Alpha synuclein, the culprit in Parkinson disease, is required for normal immune function

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

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

The role of retroelements in Parkinson's disease development

Parkinson's disease is the second most common neurodegenerative disease characterized by accumulation of alpha-synuclein and Lewy bodies in the brain's substantia nigra. Genetic studies indicate an association of various SNPs, many of which are located in intergenic and intronic regions, where retrotransposons and non-coding RNA genes derived from them reside, with this disease. Therefore, we hypothesize the influence of SNPs in retroelement genes on Parkinson's disease development. A susceptibility factor is retrotransposons activation with age, since the disease is associated with aging. We hypothesized that alpha-synuclein accumulates in the brain due to its interaction with transcripts of activated retroelements. As a result of a defective antiviral response and a large number of RNA targets for this protein, its aggregates form Lewy bodies in neurons with inflammation and neurodegeneration development in the substantia nigra. As evidence, data are presented on the role of alpha-synuclein in the antiviral response with binding to RNA viruses, which are characterized by the ability to activate retroelements that have evolved from exogenous viruses integrated into the human genome. Activation of LINE1s in the brain, endogenous retroviruses, and LINE1s in the blood serum of Parkinson's disease patients was detected. An additional mechanism contributing to the progression of the disease is mitochondrial dysfunction due to insertions of Alu elements into their genomes using LINE1 enzymes. Mechanisms of activated retrotransposons' influence on microRNAs that evolved from them are described. Analysis of the scientific literature allowed us to identify 35 such microRNAs (miR-1246, -1249, -1271, -1273, -1303, -151, -211, -28, -31, -320b, -320d, -330, -335, - 342, -374a, -374b, -421, -4293, -4317, -450b, -466, -487b, -493, -495, -5095, -520d, -576, -585, -6088, -619, -625, -626, -769, -885, -95) associated with Parkinson's disease, which may become promising targets for its treatment and diagnosis.

Myeloid FtH Regulates Macrophage Response to Kidney Injury by Modulating Snca and Ferroptosis

This study explored the role of myeloid ferritin heavy chain (FtH) in coordinating kidney iron trafficking in health and disease. Synuclein-α (Snca) was the sole iron-binding protein upregulated in response to myeloid FtH deletion (FtH Δ/Δ ). Following kidney injury, FtH Δ/Δ mice showed worsened kidney function. Transcriptome analysis revealed coupling of FtH deficiency with ferroptosis activation, a regulated cell death associated with iron accumulation. Adverse effects of ferroptosis were evidenced by upregulation of ferroptosis-related genes, increased oxidative stress markers, and significant iron deposition in kidney tissues. This iron buildup in FtH Δ/Δ kidneys stemmed from macrophage reprogramming into an iron-recycling phenotype, driven by Spic induction. Mechanistically, we establish that monomeric Snca functions as a ferrireductase catalyst, intensifying oxidative stress and triggering ferroptosis. Additionally, Snca accumulates in kidney diseases distinguished by leukocyte expansion across species. These findings position myeloid FtH as a pivotal orchestrator of the FtH-Snca-Spic axis driving macrophage reprogramming and kidney injury.

Highlights

Myeloid FtH deficiency drives kidney injury via activation of ferroptosisMΦ FtH deficiency induces Snca, linking iron dysregulation to MΦ function and response to kidney injuryFerrireductase activity of monomeric Snca augments oxidative stress, promoting lipid peroxidation and ferroptosis.

In brief

MΦ FtH modulates Snca and Spic to coordinate the injury response, linking iron trafficking to ferroptosis-induced kidney injury.

The interrelationship between intestinal immune cells and enteric α-synuclein in the progression of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder primarily characterized by motor impairment, resulting from the accumulation of α-synuclein and neuronal cell death in the substantia nigra of the midbrain. Emerging evidence suggests that α-synuclein aggregation may originate in the enteric nervous system (ENS) and subsequently propagate to the brain via the vagus nerve. Clinical observations, such as prodromal gastrointestinal dysfunction in PD patients and the increased incidence of PD among individuals with inflammatory bowel disease, support the hypothesis that abnormal intestinal inflammation may contribute to the onset of motor dysfunction and neuropathology in PD. This review examines recent findings on the interplay between intestinal immune cells and α-synuclein aggregation within the framework of gut-originated PD pathogenesis. It begins by discussing evidence linking dysbiosis and intestinal inflammation to α-synuclein aggregation in the ENS. Additionally, it explores the potential role of intestinal immune cells in influencing enteric neurons and α-synuclein aggregation, furthering the understanding of PD development.

The Micro-Structure of the Celiac Ganglia-A Two-Photon Microscopy Study on Parkinson's Disease

Background/Objectives: This study explores the micro-structure of celiac ganglia using two-photon microscopy (TPM) to highlight histological features in neurodegenerative conditions. Neurodegenerative diseases like Parkinson's disease (PD) are linked to dysautonomia, impacting autonomic regulation and leading to significant gastrointestinal and autonomic symptoms. Our research compares imaging results from TPM and SHG microscopy, visualizing neuronal integrity, collagen distribution, and the architectural organization of celiac ganglia. SHG specifically allows detailed imaging of collagen fibers and neuronal structures, revealing alterations in collagen density and organization that correlate with dysautonomia. Methods: The cross-sectional study was conducted at "Dr. Carol Davila" Central Military Emergency University Hospital, Bucharest, Romania, involving 70 participants diagnosed with PD (Hoehn and Yahr stages 2-4), including 35 with dysautonomia and 35 without. We utilized samples from PD patients with and without dysautonomia, applying immunohistochemical markers for sympathetic neurons. Results: Our findings reveal significant pathological changes in neuronal structure and collagen architecture. Immunohistochemical markers (neuropeptide Y, neurofilament heavy chain (NF-H), and tyrosine hydroxylase) were employed to characterize sympathetic neurons, while TPM and SHG provided high-resolution imaging of neuronal integrity and extracellular matrix composition. Conclusions: These imaging techniques present a promising tool for early diagnosis and assessment of neurodegeneration and dysautonomia in PD patients. Moreover, these techniques may represent a critical bridge between histopathological findings and clinical manifestations, underscoring their role in enhancing our understanding of neurodegeneration and autonomic dysfunction in Parkinson's disease.

A personalised and comprehensive approach is required to suppress or replenish SNCA for Parkinson's disease

Based on the prevailing α-synuclein "gain-of-function" hypothesis, reducing α-synuclein levels and removing its aggregates is a current focus of disease-modifying therapies for Parkinson's disease. Emerging evidence of α-synuclein "loss-of-function" suggests that it may be necessary to replenish monomeric α-synuclein levels. We propose a personalized and comprehensive approach for different Parkinson's subgroups based on whether α-synuclein is likely to contribute to disease pathogenesis through a "gain-of-function", "loss-of-function", or both mechanisms.

Chemoproteomic profiling by bioorthogonal probes to reveal the novel targets of acrylamide in microglia

Neurotoxicity studies caused by exposure to acrylamide (AA) are of wide interest, but the methods for direct analysis of AA targets in living neuronal cells by cysteine profiling are still lacking. To address this, we developed a specific bioorthogonal probe, AAPA-P2, for chemical proteomics analysis of AA covalent binding sites. AAPA-P2 captured 754 target proteins, increasing the number of identified target proteins by 20-fold. Further screening revealed 96 proteins that are both highly sensitive and heavily modified by AAPA-P2, with validation performed on some potential key targets and binding sites. AA was found to induce neurotoxicity by binding to newly identified targets, Proteasome 26S Subunit, non ATPase 9 (PSMD9) and NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 5 (NDUFA5), interfering with the ubiquitin-proteasome system, and inducing mitochondria-dependent apoptosis. The present work provides an effective bioorthogonal probe tool for identifying covalent binding targets of acrylamide and offers new insights into the molecular mechanisms underlying acrylamide-induced neurotoxicity.

Pathophysiological Significance of α-Synuclein in Sympathetic Nerves: In Vivo Observations

BACKGROUND AND OBJECTIVES

Lewy body diseases (LBDs) such as Parkinson disease (PD) feature increased deposition of α-synuclein (α-syn) in cutaneous sympathetic noradrenergic nerves. The pathophysiologic significance of sympathetic intraneuronal α-syn is unclear. We reviewed data about immunoreactive α-syn, tyrosine hydroxylase (TH, a marker of catecholaminergic fibers), and the sympathetic neurotransmitter norepinephrine (NE) in skin biopsies from control participants and patients with PD, the related LBD pure autonomic failure (PAF), the non-LBD synucleinopathy multiple system atrophy (MSA), or neurologic postacute sequelae of severe acute respiratory syndrome coronavirus 2 (neuro-PASC).

METHODS

In a retrospective observational study, we reviewed data about α-syn-TH colocalization indexes and immunoreactive α-syn and TH signal intensities in arrector pili muscles, blood vessels, and sweat glands from neck skin biopsies and NE concentrations in simultaneously obtained thigh skin biopsies from participants studied at the NIH Clinical Center. LBD, MSA, and control group data were assessed by analyses of variance with the Tukey post hoc test for multiple comparisons. Similar analyses were performed for patients with PD or neuro-PASC vs control.

RESULTS

Dermal α-syn-TH colocalization indexes and α-syn signal intensities from neck skin biopsies were examined in 18 controls (mean age 58 years, 50% female) and 53 LBD (66, 34%), 15 MSA (61, 33%), and 11 neuro-PASC (52, 82%) patients. The LBD group had higher α-syn-TH colocalization indexes than the controls (mean difference = 1.495, 95% CI 1.081-1.909, p < 0.0001) and increased α-syn signal intensities in all 3 skin constituents (arrector pili: mean difference = 2.743, 95% CI 1.608-3.879, p < 0.0001; blood vessels: mean difference = 2.157, 95% CI 1.095-3.219, p < 0.0001; sweat glands: mean difference = 4.136, 95% CI 1.704-6.567, p < 0.0001). The groups did not differ in either immunoreactive TH or NE. The neuro-PASC and PD groups had elevated α-syn-TH colocalization indexes compared with the controls, also with no group differences in immunoreactive TH or NE contents.

DISCUSSION

LBDs and neuro-PASC entail increased α-syn-TH colocalization indexes in skin biopsies, without evidence of local denervation or noradrenergic deficiency. The results fail to support toxicity of intraneuronal α-syn in cutaneous sympathetic noradrenergic nerves in either LBDs or neuro-PASC. The neuro-PASC data raise the possibility of sympathetic intraneuronal α-syn deposition as part of postinfectious immune or inflammatory processes.

Autoantibody profiles in Alzheimer´s, Parkinson´s, and dementia with Lewy bodies: altered IgG affinity and IgG/IgM/IgA responses to alpha-synuclein, amyloid-beta, and tau in disease-specific pathological patterns

BACKGROUND

Alzheimer's disease (AD) and Parkinson's disease (PD) are leading neurodegenerative disorders marked by protein aggregation, with AD featuring amyloid-beta (Aβ) and tau proteins, and PD alpha-synuclein (αSyn). Dementia with Lewy bodies (DLB) often presents with a mix of these pathologies. This study explores naturally occurring autoantibodies (nAbs), including Immunoglobulin (Ig)G, IgM, and IgA, which target αSyn, Aβ and tau to maintain homeostasis and were previously found altered in AD and PD patients, among others.

MAIN TEXT

We extended this investigation across AD, PD and DLB patients investigating both the affinities of IgGs and levels of IgGs, IgMs and IgAs towards αSyn, Aβ and tau utilizing chemiluminescence assays. We confirmed that AD and PD patients exhibited lower levels of high-affinity anti-Aβ and anti-αSyn IgGs, respectively, than healthy controls. AD patients also showed diminished levels of high-affinity anti-αSyn IgGs, while anti-tau IgG affinities did not differ significantly across groups. However, DLB patients exhibited increased anti-αSyn IgG but decreased anti-αSyn IgM levels compared to controls and PD patients, with AD patients showing a similar pattern. Interestingly, AD patients had higher anti-Aβ IgG but lower anti-Aβ IgA levels than DLB patients. DLB patients had reduced anti-Aβ IgM levels compared to controls, and anti-tau IgG levels were lower in AD than PD patients, who had reduced anti-tau IgM levels compared to controls. AD patients uniquely showed higher anti-tau IgA levels. Significant correlations were observed between clinical measures and nAbs, with negative correlations between anti-αSyn IgG affinity and levels in DLB patients and a positive correlation with anti-αSyn IgA levels in PD patients. Disease-specific changes in nAb levels and affinity correlations were identified, highlighting altered immune responses.

CONCLUSION

This study reveals distinctive nAb profiles in AD, DLB, and PD, pinpointing specific immune deficiencies against pathological proteins. These insights into the autoreactive immune system's role in neurodegeneration suggest nAbs as potential markers for vulnerability to protein aggregation, offering new avenues for understanding and possibly diagnosing these conditions.

Ancestry-specific gene expression in peripheral monocytes mediates risk of neurodegenerative disease

It is hypothesised that peripheral immune states responding to regional environmental triggers contribute to central neurodegeneration. Region-specific genetic selection pressures require this hypothesis to be assessed in an ancestry specific manner. Here we utilise genome-wide association studies and expression quantitative trait loci from African, East Asian and European ancestries to show that genes causing neurodegeneration are preferentially expressed in innate rather than adaptive immune cells, and that expression of these genes mediates the risk of neurodegenerative disease in monocytes in an ancestry-specific manner.

MAD-microbial (origin of) Alzheimer's disease hypothesis: from infection and the antimicrobial response to disruption of key copper-based systems

Microbes have been suspected to cause Alzheimer's disease since at least 1908, but this has generally remained unpopular in comparison to the amyloid hypothesis and the dominance of Aβ and Tau. However, evidence has been accumulating to suggest that these earlier theories are but a manifestation of a common cause that can trigger and interact with all the major molecular players recognized in AD. Aβ, Tau and ApoE, in particular appear to be molecules with normal homeostatic functions but also with alternative antimicrobial functions. Their alternative functions confer the non-immune specialized neuron with some innate intracellular defenses that appear to be re-appropriated from their normal functions in times of need. Indeed, signs of infection of the neurons by biofilm-forming microbial colonies, in synergy with herpes viruses, are evident from the clinical and preclinical studies we discuss. Furthermore, we attempt to provide a mechanistic understanding of the AD landscape by discussing the antimicrobial effect of Aβ, Tau and ApoE and Lactoferrin in AD, and a possible mechanistic link with deficiency of vital copper-based systems. In particular, we focus on mitochondrial oxidative respiration via complex 4 and ceruloplasmin for iron homeostasis, and how this is similar and possibly central to neurodegenerative diseases in general. In the case of AD, we provide evidence for the microbial Alzheimer's disease (MAD) theory, namely that AD could in fact be caused by a long-term microbial exposure or even long-term infection of the neurons themselves that results in a costly prolonged antimicrobial response that disrupts copper-based systems that govern neurotransmission, iron homeostasis and respiration. Finally, we discuss potential treatment modalities based on this holistic understanding of AD that incorporates the many separate and seemingly conflicting theories. If the MAD theory is correct, then the reduction of microbial exposure through use of broad antimicrobial and anti-inflammatory treatments could potentially alleviate AD although this requires further clinical investigation.

⍺-Synuclein levels in Parkinson's disease - Cell types and forms that contribute to pathogenesis

Parkinson's disease (PD) has two main pathological hallmarks, the loss of nigral dopamine neurons and the proteinaceous aggregations of ⍺-synuclein (⍺Syn) in neuronal Lewy pathology. These two co-existing features suggest a causative association between ⍺Syn aggregation and the underpinning mechanism of neuronal degeneration in PD. Both increased levels and post-translational modifications of ⍺Syn can contribute to the formation of pathological aggregations of ⍺Syn in neurons. Recent studies have shown that the protein is also expressed by multiple types of non-neuronal cells in the brain and peripheral tissues, suggesting additional roles of the protein and potential diversity in non-neuronal pathogenic triggers. It is important to determine (1) the threshold levels triggering ⍺Syn to convert from a biological to a pathologic form in different brain cells in PD; (2) the dominant form of pathologic ⍺Syn and the associated post-translational modification of the protein in each cell type involved in PD; and (3) the cell type associated biological processes impacted by pathologic ⍺Syn in PD. This review integrates these aspects and speculates on potential pathological mechanisms and their impact on neuronal and non-neuronal ⍺Syn in the brains of patients with PD.

Current insights and assumptions on α-synuclein in Lewy body disease

Lewy body disorders are heterogeneous neurological conditions defined by intracellular inclusions composed of misshapen α-synuclein protein aggregates. Although α-synuclein aggregates are only one component of inclusions and not strictly coupled to neurodegeneration, evidence suggests they seed the propagation of Lewy pathology within and across cells. Genetic mutations, genomic multiplications, and sequence polymorphisms of the gene encoding α-synuclein are also causally linked to Lewy body disease. In nonfamilial cases of Lewy body disease, the disease trigger remains unidentified but may range from industrial/agricultural toxicants and natural sources of poisons to microbial pathogens. Perhaps due to these peripheral exposures, Lewy inclusions appear at early disease stages in brain regions connected with cranial nerves I and X, which interface with inhaled and ingested environmental elements in the nasal or gastrointestinal cavities. Irrespective of its identity, a stealthy disease trigger most likely shifts soluble α-synuclein (directly or indirectly) into insoluble, cross-β-sheet aggregates. Indeed, β-sheet-rich self-replicating α-synuclein multimers reside in patient plasma, cerebrospinal fluid, and other tissues, and can be subjected to α-synuclein seed amplification assays. Thus, clinicians should be able to capitalize on α-synuclein seed amplification assays to stratify patients into potential responders versus non-responders in future clinical trials of α-synuclein targeted therapies. Here, we briefly review the current understanding of α-synuclein in Lewy body disease and speculate on pathophysiological processes underlying the potential transmission of α-synucleinopathy across the neuraxis.

Alpha-synuclein shapes monocyte and macrophage cell biology and functions by bridging alterations of autophagy and inflammatory pathways

Introduction: Abnormal spreading of alpha-synuclein (αS), a hallmark of Parkinson's disease, is known to promote peripheral inflammation, which occurs in part via functional alterations in monocytes/macrophages. However, underlying intracellular mechanisms remain unclear. Methods: Herein we investigate the subcellular, molecular, and functional effects of excess αS in human THP-1 monocytic cell line, THP-1-derived macrophages, and at least preliminarily, in primary monocyte-derived macrophages (MDMs). In cells cultured w/wo recombinant αS (1 μM) for 4 h and 24 h, by Confocal microscopy, Western Blot, RT-qPCR, Elisa, and Flow Cytometry we assessed: i) αS internalization; ii) cytokine/chemokine expression/secretion, and C-C motif chemokine receptor 2 (CCR2) levels; iii) autophagy (LC3II/I, LAMP1/LysoTracker, p62, pS6/total S6); and iv) lipid droplets (LDs) accumulation, and cholesterol pathway gene expression. Transwell migration assay was employed to measure THP-1 cell migration/chemotaxis, while FITC-IgG-bead assay was used to analyze phagocytic capacity, and the fate of phagocytosed cargo in THP-1-derived macrophages. Results: Extracellular αS was internalized by THP-1 cells, THP-1-derived macrophages, and MDMs. In THP1 cells, αS induced a general pro-inflammatory profile and conditioned media from αS-exposed THP-1 cells potently attracted unstimulated cells. However, CCL2 secretion peaked at 4 h αS, consistent with early internalization of its receptor CCR2, while this was blunted at 24 h αS exposure, when CCR2 recycled back to the plasma membrane. Again, 4 h αS-exposed THP-1 cells showed increased spontaneous migration, while 24 h αS-exposed cells showed reduced chemotaxis. This occurred in the absence of cell toxicity and was associated with upregulation of autophagy/lysosomal markers, suggesting a pro-survival/tolerance mechanism against stress-related inflammation. Instead, in THP-1-derived macrophages, αS time-dependently potentiated the intracellular accumulation, and release of pro-inflammatory mediators. This was accompanied by mild toxicity, reduced autophagy-lysosomal markers, defective LDs formation, as well as impaired phagocytosis, and the appearance of stagnant lysosomes engulfed with phagocytosed cargo, suggesting a status of macrophage exhaustion reminiscent of hypophagia. Discussion: In summary, despite an apparently similar pro-inflammatory phenotype, monocytes and macrophages respond differently to intracellular αS accumulation in terms of cell survival, metabolism, and functions. Our results suggest that in periphery, αS exerts cell- and context-specific biological effects bridging alterations of autophagy, lipid dynamics, and inflammatory pathways.

α-Synuclein pathology from the body to the brain: so many seeds so close to the central soil

ABSTRACT

α-Synuclein is a protein that mainly exists in the presynaptic terminals. Abnormal folding and accumulation of α-synuclein are found in several neurodegenerative diseases, including Parkinson's disease. Aggregated and highly phosphorylated α-synuclein constitutes the main component of Lewy bodies in the brain, the pathological hallmark of Parkinson's disease. For decades, much attention has been focused on the accumulation of α-synuclein in the brain parenchyma rather than considering Parkinson's disease as a systemic disease. Recent evidence demonstrates that, at least in some patients, the initial α-synuclein pathology originates in the peripheral organs and spreads to the brain. Injection of α-synuclein preformed fibrils into the gastrointestinal tract triggers the gut-to-brain propagation of α-synuclein pathology. However, whether α-synuclein pathology can occur spontaneously in peripheral organs independent of exogenous α-synuclein preformed fibrils or pathological α-synuclein leakage from the central nervous system remains under investigation. In this review, we aimed to summarize the role of peripheral α-synuclein pathology in the pathogenesis of Parkinson's disease. We also discuss the pathways by which α-synuclein pathology spreads from the body to the brain.

iPSC-Derived Astrocytes and Neurons Replicate Brain Gene Expression, Epigenetic, Cell Morphology and Connectivity Alterations Found in Autism

Excessive inflammatory reactions and oxidative stress are well-recognized molecular findings in autism and these processes can affect or be affected by the epigenetic landscape. Nonetheless, adequate therapeutics are unavailable, as patient-specific brain molecular markers for individualized therapies remain challenging.

METHODS

We used iPSC-derived neurons and astrocytes of patients with autism vs. controls (5/group) to examine whether they replicate the postmortem brain expression/epigenetic alterations of autism. Additionally, DNA methylation of 10 postmortem brain samples (5/group) was analyzed for genes affected in PSC-derived cells.

RESULTS

We found hyperexpression of TGFB1, TGFB2, IL6 and IFI16 and decreased expression of HAP1, SIRT1, NURR1, RELN, GPX1, EN2, SLC1A2 and SLC1A3 in the astrocytes of patients with autism, along with DNA hypomethylation of TGFB2, IL6, TNFA and EN2 gene promoters and a decrease in HAP1 promoter 5-hydroxymethylation in the astrocytes of patients with autism. In neurons, HAP1 and IL6 expression trended alike. While HAP1 promoter was hypermethylated in neurons, IFI16 and SLC1A3 promoters were hypomethylated and TGFB2 exhibited increased promoter 5-hydroxymethlation. We also found a reduction in neuronal arborization, spine size, growth rate, and migration, but increased astrocyte size and a reduced growth rate in autism. In postmortem brain samples, we found DNA hypomethylation of TGFB2 and IFI16 promoter regions, but DNA hypermethylation of HAP1 and SLC1A2 promoters in autism.

CONCLUSION

Autism-associated expression/epigenetic alterations in iPSC-derived cells replicated those reported in the literature, making them appropriate surrogates to study disease pathogenesis or patient-specific therapeutics.

A-Syn(ful) MAM: A Fresh Perspective on a Converging Domain in Parkinson's Disease

Parkinson's disease (PD) is a disease of an unknown origin. Despite that, decades of research have provided considerable evidence that alpha-synuclein (αSyn) is central to the pathogenesis of disease. Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) are functional domains formed at contact sites between the ER and mitochondria, with a well-established function of MAMs being the control of lipid homeostasis within the cell. Additionally, there are numerous proteins localized or enriched at MAMs that have regulatory roles in several different molecular signaling pathways required for cellular homeostasis, such as autophagy and neuroinflammation. Alterations in several of these signaling pathways that are functionally associated with MAMs are found in PD. Taken together with studies that find αSyn localized at MAMs, this has implicated MAM (dys)function as a converging domain relevant to PD. This review will highlight the many functions of MAMs and provide an overview of the literature that finds αSyn, in addition to several other PD-related proteins, localized there. This review will also detail the direct interaction of αSyn and αSyn-interacting partners with specific MAM-resident proteins. In addition, recent studies exploring new methods to investigate MAMs will be discussed, along with some of the controversies regarding αSyn, including its several conformations and subcellular localizations. The goal of this review is to highlight and provide insight on a domain that is incompletely understood and, from a PD perspective, highlight those complex interactions that may hold the key to understanding the pathomechanisms underlying PD, which may lead to the targeted development of new therapeutic strategies.

Contribution of CNS and extra-CNS infections to neurodegeneration: a narrative review

Central nervous system infections have been suggested as a possible cause for neurodegenerative diseases, particularly sporadic cases. They trigger neuroinflammation which is considered integrally involved in neurodegenerative processes. In this review, we will look at data linking a variety of viral, bacterial, fungal, and protozoan infections to Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis and unspecified dementia. This narrative review aims to bring together a broad range of data currently supporting the involvement of central nervous system infections in the development of neurodegenerative diseases. The idea that no single pathogen or pathogen group is responsible for neurodegenerative diseases will be discussed. Instead, we suggest that a wide range of susceptibility factors may make individuals differentially vulnerable to different infectious pathogens and subsequent pathologies.

Indoleamine 2,3-dioxygenase (IDO1) - Can dendritic cells and monocytes expressing this moonlight enzyme change the phase of Parkinson's Disease?

Parkinson's Disease (PD) is the second most common neurodegenerative disease where central and peripheral immune dysfunctions have been pointed out as a critical component of susceptibility and progression of this disease. Dendritic cells (DCs) and monocytes are key players in promoting immune response regulation and can induce the enzyme indoleamine 2,3-dioxygenase 1 (IDO1) under pro-inflammatory environments. This enzyme with catalytic and signaling activity supports the axis IDO1-KYN-aryl hydrocarbon receptor (AhR), promoting disease-specific immunomodulatory effects. IDO1 is a rate-limiting enzyme of the kynurenine pathway (KP) that begins tryptophan (Trp) catabolism across this pathway. The immune functions of the pathway, which are extensively described in cancer, have been forgotten so far in neurodegenerative diseases, where a chronic inflammatory environment underlines the progression of the disease. Despite dysfunctions of KP have been described in PD, these are mainly associated with neurotoxic functions. With this review, we aim to focus on the immune properties of IDO1+DCs and IDO1+monocytes as a possible strategy to balance the pro-inflammatory profile described in PD. We also highlight the importance of exploring the role of dopaminergic therapeutics in IDO1 modulation to possibly optimize current PD therapeutic strategies.

Ultrastructural localization of Porphyromonas gingivalis gingipains in the substantia nigra of Parkinson's disease brains

Gingipains are protease virulence factors produced by Porphyromonas gingivalis, a Gram-negative bacterium best known for its role in chronic periodontitis. Gingipains were recently identified in the middle temporal gyrus of postmortem Alzheimer's disease (AD) brains, where gingipain load correlated with AD diagnosis and tau and ubiquitin pathology. Since AD and Parkinson's disease (PD) share some overlapping pathologic features, including nigral pathology and Lewy bodies, the current study explored whether gingipains are present in the substantia nigra pars compacta of PD brains. In immunohistochemical techniques and multi-channel fluorescence studies, gingipain antigens were abundant in dopaminergic neurons in the substantia nigra of both PD and neurologically normal control brains. 3-dimensional reconstructions of Lewy body containing neurons revealed that gingipains associated with the periphery of alpha-synuclein aggregates but were occasionally observed inside aggregates. In vitro proteomic analysis demonstrated that recombinant alpha-synuclein is cleaved by lysine-gingipain, generating multiple alpha-synuclein fragments including the non-amyloid component fragments. Immunogold electron microscopy with co-labeling of gingipains and alpha-synuclein confirmed the occasional colocalization of gingipains with phosphorylated (pSER129) alpha-synuclein. In dopaminergic neurons, gingipains localized to the perinuclear cytoplasm, neuromelanin, mitochondria, and nucleus. These data suggest that gingipains localize in dopaminergic neurons in the substantia nigra and interact with alpha-synuclein.

Immunological aspects of central neurodegeneration

The etiology of various neurodegenerative disorders that mainly affect the central nervous system including (but not limited to) Alzheimer's disease, Parkinson's disease and Huntington's disease has classically been attributed to neuronal defects that culminate with the loss of specific neuronal populations. However, accumulating evidence suggests that numerous immune effector cells and the products thereof (including cytokines and other soluble mediators) have a major impact on the pathogenesis and/or severity of these and other neurodegenerative syndromes. These observations not only add to our understanding of neurodegenerative conditions but also imply that (at least in some cases) therapeutic strategies targeting immune cells or their products may mediate clinically relevant neuroprotective effects. Here, we critically discuss immunological mechanisms of central neurodegeneration and propose potential strategies to correct neurodegeneration-associated immunological dysfunction with therapeutic purposes.

Neuroimmune Connectomes in the Gut and Their Implications in Parkinson's Disease

The gastrointestinal tract is the largest immune organ and it receives dense innervation from intrinsic (enteric) and extrinsic (sympathetic, parasympathetic, and somatosensory) neurons. The immune and neural systems of the gut communicate with each other and their interactions shape gut defensive mechanisms and neural-controlled gut functions such as motility and secretion. Changes in neuroimmune interactions play central roles in the pathogenesis of diseases such as Parkinson's disease (PD), which is a multicentric disorder that is heterogeneous in its manifestation and pathogenesis. Non-motor and premotor symptoms of PD are common in the gastrointestinal tract and the gut is considered a potential initiation site for PD in some cases. How the enteric nervous system and neuroimmune signaling contribute to PD disease progression is an emerging area of interest. This review focuses on intestinal neuroimmune loops such as the neuroepithelial unit, enteric glial cells and their immunomodulatory effects, anti-inflammatory cholinergic signaling and the relationship between myenteric neurons and muscularis macrophages, and the role of α-synuclein in gut immunity. Special consideration is given to the discussion of intestinal neuroimmune connectomes during PD and their possible implications for various aspects of the disease.

The pathogenesis of Parkinson's disease

Parkinson's disease is a progressive neurodegenerative condition associated with the deposition of aggregated α-synuclein. Insights into the pathogenesis of Parkinson's disease have been derived from genetics and molecular pathology. Biochemical studies, investigation of transplanted neurons in patients with Parkinson's disease, and cell and animal model studies suggest that abnormal aggregation of α-synuclein and spreading of pathology between the gut, brainstem, and higher brain regions probably underlie the development and progression of Parkinson's disease. At a cellular level, abnormal mitochondrial, lysosomal, and endosomal function can be identified in both monogenic and sporadic Parkinson's disease, suggesting multiple potential treatment approaches. Recent work has also highlighted maladaptive immune and inflammatory responses, possibly triggered in the gut, that accelerate the pathogenesis of Parkinson's disease. Although there are currently no disease-modifying treatments for Parkinson's disease, we now have a solid basis for the development of rational neuroprotective therapies that we hope will halt the progression of this disabling neurological condition.

Alpha-synuclein dynamics bridge Type-I Interferon response and SARS-CoV-2 replication in peripheral cells

BACKGROUND

Increasing evidence suggests a double-faceted role of alpha-synuclein (α-syn) following infection by a variety of viruses, including SARS-CoV-2. Although α-syn accumulation is known to contribute to cell toxicity and the development and/or exacerbation of neuropathological manifestations, it is also a key to sustaining anti-viral innate immunity. Consistently with α-syn aggregation as a hallmark of Parkinson's disease, most studies investigating the biological function of α-syn focused on neural cells, while reports on the role of α-syn in periphery are limited, especially in SARS-CoV-2 infection.

RESULTS

Results herein obtained by real time qPCR, immunofluorescence and western blot indicate that α-syn upregulation in peripheral cells occurs as a Type-I Interferon (IFN)-related response against SARS-CoV-2 infection. Noteworthy, this effect mostly involves α-syn multimers, and the dynamic α-syn multimer:monomer ratio. Administration of excess α-syn monomers promoted SARS-CoV-2 replication along with downregulation of IFN-Stimulated Genes (ISGs) in epithelial lung cells, which was associated with reduced α-syn multimers and α-syn multimer:monomer ratio. These effects were prevented by combined administration of IFN-β, which hindered virus replication and upregulated ISGs, meanwhile increasing both α-syn multimers and α-syn multimer:monomer ratio in the absence of cell toxicity. Finally, in endothelial cells displaying abortive SARS-CoV-2 replication, α-syn multimers, and multimer:monomer ratio were not reduced following exposure to the virus and exogenous α-syn, suggesting that only productive viral infection impairs α-syn multimerization and multimer:monomer equilibrium.

CONCLUSIONS

Our study provides novel insights into the biology of α-syn, showing that its dynamic conformations are implicated in the innate immune response against SARS-CoV-2 infection in peripheral cells. In particular, our results suggest that promotion of non-toxic α-syn multimers likely occurs as a Type-I IFN-related biological response which partakes in the suppression of viral replication. Further studies are needed to replicate our findings in neuronal cells as well as animal models, and to ascertain the nature of such α-syn conformations.

Infections in the Etiology of Parkinson's Disease and Synucleinopathies: A Renewed Perspective, Mechanistic Insights, and Therapeutic Implications

Increasing evidence suggests a potential role for infectious pathogens in the etiology of synucleinopathies, a group of age-related neurodegenerative disorders including Parkinson's disease (PD), multiple system atrophy and dementia with Lewy bodies. In this review, we discuss the link between infections and synucleinopathies from a historical perspective, present emerging evidence that supports this link, and address current research challenges with a focus on neuroinflammation. Infectious pathogens can elicit a neuroinflammatory response and modulate genetic risk in PD and related synucleinopathies. The mechanisms of how infections might be linked with synucleinopathies as well as the overlap between the immune cellular pathways affected by virulent pathogens and disease-related genetic risk factors are discussed. Here, an important role for α-synuclein in the immune response against infections is emerging. Critical methodological and knowledge gaps are addressed, and we provide new future perspectives on how to address these gaps. Understanding how infections and neuroinflammation influence synucleinopathies will be essential for the development of early diagnostic tools and novel therapies.

Distinct molecular mechanisms contribute to the reduction of melanoma growth and tumor pain after systemic and local depletion of alpha-Synuclein in mice

Epidemiological studies show a coincidence between Parkinson's disease (PD) and malignant melanoma. It has been suggested that this relationship is due, at least in part, to modulation of alpha-Synuclein (αSyn/Snca). αSyn oligomers accumulate in PD, which triggers typical PD symptoms, and in malignant melanoma, which increases the proliferation of tumor cells. In addition, αSyn contributes to non-motor symptoms of PD, including pain. In this study, we investigated the role of αSyn in melanoma growth and melanoma-induced pain in a mouse model using systemic and local depletion of αSyn. B16BL6 wild-type as well as αSyn knock-down melanoma cells were inoculated into the paws of αSyn knock-out mice and wild-type mice, respectively. Tumor growth and tumor-induced pain hypersensitivity were assessed over a period of 21 days. Molecular mechanisms were analyzed by RT-PCR and Western Blot in tumors, spinal cord, and sciatic nerve. Our results indicate that both global and local ablation of Snca contribute to reduced tumor growth and to a reduction of tumor-induced mechanical allodynia, though mechanisms contributing to these effects differ. While injection of wild-type cells in Snca knock-out mice strongly increased the immune response in the tumor, local Snca knock-down decreased autophagy mechanisms and the inflammatory reaction in the tumor. In conclusion, a knockdown of αSyn might constitute a promising approach to inhibiting the progression of melanoma and reducing tumor-induced pain.

Brain-to-gut trafficking of alpha-synuclein by CD11c+ cells in a mouse model of Parkinson's disease

Inflammation in the brain and gut is a critical component of several neurological diseases, such as Parkinson's disease (PD). One trigger of the immune system in PD is aggregation of the pre-synaptic protein, α-synuclein (αSyn). Understanding the mechanism of propagation of αSyn aggregates is essential to developing disease-modifying therapeutics. Using a brain-first mouse model of PD, we demonstrate αSyn trafficking from the brain to the ileum of male mice. Immunohistochemistry revealed that the ileal αSyn aggregations are contained within CD11c+ cells. Using single-cell RNA sequencing, we demonstrate that ileal CD11c+ cells are microglia-like and the same subtype of cells is activated in the brain and ileum of PD mice. Moreover, by utilizing mice expressing the photo-convertible protein, Dendra2, we show that CD11c+ cells traffic from the brain to the ileum. Together these data provide a mechanism of αSyn trafficking between the brain and gut.

Alpha-Synuclein-Specific Regulatory T Cells Ameliorate Parkinson's Disease Progression in Mice

Parkinson's disease (PD) is a long-term neurodegenerative disease characterized by dopaminergic neuronal loss and the aggregation of alpha-synuclein (α-syn) in the brain. Cell therapy using regulatory T cells (Tregs) has therapeutic potential on PD progression in a mouse model; however, several challenges were associated with its applications. Here, we propose a strategy for α-syn specific Treg expansion (α-syn Treg). We presented α-syn to T cells via dendritic cells. This method increased the mobility of Tregs towards the site of abundant α-syn in vitro (p < 0.01; α-syn Tregs versus polyclonal Tregs (poly Tregs)) and in vivo. Consequently, α-syn Tregs showed noteworthy neuroprotective effects against motor function deficits (p < 0.05, p < 0.01; α-syn Tregs versus poly Tregs), dopaminergic neuronal loss (p < 0.001; α-syn Tregs versus poly Tregs), and α-syn accumulation (p < 0.05; α-syn Tregs versus poly Tregs) in MPTP-induced PD mice. Furthermore, the adoptive transfer of α-syn Tregs exerted immunosuppressive effects on activated microglia, especially pro-inflammatory microglia, in PD mice. Our findings suggest that α-syn presentation may provide a significant improvement in neuroprotective activities of Tregs and suggest the effective clinical application of Treg therapy in PD.

Relevance of tissue-resident memory CD8 T cells in the onset of Parkinson's disease and examination of its possible etiologies: infectious or autoimmune?

Tissue-resident memory CD8 T cells are responsible for local immune surveillance in different tissues, including the brain. They constitute the first line of defense against pathogens and cancer cells and play a role in autoimmunity. A recently published study demonstrated that CD8 T cells with markers of residency containing distinct granzymes and interferon-γ infiltrate the parenchyma of the substantia nigra and contact dopaminergic neurons in an early premotor stage of Parkinson's disease. This infiltration precedes α-synuclein aggregation and neuronal loss in the substantia nigra, suggesting a relevant role for CD8 T cells in the onset of the disease. To date, the nature of the antigen that initiates the adaptive immune response remains unknown. This review will discuss the role of tissue-resident memory CD8 T cells in brain immune homeostasis and in the onset of Parkinson's disease and other neurological diseases. We also discuss how aging and genetic factors can affect the CD8 T cell immune response and how animal models can be misleading when studying human-related immune response. Finally, we speculate about a possible infectious or autoimmune origin of Parkinson's disease.

Viral-like TLR3 induction of cytokine networks and α-synuclein are reduced by complement C3 blockade in mouse brain

Inflammatory processes and mechanisms are of central importance in neurodegenerative diseases. In the brain, α-synucleinopathies such as Parkinson's disease (PD) and Lewy body dementia (LBD) show immune cytokine network activation and increased toll like receptor 3 (TLR3) levels for viral double-stranded RNA (dsRNA). Brain inflammatory reactions caused by TLR3 activation are also relevant to understand pathogenic cascades by viral SARS-CoV-2 infection causing post- COVID-19 brain-related syndromes. In the current study, following regional brain TLR3 activation induced by dsRNA in mice, an acute complement C3 response was seen at 2 days. A C3 splice-switching antisense oligonucleotide (ASO) that promotes the splicing of a non-productive C3 mRNA, prevented downstream cytokines, such as IL-6, and α-synuclein changes. This report is the first demonstration that α-synuclein increases occur downstream of complement C3 activation. Relevant to brain dysfunction, post-COVID-19 syndromes and pathological changes leading to PD and LBD, viral dsRNA TLR3 activation in the presence of C3 complement blockade further revealed significant interactions between complement systems, inflammatory cytokine networks and α-synuclein changes.

Genome- and Exome-Wide Association Studies Revealed Candidate Genes Associated with DaTscan Imaging Features

Introduction

Despite remarkable progress in identifying Parkinson's disease (PD) genetic risk loci, the genetic basis of PD remains largely unknown. With the help of the endophenotype approach and using data from dopamine transporter single-photon emission computerized tomography (DaTscan), we identified potentially involved genes in PD.

Method

We conducted an imaging genetic study by performing exome-wide association study (EWAS) and genome-wide association study (GWAS) on the specific binding ratio (SBR) of six DaTscan anatomical areas between 489 and 559 subjects of Parkinson's progression markers initiative (PPMI) cohort and 83,623 and 36,845 single-nucleotide polymorphisms (SNPs)/insertion-deletion mutations (INDELs). We also investigated the association of cerebrospinal fluid (CSF) protein concentration of our significant genes with PD progression using PPMI CSF proteome data.

Results

Among 83,623 SNPs/INDELs in EWAS, one SNP (rs201465075) on 1 q32.1 locus was significantly (P value = 4.03 × 10-7) associated with left caudate DaTscan SBR, and 33 SNPs were suggestive. Among 36,845 SNPs in GWAS, one SNP (rs12450112) on 17 p.12 locus was significantly (P value = 1.34 × 10-6) associated with right anterior putamen DaTscan SBR, and 39 SNPs were suggestive among which 8 SNPs were intergenic. We found that rs201465075 and rs12450112 are most likely related to IGFN1 and MAP2K4 genes. The protein level of MAP2K4 in the CSF was significantly associated with PD progression in the PPMI cohort; however, proteomic data were not available for the IGFN1 gene.

Conclusion

We have shown that particular variants of IGFN1 and MAP2K4 genes may be associated with PD. Since DaTscan imaging could be positive in other Parkinsonian syndromes, caution should be taken when interpreting our results. Future experimental studies are also needed to verify these findings.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Exploring the Potential of Aptamers in Targeting Neuroinflammation and Neurodegenerative Disorders: Opportunities and Challenges

Neuroinflammation is the precursor for several neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Targeting neuroinflammation has emerged as a promising strategy to address a wide range of CNS pathologies. These NDDs still present significant challenges in terms of limited and ineffective diagnosis and treatment options, driving the need to explore innovative and novel therapeutic alternatives. Aptamers are single-stranded nucleic acids that offer the potential for addressing these challenges through diagnostic and therapeutic applications. In this review, we summarize diagnostic and therapeutic aptamers for inflammatory biomolecules, as well as the inflammatory cells in NDDs. We also discussed the potential of short nucleotides for Aptamer-Based Targeted Brain Delivery through their unique features and modifications, as well as their ability to penetrate the blood-brain barrier. Moreover, the unprecedented opportunities and substantial challenges of using aptamers as therapeutic agents, such as drug efficacy, safety considerations, and pharmacokinetics, are also discussed. Taken together, this review assesses the potential of aptamers as a pioneering approach for target delivery to the CNS and the treatment of neuroinflammation and NDDs.

Kinetic control in amyloid polymorphism: Different agitation and solution conditions promote distinct amyloid polymorphs of alpha-synuclein

Aggregation of neuronal protein α-synuclein is implicated in synucleinopathies, including Parkinson's disease. Despite abundant in vitro studies, the mechanism of α-synuclein assembly process remains ambiguous. In this work, α-synuclein aggregation was induced by its constant mixing in two separate modes, either by agitation in a 96-well microplate reader (MP) or in microcentrifuge tubes using a shaker incubator (SI). Aggregation in both modes occurred through a sigmoidal growth pattern with a well-defined lag, growth, and saturation phase. The end-stage MP- and SI-derived aggregates displayed distinct differences in morphological, biochemical, and spectral signatures as discerned through AFM, proteinase-K digestion, FTIR, Raman, and CD spectroscopy. The MP-derived aggregates showed irregular morphology with a significant random coil conformation, contrary to SI-derived aggregates, which showed typical β-sheet fibrillar structures. The end-stage MP aggregates convert to β-rich SI-like aggregates upon 1) seeding with SI-derived aggregates and 2) agitating in SI. We conclude that end-stage MP aggregates were in a kinetically trapped conformation, whose kinetic barrier was bypassed upon either seeding by SI-derived fibrils or shaking in SI. We further show that MP-derived aggregates that form in the presence of sorbitol, an osmolyte, displayed a β-rich signature, indicating that the preferential exclusion effect of osmolytes helped overcome the kinetic barrier. Our findings help in unravelling the kinetic origin of different α-synuclein aggregated polymorphs (strains) that encode diverse variants of synucleinopathies. We demonstrate that kinetic control shapes the polymorphic landscape of α-synuclein aggregates, both through de novo generation of polymorphs, and by their interconversion.

The contribution of the peripheral immune system to neurodegeneration

Microglial cells are the major immune cells of the central nervous system (CNS), and directly react to neurodegeneration, but other immune cell types are also able to react to pathology and can modify the course of neurodegenerative processes. These mainly include monocytes/macrophages and lymphocytes. While these peripheral immune cells were initially considered to act only after infiltrating the CNS, recent evidence suggests that some of them can also act directly from the periphery. We will review the existing and emerging evidence for a role of peripheral immune cells in neurodegenerative diseases, both with and without CNS infiltration. Our focus will be on amyotrophic lateral sclerosis, but we will also compare to Alzheimer's disease and Parkinson's disease to highlight similarities or differences. Peripheral immune cells are easily accessible, and therefore may be an attractive therapeutic target for neurodegenerative diseases. Thus, understanding how these peripheral immune cells communicate with the CNS deserves deeper investigation.

Controversial Properties of Amyloidogenic Proteins and Peptides: New Data in the COVID Era

For a long time, studies of amyloidogenic proteins and peptides (amyloidogenic PPs) have been focused basically on their harmful properties and association with diseases. A vast amount of research has investigated the structure of pathogenic amyloids forming fibrous deposits within or around cells and the mechanisms of their detrimental actions. Much less has been known about the physiologic functions and beneficial properties of amyloidogenic PPs. At the same time, amyloidogenic PPs have various useful properties. For example, they may render neurons resistant to viral infection and propagation and stimulate autophagy. We discuss here some of amyloidogenic PPs' detrimental and beneficial properties using as examples beta-amyloid (β-amyloid), implicated in the pathogenesis of Alzheimer's disease (AD), and α-synuclein-one of the hallmarks of Parkinson's disease (PD). Recently amyloidogenic PPs' antiviral and antimicrobial properties have attracted attention because of the COVID-19 pandemic and the growing threat of other viral and bacterial-induced diseases. Importantly, several COVID-19 viral proteins, e.g., spike, nucleocapsid, and envelope proteins, may become amyloidogenic after infection and combine their harmful action with the effect of endogenous APPs. A central area of current investigations is the study of the structural properties of amyloidogenic PPs, defining their beneficial and harmful properties, and identifying triggers that transform physiologically important amyloidogenic PPs into vicious substances. These directions are of paramount importance during the current SARS-CoV-2 global health crisis.

Advances in AAV technology for delivering genetically encoded cargo to the nonhuman primate nervous system

Modern neuroscience approaches including optogenetics, calcium imaging, and other genetic manipulations have facilitated our ability to dissect specific circuits in rodent models to study their role in neurological disease. These approaches regularly use viral vectors to deliver genetic cargo (e.g., opsins) to specific tissues and genetically-engineered rodents to achieve cell-type specificity. However, the translatability of these rodent models, cross-species validation of identified targets, and translational efficacy of potential therapeutics in larger animal models like nonhuman primates remains difficult due to the lack of efficient primate viral vectors. A refined understanding of the nonhuman primate nervous system promises to deliver insights that can guide the development of treatments for neurological and neurodegenerative diseases. Here, we outline recent advances in the development of adeno-associated viral vectors for optimized use in nonhuman primates. These tools promise to help open new avenues for study in translational neuroscience and further our understanding of the primate brain.

Effect of Electric Field on α-Synuclein Fibrils: Revealed by Molecular Dynamics Simulations

The self-association of amylogenic proteins to the fibril form is considered a pivotal factor in the pathogenesis of neurodegenerative diseases, including Parkinson’s disease (PD). PD causes unintended or uncontrollable movements in its common symptoms. α-synuclein is the major cause of PD development and thus has been the main target of numerous studies to suppress and sequester its expression or effectively degrade it. Nonetheless, to date, there are no efficient and proven ways to prevent pathological protein aggregation. Recent investigations proposed applying an external electric field to interrupt the fibrils. This method is a non-invasive approach that has a certain benefit over others. We performed molecular dynamics (MD) simulations by applying an electric field on highly toxic fibrils of α-synuclein to gain a molecular-level insight into fibril disruption mechanisms. The results revealed that the applied external electric field induces substantial changes in the conformation of the α-synuclein fibrils. Furthermore, we show the threshold value for electric field strength required to completely disrupt the α-synuclein fibrils by opening the hydrophobic core of the fibril. Thus, our findings might serve as a valuable foundation to better understand molecular-level mechanisms of the α-synuclein fibrils disaggregation process under an applied external electric field.

Distribution of phosphorylated alpha-synuclein in non-diseased brain implicates olfactory bulb mitral cells in synucleinopathy pathogenesis

Synucleinopathies are neurodegenerative diseases characterized by pathological inclusions called "Lewy pathology" (LP) that consist of aggregated alpha-synuclein predominantly phosphorylated at serine 129 (PSER129). Despite the importance for understanding disease, little is known about the endogenous function of PSER129 or why it accumulates in the diseased brain. Here we conducted several observational studies using a sensitive tyramide signal amplification (TSA) technique to determine PSER129 distribution and function in the non-diseased mammalian brain. In wild-type non-diseased mice, PSER129 was detected in the olfactory bulb (OB) and several brain regions across the neuroaxis (i.e., OB to brainstem). In contrast, PSER129 immunoreactivity was not observed in any brain region of alpha-synuclein knockout mice. We found evidence of PSER129 positive structures in OB mitral cells of non-diseased mice, rats, non-human primates, and healthy humans. Using TSA multiplex fluorescent labeling, we showed that PSER129 positive punctate structures occur within inactive (i.e., c-fos negative) T-box transcription factor 21 (TBX21) positive mitral cells and PSER129 within these cells was spatially associated with PK-resistant alpha-synuclein. Ubiquitin was found in PSER129 mitral cells but was not closely associated with PSER129. Biotinylation by antibody recognition (BAR) identified 125 PSER129-interacting proteins in the OB of healthy mice, which were significantly enriched for presynaptic vesicle trafficking/recycling, SNARE, fatty acid oxidation, oxidative phosphorylation, and RNA binding. TSA multiplex labeling confirmed the physical association of BAR-identified protein Ywhag with PSER129 in the OB and in other regions across the neuroaxis. We conclude that PSER129 accumulates in the mitral cells of the healthy OB as part of alpha-synuclein normal cellular functions. Incidental LP has been reported in the OB, and therefore we speculate that for synucleinopathies, either the disease processes begin locally in OB mitral cells or a systemic disease process is most apparent in the OB because of the natural tendency to accumulate PSER129.

Dopamine Transmission Imbalance in Neuroinflammation: Perspectives on Long-Term COVID-19

Dopamine (DA) is a key neurotransmitter in the basal ganglia, implicated in the control of movement and motivation. Alteration of DA levels is central in Parkinson’s disease (PD), a common neurodegenerative disorder characterized by motor and non-motor manifestations and deposition of alpha-synuclein (α-syn) aggregates. Previous studies have hypothesized a link between PD and viral infections. Indeed, different cases of parkinsonism have been reported following COVID-19. However, whether SARS-CoV-2 may trigger a neurodegenerative process is still a matter of debate. Interestingly, evidence of brain inflammation has been described in postmortem samples of patients infected by SARS-CoV-2, which suggests immune-mediated mechanisms triggering the neurological sequelae. In this review, we discuss the role of proinflammatory molecules such as cytokines, chemokines, and oxygen reactive species in modulating DA homeostasis. Moreover, we review the existing literature on the possible mechanistic interplay between SARS-CoV-2-mediated neuroinflammation and nigrostriatal DAergic impairment, and the cross-talk with aberrant α-syn metabolism.

The Role of Bacteria-Mitochondria Communication in the Activation of Neuronal Innate Immunity: Implications to Parkinson's Disease

Mitochondria play a key role in regulating host metabolism, immunity and cellular homeostasis. Remarkably, these organelles are proposed to have evolved from an endosymbiotic association between an alphaproteobacterium and a primitive eukaryotic host cell or an archaeon. This crucial event determined that human cell mitochondria share some features with bacteria, namely cardiolipin, N-formyl peptides, mtDNA and transcription factor A, that can act as mitochondrial-derived damage-associated molecular patterns (DAMPs). The impact of extracellular bacteria on the host act largely through the modulation of mitochondrial activities, and often mitochondria are themselves immunogenic organelles that can trigger protective mechanisms through DAMPs mobilization. In this work, we demonstrate that mesencephalic neurons exposed to an environmental alphaproteobacterium activate innate immunity through toll-like receptor 4 and Nod-like receptor 3. Moreover, we show that mesencephalic neurons increase the expression and aggregation of alpha-synuclein that interacts with mitochondria, leading to their dysfunction. Mitochondrial dynamic alterations also affect mitophagy which favors a positive feedback loop on innate immunity signaling. Our results help to elucidate how bacteria and neuronal mitochondria interact and trigger neuronal damage and neuroinflammation and allow us to discuss the role of bacterial-derived pathogen-associated molecular patterns (PAMPs) in Parkinson's disease etiology.

Are patients with Parkinson's disease at a lower risk of catching the common cold? Propensity score matching

INTRODUCTION

Accumulating evidence indicating that inflammatory responses play crucial roles in Parkinson's disease (PD) development provided a hypothesis that physiological alpha-synuclein may contribute to inflammatory responses against infections during non-advanced stages of PD. Thus, we examined the risk of catching a common cold in patients with PD as compared to other common brain diseases.

METHODS

We extracted PD (non-advanced; without dementia) and control (AD: Alzheimer's disease, migraine, epilepsy, and ischemic stroke) patient data from insurance claim data available between 2010 and 2021. After confirming the clinical PD diagnosis, we investigated factors associated with cold diagnoses and used propensity score matching to identify differences in the incidence of colds between PD and control patients.

RESULTS

Diagnosis of colds in PD patients (n = 726) and controls (AD = 377, migraine = 1019, epilepsy = 3414, ischemic stroke = 6943) was found in 1186 (9.5%) patients, which was independently associated with being female (odds ratio: OR 1.59; 95%CI 1.41-1.79; P < 0.0001), follow-up by neurologists (OR 1.30; 95%CI 1.15-1.48; P < 0.0001), diagnosis of PD (OR 0.30; 95%CI 0.20-0.45; P < 0.0001) and COVID-19 pandemic period (OR 0.58; 95%CI 0.47-0.72; P < 0.0001). After propensity score matching, the incidence of colds was significantly lower in PD (3.4%) versus in controls; AD (9.8%; P < 0.0001), migraine (13.3%; P < 0.0001), epilepsy (11.0%; P < 0.0001), ischemic stroke (8.8%; P < 0.0001).

CONCLUSIONS

Patients with PD were less likely to be diagnosed with colds. However, several confounding factors will need to be examined. Moreover, alpha-synuclein may provide protective resistance to viral infections by activating the immune system due to chronic inflammation in non-advanced PD patients.

Immunological Features of LRRK2 Function and Its Role in the Gut-Brain Axis Governing Parkinson's Disease

Emerging evidence implicates intestinal involvement in the onset and/or progression on the selective degeneration of dopaminergic neurons characterizing Parkinson's disease (PD). On the one hand, there are studies supporting the Braak hypothesis that holds that pathologic α-synuclein, a hallmark of PD, is secreted by enteric nerves into intestinal tissue and finds its way to the central nervous system (CNS) via retrograde movement in the vagus nerve. On the other hand, there is data showing that cells bearing leucine-rich repeat kinase 2 (LRRK2), a signaling molecule with genetic variants associated with both PD and with inflammatory bowel disease, can be activated in intestinal tissue and contribute locally to intestinal inflammation, or peripherally to PD pathogenesis via cell trafficking to the CNS. Importantly, these gut-centered factors affecting PD development are not necessarily independent of one another: they may interact and enhance their respective pathologic functions. In this review, we discuss this possibility by analysis of studies conducted in recent years focusing on the ability of LRRK2 to shape immunologic responses and the role of α-synuclein in influencing this ability.

HtrA2 regulates α-Synuclein-mediated mitochondrial reactive oxygen species production in the mitochondria of microglia

Aggregation and misfolding of α-Synuclein (α-Syn), a causative agent for Parkinson's disease (PD), and oxidative stress are tightly implicated in the pathogenesis of PD. Although more than 20 genes including HtrA2 have been identified as causative genes for PD, the molecular mechanisms underlying the pathophysiological functions between HtrA2 and α-Syn in the pathogenesis of PD remain unclear. This study shows that HtrA2 serine protease selectively recognizes and interacts with the NAC region of α-Syn. Interestingly, we found that HtrA2 causes proteolysis of α-Syn to prevent mitochondrial accumulation of α-Syn, thereby inhibiting the production of reactive oxygen species (ROS) in the mitochondria. We have further demonstrated that HtrA2 knockdown promotes α-Syn-mediated mitochondrial ROS production, thereby activating microglial cells. This study is the first to demonstrate that the HtrA2/α-Syn cellular partner may play a crucial role in the pathogenesis of PD and provide new insights into the pathological processes and effective therapeutic strategies for PD.

RAGE Against the Glycation Machine in Synucleinopathies: Time to Explore New Questions

Oligomerization and aggregation of misfolded forms of α-synuclein are believed to be key molecular mechanisms in Parkinson's disease (PD) and other synucleinopathies, so extensive research has attempted to understand these processes. Among diverse post-translational modifications that impact α-synuclein aggregation, glycation may take place at several lysine sites and modify α-synuclein oligomerization, toxicity, and clearance. The receptor for advanced glycation end products (RAGE) is considered a key regulator of chronic neuroinflammation through microglial activation in response to advanced glycation end products, such as carboxy-ethyl-lysine, or carboxy-methyl-lysine. The presence of RAGE in the midbrain of PD patients has been reported in the last decades and this receptor was proposed to have a role in sustaining PD neuroinflammation. However, different PD animal models demonstrated that RAGE is preferentially expressed in neurons and astrocytes, while recent evidence demonstrated that fibrillar, non-glycated α-synuclein binds to RAGE. Here, we summarize the available data on α-synuclein glycation and RAGE in the context of PD, and discuss about the questions yet to be answered that may increase our understanding of the molecular bases of PD and synucleinopathies.

⍺-Synuclein Structural Diversity and the Cellular Environment in ⍺-Synuclein Transmission Models and Humans

Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA) are termed synucleinopathies, disorders that are characterized by the intracellular aggregation of the protein ɑ-synuclein. The cellular tropism of synuclein pathology in these syndromes is notably distinct since in the Lewy disorders, PD and DLB, ɑSyn forms aggregates in neurons whereas in MSA ɑSyn forms aggregates in oligodendrocytes. Studies examining ɑSyn pathology in experimental models and in human brain have now identified fibrillar ɑSyn with unique but distinct molecular signatures, suggesting that the structure of these ɑSyn fibrils might be closely tied to their cellular ontogeny. In contrast to the native structural heterogeneity of ɑSyn in vitro, the conformational landscape of fibrillar ɑSyn in human brain and in vivo transmission models appears to be remarkably uniform. Here, we review the studies by which we propose a hypothesis that the cellular host environment might be in part responsible for how ɑSyn filaments assemble into phenotype-specific strains. We postulate that the maturation of ɑSyn strains develops as a function of their in vivo transmission routes and cell-specific risk factors. The impact of the cellular environment on the structural diversity of ɑSyn might have important implications for the design of preclinical studies and their use for the development of ɑSyn-based biomarkers and therapeutic strategies. By combining phenotype-specific fibrils and relevant synucleinopathy transmission models, preclinical models might more closely reflect unique disease phenotypes.

Evaluation of an Adoptive Cellular Therapy-Based Vaccine in a Transgenic Mouse Model of α-synucleinopathy

Aggregated α-synuclein, a major constituent of Lewy bodies plays a crucial role in the pathogenesis of α-synucleinopathies (SPs) such as Parkinson's disease (PD). PD is affected by the innate and adaptive arms of the immune system, and recently both active and passive immunotherapies targeted against α-synuclein are being trialed as potential novel treatment strategies. Specifically, dendritic cell-based vaccines have shown to be an effective treatment for SPs in animal models. Here, we report on the development of adoptive cellular therapy (ACT) for SP and demonstrate that adoptive transfer of pre-activated T-cells generated from immunized mice can improve survival and behavior, reduce brain microstructural impairment via magnetic resonance imaging (MRI), and decrease α-synuclein pathology burden in a peripherally induced preclinical SP model (M83) when administered prior to disease onset. This study provides preclinical evidence for ACT as a potential immunotherapy for LBD, PD and other related SPs, and future work will provide necessary understanding of the mechanisms of its action.

Mechanisms of Autoimmune Cell in DA Neuron Apoptosis of Parkinson's Disease: Recent Advancement

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that manifests as motor and nonmotor symptoms due to the selective loss of midbrain DArgic (DA) neurons. More and more studies have shown that pathological reactions initiated by autoimmune cells play an essential role in the progression of PD. Autoimmune cells exist in the brain parenchyma, cerebrospinal fluid, and meninges; they are considered inducers of neuroinflammation and regulate the immune in the human brain in PD. For example, T cells can recognize α-synuclein presented by antigen-presenting cells to promote neuroinflammation. In addition, B cells will accelerate the apoptosis of DA neurons in the case of PD-related gene mutations. Activation of microglia and damage of DA neurons even form the self-degeneration cycle to deteriorate PD. Numerous autoimmune cells have been considered regulators of apoptosis, α-synuclein misfolding and aggregation, mitochondrial dysfunction, autophagy, and neuroinflammation of DA neurons in PD. The evidence is mounting that autoimmune cells promote DA neuron apoptosis. In this review, we discuss the current knowledge regarding the regulation and function of B cell, T cell, and microglia as well as NK cell in PD pathogenesis, focusing on DA neuron apoptosis to understand the disease better and propose potential target identification for the treatment in the early stages of PD. However, there are still some limitations in our work, for example, the specific mechanism of PD progression caused by autoimmune cells in mitochondrial dysfunction, ferroptosis, and autophagy has not been clarified in detail, which needs to be summarized in further work.

Ingenuity pathway analysis of α-synuclein predicts potential signaling pathways, network molecules, biological functions, and its role in neurological diseases

Despite the knowledge that mutation, multiplication, and anomalous function of α-synuclein cause progressive transformation of α-synuclein monomers into toxic amyloid fibrils in neurodegenerative diseases, the understanding of canonical signaling, interaction network molecules, biological functions, and role of α-synuclein remains ambiguous. The evolution of artificial intelligence and Bioinformatics tools have enabled us to analyze a vast pool of data to draw meaningful conclusions about the events occurring in complex biological systems. We have taken the advantage of such a Bioinformatics tool, ingenuity pathway analysis (IPA) to decipher the signaling pathways, interactome, biological functions, and role of α-synuclein. IPA of the α-synuclein NCBI gene dataset revealed neuroinflammation, Huntington’s disease, TREM1, phagosome maturation, and sirtuin signaling as the key canonical signaling pathways. IPA further revealed Parkinson’s disease (PD), sumoylation, and SNARE signaling pathways specific to the toxicity of α-synuclein. A frequency distribution analysis of α-synuclein-associated genes from the NCBI dataset that appeared in the predicted canonical pathways revealed that NFKB1 was the most populated gene across the predicted pathways followed by FOS, PRKCD, TNF, GSK3B, CDC42, IL6, MTOR, PLCB1, and IL1B. Overlapping of the predicted top-five canonical signaling pathways and the α-synuclein NCBI gene dataset divulged that neuroinflammation signaling was the most overlapped pathway, while NFKB1, TNF, and CASP1 were the most shared molecules among the pathways. The major diseases associated with α-synuclein were predicted to be neurological diseases, organismal injury and abnormalities, skeletal and muscular disorders, psychological disorders, and hereditary disorders. The molecule activity predictor (MAP) analysis of the principal interaction network of α-synuclein gene SNCA revealed that SNCA directly interacts with APP, CLU, and NEDD4, whereas it indirectly communicates with CALCA and SOD1. Besides, IPA also predicted amyloid plaque forming APP, cytokines/inflammatory mediators IL1B, TNF, MIF, PTGS2, TP53, and CCL2, and kinases of MAPK family Mek, ERK, and P38 MAPK as the top upstream regulators of α-synuclein signaling cascades. Taken together, the first IPA analysis of α-synuclein predicted PD as the key toxicity pathway, neurodegeneration as the major pathological outcome, and inflammatory mediators as the critical interacting partners of α-synuclein.

Infectious origin of Alzheimer’s disease: Amyloid beta as a component of brain antimicrobial immunity

The amyloid cascade hypothesis, focusing on pathological proteins aggregation, has so far failed to uncover the root cause of Alzheimer’s disease (AD), or to provide an effective therapy. This traditional paradigm essentially explains a mechanism involved in the development of sporadic AD rather than its cause. The failure of an overwhelming majority of clinical studies (99.6%) demonstrates that a breakthrough in therapy would be difficult if not impossible without understanding the etiology of AD. It becomes more and more apparent that the AD pathology might originate from brain infection. In this review, we discuss a potential role of bacteria, viruses, fungi, and eukaryotic parasites as triggers of AD pathology. We show evidence from the current literature that amyloid beta, traditionally viewed as pathological, actually acts as an antimicrobial peptide, protecting the brain against pathogens. However, in case of a prolonged or excessive activation of a senescent immune system, amyloid beta accumulation and aggregation becomes damaging and supports runaway neurodegenerative processes in AD. This is paralleled by the recent study by Alam and colleagues (2022) who showed that alpha-synuclein, the protein accumulating in synucleinopathies, also plays a critical physiological role in immune reactions and inflammation, showing an unforeseen link between the 2 unrelated classes of neurodegenerative disorders. The multiplication of the amyloid precursor protein gene, recently described by Lee and collegues (2018), and possible reactivation of human endogenous retroviruses by pathogens fits well into the same picture. We discuss these new findings from the viewpoint of the infection hypothesis of AD and offer suggestions for future research.

More than a century after its discovery, Alzheimer’s disease (AD) remains incurable and mysterious. The dominant hypothesis of amyloid cascade has succeeded in explaining the key pathological mechanism, but not its trigger. Amyloid beta has been traditionally considered a pathological peptide, and its physiological functions remain poorly known. These knowledge gaps have contributed to repeated failures of clinical studies. The emerging infectious hypothesis of AD considers central nervous system (CNS) infection the primary trigger of sporadic AD. A closely connected hypothesis claims that amyloid beta is an antimicrobial peptide. In this review, we discuss the available evidence for the involvement of infections in AD, coming from epidemiological studies, post mortem analyses of brain tissue, and experiments in vitro and in vivo. We argue there is no unique “Alzheimer’s germ,” instead, AD is a general reaction of the CNS to chronic infections, in the milieu of an aged immune system. The pathology may become self-sustained even without continuous presence of microbes in the brain. Importantly, the infectious hypothesis leads to testable predictions. Targeting amyloid beta should be ineffective, unless the triggering pathogen and inflammatory response are addressed as well. Meticulous control of selected infections might be the best near-term strategy for AD prevention.