Intranasal administration of α-synuclein preformed fibrils triggers microglial iron deposition in the substantia nigra of Macaca fascicularis

The role of ferroptosis in Alzheimer's disease: Mechanisms and therapeutic potential (Review)

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by insidious onset and progressive symptom deterioration. It extends beyond a simple aging process, involving irreversible and progressive neurological degeneration that impairs brain function through multiple etiologies. Iron dysregulation is implicated in the pathophysiology of AD; however, the precise mechanisms remain unclear. Additionally, vitamin E and selenium are key in regulating ferroptosis through their antioxidant properties. The present review examined the mechanistic pathways by which ferroptosis contributes to AD, the regulatory roles of vitamin E, selenium, ferrostatin‑1, N‑acetylcysteine and curcumin, and their potential as therapeutic agents to mitigate neurodegeneration.

Intranasal α-Synuclein induces progressive behavioral impairments in mice

α-Synuclein (α-Syn) is implicated in the progression of Parkinson's disease, yet the disease's etiology remains unclear. This study aims to explore how α-Syn affects olfactory, motor, mood and cognitive functions if it initiates from the olfactory bulb. Mice were administered intranasal human AAV-α-Syn and subsequently evaluated for olfactory, motor, mood, and cognitive functions. Immunofluorescence was performed to assess dopaminergic neuronal damage. Results shown that olfactory dysfunction was evident as AAV-α-Syn-treated mice took longer to find buried pellets compared to controls at 3, 9, and 12 months post-instillation. Motor activity remained normal at 6 months but significantly declined at 9 months. Reduced tyrosine hydroxylase expression but increased amount of human α-Syn were observed in the substantia nigra at end of behavioral measurements. AAV-α-Syn mice showed reduced sucrose intake and decreased time in the center zone of the open field at 9 months. Cognitive deficits were observed in recognition function and social memory at 6 and 9 months, with impaired working memory at 12 months. Thus, intranasal AAV-α-Syn instillation in mice leads to progressive olfactory, motor, anxiety, depression-like, and cognitive dysfunctions, reflecting α-Syn pathology propagation.

The role of microglia in neurodegenerative diseases: from the perspective of ferroptosis

Iron plays a pivotal role in numerous fundamental biological processes in the brain. Among the various cell types in the central nervous system, microglia are recognized as the most proficient cells in accumulating and storing iron. Nonetheless, iron overload can induce inflammatory phenotype of microglia, leading to the production of proinflammatory cytokines and contributing to neurodegeneration. A growing body of evidence shows that disturbances in iron homeostasis in microglia is associated with a range of neurodegenerative disorders. Recent research has revealed that microglia are highly sensitive to ferroptosis, a form of iron-dependent cell death. How iron overload influences microglial function? Whether disbiosis in iron metabolism and ferroptosis in microglia are involved in neurodegenerative disorders and the underlying mechanisms remain to be elucidated. In this review we focus on the recent advances in research on microglial iron metabolism as well as ferroptosis in microglia. Meanwhile, we provide a comprehensive overview of the involvement of microglial ferroptosis in neurodegenerative disorders from the perspective of crosstalk between microglia and neuron, with a focus on Alzheimer's disease and Parkinson's disease.

The interplay of iron, oxidative stress, and α-synuclein in Parkinson's disease progression

The irreversible degeneration of dopamine neurons induced by α-synuclein (α-syn) aggregation in the substantia nigra is the central pathological feature of Parkinson's disease (PD). Neuroimaging and pathological autopsy studies consistently confirm significant iron accumulation in the brain of PD patients, suggesting a critical role for iron in disease progression. Current research has established that iron overload induces ferroptosis in dopaminergic neurons, evidence indicates that the impact of iron on PD pathology extends beyond ferroptosis. Iron also plays a regulatory role in modulating α-syn, affecting its aggregation, spatial conformation, post-translational modifications, and mRNA stability. Iron-induced α-syn aggregation can contribute to dopaminergic neurodegeneration through additional mechanisms, potentially creating a feedback loop in which α-syn further enhances iron accumulation, thus perpetuating a vicious cycle of neurotoxicity. Given α-syn's intrinsically disordered structure, targeting iron metabolism presents a promising therapeutic strategy for PD. Therefore, the development of iron chelators, alone or in combination with other therapeutic drugs, may offer a beneficial approach to alleviating PD symptoms and slowing disease progression.

The interplay between α-synuclein aggregation and necroptosis in Parkinson's disease: a spatiotemporal perspective

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the death of dopaminergic neurons and the aggregation of alpha-synuclein (α-Syn). It presents with prominent motor symptoms, and by the time of diagnosis, a significant number of neurons have already been lost. Current medications can only alleviate symptoms but cannot halt disease progression. Studies have confirmed that both dopaminergic neuronal loss and α-Syn aggregation are associated with necroptosis mechanisms. Necroptosis, a regulated form of cell death, has been recognized as an underexplored hotspot in PD pathogenesis research. In this review, we propose a spatiotemporal model of PD progression, highlighting the interactions between α-Syn aggregation, mitochondrial dysfunction, oxidative stress, neuroinflammation and necroptosis. These processes not only drive motor symptoms but also contribute to early non-motor symptoms, offering insights into potential diagnostic markers. Finally, we touch upon the therapeutic potential of necroptosis inhibition in enhancing current PD treatments, such as L-Dopa. This review aims to provide a new perspective on the pathogenesis of PD and to identify avenues for the development of more effective therapeutic strategies.

Lactoferrin as a Candidate Multifunctional Therapeutic in Synucleinopathies

Lactoferrin (Lf) is a multifunctional glycoprotein with well-established antimicrobial, anti-inflammatory, and iron-binding properties. Emerging evidence suggests that Lf also plays a neuroprotective role, particularly in neurodegenerative disorders characterized by protein aggregation, such as Parkinson's disease (PD). Alpha-synuclein (aSyn) aggregation is a pathological hallmark of PD and other synucleinopathies, contributing to neuronal dysfunction and disease progression. Recent studies indicate that Lf may interfere with aSyn aggregation, iron chelation, and modulation of oxidative stress and neuroinflammation. Additionally, Lf's ability to cross the blood-brain barrier and its potential impact on the gut-brain axis highlight its promise as a therapeutic agent. This review explores Lf's mechanisms of action in synucleinopathies, its potential as a disease-modifying therapy, and innovative delivery strategies that could enhance its clinical applicability. By addressing the pathological and therapeutic dimensions of aSyn aggregation, we propose Lf as a compelling candidate for future research and clinical development in neurodegenerative diseases.

Crosstalk between neuroinflammation and ferroptosis: Implications for Parkinson's disease progression

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the degeneration of dopaminergic neurons and the aggregation of α-synuclein. Neuroinflammation is triggered by the activation of microglia and astrocytes, which release pro-inflammatory factors that exacerbate neuronal damage. This inflammatory state also disrupts iron homeostasis, leading to the occurrence of ferroptosis. Ferroptosis is characterized by lipid peroxidation of cell membranes and iron overload. Abnormal accumulation of iron in the brain increases oxidative stress and lipid peroxidation, further aggravating neuroinflammation and damage to dopaminergic neurons. Natural products have garnered attention for their antioxidant, anti-inflammatory, and neuroprotective properties, with many plant extracts showing promising therapeutic potential in PD research. This study further investigates the potential therapeutic roles of various natural products in regulating neuroinflammation and ferroptosis. The results suggest that natural products have significant therapeutic potential in modulating the interaction between neuroinflammation and ferroptosis, making them potential treatments for PD. Future research should further validate the safety and efficacy of these natural compounds in clinical applications to develop novel therapeutic strategies for PD.

Corilagin Attenuates Neuronal Apoptosis and Ferroptosis of Parkinson's Disease through Regulating the TLR4/Src/NOX2 Signaling Pathway

Corilagin has shown neuroprotective potential in various neurological disorders, but its effects in Parkinson's disease (PD) have not been fully explored. In this study, we investigated the therapeutic impact and underlying mechanism of corilagin on PD using MPTP-induced mice and MPP+-treated N2a cells. Behavioral tests and immunohistochemical analysis demonstrated that corilagin significantly reduced MPTP-induced loss of TH-positive neurons in the substantia nigra. In vitro, corilagin improved cell viability, decreased MPP+-induced apoptosis, and mitigated the associated oxidative stress by lowering intracellular ROS levels and preserving mitochondrial membrane potential. Moreover, corilagin reversed MPP+-induced iron accumulation and lipid peroxidation in N2a cells. Mechanistically, Western blotting revealed that the protective effects of corilagin are linked to the TLR4/Src/NOX2 signaling pathway. The TLR4 agonist RS 09 impaired the neuroprotective effects of corilagin, further supporting its role in modulating ferroptosis via this pathway. These findings suggest that corilagin could be a promising therapeutic agent for PD by targeting the TLR4/Src/NOX2 signaling axis to inhibit ferroptosis.

Identifying potential genes driving ferroptosis in the substantia nigra and dopaminergic neurons in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder marked by dopaminergic (DA) neuron degeneration in the substantia nigra (SN). Conventional dopamine replacement therapies provide limited long-term efficacy and significant side effects. Emerging evidence suggests ferroptosis-a form of cell death driven by iron-dependent lipid peroxidation-contributes to PD pathology, though direct evidence linking dysregulation of ferroptosis-related genes in DA neuron loss in PD remains limited. This study explores the expression of ferroptosis-associated genes in the SN and DA neurons of PD patients, identifying potential therapeutic targets. We analyzed two independent RNA-seq datasets, GSE7621 and GSE8397 (GPL-96), from the GEO database to identify common differentially expressed ferroptosis-related genes in the SN of PD patients. We also conducted Gene Ontology and pathway enrichment analyses of these genes to explore the underlying mechanisms and constructed a protein-protein interaction network. The findings were further validated using an additional dataset, GSE49036. We further explored the dysregulation of these ferroptosis-related genes in DA neurons using RNA-seq data GSE169755, derived from DA neurons isolated from the SN of PD patients and controls. Lastly, the proposed hypothesis was experimentally validated in an in vitro PD model. This comprehensive multi-dataset analysis uncovers novel insights into the expression of ferroptosis-related genes in PD, suggesting potential biomarkers and therapeutic targets for mitigating DA neuron loss and PD progression.

Homeostasis and metabolism of iron and other metal ions in neurodegenerative diseases

As essential micronutrients, metal ions such as iron, manganese, copper, and zinc, are required for a wide range of physiological processes in the brain. However, an imbalance in metal ions, whether excessive or insufficient, is detrimental and can contribute to neuronal death through oxidative stress, ferroptosis, cuproptosis, cell senescence, or neuroinflammation. These processes have been found to be involved in the pathological mechanisms of neurodegenerative diseases. In this review, the research history and milestone events of studying metal ions, including iron, manganese, copper, and zinc in neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), will be introduced. Then, the upstream regulators, downstream effector, and crosstalk of mental ions under both physiologic and pathologic conditions will be summarized. Finally, the therapeutic effects of metal ion chelators, such as clioquinol, quercetin, curcumin, coumarin, and their derivatives for the treatment of neurodegenerative diseases will be discussed. Additionally, the promising results and limitations observed in clinical trials of these metal ion chelators will also be addressed. This review will not only provide a comprehensive understanding of the role of metal ions in disease development but also offer perspectives on their modulation for the prevention or treatment of neurodegenerative diseases.

Lewy body diseases and the gut

Gastrointestinal (GI) involvement in Lewy body diseases (LBDs) has been observed since the initial descriptions of patients by James Parkinson. Recent experimental and human observational studies raise the possibility that pathogenic alpha-synuclein (⍺-syn) might develop in the GI tract and subsequently spread to susceptible brain regions. The cellular and mechanistic origins of ⍺-syn propagation in disease are under intense investigation. Experimental LBD models have implicated important contributions from the intrinsic gut microbiome, the intestinal immune system, and environmental toxicants, acting as triggers and modifiers to GI pathologies. Here, we review the primary clinical observations that link GI dysfunctions to LBDs. We first provide an overview of GI anatomy and the cellular repertoire relevant for disease, with a focus on luminal-sensing cells of the intestinal epithelium including enteroendocrine cells that express ⍺-syn and make direct contact with nerves. We describe interactions within the GI tract with resident microbes and exogenous toxicants, and how these may directly contribute to ⍺-syn pathology along with related metabolic and immunological responses. Finally, critical knowledge gaps in the field are highlighted, focusing on pivotal questions that remain some 200 years after the first descriptions of GI tract dysfunction in LBDs. We predict that a better understanding of how pathophysiologies in the gut influence disease risk and progression will accelerate discoveries that will lead to a deeper overall mechanistic understanding of disease and potential therapeutic strategies targeting the gut-brain axis to delay, arrest, or prevent disease progression.

Bifenthrin Caused Parkinson's-Like Symptoms Via Mitochondrial Autophagy and Ferroptosis Pathway Stereoselectively in Parkin-/- Mice and C57BL/6 Mice

It has been proposed that pyrethroid exposure contributes to the increasing prevalence of neurodegenerative diseases. However, the potential mechanisms remain unclear. The current study aimed to investigate the effects of the widely used pyrethroid bifenthrin on Parkinson's disease (PD) risk. Bifenthrin (1S-cis-bifenthrin, 1R-cis-bifenthrin, raceme) was administered to male Parkin-/- mice and C57BL/6 mice by oral gavage at a dose of 10 mg/kg bw/day for 28 days. Bifenthrin exposure significantly increased the time of pole climbing and decreased the period of rotarod running, indicating that bifenthrin decreased motor coordination in Parkin-/- mice, which was more evident by 1S-cis-bifenthrin. Furthermore, administration of bifenthrin induced obvious decreases in tyrosine hydroxylase (TH)+ cell count and the protein expression of TH. Increased protein of mitochondrial autophagy LC3B and p62 was observed after exposure to bifenthrin. Increased iron deposition and protein expression of iron transport transferrin (Tf) and transferrin receptor 2 (TfR2) was detected. 1S-cis-bifenthrin bound with Tf, TfR2, and GPX4 with lower binding energies than 1R-cis-bifenthrin, resulting in stronger interactions with these proteins. These results show structure-dependent PD-like effects of bifenthrin on motor activity and coordination associated with the disturbed mitochondrial autophagy and ferroptosis-related pathway. These data demonstrate that pyrethroid exposure increases the potential of Parkinson's-like symptoms via the ferroptosis pathway in Parkin-/- mice that is more pronounced than in C57BL/6 mice, providing a prospective enantioselective toxic effect of environmental neurotoxins on PD risk.

Ferroptosis in Parkinson's disease -- The iron-related degenerative disease

Parkinson's disease (PD) is a prevalent and advancing age-related neurodegenerative disorder, distinguished by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Iron regional deposit in SNpc is a significant pathological characteristic of PD. Brain iron homeostasis is precisely regulated by iron metabolism related proteins, whereas disorder of these proteins can damage neurons and glial cells in the brain. Additionally, growing studies have reported iron metabolism related proteins are involved in the ferroptosis progression in PD. However, the effect of these proteins in the ferroptosis of PD has not been systematically summarized. This review focuses on the roles of iron metabolism related proteins in the ferroptosis of PD. Finally, we put forward the iron early diagnosis according to the observation of iron deposits in the brain and showed the recent advances in iron chelation therapy in PD.

Research Progress on the Relationship between Parkinson's Disease and REM Sleep Behavior Disorder

An individual's quality of life is greatly affected by Parkinson's disease (PD), a prevalent neurological degenerative condition. Rapid eye movement (REM) sleep behavior disorder (RBD) is a prominent non-motor symptom commonly associated with PD. Previous studies have shown a close relationship between PD and RBD. In addition to being a prodromal symptom of PD, RBD has a major negative impact on the prognosis of PD patients. This intrinsic connection indicates that there is a bidirectional relationship between PD and RBD. This paper provides a comprehensive review of the pathological mechanism related to PD and RBD, including the α-synuclein pathological deposition, abnormal iron metabolism, neuroinflammation, glymphatic system dysfunction and dysbiosis of the gut microbiota. Increasing evidence has shown that RBD patients have the same pathogenic mechanisms that underlie PD, but relatively little research has been done on how RBD contributes to PD progression. Therefore, a more thorough investigation is warranted to characterise how RBD affects the course of PD, in order to prepare for future therapeutic trials.

Application of quantum dots in brain diseases and their neurotoxic mechanism

The early-stage diagnosis and therapy of brain diseases pose a persistent challenge in the field of biomedicine. Quantum dots (QDs), nano-luminescent materials known for their small size and fluorescence imaging capabilities, present promising capabilities for diagnosing, monitoring, and treating brain diseases. Although some investigations about QDs have been conducted in clinical trials, the concerns about the toxicity of QDs have continued. In addition, the lack of effective toxicity evaluation methods and systems and the difference between in vivo and in vitro toxicity evaluation hinder QDs application. The primary objective of this paper is to introduce the neurotoxic effects and mechanisms attributable to QDs. First, we elucidate the utilization of QDs in brain disorders. Second, we sketch out three pathways through which QDs traverse into brain tissue. Ultimately, expound upon the adverse consequences of QDs on the brain and the mechanism of neurotoxicity in depth. Finally, we provide a comprehensive summary and outlook on the potential development of quantum dots in neurotoxicity and the difficulties to be overcome.

Cellular iron deposition patterns predict clinical subtypes of multiple system atrophy

BACKGROUND

Multiple system atrophy (MSA) is a primary oligodendroglial synucleinopathy, characterized by elevated iron burden in early-affected subcortical nuclei. Although neurotoxic effects of brain iron deposition and its relationship with α-synuclein pathology have been demonstrated, the exact role of iron dysregulation in MSA pathogenesis is unknown. Therefore, advancing the understanding of iron dysregulation at the cellular level is critical, especially in relation to α-synuclein cytopathology.

METHODS

Iron burden in subcortical and brainstem regions were histologically mapped in human post-mortem brains of 4 MSA-parkinsonian (MSA-P), 4 MSA-cerebellar (MSA-C), and 1 MSA case with both parkinsonian and cerebellar features. We then performed the first cell type-specific evaluation of pathological iron deposition in α-synuclein-affected and -unaffected cells of the globus pallidus, putamen, and the substantia nigra, regions of highest iron concentration, using a combination of iron staining with immunolabelling. Selective regional and cellular vulnerability patterns of iron deposition were compared between disease subtypes. In 7 MSA cases, expression of key iron- and closely related oxygen-homeostatic genes were examined.

RESULTS

MSA-P and MSA-C showed different patterns of regional iron burden across the pathology-related systems. We identified subcortical microglia to predominantly accumulate iron, which was more distinct in MSA-P. MSA-C showed relatively heterogenous iron accumulation, with greater or similar deposition in astroglia. Iron deposition was also found outside cellular bodies. Cellular iron burden associated with oligodendrocytic, and not neuronal, α-synuclein cytopathology. Gene expression analysis revealed dysregulation of oxygen homeostatic genes, rather than of cellular iron. Importantly, hierarchal cluster analysis revealed the pattern of cellular vulnerability to iron accumulation, distinctly to α-synuclein pathology load in the subtype-related systems, to distinguish MSA subtypes.

CONCLUSIONS

Our comprehensive evaluation of iron deposition in MSA brains identified distinct regional, and for the first time, cellular distribution of iron deposition in MSA-P and MSA-C and revealed cellular vulnerability patterns to iron deposition as a novel neuropathological characteristic that predicts MSA clinical subtypes. Our findings suggest distinct iron-related pathomechanisms in MSA clinical subtypes that are therefore not a consequence of a uniform down-stream pathway to α-synuclein pathology, and inform current efforts in iron chelation therapies at the disease and cellular-specific levels.

Targeting ferroptosis in neuroimmune and neurodegenerative disorders for the development of novel therapeutics

Neuroimmune and neurodegenerative ailments impose a substantial societal burden. Neuroimmune disorders involve the intricate regulatory interactions between the immune system and the central nervous system. Prominent examples of neuroimmune disorders encompass multiple sclerosis and neuromyelitis optica. Neurodegenerative diseases result from neuronal degeneration or demyelination in the brain or spinal cord, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. The precise underlying pathogenesis of these conditions remains incompletely understood. Ferroptosis, a programmed form of cell death characterised by lipid peroxidation and iron overload, plays a pivotal role in neuroimmune and neurodegenerative diseases. In this review, we provide a detailed overview of ferroptosis, its mechanisms, pathways, and regulation during the progression of neuroimmune and neurodegenerative diseases. Furthermore, we summarise the impact of ferroptosis on neuroimmune-related cells (T cells, B cells, neutrophils, and macrophages) and neural cells (glial cells and neurons). Finally, we explore the potential therapeutic implications of ferroptosis inhibitors in diverse neuroimmune and neurodegenerative diseases.

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.

A Comprehensive Approach to Parkinson's Disease: Addressing Its Molecular, Clinical, and Therapeutic Aspects

Parkinson's disease (PD) is a gradually worsening neurodegenerative disorder affecting the nervous system, marked by a slow progression and varied symptoms. It is the second most common neurodegenerative disease, affecting over six million people in the world. Its multifactorial etiology includes environmental, genomic, and epigenetic factors. Clinical symptoms consist of non-motor and motor symptoms, with motor symptoms being the classic presentation. Therapeutic approaches encompass pharmacological, non-pharmacological, and surgical interventions. Traditional pharmacological treatment consists of administering drugs (MAOIs, DA, and levodopa), while emerging evidence explores the potential of antidiabetic agents for neuroprotection and gene therapy for attenuating parkinsonian symptoms. Non-pharmacological treatments, such as exercise, a calcium-rich diet, and adequate vitamin D supplementation, aim to slow disease progression and prevent complications. For those patients who have medically induced side effects and/or refractory symptoms, surgery is a therapeutic option. Deep brain stimulation is the primary surgical option, associated with motor symptom improvement. Levodopa/carbidopa intestinal gel infusion through percutaneous endoscopic gastrojejunostomy and a portable infusion pump succeeded in reducing "off" time, where non-motor and motor symptoms occur, and increasing "on" time. This article aims to address the general aspects of PD and to provide a comparative comprehensive review of the conventional and the latest therapeutic advancements and emerging treatments for PD. Nevertheless, further studies are required to optimize treatment and provide suitable alternatives.

Potential convergence of olfactory dysfunction in Parkinson's disease and COVID-19: The role of neuroinflammation

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that affects 7-10 million individuals worldwide. A common early symptom of PD is olfactory dysfunction (OD), and more than 90% of PD patients suffer from OD. Recent studies have highlighted a high incidence of OD in patients with SARS-CoV-2 infection. This review investigates the potential convergence of OD in PD and COVID-19, particularly focusing on the mechanisms by which neuroinflammation contributes to OD and neurological events. Starting from our fundamental understanding of the olfactory bulb, we summarize the clinical features of OD and pathological features of the olfactory bulb from clinical cases and autopsy reports in PD patients. We then examine SARS-CoV-2-induced olfactory bulb neuropathology and OD and emphasize the SARS-CoV-2-induced neuroinflammatory cascades potentially leading to PD manifestations. By activating microglia and astrocytes, as well as facilitating the aggregation of α-synuclein, SARS-CoV-2 could contribute to the onset or exacerbation of PD. We also discuss the possible contributions of NF-κB, the NLRP3 inflammasome, and the JAK/STAT, p38 MAPK, TLR4, IL-6/JAK2/STAT3 and cGAS-STING signaling pathways. Although olfactory dysfunction in patients with COVID-19 may be reversible, it is challenging to restore OD in patients with PD. With the emergence of new SARS-CoV-2 variants and the recurrence of infections, we call for continued attention to the intersection between PD and SARS-CoV-2 infection, especially from the perspective of OD.

Research trends of ferroptosis and pyroptosis in Parkinson's disease: a bibliometric analysis

Objective

This study aims to visualize the trends and hotspots in the research of "ferroptosis in PD" and "pyroptosis in PD" through bibliometric analysis from the past to 2024.

Methods

Literature was retrieved from the Web of Science Core Collection (WoSCC) from the past to February 16, 2024, and bibliometric analysis was conducted using Vosviewer and Citespace.

Results

283 and 542 papers were collected in the field of "ferroptosis in PD" and "pyroptosis in PD." The number of publications in both fields has increased yearly, especially in "ferroptosis in PD," which will become the focus of PD research. China, the United States and England had extensive exchanges and collaborations in both fields, and more than 60% of the top 10 institutions were from China. In the fields of "ferroptosis in PD" and "pyroptosis in PD," the University of Melbourne and Nanjing Medical University stood out in terms of publication numbers, citation frequency, and centrality, and the most influential journals were Cell and Nature, respectively. The keyword time zone map showed that molecular mechanisms and neurons were the research hotspots of "ferroptosis in PD" in 2023, while memory and receptor 2 were the research hotspots of "pyroptosis in PD" in 2023, which may predict the future research direction.

Conclusion

This study provides insights into the development, collaborations, research themes, hotspots, and tendencies of "ferroptosis in PD" and "pyroptosis in PD." Overall situation of these fields is available for researchers to further explore the underlying mechanisms and potential treatments.

The Irony of Iron: The Element with Diverse Influence on Neurodegenerative Diseases

Iron accumulation in the brain is a common feature of many neurodegenerative diseases. Its involvement spans across the main proteinopathies involving tau, amyloid-beta, alpha-synuclein, and TDP-43. Accumulating evidence supports the contribution of iron in disease pathologies, but the delineation of its pathogenic role is yet challenged by the complex involvement of iron in multiple neurotoxicity mechanisms and evidence supporting a reciprocal influence between accumulation of iron and protein pathology. Here, we review the major proteinopathy-specific observations supporting four distinct hypotheses: (1) iron deposition is a consequence of protein pathology; (2) iron promotes protein pathology; (3) iron protects from or hinders protein pathology; and (4) deposition of iron and protein pathology contribute parallelly to pathogenesis. Iron is an essential element for physiological brain function, requiring a fine balance of its levels. Understanding of disease-related iron accumulation at a more intricate and systemic level is critical for advancements in iron chelation therapies.

Mapping the Research of Ferroptosis in Parkinson's Disease from 2013 to 2023: A Scientometric Review

Methods

Related studies on PD and ferroptosis were searched in Web of Science Core Collection (WOSCC) from inception to 2023. VOSviewer, CiteSpace, RStudio, and Scimago Graphica were employed as bibliometric analysis tools to generate network maps about the collaborations between authors, countries, and institutions and to visualize the co-occurrence and trends of co-cited references and keywords.

Results

A total of 160 original articles and reviews related to PD and ferroptosis were retrieved, produced by from 958 authors from 162 institutions. Devos David was the most prolific author, with 9 articles. China and the University of Melbourne had leading positions in publication volume with 84 and 12 publications, respectively. Current hot topics focus on excavating potential new targets for treating PD based on ferroptosis by gaining insight into specific molecular mechanisms, including iron metabolism disorders, lipid peroxidation, and imbalanced antioxidant regulation. Clinical studies aimed at treating PD by targeting ferroptosis remain in their preliminary stages.

Conclusion

A continued increase was shown in the literature within the related field over the past decade. The current study suggested active collaborations among authors, countries, and institutions. Research into the pathogenesis and treatment of PD based on ferroptosis has remained a prominent topic in the field in recent years, indicating that ferroptosis-targeted therapy is a potential approach to halting the progression of PD.

Parkinson's disease-derived α-synuclein assemblies combined with chronic-type inflammatory cues promote a neurotoxic microglial phenotype

Parkinson's disease (PD) is a common age-related neurodegenerative disorder characterized by the aggregation of α-Synuclein (αSYN) building up intraneuronal inclusions termed Lewy pathology. Mounting evidence suggests that neuron-released αSYN aggregates could be central to microglial activation, which in turn mounts and orchestrates neuroinflammatory processes potentially harmful to neurons. Therefore, understanding the mechanisms that drive microglial cell activation, polarization and function in PD might have important therapeutic implications. Here, using primary microglia, we investigated the inflammatory potential of pure αSYN fibrils derived from PD patients. We further explored and characterized microglial cell responses to a chronic-type inflammatory stimulation combining PD patient-derived αSYN fibrils (FPD), Tumor necrosis factor-α (TNFα) and prostaglandin E2 (PGE2) (TPFPD). We showed that FPD hold stronger inflammatory potency than pure αSYN fibrils generated de novo. When combined with TNFα and PGE2, FPD polarizes microglia toward a particular functional phenotype departing from FPD-treated cells and featuring lower inflammatory cytokine and higher glutamate release. Whereas metabolomic studies showed that TPFPD-exposed microglia were closely related to classically activated M1 proinflammatory cells, notably with similar tricarboxylic acid cycle disruption, transcriptomic analysis revealed that TPFPD-activated microglia assume a unique molecular signature highlighting upregulation of genes involved in glutathione and iron metabolisms. In particular, TPFPD-specific upregulation of Slc7a11 (which encodes the cystine-glutamate antiporter xCT) was consistent with the increased glutamate response and cytotoxic activity of these cells toward midbrain dopaminergic neurons in vitro. Together, these data further extend the structure-pathological relationship of αSYN fibrillar polymorphs to their innate immune properties and demonstrate that PD-derived αSYN fibrils, TNFα and PGE2 act in concert to drive microglial cell activation toward a specific and highly neurotoxic chronic-type inflammatory phenotype characterized by robust glutamate release and iron retention.

Cell senescence induced by toxic interaction between α-synuclein and iron precedes nigral dopaminergic neuron loss in a mouse model of Parkinson's disease

Cell senescence has been implicated in the pathology of Parkinson's disease (PD). Both abnormal α-synuclein aggregation and iron deposition are suggested to be the triggers, facilitators, and aggravators during the development of PD. In this study, we investigated the involvement of α-synuclein and iron in the process of cell senescence in a mouse model of PD. In order to overexpress α-syn-A53T in the substantia nigra pars compacta (SNpc), human α-syn-A53T was microinjected into both sides of the SNpc in mice. We found that overexpression of α-syn-A53T for one week induced significant pro-inflammatory senescence-associated secretory phenotype (SASP), increased cell senescence-related proteins (β-gal, p16, p21, H2A.X and γ-H2A.X), mitochondrial dysfunction accompanied by dysregulation of iron-related proteins (L-ferritin, H-ferritin, DMT1, IRP1 and IRP2) in the SNpc. In contrast, significant loss of nigral dopaminergic neurons and motor dysfunction were only observed after overexpression of α-syn-A53T for 4 weeks. In PC12 cells stably overexpressing α-syn-A53T, iron overload (ferric ammonium citrate, FAC, 100 μM) not only increased the level of reactive oxygen species (ROS), p16 and p21, but also exacerbated the processes of oxidative stress and cell senescence signalling induced by α-syn-A53T overexpression. Interestingly, reducing the iron level with deferoxamine (DFO) or knockdown of transferrin receptor 1 (TfR1) significantly improved both the phenotypes and dysregulated proteins of cell senescence induced by α-syn-A53T overexpression. All these evidence highlights the toxic interaction between iron and α-synuclein inducing cell senescence, which precedes nigral dopaminergic neuronal loss in PD. Further investigation on cell senescence may yield new therapeutic agents for the prevention or treatment of PD.

Gut microbiota-induced CXCL1 elevation triggers early neuroinflammation in the substantia nigra of Parkinsonian mice

Gut microbiota disturbance and systemic inflammation have been implicated in the degeneration of dopaminergic neurons in Parkinson's disease (PD). How the alteration of gut microbiota results in neuropathological events in PD remains elusive. In this study, we explored whether and how environmental insults caused early neuropathological events in the substantia nigra (SN) of a PD mouse model. Aged (12-month-old) mice were orally administered rotenone (6.25 mg·kg-1·d-1) 5 days per week for 2 months. We demonstrated that oral administration of rotenone to ageing mice was sufficient to establish a PD mouse model and that microglial activation and iron deposition selectively appeared in the SN of the mice prior to loss of motor coordination and dopaminergic neurons, and these events could be fully blocked by microglial elimination with a PLX5622-formulated diet. 16 S rDNA sequencing analysis showed that the gut microbiota in rotenone-treated mice was altered, and mice receiving faecal microbial transplantation (FMT) from ageing mice treated with rotenone for 2 months exhibited the same pathology in the SN. We demonstrated that C-X-C motif chemokine ligand-1 (CXCL1) was an essential molecule, as intravenous injection of CXCL1 mimicked almost all the pathology in serum and SN induced by oral rotenone and FMT. Using metabolomics and transcriptomics analyses, we identified the PPAR pathway as a key pathway involved in rotenone-induced neuronal damage. Inhibition of the PPARγ pathway was consistent in the above models, whereas its activation by linoleic acid (60 mg·kg-1·d-1, i.g. for 1 week) could block these pathological events in mice intravenously injected with CXCL1. Altogether, these results reveal that the altered gut microbiota resulted in neuroinflammation and iron deposition occurring early in the SN of ageing mice with oral administration of rotenone, much earlier than motor symptoms and dopaminergic neuron loss. We found that CXCL1 plays a crucial role in this process, possibly via PPARγ signalling inhibition. This study may pave the way for understanding the "brain-gut-microbiota" molecular regulatory networks in PD pathogenesis. The aged C57BL/6 male mice with rotenone intragastric administration showed altered gut microbiota, which caused systemic inflammation, PPARγ signalling inhibition and neuroinflammation, brain iron deposition and ferroptosis, and eventually dopaminergic neurodegeneration in PD.

Research progress in the molecular mechanism of ferroptosis in Parkinson's disease and regulation by natural plant products

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder of the central nervous system after Alzheimer's disease. The current understanding of PD focuses mainly on the loss of dopamine neurons in the substantia nigra region of the midbrain, which is attributed to factors such as oxidative stress, alpha-synuclein aggregation, neuroinflammation, and mitochondrial dysfunction. These factors together contribute to the PD phenotype. Recent studies on PD pathology have introduced a new form of cell death known as ferroptosis. Pathological changes closely linked with ferroptosis have been seen in the brain tissues of PD patients, including alterations in iron metabolism, lipid peroxidation, and increased levels of reactive oxygen species. Preclinical research has demonstrated the neuroprotective qualities of certain iron chelators, antioxidants, Fer-1, and conditioners in Parkinson's disease. Natural plant products have shown significant potential in balancing ferroptosis-related factors and adjusting their expression levels. Therefore, it is vital to understand the mechanisms by which natural plant products inhibit ferroptosis and relieve PD symptoms. This review provides a comprehensive look at ferroptosis, its role in PD pathology, and the mechanisms underlying the therapeutic effects of natural plant products focused on ferroptosis. The insights from this review can serve as useful references for future research on novel ferroptosis inhibitors and lead compounds for PD treatment.

Dopaminergic neurodegeneration in the substantia nigra is associated with olfactory dysfunction in mice models of Parkinson's disease

Olfactory dysfunction represents a prodromal stage in Parkinson's disease (PD). However, the mechanisms underlying hyposmia are not specified yet. In this study, we first observed an early olfactory dysfunction in mice with intragastric rotenone administration, consistent with dopaminergic neurons loss and α-synuclein pathology in the olfactory bulb. However, a much severer olfactory dysfunction was observed without severer pathology in olfactory bulb when the loss of dopaminergic neurons in the substantia nigra occurred. Then, we established the mice models by intrastriatal α-synuclein preformed fibrils injection and demonstrated the performance in the olfactory discrimination test was correlated to the loss of dopaminergic neurons in the substantia nigra, without any changes in the olfactory bulb analyzed by RNA-sequence. In mice with intranasal ferric ammonium citrate administration, we observed olfactory dysfunction when dopaminergic neurodegeneration in substantia nigra occurred and was restored when dopaminergic neurons were rescued. Finally we demonstrated that chemogenetic inhibition of dopaminergic neurons in the substantia nigra was sufficient to cause hyposmia and motor incoordination. Taken together, this study shows a direct relationship between nigral dopaminergic neurodegeneration and olfactory dysfunction in PD models and put forward the understandings that olfactory dysfunction represents the early stage of neurodegeneration in PD progression.

Metabolic reprogramming and polarization of microglia in Parkinson's disease: Role of inflammasome and iron

Parkinson's disease (PD) is a slowly progressive neurodegenerative disease characterized by α-synuclein aggregation and dopaminergic neuronal death. Recent evidence suggests that neuroinflammation is an early event in the pathogenesis of PD. Microglia are resident immune cells in the central nervous system that can be activated into either pro-inflammatory M1 or anti-inflammatory M2 phenotypes as found in peripheral macrophages. To exert their immune functions, microglia respond to various stimuli, resulting in the flexible regulation of their metabolic pathways. Inflammasomes activation in microglia induces metabolic shift from oxidative phosphorylation to glycolysis, and leads to the polarization of microglia to pro-inflammatory M1 phenotype, finally causing neuroinflammation and neurodegeneration. In addition, iron accumulation induces microglia take an inflammatory and glycolytic phenotype. M2 phenotype microglia is more sensitive to ferroptosis, inhibition of which can attenuate neuroinflammation. Therefore, this review highlights the interplay between microglial polarization and metabolic reprogramming of microglia. Moreover, it will interpret how inflammasomes and iron regulate microglial metabolism and phenotypic shifts, which provides a promising therapeutic target to modulate neuroinflammation and neurodegeneration in PD and other neurodegenerative diseases.

Iron homeostasis imbalance and ferroptosis in brain diseases

Brain iron homeostasis is maintained through the normal function of blood-brain barrier and iron regulation at the systemic and cellular levels, which is fundamental to normal brain function. Excess iron can catalyze the generation of free radicals through Fenton reactions due to its dual redox state, thus causing oxidative stress. Numerous evidence has indicated brain diseases, especially stroke and neurodegenerative diseases, are closely related to the mechanism of iron homeostasis imbalance in the brain. For one thing, brain diseases promote brain iron accumulation. For another, iron accumulation amplifies damage to the nervous system and exacerbates patients' outcomes. In addition, iron accumulation triggers ferroptosis, a newly discovered iron-dependent type of programmed cell death, which is closely related to neurodegeneration and has received wide attention in recent years. In this context, we outline the mechanism of a normal brain iron metabolism and focus on the current mechanism of the iron homeostasis imbalance in stroke, Alzheimer's disease, and Parkinson's disease. Meanwhile, we also discuss the mechanism of ferroptosis and simultaneously enumerate the newly discovered drugs for iron chelators and ferroptosis inhibitors.

Single-dose intranasal administration of α-syn PFFs induce lewy neurite-like pathology in olfactory bulbs

INTRODUCTION

Pathological α-synuclein (α-Syn) propagation may cause Parkinson's disease progression. We aimed to verify whether single-dose intranasal administration of α-Syn preformed fibrils (PFFs) induces α-Syn pathology in the olfactory bulb (OB).

METHODS

A single dose of α-Syn PFFs was administered to the left nasal cavity of wild-type mice. The untreated right side served as a control. The α-Syn pathology of the OBs was examined up to 12 months after the injection.

RESULTS

Lewy neurite-like aggregates were observed in the OB 6 and 12 months after the treatment.

CONCLUSIONS

These findings suggest that pathological α-Syn can propagate from the olfactory mucosa to the OB and reveal the potential dangers of α-Syn PFFs inhalation.

Cell-Specific Dysregulation of Iron and Oxygen Homeostasis as a Novel Pathophysiology in PSP

OBJECTIVE

Progressive supranuclear palsy (PSP) is a 4R-tauopathy showing heterogeneous tau cytopathology commencing in the globus pallidus (GP) and the substantia nigra (SN), regions also associated with age-related iron accumulation. Abnormal iron levels have been extensively associated with tau pathology in neurodegenerative brains, however, its role in PSP pathogenesis remains yet unknown. We perform the first cell type-specific evaluation of PSP iron homeostasis and the closely related oxygen homeostasis, in relation to tau pathology in human postmortem PSP brains.

METHODS

In brain regions vulnerable to PSP pathology (GP, SN, and putamen), we visualized iron deposition in tau-affected and unaffected neurons, astroglia, oligodendrocytes, and microglia, using a combination of iron staining with immunolabelling. To further explore molecular pathways underlying our observations, we examined the expression of key iron and oxygen homeostasis mRNA transcripts and proteins.

RESULTS

We found astrocytes as the major cell type accumulating iron in the early affected regions of PSP, highly associated with cellular tau pathology. The same regions are affected by dysregulated expression of alpha and beta hemoglobin and neuroglobin showing contrasting patterns. We discovered changes in iron and oxygen homeostasis-related gene expression associated with aging of the brain, and identified dysregulated expression of rare neurodegeneration with brain iron accumulation (NBIA) genes associated with tau pathology to distinguish PSP from the healthy aging brain.

INTERPRETATION

We present novel aspects of PSP pathophysiology highlighting an overlap with NBIA pathways. Our findings reveal potential novel targets for therapy development and have implications beyond PSP for other iron-associated neurodegenerative diseases. ANN NEUROL 2023;93:431-445.

Signaling pathways in Parkinson's disease: molecular mechanisms and therapeutic interventions

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, and its treatment remains a big challenge. The pathogenesis of PD may be related to environmental and genetic factors, and exposure to toxins and gene mutations may be the beginning of brain lesions. The identified mechanisms of PD include α-synuclein aggregation, oxidative stress, ferroptosis, mitochondrial dysfunction, neuroinflammation, and gut dysbiosis. The interactions among these molecular mechanisms complicate the pathogenesis of PD and pose great challenges to drug development. At the same time, the diagnosis and detection of PD are also one of obstacles to the treatment of PD due to its long latency and complex mechanism. Most conventional therapeutic interventions for PD possess limited effects and have serious side effects, heightening the need to develop novel treatments for this disease. In this review, we systematically summarized the pathogenesis, especially the molecular mechanisms of PD, the classical research models, clinical diagnostic criteria, and the reported drug therapy strategies, as well as the newly reported drug candidates in clinical trials. We also shed light on the components derived from medicinal plants that are newly identified for their effects in PD treatment, with the expectation to provide the summary and outlook for developing the next generation of drugs and preparations for PD therapy.

The link between neuroinflammation and the neurovascular unit in synucleinopathies

The neurovascular unit (NVU) is composed of vascular cells, glial cells, and neurons. As a fundamental functional module in the central nervous system, the NVU maintains homeostasis in the microenvironment and the integrity of the blood-brain barrier. Disruption of the NVU and interactions among its components are involved in the pathophysiology of synucleinopathies, which are characterized by the pathological accumulation of α-synuclein. Neuroinflammation contributes to the pathophysiology of synucleinopathies, including Parkinson's disease, multiple system atrophy, and dementia with Lewy bodies. This review aims to summarize the neuroinflammatory response of glial cells and vascular cells in the NVU. We also review neuroinflammation in the context of the cross-talk between glial cells and vascular cells, between glial cells and pericytes, and between microglia and astroglia. Last, we discuss how α-synuclein affects neuroinflammation and how neuroinflammation influences the aggregation and spread of α-synuclein and analyze different properties of α-synuclein in synucleinopathies.

Intranasal Rotenone Induces Alpha-Synuclein Accumulation, Neuroinflammation and Dopaminergic Neurodegeneration in Middle-Aged Mice

Accumulation of alpha-synuclein (α-syn) is central to the pathogenesis of Parkinson's disease (PD). Previous studies suggest that α-syn pathology may originate from the olfactory bulb (OB) or gut in response to an unknown pathogen and later progress to the different brain regions. Aging is viewed as the utmost threat to PD development. Therefore, studies depicting the role of age in α-syn accumulation and its progression in PD are important. In the present study, we gave intranasal rotenone microemulsion for 6 weeks in 12-month-old female BALB/c mice and found olfactory dysfunction after 4 and 6 weeks of rotenone administration. Interestingly, motor impairment was observed only after 6 weeks. The animals were sacrificed after 6 weeks to perform western blotting and immunohistochemical studies to detect α-syn pathology, neuroinflammation and neurodegeneration. We found α-syn accumulation in OB, striatum, substantia nigra (SN) and cortex. Importantly, we found significant glial cell activation and neurodegeneration in all the analysed regions which were absent in our previous published studies with 3 months old mice even after they were exposed to rotenone for 9 weeks indicating age is a crucial factor for α-syn induced neuroinflammation and neurodegeneration. We also observed increased iron accumulation in SN of rotenone-exposed aged mice. Moreover, inflammaging was observed in OB and striatum of 12-month-old BALB/c mice as compared to 3-month-old BALB/c mice. In conclusion, there is a difference in sensitivity between adult and aged mice in the development and progression of α-syn pathology and subsequent neurodegeneration, for which inflammaging might be the crucial probable mechanism.

Pathogenesis of α-Synuclein in Parkinson's Disease: From a Neuron-Glia Crosstalk Perspective

Parkinson's disease (PD) is a progressive neurodegenerative disorder. The classical behavioral defects of PD patients involve motor symptoms such as bradykinesia, tremor, and rigidity, as well as non-motor symptoms such as anosmia, depression, and cognitive impairment. Pathologically, the progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) and the accumulation of α-synuclein (α-syn)-composed Lewy bodies (LBs) and Lewy neurites (LNs) are key hallmarks. Glia are more than mere bystanders that simply support neurons, they actively contribute to almost every aspect of neuronal development and function; glial dysregulation has been implicated in a series of neurodegenerative diseases including PD. Importantly, amounting evidence has added glial activation and neuroinflammation as new features of PD onset and progression. Thus, gaining a better understanding of glia, especially neuron-glia crosstalk, will not only provide insight into brain physiology events but also advance our knowledge of PD pathologies. This review addresses the current understanding of α-syn pathogenesis in PD, with a focus on neuron-glia crosstalk. Particularly, the transmission of α-syn between neurons and glia, α-syn-induced glial activation, and feedbacks of glial activation on DA neuron degeneration are thoroughly discussed. In addition, α-syn aggregation, iron deposition, and glial activation in regulating DA neuron ferroptosis in PD are covered. Lastly, we summarize the preclinical and clinical therapies, especially targeting glia, in PD treatments.

New Target for Prevention and Treatment of Neuroinflammation: Microglia Iron Accumulation and Ferroptosis

Microglia play an important role in maintaining central nervous system homeostasis and are the major immune cells in the brain. In response to internal or external inflammatory stimuli, microglia are activated and release numerous inflammatory factors, thus leading to neuroinflammation. Inflammation and microglia iron accumulation promote each other and jointly promote the progression of neuroinflammation. Inhibiting microglia iron accumulation prevents neuroinflammation. Ferroptosis is an iron-dependent phospholipid peroxidation-driven type of cell death regulation. Cell iron accumulation causes the peroxidation of cell membrane phospholipids and damages the cell membrane. Ultimately, this process leads to cell ferroptosis. Iron accumulation or phospholipid peroxidation in microglia releases a large number of inflammatory factors. Thus, inhibiting microglia ferroptosis may be a new target for the prevention and treatment of neuroinflammation.

Iron metabolism mediates microglia susceptibility in ferroptosis

Ferroptosis is implicated in a range of brain disorders, but it is unknown whether neurons or glia in the brain are particularly effected. Here, we report that primary cortical astrocytes (PA), microglia (PM), and neurons (PN) varied in their sensitivities to ferroptosis. Specifically, PM were the most sensitive to ferroptosis, while PN were relatively insensitive. In contrast, PN and PM were equally susceptible to apoptosis, with PA being less affected, whereas all three cell types were similarly susceptible to autophagic cell death. In the tri-culture system containing PA, PM, and PN, the cells were more resistant to ferroptosis than that in the monoculture. These results demonstrated that brain cells exhibit different sensitivities under ferroptosis stress and the difference may be explained by the differentially regulated iron metabolism and the ability to handle iron. Continued elucidation of the cell death patterns of neurons and glia will provide a theoretical basis for related strategies to inhibit the death of brain cells.

Iron reduces the propagation of pathological α-synuclein: An Editorial Highlight for "Brain iron enrichment attenuates α-synuclein spreading after injection of preformed fibrils" on page 554

Iron accumulation and α-synuclein aggregates (e.g., Lewy bodies) have been linked with the pathogenesis of Parkinson's disease (PD), with yet-to-be-determined interaction. Previous studies have indicated that iron binds to α-synuclein and triggers its aggregation in vitro, and iron is found enriched in Lewy bodies. In the current study, Joppe et al. have found that the propagation of pathological α-synuclein caused by intrastriatal α-synuclein preformed fibrils (PFFs) injection was unexpectedly attenuated in rodent brains in a model of brain iron elevation (neonatal iron feeding). PFFs stimulated microglial activation was also reduced in mice with elevated iron. These results may provide new insight into the complex interaction between these two key pathologies of PD.

Parkinson's Disease Dementia: Synergistic Effects of Alpha-Synuclein, Tau, Beta-Amyloid, and Iron

Parkinson’s disease dementia (PDD) is a common complication of Parkinson’s disease that seriously affects patients’ health and quality of life. At present, the process and pathological mechanisms of PDD remain controversial, which hinders the development of treatments. An increasing number of clinical studies have shown that alpha-synuclein (α-syn), tau, beta-amyloid (Aβ), and iron are closely associated with PDD severity. Thus, we inferred the vicious cycle that causes oxidative stress (OS), due to the synergistic effects of α-syn, tau, Aβ, and, iron, and which plays a pivotal role in the mechanism underlying PDD. First, iron-mediated reactive oxygen species (ROS) production can lead to neuronal protein accumulation (e.g., α-syn andAβ) and cytotoxicity. In addition, regulation of post-translational modification of α-syn by iron affects the aggregation or oligomer formation of α-syn. Iron promotes tau aggregation and neurofibrillary tangles (NFTs) formation. High levels of iron, α-syn, Aβ, tau, and NFTs can cause severe OS and neuroinflammation, which lead to cell death. Then, the increasing formation of α-syn, Aβ, and NFTs further increase iron levels, which promotes the spread of α-syn and Aβ in the central and peripheral nervous systems. Finally, iron-induced neurotoxicity promotes the activation of glycogen synthase kinase 3β (GSK3β) related pathways in the synaptic terminals, which in turn play an important role in the pathological synergistic effects of α-syn, tau and Aβ. Thus, as the central factor regulating this vicious cycle, GSK3β is a potential target for the prevention and treatment of PDD; this is worthy of future study.

A Review on Lactoferrin and Central Nervous System Diseases

Central nervous system (CNS) diseases are currently one of the major health issues around the world. Most CNS disorders are characterized by high oxidative stress levels and intense inflammatory responses in affected tissues. Lactoferrin (Lf), a multifunctional iron-binding glycoprotein, plays a significant role in anti-inflammatory, antibacterial, antiviral, reactive oxygen species (ROS) modulator, antitumor immunity, and anti-apoptotic processes. Previous studies have shown that Lf is abnormally expressed in a variety of neurological diseases, especially neurodegenerative diseases. Recently, the promotion of neurodevelopment and neuroprotection by Lf has attracted widespread attention, and Lf could be exploited both as an active therapeutic agent and drug nanocarrier. However, our understanding of the roles of Lf proteins in the initiation or progression of CNS diseases is limited, especially the roles of Lf in regulating neurogenesis. This review highlights recent advances in the understanding of the major pharmacological effects of Lf in CNS diseases, including neurodegenerative diseases, cerebrovascular disease, developmental delays in children, and brain tumors.

Senescent Microglia: The Key to the Ageing Brain?

Ageing represents the single biggest risk factor for development of neurodegenerative disease. Despite being such long-lived cells, microglia have been relatively understudied for their role in the ageing process. Reliably identifying aged microglia has proven challenging, not least due to the diversity of cell populations, and the limitations of available models, further complicated by differences between human and rodent cells. Consequently, the literature contains multiple descriptions and categorisations of microglia with neurotoxic phenotypes, including senescence, without any unifying markers. The role of microglia in brain homeostasis, particularly iron storage and metabolism, may provide a key to reliable identification.

A New Rise of Non-Human Primate Models of Synucleinopathies

Synucleinopathies are neurodegenerative diseases characterized by the presence of α-synuclein-positive intracytoplasmic inclusions in the central nervous system. Multiple experimental models have been extensively used to understand better the mechanisms involved in the pathogenesis of synucleinopathy. Non-human primate (NHP) models are of interest in neurodegenerative diseases as they constitute the highest relevant preclinical model in translational research. They also contribute to bringing new insights into synucleinopathy’s pathogenicity and help in the quest and validation of therapeutical strategies. Here, we reviewed the different NHP models that have recapitulated key characteristics of synucleinopathy, and we aimed to highlight the contribution of NHP in mechanistic and translational approaches for synucleinopathies.