Tau accelerates α-synuclein aggregation and spreading in Parkinson's disease

Lycium barbarum polysaccharide ameliorates corticosterone-induced cognition decline with modulation of CRHR1

BACKGROUND

Lycium barbarum polysaccharide (LBP) has anti-inflammatory, anti-oxidation and anti-aging properties, but the mechanism of LBP on stress-induced cognitive dysfunction caused by elevated GC level is still unclear.

OBJECTIVES

Therefore, the present study aimed to investigate the mechanism of LBP on corticosterone-injected（CORT-injected） cognitive impairment.

METHODS

The rat model was induced by corticosterone in vivo. Water maze test and HE staining were used to observe the effect of LBP on cognitive function and brain morphology in CORT-injected rats. RT-qPCR, Western blot, and immunofluorescence were used to detect the expression of proteins. SH-SY5Y cells were treated with CORT and D-gal in vitro, respectively. The effect of LBP on cell proliferation was observed, and western blotting was detected in the protein expressions.

RESULTS

In this study, LBP treatment ameliorated CORT-induced learning and cognitive function and protected hypothalamic and hippocampal neurons from injury in vivo. In addition, LBP reduced plasma corticosterone concentrations in CORT-injected rats. The results also indicated that LBP enhanced the expression of synapsis-related proteins PSD95 and SYN by up-regulating the expression of CRHR1 and RGS2 in the hippocampus and hypothalamus of the model group. Meanwhile, we confirmed that LBP enhanced CORT - and D-Gal-induced proliferation of SH-SY5Y cells in vitro, and further verified the expression changes of CRHR1, RGS2, and synapse-related proteins.

CONCLUSIONS

This study demonstrates that LBP ameliorated CORT-induced cognition decline by regulating CRHR1. Therefore, LBP may represent a potential drug for the prevention of cognition dysfunction in patients caused by increased GCs.

Neurodegeneration models in Parkinson's disease: cellular and molecular paths to neuron death

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects dopaminergic neurons in the substantia nigra pars compacta. It is a complex disease that is strongly influenced by environmental and genetic factors. While the exact causes of PD are not well understood, research on the effects of toxic substances that induce neuronal death has shed some light on the etiology of the disease. In addition, studies have implicated protein aggregation and impaired mitochondrial, endoplasmic reticulum (ER), proteasome, and/or lysosomal function in the pathogenesis of PD. This review focuses on the alterations in intraneuronal organelles and the role of toxic agents that lead to organelle damage and neurodegeneration that characterize PD. We describe in vivo and in vitro models that have been used to elucidate the factors that lead to the death of dopaminergic neurons and summarize the molecular mechanisms that may underlie the changes that promote neurodegeneration. A deeper understanding of the mechanisms of neuronal death may help us to develop new therapies and interventions to delay or prevent the progression of PD.

Fibrinogen exacerbates α-synuclein aggregation and mitochondrial dysfunction via alpha5beta3 integrin in Parkinson's disease

INTRODUCTION

Blood-brain barrier(BBB) disruption promotes the influx of the fibrinogen(FG); however, it remains unknown whether FG deposit contributes to neurodegeneration in Parkinson's disease(PD).

OBJECTIVES

We aimed to examine the pathophysiologic link among FG, mitochondrial dysfunction and α-synuclein(α-syn) abnormality in PD.

METHODS

First, plasma FG levels were measured in 60 healthy controls and 60 PD patients. Second, to determine whether FG contributes to PD pathogenesis, FG was injected into the substantia nigra pars compacta(SNpc) of healthy and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)-treated PD mice. Meanwhile, intraperitoneal injections of batroxobin were used to deplete FG in the brain of PD mice. Mitochondrial ultrastructure in mouse models was observed by transmission electron microscopy(TEM), and mitochondrial functions in SH-SY5Y cells were examined by different assay kits and flow cytometry. The mechanisms underlying FG-induced α-syn abnormality and mitochondrial dysfunction were observed by RNA sequencing and validated in various experiments including western blot and immunostaining. Last, the endocytosis of FG in primary neurons were detected by confocal microscopy, and α-syn aggregation after FG co-incubation were evaluated by western blot, ThT-binding assay and TEM.

RESULTS

PD patients exhibited elevated levels of FG in peripheral blood compared to HCs, and there was a positive correlation between the plasma FG and PD clinical severity. Excessive FG in the SNpc of MPTP-treated mice promoted poly (ADP-ribose) (PAR) polymerase-1(PARP1) elevation, mediated by the αvβ3 integrin receptor. FG exacerbated α-syn abnormalities and mitochondrial dysfunctions via PARP1 activation. Moreover, FG entered neurons by αvβ3 integrin mediation, potentially enhancing α-syn fibrillation and toxicity. FG facilitated α-syn aggregation subsequently reduced ATP-dependent Clp protease(ClpP) level, impairing neuronal mitochondrial unfolded response and increasing mitochondrial ROS. Pharmacological depletion of FG by batroxobin ameliorated neurodegeneration in MPTP-treated mice.

CONCLUSION

Our study indicate that FG plays an essential pathological role in α-syn abnormality. FG-targeting therapy can be a promising strategy against neurodegeneration in PD.

Investigating glymphatic function and bed nucleus of the stria terminalis-based functional connectivity in Parkinson's disease with and without depression

Glymphatic activity and the bed nucleus of the stria terminalis (BNST) have been implicated in the pathogenesis of Parkinson's disease (PD) with depression (PDD). This study aimed to investigate glymphatic function and BNST-based functional connectivity (FC) and potential biomarkers in PDD. The diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index combined with BNST-based FC and support vector machine were applied to 24 PDD, 24 PD with non-depression (PDND), and 25 healthy controls. We found that (1) the DTI-ALPS indices (p < 0.001), the right BNST-based FC values (p < 0.001, FWE small volume correction) were significantly different among three groups; (2) the FC features in the right mPFC (mPFC_R), right MTG (MTG_R), and right ITG (ITG_R) can distinguish PDD from PDND; (3) the right BNST-based FC values, DTI-ALPS indices, and HAMD scores were correlated with each other (r = -0.620, p = 0.004; r = 0.651, p = 0.002; r = -0.53, p = 0.016). Impaired glymphatic function and altered BNST-based FC values are strongly associated with PD, and brain regions with differences in the right BNST-based FC values may serve as potential biomarkers for classifying clinical subtypes of PD. These findings provide new insights into the pathogenesis of depression in PD. This study protocol was registered on the Chinese Clinical Trial Registry (ChiCTR2000038411, September 22, 2020, https://www.chictr.org.cn/showproj.html?proj=56715 ).

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

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

Impaired Respiratory Function as an Auxiliary Marker for Disease Progression in Different Motor Subtypes of Parkinson's Disease

BACKGROUND

The mechanisms underlying respiratory function impairments in different motor subtypes of Parkinson's disease (PD) remain poorly understood.

OBJECTIVES

This study aims to elucidate the differences in respiratory function between the two main PD motor subtypes, tremor-dominant (TD) and postural instability gait difficulty (PIGD), and investigate their associations with disease severity.

METHODS

A total of 106 PD patients (59 TD and 47 PIGD) and 42 age- and sex-matched healthy controls (HCs) were enrolled. Pulmonary function tests (PFTs), respiratory muscle strength, and respiratory drive measurements were conducted. Multivariate models were employed to analyze correlations between respiratory function indices and clinical characteristics.

RESULTS

Compared to HCs, PIGD patients exhibited significant reductions in forced vital capacity (FVC%) (P = 0.018), peak expiratory flow (PEF%) (P < 0.001), diffusing capacity for carbon monoxide adjusted for hemoglobin (DLCOc%) (P = 0.013), and total lung capacity (TLC%) (P = 0.045). Although differences between the two motor subtypes were not statistically significant, a more apparent declining trend was observed in PIGD patients. Regarding respiratory muscle strength, PIGD patients showed more severe impairments in maximal inspiratory pressure (PImax%) (P < 0.001) and maximal expiratory pressure (PEmax%) (P < 0.001). Multivariate linear regression analysis confirmed that PEF% was a significant determinant of cognitive function in TD patients (β = 0.497, P < 0.001), whereas the airway occlusion pressure at 100 milliseconds (P0.1%) influenced cognitive levels in PIGD patients (β = -0.373, P = 0.015).

CONCLUSIONS

Compared to TD patients, PIGD patients have more pronounced respiratory impairments. Specific respiratory indices correlate with motor severity and cognitive decline, highlighting their potential as markers for disease progression in PD motor subtypes.

Activating autophagy to eliminate toxic protein aggregates with small molecules in neurodegenerative diseases

Neurodegenerative diseases (NDs), such as Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are well known to pose formidable challenges for their treatment due to their intricate pathogenesis and substantial variability among patients, including differences in environmental exposures and genetic predispositions. One of the defining characteristics of NDs is widely reported to be the buildup of misfolded proteins. For example, Alzheimer disease is marked by amyloid beta and hyperphosphorylated Tau aggregates, whereas Parkinson disease exhibits α-synuclein aggregates. Amyotrophic lateral sclerosis and frontotemporal dementia exhibit TAR DNA-binding protein 43, superoxide dismutase 1, and fused-in sarcoma protein aggregates, and Huntington disease involves mutant huntingtin and polyglutamine aggregates. These misfolded proteins are the key biomarkers of NDs and also serve as potential therapeutic targets, as they can be addressed through autophagy, a process that removes excess cellular inclusions to maintain homeostasis. Various forms of autophagy, including macroautophagy, chaperone-mediated autophagy, and microautophagy, hold a promise in eliminating toxic proteins implicated in NDs. In this review, we focus on elucidating the regulatory connections between autophagy and toxic proteins in NDs, summarizing the cause of the aggregates, exploring their impact on autophagy mechanisms, and discussing how autophagy can regulate toxic protein aggregation. Moreover, we underscore the activation of autophagy as a potential therapeutic strategy across different NDs and small molecules capable of activating autophagy pathways, such as rapamycin targeting the mTOR pathway to clear α-synuclein and Sertraline targeting the AMPK/mTOR/RPS6KB1 pathway to clear Tau, to further illustrate their potential in NDs' therapeutic intervention. Together, these findings would provide new insights into current research trends and propose small-molecule drugs targeting autophagy as promising potential strategies for the future ND therapies. SIGNIFICANCE STATEMENT: This review provides an in-depth overview of the potential of activating autophagy to eliminate toxic protein aggregates in the treatment of neurodegenerative diseases. It also elucidates the fascinating interrelationships between toxic proteins and the process of autophagy of "chasing and escaping" phenomenon. Moreover, the review further discusses the progress utilizing small molecules to activate autophagy to improve the efficacy of therapies for neurodegenerative diseases by removing toxic protein aggregates.

Leveraging animal models to understand non-motor symptoms of Parkinson's disease

Parkinson's disease is diagnosed based on motor symptoms, but non-motor symptoms of the disease, such as cognitive impairment, autonomic dysfunction, hyposmia, sleep disorders, and psychiatric disorders heavily impact patient and caregiver quality of life. It has proven challenging to faithfully reproduce and quantify these non-motor phenotypes. Indeed, many non-motor signs in animals that may phenotypically resemble features in patients may be caused by different mechanisms or may not be consistent within the same or similar models. In this review, we survey the existing literature on the assessment of non-motor signs in parkinsonian rodents and non-human primates. We highlight the gaps in our understanding and suggest how researchers might improve experimental designs to produce more meaningful results with the hope of better understanding the disease and developing better therapies.

Volatile oil of Acori tatarinowii rhizoma: potential candidate drugs for mitigating dementia

Objective

This study aims to elucidate the mitigating effects of the volatile oil of Acori tatarinowii rhizoma (ATR) on dementia, in order to provide a reference for future research and applications of the volatile oil of ATR in the field of dementia.

Materials and methods

A search strategy was developed using terms such as "Acori tatarinowii rhizoma," "Acorus tatarinowii Schott," "Asarone," and "Dementia." The literature search was conducted in PubMed, Web of Science, and Google Scholar, and studies not meeting the inclusion criteria were excluded. This study summarizes the main metabolites, active ingredients, toxicological properties, and pharmacokinetic characteristics of the volatile oil from ATR in mitigating dementia, with a particular focus on its potential mechanisms of action. Furthermore, the study highlights the limitations of existing research and offers insights into future research directions.

Results

The volatile oil of ATR mitigates dementia through multiple pathways, including reducing abnormal protein aggregation, promoting neurogenesis, inhibiting neuronal apoptosis, regulating neurotransmitters, improving synaptic function, modulating autophagy, countering cellular stress, reducing neuroinflammation, and alleviating vascular risk factors.

Conclusion

The multi-pathway pharmacological effects of the volatile oil of ATR are well-aligned with the complex mechanisms of dementia progression, highlighting its significant therapeutic potential for anti-dementia applications. This provides new perspectives for the development of more effective anti-dementia drugs. Nonetheless, further rigorous and high-quality preclinical and clinical investigations are required to address key issues, including the chemical characterization of the volatile oil of ATR, potential synergistic effects among active ingredients, toxicity profiles, and definitive clinical efficacy.

Role of the Intestinal Microbiota in the Molecular Pathogenesis of Atypical Parkinsonian Syndromes

The role of the intestinal microbiota and its influence on neurodegenerative disorders has recently been extensively explored, especially in the context of Parkinson's disease (PD). In particular, its role in immunomodulation, impact on inflammation, and participation in the gut-brain axis are under ongoing investigations. Recent studies have revealed new data that could be important for exploring the neurodegeneration mechanisms connected with the gut microbiota, potentially leading to the development of new methods of treatment. In this review, the potential roles of the gut microbiota in future disease-modifying therapies were discussed and the properties of the intestinal microbiota-including its impacts on metabolism and short-chain fatty acids and vitamins-were summarized, with a particular focus on atypical Parkinsonian syndromes. This review focused on a detailed description of the numerous mechanisms through which the microbiota influences neurodegenerative processes. This review explored potentially important connections between the gut microbiota and the evolution and progression of atypical Parkinsonian syndromes. Finally, a description of recently derived results regarding the microbiota alterations in atypical Parkinsonian syndromes in comparison with results previously described in PD was also included.

Irisin promotes autophagy and attenuates NLRP3 inflammasome activation in Parkinson's disease

Parkinson's disease (PD) is characterized by the aggregation and prion-like propagation of α-synuclein (α-syn). Irisin is an exercise-induced myokine that regulates energy metabolism and exerts protective effects in PD by reducing α-syn pathology. However, the molecular mechanisms underlying the role of irisin are not fully understood. Here, we show that irisin inhibits NLRP3 inflammasome activation and promotes autophagy in cultured cells. Additionally, irisin alleviates oxidative stress and reduces cell apoptosis induced by α-syn fibrils. In a PD mouse model induced by intrastriatal injection of α-syn fibrils, irisin mitigated α-syn aggregation, neuroinflammation and neurodegeneration. These observations suggest that irisin functions as a protective mediator against α-syn pathology in PD and that irisin may serve as a potential therapeutic target for the prevention and treatment of PD.

Tubulin transforms Tau and α-synuclein condensates from pathological to physiological

Proteins phase-separate to form condensates that partition and concentrate biomolecules into membraneless compartments. These condensates can exhibit dichotomous behaviors in biology by supporting cellular physiology or instigating pathological protein aggregation 1-3 . Tau and α- synuclein (αSyn) are neuronal proteins that form heterotypic (Tau:αSyn) condensates associated with both physiological and pathological processes. Tau and αSyn functionally regulate microtubules 8-12 , but are also known to misfold and co-deposit in aggregates linked to various neurodegenerative diseases 4,5,6,7 , which highlights the paradoxically ambivalent effect of Tau:αSyn condensation in health and disease. Here, we show that tubulin modulates Tau:αSyn condensates by promoting microtubule interactions, competitively inhibiting the formation of homotypic and heterotypic pathological oligomers. In the absence of tubulin, Tau-driven protein condensation accelerates the formation of toxic Tau:αSyn heterodimers and amyloid fibrils. However, tubulin partitioning into Tau:αSyn condensates modulates protein interactions, promotes microtubule polymerization, and prevents Tau and αSyn oligomerization and aggregation. We distinguished distinct Tau and αSyn structural states adopted in tubulin-absent (pathological) and tubulin-rich (physiological) condensates, correlating compact conformations with aggregation and extended conformations with function. Furthermore, using various neuronal cell models, we showed that loss of stable microtubules, which occurs in Alzheimer's disease and Parkinsons disease patients 13,14 , results in pathological oligomer formation and loss of neurites, and that functional condensation using an inducible optogenetic Tau construct resulted in microtubule stablization. Our results identify that tubulin is a critical modulator in switching Tau:αSyn pathological condensates to physiological, mechanistically relating the loss of stable microtubules with disease progression. Tubulin restoration strategies and Tau-mediated microtubule stabilization can be potential therapies targeting both Tau-specific and Tau/αSyn mixed pathologies.

Tau Pathology Drives Disease-Associated Astrocyte Reactivity in Salt-Induced Neurodegeneration

Dietary high salt intake is increasingly recognized as a risk factor for cognitive decline and dementia, including Alzheimer's disease (AD). Recent studies have identified a population of disease-associated astrocytes (DAA)-like astrocytes closely linked to amyloid deposition and tau pathology in an AD mouse model. However, the presence and role of these astrocytes in high-salt diet (HSD) models remain unexplored. In this study, it is demonstrated that HSD significantly induces enhanced reactivity of DAA-like astrocytes in the hippocampal CA3 region of mice, with this reactivity being critically dependent on neuronal tau pathology. Neuronal tau pathology activates adenosine A1R signaling, exacerbating tau pathology by inhibiting the Cers1 pathway, which sustains astrocyte reactivity. Additionally, neurons burdened with tau pathology promote astrocyte reactivity via releasing Proteins Associated with Promoting DAA-like Astrocyte Reactivity (PAPD), with Lcn2 playing a pivotal role. Knockout of Lcn2 or its receptor 24p3R significantly mitigates HSD-induced DAA reactivity and neuroinflammation. These findings suggest a vicious cycle between tau pathology and A1R signaling, driving DAA-like astrocyte reactivity. Targeting the Tau-A1R axis may provide a novel therapeutic strategy for reducing HSD-induced neuroinflammation and cognitive deficits.

Propagation of pathologic α-synuclein from kidney to brain may contribute to Parkinson's disease

The pathogenesis of Lewy body diseases (LBDs), including Parkinson's disease (PD), involves α-synuclein (α-Syn) aggregation that originates in peripheral organs and spreads to the brain. PD incidence is increased in individuals with chronic renal failure, but the underlying mechanisms remain unknown. Here we observed α-Syn deposits in the kidneys of patients with LBDs and in the kidney and central nervous system of individuals with end-stage renal disease without documented LBDs. In male mice, we found that the kidney removes α-Syn from the blood, which is reduced in renal failure, causing α-Syn deposition in the kidney and subsequent spread into the brain. Intrarenal injection of α-Syn fibrils induces the propagation of α-Syn pathology from the kidney to the brain, which is blocked by renal denervation. Deletion of α-Syn in blood cells alleviates pathology in α-Syn A53T transgenic mice. Thus, the kidney may act as an initiation site for pathogenic α-Syn spread, and compromised renal function may contribute to the onset of LBDs.

A same day α-synuclein RT-QuIC seed amplification assay for synucleinopathy biospecimens

Parkinson's disease (PD), dementia with Lewy bodies (DLB), and other synucleinopathies are characterized by the accumulation of abnormal, self-propagating aggregates of α-synuclein. RT-QuIC or seed amplification assays are currently showing unprecedented diagnostic sensitivities and specificities for synucleinopathies even in prodromal phases years in advance of the onset of Parkinsonian signs or dementia. However, commonly used α-synuclein seed amplification assays take ≥48 h to perform as applied to patients' diagnostic biospecimens. Here, we report the development of a faster α-synuclein RT-QuIC assay that is as analytically sensitive as prior assays of this type, but can be completed in ≤12 h for brain, skin, and intestinal mucosa, with positive signals often arising in <5 h. CSF assays took a few hours longer. Our same-day α-synuclein RT-QuIC (sdRT-QuIC) assay should increase the practicality, cost-effectiveness, and throughput of measurements of pathological forms of α-synuclein for fundamental research, clinical diagnosis, and therapeutics development.

Therapeutic Role of Heterocyclic Compounds in Neurodegenerative Diseases: Insights from Alzheimer's and Parkinson's Diseases

Alzheimer's and Parkinson's are the most common neurodegenerative diseases (NDDs). The development of aberrant protein aggregates and the progressive and permanent loss of neurons are the major characteristic features of these disorders. Although the precise mechanisms causing Alzheimer's disease (AD) and Parkinson's disease (PD) are still unknown, there is a wealth of evidence suggesting that misfolded proteins, accumulation of misfolded proteins, dysfunction of neuroreceptors and mitochondria, dysregulation of enzymes, and the release of neurotransmitters significantly influence the pathophysiology of these diseases. There is no effective protective medicine or therapy available even with the availability of numerous medications. There is an urgent need to create new and powerful bioactive compounds since the number of people with NDDs is rising globally. Heterocyclic compounds have consistently played a pivotal role in drug discovery due to their exceptional pharmaceutical properties. Many clinically approved drugs, such as galantamine hydrobromide, donepezil hydrochloride, memantine hydrochloride, and opicapone, feature heterocyclic cores. As these heterocyclic compounds have exceptional therapeutic potential, heterocycles are an intriguing research topic for the development of new effective therapeutic drugs for PD and AD. This review aims to provide current insights into the development and potential use of heterocyclic compounds targeting diverse therapeutic targets to manage and potentially treat patients with AD and PD.

Revealing rutaecarpine's promise: A pathway to parkinson's disease relief through PPAR modulation

The pathological mechanisms of Parkinson's disease (PD) is complex, and no definitive cure currently exists. This study identified Rutaecarpine (Rut), an alkaloid extracted from natural plants, as a potential therapeutic agent for PD. To elucidate its mechanisms of action and specific effects in PD, network pharmacology, molecular docking, and experimental validation methods were employed. Our findings demonstrated the efficacy of Rut in ameliorating PD symptoms. Network pharmacology analysis indicated that Rut exerts its therapeutic effects through the PPAR signaling pathway and the lipid pathway. Molecular docking results revealed that Rut forms stable protein-ligand complexes with PPARα and PPARγ. Animal experiments showed that Rut improved motor function in PD mice, protected dopaminergic neurons, ameliorated lipid metabolism disorders, and reduced neuroinflammation. This study identified the critical molecular mechanisms and therapeutic targets of Rut in the treatment of PD, providing a theoretical foundation for future investigations into the pharmacodynamics of Rut as a potential anti-PD agent.

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.

OTUD5 Protects Dopaminergic Neurons by Promoting the Degradation of α-Synuclein in Parkinson's Disease Model

Defective clearance and accumulation of α-synuclein (α-Syn) is the key pathogenic factor in Parkinson's disease (PD). Recent studies emphasize the importance of E3 ligases in regulating the degradation of α-Syn. However, the molecular mechanisms by which deubiquitinases regulate α-Syn degradation are scarcely studied. In this study, it is found that the protein levels of α-Syn are negatively regulated by ovarian tumor protease deubiquitinase 5 (OTUD5) which protects dopaminergic (DA) neurons in the PD model. Mechanistically, OTUD5 promotes K63-linked polyubiquitination of α-Syn independent of its deubiquitinating enzyme activity and mediates its endolysosomal degradation by recruiting the E3 ligase neural precursor cell expressed developmentally downregulated 4 (NEDD4). Furthermore, OTUD5 conditional knockout in DA neurons results in more severe α-Syn related pathology and dyskinesia after injection of α-Syn preformed fibrils (PFF). Overall, the data unveil a novel mechanism to regulate the degradation of α-Syn and provide a new therapeutic strategy to alleviate DA neurodegeneration.

Corticobasal Syndrome: Are There Central or Peripheral Triggers?

Background and Objectives

Corticobasal syndrome (CBS) is a complex of symptoms and signs comprising limb rigidity, bradykinesia, dystonia, myoclonus, apraxia, cortical sensory loss, and a variety of cognitive and language impairments. CBS is commonly seen in tauopathies. Striking asymmetry in clinical and imaging findings in CBS raises questions about potential triggers initiating neurodegeneration. The objective of this study was to investigate potential central or peripheral triggers preceding CBS symptoms.

Methods

In this retrospective observational study, we reviewed medical records of patients with CBS at our Parkinson's Disease Center and Movement Disorders Clinic, focusing on evidence of possible central or peripheral "trigger" occurring within a year before the onset of CBS. We also reviewed records of patients with Parkinson disease (PD) for comparison.

Results

Of the 72 patients with CBS, 15 (20.8%) reported potential focal triggers before the onset of CBS-related neurologic symptoms. By contrast, only 1 of 72 patients with PD (1.4%) had a documented trigger before the onset of PD-related symptoms (p < 0.001). Of potential triggers, 13 were peripheral (related to hand or shoulder surgeries or trauma) and 2 were central (stroke and head trauma). Patients with CBS with triggers were younger, had earlier symptom onset, comprised a higher proportion of men, and had a higher likelihood of limb onset of symptoms than those without.

Discussion

Our finding of relatively high frequency of focal triggers in CBS compared with PD suggests potential central or peripheral triggers initiating neurodegeneration, possibly explaining asymmetric clinical and imaging features in CBS. Further research is necessary to validate and explore this observation's implications for CBS pathogenesis.

Emerging targets of α-synuclein spreading in α-synucleinopathies: a review of mechanistic pathways and interventions

α-Synucleinopathies constitute a spectrum of neurodegenerative disorders, including Parkinson's disease (PD), Lewy body dementia (LBD), Multiple System Atrophy (MSA), and Alzheimer's disease concurrent with LBD (AD-LBD). These disorders are unified by a pathological hallmark: aberrant misfolding and accumulation of α-synuclein (α-syn). This review delves into the pivotal role of α-syn, the key agent in α-synucleinopathy pathophysiology, and provides a survey of potential therapeutics that target cell-to-cell spread of pathologic α-syn. Recognizing the intricate complexity and multifactorial etiology of α-synucleinopathy, the review illuminates the potential of various membrane receptors, proteins, intercellular spreading pathways, and pathological agents for therapeutic interventions. While significant progress has been made in understanding α-synucleinopathy, the pursuit of efficacious treatments remains challenging. Several strategies involving decreasing α-syn production and aggregation, increasing α-syn degradation, lowering extracellular α-syn, and inhibiting cellular uptake of α-syn are presented. The paper underscores the necessity of meticulous and comprehensive investigations to advance our knowledge of α-synucleinopathy pathology and ultimately develop innovative therapeutic strategies for α-synucleinopathies.

Positron emission tomography tracers for synucleinopathies

Synucleinopathies, such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, are characterized by the aggregation of α-synuclein. Variations in brain distribution allow for differentiation among these diseases and facilitate precise clinical diagnosis. However, distinguishing between synucleinopathies and Parkinsonism with tauopathies poses a challenge, significantly impacting clinical drug development. Therefore, molecular imaging is crucial for synucleinopathies, particularly for clinical diagnosis, assessment of drug efficacy, and disease surveillance. In recent years, advances in molecular imaging have led to rapid development of α-synuclein-specific tracers for positron emission tomography (PET), most of which are still in pre-clinical stages. Interestingly, some of these tracers share similar compound skeletal structures and are currently undergoing optimization for clinical application. Despite this progress, there remain challenges in developing α-synuclein tracers. This review summarizes recent findings on promising PET tracers and discusses representative compounds' characteristics while offering suggestions for further research orientation.

Unknown roles of tau pathology in neurological disorders. Challenges and new perspectives

Aging presents progressive changes that increase the susceptibility of the central nervous system (CNS) to suffer neurological disorders (NDs). Several studies have reported that an aged brain suffering from NDs shows the presence of pathological forms of tau protein, a microtubule accessory protein (MAP) critical for neuronal function. In this context, accumulative evidence has shown a pivotal contribution of pathological forms of tau to Alzheimer's disease (AD) and tauopathies. However, current investigations have implicated tau toxicity in other NDs that affect the central nervous system (CNS), including Parkinson's disease (PD), Huntington's disease (HD), Traumatic brain injury (TBI), Multiple sclerosis (MS), and Amyotrophic lateral sclerosis (ALS). These diseases are long-term acquired, affecting essential functions such as motor movement, cognition, hearing, and vision. Previous evidence indicated that toxic forms of tau do not have a critical contribution to the genesis or progression of these diseases. However, recent studies have shown that these tau forms contribute to neuronal dysfunction, inflammation, oxidative damage, and mitochondrial impairment events that contribute to the pathogenesis of these NDs. Recent studies have suggested that these neuropathologies could be associated with a prion-like behavior of tau, which induces a pathological dissemination of these toxic protein forms to different brain areas. Moreover, it has been suggested that this toxic propagation of tau from neurons into neighboring cells impairs the function of glial cells, oligodendrocytes, and endothelial cells by affecting metabolic function and mitochondrial health and inducing oxidative damage by tau pathology. Therefore, in this review, we will discuss current evidence demonstrating the critical role of toxic tau forms on NDs not related to AD and how its propagation and induced-bioenergetics failure may contribute to the pathogenic mechanism present in these NDs.

Biomarkers of mature neuronal differentiation and related diseases

The nervous system regulates perception, cognition and behavioral responses by serving as the body's primary communication system for receiving, regulating and transmitting information. Neurons are the fundamental structures and units of the nervous system. Their differentiation and maturation processes rely on the expression of specific biomarkers. Neuron-specific intracellular markers can be used to determine the degree of neuronal maturation. Neuronal cytoskeletal proteins dictate the shape and structure of neurons, while synaptic plasticity and signaling processes are intricately associated with neuronal synaptic markers. Furthermore, abnormal expression levels of biomarkers can serve as diagnostic indicators for nervous system diseases. This article reviews the markers of mature neuronal differentiation and their relationship with nervous system diseases.

Cerebrospinal fluid tau and disease progression in early Parkinson's disease: an 8-year longitudinal study

OBJECTIVE

To explore whether CSF phosphorylated tau-181 (P-tau181) and total tau (T-tau) are associated with disease progression in early PD patients.

METHODS

We analyzed 8-year longitudinal clinical data from 368 early, drug-naive PD patients and 185 matched controls from the Parkinson's Progression Markers Initiative cohort. CSF P-tau181 and T-tau were measured over 5 years, while CSF α-synuclein was measured over 3 years. Dopamine transporter (DAT) imaging was performed at baseline and at 1, 2, and 4 years.

RESULTS

PD patients exhibited significantly lower CSF P-tau181, T-tau and P-tau181/T-tau ratio than controls at each visit. Higher baseline CSF P-tau181 predicted greater increases in Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) III (estimate: 0.067, P < 0.001) and Montreal Cognitive Assessment (MoCA) scores (estimate: -0.010, P = 0.009). Similarly, higher baseline CSF T-tau predicted greater increases in MDS-UPDRS III (estimate: 0.005, P < 0.001) and MoCA scores (estimate: -0.001, P = 0.013). Higher baseline P-tau181/T-tau ratio predicted greater increases in MDS-UPDRS III (estimate: 0.552, P < 0.001) but was not significantly associated with changes in MoCA scores (estimate: -0.052, P = 0.114). CSF P-tau181 (estimate = 84.889, P < 0.001), T-tau (estimate = 8.297, P < 0.001) and P-tau181/T-tau ratio (estimate = 263.425, P < 0.001) were positively correlated with CSF α-synuclein but not correlated with striatal DAT uptake.

CONCLUSIONS

Elevated baseline CSF P-tau181, T-tau and P-tau181/T-tau ratio in early PD patients predict accelerated motor deterioration, with P-tau181 and T-tau also predicting cognitive decline, potentially through interactions with α-synuclein. However, the direct role of tau on nigrostriatal dopaminergic degeneration remains uncertain.

Posterior hippocampal sparing in Lewy body disorders with Alzheimer's copathology: An in vivo MRI study

BACKGROUND

Lewy body disorders (LBD), encompassing Parkinson disease (PD), PD dementia (PDD), and dementia with Lewy bodies (DLB), are characterized by alpha-synuclein pathology but often are accompanied by Alzheimer's disease (AD) neuropathological change (ADNC). The medial temporal lobe (MTL) is a primary locus of tau accumulation and associated neurodegeneration in AD. However, it is unclear the extent to which AD copathology in LBD (LBD/AD+) contributes to MTL-specific patterns of degeneration. We employ a MTL subregional segmentation strategy of T1-weighted (T1w) MRI in biomarker-supported or autopsy-confirmed LBD and LBD/AD+ to investigate the anatomic consequences of co-occurring LBD/AD+ pathology on neurodegeneration.

METHODS

We studied 167 individuals with clinical diagnoses of LBD (PD, n = 124 (74.3 %); PDD, n = 11 (6.6 %); DLB, n = 32 (19.2 %)) with available T1w MRI and AD biomarkers or autopsy evidence of ADNC. Individuals were further biologically classified as LBD/AD+ based on hierarchical evidence of ADNC pathology: 1) AD "intermediate" or "high" by ABC neuropathologic criteria (n = 39 (23.4 %)); 2) positive amyloid PET (n = 2 (1.2 %)); or 3) CSF β-amyloid1-42 < 185.7 pg/mL n = 126 (75.4 %)). The T1 Automated Segmentation of Hippocampal Subfields (ASHS) pipeline was used to compute volume and thickness measurements of MTL subregions in LBD/AD- and LBD/AD+. Linear regression tested the association of AD copathology and subregion volume/thickness, covarying for age and sex, and intracranial volume for volume measurements. Secondary analyses correlated MTL subregional volume/thickness with cognition and neuropathology.

RESULTS

LBD/AD+ had decreased volume/thickness compared to LBD/AD- in all MTL subregions except posterior hippocampus. The greatest effect sizes were seen in Brodmann Area 35 (BA35) (Cohen's d = 0.62, p = 0.002, β = 0.107 ± 0.034), and entorhinal cortex (ERC) (Cohen's d = 0.56, p = 0.006, β = 0.088 ± 0.031). Smaller differences were seen in the parahippocampal cortex (PHC) (Cohen's d = 0.5, p = 0.012, β = 0.082 ± 0.033), BA36 (Cohen's d = 0.47, p = 0.021, β = 0.090 ± 0.039) and anterior hippocampus (Cohen's d = 0.45, p = 0.029, β = 111.790 ± 50.595). Verbal memory scores positively correlated with volume/thickness in anterior and posterior hippocampus, BA35, ERC and PHC, while visuospatial memory positively correlated only in BA35. In the subset of participants with autopsy, lower ERC volume was associated with a higher tau load in ERC (adjusted odds ratio 0.013, 95 % CI [0.0002, 0.841], uncorrected p = 0.041).

CONCLUSIONS

Relative to LBD/AD-, LBD/AD+ has greater T1w MRI evidence of atrophy in multiple MTL subregions. Atrophy in MTL subregions associates with memory performance and tau pathological load. The observed pattern of atrophy largely follows expectation from AD Braak stages, except for posterior hippocampus. Longitudinal studies are needed to validate the hypothesized spread of neurodegeneration.

The potential therapeutic strategy in combating neurodegenerative diseases: Focusing on natural products

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington disease (HD), and Multiple sclerosis (MS), pose a significant global health challenge due to their intricate pathology and limited therapeutic interventions. Natural products represent invaluable reservoirs for combating these neurodegenerative diseases by targeting key pathological hallmarks such as protein aggregation, synaptic dysfunction, aberrant proteostasis, cytoskeletal abnormalities, altered energy homeostasis, inflammation, and neuronal cell death. This review provides an in-depth analysis of the mechanisms and therapeutic targets of natural products for their neuroprotective effects. Furthermore, it elucidates the current progress of clinical trials investigating the potential of natural products in delaying neurodegeneration. The objective of this review is to enhance the comprehension of natural products in the prevention and treatment of neurodegenerative diseases, offering new insights and potential avenues for future pharmaceutical research.

α-Synuclein seeding amplification assays for diagnosing synucleinopathies: an innovative tool in clinical implementation

The spectrum of synucleinopathies, including Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB), is characterized by α-synuclein (αSyn) pathology, which serves as the definitive diagnostic marker. However, current diagnostic methods primarily rely on motor symptoms that manifest years after the initial neuropathological changes, thereby delaying potential treatment. The symptomatic overlap between PD and MSA further complicates the diagnosis, highlighting the need for precise and differential diagnostic methods for these overlapping neurodegenerative diseases. αSyn misfolding and aggregation occur before clinical symptoms appear, suggesting that detection of pathological αSyn could enable early molecular diagnosis of synucleinopathies. Recent advances in seed amplification assay (SAA) offer a tool for detecting neurodegenerative diseases by identifying αSyn misfolding in fluid and tissue samples, even at preclinical stages. Extensive research has validated the effectiveness and reproducibility of SAAs for diagnosing synucleinopathies, with ongoing efforts focusing on optimizing conditions for detecting pathological αSyn in more accessible samples and identifying specific αSyn species to differentiate between various synucleinopathies. This review offers a thorough overview of SAA technology, exploring its applications for diagnosing synucleinopathies, addressing the current challenges, and outlining future directions for its clinical use.

Parkinson's Disease: Biomarkers for Diagnosis and Disease Progression

Parkinson's disease (PD) is a progressive neurological disease that causes both motor and nonmotor symptoms. While our understanding of putative mechanisms has advanced significantly, it remains challenging to verify biomarkers with sufficient evidence for regular clinical use. Clinical symptoms are the primary basis for diagnosing the disease, which can be mild in the early stages and overlap with other neurological disorders. As a result, clinical testing and medical records are mostly relied upon for diagnosis, posing substantial challenges during both the initial diagnosis and the continuous disease monitoring. Recent biochemical, neuroimaging, and genetic biomarkers have helped us understand the pathophysiology of Parkinson's disease. This comprehensive study focuses on these biomarkers, which were chosen based on their relevance, methodological excellence, and contribution to the field. Biochemical biomarkers, including α-synuclein and glial fibrillary acidic protein (GFAP), can predict disease severity and progression. The dopaminergic system is widely used as a neuroimaging biomarker to diagnose PD. Numerous genes and genome wide association study (GWAS) sites have been related to the development of PD. Recent research on the SNCA gene and leucine-rich repeat protein kinase 2 (LRRK2) has shown promising results. By evaluating current studies, this review intends to uncover gaps in biomarker validation and use, while also highlighting promising improvements. It emphasizes the need for dependable and reproducible indicators in improving PD diagnosis and prognosis. These biomarkers may open up new avenues for early diagnosis, disease progression tracking, and the development of personalized treatment programs.

AVE0991 ameliorates dopaminergic neuronal damage in Parkinson's disease through HOTAIRM1/miR-223-3p/α-synuclein axis

Parkinson's disease (PD) is a prevalent type of neurodegenerative disorder. AVE0991, a non-peptide analogue of Ang-(1-7), by which the progression of PD has been discovered to be ameliorated, but the specific mechanism whereby AVE0991 modulates the progression of PD re-mains unclear. The mice overexpressing human α-syn (A53T) were established to simulate PD pathology, and we also constructed an in vitro model of mouse dopaminergic neurons overexpressing hα-syn (A53T). The [18F] FDG-PET/CT method was employed to assess FDG uptake in human α-syn (A53T) overexpressing mice. Levels of lnc HOTAIRM1 and miR-223-3p were detected via qRT-PCR. Flow cytometry was deployed to assay cell apoptosis. Here, we found that AVE0991 improved behaviour disorders and decreased α-syn expression in the substantia nigra of mice with Parkinson's disease. AVE0991 inhibited the apoptosis of dopaminergic neurons overexpressing hα-syn (A53T) via lncRNA HOTAIRM1. MiR-223-3p binds to HOTAIRM1 as a ceRNA and directly targets α-syn. Moreover, miR-223-3p level in peripheral blood was found negatively correlated with the α-syn. Our present study shows that the angiotensin-(1-7) analogue AVE0991 targeted at the HOTAIRM1/miR-223-3p axis to degrade α-synuclein in PD mice, and showed neuroprotection in vitro.

Fractional Anisotropy is a More Sensitive Diagnostic Biomarker Than Mean Kurtosis for Patients with Parkinson Disease with Cognitive Dysfunction: A Diffusional Kurtosis Map Tract-Based Spatial Statistics Study

BACKGROUND AND PURPOSE

There is heterogeneity of white matter damage in Parkinson's disease patients with different cognitive states. Our aim was to find sensitive diffusional kurtosis imaging biomarkers to differentiate the white matter damage pattern of mild cognitive impairment and dementia.

MATERIALS AND METHODS

Nineteen patients with Parkinson disease with mild cognitive impairment and 18 patients with Parkinson disease with dementia were prospectively enrolled. All participants underwent MR examination with 3D-T1-weighted image and diffusional kurtosis imaging sequences. Demographic data were compared between the 2 groups. Voxelwise statistical analyses of diffusional kurtosis imaging parameters were performed using tract-based spatial statistics. The receiver operator characteristic curve of significantly different metrics was graphed. The correlation of significantly different metrics with global cognitive status was analyzed.

RESULTS

Compared with the Parkinson disease with mild cognitive impairment group, the fractional anisotropy and mean kurtosis values decreased in 4 independent clusters in the forceps minor, forceps major, inferior fronto-occipital fasciculus, and the inferior and superior longitudinal fasciculus in patients with Parkinson disease with dementia; the mean diffusivity decreased in 1 cluster in the forceps minor. The fractional anisotropy value in the inferior fronto-occipital fasciculus and inferior longitudinal fasciculus would be the diffusional kurtosis imaging marker for the differential diagnosis of Parkinson disease with mild cognitive impairment and patients with Parkinson disease with dementia, with the best diagnostic efficiency of 0.853. The fractional anisotropy values in the forceps minor (β = 84.20, P < .001) and years of education (β = 0.38, P = .014) were positively correlated with the Montreal Cognitive Assessment.

CONCLUSIONS

The diffusional kurtosis imaging-derived fractional anisotropy and mean kurtosis can detect the different white matter damage patterns of Parkinson disease with mild cognitive impairment and Parkinson disease with dementia. Fractional anisotropy is more sensitive than mean kurtosis in the differential diagnosis; fractional anisotropy derived from diffusional kurtosis imaging could become a promising imaging marker for the differential diagnosis of Parkinson disease with mild cognitive impairment and Parkinson disease with dementia.

Contrastive machine learning reveals Parkinson's disease specific features associated with disease severity and progression

Parkinson's disease (PD) exhibits heterogeneity in terms of symptoms and prognosis, likely due to diverse neuroanatomical alterations. This study employs a contrastive deep learning approach to analyze Magnetic Resonance Imaging (MRI) data from 932 PD patients and 366 controls, aiming to disentangle PD-specific neuroanatomical alterations. The results reveal that these neuroanatomical alterations in PD are correlated with individual differences in dopamine transporter binding deficit, neurodegeneration biomarkers, and clinical severity and progression. The correlation with clinical severity is verified in an external cohort. Notably, certain proteins in the cerebrospinal fluid are strongly associated with PD-specific features, particularly those involved in the immune function. The most notable neuroanatomical alterations are observed in both subcortical and temporal regions. Our findings provide deeper insights into the patterns of brain atrophy in PD and potential underlying molecular mechanisms, paving the way for earlier patient stratification and the development of treatments to slow down neurodegeneration.

Tau in neurodegenerative diseases: molecular mechanisms, biomarkers, and therapeutic strategies

The deposition of abnormal tau protein is characteristic of Alzheimer's disease (AD) and a class of neurodegenerative diseases called tauopathies. Physiologically, tau maintains an intrinsically disordered structure and plays diverse roles in neurons. Pathologically, tau undergoes abnormal post-translational modifications and forms oligomers or fibrous aggregates in tauopathies. In this review, we briefly introduce several tauopathies and discuss the mechanisms mediating tau aggregation and propagation. We also describe the toxicity of tau pathology. Finally, we explore the early diagnostic biomarkers and treatments targeting tau. Although some encouraging results have been achieved in animal experiments and preclinical studies, there is still no cure for tauopathies. More in-depth basic and clinical research on the pathogenesis of tauopathies is necessary.

Exploring Intrinsic Disorder in Human Synucleins and Associated Proteins

In this work, we explored the intrinsic disorder status of the three members of the synuclein family of proteins-α-, β-, and γ-synucleins-and showed that although all three human synucleins are highly disordered, the highest levels of disorder are observed in γ-synuclein. Our analysis of the peculiarities of the amino acid sequences and modeled 3D structures of the human synuclein family members revealed that the pathological mutations A30P, E46K, H50Q, A53T, and A53E associated with the early onset of Parkinson's disease caused some increase in the local disorder propensity of human α-synuclein. A comparative sequence-based analysis of the synuclein proteins from various evolutionary distant species and evaluation of their levels of intrinsic disorder using a set of commonly used bioinformatics tools revealed that, irrespective of their origin, all members of the synuclein family analyzed in this study were predicted to be highly disordered proteins, indicating that their intrinsically disordered nature represents an evolutionary conserved and therefore functionally important feature. A detailed functional disorder analysis of the proteins in the interactomes of the human synuclein family members utilizing a set of commonly used disorder analysis tools showed that the human α-synuclein interactome has relatively higher levels of intrinsic disorder as compared with the interactomes of human β- and γ- synucleins and revealed that, relative to the β- and γ-synuclein interactomes, α-synuclein interactors are involved in a much broader spectrum of highly diversified functional pathways. Although proteins interacting with three human synucleins were characterized by highly diversified functionalities, this analysis also revealed that the interactors of three human synucleins were involved in three common functional pathways, such as the synaptic vesicle cycle, serotonergic synapse, and retrograde endocannabinoid signaling. Taken together, these observations highlight the critical importance of the intrinsic disorder of human synucleins and their interactors in various neuronal processes.

In vivo detection of Alzheimer's and Lewy body disease concurrence: Clinical implications and future perspectives

INTRODUCTION

The recent introduction of seed amplification assays (SAAs) detecting misfolded α-synuclein, a pathology-specific marker for Lewy body disease (LBD), has allowed the in vivo identification and phenotypic characterization of patients with co-occurring Alzheimer's disease (AD) and LBD since the early clinical or even preclinical stage.

METHODS

We reviewed studies with an in vivo biomarker-based diagnosis of AD-LBD copathology.

RESULTS

Studies in large cohorts of cognitively impaired individuals have shown that cerebrospinal fluid (CSF) biomarkers detect the coexistence of AD and LB pathology in approximately 20%-25% of them, independently of the primary clinical diagnosis. Compared to those with pure AD, AD-LBD patients showed worse global cognition, especially in attentive/executive and visuospatial functions, and worse motor functions. In cognitively unimpaired individuals, concurrent AD-LBD pathologies predicted longitudinal cognitive progression with faster worsening of global cognition, memory, and attentive/executive functions.

DISCUSSION

Future research studies aiming for a better precision medicine approach should develop SAAs further to reach a quantitative evaluation or staging of each underlying pathology using a single biofluid sample.

HIGHLIGHTS

α-Synuclein seed amplification assays (SAAs) provide a specific marker for Lewy body disease (LBD). SAAs allow for the in vivo identification of co-occurring LBD in patients with Alzheimer's disease (AD). AD-LBD coexist in 20-25% of cognitively impaired elderly individuals, and ∼8% of those asymptomatic. Compared to pure AD, AD-LBD causes a faster worsening of cognitive functions. AD-LBD is associated with worse attentive/executive, memory, visuospatial and motor functions.

Cognitive dysfunction in animal models of human lewy-body dementia

Cognitive impairments are a common feature of synucleinopathies such as Parkinson's Disease Dementia and Dementia with Lewy Bodies. These pathologies are characterized by accumulation of Lewy bodies and Lewy neurites as well as neuronal cell death. Alpha-synuclein is the main proteinaceous component of Lewy bodies and Lewy neurites. To model these pathologies in vivo, toxins that selectively target certain neuronal populations or different means of inducing alpha-synuclein aggregation can be used. Alpha-synuclein accumulation can be induced by genetic manipulation, viral vector overexpression or the use of preformed fibrils of alpha-synuclein. In this review, we summarize the cognitive impairments associated with different models of synucleinopathies and relevance to observations in human diseases.

Cryo-EM structures of pathogenic fibrils and their impact on neurodegenerative disease research

Neurodegenerative diseases are commonly associated with the formation of aberrant protein aggregates within the brain, and ultrastructural analyses have revealed that the proteins within these inclusions often assemble into amyloid filaments. Cryoelectron microscopy (cryo-EM) has emerged as an effective method for determining the near-atomic structure of these disease-associated filamentous proteins, and the resulting structures have revolutionized the way we think about aberrant protein aggregation and propagation during disease progression. These structures have also revealed that individual fibril conformations may dictate different disease conditions, and this newfound knowledge has improved disease modeling in the lab and advanced the ongoing pursuit of clinical tools capable of distinguishing and targeting different pathogenic entities within living patients. In this review, we summarize some of the recently developed cryo-EM structures of ex vivo α-synuclein, tau, β-amyloid (Aβ), TAR DNA-binding protein 43 (TDP-43), and transmembrane protein 106B (TMEM106B) fibrils and discuss how these structures are being leveraged toward mechanistic research and therapeutic development.

Modulating α-synuclein propagation and decomposition: Implications in Parkinson's disease therapy

α-Synuclein (α-Syn) is closely related to the pathogenesis of Parkinson's disease (PD). Under pathological conditions, the conformation of α-syn changes and different forms of α-syn lead to neurotoxicity. According to Braak stages, α-syn can propagate in different brain regions, inducing neurodegeneration and corresponding clinical manifestations through abnormal aggregation of Lewy bodies (LBs) and lewy axons in different types of neurons in PD. So far, PD lacks early diagnosis biomarkers, and treatments are mainly targeted at some clinical symptoms. There is no effective therapy to delay the progression of PD. This review first summarized the role of α-syn in physiological and pathological states, and the relationship between α-syn and PD. Then, we focused on the origin, secretion, aggregation, propagation and degradation of α-syn as well as the important regulatory factors in these processes systematically. Finally, we reviewed some potential drug candidates for alleviating the abnormal aggregation of α-syn in order to provide valuable targets for the treatment of PD to cope with the occurrence and progression of this disease.

Serum Oligomeric α-Synuclein and p-tau181 in Progressive Supranuclear Palsy and Parkinson's Disease

Clinical differentiation of progressive supranuclear palsy (PSP) from Parkinson's disease (PD) is challenging due to overlapping phenotypes and the late onset of specific atypical signs. Therefore, easily assessable diagnostic biomarkers are highly needed. Since PD is a synucleopathy while PSP is a tauopathy, here, we investigated the clinical usefulness of serum oligomeric-α-synuclein (o-α-synuclein) and 181Thr-phosphorylated tau (p-tau181), which are considered as the most important pathological protein forms in distinguishing between these two parkinsonisms. We assessed serum o-α-synuclein and p-tau181 by ELISA and SIMOA, respectively, in 27 PSP patients, 43 PD patients, and 39 healthy controls (HC). Moreover, we evaluated the correlation between serum biomarkers and biological and clinical features of these subjects. We did not find any difference in serum concentrations of p-tau181 and o-α-synuclein nor in the o-α-synuclein/p-tau181 ratio between groups. However, we observed that serum p-tau181 positively correlated with age in HC and PD, while serum o-α-synuclein correlated positively with disease severity in PD and negatively with age in PSP. Finally, the o-α-synuclein/p-tau181 ratio showed a negative correlation with age in PD.

Role of Tau Protein in Neurodegenerative Diseases and Development of Its Targeted Drugs: A Literature Review

Tau protein is a microtubule-associated protein that is widely distributed in the central nervous system and maintains and regulates neuronal morphology and function. Tau protein aggregates abnormally and forms neurofibrillary tangles in neurodegenerative diseases, disrupting the structure and function of neurons and leading to neuronal death, which triggers the initiation and progression of neurological disorders. The aggregation of tau protein in neurodegenerative diseases is associated with post-translational modifications, which may affect the hydrophilicity, spatial conformation, and stability of tau protein, promoting tau protein aggregation and the formation of neurofibrillary tangles. Therefore, studying the role of tau protein in neurodegenerative diseases and the mechanism of aberrant aggregation is important for understanding the mechanism of neurodegenerative diseases and finding therapeutic approaches. This review describes the possible mechanisms by which tau protein promotes neurodegenerative diseases, the post-translational modifications of tau protein and associated influencing factors, and the current status of drug discovery and development related to tau protein, which may contribute to the development of new therapeutic approaches to alleviate or treat neurodegenerative diseases.

The landscape of programmed cell death-related lncRNAs in Alzheimer's disease and Parkinson's disease

This study delivers a thorough analysis of long non-coding RNAs (lncRNAs) in regulating programmed cell death (PCD), vital for neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD). We propose a new framework PCDLnc, and identified 20 significant lncRNAs, including HEIH, SNHG15, and SNHG5, associated with PCD gene sets, which were known for roles in proliferation and apoptosis in neurodegenerative diseases. By using GREAT software, we identified regulatory functions of top lncRNAs in different neurodegenerative diseases. Moreover, lncRNAs cis-regulated mRNAs linked to neurodegeneration, including JAK2, AKT1, EGFR, CDC42, SNCA, and ADIPOQ, highlighting their therapeutic potential in neurodegenerative diseases. A further exploration into the differential expression of mRNA identified by PCDLnc revealed a role in apoptosis, ferroptosis and autophagy. Additionally, protein-protein interaction (PPI) network analysis exposed abnormal interactions among key genes, despite their consistent expression levels between disease and normal samples. The randomforest model effectively distinguished between disease samples, indicating a high level of accuracy. Shared gene subsets in AD and PD might serve as potential biomarkers, along with disease-specific gene sets. Besides, we also found the strong relationship between AD and immune infiltration. This research highlights the role of lncRNAs and their associated genes in PCD in neurodegenerative diseases, offering potential therapeutic targets and diagnostic markers for future study and clinical application.

N-homocysteinylation of DJ-1 promotes neurodegeneration in Parkinson's disease

DJ-1, also known as Parkinson's disease protein 7 (Park7), is a multifunctional protein that regulates oxidative stress and mitochondrial function. Dysfunction of DJ-1 is implicated in the pathogenesis of Parkinson's disease (PD). Hyperhomocysteinemia is associated with an increased risk of PD. Here we show that homocysteine thiolactone (HTL), a reactive thioester of homocysteine (Hcy), covalently modifies DJ-1 on the lysine 182 (K182) residue in an age-dependent manner. The N-homocysteinylation (N-hcy) of DJ-1 abolishes its neuroprotective effect against oxidative stress and mitochondrial dysfunction, exacerbating cell toxicity. Blocking the N-hcy of DJ-1 restores its protective effect. These results indicate that the N-hcy of DJ-1 abolishes its neuroprotective effect and promotes the progression of PD. Inhibiting the N-hcy of DJ-1 may exert neuroprotective effect against PD.

The association between methylmalonic acid, a biomarker of mitochondrial dysfunction, and cause-specific mortality in Alzheimer's disease and Parkinson's disease

Background

Alzheimer's disease (AD) and Parkinson's disease (PD) are the leading causes of death among the elderly. Recent research has demonstrated that mitochondrial dysfunction, which is hallmark of neurodegenerative diseases, is a contributor to the development of these diseases.

Methods and materials

Methylmalonic acid (MMA), AD, PD, inflammatory markers and covariates were extracted from the National Health and Nutrition Examination Survey (NHANES). The classification of the inflammatory markers was done through quartile conversion. A restricted cubic spike function was performed to study their dose-response relationship. MMA subgroups from published studies were used to explore the correlation between different subgroups and cause-specific mortality. Multivariable weighted Cox regression was carried out to investigate MMA and cause-specific mortality in patients with AD and PD. Weighted survival analysis was used to study the survival differences among MMA subgroups.

Results

A non-linear correlation was observed between MMA and AD-specific death and PD-specific mortality. The presence of MMA Q4 was linked to increased death rates among AD patients (HR = 6.39, 95%CI: 1.19-35.24, P = 0.03) after controlling for potential confounders in a multivariable weighted Cox regression model. In PD patients, the MMA Q4 (Q4: HR: 5.51, 95 % CI: 1.26-24, P = 0.02) was also related to increased mortality. The results of survival analysis indicated that the poorer prognoses were observed in AD and PD patients with MMA Q4.

Conclusion

The higher level of mitochondria-derived circulating MMA was associated with a higher mortality rate in AD and PD patients. MMA has the potential to be a valuable indicator for evaluating AD and PD patients' prognosis in the clinic.

Pathological and physiological functional cross-talks of α-synuclein and tau in the central nervous system

α-Synuclein and tau are abundant multifunctional brain proteins that are mainly expressed in the presynaptic and axonal compartments of neurons, respectively. Previous works have revealed that intracellular deposition of α-synuclein and/or tau causes many neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Despite intense investigation, the normal physiological functions and roles of α-synuclein and tau are still unclear, owing to the fact that mice with knockout of either of these proteins do not present apparent phenotypes. Interestingly, the co-occurrence of α-synuclein and tau aggregates was found in post-mortem brains with synucleinopathies and tauopathies, some of which share similarities in clinical manifestations. Furthermore, the direct interaction of α-synuclein with tau is considered to promote the fibrillization of each of the proteins in vitro and in vivo. On the other hand, our recent findings have revealed that α-synuclein and tau are cooperatively involved in brain development in a stage-dependent manner. These findings indicate strong cross-talk between the two proteins in physiology and pathology. In this review, we provide a summary of the recent findings on the functional roles of α-synuclein and tau in the physiological conditions and pathogenesis of neurodegenerative diseases. A deep understanding of the interplay between α-synuclein and tau in physiological and pathological conditions might provide novel targets for clinical diagnosis and therapeutic strategies to treat neurodegenerative diseases.

GDF1 ameliorates cognitive impairment induced by hearing loss

Hearing loss is associated with an increased risk of Alzheimer disease (AD). However, the mechanisms of hearing loss promoting the onset of AD are poorly understood. Here we show that hearing loss aggravates cognitive impairment in both wild-type mice and mouse models of AD. Embryonic growth/differentiation factor 1 (GDF1) is downregulated in the hippocampus of deaf mice. Knockdown of GDF1 mimics the detrimental effect of hearing loss on cognition, while overexpression of GDF1 in the hippocampus attenuates the cognitive impairment induced by deafness. Strikingly, overexpression of GDF1 also attenuates cognitive impairment in APP/PS1 transgenic mice. GDF1 activates Akt, which phosphorylates asparagine endopeptidase and inhibits asparagine endopeptidase-induced synaptic degeneration and amyloid-β production. The expression of GDF1 is downregulated by the transcription factor CCAAT-enhancer binding protein-β. These findings indicate that hearing loss could promote AD pathological changes by inhibiting the GDF1 signaling pathway; thus, GDF1 may represent a therapeutic target for AD.

Overlaps and divergences between tauopathies and synucleinopathies: a duet of neurodegeneration

Proteinopathy, defined as the abnormal accumulation of proteins that eventually leads to cell death, is one of the most significant pathological features of neurodegenerative diseases. Tauopathies, represented by Alzheimer's disease (AD), and synucleinopathies, represented by Parkinson's disease (PD), show similarities in multiple aspects. AD manifests extrapyramidal symptoms while dementia is also a major sign of advanced PD. We and other researchers have sequentially shown the cross-seeding phenomenon of α-synuclein (α-syn) and tau, reinforcing pathologies between synucleinopathies and tauopathies. The highly overlapping clinical and pathological features imply shared pathogenic mechanisms between the two groups of disease. The diagnostic and therapeutic strategies seemingly appropriate for one distinct neurodegenerative disease may also apply to a broader spectrum. Therefore, a clear understanding of the overlaps and divergences between tauopathy and synucleinopathy is critical for unraveling the nature of the complicated associations among neurodegenerative diseases. In this review, we discuss the shared and diverse characteristics of tauopathies and synucleinopathies from aspects of genetic causes, clinical manifestations, pathological progression and potential common therapeutic approaches targeting the pathology, in the aim to provide a timely update for setting the scheme of disease classification and provide novel insights into the therapeutic development for neurodegenerative diseases.

Protein-protein interactions regulating α-synuclein pathology

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the formation of Lewy bodies (LBs). The main proteinaceous component of LBs is aggregated α-synuclein (α-syn). However, the mechanisms underlying α-syn aggregation are not yet fully understood. Converging lines of evidence indicate that, under certain pathological conditions, various proteins can interact with α-syn and regulate its aggregation. Understanding these protein-protein interactions is crucial for unraveling the molecular mechanisms contributing to PD pathogenesis. In this review we provide an overview of the current knowledge on protein-protein interactions that regulate α-syn aggregation. Additionally, we briefly summarize the methods used to investigate the influence of protein-protein interactions on α-syn aggregation and propagation.

ALS-linked SOD1 mutations impair mitochondrial-derived vesicle formation and accelerate aging

Oxidative stress (OS) is regarded as the dominant theory for aging. While compelling correlative data have been generated to support the OS theory, a direct cause-and-effect relationship between the accumulation of oxidation-mediated damage and aging has not been firmly established. Superoxide dismutase 1 (SOD1) is a primary antioxidant in all cells. It is, however, susceptible to oxidation due to OS and gains toxic properties to cells. This study investigates the role of oxidized SOD1 derived from amyotrophic lateral sclerosis (ALS) linked SOD1 mutations in cell senescence and aging. Herein, we have shown that the cell line NSC34 expressing the G93A mutation of human SOD1 (hSOD1G93A) entered premature senescence as evidenced by a decreased number of the 5-ethynyl-2'-deoxyuridine (EdU)-positive cells. There was an upregulation of cellular senescence markers compared to cells expressing the wild-type human SOD1 (hSOD1WT). Transgenic mice carrying the hSOD1G93A gene showed aging phenotypes at an early age (135 days) with high levels of P53 and P16 but low levels of SIRT1 and SIRT6 compared with age-matched hSOD1WT transgenic mice. Notably, the levels of oxidized SOD1 were significantly elevated in both the senescent NSC34 cells and 135-day hSOD1G93A mice. Selective removal of oxidized SOD1 by our CT4-directed autophagy significantly decelerated aging, indicating that oxidized SOD1 is a causal factor of aging. Intriguingly, mitochondria malfunctioned in both senescent NSC34 cells and middle-aged hSODG93A transgenic mice. They exhibited increased production of mitochondrial-derived vesicles (MDVs) in response to mild OS in mutant humanSOD1 (hSOD1) transgenic mice at a younger age; however, the mitochondrial response gradually declined with aging. In conclusion, our data show that oxidized SOD1 derived from ALS-linked SOD1 mutants is a causal factor for cellular senescence and aging. Compromised mitochondrial responsiveness to OS may serve as an indicator of premature aging.

Rubusoside mitigates neuroinflammation and cellular apoptosis in Parkinson's disease, and alters gut microbiota and metabolite composition

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative condition characterized by the progressive loss of dopaminergic neurons within the substantia nigra. Neuroinflammation plays a pivotal role in the pathogenesis of PD, involving the activation of microglia cells, heightened production of proinflammatory cytokines, and perturbations in the composition of the gut microbiota. Rubusoside (Ru), the principal steviol bisglucoside present in Rubus chingii var. suavissimus (S.K.Lee) L.T.Lu (Rosaceae), has been documented for its anti-inflammatory properties in diverse disease models. Nonetheless, there is an imperative need to comprehensively assess and elucidate the protective and anti-inflammatory attributes of Ru concerning PD, as well as to uncover the underlying mechanism involved.

OBJECTIVE

The aim of this study is to evaluate the neuroprotective and anti-inflammatory effects of Ru on PD and investigate its potential mechanisms associated with microbes.

RESEARCH DESIGN AND METHODS

We pre-treated mice and cell lines with Ru in order to simulate the progression of PD and the neuroinflammatory state. The mouse model was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), SN4741 cells were induced by 1-methyl-4-phenylpyridine (mpp+), and BV-2 cells were induced by lipopolysaccharide (LPS). We assessed the impact of Ru on motor function, neuroinflammation, neuron apoptosis, the composition of gut microbes, and their metabolites.

RESULTS

Ru treatment reduces the release of pro-inflammatory mediators by inhibiting microglia activation. It also prevents neuronal apoptosis, thereby safeguarding dopaminergic neurons and ameliorating motor dysfunction. Furthermore, it induces alterations in the fecal microbiota composition and metabolites profile in PD mice. In vitro experiments have demonstrated that Ru inhibits neuronal apoptosis in SN4741 cells induced by mpp+, suppresses the production of pro-inflammatory mediators, and activates the c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase (p38 MAPK), and nuclear factor kappa-B (NF-κB) signaling pathways.

CONCLUSION

Ru exhibits inhibitory effects on the MPTP-induced PD model by mitigating neuroinflammation and neuronal apoptosis while also inducing changes in the gut microbiota and metabolite composition.