Neuro-Cardio Mechanisms in Huntington's Disease and Other Neurodegenerative Disorders

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.

Brain-Periphery Interactions in Huntington's Disease: Mediators and Lifestyle Interventions

Prominent pathological features of Huntington's disease (HD) are aggregations of mutated Huntingtin protein (mHtt) in the brain and neurodegeneration, which causes characteristic motor (such as chorea and dystonia) and non-motor symptoms. However, the numerous systemic and peripheral deficits in HD have gained increasing attention recently, since those factors likely modulate disease progression, including brain pathology. While whole-body metabolic abnormalities and organ-specific pathologies in HD have been relatively well described, the potential mediators of compromised inter-organ communication in HD have been insufficiently characterized. Therefore, we applied an exploratory literature search to identify such mediators. Unsurprisingly, dysregulation of inflammatory factors, circulating mHtt, and many other messenger molecules (hormones, lipids, RNAs) were found that suggest impaired inter-organ communication, including of the gut-brain and muscle-brain axis. Based on these findings, we aimed to assess the risks and potentials of lifestyle interventions that are thought to improve communication across these axes: dietary strategies and exercise. We conclude that appropriate lifestyle interventions have great potential to reduce symptoms and potentially modify disease progression (possibly via improving inter-organ signaling) in HD. However, impaired systemic metabolism and peripheral symptoms warrant particular care in the design of dietary and exercise programs for people with HD.

Perfluorononanoic Acid Induces Neurotoxicity via Synaptogenesis Signaling in Zebrafish

Perfluorononanoic acid (PFNA), commonly used as an alternative polyfluorinated compound (PFC) of perfluorooctanoic acid (PFOA), has been widely detected in the aquatic environment. Previous ecotoxicological and epidemiological results suggested that some neurobehavioral effects were associated with PFC exposure; however, the ecological impacts and underlying neurotoxicity mechanisms remain unclear, particularly in aquatic organisms during sensitive, early developmental stages. In this study, zebrafish embryos were exposed to environmentally relevant concentrations of PFNA for 120 h, and the neurological effects of PFNA were comprehensively assessed using transcriptional, biochemical, morphological, and behavioral assays. RNA sequencing and advanced bioinformatics analyses predicted and characterized the key biological processes and pathways affected by PFNA exposure, which included the synaptogenesis signaling pathway, neurotransmitter synapse, and CREB signaling in neurons. Neurotransmitter levels (acetylcholine, glutamate, 5-hydroxytryptamine, γ-aminobutyric acid, dopamine, and noradrenaline) were significantly decreased in zebrafish larvae, and the Tg(gad67:GFP) transgenic line revealed a decreased number of GABAergic neurons in PFNA-treated larvae. Moreover, the swimming distance, rotation frequency, and activity degree were also significantly affected by PFNA, linking molecular-level changes to behavioral consequences.

Perinatal Lead Exposure Promotes Sex-Specific Epigenetic Programming of Disease-Relevant Pathways in Mouse Heart

Environmental contaminants such as the metal lead (Pb) are associated with cardiovascular disease, but the underlying molecular mechanisms are poorly understood. In particular, little is known about how exposure to Pb during early development impacts the cardiac epigenome at any point across the life course and potential differences between sexes. In a mouse model of human-relevant perinatal exposures, we utilized RNA-seq and Enhanced Reduced Representation Bisulfite Sequencing (ERRBS) to investigate the effects of Pb exposure during gestation and lactation on gene expression and DNA methylation, respectively, in the hearts of male and female mice at weaning. For ERRBS, we identified differentially methylated CpGs (DMCs) or differentially methylated 1000 bp regions (DMRs) based on a minimum absolute change in methylation of 10% and an FDR < 0.05. For gene expression data, an FDR < 0.05 was considered significant. No individual genes met the FDR cutoff for gene expression; however, we found that Pb exposure leads to significant changes in the expression of gene pathways relevant to cardiovascular development and disease. We further found that Pb promotes sex-specific changes in DNA methylation at hundreds of gene loci (280 DMCs and 99 DMRs in males, 189 DMCs and 121 DMRs in females), and pathway analysis revealed that these CpGs and regions collectively function in embryonic development. In males, differential methylation also occurred at genes related to immune function and metabolism. We then investigated whether genes exhibiting differential methylation at weaning were also differentially methylated in hearts from a cohort of Pb-exposed mice at adulthood. We found that a single gene, Galnt2, showed differential methylation in both sexes and time points. In a human cohort investigating the influence of prenatal Pb exposure on the epigenome, we also observed an inverse association between first trimester Pb concentrations and adolescent blood leukocyte DNA methylation at a locus in GALNT2, suggesting that this gene may represent a biomarker of Pb exposure across species. Together, these data, across two time points in mice and in a human birth cohort study, collectively demonstrate that Pb exposure promotes sex-specific programming of the cardiac epigenome, and provide potential mechanistic insight into how Pb causes cardiovascular disease.

A minimal region of the HSP90AB1 promoter is suitable for ubiquitous expression in different somatic tissues with applicability for gene therapy

Huntington's disease (HD) is a multi-tissue failure disorder for which there is no cure. We have previously shown an effective therapeutic approach limited mainly to the central nervous system, based on a synthetic zinc finger (ZF) transcription repressor gene therapy, but it would be important to target other tissues as well. In this study, we identify a novel minimal HSP90AB1 promoter region that can efficiently control expression not only in the CNS but also in other affected HD tissues. This promoter-enhancer is effective in driving expression of ZF therapeutic molecules in both HD skeletal muscles and the heart, in the symptomatic R6/1 mouse model. Moreover, for the first time we show that ZF molecules repressing mutant HTT reverse transcriptional pathological remodelling in HD hearts. We conclude that this HSP90AB1 minimal promoter may be used to target multiple HD organs with therapeutic genes. The new promoter has the potential to be added to the portfolio of gene therapy promoters, for use where ubiquitous expression is needed.

Transcriptomic profiling of miR-203a inhibitor and miR-34b-injected zebrafish (Danio rerio) validates oil-induced neurological, cardiovascular and eye toxicity response pathways

The global sequencing of microRNA (miRNA; miR) and integration to downstream mRNA expression profiles in early life stages (ELS) of fish following exposure to crude oil determined consistently dysregulated miRNAs regardless of the oil source or fish species. The overlay of differentially expressed miRNAs and mRNAs into in silico software determined that the key roles of these miRNAs were predicted to be involved in cardiovascular, neurological and visually-mediated pathways. Of these, altered expression of miRNAs, miR-203a and miR-34b were predicted to be primary targets of crude oil. To better characterize the effect of these miRNAs to downstream transcript changes, zebrafish embryos were microinjected at 1 h post fertilization (hpf) with either a miR-203a inhibitor or miR-34b. Since both miRs have been shown to be associated with aryl hydrocarbon receptor (AhR) function, benzo(a)pyrene (BaP), a potent AhR agonist, was used as a potential positive control. Transcriptomic profiling was conducted on injected and exposed larvae at 7 and 72 hpf, and eye morphology assessed following exposure at 72 hpf. The top predicted physiological system disease and functions between differentially expressed genes (DEGs) shared with miR-203a inhibitor-injected and miR-34b-injected embryos were involved in brain formation, and the development of the central nervous system and neurons. When DEGs of miR-203a inhibitor-injected embryos were compared with BaP-exposed DEGs, alterations in nervous system development and function, and abnormal morphology of the neurosensory retina, eye and nervous tissue were predicted, consistent with both AhR and non-AhR pathways. When assessed morphologically, the eye area of miR-203a inhibitor and miR-34b-injected and BaP-exposed embryos were significantly reduced. These results suggest that miR-203a inhibition and miR-34b overexpression contribute to neurological, cardiovascular and eye toxicity responses that are caused by oil and PAH exposure in ELS fish, and are likely mediated through both AhR and non-AhR pathways.

MiR-483-3p improves learning and memory abilities via XPO1 in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD), a common form of dementia, has been reported to influence 27 million individuals globally. Several risk factors including oxidative stress, gut microbiota imbalance, and cognitive activity are reported to be closely associated with the initiation or progression of AD. Although miR-483-3p was identified to be downregulated in AD patient serum. However, the biological role and mechanism of miR-483-3p remained unknown in AD. Here, we explored the role of miR-483-3p in AD.

METHODS

Sprague-Dawley rats were injected with homocysteine (Hcy) to establish an AD animal model. The Morris water maze tests and contextual fear tests were conducted to assess the cognitive and memory abilities of rats. TUNEL staining was utilized to determine cell apoptosis. Luciferase reporter assay was used to evaluate the binding relation between miR-483-3p and exportin 1 (XPO1).

RESULTS

Homocysteine treatment (400 μg/kg) induced the learning, cognitive and memory defects of rats. miR-483-3p was downregulated in Hcy-treated rat hippocampus. Functionally, miR-483-3p alleviated cell apoptosis and impairments of learning and memory abilities in Hcy-treated rats. In addition, miR-483-3p inhibited cell apoptosis and protein level of AD-associated factors (APP, BACE1, and Aβ1-42) in PC12 cells. In mechanism, miR-483-3p was confirmed to target XPO1 in PC12 cells. XPO1 displayed high level in rat hippocampus and was negatively correlated with miR-483-3p levels. Finally, XPO1 overexpression rescued the suppressive effect of miR-483-3p on cell apoptosis and protein levels of AD-associated factors.

CONCLUSIONS

miR-483-3p alleviates neural cell apoptosis and impairments of learning and memory abilities by targeting XPO1 in AD.

The Inflamm-Aging Model Identifies Key Risk Factors in Atherosclerosis

Background: Atherosclerosis, one of the main threats to human life and health, is driven by abnormal inflammation (i.e., chronic inflammation or oxidative stress) during accelerated aging. Many studies have shown that inflamm-aging exerts a significant impact on the occurrence of atherosclerosis, particularly by inducing an immune homeostasis imbalance. However, the potential mechanism by which inflamm-aging induces atherosclerosis needs to be studied more thoroughly, and there is currently a lack of powerful prediction models.

Methods: First, an improved inflamm-aging prediction model was constructed by integrating aging, inflammation, and disease markers with the help of machine learning methods; then, inflamm-aging scores were calculated. In addition, the causal relationship between aging and disease was identified using Mendelian randomization. A series of risk factors were also identified by causal analysis, sensitivity analysis, and network analysis.

Results: Our results revealed an accelerated inflamm-aging pattern in atherosclerosis and suggested a causal relationship between inflamm-aging and atherosclerosis. Mechanisms involving inflammation, nutritional balance, vascular homeostasis, and oxidative stress were found to be driving factors of atherosclerosis in the context of inflamm-aging.

Conclusion: In summary, we developed a model integrating crucial risk factors in inflamm-aging and atherosclerosis. Our computation pipeline could be used to explore potential mechanisms of related diseases.

Identification of the Transcriptional Biomarkers Panel Linked to Pathological Remodelling of the Eye Tissues in Various HD Mouse Models

Ocular abnormalities are becoming associated with a spectrum of pathological events in various neurodegenerative diseases. Huntington's disease (HD) is just such an example of a fatal neurological disorder, where mutated genes (CAG trinucleotide expansions in the Huntingtin gene) have widespread expression, leading to the production of mutant Huntingtin (mHTT) protein. It is well known that mutant HTT protein is prone to form toxic aggregates, which are a typical pathological feature, along with global transcriptome alterations. In this study, we employed well-established quantitative methods such as Affymetrix arrays and quantitative PCR (qPCR) to identify a set of transcriptional biomarkers that will track HD progression in three well-established mouse models: R6/2, R6/1, and HdhQ150. Our array analysis revealed significantly deregulated networks that are related to visual processes and muscle contractions. Furthermore, our targeted quantitative analysis identified a panel of biomarkers with some being dysregulated even at the presymptomatic stage of the disease, e.g., Opn1mw, Opn1sw, and Pfkfb2. Some of the deregulated genes identified in this study have been linked to other genetic ocular disorders such as: GNAT2, a source of achromatopsia, and REEP6, linked to Retinitis pigmentosa. It may thus be a useful platform for preclinical evaluations of therapeutic interventions.

Structural Abnormalities of the Optic Nerve and Retina in Huntington's Disease Pre-Clinical and Clinical Settings

Huntington's disease (HD) is a fatal neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin protein. HD-related pathological remodelling has been reported in HD mouse models and HD carriers. In this study, we studied structural abnormalities in the optic nerve by employing Spectral Domain Optical Coherence Tomography (SD-OCT) in pre-symptomatic HD carriers of Caucasian origin. Transmission Electron Microscopy (TEM) was used to investigate ultrastructural changes in the optic nerve of the well-established R6/2 mouse model at the symptomatic stage of the disease. We found that pre-symptomatic HD carriers displayed a significant reduction in the retinal nerve fibre layer (RNFL) thickness, including specific quadrants: superior, inferior and temporal, but not nasal. There were no other significant irregularities in the GCC layer, at the macula level and in the optic disc morphology. The ultrastructural analysis of the optic nerve in R6/2 mice revealed a significant thinning of the myelin sheaths, with a lamellar separation of the myelin, and a presence of myelonoid bodies. We also found a significant reduction in the thickness of myelin sheaths in peripheral nerves within the choroids area. Those ultrastructural abnormalities were also observed in HD photoreceptor cells that contained severely damaged membrane disks, with evident vacuolisation and swelling. Moreover, the outer segment of retinal layers showed a progressive disintegration. Our study explored structural changes of the optic nerve in pre- and clinical settings and opens new avenues for the potential development of biomarkers that would be of great interest in HD gene therapies.

Geographic Barriers Drive Disparities in Specialty Center Access for Older Adults with Huntington's Disease

BACKGROUND

Huntington's Disease Society of America Centers of Excellence (HDSA COEs) are primary hubs for Huntington's disease (HD) research opportunities and accessing new treatments. Data on the extent to which HDSA COEs are accessible to individuals with HD, particularly those older or disabled, are lacking.

OBJECTIVE

To describe persons with HD in the U.S. Medicare program and characterize this population by proximity to an HDSA COE.

METHODS

We conducted a cross-sectional study of Medicare beneficiaries ages ≥65 with HD in 2017. We analyzed data on benefit entitlement, demographics, and comorbidities. QGis software and Google Maps Interface were employed to estimate the distance from each patient to the nearest HDSA COE, and the proportion of individuals residing within 100 miles of these COEs at the state level.

RESULTS

Among 9,056 Medicare beneficiaries with HD, 54.5% were female, 83.0% were white; 48.5% were ≥65 years, but 64.9% originally qualified for Medicare due to disability. Common comorbidities were dementia (32.4%) and depression (35.9%), and these were more common in HD vs. non-HD patients. Overall, 5,144 (57.1%) lived within 100 miles of a COE. Race/ethnicity, sex, age, and poverty markers were not associated with below-average proximity to HDSA COEs. The proportion of patients living within 100 miles of a center varied from < 10% (16 states) to > 90% (7 states). Most underserved states were in the Mountain and West Central divisions.

CONCLUSION

Older Medicare beneficiaries with HD are frequently disabled and have a distinct comorbidity profile. Geographical, rather than sociodemographic factors, define the HD population with limited access to HDSA COEs.

Recent Advances in Modeling Mitochondrial Cardiomyopathy Using Human Induced Pluripotent Stem Cells

Around one third of patients with mitochondrial disorders develop a kind of cardiomyopathy. In these cases, severity is quite variable ranging from asymptomatic status to severe manifestations including heart failure, arrhythmias, and sudden cardiac death. ATP is primarily generated in the mitochondrial respiratory chain via oxidative phosphorylation by utilizing fatty acids and carbohydrates. Genes in both the nuclear and the mitochondrial DNA encode components of this metabolic route and, although mutations in these genes are extremely rare, the risk to develop cardiac symptoms is significantly higher in this patient cohort. Additionally, infants with cardiovascular compromise in mitochondrial deficiency display a worse late survival compared to patients without cardiac symptoms. At this point, the mechanisms behind cardiac disease progression related to mitochondrial gene mutations are poorly understood and current therapies are unable to substantially restore the cardiac performance and to reduce the disease burden. Therefore, new strategies are needed to uncover the pathophysiological mechanisms and to identify new therapeutic options for mitochondrial cardiomyopathies. Here, human induced pluripotent stem cell (iPSC) technology has emerged to provide a suitable patient-specific model system by recapitulating major characteristics of the disease in vitro, as well as to offer a powerful platform for pre-clinical drug development and for the testing of novel therapeutic options. In the present review, we summarize recent advances in iPSC-based disease modeling of mitochondrial cardiomyopathies and explore the patho-mechanistic insights as well as new therapeutic approaches that were uncovered with this experimental platform. Further, we discuss the challenges and limitations of this technology and provide an overview of the latest techniques to promote metabolic and functional maturation of iPSC-derived cardiomyocytes that might be necessary for modeling of mitochondrial disorders.

Targeted Genetic Reduction of Mutant Huntingtin Lessens Cardiac Pathology in the BACHD Mouse Model of Huntington's Disease

Individuals affected by Huntington's disease (HD) present with progressive degeneration that results in a wide range of symptoms, including cardiovascular (CV) dysfunction. The huntingtin gene (HTT) and its product are ubiquitously expressed, hence, the cardiomyopathy could also be driven by defects caused by its mutated form (mHTT) in the cardiomyocytes themselves. In the present study, we sought to determine the contribution of the mHTT expressed in the cardiomyocytes to CV symptoms. We utilized the BACHD mouse model, which exhibits many of the HD core symptoms, including CV dysfunction. This model allows the targeted genetic reduction of mHTT expression in the cardiomyocytes while maintaining the expression of the mHTT in the rest of the body. The BACHD line was crossed with a line of mice in which the expression of Cre recombinase is driven by the cardiac-specific alpha myosin-heavy chain (Myh6) promoter. The offspring of this cross (BMYO mice) exhibited a dramatic reduction in mHTT in the heart but not in the striatum. The BMYO mice were evaluated at 6 months old, as at this age, the BACHD line displays a strong CV phenotype. Echocardiogram measurements found improvement in the ejection fraction in the BMYO line compared to the BACHD, while hypertrophy was observed in both mutant lines. Next, we examined the expression of genes known to be upregulated during pathological cardiac hypertrophy. As measured by qPCR, the BMYO hearts exhibited significantly less expression of collagen1a as well as Gata4, and brain natriuretic peptide compared to the BACHD. Fibrosis in the hearts assessed by Masson's trichrome stain and the protein levels of fibronectin were reduced in the BMYO hearts compared to BACHD. Finally, we examined the performance of the mice on CV-sensitive motor tasks. Both the overall activity levels and grip strength were improved in the BMYO mice. Therefore, we conclude that the reduction of mHtt expression in the heart benefits CV function in the BACHD model, and suggest that cardiomyopathy should be considered in the treatment strategies for HD.

Do Neurotrophins Connect Neurological Disorders and Heart Diseases?

Neurotrophins (NTs) are one of the most characterized neurotrophic factor family members and consist of four members in mammals. Growing evidence suggests that there is a complex inter- and bi-directional relationship between central nervous system (CNS) disorders and cardiac dysfunction, so-called "brain-heart axis". Recent studies suggest that CNS disorders, including neurodegenerative diseases, stroke, and depression, affect cardiovascular function via various mechanisms, such as hypothalamic-pituitary-adrenal axis augmentation. Although this brain-heart axis has been well studied in humans and mice, the involvement of NT signaling in the axis has not been fully investigated. In the first half of this review, we emphasize the importance of NTs not only in the nervous system, but also in the cardiovascular system from the embryonic stage to the adult state. In the second half, we discuss the involvement of NTs in the pathogenesis of cardiovascular diseases, and then examine whether an alteration in NTs could serve as the mediator between neurological disorders and heart dysfunction. The further investigation we propose herein could contribute to finding direct evidence for the involvement of NTs in the axis and new treatment for cardiovascular diseases.

Non-Cell Autonomous and Epigenetic Mechanisms of Huntington's Disease

Huntington's disease (HD) is a rare neurodegenerative disorder caused by an expansion of CAG trinucleotide repeat located in the exon 1 of Huntingtin (HTT) gene in human chromosome 4. The HTT protein is ubiquitously expressed in the brain. Specifically, mutant HTT (mHTT) protein-mediated toxicity leads to a dramatic degeneration of the striatum among many regions of the brain. HD symptoms exhibit a major involuntary movement followed by cognitive and psychiatric dysfunctions. In this review, we address the conventional role of wild type HTT (wtHTT) and how mHTT protein disrupts the function of medium spiny neurons (MSNs). We also discuss how mHTT modulates epigenetic modifications and transcriptional pathways in MSNs. In addition, we define how non-cell autonomous pathways lead to damage and death of MSNs under HD pathological conditions. Lastly, we overview therapeutic approaches for HD. Together, understanding of precise neuropathological mechanisms of HD may improve therapeutic approaches to treat the onset and progression of HD.

Cardiac tyrosine hydroxylase activation and MB-COMT in dyskinetic monkeys

The impact of age-associated disorders is increasing as the life expectancy of the population increments. Cardiovascular diseases and neurodegenerative disorders, such as Parkinson’s disease, have the highest social and economic burden and increasing evidence show interrelations between them. Particularly, dysfunction of the cardiovascular nervous system is part of the dysautonomic symptoms of Parkinson’s disease, although more studies are needed to elucidate the role of cardiac function on it. We analyzed the dopaminergic system in the nigrostriatal pathway of Parkinsonian and dyskinetic monkeys and the expression of some key proteins in the metabolism and synthesis of catecholamines in the heart: total and phosphorylated (phospho) tyrosine hydroxylase (TH), and membrane (MB) and soluble (S) isoforms of catechol-O-methyl transferase (COMT). The dopaminergic system was significantly depleted in all MPTP-intoxicated monkeys. MPTP- and MPTP + L-DOPA-treated animals also showed a decrease in total TH expression in both right (RV) and left ventricle (LV). We found a significant increase of phospho-TH in both groups (MPTP and MPTP + L-DOPA) in the LV, while this increase was only observed in MPTP-treated monkeys in the RV. MB-COMT analysis showed a very significant increase of this isoform in the LV of MPTP- and MPTP + L-DOPA-treated animals, with no significant differences in S-COMT levels. These data suggest that MB-COMT is the main isoform implicated in the cardiac noradrenergic changes observed after MPTP treatment, suggesting an increase in noradrenaline (NA) metabolism. Moreover, the increase of TH activity indicates that cardiac noradrenergic neurons still respond despite MPTP treatment.

Systemic manifestation and contribution of peripheral tissues to Huntington's disease pathogenesis

Huntington disease (HD) is an autosomal dominant neurodegenerative disease that is caused by expansion of cytosine/adenosine/guanine repeats in the huntingtin (HTT) gene, which leads to a toxic, aggregation-prone, mutant HTT-polyQ protein. Beyond the well-established mechanisms of HD progression in the central nervous system, growing evidence indicates that also peripheral tissues are affected in HD and that systemic signaling originating from peripheral tissues can influence the progression of HD in the brain. Herein, we review the systemic manifestation of HD in peripheral tissues, and the impact of systemic signaling on HD pathogenesis. Mutant HTT induces a body wasting syndrome (cachexia) primarily via its activity in skeletal muscle, bone, adipose tissue, and heart. Additional whole-organism effects induced by mutant HTT include decline in systemic metabolic homeostasis, which stems from derangement of pancreas, liver, gut, hypothalamic-pituitary-adrenal axis, and circadian functions. In addition to spreading via the bloodstream and a leaky blood brain barrier, HTT-polyQ may travel long distance via its uptake by neurons and its axonal transport from the peripheral to the central nervous system. Lastly, signaling factors that are produced and/or secreted in response to therapeutic interventions such as exercise or in response to mutant HTT activity in peripheral tissues may impact HD. In summary, these studies indicate that HD is a systemic disease that is influenced by intertissue signaling and by the action of pathogenic HTT in peripheral tissues. We propose that treatment strategies for HD should include the amelioration of HD symptoms in peripheral tissues. Moreover, harnessing signaling between peripheral tissues and the brain may provide a means for reducing HD progression in the central nervous system.

Purine Nucleotides Metabolism and Signaling in Huntington's Disease: Search for a Target for Novel Therapies

Huntington’s disease (HD) is a multi-system disorder that is caused by expanded CAG repeats within the exon-1 of the huntingtin (HTT) gene that translate to the polyglutamine stretch in the HTT protein. HTT interacts with the proteins involved in gene transcription, endocytosis, and metabolism. HTT may also directly or indirectly affect purine metabolism and signaling. We aimed to review existing data and discuss the modulation of the purinergic system as a new therapeutic target in HD. Impaired intracellular nucleotide metabolism in the HD affected system (CNS, skeletal muscle and heart) may lead to extracellular accumulation of purine metabolites, its unusual catabolism, and modulation of purinergic signaling. The mechanisms of observed changes might be different in affected systems. Based on collected findings, compounds leading to purine and ATP pool reconstruction as well as purinergic receptor activity modulators, i.e., P2X7 receptor antagonists, may be applied for HD treatment.

Progressive cardiac arrhythmias and ECG abnormalities in the Huntington's disease BACHD mouse model

Huntington's disease (HD) is a dominantly inherited neurodegenerative disease. There is accumulating evidence that HD patients have increased prevalence of conduction abnormalities and compromised sinoatrial node function which could lead to increased risk for arrhythmia. We used mutant Huntingtin (mHTT) expressing bacterial artificial chromosome Huntington's disease mice to determine if they exhibit electrocardiogram (ECG) abnormalities involving cardiac conduction that are known to increase risk of sudden arrhythmic death in humans. We obtained surface ECGs and analyzed arrhythmia susceptibility; we observed prolonged QRS duration, increases in PVCs as well as PACs. Abnormal histological and structural changes that could lead to cardiac conduction system dysfunction were seen. Finally, we observed decreases in desmosomal proteins, plakophilin-2 and desmoglein-2, which have been reported to cause cardiac arrhythmias and reduced conduction. Our study indicates that mHTT could cause progressive cardiac conduction system pathology that could increase the susceptibility to arrhythmias and sudden cardiac death in HD patients.

Could Small Heat Shock Protein HSP27 Be a First-Line Target for Preventing Protein Aggregation in Parkinson's Disease?

Small heat shock proteins (HSPs), such as HSP27, are ubiquitously expressed molecular chaperones and are essential for cellular homeostasis. The major functions of HSP27 include chaperoning misfolded or unfolded polypeptides and protecting cells from toxic stress. Dysregulation of stress proteins is associated with many human diseases including neurodegenerative diseases, such as Parkinson's disease (PD). PD is characterized by the presence of aggregates of α-synuclein in the central and peripheral nervous system, which induces the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and in the autonomic nervous system. Autonomic dysfunction is an important non-motor phenotype of PD, which includes cardiovascular dysregulation, among others. Nowadays, the therapies for PD focus on dopamine (DA) replacement. However, certain non-motor symptoms with a great impact on quality of life do not respond to dopaminergic drugs; therefore, the development and testing of new treatments for non-motor symptoms of PD remain a priority. Since small HSP27 was shown to prevent α-synuclein aggregation and cytotoxicity, this protein might constitute a suitable target to prevent or delay the motor and non-motor symptoms of PD. In the first part of our review, we focus on the cardiovascular dysregulation observed in PD patients. In the second part, we present data on the possible role of HSP27 in preventing the accumulation of amyloid fibrils and aggregated forms of α-synuclein. We also include our own studies, highlighting the possible protective cardiac effects induced by L-DOPA treatment through the enhancement of HSP27 levels and activity.

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.

Cross-Sectional Transcriptional Analysis of the Aging Murine Heart

Cardiovascular disease accounts for millions of deaths each year and is currently the leading cause of mortality worldwide. The aging process is clearly linked to cardiovascular disease, however, the exact relationship between aging and heart function is not fully understood. Furthermore, a holistic view of cardiac aging, linking features of early life development to changes observed in old age, has not been synthesized. Here, we re-purpose RNA-sequencing data previously-collected by our group, investigating gene expression differences between wild-type mice of different age groups that represent key developmental milestones in the murine lifespan. DESeq2's generalized linear model was applied with two hypothesis testing approaches to identify differentially-expressed (DE) genes, both between pairs of age groups and across mice of all ages. Pairwise comparisons identified genes associated with specific age transitions, while comparisons across all age groups identified a large set of genes associated with the aging process more broadly. An unsupervised machine learning approach was then applied to extract common expression patterns from this set of age-associated genes. Sets of genes with both linear and non-linear expression trajectories were identified, suggesting that aging not only involves the activation of gene expression programs unique to different age groups, but also the re-activation of gene expression programs from earlier ages. Overall, we present a comprehensive transcriptomic analysis of cardiac gene expression patterns across the entirety of the murine lifespan.

Huntingtin protein maintains balanced energetics in mouse cardiomyocytes

Huntingtin (HTT) is a multifunctional protein crucial for proper embryogenesis and nervous system development. Mutation of a single allele in gene coded this protein results in the Huntington׳s disease (HD). There is growing evidence of cardiovascular system pathologies coexisting with the neurological symptoms in HD patients. Thus, this study aims to establish the role of huntingtin protein in cardiomyocytes cellular energy and nucleotides metabolism. We used HTT KO mice embryonic stem cells (ESC) obtained with CRISPR method, wild type mice ESC treated by CRISPR with Scramble control sequence (SCR) as well as wild type (WT) mice ESC and differentiate it into cardiomyocytes. Analysis of intracellular concentration of ATP, ADP, and NAD⁺, as well as nucleotide catabolites were performed with HPLC. We noted that HTT null cardiomyocytes showed diminished intracellular ATP (4.9 ± 0.5; 6.7 ± 0.4 nmol/mg protein HTT KO vs. SCR) and NAD⁺ (0.9 ± 0.1; 1.6 ± 0.1 nmol/mg HTT KO vs. SCR). We noted also reduced cellular medium concentration of total purines pool (17.1 ± 1.7; 24.7 ± 2.7 nmol/ml HTT KO vs. SCR) as well as IMP concentration (7.7 ± 0.6; 10.2 ± 0.4 nmol/ml HTT KO vs. SCR). This study indicates that HTT plays an important role in cellular energy balance as well as in nucleotide metabolism in cardiomyocytes. Furthermore, our findings underline that the deterioration in energy metabolism observed in HD may be caused not only by cellular mutant HTT accumulation but also by the loss of HTT function.

Autonomic Changes in Juvenile-Onset Huntington's Disease

Patients with adult-onset Huntington’s Disease (AOHD) have been found to have dysfunction of the autonomic nervous system that is thought to be secondary to neurodegeneration causing dysfunction of the brain–heart axis. However, this relationship has not been investigated in patients with juvenile-onset HD (JOHD). The aim of this study was to compare simple physiologic measures between patients with JOHD (n = 27 participants with 64 visits) and participants without the gene expansion that causes HD (GNE group; n = 259 participants with 395 visits). Using data from the Kids-JOHD study, we compared mean resting heart rate (rHR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) between the JOHD and GNE groups. We also divided the JOHD group into those with childhood-onset JOHD (motor diagnosis received before the age of 13, [n = 16]) and those with adolescent-onset JOHD (motor diagnosis received at or after the age of 13 [n = 11]). We used linear mixed-effects models to compare the group means while controlling for age, sex, and parental socioeconomic status and including a random effect per participant and family. For the primary analysis, we found that the JOHD group had significant increases in their rHR compared to the GNE group. Conversely, the JOHD group had significantly lower SBP compared to the GNE group. The JOHD group also had lower DBP compared to the GNE group, but the results did not reach significance. SBP and DBP decreased as disease duration of JOHD increased, but rHR did not continue to increase. Resting heart rate is more sensitive to changes in autonomic function as compared to SBP. Therefore, these results seem to indicate that early neurodegenerative changes of the central autonomic network likely lead to an increase in rHR while later progression of JOHD leads to changes in blood pressure. We hypothesize that these later changes in blood pressure are secondary to neurodegeneration in brainstem regions such as the medulla.

Influence of 3-nitropropionic acid on physiological and behavioral responses in zebrafish larvae and adults

Long-term treatment with 3-nitropropionic acid (3-NPA), a toxin derived from plants and fungi, may reproduce symptoms and biochemical characteristics of Huntington's disease (HD). Our study evaluated the effects of 3-NPA on the physiological and behavioral responses in zebrafish larvae and adults. Larvae exposed to 0.1, 0.2, or 0.5 mM 3-NPA exhibited an increase in heart rate at 2- and 5-days post-fertilization (dpf). There was a decrease in the ocular distance at 5 dpf with 0.05 mM 3-NPA treatment. However, 3-NPA did not alter larval locomotor parameters. Adult zebrafish received 3-NPA intraperitoneal injections (a total of seven injections at doses 10, 20, or 60 mg/kg every 96 h) and showed a decrease in body weight , locomotion and aggressive behavior. No changes were observed in anxiety-like behavior and social interaction between 3-NPA-exposed animals and control groups. However, 3-NPA-treated animals (at 60 mg/kg) demonstrated impaired long-term aversive memory. Overall, 3-NPA exposure induced morphological and heart rate alterations in zebrafish larvae. Additionally, our study showed behavioral changes in zebrafish that were submitted to long-term 3-NPA treatment, which could be related to HD symptoms.

Acute Disseminated Encephalomyelitis with Seizures and Myocarditis: A Fatal Triad

Autoimmune pathology of acute disseminated encephalomyelitis (ADEM) is generally restricted to the brain. Our objective is to expand the phenotype of ADEM. A four-year-old girl was admitted to the pediatric emergency room of a university medical center five days after a common upper respiratory tract infection. Acute symptoms were fever, leg pain, and headaches. She developed meningeal signs, and her level of consciousness dropped rapidly. Epileptic seizure activity started, and she became comatose, requiring intubation and mechanical ventilation. Serial brain magnetic resonance imaging (MRI) illustrated the fulminant development of ADEM. Treatment escalation with high-dose corticosteroids, immunoglobulins, and plasma exchange did not lead to clinical improvement. On day ten, the patient developed treatment-refractory cardiogenic shock and passed away. The postmortem assessment confirmed ADEM and revealed acute lymphocytic myocarditis, likely explaining the acute cardiac failure. Human metapneumovirus and picornavirus were detected in the tracheal secrete by PCR. Data sources–medical chart of the patient. This case is consistent with evidence from experimental findings of an association of ADEM with myocarditis as a postinfectious systemic autoimmune response, with life-threatening involvement of the brain and heart.

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.

Interrelationship between Alzheimer's disease and cardiac dysfunction: the brain-heart continuum?

Dementia, a devastating neurological disorder commonly found in the elderly, is characterized by severe cognitive and memory impairment. Ample clinical and epidemiological evidence has depicted a close association between dementia and heart failure. While cerebral blood under perfusion and neurohormonal activation due to the dampened cardiac pump function contribute to the loss of nutrient supply and neuronal injury, Alzheimer's disease (AD), the most common type of dementia, also provokes cardiovascular function impairment, in particular impairment of diastolic function. Aggregation of amyloid-β proteins and mutations of Presenilin (PSEN) genes are believed to participate in the pathological changes in the heart although it is still debatable with regards to the pathological cue of cardiac anomalies in AD process. In consequence, reduced cerebral blood flow triggered by cardiac dysfunction further deteriorates vascular dementia and AD pathology. Patients with atrial fibrillation, heart failure, and other cardiac anomalies are at a higher risk for cognitive decline and dementia. Conclusion: Due to the increased incidence of dementia and cardiovascular diseases, the coexistence of the two will cause more threat to public health, warranting much more attention. Here, we will update recent reports on dementia, AD, and cardiovascular diseases and discuss the causal relationship between dementia and heart dysfunction.

Adult-onset Huntington disease: An update

Appropriate nursing-care strategies depend on the early recognition of Huntington disease (HD) to prioritize a plan of care. This article offers perspective on the clinical presentation, prognosis, diagnosis, and management of adult-onset HD.

Do Disruptions in the Circadian Timing System Contribute to Autonomic Dysfunction in Huntington's Disease?

Huntington's disease (HD) patients suffer from a progressive neurodegenerative disorder that inflicts both motor and non-motor symptoms. HD is caused by a CAG repeat expansion within the first exon of the huntingtin (HTT) gene that produces a polyglutamine repeat that leads to protein misfolding, soluble aggregates, and inclusion bodies detected throughout the body. Both clinical and preclinical research indicate that cardiovascular dysfunction should be considered a core symptom in at least a subset of HD patients. There is strong evidence for dysautonomia (dysfunctional autonomic nervous system, ANS) in HD patients that can be detected early in the disease progression. The temporal patterning of ANS function is controlled by the circadian timing system based in the anterior hypothalamus. Patients with neurodegenerative diseases including HD exhibit disrupted sleep/wake cycle and, in preclinical models, there is compelling evidence that the circadian timing system is compromised early in the disease process. Here we review data from preclinical models of HD that explore the intersection between disruption of circadian rhythms and dysautonomia. This work will lead to new therapeutic strategies and standards of care for HD and other neurodegenerative diseases.

mRNA-miRNA-Seq Reveals Neuro-Cardio Mechanisms of Crude Oil Toxicity in Red Drum ( Sciaenops ocellatus)

Polycyclic aromatic hydrocarbons (PAHs) present in crude oil can cause global gene dysregulation and developmental impairment in fish. However, the mechanisms that alter gene regulation are not well understood. In this study, larval red drum ( Sciaenops ocellatus) were exposed to water accommodated fractions of source oil (6.8, 13.7, and 35.9 μg/L total PAHs) and weathered slick oil (4.7, 8.1, and 18.0 μg/L total PAHs) from the Deepwater Horizon (DWH) oil spill. The global mRNA-microRNA functional networks associated with the toxicity of DWH oil were explored by next-generation sequencing and in-depth bioinformatics analyses. Both source and slick oil significantly altered the expression of miR-18a, miR-27b, and miR-203a across all exposure concentrations. Consistent with the observed concentration-dependent morphological changes, the target mRNAs of these microRNAs were predominantly involved in neuro-cardio system development processes and associated key signaling pathways such as axonal guidance signaling, cAMP-response-element-binding protein signaling in neurons, calcium signaling, and nuclear-factor-of-activated T cells signaling in cardiac hypertrophy. The results indicated that the developmental toxicity of crude oil may result from the abnormal expression of microRNAs and associated target genes, especially for the nervous system. Moreover, we provide a case study for systematic toxicity evaluation leveraging mRNA-microRNA-seq data using nonmodel species.

Cardiac sigma receptors - an update

More than four decades passed since sigma receptors were first mentioned. Since then, existence of at least two receptor subtypes and their tissue distributions have been proposed. Nowadays, it is clear, that sigma receptors are unique ubiquitous proteins with pluripotent function, which can interact with so many different classes of proteins. As the endoplasmic resident proteins, they work as molecular chaperones - accompany various proteins during their folding, ensure trafficking of the maturated proteins between cellular organelles and regulate their functions. In the heart, sigma receptor type 1 is more dominant. Cardiac sigma 1 receptors regulate response to endoplasmic reticulum stress, modulates calcium signaling in cardiomyocyte and can affect function of voltage-gated ion channels. They contributed in pathophysiology of cardiac hypertrophy, heart failure and many other cardiovascular disorders. Therefore, sigma receptors are potential novel targets for specific treatment of cardiovascular diseases.