Molecular Mechanisms and Potential Therapeutical Targets in Huntington's Disease

Hybrid nanostructures for neurodegenerative disease theranostics: the art in the combination of biomembrane and non-biomembrane nanostructures

The diagnosis of neurodegenerative diseases (NDDs) remains challenging, and existing therapeutic approaches demonstrate little efficacy. NDD drug delivery can be achieved through the utilization of nanostructures, hence enabling multimodal NDD theranostics. Nevertheless, both biomembrane and non-biomembrane nanostructures possess intrinsic shortcomings that must be addressed by hybridization to create novel nanostructures with versatile applications in NDD theranostics. Hybrid nanostructures display improved biocompatibility, inherent targeting capabilities, intelligent responsiveness, and controlled drug release. This paper provides a concise overview of the latest developments in hybrid nanostructures for NDD theranostics and emphasizes various engineering methodologies for the integration of diverse nanostructures, including liposomes, exosomes, cell membranes, and non-biomembrane nanostructures such as polymers, metals, and hydrogels. The use of a combination technique can significantly augment the precision, intelligence, and efficacy of hybrid nanostructures, therefore functioning as a more robust theranostic approach for NDDs. This paper also addresses the issues that arise in the therapeutic translation of hybrid nanostructures and explores potential future prospects in this field.

Optical coherence tomography measurements in Huntington's disease: a systematic review and meta-analysis

BACKGROUND

A connection has been established between ocular structural changes and various neurodegenerative diseases. Several studies utilizing optical coherence tomography (OCT) have detected signs of ocular structural alterations among individuals with Huntington's disease (HD). The inconsistent results reported in the literature regarding alterations in the retina and choroid encouraged us to conduct this systematic review and meta-analysis to accumulate the findings.

METHODS

A systematic search was carried out in three electronic databases (PubMed, Embase, Scopus) to find studies reporting OCT measurements in HD cases compared with healthy controls (HC). A fixed-effects or random-effects meta-analysis was conducted according to the detected heterogeneity level. Furthermore, subgroup and sensitivity analyses, meta-regression, and quality assessment were performed.

RESULTS

Eleven studies were included in the systematic review and 9 studies with a total population of 452 participants (241 cases, and 211 HC) underwent meta-analysis. Results of the analysis denoted that subfoveal choroid had a significantly reduced thickness in HD eyes compared to HC (p < 0.0001). Moreover, our analysis indicated that HD cases had a significantly thinner average (p = 0.0130) and temporal peripapillary retinal nerve fiber layer (pRNFL) (p = 0.0012) than HC. However, subjects with pre-HD had insignificant differences in average (p = 0.44) and temporal pRNFL thickness (p = 0.33) with the HC group.

CONCLUSION

Results of the current systematic review and meta-analysis revealed the significant thinning of average and temporal pRNFL and subfoveal choroid in HD compared to HC. However, OCT currently might be considered insensitive to be applied in the pre-HD population at least until further longitudinal investigations considering variables such as the duration between OCT measurement and disease onset validating OCT as a routine diagnostic tool in HD clinics.

Neurodegenerative diseases and catechins: (-)-epigallocatechin-3-gallate is a modulator of chronic neuroinflammation and oxidative stress

Catechins, a class of phytochemicals found in various fruits and tea leaves, have garnered attention for their diverse health-promoting properties, including their potential in combating neurodegenerative diseases. Among these catechins, (-)-epigallocatechin-3-gallate (EGCG), the most abundant polyphenol in green tea, has emerged as a promising therapeutic agent due to its potent antioxidant and anti-inflammatory effects. Chronic neuroinflammation and oxidative stress are key pathological mechanisms in neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). EGCG has neuroprotective efficacy due to scavenging free radicals, reducing oxidative stress and attenuating neuroinflammatory processes. This review discusses the molecular mechanisms of EGCG's anti-oxidative stress and chronic neuroinflammation, emphasizing its effects on autoimmune responses, neuroimmune system interactions, and focusing on the related effects on AD and PD. By elucidating EGCG's mechanisms of action and its impact on neurodegenerative processes, this review underscores the potential of EGCG as a therapeutic intervention for AD, PD, and possibly other neurodegenerative diseases. Overall, EGCG emerges as a promising natural compound for combating chronic neuroinflammation and oxidative stress, offering novel avenues for neuroprotective strategies in the treatment of neurodegenerative disorders.

Divalent cations promote huntingtin fibril formation on endoplasmic reticulum derived and model membranes

Huntington's Disease (HD) is caused by an abnormal expansion of the polyglutamine (polyQ) domain within the first exon of the huntingtin protein (htt). This expansion promotes disease-related htt aggregation into amyloid fibrils and the formation of proteinaceous inclusion bodies within neurons. Fibril formation is a complex heterogenous process involving an array of aggregate species such as oligomers, protofibrils, and fibrils. In HD, structural abnormalities of membranes of several organelles develop. In particular, the accumulation of htt fibrils near the endoplasmic reticulum (ER) impinges upon the membrane, resulting in ER damage, altered dynamics, and leakage of Ca2+. Here, the aggregation of htt at a bilayer interface assembled from ER-derived liposomes was investigated, and fibril formation directly on these membranes was enhanced. Based on these observations, simplified model systems were used to investigate mechanisms associated with htt aggregation on ER membranes. As the ER-derived liposome fractions contained residual Ca2+, the role of divalent cations was also investigated. In the absence of lipids, divalent cations had minimal impact on htt structure and aggregation. However, the presence of Ca2+ or Mg2+ played a key role in promoting fibril formation on lipid membranes despite reduced htt insertion into and association with lipid interfaces, suggesting that the ability of divalent cations to promote fibril formation on membranes is mediated by induced changes to the lipid membrane physicochemical properties. With enhanced concentrations of intracellular calcium being a hallmark of HD, the ability of divalent cations to influence htt aggregation at lipid membranes may play a role in aggregation events that lead to organelle abnormalities associated with disease.

Effects of Macromolecular Cosolutes on the Kinetics of Huntingtin Aggregation Monitored by NMR Spectroscopy

The effects of two macromolecular cosolutes, specifically the polysaccharide dextran-20 and the protein lysozyme, on the aggregation kinetics of a pathogenic huntingtin exon-1 protein (hhtex1) with a 35 polyglutamine repeat, httex1Q35, are described. A unified kinetic model that establishes a direct connection between reversible tetramerization occurring on the microsecond time scale and irreversible fibril formation on a time scale of hours/days forms the basis for quantitative analysis of httex1Q35 aggregation, monitored by measuring cross-peak intensities in a series of 2D 1H-15N NMR correlation spectra acquired during the course of aggregation. The primary effects of the two cosolutes are associated with shifts in the prenucleation tetramerization equilibrium resulting in substantial changes in concentration of "preformed" httex1Q35 tetramers. Similar effects of the two cosolutes on the tetramerization equilibrium observed for a shorter, nonaggregating huntingtin variant with a 7-glutamine repeat, httex1Q7, lend confidence to the conclusions drawn from the fits to the httex1Q35 aggregation kinetics.

Superoxide dismutase and neurological disorders

Superoxide dismutase (SOD) is a common antioxidant enzyme found majorly in living cells. The main physiological role of SOD is detoxification and maintain the redox balance, acts as a first line of defence against Reactive nitrogen species (RNS), Reactive oxygen species (ROS), and other such potentially hazardous molecules. SOD catalyses the conversion of superoxide anion free radicals (O 2 -.) into molecular oxygen (O 2) and hydrogen peroxide (H 2O 2) in the cells. Superoxide dismutases (SODs) are expressed in neurons and glial cells throughout the CNS both intracellularly and extracellularly. Endogenous oxidative stress (OS) linked with enlarged production of reactive oxygen metabolites (ROMs), inflammation, deregulation of redox balance, mitochondrial dysfunction and bioenergetic crisis are found to be prerequisite for neuronal loss in neurological diseases. Clinical and genetic studies indicate a direct correlation between mutations in SOD gene and neurodegenerative diseases, like Amyotrophic Lateral Sclerosis (ALS), Huntington's disease (HD), Parkinson's Disease (PD) and Alzheimer's Disease (AD). Therefore, inhibitors of OS are considered as an optimistic approach to prevent neuronal loss. SOD mimetics like Metalloporphyrin Mn (II)-cyclic polyamines, Nitroxides and Mn (III)- Salen complexes are designed and used as therapeutic extensively in the treatment of neurological disorders. SODs and SOD mimetics are promising future therapeutics in the field of various diseases with OS-mediated pathology.

Nucleation of Huntingtin Aggregation Proceeds via Conformational Conversion of Pre-Formed, Sparsely-Populated Tetramers

Pathogenic huntingtin exon-1 protein (httex1), characterized by an expanded polyglutamine tract located between the N-terminal amphiphilic region and a C-terminal polyproline-rich domain, forms fibrils that accumulate in neuronal inclusion bodies, and is associated with a fatal, autosomal dominant neurodegenerative condition known as Huntington's disease. Here a complete kinetic model is described for aggregation/fibril formation of a httex1 construct with a 35-residue polyglutamine repeat, httex1Q35. Using exchange NMR spectroscopy, it is previously shown that the reversible formation of a sparsely-populated tetramer of the N-terminal amphiphilic domain of httex1Q35, comprising a D2 symmetric four-helix bundle, occurs on the microsecond time-scale and is a prerequisite for subsequent nucleation and fibril formation on a time scale that is many orders of magnitude slower (hours). Here a unified kinetic model of httex1Q35 aggregation is developed in which fast, reversible tetramerization is directly linked to slow irreversible fibril formation via conversion of pre-equilibrated tetrameric species to "active", chain elongation-capable nuclei by conformational re-arrangement with a finite, monomer-independent rate. The unified model permits global quantitative analysis of reversible tetramerization and irreversible fibril formation from a time series of 1H-15N correlation spectra recorded during the course of httex1Q35 aggregation.

Agmatine mitigates behavioral abnormalities and neurochemical dysregulation associated with 3-Nitropropionic acid-induced Huntington's disease in rats

Huntington's disease (HD) is a progressive neurodegenerative condition characterized by a severe motor incoordination, cognitive decline, and psychiatric complications. However, a definitive cure for this devastating disorder remains elusive. Agmatine, a biogenic amine, has gain attention for its reported neuromodulatory and neuroprotective properties. The present study was designed to examine the influence of agmatine on the behavioral, biochemical, and molecular aspects of HD in an animal model. A mitochondrial toxin, 3-nitro propionic acid (3-NP), was used to induce HD phenotype and similar symptoms such as motor incoordination, memory impairment, neuro-inflammation, and depressive-like behavior in rats. Rats were pre-treated with 3-NP (10 mg/kg, i.p.) on days 1, 3, 5, 7, and 9 and then continued on agmatine treatment (5 - 20 µg/rat, i.c.v.) from day-8 to day-27 of the treatment protocol. 3-NP-induced cognitive impairment was associated with declined in agmatine levels within prefrontal cortex, striatum, and hippocampus. Further, the 3-NP-treated rats showed an increase in IL-6 and TNF-α and a reduction in BDNF immunocontent within these brain areas. Agmatine treatment not only improved the 3-NP-induced motor incoordination, depression-like behavior, rota-rod performance, and learning and memory impairment but also normalized the GABA/glutamate, BDNF, IL-6, and TNF-α levels in discrete brain areas. Similarly, various agmatine modulators, which increase the endogenous agmatine levels in the brain, such as L-arginine (biosynthetic precursor), aminoguanidine (diamine oxidase inhibitor), and arcaine (agmatinase inhibitor) also demonstrated similar effects exhibiting the importance of endogenous agmatinergic pathway in the pathogenesis of 3-NP-induced HD like symptoms. The present study proposed the possible role of agmatine in the pathogenesis and treatment of HD associated motor incoordination, and psychiatric and cognitive complications.

Elucidating the Impact of Deleterious Mutations on IGHG1 and Their Association with Huntington's Disease

Huntington's disease (HD) is a chronic, inherited neurodegenerative condition marked by chorea, dementia, and changes in personality. The primary cause of HD is a mutation characterized by the expansion of a triplet repeat (CAG) within the huntingtin gene located on chromosome 4. Despite substantial progress in elucidating the molecular and cellular mechanisms of HD, an effective treatment for this disorder is not available so far. In recent years, researchers have been interested in studying cerebrospinal fluid (CSF) as a source of biomarkers that could aid in the diagnosis and therapeutic development of this disorder. Immunoglobulin heavy constant gamma 1 (IGHG1) is one of the CSF proteins found to increase significantly in HD. Considering this, it is reasonable to study the potential involvement of deleterious mutations in IGHG1 in the pathogenesis of this disorder. In this study, we explored the potential impact of deleterious mutations on IGHG1 and their subsequent association with HD. We evaluated 126 single-point amino acid substitutions for their impact on the structure and functionality of the IGHG1 protein while exploiting multiple computational resources such as SIFT, PolyPhen-2, FATHMM, SNPs&Go mCSM, DynaMut2, MAESTROweb, PremPS, MutPred2, and PhD-SNP. The sequence- and structure-based tools highlighted 10 amino acid substitutions that were deleterious and destabilizing. Subsequently, out of these 10 mutations, eight variants (Y32C, Y32D, P34S, V39E, C83R, C83Y, V85M, and H87Q) were identified as pathogenic by disease phenotype predictors. Finally, two pathogenic variants (Y32C and P34S) were found to reduce the solubility of the protein, suggesting their propensity to form protein aggregates. These variants also exhibited higher residual frustration within the protein structure. Considering these findings, the study hypothesized that the identified variants of IGHG1 may compromise its function and potentially contribute to HD pathogenesis.

Emerging antibody-based therapies for Huntington's disease: current status and perspectives for future development

INTRODUCTION

Being an inherited neurodegenerative disease with an identifiable genetic defect, Huntington's disease (HD) is a suitable candidate for early intervention, possibly even in the pre-symptomatic stage. Our recent advances in elucidating the pathogenesis of HD have revealed a series of novel potential therapeutic targets, among which immunotherapies are actively pursued in preclinical experiments.

AREAS COVERED

This review focuses on the potential of antibody-based treatments targeting various epitopes (of mutant huntingtin as well as phosphorylated tau) that are currently evaluated in vitro and in animal experiments. The references used in this review were retrieved from the PubMed database, searching for immunotherapies in HD, and clinical trial registries were reviewed for molecules already evaluated in clinical trials.

EXPERT OPINION

Antibody-based therapies have raised considerable interest in a series of neurodegenerative diseases characterized by deposition of aggregated of aberrantly folded proteins, HD included. Intrabodies and nanobodies can interact with mutant huntingtin inside the nervous cells. However, the conflicting results obtained with some of these intrabodies highlight the need for proper choice of epitopes and for developing animal models more closely mimicking human disease. Approval of these strategies will require a considerable financial and logistic effort on behalf of healthcare systems.

Ferroptosis regulation through Nrf2 and implications for neurodegenerative diseases

This article provides an overview of the background knowledge of ferroptosis in the nervous system, as well as the key role of nuclear factor E2-related factor 2 (Nrf2) in regulating ferroptosis. The article takes Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) as the starting point to explore the close association between Nrf2 and ferroptosis, which is of clear and significant importance for understanding the mechanism of neurodegenerative diseases (NDs) based on oxidative stress (OS). Accumulating evidence links ferroptosis to the pathogenesis of NDs. As the disease progresses, damage to the antioxidant system, excessive OS, and altered Nrf2 expression levels, especially the inhibition of ferroptosis by lipid peroxidation inhibitors and adaptive enhancement of Nrf2 signaling, demonstrate the potential clinical significance of Nrf2 in detecting and identifying ferroptosis, as well as targeted therapy for neuronal loss and mitochondrial dysfunction. These findings provide new insights and possibilities for the treatment and prevention of NDs.

Induced Pluripotent Stem Cells in Drug Discovery and Neurodegenerative Disease Modelling

Induced pluripotent stem cells (iPSCs) are derived from reprogrammed adult somatic cells. These adult cells are manipulated in vitro to express genes and factors essential for acquiring and maintaining embryonic stem cell (ESC) properties. This technology is widely applied in many fields, and much attention has been given to developing iPSC-based disease models to validate drug discovery platforms and study the pathophysiological molecular processes underlying disease onset. Especially in neurological diseases, there is a great need for iPSC-based technological research, as these cells can be obtained from each patient and carry the individual's bulk of genetic mutations and unique properties. Moreover, iPSCs can differentiate into multiple cell types. These are essential characteristics, since the study of neurological diseases is affected by the limited access to injury sites, the need for in vitro models composed of various cell types, the complexity of reproducing the brain's anatomy, the challenges of postmortem cell culture, and ethical issues. Neurodegenerative diseases strongly impact global health due to their high incidence, symptom severity, and lack of effective therapies. Recently, analyses using disease specific, iPSC-based models confirmed the efficacy of these models for testing multiple drugs. This review summarizes the advances in iPSC technology used in disease modelling and drug testing, with a primary focus on neurodegenerative diseases, including Parkinson's and Alzheimer's diseases.

Recent approaches in regenerative medicine in the fight against neurodegenerative disease

Neurodegenerative diseases arise due to slow and gradual loss of structure and/or function of neurons and glial cells and cause different degrees of loss of cognition abilities and sensation. The little success in developing effective treatments imposes a high and regressive economic impact on society, patients and their families. In recent years, regenerative medicine has provided a great opportunity to research new innovative strategies with strong potential to treatleva these diseases. These effects are due to the ability of suitable cells and biomaterials to regenerate damaged nerves with differentiated cells, creating an appropriate environment for recovering or preserving existing healthy neurons and glial cells from destruction and damage. Ultimately, a better understanding and thus a further investigation of stem cell technology, tissue engineering, gene therapy, and exosomes allows progress towards practical and effective treatments for neurodegenerative diseases. Therefore, in this review, advances currently being developed in regenerative medicine using animal models and human clinical trials in neurological disorders are summarized.

Unraveling the Puzzle of Therapeutic Peptides: A Promising Frontier in Huntington's Disease Treatment

Huntington's disease (HD) is a neurodegenerative genetic disorder characterized by a mutation in the huntingtin (HTT) gene, resulting in the production of a mutant huntingtin protein (mHTT). The accumulation of mHTT leads to the development of toxic aggregates in neurons, causing cell dysfunction and, eventually, cell death. Peptide therapeutics target various aspects of HD pathology, including mHTT reduction and aggregation inhibition, extended CAG mRNA degradation, and modulation of dysregulated signaling pathways, such as BDNF/TrkB signaling. In addition, these peptide therapeutics also target the detrimental interactions of mHTT with InsP3R1, CaM, or Caspase-6 proteins to mitigate HD. This Perspective provides a detailed perspective on anti-HD therapeutic peptides, highlighting their design, structural characteristics, neuroprotective effects, and specific mechanisms of action. Peptide therapeutics for HD exhibit promise in preclinical models, but further investigation is required to confirm their effectiveness as viable therapeutic strategies, recognizing that no approved peptide therapy for HD currently exists.

Nanomaterials for detection of biomolecules and delivering therapeutic agents in theragnosis: A review

Nanomaterials are emerging facts used to deliver therapeutic agents in living systems. Nanotechnology is used as a compliment by implementing different kinds of nanotechnological applications such as nano-porous structures, functionalized nanomaterials, quantum dots, carbon nanomaterials, and polymeric nanostructures. The applications are in the initial stage, which led to achieving several diagnoses and therapy in clinical practice. This review conveys the importance of nanomaterials in post-genomic employment, which includes the design of immunosensors, immune assays, and drug delivery. In this view, genomics is a molecular tool containing large databases that are useful in choosing an apt molecular inhibitor such as drug, ligand and antibody target in the drug delivery process. This study identifies the expression of genes and proteins in analysis and classification of diseases. Experimentally, the study analyses the design of a disease model. In particular, drug delivery is a boon area to treat cancer. The identified drugs enter different phase trails (Trails I, II, and III). The genomic information conveys more essential entities to the phase I trials and helps to move further for other trails such as trails-II and III. In such cases, the biomarkers play a crucial role by monitoring the unique pathological process. Genetic engineering with recombinant DNA techniques can be employed to develop genetically engineered disease models. Delivering drugs in a specific area is one of the challenging issues achieved using nanoparticles. Therefore, genomics is considered as a vast molecular tool to identify drugs in personalized medicine for cancer therapy.

The Therapeutic Potential and Molecular Mechanisms Underlying the Neuroprotective Effects of Sativex® - A Cannabis-derived Spray

Sativex is a cannabis-based medicine that comes in the form of an oromucosal spray. It contains equal amounts of Δ9-tetrahydrocannabinol and cannabidiol, two compounds derived from cannabis plants. Sativex has been shown to have positive effects on symptoms of amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and sleep disorders. It also has analgesic, antiinflammatory, antitumoral, and neuroprotective properties, which make it a potential treatment option for other neurological disorders. The article reviews the results of recent preclinical and clinical studies that support the therapeutic potential of Sativex and the molecular mechanisms behind its neuroprotective benefits in various neurological disorders. The article also discusses the possible advantages and disadvantages of using Sativex as a neurotherapeutic agent, such as its safety, efficacy, availability, and legal status.

Elucidating the Influence of Lipid Composition on Bilayer Perturbations Induced by the N-terminal Region of the Huntingtin Protein

Understanding the membrane interactions of the N-terminal 17 residues of the huntingtin protein (HttN) is essential for unraveling its role in cellular processes and its impact on huntingtin misfolding. In this study, we used atomic force microscopy (AFM) to examine the effects of lipid specificity in mediating bilayer perturbations induced by HttN. Across various lipid environments, the peptide consistently induced bilayer disruptions in the form of holes. Notably, our results unveiled that cholesterol enhanced bilayer perturbation induced by HttN, while phosphatidylethanolamine (PE) lipids suppressed hole formation. Furthermore, anionic phosphatidylglycerol (PG) and cardiolipin lipids, along with cholesterol at high concentrations, promoted the formation of double-bilayer patches. This unique structure suggests that the synergy among HttN, anionic lipids, and cholesterol can enhance bilayer fusion, potentially by facilitating lipid intermixing between adjacent bilayers. Additionally, our AFM-based force spectroscopy revealed that HttN enhanced the mechanical stability of lipid bilayers, as evidenced by an elevated bilayer puncture force. These findings illuminate the complex interplay between HttN and lipid membranes and provide useful insights into the role of lipid composition in modulating membrane interactions with the huntingtin protein.

Role of rafts in neurological disorders

INTRODUCTION

Rafts are protein-lipid structural nanodomains involved in efficient signal transduction and the modulation of physiological processes of the cell plasma membrane. Raft disruption in the nervous system has been associated with a wide range of disorders.

DEVELOPMENT

We review the concept of rafts, the nervous system processes in which they are involved, and their role in diseases such as Parkinson's disease, Alzheimer disease, and Huntington disease.

CONCLUSIONS

Based on the available evidence, preservation and/or reconstitution of rafts is a promising treatment strategy for a wide range of neurological disorders.

Curcumin, inflammation, and neurological disorders: How are they linked?

Background

Despite the extensive research in recent years, the current treatment modalities for neurological disorders are suboptimal. Curcumin, a polyphenol found in Curcuma genus, has been shown to mitigate the pathophysiology and clinical sequalae involved in neuroinflammation and neurodegenerative diseases.

Methods

We searched PubMed database for relevant publications on curcumin and its uses in treating neurological diseases. We also reviewed relevant clinical trials which appeared on searching PubMed database using 'Curcumin and clinical trials'.

Results

This review details the pleiotropic immunomodulatory functions and neuroprotective properties of curcumin, its derivatives and formulations in various preclinical and clinical investigations. The effects of curcumin on neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), brain tumors, epilepsy, Huntington's disorder (HD), ischemia, Parkinson's disease (PD), multiple sclerosis (MS), and traumatic brain injury (TBI) with a major focus on associated signalling pathways have been thoroughly discussed.

Conclusion

This review demonstrates curcumin can suppress spinal neuroinflammation by modulating diverse astroglia mediated cascades, ensuring the treatment of neurological disorders.

Fine scale hippocampus morphology variation cross 552 healthy subjects from age 20 to 80

The cerebral cortex varies over the course of a person's life span: at birth, the surface is smooth, before becoming more bumpy (deeper sulci and thicker gyri) in middle age, and thinner in senior years. In this work, a similar phenomenon was observed on the hippocampus. It was previously believed the fine-scale morphology of the hippocampus could only be extracted only with high field scanners (7T, 9.4T); however, recent studies show that regular 3T MR scanners can be sufficient for this purpose. This finding opens the door for the study of fine hippocampal morphometry for a large amount of clinical data. In particular, a characteristic bumpy and subtle feature on the inferior aspect of the hippocampus, which we refer to as hippocampal dentation, presents a dramatic degree of variability between individuals from very smooth to highly dentated. In this report, we propose a combined method joining deep learning and sub-pixel level set evolution to efficiently obtain fine-scale hippocampal segmentation on 552 healthy subjects. Through non-linear dentation extraction and fitting, we reveal that the bumpiness of the inferior surface of the human hippocampus has a clear temporal trend. It is bumpiest between 40 and 50 years old. This observation should be aligned with neurodevelopmental and aging stages.

The Huntington's Disease Gene in an Italian Cohort of Patients with Bipolar Disorder

BACKGROUND AND OBJECTIVES

Huntington's disease (HD) is characterized by motor, cognitive and psychiatric manifestations and caused by an expansion of CAG repeats over 35 triplets on the huntingtin (HTT) gene. However, expansions in the range 27-35 repeats (intermediate allele) can be associated with pathological phenotypes. The onset of HD is conventionally defined by the onset of motor symptoms, but psychiatric disturbances can precede the motor phase by up to twenty years. The aims of the present study are to identify HD patients in the pre-motor phase of the disease among patients diagnosed with bipolar disorders and evaluate any differences between bipolar patients carrying the normal HTT allele and patients with the expanded HTT gene.

METHODS

We assessed the HTT genotype in an Italian cohort of 69 patients who were affected by either type 1 or type 2 bipolar disorder.

RESULTS

No patient was found to be a carrier of the pathological HTT allele, but 10% of bipolar subjects carried an intermediate allele. Carriers of the intermediate allele were older at the onset of psychiatric symptoms than non-carriers.

CONCLUSION

The pathological HTT gene was not associated with bipolar disorder, while we found a higher frequency of the intermediate allele among the bipolar population with respect to healthy controls. The identification of this subset of bipolar subjects has implications for the clinical management of patients and their family members and promotes further investigation into possible pathological mechanisms common to both HD and bipolar disorder.

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

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

Chronic cholesterol administration to the brain supports complete and long-lasting cognitive and motor amelioration in Huntington's disease

Evidence that Huntington's disease (HD) is characterized by impaired cholesterol biosynthesis in the brain has led to strategies to increase its level in the brain of the rapidly progressing R6/2 mouse model, with a positive therapeutic outcome. Here we tested the long-term efficacy of chronic administration of cholesterol to the brain of the slowly progressing zQ175DN knock-in HD mice in preventing ("early treatment") or reversing ("late treatment") HD symptoms. To do this we used the most advanced formulation of cholesterol loaded brain-permeable nanoparticles (NPs), termed hybrid-g7-NPs-chol, which were injected intraperitoneally. We show that one cycle of treatment with hybrid-g7-NPs-chol, administered in the presymptomatic ("early treatment") or symptomatic ("late treatment") stages is sufficient to normalize cognitive defects up to 5 months, as well as to improve other behavioral and neuropathological parameters. A multiple cycle treatment combining both early and late treatments ("2 cycle treatment") lasting 6 months generates therapeutic effects for more than 11 months, without severe adverse reactions. Sustained cholesterol delivery to the brain of zQ175DN mice also reduces mutant Huntingtin aggregates in both the striatum and cortex and completely normalizes synaptic communication in the striatal medium spiny neurons compared to saline-treated HD mice. Furthermore, through a meta-analysis of published and current data, we demonstrated the power of hybrid-g7-NPs-chol and other strategies able to increase brain cholesterol biosynthesis, to reverse cognitive decline and counteract the formation of mutant Huntingtin aggregates. These results demonstrate that cholesterol delivery via brain-permeable NPs is a therapeutic option to sustainably reverse HD-related behavioral decline and neuropathological signs over time, highlighting the therapeutic potential of cholesterol-based strategies in HD patients. DATA AVAILABILITY: This study does not include data deposited in public repositories. Data are available on request to the corresponding authors.

Genome-wide screening in pluripotent cells identifies Mtf1 as a suppressor of mutant huntingtin toxicity

Huntington's disease (HD) is a neurodegenerative disorder caused by CAG-repeat expansions in the huntingtin (HTT) gene. The resulting mutant HTT (mHTT) protein induces toxicity and cell death via multiple mechanisms and no effective therapy is available. Here, we employ a genome-wide screening in pluripotent mouse embryonic stem cells (ESCs) to identify suppressors of mHTT toxicity. Among the identified suppressors, linked to HD-associated processes, we focus on Metal response element binding transcription factor 1 (Mtf1). Forced expression of Mtf1 counteracts cell death and oxidative stress caused by mHTT in mouse ESCs and in human neuronal precursor cells. In zebrafish, Mtf1 reduces malformations and apoptosis induced by mHTT. In R6/2 mice, Mtf1 ablates motor defects and reduces mHTT aggregates and oxidative stress. Our screening strategy enables a quick in vitro identification of promising suppressor genes and their validation in vivo, and it can be applied to other monogenic diseases.

Mitochondria in Huntington's disease: implications in pathogenesis and mitochondrial-targeted therapeutic strategies

Huntington's disease is a genetic disease caused by expanded CAG repeats on exon 1 of the huntingtin gene located on chromosome 4. Compelling evidence implicates impaired mitochondrial energetics, altered mitochondrial biogenesis and quality control, disturbed mitochondrial trafficking, oxidative stress and mitochondrial calcium dyshomeostasis in the pathogenesis of the disorder. Unfortunately, conventional mitochondrial-targeted molecules, such as cysteamine, creatine, coenzyme Q10, or triheptanoin, yielded negative or inconclusive results. However, future therapeutic strategies, aiming to restore mitochondrial biogenesis, improving the fission/fusion balance, and improving mitochondrial trafficking, could prove useful tools in improving the phenotype of Huntington's disease and, used in combination with genome-editing methods, could lead to a cure for the disease.

Transcriptional and Histone Acetylation Changes Associated with CRE Elements Expose Key Factors Governing the Regulatory Circuit in the Early Stage of Huntington's Disease Models

Huntington's disease (HD) is a disorder caused by an abnormal expansion of trinucleotide CAG repeats within the huntingtin (Htt) gene. Under normal conditions, the CREB Binding Protein interacts with CREB elements and acetylates Lysine 27 of Histone 3 to direct the expression of several genes. However, mutant Htt causes depletion of CBP, which in turn induces altered histone acetylation patterns and transcriptional deregulation. Here, we have studied a differential expression analysis and H3K27ac variation in 4- and 6-week-old R6/2 mice as a model of juvenile HD. The analysis of differential gene expression and acetylation levels were integrated into Gene Regulatory Networks revealing key regulators involved in the altered transcription cascade. Our results show changes in acetylation and gene expression levels that are related to impaired neuronal development, and key regulators clearly defined in 6-week-old mice are proposed to drive the downstream regulatory cascade in HD. Here, we describe the first approach to determine the relationship among epigenetic changes in the early stages of HD. We determined the existence of changes in pre-symptomatic stages of HD as a starting point for early onset indicators of the progression of this disease.

AAV5-miHTT-mediated huntingtin lowering improves brain health in a Huntington's disease mouse model

Huntingtin (HTT)-lowering therapies show great promise in treating Huntington's disease. We have developed a microRNA targeting human HTT that is delivered in an adeno-associated serotype 5 viral vector (AAV5-miHTT), and here use animal behaviour, MRI, non-invasive proton magnetic resonance spectroscopy and striatal RNA sequencing as outcome measures in preclinical mouse studies of AAV5-miHTT. The effects of AAV5-miHTT treatment were evaluated in homozygous Q175FDN mice, a mouse model of Huntington's disease with severe neuropathological and behavioural phenotypes. Homozygous mice were used instead of the more commonly used heterozygous strain, which exhibit milder phenotypes. Three-month-old homozygous Q175FDN mice, which had developed acute phenotypes by the time of treatment, were injected bilaterally into the striatum with either formulation buffer (phosphate-buffered saline + 5% sucrose), low dose (5.2 × 109 genome copies/mouse) or high dose (1.3 × 1011 genome copies/mouse) AAV5-miHTT. Wild-type mice injected with formulation buffer served as controls. Behavioural assessments of cognition, T1-weighted structural MRI and striatal proton magnetic resonance spectroscopy were performed 3 months after injection, and shortly afterwards the animals were sacrificed to collect brain tissue for protein and RNA analysis. Motor coordination was assessed at 1-month intervals beginning at 2 months of age until sacrifice. Dose-dependent changes in AAV5 vector DNA level, miHTT expression and mutant HTT were observed in striatum and cortex of AAV5-miHTT-treated Huntington's disease model mice. This pattern of microRNA expression and mutant HTT lowering rescued weight loss in homozygous Q175FDN mice but did not affect motor or cognitive phenotypes. MRI volumetric analysis detected atrophy in four brain regions in homozygous Q175FDN mice, and treatment with high dose AAV5-miHTT rescued this effect in the hippocampus. Like previous magnetic resonance spectroscopy studies in Huntington's disease patients, decreased total N-acetyl aspartate and increased myo-inositol levels were found in the striatum of homozygous Q175FDN mice. These neurochemical findings were partially reversed with AAV5-miHTT treatment. Striatal transcriptional analysis using RNA sequencing revealed mutant HTT-induced changes that were partially reversed by HTT lowering with AAV5-miHTT. Striatal proton magnetic resonance spectroscopy analysis suggests a restoration of neuronal function, and striatal RNA sequencing analysis shows a reversal of transcriptional dysregulation following AAV5-miHTT in a homozygous Huntington's disease mouse model with severe pathology. The results of this study support the use of magnetic resonance spectroscopy in HTT-lowering clinical trials and strengthen the therapeutic potential of AAV5-miHTT in reversing severe striatal dysfunction in Huntington's disease.

Alterations of fractional anisotropy throughout cortico-basal ganglia gray matter in a macaque model of Huntington's Disease

We recently generated a nonhuman primate (NHP) model of the neurodegenerative disorder Huntington's disease (HD) using adeno-associated viral vectors to express a fragment of mutant HTT protein (mHTT) throughout the cortico-basal ganglia circuit. Previous work by our group established that mHTT-treated NHPs exhibit progressive motor and cognitive phenotypes which are accompanied by mild volumetric reductions of cortical-basal ganglia structures and reduced fractional anisotropy (FA) in the white matter fiber pathways interconnecting these regions, mirroring findings observed in early-stage HD patients. Given the mild structural atrophy observed in cortical and sub-cortical gray matter regions characterized in this model using tensor-based morphometry, the current study sought to query potential microstructural alterations in the same gray matter regions using diffusion tensor imaging (DTI), to define early biomarkers of neurodegenerative processes in this model. Here, we report that mHTT-treated NHPs exhibit significant microstructural changes in several cortical and subcortical brain regions that comprise the cortico-basal ganglia circuit; with increased FA in the putamen and globus pallidus and decreased FA in the caudate nucleus and several cortical regions. DTI measures also correlated with motor and cognitive deficits such that animals with increased basal ganglia FA, and decreased cortical FA, had more severe motor and cognitive impairment. These data highlight the functional implications of microstructural changes in the cortico-basal ganglia circuit in early-stage HD.

Huntington's Disease in Chile: Epidemiological and Genetic Aspects

INTRODUCTION

Huntington's disease (HD) is a neurodegenerative, autosomal dominant disabling condition due to an expansion of the CAG trinucleotide in the HTT gene. Motor, psychiatric, and cognitive disorders characterize it. Chilean reports on HD in the era of molecular diagnosis were wanted.

METHODS

This is a retrospective analysis of a prospective cohort of patients with HD seen at the Center for Movement Disorders (CETRAM) in Chile between 2013 and 2019. Sociodemographic, genotype, and neuropsychiatric features were investigated.

RESULTS

One hundred three probands with HD were identified. The majority (63.1%) were born in the metropolitan region, followed by the VIII and V regions with 8.73% and 7.76%, respectively. When pedigrees were analyzed, ninety unrelated families encompassing 1,007 individuals were identified; among relatives, other 35 manifested HD, and 106 died of HD. Besides, five hundred seventy-nine individuals were at genetic risk. The minimum estimated prevalence of HD in Chile in 2019 was 0.72 × 100,000 inhabitants. The mean CAG repeats (CAGR) of 47.2 ± 10.74 for the expanded allele and 17.93 ± 2.05 for the normal allele. The mean age of onset was 41.39 ± 13.47 years. Juvenile cases represented 7.8% of this cohort, and 4.9% had a late onset. There was a negative correlation between the age of onset and the CAGR of the expanded allele (r =-0.84 p < 0.0001). Besides, 79.6% had a family history of HD.

CONCLUSIONS

This is the first report characterizing genetics, motor, and neuropsychiatric features in patients with HD in Chile. The mean length of CAGR expansion of the abnormal allele was similar to previous reports in North America (i.e., Mexico and Canada) and higher than that reported in the neighboring country of Argentina. According to previous estimations, the minimal prevalence of HD in Chile may be lower than expected.

Proteomic Analysis of Huntington's Disease Medium Spiny Neurons Identifies Alterations in Lipid Droplets

Huntington's disease (HD) is a neurodegenerative disease caused by a CAG repeat expansion in the Huntingtin (HTT) gene. The resulting polyglutamine (polyQ) tract alters the function of the HTT protein. Although HTT is expressed in different tissues, the medium spiny projection neurons (MSNs) in the striatum are particularly vulnerable in HD. Thus, we sought to define the proteome of human HD patient-derived MSNs. We differentiated HD72 induced pluripotent stem cells and isogenic controls into MSNs and carried out quantitative proteomic analysis. Using data-dependent acquisitions with FAIMS for label-free quantification on the Orbitrap Lumos mass spectrometer, we identified 6,323 proteins with at least two unique peptides. Of these, 901 proteins were altered significantly more in the HD72-MSNs than in isogenic controls. Functional enrichment analysis of upregulated proteins demonstrated extracellular matrix and DNA signaling (DNA replication pathway, double-strand break repair, G1/S transition) with the highest significance. Conversely, processes associated with the downregulated proteins included neurogenesis-axogenesis, the brain-derived neurotrophic factor-signaling pathway, Ephrin-A: EphA pathway, regulation of synaptic plasticity, triglyceride homeostasis cholesterol, plasmid lipoprotein particle immune response, interferon-γ signaling, immune system major histocompatibility complex, lipid metabolism and cellular response to stimulus. Moreover, proteins involved in the formation and maintenance of axons, dendrites, and synapses (e.g., Septin protein members) were dysregulated in HD72-MSNs. Importantly, lipid metabolism pathways were altered, and using quantitative image, we found analysis that lipid droplets accumulated in the HD72-MSN, suggesting a deficit in the turnover of lipids possibly through lipophagy. Our proteomics analysis of HD72-MSNs identified relevant pathways that are altered in MSNs and confirm current and new therapeutic targets for HD.

The structure of pathogenic huntingtin exon 1 defines the bases of its aggregation propensity

Huntington's disease is a neurodegenerative disorder caused by a CAG expansion in the first exon of the HTT gene, resulting in an extended polyglutamine (poly-Q) tract in huntingtin (httex1). The structural changes occurring to the poly-Q when increasing its length remain poorly understood due to its intrinsic flexibility and the strong compositional bias. The systematic application of site-specific isotopic labeling has enabled residue-specific NMR investigations of the poly-Q tract of pathogenic httex1 variants with 46 and 66 consecutive glutamines. Integrative data analysis reveals that the poly-Q tract adopts long α-helical conformations propagated and stabilized by glutamine side chain to backbone hydrogen bonds. We show that α-helical stability is a stronger signature in defining aggregation kinetics and the structure of the resulting fibrils than the number of glutamines. Our observations provide a structural perspective of the pathogenicity of expanded httex1 and pave the way to a deeper understanding of poly-Q-related diseases.

Brain-Derived Neurotrophic Factor: A Novel Dynamically Regulated Therapeutic Modulator in Neurological Disorders

The growth factor brain-derived neurotrophic factor (BDNF), and its receptor tropomyosin-related kinase receptor type B (TrkB) play an active role in numerous areas of the adult brain, where they regulate the neuronal activity, function, and survival. Upregulation and downregulation of BDNF expression are critical for the physiology of neuronal circuits and functioning in the brain. Loss of BDNF function has been reported in the brains of patients with neurodegenerative or psychiatric disorders. This article reviews the BDNF gene structure, transport, secretion, expression and functions in the brain. This article also implicates BDNF in several brain-related disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, major depressive disorder, schizophrenia, epilepsy and bipolar disorder.

Deletion of equilibrative nucleoside transporter 2 disturbs energy metabolism and exacerbates disease progression in an experimental model of Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease, characterized by motor dysfunction and abnormal energy metabolism. Equilibrative nucleoside transporter 1 (ENT1) and ENT2 are the major nucleoside transporters in cellular plasma membrane of the brain. Yet, unlike ENT1 whose function has been better investigated in HD, the role of ENT2 in HD remains unclear. The present study aimed to investigate the impacts of ENT2 deletion on HD using a well-characterized mouse model (R6/2). Microarray analysis, quantitative real-time polymerase chain reaction, and immunostaining of ENT2 in postmortem human brain tissues were conducted. R6/2 mice with or without genetic deletion of ENT2 were generated. Motor functions, including rotarod performance and limb-clasping test, were examined at the age of 7 to 12 weeks. Biochemical changes were evaluated by immunofluorescence staining and immunoblotting at the age of 12 to 13 weeks. In regard to energy metabolism, levels of striatal metabolites were determined by liquid chromatography coupled with the fluorescence detector or quadrupole time-of-flight mass spectrometer. Mitochondrial bioenergetics was assessed by the Seahorse assay. The results showed that ENT2 protein was detected in the neurons and astrocytes of human brains and the levels in the postmortem brain tended to be higher in patients with HD. In mice, ENT2 deletion did not alter the phenotype of the non-HD controls. Yet, ENT2 deletion deteriorated motor function and increased the number of aggregated mutant huntingtin in the striatum of R6/2 mice. Notably, disturbed energy metabolism with decreased ATP level and increased AMP/ ATP ratio was observed in R6/2-Ent2^-/- mice, compared with R6/2-Ent2^+/+ mice, resulting in the activation of AMPK in the late disease stage. Furthermore, ENT2 deletion reduced the NAD⁺/NADH ratio and impaired mitochondrial respiration in the striatum of R6/2 mice. Taken together, these findings indicate the crucial role of ENT2 in energy homeostasis, in which ENT2 deletion further impairs mitochondrial bioenergetics and deteriorates motor function in R6/2 mice.

Alpha-Pinene Alleviates Motor Activity in Animal Model of Huntington's Disease via Enhancing Antioxidant Capacity

Huntington's disease (HD) is a progressive, neurodegenerative, and inherited disease. Antioxidants have been shown to be effective in slowing disease progression in animal models of HD and are under investigation in human clinical trials. α-pinene, a member of the monoterpene class, has been shown to exert antioxidant activity. Therefore, this study aimed to investigate the impact of α-pinene on animal model of HD. Thirty-two male Wistar rats received 3-Nitropropionic acid (3-NP) for induction of the disease model or treated with α-pinene + 3-NP in different groups. Motor skill, and biochemical evaluations to detect oxidant/antioxidant markers in rat cortex and striatum were performed in all groups. We found that α-pinene significantly improved 3-NP-induced changes in the body weight, rotarod activity, time taken to cross the narrow beam, and locomotor activity. Biochemical analysis revealed that α-pinene significantly decreased the 3NP-induced elevation in oxidant markers, nitrite, and malondialdehyde in both cortex and striatum. In addition, α-pinene counteracted the 3-NP-induced fall in antioxidant enzymes, including superoxide dismutase, catalase, and glutathione in the cortex and striatum. In conclusion, we found that α-pinene prevented the motor dysfunction induced by 3-NP in the animal model of Huntington's disease. Oxidants-antioxidant balance might be involved in the protective effect of α-pinene.

Single-nuclei transcriptome analysis of Huntington disease iPSC and mouse astrocytes implicates maturation and functional deficits

Huntington disease (HD) is a neurodegenerative disorder caused by expanded CAG repeats in the huntingtin gene that alters cellular homeostasis, particularly in the striatum and cortex. Astrocyte signaling that establishes and maintains neuronal functions are often altered under pathological conditions. We performed single-nuclei RNA-sequencing on human HD patient-induced pluripotent stem cell (iPSC)-derived astrocytes and on striatal and cortical tissue from R6/2 HD mice to investigate high-resolution HD astrocyte cell state transitions. We observed altered maturation and glutamate signaling in HD human and mouse astrocytes. Human HD astrocytes also showed upregulated actin-mediated signaling, suggesting that some states may be cell-autonomous and human specific. In both species, astrogliogenesis transcription factors may drive HD astrocyte maturation deficits, which are supported by rescued climbing deficits in HD drosophila with NFIA knockdown. Thus, dysregulated HD astrocyte states may induce dysfunctional astrocytic properties, in part due to maturation deficits influenced by astrogliogenesis transcription factor dysregulation.

Transcriptional vulnerabilities of striatal neurons in human and rodent models of Huntington's disease

Striatal projection neurons (SPNs), which progressively degenerate in human patients with Huntington's disease (HD), are classified along two axes: the canonical direct-indirect pathway division and the striosome-matrix compartmentation. It is well established that the indirect-pathway SPNs are susceptible to neurodegeneration and transcriptomic disturbances, but less is known about how the striosome-matrix axis is compromised in HD in relation to the canonical axis. Here we show, using single-nucleus RNA-sequencing data from male Grade 1 HD patient post-mortem brain samples and male zQ175 and R6/2 mouse models, that the two axes are multiplexed and differentially compromised in HD. In human HD, striosomal indirect-pathway SPNs are the most depleted SPN population. In mouse HD models, the transcriptomic distinctiveness of striosome-matrix SPNs is diminished more than that of direct-indirect pathway SPNs. Furthermore, the loss of striosome-matrix distinction is more prominent within indirect-pathway SPNs. These results open the possibility that the canonical direct-indirect pathway and striosome-matrix compartments are differentially compromised in late and early stages of disease progression, respectively, differentially contributing to the symptoms, thus calling for distinct therapeutic strategies.

CRISPR/Cas9 Mediated Therapeutic Approach in Huntington's Disease

The pathogenic mechanisms of these diseases must be well understood for the treatment of neurological disorders such as Huntington's disease. Huntington's Disease (HD), a dominant and neurodegenerative disease, is characterized by the CAG re-expansion that occurs in the gene encoding the polyglutamine-expanded mutant Huntingtin (mHTT) protein. Genome editing approaches include zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and Clustered Regularly Interspaced Short Palindromic Repeats/Caspase 9 (CRISPR/Cas9) systems. CRISPR/Cas9 technology allows effective gene editing in different cell types and organisms. Through these systems are created isogenic control of human origin induced pluripotent stem cells (iPSCs). In human and mouse models, HD-iPSC lines can be continuously corrected using these systems. HD-iPSCs can be corrected through the CRISPR/Cas9 system and the cut-and-paste mechanism using isogenic control iPSCs. This mechanism is a piggyBac transposon-based selection system that can effectively switch between vectors and chromosomes. In studies conducted, it has been determined that in neural cells derived from HD-iPSC, there are isogenic controls as corrected lines recovered from phenotypic abnormalities and gene expression changes. It has been determined that trinucleotide repeat disorders occurring in HD can be cured by single-guide RNA (sgRNA) and normal exogenous DNA restoration, known as the single guideline RNA specific to Cas9. The purpose of this review in addition to give general information about HD, a neurodegenerative disorder is to explained the role of CRISPR/Cas9 system with iPSCs in HD treatment.

Dysregulation of Human Juvenile Huntington's Disease Brain Proteomes in Cortex and Putamen Involves Mitochondrial and Neuropeptide Systems

BACKGROUND

Huntington's disease (HD) is a genetic neurodegenerative disease caused by trinucleotide repeat CAG expansions in the human HTT gene. Early onset juvenile HD (JHD) in children is the most severe form of the disease caused by high CAG repeat numbers of the HTT gene.

OBJECTIVE

To gain understanding of human HD mechanisms hypothesized to involve dysregulated proteomes of brain regions that regulate motor and cognitive functions, this study analyzed the proteomes of human JHD cortex and putamen brain regions compared to age-matched controls.

METHODS

JHD and age-matched control brain tissues were assessed for CAG repeat numbers of HTT by PCR. Human brain JHD brain cortex regions of BA4 and BA6 with the putamen region (n = 5) were analyzed by global proteomics, compared to age-matched controls (n = 7). Protein interaction pathways were assessed by gene ontology (GO), STRING-db, and KEGG bioinformatics.

RESULTS

JHD brain tissues were heterozygous for one mutant HTT allele containing 60 to 120 CAG repeats, and one normal HTT allele with 10 to 19 CAG repeats. Proteomics data for JHD brain regions showed dysregulated mitochondrial energy pathways and changes in synaptic systems including peptide neurotransmitters. JHD compared to control proteomes of cortex and putamen displayed (a) proteins present only in JHD, (b) proteins absent in JHD, and (c) proteins that were downregulated or upregulated.

CONCLUSIONS

Human JHD brain cortex and putamen regions display significant dysregulation of proteomes representing deficits in mitochondrial and synaptic neurotransmission functions. These findings advance understanding of JHD brain molecular mechanisms associated with HD disabilities.

Differentiation of hPSCs to Study PRC2 Role in Cell-Fate Specification and Neurodevelopment

Several studies highlighted the importance of the polycomb repressive complex 2 (PRC2) already at the beginning of development. Although the crucial function of PRC2 in regulating lineage commitment and cell-fate specification has been well-established, the in vitro study of the exact mechanisms for which H3K27me3 is indispensable for proper differentiation is still challenging. In this chapter, we report a well-established and reproducible differentiation protocol to generate striatal medium spiny neurons as a tool to explore PRC2 role in brain development.

Generation of induced pluripotent stem cells from three individuals with Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by abnormal glutamine (Q) expansion in the huntingtin protein due to elongated CAG repeats in the gene HTT. We used non-integrative episomal plasmids to generate induced pluripotent stem cells (iPSCs) from three individuals affected by HD: CH1 (58Q), and two twin brothers CH3 (44Q) and CH4 (44Q). The iPSC lines exhibited one healthy HTT allele and one with elongated CAG repeats, as confirmed by PCR and sequencing. All iPSC lines expressed pluripotency markers, exhibited a normal karyotype, and generated cells of the three germ layers in vitro.

CRISPR-Based Genome-Editing Tools for Huntington's Disease Research and Therapy

Huntington's disease (HD) is an autosomal dominantly-inherited neurodegenerative disease, which is caused by CAG trinucleotide expansion in exon 1 of the Huntingtin (HTT) gene. Although HD is a rare disease, its monogenic nature makes it an ideal model in which to understand pathogenic mechanisms and to develop therapeutic strategies for neurodegenerative diseases. Clustered regularly-interspaced short palindromic repeats (CRISPR) is the latest technology for genome editing. Being simple to use and highly efficient, CRISPR-based genome-editing tools are rapidly gaining popularity in biomedical research and opening up new avenues for disease treatment. Here, we review the development of CRISPR-based genome-editing tools and their applications in HD research to offer a translational perspective on advancing the genome-editing technology to HD treatment.

Deep-learning analysis of micropattern-based organoids enables high-throughput drug screening of Huntington's disease models

Organoids are carrying the promise of modeling complex disease phenotypes and serving as a powerful basis for unbiased drug screens, potentially offering a more efficient drug-discovery route. However, unsolved technical bottlenecks of reproducibility and scalability have prevented the use of current organoids for high-throughput screening. Here, we present a method that overcomes these limitations by using deep-learning-driven analysis for phenotypic drug screens based on highly standardized micropattern-based neural organoids. This allows us to distinguish between disease and wild-type phenotypes in complex tissues with extremely high accuracy as well as quantify two predictors of drug success: efficacy and adverse effects. We applied our approach to Huntington's disease (HD) and discovered that bromodomain inhibitors revert complex phenotypes induced by the HD mutation. This work demonstrates the power of combining machine learning with phenotypic drug screening and its successful application to reveal a potentially new druggable target for HD.

New Therapeutic Approaches to and Mechanisms of Ginsenoside Rg1 against Neurological Diseases

Neurological diseases, including Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), stroke, cerebral infarction, ischemia-reperfusion injury, depression and, stress, have high incidence and morbidity and often lead to disability. However, there is no particularly effective medication against them. Therefore, finding drugs with a suitable efficacy, low toxicity and manageable effects to improve the quality of life of patients is an urgent problem. Ginsenoside Rg1 (Rg1) is the main active component of ginseng and has a variety of pharmacological effects. In this review, we focused on the therapeutic potential of Rg1 for improving neurological diseases. We introduce the mechanisms of Ginsenoside Rg1 in neurological diseases, including apoptosis, neuroinflammation, the microRNA (miRNA) family, the mitogen-activated protein kinase (MAPK) family, oxidative stress, nuclear factor-κB (NF-κB), and learning and memory of Rg1 in neurological diseases. In addition, Rg1 can also improve neurological diseases through the interaction of different signal pathways. The purpose of this review is to explore more in-depth ideas for the clinical treatment of neurological diseases (including PD, AD, HD, stroke, cerebral infarction, ischemia–reperfusion injury, depression, and stress). Therefore, Rg1 is expected to become a new therapeutic method for the clinical treatment of neurological diseases.

Therapeutic Strategies in Huntington’s Disease: From Genetic Defect to Gene Therapy

Despite the identification of an expanded CAG repeat on exon 1 of the huntingtin gene located on chromosome 1 as the genetic defect causing Huntington’s disease almost 30 years ago, currently approved therapies provide only limited symptomatic relief and do not influence the age of onset or disease progression rate. Research has identified various intricate pathogenic cascades which lead to neuronal degeneration, but therapies interfering with these mechanisms have been marked by many failures and remain to be validated. Exciting new opportunities are opened by the emerging techniques which target the mutant protein DNA and RNA, allowing for “gene editing”. Although some issues relating to “off-target” effects or immune-mediated side effects need to be solved, these strategies, combined with stem cell therapies and more traditional approaches targeting specific pathogenic cascades, such as excitotoxicity and bioavailability of neurotrophic factors, could lead to significant improvement of the outcomes of treated Huntington’s disease patients.

Berberine Ameliorate Haloperidol and 3-Nitropropionic Acid-Induced Neurotoxicity in Rats

Berberine due to its antioxidant properties, has been used around the globe significantly to treat several brain disorders. Also, oxidative stress is a pathological hallmark in neurodegenerative diseases like Huntington's disease (HD) and Tardive dyskinesia (TD). Berberine an alkaloid from plants has been reported to have neuroprotective potential in several animal models of neurodegenerative diseases. Hence, this study aims to evaluate the neuroprotective effect of berberine in the animal model of 3-nitropropionic acid (3-NP) induced HD and haloperidol induced tardive dyskinesia with special emphasis on its antioxidant property. The study protocol was divided into 2 phases, first phase involved the administration of 3-NP and berberine at the dose of (25, 50, and 100 mg/kg) intraperitoneally (i.p) and orally (p.o.) respectively for 21 days, and the following parameters (rotarod, narrow beam walk and photoactometer) as a measure of motor activity and striatal and cortical levels of (LPO, GSH, SOD, catalase, and nitrate) evaluated as a measure of oxidative stress were assessed for HD. Similarly in the second phase, TD was induced by using haloperidol, for 21 days and berberine at the dose of (25, 50, and 100 mg/kg) was administered, and both physical and biochemical parameters were assessed as mentioned for the HD study. The resultant data indicated that berberine attenuate 3-NP and haloperidol-induced behavioral changes and improved the antioxidant capcity in rodents. Hence berberine might be a novel therapeutic candidate to manage TD & HD.

Quantitative NMR analysis of the kinetics of prenucleation oligomerization and aggregation of pathogenic huntingtin exon-1 protein

The N-terminal region of the huntingtin protein, encoded by exon-1 (httex1) and containing an expanded polyglutamine tract, forms fibrils that accumulate in neuronal inclusion bodies, resulting in Huntington's disease. We previously showed that reversible formation of a sparsely populated tetramer of the N-terminal amphiphilic domain, comprising a dimer of dimers in a four-helix bundle configuration, occurs on the microsecond timescale and is an essential prerequisite for subsequent nucleation and fibril formation that takes place orders of magnitude slower on a timescale of hours. For pathogenic httex1, such as httex1Q35 with 35 glutamines, NMR signals decay too rapidly to permit measurement of time-intensive exchange-based experiments. Here, we show that quantitative analysis of both the kinetics and mechanism of prenucleation tetramerization and aggregation can be obtained simultaneously from a series of 1H-15N band-selective optimized flip-angle short-transient heteronuclear multiple quantum coherence (SOFAST-HMQC) correlation spectra. The equilibria and kinetics of tetramerization are derived from the time dependence of the 15N chemical shifts and 1H-15N cross-peak volume/intensity ratios, while the kinetics of irreversible fibril formation are afforded by the decay curves of 1H-15N cross-peak intensities and volumes. Analysis of data on httex1Q35 over a series of concentrations ranging from 200 to 750 μM and containing variable (7 to 20%) amounts of the Met7O sulfoxide species, which does not tetramerize, shows that aggregation of native httex1Q35 proceeds via fourth-order primary nucleation, consistent with the critical role of prenucleation tetramerization, coupled with first-order secondary nucleation. The Met7O sulfoxide species does not nucleate but is still incorporated into fibrils by elongation.

Mutant Huntingtin Protein Interaction Map Implicates Dysregulation of Multiple Cellular Pathways in Neurodegeneration of Huntington's Disease

BACKGROUND

Huntington's disease (HD) is a genetic neurodegenerative disease caused by trinucleotide repeat (CAG) expansions in the human HTT gene encoding the huntingtin protein (Htt) with an expanded polyglutamine tract.

OBJECTIVE

HD models from yeast to transgenic mice have investigated proteins interacting with mutant Htt that may initiate molecular pathways of cell death. There is a paucity of datasets of published Htt protein interactions that include the criteria of 1) defining fragments or full-length Htt forms, 2) indicating the number of poly-glutamines of the mutant and wild-type Htt forms, and 3) evaluating native Htt interaction complexes. This research evaluated such interactor data to gain understanding of Htt dysregulation of cellular pathways.

METHODS

Htt interacting proteins were compiled from the literature that meet our criteria and were subjected to network analysis via clustering, gene ontology, and KEGG pathways using rigorous statistical methods.

RESULTS

The compiled data of Htt interactors found that both mutant and wild-type Htt interact with more than 2,971 proteins. Application of a community detection algorithm to all known Htt interactors identified significant signal transduction, membrane trafficking, chromatin, and mitochondrial clusters, among others. Binomial analyses of a subset of reported protein interactor information determined that chromatin organization, signal transduction and endocytosis were diminished, while mitochondria, translation and membrane trafficking had enriched overall edge effects.

CONCLUSION

The data support the hypothesis that mutant Htt disrupts multiple cellular processes causing toxicity. This dataset is an open resource to aid researchers in formulating hypotheses of HD mechanisms of pathogenesis.

Activated or Impaired: An Overview of DNA Repair in Neurodegenerative Diseases

As the population ages, age-related neurodegenerative diseases have become a major challenge in health science. Currently, the pathology of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease, is still not fully understood. Remarkably, emerging evidence indicates a role of genomic DNA damage and repair in various neurodegenerative disorders. Here, we summarized the current understanding of the function of DNA damage repair, especially base excision repair and double strand break repair pathways, in a variety of neurodegenerative diseases. We concluded that exacerbation of DNA lesions is found in almost all types of neurodegenerative diseases, whereas the activities of different DNA repair pathways demonstrate distinct trends, depending on disease type and even brain region. Specifically, key enzymes involved in base excision repair are likely impaired in Alzheimer's disease and amyotrophic lateral sclerosis but activated in Parkinson's disease, while nonhomologous end joining is likely downregulated in most types of neurodegenerative diseases. Hence, impairment of nonhomologous end joining is likely a common etiology for most neurodegenerative diseases, while defects in base excision repair are likely involved in the pathology of Alzheimer's disease and amyotrophic lateral sclerosis but are Parkinson's disease, based on current findings. Although there are still discrepancies and further studies are required to completely elucidate the exact roles of DNA repair in neurodegeneration, the current studies summarized here provide crucial insights into the pathology of neurodegenerative diseases and may reveal novel drug targets for corresponding neurodegenerative diseases.