A role for autophagy in Huntington's disease

Unraveling the Molecular Jam: How Crowding Shapes Protein Aggregation in Neurodegenerative Disorders

Protein misfolding and aggregation are the hallmarks of neurodegenerative diseases including Huntington's disease, Parkinson's disease, Alzheimer's disease, and prion diseases. A crowded cellular environment plays a crucial role in modulating protein aggregation processes in vivo and the pathological aggregation of proteins linked to different neurodegenerative disorders. Here, we review recent studies examining the effects of various crowding agents, such as polysaccharides, polyethylene glycol, and proteins like BSA and lysozyme on the behaviors of aggregation of several amyloidogenic peptides and proteins, including amylin, huntingtin, tau, α-synuclein, prion, and amyloid-β. We also summarize how the aggregation kinetics, thermodynamic stability, and morphology of amyloid fibrils are altered significantly in the presence of crowding agents. In addition, we also discuss the molecular basis underlying the modulation of amyloidogenic aggregation, focusing on changes in the protein conformation, and the nucleation mechanism. The molecular understanding of the effects of macromolecular crowding on amyloid aggregation is essential for revealing disease pathologies and identifying possible therapeutic targets. Thus, this review offers a perspective on the complex interplay between protein aggregation and the crowded cellular environment in vivo and explains the relevance of crowding in the context of neurodegenerative disorders.

Network pharmacology-based mechanism analysis of dauricine on the alleviating Aβ-induced neurotoxicity in Caenorhabditis elegans

BACKGROUND

Dauricine (DAU), a benzyl tetrahydroisoquinoline alkaloid isolated from the root of Menispermum dauricum DC, exhibits promising anti-Alzheimer's disease (AD) effects, but its underlying mechanisms remain inadequately investigated. This paper aims to identify potential targets and molecular mechanisms of DAU in AD treatment.

METHODS

Network pharmacology and molecular docking simulation method were used to screen and focus core targets. Various transgenic Caenorhabditis elegans models were chosen to validate the anti-AD efficacy and mechanism of DAU.

RESULTS

There are 66 potential DAU-AD target intersections identified from 100 DAU and 3036 AD-related targets. Subsequent protein-protein interaction (PPI) network analysis identified 16 core targets of DAU for anti-AD. PIK3CA, AKT1 and mTOR were predicted to be the central targets with the best connectivity through the analysis of "compound-target-biological process-pathway network". Molecular docking revealed strong binding affinities between DAU and PIK3CA, AKT1, and mTOR. In vivo experiments demonstrated that DAU effectively reduced paralysis in AD nematodes caused by Aβ aggregation toxicity, downregulated expression of PIK3CA, AKT1, and mTOR homologues (age-1, akt-1, let-363), and upregulated expression of autophagy genes and the marker protein LGG-1. Simultaneously, DAU increased lysosomal content and enhanced degradation of the autophagy-related substrate protein P62. Thioflavin T（Th-T）staining experiment revealed that DAU decreased Aβ accumulation in AD nematodes. Further experiments also confirmed DAU's protein scavenging activity in polyglutamine (polyQ) aggregation nematodes.

CONCLUSION

Collectively, the mechanism of DAU against AD may be related to the activation of the autophagy-lysosomal protein clearance pathway, which contributes to the decrease of Aβ aggregation and the restoration of protein homeostasis.

Exploring molecular mechanisms, therapeutic strategies, and clinical manifestations of Huntington's disease

Huntington's disease (HD) is a paradigm of a genetic neurodegenerative disorder characterized by the expansion of CAG repeats in the HTT gene. This extensive review investigates the molecular complexities of HD by highlighting the pathogenic mechanisms initiated by the mutant huntingtin protein. Adverse outcomes of HD include mitochondrial dysfunction, compromised protein clearance, and disruption of intracellular signaling, consequently contributing to the gradual deterioration of neurons. Numerous therapeutic strategies, particularly precision medicine, are currently used for HD management. Antisense oligonucleotides, such as Tominersen, play a leading role in targeting and modulating the expression of mutant huntingtin. Despite the promise of these therapies, challenges persist, particularly in improving delivery systems and the necessity for long-term safety assessments. Considering the future landscape, the review delineates promising directions for HD research and treatment. Innovations such as Clustered regularly interspaced short palindromic repeats associated system therapies (CRISPR)-based genome editing and emerging neuroprotective approaches present unprecedented opportunities for intervention. Collaborative interdisciplinary endeavors and a more insightful understanding of HD pathogenesis are on the verge of reshaping the therapeutic landscape. As we navigate the intricate landscape of HD, this review serves as a guide for unraveling the intricacies of this disease and progressing toward transformative treatments.

Pathobiology of the autophagy-lysosomal pathway in the Huntington's disease brain

Accumulated levels of mutant huntingtin protein (mHTT) and its fragments are considered contributors to the pathogenesis of Huntington's disease (HD). Although lowering mHTT by stimulating autophagy has been considered a possible therapeutic strategy, the role and competence of autophagy-lysosomal pathway (ALP) during HD progression in the human disease remains largely unknown. Here, we used multiplex confocal and ultrastructural immunocytochemical analyses of ALP functional markers in relation to mHTT aggresome pathology in striatum and the less affected cortex of HD brains staged from HD2 to HD4 by Vonsattel neuropathological criteria compared to controls. Immunolabeling revealed the localization of HTT/mHTT in ALP vesicular compartments labeled by autophagy-related adaptor proteins p62/SQSTM1 and ubiquitin, and cathepsin D (CTSD) as well as HTT-positive inclusions. Although comparatively normal at HD2, neurons at later HD stages exhibited progressive enlargement and clustering of CTSD-immunoreactive autolysosomes/lysosomes and, ultrastructurally, autophagic vacuole/lipofuscin granules accumulated progressively, more prominently in striatum than cortex. These changes were accompanied by rises in levels of HTT/mHTT and p62/SQSTM1, particularly their fragments, in striatum but not in the cortex, and by increases of LAMP1 and LAMP2 RNA and LAMP1 protein. Importantly, no blockage in autophagosome formation and autophagosome-lysosome fusion was detected, thus pinpointing autophagy substrate clearance deficits as a basis for autophagic flux declines. The findings collectively suggest that upregulated lysosomal biogenesis and preserved proteolysis maintain autophagic clearance in early-stage HD, but failure at advanced stages contributes to progressive HTT build-up and potential neurotoxicity. These findings support the prospect that ALP stimulation applied at early disease stages, when clearance machinery is fully competent, may have therapeutic benefits in HD patients.

mTOR inhibition in Q175 Huntington's disease model mice facilitates neuronal autophagy and mutant huntingtin clearance

Huntington's disease (HD) is caused by expansion of the polyglutamine stretch in huntingtin protein (HTT) resulting in hallmark aggresomes/inclusion bodies (IBs) composed of mutant huntingtin protein (mHTT) and its fragments. Stimulating autophagy to enhance mHTT clearance is considered a potential therapeutic strategy for HD. Our recent evaluation of the autophagic-lysosomal pathway (ALP) in human HD brain reveals upregulated lysosomal biogenesis and relatively normal autophagy flux in early Vonsattel grade brains, but impaired autolysosome clearance in late grade brains, suggesting that autophagy stimulation could have therapeutic benefits as an earlier clinical intervention. Here, we tested this hypothesis by crossing the Q175 HD knock-in model with our autophagy reporter mouse TRGL ( T hy-1- R FP- G FP- L C3) to investigate in vivo neuronal ALP dynamics. In the Q175 and/or TRGL/Q175 mice, mHTT was detected in autophagic vacuoles and also exhibited high level colocalization with autophagy receptors p62/SQSTM1 and ubiquitin in the IBs. Compared to the robust lysosomal pathology in late-stage human HD striatum, ALP alterations in Q175 models are also late-onset but milder that included a lowered phospho-p70S6K level, lysosome depletion and autolysosome elevation including more poorly acidified autolysosomes and larger-sized lipofuscin granules, reflecting impaired autophagic flux. Administration of a mTOR inhibitor to 6-mo-old TRGL/Q175 normalized lysosome number, ameliorated aggresome pathology while reducing mHTT-, p62- and ubiquitin-immunoreactivities, suggesting beneficial potential of autophagy modulation at early stages of disease progression.

Role of TFEB in Huntington's Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by an expansion of the CAG trinucleotide repeat in exon 1 of the huntingtin (HTT) gene. This expansion leads to a polyglutamine (polyQ) tract at the N-terminal end of HTT, which reduces the solubility of the protein and promotes its accumulation. Inefficient clearance of mutant HTT (mHTT) by the proteasome or autophagy-lysosomal system leads to accumulation of oligomers and toxic protein aggregates in neurons, resulting in impaired proteolytic systems, transcriptional dysregulation, impaired axonal transport, mitochondrial dysfunction and cellular energy imbalance. Growing evidence suggests that the accumulation of mHTT aggregates and autophagic and/or lysosomal dysfunction are the major pathogenic mechanisms underlying HD. In this context, enhancing autophagy may be an effective therapeutic strategy to remove protein aggregates and improve cell function. Transcription factor EB (TFEB), a master transcriptional regulator of autophagy, controls the expression of genes critical for autophagosome formation, lysosomal biogenesis, lysosomal function and autophagic flux. Consequently, the induction of TFEB activity to promote intracellular clearance may be a therapeutic strategy for HD. However, while some studies have shown that overexpression of TFEB facilitates the clearance of mHTT aggregates and ameliorates the disease phenotype, others indicate such overexpression may lead to mHTT co-aggregation and worsen disease progression. Further studies are necessary to confirm whether TFEB modulation could be an effective therapeutic strategy against mHTT-mediated toxicity in different disease models.

Huntington's Disease: Complex Pathogenesis and Therapeutic Strategies

Huntington's disease (HD) arises from the abnormal expansion of CAG repeats in the huntingtin gene (HTT), resulting in the production of the mutant huntingtin protein (mHTT) with a polyglutamine stretch in its N-terminus. The pathogenic mechanisms underlying HD are complex and not yet fully elucidated. However, mHTT forms aggregates and accumulates abnormally in neuronal nuclei and processes, leading to disruptions in multiple cellular functions. Although there is currently no effective curative treatment for HD, significant progress has been made in developing various therapeutic strategies to treat HD. In addition to drugs targeting the neuronal toxicity of mHTT, gene therapy approaches that aim to reduce the expression of the mutant HTT gene hold great promise for effective HD therapy. This review provides an overview of current HD treatments, discusses different therapeutic strategies, and aims to facilitate future therapeutic advancements in the field.

The Role of Pyroptosis and Autophagy in the Nervous System

Autophagy is a conservative self-degradation system, which includes the two major processes of enveloping abnormal proteins, organelles and other macromolecules, and transferring them into lysosomes for the subsequent degradation. It holds the stability of the intracellular environment under stress. So far, three types of autophagy have been found: microautophagy, chaperone-mediated autophagy and macroautophagy. Many diseases have the pathological process of autophagy dysfunction, such as nervous system diseases. Pyroptosis is one kind of programmed cell death mediated by gasdermin (GSDM). In this process of pyroptosis, the activated caspase-3, caspase-4/5/11, or caspase-1 cleaves GSDM into the N-terminal pore-forming domain (PFD). The oligomer of PFD combines with the cell membrane to form membrane holes, thus leading to pyroptosis. Pyroptosis plays a key role in multiple tissues and organs. Many studies have revealed that autophagy and pyroptosis participate in the nervous system, but the mechanisms need to be fully clarified. Here, we focused on the recent articles on the role and mechanism of pyroptosis and autophagy in the pathological processes of the nervous system.

Nebulization of low-dose aspirin ameliorates Huntington's pathology in N171-82Q transgenic mice

Huntington Disease (HD), a devastating hereditary neurodegenerative disorder, is caused by expanded CAG trinucleotide repeats in the huntingtin gene (Htt) on chromosome 4. Currently, there is no effective therapy for HD. Although aspirin, acetylsalicylic acid, is one of the most widely-used analgesics throughout the world, it has some side effects. Even at low doses, oral aspirin can cause gastrointestinal symptoms, such as heartburn, upset stomach, or pain. Therefore, to bypass the direct exposure of aspirin to stomach, here, we described a new mode of use of aspirin and demonstrated that nebulization of low-dose of aspirin (10 μg/mouse/d=0.4 mg/kg body wt/d roughly equivalent to 28 mg/adult human/d) alleviated HD pathology in N171-82Q transgenic mice. Our immunohistochemical and western blot studies showed that daily aspirin nebulization significantly reduced glial activation, inflammation and huntingtin pathology in striatum and cortex of N171-82Q mice. Aspirin nebulization also protected transgenic mice from brain volume shrinkage and improved general motor behaviors. Collectively, these results highlight that nebulization of low-dose aspirin may have therapeutic potential in the treatment of HD.

Recent progress and future directions of the research on nanoplastic-induced neurotoxicity

Many types of plastic products, including polystyrene, have long been used in commercial and industrial applications. Microplastics and nanoplastics, plastic particles derived from these plastic products, are emerging as environmental pollutants that can pose health risks to a wide variety of living organisms, including humans. However, it is not well understood how microplastics and nanoplastics affect cellular functions and induce stress responses. Humans can be exposed to polystyrene-microplastics and polystyrene-nanoplastics through ingestion, inhalation, or skin contact. Most ingested plastics are excreted from the body, but inhaled plastics may accumulate in the lungs and can even reach the brain via the nose-to-brain route. Small-sized polystyrene-nanoplastics can enter cells by endocytosis, accumulate in the cytoplasm, and cause various cellular stresses, such as inflammation with increased pro-inflammatory cytokine production, oxidative stress with generation of reactive oxygen species, and mitochondrial dysfunction. They induce autophagy activation and autophagosome formation, but autophagic flux may be impaired due to lysosomal dysfunction. Unless permanently exposed to polystyrene-nanoplastics, they can be removed from cells by exocytosis and subsequently restore cellular function. However, neurons are very susceptible to this type of stress, thus even acute exposure can lead to neurodegeneration without recovery. This review focuses specifically on recent advances in research on polystyrene-nanoplastic-induced cytotoxicity and neurotoxicity. Furthermore, in this review, based on mechanistic studies of polystyrene-nanoplastics at the cellular level other than neurons, future directions for overcoming the negative effects of polystyrene-nanoplastics on neurons were suggested.

Upregulated pexophagy limits the capacity of selective autophagy

Selective autophagy is an essential process to maintain cellular homeostasis through the constant recycling of damaged or superfluous components. Over a dozen selective autophagy pathways mediate the degradation of diverse cellular substrates, but whether these pathways can influence one another remains unknown. We address this question using pexophagy, the autophagic degradation of peroxisomes, as a model. We show in cells that upregulated pexophagy impairs the selective autophagy of both mitochondria and protein aggregates by exhausting the autophagy initiation factor, ULK1. We confirm this finding in cell models of the pexophagy-mediated form of Zellweger Spectrum Disorder, a disease characterized by peroxisome dysfunction. Further, we extend the generalizability of limited selective autophagy by determining that increased protein aggregate degradation reciprocally reduces pexophagy using cell models of Parkinson's Disease and Huntington's Disease. Our findings suggest that the degradative capacity of selective autophagy can become limited by an increase in one substrate.

Paradigms and Success Stories of Natural Products in Drug Discovery Against Neurodegenerative Disorders (NDDs)

Neurodegenerative disorders (NDDs) are multifaceted complex disorders that have put a great health and economic burden around the globe nowadays. The multi-factorial nature of NDDs has presented a great challenge in drug discovery and continuous efforts are in progress in search of suitable therapeutic candidates. Nature has a great wealth of active principles in its lap that has cured the human population since ancient times. Natural products have revealed several benefits over conventional synthetic medications and scientists have shifted their vision towards exploring the therapeutic potentials of natural products in the past few years. The structural mimicking of natural compounds to endogenous ligands has presented them as a potential therapeutic candidate to prevent the development of NDDs. In the presented review, authors have summarized demographical facts about various NDDs including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and various types of sclerosis in the brain. The significant findings of new active principles of natural origin along with their therapeutic potentials on NDDs have been included. Also, a description of clinical trials and patents on natural products has been enlisted in this compilation. Although natural products have shown promising success in drug discovery against NDDs, still their use is associated with several ethical issues which need to be solved in the upcoming time.

Metformin: The Winding Path from Understanding Its Molecular Mechanisms to Proving Therapeutic Benefits in Neurodegenerative Disorders

Metformin, a widely prescribed medication for type 2 diabetes, has garnered increasing attention for its potential neuroprotective properties due to the growing demand for treatments for Alzheimer's, Parkinson's, and motor neuron diseases. This review synthesizes experimental and clinical studies on metformin's mechanisms of action and potential therapeutic benefits for neurodegenerative disorders. A comprehensive search of electronic databases, including PubMed, MEDLINE, Embase, and Cochrane library, focused on key phrases such as "metformin", "neuroprotection", and "neurodegenerative diseases", with data up to September 2023. Recent research on metformin's glucoregulatory mechanisms reveals new molecular targets, including the activation of the LKB1-AMPK signaling pathway, which is crucial for chronic administration of metformin. The pleiotropic impact may involve other stress kinases that are acutely activated. The precise role of respiratory chain complexes (I and IV), of the mitochondrial targets, or of the lysosomes in metformin effects remains to be established by further research. Research on extrahepatic targets like the gut and microbiota, as well as its antioxidant and immunomodulatory properties, is crucial for understanding neurodegenerative disorders. Experimental data on animal models shows promising results, but clinical studies are inconclusive. Understanding the molecular targets and mechanisms of its effects could help design clinical trials to explore and, hopefully, prove its therapeutic effects in neurodegenerative conditions.

Integrative human and murine multi-omics: Highlighting shared biomarkers in the neuronal ceroid lipofuscinoses

Neuronal ceroid lipofuscinosis (NCL) is a group of neurodegenerative disorders whose molecular mechanisms remain largely unknown. Omics approaches are among the methods that generate new information on modifying factors and molecular signatures. Moreover, omics data integration can address the need to progressively expand knowledge around the disease and pinpoint specific proteins to promote as candidate biomarkers. In this work, we integrated a total of 62 proteomic and transcriptomic datasets originating from humans and mice, employing a new approach able to define dysregulated processes across species, stages and NCL forms. Moreover, we selected a pool of differentially expressed proteins and genes as species- and form-related biomarkers of disease status/progression and evaluated local and spatial differences in most affected brain regions. Our results offer promising targets for potential new therapeutic strategies and reinforce the hypothesis of a connection between NCLs and other forms of dementia, particularly Alzheimer's disease.

Mutant-Huntingtin Molecular Pathways Elucidate New Targets for Drug Repurposing

The spectrum of neurodegenerative diseases known today is quite extensive. The complexities of their research and treatment lie not only in their diversity. Even many years of struggle and narrowly focused research on common pathologies such as Alzheimer's, Parkinson's, and other brain diseases have not brought cures for these illnesses. What can be said about orphan diseases? In particular, Huntington's disease (HD), despite affecting a smaller part of the human population, still attracts many researchers. This disorder is known to result from a mutation in the HTT gene, but having this information still does not simplify the task of drug development and studying the mechanisms of disease progression. Nonetheless, the data accumulated over the years and their analysis provide a good basis for further research. Here, we review studies devoted to understanding the mechanisms of HD. We analyze genes and molecular pathways involved in HD pathogenesis to describe the action of repurposed drugs and try to find new therapeutic targets.

Rapamycin reduces neuronal mutant huntingtin aggregation and ameliorates locomotor performance in Drosophila

Huntington's disease (HD) is a neurodegenerative disease characterized by movement and cognitive dysfunction. HD is caused by a CAG expansion in exon 1 of the HTT gene that leads to a polyglutamine (PQ) repeat in the huntingtin protein, which aggregates in the brain and periphery. Previously, we used Drosophila models to determine that Htt-PQ aggregation in the heart causes shortened lifespan and cardiac dysfunction that is ameliorated by promoting chaperonin function or reducing oxidative stress. Here, we further study the role of neuronal mutant huntingtin and how it affects peripheral function. We overexpressed normal (Htt-PQ25) or expanded mutant (Htt-PQ72) exon 1 of huntingtin in Drosophila neurons and found that mutant huntingtin caused age-dependent Htt-PQ aggregation in the brain and could cause a loss of synapsin. To determine if this neuronal dysfunction led to peripheral dysfunction, we performed a negative geotaxis assay to measure locomotor performance and found that neuronal mutant huntingtin caused an age-dependent decrease in locomotor performance. Next, we found that rapamycin reduced Htt-PQ aggregation in the brain. These results demonstrate the role of neuronal Htt-PQ in dysfunction in models of HD, suggest that brain-periphery crosstalk could be important to the pathogenesis of HD, and show that rapamycin reduces mutant huntingtin aggregation in the brain.

Gut microbiota dysbiosis and Huntington's disease: Exploring the gut-brain axis and novel microbiota-based interventions

Huntington's disease (HD) is a complex progressive neurodegenerative disorder affected by genetic, environmental, and metabolic factors contributing to its pathogenesis. Gut dysbiosis is termed as the alterations of intestinal microbial profile. Emerging research has highlighted the pivotal role of gut dysbiosis in HD, focusing on the gut-brain axis as a novel research parameter in science. This review article provides a comprehensive overview of gut microbiota dysbiosis and its relationship with HD and its pathogenesis along with the future challenges and opportunities. The focuses on the essential mechanisms which link gut dysbiosis to HD pathophysiology including neuroinflammation, immune system dysregulation, altered metabolites composition, and neurotransmitter imbalances. We also explored the impacts of gut dysbiosis on HD onset, severity, and symptoms such as cognitive decline, motor dysfunction, and psychiatric symptoms. Furthermore, we highlight recent advances in therapeutics including microbiota-based therapeutic approaches, including dietary interventions, prebiotics, probiotics, fecal microbiota transplantation, and combination therapies with conventional HD treatments and their applications in managing HD. The future challenges are also highlighted as the heterogeneity of gut microbiota, interindividual variability, establishing causality between gut dysbiosis and HD, identifying optimal therapeutic targets and strategies, and ensuring the long-term safety and efficacy of microbiota-based interventions. This review provides a better understanding of the potential role of gut microbiota in HD pathogenesis and guides the development of novel therapeutic approaches.

Dissecting the multifaced function of transcription factor EB (TFEB) in human diseases: From molecular mechanism to pharmacological modulation

The transcription factor EB (TFEB) is a transcription factor of the MiT/TFE family that translocations from the cytoplasm to the nucleus in response to various stimuli, including lysosomal stress and nutrient starvation. By activating genes involved in lysosomal function, autophagy, and lipid metabolism, TFEB plays a crucial role in maintaining cellular homeostasis. Dysregulation of TFEB has been implicated in various diseases, including cancer, neurodegenerative diseases, metabolic diseases, cardiovascular diseases, infectious diseases, and inflammatory diseases. Therefore, modulating TFEB activity with agonists or inhibitors may have therapeutic potential. In this review, we reviewed the recently discovered regulatory mechanisms of TFEB and their impact on human diseases. Additionally, we also summarize the existing TFEB inhibitors and agonists (targeted and non-targeted) and discuss unresolved issues and future research directions in the field. In summary, this review sheds light on the crucial role of TFEB, which may pave the way for its translation from basic research to practical applications, bringing us closer to realizing the full potential of TFEB in various fields.

Huntingtin Interacting Proteins and Pathological Implications

Huntington's disease (HD) is caused by an expansion of a CAG repeat in the gene that encodes the huntingtin protein (HTT). The exact function of HTT is still not fully understood, and previous studies have mainly focused on identifying proteins that interact with HTT to gain insights into its function. Numerous HTT-interacting proteins have been discovered, shedding light on the functions and structure of HTT. Most of these proteins interact with the N-terminal region of HTT. Among the various HTT-interacting proteins, huntingtin-associated protein 1 (HAP1) and HTT-interacting protein 1 (HIP1) have been extensively studied. Recent research has uncovered differences in the distribution of HAP1 in monkey and human brains compared with mice. This finding suggests that there may be species-specific variations in the regulation and function of HTT-interacting proteins. Understanding these differences could provide crucial insights into the development of HD. In this review, we will focus on the recent advancements in the study of HTT-interacting proteins, with particular attention to the differential distributions of HTT and HAP1 in larger animal models.

From Pathogenesis to Therapeutics: A Review of 150 Years of Huntington's Disease Research

Huntington's disease (HD) is a debilitating neurodegenerative genetic disorder caused by an expanded polyglutamine-coding (CAG) trinucleotide repeat in the huntingtin (HTT) gene. HD behaves as a highly penetrant dominant disorder likely acting through a toxic gain of function by the mutant huntingtin protein. Widespread cellular degeneration of the medium spiny neurons of the caudate nucleus and putamen are responsible for the onset of symptomology that encompasses motor, cognitive, and behavioural abnormalities. Over the past 150 years of HD research since George Huntington published his description, a plethora of pathogenic mechanisms have been proposed with key themes including excitotoxicity, dopaminergic imbalance, mitochondrial dysfunction, metabolic defects, disruption of proteostasis, transcriptional dysregulation, and neuroinflammation. Despite the identification and characterisation of the causative gene and mutation and significant advances in our understanding of the cellular pathology in recent years, a disease-modifying intervention has not yet been clinically approved. This review includes an overview of Huntington's disease, from its genetic aetiology to clinical presentation and its pathogenic manifestation. An updated view of molecular mechanisms and the latest therapeutic developments will also be discussed.

Chronic inflammation and the hallmarks of aging

BACKGROUND

Recently, the hallmarks of aging were updated to include dysbiosis, disabled macroautophagy, and chronic inflammation. In particular, the low-grade chronic inflammation during aging, without overt infection, is defined as "inflammaging," which is associated with increased morbidity and mortality in the aging population. Emerging evidence suggests a bidirectional and cyclical relationship between chronic inflammation and the development of age-related conditions, such as cardiovascular diseases, neurodegeneration, cancer, and frailty. How the crosstalk between chronic inflammation and other hallmarks of aging underlies biological mechanisms of aging and age-related disease is thus of particular interest to the current geroscience research.

SCOPE OF REVIEW

This review integrates the cellular and molecular mechanisms of age-associated chronic inflammation with the other eleven hallmarks of aging. Extra discussion is dedicated to the hallmark of "altered nutrient sensing," given the scope of Molecular Metabolism. The deregulation of hallmark processes during aging disrupts the delicate balance between pro-inflammatory and anti-inflammatory signaling, leading to a persistent inflammatory state. The resultant chronic inflammation, in turn, further aggravates the dysfunction of each hallmark, thereby driving the progression of aging and age-related diseases.

MAIN CONCLUSIONS

The crosstalk between chronic inflammation and other hallmarks of aging results in a vicious cycle that exacerbates the decline in cellular functions and promotes aging. Understanding this complex interplay will provide new insights into the mechanisms of aging and the development of potential anti-aging interventions. Given their interconnectedness and ability to accentuate the primary elements of aging, drivers of chronic inflammation may be an ideal target with high translational potential to address the pathological conditions associated with aging.

The Role of Autophagy in the Development of Pathological Conditions of the Body

Autophagy is the process of lysosomal elimination of the cell organelles, cytoplasmic sites, and pathogenic microorganisms that enter the cell. This process is associated with both cell death regulation and an increase in cell survival chances. Autophagy is involved in the development of various diseases (Crohn disease, cancer, atherosclerosis, etc.). For these reasons, it is of significant interest to establish the molecular targets involved in autophagy regulation and the factors that mediate its participation in pathogenesis. The review describes the potential molecular mechanisms involved in the regulation of autophagy, its contribution to the vital cell activity in a healthy organism, and pathologies.

Disruption of mitochondrial and lysosomal functions by human CACNA1C variants expressed in HEK 293 and CHO cells

Objective

To investigate the pathogenesis of three novel de novo CACNA1C variants (p.E411D, p.V622G, and p.A272V) in causing neurodevelopmental disorders and arrhythmia.

Methods

Several molecular experiments were carried out on transfected human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells to explore the effects of p.E411D, p.V622G, and p.A272V variants on electrophysiology, mitochondrial and lysosomal functions. Electrophysiological studies, RT-qPCR, western blot, apoptosis assay, mito-tracker fluorescence intensity, lyso-tracker fluorescence intensity, mitochondrial calcium concentration test, and cell viability assay were performed. Besides, reactive oxygen species (ROS) levels, ATP levels, mitochondrial copy numbers, mitochondrial complex I, II, and cytochrome c functions were measured.

Results

The p.E411D variant was found in a patient with attention deficit-hyperactive disorder (ADHD), and moderate intellectual disability (ID). This mutant demonstrated reduced calcium current density, mRNA, and protein expression, and it was localized in the nucleus, cytoplasm, lysosome, and mitochondria. It exhibited an accelerated apoptosis rate, impaired autophagy, and mitophagy. It also demonstrated compromised mitochondrial cytochrome c oxidase, complex I, and II enzymes, abnormal mitochondrial copy numbers, low ATP levels, abnormal mitochondria fluorescence intensity, impaired mitochondrial fusion and fission, and elevated mitochondrial calcium ions. The p.V622G variant was identified in a patient who presented with West syndrome and moderate global developmental delay. The p.A272V variant was found in a patient who presented with epilepsy and mild ID. Both mutants (p.V622G and p.A272V) exhibited reduced calcium current densities, decreased mRNA and protein expressions, and they were localized in the nucleus, cytoplasm, lysosome, and mitochondria. They exhibited accelerated apoptosis and proliferation rates, impaired autophagy, and mitophagy. They also exhibited abnormal mitochondrial cytochrome c oxidase, complex I and II enzymes, abnormal mitochondrial copy numbers, low ATP, high ROS levels, abnormal mitochondria fluorescence intensity, impaired mitochondrial fusion and fission, as well as elevated mitochondrial calcium ions.

Conclusion

The p.E411D, p.V622G and p.A272V mutations of human CACNA1C reduce the expression level of CACNA1C proteins, and impair mitochondrial and lysosomal functions. These effects induced by CACNA1C variants may contribute to the pathogenesis of CACNA1C-related disorders.

NOD mouse dorsal root ganglia display morphological and gene expression defects before and during autoimmune diabetes development

Introduction

During the development of Autoimmune Diabetes (AD) an autoimmune attack against the Peripheral Nervous System occurs. To gain insight into this topic, analyses of Dorsal Root Ganglia (DRG) from Non-Obese Diabetic (NOD) mice were carried out.

Methods

Histopathological analysis by electron and optical microscopy in DRG samples, and mRNA expression analyzes by the microarray technique in DRG and blood leukocyte samples from NOD and C57BL/6 mice were performed.

Results

The results showed the formation of cytoplasmic vacuoles in DRG cells early in life that could be related to a neurodegenerative process. In view of these results, mRNA expression analyses were conducted to determine the cause and/or the molecules involved in this suspected disorder. The results showed that DRG cells from NOD mice have alterations in the transcription of a wide range of genes, which explain the previously observed alterations. In addition, differences in the transcription genes in white blood cells were also detected.

Discussion

Taken together, these results indicate that functional defects are not only seen in beta cells but also in DRG in NOD mice. These results also indicate that these defects are not a consequence of the autoimmune process that takes place in NOD mice and suggest that they may be involved as triggers for its development.

In vitro methods in autophagy research: Applications in neurodegenerative diseases and mood disorders

Background

Autophagy is a conserved physiological intracellular mechanism responsible for the degradation and recycling of cytoplasmic constituents (e.g., damaged organelles, and protein aggregates) to maintain cell homeostasis. Aberrant autophagy has been observed in neurodegenerative diseases, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Huntington's Disease (HD), and recently aberrant autophagy has been associated with mood disorders, such as depression. Several in vitro methods have been developed to study the complex and tightly regulated mechanisms of autophagy. In vitro methods applied to autophagy research are used to identify molecular key players involved in dysfunctional autophagy and to screen autophagy regulators with therapeutic applications in neurological diseases and mood disorders. Therefore, the aims of this narrative review are (1) to compile information on the cell-based methods used in autophagy research, (2) to discuss their application, and (3) to create a catalog of traditional and novel in vitro methods applied in neurodegenerative diseases and depression.

Methods

Pubmed and Google Scholar were used to retrieve relevant in vitro studies on autophagy mechanisms in neurological diseases and depression using a combination of search terms per mechanism and disease (e.g., "macroautophagy" and "Alzheimer's disease"). A total of 37 studies were included (14 in PD, 8 in AD, 5 in ALS, 5 in %, and 5 in depression).

Results

A repertoire of traditional and novel approaches and techniques was compiled and discussed. The methods used in autophagy research focused on the mechanisms of macroautophagy, microautophagy, and chaperone-mediated autophagy. The in vitro tools presented in this review can be applied to explore pathophysiological mechanisms at a molecular level and to screen for potential therapeutic agents and their mechanism of action, which can be of great importance to understanding disease biology and potential therapeutic options in the context of neurodegenerative disorders and depression.

Conclusion

This is the first review to compile, discuss, and provide a catalog of traditional and novel in vitro models applied to neurodegenerative disorders and depression.

Autophagy at the synapse, an early site of dysfunction in neurodegeneration

Macroautophagy, herein referred to as autophagy, has long been implicated in the pathophysiology of neurodegenerative diseases. However, an incomplete understanding of how autophagy contributes to disease pathogenesis has limited progress in acting on this potential target for the development of disease modifying therapeutics. Research in the past few decades has revealed that autophagy plays a specialized role in the synapse, a site of early dysfunction in multiple neurodegenerative diseases. In this review we discuss the evidence suggesting that inadequate autophagy at the synapse may contribute to neurodegeneration, and why the functions of autophagy may be particularly relevant for synaptic function.

Updates on the study of lysosomal protein dynamics: possibilities for the clinic

INTRODUCTION

The lysosome is the main degradative organelle of almost all mammalian cells, fulfilling important functions in macromolecule recycling, metabolism, and signaling. Lysosomal dysfunction is connected to a continuously growing number of pathologic conditions, and lysosomal proteins present potential biomarkers for a variety of diseases. Therefore, there is an increasing interest in their analysis in patient samples.

AREAS COVERED

We provide an overview of OMICs studies which identified lysosomal proteins as potential biomarkers for pathological conditions, covering proteomics, genomics, and transcriptomics approaches, identified through PubMed searches. With respect to discovery proteomics analyses, mainly lysosomal luminal and associated proteins were detected, while membrane proteins were found less frequently. Comprehensive coverage of the lysosomal proteome was only achieved by ultra-deep-coverage studies, but targeted approaches allowed for the reproducible quantification of lysosomal proteins in diverse sample types.

EXPERT OPINION

The low abundance of lysosomal proteins complicates their reproducible analysis in patient samples. Whole proteome shotgun analyses fail in many instances to cover the lysosomal proteome, which is due to under-sampling and/or a lack of sensitivity. With the current state of the art, targeted proteomics assays provide the best performance for the characterization of lysosomal proteins in patient samples.

NAADP-Evoked Ca2+ Signaling Leads to Mutant Huntingtin Aggregation and Autophagy Impairment in Murine Astrocytes

Huntington’s disease (HD) is a progressive neurodegenerative disease characterized by mutations in the huntingtin gene (mHtt), causing an unstable repeat of the CAG trinucleotide, leading to abnormal long repeats of polyglutamine (poly-Q) in the N-terminal region of the huntingtin, which form abnormal conformations and aggregates. Alterations in Ca2+ signaling are involved in HD models and the accumulation of mutated huntingtin interferes with Ca2+ homeostasis. Lysosomes are intracellular Ca2+ storages that participate in endocytic and lysosomal degradation processes, including autophagy. Nicotinic acid adenine dinucleotide phosphate (NAADP) is an intracellular second messenger that promotes Ca2+ release from the endo-lysosomal system via Two-Pore Channels (TPCs) activation. Herein, we show the impact of lysosomal Ca2+ signals on mHtt aggregation and autophagy blockade in murine astrocytes overexpressing mHtt-Q74. We observed that mHtt-Q74 overexpression causes an increase in NAADP-evoked Ca2+ signals and mHtt aggregation, which was inhibited in the presence of Ned-19, a TPC antagonist, or BAPTA-AM, a Ca2+ chelator. Additionally, TPC2 silencing revert the mHtt aggregation. Furthermore, mHtt has been shown co-localized with TPC2 which may contribute to its effects on lysosomal homeostasis. Moreover, NAADP-mediated autophagy was also blocked since its function is dependent on lysosomal functionality. Taken together, our data show that increased levels of cytosolic Ca2+ mediated by NAADP causes mHtt aggregation. Additionally, mHtt co-localizes with the lysosomes, where it possibly affects organelle functions and impairs autophagy.

Function and Inhibition of DYRK1A: emerging roles of treating multiple human diseases

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is an evolutionarily conserved protein kinase and the most studied member of the Dual-specificity tyrosine-regulated kinase (DYRK) family. It has been shown that it participates in the development of plenty of diseases, and both the low or high expression of DYRK1A protein could lead to disorder. Thus, DYRK1A is recognized as a key target for the therapy for these diseases, and the studies on natural or synthetic DYRK1A inhibitors have become more and more popular. Here, we provide a comprehensive review for DYRK1A from the structure and function of DYRK1A, the roles of DYRK1A in various types of diseases, including diabetes mellitus, neurodegenerative diseases, and kinds of cancers, and the studies of its natural and synthetic inhibitors.

Subtyping monogenic disorders: Huntington disease

Huntington disease is a highly disabling neurodegenerative disease characterized by psychiatric, cognitive, and motor deficits. The causal genetic mutation in huntingtin (Htt, also known as IT15), located on chromosome 4p16.3, leads to an expansion of a triplet coding for polyglutamine. The expansion is invariably associated with the disease when >39 repeats. Htt encodes for the protein huntingtin (HTT), which carries out many essential biological functions in the cell, in particular in the nervous system. The precise mechanism of toxicity is not known. Based on a one-gene-one-disease framework, the prevailing hypothesis ascribes toxicity to the universal aggregation of HTT. However, the aggregation process into mutant huntingtin (mHTT) is associated with a reduction of the levels of wild-type HTT. A loss of wild-type HTT may plausibly be pathogenic, contributing to the disease onset and progressive neurodegeneration. Moreover, many other biological pathways are altered in Huntington disease, such as in the autophagic system, mitochondria, and essential proteins beyond HTT, potentially explaining biological and clinical differences among affected individuals. As one gene does not mean one disease, future efforts at identifying specific Huntington subtypes are important to design biologically tailored therapeutic approaches that correct the corresponding biological pathways-rather than continuing to exclusively target the common denominator of HTT aggregation for elimination.

Co-occurring pathogenic variants in 6q27 associated with dementia spectrum disorders in a Peruvian family

Evidence suggests that there may be racial differences in risk factors associated with the development of Alzheimer's disease and related dementia (ADRD). We used whole-genome sequencing analysis and identified a novel combination of three pathogenic variants in the heterozygous state (UNC93A: rs7739897 and WDR27: rs61740334; rs3800544) in a Peruvian family with a strong clinical history of ADRD. Notably, the combination of these variants was present in two generations of affected individuals but absent in healthy members of the family. In silico and in vitro studies have provided insights into the pathogenicity of these variants. These studies predict that the loss of function of the mutant UNC93A and WDR27 proteins induced dramatic changes in the global transcriptomic signature of brain cells, including neurons, astrocytes, and especially pericytes and vascular smooth muscle cells, indicating that the combination of these three variants may affect the neurovascular unit. In addition, known key molecular pathways associated with dementia spectrum disorders were enriched in brain cells with low levels of UNC93A and WDR27. Our findings have thus identified a genetic risk factor for familial dementia in a Peruvian family with an Amerindian ancestral background.

Brain-protective mechanisms of autophagy associated circRNAs: Kick starting self-cleaning mode in brain cells via circRNAs as a potential therapeutic approach for neurodegenerative diseases

Altered autophagy is a hallmark of neurodegeneration but how autophagy is regulated in the brain and dysfunctional autophagy leads to neuronal death has remained cryptic. Being a key cellular waste-recycling and housekeeping system, autophagy is implicated in a range of brain disorders and altering autophagy flux could be an effective therapeutic strategy and has the potential for clinical applications down the road. Tight regulation of proteins and organelles in order to meet the needs of complex neuronal physiology suggests that there is distinct regulatory pattern of neuronal autophagy as compared to non-neuronal cells and nervous system might have its own separate regulator of autophagy. Evidence has shown that circRNAs participates in the biological processes of autophagosome assembly. The regulatory networks between circRNAs, autophagy, and neurodegeneration remains unknown and warrants further investigation. Understanding the interplay between autophagy, circRNAs and neurodegeneration requires a knowledge of the multiple steps and regulatory interactions involved in the autophagy pathway which might provide a valuable resource for the diagnosis and therapy of neurodegenerative diseases. In this review, we aimed to summarize the latest studies on the role of brain-protective mechanisms of autophagy associated circRNAs in neurodegenerative diseases (including Alzheimer's disease, Parkinson's disease, Huntington's disease, Spinal Muscular Atrophy, Amyotrophic Lateral Sclerosis, and Friedreich's ataxia) and how this knowledge can be leveraged for the development of novel therapeutics against them. Autophagy stimulation might be potential one-size-fits-all therapy for neurodegenerative disease as per considerable body of evidence, therefore future research on brain-protective mechanisms of autophagy associated circRNAs will illuminate an important feature of nervous system biology and will open the door to new approaches for treating neurodegenerative diseases.

Autophagy in graves' ophthalmopathy

Graves' ophthalmopathy (GO) is an inflammatory autoimmune disease that affects the eyes. It can significantly alter the quality of life in patients because of its distinctive pathological appearance and the effect on vision. To date, the exact pathological mechanism of GO has not been explicitly discovered. However, several studies have associated autophagy with this disease. Autophagy is a catabolic process that helps maintain homeostasis in all organisms by protecting the cells and tissues from various endogenous and exogenous stress factors. Based on our results, patients affected with GO have comparatively elevated levels of autophagy, which critically affects the pathological mechanism of the GO. In this review, we have summarized the autophagy mechanism in the pathogenesis of GO.

HSF1 and Its Role in Huntington's Disease Pathology

PURPOSE OF REVIEW

Heat shock factor 1 (HSF1) is the master transcriptional regulator of the heat shock response (HSR) in mammalian cells and is a critical element in maintaining protein homeostasis. HSF1 functions at the center of many physiological processes like embryogenesis, metabolism, immune response, aging, cancer, and neurodegeneration. However, the mechanisms that allow HSF1 to control these different biological and pathophysiological processes are not fully understood. This review focuses on Huntington's disease (HD), a neurodegenerative disease characterized by severe protein aggregation of the huntingtin (HTT) protein. The aggregation of HTT, in turn, leads to a halt in the function of HSF1. Understanding the pathways that regulate HSF1 in different contexts like HD may hold the key to understanding the pathomechanisms underlying other proteinopathies. We provide the most current information on HSF1 structure, function, and regulation, emphasizing HD, and discussing its potential as a biological target for therapy.

DATA SOURCES

We performed PubMed search to find established and recent reports in HSF1, heat shock proteins (Hsp), HD, Hsp inhibitors, HSF1 activators, and HSF1 in aging, inflammation, cancer, brain development, mitochondria, synaptic plasticity, polyglutamine (polyQ) diseases, and HD.

STUDY SELECTIONS

Research and review articles that described the mechanisms of action of HSF1 were selected based on terms used in PubMed search.

RESULTS

HSF1 plays a crucial role in the progression of HD and other protein-misfolding related neurodegenerative diseases. Different animal models of HD, as well as postmortem brains of patients with HD, reveal a connection between the levels of HSF1 and HSF1 dysfunction to mutant HTT (mHTT)-induced toxicity and protein aggregation, dysregulation of the ubiquitin-proteasome system (UPS), oxidative stress, mitochondrial dysfunction, and disruption of the structural and functional integrity of synaptic connections, which eventually leads to neuronal loss. These features are shared with other neurodegenerative diseases (NDs). Currently, several inhibitors against negative regulators of HSF1, as well as HSF1 activators, are developed and hold promise to prevent neurodegeneration in HD and other NDs.

CONCLUSION

Understanding the role of HSF1 during protein aggregation and neurodegeneration in HD may help to develop therapeutic strategies that could be effective across different NDs.

Uncovering the Impact of Aggrephagy in the Development of Alzheimer's Disease: Insights Into Diagnostic and Therapeutic Approaches from Machine Learning Analysis

BACKGROUND

Alzheimer's disease (AD) stands as a widespread neurodegenerative disorder marked by the gradual onset of memory impairment, predominantly impacting the elderly. With projections indicating a substantial surge in AD diagnoses, exceeding 13.8 million individuals by 2050, there arises an urgent imperative to discern novel biomarkers for AD.

METHODS

To accomplish these objectives, we explored immune cell infiltration and the expression patterns of immune cells and immune function-related genes of AD patients. Furthermore, we utilized the consensus clustering method combined with aggrephagy-related genes (ARGs) for typing AD patients and categorized AD specimens into distinct clusters (C1, C2). A total of 272 candidate genes were meticulously identified through a combination of differential analysis and Weighted Gene Co-Expression Network Analysis (WGCNA). Subsequently, we applied three machine learning algorithms-namely random forest (RF), support vector machine (SVM), and generalized linear model (GLM)-to pinpoint a pathogenic signature comprising five genes associated with AD. To validate the predictive accuracy of these identified genes in discerning AD progression, we constructed nomograms.

RESULTS

Our analyses uncovered that cluster C2 exhibits a higher immune expression than C1. Based on the ROC(0.956). We identified five characteristic genes (PFKFB4, PDK3, KIAA0319L, CEBPD, and PHC2T) associated with AD immune cells and function. The nomograms constructed on the basis of these five diagnostic genes demonstrated effectiveness. In the validation group, the ROC values were found to be 0.760 and 0.838, respectively. These results validate the robustness and reliability of the diagnostic model, affirming its potential for accurate identification of AD.

CONCLUSION

Our findings not only contribute to a deeper understanding of the molecular mechanisms underlying AD but also offer valuable insights for drug development and clinical analysis. The limitation of our study is the limited sample size, and although AD-related genes were identified and some of the mechanisms elucidated, further experiments are needed to elucidate the more in-depth mechanisms of these characterized genes in the disease.

Modulating autophagy and mitophagy as a promising therapeutic approach in neurodegenerative disorders

The high prevalence of neurodegenerative diseases has become a major public health challenge and is associated with a tremendous burden on individuals, society and federal governments worldwide. Protein misfolding and aggregation are the major pathological hallmarks of several neurodegenerative disorders. The cells have evolved several regulatory mechanisms to deal with aberrant protein folding, namely the classical ubiquitin pathway, where ubiquitination of protein aggregates marks their degradation via lysosome and the novel autophagy or mitophagy pathways. Autophagy is a catabolic process in eukaryotic cells that allows the lysosome to recycle the cell's own contents, such as organelles and proteins, known as autophagic cargo. Their most significant role is to keep cells alive in distressed situations. Mitophagy is also crucial for reducing abnormal protein aggregation and increasing organelle clearance and partly accounts for maintaining cellular homeostasis. Furthermore, substantial data indicate that any disruption in these homeostatic mechanisms leads to the emergence of several age-associated metabolic and neurodegenerative diseases. So, targeting autophagy and mitophagy might be a potential therapeutic strategy for a variety of health conditions.

Huntingtin exon 1 deletion does not alter the subcellular distribution of huntingtin and gene transcription in mice

Huntington disease (HD) is caused by the expansion of CAG triplet repeats in exon 1 of the huntingtin (HTT) gene, which also encodes the first 17 amino acids (N-17) that can modulate the toxicity of the expanded polyQ repeat. N-17 are conserved in a wide range of species and are found to influence the subcellular distribution of mutant Htt. Moreover, N-17 is subject to many posttranslational modifications that may regulate the function, stability, and distribution of HTT. However, the function of Htt exon 1 and its influence on the normal Htt remains to be fully investigated. By investigating a knock-in mouse model that lacks Htt exon1, we found that deletion of Htt exon1 does not affect the survival of mice and differentiation of cultured mouse neurons. Furthermore, the lack of Htt exon 1 does not alter the subcellular distribution of Htt, autophagy protein expression, and global gene transcription in the mouse brain. These results suggest that removing the entire exon 1 of Htt could be a therapeutic approach to eliminate expanded polyQ toxicity.

Targeting Emerging Pathogenic Mechanisms by Natural Molecules as Potential Therapeutics for Neurodegenerative Diseases

Natural molecules with favorable safety profile and broad pharmacological activities have shown great promise in the treatment of various neurodegenerative diseases (NDDs). Current studies applying natural molecules against NDDs mainly focus on well-recognized conventional pathogenesis, such as toxic protein aggregation, oxidative stress, and neuroinflammation. However, accumulating evidence reveals that some underlying pathogenic mechanisms are involved earlier and more deeply in the occurrence and development of NDDs, such as ferroptosis, energy metabolism disorders, autophagy-lysosomal dysfunction, endoplasmic reticulum stress, and gut dysbiosis. Therefore, determining whether natural molecules can play therapeutic roles in these emerging pathogenic mechanisms will help clarify the actual targets of natural molecules and their future clinical translation. Furthermore, how to overcome the inability of most poorly water-soluble natural molecules to cross the blood-brain barrier is also critical for effective NDD treatment. This review summarizes emerging pathogenic mechanisms targeted by natural molecules for NDD treatment, proposes nanocarrier-based drug delivery and intranasal administration to enhance the intracerebral bioavailability of natural molecules, and summarizes the current state of clinical research on natural product-based therapeutics.

Convergent molecular mechanisms underlying cognitive impairment in mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder caused by pathogenic variants in the iduronate-2-sulfatase gene (IDS), responsible for the degradation of glycosaminoglycans (GAGs) heparan and dermatan sulfate. IDS enzyme deficiency results in the accumulation of GAGs within cells and tissues, including the central nervous system (CNS). The progressive neurological outcome in a representative number of MPSII patients (neuronopathic form) involves cognitive impairment, behavioral difficulties, and regression in developmental milestones. In an attempt to dissect part of the influence of axon guidance instability over the cognitive impairment presentation in MPS II, we used brain expression data, network propagation, and clustering algorithm to prioritize in the human interactome a disease module associated with the MPS II context. We identified new candidate genes and pathways that act in focal adhesion, integrin cell surface, laminin interactions, ECM proteoglycans, cytoskeleton, and phagosome that converge into functional mechanisms involved in early neural circuit formation defects and could indicate clues about cognitive impairment in patients with MPSII. Such molecular changes during neurodevelopment may precede the morphological and clinical evidence, emphasizing the importance of an early diagnosis and directing the development of potential drug leads. Furthermore, our data also support previous hypotheses pointing to shared pathogenic mechanisms in some neurodegenerative diseases.

Ube2c-inhibition alleviated amyloid pathology and memory deficits in APP/PS1 mice model of AD

Autophagy is a major intracellular degradation pathway for the clearance of damaged organelles and misfolded peptides. Previous studies have indicated that autophagy is involved in the pathogenesis of neurodegenerative disease including Alzheimer's disease (AD). Defective autophagy and highly expressed ubiquitin-conjugating enzyme 2C (Ube2c) have been found in AD patients and mouse. However, little is known about the regulation of autophagy in AD. The association of Ube2c with autophagy, amyloid pathology and cognitive deficits in AD remains unclear. In the present study, we characterized over expression of Ube2c and declined autophagy in amyloid β (Aβ)-treated microglia and demonstrated the protective effects of agomelatine (AGO) in APP/PS1 mice. We found that knockdown of Ube2c with AAV2 encoding shUbe2c resulted in an obvious enhancement of autophagy in BV2 microglia cells, and an alleviation of Aβ pathology and memory deficits in APP/PS1 mice. Further, pharmacological inhibition of Ube2c by AGO significantly reduced Aβ plaques, improved synaptic plasticity and cognitive behaviors in APP/PS1 mice, as well as promoted autophagy in microglia. Our findings uncover a potent role of Ube2c over-expression and autophagy decline in the pathogenesis of AD, and suggest that regulation of Ube2c and autophagy may provide an important clue and a potential target for the novel therapeutics of AD.

SUMO-modifying Huntington's disease

Small ubiquitin-like modifiers, SUMOs, are proteins that are conjugated to target substrates and regulate their functions in a post-translational modification called SUMOylation. In addition to its physiological roles, SUMOylation has been implicated in several neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases (HD). HD is a neurodegenerative monogenetic autosomal dominant disorder caused by a mutation in the CAG repeat of the huntingtin (htt) gene, which expresses a mutant Htt protein more susceptible to aggregation and toxicity. Besides Htt, other SUMO ligases, enzymes, mitochondrial and autophagic components are also important for the progression of the disease. Here we review the main aspects of Htt SUMOylation and its role in cellular processes involved in the pathogenesis of HD.

Realgar facilitates the Nrf2-Keap1-p62 positive feedback signaling axis via MAPKs and AKT to interfere with autophagy-induced apoptosis and oxidative stress in the hippocampus

Realgar, as a commonly used traditional Chinese medicine, exerts both pharmacological and biological effects. However, the mechanism by which it causes nervous system injury remains unclear. This study aimed to elucidate the specific mechanism underlying the hippocampal neurotoxicity caused by realgar. Nrf2 is an important receptor of exogenous toxic substances and oxidative stress. We utilized a p38-specific inhibitor (SB20358), ERK1/2-specific inhibitor (PD98059), JNK-specific inhibitor (SP600125) and AKT-specific inhibitor (LY249002) to establish the corresponding animal models and explore how realgar activates Nrf2. We established an Nrf2-shRNA gene silencing model in rats and an autophagy-specific inhibitor treatment model to further explore realgar-induced neurotoxicity and the role of Nrf2 in realgar-induced damage to the hippocampus. The results showed that realgar passed through the blood-brain barrier and accumulated in brain tissue to induce central nervous system toxicity. The specific mechanism was that realgar activated MAPKs and AKT signaling molecules to activate the Nrf2-Keap1-p62 positive feedback signaling axis, induced abnormal autophagy initiation and degradation, and promoted oxidative damage and apoptosis in neurons. Effective measures should be taken to prevent and control the arsenic poisoning caused by realgar in the early stage, and this study provides a theoretical and practical basis for the rational use of drugs in the clinic.

Harmine prevents 3-nitropropionic acid-induced neurotoxicity in rats via enhancing NRF2-mediated signaling: Involvement of p21 and AMPK

Oxidative stress induced neurotoxicity is increasingly perceived as an important neuropathologic mechanism underlying the motor and behavioral phenotypes associated with Huntington's disease (HD). Repeated exposure to 3-nitropropionic acid (3-NP) induces neurotoxic changes which closely simulate the neuropathological and behavioral characteristics of HD. This study aimed at evaluating the prophylactic effects of the dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A) inhibitor "harmine" against 3-NP-indued neurotoxicity and HD-like symptoms. The potential prophylactic effect of harmine (10 mg/kg/day; intraperitoneal) was investigated on 3-NP-induced motor and cognitive HD-like deficits, nuclear factor erythroid 2 like 2 (NRF2), AMP kinase (AMPK) and p21 protein levels and the gene expression of haem oxygenase-1 (Ho-1), NAD(P)H: quinone oxidoreductase-1 (Nqo-1) and p62 in addition to redox imbalance and histological neurotoxic changes in the striatum, prefrontal cortex, and hippocampus of male Wistar rats. Harmine successfully increased the protein levels of NRF2, AMPK and p21 and the gene expression of Ho-1, Nqo-1 and p62, restored redox homeostasis, and reduced CASPASE-3 level. This was reflected in attenuation of 3-NP-induced neurodegenerative changes and improvement of rats' motor and cognitive performance. This study draws attention to the protective role of harmine against 3-NP-induced motor and cognitive dysfunction that could be mediated via enhancing NRF2-mediated signaling with subsequent amelioration of oxidative stress injury via NRF2 activators, p21 and AMPK, in the striatum, prefrontal cortex, and hippocampus which could offer a promising therapeutic tool to slow the progression of HD.

Neuroinflammation Upregulated Neuronal Toll-Like Receptors 2 and 4 to Drive Synucleinopathy in Neurodegeneration

Background: Parkinson’s disease (PD) is characterized by intraneuronal α-synuclein aggregation called Lewy bodies and progressive dopaminergic neurodegeneration. Toll-like receptor (TLR) signaling is a major pathway mediating inflammation. The molecular link on how neuroinflammation upregulates neuronal TLRs and induces accumulation of α-synuclein aggregates to drive synucleinopathy remains to be determined.

Objective: Despite conditioned medium from microglia and TLR agonists were utilized to study their effects on neuronal cells, a Transwell coculture system, comprising lipopolysaccharide-activated microglia on top and retinoic acid-differentiated SH-SY5Y cells at the bottom more mimicking in vivo neuroinflammation, was employed to elucidate the mechanism of activated microglia on neuronal cells.

Methods: Genetic variants of TLRs in PD patients were genotyped and the multiplex cytokines, sRAGE, and HMGB1were assessed. A coculture system was employed to measure α-synuclein aggregates and neurite shortening by confocal microscope. The expression of TLR2/4 and autophagy flux was detected by western blot and immunofluorescence.

Results: PD patients showed higher plasma levels of proinflammatory cytokines and genetic TLR4 variant, c.896 A > G (p. D299G). Elevated proinflammatory cytokines in coculture medium was also seen. Phosphorylation and aggregation of α-synuclein, shortening of neurite, upregulation of TLR2/4 expression, activation of downstream p38 and JNK, and dampening of autophagic flux were seen in SH-SY5Y cells cocultured with activated microglia. Those were prevented by inhibiting TLR2/4 and p38/JNK signaling.

Conclusion: Activated microglia-derived neuroinflammation induced neuronal TLR2/4-p38/JNK activation to perturb autophagy, causing accumulation of α-synuclein aggregates and neurite shortening. Targeting neuronal TLR2/4 pathway might be a mechanistic-based therapy for neurodegenerative disease, such as PD.

Autophagy in the Neuronal Ceroid Lipofuscinoses (Batten Disease)

The neuronal ceroid lipofuscinoses (NCLs), also referred to as Batten disease, are a family of neurodegenerative diseases that affect all age groups and ethnicities around the globe. At least a dozen NCL subtypes have been identified that are each linked to a mutation in a distinct ceroid lipofuscinosis neuronal (CLN) gene. Mutations in CLN genes cause the accumulation of autofluorescent lipoprotein aggregates, called ceroid lipofuscin, in neurons and other cell types outside the central nervous system. The mechanisms regulating the accumulation of this material are not entirely known. The CLN genes encode cytosolic, lysosomal, and integral membrane proteins that are associated with a variety of cellular processes, and accumulated evidence suggests they participate in shared or convergent biological pathways. Research across a variety of non-mammalian and mammalian model systems clearly supports an effect of CLN gene mutations on autophagy, suggesting that autophagy plays an essential role in the development and progression of the NCLs. In this review, we summarize research linking the autophagy pathway to the NCLs to guide future work that further elucidates the contribution of altered autophagy to NCL pathology.

Deletion of SUMO1 attenuates behavioral and anatomical deficits by regulating autophagic activities in Huntington disease

The CAG expansion of huntingtin (mHTT) associated with Huntington disease (HD) is a ubiquitously expressed gene, yet it prominently damages the striatum and cortex, followed by widespread peripheral defects as the disease progresses. However, the underlying mechanisms of neuronal vulnerability are unclear. Previous studies have shown that SUMO1 (small ubiquitin-like modifier-1) modification of mHtt promotes cellular toxicity, but the in vivo role and functions of SUMO1 in HD pathogenesis are unclear. Here, we report that SUMO1 deletion in Q175DN HD-het knockin mice (HD mice) prevented age-dependent HD-like motor and neurological impairments and suppressed the striatal atrophy and inflammatory response. SUMO1 deletion caused a drastic reduction in soluble mHtt levels and nuclear and extracellular mHtt inclusions while increasing cytoplasmic mHtt inclusions in the striatum of HD mice. SUMO1 deletion promoted autophagic activity, characterized by augmented interactions between mHtt inclusions and a lysosomal marker (LAMP1), increased LC3B- and LAMP1 interaction, and decreased interaction of sequestosome-1 (p62) and LAMP1 in DARPP-32-positive medium spiny neurons in HD mice. Depletion of SUMO1 in an HD cell model also diminished the mHtt levels and enhanced autophagy flux. In addition, the SUMOylation inhibitor ginkgolic acid strongly enhanced autophagy and diminished mHTT levels in human HD fibroblasts. These results indicate that SUMO is a critical therapeutic target in HD and that blocking SUMO may ameliorate HD pathogenesis by regulating autophagy activities.

Recent developments in the management of Huntington's disease

Huntington's disease (HD) is a rare, incurable, inheritedneurodegenerative disorder manifested by chorea, hyperkinetic, and hypokinetic movements. The FDA has approved only two drugs, viz. tetrabenazine, and deutetrabenazine, to manage the chorea associated with HD. However, several other drugs are used as an off-label to manage chorea and other symptoms such as depression, anxiety, muscle tremors, and cognitive dysfunction associated with HD. So far, there is no disease-modifying treatment available. Drug repurposing has been a primary drive to search for new anti-HD drugs. Numerous molecular targets along with a wide range of small molecules and gene therapies are currently under clinical investigation. More than 200 clinical studies are underway for HD, 75% are interventional, and 25% are observational studies. The present review discusses the small molecule clinical pipeline and molecular targets for HD. Furthermore, the biomarkers, diagnostic tests, gene therapies, behavioral and observational studies for HD were also deliberated.