Aggregated alpha-synuclein activates microglia: a process leading to disease progression in Parkinson's disease

Phytochemicals in Parkinson's Disease: a Pathway to Neuroprotection and Personalized Medicine

Parkinson's disease (PD) is a complex neurodegenerative disorder marked by the progressive loss of dopaminergic neurons in the substantia nigra. While current treatments primarily manage symptoms, there is increasing interest in alternative approaches, particularly the use of phytochemicals from medicinal plants. These natural compounds have demonstrated promising neuroprotective potential in preclinical studies by targeting key pathological mechanisms such as oxidative stress, neuroinflammation, and protein aggregation. However, the clinical translation of these phytochemicals is limited due to a lack of robust clinical trials evaluating their safety, efficacy, and pharmacokinetics. This review provides a comprehensive overview of the neuroprotective potential of phytochemicals in PD management, examining the mechanisms underlying PD pathogenesis and emphasizing neuroprotection. It explores the historical and current research on medicinal plants like Mucuna pruriens, Curcuma longa, and Ginkgo biloba, and discusses the challenges in clinical translation, including ethical and practical considerations and the integration with conventional therapies. It further underscores the need for future research to elucidate mechanisms of action, optimize drug delivery, and conduct rigorous clinical trials to establish the safety and efficacy of phytochemicals, aiming to shape future neuroprotective strategies and develop more effective, personalized treatments for PD.

Microglial dynamics and neuroinflammation in prodromal and early Parkinson's disease

Parkinson's disease (PD) is characterized by a drastic loss of dopaminergic neurons already at diagnosis. As this loss of neurons starts decades before diagnosis, understanding the prodromal stages of the disease might offer novel strategies to curb its progression. While the precise pathogenic mechanisms underlying PD remain incompletely understood, growing evidence suggests that neuroinflammation and immune dysregulation play a central role in the development and progression of the disease. Here, we delve into the emerging roles of microglia, the resident immune cells of the central nervous system, in the pathogenesis of prodromal and early-stage PD. We emphasize that microglia contribute to neuroinflammation, protein aggregation and neurodegeneration, although the underlying mechanisms are not yet known. Neuroimaging studies have provided valuable insights into the patterns of microglial activation detected in individuals with prodromal PD and at the time of clinical diagnosis. Furthermore, we highlight the complex interplay between immune dysregulation and neurodegeneration along PD development, including alterations in the peripheral immune system, brain-gut interactions and brain-immune interfaces. Lastly, we outline existing models for investigating microglial involvement in prodromal PD, along with the impact of anti-inflammatory therapies and strategies to modify risk factors. In conclusion, targeting microglial activation and immune dysfunctions in individuals at risk of PD could represent a promising preventive measure and may offer novel therapeutic strategies for early intervention and disease modification.

TREM2 deficiency exacerbates cognitive impairment by aggravating α-Synuclein-induced lysosomal dysfunction in Parkinson's disease

Cognitive impairment in Parkinson's disease (PD) is a widespread and rapidly progressive feature that impacts prognosis. Although TREM2 has been implicated in neuroprotection across various neurodegenerative diseases, its specific role in PD remains to be clarified. In this study, we first detected the hippocampus of human PD specimens and of the mutant A53T α-Synuclein transgenic mice (A53T mice), and found a significant increase in the number of TREM2+ microglia. To evaluate the effects of TREM2 deficiency, TREM2-deficient A53T mice (TREM2-/-/A53T mice) were generated. In these mice, exacerbated cognitive impairment, neurodegeneration, disruption of synaptic plasticity, and accumulation of pathological α-Synuclein (α-Syn) in the hippocampus were observed, without any detected motor dysfunction. Despite increased infiltration of activated microglia surrounding α-Syn aggregates, lysosomal dysfunction in microglia was aggravated in the TREM2-/-/A53T mice. In addition, transcriptional analyses and in vitro experiments further found that TREM2 knockdown inhibited the nuclear distribution of TFEB via the ERK1/2 pathway, exacerbating α-Syn-induced lysosomal dysfunction and causing more pathological α-Syn accumulation. Finally, HT22 cells were cocultured with TREM2 knockdown of BV-2 cells pretreated with recombinant human A53T α-Syn preformed fibrils (PFFs). The coculture experiments showed that TREM2 knockdown in BV-2 cells pretreated with PFFs enhanced the phosphorylation of α-Syn and promoted apoptosis in HT22 cells via inhibiting α-Syn degradation. In conclusion, TREM2 deficiency exacerbates cognitive impairment in PD by exacerbating α-Syn-induced microglial lysosomal dysfunction, identifying TREM2 as a potential therapeutic target.

Exploring α-Syn's Functions Through Ablation Models: Physiological and Pathological Implications

A significant advancement in neurodegenerative research was the discovery that α-synuclein (α-Syn/SNCA) plays a part in the pathophysiology of Parkinson's disease (PD). Decades later, the protein's significant impacts on various brain disorders are still being extensively explored. In disease conditions, α-Syn misfolds and forms abnormal aggregates that accumulate in neurons, thus triggering various organellar dysfunctions and ultimately neurodegeneration. These misfolded forms are highly heterogeneous and vary significantly among different synucleinopathies, such as PD, Multiple System Atrophy, or Dementia with Lewy bodies. Though initially believed to be exclusively localized in the brain, numerous pieces of evidence suggest that α-Syn functions transcend the central nervous system, with roles in peripheral functions, such as modulation of immune responses, hematopoiesis, and gastrointestinal regulation. Here, we aim to provide a detailed compilation of cellular functions and pathological phenotypes that are altered upon attenuation of α-Syn function in vitro and in vivo and explore the effects of SNCA gene silencing in healthy and disease states using cellular and animal models.

Mechanistic insights into Alpha-Synuclein binding to P2RX7: A molecular dynamic and docking study

Alpha-synucleinopathies, characterized by extracellular alpha-synuclein (αSyn or SNCA) accumulation and aggregation, have been linked to neurological disorders including Parkinson's disease and multiple system atrophy. P2RX7 is a non-selective cationic transmembrane purinergic receptor activated by elevated levels of extracellular ATP, which typically occurs during inflammatory conditions. Activation of P2RX7 by αSyn is implicated in neuronal degeneration, potentially causing pore dilation and increased inflammation. By integrating the data curation, molecular docking, and molecular dynamics (MD) simulations, along with structural analyses, we attempted to elucidate the molecular mechanisms and binding sites for P2RX7-αSyn interaction. We elucidated interactions between P2RX7 and the N-terminal domain (NTD) of αSyn. Utilizing cryo-EM structures of P2RX7 in ATP-bound and unbound states, we assessed αSyn's effect on P2RX7 structural and functional dynamics. Initially, the analyses revealed that αSyn interactomes are mainly involved in mitochondrial functions, while P2RX7 interactors are linked to receptor internalization and calcium transport. Molecular docking with six tools identified that αSyn-NTD fragments preferentially bind to the proximal region of P2RX7's transmembrane domain. Microsecond all atom MD simulations in a POPS lipid bilayer showed significant atomic fluctuations, particularly in the head region, lower body, and large loop of P2RX7's cytoplasmic domain. Secondary structure analysis indicated unfolding in regions related to pore dilation and receptor desensitization. Further by contact-based and solvent accessibility analyses, along with protein structure network (PSN) studies, we identified crucial residues involved in αSyn-P2RX7 interactions. This understanding enhances the knowledge of how αSyn and P2RX7 interactions take place, potentially contributing to neurodegenerative diseases, and could be instrumental in developing future preventive and therapeutic approaches.

α-Synuclein condensation in synaptic vesicle function and synucleinopathies

Research into the crosstalk between α-synuclein (α-syn) and synaptic vesicles (SVs) has gained considerable attention. Notably, the recently discovered liquid-liquid phase separation of α-syn involving SVs is crucial for performing their physiological functions and mediating the transition to pathological aggregates. This review first examines the functional interactions between α-syn and SVs in the context of α-syn's condensation state. It then explores how these interactions become disrupted under pathological conditions, leading to α-syn aggregation and subsequent synaptic dysfunction. Finally, the review discusses the therapeutic potential of targeting α-syn-SV interactions to restore synaptic function in diseased states. By connecting α-syn's physiological roles with its pathological effects, the article aims to shed light on its dual role as both a regulator of SVs and a driver of neurodegeneration.

IC100 blocks inflammasome activation induced by α-synuclein aggregates and ASC specks

Parkinson's disease (PD) is associated with chronic sterile inflammation and persistent inflammasome activation involving α-synuclein and ASC protein aggregates, but the underlying mechanisms of the neuroinflammatory response remain unclear. Here, we used midbrain postmortem samples from donors with and without α-synucleinopathies to assess the expression of inflammasome proteins in patients with Parkinsonism. We show that dopaminergic neurons exhibit increased expression of ASC, NOD-like receptor protein (NLRP) 1, and modification of α-synuclein phosphorylation at serine129 (pS129) within the Lewy body inclusions, whereas NLRP3 was identified mainly in microglial. Moreover, treatment of LRRK2 cells with ASC specks from PD and Lewy body dementia patients induced inflammasome activation and cytotoxicity that was blocked by IC100. Administration of preformed α-synuclein aggregates to microglia resulted in a significant elevation in pS129, and this effect was also blocked by IC100. Thus, IC100 may be a promising therapeutic strategy for inflammatory disease modification in synucleinopathies and other diseases.

Biomimetic Nanoparticles Enhance Recovery of Movement Disorders in Parkinson's Disease by Improving Microglial Mitochondrial Homeostasis and Suppressing Neuroinflammation

Neuroinflammation is a key risk factor for cognitive impairment, and microglia are the main drivers. Metformin has been shown to suppress inflammation and reduce microglial activation, protecting neurons from damage. However, its clinical efficacy is limited by low bioavailability and metabolic challenges, especially in terms of precise delivery to specific targets. To overcome this problem, we developed biomimetic microglial nanoparticles (MePN@BM) to enhance the targeted delivery and bioavailability of metformin. Through homologous targeting, the delivery efficiency of drugs in the inflammatory site of Parkinson's disease was enhanced to improve the therapeutic effect. The results showed that MePN@BM effectively delivers metformin to the brain, promotes autophagy, restores mitochondrial membrane potential, and reduces oxidative stress. In a Parkinson's disease (PD) mouse model, MePN@BM improved motor function, repaired dopaminergic neurons, and cleared α-synuclein aggregates. Notably, transcriptome analysis revealed enriched inflammation-related pathways, and immunofluorescence showed that PD mice treated with MePN@BM had higher levels of anti-inflammatory factors and lower levels of pro-inflammatory factors. Therefore, it provides a promising strategy for the treatment of inflammation-mediated motor dysfunction.

MHCII reduction is insufficient to protect mice from alpha-synuclein-induced degeneration and the Parkinson's HLA locus exhibits epigenetic regulation

Major histocompatibility complex class II (MHCII) molecules are antigen presentation proteins and increased in post-mortem Parkinson's disease (PD) brain. Attempts to decrease MHCII expression have led to neuroprotection in PD mouse models. Our group reported that a single nucleotide polymorphism (SNP) at rs3129882 in the MHCII gene Human Leukocyte Antigen (HLA) DRA is associated with increased MHCII transcripts and surface protein and increased risk for late-onset idiopathic PD. We therefore hypothesized that decreased MHCII may mitigate dopaminergic degeneration. During an ongoing α-synuclein lesion, mice with MHCII reduction in systemic and brain innate immune cells (LysMCre + I-Abfl/fl or CRE+) displayed brain T cell repertoire shifts and greater preservation of the dopaminergic phenotype in nigrostriatal terminals. Next, we investigated a human cohort to characterize the immunophenotype of subjects with and without the high-risk GG genotype at the rs3129882 SNP. We confirmed that the high-risk GG genotype is associated with peripheral changes in MHCII inducibility, frequency of CD4 + T cells, and differentially accessible chromatin regions within the MHCII locus. Although our mouse studies indicate that myeloid MHCII reduction coinciding with an intact adaptive immune system is insufficient to fully protect dopamine neurons from α-synuclein-induced degeneration, our data are consistent with the overwhelming evidence implicating antigen presentation in PD pathophysiology.

Immunomodulatory effects of invasive and non-invasive brain stimulation in Parkinson's disease

Accumulating evidence points to a critical role of the immune system in the neurodegenerative process in Parkinson's disease (PD). This late knowledge has revolutionised our understanding of the pathogenetic mechanisms underlying PD and has opened new avenues toward disease-modifying rather than dopamine-replacement therapeutic approaches. When pharmacological treatments fail to adequately alleviate clinical symptoms, brain stimulation techniques are taken into consideration. Deep brain stimulation (DBS) constitutes the most common method for invasive brain stimulation, while the non-invasive brain stimulation paradigms comprise among others repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS). How each brain stimulation paradigm interferes with disease pathogenesis still remains elusive. In light of recent evidence supporting the involvement of the immune system in PD, a question that arises is whether brain stimulation techniques have an immunomodulatory potential. Here, we summarize the existing knowledge and provide mechanistic insights that should foster future research. Overall, it appears that DBS and rTMS can modulate both the central and the peripheral component of the immune system and can lead to clinical improvement through immunosuppressive/anti-inflammatory mechanisms. The paucity of evidence for tDCS and tACS precludes any conclusions and highlights the necessity of more mechanistic studies focusing on their immunomodulatory potential, if any. Any pre-clinical findings warrant further clinical validation using human in vivo markers and post-mortem human brain tissue. Unravelling the mechanisms that underpin the beneficial therapeutic effects of brain stimulation in PD patients can contribute substantially to the fine-tuning of the current stimulation protocols and pave the way for more efficient and clinically meaningful neuromodulation paradigms.

The A53T Mutation in α-Synuclein Enhances Proinflammatory Activation in Human Microglia Upon Inflammatory Stimulus

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease, following Alzheimer's. It is characterized by the aggregation of α-synuclein into Lewy bodies and Lewy neurites in the brain. Microglia-driven neuroinflammation may contribute to neuronal death in PD; however, the exact role of microglia remains unclear and has been understudied. The A53T mutation in the gene coding for α-synuclein has been linked to early-onset PD, and exposure to A53T mutant human α-synuclein increases the potential for inflammation of murine microglia. To date, its effect has not been studied in human microglia.

METHODS

Here, we used 2-dimensional cultures of human pluripotent stem cell-derived microglia and transplantation of these cells into the mouse brain to assess the cell autonomous effects of the A53T mutation on human microglia.

RESULTS

We found that A53T mutant human microglia had an intrinsically increased propensity toward proinflammatory activation upon inflammatory stimulus. Additionally, transplanted A53T mutant microglia showed a strong decrease in catalase expression in noninflammatory conditions and increased oxidative stress.

CONCLUSIONS

Our results indicate that A53T mutant human microglia display cell autonomous phenotypes that may worsen neuronal damage in early-onset PD.

Immune cell metabolic dysfunction in Parkinson's disease

Parkinson's disease (PD) is a multi-system disorder characterized histopathologically by degeneration of dopaminergic neurons in the substantia nigra pars compacta. While the etiology of PD remains multifactorial and complex, growing evidence suggests that cellular metabolic dysfunction is a critical driver of neuronal death. Defects in cellular metabolism related to energy production, oxidative stress, metabolic organelle health, and protein homeostasis have been reported in both neurons and immune cells in PD. We propose that these factors act synergistically in immune cells to drive aberrant inflammation in both the CNS and the periphery in PD, contributing to a hostile inflammatory environment which renders certain subsets of neurons vulnerable to degeneration. This review highlights the overlap between established neuronal metabolic deficits in PD with emerging findings in central and peripheral immune cells. By discussing the rapidly expanding literature on immunometabolic dysfunction in PD, we aim to draw attention to potential biomarkers and facilitate future development of immunomodulatory strategies to prevent or delay the progression of PD.

Tissue macrophages: origin, heterogenity, biological functions, diseases and therapeutic targets

Macrophages are immune cells belonging to the mononuclear phagocyte system. They play crucial roles in immune defense, surveillance, and homeostasis. This review systematically discusses the types of hematopoietic progenitors that give rise to macrophages, including primitive hematopoietic progenitors, erythro-myeloid progenitors, and hematopoietic stem cells. These progenitors have distinct genetic backgrounds and developmental processes. Accordingly, macrophages exhibit complex and diverse functions in the body, including phagocytosis and clearance of cellular debris, antigen presentation, and immune response, regulation of inflammation and cytokine production, tissue remodeling and repair, and multi-level regulatory signaling pathways/crosstalk involved in homeostasis and physiology. Besides, tumor-associated macrophages are a key component of the TME, exhibiting both anti-tumor and pro-tumor properties. Furthermore, the functional status of macrophages is closely linked to the development of various diseases, including cancer, autoimmune disorders, cardiovascular disease, neurodegenerative diseases, metabolic conditions, and trauma. Targeting macrophages has emerged as a promising therapeutic strategy in these contexts. Clinical trials of macrophage-based targeted drugs, macrophage-based immunotherapies, and nanoparticle-based therapy were comprehensively summarized. Potential challenges and future directions in targeting macrophages have also been discussed. Overall, our review highlights the significance of this versatile immune cell in human health and disease, which is expected to inform future research and clinical practice.

Transcranial magneto-acoustic stimulation enhances motor function and modulates cortical excitability of motor cortex in a Parkinson's disease mouse model

Parkinson's disease (PD) is a neurodegenerative disorder characterized primarily by motor dysfunction. Transcranial magneto-acoustic stimulation (TMAS), an emerging non-invasive brain neuromodulation technology, is increasingly being applied in the treatment of brain diseases. However, the effects of TMAS on PD are unknown, which is not well studied. Here, we utilized TMAS on PD model mice induced by MPTP to investigate the underlying mechanism of therapy. Our study found that TMAS improved the behavioral performance of PD model mice, enhancing the motor function and motivation for movement. Besides, it inhibited the increased beta oscillations in the motor cortex, while also reducing gamma oscillations. Moreover, the abnormally exaggerated beta-broad gamma phase amplitude coupling (PAC) was decreased after TMAS, and there was a significant negative correlation between PAC and both distance traveled and mean speed during the open filed test. Additionally, the ongoing stimulation could provide neuroprotection, implying that TMAS could ameliorate the loss of dopaminergic neurons, with no damage observed in the brain tissue of mice. Our findings suggest that TMAS could provide a non-invasive tool for the treatment of Parkinson's disease and beta-broad gamma phase amplitude coupling could be employed as a biomarker for PD.

MHCII reduction is insufficient to protect mice from alpha-synuclein-induced degeneration and the Parkinson's HLA locus exhibits epigenetic regulation

Major histocompatibility complex class II (MHCII) molecules are antigen presentation proteins and increased in post-mortem Parkinson's disease (PD) brain. Attempts to decrease MHCII expression have led to neuroprotection in PD mouse models. Our group reported that a SNP at rs3129882 in the MHCII gene Human leukocyte Antigen (HLA) DRA is associated with increased MHCII transcripts and surface protein and increased risk for late-onset idiopathic PD. We therefore hypothesized that decreased MHCII may mitigate dopaminergic degeneration. During an ongoing α-synuclein lesion, mice with MHCII reduction in systemic and brain innate immune cells (LysMCre+I-Abfl/fl or CRE+) displayed brain T cell repertoire shifts and greater preservation of the dopaminergic phenotype in nigrostriatal terminals. Next, we investigated a human cohort to characterize the immunophenotype of subjects with and without the high-risk GG genotype at the rs3129882 SNP. We confirmed that the high-risk GG genotype is associated with peripheral changes in MHCII inducibility, frequency of CD4+ T cells, and differentially accessible chromatin regions within the MHCII locus. Although our mouse studies indicate that myeloid MHCII reduction coinciding with an intact adaptive immune system is insufficient to fully protect dopamine neurons from α-synuclein-induced degeneration, our data are consistent with the overwhelming evidence implicating antigen presentation in PD pathophysiology.

Fasudil inhibits α-synuclein aggregation through ROCK-inhibition-mediated mechanisms

ROCK inhibitors such as fasudil protected against dopaminergic degeneration and other neurodegenerative processes in several experimental models through inhibition of neuroinflammation and activation of survival signaling pathways, and clinical trials have been initiated. More recently, fasudil has been suggested to inhibit α-synuclein aggregation. However, this is controversial, particularly if it is a consequence of direct binding of the fasudil molecule to α-synuclein. We studied the mechanisms involved in the effects of fasudil on α-synuclein aggregation using the α-synuclein-T/V5-synphilin-1 model. Molecule-molecule interactions were studied using real time quaking inducing conversion (RT-QuiC). Fasudil decreased the number of cells with inclusions and the size of inclusions in dopaminergic neurons and glial cells, and inhibited α-synuclein aggregation and microglial endocytosis of aggregates. These changes were not due to changes in α-synuclein protein expression or phosphorylation and were related to ROCK inhibition rather than direct interaction with α-synuclein, as confirmed with a second ROCK inhibitor (Y27632) and ROCK gene silencing. We observed that ROCK inhibition downregulates several factors that are known to promote α-synuclein aggregation such as NADPH-oxidase-derived oxidative stress, intracellular calcium increase, and α-synuclein endocytosis, and promotes autophagy. The present results support that fasudil is a useful drug against Parkinson's disease progression. In addition to other reported neuroprotective properties, fasudil inhibits α-synuclein aggregation and microglial endocytosis of aggregates, which enhances the microglial inflammatory response. The effects of fasudil are mostly related to ROCK inhibition, which we have shown using two structurally different ROCK inhibitors and knockdown data, and further supported by using RT-QuiC.

The 5-HT1F Receptor Agonist Lasmiditan improves Cognition and Ameliorates Associated Cortico-Hippocampal Pathology in Aging Parkinsonian Mice

While the etiopathology of Parkinson's disease (PD) is complex, mitochondrial dysfunction is established to have a central role. Thus, mitochondria have emerged as targets of therapeutic interventions aiming to slow or modify PD progression. We have previously identified serotonergic 5-HT1F receptors as novel mediators of mitochondrial biogenesis (MB) - the process of producing new mitochondria. Given this, here, we assessed the therapeutic potential of the FDA-approved 5-HT1F receptor agonist, lasmiditan, in a chronic progressive PD model (Thy1-aSyn 'line 61' mice). It was observed that systemic lasmiditan exhibited robust brain penetration and reversed cognitive deficits in young (4-5.5 months old) Thy1-aSyn mice (1mg/kg, every other day). Anxiety-like behavior was also improved while motor function remained unaffected. These behavioral changes were associated with enhanced MB and mitochondrial function, paired with reduced alpha-synuclein aggregation particularly in cortico-hippocampal regions. Furthermore, in older (10-11.5 months old) mice, although the effects were milder, daily lasmiditan administration increased MB and bettered cognitive abilities. In essence, these findings indicate that repurposing lasmiditan could be a potent strategy to address PD-related cognitive decline.

Intra-tumoral hemorrhage after endoscopic third ventriculostomy in a child with WNT-activated medulloblastoma: case report and literature review

Intratumoral hemorrhage is a known complication of cerebrospinal fluid (CSF) drainage surgeries, such as ventriculoperitoneal shunts or external ventricular drainage, which are usually associated with upward herniation of the posterior fossa contents. In contrast, this is extremely rare after an endoscopic third ventriculostomy (ETV). This technique should drain the CSF in a more physiological way by limiting the pressure gradient between the infratentorial and supratentorial compartments, thus avoiding upward herniation of the tumor and intratumoral hemorrhage. Only three cases of intratumoral hemorrhage after ETV have been reported in the literature. Here, we describe a 9-year-old boy affected by hydrocephalus secondary to a large posterior fossa tumor who presented intratumoral hemorrhage after ETV. He required urgent hematoma evacuation and tumor removal. Histological and molecular diagnosis was WNT-activated medulloblastoma, a tumor associated with an increased risk of hemorrhage.

Mapping of catecholaminergic denervation, neurodegeneration, and inflammation in 6-OHDA-treated Parkinson's disease mice

Efforts to develop disease-modifying treatments for Parkinson's disease (PD) have been hindered by the lack of animal models replicating all hallmarks of PD and the insufficient attention to extra-nigrostriatal regions pathologically critical for the prodromal appearance of non-motor symptoms. Among PD models, 6-hydroxydopamine (6-OHDA) infusion in mice has gained prominence since 2012, primarily focusing on the nigrostriatal region. This study characterized tyrosine hydroxylase-positive neuron and fiber loss across the brain following a unilateral 6-OHDA (20 µg) infusion into the dorsal striatum. Our analysis integrates immunolabeling, brain clearing (iDISCO+), light sheet microscopy, and computational methods, including fMRI and machine learning tools. We also examined sex differences, disease progression, neuroinflammatory responses, and pro-apoptotic signaling in nigrostriatal regions of C57BL/6 mice exposed to varying 6-OHDA dosages (5, 10, or 20 µg) followed by 1, 7, and 14 days of recovery. This comprehensive, spatiotemporal analysis of 6-OHDA-induced pathology was used to map the time course of neuronal degeneration and the onset of neuroinflammation.

Exploring the therapeutic potential of Chinese herbs on comorbid type 2 diabetes mellitus and Parkinson's disease: A mechanistic study

ETHNOPHARMACOLOGICAL RELEVANCE

Type 2 diabetes mellitus (T2DM) and Parkinson's disease (PD) are chronic conditions that affect the aging population, with increasing prevalence globally. The rising prevalence of comorbidity between these conditions, driven by demographic shifts, severely impacts the quality of life of patients, posing a significant burden on healthcare resources. Chinese herbal medicine has been used to treat T2DM and PD for millennia. Pharmacological studies have demonstrated that medicinal herbs effectively lower blood glucose levels and exert neuroprotective effects, suggesting their potential as adjunctive therapy for concurrent management of T2DM and PD.

AIM OF THE STUDY

To elucidate the shared mechanisms underlying T2DM and PD, particularly focusing on the potential mechanisms by which medicinal herbs (including herbal formulas, single herbs, and active compounds) may treat these diseases, to provide valuable insights for developing therapeutics targeting comorbid T2DM and PD.

MATERIALS AND METHODS

Studies exploring the mechanisms underlying T2DM and PD, as well as the treatment of these conditions with medicinal herbs, were extracted from several electronic databases, including PubMed, Web of Science, Google Scholar, and China National Knowledge Infrastructure (CNKI).

RESULTS

Numerous studies have shown that inflammation, oxidative stress, insulin resistance, impaired autophagy, gut microbiota dysbiosis, and ferroptosis are shared mechanisms underlying T2DM and PD mediated through the NLRP3 inflammasome, NF-κB, MAPK, Keap1/Nrf2/ARE, PI3K/AKT, AMPK/SIRT1, and System XC--GSH-GPX4 signaling pathways. Thirty-four medicinal herbs, including 2 herbal formulas, 4 single herbs, and 28 active compounds, have been reported to potentially exert anti-T2DM and anti-PD effects by targeting these shared mechanisms.

CONCLUSIONS

Traditional Chinese medicine effectively combats T2DM and PD through shared pathological mechanisms, highlighting their potential for application in treating these comorbid conditions.

Innate and adaptive immunity in neurodegenerative disease

Neurodegenerative diseases (NDs) are a group of neurological disorders characterized by the progressive loss of selected neurons. Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common NDs. Pathologically, NDs are characterized by progressive failure of neural interactions and aberrant protein fibril aggregation and deposition, which lead to neuron loss and cognitive and behavioral impairments. Great efforts have been made to delineate the underlying mechanism of NDs. However, the very first trigger of these disorders and the state of the illness are still vague. Existing therapeutic strategies can relieve symptoms but cannot cure these diseases. The human immune system is a complex and intricate network comprising various components that work together to protect the body against pathogens and maintain overall health. They can be broadly divided into two main types: innate immunity, the first line of defense against pathogens, which acts nonspecifically, and adaptive immunity, which follows a defense process that acts more specifically and is targeted. The significance of brain immunity in maintaining the homeostatic environment of the brain, and its direct implications in NDs, has increasingly come into focus. Some components of the immune system have beneficial regulatory effects, whereas others may have detrimental effects on neurons. The intricate interplay and underlying mechanisms remain an area of active research. This review focuses on the effects of both innate and adaptive immunity on AD and PD, offering a comprehensive understanding of the initiation and regulation of brain immunity, as well as the interplay between innate and adaptive immunity in influencing the progression of NDs.

Microglia Process α-Synuclein Fibrils and Enhance their Pathogenicity in a TREM2-Dependent Manner

Parkinson's disease (PD) is characterized by the deposition of misfolded α-synuclein (α-syn) in the brain. Converging evidence indicates that the intracellular transmission and subsequent templated amplification of α-syn are involved in the onset and progression of PD. However, the molecular mechanisms underlying the cell-to-cell transmission of pathological α-syn remain poorly understood. Microglia is highly activated in the brains of PD patients. Here, it is shown that depletion of microglia slows the spread of pathological α-syn pathology in mice injected with α-syn fibrils. Microglia phagocytose α-syn fibrils and transform them into more toxic species. The phagocytosis of α-syn fibrils by microglia is partially mediated by triggering a receptor expressed on myeloid cells 2 (TREM2), a transmembrane protein expressed on the surface of microglia. The endocytosed α-syn fibrils are then cleaved by the lysosomal proteinase asparagine endopeptidase (AEP) to generate truncated α-syn 1-103 fibrils with enhanced seeding activity. Knockout of TREM2 and AEP impedes the endocytosis and cleavage of α-syn fibrils, respectively. The results demonstrate that TREM2-mediated phagocytosis of α-syn fibrils by microglia and subsequent AEP-mediated cleavage of α-syn fibrils contribute to the spread of α-syn in the brain. Blocking either of these two steps attenuates the progression of α-syn pathology.

Crosstalk between SIRT1/Nrf2 signaling and NLRP3 inflammasome/pyroptosis as a mechanistic approach for the neuroprotective effect of linagliptin in Parkinson's disease

In recent years, special attention has been paid to highlighting the antiparkinsonian effect of linagliptin. However, the mechanism of its action has not yet been well investigated. The present study aimed to verify the neuroprotective effect of linagliptin in the rotenone model of Parkinson's disease (PD) and further explore its potential molecular mechanisms. Rats were intoxicated with rotenone (2 mg/kg/day; sc) and treated with linagliptin (10  mg/kg/day; po) for 14 consecutive days. The present finding showed that linagliptin ameliorated the histopathological changes of rotenone on substantia nigra and striata. Linagliptin decreased α-synuclein immunoreactivity along with an increase in tyrosine hydroxylase immunoreactivity and striatal dopamine content. This was reflected in the marked improvement of the behavior and motor deficits in rotenone-intoxicated rats. On the molecular level, linagliptin upregulated sirtuin 1 (SIRT1)/ nuclear factor erythroid 2-related factor 2 (Nrf2) signaling, reduced ionized calcium-binding adaptor molecule 1 (Iba1) protein expression, restored glutathione (GSH) content, and elevated heme oxygenase-1 (HO-1) level in rats with rotenone intoxication. Moreover, linagliptin inhibited NOD-like receptor protein 3 (NLRP3)/caspase-1/interleukin-1β (IL-1β) cascade with subsequent reduction in gasdermin D (GSDMD) expression. Therefore, the present study reveals the ability of linagliptin, through the activation of SIRT1/Nrf2 signaling, to suppress NLRP3 inflammasome-mediated pyroptosis and protect against rotenone-induced parkinsonism.

Human Microglia-Like Cells Differentiated from Monocytes with GM-CSF and IL-34 Show Phagocytosis of α-Synuclein Aggregates and C/EBPβ-Dependent Proinflammatory Activation

Microglia, the main resident immune cells in the central nervous system, are implicated in the pathogenesis of various neurological disorders. Much of our knowledge on microglial biology was obtained using rodent microglial cultures. To understand the role of microglia in human disease, reliable in vitro models of human microglia are necessary. Monocyte-derived microglia-like cells (MDMi) are a promising approach. This study aimed to characterize MDMi cells generated from adult human monocytes using granulocyte-macrophage colony-stimulating factor and interleukin-34. To this end, 49 independent cultures of MDMI were prepared, and various methodological and functional studies were performed. We show that with this protocol, adult human monocytes develop into microglia-like cells, a coating is unnecessary, and high cell density seeding is preferable. When compared to monocytes, MDMi upregulate the expression of many, but not all, microglial markers, indicating that, although these cells display a microglia-like phenotype, they cannot be considered bona fide human microglia. At the functional level, MDMi phagocytose α-synuclein aggregates and responds to lipopolysaccharide (LPS) by nuclear translocation of the transcription factor nuclear factor-kappaB (NFkappaB) and the upregulation of proinflammatory genes. Finally, a long-lasting silencing of the transcription factor CCAAT/enhancer protein β (C/EBPβ) was achieved by small interfering RNA, resulting in the subsequent downregulation of proinflammatory genes. This supports the hypothesis that C/EBPβ plays a key role in proinflammatory gene program activation in human microglia. Altogether, this study sheds new light on the properties of MDMi cells and supports these cells as a promising in vitro model for studying adult human microglia-like cells.

Uptake of alpha-synuclein preformed fibrils is suppressed by inflammation and induces an aberrant phenotype in human microglia

Microglia are brain resident immune cells that maintain proteostasis and cellular homeostasis. Recent findings suggest that microglia dysfunction could contribute to the pathogenesis of Parkinson's disease (PD). One of the hallmarks of PD is the aggregation and accumulation of alpha-synuclein (αSyn) into Lewy bodies inside nerve cells. Microglia may worsen the neuronal microenvironment by persistent inflammation, resulting in deficient clearing of aggregated αSyn. To model microglial behavior in PD, we utilized human induced pluripotent stem cells to generate functionally active microglia. We studied the microglial uptake of alpha-synuclein preformed fibrils (PFFs) and the effect of pro-inflammatory stimulation by interferon gamma. We demonstrate that combined exposure disrupts the phagosome maturation pathway while inflammatory stimuli suppress chaperone mediated autophagy and mitochondrial function. Furthermore, inflammatory stimulation impairs PFF uptake in microglia and increases cytokine production. Moreover, excessive PFF uptake by microglia results in induction of inducible nitric oxide synthase. Taken together, we demonstrate that this model is valuable for investigating the behavior of microglia in PD and provide new insights on how human microglia process aggregated αSyn.

Enhancements in Parkinson's Disease Management: Leveraging Levodopa Optimization and Surgical Breakthroughs

Parkinson's disease (PD) is a complex neurological condition caused due to inheritance, environment, and behavior among various other parameters. The onset, diagnosis, course of therapy, and future of PD are thoroughly examined in this comprehensive review. This review also presents insights into pathogenic mechanisms of reactive microgliosis, Lewy bodies, and their functions in the evolution of PD. It addresses interaction complexity with genetic mutations, especially in genes such as UCH-L1, parkin, and α-synuclein, which illuminates changes in the manner dopaminergic cells handle proteins and use proteases. This raises the improved outcomes and life quality for those with PD. Potential treatments for severe PD include new surgical methods like Deep Brain Stimulation (DBS). Further, exploration of non-motor manifestations, such as cognitive impairment, autonomic dysfunction, and others, is covered in this review article. These symptoms have a significant impact on patients' quality of life. Furthermore, one of the emerging therapeutic routes that are being investigated is neuroprotective medicines that aim to prevent the aggregation of α-synuclein and interventions that modify the progression of diseases. The review concludes by stressing the dynamic nature of PD research and the potential game-changing impact of precision medicines on current approaches to therapy.

α-Synuclein pathology as a target in neurodegenerative diseases

α-Synuclein misfolds into pathological forms that lead to various neurodegenerative diseases known collectively as α-synucleinopathies. In this Review, we provide a comprehensive overview of pivotal advances in α-synuclein research. We examine structural features and physiological functions of α-synuclein and summarize current insights into key post-translational modifications, such as nitration, phosphorylation, ubiquitination, sumoylation and truncation, considering their contributions to neurodegeneration. We also highlight the existence of disease-specific α-synuclein strains and their mechanisms of pathological spread, and discuss seed amplification assays and PET tracers as emerging diagnostic tools for detecting pathological α-synuclein in clinical settings. We also discuss α-synuclein aggregation and clearance mechanisms, and review cell-autonomous and non-cell-autonomous processes that contribute to neuronal death, including the roles of adaptive and innate immunity in α-synuclein-driven neurodegeneration. Finally, we highlight promising therapeutic approaches that target pathological α-synuclein and provide insights into emerging areas of research.

Revealing the mechanisms of blood-brain barrier in chronic neurodegenerative disease: an opportunity for therapeutic intervention

The brain microenvironment is tightly regulated, and the blood-brain barrier (BBB) plays a pivotal role in maintaining the homeostasis of the central nervous system. It effectively safeguards brain tissue from harmful substances in peripheral blood. However, both acute pathological factors and age-related biodegradation have the potential to compromise the integrity of the BBB and are associated with chronic neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD), as well as Epilepsy (EP). This association arises due to infiltration of peripheral foreign bodies including microorganisms, immune-inflammatory mediators, and plasma proteins into the central nervous system when the BBB is compromised. Nevertheless, these partial and generalized understandings do not prompt a shift from passive to active treatment approaches. Therefore, it is imperative to acquire a comprehensive and in-depth understanding of the intricate molecular mechanisms underlying vascular disease alterations associated with the onset and progression of chronic neurodegenerative disorders, as well as the subsequent homeostatic changes triggered by BBB impairment. The present article aims to systematically summarize and review recent scientific work with a specific focus on elucidating the fundamental mechanisms underlying BBB damage in AD, PD, and EP as well as their consequential impact on disease progression. These findings not only offer guidance for optimizing the physiological function of the BBB, but also provide valuable insights for developing intervention strategies aimed at early restoration of BBB structural integrity, thereby laying a solid foundation for designing drug delivery strategies centered around the BBB.

Brain organoid models for studying the function of iPSC-derived microglia in neurodegeneration and brain tumours

Microglia represent the main resident immune cells of the brain. The interplay between microglia and other cells in the central nervous system, such as neurons or other glial cells, influences the function and ability of microglia to respond to various stimuli. These cellular communications, when disrupted, can affect the structure and function of the brain, and the initiation and progression of neurodegenerative diseases including Alzheimer's disease and Parkinson's disease, as well as the progression of other brain diseases like glioblastoma. Due to the difficult access to patient brain tissue and the differences reported in the murine models, the available models to study the role of microglia in disease progression are limited. Pluripotent stem cell technology has facilitated the generation of highly complex models, allowing the study of control and patient-derived microglia in vitro. Moreover, the ability to generate brain organoids that can mimic the 3D tissue environment and intercellular interactions in the brain provide powerful tools to study cellular pathways under homeostatic conditions and various disease pathologies. In this review, we summarise the most recent developments in modelling degenerative diseases and glioblastoma, with a focus on brain organoids with integrated microglia. We provide an overview of the most relevant research on intercellular interactions of microglia to evaluate their potential to study brain pathologies.

Alpha-Synuclein and Microglia in Parkinson's Disease: From Pathogenesis to Therapeutic Prospects

Parkinson's disease (PD) is a neurodegenerative disorder characterized by both motor symptoms and non-motor features. A hallmark of PD is the misfolding and accumulation of alpha-synuclein (α-syn), which triggers neuroinflammation and drives neurodegeneration. Microglia, brain cells that play a central role in neuroinflammatory responses and help clear various unnecessary molecules within the brain, thus maintaining the brain's internal environment, respond to α-syn through mechanisms involving inflammation, propagation, and clearance. This review delves into the complex interplay between α-syn and microglia, elucidating how these interactions drive PD pathogenesis. Furthermore, we discuss emerging therapeutic strategies targeting the α-syn-microglia axis, with a focus on modulating microglial functions to mitigate neuroinflammation, enhance clearance, and prevent α-syn propagation, emphasizing their potential to slow PD progression.

Malvidin-3-O-Glucoside Mitigates α-Syn and MPTP Co-Induced Oxidative Stress and Apoptosis in Human Microglial HMC3 Cells

Parkinson's disease (PD) is a widespread age-related neurodegenerative disorder characterized by the presence of an aggregated protein, α-synuclein (α-syn), which is encoded by the SNCA gene and localized to presynaptic terminals in a normal human brain. The α-syn aggregation is induced by the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mitochondrial neurotoxin and is therefore used to mimic PD-like pathology in various in vitro and in vivo models. However, in vitro PD-like pathology using α-syn and MPTP in human microglial cells has not yet been reported. Malvidin-3-O-glucoside (M3G) is a major anthocyanin primarily responsible for pigmentation in various fruits and beverages and has been reported to possess various bioactivities. However, the neuroprotective effects of M3G in humanized in vitro PD-like pathologies have not been reported. Therefore, individual and co-treatments of α-syn and MPTP in a human microglial (HMC3) cell line were used to establish a humanized PD-like pathology model in vitro. The individual treatments were significantly less cytotoxic when compared to the α-syn and MPTP co-treatment. This study examined the neuroprotective effects of M3G by treating HMC3 cells with α-syn (8 μg/mL) and MPTP (2 mM) individually or in a co-treatment in the presence or absence of M3G (50 μM). M3G demonstrated anti-apoptotic, anti-inflammatory, and antioxidative properties against the α-syn- and MPTP-generated humanized in vitro PD-like pathology. This study determined that the cytoprotective effects of M3G are mediated by nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase (HO)-1 signaling.

Templating of Monomeric Alpha-Synuclein Induces Inflammation and SNpc Dopamine Neuron Death in a Genetic Mouse Model of Synucleinopathy

While the etiology of most cases of Parkinson's disease (PD) are idiopathic, it has been estimated that 5-10% of PD arise from known genetic mutations. The first mutations described that leads to the development of an autosomal dominant form of PD are in the SNCA gene that codes for the protein alpha-synuclein (α-syn). α-syn is an abundant presynaptic protein that is natively disordered and whose function is still unclear. In PD, α-syn misfolds into multimeric b-pleated sheets that aggregate in neurons (Lewy Bodies/neurites) and spread throughout the neuraxis in a pattern that aligns with disease progression. Here, using IHC, HC, HPLC, and cytokine analysis, we examined the sequelae of intraparenchymal brain seeding of pre-formed fibrils (PFFs) and monomeric α-syn in C57BL/6J (WT) and A53T SNCA mutant mice. We found that injection of PFFs, but not monomeric α-syn, into the striatum of C57BL/6J mice induced spread of aggregated α-syn, loss of SNpc DA neurons and increased neuroinflammation. However, in A53T SNCA mice, we found that both PFFs and monomeric α-syn induced this pathology. This suggests that the conformation changes in α-syn seen in the A53T strain can recruit wild-type α-syn to a pathological misfolded conformation which may provide a mechanism for the induction of PD in humans with SNCA duplication/triplication.

The emerging role of disease-associated microglia in Parkinson's disease

Disease-associated microglia (DAM) are a subset of microglia that appear at various stages of central nervous system neurodegenerative diseases. DAM were identified using single-cell RNA sequencing within Alzheimer's Disease (AD) where they were characterized by their unique localization near amyloid-β plaques and their phagocytic and lipid-metabolizing features. Unfortunately, activation and etiology of DAM are only understood within the context of AD where Triggering Receptor Expressed On Myeloid Cells 2 (TREM2), a receptor for amyloid-β, appears to be the key regulator in microglial transition to a DAM state. Despite this reliance on TREM2 in AD, DAM appear across other neurodegenerative diseases in which TREM2 may not be a critical player. This begs the question of if DAM are truly the same across all neurodegenerative diseases or if there exists a heterogeneity to DAM across neurodegenerative pathologies. Investigation into this critical gap in the field regarding DAM etiology and activation, as well as DAM function, could be delineated utilizing models of Parkinson's disease (PD) to complement studies in models of AD. Though highly underexplored regarding DAM, PD with its pattern of protein aggregation-associated pathology like AD could serve as the spatiotemporal comparison against AD findings to ascertain the nature of DAM. The experimental vehicle that could guide the future of such investigation is the multi-omics model. With a compound approach focusing on exploring triggers for DAM at the chromatin or mRNA level and related protein output, it becomes possible to strongly characterize and firmly answer the question of what is a DAM.

The immune system in Parkinson's disease: what we know so far

Parkinson's disease is characterized neuropathologically by the degeneration of dopaminergic neurons in the ventral midbrain, the accumulation of α-synuclein (α-syn) aggregates in neurons and chronic neuroinflammation. In the past two decades, in vitro, ex vivo and in vivo studies have consistently shown the involvement of inflammatory responses mediated by microglia and astrocytes, which may be elicited by pathological α-syn or signals from affected neurons and other cell types, and are directly linked to neurodegeneration and disease development. Apart from the prominent immune alterations seen in the CNS, including the infiltration of T cells into the brain, more recent studies have demonstrated important changes in the peripheral immune profile within both the innate and adaptive compartments, particularly involving monocytes, CD4+ and CD8+ T cells. This review aims to integrate the consolidated understanding of immune-related processes underlying the pathogenesis of Parkinson's disease, focusing on both central and peripheral immune cells, neuron-glia crosstalk as well as the central-peripheral immune interaction during the development of Parkinson's disease. Our analysis seeks to provide a comprehensive view of the emerging knowledge of the mechanisms of immunity in Parkinson's disease and the implications of this for better understanding the overall pathogenesis of this disease.

Quantitative systems pharmacology model of α-synuclein pathology in Parkinson's disease-like mouse for investigation of passive immunotherapy mechanisms

The main pathophysiological hallmark of Parkinson's disease (PD) is the accumulation of aggregated alpha-synuclein (αSyn). Microglial activation is an early event in PD and may play a key role in pathological αSyn aggregation and transmission, as well as in clearance of αSyn and immunotherapy efficacy. Our aim was to investigate how different proposed mechanisms of anti-αSyn immunotherapy may contribute to pathology reduction in various PD-like mouse models. Our mechanistic model of PD pathology in mouse includes αSyn production, aggregation, degradation and distribution in neurons, secretion into interstitial fluid, internalization, and subsequent clearance by neurons and microglia. It describes the influence of neuroinflammation on PD pathogenesis and dopaminergic neurodegeneration. Multiple data from mouse PD models were used for calibration and validation. Simulations of anti-αSyn passive immunotherapy adequately reproduce preclinical data and suggest that (1) immunotherapy is efficient in the reduction of aggregated αSyn in various models of PD-like pathology; (2) prevention of aSyn spread only does not reduce the pathology; (3) a decrease in microglial inflammatory activation and aSyn aggregation may be alternative therapy approaches in PD-like pathology.

Alpha-synuclein, autophagy-lysosomal pathway, and Lewy bodies: Mutations, propagation, aggregation, and the formation of inclusions

Research into the pathophysiology of Parkinson's disease (PD) is a fast-paced pursuit, with new findings about PD and other synucleinopathies being made each year. The involvement of various lysosomal proteins, such as TFEB, TMEM175, GBA, and LAMP1/2, marks the rising awareness about the importance of lysosomes in PD and other neurodegenerative disorders. This, along with recent developments regarding the involvement of microglia and the immune system in neurodegenerative diseases, has brought about a new era in neurodegeneration: the role of proinflammatory cytokines on the nervous system, and their downstream effects on mitochondria, lysosomal degradation, and autophagy. More effort is needed to understand the interplay between neuroimmunology and disease mechanisms, as many of the mechanisms remain enigmatic. α-synuclein, a key protein in PD and the main component of Lewy bodies, sits at the nexus between lysosomal degradation, autophagy, cellular stress, neuroimmunology, PD pathophysiology, and disease progression. This review revisits some fundamental knowledge about PD while capturing some of the latest trends in PD research, specifically as it relates to α-synuclein.

Immune responses to oligomeric α-synuclein in Parkinson's disease peripheral blood mononuclear cells

Parkinson's disease displays clinical heterogeneity, presenting with motor and non-motor symptoms. Heterogeneous phenotypes, named brain-first and body-first, may reflect distinct α-synuclein pathology starting either in the central nervous system or in the periphery. The immune system plays a prominent role in the central and peripheral pathology, with misfolded α-synuclein being placed at the intersection between neurodegeneration and inflammation. Here, we characterized the inflammatory profile and immune-phenotype of peripheral blood mononuclear cells (PBMCs) from Parkinson's disease patients upon stimulation with α-synuclein monomer or oligomer, and investigated relationships of immune parameters with clinical scores of motor and non-motor symptoms. Freshly isolated PBMCs from 21 Parkinson's disease patients and 18 healthy subjects were exposed in vitro to α-synuclein species. Cytokine/chemokine release was measured in the culture supernatant by Multiplex Elisa. The immune-phenotype was studied by FACS-flow cytometry. Correlation analysis was computed between immune parameters and parkinsonian motor and non-motor scales. We found that Parkinson's disease patients exhibited a dysregulated PBMC-cytokine profile, which remained unaltered after exposure to α-synuclein species and correlated with both motor and non-motor severity, with a strong correlation observed with olfactory impairment. Exposure of PBMCs from healthy controls to α-synuclein monomer/oligomer increased the cytokine/chemokine release up to patient's values. Moreover, the PBMCs immune phenotype differed between patients and controls and revealed a prominent association of the Mos profile with olfactory impairment, and of NK profile with constipation. Results suggest that a deranged PBMC-immune profile may reflect distinct clinical subtypes and would fit with the recent classification of Parkinson's disease into peripheral-first versus brain-first phenotype.

Alpha-synuclein and RNA viruses: Exploring the neuronal nexus

Alpha-synuclein (α-syn), known for its pivotal role in Parkinson's disease, has recently emerged as a significant player in neurotropic RNA virus infections. Upregulation of α-syn in various viral infections has been found to impact neuroprotective functions by regulating neurotransmitter synthesis, vesicle trafficking, and synaptic vesicle recycling. This review focuses on the multifaceted role of α-syn in controlling viral replication by modulating chemoattractant properties towards microglial cells, virus-induced ER stress signaling, anti-oxidative proteins expression. Furthermore, the text underlines the α-syn-mediated regulation of interferon-stimulated genes. The review may help suggest potential therapeutic avenues for mitigating the impact of RNA viruses on the central nervous system by exploiting α-syn neuroprotective biology.

Curcumin as a potential therapeutic agent for treating neurodegenerative diseases

Neurodegenerative diseases are characterized by the progressive loss of neuronal structure and function, posing a tremendous burden on health systems worldwide. Although the underlying pathological mechanisms for various neurodegenerative diseases are still unclear, a common pathological hallmark is the abundance of neuroinflammatory processes, which affect both disease onset and progression. In this review, we explore the pathways and role of neuroinflammation in various neurodegenerative diseases and further assess the potential use of curcumin, a natural spice with antioxidant and anti-inflammatory properties that has been extensively used worldwide as a traditional medicine and potential therapeutic agent. Following the examination of preclinical and clinical studies that assessed curcumin as a potential therapeutic agent, we highlight the bioavailability of curcumin in the body and discuss both the challenges and benefits of using curcumin as a therapeutic compound for treating neurodegeneration. Although elucidating the involvement of curcumin in aging and neurodegeneration has great potential for developing future CNS-related therapeutic targets, further research is required to elucidate the mechanisms by which Curcumin affects brain physiology, especially BBB integrity, under both physiological and disease conditions.

The humoral immune landscape in Parkinson's disease: Unraveling antibody and B cell changes

Parkinson's disease (PD) is a complex neurodegenerative disorder characterized by the accumulation of α-synuclein (α-syn) in the brain and progressive loss of dopaminergic neurons in the substantia nigra (SN) region of the brain. Although the role of neuroinflammation and cellular immunity in PD has been extensively studied, the involvement of humoral immunity mediated by antibodies and B cells has received less attention. This article provides a comprehensive review of the current understanding of humoral immunity in PD. Here, we discuss alterations in B cells in PD, including changes in their number and phenotype. Evidence mostly indicates a decrease in the quantity of B cells in PD, accompanied by a shift in the population from naïve to memory cells. Furthermore, the existence of autoantibodies that target several antigens in PD has been investigated (i.e., anti-α-syn autoantibodies, anti-glial-derived antigen antibodies, anti-Tau antibodies, antineuromelanin antibodies, and antibodies against the renin-angiotensin system). Several autoantibodies are generated in PD, which may either provide protection or have harmful effects on disease progression. Furthermore, we have reviewed studies focusing on the utilization of antibodies as a potential treatment for PD, both in animal and clinical trials. This review sheds light on the intricate interplay between antibodies and the pathological processes in PD, including complement system activation.

MicroRNAs Modulating Neuroinflammation in Parkinson's disease

Parkinson's disease (PD) is one of the most frequent age-associated neurodegenerative disorder. Presence of α-synuclein-containing aggregates in the substantia nigra pars compacta (SNpc) and loss of dopaminergic (DA) neurons are among the characteristic of PD. One of the hallmarks of PD pathophysiology is chronic neuroinflammation. Activation of glial cells and elevated levels of pro-inflammatory factors are confirmed as frequent features of the PD brain. Chronic secretion of pro-inflammatory cytokines by activated astrocytes and microglia exacerbates DA neuron degeneration in the SNpc. MicroRNAs (miRNAs) are among endogenous non-coding small RNA with the ability to perform post-transcriptional regulation in target genes. In that regard, the capability of miRNAs for modulating inflammatory signaling is the center of attention in many investigations. MiRNAs could enhance or limit inflammatory signaling, exacerbating or ameliorating the pathological consequences of extreme neuroinflammation. This review summarizes the importance of inflammation in the pathophysiology of PD. Besides, we discuss the role of miRNAs in promoting or protecting neural cell injury in the PD model by controlling the inflammatory pathway. Modifying the neuroinflammation by miRNAs could be considered a primary therapeutic strategy for PD.

FoxO1 Alleviates the Mitochondrial ROS Levels Induced by α-Synuclein Preformed Fibrils in BV-2 Microglial Cells

Parkinson's disease (PD) is a complex neurodegenerative disorder marked by the gradual deterioration of dopaminergic neurons, especially in the substantia nigra pars compacta (SNc). Dysregulation of the transcription factor FoxO1 is associated with various neurodegenerative conditions, including Alzheimer's disease and PD, though the specific mechanisms involved are not fully understood. This study explores the effects of α-Synuclein preformed fibrils (PFF) on BV-2 microglial cells, focusing on changes in molecular characteristics and their impact on neuronal degeneration. Our results demonstrate that PFF treatment significantly increases FoxO1 mRNA (p = 0.0443) and protein (p = 0.0216) levels, leading to its nuclear translocation (p = 0.0142) and enhanced expression of genes involved in the detoxification of reactive oxygen species (ROS), such as Catalase (Cat, p = 0.0249) and superoxide dismutase 2 (Sod2, p = 0.0313). Furthermore, we observed that PFF treatment elevates mitochondrial ROS levels. However, cells lacking FoxO1 or treated with FoxO1 inhibitors showed increased vulnerability to PFF-induced ROS, attributed to reduced expression of ROS detoxifying enzymes Cat and Sod2 (p < 0.0001). Besides enhancing ROS production, inhibiting FoxO1 also heightens neurotoxicity induced by PFF treatment in microglia-conditioned medium (p < 0.0001). Conversely, treatment with N-acetylcysteine or bacterial superoxide dismutase A mitigated the ROS increase induced by PFF (p < 0.0001). These findings suggest the essential role of FoxO1 in regulating ROS levels, which helps alleviate pathology in PFF-induced PD models. Our study provides insights into the genetic mechanisms of PD and suggests potential pathways for developing novel therapeutic strategies.

Calcium Deregulation in Neurodegeneration and Neuroinflammation in Parkinson's Disease: Role of Calcium-Storing Organelles and Sodium-Calcium Exchanger

Parkinson's disease (PD) is a progressive neurodegenerative disorder that lacks effective treatment strategies to halt or delay its progression. The homeostasis of Ca2+ ions is crucial for ensuring optimal cellular functions and survival, especially for neuronal cells. In the context of PD, the systems regulating cellular Ca2+ are compromised, leading to Ca2+-dependent synaptic dysfunction, impaired neuronal plasticity, and ultimately, neuronal loss. Recent research efforts directed toward understanding the pathology of PD have yielded significant insights, particularly highlighting the close relationship between Ca2+ dysregulation, neuroinflammation, and neurodegeneration. However, the precise mechanisms driving the selective loss of dopaminergic neurons in PD remain elusive. The disruption of Ca2+ homeostasis is a key factor, engaging various neurodegenerative and neuroinflammatory pathways and affecting intracellular organelles that store Ca2+. Specifically, impaired functioning of mitochondria, lysosomes, and the endoplasmic reticulum (ER) in Ca2+ metabolism is believed to contribute to the disease's pathophysiology. The Na+-Ca2+ exchanger (NCX) is considered an important key regulator of Ca2+ homeostasis in various cell types, including neurons, astrocytes, and microglia. Alterations in NCX activity are associated with neurodegenerative processes in different models of PD. In this review, we will explore the role of Ca2+ dysregulation and neuroinflammation as primary drivers of PD-related neurodegeneration, with an emphasis on the pivotal role of NCX in the pathology of PD. Consequently, NCXs and their interplay with intracellular organelles may emerge as potentially pivotal players in the mechanisms underlying PD neurodegeneration, providing a promising avenue for therapeutic intervention aimed at halting neurodegeneration.

Neurodegenerative diseases and catechins: (-)-epigallocatechin-3-gallate is a modulator of chronic neuroinflammation and oxidative stress

Catechins, a class of phytochemicals found in various fruits and tea leaves, have garnered attention for their diverse health-promoting properties, including their potential in combating neurodegenerative diseases. Among these catechins, (-)-epigallocatechin-3-gallate (EGCG), the most abundant polyphenol in green tea, has emerged as a promising therapeutic agent due to its potent antioxidant and anti-inflammatory effects. Chronic neuroinflammation and oxidative stress are key pathological mechanisms in neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). EGCG has neuroprotective efficacy due to scavenging free radicals, reducing oxidative stress and attenuating neuroinflammatory processes. This review discusses the molecular mechanisms of EGCG's anti-oxidative stress and chronic neuroinflammation, emphasizing its effects on autoimmune responses, neuroimmune system interactions, and focusing on the related effects on AD and PD. By elucidating EGCG's mechanisms of action and its impact on neurodegenerative processes, this review underscores the potential of EGCG as a therapeutic intervention for AD, PD, and possibly other neurodegenerative diseases. Overall, EGCG emerges as a promising natural compound for combating chronic neuroinflammation and oxidative stress, offering novel avenues for neuroprotective strategies in the treatment of neurodegenerative disorders.

Challenges and Future Perspectives in Modeling Neurodegenerative Diseases Using Organ-on-a-Chip Technology

Neurodegenerative diseases (NDDs) affect more than 50 million people worldwide, posing a significant global health challenge as well as a high socioeconomic burden. With aging constituting one of the main risk factors for some NDDs such as Alzheimer's disease (AD) and Parkinson's disease (PD), this societal toll is expected to rise considering the predicted increase in the aging population as well as the limited progress in the development of effective therapeutics. To address the high failure rates in clinical trials, legislative changes permitting the use of alternatives to traditional pre-clinical in vivo models are implemented. In this regard, microphysiological systems (MPS) such as organ-on-a-chip (OoC) platforms constitute a promising tool, due to their ability to mimic complex and human-specific tissue niches in vitro. This review summarizes the current progress in modeling NDDs using OoC technology and discusses five critical aspects still insufficiently addressed in OoC models to date. Taking these aspects into consideration in the future MPS will advance the modeling of NDDs in vitro and increase their translational value in the clinical setting.

Calcium influx: An essential process by which α-Synuclein regulates morphology of erythrocytes

INTRODUCTION

Morphological abnormalities of erythrocytes/red blood cells (RBCs), e.g., increased acanthocytes, in Parkinson's disease (PD) have been reported previously, although the underlying mechanisms remain to be characterized. In this study, the potential roles of α-synuclein (α-syn), a protein critically involved in PD and highly abundant in RBCs, were studied in PD patients as well as in a PD mouse model.

METHODS

Transgenic [PAC-Tg (SNCAA53T), A53T] mice overexpressing A53T mutant α-syn and SNCA knockout mice were employed to characterize the effect of α-syn on RBC morphology. In addition to A53T and SNCA knockout mice, the morphology of RBCs of PD patients was also examined using scanning electron microscopy. The potential roles of α-syn were further investigated in cultured RBCs and mice.

RESULTS

Morphological abnormalities of RBCs and increased accumulation of aggregated α-syn on the RBC membrane were observed in PD patients. A similar phenomenon was also observed in A53T mice. Furthermore, while mice lacking α-syn expression showed a lower proportion of acanthocytes, treating RBCs derived from SNCA knockout mice with aggregated α-syn resulted in a higher percentage of acanthocytes. In a follow-up proteomic investigation, several major classes of proteins were identified as α-syn-associated proteins on the RBC membrane, seven of which were calcium-binding proteins. Applying aggregated α-syn to the RBC membrane directly induced extracellular calcium influx along with morphological changes; both observations were adequately reversed by blocking calcium influx.

CONCLUSIONS

This study demonstrated that α-syn plays a critical role in PD-associated morphological abnormalities of RBCs, at least partially via a process mediated by extracellular calcium influx.

Neuroanatomical and cognitive biomarkers of alpha-synuclein propagation in a mouse model of synucleinopathy prior to onset of motor symptoms

Significant evidence suggests that misfolded alpha-synuclein (aSyn), a major component of Lewy bodies, propagates in a prion-like manner contributing to disease progression in Parkinson's disease (PD) and other synucleinopathies. In fact, timed inoculation of M83 hemizygous mice with recombinant human aSyn preformed fibrils (PFF) has shown symptomatic deficits after substantial spreading of pathogenic alpha-synuclein, as detected by markers for the phosphorylation of S129 of aSyn. However, whether accumulated toxicity impact human-relevant cognitive and structural neuroanatomical measures is not fully understood. Here we performed a single unilateral striatal PFF injection in M83 hemizygous mice, and using two assays with translational potential, ex vivo magnetic resonance imaging (MRI) and touchscreen testing, we examined the combined neuroanatomical and behavioral impact of aSyn propagation. In PFF-injected mice, we observed widespread atrophy in bilateral regions that project to or receive input from the injection site using MRI. We also identified early deficits in reversal learning prior to the emergence of motor symptoms. Our findings highlight a network of regions with related cellular correlates of pathology that follow the progression of aSyn spreading, and that affect brain areas relevant for reversal learning. Our experiments suggest that M83 hemizygous mice injected with human PFF provides a model to understand how misfolded aSyn affects human-relevant pre-clinical measures and suggest that these pre-clinical biomarkers could be used to detect early toxicity of aSyn and provide better translational measures between mice and human disease.

TGF-β1 mediates hypoxia-preconditioned olfactory mucosa mesenchymal stem cells improved neural functional recovery in Parkinson's disease models and patients

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the degeneration of dopaminergic neurons in the substantia nigra (SN). Activation of the neuroinflammatory response has a pivotal role in PD. Mesenchymal stem cells (MSCs) have emerged as a promising therapeutic approach for various nerve injuries, but there are limited reports on their use in PD and the underlying mechanisms remain unclear.

METHODS

We investigated the effects of clinical-grade hypoxia-preconditioned olfactory mucosa (hOM)-MSCs on neural functional recovery in both PD models and patients, as well as the preventive effects on mouse models of PD. To assess improvement in neuroinflammatory response and neural functional recovery induced by hOM-MSCs exposure, we employed single-cell RNA sequencing (scRNA-seq), assay for transposase accessible chromatin with high-throughput sequencing (ATAC-seq) combined with full-length transcriptome isoform-sequencing (ISO-seq), and functional assay. Furthermore, we present the findings from an initial cohort of patients enrolled in a phase I first-in-human clinical trial evaluating the safety and efficacy of intraspinal transplantation of hOM-MSC transplantation into severe PD patients.

RESULTS

A functional assay identified that transforming growth factor-β1 (TGF-β1), secreted from hOM-MSCs, played a critical role in modulating mitochondrial function recovery in dopaminergic neurons. This effect was achieved through improving microglia immune regulation and autophagy homeostasis in the SN, which are closely associated with neuroinflammatory responses. Mechanistically, exposure to hOM-MSCs led to an improvement in neuroinflammation and neural function recovery partially mediated by TGF-β1 via activation of the anaplastic lymphoma kinase/phosphatidylinositol-3-kinase/protein kinase B (ALK/PI3K/Akt) signaling pathway in microglia located in the SN of PD patients. Furthermore, intraspinal transplantation of hOM-MSCs improved the recovery of neurologic function and regulated the neuroinflammatory response without any adverse reactions observed in patients with PD.

CONCLUSIONS

These findings provide compelling evidence for the involvement of TGF-β1 in mediating the beneficial effects of hOM-MSCs on neural functional recovery in PD. Treatment and prevention of hOM-MSCs could be a promising and effective neuroprotective strategy for PD. Additionally, TGF-β1 may be used alone or combined with hOM-MSCs therapy for treating PD.

Herpes simplex virus 1 accelerates the progression of Alzheimer's disease by modulating microglial phagocytosis and activating NLRP3 pathway

Accumulating evidence implicates that herpes simplex virus type 1 (HSV-1) has been linked to the development and progression of Alzheimer's disease (AD). HSV-1 infection induces β-amyloid (Aβ) deposition in vitro and in vivo, but the effect and precise mechanism remain elusive. Here, we show that HSV-1 infection of the brains of transgenic 5xFAD mice resulted in accelerated Aβ deposition, gliosis, and cognitive dysfunction. We demonstrate that HSV-1 infection induced the recruitment of microglia to the viral core to trigger microglial phagocytosis of HSV-GFP-positive neuronal cells. In addition, we reveal that the NLRP3 inflammasome pathway induced by HSV-1 infection played a crucial role in Aβ deposition and the progression of AD caused by HSV-1 infection. Blockade of the NLRP3 inflammasome signaling reduces Aβ deposition and alleviates cognitive decline in 5xFAD mice after HSV-1 infection. Our findings support the notion that HSV-1 infection is a key factor in the etiology of AD, demonstrating that NLRP3 inflammasome activation functions in the interface of HSV-1 infection and Aβ deposition in AD.

Allopregnanolone and its antagonist modulate neuroinflammation and neurological impairment

Neuroinflammation accompanies several brain disorders, either as a secondary consequence or as a primary cause and may contribute importantly to disease pathogenesis. Neurosteroids which act as Positive Steroid Allosteric GABA-A receptor Modulators (Steroid-PAM) appear to modulate neuroinflammation and their levels in the brain may vary because of increased or decreased local production or import from the systemic circulation. The increased synthesis of steroid-PAMs is possibly due to increased expression of the mitochondrial cholesterol transporting protein (TSPO) in neuroinflammatory tissue, and reduced production may be due to changes in the enzymatic activity. Microglia and astrocytes play an important role in neuroinflammation, and their production of inflammatory mediators can be both activated and inhibited by steroid-PAMs and GABA. What is surprising is the finding that both allopregnanolone, a steroid-PAM, and golexanolone, a novel GABA-A receptor modulating steroid antagonist (GAMSA), can inhibit microglia and astrocyte activation and normalize their function. This review focuses on the role of steroid-PAMs in neuroinflammation and their importance in new therapeutic approaches to CNS and liver disease.