Alpha-Synuclein Targeting Therapeutics for Parkinson's Disease and Related Synucleinopathies

Harnessing Graphdiyne for Selective Cu2+ Detection: A Promising Tool for Parkinson's Disease Diagnostics and Pathogenesis

Cu2+ accelerates the viral-like propagation of α-synuclein fibrils and plays a key role in the pathogenesis of Parkinson's disease (PD). Therefore, the accurate detection of Cu2+ is essential for the diagnosis of PD and other neurological diseases. The Cu2+ detection process is impeded by substances that have similar electrochemical properties. In this study, graphdiyne (GDY), a new kind of carbon allotrope with strong electron-donating ability, was utilized for the highly selective detection of Cu2+ by taking advantage of its outstanding adsorption capacity for Cu2+. Density functional theory (DFT) calculations show that Cu atoms are adsorbed in the cavity of GDY, and the absorption energy between Cu and C atoms is higher than that of graphene (GR), indicating that the cavity of GDY is favorable for the adsorption of Cu atoms and electrochemical sensing. The GDY-based electrochemical sensor can effectively avoid the interference of amino acids, metal ions and neurotransmitters and has a high sensitivity of 9.77 μA·μM-1·cm-2, with a minimum detectable concentration of 200 nM. During the investigating pathogenesis and therapeutic process of PD with α-synuclein as the diagnostic standard, the concentration of Cu2+ in cells before and after L-DOPA and GSH treatments were examined, and it was found that Cu2+ exhibits high potential as a biomarker for PD. This study not only harnesses the favorable adsorption of the GDY and Cu2+ to improve the specificity of ion detection but also provide clues for deeper understanding of the role of Cu2+ in neurobiology and neurological diseases.

Refining the clinical diagnosis of Parkinson's disease

Our ability to define, understand, and classify Parkinson's disease (PD) has undergone significant changes since the disorder was first described in 1817. Clinical features and neuropathologic signatures can now be supplemented by in-vivo interrogation of genetic and biological substrates of disease, offering great opportunity for further refining the diagnosis of PD. In this mini-review, we discuss the historical perspectives which shaped our thinking surrounding the definition and diagnosis of PD. We highlight the clinical, genetic, pathologic and biologic diversity which underpins the condition, and proceed to discuss how recent developments in our ability to define biologic and pathologic substrates of disease might impact PD definition, diagnosis, individualised prognostication, and personalised clinical care. We argue that Parkinson's 'disease', as currently diagnosed in the clinic, is actually a syndrome. It is the outward manifestation of any array of potential dysfunctional biologic processes, neuropathological changes, and disease aetiologies, which culminate in common outward clinical features which we term PD; each person has their own unique disease, which we can now define with increasing precision. This is an exciting time in PD research and clinical care. Our ability to refine the clinical diagnosis of PD, incorporating in-vivo assessments of disease biology, neuropathology, and neurogenetics may well herald the era of biologically-based, precision medicine approaches PD management. With this however comes a number of challenges, including how to integrate these technologies into clinical practice in a way which is acceptable to patients, promotes meaningful changes to care, and minimises health economic impact.

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.

Unraveling Dysregulated Cell Signaling Pathways, Genetic and Epigenetic Mysteries of Parkinson's Disease

Parkinson's disease (PD) is a prevalent and burdensome neurodegenerative disorder that has been extensively researched to understand its complex etiology, diagnosis, and treatment. The interplay between genetic and environmental factors in PD makes its pathophysiology difficult to comprehend, emphasizing the need for further investigation into genetic and epigenetic markers involved in the disease. Early diagnosis is crucial for optimal management of the disease, and the development of novel diagnostic biomarkers is ongoing. Although many efforts have been made in the field of recognition and interpretation of the mechanisms involved in the pathophysiology of the disease, the current knowledge about PD is just the tip of the iceberg. By scrutinizing genetic and epigenetic patterns underlying PD, new avenues can be opened for dissecting the pathology of the disorder, leading to more precise and efficient diagnostic and therapeutic approaches. This review emphasizes the importance of studying dysregulated cell signaling pathways and molecular processes associated with genes and epigenetic alterations in understanding PD, paving the way for the development of novel therapeutic strategies to combat this devastating disease.

Molecular docking analysis of α-Synuclein aggregation with Anle138b

α-Synuclein aggregation into toxic oligomeric species is central to Parkinson's disease pathogenesis. Anle138b is a recently identified inhibitor of α-synuclein oligomerization showing promise in preclinical studies. This study employed computational approaches to elucidate Anle138b's mechanism of oligomer-specific action. The inhibitory potential of Anle138b against α-synuclein oligomers was evaluated by performing molecular docking studies using AutoDock Tools, followed by their binding pocket analysis. Further, protein-protein docking studies were performed using Hex8.0 to validate the aggregation inhibitory potential of Anle138b. Molecular docking revealed increasing binding affinity of Anle138b against higher order α-synuclein oligomers (dimer to decamer). Anle138b occupied oligomeric cavity and interacted with residues Thr54, Gly73, Val74 and Thr75 across several oligomers. Protein-protein docking showed that Anle138b interferes with α-synuclein decamer formation. These results highlight the oligomer-directed inhibitory mechanism of Anle138b, without hindering the monomeric forms and provide molecular insights to advance its therapeutic development for Parkinson's and related synucleinopathies.

ENGINEERED NANOBODIES WITH PROGRAMMABLE TARGET ANTIGEN PROTEOLYSIS (PTAP) FUSIONS REGULATE INTRACELLULAR ALPHA-SYNUCLEIN IN VITRO AND IN VIVO

Alpha-synuclein (αSyn) aggregation and the formation of Lewy pathology (LP) is a foundational pathophysiological phenomenon in synucleinopathies. Delivering therapeutic single-chain and single-domain antibodies that bind pathogenic targets can disrupt intracellular aggregation. The fusion of antibody fragments to a negatively-charged proteasomal targeting motif (PEST) creates bifunctional constructs that enhance both solubility and turnover. With sequence-specific point mutations of PEST sequences that modulate proteasomal degradation efficiency, we report the creation of Programmable Target Antigen Proteolysis (PTAP) technology that can provide graded control over the levels of target antigens. We have previously demonstrated our lead anti-αSyn intrabody, VH14-PEST, is capable of reducing the pathological burden of synucleinopathy in vitro and in vivo. Here, we report a family of fully humanized VH14-PTAP constructs for controllable, therapeutic targeting of intracellular α-Syn. In cells, we demonstrate successful target engagement and efficacy of VH14-hPEST intrabodies, and validate proof-of-principle in human cells using 3D human organoids derived from PD-patient induced pluripotent stem cells (iPSC). In two synuclein-based rat models, PTAP intrabodies attenuated nigral αSyn pathology, preserved nigrostriatal dopaminergic tone, and slowed the propagation of αSyn pathology. These data demonstrate the potency of intracellular αSyn targeting as a method to alleviate pathology and highlight the potential clinical utility of PTAP intrabodies.

Recombinant Antibody Fragments for Immunotherapy of Parkinson's Disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder. Multiple genetic and environmental factors leading to progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SN) and consequent depletion of dopamine were described. Current clinical approaches, such as dopamine replacement or deep brain stimulation using surgically implanted probes, provide symptomatic relief but cannot modify disease progression. Therefore, disease-modifying therapeutic tools are urgently needed. Immunotherapy approaches, including passive transfer of protective antibodies and their fragments, have shown therapeutic efficacy in several animal models of neurodegenerative diseases, including PD. Recombinant antibody fragments are promising alternatives to conventional full-length antibodies. Modern computational approaches and molecular biology tools, directed evolution methodology, and the design of tissue-penetrating fusion peptides allowed for the development of recombinant antibody fragments with superior specificity and affinity, reduced immunogenicity, the capacity to target hidden epitopes and cross the blood-brain barrier (BBB), higher solubility and stability, the ability to refold after heat denaturation, and inexpensive large-scale production. In addition, antibody fragments do not induce microglia Fcγ receptor (FcγR)-mediated proinflammatory response and tissue damage in the central nervous system (CNS), because they lack the Fc portion of the immunoglobulin molecule. In the present review, we summarized data on recombinant antibody fragments evaluated as immunotherapeutics in preclinical models of PD and discussed their potential for developing therapeutic and preventive protocols for patients with PD.

α-Synuclein oligomers and fibrils: partners in crime in synucleinopathies

The misfolding and aggregation of α-synuclein is the general hallmark of a group of devastating neurodegenerative pathologies referred to as synucleinopathies, such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. In such conditions, a range of different misfolded aggregates, including oligomers, protofibrils, and fibrils, are present both in neurons and glial cells. Growing experimental evidence supports the proposition that soluble oligomeric assemblies, formed during the early phases of the aggregation process, are the major culprits of neuronal toxicity; at the same time, fibrillar conformers appear to be the most efficient at propagating among interconnected neurons, thus contributing to the spreading of α-synuclein pathology. Moreover, α-synuclein fibrils have been recently reported to release soluble and highly toxic oligomeric species, responsible for an immediate dysfunction in the recipient neurons. In this review, we discuss the current knowledge about the plethora of mechanisms of cellular dysfunction caused by α-synuclein oligomers and fibrils, both contributing to neurodegeneration in synucleinopathies.

E46K Mutation of α-Synuclein Preorganizes the Intramolecular Interactions Crucial for Aggregation

Aggregation of α-synuclein is central to the pathogenesis of Parkinson's disease. The most toxic familial mutation E46K accelerates the aggregation process by an unknown mechanism. Herein, we provide a clue by investigating the influence of E46K on monomeric α-synuclein and its relation to aggregation with molecular dynamics simulations. The E46K mutation suppresses β-sheet structures in the N-terminus while promoting those at the key fibrillization region named NACore. Even though WT and E46K monomers share conserved intramolecular interactions with fibrils, E46K abolishes intramolecular contacts within the N-terminus which are present in the WT monomer but absent in fibrils. Network analysis identifies residues 36-53 as the interaction core of the WT monomer. Upon mutation, residues 36-46 are expelled to water due to aggravated electrostatic repulsion in the 43KTKK46 segment. Instead, NACore (residues 68-78) becomes the interaction hub and connects preceding residues 47-56 and the C-terminus. Consequently, residues 47-95 which belong to the fibril core form more compact β-sheets. Overall, the interaction network of E46K is more like fibrils than WT, stabilizing the fibril-like conformations. Our work provides mechanistic insights into the faster aggregation of the E46K mutant. It implies a close link between monomeric conformations and fibrils, which would spur the development of therapeutic strategies.

Effect of Electric Field on α-Synuclein Fibrils: Revealed by Molecular Dynamics Simulations

The self-association of amylogenic proteins to the fibril form is considered a pivotal factor in the pathogenesis of neurodegenerative diseases, including Parkinson’s disease (PD). PD causes unintended or uncontrollable movements in its common symptoms. α-synuclein is the major cause of PD development and thus has been the main target of numerous studies to suppress and sequester its expression or effectively degrade it. Nonetheless, to date, there are no efficient and proven ways to prevent pathological protein aggregation. Recent investigations proposed applying an external electric field to interrupt the fibrils. This method is a non-invasive approach that has a certain benefit over others. We performed molecular dynamics (MD) simulations by applying an electric field on highly toxic fibrils of α-synuclein to gain a molecular-level insight into fibril disruption mechanisms. The results revealed that the applied external electric field induces substantial changes in the conformation of the α-synuclein fibrils. Furthermore, we show the threshold value for electric field strength required to completely disrupt the α-synuclein fibrils by opening the hydrophobic core of the fibril. Thus, our findings might serve as a valuable foundation to better understand molecular-level mechanisms of the α-synuclein fibrils disaggregation process under an applied external electric field.

Real-life ankle submovements and computer mouse use reflect patient-reported function in adult ataxias

Novel disease-modifying therapies are being evaluated in spinocerebellar ataxias and multiple system atrophy. Clinician-performed disease rating scales are relatively insensitive for measuring disease change over time, resulting in large and long clinical trials. We tested the hypothesis that sensors worn continuously at home during natural behaviour and a web-based computer mouse task performed at home could produce interpretable, meaningful and reliable motor measures for potential use in clinical trials. Thirty-four individuals with degenerative ataxias (spinocerebellar ataxia types 1, 2, 3 and 6 and multiple system atrophy of the cerebellar type) and eight age-matched controls completed the cross-sectional study. Participants wore an ankle and wrist sensor continuously at home for 1 week and completed the Hevelius computer mouse task eight times over 4 weeks. We examined properties of motor primitives called 'submovements' derived from the continuous wearable sensors and properties of computer mouse clicks and trajectories in relationship to patient-reported measures of function (Patient-Reported Outcome Measure of Ataxia) and ataxia rating scales (Scale for the Assessment and Rating of Ataxia and the Brief Ataxia Rating Scale). The test-retest reliability of digital measures and differences between ataxia and control participants were evaluated. Individuals with ataxia had smaller, slower and less powerful ankle submovements during natural behaviour at home. A composite measure based on ankle submovements strongly correlated with ataxia rating scale scores (Pearson's r = 0.82-0.88), strongly correlated with self-reported function (r = 0.81), had high test-retest reliability (intraclass correlation coefficient = 0.95) and distinguished ataxia and control participants, including preataxic individuals (n = 4) from controls. A composite measure based on computer mouse movements and clicks strongly correlated with ataxia rating scale total (r = 0.86-0.88) and arm scores (r = 0.65-0.75), correlated well with self-reported function (r = 0.72-0.73) and had high test-retest reliability (intraclass correlation coefficient = 0.99). These data indicate that interpretable, meaningful and highly reliable motor measures can be obtained from continuous measurement of natural movement, particularly at the ankle location, and from computer mouse movements during a simple point-and-click task performed at home. This study supports the use of these two inexpensive and easy-to-use technologies in longitudinal natural history studies in spinocerebellar ataxias and multiple system atrophy of the cerebellar type and shows promise as potential motor outcome measures in interventional trials.

Current Treatments and New, Tentative Therapies for Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative pathology, the origin of which is associated with the death of neuronal cells involved in the production of dopamine. The prevalence of PD has increased exponentially. The aim of this review was to describe the novel treatments for PD that are currently under investigation and study and the possible therapeutic targets. The pathophysiology of this disease is based on the formation of alpha-synuclein folds that generate Lewy bodies, which are cytotoxic and reduce dopamine levels. Most pharmacological treatments for PD target alpha-synuclein to reduce the symptoms. These include treatments aimed at reducing the accumulation of alpha-synuclein (epigallocatechin), reducing its clearance via immunotherapy, inhibiting LRRK2, and upregulating cerebrosidase (ambroxol). Parkinson’s disease continues to be a pathology of unknown origin that generates a significant social cost for the patients who suffer from it. Although there is still no definitive cure for this disease at present, there are numerous treatments available aimed at reducing the symptomatology of PD in addition to other therapeutic alternatives that are still under investigation. However, the therapeutic approach to this pathology should include a combination of pharmacological and non-pharmacological strategies to maximise outcomes and improve symptomatological control in these patients. It is therefore necessary to delve deeper into the pathophysiology of the disease in order to improve these treatments and therefore the quality of life of the patients.

α-Synuclein in synaptic function and dysfunction

α-Synuclein is a neuronal protein that is enriched in presynaptic terminals. Under physiological conditions, it binds to synaptic vesicle membranes and functions in neurotransmitter release, although the molecular details remain unclear, and it is controversial whether α-synuclein inhibits or facilitates neurotransmitter release. Pathologically, in synucleinopathies including Parkinson's disease (PD), α-synuclein forms aggregates that recruit monomeric α-synuclein and spread throughout the brain, which triggers neuronal dysfunction at molecular, cellular, and organ levels. Here, we present an overview of the effects of α-synuclein on SNARE-complex assembly, neurotransmitter release, and synaptic vesicle pool homeostasis, and discuss how the observed divergent effects of α-synuclein on neurotransmitter release can be reconciled. We also discuss how gain-of-function versus loss-of-function of α-synuclein may contribute to pathogenesis in synucleinopathies.

The Hidden Cell-to-Cell Trail of α-Synuclein Aggregates

The progressive accumulation of insoluble aggregates of the presynaptic protein alpha-synuclein (α-Syn) is a hallmark of neurodegenerative disorders including Parkinson's disease (PD), Multiple System Atrophy, and Dementia with Lewy Bodies, commonly referred to as synucleinopathies. Despite considerable progress on the structural biology of these aggregates, the molecular mechanisms mediating their cell-to-cell transmission, propagation, and neurotoxicity remain only partially understood. Numerous studies have highlighted the stereotypical spatiotemporal spreading of pathological α-Syn aggregates across different tissues and anatomically connected brain regions over time. Experimental evidence from various cellular and animal models indicate that α-Syn transfer occurs in two defined steps: the release of pathogenic α-Syn species from infected cells, and their uptake via passive or active endocytic pathways. Once α-Syn aggregates have been internalized, little is known about what drives their toxicity or how they interact with the endogenous protein to promote its misfolding and subsequent aggregation. Similarly, unknown genetic factors modulate different cellular responses to the aggregation and accumulation of pathogenic α-Syn species. Here we discuss the current understanding of the molecular phenomena associated with the intercellular spreading of pathogenic α-Syn seeds and summarize the evidence supporting the transmission hypothesis. Understanding the molecular mechanisms involved in α-Syn aggregates transmission is essential to develop novel targeted therapeutics against PD and related synucleinopathies.

Curcumin Interacts with α-Synuclein Condensates To Inhibit Amyloid Aggregation under Phase Separation

The amyloid aggregation of α-synuclein (α-Syn) is highly associated with Parkinson's disease (PD). Discovering α-Syn amyloid inhibitors is one of the strategies for PD therapies. Recent studies suggested that α-Syn undergoes phase separation to accelerate amyloid aggregation. Molecules modulating α-Syn phase separation or transition have the potential to regulate amyloid aggregation. Here, we discovered that curcumin, a small natural molecule, interacts with α-Syn during phase separation. Our study showed that curcumin neither affects the formation of α-Syn condensates nor influences the initial morphology of α-Syn condensates. However, curcumin decreases the fluidity of α-Syn inside the condensates and efficiently inhibits α-Syn from turning into an amyloid. It also inhibits the amyloid aggregations of PD disease-related α-Syn E46K and H50Q mutants under phase separation. Furthermore, curcumin can destabilize preformed α-Syn amyloid aggregates in the condensates. Together, our findings demonstrate that curcumin regulates α-Syn amyloid formation during protein phase separation and reveal that α-Syn amyloid aggregation under phase separation can be modulated by small molecules.

Myricetin Inhibits α-Synuclein Amyloid Aggregation by Delaying the Liquid-to-Solid Phase Transition

The aggregation of α-synuclein (α-Syn) is a critical pathological hallmark of Parkinson's disease (PD). Prevention of α-Syn aggregation has become a key strategy for treating PD. Recent studies have suggested that α-Syn undergoes liquid-liquid phase separation (LLPS) to facilitate nucleation and amyloid formation. Here, we examined the modulation of α-Syn aggregation by myricetin, a polyhydroxyflavonol compound, under the conditions of LLPS. Unexpectedly, neither the initial morphology nor the phase-separated fraction of α-Syn was altered by myricetin. However, the dynamics of α-Syn condensates decreased upon myricetin binding. Further studies showed that myricetin dose-dependently inhibits amyloid aggregation in the condensates by delaying the liquid-to-solid phase transition. In addition, myricetin could disassemble the preformed α-Syn amyloid aggregates matured from the condensates. Together, our study shows that myricetin inhibits α-Syn amyloid aggregation in the condensates by retarding the liquid-to-solid phase transition and reveals that α-Syn phase transition can be targeted to inhibit amyloid aggregation.