Transcriptional Signature of an Altered Purine Metabolism in the Skeletal Muscle of a Huntington's Disease Mouse Model

The microbiota-gut-brain axis in Huntington's disease: pathogenic mechanisms and therapeutic targets

Huntington's disease (HD) is a currently incurable neurogenerative disorder and is typically characterized by progressive movement disorder (including chorea), cognitive deficits (culminating in dementia), psychiatric abnormalities (the most common of which is depression), and peripheral symptoms (including gastrointestinal dysfunction). There are currently no approved disease-modifying therapies available for HD, with death usually occurring approximately 10-25 years after onset, but some therapies hold promising potential. HD subjects are often burdened by chronic diarrhea, constipation, esophageal and gastric inflammation, and a susceptibility to diabetes. Our understanding of the microbiota-gut-brain axis in HD is in its infancy and growing evidence from preclinical and clinical studies suggests a role of gut microbial population imbalance (gut dysbiosis) in HD pathophysiology. The gut and the brain can communicate through the enteric nervous system, immune system, vagus nerve, and microbiota-derived-metabolites including short-chain fatty acids, bile acids, and branched-chain amino acids. This review summarizes supporting evidence demonstrating the alterations in bacterial and fungal composition that may be associated with HD. We focus on mechanisms through which gut dysbiosis may compromise brain and gut health, thus triggering neuroinflammatory responses, and further highlight outcomes of attempts to modulate the gut microbiota as promising therapeutic strategies for HD. Ultimately, we discuss the dearth of data and the need for more longitudinal and translational studies in this nascent field. We suggest future directions to improve our understanding of the association between gut microbes and the pathogenesis of HD, and other 'brain and body disorders'.

Targeting Gut Microbiota in Cancer Cachexia: Towards New Treatment Options

Cancer cachexia is a complex multifactorial syndrome whose hallmarks are weight loss due to the wasting of muscle tissue with or without the loss of adipose tissue, anorexia, systemic inflammation, and multi-organ metabolic alterations, which negatively impact patients' response to anticancer treatments, quality of life, and overall survival. Despite its clinical relevance, cancer cachexia often remains an underestimated complication due to the lack of rigorous diagnostic and therapeutic pathways. A number of studies have shown alterations in gut microbiota diversity and composition in association with cancer cachexia markers and symptoms, thus supporting a central role for dysbiosis in the pathogenesis of this syndrome. Different tools of microbiota manipulation, including probiotics, prebiotics, synbiotics, and fecal microbiota transplantation, have been investigated, demonstrating encouraging improvements in cachexia outcomes. Albeit pioneering, these studies pave the way for future research with the aim of exploring the role of gut microbiota in cancer cachexia more deeply and setting up effective microbiota-targeting interventions to be translated into clinical practice.

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.

Rosiglitazone Ameliorates Cardiac and Skeletal Muscle Dysfunction by Correction of Energetics in Huntington’s Disease

Huntington’s disease (HD) is a rare neurodegenerative disease that is accompanied by skeletal muscle atrophy and cardiomyopathy. Tissues affected by HD (central nervous system [CNS], skeletal muscle, and heart) are known to suffer from deteriorated cellular energy metabolism that manifests already at presymptomatic stages. This work aimed to test the effects of peroxisome proliferator-activated receptor (PPAR)-γ agonist—rosiglitazone on grip strength and heart function in an experimental HD model—on R6/1 mice and to address the mechanisms. We noted that rosiglitazone treatment lead to improvement of R6/1 mice grip strength and cardiac mechanical function. It was accompanied by an enhancement of the total adenine nucleotides pool, increased glucose oxidation, changes in mitochondrial number (indicated as increased citric synthase activity), and reduction in mitochondrial complex I activity. These metabolic changes were supported by increased total antioxidant status in HD mice injected with rosiglitazone. Correction of energy deficits with rosiglitazone was further indicated by decreased accumulation of nucleotide catabolites in HD mice serum. Thus, rosiglitazone treatment may not only delay neurodegeneration but also may ameliorate cardio- and myopathy linked to HD by improvement of cellular energetics.

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.

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.

A Glimpse of Molecular Biomarkers in Huntington's Disease

Huntington's disease (HD) is a devastating neurodegenerative disorder that is caused by an abnormal expansion of CAG repeats in the Huntingtin (HTT) gene. Although the main symptomatology is explained by alterations at the level of the central nervous system, predominantly affecting the basal ganglia, a peripheral component of the disease is being increasingly acknowledged. Therefore, the manifestation of the disease is complex and variable among CAG expansion carriers, introducing uncertainty in the appearance of specific signs, age of onset and severity of disease. The monogenic nature of the disorder allows a precise diagnosis, but the use of biomarkers with prognostic value is still needed to achieve clinical management of the patients in an individual manner. In addition, we need tools to evaluate the patient's response to potential therapeutic approaches. In this review, we provide a succinct summary of the most interesting molecular biomarkers that have been assessed in patients, mostly obtained from body fluids such as cerebrospinal fluid, peripheral blood and saliva.

Huntingtin Ubiquitination Mechanisms and Novel Possible Therapies to Decrease the Toxic Effects of Mutated Huntingtin

Huntington Disease (HD) is a dominant, lethal neurodegenerative disorder caused by the abnormal expansion (>35 copies) of a CAG triplet located in exon 1 of the HTT gene encoding the huntingtin protein (Htt). Mutated Htt (mHtt) easily aggregates, thereby inducing ER stress that in turn leads to neuronal injury and apoptosis. Therefore, both the inhibition of mHtt aggregate formation and the acceleration of mHtt degradation represent attractive strategies to delay HD progression, and even for HD treatment. Here, we describe the mechanism underlying mHtt degradation by the ubiquitin–proteasome system (UPS), which has been shown to play a more important role than the autophagy–lysosomal pathway. In particular, we focus on E3 ligase proteins involved in the UPS and detail their structure–function relationships. In this framework, we discuss the possible exploitation of PROteolysis TArgeting Chimeras (PROTACs) for HD therapy. PROTACs are heterobifunctional small molecules that comprise two different ligands joined by an appropriate linker; one of the ligands is specific for a selected E3 ubiquitin ligase, the other ligand is able to recruit a target protein of interest, in this case mHtt. As a consequence of PROTAC binding, mHtt and the E3 ubiquitin ligase can be brought to a relative position that allows mHtt to be ubiquitinated and, ultimately, allows a reduction in the amount of mHtt in the cell.

Kinetin stimulates differentiation of C2C12 myoblasts

Kinetin or N6-furfuryladenine (K) belongs to a class of plant hormones called cytokinins, which are biologically active molecules modulating many aspects of plant growth and development. However, biological activities of cytokinins are not only limited to plants; their effects on animals have been widely reported in the literature. Here, we found that Kinetin is a potent small molecule that efficiently stimulates differentiation of C2C12 myoblasts into myotubes in vitro. The highest efficacy was achieved at 1μM and 10μM Kinetin concentrations, in both mitogen-poor and rich media. More importantly, Kinetin was able to strongly stimulate the MyoD-dependent conversion of fibroblasts into myotubes. Kinetin alone did not give rise to fibroblast conversion and required MyoD; this demonstrates that Kinetin augments the molecular repertoire of necessary key regulatory factors to facilitate MyoD-mediated myogenic differentiation. This novel Kinetin pro-myogenic function may be explained by its ability to alter intracellular calcium levels and by its potential to impact on Reactive Oxygen Species (ROS) signalling. Taken together, our findings unravel the effects of a new class of small molecules with potent pro-myogenic activities. This opens up new therapeutic avenues with potential for treating skeletal muscle diseases related to muscle aging and wasting.

Brain Region and Cell Compartment Dependent Regulation of Electron Transport System Components in Huntington's Disease Model Mice

Huntington’s disease (HD) is a rare hereditary neurodegenerative disorder characterized by multiple metabolic dysfunctions including defects in mitochondrial homeostasis and functions. Although we have recently reported age-related changes in the respiratory capacities in different brain areas in HD mice, the precise mechanisms of how mitochondria become compromised in HD are still poorly understood. In this study, we investigated mRNA and protein levels of selected subunits of electron transport system (ETS) complexes and ATP-synthase in the cortex and striatum of symptomatic R6/2 mice. Our findings reveal a brain-region-specific differential expression of both nuclear and mitochondrial-encoded ETS components, indicating defects of transcription, translation and/or mitochondrial import of mitochondrial ETS components in R6/2 mouse brains.

Purinergic Signaling in the Pathophysiology and Treatment of Huntington's Disease

Huntington’s disease (HD) is a devastating, progressive, and fatal neurodegenerative disorder inherited in an autosomal dominant manner. This condition is characterized by motor dysfunction (chorea in the early stage, followed by bradykinesia, dystonia, and motor incoordination in the late stage), psychiatric disturbance, and cognitive decline. The neuropathological hallmark of HD is the pronounced neuronal loss in the striatum (caudate nucleus and putamen). The striatum is related to the movement control, flexibility, motivation, and learning and the purinergic signaling has an important role in the control of these events. Purinergic signaling involves the actions of purine nucleotides and nucleosides through the activation of P2 and P1 receptors, respectively. Extracellular nucleotide and nucleoside-metabolizing enzymes control the levels of these messengers, modulating the purinergic signaling. The striatum has a high expression of adenosine A_2A receptors, which are involved in the neurodegeneration observed in HD. The P2X7 and P2Y2 receptors may also play a role in the pathophysiology of HD. Interestingly, nucleotide and nucleoside levels may be altered in HD animal models and humans with HD. This review presents several studies describing the relationship between purinergic signaling and HD, as well as the use of purinoceptors as pharmacological targets and biomarkers for this neurodegenerative disorder.

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.

Quantitative Proteomics Analysis for the Identification of Differential Protein Expression in Calf Muscles between Young and Old SD Rats Using Mass Spectrometry

Aging is associated with loss of muscle mass and strength that leads to a condition termed sarcopenia. Impaired conditions, morbidity, and malnutrition are the factors of devaluation of muscle fibers in aged animals. Satellite cells play an important role in maintaining muscle homeostasis during tissue regeneration and repair. Proteomic profiling on the skeletal muscle tissues of different age group rats helps to determine the differentially expressed (DE) proteins, which may eventually lead to the development of biomarkers in treating the conditions of sarcopenia. In this study, nanoscale liquid chromatography coupled to tandem mass spectrometry (nano-LC-MS/MS) analysis was implemented in the calf tissues of young and old groups of rats. The mass spectrometry (MS) analysis revealed the presence of 335 differentially expressed proteins between the two different age conditions, among which those based on log-fold change 25 proteins were upregulated and 77 were downregulated. The protein-protein interaction network analysis revealed 18 upregulated proteins with three distinct interconnected networks and 57 downregulated proteins with two networks. Further, gene ontology (GO) enrichment analysis showed the biological process, cellular component, and molecular function of the differential proteins. Pathway enrichment analysis of the DE proteins identified nine significantly enriched pathways with a list of eight significant genes (Cryab, Hspb2, Acat1, Ak1, Adssl1, Anxa5, Gys1, Ogdh, Gc, and Adssl1). Quantification of significant genes by quantitative real-time polymerase chain reaction (qRT-PCR) confirmed the downregulation at the mRNA level. Western blot analysis of their protein expression showed concordant results on two candidate proteins (Ogdh and annexin 5) confirming their differential regulation between the two age groups of rats. Thus, these proteomic approaches on young and aged rats provide insights into the development of protein targets in the treatment of sarcopenia (muscle loss).

Abnormalities in the Motor Unit of a Fast-Twitch Lower Limb Skeletal Muscle in Huntington's Disease

Huntington’s disease (HD) is a disorder characterized by chronic involuntary movements, dementia, and psychiatric symptoms. It is caused by a mutation in the gene that encodes for huntingtin protein (HTT), leading to the formation of mutant proteins expressed in various tissues. Although brain pathology has become the hallmark for HD, recent studies suggest that damage of peripheral structures also contributes to HD progression. We previously identified severe alterations in the motor units that innervate cervical muscles in 12-month-old BACHD (Bacterial Artificial Chromosome Huntington’s Disease) mice, a well-established mouse model for HD. Here, we studied lumbar motoneurons and their projections onto hind limb fast-twitch skeletal muscles (tibialis anterior), which control balance and gait in HD patients. We found that lumbar motoneurons were altered in the HD mouse model; the number and size of lumbar motoneurons were reduced in BACHD. Structural alterations were also present in the sciatic nerve and neuromuscular junctions. Acetylcholine receptors were organized in several small patches (acetylcholine receptor fragmentation), many of which were partially innervated. In BACHD mice, we observed atrophy of tibialis anterior muscles, decreased expression of glycolytic fast Type IIB fibers, and at the ultrastructural level, alterations of sarcomeres and mitochondria. Corroborating all these findings, BACHD animals performed worse on motor behavior tests. Our results provide additional evidences that nerve–muscle communication is impaired in HD and that motoneurons from distinct spinal cord locations are similarly affected in the disease.

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.

Increased Adenine Nucleotide Degradation in Skeletal Muscle Atrophy

Adenine nucleotides (AdNs: ATP, ADP, AMP) are essential biological compounds that facilitate many necessary cellular processes by providing chemical energy, mediating intracellular signaling, and regulating protein metabolism and solubilization. A dramatic reduction in total AdNs is observed in atrophic skeletal muscle across numerous disease states and conditions, such as cancer, diabetes, chronic kidney disease, heart failure, COPD, sepsis, muscular dystrophy, denervation, disuse, and sarcopenia. The reduced AdNs in atrophic skeletal muscle are accompanied by increased expression/activities of AdN degrading enzymes and the accumulation of degradation products (IMP, hypoxanthine, xanthine, uric acid), suggesting that the lower AdN content is largely the result of increased nucleotide degradation. Furthermore, this characteristic decrease of AdNs suggests that increased nucleotide degradation contributes to the general pathophysiology of skeletal muscle atrophy. In view of the numerous energetic, and non-energetic, roles of AdNs in skeletal muscle, investigations into the physiological consequences of AdN degradation may provide valuable insight into the mechanisms of muscle atrophy.

Satellite cell content in Huntington's disease patients in response to endurance training

Background

Skeletal muscle wasting is a hallmark of Huntington’s disease (HD). However, data on myocellular characteristics and myofiber remodeling in HD patients are scarce. We aimed at gaining insights into myocellular characteristics of HD patients as compared to healthy controls at rest and after a period of increased skeletal muscle turnover.

Methods

Myosin heavy chain (MyHC)-specific cross-sectional area, satellite cell content, myonuclear number, myonuclear domain, and muscle fiber type distribution were determined from vastus lateralis muscle biopsies at rest and after 26 weeks of endurance training in HD patients and healthy controls.

Results

At the beginning of the study, there were no differences in myocellular characteristics between HD patients and healthy controls. Satellite cell content per MyHC-1 fiber (P = 0.014) and per MyHC-1 myonucleus (P = 0.006) increased significantly in healthy controls during the endurance training intervention, whereas it remained constant in HD patients (P = 0.804 and P = 0.975 for satellite cell content per MyHC-1 fiber and myonucleus, respectively). All further variables were not altered during the training intervention in HD patients and healthy controls.

Conclusions

Similar skeletal muscle characteristics between HD patients and healthy controls at baseline suggested similar potential for myofiber remodeling in response to exercise. However, the missing satellite cell response in MyHC-1 myofibers following endurance training in HD patients points to a potential dysregulation in the exercise-induced activation and/or proliferation of satellite cells. In the longer-term, impaired myonuclear turnover might be associated with the clinical observation of skeletal muscle wasting.

Characterization of adenine nucleotide metabolism in the cellular model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder that is caused by expanded CAG repeats within the exon-1 of the huntingtin (HTT) gene. It has been shown that HTT interacts with the proteins involved in the gene transcription, endocytosis and metabolism, nevertheless the biochemical pathways by which mutant HTT causes a cellular dysfunction remain unclear. Thus, this study aimed to establish the role of mutant HTT expansion in energy and nucleotide metabolism deteriorations. We examined HEK 293 T cell line transfected with plasmids expressing wild-type (control) or mutant exon 1 of the HTT gene (HD). Analysis of intracellular concentration of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD⁺), as well as activities of intra- and extracellular enzymes of nucleotide catabolism (such as adenine monophosphate deaminase (AMPD), adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) and ectonucleoside triphosphate diphosphohydrolase (eNTPD), ecto-5'-nucleotidase (e5NT), ecto-adenosine deaminase (eADA) were performed with high pressure liquid chromatography. Protein concentration was measured with Bradford method. We found diminished intracellular ATP concentration (22.5 ± 1.7 in HD; 29.3 ± 1.4 nmol/mg protein in control), increased ADA activity (27.9 ± 1.0 in HD; 21.1 ± 1.6 nmol/min/mg protein in control) and reduced activities of eNTPD (2.4 ± 0.5 in HD; 5.8 ± 0.7 nmol/min/mg protein in control), e5NT (0.1 ± 0.01 in HD; 0.2 ± 0.01 nmol/min/mg protein in control) and eADA (0.3 ± 0.03 in HD; 0.4 ± 0.04 nmol/min/mg protein in control) while NAD⁺ concentration, AMPD and PNP activities remained unchanged. This study highlights that the mutant HTT expansion resulted in depletion of cellular ATP concentration and reduced rates of extracellular nucleotide breakdown. In conclusion, such changes may contribute to the pathology of HD.

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

Although Huntington's disease is generally considered to be a neurological disorder, there is mounting evidence that heart malfunction plays an important role in disease progression. This is perhaps not unexpected since both cardiovascular and nervous systems are strongly connected - both developmentally and subsequently in health and disease. This connection occurs through a system of central and peripheral neurons that control cardiovascular performance, while in return the cardiovascular system works as a sensor for the nervous system to react to physiological events. Hence, given their permanent interconnectivity, any pathological events occurring in one system might affect the second. In addition, some pathological signals from Huntington's disease might occur simultaneously in both the cardiovascular and nervous systems, since mutant huntingtin protein is expressed in both. Here we aim to review the source of HD-related cardiomyopathy in the light of recently published studies, and to identify similarities between HD-related cardiomyopathy and other neuro-cardio disorders.