Elevated tauopathy and alpha-synuclein pathology in postmortem Parkinson's disease brains with and without dementia

Early diagnosis of Parkinson's disease: biomarker study

Parkinson's disease (PD) is a common chronic degenerative disease with age-dependent increasing prevalence in the elderly. Non-motor symptoms include sensory deficiencies, autonomic dysfunction, psychological and cognitive abnormalities; while motor symptoms are bradykinesia, myotonia, resting tremor, and postural balance difficulties. The clinical diagnosis of PD depends mainly on patients' medical history and physical examination. It is highly important to realize early detection of PD, and biomarkers are a valuable tool in this regard. The present study reviewed the findings of researches from the last few years, involving the advancements in the study of PD biomarkers in blood, cerebrospinal fluid, saliva, urine, tears, imaging, and pathology.

Metabolic dysregulation and resistance to high-fat diet-induced weight gain in mice overexpressing human wild-type α-synuclein

Unintentional weight loss is common among patients with Parkinson's disease (PD) and is associated with poor quality of life and accelerated disease progression. To explore how early α-synuclein pathology contributes to metabolic dysregulation leading to weight loss in PD, transgenic mice overexpressing human wild-type α-synuclein (α-Syn) and controls were fed a high-fat diet (HFD) chow for 4 months. Compared with controls on HFD, α-Syn mice on HFD exhibited a dramatically leaner phenotype, improved glucose tolerance, a major decrease in fat mass, an increase in energy expenditure, a decrease in insulin signaling in the olfactory bulb, aggravated olfactory and motor dysfunctions, and an increase in mortality. Our results show that high-fat diet in α-Syn mice provides a sensitive tool for assessing the underlying mechanism of metabolic dysfunction and its impact on weight loss and disease progression in PD. Moreover, a role is proposed for olfactory dysfunction in PD-related unintentional weight loss.

Alpha-Synuclein Demonstrates Varying Binding Affinities With Different Tau Isoforms

The hallmark of various neurodegenerative diseases is the accumulation and aggregation of amyloidogenic proteins, such as amyloid-beta (Aβ) and tau in Alzheimer's disease (AD) and alpha-synuclein (aSyn) in synucleinopathies. Many neurodegenerative diseases express mixed pathology. For instance, Lewy bodies are reported in tauopathies and neurofibrillary tau-tangles are detected in synucleinopathies, suggesting a potential co-existence or crosstalk of misfolded aSyn and tau. In the present study, we investigated the binding characteristics of monomeric aSyn with different tau isoforms by using surface plasmon resonance (SPR) spectroscopy allowing monitoring direct protein-protein interactions and their potential co-localization using SH-SY5Y cells. The calculation of the binding parameters (association and dissociation rate constants) indicated the strongest binding affinity between aSyn and tau isoform 1N3R followed by tau 2N3R and tau 2N4R. Co-localization studies in SH-SY5Y cells, treated with aSyn and all six tau isoforms revealed an intracellular co-localization of aSyn with different isoforms of tau. Subcellular fractionation confirmed the cellular uptake and colocalization of tau and aSyn in the same compartment, showing their expression in membrane, nuclear, and cytoskeletal fractions. Understanding the intricate interplay between aSyn and tau is crucial for unraveling the pathophysiology of PD, AD, and related neurodegenerative disorders, ultimately paving the way for the development of effective treatments targeting this interaction. In conclusion, our data indicate that aSyn and tau are direct interaction partners with varying binding affinities depending on the tau isoform. This interaction may be significant for understanding the pathophysiology of dementia with mixed pathologies.

Microbial Trojan Horses: Virulence Factors as Key Players in Neurodegenerative Diseases

Changes in population demographics indicate that the elderly population will reach 2.1 billion worldwide by 2050. In parallel, there will be an increase in neurodegenerative diseases such as Alzheimer's and Parkinson's. This review explores dysbiosis occurring in these pathologies and how virulence factors contribute to the worsening or development of clinical conditions, and it summarizes existing and potential ways to combat microorganisms related to these diseases. Microbiota imbalances can contribute to the progression of neurodegenerative diseases by increasing intestinal permeability, exchanging information through innervation, and even acting as a Trojan horse affecting immune cells. The microorganisms of the microbiota produce virulence factors to protect themselves from host defenses, many of which contribute to neurodegenerative diseases. These virulence factors are expressed according to the genetic composition of each microorganism, leading to a wide range of factors to be considered. Among the main virulence factors are LPS, urease, curli proteins, amyloidogenic proteins, VacA, and CagA. These factors can also be packed into bacterial outer membrane vesicles, which transport proteins, RNA, and DNA, enabling distal communication that impacts various diseases, including Alzheimer's and Parkinson's.

Increased dementia risk in patients with Parkinson's disease attributed to metabolic syndrome

INTRODUCTION

Metabolic syndrome (MetS) manifests resembling pathophysiological mechanisms with Parkinson's disease (PD). Current research on the overall population has emphasized MetS as a freestanding risk factor for cognition. This research aims to explore the impact of MetS on cognition in Parkinson's patients.

METHOD

We involved subjects identified as having early-stage PD patients. The MetS was diagnosed dependent on parameters overviewed in the National Cholesterol Education Program's Adult Treatment Panel III. The clinical severity and stages in patients with PD were dependent on the disease rating scales. The cognition was evaluated by the Turkısh version of the Montreal Cognitive Assessment Scale (MoCA-TR). The cases were categorized according to cognitive failure: mild cognitive impairment in PD (PD-MCI), and PD dementia (PDD).

RESULTS

Metabolic syndrome was present in 39.6% of the participants. 22.0% of patients were in the normal cognition, 29.1% in the PD-MCI group, and 48.9% in the PD-D group. The cognitive scores in patients with MetS is considerably lower than MetS negative group. A statistically notable inverse association was detected between fasting blood glucose levels and the visual-spatial/executive functions, naming, language, and orientation scores. The multivariate logistic regression analysis showed individuals with MetS were found to have an 11.308 times higher risk of PD-D (odds ratio [OR]: 11,3, 95% confidence interval [CI]: 1.61-79.2 ).

CONCLUSION

We discerned the occurrence of MetS in PD raises the possibility of advancing dementia. This suggests that considering MetS in this patient group could contribute to the effective management of dementia.

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.

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

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

Vanillin Mitigates the MPTP-Induced α-Synucleinopathy in a Mouse Model of Parkinson's Disease: Insights into the Involvement of Wnt/β-Catenin Signaling

BACKGROUND

The abnormal aggregation of α-synuclein (α-syn) in the substantia nigra pars compacta (SNpc) region of the brain is characteristic of Parkinson's disease (PD), leading to the selective demise of neurons. Modifications in the post-translational processing of α-syn, phosphorylation at Ser129 in particular, are implicated in α-syn aggregation and are considered key hallmarks of PD. Furthermore, dysregulated Wnt/β-catenin signaling, influenced by glycogen synthase kinase-3 beta (GSK-3β), is implicated in PD pathogenesis. Inhibition of GSK-3β holds promise in promoting neuroprotection by enhancing the Wnt/β-catenin pathway.

METHODS

In our previous study utilizing 1-methyl-4-phenylpyridinium (MPP+)-administered differentiated SH-SY5Y cells and a PD mouse model, we explored Vanillin's neuroprotective properties and related mechanisms against neuronal loss induced by MPP+/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. In the current study, we elucidated the mitigating effects of Vanillin on motor impairments, P-Ser129-α-syn expression, Wnt/β-catenin signaling, and autophagic neuron death induced by MPTP in a mouse model of PD by performing motor function tests, western blot analysis and immunostaining.

RESULTS

Our results show that Vanillin effectively modulated the motor dysfunctions, GSK-3β expression, and activity, activated the Wnt/β-catenin signaling, and reduced autophagic neuronal demise in the MPTP-lesioned mice, highlighting its neuroprotective effects.

CONCLUSIONS

These findings underscore the complex interplay between α-syn pathology, GSK-3β, Wnt/β-catenin signaling, and autophagic-cell death in PD pathogenesis. Targeting these pathways, particularly with Vanillin, can be a promising therapeutic strategy for restoring dopaminergic (DA-ergic) neuronal homeostasis and slowing the progression of PD. Further research is crucial to resolving existing disputes and translating these discoveries into effective therapeutic interventions for PD patients.

The potential of exosomal biomarkers: Revolutionizing Parkinson's disease: How do they influence pathogenesis, diagnosis, and therapeutic strategies?

Parkinson's disease (PD) is characterized by the pathological accumulation of α-synuclein, which has driven extensive research into the role of exosomes in disease mechanisms. Exosomes are nanoscale vesicles enriched with proteins, RNA, and lipids that facilitate critical intercellular communication processes. Recent studies have elucidated the role of exosomes in transmitting misfolded proteins among neurons, which significantly impacts the progression of PD. The presence of disease-associated exosomes in cerebrospinal fluid and blood highlights their substantial diagnostic potential for PD. Specifically, exosomes derived from the central nervous system (CNS) have emerged as promising biomarkers because of their ability to accurately reflect pathological states. Furthermore, the isolation of exosomes from distinct brain cell types allows the identification of precise biomarkers, increasing diagnostic specificity and accuracy. In addition to being useful for diagnostics, exosomes hold therapeutic promise given their ability to cross the blood-brain barrier (BBB) and selectively modulate their cargo. These findings suggest that these materials could be used as delivery systems for therapeutic drugs for the treatment of neurodegenerative diseases. This review comprehensively examines the multifaceted roles of exosomes in PD pathogenesis, diagnosis, and treatment. It also addresses the associated clinical challenges and underscores the urgent need for further research and development to fully leverage exosome-based strategies in PD management.

Therapeutic Potential Effect of Glycogen Synthase Kinase 3 Beta (GSK-3β) Inhibitors in Parkinson Disease: Exploring an Overlooked Avenue

Parkinson's disease (PD) is a progressive neurodegenerative disease of the brain due to degeneration of dopaminergic neurons in the substantia nigra (SN). Glycogen synthase kinase 3 beta (GSK-3β) is implicated in the pathogenesis of PD. Therefore, the purpose of the present review was to revise the mechanistic role of GSK-3β in PD neuropathology, and how GSK-3β inhibitors affect PD neuropathology. GSK-3 is a conserved threonine/serine kinase protein that is intricate in the regulation of cellular anabolic and catabolic pathways by modulating glycogen synthase. Over-expression of GSK-3β is also interconnected with the development of different neurodegenerative diseases. However, the underlying mechanism of GSK-3β in PD neuropathology is not fully clarified. Over-expression of GSK-3β induces the development of PD by triggering mitochondrial dysfunction and oxidative stress in the dopaminergic neurons of the SN. NF-κB and NLRP3 inflammasome are activated in response to dysregulated GSK-3β in PD leading to progressive neuronal injury. Higher expression of GSK-3β in the early stages of PD neuropathology might contribute to the reduction of neuroprotective brain-derived neurotrophic factor (BDNF). Thus, GSK-3β inhibitors may be effective in PD by reducing inflammatory and oxidative stress disorders which are associated with degeneration of dopaminergic in the SN.

Resistance to high-fat diet-induced weight gain in transgenic mice overexpressing human wild-type α-synuclein: A model for metabolic dysfunction in Parkinson's disease

Unintentional weight loss, primarily due to the loss of fat mass rather than muscle mass, is common among patients with Parkinson's disease (PD) and is associated with poor quality of life and accelerated disease progression. Since transgenic mice overexpressing human wild-type α-synuclein (α-Syn mice) are modestly leaner than control mice, and since diabetes, a metabolic disorder, is a major risk factor for PD, we reasoned that high-fat diet-induced diabetes/metabolic dysregulation in α-Syn mice may serve as a robust tool for exploring how early α-synuclein pathology contributes to metabolic dysregulation, leading to weight loss in PD. Thus, α-Syn and age-matched controls were fed a high-fat diet (HFD) chow (60% fat calories) ad libitum for four months. Compared with controls on HFD (control-HFD), α-Syn mice on HFD (α-Syn-HFD) were dramatically leaner. The resistance to gaining weight in α-Syn-HFD mice was accompanied by improved glucose tolerance, a dramatic decrease in fat mass, and an increase in energy expenditure. Despite this leaner phenotype and better glucose tolerance, the mortality was much higher in male α-Syn-HFD mice than in all controls, but was unaffected in females, suggesting protective effects of female sex hormones, as well as lower α-synuclein levels. Immunoblot analysis of insulin signaling in the olfactory bulb, the proposed initial seeding site of α-synuclein pathology, revealed a decrease of IGF-IRβ, p GSK, and p mTOR in α-Syn-HFD mice. Since GSK-3β and mTOR regulate synaptic plasticity, we assessed levels of PSD-95 and synaptophysin in the olfactory bulb. As anticipated, we observed a significant decrease in the levels of PSD-95, along with a potentially compensatory increase in synaptophysin levels. Our results show that α-Syn mice, when challenged with diet-induced diabetes/metabolic dysregulation, clearly reveal a profile of robust metabolic dysfunction, thus providing a sensitive tool for assessing the underlying mechanism of metabolic dysfunction and its impact on weight loss and disease progression in PD. We propose a role for olfactory dysfunction in PD-related unintentional weight loss and suggest that strategies aimed at increasing body weight/BMI will improve the quality of life and prognosis for people living with PD.

Association between dipeptidyl peptidase-4 inhibitor use and risk of Parkinson's disease among patients with diabetes mellitus: a retrospective cohort study

BACKGROUND

How a person's Parkinson disease (PD) risk is affected by dipeptidyl peptidase-4 (DPP-4) inhibitors remains unclear. We evaluated the association of PD risk with use of these inhibitors in individuals diagnosed as having diabetes mellitus (DM).

METHODS

Individuals diagnosed as having new-onset DM were enrolled into the case group and comparison group, comprising patients who received a DPP-4 inhibitor and a sulfonylurea, respectively. These groups were matched through propensity score matching on the basis of income level, gender, urbanization level, enrollment year, age, and diabetes complications severity index score. The case group was divided into subgroups on the basis of whether they had a cumulative defined daily dose (cDDD) of <75, 75-150, or >150. The DPP-4 inhibitor-PD risk association was evaluated through a Cox proportional hazards model. The Bonferroni adjustment test was employed to adjust P-values and reduce the false positive rate.

RESULTS

Compared with those in the comparison group (treatment with a sulfonylurea), patients with a DPP-4 inhibitor cDDD of >150 had a hazard ratio (HR) of 1.30 for PD development (95% confidence interval [CI]: 0.97-1.73; adjusted P = .263); the HRs for patients with a cDDD of <75 or 75-150 were 0.95 (95% CI: 0.71-1.27; adjusted P = .886) and 1.06 (95% CI: 0.75-1.50; adjusted P = .886), respectively. We noted nonsignificant differences regarding the associations between the use of the various DPP-4 inhibitors (linagliptin, saxagliptin, sitagliptin, and vildagliptin) and PD risk after adjustment for any individual inhibitor (adjusted P > .05).

CONCLUSIONS

DPP-4 inhibitors were discovered in this study to not be associated with increased PD risk. This result was confirmed when the analysis was conducted individually for the 4 investigated DPP-4 inhibitors (sitagliptin, saxagliptin, linagliptin, and vildagliptin).

Protein modification in neurodegenerative diseases

Posttranslational modifications play a crucial role in governing cellular functions and protein behavior. Researchers have implicated dysregulated posttranslational modifications in protein misfolding, which results in cytotoxicity, particularly in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease. These aberrant posttranslational modifications cause proteins to gather in certain parts of the brain that are linked to the development of the diseases. This leads to neuronal dysfunction and the start of neurodegenerative disease symptoms. Cognitive decline and neurological impairments commonly manifest in neurodegenerative disease patients, underscoring the urgency of comprehending the posttranslational modifications' impact on protein function for targeted therapeutic interventions. This review elucidates the critical link between neurodegenerative diseases and specific posttranslational modifications, focusing on Tau, APP, α-synuclein, Huntingtin protein, Parkin, DJ-1, and Drp1. By delineating the prominent aberrant posttranslational modifications within Alzheimer disease, Parkinson disease, and Huntington disease, the review underscores the significance of understanding the interplay among these modifications. Emphasizing 10 key abnormal posttranslational modifications, this study aims to provide a comprehensive framework for investigating neurodegenerative diseases holistically. The insights presented herein shed light on potential therapeutic avenues aimed at modulating posttranslational modifications to mitigate protein aggregation and retard neurodegenerative disease progression.

Autophagy-associated non-coding RNAs: Unraveling their impact on Parkinson's disease pathogenesis

BACKGROUND

Parkinson's disease (PD) is a degenerative neurological condition marked by the gradual loss of dopaminergic neurons in the substantia nigra pars compacta. The precise etiology of PD remains unclear, but emerging evidence suggests a significant role for disrupted autophagy-a crucial cellular process for maintaining protein and organelle integrity.

METHODS

This review focuses on the role of non-coding RNAs (ncRNAs) in modulating autophagy in PD. We conducted a comprehensive review of recent studies to explore how ncRNAs influence autophagy and contribute to PD pathophysiology. Special attention was given to the examination of ncRNAs' regulatory impacts in various PD models and patient samples.

RESULTS

Findings reveal that ncRNAs are pivotal in regulating key processes associated with PD progression, including autophagy, α-synuclein aggregation, mitochondrial dysfunction, and neuroinflammation. Dysregulation of specific ncRNAs appears to be closely linked to these pathogenic processes.

CONCLUSION

ncRNAs hold significant therapeutic potential for addressing autophagy-related mechanisms in PD. The review highlights innovative therapeutic strategies targeting autophagy-related ncRNAs and discusses the challenges and prospective directions for developing ncRNA-based therapies in clinical practice. The insights from this study underline the importance of ncRNAs in the molecular landscape of PD and their potential in novel treatment approaches.

Icariin attenuates dopaminergic neural loss in haloperidol-induced Parkinsonism in rats via GSK-3β and tyrosine hydroxylase regulation mechanism

Parkinson's Disease (PD) is an age-dependent, incessant, dynamic neurodegenerative illness. In animal models, the administration of the dopaminergic D2 antagonist Haloperidol (HP) affects the nigrostriatal pathway, inducing catalepsy, a state of immobility like PD, bradykinesia, and akinesia. The present study investigated the neural effects of Icariin (ICA), a flavonoid derived from Herba Epimedii, against HP-induced PD in rats compared to a standard drug levodopa (L-DOPA). Twenty-four adult male rats were divided into 4 groups: the control group treated with vehicle, the 2nd group treated with HP intraperitoneally, the 3rd group treated with the same dose of HP+L-DOPA orally, and the 4th one, treated with the same dose of HP+ICA orally. All the groups were treated for fourteen consecutive days. Two days before the last dose, locomotor activity was assessed in open field and rotarod tasks. At the end of the experiment, the malondialdehyde, nitric oxide (NO), iron, glycogen synthase kinase-3beta (GSK-3β), and tyrosine hydroxylase (TH) contents, glutathione S-transferase, catalase, superoxide dismutase, activities were estimated in the midbrain. Also, cortex and midbrain monoamine contents (norepinephrine, dopamine, and serotonin) were determined. Moreover, the midbrain histopathology was detected in all treated groups. The results suggested that the neuroleptic effect of HP was completely improved by ICA. This improvement occurred by decreasing the neurotoxicity via lowering midbrain lipid peroxidation, NO, GSK-3β contents, increasing antioxidant biomarkers, TH, and recovering the treated groups' cortex and midbrain monoamines contents. In conclusion, this study suggests that ICA is a suitable treatment for Parkinson's induced by HP.

α-synuclein-lack expression rescues methamphetamine-induced mossy fiber degeneration in dorsal hippocampal CA3

Methamphetamine (METH) - induced cognitive impairments may be related to synaptic degeneration at mossy fiber terminals, critical for spatial memory formation in hippocampal circuits. We have previously found METH-induced neurodegeneration in the striatum by increasing the α-synuclein (α-SYN) level. However, whether and how the METH-induced mossy fiber degeneration is also blamed for the abnormal accumulation of α-SYN remains to be elucidated. Chronic METH exposure decreased mossy fiber density but upregulatedα-SYN and phosphorylated TAU (TAU-pSer396) in hippocampal CA3, associated with glial cell overactivation, axonal neuropathies, and memory impairment. Notably, the knockout of the α-SYN gene significantly alleviated the METH-induced mossy fiber degeneration and memory impairment. Meanwhile, the TAU-pSer396 accumulation and glial activation were ameliorated by α-SYN knockout. Our findings suggest an essential role of α-SYN in mediating METH-induced mossy fiber degeneration, providing promising therapeutic and prophylactic targets for METH-related neurodegenerative diseases.

Insulin and TLR4 Inhibitor Improve Motor Impairments in a Rat Model of Parkinson's Disease

Background

Insulin resistance is an important pathological hallmark of Parkinson's disease (PD). Proinflammatory cytokines during neuroinflammation decrease insulin sensitivity by suppressing insulin signaling elements. Toll-like receptor 4 (TLR4), the main receptor involved in neuroinflammation, is also associated with the pathogenesis of PD.

Objectives

The present study evaluated the effect of insulin, an insulin receptor antagonist, and a TLR4 inhibitor on behavioral deficits and insulin resistance induced by 6-hydroxydopamine (6-OHDA).

Methods

Male Wistar rats were divided into nine groups: (1) sham (normal saline [NS] in the medial forebrain bundle [MFB]); (2) 6-OHDA (20 µg in the MFB); (3) 6-OHDA + NS; (4) 6-OHDA + dimethyl sulfoxide (DMSO); (5) 6-OHDA + insulin (2.5 IU/day, intracerebroventricular ([ICV]); (6) 6-OHDA + insulin (5 IU/day, intranasal [IN]); (7) 6-OHDA + insulin receptor antagonist (S961; 6.5 nM/kg, ICV); (8) 6-OHDA + TLR4 inhibitor (TAK242; 0.01 µg/rat, ICV); (9) 6-OHDA + insulin + TLR4 inhibitor. All treatments were administered for seven consecutive days. Motor performance was evaluated using apomorphine-induced rotation and cylinder tests. Gene expression and protein levels of α-synuclein, TLR4, insulin receptor substrate (IRS) 1, IRS2, and glycogen synthase kinase 3β (GSK3β) were measured by real-time PCR and western blotting, respectively, in the striatum.

Results

Insulin, alone and with TAK242, improved motor deficits induced by 6-OHDA. Administration of the insulin receptor antagonist had no effect on motor deficits. The increased expression of α-synuclein and TLR4 following 6-OHDA was attenuated by insulin and TAK242. GSK3β levels, both mRNA and protein, were significantly increased by 6-OHDA and attenuated with insulin and TAK242.

Conclusions

The findings suggest that 6-OHDA induces neurodegeneration via activation of TLR4 and GSK3β, indicating insulin resistance, and that insulin can improve these impairments. Moreover, TLR4 inhibition prevents insulin signaling dysfunction and improves behavioral and molecular impairments, highlighting the critical role of TLR4 in the development of insulin resistance in PD pathology.

Pathobiology of Cognitive Impairment in Parkinson Disease: Challenges and Outlooks

Cognitive impairment (CI) is a characteristic non-motor feature of Parkinson disease (PD) that poses a severe burden on the patients and caregivers, yet relatively little is known about its pathobiology. Cognitive deficits are evident throughout the course of PD, with around 25% of subtle cognitive decline and mild CI (MCI) at the time of diagnosis and up to 83% of patients developing dementia after 20 years. The heterogeneity of cognitive phenotypes suggests that a common neuropathological process, characterized by progressive degeneration of the dopaminergic striatonigral system and of many other neuronal systems, results not only in structural deficits but also extensive changes of functional neuronal network activities and neurotransmitter dysfunctions. Modern neuroimaging studies revealed multilocular cortical and subcortical atrophies and alterations in intrinsic neuronal connectivities. The decreased functional connectivity (FC) of the default mode network (DMN) in the bilateral prefrontal cortex is affected already before the development of clinical CI and in the absence of structural changes. Longitudinal cognitive decline is associated with frontostriatal and limbic affections, white matter microlesions and changes between multiple functional neuronal networks, including thalamo-insular, frontoparietal and attention networks, the cholinergic forebrain and the noradrenergic system. Superimposed Alzheimer-related (and other concomitant) pathologies due to interactions between α-synuclein, tau-protein and β-amyloid contribute to dementia pathogenesis in both PD and dementia with Lewy bodies (DLB). To further elucidate the interaction of the pathomechanisms responsible for CI in PD, well-designed longitudinal clinico-pathological studies are warranted that are supported by fluid and sophisticated imaging biomarkers as a basis for better early diagnosis and future disease-modifying therapies.

Alpha-Synuclein Contribution to Neuronal and Glial Damage in Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disease characterized by the progressive loss of dopaminergic neurons in the substantia nigra and the widespread accumulation of alpha-synuclein (αSyn) protein aggregates. αSyn aggregation disrupts critical cellular processes, including synaptic function, mitochondrial integrity, and proteostasis, which culminate in neuronal cell death. Importantly, αSyn pathology extends beyond neurons-it also encompasses spreading throughout the neuronal environment and internalization by microglia and astrocytes. Once internalized, glia can act as neuroprotective scavengers, which limit the spread of αSyn. However, they can also become reactive, thereby contributing to neuroinflammation and the progression of PD. Recent advances in αSyn research have enabled the molecular diagnosis of PD and accelerated the development of targeted therapies. Nevertheless, despite more than two decades of research, the cellular function, aggregation mechanisms, and induction of cellular damage by αSyn remain incompletely understood. Unraveling the interplay between αSyn, neurons, and glia may provide insights into disease initiation and progression, which may bring us closer to exploring new effective therapeutic strategies. Herein, we provide an overview of recent studies emphasizing the multifaceted nature of αSyn and its impact on both neuron and glial cell damage.

New insights into the role of GSK-3β in the brain: from neurodegenerative disease to tumorigenesis

Glycogen synthase kinase 3 (GSK-3) is a serine/threonine kinase widely expressed in various tissues and organs. Unlike other kinases, GSK-3 is active under resting conditions and is inactivated upon stimulation. In mammals, GSK-3 includes GSK-3 α and GSK-3β isoforms encoded by two homologous genes, namely, GSK3A and GSK3B. GSK-3β is essential for the control of glucose metabolism, signal transduction, and tissue homeostasis. As more than 100 known proteins have been identified as GSK-3β substrates, it is sometimes referred to as a moonlighting kinase. Previous studies have elucidated the regulation modes of GSK-3β. GSK-3β is involved in almost all aspects of brain functions, such as neuronal morphology, synapse formation, neuroinflammation, and neurological disorders. Recently, several comparatively specific small molecules have facilitated the chemical manipulation of this enzyme within cellular systems, leading to the discovery of novel inhibitors for GSK-3β. Despite these advancements, the therapeutic significance of GSK-3β as a drug target is still complicated by uncertainties surrounding the potential of inhibitors to stimulate tumorigenesis. This review provides a comprehensive overview of the intricate mechanisms of this enzyme and evaluates the existing evidence regarding the therapeutic potential of GSK-3β in brain diseases, including Alzheimer's disease, Parkinson's disease, mood disorders, and glioblastoma.

Upregulation of LRRK2 following traumatic brain injury does not directly phosphorylate Thr175 tau

Phosphorylated microtubule-associated protein tau (tau) aggregates are a pathological hallmark of various neurodegenerative diseases, including chronic traumatic encephalopathy and amyotrophic lateral sclerosis with cognitive impairment. While there are many residues phosphorylated on tau, phosphorylation of threonine 175 (pThr175 tau) has been shown to initiate fibril formation in vitro and is present in pathological tau aggregates in vivo. Given this, preventing Thr175 tau phosphorylation presents a potential approach to reduce fibril formation; however, the kinase(s) acting on Thr175 are not yet fully defined. Using a single controlled cortical impact rodent model of traumatic brain injury (TBI), which rapidly induces Thr175 tau phosphorylation, we observed an upregulation and alteration in subcellular localization of leucine-rich repeat kinase 2 (LRRK2), a kinase that has been implicated in tau phosphorylation. LRRK2 upregulation was evident by one-day post-injury and persisted to day 10. The most notable changes were observed in microglia at the site of injury in the cortex. To determine if the appearance of pThr175 tau was causally related to the upregulation of LRRK2 expression, we examined the ability of LRRK2 to phosphorylate Thr175in vitro by co-transfecting 2N4R human WT-tau with either LRRK2-WT, constitutively-active LRRK2-G2019S or inactive LRRK2-3XKD. We found no significant difference in the level of pThr175 tau between the overexpression of LRRK2-WT, -G2019S or -3XKD, suggesting LRRK2 does not phosphorylate tau at Thr175. Further, downstream events known to follow Thr175 phosphorylation and known to be associated with pathological tau fibril formation (pSer9-GSK3β and pThr231 tau induction) also remained unchanged. We conclude that while LRRK2 expression is altered in TBI, it does not contribute directly to pThr175 tau generation.

Recent research progress on metabolic syndrome and risk of Parkinson's disease

Parkinson's disease (PD) is one of the most widespread neurodegenerative diseases. PD is associated with progressive loss of substantia nigra dopaminergic neurons, including various motor symptoms (e.g., bradykinesia, rigidity, and resting tremor), as well as non-motor symptoms (e.g., cognitive impairment, constipation, fatigue, sleep disturbance, and depression). PD involves multiple biological processes, including mitochondrial or lysosomal dysfunction, oxidative stress, insulin resistance, and neuroinflammation. Metabolic syndrome (MetS), a collection of numerous connected cerebral cardiovascular conditions, is a common and growing public health problem associated with many chronic diseases worldwide. MetS components include central/abdominal obesity, systemic hypertension, diabetes, and atherogenic dyslipidemia. MetS and PD share multiple pathophysiological processes, including insulin resistance, oxidative stress, and chronic inflammation. In recent years, MetS has been linked to an increased risk of PD, according to studies; however, the specific mechanism remains unclear. Researchers also found that some related metabolic therapies are potential therapeutic strategies to prevent and improve PD. This article reviews the epidemiological relationship between components of MetS and the risk of PD and discusses the potentially relevant mechanisms and recent progress of MetS as a risk factor for PD. Furthermore, we conclude that MetS-related therapies are beneficial for the prevention and treatment of PD.

The role of exosomes in the diagnosis of Parkinson's disease

Parkinson's disease is a common neurodegenerative disease characterized by intracellular aggregation of misfolded α-synuclein as a major pathological hallmark. Exosomes are cell-derived lipid bilayer membrane vesicles with various components, including proteins, RNA, and lipids, that mediate intercellular communication. Currently, exosomes are found to be responsible for transporting misfolded proteins from unhealthy neurons to nearby cells, spreading the disease from cell to cell. Such exosomes can also be found in the cerebrospinal fluid and blood. Thus, exosomes may serve as a potential tool to detect the pathology of Parkinson's disease for clinical diagnosis. In this article, the role and challenges of exosomes in the diagnosis of Parkinson's disease are outlined.

Cogs in the autophagic machine-equipped to combat dementia-prone neurodegenerative diseases

Neurodegenerative diseases are often characterized by hydrophobic inclusion bodies, and it may be the case that the aggregate-prone proteins that comprise these inclusion bodies are in fact the cause of neurotoxicity. Indeed, the appearance of protein aggregates leads to a proteostatic imbalance that causes various interruptions in physiological cellular processes, including lysosomal and mitochondrial dysfunction, as well as break down in calcium homeostasis. Oftentimes the approach to counteract proteotoxicity is taken to merely upregulate autophagy, measured by an increase in autophagosomes, without a deeper assessment of contributors toward effective turnover through autophagy. There are various ways in which autophagy is regulated ranging from the mammalian target of rapamycin (mTOR) to acetylation status of proteins. Healthy mitochondria and the intracellular energetic charge they preserve are key for the acidification status of lysosomes and thus ensuring effective clearance of components through the autophagy pathway. Both mitochondria and lysosomes have been shown to bear functional protein complexes that aid in the regulation of autophagy. Indeed, it may be the case that minimizing the proteins associated with the respective neurodegenerative pathology may be of greater importance than addressing molecularly their resulting inclusion bodies. It is in this context that this review will dissect the autophagy signaling pathway, its control and the manner in which it is molecularly and functionally connected with the mitochondrial and lysosomal system, as well as provide a summary of the role of autophagy dysfunction in driving neurodegenerative disease as a means to better position the potential of rapamycin-mediated bioactivities to control autophagy favorably.

Assessment of Aggregated and Exosome-Associated α-Synuclein in Brain Tissue and Cerebrospinal Fluid Using Specific Immunoassays

Even though it is currently well-established that α-synuclein aggregation is closely associated with the pathological events in Parkinson's disease (PD) and several other neurodegenerative disorders, collectively called synucleinopathies, the mechanistic link between α-synuclein aggregates and the onset and progression of neurodegeneration in these diseases remain unclear. The process of aggregation initiates from a structurally distorted monomer that gradually oligomerizes to generate a repertoire of fibrillar and oligomeric multimers that deposit within diseased cells in the brain. Total α-synuclein has been proposed as a potential biomarker in PD, but most of the studies do not discriminate between distinct α-synuclein conformers. To correlate protein measurements to disease pathology, we have developed a conformation-specific ELISA method that selectively detects fibrillar and oligomeric forms of α-synuclein without cross-reacting with monomers. We have used this assay to determine the levels of aggregated α-synuclein in human and mouse brain tissue as well as in CSF and CSF-derived exosomes from patients with synucleinopathy and control subjects. Our results verify the ability of the new assay to detect aggregated α-synuclein in complex matrices and support the idea that the levels of these conformers are related to the age of onset in PD patients, while CSF analysis showed that these species exist in low abundance in CSF and CSF-derived exosomes. Future studies will be required to fully assess the diagnostic usefulness of this ELISA in synucleinopathies.

Necrosulfonamide exerts neuroprotective effect by inhibiting necroptosis, neuroinflammation, and α-synuclein oligomerization in a subacute MPTP mouse model of Parkinson's disease

Parkinson's disease (PD) is an incurable movement disorder characterized by dopaminergic cell loss, neuroinflammation, and α-synuclein pathology. Herein, we investigated the therapeutic effects of necrosulfonamide (NSA), a specific inhibitor of mixed lineage kinase domain-like protein (MLKL), in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MLKL is an executor of necroptosis, a programmed cell death pathway that causes inflammation. Repeated administration of NSA resulted in the recovery of impaired motor performance and dopaminergic degeneration. Furthermore, NSA inhibited the phosphorylation, ubiquitylation, and oligomerization of MLKL, all of which are associated with MLKL cell death-inducing activity in dopaminergic cells in the substantia nigra (SN). NSA also inhibited microglial activation and reactive astrogliosis as well as the MPTP-induced expression of proinflammatory molecules such as tumor necrosis factor-α, interleukin-1β, inducible nitric oxide synthase, and cystatin F. Furthermore, NSA inhibited α-synuclein oligomerization and phosphorylation in the SN of MPTP-treated mice by inhibiting the activity of glycogen synthase kinase 3β and matrix metalloproteinase-3. In conclusion, NSA has anti-necroptotic, anti-inflammatory, and anti-synucleinopathic effects on PD pathology. Therefore, NSA is a potential therapeutic candidate for PD.

Therapeutic effects of phlorotannins in the treatment of neurodegenerative disorders

Phlorotannins are natural polyphenolic compounds produced by brown marine algae and are currently found in nutritional supplements. Although they are known to cross the blood-brain barrier, their neuropharmacological actions remain unclear. Here we review the potential therapeutic benefits of phlorotannins in the treatment of neurodegenerative diseases. In mouse models of Alzheimer's disease, ethanol intoxication and fear stress, the phlorotannin monomer phloroglucinol and the compounds eckol, dieckol and phlorofucofuroeckol A have been shown to improve cognitive function. In a mouse model of Parkinson's disease, phloroglucinol treatment led to improved motor performance. Additional neurological benefits associated with phlorotannin intake have been demonstrated in stroke, sleep disorders, and pain response. These effects may stem from the inhibition of disease-inducing plaque synthesis and aggregation, suppression of microglial activation, modulation of pro-inflammatory signaling, reduction of glutamate-induced excitotoxicity, and scavenging of reactive oxygen species. Clinical trials of phlorotannins have not reported significant adverse effects, suggesting these compounds to be promising bioactive agents in the treatment of neurological diseases. We therefore propose a putative biophysical mechanism of phlorotannin action in addition to future directions for phlorotannin research.

Cerebrospinal fluid alpha-synuclein, amyloid beta, total tau, and phosphorylated tau in tremor-dominant Parkinson's disease

BACKGROUND

Protein misfolding within specific brain regions is a common characteristic of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease (PD). Therefore, a common term often used for these disorders is "proteinopathy". Currently, there has been increasing attention toward the overlap of pathogenesis between proteinopathies.

AIMS

We aimed to explore the cross-sectional and longitudinal level of the CSF α-synuclein (α-syn), amyloid βeta (Aβ1-42), total tau (t-tau), and phosphorylated tau (p-tau) in PD subjects with tremor dominant (TD) and a non-tremor dominant (nonTD) subtype from the Parkinson Progression Markers Initiative (PPMI).

METHODS

We enrolled 411 early-stage PD patients and 187 healthy controls (HCs) from the PPMI. We compared the level of CSF biomarkers at four time points including baseline, 6 months, 1 year, and 2 years. To investigate longitudinal changes in CSF proteins within each group, we used linear mixed models.

RESULTS

The level of CSF biomarkers was significantly lower in PD patients compared to HCs at any visit. Moreover, there was no statistically significant difference in the level of CSF α-syn, Aβ1-42, t-tau, and p-tau between PD-TD and PD-nonTD. Longitudinal analysis showed significant CSF α-syn reduction after one year from baseline in PD-TD patients (P = 0.047). Also, there was a significant reduction in the level of CSF Aβ1-42 after two years in PD-nonTD patients but not HCs and PD-TD (P = 0.033).

CONCLUSION

Our results indicate that different patterns in longitudinal changes of CSF biomarkers could be due to different pathophysiological mechanisms involved in each PD motor subtype.

Suppression of neuroinflammation and α-synuclein oligomerization by rotarod walking exercise in subacute MPTP model of Parkinson's disease

Parkinson's disease (PD) belongs to an α-synucleinopathy and manifests motor dysfunction attributed to nigrostriatal dopaminergic degeneration. In clinical practice, the beneficial role of physical therapy such as motor skill learning training has been recognized in PD-linked motor defects. Nevertheless, the disease-modifying effects of motor skill learning training on PD-related pathology remain unclear. Here, we investigated the disease-modifying effects of rotarod walking exercise (RWE), a modality of motor skill learning training, in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. In motor function and dopaminergic degeneration, RWE improved MPTP-induced deficits. In addition, RWE enhanced the expression of neurotrophic factors BDNF/GDNF, PGC1-α, Nurr1, and p-AMPK, thereby recovering dopaminergic neuronal cell death. Moreover, RWE inhibited microglial activation and the expression of pro-inflammatory markers, such as p-IκBα, iNOS, IL-1β, TNF-α, and cathepsin D, while elevating anti-inflammatory IL-10 and TGF-β. RWE also decreased oxidative stress markers in the substantia nigra, such as 4-HNE and 8-OHdG-positive cells, while increasing Nrf2-controlled antioxidant enzymes. Regarding the effect of RWE on α-synuclein, it reduced the monomer/oligomer forms of α-synuclein and phosphorylation at serine 129. Further mechanistic studies revealed that RWE suppressed the expression of matrix metalloproteinase-3 and p-GSK3β (Y216), which play key roles in α-synuclein aggregation. These data collectively suggest that inhibition of neuroinflammation and α-synuclein oligomerization by RWE may contribute to the improvement of PD pathology.

Different MAPT haplotypes influence expression of total MAPT in postmortem brain tissue

The MAPT gene, encoding the microtubule-associated protein tau on chromosome 17q21.31, is result of an inversion polymorphism, leading to two allelic variants (H1 and H2). Homozygosity for the more common haplotype H1 is associated with an increased risk for several tauopathies, but also for the synucleinopathy Parkinson's disease (PD). In the present study, we aimed to clarify whether the MAPT haplotype influences expression of MAPT and SNCA, encoding the protein α-synuclein (α-syn), on mRNA and protein levels in postmortem brains of PD patients and controls. We also investigated mRNA expression of several other MAPT haplotype-encoded genes. Postmortem tissues from cortex of fusiform gyrus (ctx-fg) and of the cerebellar hemisphere (ctx-cbl) of neuropathologically confirmed PD patients (n = 95) and age- and sex-matched controls (n = 81) were MAPT haplotype genotyped to identify cases homozygous for either H1 or H2. Relative expression of genes was quantified using real-time qPCR; soluble and insoluble protein levels of tau and α-syn were determined by Western blotting. Homozygosity for H1 versus H2 was associated with increased total MAPT mRNA expression in ctx-fg regardless of disease state. Inversely, H2 homozygosity was associated with markedly increased expression of the corresponding antisense MAPT-AS1 in ctx-cbl. PD patients had higher levels of insoluble 0N3R and 1N4R tau isoforms regardless of the MAPT genotype. The increased presence of insoluble α-syn in PD patients in ctx-fg validated the selected postmortem brain tissue. Our findings in this small, but well controlled cohort of PD and controls support a putative biological relevance of tau in PD. However, we did not identify any link between the disease-predisposing H1/H1 associated overexpression of MAPT with PD status. Further studies are required to gain a deeper understanding of the potential regulatory role of MAPT-AS1 and its association to the disease-protective H2/H2 condition in the context of PD.

An Update on Peripheral Blood Extracellular Vesicles as Biomarkers for Parkinson's Disease Diagnosis

Parkinson's disease (PD) is the world's second primary neurodegenerative disease, and the diagnosis and treatment of PD have become mainstream research. Over the past decades, several studies have identified potential biomarkers for diagnosing PD. Among them, extracellular vesicles (EVs) can carry specific biomarkers reflecting the physiological and pathological state of the body. Due to the blood-brain barrier (BBB) limitation, peripheral blood is limited in diagnosing neurodegenerative diseases. With the increasing research on EVs, their ability to pass through BBB indicated that peripheral blood could depict disease status like cerebrospinal fluid (CSF). Peripheral blood is a clinically available sample and has recently been widely used by researchers in various studies. In this review, we summarized previous studies on PD diagnosis biomarkers in peripheral blood EVs and evaluated their diagnostic value. Some EV surface markers were also described, which can extract EVs from specific cell origins. In addition, the combination of several biomarkers demonstrated good diagnostic performance in PD diagnosis compared with a single biomarker, suggesting the focus of future research.

Stimulation of synaptic activity promotes TFEB-mediated clearance of pathological MAPT/Tau in cellular and mouse models of tauopathies

Synapses represent an important target of Alzheimer disease (AD), and alterations of their excitability are among the earliest changes associated with AD development. Synaptic activation has been shown to be protective in models of AD, and deep brain stimulation (DBS), a surgical strategy that modulates neuronal activity to treat neurological and psychiatric disorders, produced positive effects in AD patients. However, the molecular mechanisms underlying the protective role(s) of brain stimulation are still elusive. We have previously demonstrated that induction of synaptic activity exerts protection in mouse models of AD and frontotemporal dementia (FTD) by enhancing the macroautophagy/autophagy flux and lysosomal degradation of pathological MAPT/Tau. We now provide evidence that TFEB (transcription factor EB), a master regulator of lysosomal biogenesis and autophagy, is a key mediator of this cellular response. In cultured primary neurons from FTD-transgenic mice, synaptic stimulation inhibits MTORC1 signaling, thus promoting nuclear translocation of TFEB, which, in turn, induces clearance of MAPT/Tau oligomers. Conversely, synaptic activation fails to promote clearance of toxic MAPT/Tau in neurons expressing constitutively active RRAG GTPases, which sequester TFEB in the cytosol, or upon TFEB depletion. Activation of TFEB is also confirmed in vivo in DBS-stimulated AD mice. We also demonstrate that DBS reduces pathological MAPT/Tau and promotes neuroprotection in Parkinson disease patients with tauopathy. Altogether our findings indicate that stimulation of synaptic activity promotes TFEB-mediated clearance of pathological MAPT/Tau. This mechanism, underlying the protective effect of DBS, provides encouraging support for the use of synaptic stimulation as a therapeutic treatment against tauopathies.Abbreviations: 3xTg-AD: triple transgenic AD mice; AD: Alzheimer disease; CSA: cyclosporine A; DBS: deep brain stimulation; DIV: days in vitro; EC: entorhinal cortex; FTD: frontotemporal dementia; gLTP: glycine-induced long-term potentiation; GPi: internal segment of the globus pallidus; PD: Parkinson disease; STN: subthalamic nucleus; TFEB: transcription factor EB.

Nanodelivery of Histamine H3/H4 Receptor Modulators BF-2649 and Clobenpropit with Antibodies to Amyloid Beta Peptide in Combination with Alpha Synuclein Reduces Brain Pathology in Parkinson's Disease

Parkinson's disease (PD) in military personnel engaged in combat operations is likely to develop in their later lives. In order to enhance the quality of lives of PD patients, exploration of novel therapy based on new research strategies is highly warranted. The hallmarks of PD include increased alpha synuclein (ASNC) and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) leading to brain pathology. In addition, there are evidences showing increased histaminergic nerve fibers in substantia niagra pars compacta (SNpc), striatum (STr), and caudate putamen (CP) associated with upregulation of histamine H3 receptors and downregulation of H4 receptors in human brain. Previous studies from our group showed that modulation of potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist induces neuroprotection in PD brain pathology. Recent studies show that PD also enhances amyloid beta peptide (AβP) depositions in brain. Keeping these views in consideration in this review, nanowired delivery of monoclonal antibodies to AβP together with ASNC and H3/H4 modulator drugs on PD brain pathology is discussed based on our own observations. Our investigation shows that TiO₂ nanowired BF-2649 (1 mg/kg, i.p.) or CLBPT (1 mg/kg, i.p.) once daily for 1 week together with nanowired delivery of monoclonal antibodies (mAb) to AβP and ASNC induced superior neuroprotection in PD-induced brain pathology. These observations are the first to show the modulation of histaminergic receptors together with antibodies to AβP and ASNC induces superior neuroprotection in PD. These observations open new avenues for the development of novel drug therapies for clinical strategies in PD.

Role of Nrf2 Pathway Activation in Neurological Disorder: A Brief Review

Oxidative stress plays a crucial role in the emergence of numerous neurodegenerative diseases, with protein accumulation and mitochondrial damage, which result in neurological disorders. To minimize oxidative stress, several defensive mechanisms protect nerve cells by releasing antioxidants such as nuclear erythroid factor2 (Nrf2)-Kelch-like ECH-associated protein1 (Keap1) signaling pathway activation has been proved to be a prospective treatment to reduce oxidative stress and neuroinflammation for protection of neurons in a variety of neurological disorders. In this review, we focus beneficial role of Nrf2 in Alzheimer’s and Parkinson’s diseases. Nrf2 is proved to be a master regulator of antioxidants by releasing over 250 cytoprotective genes aimed at oxidative stress and neuroinflammation. In animal studies Nrf2 activation is proved to improve autophagy, mitochondrial biogenesis, and Suppression of inflammatory cytokinin which protects neuronal cells and inhibit progressive neurodegeneration.

CSF α-Synuclein and Tau as Biomarkers for Dementia With Lewy Bodies: A Systematic Review and Meta-analysis

OBJECTIVE

This study investigated whether α-synuclein and tau in cerebrospinal fluid (CSF) can be used as biomarkers to diagnose dementia with Lewy bodies (DLB).

MATERIALS AND METHODS

We retrieved 3303 studies with "Dementia with Lewy bodies," "α-synuclein," and "tau" as keywords. We formulated screening criteria, and 2 researchers completed the screening, quality evaluation, and data extraction tasks. Finally, 35 studies related to tau, and 14 studies related to α-synuclein were included. Review Manager 5.4 and Stata16 were used for meta-analysis. Subgroup, sensitivity, and meta-regression analyses were performed to identify sources of heterogeneity and strengthen the results.

RESULTS

Compared with the control group, DLB patients showed significantly higher CSF levels of tau [weighted mean difference=81.36 (59.82, 102.91); Z =7.40; P <0.00001], and lower CSF levels of α-synuclein [weighted mean difference=-95.25 (-162.02, -28.48); Z =2.80; P =0.005]. Mini-Mental State Examination (MMSE) score, male ratio, and disease duration were not sources of heterogeneity on subgroup and meta-regression analyses. Sensitivity analysis revealed no significant differences.

CONCLUSIONS

Higher levels of tau and lower levels of α-synuclein were found in the CSF of patients with DLB compared with the control group. Therefore, CSF tau and α-synuclein levels may be diagnostic biomarkers for DLB.

Crosstalk between neurological, cardiovascular, and lifestyle disorders: insulin and lipoproteins in the lead role

Insulin resistance and impaired lipoprotein metabolism contribute to a plethora of metabolic and cardiovascular disorders. These alterations have been extensively linked with poor lifestyle choices, such as consumption of a high-fat diet, smoking, stress, and a redundant lifestyle. Moreover, these are also known to increase the co-morbidity of diseases like Type 2 diabetes mellitus and atherosclerosis. Under normal physiological conditions, insulin and lipoproteins exert a neuroprotective role in the central nervous system. However, the tripping of balance between the periphery and center may alter the normal functioning of the brain and lead to neurological disorders such as Alzheimer's disease, Parkinson's disease, stroke, depression, and multiple sclerosis. These neurological disorders are further characterized by certain behavioral and molecular changes that show consistent overlap with alteration in insulin and lipoprotein signaling pathways. Therefore, targeting these two mechanisms not only reveals a way to manage the co-morbidities associated with the circle of the metabolic, central nervous system, and cardiovascular disorders but also exclusively work as a disease-modifying therapy for neurological disorders. In this review, we summarize the role of insulin resistance and lipoproteins in the progression of various neurological conditions and discuss the therapeutic options currently in the clinical pipeline targeting these two mechanisms; in addition, challenges faced in designing these therapeutic approaches have also been touched upon briefly.

Morphological basis of Parkinson disease-associated cognitive impairment: an update

Cognitive impairment is one of the most salient non-motor symptoms of Parkinson disease (PD) that poses a significant burden on the patients and carers as well as being a risk factor for early mortality. People with PD show a wide spectrum of cognitive dysfunctions ranging from subjective cognitive decline and mild cognitive impairment (MCI) to frank dementia. The mean frequency of PD with MCI (PD-MCI) is 25.8% and the pooled dementia frequency is 26.3% increasing up to 83% 20 years after diagnosis. A better understanding of the underlying pathological processes will aid in directing disease-specific treatment. Modern neuroimaging studies revealed considerable changes in gray and white matter in PD patients with cognitive impairment, cortical atrophy, hypometabolism, dopamine/cholinergic or other neurotransmitter dysfunction and increased amyloid burden, but multiple mechanism are likely involved. Combined analysis of imaging and fluid markers is the most promising method for identifying PD-MCI and Parkinson disease dementia (PDD). Morphological substrates are a combination of Lewy- and Alzheimer-associated and other concomitant pathologies with aggregation of α-synuclein, amyloid, tau and other pathological proteins in cortical and subcortical regions causing destruction of essential neuronal networks. Significant pathological heterogeneity within PD-MCI reflects deficits in various cognitive domains. This review highlights the essential neuroimaging data and neuropathological changes in PD with cognitive impairment, the amount and topographical distribution of pathological protein aggregates and their pathophysiological relevance. Large-scale clinicopathological correlative studies are warranted to further elucidate the exact neuropathological correlates of cognitive impairment in PD and related synucleinopathies as a basis for early diagnosis and future disease-modifying therapies.

Vocal changes in a zebra finch model of Parkinson's disease characterized by alpha-synuclein overexpression in the song-dedicated anterior forebrain pathway

Deterioration in the quality of a person's voice and speech is an early marker of Parkinson's disease (PD). In humans, the neural circuit that supports vocal motor control consists of a cortico-basal ganglia-thalamo-cortico loop. The basal ganglia regions, striatum and globus pallidus, in this loop play a role in modulating the acoustic features of vocal behavior such as loudness, pitch, and articulatory rate. In PD, this area is implicated in pathogenesis. In animal models of PD, the accumulation of toxic aggregates containing the neuronal protein alpha-synuclein (αsyn) in the midbrain and striatum result in limb and vocal motor impairments. It has been challenging to study vocal impairments given the lack of well-defined cortico-basal ganglia circuitry for vocalization in rodent models. Furthermore, whether deterioration of voice quality early in PD is a direct result of αsyn-induced neuropathology is not yet known. Here, we take advantage of the well-characterized vocal circuits of the adult male zebra finch songbird to experimentally target a song-dedicated pathway, the anterior forebrain pathway, using an adeno-associated virus expressing the human wild-type αsyn gene, SNCA. We found that overexpression of αsyn in this pathway coincides with higher levels of insoluble, monomeric αsyn compared to control finches. Impairments in song production were also detected along with shorter and poorer quality syllables, which are the most basic unit of song. These vocal changes are similar to the vocal abnormalities observed in individuals with PD.

Tau protein quantification in skin biopsies differentiates tauopathies from alpha-synucleinopathies

Abnormal accumulation of microtubule-associated protein tau (τ) is a characteristic feature of atypical parkinsonisms with tauopathies such as Progressive Supranuclear Palsy (PSP) and Corticobasal Degeneration (CBD). However, pathological τ has also been observed in α-synucleinopathies like Parkinson's Disease (PD) and Multiple System Atrophy (MSA). Based on the involvement of peripheral nervous system in several neurodegenerative diseases, we characterized and compared τ expression in skin biopsies of patients clinically diagnosed with PD, MSA, PSP, CBD, and in healthy control subjects. In all groups, τ protein was detected along both somatosensory and autonomic nerve fibers in the epidermis and dermis by immunofluorescence. We found by western blot the presence of mainly two different bands at 55 and 70 KDa, co-migrating with 0N4R/1N3R and 2N4R isoforms, respectively. At the RNA level, the main transcript variants were 2N and 4R, and both resulted more expressed in PSP/CBD by real-time PCR. ELISA assay demonstrated significantly higher levels of total τ protein in skin lysates of PSP/CBD compared to the other groups. Multivariate regression analysis and ROC curves analysis of τ amount at both sites showed a clinical association with tauopathies diagnosis and high diagnostic value for PSP/CBD vs. PD (sensitivity 90%, specificity 69%) and PSP/CBD vs. MSA (sensitivity 90%, specificity 86%). τ protein increase correlated with cognitive impairment in PSP/CBD. This study is a comprehensive characterization of τ in the human cutaneous peripheral nervous system in physiologic and pathologic conditions. The differential expression of τ, both at transcript and protein levels, suggests that skin biopsy, an easily accessible and minimally invasive exam, can help in discriminating among different neurodegenerative diseases.

Paraquat Inhibits Autophagy Via Intensifying the Interaction Between HMGB1 and α-Synuclein

Paraquat, a widely used herbicide, is associated with an increased risk of Parkinson's disease (PD). PQ induces upregulation and accumulation of α-synuclein in neurons, which is one of the major pathological hallmarks of PD. Autophagy, as the major mechanism for the clearance of α-synuclein, is disrupted upon pesticide exposure as well as in PD patients. Meanwhile, HMGB1 is involved in autophagy dysfunction and particularly relevant to PD. However, whether PQ exposure affects HMGB1, α-synuclein, and autophagy function have rarely been reported. In this study, we found that PQ exposure impaired autophagy function via disturbing the complex formation of HMGB1 and Beclin1. Moreover, the expression of α-synuclein is modulated by HMGB1 and the interaction between HMGB1 and α-synuclein was intensified by PQ exposure. Taken together, our results revealed that HMGB1-mediated α-synuclein accumulation could competitively perturb the complex formation of HMGB1 and Beclin1, thereby inhibiting the autophagy function in SH-SY5Y cells.

Multi-Target Approach of Murraya koenigii Leaves in Treating Neurodegenerative Diseases

Neurodegenerative diseases (NDs) mainly affect neurons and gradually lead to a loss of normal motor and cognitive functions. Atypical protein homeostasis-misfolding, aggregations and accumulations, oxidative stress, inflammation, and apoptosis-are common features in most NDs. To date, due to the complex etiology and pathogenesis of NDs, no defined treatment is available. There has been increasing interest in plant extracts as potential alternative medicines as the presence of various active components may exert synergistic and multi-pharmacological effects. Murraya koenigii (Rutaceae) is utilized in Ayurvedic medicine for various ailments. Pharmacological studies evidenced its potential antioxidant, anti-inflammatory, anticancer, hepatoprotective, immunomodulatory, antimicrobial, and neuroprotective activities, among others. In line with our interest in exploring natural agents for the treatment of neurodegenerative diseases, this review presents an overview of literature concerning the mechanisms of action and the safety profile of significant bioactive components present in M. koenigii leaves to support further investigations into their neuroprotective therapeutic potential.

Glycogen Synthase Kinase-3 Inhibitors: Preclinical and Clinical Focus on CNS-A Decade Onward

The protein kinase, GSK-3, participates in diverse biological processes and is now recognized a promising drug discovery target in treating multiple pathological conditions. Over the last decade, a range of newly developed GSK-3 inhibitors of diverse chemotypes and inhibition modes has been developed. Even more conspicuous is the dramatic increase in the indications that were tested from mood and behavior disorders, autism and cognitive disabilities, to neurodegeneration, brain injury and pain. Indeed, clinical and pre-clinical studies were largely expanded uncovering new mechanisms and novel insights into the contribution of GSK-3 to neurodegeneration and central nerve system (CNS)-related disorders. In this review we summarize new developments in the field and describe the use of GSK-3 inhibitors in the variety of CNS disorders. This remarkable volume of information being generated undoubtedly reflects the great interest, as well as the intense hope, in developing potent and safe GSK-3 inhibitors in clinical practice.

Biomarkers of Cerebral Glucose Metabolism and Neurodegeneration in Parkinson's Disease: A Cerebrospinal Fluid-Based Study

BACKGROUND

Several biomarkers have been evaluated in Parkinson's disease (PD); cerebrospinal fluid (CSF) levels of lactate may reflect cerebral metabolism function and CSF amyloid-β42 (Aβ42), total tau (t-tau) and phosphorylated tau (p-tau) concentrations may detect an underlying neurodegenerative process.

OBJECTIVE

CSF levels of lactate, Aβ42, t-tau, and p-tau were measured in patients with mild to moderate PD. CSF levels of dopamine (DA) and its metabolite 3,4-Dihydroxyphenylacetic acid (DOPAC) were also assessed, exploring their relations with the other CSF biomarkers.

METHODS

101 drug-naive PD patients and 60 controls were included. Participants underwent clinical assessments and CSF biomarker analysis. Patients were divided into subgroups according to their Hoehn & Yahr stage (PD-1, PD-2, PD-3).

RESULTS

PD patients showed higher lactate levels (M = 1.91; p = 0.03) and lower Aβ42 (M = 595; p < 0.001) and DA levels (M = 0.32; p = 0.04) than controls (Mlactate = 1.72; MAβ42 = 837; MDA = 0.50), while no significant differences were found in t-tau, p-tau and DOPAC concentrations. Considering the subgroup analysis, PD-3 group had higher lactate (M = 2.12) and t-tau levels (M = 333) than both PD-1 (Mlactate = 1.75, p = 0.006; Mt - tau = 176, p = 0.008) and PD-2 groups (Mlactate = 1.91, p = 0.01; Mt - tau = 176, p = 0.03), as well as the controls (Mlactate = 1.72, p = 0.04; Mt - tau = 205, p = 0.04). PD-2 group showed higher lactate levels than PD-1 group (p = 0.04) and controls (p = 0.03). Finally, CSF lactate levels negatively correlated with DA (r = -0.42) and positively with t-tau CSF levels (r = 0.33).

CONCLUSION

This CSF-based study shows that lactate levels in PD correlated with both clinical disease progression and neurodegeneration biomarkers, such as tau proteins and DA. Further studies should explore the clinical potential of measuring CSF biomarkers for better understanding the role of brain energy metabolism in PD, for research and therapeutic options.

Neuronal TNFα, Not α-Syn, Underlies PDD-Like Disease Progression in IFNβ-KO Mice

OBJECTIVE

Parkinson's disease (PD) manifests in motor dysfunction, non-motor symptoms, and eventual dementia (PDD). Neuropathological hallmarks include nigrostriatal neurodegeneration, Lewy body (LB) pathology, and neuroinflammation. Alpha-synuclein (α-syn), a primary component of LBs, is implicated in PD pathogenesis, accumulating, and aggregating in both familial and sporadic PD. However, as α-syn pathology is often comorbid with amyloid-beta (Aβ) plaques and phosphorylated tau (pTau) tangles in PDD, it is still unclear whether α-syn is the primary cause of neurodegeneration in sporadic PDD. We aimed to determine how the absence of α-syn would affect PDD manifestation.

METHODS

IFN-β knockout (Ifnb-/- ) mice spontaneously develop progressive behavior abnormalities and neuropathology resembling PDD, notably with α-syn+ LBs. We generated Ifnb/Snca double knockout (DKO) mice and evaluated their behavior and neuropathology compared with wild-type (Wt), Ifnb-/- , and Snca-/- mice using immunohistochemistry, electron microscopy, immunoblots, qPCR, and modification of neuronal signaling.

RESULTS

Ifnb/Snca DKO mice developed all clinical PDD-like behavioral manifestations induced by IFN-β loss. Independently of α-syn expression, lack of IFN-β alone induced Aβ plaques, pTau tangles, and LB-like Aβ+ /pTau+ inclusion bodies and neuroinflammation. IFN-β loss caused significant elevated glial and neuronal TNF-α and neuronal TNFR1, associated with neurodegeneration. Restoring neuronal IFN-β signaling or blocking TNFR1 rescued caspase 3/t-BID-mediated neuronal-death through upregulation of c-FLIPS and lowered intraneuronal Aβ and pTau accumulation.

INTERPRETATION

These findings increase our understanding of PD pathology and suggest that targeting α-syn alone is not sufficient to mitigate disease. Targeting specific aspects of neuroinflammation, such as aberrant neuronal TNF-α/TNFR1 or IFN-β/IFNAR signaling, may attenuate disease. ANN NEUROL 2021;90:789-807.

Plasma extracellular vesicles tau and β-amyloid as biomarkers of cognitive dysfunction of Parkinson's disease

The contribution of circulatory tau and β-amyloid in Parkinson's disease (PD), especially the cognitive function, remains inconclusive. Extracellular vesicles (EVs) cargo these proteins throughout the bloodstream after they are directly secreted from many cells, including neurons. The present study aims to investigate the role of the plasma EV-borne tau and β-amyloid as biomarkers for cognitive dysfunction in PD by investigating subjects with mild to moderate stage of PD (n = 116) and non-PD controls (n = 46). Plasma EVs were isolated, and immunomagnetic reduction-based immunoassay was used to assess the levels of α-synuclein, tau, and β-amyloid 1-42 (Aβ1-42) within the EVs. Artificial neural network (ANN) models were then applied to predict cognitive dysfunction. We observed no significant difference in plasma EV tau and Aβ1-42 between PD patients and controls. Plasma EV tau was significantly associated with cognitive function. Moreover, plasma EV tau and Aβ1-42 were significantly elevated in PD patients with cognitive impairment when compared to PD patients with optimal cognition. The ANN model used the plasma EV α-synuclein, tau, and Aβ1-42, as well as the patient's age and gender, as predicting factors. The model achieved an accuracy of 91.3% in identifying cognitive dysfunction in PD patients, and plasma EV tau and Aβ1-42 are the most valuable factors. In conclusion, plasma EV tau and Aβ1-42 are significant markers of cognitive function in PD patients. Combining with the plasma EV α-synuclein, age, and sex, plasma EV tau and Aβ1-42 can identify cognitive dysfunction in PD patients. This study corroborates the prognostic roles of plasma EV tau and Aβ1-42 in PD.

Decoupling of Global Brain Activity and Cerebrospinal Fluid Flow in Parkinson's Disease Cognitive Decline

BACKGROUND

Deposition and spreading of misfolded proteins (α-synuclein and tau) have been linked to Parkinson's disease cognitive dysfunction. The glymphatic system may play an important role in the clearance of these toxic proteins via cerebrospinal fluid (CSF) flow through perivascular and interstitial spaces. Recent studies discovered that sleep-dependent global brain activity is coupled to CSF flow, which may reflect glymphatic function.

OBJECTIVE

The objective of this current study was to determine if the decoupling of brain activity-CSF flow is linked to Parkinson's disease cognitive dysfunction.

METHODS

Functional and structural MRI data, clinical motor (Unified Parkinson's Disease Rating Scale), and cognitive (Montreal Cognitive Assessment [MoCA]) scores were collected from 60 Parkinson's disease and 58 control subjects. Parkinson's disease patients were subgrouped into those with mild cognitive impairment (MoCA < 26), n = 31, and those without mild cognitive impairment (MoCA ≥ 26), n = 29. The coupling strength between the resting-state global blood-oxygen-level-dependent signal and associated CSF flow was quantified, compared among groups, and associated with clinical and structural measurements.

RESULTS

Global blood-oxygen-level-dependent signal-CSF coupling decreased significantly (P < 0.006) in Parkinson's disease patients showing mild cognitive impairment, compared with those without mild cognitive impairment and controls. Reduced global blood-oxygen-level-dependent signal-CSF coupling was associated with decreased MoCA scores present in Parkinson's disease patients (P = 0.005) but not in controls (P = 0.65). Weaker global blood-oxygen-level-dependent signal-CSF coupling in Parkinson's disease patients also was associated with a thinner right entorhinal cortex (Spearman's correlation, -0.36; P = 0.012), an early structural change often seen in Alzheimer's disease.

CONCLUSIONS

The decoupling between global brain activity and associated CSF flow is related to Parkinson's disease cognitive impairment. © 2021 International Parkinson and Movement Disorder Society.

The Prion-Like Spreading of Alpha-Synuclein in Parkinson's Disease: Update on Models and Hypotheses

The pathological aggregation of the presynaptic protein α-synuclein (α-syn) and propagation through synaptically coupled neuroanatomical tracts is increasingly thought to underlie the pathophysiological progression of Parkinson's disease (PD) and related synucleinopathies. Although the precise molecular mechanisms responsible for the spreading of pathological α-syn accumulation in the CNS are not fully understood, growing evidence suggests that de novo α-syn misfolding and/or neuronal internalization of aggregated α-syn facilitates conformational templating of endogenous α-syn monomers in a mechanism reminiscent of prions. A refined understanding of the biochemical and cellular factors mediating the pathological neuron-to-neuron propagation of misfolded α-syn will potentially elucidate the etiology of PD and unravel novel targets for therapeutic intervention. Here, we discuss recent developments on the hypothesis regarding trans-synaptic propagation of α-syn pathology in the context of neuronal vulnerability and highlight the potential utility of novel experimental models of synucleinopathies.

Hot Topics in Recent Parkinson's Disease Research: Where We are and Where We Should Go

Parkinson's disease (PD), the second most common neurodegenerative disease, is clinically characterized by both motor and non-motor symptoms. Although overall great achievements have been made in elucidating the etiology and pathogenesis of PD, the exact mechanisms of this complicated systemic disease are still far from being clearly understood. Consequently, most of the currently-used diagnostic tools and therapeutic options for PD are symptomatic. In this perspective review, we highlight the hot topics in recent PD research for both clinicians and researchers. Some of these hot topics, such as sleep disorders and gut symptoms, have been neglected but are currently emphasized due to their close association with PD. Following these research directions in future PD research may help understand the nature of the disease and facilitate the discovery of new strategies for the diagnosis and therapy of PD.