alpha-Synuclein in filamentous inclusions of Lewy bodies from Parkinson's disease and dementia with lewy bodies

Lasting Impact: Exploring the Brain Mechanisms that Link Traumatic Brain Injury to Parkinson's Disease

Development of Parkinson's Disease (PD) is linked with a history of traumatic brain injury (TBI), although the mechanisms driving this remain unclear. Of note, many key parallels have been identified between the pathologies of PD and TBI; in particular, PD is characterised by loss of dopaminergic neurons from the substantia nigra (SN), accompanied by broader changes to dopaminergic signalling, disruption of the Locus Coeruleus (LC) and noradrenergic system, and accumulation of aggregated α-synuclein in Lewy Bodies, which spreads in a stereotypical pattern throughout the brain. Widespread disruptions to the dopaminergic and noradrenergic systems, including progressive neuronal loss from the SN and LC, have been observed acutely following injury, some of which have also been identified chronically in TBI patients and preclinical models. Furthermore, changes to α-synuclein expression are also seen both acutely and chronically following injury throughout the brain, although detailed characterisation of these changes and spread of pathology is limited. In this review, we detail the current literature regarding dopaminergic and noradrenergic disruption and α-synuclein pathology following injury, with particular focus on how these changes may predispose individuals to prolonged pathology and progressive neurodegeneration, particularly the development of PD. While it is increasingly clear that TBI is a key risk factor for the development of PD, significant gaps remain in current understanding of neurodegenerative pathology following TBI, particularly chronic manifestations of injury.

Brain O-GlcNAcylation: Bridging physiological functions, disease mechanisms, and therapeutic applications

O-GlcNAcylation, a dynamic post-translational modification occurring on serine or threonine residues of numerous proteins, plays a pivotal role in various cellular processes, including gene regulation, metabolism, and stress response. Abundant in the brain, O-GlcNAcylation intricately governs neurodevelopment, synaptic assembly, and neuronal functions. Recent investigations have established a correlation between the dysregulation of brain O-GlcNAcylation and a broad spectrum of neurological disorders and injuries, spanning neurodevelopmental, neurodegenerative, and psychiatric conditions, as well as injuries to the central nervous system (CNS). Manipulating O-GlcNAcylation has demonstrated neuroprotective properties against these afflictions. This review delineates the roles and mechanisms of O-GlcNAcylation in the CNS under both physiological and pathological circumstances, with a focus on its neuroprotective effects in neurological disorders and injuries. We discuss the involvement of O-GlcNAcylation in key processes such as neurogenesis, synaptic plasticity, and energy metabolism, as well as its implications in conditions like Alzheimer's disease, Parkinson's disease, and ischemic stroke. Additionally, we explore prospective therapeutic approaches for CNS disorders and injuries by targeting O-GlcNAcylation, highlighting recent clinical developments and future research directions. This comprehensive overview aims to provide insights into the potential of O-GlcNAcylation as a therapeutic target and guide future investigations in this promising field.

Identification of novel small molecule chaperone activators for neurodegenerative disease treatment

A pathological hallmark of neurodegenerative disease is the accumulation of aberrant protein aggregates which contribute to the cytotoxicity and are therefore a target for therapy development. One key mechanism to manage cellular protein homeostasis is heat shock proteins (HSPs), protein chaperones which are known to target aberrant protein accumulation. Activation of HSPs target aberrant TDP-43, tau and amyloid to rescue neurodegenerative disease. As an attempt to target HSP activation for neurodegeneration therapy, we here develop a drug screening assay to identify compounds that will activate the master regulator of HSPs, the transcription factor heat shock factor 1 (HSF1). As HSF1 is bound by HSP90 which prevents its activation, we developed a NanoBRET assay, which allows us to monitor and quantify the HSF1-HSP90 interaction in living cells to screen for compounds disrupting this interaction and thereby releasing HSF1 for activation. After the optimisation and validation of the assay, a two thousand compound library was screened which produced 10 hits including two known HSP90 inhibitors. Follow-up functional study showed that one of the hits oxyphenbutazone (OPB) significantly reduces the accumulation of insoluble TDP-43 in a cell model, eliciting no signs of stress or toxicity. Overall, this study demonstrates a viable strategy for new drug discovery in targeting aberrant proteins and identifies potential candidates for translation into neurodegenerative disease treatment.

Protective Effect of the LRRK2 Kinase Inhibition in Human Fibroblasts Bearing the Genetic Variant GBA1 K198E: Implications for Parkinson's Disease

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder for which there are currently no curative therapies. Therefore, the need for innovative treatments for this illness is critical. The glucosylceramidase beta 1 (GBA1) and leucine-rich repeated kinase 2 (LRRK2) genes have been postulated as potential genetically defined drug targets. We report for the first time that the LRRK2 inhibitor PF-06447475 (PF-475) not only restores GCase enzyme activity, but also increases mitochondrial membrane potential, significantly decreases DJ-1 Cys106-SO3, reduces lysosome accumulation, and diminishes cleaved caspase-3 (CC3) in GBA1 K198E fibroblasts. Furthermore, in addition to a significant reduction in p-Ser935 LRRK2 kinase, we found that PF-475 reduced p-Thr73 RAB 10 and p-Ser129 α-Syn in mutant skin fibroblasts. In addition, we found that the GCase activator GCA (NCGC00188758) increased GCase activity and decreased lysosomal accumulation, but did not affect p-Ser935 LRRK2, ∆Ψm, p-Ser129 α-Syn, DJ-1 Cys106-SO3, or CC3 in K198E GBA1 fibroblasts. The GCase inhibitor conduritol-β-epoxide (CBE), used as an internal control, significantly reduced GCase and left the other pathological markers largely unaltered in GBA1 K198E, but reduced GCase and increased the accumulation of lysosomes only in WT GBA1 fibroblasts. Taken together, these results suggest that LRRK2 is a critical signaling kinase in the pathogenic mechanism associated with the lysosomal GBA1/GCase K198E variant. Our findings suggest that the use of LRRK2 inhibitors in PD patients with GBA1 mutations, such as K198E, may be effective in reversing GBA1/GCase deficiency, autophagy impairment, oxidative stress, and neuronal death.

MEK1/2 inhibitors suppress pathological α-synuclein and neurotoxicity in cell models and a humanized mouse model of Parkinson's disease

The abnormal accumulation of misfolded proteins is a common hallmark of many neurodegenerative disorders. Among these proteins, α-synuclein (αsyn) is a well-characterized pathogenic protein in Parkinson's disease (PD) and other synucleinopathies. αsyn can be hyperphosphorylated and form pathological aggregates, leading to neurodegeneration. Thus, chemical modulators of pathological αsyn may suppress its downstream toxicity and provide entry points to therapeutic intervention. Here, we identified mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitors as negative modulators of basal αsyn in wild-type cells and that pathological αsyn in αsyn preformed fibrils (αsyn-PFF) induced the neuroblastoma cell line SHSY-5Y, PC12 cells, and primary cultured neurons. We further demonstrated that these inhibitors suppressed Ser129 phosphorylated αsyn (p-αsyn) through the kinase PLK2 downstream of MEK1/2-ERK2 in PD cell models. We established a humanized PD mouse model by injecting human αsyn-PFF into mice with homozygous knock-in of human SNCA. Oral administration of blood-brain barrier-penetrable MEK1/2 inhibitors lowered pathological αsyn and rescued PD-relevant phenotypes with an acceptable safety profile in these mice. Collectively, these data highlight MEK1/2 inhibitors as a potential therapeutic strategy for PD.

Identifying Immune Response Protein Biomarkers in Parkinson's-Related Cognitive Impairment and Depression

A distinct immune microenvironment may develop in patients with Parkinson's disease (PD), influenced by the severity of cognitive impairment and the presence of depression. We aimed to identify blood-based immune response markers in patients with PD using a proximity extension assay (PEA). Peripheral plasma samples from 58 patients with PD and 30 healthy controls (HCs) were analyzed for 92 immune response-associated proteins using Olink's PEA technology. A panel of four proteins (SIT1, CLEC4C, EIF5A, and NFATC3) was identified, effectively differentiating patients with PD from HCs, with a combined area under the receiver operating characteristic (ROC) curve of 0.863. Among these, ITGA11 and EIF5A were particularly associated with the degree of cognitive impairment. After applying Bonferroni correction, five proteins-PPP1R9B, MILR1, BTN3A2, IRAK1, and TANK-demonstrated potentially significant differences between depressed and non-depressed patients with PD-cognitively normal (PD-CN). In the correlation analyses, PPP1R9B exhibited a positive correlation with the Hamilton Depression Rating Scale (HAMD) score (r = 0.509, P = 0.019). Furthermore, after adjusting for potential confounding factors in binary logistic regression analysis, PPP1R9B remained significantly associated with depression (P = 0.042). We identified potential blood-based immune response markers associated with the severity of cognitive impairment and depression in patients with PD. These findings provide preliminary insights into the immune-related pathology underlying non-motor symptoms of PD, potentially guiding future studies aimed at targeted therapeutic strategies. Further validation in larger, independent cohorts is warranted to confirm these associations and their clinical utility.

Autonomic dysfunction in neurodegenerative disease

In addition to their more studied cognitive and motor effects, neurodegenerative diseases are also associated with impairments in autonomic function - the regulation of involuntary physiological processes. These autonomic impairments manifest in different ways and at different stages depending on the specific disease. The neural networks responsible for autonomic regulation in the brain and body have characteristics that render them particularly susceptible to the prion-like spread of protein aggregation involved in neurodegenerative diseases. Specifically, the axons of these neurons - in both peripheral and central networks - are long and poorly myelinated axons, which make them preferential targets for pathological protein aggregation. Moreover, cortical regions integrating information about the internal state of the body are highly connected with other brain regions, which increases the likelihood of intersection with pathological pathways and prion-like spread of abnormal proteins. This leads to an autonomic 'signature' of dysfunction, characteristic of each neurodegenerative disease, that is linked to the affected networks and regions undergoing pathological aggregation.

No structure, no problem: Protein stabilization by Hero proteins and other chaperone-like IDPs

In order for a protein to function, it must fold into its proper three-dimensional structure. Otherwise, improperly folded proteins are typically prone to aggregate through a process that is detrimental to cellular health. It is widely known that a diverse group of proteins, called molecular chaperones, function to promote proper folding of other proteins and prevent aggregation. In contrast, intrinsically disordered proteins (IDPs) lack substantial tertiary structures, but nonetheless serve important functional roles. In some cases, IDPs have been observed to display remarkably chaperone-like activities, where they stabilize the activities of client proteins and prevent their aggregation. While it was previously thought that chaperone-like IDPs were mainly utilized by extremophilic organisms in their survival of extreme stress, we recently showed that a group of chaperone-like IDPs, we named heat-resistant obscure (Hero) proteins, are also widespread in non-extremophile animals, including humans and flies. Thus, we should consider the possibility that IDPs serve significant chaperone-like functions in protein stabilization relevant to physiological conditions. However, as most of our understanding of how chaperones function is based on insights from their structured domains, it is unclear how chaperone-like IDPs elicit chaperone-like effects without these structures. Here we summarize our understanding of Hero proteins to date and, based on experimental evidence, outline the features that are likely important for their protein stabilizing activities. We draw on concepts from the studies of chaperones and chaperone-like IDPs, in order to draft potential models of how chaperone-like IDPs achieve chaperone-like effects in the absence of well-defined structures.

A Novel Small Molecule Enhances Stable Dopamine Delivery to the Brain in Models of Parkinson's Disease

Levodopa is the gold standard symptomatic treatment for Parkinson's disease. Disease progression due to alpha-synuclein accumulation, brain inflammation, and the loss of dopamine neurons, as well as motor fluctuations, due to variations in levodopa plasma levels, remain a significant problem for Parkinson's patients. Developing a therapeutic option that can simultaneously reduce the neuropathology associated with alpha-synuclein aggregation, attenuate oxidative stress and inflammation, and overcome variations in levodopa plasma levels is an unmet need to treat Parkinson's disease. We determined the pharmacokinetics and pharmacodynamics of a small molecule, dubbed Pegasus, that conjugates dopamine with a nonantibiotic doxycycline derivative via a molecular linker. Mice harboring the human A53T mutation of alpha-synuclein or treated with MPTP were injected once daily with 50 mg/kg Pegasus for 2 weeks and assessed for motor, behavioral, and cognitive effects, followed by biochemical and histochemical analysis. Pegasus is a poor brain penetrant but it was metabolized to stable dopamine and tetracycline derivatives, and abundant plasma and brain levels of these metabolites were detected. Pegasus reduced soluble and insoluble alpha-synuclein levels, protected dopamine-producing neurons, and reduced astrocytic activation in A53T mice. Mice treated with Pegasus exhibited motor improvement (6.5 h) and reduction in anxiety-like behavior. Rotarod and grip strength improved in MPTP-treated mice when mice were treated with Pegasus or levodopa. Pegasus may be a multi-modal therapeutic option that can deliver stable dopamine into the CNS and reduce misfolded alpha-synuclein, activate dopamine receptors, and attenuate variations in dopamine levels.

Biofunctionalized nanomaterials for Parkinson's disease theranostics: potential for efficient PD biomarker detection and effective therapy

α-Synuclein (α-Syn) is a primary pathological indicator for Parkinson's disease (PD). The α-Syn oligomer is even more toxic and is responsible for PD. Hence, identifying α-Syn and its oligomers is an interesting approach to diagnosing PD. The prevention strategies for oligomer formation could be therapeutic in treating PD. Various conventional strategies have been developed for the management of PD. However, their clinical applications are limited due to toxicity, off-targeting, side effects, and poor bioavailability. Recently, nanomaterials have gained significant attention due to unique physicochemical characteristics such as nanoscale size, large surface area, flexibility of functionalization, and ability to protect and control a loaded payload. Functionalizing the surface of nanoparticles with a desired targeting agent could offer targeted delivery of the payload at the site of action due to specificity and selectivity against complementary molecules. Among various functionalization approaches, biomolecule-functionalized nanomaterials offer benefits such as enhanced bioavailability, improved internalization into target cells through receptor-mediated endocytosis, and delivery of therapeutics across the BBB (blood-brain barrier). In this review, we initially discussed the major milestones related to PD and highlighted the therapeutic strategies focused on clinical trials. The strategies of biomolecule functionalization of nanomaterials and their application in detecting and preventing α-Syn oligomer for the diagnosis and therapy of PD, respectively, have been reviewed comprehensively. Ultimately, we have outlined the conclusions, highlighted the limitations and challenges, and provided insight into future perspectives and alternative approaches that must be investigated.

The potential of brain organoids in addressing the heterogeneity of synucleinopathies

Synucleinopathies are a group of diseases characterized by neuronal and glial accumulation of α-synuclein (aSyn) linked with different clinical presentations, including Parkinson's disease (PD), Parkinson's disease with dementia (PDD), Dementia with Lewy Bodies (DLB) and Multiple system atrophy (MSA). Interestingly, the structure of the aSyn aggregates can vary across different synucleinopathies. Currently, it is unclear how the aSyn protein can aggregate into diverse structures and affect distinct cell types and various brain regions, leading to different clinical symptoms. Recent advances in induced pluripotent stem cells (iPSCs)-based brain organoids (BOs) technology provide an unprecedented opportunity to define the etiology of synucleinopathies in human brain cells within their three-dimensional (3D) context. In this review, we will summarize current advances in investigating the mechanisms of synucleinopathies using BOs and discuss the scope of this platform to define mechanisms underlining the selective vulnerability of cell types and brain regions in synucleinopathies.

Defining essential charged residues in fibril formation of a lysosomal derived N-terminal α-synuclein truncation

N- and C-terminal α-synuclein (α-syn) truncations are prevalent in Parkinson's disease. Effects of the N- and C-terminal residues on α-syn aggregation and fibril propagation are distinct, where the N-terminus dictates fibril structure. Here, the majority of α-syn truncations are assigned by intact mass spectrometry to lysosomal activity. To delineate essential charged residues in fibril formation, we selected an N-terminal truncation (66-140) that is generated solely from soluble α-syn by asparagine endopeptidase. Ala-substitutions at K80 and E83 impact aggregation kinetics, revealing their vital roles in defining fibril polymorphism. K80, E83, and K97 are identified to be critical for fibril elongation. Based on solid-state NMR, mutational and Raman studies, and molecular dynamics simulations, a E83-K97 salt bridge is proposed. Finally, participation of C-terminal Lys residues in the full-length α-syn fibril assembly process is also shown, highlighting that individual residues can be targeted for therapeutic intervention.

Liganded magnetic nanoparticles for magnetic resonance imaging of α-synuclein

Aggregation of the protein α-synuclein (α-syn) is the histopathological hallmark of neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), which are collectively known as synucleinopathies. Currently, patients with synucleinopathies are diagnosed by physical examination and medical history, often at advanced stages of disease. Because synucleinopathies are associated with α-syn aggregates, and α-syn aggregation often precedes onset of symptoms, detecting α-syn aggregates would be a valuable early diagnostic for patients with synucleinopathies. Here, we design a liganded magnetic nanoparticle (LMNP) functionalized with an α-syn-targeting peptide to be used as a magnetic resonance imaging (MRI)-based biomarker for α-syn. Our LMNPs bind to aggregates of α-syn in vitro, cross the blood-brain barrier in mice with mannitol adjuvant, and can be used as an MRI contrast agent to distinguish mice with α-synucleinopathy from age-matched, wild-type control mice in vivo. These results provide evidence for the potential of magnetic nanoparticles that target α-syn for diagnosis of synucleinopathies.

The basolateral amygdala and striatum propagate alpha-synuclein pathology causing increased fear response in a Parkinson's disease model

Alpha-synuclein (aSyn)-related pathology crucially contributes to the pathogenesis of Parkinson's disease, a frequent and incurable neurodegenerative disease characterized by progressive motor and non-motor symptoms. Anxiety and fear- related neuropsychiatric symptoms develop frequently and early in the disease, but a lack of understanding of pathogenesis hampers rational therapy. This study aimed to decipher whether aSyn pathology in the basolateral amygdala (BLA) is causative of fear and anxiety. Bilateral stereotaxic injections of human aSyn-preformed amyloid fibrils (PFF) in BLA, striatum, or substantia nigra were conducted in female mice overexpressing human aSyn (Thy1-aSyn) and in wildtype littermates (WT). We characterized the propagation of aSyn pathology and related neuropathological changes across brain regions and examined the behavioral and fear responses in mice up to 2 months post-injection of PFF. While PFF injections induced local aSyn fibril pathology close to all respective injection sites in transgenic mice, we observed differences in propagation, downstream pathology and behavioral alterations. The BLA and the striatum, but not the substantia nigra, effectively propagated aSyn pathology to connected brain regions at 2.5 months post injection. This involved enhanced microgliosis and astrogliosis in the nigrostriatal system and loss of GABAergic parvalbuminergic interneurons in the striatum and corticolimbic brain regions. Intra-BLA PFF injections resulted in increased cued fear response in both transgenic mice and WT mice at 1 month post injection. The effect was more pronounced in the transgenic mice. Conversely, intra-striatal PFF injections enhanced contextual fear in WT at 2 months post injection. These findings imply that increased fear is inducible by aSyn pathology, especially if originating in the BLA or striatum. Furthermore, both regions are hub regions of aSyn pathology propagation, thereby contributing to disease progression. These insights provide mechanisms that can guide rational therapeutic development.

Zinc oxide nanoparticle interface moderation enhances the extent of α-synuclein sequestering against the protein amyloidosis

Parkinson's disease is a progressive neurodegenerative disorder that is often associated with plaque deposition, known as Lewy Bodies. Lewy Bodies are predominantly composed of α-synuclein amyloid fibrils. α-Synuclein is a soluble intrinsically disordered protein (IDP) with proposed multiple physiological functions, consisting of aggregation-prone non-amyloid β component (NAC) region in its sequence. Amyloid aggregation of α-synuclein goes through a cytotoxic intermediate(s), leading to structurally mature cross-β sheet-rich fibrils as its end product. Metal nanoparticles with a biocompatible nature have been adopted for different biological applications. Thus, sequestering of α-synuclein monomer onto the metal nanoparticle will potentially impede Parkinson's onset/progression. In this study, interaction of α-synuclein with zinc oxide nanoparticle (ZnONP) having positive surface potential, and moderated ZnONP with negative surface-functional group(s), were explored. The interaction studies indicate that the NAC region interacts with the nanoparticle to sequester the monomeric protein into an amorphous aggregate, thus extending the lag phase of protein fibrillation. Interestingly, α-synuclein complexed with ZnONP exhibits remarkably lowered cytotoxicity against the SH-SY5Y cell in-vitro, compared to the treatment with only ZnONP interfaces or α-synuclein fibrils.

Alpha-synuclein regulates nucleolar DNA double-strand break repair in melanoma

Although an increased risk of the skin cancer melanoma in people with Parkinson's disease (PD) has been shown in multiple studies, the mechanisms involved are poorly understood, but increased expression of the PD-associated protein alpha-synuclein (αSyn) in melanoma cells may be important. Our previous work suggests that αSyn can facilitate DNA double-strand break (DSB) repair, promoting genomic stability. We now show that αSyn is preferentially enriched within the nucleolus in melanoma, where it colocalizes with DNA damage markers and DSBs. Inducing DSBs specifically within nucleolar ribosomal DNA (rDNA) increases αSyn levels near sites of damage. αSyn knockout increases DNA damage within the nucleolus at baseline, after specific rDNA DSB induction, and prolongs the rate of recovery from this induced damage. αSyn is important downstream of ataxia-telangiectasia-mutated signaling to facilitate MDC1-mediated 53BP1 recruitment to DSBs, reducing micronuclei formation and promoting cellular proliferation, migration, and invasion.

Platelet miRNAs as early biomarkers for progression of idiopathic REM sleep behavior disorder to a synucleinopathy

Individuals diagnosed with isolated REM sleep behavior disorder (IRBD) have a high risk of developing Lewy body disorders (LBD), mainly Parkinson's disease (PD) or dementia with Lewy bodies (DLB). As we have previously identified seven platelet-derived miRNAs as potential biomarkers for DLB, in this pilot study we aimed to investigate whether specific expression changes of these miRNAs are also present in IRBD. RNA was obtained from platelets of individuals with IRBD (n = 29) and controls (n = 34), and miRNA levels were determined with a miRCURY LNA miRNA Custom PCR Panel. miRNA interactomes of deregulated miRNAs were determined, and mRNA quantification of miRNA target genes was carried out using real-time PCR and the ΔΔCt method. We found that the expression of hsa-miR- 139 - 5p (p = 0.010) and hsa-miR- 142 - 3p (p = 0.017) was diminished, while hsa-miR- 191 - 5p (p = 0.023) was increased in platelets of IRBD patients compared with controls. Interactome analysis of these miRNAs showed that hsa-miR- 142 - 3p regulates genes related to the structure and maintenance of the cytoskeleton. Of the 15 genes expressed in platelets, the expression of WASL, a gene involved in actin filament organization, was increased in platelets of IRBD patients. Additionally, WASL expression correlated inversely with hsa-miR- 142 - 3p expression. Since the interactomes of hsa-miR- 139 - 5p and hsa-miR- 191 - 5p play a role in several cancer types, their expression was not addressed. Changes in hsa-miR- 142 - 3p, hsa-miR- 139 - 5p, and hsa-miR- 191 - 5p expression were found in IRBD platelets and might represent early biomarkers for LBD involving cytoskeleton dysfunction. Increased expression of WASL could indicate that altered platelet activation occurs early during the development of LBD.

The interplay between α-synuclein aggregation and necroptosis in Parkinson's disease: a spatiotemporal perspective

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the death of dopaminergic neurons and the aggregation of alpha-synuclein (α-Syn). It presents with prominent motor symptoms, and by the time of diagnosis, a significant number of neurons have already been lost. Current medications can only alleviate symptoms but cannot halt disease progression. Studies have confirmed that both dopaminergic neuronal loss and α-Syn aggregation are associated with necroptosis mechanisms. Necroptosis, a regulated form of cell death, has been recognized as an underexplored hotspot in PD pathogenesis research. In this review, we propose a spatiotemporal model of PD progression, highlighting the interactions between α-Syn aggregation, mitochondrial dysfunction, oxidative stress, neuroinflammation and necroptosis. These processes not only drive motor symptoms but also contribute to early non-motor symptoms, offering insights into potential diagnostic markers. Finally, we touch upon the therapeutic potential of necroptosis inhibition in enhancing current PD treatments, such as L-Dopa. This review aims to provide a new perspective on the pathogenesis of PD and to identify avenues for the development of more effective therapeutic strategies.

Alpha-synuclein aggregation induces prominent cellular lipid changes as revealed by Raman spectroscopy and machine learning analysis

The aggregation of α-synuclein is a central neuropathological hallmark in neurodegenerative disorders known as Lewy body diseases, including Parkinson's disease and dementia with Lewy bodies. In the aggregation process, α-synuclein transitions from its native disordered/α-helical form to a β-sheet-rich structure, forming oligomers and protofibrils that accumulate into Lewy bodies, in a process that is thought to underlie neurodegeneration. Lipids are thought to play a critical role in this process by facilitating α-synuclein aggregation and contributing to cell toxicity, possibly through ceramide production. This study aimed to investigate biochemical changes associated with α-synuclein aggregation, focusing on lipid changes, using Raman spectroscopy coupled with machine learning. HEK293, Neuro2a and SH-SY5Y expressing increased levels of α-synuclein were treated with sonicated α-synuclein pre-formed fibrils, to model seeded aggregation. Raman spectroscopy, complemented by an in-house lipid spectral library, was used to monitor the aggregation process and its effects on cellular viability over 14 days. We detected α-synuclein aggregation by assessing β-sheet peaks at 1045 cm⁻1, in cells treated with α-synuclein pre-formed fibrils, using machine learning (principal component analysis and uniform manifold approximation and projection) analysis based on Raman spectral features. Changes in lipid profiles, and especially sphingolipids, including a decrease in sphingomyelin and increase in ceramides, were observed, consistent with oxidative stress and apoptosis. Altogether, our study informs on biochemical alterations that can be considered for the design of therapeutic strategies for Parkinson's disease and related synucleinopathies.

Neurotropic Viruses as Acute and Insidious Drivers of Aging

Aging is the result of various compounding stresses that gradually overcome the homeostatic regulation of the cell, resulting in irreversible damage. This manifests as many acute and chronic conditions, the most common of which are neurodegeneration and dementia. Epidemiological studies have shown significant, strong correlations between viral infection and neurodegenerative diseases. This review overlays the characteristics of viral pathogenesis with the hallmarks of aging to discuss how active and latent viruses contribute to aging. Through our contextualization of myriad basic science papers, we offer explanations for premature aging via viral induction of common stress response pathways. Viruses induce many stresses: dysregulated homeostasis by exogenous viral proteins and overwhelmed protein quality control mechanisms, DNA damage through direct integration and epigenetic manipulation, immune-mediated oxidative stress and immune exhaustion, and general energy theft that is amplified in an aging system. Overall, this highlights the long-term importance of vaccines and antivirals in addition to their acute benefits.

Luteolin Exhibits Anxiolytic and Antidepressant Potential in Parkinson's Disease Rat: Antioxidant and Anti-Inflammatory Effects

Parkinson's disease (PD) is accompanied by a complex array of nonmotor and motor manifestations. The exploration of anti-inflammatory and antioxidant active ingredient as potential therapeutic interventions in PD-associated mood alterations has gained significant attention. This study aimed to assess the antidepressant and anxiolytic properties of luteolin (LTN), a potent antioxidant and anti-inflammatory component, using a 6-hydroxydopamine (6-OHDA)-induced animal model of PD. Rats were administered LTN (10, 25, and 50 mg/kg, per oral) and fluoxetine (10 mg/kg/per oral) over a 28-day period. Behavioral tests were employed to estimate the depression- and anxiety-like behaviors. Rats treated with LTN exhibited significant improvement in 6-OHDA-induced mood alterations, as per behavioral tests. Additionally, LTN treatment led to increased hippocampal levels of catalase and superoxide dismutase, and a reduction in malondialdehyde. LTN downregulated the gene expression of nuclear factor kappa B (NF-κB)/nod-like receptor (NLR) pyrin domain-containing 3 (NLRP3) axis components, including NF-κB, NLRP3, ASC, and Caspase1 and reduced the protein level of pro-inflammatory cytokines, including interleukin (IL)-6, interleukin (IL)-1β, and tumor necrosis factor alpha (TNF-α), in addition to augmenting the protein levels of TNF-α, IL-1β, and IL-6. Furthermore, LTN exhibited an upregulatory effect on the anti-inflammatory cytokine IL-10 within the hippocampus of 6-OHDA-induced PD rats. Also, molecular docking showed higher affinity between LTN and NF-κB/NLRP3 axis components. These findings highlight the potential anxiolytic and antidepressant impacts of LTN through its antioxidant and anti-inflammatory mechanisms against 6-OHDA-induced alterations in a rat PD model.

Criterion for Assessing Accumulated Neurotoxicity of Alpha-Synuclein Oligomers in Parkinson's Disease

The paper introduces a parameter called "accumulated neurotoxicity" of α-syn oligomers, which measures the cumulative damage these toxic species inflict on neurons over time, given the years it typically takes for such damage to manifest. A threshold value for accumulated neurotoxicity is estimated, beyond which neuron death is likely. Numerical results suggest that rapid deposition of α-syn oligomers into fibrils minimizes neurotoxicity, indicating that the formation of Lewy bodies might play a neuroprotective role. Strategies such as reducing α-syn monomer production or enhancing degradation can decrease accumulated neurotoxicity. In contrast, slower degradation (reflected by longer half-lives of monomers and free aggregates) increases neurotoxicity, supporting the idea that impaired protein degradation may contribute to Parkinson's disease progression. Accumulated neurotoxicity is highly sensitive to the half-deposition time of free α-syn aggregates into fibrils, exhibiting a sharp increase as it transitions from negligible to elevated levels, indicative of neural damage.

Alpha-Synuclein Pathophysiology in Neurodegenerative Disorders: A Review Focusing on Molecular Mechanisms and Treatment Advances in Parkinson's Disease

Worldwide aging has contributed to the growth of prevalence of neurodegenerative diseases (NDDs), including Parkinson's disease among the elderlies. The advanced destruction of dopaminergic neurons in the substantia nigra, due to many accelerator factors in the brain is the main mechanism of Parkinson's disease. The pathological aggregated alpha-synuclein (α-syn), a protein implicated in multiple neurodegenerative disorders, is one of the critical factors in this neurodegenerative disease and other similar disorders. The misfolding and aggregation of α-syn may interrupt critical processes, including functions of synaptic vesicles and can lead to neuronal death. This protein is encoded by Alpha-Synuclein Gene (SNCA) and mutation in this gene can lead to dysfunctions of the protein structure. Since, therapeutic policies that aim α-syn are promising approaches. Advances in immunotherapies, molecular chaperones, gene therapy targeting SNCA, and DNA aptamers are some examples of this strategy. This review aims to comprehensively assess the current knowledge and evidence on α-syn pathology, genetic determinants, and novel therapeutic methods in Parkinson,'s disease and other synucleinopathies. Continued investigation to discover interventions in this system could result in finding of effective and safe treatments for NDDs.

Alpha-synuclein knockout impairs melanoma development and alters DNA damage repair in the TG3 mouse model in a sex-dependent manner

Introduction

Strong evidence suggests links between Parkinson's Disease (PD) and melanoma, as studies have found that people with PD are at an increased risk of developing melanoma and those with melanoma are at increased risk of developing PD. Although these clinical associations are well-established, the cellular and molecular pathways linking these diseases are poorly understood. Recent studies have found a previously unrecognized role for the neurodegeneration-associated protein alpha-synuclein (αSyn) in melanoma; the overexpression of αSyn promotes melanoma cell proliferation and metastasis. However, to our knowledge, no studies have investigated the role of αSyn in in vivo melanoma models outside of a xenograft paradigm.

Methods

Our study created and characterized Snca knockout in the spontaneously developing melanoma TG3 mouse line, TG3+/+Snca-/-.

Results

We show that αSyn loss-of-function significantly delays melanoma onset and slows tumor growth in vivo in males. Furthermore, decreased tumor volume is correlated with a decreased DNA damage signature and increased apoptotic markers, indicating a role for αSyn in modulating the DNA damage response (DDR) pathway.

Discussion

Overall, our study may suggest that targeting αSyn and its role in modulating the DDR and melanomagenesis could serve as a promising new therapeutic target.

α-synuclein expression in glioblastoma restores tumor suppressor function and rescues temozolomide drug resistance

Several studies have shown that Parkinson's disease causative gene products, including α-synuclein (α-syn), display tight links with the tumor suppressor p53. The purpose of this study is to determine the implication of α-syn in glioblastoma development and elucidate how it elicits a tumor suppressor function. We show that the expression of α-syn, a TP53 transcriptional target and a key molecular player in Parkinson's disease, is detected in 1p/19q-codeleted and isocitrate dehydrogenase (IDH)-mutant oligodendroglioma and in IDH-wild-type glioblastoma, while reduced in glioblastoma biopsies, corroborating the link of α-syn expression with a better prognosis among all glioma patients. Accordingly, protein expression is drastically reduced in oligodendrogliomas and glioblastoma biopsies. This could be accounted for by a reduction of p53 transcriptional activity in these samples. Interestingly, genetic manipulation of p53 in glioblastoma cells and in mouse brain shows that p53 up-regulates α-synuclein, a phenotype fully abolished by the prominent p53 hot spot mutation R175H. Downstream to its p53-linked control, α-syn lowers cyclin D1 protein and mRNA levels and reduces glioblastoma cells proliferation in a cyclin D1-dependent-manner. Further, in temozolomide (TMZ)-resistant U87 cells, α-syn reduces O6-methylguanine-DNA methyltransferase (MGMT) expression and rescues drug sensitivity by a mechanism implying its transcriptional activation by X-box binding protein 1 (XBP1), an effector of the UPR response. Furthermore, α-syn lowers MGMT and cyclin D1 (CCDN1) expressions and reduces tumor development in allografted mice. Overall, our data reveals a new role of α-syn as an oligodendroglioma biomarker and as a glioblastoma tumor suppressor capable of either potentiate TMZ effect or avoid TMZ-associated resistance.

Revealing protein sequence organization via contiguous hydrophobicity with the blobulator toolkit

Clusters of hydrophobic residues are known to promote structured protein stability and drive protein aggregation. Recent work has shown that identifying contiguous hydrophobic residue clusters within protein sequences (termed "blobs") has proven useful in both intrinsically disordered protein (IDP) simulation and human genome studies. However, an accessible toolkit was unavailable, and the role that blobs play across the structural context of a variety of protein families remained unclear. Here, we present the blobulator toolkit: consisting of a webtool, a command line interface, and a VMD plugin. We demonstrate how identifying blobs using biologically relevant parameters provides useful information about a globular protein, two orthologous membrane proteins, and an IDP. Other potential applications are discussed, including: predicting protein segments with critical roles in tertiary interactions, providing a definition of local order and disorder with clear edges, and aiding in predicting protein features from sequence. The blobulator webtool can be found at www.blobulator.branniganlab.org, and the source code with pip installable command line tool, as well as the VMD plugin with installation instructions, can be found on GitHub at www.GitHub.com/BranniganLab/blobulator.

Human biodistribution and radiation dosimetry of two novel α-synuclein PET tracers, 18F-SPAL-T-06 and 18F-C05-05

18F-SPAL-T-06 and 18F-C05-05 are two novel positron emission tomography (PET) radioligands targeting α-synuclein fibrils. Our study aimed to evaluate the biodistribution, safety, and radiation dosimetry of each tracer in humans. Biodistribution and radiation dosimetry studies were carried out with two healthy volunteers for each tracer, 18F-SPAL-T-06 (one female and one male volunteer, both aged 63 years) and 18F-C05-05 (one female and one male volunteer, aged 63 and 73 years, respectively). After injection of either tracer, dynamic PET images were acquired from head to upper thigh. Effective dose of each tracer was estimated using OLINDA/EXM Version 2.2. Injection of either of the tracers caused no adverse effects. Greatest uptake of both tracers was observed in the liver and small intestine. The estimated absorbed doses were highest in the biliary tract, followed by the lower large intestinal wall. Effective doses were 35.9 µSv/MBq for 18F-SPAL-T-06 and 30.5 µSv/MBq for 18F-C05-05. 18F-SPAL-T-06 and 18F-C05-05 are safe for in vivo PET imaging of humans. Their mean effective doses were 6.6 mSv for 18F-SPAL-T-06 and 5.6 mSv for 18F-C05-05 when 185 MBq of either tracer was given to a subject, and they were comparable to other amyloid and tau PET tracers labelled with 18F.Trial registration Trial registration number: jRCTs031210180, Registered date: 2nd July 2021 (18F-SPAL-T-06) https://jrct.niph.go.jp/en-latest-detail/jRCTs031210180 and Trial registration number: jRCTs031220123, Registered date: 9th June 2022 (18F-C05-05) https://jrct.niph.go.jp/en-latest-detail/jRCTs031220123 .

Distinguish risk genes functioning at presynaptic or postsynaptic regions and key connectomes associated with pathological α-synuclein spreading

Previous studies have suggested that pathological α-synuclein (α-Syn) mainly transmits along the neuronal network, but several key questions remain unanswered: (1) How many and which connections in the connectome are necessary for predicting the progression of pathological α-Syn? (2) How to identify risk gene that affects pathology spreading functioning at presynaptic or postsynaptic regions, and are these genes enriched in different cell types? Here, we addressed these key questions with novel mathematical models. Strikingly, the spreading of pathological α-Syn is predominantly determined by the key subnetworks composed of only 2% of the strongest connections in the connectome. We further explored the genes that are responsible for the selective vulnerability of different brain regions to transmission to distinguish the genes that play roles in presynaptic from those in postsynaptic regions. Those risk genes were significantly enriched in microglial cells of presynaptic regions and neurons of postsynaptic regions. Gene regulatory network analyses were then conducted to identify 'key drivers' of genes responsible for selective vulnerability and overlapping with Parkinson's disease risk genes. By identifying and discriminating between key gene mediators of transmission operating at presynaptic and postsynaptic regions, our study has demonstrated for the first time that these are functionally distinct processes.

Associations among blood biomarkers, clinical subtypes, and prognosis in Parkinson's disease

Background

Early identification of the poor prognosis subtype by surrogate markers would be advantageous for selecting treatments for Parkinson's disease (PD). The aim of the present study was to test whether plasma neurofilament light chain (NF-L), total tau (t-tau), ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1), fatty acid-binding protein 3 (FABP3), and phosphorylated tau (p-tau) can be used as prognostic biomarkers in PD.

Methods

In the present study, both retrospective and prospective studies were performed. Plasma samples at baseline from 81 PD patients were included in the prospective study. Plasma samples at baseline from 60 patients who underwent cognitive assessment were subjected to the hierarchical cluster analysis for a retrospective study.

Results

On the basis of the results of the cluster analysis, patients were classified into three groups: groups (G)1, G2 and G3. Individuals in the G1 cluster, who had an older age at onset and were prone to early progression with dementia, had significantly greater plasma NF-L levels than those in the G3 cluster, who did not present with dementia at an early stage. A Cox proportional hazards regression model adjusted for age and sex revealed that high NF-L and UCH-L1 levels at baseline predicted the four future milestones (i.e., nursing care, dysphagia, wheelchair use, and repeated falls), and high plasma t-tau at baseline predicted future dysphagia.

Conclusions

Although further studies with a larger number of patients will be required, plasma NF-L may be a useful biomarker for identifying the rapidly progressive subtype of PD, and plasma NF-L and UCH-L1 may serve as biomarkers of overall PD prognosis, whereas plasma t-tau could be a biomarker for future dysphagia in PD.

Longitudinal multi-omics in alpha-synuclein Drosophila model discriminates disease- from age-associated pathologies in Parkinson's disease

Parkinson's disease (PD) starts decades before symptoms appear, usually in the later decades of life, when age-related changes are occurring. To identify molecular changes early in the disease course and distinguish PD pathologies from aging, we generated Drosophila expressing alpha-synuclein (αSyn) in neurons and performed longitudinal bulk transcriptomics and proteomics on brains at six time points across the lifespan and compared the data to healthy control flies as well as human post-mortem brain datasets. We found that translational and energy metabolism pathways were downregulated in αSyn flies at the earliest timepoints; comparison with the aged control flies suggests that elevated αSyn accelerates changes associated with normal aging. Unexpectedly, single-cell analysis at a mid-disease stage revealed that neurons upregulate protein synthesis and nonsense-mediated decay, while glia drive their overall downregulation. Longitudinal multi-omics approaches in animal models can thus help elucidate the molecular cascades underlying neurodegeneration vs. aging and co-pathologies.

Correlative light and electron microscopy imaging of proteinaceous deposits in cell cultures and brain tissues

Identifying protein deposits and associated components is crucial for understanding the pathogenesis of neurodegenerative disorders with intracellular or extracellular deposits. Correlative light and electron microscopy (CLEM) has emerged as a powerful tool to accurately study tissue and cellular pathology by examination of the same target at both microstructural and ultrastructural levels. However, the technical challenges with CLEM have limited its application to neuropathology. Here, we developed a simplified efficient CLEM method and applied it to a cell model that produces a high proportion of α-synuclein (αS) inclusions with immunopositivity to phosphorylated αS and the synaptic vesicle marker SV2A and synaptophysin. This approach incorporates modifications in sample processing and innovative fiducial marking techniques, which enhance antigen preservation and improve target registration, respectively. These advancements achieve an optimal balance in sensitivity, accuracy, efficiency, and cost-effectiveness compared to current CLEM methods employing different strategies. Using this method, we identified and analyzed αS inclusions in cell cultures, as well as various pathological protein deposits in postmortem brain tissues from individuals with a range of neurodegenerative disorders. Our findings replicate recently reported new features of αS pathology and also reveal unrecognized a variety forms of small αS inclusions in human brain, which provide valuable insights into mechanisms underlying Lewy-related pathology. Application of this enhanced CLEM method is a powerful tool in research on neurodegenerative disorders, including αS-opathies.

Tissue macrophages: origin, heterogenity, biological functions, diseases and therapeutic targets

Macrophages are immune cells belonging to the mononuclear phagocyte system. They play crucial roles in immune defense, surveillance, and homeostasis. This review systematically discusses the types of hematopoietic progenitors that give rise to macrophages, including primitive hematopoietic progenitors, erythro-myeloid progenitors, and hematopoietic stem cells. These progenitors have distinct genetic backgrounds and developmental processes. Accordingly, macrophages exhibit complex and diverse functions in the body, including phagocytosis and clearance of cellular debris, antigen presentation, and immune response, regulation of inflammation and cytokine production, tissue remodeling and repair, and multi-level regulatory signaling pathways/crosstalk involved in homeostasis and physiology. Besides, tumor-associated macrophages are a key component of the TME, exhibiting both anti-tumor and pro-tumor properties. Furthermore, the functional status of macrophages is closely linked to the development of various diseases, including cancer, autoimmune disorders, cardiovascular disease, neurodegenerative diseases, metabolic conditions, and trauma. Targeting macrophages has emerged as a promising therapeutic strategy in these contexts. Clinical trials of macrophage-based targeted drugs, macrophage-based immunotherapies, and nanoparticle-based therapy were comprehensively summarized. Potential challenges and future directions in targeting macrophages have also been discussed. Overall, our review highlights the significance of this versatile immune cell in human health and disease, which is expected to inform future research and clinical practice.

Autoantibodies against α-synuclein inhibit its aggregation and cytotoxicity

Aggregates of α-synuclein (α-Syn) are the major component of the Lewy bodies associated with Parkinson's disease. Recently, naturally occurring autoantibodies against α-synuclein (α-Syn-nAbs) were detected. Herein we have isolated and further characterized such α-Syn-nAbs. Using an affinity column coated with α-Syn, we have isolated α-Syn-nAbs from a commercially available intravenous Immunoglobulin (IVIg) preparation. A methodological approach based on ELISA, Western blotting and immunoprecipitation as well as surface plasmon resonance, was used to determine binding capacity to α-Syn. The epitope was determined via peptide array membrane and the functionality was tested in vitro using a toxicity and a fibrillation assay. The autoantibodies display strong binding capacity to α-Syn as demonstrated by ELISA, immunoprecipitation and Western blotting analysis. The binding affinities of the purified autoantibodies were analyzed in detail by surface plasmon resonance (Biacore). The epitope on α-Syn that is recognized by the α-Syn nAbs was fully determined. A sequence within the non-amyloid component (NAC)-Region of α-Syn is crucial for the binding of α-Syn-nAbs to α-Syn. Furthermore, the α-Syn-nAbs had an inhibitory effect on α-Syn fibril formation and were also able to specifically reverse the toxicity of α-Syn oligomers species in human neuroblastoma (SH-SY5Y) cells. Our results emphasize the possible importance of naturally occurring autoantibodies for the pathogenesis of Parkinson's disease. Since autoantibodies against α-Syn are detectable in human serum and cerebrospinal fluid and interfere with pathological events associated with α-Syn, they may provide a candidate for the treatment of Parkinson's disease.

PD-Like Pathogenesis in Caenorhabditis elegans Intestinally Infected with Nocardia farcinica and the Underlying Molecular Mechanisms

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the abnormal aggregation of α-synuclein (α-syn) and the loss of dopaminergic neurons. Although microbial infection has been implicated in the pathogenesis of PD, the associated virulence factors and the underlying molecular mechanisms require further elucidation. Here, we found that intestinal infection with Nocardia farcinica induced a series of PD-like symptoms in Caenorhabditis elegans, such as the accelerated degeneration of dopaminergic neurons, impaired locomotion capacity, and enhanced α-syn aggregation, through the disturbance of mitochondrial functions. To identify the potential virulence factors involved in these effects, we knocked out the nbtB/C and nbtS genes in N. farcinica, which are localized in the gene clusters responsible for nocobactin biosynthesis. The deletion of either gene partially rescued the degenerative effects of wild-type N. farcinica on dopaminergic neurons by attenuating mitochondrial dysfunction. LC-MS analysis further identified a decrease in the abundance of several siderophores in the two mutants, including nocobactin NA-a, nocobactin NA-b, and nocardimicin B. Collectively, our results demonstrated that intestinal N. farcinica infection in C. elegans facilitates PD-like pathogenesis and provides novel evidence for the involvement of pathogenic bacteria in neurodegenerative diseases via non-neuroinvasive mechanisms.

Structural and functional connectomics of the olfactory system in Parkinson's disease: a systematic review

Olfactory dysfunction, affecting 75-90 % of Parkinson's disease (PD) patients, holds significant predictive value for PD development. Advanced imaging techniques, such as diffusion MRI (dMRI) and functional MRI (fMRI), offer insights into structural and functional changes within olfactory pathways. This review summarizes a decade of research on MRI-based connectivity of the olfactory system in PD, focusing on structural and functional alterations in olfactory brain areas and their links to early olfactory processing changes. Fifteen dMRI and eighteen fMRI studies met inclusion criteria and were carefully reviewed. Among the studies investigating diffusion metrics, the most consistent finding was the reduction of fractional anisotropy in the olfactory tract and anterior olfactory structures, though evidence correlating this result to olfactory dysfunction is limited and contrasting. dMRI support the hypothesis that olfactory function may be correlated to structural alterations at the network-level. In contrast, fMRI studies found more consistent evidence of dysconnectivity in both primary and secondary olfactory areas as directly correlated to olfactory processing and dysfunction. Results suggest a potential dissociation between structural alterations in olfactory brain regions and early functional impairment in olfactory processing, likely related to different patient subtypes. Heterogeneity in clinical and technical factors may limit the generalizability of the results, leaving room for further investigations. By providing a comprehensive perspective on the use of dMRI and fMRI to explore the olfactory connectome in PD, our review might facilitate future research towards earlier diagnosis and more targeted therapeutic and neurorehabilitation strategies.

Limitations and Applications of Rodent Models in Tauopathy and Synucleinopathy Research

Rodent models that accurately recapitulate key aspects of human disease have long been fundamental to the successful development of clinical interventions. This is greatly underscored in the neurodegenerative disease field, where preclinical testing of anti-prion therapeutics against rodent-adapted prions resulted in the development of small molecules effective against rodent-adapted prions but not against human prions. These findings provided critical lessons for ongoing efforts to develop treatments for patients with neurodegenerative diseases caused by misfolding and accumulation of the proteins tau and α-synuclein, or tauopathies and synucleinopathies, respectively. To avoid the potential pitfalls previously identified in the prion field, this review focuses on rodent models currently available to study tau and α-synuclein disease pathogenesis, emphasizing the strengths and limitations of each with the particular goal of better supporting preclinical research.

Salivary biomarkers for the molecular diagnosis of dementia with Lewy bodies

BackgroundDespite dementia with Lewy bodies (DLB) being the second most common form of neurodegenerative dementia, more than 80% of DLB cases are initially misdiagnosed. Alpha-synuclein (a-syn) and tau species have been detected in peripheral tissues and biological fluids of DLB patients and among different biological fluids, saliva represent an easely accessible and non-invasive source for biomarker detection.ObjectiveThis study aimed to investigate salivary a-syn and tau species as molecular disease biomarkers, assessing their potential in the diagnosis of DLB and in the differential diagnosis on respect to Alzheimer's disease (AD) and Parkinson's disease (PD).MethodsWe measured total and oligomeric a-syn, total-tau, and S199-phosphorylated-tau (pS199-tau) in the saliva of 21 DLB, 20 AD, 20 PD patients, and 20 healthy subjects (HS) using quantitative enzyme-linked immunosorbent assay (ELISA) analyses.ResultsSalivary total a-syn was not significantly changed between the different groups, whereas all pathological groups had a higher oligomeric a-syn concentration than HS. Salivary total-tau concentration was higher in all the pathological groups than HS, whereas the concentrations did not differ among patients' groups. Conversely, salivary levels of pS199-tau was higher in DLB and AD patients than in HS and PD patients. Both correlation matrix and principal component analysis showed that core clinical DLB features were related to a-syn pathology, while cognitive decline was associated with salivary levels of pS199-tau in both DLB and AD patients. Receiver operating characteristic analysis reported high diagnostic accuracy for both a-syn oligomers and pS199-tau, between DLB and HS, and an adequate accuracy between DLB and PD. Conversely, the diagnostic accuracy was not optimal between DLB patients and AD patients.ConclusionsThese findings provide preliminary evidence that salivary a-syn and tau species might be promising in identifying DLB patients on respect to PD patients and HS, while the diagnostic potential is limited on respect to AD.

SENP2-based N-terminal truncation of α-synuclein in Lewy pathology propagation

α-Synuclein (αSyn) is a major component of Lewy bodies (LBs) and Lewy neurites (LNs), which are pathological features of Parkinson's disease (PD) and dementia with Lewy bodies. In the PD brain, with disease progression, LB/LN formation is propagated from the lower brainstem to the cerebral cortex. Prion-like cell-to-cell seed transmission has been implicated as an underlying mechanism for Lewy-pathology propagation. However, the biochemical properties and production mechanism of those pathogenic seeds are unelucidated. In this study, we ascertained that the seeds released from pathological neurons that harbor LB/LN-like aggregates have the N-terminally truncated form of αSyn. This N-terminal truncation is directly catalyzed by SENP2, which is a well-known deSUMOylation enzyme. After SENP2 processing of recombinant αSyn, the SDS-resistant high-molecular oligomer formation was promoted in vitro. Inhibition of SENP2 activity suppressed aggregate formation and propagation in cultured neurons and mouse brains. Thus, SENP2 might be a therapeutic target in LB diseases.

Molecular Insights into α-Synuclein Fibrillation: A Raman Spectroscopy and Machine Learning Approach

The aggregation of α-synuclein is crucial to the development of Lewy body diseases, including Parkinson's disease and dementia with Lewy bodies. The aggregation pathway of α-synuclein typically involves a defined sequence of nucleation, elongation, and secondary nucleation, exhibiting prion-like spreading. This study employed Raman spectroscopy and machine learning analysis, alongside complementary techniques, to characterize the biomolecular changes during the fibrillation of purified recombinant wild-type α-synuclein protein. Monomeric α-synuclein was produced, purified, and subjected to a 7-day fibrillation assay to generate preformed fibrils. Stages of α-synuclein fibrillation were analyzed using Raman spectroscopy, with aggregation confirmed through negative staining transmission electron microscopy, mass spectrometry, and light scattering analyses. A machine learning pipeline incorporating principal component analysis and uniform manifold approximation and projection was used to analyze the Raman spectral data and identify significant peaks, resulting in differentiation between sample groups. Notable spectral shifts in α-synuclein were found in various stages of aggregation. Early changes (D1) included increases in α-helical structures (1303, 1330 cm-1) and β-sheet formation (1045 cm-1), with reductions in COO- and CH2 bond regions (1406, 1445 cm-1). By D4, these structural shifts persist with additional β-sheet features. At D7, a decrease in β-sheet H-bonding (1625 cm-1) and tyrosine ring breathing (830 cm-1) indicates further structural stabilization, suggesting a shift from initial helical structures to stabilized β-sheets and aggregated fibrils. Additionally, alterations in peaks related to tyrosine, alanine, proline, and glutamic acid were identified, emphasizing the role of these amino acids in intramolecular interactions during the transition from α-helical to β-sheet conformational states in α-synuclein fibrillation. This approach offers insight into α-synuclein aggregation, enhancing the understanding of its role in Lewy body disease pathophysiology and potential diagnostic relevance.

Cathepsin B prevents cell death by fragmentation and destruction of pathological amyloid fibrils

Amyloid fibrils cause organ and tissue dysfunction in numerous severe diseases. Despite the prevalence and severity of amyloidoses, there is still no effective and safe anti-amyloid therapy. This study investigates the impact of cysteine protease cathepsin B (CTSB) on amyloids associated with Alzheimer's and Parkinson's diseases, hemodialysis, and lysozyme amyloidosis. We analyzed the effect of CTSB on the size, structure, and proteotoxicity of amyloid fibrils formed from alpha-synuclein, abeta peptide (1-42), insulin, and lysozyme using a combination of spectroscopic, microscopic, electrophoretic, and colorimetric methods. Our comprehensive research revealed a dual effect of CTSB on amyloid fibrils. Firstly, CTSB induced amyloid fragmentation while preserving their ordered morphology, and, secondly, it "loosened" the tertiary structure of amyloids and reduced the regularity of the secondary structure. This dual mechanism of action was universal across fibrils associated with different pathologies, although the disruption efficacy and predominant type of degradation products depended on the amyloids' structure, size, and clustering. Notably, CTSB-induced irreversible degradation significantly reduced the toxicity for immortalized and primary cell lines of low-clustered fibrils, such as alpha-synuclein amyloids associated with Parkinson's disease. These findings enhance our understanding of how endogenous CTSB may regulate amyloid content at the molecular level in different neuropathologies. In addition, our results suggest the potential of CTSB as a component of anti-amyloid drugs in combination with agents that enhance the accessibility of proteolytic sites within amyloid clots and reduce these clusters stability.

α-Synuclein Degradation in Brain Pericytes Is Mediated via Akt, ERK, and p38 MAPK Signaling Pathways

Parkinson's disease (PD) is characterized by widespread distribution of Lewy bodies, which are composed of phosphorylated and aggregated forms of α-Synuclein (α-Syn), in the brain. Although the accumulation and propagation of α-Syn contribute to the development of PD, the involvement of the blood-brain barrier (BBB) in these processes remains unknown. Pericytes, one of the cell types that constitute the BBB, degrade various forms of α-Syn. However, the detailed mechanisms involved in α-Syn degradation by pericytes remain poorly understood. Therefore, in this study, we aimed to determine the ability of the BBB-constituting cells, particularly primary cultures of rat pericytes, brain endothelial cells, and astrocytes, to degrade α-Syn. After α-Syn uptake by the cells, intracellular α-Syn decreased only in pericytes. This pericyte-specific α-Syn decrease was inhibited by an autophagy inhibitor, bafilomycin A1, and a proteasome inhibitor, MG132. siRNA-mediated knockdown of degradation enzymes or familial PD-associated genes, including cathepsin D, DJ-1, and LRRK2, did not affect α-Syn clearance in pericytes. However, pharmacological inhibitors of Akt, ERK, and p38 MAPK inhibited α-Syn degradation by pericytes. In conclusion, our results suggest that α-Syn degradation by pericytes is mediated by an autophagy-lysosome system and a ubiquitin-proteasome system via α-Syn-activated Akt, ERK, and p38 MAPK signaling pathways.

Current trends in blood biomarkers detection and neuroimaging for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by both motor and cognitive impairments. A significant challenge in managing PD is the variability of symptoms and disease progression rates. This variability is primarily attributed to unclear biomarkers associated with the disease and the lack of early diagnostic technologies and effective imaging methods. PD-specific biomarkers are essential for developing practical tools that facilitate accurate diagnosis, patient stratification, and monitoring of disease progression. Hence, creating valuable tools for detecting and diagnosing PD based on specific biomarkers is imperative. Blood testing, less invasive than obtaining cerebrospinal fluid through a lumbar puncture, is an ideal source for these biomarkers. Although such biomarkers were previously lacking, recent advancements in various detection techniques related to PD biomarkers and new imaging methods have emerged. However, basic research requires more detailed guidelines on effectively implementing these biomarkers in diagnostic procedures to enhance the diagnostic accuracy of PD blood testing in clinical practice. This review discusses the developmental trends of PD-related blood biomarker detection technologies, including optical analysis platforms. Despite the progress in developing various biomarkers for PD, their specificity and sensitivity remain suboptimal. Therefore, the integration of multimodal biomarkers along with optical and imaging technologies is likely to significantly improve diagnostic accuracy and facilitate the implementation of personalized medicine. This review forms valid research hypotheses for PD research and guides future empirical studies.

TMEM106B C-terminal fragments aggregate and drive neurodegenerative proteinopathy in transgenic Caenorhabditis elegans

INTRODUCTION

Genetic variation in the lysosomal and transmembrane protein 106B (TMEM106B) modifies risk for several neurodegenerative disorders, especially frontotemporal lobar degeneration (FTLD). The C-terminal (CT) domain of TMEM106B occurs as fibrillar protein deposits in the brains of dementia patients.

METHODS

To determine the TMEM CT aggregation propensity and neurodegenerative potential, we generated transgenic Caenorhabditis elegans expressing the human TMEM CT fragment aggregating in FTLD cases.

RESULTS

Pan-neuronal expression of human TMEM CT in C. elegans causes severe neuronal dysfunction driving neurodegeneration.  Cytosolic aggregation of TMEM CT proteins accompanied by behavioral dysfunction and neurodegeneration. Loss of pgrn-1 did not modify TMEM CT phenotypes suggesting TMEM CT aggregation occurs downstream of PGRN loss of function. The mechanistic drivers of TMEM106B proteinopathy appear distinct from known modifiers of tauopathy.

DISCUSSION

Our data demonstrate that TMEM CT aggregation can kill neurons. TMEM106B transgenic C.elegans provide a useful model for characterizing TMEM106B proteinopathy-mediated neurodegeneration in FTLD.

HIGHLIGHTS

Pan-neuronal expression of human TMEM106B C-terminal fragments (TMEM CT) in C. elegans neurons drives a suite of disease-related phenotypes useful for modeling the molecular and cellular features of TMEM106B neuropathology. TMEM CT expression results in extensive TMEM aggregation and accumulation of highly detergent insoluble protein species. TMEM CT expression causes moderate to severe neuronal dysfunction dependent on TMEM CT abundance as measured by stereotypical behavioral readouts. TMEM CT expression drives significant neurodegenerative changes. Dendra2 tagged TMEM exhibits similar properties to untagged TMEM allowing ready visualization of the protein. TMEM CT aggregates accumulate adjacent to but not within lysosomes. PGRN loss of function does not impact TMEM CT toxicity. Modifiers of tau and TDP-43 proteinopathies have little impact on TMEM CT-related neurodegenerative phenotypes.

Individualized brain radiomics-based network tracks distinct subtypes and abnormal patterns in prodromal Parkinson's disease

Individuals in the prodromal phase of Parkinson's disease (PD) exhibit significant heterogeneity and can be divided into distinct subtypes based on clinical symptoms, pathological mechanisms, and brain network patterns. However, little has been done regarding the valid subtyping of prodromal PD, which hinders the early diagnosis of PD. Therefore, we aimed to identify the subtypes of prodromal PD using the brain radiomics-based network and examine the unique patterns linked to the clinical presentations of each subtype. Individualized brain radiomics-based network was constructed for normal controls (NC; N = 110), prodromal PD patients (N = 262), and PD patients (N = 108). A data-driven clustering approach using the radiomics-based network was carried out to cluster prodromal PD patients into higher-/lower-risk subtypes. Then, the dissociated patterns of clinical manifestations, anatomical structure alterations, and gene expression between these two subtypes were evaluated. Clustering findings indicated that one prodromal PD subtype closely resembled the pattern of NCs (N-P; N = 159), while the other was similar to the pattern of PD (P-P; N = 103). Significant differences were observed between the subtypes in terms of multiple clinical measurements, neuroimaging for morphological changes, and gene enrichment for synaptic transmission. Identification of prodromal PD subtypes based on brain connectomes and a full understanding of heterogeneity at this phase could inform early and accurate PD diagnosis and effective neuroprotective interventions.

Alpha-synuclein pathology enhances peripheral and CNS immune responses to bacterial endotoxins

Increasing evidence points to infectious diseases as contributor to the pathogenesis of neurodegeneration in Parkinson's disease (PD), probably driven by a peripheral and CNS inflammatory response together with alpha-synuclein (aSyn) pathology. Pro-inflammatory lipopolysaccharide (LPS) endotoxin is suggested as a risk factor, and LPS shedding gram-negative bacteria are more prevalent in the gut-microbiome of PD patients. Here, we investigated whether LPS could contribute to the neurodegenerative disease progression via neuroinflammation, especially under conditions of aSyn pathology. To investigate this, we created a double-hit model based on the Thy1-aSyn mouse line (line 61), an established aSyn-overexpression model of PD, exposed to a single intraperitoneal injection of LPS at a dose of 0.8 mg/kg (equivalent to approximately 1,200,000 EU/kg). Clinical parameters, flow cytometry of blood and immune cells in the brain, brain immunohistology and motor behavior were evaluated over time. As expected, the LPS dosage induced transient acute symptoms and mild weight loss in mice, with full recovery after 7 days. In aSyn over-expressing mice, this single low dose of LPS was sufficient to alter the expression of specific markers on blood and brain immune cells and induced brain region-specific microgliosis that were present at 7 days post LPS injection. At 14 days post injection of LPS, aSyn expression was reduced in wild-type mice, indicating a specific response of the endogenous protein to the endotoxin. At this early time point, motor behavior is not yet robustly impacted by the observed pathological alterations. In conclusion, aSyn pathology renders the peripheral and central immune response more sensitive to a single low dose of bacterial endotoxin, which mimics a transient dysbiosis or gut infection. Thus, this data suggests that such peripheral triggers should be monitored in PD patients for instance by blood immune cell response as biomarkers. Furthermore, results from this study lend further support to the development of treatments aiming to reduce the impact of bacterial dysbiosis as a promising strategy to mitigate PD progression.

α-Synuclein interaction with POPC/POPS vesicles

We have investigated the adsorption of the amyloid-forming protein α-Synuclein (αSyn) onto small unilamellar vesicles composed of a mixture of zwitterionic POPC and anionic POPS lipids. αSyn monomers adsorb onto the anionic lipid vesicles where they adopt an α-helical secondary structure. The degree of adsorption depends on the fraction of anionic lipid in the mixed lipid membrane, but one needs to consider the electrostatic shift of the serine pKa with increasing fraction of POPS. The vesicles with adsorbed αSyn monomers are kinetically stable. However, after fibrils have been formed, here triggered by the addition of a small concentration of pre-formed fibrils (seeds), we observed that the average vesicle size increased by approximately a factor of two. This increase in the vesicle size can be explained by vesicle fusion taking place during the fibril formation process.

Synaptic phosphoproteome modifications and cortical circuit dysfunction are linked to the early-stage progression of alpha-synuclein aggregation

Cortical dysfunction is increasingly recognized as a major contributor to the non-motor symptoms associated with Parkinson's disease (PD) and other synucleinopathies. Although functional alterations in cortical circuits have been observed in preclinical PD models, the underlying molecular mechanisms are unclear. To bridge this knowledge gap, we investigated tissue-level changes in the cortices of rats and mice treated with alpha-synuclein (aSyn) seeds using a multi-omics approach. Our study revealed significant phosphoproteomic changes, but not global proteomic or lipid profiling changes, in the rat sensorimotor cortex 3 months after intrastriatal injection with aSyn preformed fibrils (PFFs). Gene ontology analysis of the phosphoproteomic data indicated that PFF administration impacted pathways related to synaptic transmission and cytoskeletal organization. Similar phosphoproteomic perturbations were observed in the sensorimotor cortex of mice injected intrastriatally or intracortically with aSyn PFFs. Functional analyses demonstrated increased neuronal firing rates and enhanced spike-spike coherence in the sensorimotor cortices of PFF-treated mice, indicating seed-dependent cortical circuit dysfunction. Bioinformatic analysis of the altered phosphosites suggested the involvement of several kinases, including casein kinase-2 (CK2), which has been previously implicated in PD pathology. Collectively, these findings highlight the importance of phosphorylation-mediated signaling pathways in the cortical response to aSyn pathology spread in PD and related synucleinopathies, setting the stage for developing new therapeutic strategies.

Acute lipid droplet accumulation induced by the inhibition of the phospholipase DDHD2 does not affect the level, solubility, or phosphoserine-129 status of α-synuclein

α-Synuclein (αS) is a 140 amino-acid neuronal protein highly enriched in presynaptic nerve terminals. Its progressive accumulation in Lewy bodies and neurites is the hallmark of Parkinson's disease (PD). A growing number of studies highlights a critical interplay between lipid metabolism and αS biology. Some of these works postulate a physical interaction between αS and lipid droplets (LDs), but further clarity is needed, not least because typically exogenous αS and/or heterologous systems have been studied. Here, we investigated the effects of acute LD accumulation on endogenous wild-type αS in primary rat cortical neurons. To induce robust LD accumulation within hours, we inhibited the neuronal triacylglycerol hydrolase DDHD2, a phospholipase, using the compound KLH45. KLH45-induced LD accumulation did not affect total levels, phosphoserine-129 status, or solubility of αS, and no co-localization between LDs and αS was observed under these conditions. These findings suggest that a "second hit" and/or a specific LD lipid composition may be necessary for lipid excess to affect αS homeostasis. Our work thus contributes to the debate on αS structure and lipid interaction.

Deciphering the Seed Size-Dependent Cellular Internalization Mechanism for α-Synuclein Fibrils

Aggregation of α-synuclein (α-Syn) and Lewy body (LB) formation are the key pathological events implicated in Parkinson's disease (PD) that spread in a prion-like manner. However, biophysical and structural characteristics of toxic α-Syn species and molecular events that drive early events in the propagation of α-Syn amyloids in a prion-like manner remain elusive. We used a neuronal cell model to demonstrate the size-dependent native biological activities of α-Syn fibril seeds. Biophysical characterization of the fibril seeds generated by controlled fragmentation indicated that increased fragmentation leads to a reduction in fibril size, correlating directly with the extent of fragmentation events. Although the size-based complexity of amyloid fibrils modulates their biological activities and fibril amplification pathways, it remains unclear how the variability of fibril seed size dictates its specific uptake mechanism into the cells. The present study elucidates the mechanism of α-Syn fibril internalization and how it is regulated by the size of fibril seeds. Further, we demonstrate that size-dependent endocytic pathways (dynamin-dependent clathrin/caveolin-mediated) are more prominent for the differential uptake of short fibril seeds compared to their longer counterparts. This size-dependent preference might contribute to the enhanced uptake and transcellular propagation of short α-Syn fibril seeds in a prion-like manner. Overall, the present study suggests that the physical dimension of α-Syn amyloid fibril seeds significantly influences their cellular uptake and pathological responses in the initiation and progression of PD.

Lipid Packing Defects are Necessary and Sufficient for Membrane Binding of α-Synuclein

α-Synuclein (αSyn), an intrinsically disordered protein implicated in Parkinson's disease, is potentially thought to initiate aggregation through binding to cellular membranes. Previous studies have suggested that anionic membrane charge is necessary for this binding. However, these studies largely focus on unmodified αSyn, while nearly all αSyn in the body is N-terminally acetylated (NTA). NTA dramatically shifts the narrative by diminishing αSyn's reliance on anionic charge for membrane binding. Instead, we demonstrate that membrane packing defects are the dominant forces driving NTA-αSyn interactions, challenging the long-standing paradigm that anionic membranes are essential for αSyn binding. Using fluorescence microscopy and circular dichroism spectroscopy, we monitored the binding of NTA-αSyn to reconstituted membrane surfaces with different lipid compositions. Phosphatidylcholine and phosphatidylserine concentrations were varied to control surface charge, while phospholipid tail unsaturation and methylation were varied to control lipid packing. All-atom molecular dynamics simulations of lipid bilayers supported the observation that membrane packing defects are necessary for NTA-αSyn binding and that defect-rich membranes are sufficient for NTA-αSyn binding regardless of membrane charge. We further demonstrated that this affinity for membrane defects persisted in reconstituted, cholesterol-containing membranes that mimicked the physiological lipid composition of synaptic vesicles. Increasing phospholipid unsaturation in these mimics led to more membrane packing defects and a corresponding increase in NTA-αSyn binding. Altogether, our results point to a mechanism for the regulation of NTA-αSyn binding in biological membranes that extends beyond phospholipid charge to the structural properties of the lipids themselves.