT-positive inclusion bodies, gene dysregulation, reduced levels of adult dentate gyrus neurogenesis and neuron loss throughout many regions of the brain. Additionally, because HTT is ubiquitously expressed, several peripheral tissues are also affected. HD patients suffer from progressive motor, cognitive, psychiatric, and metabolic symptoms, including weight loss and skeletal muscle wasting. HD patients also show neuroendocrine changes including a robust, significant elevation in circulating levels of the glucocorticoid, cortisol. Previously, we confirmed that the R6/2 mouse model of HD exhibits elevated corticosterone (the rodent homolog of cortisol) levels and demonstrated that experimentally elevated corticosterone exacerbates R6/2 HD symptomology, resulting in severe and rapid weight loss and a shorter latency to death. Given that efficacious therapeutics are lacking for HD, here we investigated whether normalizing glucocorticoid levels could serve as a viable therapeutic approach for this disease. We tested the hypothesis that normalizing glucocorticoids to wild-type levels would ameliorate HD symptomology. Wild-type (WT) and transgenic R6/2 mice were allocated to three treatment groups: 1) adrenalectomy with normalized, WT-level corticosterone replacement (10 μg/ml), 2) adrenalectomy with high HD-level corticosterone replacement (35 μg/ml), or 3) sham surgery with no corticosterone replacement. Normalizing corticosterone to WT levels led to an improvement in metabolic rate in male R6/2 mice, as indicated by indirect calorimetry, including a reduction in oxygen consumption and normalization of respiratory exchange ratio values (p < .05 for both). Normalizing corticosterone also ameliorated brain atrophy in female R6/2 mice and skeletal muscle wasting in both male and female R6/2 mice (p < .05 for all). Female R6/2 mice given WT-level corticosterone replacement also showed a reduction in HD neuropathological markers, including a reduction in mHTT inclusion burden in the striatum, cortex, and hippocampus (p < .05 for all). This data illustrates that ameliorating glucocorticoid dysregulation leads to a significant improvement in HD symptomology in the R6/2 mouse model and suggests that cortisol-reducing therapeutics may be of value in improving HD patient quality of life.

Commonalities in Biological Pathways, Genetics, and Cellular Mechanism between Alzheimer Disease and Other Neurodegenerative Diseases: An In Silico-Updated Overview

BACKGROUND

Alzheimer's disease (AD) is the most common and well-studied neurodegenerative disease (ND). Biological pathways, pathophysiology and genetics of AD show commonalities with other NDs viz. Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), Prion disease and Dentatorubral-pallidoluysian atrophy (DRPLA). Many of the NDs, sharing the common features and molecular mechanisms suggest that pathology may be directly comparable and be implicated in disease prevention and development of highly effective therapies.

METHOD

In this review, a brief description of pathophysiology, clinical symptoms and available treatment of various NDs have been explored with special emphasis on AD. Commonalities in these fatal NDs provide support for therapeutic advancements and enhance the understanding of disease manifestation.

CONCLUSION

The studies concentrating on the commonalities in biological pathways, cellular mechanisms and genetics may provide the scope to researchers to identify few novel common target(s) for disease prevention and development of effective common drugs for multi-neurodegenerative diseases.

XJB-5-131-mediated improvement in physiology and behaviour of the R6/2 mouse model of Huntington's disease is age- and sex- dependent

We have reported that the radical scavenger XJB-5-131 attenuates or reverses progression of the disease phenotype in the HdhQ(150/150) mouse, a slow onset model of HD. Here, we tested whether XJB-5-131 has beneficial effects in R6/2 mice, a severe early onset model of HD. We found that XJB-5-131 has beneficial effects in R6/2 mice, by delaying features of the motor and histological phenotype. The impact was sex-dependent, with a stronger effect in male mice. XJB-5-131 treatment improved some locomotor deficits in female R6/2 mice, but the effects were, in general, greater in male mice. Chronic treatment of male R6/2 mice with XJB-5-1-131 reduced weight loss, and improved the motor and temperature regulation deficits, especially in male mice. Treatment with XJB-5-131 had no effect on the lifespan of R6/2 mice. Nevertheless, it significantly slowed somatic expansion at 90 days, and reduced the density of inclusions. Our data show that while treatment with XJB-5-131 had complex effects on the phenotype of R6/2 mice, it produced a number of significant improvements in this severe model of HD.

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.

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.

Therapy development in Huntington disease: From current strategies to emerging opportunities

Huntington disease (HD) is a progressive autosomal dominant neurodegenerative disorder in which patients typically present with uncontrolled involuntary movements and subsequent cognitive decline. In 1993, a CAG trinucleotide repeat expansion in the coding region of the huntingtin (HTT) gene was identified as the cause of this disorder. This extended CAG repeat results in production of HTT protein with an expanded polyglutamine tract, leading to pathogenic HTT protein conformers that are resistant to protein turnover, culminating in cellular toxicity and neurodegeneration. Research into the mechanistic basis of HD has highlighted a role for bioenergetics abnormalities stemming from mitochondrial dysfunction, and for synaptic defects, including impaired neurotransmission and excitotoxicity. Interference with transcription regulation may underlie the mitochondrial dysfunction. Current therapies for HD are directed at treating symptoms, as there are no disease-modifying therapies. Commonly prescribed drugs for involuntary movement control include tetrabenazine, a potent and selective inhibitor of vesicular monoamine transporter 2 that depletes synaptic monoamines, and olanzapine, an atypical neuroleptic that blocks the dopamine D2 receptor. Various drugs are used to treat non-motor features. The HD therapeutic pipeline is robust, as numerous efforts are underway to identify disease-modifying treatments, with some small compounds and biological agents moving into clinical trials. Especially encouraging are dosage reduction strategies, including antisense oligonucleotides, and molecules directed at transcription dysregulation. Given the depth and breadth of current HD drug development efforts, there is reason to believe that disease-modifying therapies for HD will emerge, and this achievement will have profound implications for the entire neurotherapeutics field.

Ghrelin rescues skeletal muscle catabolic profile in the R6/2 mouse model of Huntington's disease

Accumulating evidence suggests altered energy metabolism as a key feature in Huntington’s disease (HD) pathology. Hyper-catabolism, including weight loss and muscle atrophy, is seen in HD patients and HD mouse models. Metabolic hormones are key players, not only in energy metabolism, but also in neurodegenerative processes. Ghrelin, a gut peptide-hormone, plays an important role in regulating energy metabolism, stimulating appetite, and affects brain function and increases neuronal survival. The R6/2 mouse model of HD has previously been shown to exhibit progressive weight loss, dysregulated glucose metabolism, skeletal muscle atrophy and altered body composition. In this study, we targeted energy metabolism in R6/2 mice using ghrelin administration, with the primary aim to delay weight loss and reduce muscle atrophy. We also evaluated glucose metabolism and behaviour. We here demonstrate that ghrelin administration (subcutaneous 150 μg/kg daily injections) for 4 weeks, reversed the catabolic gene expression profile (increased expression of Caspase 8, Traf-5 and Creb1) seen in R6/2 mouse skeletal muscle. Skeletal muscle morphology was also improved with ghrelin, and importantly, ghrelin administration normalized behavioural deficits in R6/2 mice. Taken together, our findings encourage further studies targeting metabolism in HD.

Triheptanoin for the treatment of brain energy deficit: A 14-year experience

Triheptanoin is an odd-chain triglyceride with anaplerotic properties-that is, replenishing the pool of metabolic intermediates in the Krebs cycle. Unlike even-chain fatty acids metabolized to acetyl-CoA only, triheptanoin can indeed provide both acetyl-CoA and propionyl-CoA, two key carbon sources for the Krebs cycle. Triheptanoin was initially used in patients with long-chain fatty acid oxidation disorders. The first demonstration of the possible benefit of triheptanoin for brain energy deficit came from a patient with pyruvate carboxylase deficiency, a severe metabolic disease that affects anaplerosis in the brain. In an open-label study, triheptanoin was then shown to decrease nonepileptic paroxysmal manifestations by 90% in patients with glucose transporter 1 deficiency syndrome, a disease that affects glucose transport into the brain. ³¹ P magnetic resonance spectroscopy studies also indicated that triheptanoin was able to correct bioenergetics in the brain of patients with Huntington disease, a neurodegenerative disease associated with brain energy deficit. Altogether, these studies indicate that triheptanoin can be a treatment for brain energy deficit related to altered anaplerosis and/or glucose metabolism. © 2017 Wiley Periodicals, Inc.

Manganese and the Insulin-IGF Signaling Network in Huntington's Disease and Other Neurodegenerative Disorders

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease resulting in motor impairment and death in patients. Recently, several studies have demonstrated insulin or insulin-like growth factor (IGF) treatment in models of HD, resulting in potent amelioration of HD phenotypes via modulation of the PI3K/AKT/mTOR pathways. Administration of IGF and insulin can rescue microtubule transport, metabolic function, and autophagy defects, resulting in clearance of Huntingtin (HTT) aggregates, restoration of mitochondrial function, amelioration of motor abnormalities, and enhanced survival. Manganese (Mn) is an essential metal to all biological systems but, in excess, can be toxic. Interestingly, several studies have revealed the insulin-mimetic effects of Mn-demonstrating Mn can activate several of the same metabolic kinases and increase peripheral and neuronal insulin and IGF-1 levels in rodent models. Separate studies have shown mouse and human striatal neuroprogenitor cell (NPC) models exhibit a deficit in cellular Mn uptake, indicative of a Mn deficiency. Furthermore, evidence from the literature reveals a striking overlap between cellular consequences of Mn deficiency (i.e., impaired function of Mn-dependent enzymes) and known HD endophenotypes including excitotoxicity, increased reactive oxygen species (ROS) accumulation, and decreased mitochondrial function. Here we review published evidence supporting a hypothesis that (1) the potent effect of IGF or insulin treatment on HD models, (2) the insulin-mimetic effects of Mn, and (3) the newly discovered Mn-dependent perturbations in HD may all be functionally related. Together, this review will present the intriguing possibility that intricate regulatory cross-talk exists between Mn biology and/or toxicology and the insulin/IGF signaling pathways which may be deeply connected to HD pathology and, perhaps, other neurodegenerative diseases (NDDs) and other neuropathological conditions.

The chicken or the egg: mitochondrial dysfunction as a cause or consequence of toxicity in Huntington's disease

Mitochondrial dysfunction and ensuing oxidative damage is typically thought to be a primary cause of Huntington's disease, Alzheimer's disease, and Parkinson disease. There is little doubt that mitochondria (MT) become defective as neurons die, yet whether MT defects are the primary cause or a detrimental consequence of toxicity remains unanswered. Oxygen consumption rate (OCR) and glycolysis provide sensitive and informative measures of the functional status MT and the cells metabolic regulation, yet these measures differ depending on the sample source; species, tissue type, age at measurement, and whether MT are measured in purified form or in a cell. The effects of these various parameters are difficult to quantify and not fully understood, but clearly have an impact on interpreting the bioenergetics of MT or their failure in disease states. A major goal of the review is to discuss issues and coalesce detailed information into a reference table to help in assessing mitochondrial dysfunction as a cause or consequence of Huntington's disease.

Prolonged day length exposure improves circadian deficits and survival in a transgenic mouse model of Huntington's disease

The circadian disruption seen in patients of Huntington's disease (HD) is recapitulated in the R6/2 mouse model. As the disease progresses, the activity of R6/2 mice increases dramatically during the rest (light) period and decreases during the active (dark) period, eventually leading to a complete disintegration of rest-activity rhythms by the age of ~16 weeks. The suprachiasmatic nucleus controls circadian rhythms by entraining the rest-activity rhythms to the environmental light-dark cycle. Since R6/2 mice can shift their rest-activity rhythms in response to a jet-lag paradigm and also respond positively to bright light therapy (1000 lx), we investigated whether or not a prolonged day length exposure could reduce their daytime activity and improve their behavioural circadian rhythms. We found that a long-day photoperiod (16 h light/8 h dark cycle; 100 lx) significantly improved the survival of R6/2 female mice by 2.4 weeks, compared to mice kept under standard conditions (12 h light/12 h dark cycle). Furthermore, a long-day photoperiod improved the nocturnality of R6/2 female mice. Mice kept under long-day photoperiod also maintained acrophase in activity rhythms (a parameter of rhythmicity strength) in phase with that of WT mice, even if they were symptomatic. By contrast, a short-day photoperiod (8 h light/16 h dark cycle) was deleterious to R6/2 female mice and further reduced the survival by ~1 week. Together, our results support the idea that light therapy may be beneficial for improving circadian dysfunction in HD patients.

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Chronic exposure to a long day (16:8 LD) is beneficial to R6/2 female mice.

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The 16:8 LD cycle slowed body weight loss and improved survival of R6/2 mice.

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Lifespan of R6/2 female mice was extended by ~2.4 weeks under 16:8 LD cycle.

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R6/2 female mice under 16:8 LD had stabilised acrophase in activity rhythms.

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Lifespan of R6/2 female mice was reduced by chronic exposure to a short day (8:16 LD).

Cross-phenotype association tests uncover genes mediating nutrient response in Drosophila

Background

Obesity-related diseases are major contributors to morbidity and mortality in the developed world. Molecular diagnostics and targets of therapies to combat nutritional imbalance are urgently needed in the clinic. Invertebrate animals have been a cornerstone of basic research efforts to dissect the genetics of metabolism and nutrient response. We set out to use fruit flies reared on restricted and nutrient-rich diets to identify genes associated with starvation resistance, body mass and composition, in a survey of genetic variation across the Drosophila Genetic Reference Panel (DGRP).

Results

We measured starvation resistance, body weight and composition in DGRP lines on each of two diets and used several association mapping strategies to harness this panel of phenotypes for molecular insights. We tested DNA sequence variants for a relationship with single metabolic traits and with multiple traits at once, using a scheme for cross-phenotype association mapping; we focused our association tests on homologs of human disease genes and common polymorphisms; and we tested for gene-by-diet interactions. The results revealed gene and gene-by-diet associations between 17 variants and body mass, whole-body triglyceride and glucose content, or starvation resistance. Focused molecular experiments validated the role in body mass of an uncharacterized gene, CG43921 (which we rename heavyweight), and previously unknown functions for the diacylglycerol kinase rdgA, the huntingtin homolog htt, and the ceramide synthase schlank in nutrient-dependent body mass, starvation resistance, and lifespan.

Conclusions

Our findings implicate a wealth of gene candidates in fly metabolism and nutrient response, and ascribe novel functions to htt, rdgA, hwt and schlank.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3137-9) contains supplementary material, which is available to authorized users.

White Adipose Tissue Browning in the R6/2 Mouse Model of Huntington's Disease

Huntington’s disease (HD) is a fatal, autosomal dominantly inherited neurodegenerative disorder, characterised not only by progressive cognitive, motor and psychiatric impairments, but also of peripheral pathology. In both human HD and in mouse models of HD there is evidence of increased energy expenditure and weight loss, alongside altered body composition. Unlike white adipose tissue (WAT), brown adipose tissue (BAT), as well as brown-like cells within WAT, expresses the mitochondrial protein, uncoupling protein 1 (UCP1). UCP1 enables dissociation of cellular respiration from ATP utilization, resulting in the release of stored energy as heat. Hyperplasia of brown/beige cells in WAT has been suggested to enhance energy expenditure. In this study, we therefore investigated the gene expression profile, histological appearance, response to cold challenge and functional aspects of WAT in the R6/2 HD mouse model and selected WAT gene expression in the full-length Q175 mouse model of HD. WAT from R6/2 mice contained significantly more brown-like adipocyte regions and had a gene profile suggestive of the presence of brown-like adipocytes, such as higher Ucp1 expression. Cold exposure induced Ucp1 expression in R6/2 inguinal WAT to a markedly higher degree as compared to the thermogenic response in WT WAT. Alongside this, gene expression of transcription factors (Zfp516 and Pparα), important inducers of WAT browning, were increased in R6/2 inguinal WAT, and Creb1 was highlighted as a key transcription factor in HD. In addition to increased WAT Ucp1 expression, a trend towards increased mitochondrial oxygen consumption due to enhanced uncoupling activity was found in inguinal R6/2 WAT. Key gene expressional changes (increased expression of (Zfp516 and Pparα)) were replicated in inguinal WAT obtained from Q175 mice. In summary, for the first time, we here show that HD mouse WAT undergoes a process of browning, resulting in molecular and functional alterations that may contribute to the weight loss and altered metabolism observed with disease progression.

Mutant Huntingtin and Elusive Defects in Oxidative Metabolism and Mitochondrial Calcium Handling

Elongation of a polyglutamine (polyQ) stretch in huntingtin protein (Htt) is linked to Huntington's disease (HD) pathogenesis. The mutation in Htt correlates with neuronal dysfunction in the striatum and cerebral cortex and eventually leads to neuronal cell death. The exact mechanisms of the injurious effect of mutant Htt (mHtt) on neurons are not completely understood but might include aberrant gene transcription, defective autophagy, abnormal mitochondrial biogenesis, anomalous mitochondrial dynamics, and trafficking. In addition, deficiency in oxidative metabolism and defects in mitochondrial Ca(2+) handling are considered essential contributing factors to neuronal dysfunction in HD and, consequently, in HD pathogenesis. Since the discovery of the mutation in Htt, the questions whether mHtt affects oxidative metabolism and mitochondrial Ca(2+) handling and, if it does, what mechanisms could be involved were in focus of numerous investigations. However, despite significant research efforts, the detrimental effect of mHtt and the mechanisms by which mHtt might impair oxidative metabolism and mitochondrial Ca(2+) handling remain elusive. In this paper, I will briefly review studies aimed at clarifying the consequences of mHtt interaction with mitochondria and discuss experimental results supporting or arguing against the mHtt effects on oxidative metabolism and mitochondrial Ca(2+) handling.

Novel targets for Huntington's disease: future prospects

Huntington's disease (HD) is an incurable, inherited, progressive, neurodegenerative disorder that is characterized by a triad of motor, cognitive, and psychiatric problems. Despite the noticeable increase in therapeutic trials in HD in the last 20 years, there have, to date, been very few significant advances. The main hope for new and emerging therapeutics for HD is to develop a neuroprotective compound capable of slowing down or even stopping the progression of the disease and ultimately prevent the subtle early signs from developing into manifest disease. Recently, there has been a noticeable shift away from symptomatic therapies in favor of more mechanistic-based interventions, a change driven by a better understanding of the pathogenesis of this disorder. In this review, we discuss the status of, and supporting evidence for, potential novel treatments of HD that are currently under development or have reached the level of early Phase I/II clinical trials.

Metabolic disruption identified in the Huntington's disease transgenic sheep model

Huntington’s disease (HD) is a dominantly inherited, progressive neurodegenerative disorder caused by a CAG repeat expansion within exon 1 of HTT, encoding huntingtin. There are no therapies that can delay the progression of this devastating disease. One feature of HD that may play a critical role in its pathogenesis is metabolic disruption. Consequently, we undertook a comparative study of metabolites in our transgenic sheep model of HD (OVT73). This model does not display overt symptoms of HD but has circadian rhythm alterations and molecular changes characteristic of the early phase disease. Quantitative metabolite profiles were generated from the motor cortex, hippocampus, cerebellum and liver tissue of 5 year old transgenic sheep and matched controls by gas chromatography-mass spectrometry. Differentially abundant metabolites were evident in the cerebellum and liver. There was striking tissue-specificity, with predominantly amino acids affected in the transgenic cerebellum and fatty acids in the transgenic liver, which together may indicate a hyper-metabolic state. Furthermore, there were more strong pair-wise correlations of metabolite abundance in transgenic than in wild-type cerebellum and liver, suggesting altered metabolic constraints. Together these differences indicate a metabolic disruption in the sheep model of HD and could provide insight into the presymptomatic human disease.

Factors Associated with Low Body Mass Index in Huntington's Disease: A Spanish Multicenter Study of the European Huntington's Disease Registry

Background

Patients with Huntington's disease (HD) are at risk for body weight loss and increased risk for institutionalization, morbidity, and mortality. The aim of this study was to determine the factors associated with low body mass index (BMI) in patients with HD.

Methods

In this national, observational, cross-sectional study of the European Huntington's Disease Network, the frequency of food consumption, calories, and nutrient intake in patients with HD was assessed using questionnaires validated for the Spanish population and were calculated using the software package Alimentación and Salud (Diet and Health), version 2.0. Nutritional status was estimated using the BMI, and disease severity was assessed using the Unified Huntington's Disease Rating Scale and a total functional capacity (TFC) score. Linear regression models were performed using BMI as the dependent variable and using energy balance (energy caloric intake - energy expenditure); the TFC score; the presence of a caregiver; dysphagia; cytosine, adenine, guanine (CAG) repeats; comorbidities; intake of supplements; pharmacologic treatments; age; gender; education; and physical activity as the independent variables.

Results

Two hundred twenty-four patients with HD were included (59% women), and their mean age was 47.41 ± 14.26 years, a median TFC score of 9 (range, 3-13), normal BMI in 124 patients (55.4%), and low BMI in 13 patients (6.7%). In the linear regression model, older age (β = 0.003; P = 0.01), male gender (β = 0.13; P = 0.003), and lower energy balance (β = -0.0001; P = 0.0003) were associated with a higher log-transformed BMI.

Conclusions

Younger female HD patients are at risk for low BMI. To counteract the influence of the HD gene mutation on decreased BMI, an increase in kilocalories per day should be encouraged.

A Metabolic Study of Huntington's Disease

Background

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

Methods

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

Results

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

Conclusions

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

Advancing pharmacotherapy for treating Huntington's disease: a review of the existing literature

INTRODUCTION

Huntington's disease (HD) is an incurable chronic neurodegenerative disorder that typically presents in mid-life with a range of motor, cognitive and affective problems. Patients are currently managed using a combination of drug treatments and non-pharmacological therapies but at present there is no "gold standard" treatment for any aspect of the disease.

AREAS COVERED

In this review the empirical evidence supporting the use of drugs commonly used to treat HD was discussed. In particular, we focus on therapeutics that have either reached phase 3 clinical trials or are already in clinical use.

EXPERT OPINION

The results confirmed that there is a striking lack of evidence to support the efficacy of the drugs currently used in the management of HD. In fact, many drugs are prescribed on the basis of case reports, open label studies, small double blind placebo control trials of limited duration, or personal clinical experience. However of late, the establishment of large international databases, capturing all patients and their clinical details regardless of stage or geographical location has led to an increase in the number of clinical trials conducted on new therapies. Unfortunately, the same is not true for the existing therapies which look set to remain untested for the foreseeable future.

Energy Balance in Huntington's Disease

INTRODUCTION

Little is known about the energy needs in Huntington's disease (HD). The aims of this study are to analyze and compare the total energy expenditure (TEE) and energy balance (EB) in a representative sample of HD patients with healthy controls.

METHODS

This is an observational, case-control single-center study. Food caloric energy intake (EI) and TEE were considered for estimating EB. A dietary recall questionnaire was used to assess the EI. TEE was computed as the sum of resting energy expenditure (REE), measured by indirect calorimetry and physical activity (PA) monitored by an actigraph.

RESULTS

A total of 22 patients were included (36% men, mean age 50.3 ± 15.6 years, motor Unified Huntington's Disease Scale 27.9 ± 23.7, total functional capacity 11.0 (7.0-13.0), EI 38.6 ± 10.0 kcal/kg, PA 5.3 (3.0-7.4) kcal/kg, REE 30.9 ± 6.4 kcal/kg, TEE 2,023.4 (1,592.0-2,226.5) kcal/day) and 18 controls (50% men, mean age 47.4 ± 13.8 years, EI 38.6 ± 10.3 kcal/kg, PA 8.4 (5.0-13.8) kcal/kg, REE 30.8 ± 6.6 kcal/kg, TEE 2,281.0 (2,057.3-2,855.3) kcal/day). TEE was significantly lower in patients compared to controls (p = 0.03). PA was lower in patients compared to controls (p = 0.02).

CONCLUSIONS

Although patients with HD appeared to have lower energy expenditure, mainly due to decreased voluntary PA, they were still able to maintain their energy needs with an adequate food intake. © 2015 S. Karger AG, Basel.

A 24-Hour Study of the Hypothalamo-Pituitary Axes in Huntington's Disease

Background

Huntington’s disease is an inherited neurodegenerative disorder characterised by motor, cognitive and psychiatric disturbances. Patients exhibit other symptoms including sleep and mood disturbances, muscle atrophy and weight loss which may be linked to hypothalamic pathology and dysfunction of hypothalamo-pituitary axes.

Methods

We studied neuroendocrine profiles of corticotropic, somatotropic and gonadotropic hypothalamo-pituitary axes hormones over a 24-hour period in controlled environment in 15 healthy controls, 14 premanifest and 13 stage II/III Huntington’s disease subjects. We also quantified fasting levels of vasopressin, oestradiol, testosterone, dehydroepiandrosterone sulphate, thyroid stimulating hormone, free triiodothyronine, free total thyroxine, prolactin, adrenaline and noradrenaline. Somatotropic axis hormones, growth hormone releasing hormone, insulin-like growth factor-1 and insulin-like factor binding protein-3 were quantified at 06:00 (fasting), 15:00 and 23:00. A battery of clinical tests, including neurological rating and function scales were performed.

Results

24-hour concentrations of adrenocorticotropic hormone, cortisol, luteinizing hormone and follicle-stimulating hormone did not differ significantly between the Huntington’s disease group and controls. Daytime growth hormone secretion was similar in control and Huntington’s disease subjects. Stage II/III Huntington’s disease subjects had lower concentration of post-sleep growth hormone pulse and higher insulin-like growth factor-1:growth hormone ratio which did not reach significance. In Huntington’s disease subjects, baseline levels of hypothalamo-pituitary axis hormones measured did not significantly differ from those of healthy controls.

Conclusions

The relatively small subject group means that the study may not detect subtle perturbations in hormone concentrations. A targeted study of the somatotropic axis in larger cohorts may be warranted. However, the lack of significant results despite many variables being tested does imply that the majority of them do not differ substantially between HD and controls.

Sleep deficits but no metabolic deficits in premanifest Huntington's disease

Objective

Huntington disease (HD) is a fatal autosomal dominant, neurodegenerative condition characterized by progressively worsening motor and nonmotor problems including cognitive and neuropsychiatric disturbances, along with sleep abnormalities and weight loss. However, it is not known whether sleep disturbances and metabolic abnormalities underlying the weight loss are present at a premanifest stage.

Methods

We performed a comprehensive sleep and metabolic study in 38 premanifest gene carrier individuals and 36 age‐ and sex‐matched controls. The study consisted of 2 weeks of actigraphy at home, 2 nights of polysomnography and multiple sleep latency tests in the laboratory, and body composition assessment using dual energy x‐ray absorptiometry scanning with energy expenditure measured over 10 days at home by doubly labeled water and for 36 hours in the laboratory by indirect calorimetry along with detailed cognitive and clinical assessments. We performed a principal component analyses across all measures within each studied domain.

Results

Compared to controls, premanifest gene carriers had more disrupted sleep, which was best characterized by a fragmented sleep profile. These abnormalities, as well as a theta power (4–7Hz) decrease in rapid eye movement sleep, were associated with disease burden score. Objectively measured sleep problems coincided with the development of cognitive, affective, and subtle motor deficits and were not associated with any metabolic alterations.

Interpretation

The results show that among the earliest abnormalities in premanifest HD is sleep disturbances. This raises questions as to where the pathology in HD begins and also whether it could drive some of the early features and even possibly the pathology. Ann Neurol 2015;78:630–648

Characterization of Gastric Mucosa Biopsies Reveals Alterations in Huntington's Disease

Weight loss is an important complication of Huntington’s disease (HD), however the mechanism for weight loss in HD is not entirely understood. Mutant huntingtin is expressed in the gastrointestinal (GI) tract and, in HD mice, mutant huntingtin inclusions are found within the enteric nervous system along the GI tract. A reduction of neuropeptides, decreased mucosal thickness and villus length, as well as gut motility impairment, have also been shown in HD mice. We therefore set out to study gastric mucosa of patients with HD, looking for abnormalities of mucosal cells using immunohistochemistry. In order to investigate possible histological differences related to gastric acid production, we evaluated the cell density of acid producing parietal cells, as well as gastrin producing cells (the endocrine cell controlling parietal cell function). In addition, we looked at chief cells and somatostatin-containing cells. In gastric mucosa from HD subjects, compared to control subject biopsies, a reduced expression of gastrin (a marker of G cells) was found. This is in line with previous HD mouse studies showing reduction of GI tract neuropeptides.

Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases?

There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.

Analysis of White Adipose Tissue Gene Expression Reveals CREB1 Pathway Altered in Huntington's Disease

BACKGROUND

In addition to classical neurological symptoms, Huntington's disease (HD) is complicated by peripheral pathology and both the mutant gene and the protein are found in cells and tissues throughout the body. Despite the adipose tissue gene expression alterations described in HD mouse models, adipose tissue and its gene expression signature have not been previously explored in human HD.

OBJECTIVE

We investigated gene expression signatures in subcutaneous adipose tissue obtained from control subjects, premanifest HD gene carriers and manifest HD subjects with the aim to identify gene expression changes and signalling pathway alterations in adipose tissue relevant to HD.

METHODS

Gene expression was assessed using Affymetrix GeneChip® Human Gene 1.0 ST Array. Target genes were technically validated using real-time quantitative PCR and the expression signature was validated in an independent subject cohort.

RESULTS

In subcutaneous adipose tissue, more than 500 genes were significantly different in premanifest HD subjects as compared to healthy controls. Pathway analysis suggests that the differentially expressed genes found here in HD adipose tissue are involved in fatty acid metabolism pathways, angiotensin signalling pathways and immune pathways. Transcription factor analysis highlights CREB1. Using RT-qPCR, we found that MAL2, AGTR2, COBL and the transcription factor CREB1 were significantly upregulated, with CREB1 and AGT also being significantly upregulated in a separate cohort.

CONCLUSIONS

Distinct gene expression profiles can be seen in HD subcutaneous adipose tissue, with CREB1 highlighted as a key transcription factor.