Pathological α-synuclein transmission initiates Parkinson-like neurodegeneration in nontransgenic mice

Possible regulation of the immune modulator tetraspanin CD81 by alpha-synuclein in melanoma

We probed the mechanism by which the Parkinson's disease-associated protein α-synuclein (α-syn)/SNCA promotes the pathogenesis and progression of melanoma. We found that the human melanoma cell line SK-MEL-28 in which SNCA is knocked out (SNCA-KO) has low levels of tetraspanin CD81, which is a cell-surface protein that promotes invasion, migration, and immune suppression. Analyzing data from the Cancer Genome Atlas, we show that SNCA and CD81 mRNA levels are positively correlated in melanoma; melanoma survival is inversely related to the levels of SNCA and CD81; and SNCA/CD81 are inversely related to the expression of key cytokine genes (IL12A, IL12B, IFN, IFNG, PRF1 and GZMB) for immune activation and immune cell-mediated killing of melanoma cells. We propose that high levels of α-syn and CD81 in melanoma and in immune cells drive invasion and migration and in parallel cause an immunosuppressive microenvironment; these contributing factors lead to aggressive melanomas.

Intracerebroventricular injection of α-synuclein preformed fibrils do not induce motor and olfactory impairment in C57BL/6 mice

INTRODUCTION

Alpha-synuclein (αSyn) is believed to play a central role in the pathogenesis of Parkinson's disease (PD). Cerebrospinal fluid (CSF) total αSyn were significantly lower in PD patients, whereas the aggregates were higher, and this phenomenon was further exacerbated with longer disease duration. However, whether CSF αSyn can be the cause and/or a consequence in PD is not fully elucidated.

METHOD

We administered 2 ng or 200 ng αSyn preformed fibrils (PFFs) by intracerebroventricular injection for consecutive 7 days in C57BL/6 mice. The olfactory function was assessed by the olfactory discrimination test and buried food-seeking test. The locomotor function was assessed by the rotarod test, pole test, open field test and CatWalk gait analysis. Phosphorylated αSyn at serine 129 was detected by the immunohistochemistry staining. Iron levels was determined by Perl's-diaminobenzidine iron staining and synchrotron-based X-ray fluorescence.

RESULTS

The mice did not exhibit any diffuse synucleinopathy in the brain for up to 30 weeks, although αSyn PFFs induced aggregation in SH-SY5Y cells and in the substantia nigra and striatum of mice with stereotactic injection. No impairment of motor behaviors or olfactory functions were observed, although there was a temporary motor enhancement at 1 week. We then demonstrated iron levels were comparable in certain brain regions, suggesting there was no iron deposition/redistribution occurred.

CONCLUSION

The intraventricular injection of αSyn PFFs does not induce synucleinopathy or behavioral symptoms. These findings have implications that CSF αSyn aggregates may not necessarily contribute to the onset or progression in PD.

Posttranslational Modifications of -Synuclein, Their Therapeutic Potential, and Crosstalk in Health and Neurodegenerative Diseases

α-Synuclein (α-Syn) aggregation in Lewy bodies and Lewy neurites has emerged as a key pathogenetic feature in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Various factors, including posttranslational modifications (PTMs), can influence the propensity of α-Syn to misfold and aggregate. PTMs are biochemical modifications of a protein that occur during or after translation and are typically mediated by enzymes. PTMs modulate several characteristics of proteins including their structure, activity, localization, and stability. α-Syn undergoes various posttranslational modifications, including phosphorylation, ubiquitination, SUMOylation, acetylation, glycation, O-GlcNAcylation, nitration, oxidation, polyamination, arginylation, and truncation. Different PTMs of a protein can physically interact with one another or work together to influence a particular physiological or pathological feature in a process known as PTMs crosstalk. The development of detection techniques for the cooccurrence of PTMs in recent years has uncovered previously unappreciated mechanisms of their crosstalk. This has led to the emergence of evidence supporting an association between α-Syn PTMs crosstalk and synucleinopathies. In this review, we provide a comprehensive evaluation of α-Syn PTMs, their impact on misfolding and pathogenicity, the pharmacological means of targeting them, and their potential as biomarkers of disease. We also highlight the importance of the crosstalk between these PTMs in α-Syn function and aggregation. Insight into these PTMS and the complexities of their crosstalk can improve our understanding of the pathogenesis of synucleinopathies and identify novel targets of therapeutic potential. SIGNIFICANCE STATEMENT: α-Synuclein is a key pathogenic protein in Parkinson's disease and other synucleinopathies, making it a leading therapeutic target for disease modification. Multiple posttranslational modifications occur at various sites in α-Synuclein and alter its biophysical and pathological properties, some interacting with one another to add to the complexity of the pathogenicity of this protein. This review details these modifications, their implications in disease, and potential therapeutic opportunities.

From Prodromal Stages to Clinical Trials: The Promise of Digital Speech Biomarkers in Parkinson's Disease

Speech impairment is a common and disabling symptom in Parkinson's disease (PD), affecting communication and quality of life. Advances in digital speech processing and artificial intelligence have revolutionized objective speech analysis. Given the complex nature of speech impairment, acoustic speech analysis offers unique biomarkers for neuroprotective treatments from the prodromal stages of PD. Digital speech biomarkers can monitor levodopa-induced motor complications, detect the effects of deep brain stimulation, and provide feedback for behavioral speech therapy. This review updates the mechanisms underlying speech impairment, the impact of speech phenotypes, and the effects of interventions on speech. We evaluate the strengths, potential weaknesses, and suitability of promising digital speech biomarkers in PD for capturing disease progression and treatment efficacy. Additionally, we explore the translational potential of PD speech biomarkers to other neuropsychiatric diseases, offering insights into motion, cognition, and emotion. Finally, we highlight knowledge gaps and suggest directions for future research to enhance the use of quantitative speech measures in disease-modifying clinical trials. The findings demonstrate that one year is sufficient to detect disease progression in early PD through speech biomarkers. Voice quality, pitch, loudness, and articulation measures appear to capture the efficacy of treatment interventions most effectively. Certain speech features, such as loudness and articulation rate, behave oppositely in different neurological diseases, offering valuable insights for differential diagnosis. In conclusion, this review highlights speech as a biomarker in tracking disease progression, especially in the prodromal stages of PD, and calls for further longitudinal studies to establish its efficacy across diverse populations.

RNA G-quadruplexes form scaffolds that promote neuropathological α-synuclein aggregation

Synucleinopathies, including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, are triggered by α-synuclein aggregation, triggering progressive neurodegeneration. However, the intracellular α-synuclein aggregation mechanism remains unclear. Herein, we demonstrate that RNA G-quadruplex assembly forms scaffolds for α-synuclein aggregation, contributing to neurodegeneration. Purified α-synuclein binds RNA G-quadruplexes directly through the N terminus. RNA G-quadruplexes undergo Ca2+-induced phase separation and assembly, accelerating α-synuclein sol-gel phase transition. In α-synuclein preformed fibril-treated neurons, RNA G-quadruplex assembly comprising synaptic mRNAs co-aggregates with α-synuclein upon excess cytoplasmic Ca2+ influx, eliciting synaptic dysfunction. Forced RNA G-quadruplex assembly using an optogenetic approach evokes α-synuclein aggregation, causing neuronal dysfunction and neurodegeneration. The administration of 5-aminolevulinic acid, a protoporphyrin IX prodrug, prevents RNA G-quadruplex phase separation, thereby attenuating α-synuclein aggregation, neurodegeneration, and progressive motor deficits in α-synuclein preformed fibril-injected synucleinopathic mice. Therefore, Ca2+ influx-induced RNA G-quadruplex assembly accelerates α-synuclein phase transition and aggregation, potentially contributing to synucleinopathies.

Neuropathology in an α-synuclein preformed fibril mouse model occurs independent of the Parkinson's disease-linked lysosomal ATP13A2 protein

Loss-of-function mutations in the ATP13A2 (PARK9) gene are implicated in early-onset autosomal recessive Parkinson's disease (PD) and other neurodegenerative disorders. ATP13A2 encodes a lysosomal transmembrane P5B-type ATPase that is highly expressed in brain and specifically within the substantia nigra pars compacta (SNc). Recent studies have revealed its normal role as a lysosomal polyamine transporter, although its contribution to PD-related pathology remains unclear. Cellular studies report that ATP13A2 can regulate α-synuclein (α-syn) secretion via exosomes. However, the relationship between ATP13A2 and α-syn in animal models remains inconclusive. ATP13A2 knockout (KO) mice exhibit lysosomal abnormalities and reactive astrogliosis but do not develop PD-related neuropathology. Studies manipulating α-syn levels in mice lacking ATP13A2 indicate minimal effects on pathology. The delivery of α-syn preformed fibrils (PFFs) into the mouse striatum is a well-defined model to study the development and spread of α-syn pathology. In this study we unilaterally injected wild-type (WT) and homozygous ATP13A2 KO mice with mouse α-syn PFFs in the striatum and evaluated mice for neuropathology after 6 months. The distribution, spread and extent of α-syn aggregation in multiple regions of the mouse brain was largely independent of ATP13A2 expression. The loss of nigrostriatal pathway dopaminergic neurons and their nerve terminals induced by PFFs were equivalent in WT and ATP13A2 KO mice. Reactive astrogliosis was induced equivalently by α-syn PFFs in WT and KO mice but was already significantly higher in ATP13A2 KO mice due to pre-existing reactive gliosis. We did not identify asymmetric motor disturbances, microglial activation, or axonal damage induced by α-syn PFFs in WT or KO mice. Although α-syn PFFs induce an increase in lysosomal number in the SNc in general, TH-positive dopaminergic neurons did not exhibit either increased lysosomal area or intensity, regardless of genotype. Our study evaluating the spread of α-syn pathology reveals no exacerbation of α-syn pathology, neuronal loss, astrogliosis or motor deficits in ATP13A2 KO mice, suggesting that selective lysosomal abnormalities resulting from ATP13A2 loss do not play a major role in α-syn clearance or propagation in vivo.

α-Synuclein aggregation decreases cortico-amygdala connectivity and impairs social behavior in mice

Abnormal accumulation of insoluble α-synuclein (α-Syn) inclusions in neurons, neurites, and glial cells is the defining neuropathology of synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy. Accumulation of α-Syn inclusions in the amygdala has been well-documented in post-mortem studies of PD and DLB brains, as well as preclinical animal models of these conditions. Though α-Syn pathology is closely associated with neurodegeneration, there is a poor correlation between neuronal loss in the amygdala and the clinical features of PD and DLB. Moreover, functional interaction between the cerebral cortex and the amygdala is critical to regulating emotion, motivation, and social behaviors. The cortico-amygdala functional interaction is likely to be disrupted by the development of α-Syn pathology in the brain. Thus, we hypothesize that neuronal α-Syn inclusions disrupt cortical modulation of the amygdala circuits and are sufficient to drive social behavioral deficits. In the present work, we designed a series of longitudinal studies to rigorously measure the time courses of neurodegeneration, functional impairment of cortico-amygdala connectivity, and development of amygdala-dependent social behavioral deficits to test this hypothesis. We injected α-Syn preformed fibrils (PFFs) into the dorsal striatum to induce α-Syn aggregation in the amygdala and the medial prefrontal cortex (mPFC) of C57BL6 mice of both sexes, followed by a detailed analysis of temporal development of α-Syn pathology, synaptic deficits, and neuronal loss in the amygdala, as well as behavioral deficits at 3-12 months post injections. Development of α-Syn inclusions caused losses of cortical axon terminals and cell death in the basolateral amygdala (BLA) at 6- and 12-months post injections, respectively. At a relatively early stage of 3 months post injections, the connection strength of the mPFC-BLA synapse was decreased in PFFs-injection mice compared to controls. Meanwhile, the PFFs-injected mice showed impaired social interaction behavior, which was rescued by chemogenetic stimulation of mPFC-BLA connections. Altogether, we presented a series of evidence to delineate circuit events in the amygdala associated with the accumulation of α-Syn inclusions in the mouse brain, highlighting that functional impairment of the amygdala is sufficient to cause social behavior deficits. The present work further suggests that early circuit modulation could be an effective approach to alleviate symptoms associated with α-Syn pathology, necessitating studies of functional consequences of α-Syn aggregation.

An accelerated Parkinson's disease monkey model using AAV-α-synuclein plus poly(ADP-ribose)

The etiology of Parkinson's disease (PD) remains elusive, and the limited availability of suitable animal models hampers research on pathogenesis and drug development. We report the development of a cynomolgus monkey model of PD that combines adeno-associated virus (AAV)-mediated overexpression of α-synuclein into the substantia nigra with an injection of poly(ADP-ribose) (PAR) into the striatum. Our results show that pathological processes were accelerated, including dopaminergic neuron degeneration, Lewy body aggregation, and hallmarks of inflammation in microglia and astrocytes. Behavioral phenotypes, dopamine transporter imaging, and transcriptomic profiling further demonstrate consistencies between the model and patients with PD. This model can help to determine the mechanisms underlying PD impacted by α-synuclein and PAR and aid in the accelerated development of therapeutic strategies for PD.

α-Synuclein pathology disrupts mitochondrial function in dopaminergic and cholinergic neurons at-risk in Parkinson's disease

BACKGROUND

Pathological accumulation of aggregated α-synuclein (aSYN) is a common feature of Parkinson's disease (PD). However, the mechanisms by which intracellular aSYN pathology contributes to dysfunction and degeneration of neurons in the brain are still unclear. A potentially relevant target of aSYN is the mitochondrion. To test this hypothesis, genetic and physiological methods were used to monitor mitochondrial function in substantia nigra pars compacta (SNc) dopaminergic and pedunculopontine nucleus (PPN) cholinergic neurons after stereotaxic injection of aSYN pre-formed fibrils (PFFs) into the mouse brain.

METHODS

aSYN PFFs were stereotaxically injected into the SNc or PPN of mice. Twelve weeks later, mice were studied using a combination of approaches, including immunocytochemical analysis, cell-type specific transcriptomic profiling, electron microscopy, electrophysiology and two-photon-laser-scanning microscopy of genetically encoded sensors for bioenergetic and redox status.

RESULTS

In addition to inducing a significant neuronal loss, SNc injection of PFFs induced the formation of intracellular, phosphorylated aSYN aggregates selectively in dopaminergic neurons. In these neurons, PFF-exposure decreased mitochondrial gene expression, reduced the number of mitochondria, increased oxidant stress, and profoundly disrupted mitochondrial adenosine triphosphate production. Consistent with an aSYN-induced bioenergetic deficit, the autonomous spiking of dopaminergic neurons slowed or stopped. PFFs also up-regulated lysosomal gene expression and increased lysosomal abundance, leading to the formation of Lewy-like inclusions. Similar changes were observed in PPN cholinergic neurons following aSYN PFF exposure.

CONCLUSIONS

Taken together, our findings suggest that disruption of mitochondrial function, and the subsequent bioenergetic deficit, is a proximal step in the cascade of events induced by aSYN pathology leading to dysfunction and degeneration of neurons at-risk in PD.

Different neurotoxicity and seeding activity between α-synuclein oligomers formed in plasma of patients with Parkinson's disease and multiple system atrophy

Previous studies have shown that α-synuclein (α-Syn) aggregates derived from the brains of patients with Parkinson's disease (PD) and multiple system atrophy (MSA) exhibit different phosphorylation, cytotoxicity, and seeding activity. However, the mechanism underlying the differences remains poorly understood. Here, recombinant human α-Syn was incubated in the plasma of patients with PD and MSA, and the oligomers formed in the plasma (PD-O-α-Syn and MSA-O-α-Syn) were purified and analyzed for their phosphorylation, cytotoxicity and seeding activity. In vitro assays revealed that both PD-O-α-Syn and MSA-O-α-Syn were phosphorylated at serine 129. However, the phosphorylation degree of MSA-O-α-Syn was significantly higher than that of PD-O-α-Syn. In addition, MSA-O-α-Syn exhibited stronger cytotoxicity and seeding activity compared with PD-O-α-Syn. In vivo experiments showed that mice receiving intrastriatal inoculation of MSA-O-α-Syn developed more severe motor dysfunction and dopaminergic degeneration than mice receiving intrastriatal inoculation of PD-O-α-Syn. Compared with the mice inoculated with PD-O-α-Syn, the mice inoculated with MSA-O-α-Syn accumulated more phosphorylated and oligomerized α-Syn in the striatum and brain regions (substantia nigra, hippocampus and prefrontal cortex) away from the inoculated site. The results obtained suggest that α-Syn oligomers formed in PD and MSA plasma are different in phosphorylation, cytotoxicity, and seeding activity.

α-Synuclein: Multiple pathogenic roles in trafficking and proteostasis pathways in Parkinson's disease

Parkinson's disease (PD) is a common age-related neurodegenerative disorder characterized by the loss of dopaminergic neurons in the midbrain. A hallmark of both familial and sporadic PD is the presence of Lewy body inclusions composed mainly of aggregated α-synuclein (α-syn), a presynaptic protein encoded by the SNCA gene. The mechanisms driving the relationship between α-syn accumulation and neurodegeneration are not completely understood, although recent evidence indicates that multiple branches of the proteostasis pathway are simultaneously perturbed when α-syn aberrantly accumulates within neurons. Studies from patient-derived midbrain cultures that develop α-syn pathology through the endogenous expression of PD-causing mutations show that proteostasis disruption occurs at the level of synthesis/folding in the endoplasmic reticulum (ER), downstream ER-Golgi trafficking, and autophagic-lysosomal clearance. Here, we review the fundamentals of protein transport, highlighting the specific steps where α-syn accumulation may intervene and the downstream effects on proteostasis. Current therapeutic efforts are focused on targeting single pathways or proteins, but the multifaceted pathogenic role of α-syn throughout the proteostasis pathway suggests that manipulating several targets simultaneously will provide more effective disease-modifying therapies for PD and other synucleinopathies.

Research Priorities on the Role of α-Synuclein in Parkinson's Disease Pathogenesis

Various forms of Parkinson's disease, including its common sporadic form, are characterized by prominent α-synuclein (αSyn) aggregation in affected brain regions. However, the role of αSyn in the pathogenesis and evolution of the disease remains unclear, despite vast research efforts of more than a quarter century. A better understanding of the role of αSyn, either primary or secondary, is critical for developing disease-modifying therapies. Previous attempts to hone this research have been challenged by experimental limitations, but recent technological advances may facilitate progress. The Scientific Issues Committee of the International Parkinson and Movement Disorder Society (MDS) charged a panel of experts in the field to discuss current scientific priorities and identify research strategies with potential for a breakthrough. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Interorganelle phospholipid communication, a house not so divided

The presence of membrane-bound organelles with specific functions is one of the main hallmarks of eukaryotic cells. Organelle membranes are composed of specific lipids that govern their function and interorganelle communication. Discoveries in cell biology using imaging and omic technologies have revealed the mechanisms that drive membrane remodeling, organelle contact sites, and metabolite exchange. The interplay between multiple organelles and their interdependence is emerging as the next frontier for discovery using 3D reconstruction of volume electron microscopy (vEM) datasets. We discuss recent findings on the links between organelles that underlie common functions and cellular pathways. Specifically, we focus on the metabolism of ether glycerophospholipids that mediate organelle dynamics and their communication with each other, and the new imaging techniques that are powering these discoveries.

Galantamine suppresses α-synuclein aggregation by inducing autophagy via the activation of α7 nicotinic acetylcholine receptors

Synucleinopathies, including Parkinson's disease and dementia with Lewy bodies, are neurodegenerative disorders characterized by the aberrant accumulation of α-synuclein (α-syn). Although no treatment is effective for synucleinopathies, the suppression of α-syn aggregation may contribute to the development of numerous novel therapeutic targets. Recent research revealed that nicotinic acetylcholine (nACh) receptor activation has neuroprotective effects and promotes the degradation of amyloid protein by activating autophagy. In an in vitro human-derived cell line model, we demonstrated that galantamine, the nAChR allosteric potentiating ligand, significantly reduced the cell number of SH-SY5Y cells with intracellular Lewy body-like aggregates by enhancing the sensitivity of α7-nAChR. In addition, galantamine promoted autophagic flux, and prevented the formation of Lewy body-resembled aggregates. In an in vivo synucleinopathy mouse model, the propagation of α-syn aggregation in the cerebral cortex was inhibited by galantamine administration for 90 days. These results suggest that α7-nAChR is expected to be a novel therapeutic target, and galantamine is a potential agent for synucleinopathies.

Inhibitor Development for α-Synuclein Fibril's Disordered Region to Alleviate Parkinson's Disease Pathology

The amyloid fibrils of α-synuclein (α-syn) are crucial in the pathology of Parkinson's disease (PD), with the intrinsically disordered region (IDR) of its C-terminal playing a key role in interacting with receptors like LAG3 and RAGE, facilitating pathological neuronal spread and inflammation. In this study, we identified Givinostat (GS) as an effective inhibitor that disrupts the interaction of α-syn fibrils with receptors such as LAG3 and RAGE through high-throughput screening. By exploring the structure-activity relationship and optimizing GS, we developed several lead compounds, including GSD-16-24. Utilizing solution-state and solid-state NMR, along with cryo-EM techniques, we demonstrated that GSD-16-24 binds directly to the C-terminal IDR of α-syn monomer and fibril, preventing the fibril from binding to the receptors. Furthermore, GSD-16-24 significantly inhibits the association of α-syn fibrils with membrane receptors, thereby reducing neuronal propagation and pro-inflammatory effects of α-syn fibrils. Our findings introduce a novel approach to mitigate the pathological effects of α-syn fibrils by targeting their IDR with small molecules, offering potential leads for the development of clinical drugs to treat PD.

Circadian disruption promotes the neurotoxicity of oligomeric alpha-synuclein in mice

Circadian disruption often arises prior to the onset of typical motor deficits in patients with Parkinson's disease (PD). It remains unclear whether such a prevalent non-motor manifestation would contribute to the progression of PD. Diffusible oligomeric alpha-synuclein (O-αSyn) is perceived as the most toxic and rapid-transmitted species in the early stages of PD. Exploring the factors that influence the spread and toxicity of O-αSyn should be helpful for developing effective interventions for the disease. The aim of this study was to explore the effects of circadian disruption on PD pathology and parkinsonism-like behaviors in a novel mouse model induced by O-αSyn. We discovered that O-αSyn could enter the brain rapidly following intranasal administration, resulting in the formation of nitrated-αSyn pathology and non-motor symptoms of the mice. Meanwhile, circadian disruption exacerbated the burden of nitrated-αSyn pathology and accelerated the loss of dopaminergic neurons in O-αSyn-treated mice. Subsequent experiments demonstrated that circadian disruption might act via promoting nitrative stress and neuroinflammation. These findings could highlight the circadian rhythms as a potential diagnostic and therapeutic target in early-stage PD.

Navigating through the complexities of synucleinopathies: Insights into pathogenesis, heterogeneity, and future perspectives

The aggregation of alpha-synuclein (aSyn) represents a neuropathological hallmark observed in a group of neurodegenerative disorders collectively known as synucleinopathies. Despite their shared characteristics, these disorders manifest diverse clinical and pathological phenotypes. The mechanism underlying this heterogeneity is thought to be due to the diversity in the aSyn strains present across the diseases. In this perspective, we will explore recent findings on aSyn strains and discuss recent discoveries about Lewy bodies' composition. We further discuss the current hypothesis for aSyn spreading and emphasize the emerging biomarker field demonstrating promising results. A comprehension of these mechanisms holds substantial promise for future clinical applications. This understanding can pave the way for the development of personalized medicine strategies, specifically targeting the unique underlying causes of each synucleinopathy. Such advancements can revolutionize therapeutic approaches and significantly contribute to more effective interventions in the intricate landscape of neurodegenerative disorders.

Olfactory deficit and gastrointestinal dysfunction precede motor abnormalities in alpha-Synuclein G51D knock-in mice

Parkinson's disease (PD) is typically a sporadic late-onset disorder, which has made it difficult to model in mice. Several transgenic mouse models bearing mutations in SNCA, which encodes alpha-Synuclein (α-Syn), have been made, but these lines do not express SNCA in a physiologically accurate spatiotemporal pattern, which limits the ability of the mice to recapitulate the features of human PD. Here, we generated knock-in mice bearing the G51D SNCA mutation. After establishing that their motor symptoms begin at 9 mo of age, we then sought earlier pathologies. We assessed the phosphorylation at Serine 129 of α-Syn in different tissues and detected phospho-α-Syn in the olfactory bulb and enteric nervous system at 3 mo of age. Olfactory deficit and impaired gut transit followed at 6 mo, preceding motor symptoms. The SncaG51D mice thus parallel the progression of human PD and will enable us to study PD pathogenesis and test future therapies.

Alpha-synuclein preformed fibril-induced aggregation and dopaminergic cell death in cathepsin D overexpression and ZKSCAN3 knockout mice

α-synuclein accumulation is recognized as a prominent feature in the majority of Parkinson's disease cases and also occurs in a broad range of neurodegenerative disorders including Alzheimer's disease. It has been shown that α-synuclein can spread from a donor cell to neighboring cells and thus propagate cellular damage, antagonizing the effectiveness of therapies such as transplantation of fetal or iPSC derived dopaminergic cells. As we and others previously have shown, insufficient lysosomal function due to genetic mutations or targeted disruption of cathepsin D can cause α-synuclein accumulation. We here investigated whether overexpression of cathepsin D or knockout (KO) of the transcriptional suppressor of lysosomal biogenesis ZKSCAN3 can attenuate propagation of α-synuclein aggregation and cell death. We examined dopaminergic neurodegeneration in the substantia nigra using stereology of tyrosine hydroxylase-immunoreactive cells 4 months and 6 months after intrastriatal injection of α-synuclein preformed fibrils or monomeric α-synuclein control in control, central nervous system (CNS)-cathepsin D overexpressing and CNS-specific ZKSCAN3 KO mice. We also examined pS129-α-synuclein aggregates in the substantia nigra, cortex, amygdala and striatum. The extent of dopaminergic neurodegeneration and pS129-α-synuclein aggregation in the brains of CNS-specific ZKSCAN3 knockout mice and CNS-cathepsin D overexpressing mice was similar to that observed in wild-type mice. Our results indicate that neither enhancing cathepsin D expression nor disrupting ZKSCAN3 in the CNS is sufficient to attenuate pS129-α-synuclein aggregate accumulation or dopaminergic neurodegeneration.

Astrocyte-neuron communication through the complement C3-C3aR pathway in Parkinson's disease

Neuroinflammation and autoimmunity are pivotal in the pathogenesis of neurodegenerative diseases. Complement activation and involvement of astrocyte-neuron C3/C3aR pathway have been observed, yet the mechanisms influencing α-synuclein (α-syn) pathology and neurodegeneration remain unclear. In this study, elevated levels of complement C3 were detected in the plasma of α-syn PFF-induced mice and the substantia nigra of A53T transgenic mice. Colocalization of complement C3 with astrocytes was also observed. Overexpression of complement C3 exacerbated motor dysfunction, dopaminergic neuron loss, and phosphorylated α-syn expression in mice injected with α-syn preformed fibrils (α-syn PFFs). Conversely, downregulation of complement C3 protected α-syn PFF-induced mice. Molecular investigations revealed that inhibition of Toll-like receptor 2 (TLR2) or NF-κB reduced complement C3 expression in primary astrocytes following α-syn PFF treatment. Astrocyte-neuron communication via the C3/C3aR pathway influenced α-syn PFF-induced neuronal apoptosis and α-syn pathology, potentially through modulation of GSK3β. These findings underscore the critical role of astrocyte-neuron communication via the C3/C3aR pathway in PD pathogenesis, highlighting its potential as a therapeutic target.

The role of gut-derived short-chain fatty acids in Parkinson's disease

The emerging function of short-chain fatty acids (SCFAs) in Parkinson's disease (PD) has been investigated in this article. SCFAs, which are generated via the fermentation of dietary fiber by gut microbiota, have been associated with dysfunction of the gut-brain axis and, neuroinflammation. These processes are integral to the development of PD. This article examines the potential therapeutic implications of SCFAs in the management of PD, encompassing their capacity to modulate gastrointestinal permeability, neuroinflammation, and neuronal survival, by conducting an extensive literature review. As a whole, this article emphasizes the potential therapeutic utility of SCFAs as targets for the management and treatment of PD.

Intercellular transmission of alpha-synuclein

An emerging theme in Parkinson's disease (PD) is the propagation of α-synuclein pathology as the disease progresses. Research involving the injection of preformed α-synuclein fibrils (PFFs) in animal models has recapitulated the pathological spread observed in PD patients. At the cellular and molecular levels, this intercellular spread requires the translocation of α-synuclein across various membrane barriers. Recent studies have identified subcellular organelles and protein machineries that facilitate these processes. In this review, we discuss the proposed pathways for α-synuclein intercellular transmission, including unconventional secretion, receptor-mediated uptake, endosome escape and nanotube-mediated transfer. In addition, we advocate for a rigorous examination of the evidence for the localization of α-synuclein in extracellular vesicles.

Rapid iPSC inclusionopathy models shed light on formation, consequence, and molecular subtype of α-synuclein inclusions

The heterogeneity of protein-rich inclusions and its significance in neurodegeneration is poorly understood. Standard patient-derived iPSC models develop inclusions neither reproducibly nor in a reasonable time frame. Here, we developed screenable iPSC "inclusionopathy" models utilizing piggyBac or targeted transgenes to rapidly induce CNS cells that express aggregation-prone proteins at brain-like levels. Inclusions and their effects on cell survival were trackable at single-inclusion resolution. Exemplar cortical neuron α-synuclein inclusionopathy models were engineered through transgenic expression of α-synuclein mutant forms or exogenous seeding with fibrils. We identified multiple inclusion classes, including neuroprotective p62-positive inclusions versus dynamic and neurotoxic lipid-rich inclusions, both identified in patient brains. Fusion events between these inclusion subtypes altered neuronal survival. Proteome-scale α-synuclein genetic- and physical-interaction screens pinpointed candidate RNA-processing and actin-cytoskeleton-modulator proteins like RhoA whose sequestration into inclusions could enhance toxicity. These tractable CNS models should prove useful in functional genomic analysis and drug development for proteinopathies.

Motor Cortical Neuronal Hyperexcitability Associated with α-Synuclein Aggregation

Dysfunction of the cerebral cortex is thought to underlie motor and cognitive impairments in Parkinson disease (PD). While cortical function is known to be suppressed by abnormal basal ganglia output following dopaminergic degeneration, it remains to be determined how the deposition of Lewy pathology disrupts cortical circuit integrity and function. Moreover, it is also unknown whether cortical Lewy pathology and midbrain dopaminergic degeneration interact to disrupt cortical function in late-stage. To begin to address these questions, we injected α-synuclein (αSyn) preformed fibrils (PFFs) into the dorsolateral striatum of mice to seed αSyn pathology in the cortical cortex and induce degeneration of midbrain dopaminergic neurons. Using this model system, we reported that αSyn aggregates accumulate in the motor cortex in a layer- and cell-subtype-specific pattern. Particularly, intratelencephalic neurons (ITNs) showed earlier accumulation and greater extent of αSyn aggregates relative to corticospinal neurons (CSNs). Moreover, we demonstrated that the intrinsic excitability and inputs resistance of αSyn aggregates-bearing ITNs in the secondary motor cortex (M2) are increased, along with a noticeable shrinkage of cell bodies and loss of dendritic spines. Last, neither the intrinsic excitability of CSNs nor their thalamocortical input was altered by a partial striatal dopamine depletion associated with αSyn pathology. Our results documented motor cortical neuronal hyperexcitability associated with αSyn aggregation and provided a novel mechanistic understanding of cortical circuit dysfunction in PD.

Hope vs. Hype I: Spreading alpha-synuclein explains cognitive deficits in Parkinson disease

The Parkinson Study Group (PSG) gathered North American experts in Parkinson disease during the 9th Annual Symposium on "Shaping the Management of Parkinson Disease: Debating Current Controversies". Debaters were tasked with agree or disagree positions to a particular prompt. This is the first in three-part series of "Hype vs. Hope" debates involving current trends and advances in Parkinson disease. With the prompt of "Spreading alpha-synuclein explains cognitive deficits in Parkinson disease," Dr. Kelly Mills, MD, MHS was tasked with the "agree" stance and Dr. Abhimanyu Mahajan, MD, MHS was tasked with the "disagree" stance. The following point-of-view article is an adaptation of this debate.

Autophagy in aging-related diseases and cancer: Principles, regulatory mechanisms and therapeutic potential

Macroautophagy/autophagy is primarily accountable for the degradation of damaged organelles and toxic macromolecules in the cells. Regarding the essential function of autophagy for preserving cellular homeostasis, changes in, or dysfunction of, autophagy flux can lead to disease development. In the current paper, the complicated function of autophagy in aging-associated pathologies and cancer is evaluated, highlighting the underlying molecular mechanisms that can affect longevity and disease pathogenesis. As a natural biological process, a reduction in autophagy is observed with aging, resulting in an accumulation of cell damage and the development of different diseases, including neurological disorders, cardiovascular diseases, and cancer. The MTOR, AMPK, and ATG proteins demonstrate changes during aging, and they are promising therapeutic targets. Insulin/IGF1, TOR, PKA, AKT/PKB, caloric restriction and mitochondrial respiration are vital for lifespan regulation and can modulate or have an interaction with autophagy. The specific types of autophagy, such as mitophagy that degrades mitochondria, can regulate aging by affecting these organelles and eliminating those mitochondria with genomic mutations. Autophagy and its specific types contribute to the regulation of carcinogenesis and they are able to dually enhance or decrease cancer progression. Cancer hallmarks, including proliferation, metastasis, therapy resistance and immune reactions, are tightly regulated by autophagy, supporting the conclusion that autophagy is a promising target in cancer therapy.

Excitatory synaptic structural abnormalities produced by templated aggregation of α-syn in the basolateral amygdala

Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are characterized by neuronal α-synuclein (α-syn) inclusions termed Lewy Pathology, which are abundant in the amygdala. The basolateral amygdala (BLA), in particular, receives projections from the thalamus and cortex. These projections play a role in cognition and emotional processing, behaviors which are impaired in α-synucleinopathies. To understand if and how pathologic α-syn impacts the BLA requires animal models of α-syn aggregation. Injection of α-syn pre-formed fibrils (PFFs) into the striatum induces robust α-syn aggregation in excitatory neurons in the BLA that corresponds with reduced contextual fear conditioning. At early time points after aggregate formation, cortico-amygdala excitatory transmission is abolished. The goal of this project was to determine if α-syn inclusions in the BLA induce synaptic degeneration and/or morphological changes. In this study, we used C57BL/6 J mice injected bilaterally with PFFs in the dorsal striatum to induce α-syn aggregate formation in the BLA. A method was developed using immunofluorescence and three-dimensional reconstruction to analyze excitatory cortico-amygdala and thalamo-amygdala presynaptic terminals closely juxtaposed to postsynaptic densities. The abundance and morphology of synapses were analyzed at 6- or 12-weeks post-injection of PFFs. α-Syn aggregate formation in the BLA did not cause a significant loss of synapses, but cortico-amygdala and thalamo-amygdala presynaptic terminals and postsynaptic densities with aggregates of α-syn show increased volumes, similar to previous findings in human DLB cortex, and in non-human primate models of PD. Transmission electron microscopy showed that asymmetric synapses in mice with PFF-induced α-syn aggregates have reduced synaptic vesicle intervesicular distances, similar to a recent study showing phospho-serine-129 α-syn increases synaptic vesicle clustering. Thus, pathologic α-syn causes major alterations to synaptic architecture in the BLA, potentially contributing to behavioral impairment and amygdala dysfunction observed in synucleinopathies.

Suppression of the JAK/STAT pathway inhibits neuroinflammation in the line 61-PFF mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by neuroinflammation, progressive loss of dopaminergic neurons, and accumulation of α-synuclein (α-Syn) into insoluble aggregates called Lewy pathology. The Line 61 α-Syn mouse is an established preclinical model of PD; Thy-1 is used to promote human α-Syn expression, and features of sporadic PD develop at 9-18 months of age. To accelerate the PD phenotypes, we injected sonicated human α-Syn preformed fibrils (PFFs) into the striatum, which produced phospho-Syn (p-α-Syn) inclusions in the substantia nigra pars compacta and significantly increased MHC Class II-positive immune cells. Additionally, there was enhanced infiltration and activation of innate and adaptive immune cells in the midbrain. We then used this new model, Line 61-PFF, to investigate the effect of inhibiting the JAK/STAT signaling pathway, which is critical for regulation of innate and adaptive immune responses. After administration of the JAK1/2 inhibitor AZD1480, immunofluorescence staining showed a significant decrease in p-α-Syn inclusions and MHC Class II expression. Flow cytometry showed reduced infiltration of CD4+ T-cells, CD8+ T-cells, CD19+ B-cells, dendritic cells, macrophages, and endogenous microglia into the midbrain. Importantly, single-cell RNA-Sequencing analysis of CD45+ cells from the midbrain identified 9 microglia clusters, 5 monocyte/macrophage (MM) clusters, and 5 T-cell (T) clusters, in which potentially pathogenic MM4 and T3 clusters were associated with neuroinflammatory responses in Line 61-PFF mice. AZD1480 treatment reduced cell numbers and cluster-specific expression of the antigen-presentation genes H2-Eb1, H2-Aa, H2-Ab1, and Cd74 in the MM4 cluster and proinflammatory genes such as Tnf, Il1b, C1qa, and C1qc in the T3 cluster. Together, these results indicate that inhibiting the JAK/STAT pathway suppresses the activation and infiltration of innate and adaptive cells, reducing neuroinflammation in the Line 61-PFF mouse model.

α-Synuclein strain propagation is independent of cellular prion protein expression in a transgenic synucleinopathy mouse model

The cellular prion protein, PrPC, has been postulated to function as a receptor for α-synuclein, potentially facilitating cell-to-cell spreading and/or toxicity of α-synuclein aggregates in neurodegenerative disorders such as Parkinson's disease. Previously, we generated the "Salt (S)" and "No Salt (NS)" strains of α-synuclein aggregates that cause distinct pathological phenotypes in M83 transgenic mice overexpressing A53T-mutant human α-synuclein. To test the hypothesis that PrPC facilitates the propagation of α-synuclein aggregates, we produced M83 mice that either express or do not express PrPC. Following intracerebral inoculation with the S or NS strain, the absence of PrPC in M83 mice did not prevent disease development and had minimal influence on α-synuclein strain-specified attributes such as the extent of cerebral α-synuclein deposition, selective targeting of specific brain regions and cell types, the morphology of induced α-synuclein deposits, and the structural fingerprints of protease-resistant α-synuclein aggregates. Likewise, there were no appreciable differences in disease manifestation between PrPC-expressing and PrPC-lacking M83 mice following intraperitoneal inoculation of the S strain. Interestingly, intraperitoneal inoculation with the NS strain resulted in two distinct disease phenotypes, indicative of α-synuclein strain evolution, but this was also independent of PrPC expression. Overall, these results suggest that PrPC plays at most a minor role in the propagation, neuroinvasion, and evolution of α-synuclein strains in mice that express A53T-mutant human α-synuclein. Thus, other putative receptors or cell-to-cell propagation mechanisms may have a larger effect on the spread of α-synuclein aggregates during disease.

Inflammation and heterogeneity in synucleinopathies

Neurodegenerative diseases represent a huge healthcare challenge which is predicted to increase with an aging population. Synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), present complex challenges in understanding their onset and progression. They are characterized by the abnormal aggregation of α-synuclein in the brain leading to neurodegeneration. Accumulating evidence supports the existence of distinct subtypes based on the site of α-synuclein aggregation initiation, genetics, and, more recently, neuroinflammation. Mediated by both central nervous system-resident cells, peripheral immune cells, and gut dysbiosis, neuroinflammation appears as a key process in the onset and progression of neuronal loss. Sex-based differences add another layer of complexity to synucleinopathies, influencing disease prevalence - with a known higher incidence of PD in males compared to females - as well as phenotype and immune responses. Biological sex affects neuroinflammatory pathways and the immune response, suggesting the need for sex-specific therapeutic strategies and biomarker identification. Here, we review the heterogeneity of synucleinopathies, describing the etiology, the mechanisms by which the inflammatory processes contribute to the pathology, and the consideration of sex-based differences to highlight the need for personalized therapeutics.

A charged tail on anti-α-Synuclein antibodies does not enhance their affinity to α-Synuclein fibrils

The aggregation of α-Synuclein (αSyn) is strongly linked to neuronal death in Parkinson's disease and other synucleinopathies. The spreading of aggregated αSyn between neurons is at least partly dependent on electrostatic interactions between positively charged stretches on αSyn fibrils and the negatively charged heparan sulphate proteoglycans on the cell surface. To date there is still no therapeutic option available that could halt the progression of Parkinson's disease and one of the major limitations is likely the relatively low proportion of αSyn aggregates accessible to drugs in the extracellular space. Here, we investigated whether a negatively charged peptide tail fused to the αSyn aggregate-specific antibodies SynO2 and 9E4 could enhance the antibodies' avidity to αSyn aggregates in order to improve their potential therapeutic effect through inhibiting cell-to-cell spreading and enhancing the clearance of extracellular aggregates. We performed ELISAs to test the avidity to αSyn aggregates of both monovalent and bivalent antibody formats with and without the peptide tail. Our results show that the addition of the negatively charged peptide tail decreased the binding strength of both antibodies to αSyn aggregates at physiological salt conditions, which can likely be explained by intermolecular repulsions between the tail and the negatively charged C-terminus of αSyn. Additionally, the tail might interact with the paratopes of the SynO2 antibody abolishing its binding to αSyn aggregates. Conclusively, our peptide tail did not fulfil the required characteristics to improve the antibodies' binding to αSyn aggregates. Fine-tuning the design of the peptide tail to avoid its interaction with the antibodies' CDR and to better mimic relevant characteristics of heparan sulphates for αSyn aggregate binding may help overcome the limitations observed in this study.

Spatial-temporal dynamic evolution of lewy body dementia by metabolic PET imaging

PURPOSE

Lewy body dementia (LBD) is a neurodegenerative disease with high heterogeneity and complex pathogenesis. Our study aimed to use disease progression modeling to uncover spatial-temporal dynamic evolution of LBD in vivo, and to explore differential profiles of clinical features, glucose metabolism, and dopaminergic function among different evolution-related subtypes.

METHODS

A total of 123 participants (31 healthy controls and 92 LBD patients) who underwent 18F-FDG PET scans were retrospectively enrolled. 18F-FDG PET-based Subtype and Stage Inference (SuStaIn) model was established to illustrate spatial-temporal evolutionary patterns and categorize relevant subtypes. Then subtypes and stages were further related to clinical features, glucose metabolism, and dopaminergic function of LBD patients.

RESULTS

This 18F-FDG PET imaging-based approach illustrated two distinct patterns of neurodegenerative evolution originating from the neocortex and basal ganglia in LBD and defined them as subtype 1 and subtype 2, respectively. There were obvious differences between subtypes. Compared with subtype 1, subtype 2 exhibited a greater proportion of male patients (P = 0.045) and positive symptoms such as visual hallucinations (P = 0.033) and fluctuating cognitions (P = 0.033). Cognitive impairment, metabolic abnormalities, dopaminergic dysfunction and progression were all more severe in subtype 2 (all P < 0.05). In addition, a strong association was observed between SuStaIn subtypes and two clinical phenotypes (Parkinson's disease dementia and dementia with Lewy bodies) (P = 0.005).

CONCLUSIONS

Our findings based on 18F-FDG PET and data-driven model illustrated spatial-temporal dynamic evolution of LBD and categorized novel subtypes with different evolutionary patterns, clinical and imaging features in vivo. The evolution-related subtypes are associated with LBD clinical phenotypes, which supports the perspective of existence of distinct entities in LBD spectrum.

Construct, Face, and Predictive Validity of Parkinson's Disease Rodent Models

Parkinson's disease (PD) is the second most common neurodegenerative disease globally. Current drugs only alleviate symptoms without halting disease progression, making rodent models essential for researching new therapies and understanding the disease better. However, selecting the right model is challenging due to the numerous models and protocols available. Key factors in model selection include construct, face, and predictive validity. Construct validity ensures the model replicates pathological changes seen in human PD, focusing on dopaminergic neurodegeneration and a-synuclein aggregation. Face validity ensures the model's symptoms mirror those in humans, primarily reproducing motor and non-motor symptoms. Predictive validity assesses if treatment responses in animals will reflect those in humans, typically involving classical pharmacotherapies and surgical procedures. This review highlights the primary characteristics of PD and how these characteristics are validated experimentally according to the three criteria. Additionally, it serves as a valuable tool for researchers in selecting the most appropriate animal model based on established validation criteria.

Role of Lipids in the Pathogenesis of Parkinson's Disease

Aggregation of α-synuclein (αSyn) and its accumulation as Lewy bodies play a central role in the pathogenesis of Parkinson's disease (PD). However, the mechanism by which αSyn aggregates in the brain remains unclear. Biochemical studies have demonstrated that αSyn interacts with lipids, and these interactions affect the aggregation process of αSyn. Furthermore, genetic studies have identified mutations in lipid metabolism-associated genes such as glucocerebrosidase 1 (GBA1) and synaptojanin 1 (SYNJ1) in sporadic and familial forms of PD, respectively. In this review, we focus on the role of lipids in triggering αSyn aggregation in the pathogenesis of PD and propose the possibility of modulating the interaction of lipids with αSyn as a potential therapy for PD.

FoxO1 Alleviates the Mitochondrial ROS Levels Induced by α-Synuclein Preformed Fibrils in BV-2 Microglial Cells

Parkinson's disease (PD) is a complex neurodegenerative disorder marked by the gradual deterioration of dopaminergic neurons, especially in the substantia nigra pars compacta (SNc). Dysregulation of the transcription factor FoxO1 is associated with various neurodegenerative conditions, including Alzheimer's disease and PD, though the specific mechanisms involved are not fully understood. This study explores the effects of α-Synuclein preformed fibrils (PFF) on BV-2 microglial cells, focusing on changes in molecular characteristics and their impact on neuronal degeneration. Our results demonstrate that PFF treatment significantly increases FoxO1 mRNA (p = 0.0443) and protein (p = 0.0216) levels, leading to its nuclear translocation (p = 0.0142) and enhanced expression of genes involved in the detoxification of reactive oxygen species (ROS), such as Catalase (Cat, p = 0.0249) and superoxide dismutase 2 (Sod2, p = 0.0313). Furthermore, we observed that PFF treatment elevates mitochondrial ROS levels. However, cells lacking FoxO1 or treated with FoxO1 inhibitors showed increased vulnerability to PFF-induced ROS, attributed to reduced expression of ROS detoxifying enzymes Cat and Sod2 (p < 0.0001). Besides enhancing ROS production, inhibiting FoxO1 also heightens neurotoxicity induced by PFF treatment in microglia-conditioned medium (p < 0.0001). Conversely, treatment with N-acetylcysteine or bacterial superoxide dismutase A mitigated the ROS increase induced by PFF (p < 0.0001). These findings suggest the essential role of FoxO1 in regulating ROS levels, which helps alleviate pathology in PFF-induced PD models. Our study provides insights into the genetic mechanisms of PD and suggests potential pathways for developing novel therapeutic strategies.

Prion diseases, always a threat?

Prion diseases are caused by prions, which are proteinaceous infectious particles that have been identified as causative factors of transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease (CJD). Prion diseases are devastating neurodegenerative disorders in humans and many animals, including sheep, cows, deer, cats, and camels. Prion diseases are classified into sporadic and genetic forms. Additionally, a third, environmentally acquired category exists. This type includes kuru, iatrogenic CJD caused by human dura mater grafts or human pituitary-derived hormones, and variant CJD transmitted through food contaminated with bovine spongiform encephalopathy prions. Bovine spongiform encephalopathy and variant CJD have nearly been controlled, but chronic wasting disease, a prion disease affecting deer, is spreading widely in North America and South Korea and recently in Northern Europe. Recently, amyloid-beta, alpha-synuclein, and other proteins related to Alzheimer's disease, Parkinson's disease, and other neurodegenerative diseases were reported to have prion features such as transmission to animals. Amyloid-beta transmission to humans has been suggested in iatrogenic CJD cases and in cerebral amyloid angiopathy cases with cerebral bleeding occurring long after childhood neurosurgery with or without cadaveric dura mater transplantation. These findings indicate that diseases caused by various prions, namely various transmissible proteins, appear to be a threat, particularly in the current longevity society. Prion disease represented by CJD has obvious transmissibility and is considered to be an "archetype of various neurodegenerative diseases". Overcoming prion diseases is a top priority currently in our society, and this strategy will certainly contribute to elucidating pathomechanism of other neurodegenerative diseases and developing new therapies for them.

Current insights and assumptions on α-synuclein in Lewy body disease

Lewy body disorders are heterogeneous neurological conditions defined by intracellular inclusions composed of misshapen α-synuclein protein aggregates. Although α-synuclein aggregates are only one component of inclusions and not strictly coupled to neurodegeneration, evidence suggests they seed the propagation of Lewy pathology within and across cells. Genetic mutations, genomic multiplications, and sequence polymorphisms of the gene encoding α-synuclein are also causally linked to Lewy body disease. In nonfamilial cases of Lewy body disease, the disease trigger remains unidentified but may range from industrial/agricultural toxicants and natural sources of poisons to microbial pathogens. Perhaps due to these peripheral exposures, Lewy inclusions appear at early disease stages in brain regions connected with cranial nerves I and X, which interface with inhaled and ingested environmental elements in the nasal or gastrointestinal cavities. Irrespective of its identity, a stealthy disease trigger most likely shifts soluble α-synuclein (directly or indirectly) into insoluble, cross-β-sheet aggregates. Indeed, β-sheet-rich self-replicating α-synuclein multimers reside in patient plasma, cerebrospinal fluid, and other tissues, and can be subjected to α-synuclein seed amplification assays. Thus, clinicians should be able to capitalize on α-synuclein seed amplification assays to stratify patients into potential responders versus non-responders in future clinical trials of α-synuclein targeted therapies. Here, we briefly review the current understanding of α-synuclein in Lewy body disease and speculate on pathophysiological processes underlying the potential transmission of α-synucleinopathy across the neuraxis.

Motor Cortical Neuronal Hyperexcitability Associated with α-Synuclein Aggregation

Dysfunction of the cerebral cortex is thought to underlie motor and cognitive impairments in Parkinson disease (PD). While cortical function is known to be suppressed by abnormal basal ganglia output following dopaminergic degeneration, it remains to be determined how the deposition of Lewy pathology disrupts cortical circuit integrity and function. Moreover, it is also unknown whether cortical Lewy pathology and midbrain dopaminergic degeneration interact to disrupt cortical function in late-stage. To begin to address these questions, we injected α-synuclein (αSyn) preformed fibrils (PFFs) into the dorsolateral striatum of mice to seed αSyn pathology in the cortical cortex and induce degeneration of midbrain dopaminergic neurons. Using this model system, we reported that αSyn aggregates accumulate in the motor cortex in a layer- and cell-subtype-specific pattern. Particularly, intratelencephalic neurons (ITNs) showed earlier accumulation and greater extent of αSyn aggregates relative to corticospinal neurons (CSNs). Moreover, we demonstrated that the intrinsic excitability and inputs resistance of αSyn aggregates-bearing ITNs in the secondary motor cortex (M2) are increased, along with a noticeable shrinkage of cell bodies and loss of dendritic spines. Last, neither the intrinsic excitability of CSNs nor their thalamocortical input was altered by a partial striatal dopamine depletion associated with αSyn pathology. Our results documented motor cortical neuronal hyperexcitability associated with αSyn aggregation and provided a novel mechanistic understanding of cortical circuit dysfunction in PD.

Aptamer binding footprints discriminate α-synuclein fibrillar polymorphs from different synucleinopathies

Synucleinopathies, including dementia with Lewy bodies (DLB), Parkinson's disease (PD), and multiple system atrophy (MSA), are characterized by the presence of α-synuclein (α-syn) aggregates in the central nervous system. Recent evidence suggests that the heterogeneity of synucleinopathies may be partly explained by the fact that patients may have different α-syn fibrillar polymorphs with structural differences. In this study, we identify nuclease resistant 2'fluoro-pyrimidine RNA aptamers that can differentially bind to structurally distinct α-syn fibrillar polymorphs. Moreover, we introduce a method, AptaFOOT-Seq, designed to rapidly assess the affinity of a mixture of these aptamers for different α-SYN fibrillar polymorphs using next-generation sequencing. Our findings reveal that the binding behavior of aptamers can be very different when they are tested separately or in the presence of other aptamers. In this case, competition and cooperation can occur, providing a higher level of information, which can be exploited to obtain specific 'footprints' for different α-Syn fibrillar polymorphs. Notably, these footprints can distinguish polymorphs obtained from patients with PD, DLB or MSA. This result suggests that aptaFOOT-Seq could be used for the detection of misfolded or abnormal protein conformations to improve the diagnosis of synucleinopathies.

Interplay between Copper, Phosphatidylserine, and α-Synuclein Suggests a Link between Copper Homeostasis and Synaptic Vesicle Cycling

Copper homeostasis is critical to the functioning of the brain, and its breakdown is linked with many brain diseases. Copper is also known to interact with the negatively charged lipid, phosphatidylserine (PS), as well as α-synuclein, an aggregation-prone protein enriched in the synapse, which plays a role in synaptic vesicle docking and fusion. However, the interplay between copper, PS lipid, and α-synuclein is not known. Herein, we report a detailed and predominantly kinetic study of the interactions among these three components pertinent to copper homeostasis and neurotransmission. We found that synaptic vesicle-mimicking small unilamellar vesicles (SUVs) can sequester any excess free Cu2+ within milliseconds, and bound Cu2+ on SUVs can be reduced to Cu+ by GSH at a nearly constant rate under physiological conditions. Moreover, we revealed that SUV-bound Cu2+ does not affect the binding between wild-type α-synuclein and SUVs but affect that between N-terminal acetylated α-synuclein and SUVs. In contrast, Cu2+ can effectively displace both types of α-synuclein from the vesicles. Our results suggest that synaptic vesicles may mediate copper transfer in the brain, while copper could participate in synaptic vesicle docking to the plasma membrane via its regulation of the interaction between α-synuclein and synaptic vesicle.

Imaging α-synuclein pathologies in animal models and patients with Parkinson's and related diseases

Deposition of α-synuclein fibrils is implicated in Parkinson's disease (PD) and dementia with Lewy bodies (DLB), while in vivo detection of α-synuclein pathologies in these illnesses has been challenging. Here, we have developed a small-molecule ligand, C05-05, for visualizing α-synuclein deposits in the brains of living subjects. In vivo optical and positron emission tomography (PET) imaging of mouse and marmoset models demonstrated that C05-05 captured a dynamic propagation of fibrillogenesis along neural pathways, followed by disruptions of these structures. High-affinity binding of 18F-C05-05 to α-synuclein aggregates in human brain tissues was also proven by in vitro assays. Notably, PET-detectable 18F-C05-05 signals were intensified in the midbrains of PD and DLB patients as compared with healthy controls, providing the first demonstration of visualizing α-synuclein pathologies in these illnesses. Collectively, we propose a new imaging technology offering neuropathology-based translational assessments of PD and allied disorders toward diagnostic and therapeutic research and development.

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

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

Image post-processing for SILMAS: structured illumination light sheet microscopy with axial sweeping

In this article, we propose a post-processing scheme for the novel volumetric microscopy technique SILMAS. We demonstrate this scheme on data from an alpha-synuclein transgenic mouse brain. By combining structured illumination and axial sweeping, a SILMAS measurement provides a prerequisite for quantitative data extraction through improved contrast and optical sectioning. However, due to the technique's efficient removal ofb multiple scattered light, image artifacts such as illumination inhomogeneity, shadowing stripes, and signal attenuation, are highlighted in the recorded volumes. To suppress these artifacts, we rely on the strengths of the imaging method. The SILMAS data, together with the Beer-Lambert law, allow for an approximation of real light extinction, which can be used to compensate for light attenuation in a near-quantitative way. Shadowing stripes can be suppressed efficiently using a computational strategy thanks to the large numerical aperture of an axially swept light sheet. Here, we build upon prior research that employed wavelet-Fourier filtering by incorporating an extra bandpass step. This allows us to filter high-contrast light sheet microscopy data without introducing new artifacts and with minimal distortion of the data. The combined technique is suitable for imaging cleared tissue samples of up to a centimeter scale with an isotropic resolution of a few microns. The combination of a thin and uniform light sheet, scattered light suppression, light attenuation compensation, and shadowing suppression produces volumetric data that is seamless and highly uniform.

Elucidating the mechanisms of α-Synuclein-lipid interactions using site-directed mutagenesis

α-Synuclein (α-syn) is a small protein that is involved in cell vesicle trafficking in neuronal synapses. A progressive aggregation of this protein is the expected molecular cause of Parkinson's disease, a disease that affects millions of people around the world. A growing body of evidence indicates that phospholipids can strongly accelerate α-syn aggregation and alter the toxicity of α-syn oligomers and fibrils formed in the presence of lipid vesicles. This effect is attributed to the presence of high copies of lysines in the N-terminus of the protein. In this study, we performed site-directed mutagenesis and replaced one out of two lysines at each of the five sites located in the α-syn N-terminus. Using several biophysical and cellular approaches, we investigated the extent to which six negatively charged fatty acids (FAs) could alter the aggregation properties of K10A, K23A, K32A, K43A, and K58A α-syn. We found that FAs uniquely modified the aggregation properties of K43A, K58A, and WT α-syn, as well as changed morphology of amyloid fibrils formed by these mutants. At the same time, FAs failed to cause substantial changes in the aggregation rates of K10A, K23A, and K32A α-syn, as well as alter the morphology and toxicity of the corresponding amyloid fibrils. Based on these results, we can conclude that K10, K23, and K32 amino acid residues play a critical role in protein-lipid interactions since their replacement on non-polar alanines strongly suppressed α-syn-lipid interactions.

Transcellular transmission and molecular heterogeneity of aggregation-prone proteins in neurodegenerative diseases

The accumulation of aggregation-prone proteins in a specific neuronal population is a common feature of neurodegenerative diseases, which is correlated with the development of pathological lesions in diseased brains. The formation and progression of pathological protein aggregates in susceptible neurons induce cellular dysfunction, resulting in progressive degeneration. Moreover, recent evidence supports the notion that the cell-to-cell transmission of pathological protein aggregates may be involved in the onset and progression of many neurodegenerative diseases. Indeed, several studies have identified different pathological aggregate strains. Although how these different aggregate strains form remains unclear, a variety of biomolecular compositions or cross-seeding events promoted by the presence of other protein aggregates in the cellular environment may affect the formation of different strains of pathological aggregates, which in turn can influence complex pathologies in diseased brains. In this review, we summarize the recent results regarding cell-to-cell transmission and the molecular heterogeneity of pathological aggregate strains, raising key questions for future research directions.

Ion channel dysregulation and cellular adaptations to alpha-synuclein in stressful pacemakers of the parkinsonian brainstem

Parkinson's disease (PD) is diagnosed by its cardinal motor symptoms that are associated with the loss of dopamine neurons in the substantia nigra pars compacta (SNc). However, PD patients suffer from various non-motor symptoms years before diagnosis. These prodromal symptoms are thought to be associated with the appearance of Lewy body pathologies (LBP) in brainstem regions such as the dorsal motor nucleus of the vagus (DMV), the locus coeruleus (LC) and others. The neurons in these regions that are vulnerable to LBP are all slow autonomous pacemaker neurons that exhibit elevated oxidative stress due to their perpetual influx of Ca2+ ions. Aggregation of toxic α-Synuclein (aSyn) - the main constituent of LBP - during the long prodromal period challenges these vulnerable neurons, presumably altering their biophysics and physiology. In contrast to pathophysiology of late stage parkinsonism which is well-documented, little is known about the pathophysiology of the brainstem during prodromal PD. In this review, we discuss ion channel dysregulation associated with aSyn aggregation in brainstem pacemaker neurons and their cellular responses to them. While toxic aSyn elevates oxidative stress in SNc and LC pacemaker neurons and exacerbates their phenotype, DMV neurons mount an adaptive response that mitigates the oxidative stress. Ion channel dysregulation and cellular adaptations may be the drivers of the prodromal symptoms of PD. For example, selective targeting of toxic aSyn to DMV pacemakers, elevates the surface density of K+ channels, which slows their firing rate, resulting in reduced parasympathetic tone to the gastrointestinal tract, which resembles the prodromal PD symptoms of dysphagia and constipation. The divergent responses of SNc & LC vs. DMV pacemaker neurons may explain why the latter outlive the former despite presenting LBPs earlier. Elucidation the brainstem pathophysiology of prodromal PD could pave the way for physiological biomarkers, earlier diagnosis and novel neuroprotective therapies for PD.

Neuroanatomical and cognitive biomarkers of alpha-synuclein propagation in a mouse model of synucleinopathy prior to onset of motor symptoms

Significant evidence suggests that misfolded alpha-synuclein (aSyn), a major component of Lewy bodies, propagates in a prion-like manner contributing to disease progression in Parkinson's disease (PD) and other synucleinopathies. In fact, timed inoculation of M83 hemizygous mice with recombinant human aSyn preformed fibrils (PFF) has shown symptomatic deficits after substantial spreading of pathogenic alpha-synuclein, as detected by markers for the phosphorylation of S129 of aSyn. However, whether accumulated toxicity impact human-relevant cognitive and structural neuroanatomical measures is not fully understood. Here we performed a single unilateral striatal PFF injection in M83 hemizygous mice, and using two assays with translational potential, ex vivo magnetic resonance imaging (MRI) and touchscreen testing, we examined the combined neuroanatomical and behavioral impact of aSyn propagation. In PFF-injected mice, we observed widespread atrophy in bilateral regions that project to or receive input from the injection site using MRI. We also identified early deficits in reversal learning prior to the emergence of motor symptoms. Our findings highlight a network of regions with related cellular correlates of pathology that follow the progression of aSyn spreading, and that affect brain areas relevant for reversal learning. Our experiments suggest that M83 hemizygous mice injected with human PFF provides a model to understand how misfolded aSyn affects human-relevant pre-clinical measures and suggest that these pre-clinical biomarkers could be used to detect early toxicity of aSyn and provide better translational measures between mice and human disease.

Design of amyloidogenic peptide traps

Segments of proteins with high β-strand propensity can self-associate to form amyloid fibrils implicated in many diseases. We describe a general approach to bind such segments in β-strand and β-hairpin conformations using de novo designed scaffolds that contain deep peptide-binding clefts. The designs bind their cognate peptides in vitro with nanomolar affinities. The crystal structure of a designed protein-peptide complex is close to the design model, and NMR characterization reveals how the peptide-binding cleft is protected in the apo state. We use the approach to design binders to the amyloid-forming proteins transthyretin, tau, serum amyloid A1 and amyloid β1-42 (Aβ42). The Aβ binders block the assembly of Aβ fibrils as effectively as the most potent of the clinically tested antibodies to date and protect cells from toxic Aβ42 species.