Neuroendocrine disturbances in Huntington's disease

Neuroprotective potential of epigallocatechin gallate in Neurodegenerative Diseases: Insights into molecular mechanisms and clinical Relevance

Neurodegenerative diseases (NDs) such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis pose significant challenges due to their complex pathophysiology and lack of effective treatments. Green tea, rich in the epigallocatechin gallate (EGCG) polyphenolic component, has demonstrated potential as a neuroprotective agent with numerous medicinal applications. EGCG effectively reduces tau and Aβ aggregation in ND models, promotes autophagy, and targets key signaling pathways like Nrf2-ARE, NF-κB, and MAPK. This review explores the molecular processes that underlie EGCG's neuroprotective properties, including its ability to regulate mitochondrial dysfunction, oxidative stress, neuroinflammation, and protein misfolding. Clinical research indicates that EGCG may enhance cognitive and motor abilities, potentially inhibiting disease progression despite absorption and dose optimization limitations. The substance has been proven to slow the amyloidogenic process, prevent protein aggregation, decrease amyloid cytotoxicity, inhibit fibrillogenesis, and restructure fibrils for synergistic therapeutic effects. The review highlights the potential of EGCG as a natural, multi-targeted strategy for NDs but emphasizes the need for further clinical trials to enhance its therapeutic efficacy.

Insights into therapeutic approaches for the treatment of neurodegenerative diseases targeting metabolic syndrome

Due to the significant energy requirements of nerve cells, glucose is rapidly oxidized to generate ATP and works in conjunction with mitochondria in metabolic pathways, resulting in a combinatorial impact. The purpose of this review is to show how glucose metabolism disorder invariably disrupts the normal functioning of neurons, a phenomenon commonly observed in neurodegenerative diseases. Interventions in these systems may alleviate the degenerative load on neurons. Research on the concepts of metabolic adaptability during disease progression has become a key focus. The majority of the existing treatments are effective in mitigating some clinical symptoms, but they are unsuccessful in preventing neurodegeneration. Hence, there is an urgent need for breakthrough and highly effective therapies for neurodegenerative diseases. Here, we summarise the interactions that various neurodegenerative diseases have with abnormalities in insulin signalling, lipid metabolism, glucose control, and mitochondrial bioenergetics. These factors have a crucial role in brain activity and cognition, and also significantly contribute to neuronal degeneration in pathological conditions. In this article, we have discussed the latest and most promising treatment methods, ranging from molecular advancements to clinical trials, that aim at improving the stability of neurons.

Epigallocatechin 3-gallate-induced neuroprotection in neurodegenerative diseases: molecular mechanisms and clinical insights

Neurodegenerative diseases (NDs) are caused by progressive neuronal death and cognitive decline. Epigallocatechin 3-gallate (EGCG) is a polyphenolic molecule in green tea as a neuroprotective agent. This review evaluates the therapeutic effects of EGCG and explores the molecular mechanisms that show its neuroprotective properties. EGCG protects neurons in several ways, such as by lowering oxidative stress, stopping Aβ from aggregation together, changing cell signaling pathways, and decreasing inflammation. Furthermore, it promotes autophagy and improves mitochondrial activity, supporting neuronal survival. Clinical studies have demonstrated that EGCG supplementation can reduce neurodegenerative biomarkers and enhance cognitive function. This review provides insights into the molecular mechanisms and therapeutic potential of EGCG in treating various NDs. EGCG reduces oxidative stress by scavenging free radicals and enhancing antioxidant enzyme activity, aiding neuronal defense. It also protects neurons and improves cognitive abilities by inhibiting the toxicity and aggregation of Aβ peptides. It changes important cell signaling pathways like Nrf2, PI3K/Akt, and MAPK, which are necessary for cell survival, cell death, and inflammation. Additionally, it has strong anti-inflammatory properties because it inhibits microglial activation and downregulates pro-inflammatory cytokines. It improves mitochondrial function by reducing oxidative stress, increasing ATP synthesis, and promoting mitochondrial biogenesis, which promotes neurons' survival and energy metabolism. In addition, it also triggers autophagy, a cellular process that breaks down and recycles damaged proteins and organelles, eliminating neurotoxic aggregates and maintaining cellular homeostasis. Moreover, it holds significant promise as an ND treatment, but future research should focus on increasing bioavailability and understanding its long-term clinical effects. Future studies should focus on improving EGCG delivery and understanding its long-term effects in therapeutic settings. It can potentially be a therapeutic agent for managing NDs, indicating a need for further research.

GHRH and its analogues in central nervous system diseases

Growth hormone-releasing hormone (GHRH) is primarily produced by the hypothalamus and stimulates the release of growth hormone (GH) in the anterior pituitary gland, which subsequently regulates the production of hepatic insulin-like growth factor-1 (IGF-1). GH and IGF-1 have potent effects on promoting cell proliferation, inhibiting cell apoptosis, as well as regulating cell metabolism. In central nerve system (CNS), GHRH/GH/IGF-1 promote brain development and growth, stimulate neuronal proliferation, and regulate neurotransmitter release, thereby participating in the regulation of various CNS physiological activities. In addition to hypothalamus-pituitary gland, GHRH and GHRH receptor (GHRH-R) are also expressed in other brain cells or tissues, such as endogenous neural stem cells (NSCs) and tumor cells. Alternations in GHRH/GH/IGF-1 axis are associated with various CNS diseases, for example, Alzheimer's disease, amyotrophic lateral sclerosis and emotional disorders manifest GHRH, GH or IGF-1 deficiency, and GH or IGF-1 supplementation exerts beneficial therapeutic effects on these diseases. CNS tumors, such as glioma, can express GHRH and GHRH-R, and activating this signaling pathway promotes tumor cell growth. The synthesized GHRH antagonists have shown to inhibit glioma cell growth and may hold promising as an adjuvant therapy for treating glioma. In addition, we have shown that GHRH agonist MR-409 can improve neurological sequelae after ischemic stroke by activating extrapituitary GHRH-R signaling and promoting endogenous NSCs-derived neuronal regeneration. This article reviews the involvement of GHRH/GH/IGF-1 in CNS diseases, and potential roles of GHRH agonists and antagonists in treating CNS diseases.

Circadian Interventions in Preclinical Models of Huntington's Disease: A Narrative Review

Huntington's Disease (HD) is a neurodegenerative disorder caused by an autosomal-dominant mutation in the huntingtin gene, which manifests with a triad of motor, cognitive and psychiatric declines. Individuals with HD often present with disturbed sleep/wake cycles, but it is still debated whether altered circadian rhythms are intrinsic to its aetiopathology or a consequence. Conversely, it is well established that sleep/wake disturbances, perhaps acting in concert with other pathophysiological mechanisms, worsen the impact of the disease on cognitive and motor functions and are a burden to the patients and their caretakers. Currently, there is no cure to stop the progression of HD, however, preclinical research is providing cementing evidence that restoring the fluctuation of the circadian rhythms can assist in delaying the onset and slowing progression of HD. Here we highlight the application of circadian-based interventions in preclinical models and provide insights into their potential translation in clinical practice. Interventions aimed at improving sleep/wake cycles' synchronization have shown to improve motor and cognitive deficits in HD models. Therefore, a strong support for their suitability to ameliorate HD symptoms in humans emerges from the literature, albeit with gaps in our knowledge on the underlying mechanisms and possible risks associated with their implementation.

Systemic Symptoms in Huntington's Disease: A Comprehensive Review

BACKGROUND

Although Huntington's disease (HD) is usually thought of as a triad of motor, cognitive, and psychiatric symptoms, there is growing appreciation of HD as a systemic illness affecting the entire body.

OBJECTIVES

This review aims to draw attention to these systemic non-motor symptoms in HD.

METHODS

We identified relevant studies published in English by searching MEDLINE (from 1966 to September 2023), using the following subject headings: Huntington disease, autonomic, systemic, cardiovascular, respiratory, gastrointestinal, urinary, sexual and cutaneous, and additional specific symptoms.

RESULTS

Data from 123 articles were critically reviewed with focus on systemic features associated with HD, such as cardiovascular, respiratory, gastrointestinal, urinary, sexual and sweating.

CONCLUSION

This systematic review draws attention to a variety of systemic and autonomic co-morbidities in patients with HD. Not all of them correlate with the severity of the primary HD symptoms or CAG repeats. More research is needed to better understand the pathophysiology and treatment of systemic and autonomic dysfunction in HD.

Association between sex and Huntington's disease: an updated review on symptomatology and prognosis of neurodegenerative disorders

Huntington's disease is a rare autosomal dominant disorder presenting with chorea, rigidity, hypo-/akinesia, cognitive decline, and psychiatric disturbances. Numerous risk factors have been defined in the onset of this disease. However, the number of CAG repeats in the genes are the most crucial factor rendering patients susceptible to the disease. Studies have shown significant differences in onset and disease presentation among the sexes, which prompts analysis of the impact of different sexes on disease etiology and progression. This article therefore discusses the evidence-based role of sex in aspects of symptomatology, pathogenesis, biomarkers, progression, and prognosis of Huntington's disease, with a secondary review of sex-linked differences in Alzheimer's and Parkinson's disease.

Increase in brain glycogen levels ameliorates Huntington's disease phenotype and rescues neurodegeneration in Drosophila

Under normal physiological conditions, the mammalian brain contains very little glycogen, most of which is stored in astrocytes. However, the aging brain and the subareas of the brain in patients with neurodegenerative disorders tend to accumulate glycogen, the cause and significance of which remain largely unexplored. Using cellular models, we have recently demonstrated a neuroprotective role for neuronal glycogen and glycogen synthase in the context of Huntington's disease. To gain insight into the role of brain glycogen in regulating proteotoxicity, we utilized a Drosophila model of Huntington's disease, in which glycogen synthase is either knocked down or expressed ectopically. Enhancing glycogen synthesis in the brains of flies with Huntington's disease decreased mutant Huntingtin aggregation and reduced oxidative stress by activating auto-lysosomal functions. Further, overexpression of glycogen synthase in the brain rescues photoreceptor degeneration, improves locomotor deficits and increases fitness traits in this Huntington's disease model. We, thus, provide in vivo evidence for the neuroprotective functions of glycogen synthase and glycogen in neurodegenerative conditions, and their role in the neuronal autophagy process.

The Urine Metabolome of R6/2 and zQ175DN Huntington's Disease Mouse Models

Huntington's disease (HD) is caused by the expansion of a polyglutamine (polyQ)-encoding tract in exon 1 of the huntingtin gene to greater than 35 CAG repeats. It typically has a disease course lasting 15-20 years, and there are currently no disease-modifying therapies available. Thus, there is a need for faithful mouse models of HD to use in preclinical studies of disease mechanisms, target validation, and therapeutic compound testing. A large variety of mouse models of HD were generated, none of which fully recapitulate human disease, complicating the selection of appropriate models for preclinical studies. Here, we present the urinary liquid chromatography-high-resolution mass spectrometry analysis employed to identify metabolic alterations in transgenic R6/2 and zQ175DN knock-in mice. In R6/2 mice, the perturbation of the corticosterone metabolism and the accumulation of pyrraline, indicative of the development of insulin resistance and the impairment of pheromone excretion, were observed. Differently from R6/2, zQ175DN mice showed the accumulation of oxidative stress metabolites. Both genotypes showed alterations in the tryptophan metabolism. This approach aims to improve our understanding of the molecular mechanisms involved in HD neuropathology, facilitating the selection of appropriate mouse models for preclinical studies. It also aims to identify potential biomarkers specific to HD.

Brain-Derived Neurotrophic Factor Dysregulation as an Essential Pathological Feature in Huntington's Disease: Mechanisms and Potential Therapeutics

Brain-derived neurotrophic factor (BDNF) is a major neurotrophin whose loss or interruption is well established to have numerous intersections with the pathogenesis of progressive neurological disorders. There is perhaps no greater example of disease pathogenesis resulting from the dysregulation of BDNF signaling than Huntington's disease (HD)-an inherited neurodegenerative disorder characterized by motor, psychiatric, and cognitive impairments associated with basal ganglia dysfunction and the ultimate death of striatal projection neurons. Investigation of the collection of mechanisms leading to BDNF loss in HD highlights this neurotrophin's importance to neuronal viability and calls attention to opportunities for therapeutic interventions. Using electronic database searches of existing and forthcoming research, we constructed a literature review with the overarching goal of exploring the diverse set of molecular events that trigger BDNF dysregulation within HD. We highlighted research that investigated these major mechanisms in preclinical models of HD and connected these studies to those evaluating similar endpoints in human HD subjects. We also included a special focus on the growing body of literature detailing key transcriptomic and epigenetic alterations that affect BDNF abundance in HD. Finally, we offer critical evaluation of proposed neurotrophin-directed therapies and assessed clinical trials seeking to correct BDNF expression in HD individuals.

The neurobiology of insulin-like growth factor I: From neuroprotection to modulation of brain states

After decades of research in the neurobiology of IGF-I, its role as a prototypical neurotrophic factor is undisputed. However, many of its actions in the adult brain indicate that this growth factor is not only involved in brain development or in the response to injury. Following a three-layer assessment of its role in the central nervous system, we consider that at the cellular level, IGF-I is indeed a bona fide neurotrophic factor, modulating along ontogeny the generation and function of all the major types of brain cells, contributing to sculpt brain architecture and adaptive responses to damage. At the circuit level, IGF-I modulates neuronal excitability and synaptic plasticity at multiple sites, whereas at the system level, IGF-I intervenes in energy allocation, proteostasis, circadian cycles, mood, and cognition. Local and peripheral sources of brain IGF-I input contribute to a spatially restricted, compartmentalized, and timed modulation of brain activity. To better define these variety of actions, we consider IGF-I a modulator of brain states. This definition aims to reconcile all aspects of IGF-I neurobiology, and may provide a new conceptual framework in the design of future research on the actions of this multitasking neuromodulator in the brain.

Comorbidities and clinical outcomes in adult- and juvenile-onset Huntington's disease: a study of linked Swedish National Registries (2002-2019)

BACKGROUND

Huntington's disease (HD) is a rare, neurodegenerative disease and its complex motor, cognitive and psychiatric symptoms exert a lifelong clinical burden on both patients and their families.

OBJECTIVE

To describe the clinical burden and natural history of HD.

METHODS

This longitudinal cohort study used data from the linked Swedish national registries to describe the occurrence of comorbidities (acute and chronic), symptomatic treatments and mortality in an incident cohort of individuals who either received the first diagnosis of HD above (adult onset HD; AoHD) or below (juvenile-onset HD; JoHD) 20 years of age, compared with a matched cohort without HD from the general population. Disease burden of all individuals alive in Sweden was described during a single calendar year (2018), including the occurrence of key symptoms, treatments and hospitalizations.

RESULTS

The prevalence of HD in 2018 was approximately 10.2 per 100,000. Of 1492 individuals with a diagnosis of HD during 2002 and 2018, 1447 had AoHD and 45 had JoHD. Individuals with AoHD suffered a higher incidence of obsessive-compulsive disorder, acute psychotic episodes, pneumonia, constipation and fractures compared with matched controls. Individuals with JoHD had higher incidence rates of epilepsy, constipation and acute respiratory symptoms. Median time to all-cause mortality in AoHD was 12.1 years from diagnosis. Patients alive with HD in Sweden in 2018 displayed a pattern of increased clinical burden for a number of years since diagnosis.

CONCLUSIONS

This study demonstrates the significant and progressive clinical burden in individuals with HD and presents novel insights into the natural history of JoHD.

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.

Amendment of Altered Immune Response by Curcumin in Drosophila Model of Huntington's Disease

BACKGROUND

Though primarily classified as a brain disorder, surplus studies direct Huntington's disease (HD) to be a multi-system disorder affecting various tissues and organs, thus affecting overall physiology of host. Recently, we have reported that neuronal expression of mutant huntingtin induces immune dysregulation in Drosophila and may pose chronic threat to challenged individuals. Therefore, we tested the polyphenolic compound curcumin to circumvent the impact of immune dysregulation in Drosophila model of HD.

OBJECTIVE

The present study examined the molecular basis underlying immune derangements and immunomodulatory potential of curcumin in HD.

METHODS

UAS-GAL4 system was used to imitate the HD symptoms in Drosophila, and the desired female progenies (elav > Httex1pQ25; control and elav > Httex1pQ93; diseased) were cultured on food mixed without and with 10 μM concentration of curcumin since early development. Effect of curcumin supplementation was investigated by monitoring the hemocytes' count and their functional abilities in diseased condition. Reactive oxygen species (ROS) level in cells was assessed by DHE staining and mitochondrial dysfunction was assessed by CMXros red dye. In addition, transcript levels of pro-inflammatory cytokines and anti-microbial peptides were monitored by qRT-PCR.

RESULTS

We found that curcumin supplementation commendably reduced higher crystal cell count and phenoloxidase activity in diseased flies. Interestingly, curcumin significantly managed altered plasmatocytes count, improved their phagocytic activity by upregulating the expression of key phagocytic receptors in HD condition. Moreover, substantial alleviation of ROS levels and mitochondria dysfunction was observed in plasmatocytes of diseased flies upon curcumin supplementation. Furthermore, curcumin administration effectively attenuated transcriptional expression of pro-inflammatory cytokines and AMPs in diseased flies.

CONCLUSIONS

Our results indicate that curcumin efficiently attenuates immune derangements in HD flies and may prove beneficial in alleviating complexities associated with HD.

Metabolism in Huntington's disease: a major contributor to pathology

Huntington's disease (HD) is a progressively debilitating neurodegenerative disease exhibiting autosomal-dominant inheritance. It is caused by an unstable expansion in the CAG repeat tract of HD gene, which transforms the disease-specific Huntingtin protein (HTT) to a mutant form (mHTT). The profound neuronal death in cortico-striatal circuits led to its identification and characterisation as a neurodegenerative disease. However, equally disturbing are the concomitant whole-body manifestations affecting nearly every organ of the diseased individuals, at varying extents. Altered central and peripheral metabolism of energy, proteins, nucleic acids, lipids and carbohydrates encompass the gross pathology of the disease. Intense fluctuation of body weight, glucose homeostasis and organ-specific subcellular abnormalities are being increasingly recognised in HD. Many of these metabolic abnormalities exist years before the neuropathological manifestations such as chorea, cognitive decline and behavioural abnormalities develop, and prove to be reliable predictors of the disease progression. In this review, we provide a consolidated overview of the central and peripheral metabolic abnormalities associated with HD, as evidenced from clinical and experimental studies. Additionally, we have discussed the potential of metabolic biomolecules to translate into efficient biomarkers for the disease onset as well as progression. Finally, we provide a brief outlook on the efficacy of existing therapies targeting metabolic remediation. While it is clear that components of altered metabolic pathways can mark many aspects of the disease, it is only conceivable that combinatorial therapies aiming for neuronal protection in consort with metabolic upliftment will prove to be more efficient than the existing symptomatic treatment options.

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

Research Progress on Neuroprotection of Insulin-like Growth Factor-1 towards Glutamate-Induced Neurotoxicity

Insulin-like growth factor-1 (IGF-1) and its binding proteins and receptors are widely expressed in the central nervous system (CNS), proposing IGF-1-induced neurotrophic actions in normal growth, development, and maintenance. However, while there is convincing evidence that the IGF-1 system has specific endocrine roles in the CNS, the concept is emerging that IGF-I might be also important in disorders such as ischemic stroke, brain trauma, Alzheimer’s disease, epilepsy, etc., by inducing neuroprotective effects towards glutamate-mediated excitotoxic signaling pathways. Research in rodent models has demonstrated rescue of pathophysiological and behavioral abnormalities when IGF-1 was administered by different routes, and several clinical studies have shown safety and promise of efficacy in neurological disorders of the CNS. Focusing on the relationship between IGF-1-induced neuroprotection and glutamate-induced excitatory neurotoxicity, this review addresses the research progress in the field, intending to provide a rationale for using IGF-I clinically to confer neuroprotective therapy towards neurological diseases with glutamate excitotoxicity as a common pathological pathway.

Association between Serum Prolactin Levels and Neurodegenerative Diseases: Systematic Review and Meta-Analysis

INTRODUCTION

Prolactin (PRL) exerts inflammatory and anti-inflammatory properties and is also thought to play an important role in the pathogenesis of neurodegenerative diseases (NDs). However, serum PRL levels in patients with NDs were inconsistent in the research literature.

OBJECTIVE

We aimed to assess the serum PRL levels in patients with NDs.

METHODS

Electronic databases, including MEDLINE, Embase, Cochrane Library database, clinicaltrials.gov, Web of Science, and Google Scholar, and reference lists of articles were searched up to December 31, 2020. Pooled standard mean difference (SMD) with 95% confidence interval (CI) was calculated by fixed-effect or random-effect model analysis.

RESULTS

A total of 36 comparisons out of 29 studies (3 RCTs and 26 case controls) focusing on NDs (including Parkinson's disease, Alzheimer's disease, Huntington's disease [HD], multiple sclerosis [MS], and epilepsy) were reported. The meta-analysis showed that there was no statistically significant difference in serum PRL levels between patients with NDs and healthy controls (SMD = 0.40, 95% CI: -0.16 to 0.96, p = 0.16). Subgroup analysis showed that serum PRL levels in patients with HD and MS were higher than those of healthy controls. Furthermore, patients with NDs aged <45 years had higher serum PRL levels (SMD = 0.97, 95% CI: 0.16-1.78, p = 0.018) than healthy controls. High serum PRL levels were found in subgroups such as the microenzymatic method, Asia, and the Americas.

CONCLUSIONS

Our meta-analysis showed serum PRL levels in patients with HD and MS were significantly higher than those in healthy controls. Serum PRL levels were associated with age, region, and detection method. Other larger sample studies using more uniform detection methods are necessary to confirm our results.

Mini Review: Effect of GLP-1 Receptor Agonists and SGLT-2 Inhibitors on the Growth Hormone/IGF Axis

Accumulating evidence supports the early use of glucagon-like peptide-1 receptor agonists (GLP-1RAs) and sodium glucose transporter-2 inhibitors (SGLT-2is) for the treatment of type 2 diabetes. Indeed, these compounds exert numerous pleiotropic actions that favorably affect metabolism and diabetes comorbidities, showing an additional effect beyond glucose control. Although a substantial amount of knowledge has been generated regarding the mechanism of action of both drug classes, much remains to be understood. Growth hormone (GH) is an important driver for multiple endocrine responses involving changes in glucose and lipid metabolism, and affects several tissues and organs (e.g., bone, heart). It acts directly on several target tissues, including skeletal muscle and bone, but several effects are mediated indirectly by circulating (liver-derived) or locally produced IGF-1. In consideration of the multiple metabolic and cardiovascular effects seen in subjects treated with GLP-1RAs and SGLT-2is (e.g., reduction of hyperglycemia, weight loss, free/fat mass and bone remodeling, anti-atherosclerosis, natriuresis), it is reasonable to speculate that GH and IGF-1 may play a about a relevant role in this context. This narrative mini-review aims to describe the involvement of the GH/IGF-1/IGF-1R axis in either mediating or responding to the effects of each of the two drug classes.

Circadian rhythms in neurodegenerative disorders

Endogenous biological clocks, orchestrated by the suprachiasmatic nucleus, time the circadian rhythms that synchronize physiological and behavioural functions in humans. The circadian system influences most physiological processes, including sleep, alertness and cognitive performance. Disruption of circadian homeostasis has deleterious effects on human health. Neurodegenerative disorders involve a wide range of symptoms, many of which exhibit diurnal variations in frequency and intensity. These disorders also disrupt circadian homeostasis, which in turn has negative effects on symptoms and quality of life. Emerging evidence points to a bidirectional relationship between circadian homeostasis and neurodegeneration, suggesting that circadian function might have an important role in the progression of neurodegenerative disorders. Therefore, the circadian system has become an attractive target for research and clinical care innovations. Studying circadian disruption in neurodegenerative disorders could expand our understanding of the pathophysiology of neurodegeneration and facilitate the development of novel, circadian-based interventions for these disabling disorders. In this Review, we discuss the alterations to the circadian system that occur in movement (Parkinson disease and Huntington disease) and cognitive (Alzheimer disease and frontotemporal dementia) neurodegenerative disorders and provide directions for future investigations in this field.

Defining circadian disruption in neurodegenerative disorders

Neurodegenerative diseases encompass a large group of conditions that are clinically and pathologically diverse yet are linked by a shared pathology of misfolded proteins. The accumulation of insoluble aggregates is accompanied by a progressive loss of vulnerable neurons. For some patients, the symptoms are motor focused (ataxias), while others experience cognitive and psychiatric symptoms (dementias). Among the shared symptoms of neurodegenerative diseases is a disruption of the sleep/wake cycle that occurs early in the trajectory of the disease and may be a risk factor for disease development. In many cases, the disruption in the timing of sleep and other rhythmic physiological markers immediately raises the possibility of neurodegeneration-driven disruption of the circadian timing system. The aim of this Review is to summarize the evidence supporting the hypothesis that circadian disruption is a core symptom within neurodegenerative diseases, including Alzheimer's disease, Huntington's disease, and Parkinson's disease, and to discuss the latest progress in this field. The Review discusses evidence that neurodegenerative processes may disrupt the structure and function of the circadian system and describes circadian-based interventions as well as timed drug treatments that may improve a wide range of symptoms associated with neurodegenerative disorders. It also identifies key gaps in our knowledge.

Gastrointestinal disorders in hyperkinetic movement disorders and ataxia

BACKGROUND

Gastrointestinal (GI) disorders have been thoroughly investigated in hypokinetic disorders such as Parkinson's disease, but much less is known about GI disorders in hyperkinetic movement disorders and ataxia. The aim of this review is to draw attention to the GI disorders that are associated with these movement disorders.

METHODS

References for this systematic review were identified by searches of PubMed through May 2020. Only publications in English were reviewed.

RESULTS

Data from 249 articles were critically reviewed, compared, and integrated. The most frequently reported GI symptoms overall in hyperkinetic movement disorders and ataxia are dysphagia, sialorrhea, weight changes, esophago-gastritis, gastroparesis, constipation, diarrhea, and malabsorption. We report in detail on the frequency, characteristics, pathophysiology, and management of GI symptoms in essential tremor, restless legs syndrome, chorea, and spinocerebellar ataxias. The limited available data on GI disorders in dystonias, paroxysmal movement disorders, tardive dyskinesias, myoclonus, and non-SCA ataxias are also summarized.

CONCLUSION

The purpose of our systematic review is to draw attention that, although primarily motor disorders, hyperkinetic movement disorders and ataxia can involve the GI system. Raising awareness about the GI symptom burden in hyperkinetic movement disorders and ataxia could contribute to a new research interest in that field, as well as improved patient care.

Testosterone Levels Are Decreased and Associated with Disease Duration in Male Spinocerebellar Ataxia Type 2 Patients

Spinocerebellar ataxia type 2 (SCA2) is a progressive neurodegenerative disorder due to an unstable expansion of a CAG repeat in the ATXN2 gene. Despite clinical and experimental evidence indicating the relevance of the gonadotropic axis to the prognosis and therapeutics for several late-onset neurodegenerative disorders, its functioning and association with disease severity have not been previously explored in SCA2. To assess serum levels of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH), and their clinical relevance in SCA2 patients. A case-control study involving 94 Cuban SCA2 patients and 101 gender- and age-matched healthy controls was conducted. Testosterone, LH, and FSH serum levels were determined by radioimmunoassay or immunoradiometric assay systems. Clinical outcomes included age at onset, disease duration, Scale for the Assessment and Rating of Ataxia (SARA) score, and progression rate. Univariate general linear models were generated. Testosterone, LH, and FSH serum levels were significantly reduced in male SCA2 patients relative to control individuals. On average, there was a 35% reduction in testosterone levels in male patients versus male control individuals. Testosterone levels were associated with disease duration (r = 0.383; p = 0.025) and age at onset (r = 0.414; p = 0.011) in male SCA2 patients, but no association was observed between testosterone and CAG expansion size, SARA score, or progression rate. Testosterone levels might be a biomarker of disease progression in male SCA2 patients. Further studies are needed to explore the effects of low testosterone levels on non-motor symptoms, and to assess the potential of testosterone replacement therapy in male SCA2 patients.

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.

Thyroid hormone: sex-dependent role in nervous system regulation and disease

Thyroid hormone (TH) regulates many functions including metabolism, cell differentiation, and nervous system development. Alteration of thyroid hormone level in the body can lead to nervous system-related problems linked to cognition, visual attention, visual processing, motor skills, language, and memory skills. TH has also been associated with neuropsychiatric disorders including schizophrenia, bipolar disorder, anxiety, and depression. Males and females display sex-specific differences in neuronal signaling. Steroid hormones including testosterone and estrogen are considered to be the prime regulators for programing the neuronal signaling in a male- and female-specific manner. However, other than steroid hormones, TH could also be one of the key signaling molecules to regulate different brain signaling in a male- and female-specific manner. Thyroid-related diseases and neurological diseases show sex-specific incidence; however, the molecular mechanisms behind this are not clear. Hence, it will be very beneficial to understand how TH acts in male and female brains and what are the critical genes and signaling networks. In this review, we have highlighted the role of TH in nervous system regulation and disease outcome and given special emphasis on its sex-specific role in male and female brains. A network model is also presented that provides critical information on TH-regulated genes, signaling, and disease.

Body Mass Index Is Significantly Associated With Disease Severity in Spinocerebellar Ataxia Type 2 Patients

BACKGROUND

Spinocerebellar ataxia type 2 is a progressive neurodegenerative disorder due to an unstable expansion of a CAG repeat in the ATXN2 gene. Although weight loss has been associated with disease progression in several neurodegenerative conditions, it has been barely assessed in patients with spinocerebellar ataxia type 2.

OBJECTIVE

The objective of this study was to test whether body mass index is altered in patients with spinocerebellar ataxia type 2 with varying expansion sizes from early to late disease stages.

METHODS

A cross-sectional case-control study was performed, which included 222 clinically and molecularly diagnosed patients and 214 sex- and age-matched healthy individuals. ATXN2 genotypes and sex were considered as risk factors. Clinical outcomes included the body mass index, age at onset, disease duration, Scale for the Assessment and Rating of Ataxia score, disease stage, dysphagia, and progression rate. Multiple linear regression models were generated.

RESULTS

Body mass index was significantly decreased in male patients, but not in female patients, relative to control subjects. In addition to sex, body mass index was significantly associated with age at onset and progression rate. Conversely, body mass index, along with repeat length in ATXN2 expanded alleles and disease duration, was associated with Scale for the Assessment and Rating of Ataxia score. In addition, body mass index, along with the age at onset and the repeat length in ATXN2 normal and expanded alleles, has a significant influence on progression rate.

CONCLUSIONS

Body mass index might be a useful biomarker of disease severity, particularly in male patients with spinocerebellar ataxia type 2 in the context of nutritional interventions or clinical trials assessing the efficacy of promising new drugs. © 2021 International Parkinson and Movement Disorder Society.

What, When and How to Measure-Peripheral Biomarkers in Therapy of Huntington's Disease

Among the main challenges in further advancing therapeutic strategies for Huntington’s disease (HD) is the development of biomarkers which must be applied to assess the efficiency of the treatment. HD is a dreadful neurodegenerative disorder which has its source of pathogenesis in the central nervous system (CNS) but is reflected by symptoms in the periphery. Visible symptoms include motor deficits and slight changes in peripheral tissues, which can be used as hallmarks for prognosis of the course of HD, e.g., the onset of the disease symptoms. Knowing how the pathology develops in the context of whole organisms is crucial for the development of therapy which would be the most beneficial for patients, as well as for proposing appropriate biomarkers to monitor disease progression and/or efficiency of treatment. We focus here on molecular peripheral biomarkers which could be used as a measurable outcome of potential therapy. We present and discuss a list of wet biomarkers which have been proposed in recent years to measure pre- and postsymptomatic HD. Interestingly, investigation of peripheral biomarkers in HD can unravel new aspects of the disease pathogenesis. This especially refers to inflammatory proteins or specific immune cells which attract scientific attention in neurodegenerative disorders.

The supraoptic and paraventricular nuclei in healthy aging and neurodegeneration

The supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus undergo structural and functional changes over the course of healthy aging. These nuclei and their connections are also heterogeneously affected by several different neurodegenerative diseases. This chapter reviews the involvement of the SON and PVN, the hypothalamic-pituitary axes, and the peptide hormones produced in both nuclei in healthy aging and in neurodegeneration, with a focus on Alzheimer's disease (AD), frontotemporal dementia (FTD), amyotrophic lateral sclerosis, progressive supranuclear palsy, Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy, and Huntington's disease. Although age-related changes occur in several regions of the hypothalamus, the SON and PVN are relatively preserved during aging and in many neurodegenerative disorders. With aging, these nuclei do undergo some sexually dimorphic changes including changes in size and levels of vasopressin and corticotropin-releasing hormone, likely due to age-related changes in sex hormones. In contrast, oxytocinergic cells and circulating levels of thyrotropin-releasing hormone remain stable. A relative resistance to many forms of neurodegenerative pathology is also observed, in comparison to other hypothalamic and brain regions. Mirroring the pattern observed in aging, pathologic hallmarks of AD, and some subtypes of FTD are observed in the PVN, though to a milder degree than are observed in other brain regions, while the SON is relatively spared. In contrast, the SON appears more vulnerable to alpha-synuclein pathology of DLB and PD. The consequences of these alterations may help to inform several of the physiologic changes observed in aging and neurodegenerative disease.

Cardiac electrical remodeling and neurodegenerative diseases association

Cardiac impairment contributes significantly to the mortality associated with several neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), primarily recognized as brain pathologies. These diseases may be caused by aggregation of a misfolded protein, most often, in the brain, although new evidence also reveals peripheral abnormalities. After characterization of the cardiac involvement in neurodegenerative diseases, several studies concentrated on elucidating the cause of the impaired cardiac function. However, most of the current knowledge is focused on the mechanical aspects of the heart rather than the electrical disturbances. The main objective of this review is to summarize the most recent advances in the elucidation of cardiac electrical remodeling in the neurodegenerative environment. We aimed to determine a crosstalk between the heart and the brain in three neurodegenerative conditions: AD, PD, and HD. We found that the most studies demonstrated important alterations in the electrocardiogram (ECG) of patients with neurodegeneration and in animal models of the conditions. We also showed that little is described when considering excitability disruptions in cardiomyocytes, for example, action potential impairments. It is a matter of contention whether central nervous system abnormalities or the peripheral ones increase the risk of heart diseases in patients with neurodegenerative conditions. To determine this notion, there is a need for new heart studies focusing specifically on the cardiac electrophysiology (e.g., ECG and cardiomyocyte excitability). This review could serve as an important guide in designing novel accurate approaches targeting the heart in neuronal conditions.

Inflammation in Huntington's disease: A few new twists on an old tale

Huntington's disease (HD) is a neurodegenerative disease characterized by prominent loss of neurons in the striatum and cortex. Traditionally research in HD has focused on brain changes as they cause progressive motor dysfunction, cognitive decline and psychiatric disorders. The discovery that huntingtin protein (HTT) and its mutated form (mHTT) are expressed not only in the brain but also in different organs and tissues paved the way for the hypothesis that HD might affect regions beyond the central nervous system (CNS). Besides pathological deposition of mHTT, other mechanisms, including inflammation, seem to underlie HD pathogenesis and progression. Altered inflammation can be evidenced even before the onset of classical symptoms of HD. Herein, we will discuss current pre-clinical and clinical evidence on immune/inflammatory changes in peripheral organs during HD development and progression. The understanding of the impact of inflammation on peripheral organs may open new venues for the development of novel therapeutic targets in HD.

Androgen Therapy in Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and Huntington disease, are characterized by the loss of neurons as well as neuronal function in multiple regions of the central and peripheral nervous systems. Several studies in animal models have shown that androgens have neuroprotective effects in the brain and stimulate axonal regeneration. The presence of neuronal androgen receptors in the peripheral and central nervous system suggests that androgen therapy might be useful in the treatment of neurodegenerative diseases. To illustrate, androgen therapy reduced inflammation, amyloid-β deposition, and cognitive impairment in patients with AD. As well, improvements in remyelination in MS have been reported; by comparison, only variable results are observed in androgen treatment of PD. In ALS, androgen administration stimulated motoneuron recovery from progressive damage and regenerated both axons and dendrites. Only a few clinical studies are available in human individuals despite the safety and low cost of androgen therapy. Clinical evaluations of the effects of androgen therapy on these devastating diseases using large populations of patients are strongly needed.

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.

Prevalence of Non-psychiatric Comorbidities in Pre-symptomatic and Symptomatic Huntington's Disease Gene Carriers in Poland

Huntington's disease (HD) is monogenic neurodegenerative disorder caused by CAG expansions within the Huntingtin gene (Htt); it has a prevalence of 1 in 10,000 worldwide and is invariably fatal. Typically, healthy individuals have fewer than 35 CAG repeats, while the CAG expansions range from 36 to ~200 in HD patients. The hallmark of HD is neurodegeneration, especially in the striatal nuclei, basal ganglia and cerebral cortex, leading to neurological symptoms that involve motor, cognitive, and psychiatric events. However, HD is a complex disorder that may also affect peripheral organs, so it is possible that HD patients could be affected by comorbidities. Hence, we investigated the prevalence of comorbid conditions in HD patients (pre-symptomatic and symptomatic groups) and compared the frequency of those conditions to a control group. Our groups represent 65% of HD gene carriers registered in Poland. We identified 8 clusters of comorbid conditions in both HD groups, namely: musculoskeletal, allergies, cardiovascular, neurological, gastrointestinal, thyroid, psychiatric, and ophthalmologic. We found that HD patients have a significantly higher percentage of co-existing conditions in comparison to the control group. Among the 8 clusters of diseases, musculoskeletal, psychiatric, and cardiovascular events were significantly more frequent in both pre- and symptomatic HD patients, while neurological and gastrointestinal clusters showed significantly higher occurrence in the HD symptomatic group. A greater recognition of comorbidity in HD might help to better understand health outcomes and improve clinical management.

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.

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.

Fluid and imaging biomarkers for Huntington's disease

Huntington's disease is a chronic progressive neurodegenerative condition for which there is no disease-modifying treatment. The known genetic cause of Huntington's disease makes it possible to identify individuals destined to develop the disease and instigate treatments before the onset of symptoms. Multiple trials are already underway that target the cause of HD, yet clinical measures are often insensitive to change over typical clinical trial duration. Robust biomarkers of drug target engagement, disease severity and progression are required to evaluate the efficacy of treatments and concerted efforts are underway to achieve this. Biofluid biomarkers have potential advantages of direct quantification of biological processes at the molecular level, whilst imaging biomarkers can quantify related changes at a structural level in the brain. The most robust biofluid and imaging biomarkers can offer complementary information, providing a more comprehensive evaluation of disease stage and progression to inform clinical trial design and endpoints.

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.

Transcriptomic Biomarkers for Huntington's Disease: Are Gene Expression Signatures in Whole Blood Reliable Biomarkers?

Huntington's disease (HD) is a severe neurodegenerative disorder manifesting as progressive impairment of motor function, cognitive decline, psychiatric symptoms, and immunological and endocrine dysfunction. We explored the consistency of blood transcriptomic biomarkers in HD based on a novel Slovene patient cohort and expert review of previous studies. HumanHT-12 v4 BeadChip microarrays were performed on the whole blood samples of a cohort of 23 HD mutation carriers and 23 controls to identify differentially expressed (DE) transcripts. In addition, we performed an expert review of DE transcripts identified in comparable HD studies from whole blood, to identify any consistent signature of HD. In the Slovene cohort, we identified 740 DE transcripts (p < 0.01 and a false discovery rate (FDR) of <0.1) of which 414 were downregulated and 326 were upregulated. Pathway analyses of DE transcripts showed enrichment for pathways involved in systemic, rather than neural processes in HD. With an expert review of comparable studies, we have further identified 15 DE transcripts shared by 3 studies. We suggest transcriptomic changes in blood reflect systemic changes in HD pathogenesis, rather than being a direct result of the neuropathological processes in the central nervous system during HD progression, and thus, have limited value as disease 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.

Huntington's Disease and Diabetes: Chronological Sequence of its Association

Although Huntington’s disease (HD) is primarily considered a rare neurodegenerative disorder, it has been linked to glucose metabolism alterations and diabetes, as has been described in other neuro syndromes such as Friedreich’s ataxia or Alzheimer’s disease. This review surveys the existing literature on HD and its potential relationship with diabetes, glucose metabolism-related indexes and pancreas morphology, in humans and in animal’s models. The information is reported in chronological sequence. That is, studies performed before and after the identification of the genetic defect underlying HD (CAG: encoding glutamine ≥36 repeats located in exon 1 of the HTT gene) and with the development and evolution of HD animal models. The aim of the review is to evaluate whether impaired glucose metabolism contributes to the development of HD, and whether optimized glycemic control may ameliorate the symptoms of HD.

Biofluid Biomarkers in Huntington's Disease

Huntington's disease (HD) is a chronic progressive neurodegenerative condition where new markers of disease progression are needed. So far no disease-modifying interventions have been found, and few interventions have been proven to alleviate symptoms. This may be partially explained by the lack of reliable indicators of disease severity, progression, and phenotype.Biofluid biomarkers may bring advantages in addition to clinical measures, such as reliability, reproducibility, price, accuracy, and direct quantification of pathobiological processes at the molecular level; and in addition to empowering clinical trials, they have the potential to generate useful hypotheses for new drug development.In this chapter we review biofluid biomarker reports in HD, emphasizing those we feel are likely to be closest to clinical applicability.

Therapeutic Effects of Anthocyanins and Environmental Enrichment in R6/1 Huntington's Disease Mice

BACKGROUND

Huntington's disease (HD) is a progressive neurodegenerative disease with no effective treatment or cure. Environmental enrichment has been used to slow processes leading to ageing and neurodegenerative diseases including HD. Phenolic phytochemicals including anthocyanins have also been shown to improve brain function in ageing and neurodegenerative diseases.

OBJECTIVE

This study examined the effects of anthocyanin dietary supplementation and environmental enrichment on behavioural phenotypes and brain cholesterol metabolic alterations in the R6/1 mouse model of HD.

METHODS

R6/1 HD mice and their wild-type littermate controls were randomised into the different experimental conditions, involving either environmentally enriched versus standard housing conditions, or anthocyanin versus control diet. Motor dysfunction was assessed from 6 to 26 weeks using the RotaRod and the hind-paw clasping tests. Gas chromatography - tandem mass spectrometry was used to quantify a broad range of sterols in the striatum and cortex of R6/1 HD mice.

RESULTS

Anthocyanin dietary supplementation delayed the onset of motor dysfunction in female HD mice. Environmental enrichment improved motor function and the hind paw clasping phenotype in male HD mice only. These mice also had lower levels of cholesterol oxidation products in the cortex compared to standard-housed mice.

CONCLUSION

Both anthocyanin supplementation and environmental enrichment are able to improve the motor dysfunction phenotype of R6/1 mice, however the effectiveness of these interventions was different between the two sexes. The interventions examined did not alter brain cholesterol metabolic deficits that have been reported previously in this mouse model of HD.

Huntington's disease blood and brain show a common gene expression pattern and share an immune signature with Alzheimer's disease

There is widespread transcriptional dysregulation in Huntington's disease (HD) brain, but analysis is inevitably limited by advanced disease and postmortem changes. However, mutant HTT is ubiquitously expressed and acts systemically, meaning blood, which is readily available and contains cells that are dysfunctional in HD, could act as a surrogate for brain tissue. We conducted an RNA-Seq transcriptomic analysis using whole blood from two HD cohorts, and performed gene set enrichment analysis using public databases and weighted correlation network analysis modules from HD and control brain datasets. We identified dysregulated gene sets in blood that replicated in the independent cohorts, correlated with disease severity, corresponded to the most significantly dysregulated modules in the HD caudate, the most prominently affected brain region, and significantly overlapped with the transcriptional signature of HD myeloid cells. High-throughput sequencing technologies and use of gene sets likely surmounted the limitations of previously inconsistent HD blood expression studies. Our results suggest transcription is disrupted in peripheral cells in HD through mechanisms that parallel those in brain. Immune upregulation in HD overlapped with Alzheimer's disease, suggesting a common pathogenic mechanism involving macrophage phagocytosis and microglial synaptic pruning, and raises the potential for shared therapeutic approaches.

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.

Insulin-Like Growth Factor-1 but Not Insulin Predicts Cognitive Decline in Huntington's Disease

Background

Huntington's disease (HD) is one of several neurodegenerative disorders that have been associated with metabolic alterations. Changes in Insulin Growth Factor 1 (IGF-1) and/or insulin input to the brain may underlie or contribute to the progress of neurodegenerative processes. Here, we investigated the association over time between changes in plasma levels of IGF-1 and insulin and the cognitive decline in HD patients.

Methods

We conducted a multicentric cohort study in 156 patients with genetically documented HD aged from 22 to 80 years. Among them, 146 patients were assessed at least twice with a follow-up of 3.5 ± 1.8 years. We assessed their cognitive decline using the Unified Huntington’s Disease Rating Scale, and their IGF-1 and insulin plasmatic levels, at baseline and once a year during the follow-up. Associations were evaluated using a mixed-effect linear model.

Results

In the cross-sectional analysis at baseline, higher levels of IGF-1 and insulin were associated with lower cognitive scores and thus with a higher degree of cognitive impairment. In the longitudinal analysis, the decrease of all cognitive scores, except the Stroop interference, was associated with the IGF-1 level over time but not of insulin.

Conclusions

IGF-1 levels, unlike insulin, predict the decline of cognitive function in HD.

Regulation of L-type Ca2+ Channel Activity and Insulin Secretion by Huntingtin-associated Protein 1

Huntingtin-associated protein 1 (Hap1) was originally identified as a protein that binds to the Huntington disease protein, huntingtin. Growing evidence has shown that Hap1 participates in intracellular trafficking via its association with various microtubule-dependent transporters and organelles. Recent studies also revealed that Hap1 is involved in exocytosis such as insulin release from pancreatic β-cells. However, the mechanism underlying the action of Hap1 on insulin release remains to be investigated. We found that Hap1 knock-out mice had a lower plasma basal insulin level than control mice. Using cultured pancreatic β-cell lines, INS-1 cells, we confirmed that decreasing Hap1 reduces the number of secreted vesicles and inhibits vesicle exocytosis. Electrophysiology and imaging of intracellular Ca²⁺ measurements demonstrated that Hap1 depletion significantly reduces the influx of Ca²⁺ mediated by L-type Ca²⁺ channels (Cav). This decrease is not due to reduced expression of Cav1.2 channel mRNA but results from the decreased distribution of Cav1.2 on the plasma membrane of INS-1 cells. Fluorescence recovery after photobleaching showed a defective movement of Cav1.2 in Hap1 silencing INS-1 cells. Our findings suggest that Hap1 is important for insulin secretion of pancreatic β-cells via regulating the intracellular trafficking and plasma membrane localization of Cav1.2, providing new insight into the mechanisms that regulate insulin release from pancreatic β-cells.

Corticosterone dysregulation exacerbates disease progression in the R6/2 transgenic mouse model of Huntington's disease

Huntington's disease (HD) is a genetic neurological disorder that causes severe and progressive motor, cognitive, psychiatric, and metabolic symptoms. There is a robust, significant elevation in circulating levels of the stress hormone, cortisol, in HD patients; however, the causes and consequences of this elevation are largely uncharacterized. Here, we evaluated whether elevated levels of corticosterone, the rodent homolog of cortisol, contributed to the development of symptomology in transgenic HD mice. Wild-type (WT) and transgenic R6/2 mice were given either 1) adrenalectomy with WT-level corticosterone replacement (10ng/ml), 2) adrenalectomy with high HD-level corticosterone replacement (60ng/ml), or 3) sham surgery without replacement. R6/2 mice on HD-level replacement showed severe and rapid weight loss (p<0.05) and a shorter latency to death (p<0.01) relative to the HD mice on WT-level replacement. We further evaluated basal and stress-induced levels of circulating corticosterone in R6/2 mice throughout the course of their life. We found that R6/2 transgenic HD mice display a spontaneous elevation in circulating corticosterone levels that became significant at 10weeks of age. Furthermore, we identified significant dysregulation of circadian rhythmicity of corticosterone release measured over a 24h period compared to wild-type controls. Unexpectedly, we found that R6/2 transgenic mice show a blunted corticosterone response to restraint stress, compared to wild-type mice. Together, these data provide further evidence that HPA-axis activity is abnormal in R6/2 mice, and highlight the important role that cortisol plays in HD symptom development. Our findings suggest that cortisol-reducing therapeutics may be of value in improving HD patient quality of life.