The Huntington's disease-related cardiomyopathy prevents a hypertrophic response in the R6/2 mouse model

A Comprehensive Bioinformatics Approach to Identify Molecular Signatures and Key Pathways for the Huntington Disease

Huntington disease (HD) is a degenerative brain disease caused by the expansion of CAG (cytosine-adenine-guanine) repeats, which is inherited as a dominant trait and progressively worsens over time possessing threat. Although HD is monogenetic, the specific pathophysiology and biomarkers are yet unknown specifically, also, complex to diagnose at an early stage, and identification is restricted in accuracy and precision. This study combined bioinformatics analysis and network-based system biology approaches to discover the biomarker, pathways, and drug targets related to molecular mechanism of HD etiology. The gene expression profile data sets GSE64810 and GSE95343 were analyzed to predict the molecular markers in HD where 162 mutual differentially expressed genes (DEGs) were detected. Ten hub genes among them (DUSP1, NKX2-5, GLI1, KLF4, SCNN1B, NPHS1, SGK2, PITX2, S100A4, and MSX1) were identified from protein-protein interaction (PPI) network which were mostly expressed as down-regulated. Following that, transcription factors (TFs)-DEGs interactions (FOXC1, GATA2, etc), TF-microRNA (miRNA) interactions (hsa-miR-340, hsa-miR-34a, etc), protein-drug interactions, and disorders associated with DEGs were predicted. Furthermore, we used gene set enrichment analysis (GSEA) to emphasize relevant gene ontology terms (eg, TF activity, sequence-specific DNA binding) linked to DEGs in HD. Disease interactions revealed the diseases that are linked to HD, and the prospective small drug molecules like cytarabine and arsenite was predicted against HD. This study reveals molecular biomarkers at the RNA and protein levels that may be beneficial to improve the understanding of molecular mechanisms, early diagnosis, as well as prospective pharmacologic targets for designing beneficial HD treatment.

Return of the Tbx5; lineage-tracing reveals ventricular cardiomyocyte-like precursors in the injured adult mammalian heart

The single curative measure for heart failure patients is a heart transplantation, which is limited due to a shortage of donors, the need for immunosuppression and economic costs. Therefore, there is an urgent unmet need for identifying cell populations capable of cardiac regeneration that we will be able to trace and monitor. Injury to the adult mammalian cardiac muscle, often leads to a heart attack through the irreversible loss of a large number of cardiomyocytes, due to an idle regenerative capability. Recent reports in zebrafish indicate that Tbx5a is a vital transcription factor for cardiomyocyte regeneration. Preclinical data underscore the cardioprotective role of Tbx5 upon heart failure. Data from our earlier murine developmental studies have identified a prominent unipotent Tbx5-expressing embryonic cardiac precursor cell population able to form cardiomyocytes, in vivo, in vitro and ex vivo. Using a developmental approach to an adult heart injury model and by employing a lineage-tracing mouse model as well as the use of single-cell RNA-seq technology, we identify a Tbx5-expressing ventricular cardiomyocyte-like precursor population, in the injured adult mammalian heart. The transcriptional profile of that precursor cell population is closer to that of neonatal than embryonic cardiomyocyte precursors. Tbx5, a cardinal cardiac development transcription factor, lies in the center of a ventricular adult precursor cell population, which seems to be affected by neurohormonal spatiotemporal cues. The identification of a Tbx5-specific cardiomyocyte precursor-like cell population, which is capable of dedifferentiating and potentially deploying a cardiomyocyte regenerative program, provides a clear target cell population for translationally-relevant heart interventional studies.

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.

Huntington’s disease phenotypes are improved via mTORC1 modulation by small molecule therapy

Huntington’s Disease (HD) is a dominantly inherited neurodegenerative disease for which the major causes of mortality are neurodegeneration-associated aspiration pneumonia followed by cardiac failure. mTORC1 pathway perturbations are present in HD models and human tissues. Amelioration of mTORC1 deficits by genetic modulation improves disease phenotypes in HD models, is not a viable therapeutic strategy. Here, we assessed a novel small molecule mTORC1 pathway activator, NV-5297, for its improvement of the disease phenotypes in the N171-82Q HD mouse model. Oral dosing of NV-5297 over 6 weeks activated mTORC1, increased striatal volume, improved motor learning and heart contractility. Further, the heart contractility, heart fibrosis, and survival were improved in response to the cardiac stressor isoprenaline when compared to vehicle-treated mice. Cummulatively, these data support mTORC1 activation as a therapeutic target in HD and consolidates NV-5297 as a promising drug candidate for treating central and peripheral HD phenotypes and, more generally, mTORC1-deficit 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.

A Systematic Review of Transcriptional Dysregulation in Huntington's Disease Studied by RNA Sequencing

Huntington's disease (HD) is a chronic neurodegenerative disorder caused by an expansion of polyglutamine repeats in exon 1 of the Huntingtin gene. Transcriptional dysregulation accompanied by epigenetic alterations is an early and central disease mechanism in HD yet, the exact mechanisms and regulators, and their associated gene expression programs remain incompletely understood. This systematic review investigates genome-wide transcriptional studies that were conducted using RNA sequencing (RNA-seq) technology in HD patients and models. The review protocol was registered at the Open Science Framework (OSF). The biomedical literature and gene expression databases, PubMed and NCBI BioProject, Array Express, European Nucleotide Archive (ENA), European Genome-Phenome Archive (EGA), respectively, were searched using the defined terms specified in the protocol following the PRISMA guidelines. We conducted a complete literature and database search to retrieve all RNA-seq-based gene expression studies in HD published until August 2020, retrieving 288 articles and 237 datasets from PubMed and the databases, respectively. A total of 27 studies meeting the eligibility criteria were included in this review. Collectively, comparative analysis of the datasets revealed frequent genes that are consistently dysregulated in HD. In postmortem brains from HD patients, DNAJB1, HSPA1B and HSPB1 genes were commonly upregulated across all brain regions and cell types except for medium spiny neurons (MSNs) at symptomatic disease stage, and HSPH1 and SAT1 genes were altered in expression in all symptomatic brain datasets, indicating early and sustained changes in the expression of genes related to heat shock response as well as response to misfolded proteins. Specifically in indirect pathway medium spiny neurons (iMSNs), mitochondria related genes were among the top uniquely dysregulated genes. Interestingly, blood from HD patients showed commonly differentially expressed genes with a number of brain regions and cells, with the highest number of overlapping genes with MSNs and BA9 region at symptomatic stage. We also found the differential expression and predicted altered activity of a set of transcription factors and epigenetic regulators, including BCL6, EGR1, FOSL2 and CREBBP, HDAC1, KDM4C, respectively, which may underlie the observed transcriptional changes in HD. Altogether, our work provides a complete overview of the transcriptional studies in HD, and by data synthesis, reveals a number of common and unique gene expression and regulatory changes across different cell and tissue types in HD. These changes could elucidate new insights into molecular mechanisms of differential vulnerability in HD. Systematic Review Registration: https://osf.io/pm3wq.

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.

Transcriptional Dysregulation in Huntington's Disease: The Role in Pathogenesis and Potency for Pharmacological Targeting

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by a mutation in the gene that encodes a critical cell regulatory protein, huntingtin (Htt). The expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats causes improper folding of functional proteins and is an initial trigger of pathological changes in the brain. Recent research has indicated that the functional dysregulation of many transcription factors underlies the neurodegenerative processes that accompany HD. These disturbances are caused not only by the loss of wild-type Htt (WT Htt) function but also by the occurrence of abnormalities that result from the action of mutant Htt (mHtt). In this review, we aim to describe the role of transcription factors that are currently thought to be strongly associated with HD pathogenesis, namely, RE1-silencing transcription factor, also known as neuron-restrictive silencer factor (REST/NRSF), forkhead box proteins (FOXPs), peroxisome proliferator-activated receptor gamma coactivator-1a (PGC1α), heat shock transcription factor 1 (HSF1), and nuclear factor κ light-chain-enhancer of activated B cells (NF- κB). We also take into account the role of these factors in the phenotype of HD as well as potential pharmacological interventions targeting the analyzed proteins. Furthermore, we considered whether molecular manipulation resulting in changes in transcription factor function may have clinical potency for treating HD.

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.

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.

Cardiac mTORC1 Dysregulation Impacts Stress Adaptation and Survival in Huntington's Disease

Huntington’s disease (HD) is a dominantly inherited neurological disorder caused by CAG-repeat expansion in exon 1 of Huntingtin (HTT). But in addition to the neurological disease, mutant HTT (mHTT), which is ubiquitously expressed, impairs other organ systems. Indeed, epidemiological and animal model studies suggest higher incidence of and mortality from heart disease in HD. Here, we show that the protein complex mTORC1 is dysregulated in two HD mouse models through a mechanism that requires intrinsic mHTT expression. Moreover, restoring cardiac mTORC1 activity with constitutively active Rheb prevents mortality and relieves the mHTT-induced block to hypertrophic adaptation to cardiac stress. Finally, we show that chronic mTORC1 dysregulation is due in part to mislocalization of endogenous Rheb. These data provide insight into the increased cardiac-related mortality of HD patients, with cardiac mHTT expression inhibiting mTORC1 activity, limiting heart growth, and decreasing the heart’s ability to compensate to chronic stress.

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.

The effect of calorie restriction on mouse skeletal muscle is sex, strain and time-dependent

Loss of skeletal muscle mass and function occurs with increasing age. Calorie restriction (CR) increases the lifespan of C57Bl/6 mice, but not in the shorter-lived DBA/2 strain. There is some evidence that calorie restriction reduces or delays many of the age-related defects that occur in rodent skeletal muscle. We therefore investigated the effect of short (2.5 month) and longer term (8.5 and 18.5 months) CR on skeletal muscle in male and female C57Bl/6 and DBA/2 mice. We found that short-term CR increased the satellite cell number and collagen VI content of muscle, but resulted in a delayed regenerative response to injury.Consistent with this, the in vitro proliferation of satellite cells derived from these muscles was reduced by CR. The percentage of stromal cells, macrophages, hematopoietic stem cells and fibroadipogenic cells in the mononucleated cell population derived from skeletal muscle was reduced by CR at various stages. But overall, these changes are neither consistent over time, nor between strain and sex. The fact that changes induced by CR do not persist with time and the dissimilarities between the two mouse strains, combined with sex differences, urge caution in applying CR to improve skeletal muscle function across the lifespan in humans.

Early transcriptional alteration of histone deacetylases in a murine model of doxorubicin-induced cardiomyopathy

Doxorubicin is a potent chemotherapeutic agent that is widely-used to treat a variety of cancers but causes acute and chronic cardiac injury, severely limiting its use. Clinically, the acute side effects of doxorubicin are mostly manageable, whereas the delayed consequences can lead to life-threatening heart failure, even decades after cancer treatment. The cardiotoxicity of doxorubicin is subject to a critical cumulative dose and so dosage limitation is considered to be the best way to reduce these effects. Hence, a number of studies have defined a "safe dose" of the drug, both in animal models and clinical settings, with the aim of avoiding long-term cardiac effects. Here we show that a dose generally considered as safe in a mouse model can induce harmful changes in the myocardium, as early as 2 weeks after infusion. The adverse changes include the development of fibrotic lesions, disarray of cardiomyocytes and a major transcription dysregulation. Importantly, low-dose doxorubicin caused specific changes in the transcriptional profile of several histone deacetylases (HDACs) which are epigenetic regulators of cardiac remodelling. This suggests that cardioprotective therapies, aimed at modulating HDACs during doxorubicin treatment, deserve further exploration.

3-NP-induced Huntington's-like disease impairs Nrf2 activation without loss of cardiac function in aged rats

Cardiovascular diseases (CVDs) are one of the leading causes of death in patients over 60years with Huntington's disease (HD). Here, we investigated if age-related oxidative stress (OS) is a relevant factor to develop cardiac damage in an in vivo model of striatal neurodegeneration induced by 3-nitropropionic acid (3-NP). We also evaluated the potential effect of tert-butylhydroquinone (tBHQ) to increase the Nrf2-regulated antioxidant response in hearts from adult and aged rats intoxicated with 3-NP. Our results showed that 3-NP-treatment did not induce cardiac dysfunction, neither in adult nor in aged rats. However, at the cellular level, adult animals showed higher susceptibility to 3-NP-induced damage than aged rats, which suggest that chronic oxidative stress ongoing during aging might have induced an hormetic response that probably prevented from further 3-NP damage. We also found that the oxidative unbalance concurs with unresponsiveness of the Nrf2-mediated antioxidant response in old animals.

Huntington's Disease-Induced Cardiac Disorders Affect Multiple Cellular Pathways

Huntington's disease (HD) is a rare, inherited, progressive, and fatal neurological disorder resulting from expanded polyglutamine repeats in the huntingtin protein. While HD is predominately characterized as a disease of the central nervous system, mortality surveys and epidemiological studies reveal heart disease as one of the leading causes of death in HD patients. Emerging evidence supports a link between HD and cardiovascular disease, such as cardiac amyloidosis (accumulation of aggregates in the heart). Experimental animal and clinical studies have attempted to explain the mechanisms of HD-induced cardiac pathology in the association of protein misfolding, autophagic defects, oxidative stress, mitochondrial dysfunction, and cell death. HD is increasingly understood as a complex disease with peripheral components of cardiac and skeletal muscle pathophysiology. While the discovery of these linkages and apparent pathological markers is promising, the mechanism of HD-induced cardiac pathology and the nature of its cell autonomy remain elusive. Further study of the wide-ranging cardiac function in HD patients is needed. This review highlights published literature on the pathological factors associated with HD-induced cardiac amyloidosis and other cardiovascular diseases, and addresses gaps in this expanding area of study. Through comprehensive experimental and clinical studies, potential drugs can be tested to attenuate and/or ameliorate HD-induced cardiac pathology and mortality.

An impaired metabolism of nucleotides underpins a novel mechanism of cardiac remodeling leading to Huntington's disease related cardiomyopathy

Huntington's disease (HD) is mainly thought of as a neurological disease, but multiple epidemiological studies have demonstrated a number of cardiovascular events leading to heart failure in HD patients. Our recent studies showed an increased risk of heart contractile dysfunction and dilated cardiomyopathy in HD pre-clinical models. This could potentially involve metabolic remodeling, that is a typical feature of the failing heart, with reduced activities of high energy phosphate generating pathways. In this study, we sought to identify metabolic abnormalities leading to HD-related cardiomyopathy in pre-clinical and clinical settings. We found that HD mouse models developed a profound deterioration in cardiac energy equilibrium, despite AMP-activated protein kinase hyperphosphorylation. This was accompanied by a reduced glucose usage and a significant deregulation of genes involved in de novo purine biosynthesis, in conversion of adenine nucleotides, and in adenosine metabolism. Consequently, we observed increased levels of nucleotide catabolites such as inosine, hypoxanthine, xanthine and uric acid, in murine and human HD serum. These effects may be caused locally by mutant HTT, via gain or loss of function effects, or distally by a lack of trophic signals from central nerve stimulation. Either may lead to energy equilibrium imbalances in cardiac cells, with activation of nucleotide catabolism plus an inhibition of re-synthesis. Our study suggests that future therapies should target cardiac mitochondrial dysfunction to ameliorate energetic dysfunction. Importantly, we describe the first set of biomarkers related to heart and skeletal muscle dysfunction in both pre-clinical and clinical HD settings.

A shared mechanism of muscle wasting in cancer and Huntington's disease

Skeletal muscle loss and dysfunction in aging and chronic diseases is one of the major causes of mortality in patients, and is relevant for a wide variety of diseases such as neurodegeneration and cancer. Muscle loss is accompanied by changes in gene expression and metabolism that lead to contractile impairment and likely affect whole-body metabolism and function. The changes may be caused by inactivity, inflammation, age-related factors or unbalanced nutrition. Although links with skeletal muscle loss have been found in diseases with disparate aetiologies, for example both in Huntington’s disease (HD) and cancer cachexia, the outcome is a similar impairment and mortality. This short commentary aims to summarize recent achievements in the identification of common mechanisms leading to the skeletal muscle wasting syndrome seen in diseases as different as cancer and HD. The latter is the most common hereditary neurodegenerative disorder and muscle wasting is an important component of its pathology. In addition, possible therapeutic strategies for anti-cachectic treatment will be also discussed in the light of their translation into possible therapeutic approaches for HD.

Transcriptional dysregulation in Huntington's disease: The role of histone deacetylases

Huntington's disease (HD) is a progressive neurological disorder for which there are no disease-modifying treatments. Although, the exact underlying mechanism(s) leading to the neural cell death in HD still remains elusive, the transcriptional dysregulation is a major molecular feature. Recently, the transcriptional activation and repression regulated by chromatin acetylation has been found to be impaired in HD pathology. The acetylation and deacetylation of histone proteins is carried out by opposing actions of histone acetyl-transferases and histone deacetylases (HDACs), respectively. Studies carried out in cell culture, yeast, Drosophila and rodent model(s) have indicated that HDAC inhibitors (HDACIs) might provide useful class of therapeutic agents for HD. Clinical trials have also reported the beneficial effects of HDACIs in patients suffering from HD. Therefore, the development of HDACIs as therapeutics for HD has been vigorously pursued. In this review, we highlight and summarize the putative role of HDACs in HD like pathology and further discuss the potential of HDACIs as new therapeutic avenues for the treatment of HD.

Non-Hsp genes are essential for HSF1-mediated maintenance of whole body homeostasis

Mammalian tissues are always exposed to diverse threats from pathological conditions and aging. Therefore, the molecular systems that protect the cells from these threats are indispensable for cell survival. A variety of diseases, including neurodegenerative diseases, cause intracellular damage and disturb homeostasis. Heat shock transcription factor 1 (HSF1) positively regulates heat shock protein (Hsp) and maintains the precise folding of proteins. Moreover, HSF1 induces the non-Hsp genes expression, and degrades damaged/misfolded protein. Recently, my colleagues and I revealed non-Hsp genes have more protective roles than Hsps at the cellular level. However, whether these protective systems are similarly important to cellular defense in each tissue is still elusive. In this study, I compared polyglutamine (polyQ) protein aggregations/inclusion development in each tissue of WT- and HSF1KO-Huntington’s disease (HD) mice, and examined the expression of the eight non-Hsp HSF1 target genes that have a strong suppressive effect on polyQ protein aggregation. Of these genes, Nfatc2, Pdzk3, Cryab, Csrp2, and Prame were detected in most tissues, but the other genes were not. Surprisingly, the obvious effect of HSF1 deficiency on the expression of these five genes was detected in only heart, spleen, and stomach. In addition, polyQ protein aggregations/inclusion was not detected in any tissues of WT-HD and HSF1KO-HD mice, but higher level of pre-aggregative polyQ protein was detected in HSF1KO-HD tissues. These results indicate non-Hsp genes are indispensable for the maintenance of intracellular homeostasis in mammalian tissues, resulting in whole body homeostasis.

Huntington's disease is a multi-system disorder

Huntington's disease (HD) is one of the most common non-curable rare diseases and is characterized by choreic movements, psychiatric symptoms, and slowly progressive dementia. HD is inherited as an autosomal dominant disorder with complete penetrance. Although brain pathology has become a hallmark of HD, there is a critical mass of new studies suggesting peripheral tissue pathology as an important factor in disease progression. In particular, recently published studies about skeletal muscle malfunction and HD-related cardiomyopathy in HD mouse models strongly suggest their important roles, leading to upcoming preclinical and clinical trials. One might conclude that therapeutic approaches in HD should not be restricted only to the brain pathology but instead major efforts should also be made to understand the cross-talk between diseased tissues like the CNS-Heart or CNS-skeletal muscle axes.

HDAC4-myogenin axis as an important marker of HD-related skeletal muscle atrophy

Skeletal muscle remodelling and contractile dysfunction occur through both acute and chronic disease processes. These include the accumulation of insoluble aggregates of misfolded amyloid proteins that is a pathological feature of Huntington’s disease (HD). While HD has been described primarily as a neurological disease, HD patients’ exhibit pronounced skeletal muscle atrophy. Given that huntingtin is a ubiquitously expressed protein, skeletal muscle fibres may be at risk of a cell autonomous HD-related dysfunction. However the mechanism leading to skeletal muscle abnormalities in the clinical and pre-clinical HD settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of HD. We found that symptomatic animals developed a progressive impairment of the contractile characteristics of the hind limb muscles tibialis anterior (TA) and extensor digitorum longus (EDL), accompanied by a significant loss of motor units in the EDL. In symptomatic animals, these pronounced functional changes were accompanied by an aberrant deregulation of contractile protein transcripts and their up-stream transcriptional regulators. In addition, HD mouse models develop a significant reduction in muscle force, possibly as a result of a deterioration in energy metabolism and decreased oxidation that is accompanied by the re-expression of the HDAC4-DACH2-myogenin axis. These results show that muscle dysfunction is a key pathological feature of HD.

Huntington’s disease (HD) is a neurodegenerative disorder in which the mutation results in an extra-long tract of glutamines that causes the huntingtin protein to aggregate. It is characterized by neurological symptoms and brain pathology, which is associated with nuclear and cytoplasmic protein aggregates and with transcriptional deregulation. Despite the fact that HD has been recognized principally as a neurological disease, there are multiple studies indicating that peripheral pathologies including cardiac dysfunction and skeletal muscle atrophy, contribute to the overall progression of HD. To unravel the cause of the skeletal muscle dysfunction, we applied a wide range of molecular and physiological methods to the analysis of two well established genetic mouse models of this disease. We found that symptomatic animals developed muscle dysfunction characterised by a change in the contractile characteristics of fast twitch muscles and a decrease in twitch and tetanic force of hindlimb muscles. In addition, there is a significant decrease in the number of motor units innervating the EDL muscle, and this motor unit loss progresses during the course of the disease. These changes were accompanied by the re-expression of contractile transcripts and markers of muscle denervation such as the HDAC4-Dach2-myogenin axis, as well as the apparent deterioration in energy metabolism and decreased oxidation. Therefore, we conclude, that the HD-related skeletal muscle atrophy is accompanied by progressive loss of functional motor units.

HDAC4 as a potential therapeutic target in neurodegenerative diseases: a summary of recent achievements

For the past decade protein acetylation has been shown to be a crucial post-transcriptional modification involved in the regulation of protein functions. Histone acetyltransferases (HATs) mediate acetylation of histones which results in the nucleosomal relaxation associated with gene expression. The reverse reaction, histone deacetylation, is mediated by histone deacetylases (HDACs) leading to chromatin condensation followed by transcriptional repression. HDACs are divided into distinct classes: I, IIa, IIb, III, and IV, on the basis of size and sequence homology, as well as formation of distinct repressor complexes. Implications of HDACs in many diseases, such as cancer, heart failure, and neurodegeneration, have identified these molecules as unique and attractive therapeutic targets. The emergence of HDAC4 among the members of class IIa family as a major player in synaptic plasticity raises important questions about its functions in the brain. The characterization of HDAC4 specific substrates and molecular partners in the brain will not only provide a better understanding of HDAC4 biological functions but also might help to develop new therapeutic strategies to target numerous malignancies. In this review we highlight and summarize recent achievements in understanding the biological role of HDAC4 in neurodegenerative processes.

Update on Huntington's disease: advances in care and emerging therapeutic options

INTRODUCTION

Huntington's disease (HD) is the most common hereditary neurodegenerative disorder. Despite the fact that both the gene and the mutation causing this monogenetic disorder were identified more than 20 years ago, disease-modifying therapies for HD have not yet been established.

REVIEW

While intense preclinical research and large cohort studies in HD have laid foundations for tangible improvements in understanding HD and caring for HD patients, identifying targets for therapeutic interventions and developing novel therapeutic modalities (new chemical entities and advanced therapies using DNA and RNA molecules as therapeutic agents) continues to be an ongoing process. The authors review recent achievements in HD research and focus on approaches towards disease-modifying therapies, ranging from huntingtin-lowering strategies to improving huntingtin clearance that may be promoted by posttranslational HTT modifications.

CONCLUSION

The nature and number of upcoming clinical studies/trials in HD is a reason for hope for HD patients and their families.