Normalization of Overexpressed α-Synuclein Causing Parkinson's Disease By a Moderate Gene Silencing With RNA Interference

Navigating the Neurobiology of Parkinson's: The Impact and Potential of α-Synuclein

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease worldwide; therefore, since its initial description, significant progress has been made, yet a mystery remains regarding its pathogenesis and elusive root cause. The widespread distribution of pathological α-synuclein (αSyn) aggregates throughout the body raises inquiries regarding the etiology, which has prompted several hypotheses, with the most prominent one being αSyn-associated proteinopathy. The identification of αSyn protein within Lewy bodies, coupled with genetic evidence linking αSyn locus duplication, triplication, as well as point mutations to familial Parkinson's disease, has underscored the significance of αSyn in initiating and propagating Lewy body pathology throughout the brain. In monogenic and sporadic PD, the presence of early inflammation and synaptic dysfunction leads to αSyn aggregation and neuronal death through mitochondrial, lysosomal, and endosomal functional impairment. However, much remains to be understood about αSyn pathogenesis, which is heavily grounded in biomarkers and treatment strategies. In this review, we provide emerging new evidence on the current knowledge about αSyn's pathophysiological impact on PD, and its presumable role as a specific disease biomarker or main target of disease-modifying therapies, highlighting that this understanding today offers the best potential of disease-modifying therapy in the near future.

Identification of selective and non-selective C9ORF72 targeting in vivo active siRNAs

A hexanucleotide (G4C2) repeat expansion (HRE) within intron one of C9ORF72 is the leading genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). C9ORF72 haploinsufficiency, formation of RNA foci, and production of dipeptide repeat (DPR) proteins have been proposed as mechanisms of disease. Here, we report the first example of disease-modifying siRNAs for C9ORF72 driven ALS/FTD. Using a combination of reporter assay and primary cortical neurons derived from a C9-ALS/FTD mouse model, we screened a panel of more than 150 fully chemically stabilized siRNAs targeting different C9ORF72 transcriptional variants. We demonstrate the lack of correlation between siRNA efficacy in reporter assay versus native environment; repeat-containing C9ORF72 mRNA variants are found to preferentially localize to the nucleus, and thus C9ORF72 mRNA accessibility and intracellular localization have a dominant impact on functional RNAi. Using a C9-ALS/FTD mouse model, we demonstrate that divalent siRNAs targeting C9ORF72 mRNA variants specifically or non-selectively reduce the expression of C9ORF72 mRNA and significantly reduce DPR proteins. Interestingly, siRNA silencing all C9ORF72 mRNA transcripts was more effective in removing intranuclear mRNA aggregates than targeting only HRE-containing C9ORF72 mRNA transcripts. Combined, these data support RNAi-based degradation of C9ORF72 as a potential therapeutic paradigm.

Non-coding RNAs in Parkinson's disease: Regulating SNCA and alpha-synuclein aggregation

Parkinson's disease is one of the vital neurodegenerative ailments attributed to a rise in Alpha-synuclein proteins leading to the advancement of motor and cognitive deterioration. Interestingly, in PD lncRNAs, miRNAs and siRNAs are also key regulators of SNCA and alpha-synuclein aggregation. This review will focus on the roles of these three types of small RNAs in trebling the development of PD through regulating SNCA expression or alpha-synuclein protein mediating the RNA from acting. Parkinson's disease is defined by the build-up of alpha-synuclein protein resulting predominantly from the elevated expression level of the SNCA gene. Non-coding RNAs have gained broad appeal as fundamental modulators of gene expression and protein aggregation dynamics, with significant implications on the aetiology of PD. LncRNAs modulate SNCA transcription and edit epigenetic modifications, while miRNA target mRNA is involved in the stability and translation of count alpha-synuclein. Considering all these data, siRNAs can achieve the precise gene silencing effect that directly induces the downregulation of SNCA mRNA. This review also summarizes some recent reports about the interaction between these ncRNAs with the SNCA gene and alpha-synuclein protein, each through its independent in addition to synergistic mechanisms. This review highlights the possibility of therapeutic interventions to perturb SNCA expression to prevent alpha-synuclein aggregation via targeting ncRNAs that might be spun off novel drug development for PD.

2-Butoxytetrahydrofuran, Isolated from Holothuria scabra, Attenuates Aggregative and Oxidative Properties of α-Synuclein and Alleviates Its Toxicity in a Transgenic Caenorhabditis elegans Model of Parkinson's Disease

Aggregative α-synuclein and incurring oxidative stress are pivotal cascading events, leading to dopaminergic (DAergic) neuronal loss and contributing to clinical manifestations of Parkinson's disease (PD). Our previous study demonstrated that 2-butoxytetrahydrofuran (2-BTHF), isolated from Holothuria scabra (H. scabra), could inhibit amyloid-β aggregation and its ensuing toxicity, which leads to Alzheimer's disease. In the present study, we found that 2-BTHF also attenuated the aggregative and oxidative activities of α-synuclein and lessened its toxicity in a transgenic Caenorhabditis elegans (C. elegans) PD model. Such worms treated with 100 μM of 2-BTHF showed substantial reductions in α-synuclein accumulation and DAergic neurodegeneration. Mechanistically, 2-BTHF, at this concentration, significantly decreased aggregation of monomeric α-synuclein and restored locomotion and dopamine-dependent behaviors. Molecular docking exhibited potential bindings of 2-BTHF to HSF-1 and DAF-16 transcription factors. Additionally, 2-BTHF significantly increased the mRNA transcripts of genes encoding proteins involved in proteostasis, including the molecular chaperones hsp-16.2 and hsp-16.49, the ubiquitination/SUMOylation-related ubc-9 gene, and the autophagy-related genes atg-7 and lgg-1. Transcriptomic profiling revealed an additional mechanism of 2-BTHF in α-synuclein-expressing worms, which showed upregulation of PPAR signaling cascades that mediated fatty acid metabolism. 2-BTHF significantly restored lipid deposition, upregulated the fat-7 gene, and enhanced gcs-1-mediated glutathione synthesis in the C. elegans PD model. Taken together, this study demonstrated that 2-BTHF could abrogate aggregative and oxidative properties of α-synuclein and attenuate its toxicity, thus providing a possible therapeutic application for the treatment of α-synuclein-induced PD.

Antisense therapy: a potential breakthrough in the treatment of neurodegenerative diseases

Neurodegenerative diseases are a group of disorders characterized by the progressive degeneration of neurons in the central or peripheral nervous system. Currently, there is no cure for neurodegenerative diseases and this means a heavy burden for patients and the health system worldwide. Therefore, it is necessary to find new therapeutic approaches, and antisense therapies offer this possibility, having the great advantage of not modifying cellular genome and potentially being safer. Many preclinical and clinical studies aim to test the safety and effectiveness of antisense therapies in the treatment of neurodegenerative diseases. The objective of this review is to summarize the recent advances in the development of these new technologies to treat the most common neurodegenerative diseases, with a focus on those antisense therapies that have already received the approval of the U.S. Food and Drug Administration.

Nonintuitive Immunogenicity and Plasticity of Alpha-Synuclein Conformers: A Paradigm for Smart Delivery of Neuro-Immunotherapeutics

Despite the extensive research successes and continuous developments in modern medicine in terms of diagnosis, prevention, and treatment, the lack of clinically useful disease-modifying drugs or immunotherapeutic agents that can successfully treat or prevent neurodegenerative diseases is an ongoing challenge. To date, only one of the 244 drugs in clinical trials for the treatment of neurodegenerative diseases has been approved in the past decade, indicating a failure rate of 99.6%. In corollary, the approved monoclonal antibody did not demonstrate significant cognitive benefits. Thus, the prevalence of neurodegenerative diseases is increasing rapidly. Therefore, there is an urgent need for creative approaches to identifying and testing biomarkers for better diagnosis, prevention, and disease-modifying strategies for the treatment of neurodegenerative diseases. Overexpression of the endogenous α-synuclein has been identified as the driving force for the formation of the pathogenic α-synuclein (α-Syn) conformers, resulting in neuroinflammation, hypersensitivity, endogenous homeostatic responses, oxidative dysfunction, and degeneration of dopaminergic neurons in Parkinson's disease (PD). However, the conformational plasticity of α-Syn proffers that a certain level of α-Syn is essential for the survival of neurons. Thus, it exerts both neuroprotective and neurotoxic (regulatory) functions on neighboring neuronal cells. Furthermore, the aberrant metastable α-Syn conformers may be subtle and difficult to detect but may trigger cellular and molecular events including immune responses. It is well documented in literature that the misfolded α-Syn and its conformers that are released into the extracellular space from damaged or dead neurons trigger the innate and adaptive immune responses in PD. Thus, in this review, we discuss the nonintuitive plasticity and immunogenicity of the α-Syn conformers in the brain immune cells and their physiological and pathological consequences on the neuroimmune responses including neuroinflammation, homeostatic remodeling, and cell-specific interactions that promote neuroprotection in PD. We also critically reviewed the novel strategies for immunotherapeutic delivery interventions in PD pathogenesis including immunotherapeutic targets and potential nanoparticle-based smart drug delivery systems. It is envisioned that a greater understanding of the nonintuitive immunogenicity of aberrant α-Syn conformers in the brain's microenvironment would provide a platform for identifying valid therapeutic targets and developing smart brain delivery systems for clinically effective disease-modifying immunotherapeutics that can aid in the prevention and treatment of PD in the future.

Ultrasound-Assisted CRISPRi-Exosome for Epigenetic Modification of α-Synuclein Gene in a Mouse Model of Parkinson's Disease

Currently, there is a lack of effective treatment for Parkinson's disease (PD). In PD patients, aberrant methylation of SNCA (α-synuclein gene) has been reported and may be a potential therapeutic target. In this study, we established an epigenetic regulation platform based on an exosomal CRISPR intervention system. With the assist of focused ultrasound (FUS) opening the blood-brain barrier, engineered exosomes carrying RVG (rabies viral glycoprotein) targeting peptide, sgRNA (single guide RNA), and dCas9-DNMT3A (named RVG-CRISPRi-Exo) were efficiently delivered into the brain lesions and induced specific methylation of SNCA. In vivo, FUS combined with RVG-CRISPRi-Exo significantly improved motor performance, balance coordination, and neurosensitivity in PD mice, greatly down-regulated the elevation of α-synuclein (α-syn) caused by modeling, rescued cell apoptosis, and alleviated the progression of PD in mice. [18F]-FP-DTBZ imaging suggested that the synaptic function of the nigrostriatal pathway could be restored, which was conducive to the control of motor behavior in PD mice. Pyrosequencing results showed that RVG-CRISPRi-Exo could methylate CpG at specific sites of SNCA, and this fine-tuned editing achieved good therapeutic effects in PD model mice. In vitro, RVG-CRISPRi-Exo down-regulated SNCA transcripts and α-syn expression and relieved neuronal cell damage. Collectively, our findings provide a proof-of-principle for the development of targeted brain nanodelivery based on engineered exosomes and provide insights into epigenetic regulation of brain diseases.

Neuronal-type-specific epigenome editing to decrease SNCA expression: Implications for precision medicine in synucleinopathies

Overexpression of SNCA has been implicated in the pathogenesis of synucleinopathies, particularly Parkinson's disease (PD) and dementia with Lewy bodies (DLB). While PD and DLB share some clinical and pathological similarities, each disease presents distinct characteristics, including the primary affected brain region and neuronal type. We aimed to develop neuronal-type-specific SNCA-targeted epigenome therapies for synucleinopathies. The system is based on an all-in-one lentiviral vector comprised of CRISPR-dSaCas9 and guide RNA (gRNA) targeted at SNCA intron 1 fused with a synthetic repressor molecule of Krüppel-associated box (KRAB)/ methyl CpG binding protein 2 (MeCp2) transcription repression domain (TRD). To achieve neuronal-type specificity for dopaminergic and cholinergic neurons, the system was driven by tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) promoters, respectively. Delivering the system into human induced pluripotent stem cell (hiPSC)-derived dopaminergic and cholinergic neurons from a patient with the SNCA triplication resulted in efficient and neuronal-type-specific downregulation of SNCA-mRNA and protein. Furthermore, the reduction in SNCA levels by the gRNA-dSaCas9-repressor system rescued disease-related cellular phenotypes including Ser129-phophorylated α-synuclein, neuronal viability, and mitochondrial dysfunction. We established a novel neuronal-type-specific SNCA-targeted epigenome therapy and provided in vitro proof of concept using human-based disease models. Our results support the therapeutic potential of our system for PD and DLB and provide the foundation for further preclinical studies in animal models toward investigational new drug (IND) enablement and clinical trials.

Tet1 peptide and zinc (II)-adenine multifunctional module functionalized polycations as efficient siRNA carriers for Parkinson's disease

A bioreducible Zn (II)-adenine multifunctional module (BS) and Tet1 peptide were used to modify low-molecular-weight PEI3.5k (polyethyleneimine with molecular weight of 3.5 kDa)into a siRNA vector Zn-PB-T with high transfection efficiency in neurons. A GSH-responsive breakable disulfide spacer was introduced into BS to realize the controlled release of siRNA from the polyplexes in cytoplasm. Zn-PB showed >90% transfection rates in multiple cell lines (3 T3, HK-2, HepG2, 293 T, HeLa, PANC-1)，and 1.8-folds higher EGFP knockdown rates than commercial Lipo2k in normal cell line 293 T and cancer cell line HepG2. And Zn-PB-T1 showed 4.7-4.9- and 8.0-8.1-folds higher transfection efficiency comparing to commercial Lipo2k and PEI25k (polyethyleneimine with molecular weight of 25 kDa) in PC12 cells respectively, 2.1-fold EGFP gene silencing efficiency (96.6% EGFP knockdown rates) superior to commercial Lipo2k in neurons. In Parkinson's model, Zn-PB-T1/SNCA-siRNA can effectively protect neurons against MPP+-induced cell death and apoptosis, increasing the cell survival rate to 84.6% and reducing the cell apoptosis rate to 10.8%. This work demonstrated the promising application prospects of the resulting efficient siRNA carriers in siRNA-mediated gene therapy of Parkinson's disease.

Supplementation of probiotic Bifidobacterium breve Bif11 reverses neurobehavioural deficits, inflammatory changes and oxidative stress in Parkinson's disease model

Human gut microbiota are thought to affect different physiological processes in the body, including brain functions. Gut dysbiosis has been linked to the progression of Parkinson's disease (PD) and thus, restoring the healthy gut microbiota with supplementation of putative probiotic strains can confer some benefits in PD. In the current study, we explored the neuroprotective potential of Bifidobacterium breve Bif11 supplementation in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) treated female Sprague Dawley rats. This study investigated the behavioural, molecular and biochemical parameters in the MPTP rat model. A pharmacological intervention of Bif11 at doses of 1 × 1010 CFU and 2 × 1010 CFU for 21 days was found to attenuate the cognitive and motor changes in the MPTP rat model. Furthermore, it also increased the tyrosine hydroxylase levels, reduced pro-inflammatory markers and decreased oxidative and nitrosative stress in the mid brain of MPTP-lesioned rats. Bif11 supplementation even restored the levels of short-chain fatty acids and decreased intestinal epithelial permeability in MPTP-induced PD model rats. In summary, these findings demonstrate that B. breve Bif11 has the potential to ameliorate symptoms of PD. However, this therapy needs to be further investigated with in-depth mechanistic insights in the future for the treatment of PD.

Combined RNA interference and gene replacement therapy targeting MFN2 as proof of principle for the treatment of Charcot-Marie-Tooth type 2A

Mitofusin-2 (MFN2) is an outer mitochondrial membrane protein essential for mitochondrial networking in most cells. Autosomal dominant mutations in the MFN2 gene cause Charcot-Marie-Tooth type 2A disease (CMT2A), a severe and disabling sensory-motor neuropathy that impacts the entire nervous system. Here, we propose a novel therapeutic strategy tailored to correcting the root genetic defect of CMT2A. Though mutant and wild-type MFN2 mRNA are inhibited by RNA interference (RNAi), the wild-type protein is restored by overexpressing cDNA encoding functional MFN2 modified to be resistant to RNAi. We tested this strategy in CMT2A patient-specific human induced pluripotent stem cell (iPSC)-differentiated motor neurons (MNs), demonstrating the correct silencing of endogenous MFN2 and replacement with an exogenous copy of the functional wild-type gene. This approach significantly rescues the CMT2A MN phenotype in vitro, stabilizing the altered axonal mitochondrial distribution and correcting abnormal mitophagic processes. The MFN2 molecular correction was also properly confirmed in vivo in the MitoCharc1 CMT2A transgenic mouse model after cerebrospinal fluid (CSF) delivery of the constructs into newborn mice using adeno-associated virus 9 (AAV9). Altogether, our data support the feasibility of a combined RNAi and gene therapy strategy for treating the broad spectrum of human diseases associated with MFN2 mutations.

Neuromodulation in Parkinson's disease targeting opioid and cannabinoid receptors, understanding the role of NLRP3 pathway: a novel therapeutic approach

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, resulting in motor and non-motor symptoms. Although levodopa is the primary medication for PD, its long-term use is associated with complications such as dyskinesia and drug resistance, necessitating novel therapeutic approaches. Recent research has highlighted the potential of targeting opioid and cannabinoid receptors as innovative strategies for PD treatment. Modulating opioid transmission, particularly through activating µ (MOR) and δ (DOR) receptors while inhibiting κ (KOR) receptors, shows promise in preventing motor complications and reducing L-DOPA-induced dyskinesia. Opioids also possess neuroprotective properties and play a role in neuroprotection and seizure control. Similar to this, endocannabinoid signalling via CB1 and CB2 receptors influences the basal ganglia and may contribute to PD pathophysiology, making it a potential therapeutic target. In addition to opioid and cannabinoid receptor targeting, the NLRP3 pathway, implicated in neuroinflammation and neurodegeneration, emerges as another potential therapeutic avenue for PD. Recent studies suggest that targeting this pathway holds promise as a therapeutic strategy for PD management. This comprehensive review focuses on neuromodulation and novel therapeutic approaches for PD, specifically highlighting the targeting of opioid and cannabinoid receptors and the NLRP3 pathway. A better understanding of these mechanisms has the potential to enhance the quality of life for PD patients.

Translational molecular imaging and drug development in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that primarily affects elderly people and constitutes a major source of disability worldwide. Notably, the neuropathological hallmarks of PD include nigrostriatal loss and the formation of intracellular inclusion bodies containing misfolded α-synuclein protein aggregates. Cardinal motor symptoms, which include tremor, rigidity and bradykinesia, can effectively be managed with dopaminergic therapy for years following symptom onset. Nonetheless, patients ultimately develop symptoms that no longer fully respond to dopaminergic treatment. Attempts to discover disease-modifying agents have increasingly been supported by translational molecular imaging concepts, targeting the most prominent pathological hallmark of PD, α-synuclein accumulation, as well as other molecular pathways that contribute to the pathophysiology of PD. Indeed, molecular imaging modalities such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can be leveraged to study parkinsonism not only in animal models but also in living patients. For instance, mitochondrial dysfunction can be assessed with probes that target the mitochondrial complex I (MC-I), while nigrostriatal degeneration is typically evaluated with probes designed to non-invasively quantify dopaminergic nerve loss. In addition to dopaminergic imaging, serotonin transporter and N-methyl-D-aspartate (NMDA) receptor probes are increasingly used as research tools to better understand the complexity of neurotransmitter dysregulation in PD. Non-invasive quantification of neuroinflammatory processes is mainly conducted by targeting the translocator protein 18 kDa (TSPO) on activated microglia using established imaging agents. Despite the overwhelming involvement of the brain and brainstem, the pathophysiology of PD is not restricted to the central nervous system (CNS). In fact, PD also affects various peripheral organs such as the heart and gastrointestinal tract - primarily via autonomic dysfunction. As such, research into peripheral biomarkers has taken advantage of cardiac autonomic denervation in PD, allowing the differential diagnosis between PD and multiple system atrophy with probes that visualize sympathetic nerve terminals in the myocardium. Further, α-synuclein has recently gained attention as a potential peripheral biomarker in PD. This review discusses breakthrough discoveries that have led to the contemporary molecular concepts of PD pathophysiology and how they can be harnessed to develop effective imaging probes and therapeutic agents. Further, we will shed light on potential future trends, thereby focusing on potential novel diagnostic tracers and disease-modifying therapeutic interventions.

Inhibition of α-Synuclein Seeding-Dependent Aggregation by ssDNA Aptamers Specific to C-Terminally Truncated α-Synuclein Fibrils

Neuropathologically, Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are characterized by the accumulation of insoluble aggregates of α-synuclein (α-syn) in the Lewy bodies (LBs). In addition to full-length α-syn fibrils, C-terminally truncated α-syn is also abundant in the LBs that acts as seeds and facilitates the aggregation of the full-length α-syn in vitro and in vivo and induces toxicity. Hence, identifying molecules that can inhibit the seeding activity of these truncated forms is of great importance. Here, we report the first in vitro selection of aptamers targeting the fibrillar forms of different C-terminally truncated α-syn using systematic evolution by an exponential enrichment method followed by quantitative high-throughput DNA sequencing. We identify a panel of aptamers that bound with high specificity to different truncated forms of α-syn fibrils with no cross-reactivity toward other amyloid fibrils. Interestingly, two of the aptamers (named Apt11 and Apt15) show higher affinity to most C-terminally truncated forms of α-syn fibrils with an evident inhibition of α-syn-seeded aggregation in vitro by Apt11. This inhibition is further confirmed by circular dichroism, Congo red binding assay, and electronic microscopy. Moreover, Apt11 is also found to reduce the insoluble phosphorylated form of α-syn at Ser-129 (pS129-α-syn) in the cell model and also can inhibit α-syn aggregation using RT-QuIC reactions seeded with brain homogenates extracted from patients affected by PD. The aptamers discovered in this study represent potential useful tools for research and diagnostics or therapy toward PD and DLB.

Intronic enhancers of the human SNCA gene predominantly regulate its expression in brain in vivo

Evidence from patients with Parkinson's disease (PD) and our previously reported α-synuclein (SNCA) transgenic rat model support the idea that increased SNCA protein is a substantial risk factor of PD pathogenesis. However, little is known about the transcription control of the human SNCA gene in the brain in vivo. Here, we identified that the DYT6 gene product THAP1 (THAP domain-containing apoptosis-associated protein 1) and its interaction partner CTCF (CCCTC-binding factor) act as transcription regulators of SNCA. THAP1 controls SNCA intronic enhancers' activities, while CTCF regulates its enhancer-promoter loop formation. The SNCA intronic enhancers present neurodevelopment-dependent activities and form enhancer clusters similar to "super-enhancers" in the brain, in which the PD-associated single-nucleotide polymorphisms are enriched. Deletion of the SNCA intronic enhancer clusters prevents the release of paused RNA polymerase II from its promoter and subsequently reduces its expression drastically in the brain, which may provide new therapeutic approaches to prevent its accumulation and thus related neurodegenerative diseases defined as synucleinopathies.

Transcriptomics analysis of human iPSC-derived dopaminergic neurons reveals a novel model for sporadic Parkinson's disease

Parkinson's disease (PD) is a progressive, neurodegenerative disease affecting over 1% of the population beyond 65 years of age. Although some PD cases are inheritable, the majority of PD cases occur in a sporadic manner. Risk factors comprise next to heredity, age, and gender also exposure to neurotoxins from for instance pesticides and herbicides. As PD is characterized by a loss of dopaminergic neurons in the substantia nigra, it is nearly impossible to access and extract these cells from patients for investigating disease mechanisms. The emergence of induced pluripotent stem (iPSC) technology allows differentiating and growing human dopaminergic neurons, which can be used for in vitro disease modeling. Here, we differentiated human iPSCs into dopaminergic neurons, and subsequently exposed the cells to increasing concentrations of the neurotoxin MPP⁺. Temporal transcriptomics analysis revealed a strong time- and dose-dependent response with genes over-represented across pathways involved in PD etiology such as "Parkinson's Disease", "Dopaminergic signaling" and "calcium signaling". Moreover, we validated this disease model by showing robust overlap with a meta-analysis of transcriptomics data from substantia nigra from post-mortem PD patients. The overlap included genes linked to e.g. mitochondrial dysfunction, neuron differentiation, apoptosis and inflammation. Our data shows, that MPP⁺-induced, human iPSC-derived dopaminergic neurons present molecular perturbations as observed in the etiology of PD. Therefore we propose iPSC-derived dopaminergic neurons as a foundation for a novel sporadic PD model to study the pathomolecular mechanisms of PD, but also to screen for novel anti-PD drugs and to develop and test new treatment strategies.

Modeling neurodegenerative disorders in zebrafish

Neurodegeneration is a major cause of Alzheimer's, Parkinson's, Huntington's, multiple and amyotrophic lateral sclerosis, pontocerebellar hypoplasia, dementia and other related brain disorders. Their complex pathogenesis commonly includes genetic and neurochemical deficits, misfolded protein toxicity, demyelination, apoptosis and mitochondrial dysfunctions. Albeit differing in specific underlying mechanisms, neurodegenerative disorders typically display evolutionarily conserved mechanisms across taxa. Here, we review the role of zebrafish models in recapitulating major human and rodent neurodegenerative conditions, demonstrating this species as a highly relevant experimental model for research on neurodegenerative diseases, and discussing how these fish models can further clarify the underlying genetic, neurochemical, neuroanatomical and behavioral pathogenic mechanisms.

The role of Tumour Necrosis Factor in neuroinflammation associated with Parkinson's disease and targeted therapies

Neurodegenerative disorders Parkinson's disease is a progressive neurodegenerative disorder associated with neuroinflammatory responses that lead to the neurodegeneration of the dopaminergic neurons. These neuroinflammatory mechanisms involve various cytokines produced by the activated glial cells. Tumour Necrosis factor α (TNF α) is one of the major mediators of the neuroinflammation associated with neurodegeneration. TNF α has a dual role of neuroprotection and neurotoxicity in the brain. The effective pathways of TNF involve various signalling pathways transduced by the receptors TNFR1 and TNFR2. Effective therapeutic strategies have been produced targeting the neurotoxic behaviour of the Tumour Necrosis Factor and the associated neurodegeneration which includes the use of Dominant Negative Tumour Necrosis Factor (DN-TNF) inhibitors like XENP 345 and XPro®1595 and peroxisome proliferator receptor gamma (PPAR-γ) agonists.

Alpha-Synuclein Aggregation Pathway in Parkinson's Disease: Current Status and Novel Therapeutic Approaches

Following Alzheimer’s, Parkinson’s disease (PD) is the second-most common neurodegenerative disorder, sharing an unclear pathophysiology, a multifactorial profile, and massive social costs worldwide. Despite this, no disease-modifying therapy is available. PD is tightly associated with α-synuclein (α-Syn) deposits, which become organised into insoluble, amyloid fibrils. As a typical intrinsically disordered protein, α-Syn adopts a monomeric, random coil conformation in an aqueous solution, while its interaction with lipid membranes drives the transition of the molecule part into an α-helical structure. The central unstructured region of α-Syn is involved in fibril formation by converting to well-defined, β-sheet rich secondary structures. Presently, most therapeutic strategies against PD are focused on designing small molecules, peptides, and peptidomimetics that can directly target α-Syn and its aggregation pathway. Other approaches include gene silencing, cell transplantation, stimulation of intracellular clearance with autophagy promoters, and degradation pathways based on immunotherapy of amyloid fibrils. In the present review, we sum marise the current advances related to α-Syn aggregation/neurotoxicity. These findings present a valuable arsenal for the further development of efficient, nontoxic, and non-invasive therapeutic protocols for disease-modifying therapy that tackles disease onset and progression in the future.

Passive Immunization in Alpha-Synuclein Preclinical Animal Models

Alpha-synucleinopathies include Parkinson’s disease, dementia with Lewy bodies, pure autonomic failure and multiple system atrophy. These are all progressive neurodegenerative diseases that are characterized by pathological misfolding and accumulation of the protein alpha-synuclein (αsyn) in neurons, axons or glial cells in the brain, but also in other organs. The abnormal accumulation and propagation of pathogenic αsyn across the autonomic connectome is associated with progressive loss of neurons in the brain and peripheral organs, resulting in motor and non-motor symptoms. To date, no cure is available for synucleinopathies, and therapy is limited to symptomatic treatment of motor and non-motor symptoms upon diagnosis. Recent advances using passive immunization that target different αsyn structures show great potential to block disease progression in rodent studies of synucleinopathies. However, passive immunotherapy in clinical trials has been proven safe but less effective than in preclinical conditions. Here we review current achievements of passive immunotherapy in animal models of synucleinopathies. Furthermore, we propose new research strategies to increase translational outcome in patient studies, (1) by using antibodies against immature conformations of pathogenic αsyn (monomers, post-translationally modified monomers, oligomers and protofibrils) and (2) by focusing treatment on body-first synucleinopathies where damage in the brain is still limited and effective immunization could potentially stop disease progression by blocking the spread of pathogenic αsyn from peripheral organs to the brain.

Therapeutics in the Pipeline Targeting α-Synuclein for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and the fastest growing neurologic disease in the world, yet no disease-modifying therapy is available for this disabling condition. Multiple lines of evidence implicate the protein α-synuclein (α-Syn) in the pathogenesis of PD, and as such, there is intense interest in targeting α-Syn for potential disease modification. α-Syn is also a key pathogenic protein in other synucleionpathies, most commonly dementia with Lewy bodies. Thus, therapeutics targeting this protein will have utility in these disorders as well. Here we discuss the various approaches that are being investigated to prevent and mitigate α-Syn toxicity in PD, including clearing its pathologic aggregates from the brain using immunization strategies, inhibiting its misfolding and aggregation, reducing its expression level, enhancing cellular clearance mechanisms, preventing its cell-to-cell transmission within the brain and perhaps from the periphery, and targeting other proteins associated with or implicated in PD that contribute to α-Syn toxicity. We also discuss the therapeutics in the pipeline that harness these strategies. Finally, we discuss the challenges and opportunities for the field in the discovery and development of therapeutics for disease modification in PD. SIGNIFICANCE STATEMENT: PD is the second most common neurodegenerative disorder, for which disease-modifying therapies remain a major unmet need. A large body of evidence points to α-synuclein as a key pathogenic protein in this disease as well as in dementia with Lewy bodies, making it of leading therapeutic interest. This review discusses the various approaches being investigated and progress made to date toward discovering and developing therapeutics that would slow and stop progression of these disabling diseases.

Roles of α‑synuclein in gastrointestinal microbiome dysbiosis‑related Parkinson's disease progression (Review)

Parkinson's disease (PD) is the second most common neurodegenerative disease amongst the middle-aged and elderly populations. Several studies have confirmed that the microbiota-gut-brain axis (MGBA) serves a key role in the pathogenesis of PD. Changes to the gastrointestinal microbiome (GM) cause misfolding and abnormal aggregation of α-synuclein (α-syn) in the intestine. Abnormal α-syn is not eliminated via physiological mechanisms and is transported into the central nervous system (CNS) via the vagus nerve. The abnormal levels of α-syn aggregate in the substantia nigra pars compacta, not only leading to the formation of eosinophilic Lewis Bodies in the cytoplasm and mitochondrial dysfunction in dopaminergic (DA) neurons, but also leading to the stimulation of an inflammatory response in the microglia. These pathological changes result in an increase in oxidative stress (OS), which triggers nerve cell apoptosis, a characteristic of PD. This increase in OS further oxidizes and intensifies abnormal aggregation of α-syn, eventually forming a positive feedback loop. The present review discusses the abnormal accumulation of α-syn in the intestine caused by the GM changes and the increased levels of α-syn transport to the CNS via the MGBA, resulting in the loss of DA neurons and an increase in the inflammatory response of microglial cells in the brain of patients with PD. In addition, relevant clinical therapeutic strategies for improving the GM and reducing α-syn accumulation to relieve the symptoms and progression of PD are described.

"Janus-Faced" α-Synuclein: Role in Parkinson's Disease

Parkinson's disease (PD) is a pathological condition characterized by the aggregation and the resultant presence of intraneuronal inclusions termed Lewy bodies (LBs) and Lewy neurites which are mainly composed of fibrillar α-synuclein (α-syn) protein. Pathogenic aggregation of α-syn is identified as the major cause of LBs deposition. Several mutations in α-syn showing varied aggregation kinetics in comparison to the wild type (WT) α-syn are reported in PD (A30P, E46K, H 50Q, G51D, A53E, and A53T). Also, the cell-to-cell spread of pathological α-syn plays a significant role in PD development. Interestingly, it has also been suggested that the pathology of PD may begin in the gastrointestinal tract and spread via the vagus nerve (VN) to brain proposing the gut-brain axis of α-syn pathology in PD. Despite multiple efforts, the behavior and functions of this protein in normal and pathological states (specifically in PD) is far from understood. Furthermore, the etiological factors responsible for triggering aggregation of this protein remain elusive. This review is an attempt to collate and present latest information on α-syn in relation to its structure, biochemistry and biophysics of aggregation in PD. Current advances in therapeutic efforts toward clearing the pathogenic α-syn via autophagy/lysosomal flux are also reviewed and reported.

Synthesis of Double Interfering Biodegradable Nano-MgO Micelle Composites and Their Effect on Parkinson's Disease

Although gene therapy targeting the α-synuclein gene (SNCA) has achieved outstanding results in the treatment of Parkinson's disease (PD), the lack of a suitable gene delivery system and inadequate therapeutic effects remains a tremendous obstacle for RNAi therapy. Here, a degradable nano-MgO micelle composite (MgO(pDNA)-INS-Plu-mRNA-NGF) with double interference (mediated by RNAi and α-synuclein (α-syn)-targeted mRNA) was constructed. Binding mRNA treatment significantly increased the inhibitory effect compared to the reduction of α-syn expression by RNAi alone. Moreover, the cell experiments demonstrated that the viability of the PD cell model can be significantly improved by nano-MgO micelle composite treatment. More importantly, the composite has the ability to penetrate the blood brain barrier and deliver genes and mRNA to neurons through endocytosis mediated by the nerve growth factor and its receptors, thus significantly downregulating the expression of α-syn in the PD mice model without causing damage to other major organs. Overall, this work provides a novel insight into the design of biomaterials for gene therapy for PD.

Novel targeted therapies for Parkinson's disease

Parkinson’s disease (PD) is the second more common neurodegenerative disease with increasing incidence worldwide associated to the population ageing. Despite increasing awareness and significant research advancements, treatment options comprise dopamine repleting, symptomatic therapies that have significantly increased quality of life and life expectancy, but no therapies that halt or reverse disease progression, which remain a great, unmet goal in PD research. Large biomarker development programs are undertaken to identify disease signatures that will improve patient selection and outcome measures in clinical trials. In this review, we summarize PD-related mechanisms that can serve as targets of therapeutic interventions aiming to slow or modify disease progression, as well as previous and ongoing clinical trials in each field, and discuss future perspectives.

siRNA Therapeutics: Future Promise for Neurodegenerative Diseases

Neurodegenerative diseases (ND), as a group of central nervous system (CNS) disorders, are among the most prominent medical problems of the 21st century. They are often associated with considerable disability, motor dysfunction and dementia and are more common in the aged population. ND imposes a psychologic, economic and social burden on the patients and their families. Currently, there is no effective treatment for ND. Since many ND result from the gain of function of a mutant allele, small interference RNA (siRNA) can be a potential therapeutic agent for ND management. Based on the RNA interference (RNAi) approach, siRNA is a powerful tool for modulating gene expression through gene silencing. However, there are some obstacles in the clinical application of siRNA, including unfavorable immune response, off-target effects, instability of naked siRNA, nuclease susceptibility and a need to develop a suitable delivery system. Since there are some issues related to siRNA delivery routes, in this review, we focus on the application of siRNA in the management of ND treatment from 2000 to 2020.

Revisiting gene delivery to the brain: silencing and editing

Neurodegenerative disorders, ischemic brain diseases, and brain tumors are debilitating diseases that severely impact a person's life and could possibly lead to their demise if left untreated. Many of these diseases do not respond to small molecule therapeutics and have no effective long-term therapy. Gene therapy offers the promise of treatment or even a cure for both genetic and acquired brain diseases, mediated by either silencing or editing disease-specific genes. Indeed, in the last 5 years, significant progress has been made in the delivery of non-coding RNAs as well as gene-editing formulations to the brain. Unfortunately, the delivery is a major limiting factor for the success of gene therapies. Both viral and non-viral vectors have been used to deliver genetic information into a target cell, but they have limitations. Viral vectors provide excellent transduction efficiency but are associated with toxic effects and have limited packaging capacity; however, non-viral vectors are less toxic and show a high packaging capacity at the price of low transfection efficiency. Herein, we review the progress made in the field of brain gene therapy, particularly in the design of non-toxic and trackable non-viral vectors, capable of controlled release of genes in response to internal/external triggers, and in the delivery of formulations for gene editing. The application of these systems in the context of various brain diseases in pre-clinical and clinical tests will be discussed. Such promising approaches could potentially pave the way for clinical realization of brain gene therapies.

Extracellular Vesicles as Nanotherapeutics for Parkinson's Disease

Extracellular vesicles (EVs) are naturally occurring membranous structures secreted by normal and diseased cells, and carrying a wide range of bioactive molecules. In the central nervous system (CNS), EVs are important in both homeostasis and pathology. Through receptor-ligand interactions, direct fusion, or endocytosis, EVs interact with their target cells. Accumulating evidence indicates that EVs play crucial roles in the pathogenesis of many neurodegenerative disorders (NDs), including Parkinson's disease (PD). PD is the second most common ND, characterized by the progressive loss of dopaminergic (DAergic) neurons within the Substantia Nigra pars compacta (SNpc). In PD, EVs are secreted by both neurons and glial cells, with either beneficial or detrimental effects, via a complex program of cell-to-cell communication. The functions of EVs in PD range from their etiopathogenetic relevance to their use as diagnostic tools and innovative carriers of therapeutics. Because they can cross the blood-brain barrier, EVs can be engineered to deliver bioactive molecules (e.g., small interfering RNAs, catalase) within the CNS. This review summarizes the latest findings regarding the role played by EVs in PD etiology, diagnosis, prognosis, and therapy, with a particular focus on their use as novel PD nanotherapeutics.

Anti-α-synuclein ASO delivered to monoamine neurons prevents α-synuclein accumulation in a Parkinson's disease-like mouse model and in monkeys

BACKGROUND

Progressive neuronal death in monoaminergic nuclei and widespread accumulation of α-synuclein are neuropathological hallmarks of Parkinson's disease (PD). Given that α-synuclein may be an early mediator of the pathological cascade that ultimately leads to neurodegeneration, decreased α-synuclein synthesis will abate neurotoxicity if delivered to the key affected neurons.

METHODS

We used a non-viral gene therapy based on a new indatraline-conjugated antisense oligonucleotide (IND-ASO) to disrupt the α-synuclein mRNA transcription selectively in monoamine neurons of a PD-like mouse model and elderly nonhuman primates. Molecular, cell biology, histological, neurochemical and behavioral assays were performed.

FINDINGS

Intracerebroventricular and intranasal IND-ASO administration for four weeks in a mouse model with AAV-mediated wild-type human α-synuclein overexpression in dopamine neurons prevented the synthesis and accumulation of α-synuclein in the connected brain regions, improving dopamine neurotransmission. Likewise, the four-week IND-ASO treatment led to decreased levels of endogenous α-synuclein protein in the midbrain monoamine nuclei of nonhuman primates, which are affected early in PD.

CONCLUSIONS

The inhibition of α-synuclein production in dopamine neurons and its accumulation in cortical/striatal projection areas may alleviate the early deficits of dopamine function, showing the high translational value of antisense oligonucleotides as a disease modifying therapy for PD and related synucleinopathies.

FUNDING

Grants SAF2016-75797-R, RTC-2014-2812-1 and RTC-2015-3309-1, Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (ERDF), UE; Grant ID 9238, Michael J. Fox Foundation; and Centres for Networked Biomedical Research on Mental Health (CIBERSAM), and on Neurodegenerative Diseases (CIBERNED).

Gene-Editing Technologies Paired With Viral Vectors for Translational Research Into Neurodegenerative Diseases

Diseases of the central nervous system (CNS) have historically been among the most difficult to treat using conventional pharmacological approaches. This is due to a confluence of factors, including the limited regenerative capacity and overall complexity of the brain, problems associated with repeated drug administration, and difficulties delivering drugs across the blood-brain barrier (BBB). Viral-mediated gene transfer represents an attractive alternative for the delivery of therapeutic cargo to the nervous system. Crucially, it usually requires only a single injection, whether that be a gene replacement strategy for an inherited disorder or the delivery of a genome- or epigenome-modifying construct for treatment of CNS diseases and disorders. It is thus understandable that considerable effort has been put towards the development of improved vector systems for gene transfer into the CNS. Different viral vectors are of course tailored to their specific applications, but they generally should share several key properties. The ideal viral vector incorporates a high-packaging capacity, efficient gene transfer paired with robust and sustained expression, lack of oncogenicity, toxicity and pathogenicity, and scalable manufacturing for clinical applications. In this review, we will devote attention to viral vectors derived from human immunodeficiency virus type 1 (lentiviral vectors; LVs) and adeno-associated virus (AAVs). The high interest in these viral delivery systems vectors is due to: (i) robust delivery and long-lasting expression; (ii) efficient transduction into postmitotic cells, including the brain; (iii) low immunogenicity and toxicity; and (iv) compatibility with advanced manufacturing techniques. Here, we will outline basic aspects of LV and AAV biology, particularly focusing on approaches and techniques aiming to enhance viral safety. We will also allocate a significant portion of this review to the development and use of LVs and AAVs for delivery into the CNS, with a focus on the genome and epigenome-editing tools based on clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas 9) and the development of novel strategies for the treatment of neurodegenerative diseases (NDDs).

Progress in the molecular pathogenesis and nucleic acid therapeutics for Parkinson's disease in the precision medicine era

Parkinson's disease (PD) is one of the most common neurodegenerative disorders that manifest various motor and nonmotor symptoms. Although currently available therapies can alleviate some of the symptoms, the disease continues to progress, leading eventually to severe motor and cognitive decline and reduced life expectancy. The past two decades have witnessed rapid progress in our understanding of the molecular and genetic pathogenesis of the disease, paving the way for the development of new therapeutic approaches to arrest or delay the neurodegenerative process. As a result of these advances, biomarker‐driven subtyping is making it possible to stratify PD patients into more homogeneous subgroups that may better respond to potential genetic‐molecular pathway targeted disease‐modifying therapies. Therapeutic nucleic acid oligomers can bind to target gene sequences with very high specificity in a base‐pairing manner and precisely modulate downstream molecular events. Recently, nucleic acid therapeutics have proven effective in the treatment of a number of severe neurological and neuromuscular disorders, drawing increasing attention to the possibility of developing novel molecular therapies for PD. In this review, we update the molecular pathogenesis of PD and discuss progress in the use of antisense oligonucleotides, small interfering RNAs, short hairpin RNAs, aptamers, and microRNA‐based therapeutics to target critical elements in the pathogenesis of PD that could have the potential to modify disease progression. In addition, recent advances in the delivery of nucleic acid compounds across the blood–brain barrier and challenges facing PD clinical trials are also reviewed.

Alterations in the nigrostriatal system following conditional inactivation of α-synuclein in neurons of adult and aging mice

The etiology and pathogenesis of Parkinson's disease (PD) are tightly linked to the gain-of-function of α-synuclein. However, gradual accumulation of α-synuclein aggregates in dopaminergic neurons of substantia nigra pars compacta (SNpc) leads to the depletion of the functional pool of soluble α-synuclein, and therefore, creates loss-of-function conditions, particularly in presynaptic terminals of these neurons. Studies of how this late-onset depletion of a protein involved in many important steps of neurotransmission contributes to PD progression and particularly, to worsening the nigrostriatal pathology at late stages of the disease are limited and obtained data, are controversial. Recently, we produced a mouse line for conditional knockout of the gene encoding α-synuclein, and here we used its tamoxifen-inducible pan-neuronal inactivation to study consequences of the adult-onset (from the age of 6 months) and late-onset (from the age of 12 months) α-synuclein depletion to the nigrostriatal system. No significant changes of animal balance/coordination, the number of dopaminergic neurons in the SNpc and the content of dopamine and its metabolites in the striatum were observed after adult-onset α-synuclein depletion, but in aging (18-month-old) late-onset depleted mice we found a significant reduction of major dopamine metabolites without changes to the content of dopamine itself. Our data suggest that this might be caused, at least partially, by reduced expression of aldehyde dehydrogenase ALDH1a1 and could lead to the accumulation of toxic intermediates of dopamine catabolism. By extrapolating our findings to a potential clinical situation, we suggest that therapeutic downregulation of α-synuclein expression in PD patients is a generally safe option as it should not cause adverse side effects on the functionality of their nigrostriatal system. However, if started in aged patients, this type of therapy might trigger slight functional changes of the nigrostriatal system with potentially unwanted additive effect to already existing pathology.

Gene Therapy Options as New Treatment for Inherited Peripheral Neuropathy

Inherited peripheral neuropathy (IPN) is caused by heterogeneous genetic mutations in more than 100 genes. So far, several treatment options for IPN have been developed and clinically evaluated using small molecules. However, gene therapy-based therapeutic strategies have not been aggressively investigated, likely due to the complexities of inheritance in IPN. Indeed, because the majority of the causative mutations of IPN lead to gain-of-function rather than loss-of-function, developing a therapeutic strategy is more difficult, especially considering gene therapy for genetic diseases began with the simple idea of replacing a defective gene with a functional copy. Recent advances in gene manipulation technology have brought novel approaches to gene therapy and its clinical application for IPN treatment. For example, in addition to the classically used gene replacement for mutant genes in recessively inherited IPN, other techniques including gene addition to modify the disease phenotype, modulations of target gene expression, and techniques to edit mutant genes have been developed and evaluated as potent therapeutic strategies for dominantly inherited IPN. In this review, the current status of gene therapy for IPN and future perspectives will be discussed.

CRISPR System: A High-throughput Toolbox for Research and Treatment of Parkinson's Disease

In recent years, the innovation of gene-editing tools such as the CRISPR/Cas9 system improves the translational gap of treatments mediated by gene therapy. The privileges of CRISPR/Cas9 such as working in living cells and organs candidate this technology for using in research and treatment of the central nervous system (CNS) disorders. Parkinson's disease (PD) is a common, debilitating, neurodegenerative disorder which occurs due to loss of dopaminergic neurons and is associated with progressive motor dysfunction. Knowledge about the pathophysiological basis of PD has altered the classification system of PD, which manifests in familial and sporadic forms. The first genetic linkage studies in PD demonstrated the involvement of Synuclein alpha (SNCA) mutations and SNCA genomic duplications in the pathogenesis of PD familial forms. Subsequent studies have also insinuated mutations in leucine repeat kinase-2 (LRRK2), Parkin, PTEN-induced putative kinase 1 (PINK1), as well as DJ-1 causing familial forms of PD. This review will attempt to discuss the structure, function, and development in genome editing mediated by CRISP/Cas9 system. Further, it describes the genes involved in the pathogenesis of PD and the pertinent alterations to them. We will pursue this line by delineating the PD linkage studies in which CRISPR system was employed. Finally, we will discuss the pros and cons of CRISPR employment vis-à-vis the process of genome editing in PD patients' iPSCs.

Targeting α-synuclein for PD Therapeutics: A Pursuit on All Fronts

Parkinson's Disease (PD) is characterized both by the loss of dopaminergic neurons in the substantia nigra and the presence of cytoplasmic inclusions called Lewy Bodies. These Lewy Bodies contain the aggregated α-synuclein (α-syn) protein, which has been shown to be able to propagate from cell to cell and throughout different regions in the brain. Due to its central role in the pathology and the lack of a curative treatment for PD, an increasing number of studies have aimed at targeting this protein for therapeutics. Here, we reviewed and discussed the many different approaches that have been studied to inhibit α-syn accumulation via direct and indirect targeting. These analyses have led to the generation of multiple clinical trials that are either completed or currently active. These clinical trials and the current preclinical studies must still face obstacles ahead, but give hope of finding a therapy for PD with time.

Exosomal DNA Aptamer Targeting α-Synuclein Aggregates Reduced Neuropathological Deficits in a Mouse Parkinson's Disease Model

The α-synuclein aggregates are the main component of Lewy bodies in Parkinson's disease (PD) brain, and they showed immunotherapy could be employed to alleviate α-synuclein aggregate pathology in PD. Recently we have generated DNA aptamers that specifically recognize α-synuclein. In this study, we further investigated the in vivo effect of these aptamers on the neuropathological deficits associated with PD. For efficient delivery of the aptamers into the mouse brain, we employed modified exosomes with the neuron-specific rabies viral glycoprotein (RVG) peptide on the membrane surface. We demonstrated that the aptamers were efficiently packaged into the RVG-exosomes and delivered into neurons in vitro and in vivo. Functionally, the aptamer-loaded RVG-exosomes significantly reduced the α-synuclein preformed fibril (PFF)-induced pathological aggregates, and rescued synaptic protein loss and neuronal death. Moreover, intraperitoneal administration of these exosomes into the mice with intra-striatally injected α-synuclein PFF reduced the pathological α-synuclein aggregates and improved motor impairments. In conclusion, we demonstrated that the aptamers targeting α-synuclein aggregates could be effectively delivered into the mouse brain by the RVG-exosomes and reduce the neuropathological and behavioral deficits in the mouse PD model. This study highlights the therapeutic potential of the RVG-exosome delivery of aptamer to alleviate the brain α-synuclein pathology.

Systemic peptide mediated delivery of an siRNA targeting α-syn in the CNS ameliorates the neurodegenerative process in a transgenic model of Lewy body disease

Neurodegenerative disorders of the aging population are characterized by progressive accumulation of neuronal proteins such as α-synuclein (α-syn) in Parkinson's Disease (PD) and Amyloid ß (Aß) and Tau in Alzheimer's disease (AD) for which no treatments are currently available. The ability to regulate the expression at the gene transcription level would be beneficial for reducing the accumulation of these proteins or regulating expression levels of other genes in the CNS. Short interfering RNA molecules can bind specifically to target RNAs and deliver them for degradation. This approach has shown promise therapeutically in vitro and in vivo in mouse models of PD and AD and other neurological disorders; however, delivery of the siRNA to the CNS in vivo has been achieved primarily through intra-cerebral or intra-thecal injections that may be less amenable for clinical translation; therefore, alternative approaches for delivery of siRNAs to the brain is needed. Recently, we described a small peptide from the envelope protein of the rabies virus (C2-9r) that was utilized to deliver an siRNA targeting α-syn across the blood brain barrier (BBB) following intravenous injection. This approach showed reduced expression of α-syn and neuroprotection in a toxic mouse model of PD. However, since receptor-mediated delivery is potentially saturable, each allowing the delivery of a limited number of molecules, we identified an alternative peptide for the transport of nucleotides across the BBB based on the apolipoprotein B (apoB) protein targeted to the family of low-density lipoprotein receptors (LDL-R). We used an 11-amino acid sequence from the apoB protein (ApoB11) that, when coupled with a 9-amino acid arginine linker, can transport siRNAs across the BBB to neuronal and glial cells. To examine the value of this peptide mediated oligonucleotide delivery system for PD, we delivered an siRNA targeting the α-syn (siα-syn) in a transgenic mouse model of PD. We found that ApoB11 was effective (comparable to C2-9r) at mediating the delivery of siα-syn into the CNS, co-localized to neurons and glial cells and reduced levels of α-syn protein translation and accumulation. Delivery of ApoB11/siα-syn was accompanied by protection from degeneration of selected neuronal populations in the neocortex, limbic system and striato-nigral system and reduced neuro-inflammation. Taken together, these results suggest that systemic delivery of oligonucleotides targeting α-syn using ApoB11 might be an interesting alternative strategy worth considering for the experimental treatment of synucleinopathies.

Amido-bridged nucleic acid (AmNA)-modified antisense oligonucleotides targeting α-synuclein as a novel therapy for Parkinson's disease

Parkinson’s disease (PD) is a neurodegenerative disease caused by the loss of dopaminergic neurons in the substantia nigra. A characteristic pathological feature of PD is cytoplasmic accumulation of α-synuclein (SNCA) protein. Multiplication of the SNCA gene in familial PD and pathological accumulation of SNCA protein during progression of sporadic PD suggest that increased SNCA protein levels increase the risk of PD. Thus, reducing SNCA expression levels could delay PD onset or modify the disease course. For efficient knock down, we designed and synthesized an amido-bridged nucleic acids (AmNA)-modified antisense oligonucleotide (ASO) that targeted SNCA with improved stability and cellular uptake in vivo. AmNA-ASO efficiently downregulated SNCA at both the mRNA and protein level in vitro and in vivo. Notably, AmNA-ASO was efficiently delivered into the mouse brain by intracerebroventricular injection without the aid of additional chemicals. Furthermore, administration of AmNA-ASO ameliorated neurological defects in PD model mice expressing human wild type SNCA. Taken together, these findings suggest that AmNA-ASO is a promising therapeutic strategy for SNCA-associated pathology in PD.

Progress of immunotherapy of anti-α-synuclein in Parkinson's disease

Many neurodegenerative diseases are characterized by progressive loss of neurons and abnormal protein accumulation, including amyloid (A)β and tau in Alzheimer's disease and Lewy bodies and α-synuclein (α-syn) in Parkinson's disease (PD). Recent evidence suggests that adaptive immunity plays an important role in PD, and that anti-α-syn antibodies can be used as therapy in neurodegenerative diseases; monoclonal antibodies were shown to inhibit α-syn propagation and aggregation in PD models and patients. In this review, we summarize the different pathological states of α-syn, including gene mutations, truncation, phosphorylation, and the high molecular weight form, and describe the specific antibodies that recognize the α-syn monomer or oligomer, some of which have been tested in clinic trials. We also discuss future research directions and potential targets in PD therapy.

Identification of potential blood biomarkers for Parkinson's disease by gene expression and DNA methylation data integration analysis

BACKGROUND

Blood-based gene expression or epigenetic biomarkers of Parkinson's disease (PD) are highly desirable. However, accuracy and specificity need to be improved, and methods for the integration of gene expression with epigenetic data need to be developed in order to make this feasible.

METHODS

Whole blood gene expression data and DNA methylation data were downloaded from Gene Expression Omnibus (GEO) database. A linear model was used to identify significantly differentially expressed genes (DEGs) and differentially methylated genes (DMGs) according to specific gene regions 5'-C-phosphate-G-3' (CpGs) or all gene regions CpGs in PD. Gene set enrichment analysis was then applied to DEGs and DMGs. Subsequently, data integration analysis was performed to identify robust PD-associated blood biomarkers. Finally, the random forest algorithm and a leave-one-out cross validation method were performed to construct classifiers based on gene expression data integrated with methylation data.

RESULTS

Eighty-five (85) significantly hypo-methylated and upregulated genes in PD patients compared to healthy controls were identified. The dominant hypo-methylated regions of these genes were significantly different. Some genes had a single dominant hypo-methylated region, while others had multiple dominant hypo-methylated regions. One gene expression classifier and two gene methylation classifiers based on all or dominant methylation-altered region CpGs were constructed. All have a good prediction power for PD.

CONCLUSIONS

Gene expression and methylation data integration analysis identified a blood-based 53-gene signature, which could be applied as a biomarker for PD.

Prospective treatment of Parkinson's disease by a siRNA-LDH nanoconjugate

In the world, among the neurodegenerative diseases, Parkinson's is the second most common disease. Although several medications are available in the market, this disease still remains incurable and only the symptoms are controlled to a certain extent with severe side effects. For these reasons we decided to search for a novel therapeutic measure. The objective of this publication was to find a therapeutic procedure to cure this devastating disease. In this study, a biocompatible, easily permeable, cationic nanoparticle-layered double hydroxide was synthesized. Within the layers of these nanoparticles we intercalated α synuclein siRNA, which helps to silence the α synuclein gene. After the intercalation, which was optimized at a 1 : 40 ratio of siRNA : (LDH), we studied its stability in blood by a RNase protection test and serum protection assay. Both proved that LDH was an excellent nanocarrier that can protect intercalated molecules within its layers. After that, several cellular studies were performed by FACS to evaluate its biocompatibility after intercalation and cellular internalization. Results of the biocompatibility studies found it to be nontoxic and in the cellular internalization study, 51.55% of cells were taken into the nanoconjugate and confocal microscopy supported the data from FACS. Lastly, ELISA was performed to discover protein levels in the control, overexpressed, and treated groups of the SH-SY5Y cell line. These results verified that this nanoconjugate is a protective treatment procedure for Parkinson's disease.

Downregulation of SNCA Expression by Targeted Editing of DNA Methylation: A Potential Strategy for Precision Therapy in PD

Elevated levels of SNCA have been implicated in the pathogenesis of Parkinson's disease (PD), while normal physiological levels of SNCA are needed to maintain neuronal function. We ought to develop new therapeutic strategies targeting the regulation of SNCA expression. DNA methylation at SNCA intron 1 regulates SNCA transcription, and PD brains showed differential methylation levels compared to controls. Thus, DNA methylation at SNCA intron 1 is an attractive target for fine-tuned downregulation of SNCA levels. Here we developed a system, comprising an all-in-one lentiviral vector, for targeted DNA methylation editing within intron 1. The system is based on CRISPR-deactivated Cas9 (dCas9) fused with the catalytic domain of DNA-methyltransferase 3A (DNMT3A). Applying the system to human induced pluripotent stem cell (hiPSC)-derived dopaminergic neurons from a PD patient with the SNCA triplication resulted in fine downregulation of SNCA mRNA and protein mediated by targeted DNA methylation at intron 1. Furthermore, the reduction in SNCA levels by the guide RNA (gRNA)-dCas9-DMNT3A system rescued disease-related cellular phenotype characteristics of the SNCA triplication hiPSC-derived dopaminergic neurons, e.g., mitochondrial ROS production and cellular viability. We established that DNA hypermethylation at SNCA intron 1 allows an effective and sufficient tight downregulation of SNCA expression levels, suggesting the potential of this target sequence combined with the CRISPR-dCas9 technology as a novel epigenetic-based therapeutic approach for PD.

Origination, change, and modulation of geriatric disease-related gut microbiota during life

The age-related changes in the diversity and composition of the gut microbiota are well described in recent studies. These changes have been suggested to be influenced by age-associated weakening of the immune system and low-grade chronic inflammation, resulting in numerous age-associated pathological conditions. Gut microbiota homeostasis is important throughout the life of the host by providing vital functions to regulate various immunological functions and homeostasis. Based on published results, we summarize the relationship between the gut microbiota and aging-related diseases, especially Parkinson's disease, immunosenescence, rheumatoid arthritis, bone loss, and metabolic syndrome. The change in composition of the gut microbiota and gut ecosystem during life and its influence on the host immunologic and metabolic phenotype are also analyzed to determine factors that affect aging-related diseases. Approaches to maintain host health and prevent or cure geriatric diseases are also discussed.

CRISPR/Cas9 Technology as an Emerging Tool for Targeting Amyotrophic Lateral Sclerosis (ALS)

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9) is a genome editing tool that has recently caught enormous attention due to its novelty, feasibility, and affordability. This system naturally functions as a defense mechanism in bacteria and has been repurposed as an RNA-guided DNA editing tool. Unlike zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), CRISPR/Cas9 takes advantage of an RNA-guided DNA endonuclease enzyme, Cas9, which is able to generate double-strand breaks (DSBs) at specific genomic locations. It triggers cellular endogenous DNA repair pathways, contributing to the generation of desired modifications in the genome. The ability of the system to precisely disrupt DNA sequences has opened up new avenues in our understanding of amyotrophic lateral sclerosis (ALS) pathogenesis and the development of new therapeutic approaches. In this review, we discuss the current knowledge of the principles and limitations of the CRISPR/Cas9 system, as well as strategies to improve these limitations. Furthermore, we summarize novel approaches of engaging the CRISPR/Cas9 system in establishing an adequate model of neurodegenerative disease and in the treatment of SOD1-linked forms of ALS. We also highlight possible applications of this system in the therapy of ALS, both the inherited type as well as ALS of sporadic origin.

Novel DNA Aptamers for Parkinson's Disease Treatment Inhibit α-Synuclein Aggregation and Facilitate its Degradation

Parkinson’s disease (PD) is one of the most prevalent forms of synucleinopathies, and it is characterized neuropathologically by the presence of intracellular inclusions composed primarily of the protein α-synuclein (α-syn) in neurons. The previous immunotherapy targeting the α-syn in PD models with monoclonal antibodies has established α-syn protein as an effective target for neuronal cell death. However, due to the essential weaknesses of antibody and the unique features of aptamers, the aptamers could represent a promising alternative to the currently used antibodies in immunotherapy for PD. In this study, the purified human α-syn was used as the target for in vitro selection of aptamers using systematic evolution by exponential enrichment. This resulted in the identification of two 58-base DNA aptamers with a high binding affinity and good specificity to the α-syn, with K_D values in the nanomolar range. Both aptamers could effectively reduce α-syn aggregation in vitro and in cells and target the α-syn to intracellular degradation through the lysosomal pathway. These effects consequently rescued the mitochondrial dysfunction and cellular defects caused by α-syn overexpression. To our knowledge, this is the first study to employ aptamers to block the aberrant cellular effects of the overexpressed α-syn in cells.

Neuroprotective effect of gold nanoparticles composites in Parkinson's disease model

Parkinson's disease (PD) is second most common neurodegenerative disorder worldwide. Although drugs and surgery can relieve the symptoms of PD, these therapies are incapable of fundamentally treating the disease. For PD patients, over-expression of α-synuclein (SNCA) leads to the death of dopaminergic neurons. This process can be prevented by suppressing SNCA over-expression through RNA interference. Here, we successfully synthesized gold nanoparticles (GNP) composites (CTS@GNP-pDNA-NGF) via the combination of electrostatic adsorption and photochemical immobilization, which could load plasmid DNA (pDNA) and target specific cell types. GNP was transfected into cells via endocytosis to inhibiting the apoptosis of PC12 cells and dopaminergic neurons. Simultaneously, GNP composites are also used in PD models in vivo, and it can successfully cross the blood-brain barrier by contents of GNP in the mice brain. In general, all the works demonstrated that GNP composites have good therapeutic effects for PD models in vitro and in vivo.

ASPsiRNA: A Resource of ASP-siRNAs Having Therapeutic Potential for Human Genetic Disorders and Algorithm for Prediction of Their Inhibitory Efficacy

Allele-specific siRNAs (ASP-siRNAs) have emerged as promising therapeutic molecules owing to their selectivity to inhibit the mutant allele or associated single-nucleotide polymorphisms (SNPs) sparing the expression of the wild-type counterpart. Thus, a dedicated bioinformatics platform encompassing updated ASP-siRNAs and an algorithm for the prediction of their inhibitory efficacy will be helpful in tackling currently intractable genetic disorders. In the present study, we have developed the ASPsiRNA resource (http://crdd.osdd.net/servers/aspsirna/) covering three components viz (i) ASPsiDb, (ii) ASPsiPred, and (iii) analysis tools like ASP-siOffTar. ASPsiDb is a manually curated database harboring 4543 (including 422 chemically modified) ASP-siRNAs targeting 78 unique genes involved in 51 different diseases. It furnishes comprehensive information from experimental studies on ASP-siRNAs along with multidimensional genetic and clinical information for numerous mutations. ASPsiPred is a two-layered algorithm to predict efficacy of ASP-siRNAs for fully complementary mutant (Eff^mut) and wild-type allele (Eff^wild) with one mismatch by ASPsiPred^SVM and ASPsiPred^matrix, respectively. In ASPsiPred^SVM, 922 unique ASP-siRNAs with experimentally validated quantitative Eff^mut were used. During 10-fold cross-validation (10nCV) employing various sequence features on the training/testing dataset (T737), the best predictive model achieved a maximum Pearson’s correlation coefficient (PCC) of 0.71. Further, the accuracy of the classifier to predict Eff^mut against novel genes was assessed by leave one target out cross-validation approach (LOTOCV). ASPsiPred^matrix was constructed from rule-based studies describing the effect of single siRNA:mRNA mismatches on the efficacy at 19 different locations of siRNA. Thus, ASPsiRNA encompasses the first database, prediction algorithm, and off-target analysis tool that is expected to accelerate research in the field of RNAi-based therapeutics for human genetic diseases.

Current Experimental Studies of Gene Therapy in Parkinson's Disease

Parkinson's disease (PD) was characterized by late-onset, progressive dopamine neuron loss and movement disorders. The progresses of PD affected the neural function and integrity. To date, most researches had largely addressed the dopamine replacement therapies, but the appearance of L-dopa-induced dyskinesia hampered the use of the drug. And the mechanism of PD is so complicated that it's hard to solve the problem by just add drugs. Researchers began to focus on the genetic underpinnings of Parkinson's disease, searching for new method that may affect the neurodegeneration processes in it. In this paper, we reviewed current delivery methods used in gene therapies for PD, we also summarized the primary target of the gene therapy in the treatment of PD, such like neurotrophic factor (for regeneration), the synthesis of neurotransmitter (for prolong the duration of L-dopa), and the potential proteins that might be a target to modulate via gene therapy. Finally, we discussed RNA interference therapies used in Parkinson's disease, it might act as a new class of drug. We mainly focus on the efficiency and tooling features of different gene therapies in the treatment of PD.