Parkinson’s disease dementia: convergence of α-synuclein, tau and amyloid-β pathologies. Nat Rev Neurosci. 2013;14:626-636. [PMID: 23900411 DOI: 10.1038/nrn3549]

Dysregulation of serotonergic neurotransmission in Parkinson disease: A key duet

Parkinson's disease (PD) is the most common movement disorder, affecting approximately 1% of the general population over 65 years of age. PD is commonly associated with the development of motor and non-motor symptoms. Non-motor symptoms arise decades earlier than motor symptoms due to the degeneration of GABAergic, serotonergic, and other neurons involved in autonomic regulation. However, motor symptoms in PD are developed due to degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNpc) of midbrain. The PD neuropathology is related to the progressive loss of the dopaminergic neurons in the SNpc of midbrain. Particularly, dysfunction of serotonergic system is implicated in the development of non-motor symptoms such as sleep disorders, cognitive dysfunction, depression and anxiety. In addition, dysfunction of serotonergic neurons which affects the dopaminergic neurons in the SNpc leads to the development of motor symptoms. Moreover, dysfunction of serotonergic neurons is associated with the development of L-dopamine (L-DOPA)-induced dyskinesia. Consistently, administration of serotonin (5-HT) receptor agonist attenuates the development of L-DOPA-induced dyskinesia. These findings emphasized the possible role of serotonergic system in PD. However, the underlying mechanisms that mediate the latent effect of 5-HT in PD are not completely elucidated. Therefore, this mini-review aims to discuss the exact role of 5-HT in PD, and how the 5-HT modulators affect PD neuropathology.

Off-pathway oligomers of α-synuclein and Aβ inhibit secondary nucleation of α-synuclein amyloid fibrils

α-Synuclein (αSyn) is a key culprit in the pathogenesis of synucleinopathies such as Parkinson's Disease (PD), in which it forms not only insoluble aggregates called amyloid fibrils but also smaller, likely more detrimental species termed oligomers. This property is shared with other amyloidogenic proteins such as the Alzheimer's Disease-associated amyloid-β (Aβ). We previously found an intriguing interplay between off-pathway Aβ oligomers and Aβ fibrils, in which the oligomers interfere with fibril formation via inhibition of secondary nucleation by blocking secondary nucleation sites on the fibril surface. Here, using ThT aggregation kinetics and atomic force microscopy (AFM), we tested if the same interplay applies to αSyn fibrils. Both homotypic (i.e. αSyn) and heterotypic (i.e. Aβ) off-pathway oligomers inhibited αSyn aggregation in kinetic assays of secondary nucleation. Initially soluble, kinetically trapped Aβ oligomers co-precipitated with αSyn(1-108) fibrils. The resulting co-assemblies were imaged as clusters of curvilinear oligomers by AFM. The results indicate that off-pathway oligomers have a general tendency to bind amyloid fibril surfaces, also in the absence of sequence homology between fibril and oligomer. The interplay between off-pathway oligomers and amyloid fibrils adds another level of complexity to the homo- and hetero-assembly processes of amyloidogenic proteins.

Comparative mapping of single-cell transcriptomic landscapes in neurodegenerative diseases

INTRODUCTION

Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and Parkinson's disease (PD) represent a spectrum of neurodegenerative diseases (NDDs). Here, we performed the first direct comparison of their transcriptomic landscapes.

METHODS

We profiled whole transcriptomes of NDD cortical tissue by single-nucleus RNA sequencing, using computational analyses to identify common and distinct differentially expressed genes (DEGs), pathways, vulnerable and disease-driver cell subtypes, and altered cell-to-cell interactions.

RESULTS

The same inhibitory neuron subtype was depleted in both AD and DLB. Potentially disease-driving neuronal cell subtypes were identified in both PD and DLB. Cell-cell communication was predicted to be increased in AD but decreased in DLB and PD. DEGs were most commonly shared across NDDs within inhibitory neuron subtypes. Overall, AD and PD showed greatest transcriptomic divergence, while DLB exhibited an intermediate signature.

DISCUSSION

These results may help explain the clinicopathological spectrum of these NDDs and provide unique insights into shared and distinct molecular mechanisms underlying pathogenesis.

HIGHLIGHTS

The same vulnerable inhibitory neuron subtype population was depleted in both Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). Potentially disease-driving neuronal cell subtypes were discovered in both Parkinson's disease (PD) and DLB. Cell-cell communication was predicted to be increased in AD but decreased in DLB and PD. Differentially expressed genes were most commonly shared across neurodegenerative diseases in inhibitory neuron types. AD and PD had the greatest transcriptomic divergence, with DLB showing an intermediate signature.

Microglia-driven inflammation induces progressive tauopathies and synucleinopathies

Alzheimer's disease and Parkinson's disease are characterized by distinct types of abnormal protein aggregates within neurons. These aggregates are known as neurofibrillary tangles and Lewy bodies, which consist of tau and α-synuclein, respectively. As the diseases progress, these aggregates spread from one cell to another, causing protein pathology to affect broader regions of the brain. Another notable characteristic of these diseases is neuroinflammation, which occurs when microglia become activated. Recent studies have suggested that inflammation may contribute to the formation and propagation of protein aggregates. However, it remains unclear whether microglia-driven inflammation can initiate and propagate different proteinopathies and associated neuropathology in neurodegenerative diseases. Here, using single-cell RNA sequencing, we observed that microglia exposed to α-synuclein or tau underwent changes in their characteristics and displayed distinct types of inflammatory response. The naive mice that received these microglial cell transplants developed both tauopathy and synucleinopathy, along with gliosis and inflammation. Importantly, these pathological features were not limited to the injection sites but also spread to other regions of the brain, including the opposite hemisphere. In conjunction with these pathological changes, the mice experienced progressive motor and cognitive deficits. These findings conclusively demonstrate that microglia-driven inflammation alone can trigger the full range of pathological features observed in neurodegenerative diseases, and that inflammation-induced local neuropathology can spread to larger brain regions. Consequently, these results suggest that microglia-driven inflammation plays an early and pivotal role in the development of neurodegenerative diseases. The transplantation of microglia activated by αSyn or tau proteins into the brains of naive mice resulted in the formation of synucleinopathy, tauopathy, gliosis, neuroinflammation and behavioral abnormalities. Activated microglia displayed alterations in subclusters as well as the corresponding feature genes.

Cognition-Associated Changes in Retinal Thickness Relate to Limbic and Temporal Cortical Atrophy in Parkinson's Disease

BACKGROUND

Research links retinal changes to cognitive decline in Parkinson's disease (PD), paralleling findings in Alzheimer's, raising questions about specific cortical patterns of cognition-related retinal abnormalities in PD.

OBJECTIVE

The study aimed to explore whether retinal thinning linked to cognitive decline could act as a potential biomarker for cerebral atrophy in PD.

METHODS

Twenty seven patients with PD underwent cognitive and neurological assessments, along with retinal imaging using OCT and cerebral imaging using structural MRI. After identifying abnormal retinal layers associated with cognitive dysfunction through partial correlation analyses controlling for age-related effects, associations between these retinal layers and the parcellated cerebral gray matter were assessed using multiple comparison-corrected partial correlation analyses adjusted for age and gender.

RESULTS

Significant positive correlations were found between cognitive impairment measured by MoCA and specific retinal layers (IPL, GCL, and RNFL). Of these, strong associations were observed between the IPL and GCL and cortical thickness in brain the temporal lobe and limbic cortex, with more detailed further analysis showing significant correlations particularly within the middle and posterior cingulate cortex in the limbic cortex and the middle and superior temporal gyrus in the temporal lobe.

CONCLUSION

Correlations between retinal thinning, cognitive decline, and specific patterns of cortical atrophy in PD support a potential of retinal measurements as a biomarker for cognitive impairment linked to cerebral neurodegeneration.

Apolipoprotein E genotypes and amyloid burden associated with cognitive decline in non-demented Parkinson's disease patients: A preliminary analysis

BACKGROUND

Cognitive impairment is a common non-motor manifestation in Parkinson's disease (PD). Amyloidosis seems to accelerate the onset of dementia in PD. The Apolipoprotein (APOE) ε4 genotype is linked to amyloid aggregation and has been suggested to be a candidate for development of PD dementia, while other APOE alleles have been less investigated.

METHODS

Forty-eight non-demented PD patients were included (ε2/ε3 carriers: n = 8; ε3/ε3 carriers: n = 35; and ε3/ε4 carriers: n = 5). Patients underwent APOE genotyping, a neuropsychological exam and a [18F]-Flutemetamol PET. Statistical Parametric Mapping 12 was used to analyze regional amyloid differences by APOE genotypes. Cognitive assessment was re-administered after follow-up.

RESULTS

APOE ε3/ε4 carriers showed significant amyloid load in left middle occipital areas in comparison with APOE ε3/ε3, whereas APOE ε3/ε4 exhibited several areas of amyloid accumulation in comparison with APOE ε2/ε3 that disappeared after family-wise error cluster level correction, but which hold in nonparametric analyses. No amyloid load differences were found between APOE ε2/ε3 and APOE ε3/ε3. The frequency of progression of cognitive decline was 80 % in ε3/ε4, 50 % in ε2/ε3, and 22.86 % in ε3/ε3 carriers.

CONCLUSIONS

This compared regional amyloid deposition and cognitive evolution among APOE genotypes. Our preliminary findings suggest an association between APOE ε4 and amyloid burden in posterior cortical areas in non-demented PD and a tendency to a higher frequency of cognitive decline. Larger studies should explore cognition and amyloid burden in APOE ε2 carriers.

Unravelling the Proteinopathic Engagement of α-Synuclein, Tau, and Amyloid Beta in Parkinson's Disease: Mitochondrial Collapse as a Pivotal Driver of Neurodegeneration

Parkinson's disease is a complex neurological ailment manifested by dopaminergic neurodegeneration in the substantia nigra of the brain. This study investigates the molecular tripartite interaction between Lewy bodies, amyloid beta, and tau protein in the pathogenesis of Parkinson's disease. Lewy bodies which have been found as the important pathological hallmark in the degenerative neurons of Parkinson's patients, are mainly composed of α-synuclein. The accumulation of α-synuclein has been directly and indirectly linked to the severity and degree of progression of the disease. In addition, approximately 50% of Parkinson's disease cases are also described by hyperphosphorylation of tau protein indicating its significant involvement in the disease. The study further explains how α-synuclein, tau and amyloid beta can spread via cross-seeding mechanisms and accelerate each other's aggregation leading to neuronal death. Both GSK-3β and CDK5 are involved in phosphorylation which among other effects contributes to the misfolding of both α-synuclein and tau proteins that lead to neurodegeneration in Alzheimer's disease. Several mediators, that contribute to mitochondrial damage through elevated oxidative stress pathology are clearly described. Because of the increase in the incidence of Parkinson's disease, as predicted to be 17 million when the study was being conducted, studying these pathological mechanisms is very important in trying to establish treatments. This work contributes a path to finding a multi-target treatment regimen to alleviate the burden of this devastating disease.

Additive effect of distant Lewy bodies and tau seeds injections on nigral degeneration in macaques

The influence of Lewy body (LB) and tau co-pathologies is increasingly acknowledged as putatively affecting neurodegeneration and clinical phenotypes. Here, we injected rhesus macaques with LB fractions or/and tau seeds derived from patients brains into distinct brain areas connected to the mesencephalon. Compared to control macaques, we observed increased mesencephalic staining of pathological α-synuclein and tau, as well as nigrostriatal dopaminergic neuronal loss, with a cumulative effect of co-pathology.

Impact of 6-OHDA injection and microtrauma in the rat substantia nigra on local brain amyloid beta protein concentrations in the affected area

Amyloid beta peptides (Aβ) are key indicators of Alzheimer's disease and are also linked to cognitive decline in Parkinson's disease (PD) and other neurodegenerative disorders. This study explored the accumulation of Aβ in a standard 6-Hydroxydopamine (6-OHDA) model of PD. We unilaterally injected 6-OHDA into the substantia nigra of Wistar rats to induce dopaminergic cell degeneration and death, a characteristic of PD. The goal was to detect Aβ protein in tissues and blood vessels showing inflammation or degeneration from the 6-OHDA injection. Our results showed that 6-OHDA injection produced a statistically significant rise in Aβ concentration at the injection site 60 minutes after injection, which was slightly reduced 24 hours post-injection but still significantly higher than in controls. We also tried Gp120 injection in the same zone but it only produced effects comparable to control needle trauma. The presence of Aβ in tissues and blood vessel walls after injection was confirmed through ELISA tests and was supported by immunohistochemical staining of injection areas. We found that the increased Aβ concentration was visible in and around blood vessels and inside blood vessel walls, and also, to a lesser extent in some cells, most probably neurons, in the area. This research highlights the connection between dopaminergic cell poisoning and the accumulation of Aβ, offering insights into the progression of PD to cognitive disorders and dementia.

Identification of Common Brain Protein and Genetic Loci Between Parkinson's Disease and Lewy Body Dementia

BACKGROUND

Parkinson's disease (PD) and Lewy body dementia (LBD) have many common features, including clinical manifestations, neurochemistry, and pathology, but little is known about their shared brain proteins and genetic factors.

METHODS

To identify susceptibility-related brain proteins that are shared between PD and LBD patients, proteome-wide association studies (PWASs) were conducted by integrating human brain protein quantitative trait loci (pQTLs) with large-scale genome-wide association studies (GWASs) of both diseases. Subsequently, pleiotropy-informed conditional false discovery rate (pleioFDR) analysis was performed to identify common risk genetic loci between PD and LBD. Finally, the downregulation of these risk genes in different disease states was validated by differential gene expression analysis.

RESULTS

PWASs identified 12 PD risk proteins and nine LBD risk proteins, among which TMEM175 (zPD = -7.25, PPD = 4.12E-13; zLBD = -6.02, PLBD = 1.75E-09) and DOC2A (zPD = -4.13, PPD = 3.71E-05; zLBD = -3.91, PLBD = 9.08E-05) were shared. PleioFDR analysis revealed that five genetic risk loci mapped to eight genes associated with PD and LBD, including the proteome-wide significant risk gene TMEM175 (ConjFDR = 5.74E-03). Differential expression analysis verified that TMEM175 was significantly downregulated in the midbrains of PD patients (p = 1.19E-02), and further exploration revealed that TMEM175 was also dramatically downregulated in the substantia nigra of PD patients (p = 1.16E-02) and incidental Lewy body disease patients (p = 7.52E-03). Moreover, TMEM175 was significantly downregulated in induced pluripotent stem cell-derived dopaminergic neurons from PD patients (p = 4.60E-02).

CONCLUSION

Dysregulation of TMEM175 may confer PD and LBD risk and may be partly responsible for their comorbidity. Our results revealed the common genetic risk factors between PD and LBD, which elucidated the shared genetic basis of these diseases.

Changing the amyloid nucleation process using small molecules and substrates: a way to build two-dimensional materials

The assembly of two-dimensional (2D) materials on substrates presents a wide range of potential applications in nanomaterials. However, there is limited information available in the literature regarding the tunable nucleation process in molecular assembly. In this paper, a neurodegenerative disease-related short peptide and a small molecule named Fast Green (FG) were selected for their binding affinity with mica/highly oriented pyrolytic graphite (HOPG) substrates. Based on atomic force microscopy (AFM) and molecular dynamics (MD) simulation, we investigated the control of 2D assemblies. By tuning FG small molecules and substrates, the assemblies grew epitaxially from nanosheets to nanofilms on mica and highly ordered nanofilaments on HOPG substrates. Notably, the nuclei formed an orderly array without a critical size or lag phase in the presence of FG molecules on the HOPG substrate, facilitating a quicker co-assembly of ordered filaments compared to bulk conditions. Our MD simulations further demonstrated that the interaction between Aβ16-22 molecules and the HOPG substrate was primarily due to π-π interactions between aromatic rings, which led to the formation of single-layer filaments by lying on the surface of HOPG. Additionally, parallel π-π stacking acted as the primary force to inhibit the aggregation of peptides into fibrils. Overall, our results provide a strategy for modulating the interaction of amyloid peptides with small molecules and substrates in the assembly of 2D nanomaterials.

Dissecting the molecular landscape of Parkinson's disease and Parkinson's disease dementia using highly efficient snRNA-seq (HIF-snRNA-seq)

This study presents a transcriptomic analysis of the cingulate cortex (CING) in Parkinson's disease (PD) and Parkinson's disease dementia (PDD) using a High-efficiency single-nucleus RNA sequencing (HiF-snRNA-seq) protocol optimized for post-mortem brain samples. RNA quality prediction, poly-A tailing, and dCas9-targeted depletion enabled analysis of 77 high-quality samples from 240 cases, yielding over 2 million nuclei classified into seven major cell types. Disease conditions revealed altered astrocyte and microglia proportions, implicating their roles in neuroinflammation. Differential expression analysis identified unique and shared genes across PD and PDD, linked to synaptic remodeling, stress responses, and inflammation. Stage-specific analysis uncovered tau-dependent early-stage genes and inflammation-associated late-stage genes. This study highlights the CING's central role in PD and PDD pathophysiology, offering insights into disease mechanisms and identifying candidate genes and pathways for therapeutic and biomarker development.

Mitochondrial DNA Copy Number as a Potential Biomarker for the Severity of Motor Symptoms and Prognosis in Parkinson's Disease

BACKGROUND

Mitochondrial function influences Parkinson's disease (PD) through the accumulation of pathogenic alpha-synuclein, oxidative stress, impaired autophagy, and neuroinflammation. The mitochondrial DNA copy number (mtDNA-CN), representing the number of mitochondrial DNA copies within a cell, serves as an easily assessable proxy for mitochondrial function.

OBJECTIVE

This study aimed to assess the diagnostic and prognostic capabilities of mtDNA-CN in PD.

METHODS

We assessed mtDNA-CN in blood samples using whole genome sequencing from 405 patients with PD and 200 healthy controls (HC). We examined the relationship between mtDNA-CN levels and motor symptom severity in PD, as well as their association with dementia development in patients with early-PD (within 3 years of diagnosis).

RESULTS

mtDNA-CN levels were significantly lower in patients with PD compared with HC (P = 1.1 × 10-5). A negative correlation was discovered between mtDNA-CN level and motor severity in PD (correlation coefficient = -0.20; P = 0.008). Among 210 patients with early-PD, Cox regression analysis demonstrated an association between lower mtDNA-CN levels and a higher risk of developing dementia (hazard ratio [HR] = 0.41, 95% confidence interval: 0.20-0.86, P = 0.02), even after adjusting for age and blood cell count (HR = 0.41, 95% confidence interval: 0.18-0.92, P = 0.03). However, mtDNA-CN levels did not significantly correlate with motor progression in PD.

CONCLUSION

Our findings suggest that blood mtDNA-CN may function as a diagnostic biomarker for PD and a prognostic marker for dementia in patients with PD. © 2025 International Parkinson and Movement Disorder Society.

Comprehensive mapping of mutations in TDP-43 and α-Synuclein that affect stability and binding

Abnormal aggregation and amyloid inclusions of TAR DNA-binding protein 43 (TDP-43) and α-Synuclein (α-Syn) are frequently co-observed in amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease. Several reports showed TDP-43 C-terminal domain (CTD) and α-Syn interact with each other and the aggregates of these two proteins colocalized together in different cellular and animal models. Molecular dynamics simulation was conducted to elucidate the stability of the TDP-43 and Syn complex structure. The interfacial mutations in protein complexes changes the stability and binding affinity of the protein that may cause diseases. Here, we have utilized the computational saturation mutagenesis approach including structure-based stability and binding energy calculations to compute the systemic effects of missense mutations of TDP-43 CTD and α-Syn on protein stability and binding affinity. Most of the interfacial mutations of CTD and α-Syn were found to destabilize the protein and reduced the protein binding affinity. The results thus shed light on the functional consequences of missense mutations observed in TDP-43 associated proteinopathies and may provide the mechanisms of co-morbidities involving these two proteins.Communicated by Ramaswamy H. Sarma.

RNA methylation homeostasis in ocular diseases: All eyes on Me

RNA methylation is a pivotal epigenetic modification that adjusts various aspects of RNA biology, including nuclear transport, stability, and the efficiency of translation for specific RNA candidates. The methylation of RNA involves the addition of methyl groups to specific bases and can occur at different sites, resulting in distinct forms, such as N6-methyladenosine (m6A), N1-methyladenosine (m1A), 5-methylcytosine (m5C), and 7-methylguanosine (m7G). Maintaining an optimal equilibrium of RNA methylation is crucial for fundamental cellular activities such as cell survival, proliferation, and migration. The balance of RNA methylation is linked to various pathophysiological conditions, including senescence, cancer development, stress responses, and blood vessel formation, all of which are pivotal for comprehending a spectrum of eye diseases. Recent findings have highlighted the significant role of diverse RNA methylation patterns in ophthalmological conditions such as age-related macular degeneration, diabetic retinopathy, cataracts, glaucoma, uveitis, retinoblastoma, uveal melanoma, thyroid eye disease, and myopia, which are critical for vision health. This thorough review endeavors to dissect the influence of RNA methylation on common and vision-impairing ocular disorders. It explores the nuanced roles that RNA methylation plays in key pathophysiological mechanisms, such as oxidative stress and angiogenesis, which are integral to the onset and progression of these diseases. By synthesizing the latest research, this review offers valuable insights into how RNA methylation could be harnessed for therapeutic interventions in the field of ophthalmology.

Engrams across diseases: Different pathologies - unifying mechanisms?

Memories are our reservoir of knowledge and thus, are crucial for guiding decisions and defining our self. The physical correlate of a memory in the brain is termed an engram and since decades helps researchers to elucidate the intricate nature of our imprinted experiences and knowledge. Given the importance that memories have for our lives, their impairment can present a tremendous burden. In this review we aim to discuss engram malfunctioning across diseases, covering dementia-associated pathologies, epilepsy, chronic pain and psychiatric disorders. Current neuroscientific tools allow to witness the emergence and fate of engram cells and enable their manipulation. We further suggest that specific mechanisms of mnemonic malfunction can be derived from engram cell readouts. While depicting the way diseases act on the mnemonic component - specifically, on the cellular engram - we emphasize a differentiation between forms of amnesia and hypermnesia. Finally, we highlight commonalities and distinctions of engram impairments on the cellular level across diseases independent of their pathogenic origins and discuss prospective therapeutic measures.

Mandragora autumnalis Distribution, Phytochemical Characteristics, and Pharmacological Bioactivities

In the Mediterranean and Himalayan regions, the genus Mandragora (family Solanaceae), sometimes called mandrake, is widely utilized in herbal therapy and is well-known for its mythical associations. Objective: To compile up-to-date information on M. autumnalis's therapeutic properties. Its pharmacological properties and phytochemical composition are particularly covered in managing several illnesses, including diabetes, cancer, and heart disease. Methods: Articles on the review topic were found by searching major scientific literature databases, such as PubMed, Scopus, ScienceDirect, SciFinder, Chemical Abstracts, and Medicinal and Aromatic Plants Abstracts. Additionally, general online searches were conducted using Google Scholar and Google. The time frame for the search included items released from 1986 to 2023. Results:Mandragora has been shown to contain a variety of phytochemicals, including coumarins, withanolides, and alkaloids. The pharmacological characteristics of M. autumnalis, such as increasing macrophage anti-inflammatory activity, free radicals inhibition, bacterial and fungal growth inhibition, cytotoxic anticancer activities in vivo and in vitro against cancer cell lines, and enzyme-inhibitory properties, are attributed to these phytochemicals. Furthermore, M. autumnalis also inhibits cholinesterase, tyrosinase, α-amylase, α-glucosidase, and free radicals. On the other hand, metabolic risk factors, including the inhibition of diabetes-causing enzymes and obesity, have been treated using dried ripe berries. Conclusions: Investigations into the pharmacological and phytochemical characteristics of M. autumnalis have revealed that this plant is a rich reservoir of new bioactive substances. This review aims to provide insight into the botanical and ecological characteristics of Mandragora autumnalis, including a summary of its phytochemical components and antioxidant, antimicrobial, antidiabetic, anticancer, enzyme-inhibitory properties, as well as toxicological implications, where its low cytotoxic activity against the normal VERO cell line has been shown. More research on this plant is necessary to ensure its efficacy and safety. Still, it is also necessary to understand the molecular mechanism of action behind the observed effects to clarify its therapeutic potential.

Structural basis of a distinct α-synuclein strain that promotes tau inclusion in neurons

Amyloidoses are predominantly associated with the accumulation of persistent aggregates of a particular protein. For example, the protein α-synuclein characteristically aggregates in Parkinson's disease (PD), while amyloid beta and tau deposits are associated with Alzheimer's disease (AD). However, α-synuclein-positive inclusions have been reportedly found in some tauopathies, and vice versa; tau-positive inclusions can be found in synucleinopathies. This suggests that there may be coexistence or crosstalk between these proteinopathies. This coexistence suggests that the simultaneous presence of these misfolded proteins may amplify pathogenic mechanisms. However, the crosstalk between these two types of proteopathies remains poorly understood. We now determine the structure of α-synuclein fibrils that directly promote tau aggregation by cryogenic electron microscopy. Helical reconstruction at 2.6 Å resolution reveals a new α-synuclein fibril polymorph we term "strain B"; its core is unique, incorporating both the N- and C-termini of α-synuclein. The design of peptides meant to inhibit the formation of this structure demonstrates that the C-terminal domain fragment (D105-E115) of α-synuclein is critical for the formation of "strain B" fibrils and may play a key role in its interaction with tau. We hypothesize that the unique structure of pathological α-synuclein significantly contributes to tau co-aggregation and plays a role in the intricate interactions among Alzheimer's, Parkinson's, and other neurodegenerative diseases. These findings open new avenues for drug targeting, discovery, and improve our understanding of neurodegenerative pathology.

Dissecting the immune response of CD4+ T cells in Alzheimer's disease

The formation of amyloid-β (Aβ) plaques is a neuropathological hallmark of Alzheimer's disease (AD), however, these pathological aggregates can also be found in the brains of cognitively unimpaired elderly population. In that context, individual variations in the Aβ-specific immune response could be key factors that determine the level of Aβ-induced neuroinflammation and thus the propensity to develop AD. CD4+ T cells are the cornerstone of the immune response that coordinate the effector functions of both adaptive and innate immunity. However, despite intensive research efforts, the precise role of these cells during AD pathogenesis is still not fully elucidated. Both pathogenic and beneficial effects have been observed in various animal models of AD, as well as in humans with AD. Although this functional duality of CD4+ T cells in AD can be simply attributed to the vast phenotype heterogeneity of this cell lineage, disease stage-specific effect have also been proposed. Therefore, in this review, we summarized the current understanding of the role of CD4+ T cells in the pathophysiology of AD, from the aspect of their antigen specificity, activation, and phenotype characteristics. Such knowledge is of practical importance as it paves the way for immunomodulation as a therapeutic option for AD treatment, given that currently available therapies have not yielded satisfactory results.

The role of Apolipoprotein E4 on cognitive impairment in Parkinson's disease and Parkinsonisms

Cognitive impairment is a prevalent non-motor symptom of Parkinson's disease (PD), increasing the risk of dementia as the disease progresses. Despite its clinical significance, the etiology of cognitive impairment in PD remains unclear. Apolipoprotein E4 (APOE4), a well-known genetic risk factor of Alzheimer's disease, has been studied for its potential role in PD-related cognitive impairment. However, findings have been conflicting and thus inconclusive, highlighting a need to critically evaluate the current research. Several studies using neuroimaging modalities have explored the brains of individuals with PD and atypical parkinsonian disorders who have APOE4. Some of these studies have identified distinct neuropathological changes that have been previously reported to be associated with cognitive impairments in those with Parkinsonisms. Here, we review the role of APOE4 on cognitive impairment in PD and atypical Parkinsonisms using neuroimaging evidence. We will examine how APOE4 may contribute to pathological changes within the brain and its association with cognitive impairment.

Neuropathological stages of neuronal, astrocytic and oligodendrocytic alpha-synuclein pathology in Parkinson's disease

Alpha-synucleinopathies are neurodegenerative diseases characterized by the spread of alpha-synuclein (α-syn) aggregates throughout the central nervous system in a stereotypical manner. These diseases include Lewy body disease (LBD), which encompass Dementia with Lewy bodies (DLB), Parkinson's Disease (PD), and Parkinson's Disease Dementia (PDD), and Multiple System Atrophy (MSA). LBD and MSA chiefly contain α-syn aggregates in neurons and oligodendrocytes, respectively, although glial α-syn pathology in LBD is increasingly being recognized. Semi-quantitative and machine learning-based quantifications of neuronal, oligodendrocytic and astrocytic α-syn pathology were implemented on a cohort of LBD and MSA post-mortem tissue samples. The neuroanatomical distribution of each cell-type specific α-syn pathology was evaluated using conditional probability matrices and Subtype and Stage Inference (SuStaIn) algorithm. We revealed extensive glial α-syn pathology in LBD, emphasizing the disease- and region-specific profile of astrocytic α-syn pathology, which was absent in MSA and minimal in the substantia nigra of LBD. Furthermore, we have described distinct morphologies of astrocytic α-syn pathology, which were found to correlate with the density of astrocytic α-syn inclusions. Astrocytic α-syn pathology was mainly centered in the amygdala and exhibited a unique stereotypical progression whilst oligodendrocytes displayed a distribution akin to the established neuronal progression pattern. SuStaIn modeling was further used to test for heterogeneity in the spatiotemporal progression, revealing that a subset of cases might follow an alternative pattern. Based on these findings, we introduce a novel multimodal progression framework that integrates, for the first time, the temporal and spatial progression of astrocytic and oligodendrocytic α-syn pathology alongside neuronal pathology in PD, providing further information regarding the role of neurons and glia in disease pathogenesis.

Beyond CO2 Storage: Enzyme-Amyloid Fibril Catalytic Hybrids for Long Cascade Reactions Converting CO2 into Fructose

Enzyme immobilization is an efficient and cost-effective approach to recovering, stabilizing, and enhancing enzyme catalytic properties. It is a challenge, however, for coimmobilized multiple enzymes to perform consecutive reactions without being inactivated under similar conditions. Here, we present a facile enzyme immobilization platform using β-lactoglobulin amyloid fibril hydrogels. Two different hydrogels, loading either RuBisCO alone (hereby termed AFR*) or seven enzymes related to the Calvin Cycle (hereby termed AF7E hydrogel), show immobilization efficiency of over ∼95% while simultaneously exhibiting excellent activity and stability. The AFR* hydrogel enables the fixation of CO2 into 3-phosphoglycerate (3-PGA), which is then utilized as the initial step in the Calvin Cycle cascade catalytic reactions if the AF7E hydrogel is used, mimicking the light-independent part of the more complex natural photosynthesis full process. The converted substrates of this process contain precursors (α-glycerophosphate dehydrogenase and dihydroxyacetone phosphate), which can be further converted to fructose by additional aldolase. Due to the proteinaceous nature of the amyloid substrate, the AF7E hydrogel is completely biodegradable by pepsin, as confirmed via atomic force microscopy and circular dichroism spectroscopy analysis. This original enzyme-amyloid hybrid is biocompatible, sustainable, and scalable and may serve as a general template for multienzymatic catalytic platforms.

Targeting tau in Alzheimer's and beyond: Insights into pathology and therapeutic strategies

Tauopathies encompass a group of approximately 20 neurodegenerative diseases characterized by the accumulation of the microtubule-associated protein tau in brain neurons. The pathogenesis of intracellular neurofibrillary tangles, a hallmark of tauopathies, is initiated by hyperphosphorylated tau protein isoforms that cause neuronal death and lead to diseases like Alzheimer's, Parkinson's disease, frontotemporal dementia, and other complex neurodegenerative diseases. Current applications of tau biomarkers, including imaging, cerebrospinal fluid, and blood-based assays, assist in the evaluation and diagnosis of tauopathies. Emerging research is providing various potential strategies to prevent cellular toxicity caused by tau aggregation such as: 1) suppressing toxic tau aggregation, 2) preventing post-translational modifications of tau, 3) stabilizing microtubules and 4) designing tau-directed immunogens. This review aims to discuss the role of tau in tauopathies along with neuropathological features of the different tauopathies and the new developments in treating tau aggregation with the therapeutics for treating and possibly preventing tauopathies.

Cholinergic degeneration and early cognitive signs in prodromal Lewy body dementia

INTRODUCTION

Isolated REM sleep behavior disorder (iRBD) is a strong prodromal marker of Lewy body diseases (LBDs) - Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Cholinergic loss is linked to cognitive decline in these conditions, but its trajectory remains unclear.

METHODS

In a cohort of 92 iRBD participants with baseline MRI, cholinergic basal forebrain (cBF) volume was measured, with longitudinal changes analyzed in 49 with follow-up scans. Cross-sectional neuropsychological associations were examined across a broader RBD-LBD continuum, including the iRBD cohort plus 65 PD and 15 DLB patients with probable RBD.

RESULTS

cBF volume declined at comparable rates in iRBD-to-PD and iRBD-to-DLB converters, but atrophy was more severe at DLB phenoconversion. cBF atrophy correlated with attention, executive, and memory deficits. In iRBD, baseline cBF z-score < -1.0 predicted dementia (hazard ratio = 9.57, p = .009).

CONCLUSION

cBF degeneration evolves from the prodromal iRBD stage of LBDs and predicts dementia, highlighting a window for cholinergic-targeted intervention.

HIGHLIGHTS

Basal forebrain links to attention, executive function, and memory in the RBD continuum. Basal forebrain atrophy progresses at similar rates in prodromal PD and prodromal DLB. At phenoconversion, basal forebrain atrophy is greater in DLB than in PD converters. Basal forebrain atrophy strongly predicts future dementia in iRBD. Executive dysfunction predicts faster basal forebrain degeneration in iRBD.

Distinct CSF α-synuclein aggregation profiles associated with Alzheimer's disease phenotypes and MCI-to-AD conversion

BACKGROUND

α-Synuclein (α-Syn) pathology is present in 30-50 % of Alzheimer's disease (AD) patients, and its interactions with tau proteins may further exacerbate pathological changes in AD. However, the specific role of different aggregation forms of α-Syn in the progression of AD remains unclear.

OBJECTIVES

To explore the relationship between various aggregation types of CSF α-Syn and Alzheimer's disease progression.

DESIGN

We conducted a retrospective analysis of data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) to examine the association between different α-Syn aggregation forms-Syn0 (no detectable α-Syn aggregates) and Syn1 (α-Syn aggregates detected, resembling those found in Parkinson's disease)-with the pathological and clinical features of AD. Additionally, we evaluated their potential as predictors of conversion from mild cognitive impairment (MCI) to AD.

SETTING

The ADNI database.

PARTICIPANTS

A total of 250 participants, including 70 cognitively normal controls, 119 patients diagnosed with MCI, and 61 patients diagnosed with AD.

MEASUREMENTS

Pearson correlation was employed to assess the relationship between α-Syn levels and cerebrospinal fluid (CSF) biomarkers, including total tau (T-tau), phosphorylated tau (p-tau), and amyloid-β42 (Aβ42). Multivariate Cox proportional hazards models were applied, adjusting for APOE4 status, age, and sex, to determine the association between α-Syn forms and AD-related pathological and clinical outcomes. Kaplan-Meier curves were used to evaluate the prognostic value of different α-Syn aggregation states in predicting the conversion from MCI to AD.

RESULTS

Compared with controls, overall MCI and AD patients had elevated α-Syn levels. Notably, in the α-Syn0 group, α-Syn levels were increased in the MCI patients and further increased in AD patients, whereas in the α-Syn1 group, α-Syn levels did not significantly differ across diagnostic groups. Both in the α-Syn0 and α-Syn1 groups, α-Syn levels were found to correlate more strongly with CSF tau levels than with Aβ42, indicating a possible role for α-Syn in tau-related pathology in AD. Importantly, α-Syn0-AD patients exhibited more rapid cognitive decline and greater hippocampal atrophy than α-Syn1-AD patients. However, MCI patients with CSF α-Syn1 aggregation status had an increased risk of conversion to AD.

CONCLUSIONS

CSF α-Syn is associated with tau pathology and neurodegeneration in Alzheimer's disease. The distinct aggregation profiles of α-Syn serve as valuable biomarkers, offering insights into differing prognoses in AD and aiding in the prediction of early disease progression.

HDAC6 inhibitor-loaded brain-targeted nanocarrier-mediated neuroprotection in methamphetamine-driven Parkinson's disease

The dynamic equilibrium between acetylation and deacetylation is vital for cellular homeostasis. Parkinson's disease (PD), a neurodegenerative disorder marked by α-synuclein (α-syn) accumulation and dopaminergic neuron loss in the substantia nigra, is associated with a disruption of this balance. Therefore, correcting this imbalance with histone deacetylase (HDAC) inhibitors represents a promising treatment strategy for PD. CAY10603 (CAY) is a potent and selective HDAC6 inhibitor. However, because of its poor water solubility and short biological half-life, it faces clinical limitations. Herein, we engineered lactoferrin-decorated CAY-loaded poly(lactic-co-glycolic acid) nanoparticles (denoted as PLGA@CAY@Lf NPs) to effectively counter methamphetamine (Meth)-induced PD. PLGA@CAY@Lf NPs showed enhanced blood-brain barrier crossing and significant brain accumulation. Notably, CAY released from PLGA@CAY@Lf NPs restored the disrupted acetylation balance in PD, resulting in neuroprotection by reversing mitochondrial dysfunction, suppressing reactive oxygen species, and inhibiting α-syn accumulation. Additionally, PLGA@CAY@Lf NPs treatment normalized dopamine and tyrosine hydroxylase levels, reduced neuroinflammation, and improved behavioral impairments. These findings underscore the potential of PLGA@CAY@Lf NPs in treating Meth-induced PD and suggest that an innovative HDAC6-inhibitor-based strategy can be used to treat PD.

Nanotechnology in Parkinson's Disease: overcoming drug delivery challenges and enhancing therapeutic outcomes

The global prevalence of Parkinson's Disease (PD) is on the rise, driven by an ageing population and ongoing environmental conditions. To gain a better understanding of PD pathogenesis, it is essential to consider its relationship with the ageing process, as ageing stands out as the most significant risk factor for this neurodegenerative condition. PD risk factors encompass genetic predisposition, exposure to environmental toxins, and lifestyle influences, collectively increasing the chance of PD development. Moreover, early and precise PD diagnosis remains elusive, relying on clinical assessments, neuroimaging techniques, and emerging biomarkers. Conventional management of PD involves dopaminergic medications and surgical interventions, but these treatments often become less effective over time and do not address disease treatment. Challenges persist due to the blood-brain barrier's (BBB) impermeability, hindering drug delivery. Recent advancements in nanotechnology offer promising novel approaches for PD management. Various drug delivery systems (DDS), including nanosized polymers, lipid-based carriers, and nanoparticles (such as metal/metal oxide, protein, and carbonaceous particles), aim to enhance drug and gene delivery. These modifications seek to improve BBB permeability, ultimately benefiting PD patients. This review underscores the critical role of ageing in PD development and explores how age-related neuronal decline contributes to substantia nigra loss and PD manifestation in susceptible individuals. The review also highlights the advancements and ongoing challenges in nanotechnology-based therapies for PD.

α-Synuclein fibrils enhance HIV-1 infection of human T cells, macrophages and microglia

HIV-associated neurocognitive disorders (HAND) and viral reservoirs in the brain remain a significant challenge. Despite their importance, the mechanisms allowing HIV-1 entry and replication in the central nervous system (CNS) are poorly understood. Here, we show that α-synuclein and (to a lesser extent) Aβ fibrils associated with neurological diseases enhance HIV-1 entry and replication in human T cells, macrophages, and microglia. Additionally, an HIV-1 Env-derived amyloidogenic peptide accelerated amyloid formation by α-synuclein and Aβ peptides. Mechanistic studies show that α-synuclein and Aβ fibrils interact with HIV-1 particles and promote virion attachment and fusion with target cells. Despite an overall negative surface charge, these fibrils facilitate interactions between viral and cellular membranes. The enhancing effects of human brain extracts on HIV-1 infection correlated with their binding to Thioflavin T, a dye commonly used to stain amyloids. Our results suggest a detrimental interplay between HIV-1 and brain amyloids that may contribute to the development of neurodegenerative diseases.

Quantification of cinpanemab (BIIB054) binding to α-synuclein in cerebrospinal fluid of phase 1 single ascending dose samples

Through its pathological and genetic association with Parkinson disease (PD), α-synuclein (α-syn) remains a favorable therapeutic target that is being investigated using various modalities, including many passive immunotherapy approaches clinically targeting different forms of α-syn and epitopes. Although published studies from some immunotherapy trials have demonstrated engagement in plasma, none has shown direct drug-antigen interactions in the disease-relevant compartment, the central nervous system. Cinpanemab (BIIB054) selectively targets pathological aggregated α-syn with low-affinity binding to monomeric forms. The avidity-driven binding, low drug concentration, and the very low α-syn levels, plus its heterogeneous nature in cerebrospinal fluid (CSF), made it impossible to measure drug-target interactions by conventional assays. Here we overcame these challenges by using zero-length crosslinking to stabilize the BIIB054-α-syn complexes and then quantified the crosslinked complexes using a Meso Scale Discovery electrochemiluminescence assay. CSF samples from healthy volunteers (HVs, n = 46) and individuals with PD (PD, n = 18) from study 228HV101 (phase 1 clinical trial of BIIB054) demonstrated dose- and time-dependent binding of cinpanemab to α-syn with measurable complexes detected at doses ≥15 mg/kg. Complex formation displayed a direct positive correlation to drug concentration (Spearman rank correlation = 0.8295 [HV], 0.8032 [PD] P < .0001 [HV, PD]). The observed binding of cinpanemab to α-syn in CSF is consistent with its low intrinsic affinity for α-syn monomer and provides evidence that the drug is behaving with expected binding dynamics in the central nervous system compartment. SIGNIFICANCE STATEMENT: A zero-length crosslinking method with Meso Scale Discovery detection was developed to enable quantification of cinpanemab-α-synuclein (α-syn) complexes in clinical cerebrospinal fluid samples by preventing signal loss caused by their rapid dissociation. Observed dose- and time-dependent binding was consistent with cinpanemab's affinity for α-syn and provided confidence the drug had engaged its target at the desired site of action. This is the first demonstration of α-syn binding by an antibody in clinical samples from the central nervous system.

Site-specific seeding of Lewy pathology induces distinct pre-motor cellular and dendritic vulnerabilities in the cortex

Circuit-based biomarkers distinguishing the gradual progression of Lewy pathology across synucleinopathies remain unknown. Here, we show that seeding of α-synuclein preformed fibrils in mouse dorsal striatum and motor cortex leads to distinct prodromal-phase cortical dysfunction across months. Our findings reveal that while both seeding sites had increased cortical pathology and hyperexcitability, distinct differences in electrophysiological and cellular ensemble patterns were crucial in distinguishing pathology spread between the two seeding sites. Notably, while beta-band spike-field-coherence reflected a significant increase beginning in Layer-5 and then spreading to Layer-2/3, the rate of entrainment and the propensity of stochastic beta-burst dynamics was markedly seeding location-specific. This beta dysfunction was accompanied by gradual superficial excitatory ensemble instability following cortical, but not striatal, preformed fibrils injection. We reveal a link between Layer-5 dendritic vulnerabilities and translaminar beta event dysfunction, which could be used to differentiate symptomatically similar synucleinopathies.

Role of oral-gut-brain axis in psychiatric and neurological disorders

The oral cavity and gut are two important microbial habitats in the human body, harboring the most ecologically rich and taxonomically diverse microbial communities in humans, which play a key role in microbiome related diseases. In recent years, the emerging concept of the oral-gut-brain axis has attracted widespread attention in the fields of neuroscience, digestive science, and microbiology. It is not only an anatomical description, but also a comprehensive concept that covers multiple physiological functions and pathological mechanisms. Simply put, the oral-gut-brain axis refers to the complex network that connects the mouth, gut, and brain tightly together through neural connections and hormonal and immune pathways. With the deepening of research on the oral-gut-brain axis theory, more and more evidence shows that it plays an important role in depression, Parkinson's disease, and other neurodegenerative diseases. This article reviews the recent progress in research of the oral-gut-brain axis in psychiatric and neurological diseases.

Pharmacogenomics for neurodegenerative disorders - a focused review

Neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) are characterized by the progressive degeneration of neuronal structure and function, leading to severe cognitive and motor impairments. These conditions present significant challenges to healthcare systems, and traditional treatments often fail to account for genetic variability among patients, resulting in inconsistent therapeutic outcomes. Pharmacogenomics aims to tailor medical treatments based on an individual's genetic profile, thereby improving therapeutic efficacy and reducing adverse effects. This focused review explores the genetic factors influencing drug responses in neurodegenerative diseases and the potential of pharmacogenomics to revolutionize their treatment. Key genetic markers, such as the APOE ε4 allele in AD and the CYP2D6 polymorphisms in PD, are highlighted for their roles in modulating drug efficacy. Additionally, advancements in pharmacogenomic tools, including genome-wide association studies (GWAS), next-generation sequencing (NGS), and CRISPR-Cas9, are discussed for their contributions to personalized medicine. The application of pharmacogenomics in clinical practice and its prospects, including ethical and data integration challenges, are also examined.

Comparative mapping of single-cell transcriptomic landscapes in neurodegenerative diseases

INTRODUCTION

Alzheimer's disease (AD), Dementia with Lewy bodies (DLB), and Parkinson's disease (PD) represent a spectrum of neurodegenerative disorders (NDDs). Here, we performed the first direct comparison of their transcriptomic landscapes.

METHODS

We profiled the whole transcriptomes of NDD cortical tissue by snRNA-seq. We used computational analyses to identify common and distinct differentially expressed genes (DEGs), biological pathways, vulnerable and disease-driver cell subtypes, and alteration in cell-to-cell interactions.

RESULTS

The same vulnerable inhibitory neuron subtype was depleted in both AD and DLB. Potentially disease-driving neuronal cell subtypes were present in both PD and DLB. Cell-cell communication was predicted to be increased in AD but decreased in DLB and PD. DEGs were most commonly shared across NDDs within inhibitory neuron subtypes. Overall, we observed the greatest transcriptomic divergence between AD and PD, while DLB exhibited an intermediate transcriptomic signature.

DISCUSSION

These results help explain the clinicopathological spectrum of this group of NDDs and provide unique insights into the shared and distinct molecular mechanisms underlying the pathogenesis of NDDs.

Alpha-synuclein expression in neurons modulates Japanese encephalitis virus infection

Japanese encephalitis virus (JEV) stands as a prominent vector-borne zoonotic pathogen, displaying neurotropism and eliciting Parkinson's disease (PD)-like symptoms among most symptomatic survivors. A characteristic feature of PD is the aggregation of mutated α-synuclein (α-syn) that damages the dopaminergic neurons. Considering this link between JEV-induced PD-like symptoms and α-syn pathogenesis, we explored the role of α-syn in JEV infectivity in neuronal cells. Our investigation revealed a significant increase in endogenous α-syn expression in JEV-infected cells. In addition, exogenous α-syn (Exoα-syn) treatment substantially reduced JEV replication, suggesting its anti-JEV effect. Furthermore, Exoα-syn treatment led to the upregulation of superoxide dismutase 1 (SOD1) and reduction in reactive oxygen species (ROS). The results were validated by endogenous α-syn-silencing, which decreased SOD1 and raised ROS levels in neuronal cells. Similarly, the SOD1 inhibition via LCS-1 also intensified ROS and JEV infection. Silencing of SOD1 in α-syn overexpressing neuro2a cells exhibited increased JEV replication. Overall, our results suggest that α-syn exerts an anti-JEV effect by regulating protein involved in oxidative stress inside neuronal cells. This study contributes valuable insights into the interplay between α-syn expression and JEV infectivity, shedding light on avenues further to investigate the potential role of α-syn in JEV pathogenesis.

IMPORTANCE

Japanese encephalitis virus (JEV) poses a significant threat, particularly to children. Despite extensive research efforts, the development of effective treatments against JEV has been impeded. One of the major setbacks is a lack of comprehensive understanding of neurotropism. The study focuses on alpha-synuclein (α-syn), a neuronal protein, and aims to determine its role in JEV pathogenesis. The present study reveals that the host cell upregulates α-syn in response to JEV infection. α-syn restrains JEV propagation by modulating superoxide dismutase 1 (SOD1) expression which further blocks JEV-induced ROS generation. Endogenous α-syn silencing led to a decrease in SOD1 expression and increased viral titer. α-syn plays a crucial role in counteracting oxidative stress through SOD1, which is essential for limiting JEV replication. This study provides broader implications for antiviral strategies and their possible role in neurodegenerative diseases; however, there is still much to explore, particularly regarding α-syn aggregation kinetics in JEV infection.

Heterotypic Interactions of Amyloid β and the Islet Amyloid Polypeptide Produce Mixed Aggregates with Non-Native Fibril Structure

Amyloid aggregates are hallmarks of the pathology of a wide range of diseases, including type 2 diabetes (T2D) and Alzheimer's disease (AD). Much epidemiological and pathological evidence points to significant overlap between AD and T2D. Individuals with T2D have a higher likelihood of developing AD; moreover, colocalized aggregates of amyloid β (Aβ) and the islet amyloid polypeptide (IAPP), the two main peptides implicated in the formation of toxic amyloid aggregates in AD and T2D, have also been identified in the brain. However, how these peptides interact with each other is not well understood, and the structural facets of heterotypic mixed fibrils formed via such interactions remain elusive. Here we use atomic force microscopy augmented with infrared spectroscopy to probe the secondary structure of individual aggregates formed via heterotypic interactions of Aβ and IAPP and provide unequivocal direct evidence of mixed aggregates. Furthermore, we show that co-aggregation of the peptides from the monomeric stage leads to the formation of unique polymorphs, in which both peptides undergo structural deviation from their native states, whereas seeding with preformed IAPP fibrils leads to aggregates similar to native Aβ. These findings highlight how heterotypic interactions between amyloidogenic peptides can lead to polymorphic diversity proteinopathies.

Cognitive Impact of β-Amyloid Load in the Rapid Eye Movement Sleep Behavior Disorder-Lewy Body Disease Continuum

BACKGROUND

Rapid eye movement sleep behavior disorder (RBD) is linked to the diffuse-malignant subtype and higher cognitive burden in Lewy body disease (LBD).

OBJECTIVE

This study explores brain β-amyloid deposition and its association with cognitive decline across the RBD-LBD continuum.

METHODS

Patients with isolated RBD (iRBD), Parkinson's disease with probable RBD (PDRBD), and dementia with Lewy bodies with probable RBD (DLBRBD) underwent 18F-florbetaben positron emission tomography, 3T magnetic resonance imaging scans, and comprehensive neuropsychological assessments. Subjects were categorized as cognitively normal (NC), mild cognitive impairment (MCI), or dementia. Global and regional standardized uptake value ratios (SUVR) were estimated in predefined cognitive volumes of interest (VOI) derived from voxel-wise comparison analysis among the cognitive groups, namely the prefrontal, parietal, precentral cortices, lingual gyrus, and supplementary motor area. Generalized linear models assessed the relationship between 18F-florbetaben SUVRs and neuropsychological testing, adjusting for age and sex. Subgroup analysis focused on the polysomnography-confirmed iRBD-continuum subset (n = 41) encompassing phenoconverters and nonconverters in our prospective iRBD cohort.

RESULTS

Eighty-six subjects were classified as follows: 14 NC, 54 MCI, and 18 dementia. The proportion of positive β-amyloid scans increased with advanced cognitive stages (P = 0.038). β-Amyloid signals in cognitive VOIs were elevated in subgroups showing impairment in Trail-Making Test B (TMT-B). A linear association between TMT-B z score and global cortical β-amyloid levels was observed in the iRBD-continuum subset (P = 0.013).

CONCLUSION

Cortical β-amyloid accumulates with declines in executive function within the RBD-LBD continuum. TMT-B performance may be a useful marker associating with β-amyloid load, particularly in the iRBD population. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

A systematic review of salivary biomarkers in Parkinson's disease

The search for reliable and easily accessible biomarkers in Parkinson's disease is receiving a growing emphasis, to detect neurodegeneration from the prodromal phase and to enforce disease-modifying therapies. Despite the need for non-invasively accessible biomarkers, the majority of the studies have pointed to cerebrospinal fluid or peripheral biopsies biomarkers, which require invasive collection procedures. Saliva represents an easily accessible biofluid and an incredibly wide source of molecular biomarkers. In the present study, after presenting the morphological and biological bases for looking at saliva in the search of biomarkers for Parkinson's disease, we systematically reviewed the results achieved so far in the saliva of different cohorts of Parkinson's disease patients. A comprehensive literature search on PubMed and SCOPUS led to the discovery of 289 articles. After screening and exclusion, 34 relevant articles were derived for systematic review. Alpha-synuclein, the histopathological hallmark of Parkinson's disease, has been the most investigated Parkinson's disease biomarker in saliva, with oligomeric alpha-synuclein consistently found increased in Parkinson's disease patients in comparison to healthy controls, while conflicting results have been reported regarding the levels of total alpha-synuclein and phosphorylated alpha-synuclein, and few studies described an increased oligomeric alpha-synuclein/total alpha-synuclein ratio in Parkinson's disease. Beyond alpha-synuclein, other biomarkers targeting different molecular pathways have been explored in the saliva of Parkinson's disease patients: total tau, phosphorylated tau, amyloid-β1-42 (pathological protein aggregation biomarkers); DJ-1, heme-oxygenase-1, metabolites (altered energy homeostasis biomarkers); MAPLC-3beta (aberrant proteostasis biomarker); cortisol, tumor necrosis factor-alpha (inflammation biomarkers); DNA methylation, miRNA (DNA/RNA defects biomarkers); acetylcholinesterase activity (synaptic and neuronal network dysfunction biomarkers); Raman spectra, proteome, and caffeine. Despite a few studies investigating biomarkers targeting molecular pathways different from alpha-synuclein in Parkinson's disease, these results should be replicated and observed in studies on larger cohorts, considering the potential role of these biomarkers in determining the molecular variance among Parkinson's disease subtypes. Although the need for standardization in sample collection and processing, salivary-based biomarkers studies have reported encouraging results, calling for large-scale longitudinal studies and multicentric assessments, given the great molecular potentials and the non-invasive accessibility of saliva.

Loss of calcium/calmodulin-dependent protein kinase kinase 2, transferrin, and transferrin receptor proteins in the temporal cortex of Alzheimer's patients postmortem is associated with abnormal iron homeostasis: implications for patient survival

Introduction

Iron is crucial for brain function, but excessive iron is neurotoxic. Abnormally high brain iron accumulation is one of the pathogenic factors in Alzheimer's disease (AD). Therefore, understanding the mechanistic basis of iron dyshomeostasis in AD is vital for disease mitigation. Calcium, another essential bioelement involved in cell signaling, also exhibits dysregulated homeostasis in AD. Calcium ion (Ca2+) signaling can influence iron homeostasis through multiple effectors. Our previous studies identified Ca2+/calmodulin (CAM)-dependent protein kinase kinase 2 (CAMKK2) as a regulator of transferrin (TF)-bound iron trafficking through the TF receptor (TFRC). Given CAMKK2's high expression in brain cells, it was hypothesized that abnormal CAMKK2-TF/TFRC signaling may underlie excessive iron deposition in AD brains. This study aims to retrospectively investigate CAMKK2, TF, TFRC proteins, and iron content in temporal cortex tissues from AD patients and cognitively normal (CN) individuals, postmortem.

Methods

Postmortem temporal cortex tissues from 74 AD patients, 27 Parkinson's disease (PD) patients, and 17 CN individuals were analyzed for CAMKK2, TF, and TFRC protein levels by Western blotting. Additionally, prefrontal/temporal cortex tissues from 30 CN individuals of various ages were examined for age-related effects. Iron content in cortical tissues was measured using a colorimetric assay.

Results

CAMKK2, TF, and TFRC levels were significantly decreased in AD patients' temporal cortices compared to CN individuals, independent of age or postmortem interval-related changes. PD patients' also exhibited similar reductions in CAMKK2/TF/TFRC levels. The increased iron content in AD brains was significantly correlated with reduced TF/TFRC protein levels.

Discussion

Building on the previous identification of CAMKK2 as a regulator of TF/TFRC trafficking and iron homeostasis, the findings from this study suggest that downregulation of CAMKK2 in AD cortices may disrupt TF/TFRC signaling and contribute to iron overloading and neurodegeneration through iron-induced toxicity. The decreased levels of TF/TFRC and increased iron in AD brains may result from enhanced clearance or post-trafficking degradation of TF/TFRC due to CAMKK2 downregulation. Restoring CAMKK2 levels in the AD brain could offer a novel therapeutic approach to reestablish iron homeostasis. Further studies are needed to explore the pathways linking CAMKK2 and iron dysregulation in AD and other neurodegenerative diseases.

Green synthesis of nanoparticles using medicinal plants as an eco-friendly and therapeutic potential approach for neurodegenerative diseases: a comprehensive review

Central nervous system disorders impact over 1.5 billion individuals globally, with neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's diseases being particularly prominent. These conditions, often associated with aging, present debilitating symptoms including memory loss and movement difficulties. The growing incidence of neurological disorders, alongside a scarcity of effective anti-amyloidogenic therapies, highlights an urgent need for innovative treatment methodologies. Nanoparticles (NPs), derived from medicinal plants and characterized by their favorable pharmacological properties and minimal side effects, offer a promising solution. Their inherent attributes allow for successful traversal of the blood-brain barrier (BBB), enabling targeted delivery to the brain and the modulation of specific molecular pathways involved in neurodegeneration. NPs are crucial in managing oxidative stress, apoptosis, and neuroinflammation in ND. This study reviews the efficacy of green-synthesized nanoparticles in conjunction with various medicinal plants for treating neurodegenerative diseases, advocating for further research to refine these formulations for enhanced clinical applicability and improved patient outcomes.

Apolipoprotein E aggregation in microglia initiates Alzheimer's disease pathology by seeding β-amyloidosis

The seeded growth of pathogenic protein aggregates underlies the pathogenesis of Alzheimer's disease (AD), but how this pathological cascade is initiated is not fully understood. Sporadic AD is linked genetically to apolipoprotein E (APOE) and other genes expressed in microglia related to immune, lipid, and endocytic functions. We generated a transgenic knockin mouse expressing HaloTag-tagged APOE and optimized experimental protocols for the biochemical purification of APOE, which enabled us to identify fibrillary aggregates of APOE in mice with amyloid-β (Aβ) amyloidosis and in human AD brain autopsies. These APOE aggregates that stained positive for β sheet-binding dyes triggered Aβ amyloidosis within the endo-lysosomal system of microglia, in a process influenced by microglial lipid metabolism and the JAK/STAT signaling pathway. Taking these observations together, we propose a model for the onset of Aβ amyloidosis in AD, suggesting that the endocytic uptake and aggregation of APOE by microglia can initiate Aβ plaque formation.

Gastrointestinal tract cleavage of α-synuclein by asparaginyl endopeptidase leads to Parkinson's disease

Pathologic α-synuclein (α-syn) aggregates from the gastrointestinal (GI) tract may contribute to Parkinson's disease (PD). Xiang et al.1 report in Neuron that enteric nervous system-specific expression of asparaginyl endopeptidase (AEP)-truncated α-syn and tau spreads to the brain, synergistically causing PD-related neurodegeneration and neurobehavioral deficits.

Oral Microbiota and Porphyromonas gingivalis Kgp Genotypes Altered in Parkinson's Disease with Mild Cognitive Impairment

Cognitive impairment (CI) is a common complication of the non-motor symptoms in Parkinson's disease (PD), including PD with mild cognitive impairment (PD-MCI) and PD dementia. Recent studies reported the oral dysbiosis in PD and CI, respectively. Porphyromonas gingivalis (P. gingivalis), a pathogen of oral dysbiosis, plays an important role in PD, whose lysine-gingipain (Kgp) could lead to AD-type pathologies. No previous study investigated the composition of oral microbiota and role of P. gingivalis in PD-MCI. This study aimed to investigate the differences of oral microbiota composition, P. gingivalis copy number, and Kgp genotypes among PD-MCI, PD with normal cognition (PD-NC) and periodontal status-matched control (PC) groups. The oral bacteria composition, the copy number of P. gingivalis, and the Kgp genotypes in gingival crevicular fluid from PD-MCI, PD-NC, and PC were analyzed using 16S ribosomal RNA sequencing, quantitative real-time PCR, and MseI restriction. We found that the structures of oral microbiota in PD-MCI group were significantly different compared to that in PD-NC and PC group. The relative abundances of Prevotella, Lactobacillus, Megasphaera, Atopobium, and Howardella were negatively correlated with cognitive score. Moreover, there was a significant difference of Kgp genotypes among the three groups. The predominant Kgp genotypes of P. gingivalis in the PD-MCI group were primarily Kgp II, whereas in the PD-NC group, it was mainly Kgp I. The Kgp II correlated with lower MMSE and MoCA scores, which suggested that Kgp genotypes II is related to cognitive impairment in PD.

Oxyphylla A exerts antiparkinsonian effects by ameliorating 6-OHDA-induced mitochondrial dysfunction and dyskinesia in vitro and in vivo

Parkinson's disease (PD) poses a formidable challenge in neurology, marked by progressive neuronal loss in the substantia nigra. Despite extensive investigations, understanding PD's pathophysiology remains elusive, with no effective therapeutic intervention identified to alter its course. Oxyphylla A (OPA), a natural compound extracted from Alpinia oxyphylla, exhibits promise in experimental models of various neurodegenerative disorders (ND), notably through novel mechanisms like α-synuclein degradation. The purpose of this investigation was to explore the neuroprotective potential of OPA on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in PD models, with a focus on mitochondrial functions. Additionally, potential OPA targets for neuroprotection were explored. PC12 cells and C57BL/6 mice were lesioned with 6-OHDA as PD models. Impaired mitochondrial membrane potential (Δψm) was assessed using JC-1 staining. The oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were also detected to evaluate mitochondrial function and glucose metabolism in PC12 cells. Behavioral analysis and immunohistochemistry were performed to evaluate pathological lesions in the mouse brain. Moreover, bioinformatics tools predicted OPA targets. OPA restored cellular energy metabolism and mitochondrial biogenesis, preserving Δψm in 6-OHDA-induced neuronal damage. Pre-treatment mitigated loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra and striatal dopaminergic fibers, restoring dopamine levels and ameliorating motor deficits in PD mice. Mechanistically, OPA may activate PKA/Akt/GSK-3β and CREB/PGC-1α/NRF-1/TFAM signaling cascades. Bioinformatics analysis identified potential OPA targets, including CTNNB1, ESR1, MAPK1, MAPK14, and SRC. OPA, derived from Alpinia oxyphylla, exhibited promising neuroprotective activity against PD through addressing mitochondrial dysfunction, suggesting its potential as a multi-targeted therapeutic for PD.

Optineurin regulates motor and learning behaviors by affecting dopaminergic neuron survival in mice

Optineurin (OPTN) is an autophagy receptor that participates in the degradation of damaged mitochondria, protein aggregates, and invading pathogens. OPTN is closely related to various types of neurodegenerative diseases. However, the role of OPTN in the central nervous system is unclear. Here, we found that OPTN dysregulation in the compact part of substantia nigra (SNc) led to motor and learning deficits in animal models. Knockdown of OPTN increased total and phosphorylated α-synuclein levels which induced microglial activation and dopaminergic neuronal loss in the SNc. Overexpression of OPTN can't reverse the motor and learning phenotypes. Mechanistic analysis revealed that upregulation of OPTN increased α-synuclein phosphorylation independent of its autophagy receptor activity, which further resulted in microglial activation and dopaminergic neuronal loss similar to OPTN downregulation. Our study uncovers the crucial role of OPTN in maintaining dopaminergic neuron survival and motor and learning functions which are disrupted in PD patients.

Clinical and diagnostic implications of Alzheimer's disease copathology in Lewy body disease

Concomitant Alzheimer's disease (AD) pathology is a frequent event in the context of Lewy body disease (LBD), occurring in approximately half of all cases. Evidence shows that LBD patients with AD copathology show an accelerated disease course, a greater risk of cognitive decline and an overall poorer prognosis. However, LBD-AD cases may show heterogeneous motor and non-motor phenotypes with a higher risk of dementia and, consequently, be not rarely misdiagnosed. In this review, we summarize the current understanding of LBD-AD by discussing the synergistic effects of AD neuropathological changes and Lewy pathology and their clinical relevance. Furthermore, we provide an extensive overview of neuroimaging and fluid biomarkers under assessment for use in LBD-AD and their possible diagnostic and prognostic values. AD pathology can be predicted in vivo by means of CSF, MRI and PET markers, whereas the most promising technique to date for identifying Lewy pathology in different biological tissues is the α-synuclein seed amplification assay. Pathological imaging and CSF AD biomarkers are associated with a higher likelihood of cognitive decline in LBD but do not always mirror the neuropathological severity as in pure AD. Implementing the use of blood-based AD biomarkers might allow faster screening of LBD patients for AD copathology, thus improving the overall diagnostic sensitivity for LBD-AD. Finally, we discuss the literature on novel candidate biomarkers being exploited in LBD-AD to investigate other aspects of neurodegeneration, such as neuroaxonal injury, glial activation and synaptic dysfunction. The thorough characterization of AD copathology in LBD should be taken into account when considering differential diagnoses of dementia syndromes, to allow prognostic evaluation on an individual level, and to guide symptomatic and disease-modifying therapies.

Exploratory Analysis of the Association Between Plasma Ceramide Alterations and Cognitive Dysfunction in Parkinson's Disease

OBJECTIVE

Prior research has underscored the importance of sphingolipid metabolism in Parkinson's disease (PD) pathogenesis. Our objective was to explore the associations between plasma ceramide levels and PD patients with cognitive dysfunction (PD-CD).

METHODS

We enrolled two study populations from Eastern China and the Parkinson's Progression Markers Initiative (PPMI), comprising 290 (100 HCs, 160 PDs, and 30 MSAs) and 429 (125 HCs and 304 PDs) participants, respectively. The plasma levels of ceramides (Cer 16:0, Cer 18:0, Cer 24:0, and Cer 24:1) were tested via HPLC-MS/MS analysis.

RESULTS

Compared with those in the HC group, the plasma levels of Cer 18:0, Cer 24:1, Cer 16:0/Cer 24:0, Cer 18:0/Cer 24:0, and Cer 24:1/Cer 24:0 were higher in both the PD and MSA groups. Significant differences in the plasma levels of Cer 16:0/Cer 24:0, Cer 18:0/Cer 24:0, and Cer 24:1/Cer 24:0 were observed among the PD-NC (PD with normal cognition), PD-MCI (PD with mild cognitive impairment), and PDD (PD dementia) groups, with the PDD group exhibiting the highest levels. PD patients with higher baseline levels of plasma ceramides (specifically, Cer 18:0, Cer 16:0/Cer 24:0, Cer 18:0/Cer 24:0, and Cer 24:1/Cer 24:0) demonstrated accelerated cognitive decline compared with individuals who had lower baseline plasma ceramide levels during the 5-year follow-up period. A biomarker panel including Cer 18:0/Cer 24:0 and Cer 24:1/Cer 24:0 could effectively differentiate PD-CD from PD-NC with notable diagnostic accuracy.

CONCLUSIONS

Our results indicate that plasma ceramide levels could potentially be used as diagnostic biomarkers for PD-CD.

A comprehensive review on the pharmacological role of gut microbiome in neurodegenerative disorders: potential therapeutic targets

Neurological disorders, including Alzheimer and Parkinson's, pose significant challenges to public health due to their complex etiologies and limited treatment options. Recent advances in research have highlighted the intricate bidirectional communication between the gut microbiome and the central nervous system (CNS), revealing a potential therapeutic avenue for neurological disorders. Thus, this review aims to summarize the current understanding of the pharmacological role of gut microbiome in neurological disorders. Mounting evidence suggests that the gut microbiome plays a crucial role in modulating CNS function through various mechanisms, including the production of neurotransmitters, neuroactive metabolites, and immune system modulation. Dysbiosis, characterized by alterations in gut microbial composition and function, has been observed in many neurological disorders, indicating a potential causative or contributory role. Pharmacological interventions targeting the gut microbiome have emerged as promising therapeutic strategies for neurological disorders. Probiotics, prebiotics, antibiotics, and microbial metabolite-based interventions have shown beneficial effects in animal models and some human studies. These interventions aim to restore microbial homeostasis, enhance microbial diversity, and promote the production of beneficial metabolites. However, several challenges remain, including the need for standardized protocols, identification of specific microbial signatures associated with different neurological disorders, and understanding the precise mechanisms underlying gut-brain communication. Further research is necessary to unravel the intricate interactions between the gut microbiome and the CNS and to develop targeted pharmacological interventions for neurological disorders.

Effective lowering of α-synuclein expression by targeting G-quadruplex structures within the SNCA gene

Alpha-synuclein, encoded by the SNCA gene, is a pivotal protein implicated in the pathogenesis of synucleinopathies, including Parkinson's disease. Current approaches for modulating alpha-synuclein levels involve antisense nucleotides, siRNAs, and small molecules targeting SNCA's 5'-UTR mRNA. Here, we propose a groundbreaking strategy targeting G-quadruplex structures to effectively modulate SNCA gene expression and lowering alpha-synuclein amount. Novel G-quadruplex sequences, identified on the SNCA gene's transcription starting site and 5'-UTR of SNCA mRNAs, were experimentally confirmed for their stability through biophysical assays and in vitro experiments on human genomic DNA. Biological validation in differentiated SH-SY5Y cells revealed that well-known G-quadruplex ligands remarkably stabilized these structures, inducing the modulation of SNCA mRNAs expression, and the effective decrease in alpha-synuclein amount. Besides, a novel peptide nucleic acid conjugate, designed to selectively disrupt of G-quadruplex within the SNCA gene promoter, caused a promising lowering of both SNCA mRNA and alpha-synuclein protein. Altogether our findings highlight G-quadruplexes' key role as intriguing biological targets in achieving a notable and successful reduction in alpha-synuclein expression, pointing to a novel approach against synucleinopathies.