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

Decreased levels of phosphorylated synuclein in plasma are correlated with poststroke cognitive impairment

JOURNAL/nrgr/04.03/01300535-202509000-00022/figure1/v/2024-11-05T132919Z/r/image-tiff Poststroke cognitive impairment is a major secondary effect of ischemic stroke in many patients; however, few options are available for the early diagnosis and treatment of this condition. The aims of this study were to (1) determine the specific relationship between hypoxic and α-synuclein during the occur of poststroke cognitive impairment and (2) assess whether the serum phosphorylated α-synuclein level can be used as a biomarker for poststroke cognitive impairment. We found that the phosphorylated α-synuclein level was significantly increased and showed pathological aggregation around the cerebral infarct area in a mouse model of ischemic stroke. In addition, neuronal α-synuclein phosphorylation and aggregation were observed in the brain tissue of mice subjected to chronic hypoxia, suggesting that hypoxia is the underlying cause of α-synuclein-mediated pathology in the brains of mice with ischemic stroke. Serum phosphorylated α-synuclein levels in patients with ischemic stroke were significantly lower than those in healthy subjects, and were positively correlated with cognition levels in patients with ischemic stroke. Furthermore, a decrease in serum high-density lipoprotein levels in stroke patients was significantly correlated with a decrease in phosphorylated α-synuclein levels. Although ischemic stroke mice did not show significant cognitive impairment or disrupted lipid metabolism 14 days after injury, some of them exhibited decreased cognitive function and reduced phosphorylated α-synuclein levels. Taken together, our results suggest that serum phosphorylated α-synuclein is a potential biomarker for poststroke cognitive impairment.

A model of L-DOPA-induced dyskinesia in parkinsonian mice produced by AAV vector-mediated overexpression of α-synuclein

L-3,4-dihydroxyphenylalanin (L-DOPA) is the most effective drug for treating Parkinson's disease (PD); however, long-term L-DOPA therapy can lead to L-DOPA-induced dyskinesia (LID). While the 6-hydroxydopamine-lesioned rodent model for LID fails to reproduce the pathological hallmarks of PD, a newly introduced rodent model using adeno-associated virus (AAV)-mediated overexpression of α-synuclein results in α-synuclein aggregation and progressive loss of dopaminergic neurons. The present study aimed to provoke LID in parkinsonian mice generated by AAV vector-mediated overexpression of α-synuclein and to explore histologic features associated with LID. A recombinant AAV2/7 vector containing the human α-synuclein transgene was injected into the substantia nigra (SN) of wild-type mice. Eight weeks later, mice received daily injections of 10 mg/kg of L-DOPA for one week, followed by 25 mg/kg of L-DOPA daily for the subsequent week. LID was observed in 3 out of 19 mice at the 10 mg/kg L-DOPA dose and in 14 mice at 25 mg/kg dose. The number of tyrosine hydroxylase (TH)-positive neurons in the AAV vector-injected side of the SN was reduced to an average of 59 % of the intact side, and the optical density of TH-positive fibers in the ipsilateral striatum was reduced to an average of 37 %. Abnormal Involuntary Movement scores were correlated with decrease in both the number of TH-positive neurons in SN and optical density of striatal TH-positive fibers. This study establishes a mouse model for LID using AAV vector-mediated overexpression of α-synuclein, providing a useful tool for investigating the progressive changes and associated pathophysiology during occurrence of LID.

Early α-synuclein aggregation decreases corticostriatal glutamate drive and synapse density

Neuronal inclusions of α-synuclein (α-syn) are pathological hallmarks of Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB). α-Syn pathology accumulates in cortical neurons which project to the striatum. To understand how α-syn pathology affects cortico-striatal synapses at early time points before significant dopamine neuron loss, pre-formed α-syn fibrils (PFF) were injected into the striatum to induce endogenous α-syn aggregation in corticostriatal-projecting neurons. Electrophysiological recordings of striatal spiny projection neurons (SPNs) from acute slices found a significant decrease in evoked corticostriatal glutamate release and corticostriatal synaptic release sites in mice with PFF-induced aggregates compared to monomer injected mice. Expansion microscopy, confocal microscopy and Imaris reconstructions were used to identify VGLUT1 positive presynaptic terminals juxtaposed to Homer1 positive postsynaptic densities, termed synaptic loci. Quantitation of synaptic loci density revealed an early loss of corticostriatal synapses. Immunoblots of the striatum showed reductions in expression of pre-synaptic proteins VGLUT1, VAMP2 and Snap25, in mice with α-syn aggregates compared to controls. Paradoxically, a small percentage of remaining VGLUT1+ synaptic loci positive for pS129-α-syn aggregates showed enlarged volumes compared to nearby synapses without α-syn aggregates. Our combined physiology and high-resolution imaging data point to an early loss of corticostriatal synapses in mice harboring α-synuclein inclusions, which may contribute to impaired basal ganglia circuitry in PD and DLB.

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.

α-Synuclein pathology and mitochondrial dysfunction: Toxic partners in Parkinson's disease

Two major neuropathological features of Parkinson's disease (PD) are α-synuclein Lewy pathology and mitochondrial dysfunction. Although both α-synuclein pathology and mitochondrial dysfunction may independently contribute to PD pathogenesis, the interaction between these two factors is not yet fully understood. In this review, we discuss the physiological functions of α-synuclein and mitochondrial homeostasis in neurons as well as the pathological defects that ensue when these functions are disturbed in PD. Recent studies have highlighted that dysfunctional mitochondria can become sequestered within Lewy bodies, and cell biology studies have suggested that α-synuclein can directly impair mitochondrial function. There are also PD cases caused by genetic or environmental perturbation of mitochondrial homeostasis. Together, these studies suggest that mitochondrial dysfunction may be a common pathway to neurodegeneration in PD, triggered by multiple insults. We review the literature surrounding the interaction between α-synuclein and mitochondria and highlight open questions in the field that may be explored to advance our understanding of PD and develop novel, disease-modifying therapies.

Mesenchymal stem cells enhance selective ER-phagy to promote α-synuclein clearance in Parkinson's disease

Ample evidence suggests that α-synuclein (αSyn) accumulation in the endoplasmic reticulum (ER) leads to ER stress, resulting in neurodegeneration in Parkinson's disease (PD). Selective degradation of accumulated αSyn through ER-phagy can alleviate ER stress and rescue neurodegeneration. In the present study, we investigated whether mesenchymal stem cells (MSCs) exert neuroprotective effects against PD by modulating ER-phagy. In a cellular model overexpressing αSyn specifically in the ER (ER-αSyn), co-culture with MSCs promoted ER-αSyn clearance through selective ER-phagy and also recovered cell viability. Injection of MSCs to an animal model using adeno-associated virus vectors to overexpress αSyn in the ER (AAV-ER- αSyn), also decreased the expression of aSyn in the ER and attenuated the dopaminergic neuronal loss in substantia nigra (SN) and denervation in striatum (ST), followed by functional improvement of motor deficits. In vitro screening identified that MSCs promoted family with sequence similarity 134 member B (FAM134B)-mediated ER-phagy via regulating transcription factor of nuclear subfamily 4 group A member 1 (NR4A1), and it underwent in vivo validation. This study suggests that MSCs modulate FAM134B-mediated ER-phagy under the regulation of NR4A1, promoting the clearance of ER-accumulated αSyn in PD cellular and murine models.

Convergent large-scale network and local vulnerabilities underlie brain atrophy across Parkinson's disease stages: a worldwide ENIGMA study

Parkinson's disease (PD) is associated with extensive structural brain changes. Recent work has proposed that the spatial pattern of disease pathology is shaped by both network spread and local vulnerability. However, only few studies assessed these biological frameworks in large patient samples across disease stages. Analyzing the largest imaging cohort in PD to date (N = 3,096 patients), we investigated the roles of network architecture and local brain features by relating regional abnormality maps to normative profiles of connectivity, intrinsic networks, cytoarchitectonics, neurotransmitter receptor densities, and gene expression. We found widespread cortical and subcortical atrophy in PD to be associated with advancing disease stage, longer time since diagnosis, and poorer global cognition. Structural brain connectivity best explained cortical atrophy patterns in PD and across disease stages. These patterns were robust among individual patients. The precuneus, lateral temporal cortex, and amygdala were identified as likely network-based epicentres, with high convergence across disease stages. Individual epicentres varied significantly among patients, yet they consistently localized to the default mode and limbic networks. Furthermore, we showed that regional overexpression of genes implicated in synaptic structure and signalling conferred increased susceptibility to brain atrophy in PD. In summary, this study demonstrates in a well-powered sample that structural brain abnormalities in PD across disease stages and within individual patients are influenced by both network spread and local vulnerability.

Identification of biomarkers associated with inflammatory response in Parkinson's disease by bioinformatics and machine learning

Parkinson's disease (PD) is a common and debilitating neurodegenerative disorder. The inflammatory response is essential in the pathogenesis and progression of PD. The goal of this study is to combine bioinformatics and machine learning to screen for biomarker genes related to the inflammatory response in PD. First, differentially expressed genes associated with inflammatory response were screened, PPI networks were constructed and enriched for analysis. LASSO, SVM-RFE and Random Forest algorithms were used to screen biomarker genes. Then, ROC curves were drawn and PD risk predicting models were constructed on the basis of the biomarker genes. Finally, drug sensitivity analysis, mRNA-miRNA network construction and single-cell transcriptome data analysis were performed. The experimental results showed that we screened 31 differentially expressed genes related to inflammatory response. Signaling pathways such as cytokine activity were associated with these genes. Three biomarkers were identified using machine learning algorithms: IL18R1, NMUR1 and RELA. Seventeen co-associated miRNAs were identified by the mRNA-miRNA network as possible regulatory nodes in PD. Finally, these three biomarkers were found to be closely associated with T cells, Endothelial cells, excitatory neurons, inhibitory neurons, and other cells in single-cell transcriptomic analysis. In conclusion, IL18R1, NMUR1 and RELA could be potential therapeutic targets for PD in inflammatory response and new biomarkers for PD diagnosis.

Key Connectomes and Synaptic-Compartment-Specific Risk Genes Drive 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 genes that affect pathology spreading functioning at presynaptic or postsynaptic regions, and are these genes enriched in different cell types? Here, these questions are addressed 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. Genes associated with the selective vulnerability of brain regions to pathological α-Syn transmission are further analyzed to distinguish those functioning at presynaptic versus postsynaptic regions. Those risk genes are significantly enriched in microglial cells of presynaptic regions and neurons of postsynaptic regions. Gene regulatory network analyses are 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, this study has demonstrated for the first time that these are functionally distinct processes.

Development of human targeted extracellular vesicles loaded with shRNA minicircles to prevent parkinsonian pathology

BACKGROUND

Neurological disorders are the second leading cause of death and the leading cause of disability in the world. Thus, the development of novel disease-modifying strategies is clearly warranted. We have previously developed a therapeutic approach using mouse targeted rabies virus glycoprotein (RVG) extracellular vesicles (EVs) to deliver minicircles (MCs) expressing shRNA (shRNA-MCs) to induce long-term α-synuclein down-regulation. Although the previous therapy successfully reduced the pathology, the clinical translation was extremely unlikely since they were mouse extracellular vesicles.

METHODS

To overcome this limitation, we developed a source of human RVG-EVs compatible with a personalized therapy using immature dendritic cells. Human peripheral blood monocytes were differentiated in vitro into immature dendritic cells, which were transfected to express the RVG peptide. RVG-EVs containing shRNA-MCs, loaded by electroporation, were injected intravenously in the α-synuclein performed fibril (PFF) mouse model. Level of α-synuclein, phosphorylated α-synuclein aggregates, dopaminergic neurons and motor function were evaluated 90 days after the treatment. To confirm that EVs derived from patients were suitable as a vehicle, proteomic analysis of EVs derived from control, initial and advanced Parkinson's disease was performed.

RESULTS

The shRNA-MCs could be successfully loaded into human RVG-EVs and downregulate α-synuclein in SH-SY5Y cells. Intravenous injection of the shRNA-MC-loaded RVG-EVs induced long-term downregulation of α-synuclein mRNA expression and protein level, decreased α-synuclein aggregates, prevented dopaminergic cell death and ameliorated motor impairment in the α-synuclein PFF mouse model. Moreover, we confirmed that the EVs from PD patients are suitable as a personalized therapeutic vehicle.

CONCLUSION

Our study confirmed the therapeutic potential of shRNA-MCs delivered by human RVG-EVs for long-term treatment of neurodegenerative diseases. These results pave the way for clinical use of this approach.

Rational selection of the monoclonal α-synuclein antibody amlenetug (Lu AF82422) for the treatment of α-synucleinopathies

Amlenetug (Lu AF82422) is a human monoclonal antibody targeting α-synuclein in clinical development for multiple system atrophy. We describe a series of studies that characterize its functional properties and supported its selection as a viable clinical candidate. Amlenetug inhibits seeding induced in mouse primary neurons by various α-synuclein fibrillar assemblies and by aggregates isolated from MSA brain homogenate. In vivo, both co-injection of amlenetug with α-synuclein assemblies in mouse brain and peripheral administration inhibit α-synuclein seeding. Amlenetug inhibits uptake of α-synuclein seeds as well as accumulation of C-terminal truncated α-synuclein seeds and demonstrates binding to monomeric, aggregated, and truncated forms of human α-synuclein. The epitope of amlenetug was mapped to amino acids 112-117 and further characterized by crystallographic structure analysis. Based on our data, we hypothesize that targeting α-synuclein will potentially slow further disease progression by inhibiting further pathology development but be without impact on established pathology and symptoms.

TIGAR plays neuroprotective roles in MPP+/MPTP-induced Parkinson's disease by alleviating ferroptosis

Parkinson's disease (PD) is a common neurodegenerative disorder worldwide, characterized by the loss of dopaminergic (DA) neurons in the substantia nigra and is associated with iron dyshomeostasis. Ferroptosis, a form of programmed cell death, involves iron-dependent lipid peroxidation and serves as a significant regulatory mechanism in PD. This study identified Tp53-induced glycolysis and apoptosis regulator (TIGAR) as a potential regulator of ferroptosis resistance in PD development. In this study, we demonstrated that in HT22 cells, 1-methyl-4-phenylpyridinium (MPP+) increased lipid peroxidation levels and reduced cell viability. These effects were reversed by the ferroptosis inhibitor ferrostatin-1 (Fer-1). MPP+ also induced elevated intracellular iron ion deposition, reactive oxygen species (ROS), and the lipid peroxidation product malondialdehyde (MDA). Meanwhile, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) significantly decreased glutathione (GSH) and nicotinamide adenine dinucleotide phosphate (NADPH) levels, glutathione peroxidase (GPX) activity, and TIGAR expression, all of which were reversible with TIGAR overexpression. In an MPTP-induced in vivo PD model, TIGAR overexpression markedly increased DA neurons and reduced iron deposition. To summarize, TIGAR enhances intracellular NADPH production via the promotion of the pentose phosphate pathway (PPP), reduces intracellular glutathione disulfide (GSSG) to GSH, boosts GPX activity, and inhibits ferroptosis, thus providing neuronal protection.

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.

Intracellular Inclusions Induced by Patient-Derived and Amplified α-Synuclein Aggregates Are Morphologically Indistinguishable

Lewy Body Disease (LBD) and Multiple System Atrophy (MSA) are synucleinopathies with distinct prognoses and neuropathologies, however, with overlapping clinical symptoms. Different disease characteristics are proposed to be determined by distinct conformations of alpha-synuclein (α-Syn) aggregates, which can self-propagate and spread between cells via a prion-like mechanism. The goal of this study is to investigate whether α-syn aggregates amplified from brain and CSF samples of LBD and MSA patients using the Seed Amplification Assay (SAA) maintain α-Syn seeding properties similar to those of α-syn aggregates derived from patients' brains. To address this, SAA-amplified and un-amplified α-Syn aggregates from LBD and MSA patients' brains, as well as SAA-amplified α-Syn aggregates from LBD and MSA patients' CSF samples, were used to treat synuclein biosensor cells, and induced intracellular α-Syn inclusions were analyzed by confocal microscopy. Our data indicate that induced α-Syn aggregates from LBD and MSA patients' brains have similar seeding properties and morphological characteristics in the α-Syn biosensor cells as those amplified from LBD and MSA patients' brains, as well as those amplified from LBD and MSA patients' CSF samples. In this study, we demonstrated that, regardless of the source of aggregates, the seeds from LBD and MSA produce cellular accumulation of α-Syn with distinct morphologies, confirming the presence of different conformational strains of α-Syn in LBD and MSA and allowing us to differentiate synucleinopathies based on the morphology of aggregates and seeding properties.

Effect of RNA on the supramolecular architecture of α-synuclein fibrils

Structural changes associated with protein aggregation are challenging to study, requiring the combination of experimental techniques providing insights at the molecular level across diverse scales, ranging from nanometers to microns. Understanding these changes is even more complex when aggregation occurs in the presence of molecular cofactors such as nucleic acids and when the resulting aggregates are highly polymorphic. Infrared (IR) spectroscopy is a powerful tool for studying protein aggregates since it combines the label-free sensitivity to the cross-β architecture, an inherent feature of protein supramolecular aggregates, with the possibility to reach nanoscale sensitivity by leveraging atomic force microscopy (AFM)-assisted detection. Here, we present a combined approach that detects IR spectral markers of aggregation using various IR spectroscopy techniques, covering micro-to-nanoscale ranges, to study the effect of RNA on the supramolecular architecture of α-synuclein amyloid aggregates. We show a clear impact of RNA consistent with enhanced intermolecular forces, likely via a stronger hydrogen-bonded network stabilizing the cross-β architecture. AFM-assisted IR spectroscopy was crucial to assess that the more ordered the aggregates are, the stronger the structural impact of RNA. In addition, an RNA-induced reduction of the degree of polymorphism within the aggregate population is obtained.

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.

The relationship between serum GDF15 levels and non-motor symptoms in Parkinson's disease

OBJECTIVES

The primary aim was to investigate the relationship between serum growth differentiation factor-15 (GDF15) levels and non-motor symptom (NMS) in Parkinson's disease (PD) patients. The secondary aim was to explore the diagnostic value of GDF15 for specific NMS.

METHODS

A total of 102 PD patients were enrolled in this study, including 47 males and 55 females. Doctors collected the clinical and demographic information of patients and detected the level of serum GDF15. Next, linear univariate and multivariate linear regression analyses were used to assess the correlation between GDF15 and NMS. Receiver operating characteristic curve analysis was performed to determine the optimal cut-off value of GDF15 and evaluate its diagnostic value.

RESULTS

In PD patients, there was no significant difference in serum GDF15 levels between males and females (p = 0.831). Age of PD onset, pesticide use, depression, sexual dysfunction, Epworth Sleepiness Scale (ESS) and Hamilton Depression Scale (HAMD) were associated with serum GDF15. Serum GDF15 was negatively correlated with HAMD, depression and sexual dysfunction and positively correlated with ESS. Each 10 pg/ml increase in serum GDF15 levels was associated with a 4% lower risk of depression and a 5% lower risk of sexual dysfunction. Notably, serum GDF15 may be a biomarker for distinguishing depression and sexual dysfunction in PD patients.

CONCLUSION

Elevated serum GDF15 reduced the risk of PD with depression and sexual dysfunction. Serum GDF15 may be a biomarker for distinguishing depression and sexual dysfunction in PD patients.

GDNF reduces fibril-induced early-stage alpha-synuclein pathology after delivery of 20S proteasome inhibitor lactacystin

Failures in protein homeostasis are linked to Parkinson's disease (PD) and other neurodegenerative diseases. Lewy bodies, proteinaceous inclusions rich in phosphorylated alpha-synuclein are a hallmark of PD. Glial cell line-derived neurotrophic factor (GDNF) can eliminate Lewy body-like inclusions in mouse dopamine neurons. This study explores whether GDNF has protective effects against alpha-synuclein protofibril toxicity under proteasome inhibition by lactacystin, both in vitro and in vivo. GDNF did not shield midbrain dopamine neurons from lactacystin-induced neurodegeneration, but still prevented phosphorylated alpha-synuclein accumulation. In vivo experiment with control or GDNF-expressing viral vectors assessed alpha-synuclein pathology spread in the nigrostriatal pathway and lactacystin-caused damage in the midbrain. GDNF overexpression reduced phosphorylated alpha-synuclein inclusions. Lactacystin-treated mice showed motor asymmetry and decreased spontaneous activity, exacerbated without AAV-GDNF pre-treatment. However, GDNF's neuroprotective effect could not be confirmed in vivo, due to side-effects from overexpression in the midbrain. Importantly, these findings show that GDNF continues to eliminate alpha-synuclein aggregation despite lactacystin-induced proteasome inhibition. Activating neurotrophic signaling pathways may protect against alpha-synuclein pathology in PD, even with impaired protein degradation mechanisms.

α-Synuclein in Parkinson's Disease: From Bench to Bedside

α-Synuclein (α-syn), a pathological hallmark of PD, is emerging as a bridging element at the crossroads between neuro/immune-inflammatory responses and neurodegeneration in PD. Several evidence show that pathological α-syn accumulates in neuronal and non-neuronal cells (i.e., neurons, microglia, macrophages, skin cells, and intestinal cells) in central and peripheral tissues since the prodromal phase of the disease, contributing to brain pathology. Indeed, pathological α-syn deposition can promote neurogenic/immune-inflammatory responses that contribute to systemic and central neuroinflammation associated with PD. After providing an overview of the structure and functions of physiological α-syn as well as its pathological forms, we review current studies about the role of neuronal and non-neuronal α-syn at the crossroads between neuroinflammation and neurodegeneration in PD. In addition, we provide an overview of the correlation between the accumulation of α-syn in central and peripheral tissues and PD, related symptoms, and neuroinflammation. Special attention was paid to discussing whether targeting α-syn can represent a suitable therapeutical approach for PD.

Nicotine Ameliorates α-Synuclein Preformed Fibril-Induced Behavioral Deficits and Pathological Features in Mice

Epidemiologic study suggests that nicotine reduces the risk of Parkinson's disease (PD) and thus could serve as a potential treatment. In this study, we aimed to investigate the effect of nicotine on the behavioral phenotypes and pathological characteristics of mice induced by human alpha-synuclein preformed fibers (α-syn-PFF). Mice were injected with 5 µg of human α-syn-PFF in the hippocampus while administering nicotine-containing drinking water (200 µg/mL). After 1 month, the motor ability, mood, spatial learning, and memory ability of the PD phenotype-like model mice were detected using open field, rotarod, Y maze, and O maze tests. The expression of pathological α-syn and apoptotic proteins, as well as the number of glial and neural stem cells in the hippocampus of mice, was detected using western blot and immunofluorescence. The results demonstrated that nicotine significantly reduced pathological α-syn accumulation, α-syn serine 129 phosphorylation, and apoptosis induced by α-syn-PFF injection in the hippocampus of mice. Nicotine also inhibited the increase in the number of glia, microglia, and neuronal apoptotic cells, and it decreased the expression of PI3K and Akt while also exhibiting significant memory impairment, motor deficits, and anxiety-like behavior. In conclusion, our findings suggest that nicotine ameliorates behavioral deficits and pathological changes in mice by inhibiting human α-syn-PFF-induced neuroinflammation and apoptosis.

Fibril-seeded animal models of synucleinopathies: Pathological mechanisms, disease modeling, and therapeutic implications

Accumulating evidence suggests that prion-like spread of misfolded α-Synuclein (αSyn) underlies the pathological progression of Lewy body diseases (LBD). Animal models injected with αSyn preformed fibrils (PFFs) have provided strong evidence for the prion hypothesis in LBD. Moreover, αSyn PFFs can be administered to various hosts and regions, contributing to the elucidation of pathological mechanisms and disease modeling. These models have also been used to identify biomarkers and develop new disease-modifying therapies for LBD. In contrast, it remains unknown how the prion-like properties of αSyn contribute to the pathogenesis of multiple system atrophy (MSA). Recent studies indicate that conformationally distinct αSyn fibrils induce different pathological features in animals, supporting the strain hypothesis, which suggests that conformational variations in αSyn fibrils contribute to the clinicopathological heterogeneity in synucleinopathies. However, the study of disease-specific αSyn fibrils in pathological mechanisms and disease modeling is still in its early stages. This review aims to highlight recent advances in αSyn fibril-seeded animal models with an emphasis on their unique features and utility in exploring pathological mechanisms and identifying novel disease-modifying therapies. In addition, I discuss future directions for refining these models in light of the emerging strain hypothesis in synucleinopathies.

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.

SLC7A11 is an unconventional H+ transporter in lysosomes

Lysosomes maintain an acidic pH of 4.5-5.0, optimal for macromolecular degradation. Whereas proton influx is produced by a V-type H+ ATPase, proton efflux is mediated by a fast H+ leak through TMEM175 channels, as well as an unidentified slow pathway. A candidate screen on an orphan lysosome membrane protein (OLMP) library enabled us to discover that SLC7A11, the protein target of the ferroptosis-inducing compound erastin, mediates a slow lysosomal H+ leak through downward flux of cystine and glutamate, two H+ equivalents with uniquely large but opposite concentration gradients across lysosomal membranes. SLC7A11 deficiency or inhibition caused lysosomal over-acidification, reduced degradation, accumulation of storage materials, and ferroptosis, as well as facilitated α-synuclein aggregation in neurons. Correction of abnormal lysosomal acidity restored lysosome homeostasis and prevented ferroptosis. These studies have revealed an unconventional H+ transport conduit that is integral to lysosomal flux of protonatable metabolites to regulate lysosome function, ferroptosis, and Parkinson's disease (PD) pathology.

The Gut-Brain Axis Based on α-Synuclein Propagation-Clinical, Neuropathological, and Experimental Evidence

The cytopathological hallmark of Parkinson's disease (PD) is a neuronal cytoplasmic inclusion called Lewy body (LB). Lewy bodies are composed of alpha-synuclein (aSyn), a 140 aa protein that is predominantly expressed in the presynaptic terminal and which is implicated in neurotransmitter release. Recently, aSyn was found to propagate from neuron to neuron in a trans-synaptic manner. Although the precise molecular mechanisms are unclear, the propagation of aSyn is believed to play a major role in the progression of Lewy pathology in PD. Neuropathologically, the initial Lewy pathology has been shown to be formed in the dorsal motor nucleus of the vagus (DMV) or olfactory bulb by neuropathological studies. Since the DMV innervates the enteric nervous system (ENS) and LBs are formed in the gut nerve plexuses, it is conceivable that LBs propagate from the gut to the DMV and then to other regions of the brain. In this article, clinical, neuropathological, and experimental evidence supporting or negating the idea that aSyn propagation from the ENS to the brain leads to PD is reviewed. Moreover, the propagation of aSyn seeds through systemic circulation or multifocal generation of aSyn seeds is discussed as a potential alternative scenario for aSyn spreading.

Research models to study lewy body dementia

Lewy body dementia (LBD) encompasses neurodegenerative dementias characterized by cognitive fluctuations, visual hallucinations, and parkinsonism. Clinical differentiation of LBD from Alzheimer's disease (AD) remains complex due to symptom overlap, yet approximately 25% of dementia cases are diagnosed as LBD postmortem, primarily identified by the presence of α-synuclein aggregates, tau tangles, and amyloid plaques. These pathological features position LBD as a comorbid condition of both Parkinson's disease (PD) and AD, with over 50% of LBD cases exhibiting co-pathologies. LBD's mixed pathology complicates the development of comprehensive models that reflect the full spectrum of LBD's etiological, clinical, and pathological features. While existing animal and cellular models have facilitated significant discoveries in PD and AD research, they lack specificity in capturing LBD's unique pathogenic mechanisms, limiting the exploration of therapeutic avenues for LBD specifically. This review assesses widely used PD and AD models in terms of their relevance to LBD, particularly focusing on their ability to replicate human disease pathology and assess treatment efficacy. Furthermore, we discuss potential modifications to these models to advance the understanding of LBD mechanisms and propose innovative research directions aimed at developing models with enhanced etiological, face, predictive, and construct validity.

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.

A high-fidelity microfluidic platform reveals retrograde propagation as the main mechanism of α-Synuclein spread in human neurons

α-Synuclein (αSyn) is a major component of Lewy bodies and Lewy neurites, which are a pathological hallmark of Parkinson's disease (PD). Pathologically aggregated forms of αSyn can spread along neurites and induce the misfolding of normal αSyn. To elucidate how αSyn pathology propagates between brain areas, we developed a novel in vitro microfluidic platform to study the intracellular transport of preformed fibrils and the induction and spread of αSyn aggregates. Patient-derived midbrain dopaminergic (mDA) neurons were cultured in microfluidic devices designed to maintain unidirectional axonal connections between fluidically isolated mDA neuronal cultures for over 3 months. Using αSyn preformed fibrils to induce Lewy-like pathology, we found that anterograde spread of αSyn fibrils was slow and occurred at low levels, while retrograde spread was significantly more efficient. This is in line with observations in animal models and shows that the platform provides an innovative new tool for studying PD in vitro.

A No-Brainer! The Therapeutic Potential of TRIM Proteins in Viral and Central Nervous System Diseases

Tripartite motif (TRIM) proteins comprise an important class of E3 ubiquitin ligases that regulate numerous biological processes including protein expression, cellular signaling pathways, and innate immunity. This ubiquitous participation in fundamental aspects of biology has made TRIM proteins a focus of study in many fields and has illuminated the negative impact they exert when functioning improperly. Disruption of TRIM function has been linked to the success of various pathogens and separately to the occurrence and development of several neurodegenerative diseases, making TRIM proteins an appealing candidate to study for novel therapeutic approaches. Here, we review the current findings on TRIM proteins that demonstrate their analogous properties in the distinct fields of viral infection and central nervous system (CNS) disorders. We also examine recent advancements in drug development and targeted protein degradation as potential strategies for TRIM-mediated therapeutic treatments and discuss the implications these technologies have on future research directions.

OAB-14 Attenuated Glymphatic System Disorder, Neuroinflammation and Dyskinesia in Parkinson's Disease Model Mice Induced by Rotenone

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by the pathological accumulation of alpha-synuclein (α-syn) in the neuronal cell bodies of the substantia nigra. The glymphatic system within the Central Nervous System (CNS) is responsible for clearing metabolic waste and abnormal proteins and its dysfunction may significantly contribute to the pathogenesis of PD. Our previous study showed that OAB-14, the novel small molecular compound, showed a great potential effect in APP/PS1 transgenic mice. Given the similarities in the pathogenesis of PD and Alzheimer's disease (AD), it is pertinent to explore the therapeutic potential of OAB-14 in the context of PD. This study utilized a rotenone-induced PD mice model to evaluate the effects of oral administration of OAB-14, and its underlying mechanisms. Here we confirmed the neuroprotective effect and motor improvement of OAB-14 in rotenone-induced PD model mice. Our research has shown that OAB-14 is capable of enhancing the glymphatic system function by promoting the influx and efflux of the CSF tracers to the brain and deep cervical lymph nodes, respectively, to promote the clearance of α-syn. In addition, OAB-14 could down-regulate MyD88, NF-kB (Ser 536) phosphorylation, and TLR4 to reduce glial cell activation; and down-regulate cleaved-caspase1, NLRP3, ASC, IL-1β, IL-6, IL-18, TNF-α, and IL-10 to reduce the expression of inflammatory vesicles and pro-inflammatory factors, and to reduce neuronal oxidative stress. In summary, OAB-14 may promote the clearance of brain α-syn through the glial lymphatic system, inhibit the α-syn/TLR4/NF-κB/NLRP3 inflammatory pathway, and improve movement disorders.

An update on mammalian and non-mammalian animal models for biomarker development in neurodegenerative disorders

Neurodegeneration is one of the leading factor for death globally, affecting millions of people. Developing animal models are critical to understand biological processes and comprehend pathological hallmarks of neurodegenerative diseases. For decades, many animal models have served as excellent tools to determine the disease progression, develop diagnostic methods and design novel therapies against distinct pathologies. Here, we provide a comprehensive overview of both, mammalian and non-mammalian animal models, with a focus on three most common and aggressive neurodegenerative disorders: Alzheimer's disease, Parkinson's disease and Spinocerebellar ataxia-1. We highlight various approaches including transgene, gene transfer, and chemically-induced methods used to develop disease models. In particular, we discuss applications of both non-mammalian and mammalian contributions in research on neurodegeneration. It is exciting to learn the roles of animal models in disease pathomechanisms, identifying biomarkers and hence devising novel interventions to treat neuropathological conditions.

Tet2 loss and enhanced ciliogenesis suppress α-synuclein pathology

There are no approved treatments that slow Parkinson's disease (PD) progression and therefore it is important to identify novel pathogenic mechanisms that can be targeted. Loss of the epigenetic marker, Tet2 appears to have some beneficial effects in PD models, but the underlying mechanism of action is not well understood. We performed an unbiased transcriptomic analysis of cortical neurons isolated from patients with PD to identify dysregulated pathways and determine their potential contributions to the disease process. We discovered that genes associated with primary cilia, non-synaptic sensory and signaling organelles, are upregulated in both early and late stage PD patients. Enhancing ciliogenesis in primary cortical neurons via sonic hedgehog signaling suppressed the accumulation of α-synuclein pathology in vitro. Interestingly, deletion of Tet2 in mice also enhanced the expression of primary cilia and sonic hedgehog signaling genes and reduced the accumulation of α-synuclein pathology and dopamine neuron degeneration in vivo. Our findings demonstrate the crucial role of TET2 loss in regulating ciliogenesis and potentially affecting the progression of PD pathology.

Biological frameworks for Parkinson's disease: the heterogeneity SAAgged

Recent biological frameworks of Parkinson's disease (PD) rely on the new advances in α-synuclein detection in biological tissues, mostly through α-synuclein seed amplification assays, and are mainly aimed at intercepting pre-clinical or early phases of disease to be subjected to disease-modifying therapies targeting α-synuclein. However, α-synuclein pathology alone is insufficient to explain the observed clinical heterogeneity of PD. Indeed, it has been demonstrated that a number of additional elements, such as genetics, comorbidities, co-pathology, and environmental factors, may influence PD phenotype and progression. Such factors have been partially accounted for or completely overlooked by both biological frameworks and would instead represent features which could explain, at least partially, the clinical and pathophysiologic diversities of PD and further represent potential druggable targets. Recognizing that the clinical heterogeneity of PD is a window to understand the pathophysiologic complexity of the disease might turn useful for a refinement of the current biological frameworks and move the field to satisfy the unmet need of establishing a precision medicine framework for this prevalent disorder.

Novel subcellular regulatory mechanisms of protein homeostasis and its implications in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron degenerative disorder. Protein aggregates induce various forms of neuronal dysfunction and represent pathological hallmarks in ALS patients. Reducing protein aggregates could be a promising therapeutic strategy for ALS. While most studies have focused on cytoplasmic protein homeostasis, neurons adaptively reduce aggregates across subcellular compartments during stress through previously uncharacterized mechanisms. Here, we summarize novel compartment-specific proteostatic mechanisms: (1) the ERAD/RESET pathways, (2) HSPs-mediated nuclear sequestration, (3) mitochondrial aggregate import (MAGIC), (4) neurite-localized UPS/autophagosome and NMP, and (5) exopher-mediated extracellular disposal. These mechanisms collectively ensure cellular stress adaptation and provide novel therapeutic targets for ALS treatment.

Gene delivery of SUMO1-derived peptide rescues neuronal degeneration and motor deficits in a mouse model of Parkinson's disease

Developing α-synuclein aggregation inhibitors is challenging because its aggregation process involves several microscopic steps and heterogeneous intermediates. Previously, we identified a SUMO1-derived peptide, SUMO1(15-55), that exhibits tight binding to monomeric α-synuclein via SUMO-SUMO-interacting motif (SIM) interactions, and effectively blocks the initiation of aggregation and formation of toxic aggregates in vitro. In cellular and Drosophila models, SUMO1(15-55) was efficacious in protecting neuronal cells from α-synuclein-induced neurotoxicity and neuronal degeneration. Given the demonstrated ability of SUMO1(15-55) to sequester α-synuclein monomers thereby blocking oligomer formation, we sought to evaluate whether it could be equally effective against the aggregation-prone familial mutant α-synuclein-A53T. Herein, we show that SUMO1(15-55) selectively binds to monomeric α-synuclein-A53T, inhibits primary nucleation, and prevents the formation of structured protofibrils in vitro, thereby protecting neuronal cells from protofibril-induced cell death. We further demonstrate that larval feeding of a designed His10-SUMO1(15-55) that exhibits enhanced sub-stoichiometric suppression of α-synuclein-A53T aggregation in vitro can ameliorate Parkinson's disease (PD)-related symptoms in α-synuclein-A53T transgenic Drosophila models, while its rAAV-mediated gene delivery can relieve the PD-related histological and behavioral deficiencies in an rAAV-α-synuclein-A53T mouse PD model. Our findings suggest that gene delivery of His10-SUMO1(15-55) may serve as a clinical therapy for a spectrum of α-synuclein-aggregation associated synucleinopathies.

Distinct alpha-synuclein strains derived from Parkinson's disease patient tissues trigger differential inclusion pathology in a novel biosensor cell model

Background

α-Synuclein (αSyn) can misfold and aggregate to form fibrillar ß-sheet-rich aggregates ("strains") that are phosphorylated (p-αSyn) and deposited into intracellular inclusions in the brain, the pathological hallmark of synucleinopathies including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Previously, we reported that seed amplification assays such as real-time quaking-induced conversion (RT-QuIC) amplifies and detects αSyn strains from the patient skin. However, whether skin-derived αSyn strains induce disease-specific pathological features in a biological system is unknown.

Methods

We generated a U251 human glioblastoma cell line expressing fluorescently tagged αSyn carrying the PD-linked A53T mutation and Förster resonance energy transfer (FRET)-based U251 biosensor cells. Using fluorescence microscopy coupled with in situ detergent extraction, FRET-Flow cytometry and high-content confocal imaging, we examined the pathological burden and morphology of p-αSyn inclusions seeded by RT-QuIC-amplified patient skin and brain αSyn strains in αSyn-expressing U251 cells, FRET-based αSyn biosensor cells and αSyn biosensor cell-derived neurons.

Results

U251 cells allow robust and rapid in situ detection of detergent-insoluble intracellular αSyn inclusions triggered by exogenous αSyn seeds. In U251 FRET-based biosensor cells, PD skin-amplified strains induce a greater pathological burden and distinct p-αSyn inclusion morphology from PD brain-amplified and DLB skin-amplified strains. Inclusion morphology of DLB and MSA skin- and brain-amplified strains are comparable. Furthermore, skin-amplified αSyn strains induce neuronal inclusions and cause degeneration of induced neurons reprogrammed from the U251 biosensor cells. Finally, biosensor cell-propagated PD skin αSyn strains induce higher seeding activity measured by RT-QuIC than PD brain and DLB skin αSyn strains, linking intracellular pathological burden to in vitro seeding activity.

Conclusions

We report the detection of distinct PD strains derived from patient skin and brain tissues that trigger unique pathological phenotypes in U251 αSyn biosensor cells and cause degeneration of reprogrammed neurons from the same cell lineage. Moreover, DLB and MSA skin αSyn strains mimic pathological features of their brain αSyn strains in these biosensor cells. Therefore, the U251 αSyn biosensor cell model is a robust tool to potentially discriminate PD and DLB synucleinopathies and to study αSyn tissue- and strain-specific etiology and pathogenesis.

Graphical abstract

Parkinson's Paradox: Alpha-synuclein's Selective Strike on SNc Dopamine Neurons over VTA

In synucleinopathies, including Parkinson's disease (PD), dopamine neurons in the substantia nigra pars compacta (SNc) exhibit greater vulnerability to degeneration than those in the ventral tegmental area (VTA). While α-synuclein (αSyn) pathology is implicated in nigral dopamine neuron loss, the mechanisms by which αSyn affects neuronal activity and midbrain dopamine network connectivity prior to cell death remain unclear. This study tested the hypothesis that elevated αSyn expression induces pathophysiological changes in firing activity and disrupts network connectivity dynamics of dopamine neurons before neuronal loss. We employed two mouse models of synucleinopathy: preformed αSyn fibril (PFF) injection and AAV-mediated expression of human αSyn (hαSyn) under the control of the tyrosine hydroxylase (TH) promoter, both targeting the VTA and SNc. Four weeks post-injection, brain sections underwent histological, electrophysiological, and network analyses. Immunohistochemistry for TH, hαSyn, and phospho-Ser129 αSyn assessed αSyn expression and dopaminergic neuron alterations. Neuronal viability was evaluated using two complementary approaches: quantification of TH + or FOX3 + and TUNEL labeling. Importantly, these analyses revealed no significant changes in neuronal counts or TUNEL + cells at this time point, confirming that subsequent functional assessments captured pre-neurodegenerative, αSyn-induced alterations rather than late-stage neurodegeneration. Electrophysiological recordings revealed a differential effect of hαSyn expression. SNc dopamine neurons exhibited significantly increased baseline firing rates, whereas VTA dopamine neurons remained unchanged. These findings indicate a region-specific vulnerability to αSyn-induced hyperactivity of dopamine neurons. Further analysis revealed impaired homeostatic firing rate regulation in SNc, but not VTA, dopamine neurons, demonstrated by a reduced capacity to recover baseline firing following hyperpolarization. Collectively, our results demonstrate that, prior to neurodegeneration, elevated αSyn expression differentially disrupts both basal firing activity and network stability of SNc dopamine neurons, while sparing VTA dopamine neurons. By identifying neurophysiological changes preceding dopaminergic neuron loss, these findings provide critical insights into the pathophysiological mechanisms predisposing SNc neurons to degeneration in Parkinson's disease.

Significance Statement

A central question in Parkinson's disease research is why dopamine neurons in the substantia nigra pars compacta (SNc) are more vulnerable than those in the ventral tegmental area (VTA). This study reveals that alpha-synuclein (αSyn) pathology differentially impacts dopamine neuronal activity and network connectivity, causing changes in the SNc before neuronal loss occurs, but not in the VTA. These findings provide a mechanism to explain the differential resilience of these neighboring dopamine neuron populations and provide insights into Parkinson's disease progression. The methodologies developed in this study establish a foundation for investigating network topology in deep brain structures and its role in neurodegenerative disorders.

Intrastriatal injection of alpha-synuclein preformed fibrils to rats results in L-DOPA reversible sensorimotor impairments and alterations in non-motor function

Introduction

The alpha-synuclein (α-syn) preformed fibril (PFF) model of Parkinson's disease (PD) is widely used in rodents to understand the mechanisms contributing to progression of pathology and neurodegeneration in the disorder. While the time course of pathology in the α-syn PFF rat model has been well characterized, it has been more challenging to determine reliable and reproducible behavior impairments. This is mainly due to α-syn PFF injections resulting in a partial nigrostriatal lesion that make motor anomalies more subtle and difficult to detect, just as in patients with PD. In the present study we sought to examine the effect of increased striatal distribution and injection quantity of α-syn PFFs in rats on accumulation of phosphorylated α-syn inclusions, nigrostriatal degeneration, sensorimotor behavior, and nonmotor function related to PD.

Methods

Male Fischer 344 rats were injected unilaterally in the striatum with a total of 24μg α-syn PFFs distributed into three sites, or an equal volume of phosphate buffered saline (PBS) as a control condition. Sensorimotor function was assessed using a battery of behavioral tests sensitive to varying degrees of nigrostriatal neurodegeneration. Non-motor testing included assays for olfaction, emotional reactivity, cognitive function, and sleep.

Results

At six months post injection, α-syn PFF rats displayed significant movement and somatosensory asymmetries compared with control rats. Time to initiate a forelimb step and time to contact an adhesive stimulus on the forepaw took significantly longer with the contralateral limb compared with the ipsilateral limb in α-syn PFF rats. Further, hindlimb stepping in the cylinder was significantly reduced in α-syn PFF-injected rats compared with controls. Cognitive function was also affected in the α-syn PFF rats, with investigation time significantly decreased in an object recognition test. Levodopa reversibility was observed in the movement initiation and cylinder tests. Postmortem analysis revealed a 55% loss of nigral tyrosine hydroxylase immunoreactive neurons and a 63% reduction in striatal dopamine content in α-syn PFF-injected rats.

Conclusion

Thus, using the present α-syn PFF surgical parameters, sufficient nigrostriatal degeneration can be achieved to manifest significant motor and non-motor deficits. These rat α-syn PFF surgical parameters will be important for preclinical assessment of novel diseasemodifying therapies.

Targeted Raman Visualization and Mitigation of α-Synuclein Amyloidogenesis in Living Zebrafish by a Nanobody-Decorated Polydiacetylene

α-Synuclein (α-Syn) amyloidogenesis is considered a promising diagnostic marker and therapeutic target for Parkinson's disease (PD). Simultaneously visualizing and mitigating α-Syn amyloidogenesis are essential for future PD theranostics, yet they continue to pose an insurmountable challenge. This study have herein developed a nanobody-decorated polydiacetylene to approach a straightforward solution. Grafting α-Syn61-95 segment into the third complementary determining region of a parent nanobody generates an engineered nanobody X30 that can bind with α-Syn and prevent its amyloidogenesis through homotypic interaction. It next use X30 to decorate poly(deca-4,6-diynedioic acid) (PDDA), a polydiacetylene with an ultrastrong alkyne Raman signal (2120 cm-1) in the cellular silent region, to create an α-Syn targeting Raman probe PX30. The binding affinity between X30 and α-Syn can be further boosted for over 150 times attributed to the rigidity of PDDA backbone and the multivalent effect. Therefore, PX30 not only enables real-time Raman visualization of α-Syn amyloidogenesis with a high signal-to-noise ratio in living zebrafish, but also alleviates amyloidogenesis-mediated damage to zebrafish embryos by effectively inhibiting α-Syn amyloidogenesis at low stoichiometric concentrations and scavenging pathologic reactive oxygen species.

Single-Molecule Insight Into α-Synuclein Fibril Structure and Mechanics Modulated by Chemical Compounds

α-Syn fibrils, a key pathological hallmark of Parkinson's disease, is closely associated with disease initiation and progression. Several small molecules are found to bind or dissolve α-syn fibrils, offering potential therapeutic applications. Here, an innovative optical tweezers-based, fluorescence-combined approach is developed to probe the mechanical characteristics of α-syn fibrils at the single-molecule level. When subjected to axial stretching, local deformation within α-syn fibrils appeared at forces above 50 pN. These structural alternations occurred stepwise and are irreversible, suggesting unfolding of individual α-syn molecules or subdomains. Additionally, α-syn fibrils exhibits high heterogeneity in lateral disruption, with rupture force ranging from 50 to 500 pN. The impact of different compounds on the structure and mechanical features of α-syn fibrils is further examined. Notably, epigallocatechin gallate (EGCG) generally attenuates the rupture force of fibrils by wedging into the N-terminal polar groove and induces fibril dissociation. Conversely, copper chlorophyllin A (CCA) attaches to four different sites wrapping around the fibril core, reinforcing the stability of the fibril against rupture forces. The work offers an effective method for characterizing single-fibril properties and bridges compound-induced structural alternations with mechanical response. These insights are valuable for understanding amyloid fibril mechanics and their regulation by small molecules.

Current amyloid inhibitors: Therapeutic applications and nanomaterial-based innovations

Amyloid proteins have long been in the spotlight for being involved in many degenerative diseases including Alzheimer´s, Parkinson´s or type 2 diabetes, which currently cannot be prevented and for which there is no effective treatment or cure. Here we provide a comprehensive review of inhibitors that act directly on the amyloidogenic pathway (at the monomer, oligomer or fibril level) of key pathological amyloids, focusing on the most representative amyloid-related diseases. We discuss the latest advances in preclinical and clinical trials, focusing on cutting-edge developments, particularly on nanomaterials-based inhibitors, which offer unprecedented opportunities to address the complexity of protein misfolding disorders and are revolutionizing the landscape of anti-amyloid therapeutics. Notably, nanomaterials are impacting critical areas such as bioavailability, penetrability and functionality of compounds currently used in biomedicine, paving the way for more specific therapeutic solutions tailored to various amyloid-related diseases. Finally, we highlight the window of opportunity opened by comparative analysis with so-called functional amyloids for the development of innovative therapeutic approaches for these devastating diseases.

A Multi-omics Framework Based on Machine Learning as a Predictor of Cognitive Impairment Progression in Early Parkinson's Disease

INTRODUCTION

Cognitive impairment (CI) is a common non-motor symptom of Parkinson's disease (PD). However, the diagnosis and prediction of CI progression in PD remain challenging. We aimed to explore a multi-omics framework based on machine learning integrating comprehensive radiomics, cerebrospinal fluid biomarkers, and genetics information to identify CI progression in early PD.

METHODS

Patients were first diagnosed with PD without CI at baseline. According to whether CI progressed within 5 years, patients were divided into two groups: PD without CI and PD with CI. Radiomics signatures were extracted from patients' T1-weighted MRI. We used machine learning methods to construct radiomics, hybrid, and multi-omics models in the training set and validated the models in the testing set.

RESULT

In the two groups, we found 7, 23, and 25 radiomics signatures with significant differences in the parietal, temporal, and frontal lobes, respectively. The radiomics model using the 25 signatures of the frontal lobe had an accuracy of 0.833 and an AUC (area under the curve) of 0.879 to predict CI progression. In addition, the hybrid model fused with the cerebrospinal fluid Aβ level had an accuracy of 0.867 and an AUC of 0.916. In our study, the multi-omics model showed the best predictive performance. The accuracy of the multi-omics model was 0.900, and the average AUC value after five-fold cross-validation was 0.928.

CONCLUSION

Radiomics signatures have a recognition effect in the CI progression in early PD. Multi-omics frameworks combining radiomics, cerebrospinal fluid biomarkers, and genetic information may be a potential predictor of CI progression in PD.

KCa3.1 Contributes to Neuroinflammation and Nigral Dopaminergic Neurodegeneration in Experimental models of Parkinson's Disease

Chronic neuroinflammation and misfolded α-synuclein (αSyn) have been identified as key pathological correlates driving Parkinson's disease (PD) pathogenesis; however, the contribution of ion channels to microglia activation in the context of α-synucleinopathy remains elusive. Herein, we show that KCa3.1, a calcium-activated potassium channel, is robustly upregulated within microglia in multiple preclinical models of PD and, most importantly, in human PD and dementia with Lewy bodies (DLB) brains. Pharmacological inhibition of KCa3.1 via senicapoc or TRAM-34 inhibits KCa3.1 channel activity and the associated reactive microglial phenotype in response to aggregated αSyn, as well as ameliorates of PD like pathology in diverse PD mouse models. Additionally, proteomic and transcriptomic profiling of microglia revealed that senicapoc ameliorates aggregated αSyn-induced, inflammation-associated pathways and dysregulated metabolism in primary microglial cells. Mechanistically, FYN kinase in a STAT1 dependent manner regulates KCa3.1 mediated the microglial reactive activation phenotype after α-synucleinopathy. Moreover, reduced neuroinflammation and subsequent PD-like neuropathology were observed in SYN AAV inoculated KCa3.1 knockout mice. Together, these findings suggest that KCa3.1 inhibition represents a novel therapeutic strategy for treating patients with PD and related α-synucleinopathies.

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.

Coronin1A Regulates the Trafficking of Alpha Synuclein in Microglia

Microglia respond to cytotoxic protein aggregates associated with the progression of neurodegenerative disease. Pathological protein aggregates activate the microglial NLRP3 inflammasome resulting in proinflammatory signaling, secretion, and potentially pyroptotic cell death. We characterized mixed sex primary mouse microglia exposed to microbial stressors and alpha synuclein preformed fibrils (αsyn PFFs) to identify cellular mechanisms related to Parkinson's disease. Microglia package and release the endosome fate regulator Coronin1A (Coro1A) in EVs in an Nlrp3-dependent manner in widely used experimental activation conditions. We were surprised to find that Coro1A packaging and release was not Nlrp3-dependent in αsyn PFF exposure conditions. Coro1A-/- microglia exposed to αsyn PFFs trafficked more αsyn to the lysosomal compartment increasing lysosomal membrane permeabilization. This corresponds to a decrease in αsyn released in EVs suggesting that Coro1A functions to shunt pathological proteins to a secretory pathway to attenuate lysosomal stress. αsyn PFF-driven lysosomal stress resulting from Coro1a loss was associated with enhanced cytotoxicity. Intrinsic apoptosis signaling was unaffected, but we observed elevated cytosolic cathepsin B and the presence of a cathepsin-associated 55 kD PARP cleavage product. Postmortem analysis of the PD mesencephalon supported a role for Coro1A in microglia, revealing elevated levels of Coro1A protein in human PD brains compared with those of healthy donors. Findings are relevant to the distribution of pathological αsyn and indicate that Coro1a protects microglia from lysosomal overload, inflammasome activation, and pyroptotic demise.

Connectome architecture for gray matter atrophy and surgical outcomes in temporal lobe epilepsy

OBJECTIVE

Temporal lobe epilepsy (TLE) has been recognized as a network disorder with widespread gray matter atrophy. However, the role of connectome architecture in shaping morphological alterations and identifying atrophy epicenters remains unclear. Furthermore, individualized modeling of atrophy epicenters and their potential clinical applications have not been well established. This study aims to explore how gray matter atrophy correlates with normal connectome architecture, identify potential atrophy epicenters, and employ individualized modeling approach to evaluate the impact of different epicenter patterns on surgical outcomes in patients with TLE.

METHODS

This study utilized anatomic MRI data from 126 refractory TLE patients who underwent anterior temporal lobectomy and 60 healthy controls (HCs), along with normative functional and structural connectome data, to investigate the relationship between gray matter volume (GMV) changes and functional or structural connectivity. Two models were employed to identify atrophy epicenters: a data-driven approach evaluating nodal and neighbor atrophy rankings, and a network diffusion model (NDM) simulating the spread of pathology from different seed regions. K-means clustering was applied in patient-tailored modeling to uncover distinct epicenter subtypes.

RESULTS

Our findings indicate that the pattern of gray matter atrophy in TLE is constrained primarily by structural connectivity rather than by functional connectivity. Using the structural connectome, we pinpointed the hippocampus and adjacent temporo-limbic regions as key atrophy epicenters. The patient-tailored modeling revealed significant variability in epicenter distribution, allowing us to categorize them into two distinct subtypes. Notably, patients in subtype 2, with epicenters localized to the ipsilateral temporal pole and medial temporal lobe, exhibited significantly higher seizure-free rates compared to patients in subtype 1, whose epicenters situated in frontocentral regions.

SIGNIFICANCE

These findings highlight the central role of structural connectivity in shaping TLE-related morphological changes. Individualized epicenter modeling may enhance surgical decisions and improve prognostic stratification in TLE management.

Age-dependent progression from clearance to vulnerability in the early response of periventricular microglia to α-synuclein toxic species

Cytoplasmic alpha-synuclein (αSyn) aggregates are a typical feature of Parkinson's disease (PD). Extracellular insoluble αSyn can induce pathology in healthy neurons suggesting that PD neurodegeneration may spread through cell-to-cell transfer of αSyn proteopathic seeds. Early pro-homeostatic reaction of microglia to toxic forms of αSyn remains elusive, which is especially relevant considering the recently uncovered microglial molecular diversity. Here, we show that periventricular microglia of the subependymal neurogenic niche monitor the cerebrospinal fluid and can rapidly phagocytize and degrade different aggregated forms of αSyn delivered into the lateral ventricle. However, this clearing ability worsens with age, leading to an increase in microglia with aggregates in aged treated mice, an accumulation also observed in human PD samples. We also show that exposure of aged microglia to aggregated αSyn isolated from human PD samples results in the phosphorylation of the endogenous protein and the generation of αSyn seeds that can transmit the pathology to healthy neurons. Our data indicate that while microglial phagocytosis rapidly clears toxic αSyn, aged microglia can contribute to synucleinopathy spreading.

Human induced pluripotent stem cell-derived dopaminergic neurons release alpha-synuclein through neuronal activity

Lewy body diseases, including Parkinson's disease (PD), are characterized by the spread of alpha-synuclein (αSyn) between neurons across synapses, a process crucial for understanding their pathophysiology and developing effective treatments. In this study, we aimed to investigate the role of neuronal activity in releasing αSyn from human induced pluripotent stem cell-derived dopaminergic neurons. We examined human induced pluripotent stem cell-derived dopaminergic neurons, both healthy and those with the αSyn gene mutation associated with PD. We employed pharmacological agents and optogenetic techniques and demonstrated that increased neuronal activity, induced by bicuculline or optogenetic stimulation, significantly enhances αSyn release. However, suppression of neuronal activity with cyanquixaline reduces αSyn secretion. These findings underscore the pivotal role of neuronal activity in αSyn transmission between neurons, showing its potential impact on the spread of Lewy pathology in patients with neurodegenerative diseases like PD. Therefore, this study advances our understanding of PD and opens new avenues for therapeutic strategies to mitigate Lewy body disease progression.

Identification of novel phenolic inhibitors from traditional Chinese medicine against toxic α-synuclein aggregation via regulating phase separation

Parkinson's disease (PD), a neurodegenerative disorder without cure, is characterized by the pathological aggregation of α-synuclein (α-Syn) in Lewy bodies. Classic deposition pathway and condensation pathway contribute to α-Syn aggregation, and liquid-liquid phase separation is the driving force for condensate formation, which subsequently undergo liquid-solid phase separation to form toxic fibrils. Traditional Chinese Medicine (TCM) has a long history in treating neurodegenerative disease; herein, we identified chemicals from herbs that inhibit α-Syn aggregation. We screened commonly prescribed TCMs for PD from the CNKI database and registered patents, 13 chemicals were identified in the TCMSP databases as candidate inhibitors, among which three phenols, forsythoside B (FTSB), echinacoside (ECH), and 4-hydroxyindole (C4-OH) efficiently inhibit α-Syn aggregation. Moreover, FTSB and ECH increase α-Syn fluidity within condensates, inhibit α-Syn transition into amyloid fibrils and reduce fibril-induced toxicity in SH-SY5Y cells. Importantly, they disaggregated preformed α-Syn amyloid fibrils. Notably, in an α-Syn overexpressing NL5901 C. elegans PD model, either FTSB or ECH treatment significantly extended the lifespan and improved the PD-like movement disorders, both in the preventive and therapeutic treatment approaches, by reducing toxic α-Syn inclusion formation and improving the fluidity of α-Syn. Together, we offer new therapeutic candidates targeting phase separation-associated aggregation for PD.

Aging, cellular senescence and Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, affecting 1-2% of people over age 65. The risk of developing PD dramatically increases with advanced age, indicating that aging is likely a driving factor in PD neuropathogenesis. Several age-associated biological changes are also hallmarks of PD neuropathology, including mitochondrial dysfunction, oxidative stress, and neuroinflammation. Accumulation of senescent cells is an important feature of aging that contributes to age-related diseases. How age-related cellular senescence affects brain health and whether this phenomenon contributes to neuropathogenesis in PD is not yet fully understood. In this review, we highlight hallmarks of aging, including mitochondrial dysfunction, loss of proteostasis, genomic instability and telomere attrition in relation to well established PD neuropathological pathways. We then discuss the hallmarks of cellular senescence in the context of neuroscience and review studies that directly examine cellular senescence in PD. Studying senescence in PD presents challenges and holds promise for advancing our understanding of disease mechanisms, which could contribute to the development of effective disease-modifying therapeutics. Targeting senescent cells or modulating the senescence-associated secretory phenotype (SASP) in PD requires a comprehensive understanding of the complex relationship between PD pathogenesis and cellular senescence.

Current safety recommendations for handling mouse and human αsynuclein pre-formed fibrils

α-Synuclein (α-syn) can form amyloid fibrils. Lewy bodies and Lewy neurites containing aggregated α-syn are pathological markers of Parkinson's Disease and Dementia with Lewy Bodies. To better understand the role of pathological α-syn in disease, many labs use α-syn preformed fibrils (PFFs). Neurons take up the PFFs, which act as seeds to corrupt endogenously expressed α-syn, inducing it to form aggregates very similar to those found in diseased brains. The PFFs are typically generated using recombinant mouse or human α-syn. α-Syn fibrils can also be extracted or amplified from brain tissue extracts, cerebrospinal fluid, or skin biopsies from patients with known synucleinopathy. The PFFs are then added to cell culture, or injected into rodents or primates to induce pathology. Because PFFs can corrupt endogenous α-syn, researchers should adhere to strict safety protocols when handling PFFs to minimize potential exposures. Our group consulted with biosafety professionals at the University of Alabama at Birmingham (UAB) to identify potential risks related to working with α-syn PFFs and offer containment controls to mitigate those risks. Potential exposures include pipetting, opening tubes, and sonication of the PFFs to generate fragments, all of which could potentially generate aerosols. Here, we outline best practices for the safe conduct of research with α-syn fibrils, including personal protective equipment and decontamination procedures. We highlight steps in which extra precautions should be taken and how to minimize exposure and potential risk associated with use of PFFs in scientific research.