α-Synuclein and neuronal cell death

Transcriptional mutagenesis of α-synuclein caused by DNA oxidation in Parkinson's disease pathogenesis

Oxidative stress plays an essential role in the development of Parkinson's disease (PD). 8-oxo-7,8-dihydroguanine (8-oxodG, oxidized guanine) is the most abundant oxidative stress-mediated DNA lesion. However, its contributing role in underlying PD pathogenesis remains unknown. In this study, we hypothesized that 8-oxodG can generate novel α-synuclein (α-SYN) mutants with altered pathologic aggregation through a phenomenon called transcriptional mutagenesis (TM). We observed a significantly higher accumulation of 8-oxodG in the midbrain genomic DNA from PD patients compared to age-matched controls, both globally and region specifically to α-SYN. In-silico analysis predicted that forty-three amino acid positions can contribute to TM-derived α-SYN mutation. Here, we report a significantly higher load of TM-derived α-SYN mutants from the midbrain of PD patients compared to controls using a sensitive PCR-based technique. We found a novel Serine42Tyrosine (S42Y) α-SYN as the most frequently detected TM mutant, which incidentally had the highest predicted aggregation score amongst all TM variants. Immunohistochemistry of midbrain sections from PD patients using a newly characterized antibody for S42Y identified S42Y-laden Lewy bodies (LB). We further demonstrated that the S42Y TM variant significantly accelerates WT α-SYN aggregation by cell and recombinant protein-based assays. Cryo-electron tomography revealed that S42Y exhibits considerable conformational heterogeneity compared to WT fibrils. Moreover, S42Y exhibited higher neurotoxicity compared to WT α-SYN as shown in mouse primary cortical cultures and AAV-mediated overexpression in the substantia nigra of C57BL/6 J mice. To our knowledge, this is the first report describing the possible contribution of TM-generated mutations of α-SYN to LB formation and PD pathogenesis.

Extracellular high molecular weight α-synuclein oligomers induce cell death by disrupting the plasma membrane

α-Synuclein (αS), the causative protein of Parkinson's disease and other α-synucleinopathies, aggregates from a low molecular weight form (LMW-αS) to a high molecular weight αS oligomer (HMW-αSo). Aggregated αS accumulates intracellularly, induces intrinsic apoptosis, is released extracellularly, and appears to propagate disease through prion-like spreading. Whether extracellular αS aggregates are cytotoxic, damage cell wall, or induce cell death is unclear. We investigated cytotoxicity and cell death caused by HMW-αSo or LMW-αS. Extracellular HMW-αSo was more cytotoxic than LMW-αS and was a crucial factor for inducing plasma membrane damage and cell death. HMW-αSo induced reactive oxygen species production and phospholipid peroxidation in the membrane, thereby impairing calcium homeostasis and disrupting plasma membrane integrity. HMW-αSo also induced extrinsic apoptosis and cell death by activating acidic sphingomyelinase. Thus, as extracellular HMW-αSo causes neuronal injury and death via cellular transmission and direct plasma membrane damage, we propose an additional disease progression pathway for α-synucleinopathies.

Sporadic SNCA mutations A18T and A29S exhibit variable effects on protein aggregation, cell viability and oxidative stress

BACKGROUND

α-synuclein aggregation is the hallmark feature of Parkinson's disease. Both familial and sporadic forms of the disease exhibit this feature. Several mutations have been identified in patients and are associated with the disease pathology.

METHODS AND RESULTS

We have used site-directed mutagenesis to generate α-synuclein mutant variants tagged with GFP. Fluorescence microscopy, flow cytometry, western blotting, cell viability and oxidative stress analysis were performed to investigate the effect of two less studied α-synuclein variants. In this study we characterized two less studied α-synuclein mutations, A18T and A29S, in the well-established yeast model. Our data shows variable expression, distribution and toxicity of the protein in the mutant variants A18T, A29S, A53T and WT. The cells expressing the double mutant variant A18T/A53T showed the most increase in the aggregation phenotype and also depicted reduced viability suggesting a more substantial effect of this variant.

CONCLUSION

The outcome of our study highlights the variable localization, aggregation phenotype and toxicity of the studied α-synuclein variants. This underscores the importance of in-depth analysis of every disease-associated mutation which may result in variable cellular phenotype.

L-Theanine alleviates MPTP-induced Parkinson's disease by targeting Wnt/β-catenin signaling mediated by the MAPK signaling pathway

We evaluated the neuroprotective effect of L-theanine in Parkinson's disease and the underlying mechanism focusing on WNT/β-catenin signaling mediated by the MAPK pathway. We treated MPTP-induced SH-SY5Y cells with various concentrations of L-theanine (50, 100, 200, and 500 μg/mL), and we also treated Parkinson's model mice with L-theanine. L-theanine treatment effectively reduced the immunohistochemical hallmarks of Parkinson's disease, particularly Lewy bodies and α-synuclein, and increased the number of tyrosine hydroxylase-positive cells. L-theanine also improved the motor dysfunction in MPTP-induced Parkinson's disease model mice as measured by the rotarod test. The levels of several pro-inflammatory mediators that are overexpressed in Parkinson's disease, namely TNF-α, IL-6, COX-2, and MAC-1, were reduced following L-theanine treatment, and the levels of the pro-apoptotic proteins Bcl-2, caspase-3, p53, and PARP-1 were significantly reduced. L-theanine regulated the oxidative stress-related factors SOD-1, GST, and NOX-4 by targeting several proteins related to WNT/β-catenin signaling, i.e., β-catenin, WNT-3a, WNT-5a, TCF1/TCF7, and LEF1, via the MAPK pathway (p-JNK, p-ERK, and p-p38). Our results indicate that L-theanine is neuroprotective and has anti-inflammatory effects that could be beneficial for treating Parkinson's disease.

Salsolinol Induces Parkinson's Disease Through Activating NLRP3-Dependent Pyroptosis and the Neuroprotective Effect of Acteoside

Endogenous neurotoxin 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroiso-quinoline (Salsolinol, SAL) is a dopamine metabolite that is toxic to dopaminergic neurons in vitro and in vivo, and is involved in the pathogenesis of Parkinson's disease (PD). However, the molecular mechanism by which SAL induces neurotoxicity in PD remains challenging for future investigations. This study found that SAL induced neurotoxicity in SH-SY5Y cells and mice. RNA sequencing (RNAseq) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used to detect differentially expressed genes in SAL-treated SH-SY5Y cells. We found that NLR family pyrin domain-containing 3 (NLRP3)-dependent pyroptosis was enriched by SAL, which was validated by in vitro and in vivo SAL models. Further, NLRP3 inflammasome-related genes (ASC, NLRP3, active caspase 1, IL-1β, and IL-18) were increased at the mRNA and protein level. Acteoside mitigates SAL-induced neurotoxicity by inhibiting NLRP3 inflammasome-related pyroptosis in in vitro and in vivo PD models. In summary, the present study suggests for the first time that NLRP3-dependent pyroptosis plays a role in the pathogenesis of SAL-induced PD, and acteoside mitigates SAL-induced pyroptosis-dependent neurotoxicity in in vitro and in vivo PD models. The present results demonstrated a new mechanism whereby SAL mediates neurotoxicity by activating NLRP3-dependent pyroptosis, further highlighting SAL-induced pyroptosis-dependent neurotoxicity as a potential therapeutic target in PD.

Molecular Insights into the Misfolding and Dimerization Dynamics of the Full-Length α-Synuclein from Atomistic Discrete Molecular Dynamics Simulations

The misfolding and pathological aggregation of α-synuclein forming insoluble amyloid deposits is associated with Parkinson's disease, the second most common neurodegenerative disease in the world population. Characterizing the self-assembly mechanism of α-synuclein is critical for discovering treatments against synucleinopathies. The intrinsically disordered property, high degrees of freedom, and macroscopic timescales of conformational conversion make its characterization extremely challenging in vitro and in silico. Here, we systematically investigated the dynamics of monomer misfolding and dimerization of the full-length α-synuclein using atomistic discrete molecular dynamics simulations. Our results suggested that both α-synuclein monomers and dimers mainly adopted unstructured formations with partial helices around the N-terminus (residues 8-32) and various β-sheets spanning the residues 35-56 (N-terminal tail) and residues 61-95 (NAC region). The C-terminus mostly assumed an unstructured formation wrapping around the lateral surface and the elongation edge of the β-sheet core formed by an N-terminal tail and NAC regions. Dimerization enhanced the β-sheet formation along with a decrease in the unstructured content. The inter-peptide β-sheets were mainly formed by the N-terminal tail and NACore (residues 68-78) regions, suggesting that these two regions played critical roles in the amyloid aggregation of α-synuclein. Interactions of the C-terminus with the N-terminal tail and the NAC region were significantly suppressed in the α-synuclein dimer, indicating that the interaction of the C-terminus with the N-terminal tail and NAC regions could prevent α-synuclein aggregation. These results on the structural ensembles and early aggregation dynamics of α-synuclein will help understand the nucleation and fibrillization of α-synuclein.

Vexed mutations promote degeneration of dopaminergic neurons through excessive activation of the innate immune response

The hallmark of Parkinson's disease (PD) is the loss of dopaminergic (DA) neurons in the brain. However, little is known about why DA neurons are selectively vulnerable to PD. We previously completed a screen identifying genes associated with the progressive degeneration of DA neurons. Here we describe the role of a previously uncharacterized gene, CG42339, in the loss of DA neurons using Drosophila Melanogaster. CG42339 mutants display a progressive loss of DA neurons and locomotor dysfunction, along with an accumulation of advanced glycation end products (AGEs) in the brain. Based on this phenotype, we refer to CG42339 as vexed. We demonstrate that vexed is specifically required within cortex glia to maintain neuronal viability. Loss of vexed function results in excessive activation of the innate immune response in the brain, leading to loss of DA neurons. We show that activation of the innate immune response leads to increased nitric oxide signaling and accumulation of AGEs, which ultimately result in neurodegeneration. These results provide further insight into the relationship between the role of the immune response in the central nervous system and how this impacts neuronal viability.

Liquid-Liquid Phase Separation Promotes Protein Aggregation and Its Implications in Ferroptosis in Parkinson’s Disease Dementia

The pathological features of PDD are represented by dopaminergic neuronal death and intracellular α-synuclein (α-syn) aggregation. The interaction of iron accumulation with α-syn and tau was further explored as an essential pathological mechanism of PDD. However, the links and mechanisms between these factors remain unclear. Studies have shown that the occurrence and development of neurodegenerative diseases such as PDD are closely related to the separation of abnormal phases. Substances such as proteins can form droplets through liquid-liquid phase separation (LLPS) under normal physiological conditions and even undergo further liquid-solid phase transitions to form solid aggregates under disease or regulatory disorders, leading to pathological phenomena. By analyzing the existing literature, we propose that LLPS is the crucial mechanism causing abnormal accumulation of α-syn, tau, and other proteins in PDD, and its interaction with iron metabolism disorder is the key factor driving ferroptosis in PDD. Therefore, we believe that LLPS can serve as one of the means to explain the pathological mechanism of PDD. Determining the significance of LLPS in neurodegenerative diseases such as PDD will stimulate interest in research into treatments based on interference with abnormal LLPS.

Role of post-translational modifications on the alpha-synuclein aggregation-related pathogenesis of Parkinson’s disease

Together with neuronal loss, the existence of insoluble inclusions of alpha-synuclein (α-syn) in the brain is widely accepted as a hallmark of synucleinopathies including Parkinson’s disease (PD), multiple system atrophy, and dementia with Lewy body. Because the α-syn aggregates are deeply involved in the pathogenesis, there have been many attempts to demonstrate the mechanism of the aggregation and its potential causative factors including post-translational modifications (PTMs). Although no concrete conclusions have been made based on the previous study results, growing evidence suggests that modifications such as phosphorylation and ubiquitination can alter α-syn characteristics to have certain effects on the aggregation process in PD; either facilitating or inhibiting fibrillization. In the present work, we reviewed studies showing the significant impacts of PTMs on α-syn aggregation. Furthermore, the PTMs modulating α-syn aggregation-induced cell death have been discussed. 

The use of fibroblasts as a valuable strategy for studying mitochondrial impairment in neurological disorders

Neurological disorders (NDs) are characterized by progressive neuronal dysfunction leading to synaptic failure, cognitive impairment, and motor injury. Among these diseases, Alzheimer's disease (AD), Parkinson's disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS) have raised a significant research interest. These disorders present common neuropathological signs, including neuronal dysfunction, protein accumulation, oxidative damage, and mitochondrial abnormalities. In this context, mitochondrial impairment is characterized by a deficiency in ATP production, excessive production of reactive oxygen species, calcium dysregulation, mitochondrial transport failure, and mitochondrial dynamics deficiencies. These defects in mitochondrial health could compromise the synaptic process, leading to early cognitive dysfunction observed in these NDs. Interestingly, skin fibroblasts from AD, PD, HD, and ALS patients have been suggested as a useful strategy to investigate and detect early mitochondrial abnormalities in these NDs. In this context, fibroblasts are considered a viable model for studying neurodegenerative changes due to their metabolic and biochemical relationships with neurons. Also, studies of our group and others have shown impairment of mitochondrial bioenergetics in fibroblasts from patients diagnosed with sporadic and genetic forms of AD, PD, HD, and ALS. Interestingly, these mitochondrial abnormalities have been observed in the brain tissues of patients suffering from the same pathologies. Therefore, fibroblasts represent a novel strategy to study the genesis and progression of mitochondrial dysfunction in AD, PD, HD, and ALS. This review discusses recent evidence that proposes fibroblasts as a potential target to study mitochondrial bioenergetics impairment in neurological disorders and consequently to search for new biomarkers of neurodegeneration.

The Therapeutic Role of Ketogenic Diet in Neurological Disorders

The ketogenic diet (KD) is a high-fat, low-carbohydrate and adequate-protein diet that has gained popularity in recent years in the context of neurological diseases (NDs). The complexity of the pathogenesis of these diseases means that effective forms of treatment are still lacking. Conventional therapy is often associated with increasing tolerance and/or drug resistance. Consequently, more effective therapeutic strategies are being sought to increase the effectiveness of available forms of therapy and improve the quality of life of patients. For the moment, it seems that KD can provide therapeutic benefits in patients with neurological problems by effectively controlling the balance between pro- and antioxidant processes and pro-excitatory and inhibitory neurotransmitters, and modulating inflammation or changing the composition of the gut microbiome. In this review we evaluated the potential therapeutic efficacy of KD in epilepsy, depression, migraine, Alzheimer’s disease and Parkinson’s disease. In our opinion, KD should be considered as an adjuvant therapeutic option for some neurological diseases.

Protective Effect of CP690550 in MPTP-Induced Parkinson's Like Behavioural, Biochemical and Histological Alterations in Mice

Janus-activated kinases (JAKs) are well known to play a physiological as well as pathological role in several disease conditions such as autoimmune disorders. The present study evaluated the therapeutic potential of CP690550 (pan-JAK inhibitor) in 1-methyl-4-phenyl-1,2,3,6-tertahydropyridine (MPTP) model of Parkinson's disease. Intrastriatal administration of MPTP (30 micromol in 2 microl) produced a significant alteration in behavioural (bar test and block test). Biochemical investigations in serum and brain homogenate revealed a significant alteration in the JAK-mediated cytokine levels. MPTP administration also showed significant imbalance of inflammatory (increased TNF-α, IL-6 and NF-κb) versus anti-inflammatory cytokines (decreased IL-10 levels). MPTP-treated brain sections revealed alteration in the tissue architecture as well as undifferentiated bodies of varying contour and lesions. Chronic administration of CP690550 (3 and 10 mg/kg, po) for 7 days significantly reversed the behavioural, biochemical and histological alterations induced by MPTP. In conclusion, the findings of the present study govern the possible therapeutic potential of CP690550 in MPTP-treated mice and thus highlight the therapeutic potential of JAK inhibitors in treatment of Parkinson's disease.

Exposure of α-Synuclein Aggregates to Organotypic Slice Cultures Recapitulates Key Molecular Features of Parkinson's Disease

The accumulation of proteinaceous deposits comprised largely of the α-synuclein protein is one of the main hallmarks of Parkinson's disease (PD) and related synucleinopathies. Their progressive development coincides with site-specific phosphorylation, oxidative stress and eventually, compromised neuronal function. However, modeling protein aggregate formation in animal or in vitro models has proven notably difficult. Here, we took advantage of a preclinical organotypic brain slice culture model to study α-synuclein aggregate formation ex vivo. We monitored the progressive and gradual changes induced by α-synuclein such as cellular toxicity, autophagy activation, mitochondrial dysfunction, cellular death as well as α-synuclein modification including site-specific phosphorylation. Our results demonstrate that organotypic brain slice cultures can be cultured for long periods of time and when cultured in the presence of aggregated α-synuclein, the molecular features of PD are recapitulated. Taken together, this ex vivo model allows for detailed modeling of the molecular features of PD, thus enabling studies on the cumulative effects of α-synuclein in a complex environment. This provides a platform to screen potential disease-modifying therapeutic candidates aimed at impeding α-synuclein aggregation and/or cellular transmission. Moreover, this model provides a robust replacement for in vivo studies that do not include behavioral experiments, thus providing a way to reduce the number of animals used in an accelerated timescale.

Modifying the diet and gut microbiota to prevent and manage neurodegenerative diseases

The global prevalence of Alzheimer's disease and Parkinson's disease is steadily increasing due to the aging population. The lack of effective drugs against these neurodegenerative disorders makes it imperative to identify new strategies for their prevention and treatment. Recent studies have revealed that harnessing the power of the gut microbiota through modification of diet may be a valuable approach for reducing the risk, modulating the symptoms, and ameliorating the pathophysiological aspects of neurodegenerative diseases. Consuming specific dietary components can alter the prevalence of bacterial communities within the gut to a healthy enterotype, which can influence the production of beneficial metabolites by microbiota. This article focuses on several dietary components, which have been demonstrated to affect the gut microbiota-brain axis and therefore could lead to attenuation of specific pathological processes in neurodegenerative diseases. Published evidence indicates that fermented foods, including kefir, and foods that are high in bioactive polyphenols and complex carbohydrates, such as grapes, pomegranates, and seaweed, may be effective at reducing neuroinflammation, oxidative stress, neurotransmitter dysfunction, and neuronal death associated with Alzheimer's and Parkinson's diseases. Even though experimental evidence supporting the protective properties of the above dietary components in these diseases is emerging, it is evident that further human clinical studies are required to conclusively establish the benefits of any suggested dietary interventions. The translational potential of such research is illustrated by the clinical success of the recently developed Alzheimer's drug, GV-971, which is a seaweed derivative that works by modulating the gut microbiota-brain axis.

Pharmacological Intervention Targeting FAF1 Restores Autophagic Flux for α-Synuclein Degradation in the Brain of a Parkinson's Disease Mouse Model

α-Synuclein accumulation is implicated in the pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD). Previously, we reported that Fas-associated factor 1 (FAF1), which plays a role in PD pathogenesis, potentiates α-synuclein accumulation through autophagy impairment in dopaminergic neurons. In this study, we show that KM-819, a FAF1-targeting compound, which has completed phase I clinical trials, interferes with α-synuclein accumulation in the mouse brain, as well as in human neuronal cells (SH-SY5Ys). KM-819 suppressed the accumulation of monomeric, oligomeric, and aggregated forms of α-synuclein in neuronal cells. Furthermore, KM-819 restored the turnover rate of α-synuclein in FAF1-overexpressing SH-SY5Y cells, implicating KM-819-mediated reconstitution of the α-synuclein degradative pathway. In addition, KM-819 reconstituted autophagic flux in FAF1-transfected SH-SY5Y cells, also suppressing α-synuclein-induced mitochondrial dysfunction. Moreover, oral administration of KM-819 also interfered with α-synuclein accumulation in the midbrain of mice overexpressing FAF1 via an adeno-associated virus system. Consistently, KM-819 reduced α-synuclein accumulation in both the hippocampus and the midbrain of human A53T α-synuclein transgenic mice. Collectively, these data imply that KM-819 may have therapeutic potential for patients with PD.

Imaging modalities in differential diagnosis of Parkinson’s disease: opportunities and challenges

Background

Parkinson’s disease (PD) diagnosis is yet largely based on the related clinical aspects. However, genetics, biomarkers, and neuroimaging studies have demonstrated a confirming role in the diagnosis, and future developments might be used in a pre-symptomatic phase of the disease.

Main text

This review provides an update on the current applications of neuroimaging modalities for PD diagnosis. A literature search was performed to find published studies that were involved on the application of different imaging modalities for PD diagnosis. An organized search of PubMed/MEDLINE, Embase, ProQuest, Scopus, Cochrane, and Google Scholar was performed based on MeSH keywords and suitable synonyms. Two researchers (TM and JPI) independently and separately performed the literature search. Our search strategy in each database was done by the following terms: ((Parkinson [Title/Abstract]) AND ((“Parkinsonian syndromes ”[Mesh]) OR Parkinsonism [Title/Abstract])) AND ((PET [Title/Abstract]) OR “SPECT”[Mesh]) OR ((Functional imaging, Transcranial sonography [Title/Abstract]) OR “Magnetic resonance spectroscopy ”[Mesh]). Database search had no limitation in time, and our last update of search was in February 2021. To have a comprehensive search and to find possible relevant articles, a manual search was conducted on the reference list of the articles and limited to those published in English.

Conclusion

Early diagnosis of PD could be vital for early management and adequate neuroprotection. Recent neuroimaging modalities such as SPECT and PET imaging using radiolabeled tracers, MRI, and CT are used to discover the disease. By the modalities, it is possible to early diagnose dopaminergic degeneration and also to differentiate PD from others parkinsonian syndromes, to monitor the natural progression of the disease and the effect of neuroprotective treatments on the progression. In this regard, functional imaging techniques have provided critical insights and roles on PD.

Exposure to anesthesia is not associated with development of α-synucleinopathies: A nested case-control study

INTRODUCTION

Preclinical studies suggest that inhalational anesthetics may induce neuropathology changes in the nigrostriatal system, leading to development of α-synucleinopathies. We explored the role of general anesthesia in the development of Parkinson disease (PD) and other α-synucleinopathies.

METHODS

All α-synucleinopathy cases in Olmsted County, Minnesota, from January 1991, to December 2010, were identified from diagnostic codes, and then reviewed for type and index date of diagnosis. Cases were matched by sex and age (±1 year) to a referent control, a resident living in Olmsted County, and free of α-synucleinopathies before the index date (year of onset of the α-synucleinopathy). Medical records of both cases and controls were reviewed for lifetime exposure to anesthesia prior to the index date.

RESULTS

A total of 431 cases with clinically defined α-synucleinopathies were identified. Of these, 321 (74%) underwent 1,069 procedures under anesthesia before the diagnosis date, and in the control group, 341 (79%) underwent 986 procedures. When assessed as a dichotomous variable, anesthetic exposure was not significantly associated with α-synucleinopathies (odds ratio [OR], 0.75; 95% CI, 0.54-1.05; P=.094). No association was observed when anesthetic exposure was quantified by the number of exposures (OR, 0.64, 0.89, and  0.74, for 1, 2-3, and ≥4 exposures, respectively, compared to no exposure as the reference; P=.137) or quantified by the cumulative duration of exposure assessed as a continuous variable (OR, 1.00; 95% CI, 0.97-1.02 per 1-h increase of anesthetic exposure; P=.776).

CONCLUSIONS

We did not observe a significant association between exposure to general anesthesia and risk for the development of α-synucleinopathies.

Proteolytic α-Synuclein Cleavage in Health and Disease

In Parkinson's disease, aggregates of α-synuclein within Lewy bodies and Lewy neurites represent neuropathological hallmarks. However, the cellular and molecular mechanisms triggering oligomeric and fibrillary α-synuclein aggregation are not fully understood. Recent evidence indicates that oxidative stress induced by metal ions and post-translational modifications such as phosphorylation, ubiquitination, nitration, glycation, and SUMOylation affect α-synuclein conformation along with its aggregation propensity and neurotoxic profiles. In addition, proteolytic cleavage of α-synuclein by specific proteases results in the formation of a broad spectrum of fragments with consecutively altered and not fully understood physiological and/or pathological properties. In the present review, we summarize the current knowledge on proteolytical α-synuclein cleavage by neurosin, calpain-1, cathepsin D, and matrix metalloproteinase-3 in health and disease. We also shed light on the contribution of the same enzymes to proteolytical processing of pathogenic proteins in Alzheimer's disease and report potential cross-disease mechanisms of pathogenic protein aggregation.

Combating deleterious phase transitions in neurodegenerative disease

Protein aggregation is a hallmark of neurodegenerative diseases. However, the mechanism that induces pathogenic aggregation is not well understood. Recently, it has emerged that several of the pathological proteins found in an aggregated or mislocalized state in neurodegenerative diseases are also able to undergo liquid-liquid phase separation (LLPS) under physiological conditions. Although these phase transitions are likely important for various physiological functions, neurodegenerative disease-related mutations and conditions can alter the LLPS behavior of these proteins, which can elicit toxicity. Therefore, therapeutics that antagonize aberrant LLPS may be able to mitigate toxicity and aggregation that is ubiquitous in neurodegenerative disease. Here, we discuss the mechanisms by which aberrant protein phase transitions may contribute to neurodegenerative disease. We also outline potential therapeutic strategies to counter deleterious phases. State without borders: Membrane-less organelles and liquid-liquid phase transitions edited by Vladimir N Uversky.

Inflammatory Responses to Monomeric and Aggregated α-Synuclein in Peripheral Blood of Parkinson Disease Patients

To investigate whether different forms of α-synuclein (α-syn) proteins can induce inflammation and activate the NLRP3 inflammasome, we stimulated with monomeric or aggregated α-syn peripheral blood mononuclear cells of Parkinson disease (PD) patients and age- and sex-matched healthy controls (HC). ASC-speck formation, i.e., the intracellular generation of functionally active inflammasome complexes, as well as the production of inflammasome-related [caspase-1, interleukin 1β (IL-18), and IL-1β], and pro–IL-6, or anti–IL-10 inflammatory cytokines were evaluated. Gastrointestinal permeability, suggested to be altered in PD, was also investigated by measuring plasma concentration of lipopolysaccharide (LPS) and I-FABP (fatty acid–binding protein). ASC-speck expression, as well as IL-18 and caspase-1 production and LPS and I-FABP plasma concentration, was comparable in PD and HC, indicating that α-syn does not stimulate the NLRP3 inflammasome and that PD does not associate with alterations of intestinal permeability. Interestingly, though, IL-1β and IL-6 production was increased, whereas that of IL-10 was reduced in α-syn–stimulated cells of PD compared to HC, suggesting that PD-associated neuroinflammation is not the consequence of the activation of the NLRP3 inflammasome but rather of an imbalance between proinflammatory and anti-inflammatory cytokines.

Activation of α7-nAChRs Promotes the Clearance of α-Synuclein and Protects Against Apoptotic Cell Death Induced by Exogenous α-Synuclein Fibrils

Misfolding and abnormal aggregation of α-synuclein (αSyn) have been shown to increase the risk of developing Parkinson's disease (PD). Finding some way to reduce the aggregation of αSyn is particularly important for the treatment of PD. The main route in prion-like αSyn spreading is the cholinergic innervated vagus nervous system and central cholinergic neurons. Since the degenerative changes and death of cholinergic neurons also run through the pathological process of PD, we hypothesize an involvement of the cholinergic system in αSyn aggregation. The α7 nicotinic acetylcholine receptors (α7-nAChRs) are one of the most abundant nAChRs in the mammalian brain. Using nicotine and a selective α7-nAChRs agonist PNU-282987, we found a protective effect of α7-nAChRs on the cell damage induced by αSyn-PFF (preformed fibrils) through inhibiting apoptotic cell death. We further discovered an additive effect of α7-nAChRs on the clearance of αSyn in normal and αSyn stably transduced SH-SY5Y cells. Moreover, using α7-nAChRs knockout mice, we noticed that α7-nAChRs deficiency increased the deposition of αSyn and aggravated the loss of dopaminergic neurons in a chronic MPTP mouse model of PD. Our findings for the first time indicated that α7-nAChRs activation exhibited a neuroprotective effect on αSyn pathology and aggregation by promoting the clearance of αSyn.

C/EBPβ/δ-secretase signaling mediates Parkinson's disease pathogenesis via regulating transcription and proteolytic cleavage of α-synuclein and MAOB

Parkinson's disease (PD) is characterized by dopaminergic neuronal loss and the presence of intra-neuronal Lewy body (LB) inclusions with aggregated α-synuclein (α-Syn) as the major component. MAOB, a crucial monoamine oxidase for dopamine metabolism, triggers oxidative stress in dopaminergic neurons and α-Syn aggregation. However, the key molecular mechanism that mediates PD pathogenesis remains elusive. Here we show that C/EBPβ acts as an age-dependent transcription factor for both α-Syn and MAOB, and initiates the PD pathologies by upregulating these two pivotal players, in addition to escalating δ-secretase activity to cleave α-Syn and promotes its neurotoxicity. Overexpression of C/EBPβ in human wild-type α-Syn transgenic mice facilitates PD pathologies and elicits motor disorders associated with augmentation of δ-secretase, α-Syn, and MAOB. In contrast, depletion of C/EBPβ from human α-Syn Tg mice abolishes rotenone-elicited PD pathologies and motor impairments via downregulating the expression of these key factors. Hence, our study supports that C/EBPβ/δ-secretase signaling mediates PD pathogenesis via regulating the expression and cleavage of α-Syn and MAOB.

Mitophagy impairment in neurodegenerative diseases: Pathogenesis and therapeutic interventions

Neurons are specialized cells, requiring a lot of energy for its proper functioning. Mitochondria are the key cellular organelles and produce most of the energy in the form of ATP, required for all the crucial functions of neurons. Hence, the regulation of mitochondrial biogenesis and quality control is important for maintaining neuronal health. As a part of mitochondrial quality control, the aged and damaged mitochondria are removed through a selective mode of autophagy called mitophagy. However, in different pathological conditions, this process is impaired in neuronal cells and lead to a variety of neurodegenerative disease (NDD). Various studies indicate that specific protein aggregates, the characteristics of different NDDs, affect this process of mitophagy, adding to the severity and progression of diseases. Though, the detailed process of this association is yet to be explored. In light of the significant role of impaired mitophagy in NDDs, further studies have also investigated a large number of therapeutic strategies to target mitophagy in these diseases. Our current review summarizes the abnormalities in different mitophagy pathways and their association with different NDDs. We have also elaborated upon various novel therapeutic strategies and their limitations to enhance mitophagy in NDDs that may help in the management of symptoms and increasing the life expectancy of NDD patients. Thus, our study provides an overview of mitophagy in NDDs and emphasizes the need to elucidate the mechanism of impaired mitophagy prevalent across different NDDs in future research. This will help designing better treatment options with high efficacy and specificity.

Do caffeine and more selective adenosine A2A receptor antagonists protect against dopaminergic neurodegeneration in Parkinson's disease?

The adenosine A_2A receptor is a major target of caffeine, the most widely used psychoactive substance worldwide. Large epidemiological studies have long shown caffeine consumption is a strong inverse predictor of Parkinson’s disease (PD). In this review, we first examine the epidemiology of caffeine use vis-à-vis PD and follow this by looking at the evidence for adenosine A_2A receptor antagonists as potential neuroprotective agents. There is a wealth of accumulating biological, epidemiological and clinical evidence to support the further investigation of selective adenosine A_2A antagonists, as well as caffeine, as promising candidate therapeutics to fill the unmet need for disease modification of PD.

Caffeine and Parkinson's Disease: Multiple Benefits and Emerging Mechanisms

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, characterized by dopaminergic neurodegeneration, motor impairment and non-motor symptoms. Epidemiological and experimental investigations into potential risk factors have firmly established that dietary factor caffeine, the most-widely consumed psychoactive substance, may exerts not only neuroprotective but a motor and non-motor (cognitive) benefits in PD. These multi-benefits of caffeine in PD are supported by convergence of epidemiological and animal evidence. At least six large prospective epidemiological studies have firmly established a relationship between increased caffeine consumption and decreased risk of developing PD. In addition, animal studies have also demonstrated that caffeine confers neuroprotection against dopaminergic neurodegeneration using PD models of mitochondrial toxins (MPTP, 6-OHDA, and rotenone) and expression of α-synuclein (α-Syn). While caffeine has complex pharmacological profiles, studies with genetic knockout mice have clearly revealed that caffeine’s action is largely mediated by the brain adenosine A_2A receptor (A_2AR) and confer neuroprotection by modulating neuroinflammation and excitotoxicity and mitochondrial function. Interestingly, recent studies have highlighted emerging new mechanisms including caffeine modulation of α-Syn degradation with enhanced autophagy and caffeine modulation of gut microbiota and gut-brain axis in PD models. Importantly, since the first clinical trial in 2003, United States FDA has finally approved clinical use of the A_2AR antagonist istradefylline for the treatment of PD with OFF-time in Sept. 2019. To realize therapeutic potential of caffeine in PD, genetic study of caffeine and risk genes in human population may identify useful pharmacogenetic markers for predicting individual responses to caffeine in PD clinical trials and thus offer a unique opportunity for “personalized medicine” in PD.

Pro-cathepsin D, Prosaposin, and Progranulin: Lysosomal Networks in Parkinsonism

Mutations in GBA1, the gene encoding the lysosomal hydrolase glucocerebrosidase (GCase), are a risk factor for parkinsonism. Pursuing the potential mechanisms underlying this risk in aging neurons, we propose a new network uniting three major lysosomal proteins: (i) cathepsin D (CTSD), which plays a major role in α-synuclein (SNCA) degradation and prosaposin (PSAP) cleavage; (ii) PSAP, essential for GCase activation and progranulin (PGRN) transport; and (iii) PGRN, impacting lysosomal biogenesis, PSAP trafficking, and CTSD maturation. We hypothesize that alterations to this network and associated receptors modify lysosomal function and subsequently impact both SNCA degradation and GCase activity. By exploring the interactions between this protein trio and each of their respective transporters and receptors, we may identify secondary risk factors that provide insight into the relationship between these lysosomal proteins, GCase, and SNCA, and reveal novel therapeutic targets.

Mapping of Photochemically-Derived Dityrosine across Fe-Bound N-Acetylated α-Synuclein

Parkinson’s disease (PD) is the second most common neurological disease and belongs to a group of neurodegenerative disorders called synucleinopathies in which pathological aggregates of N-terminally acetylated α-synuclein (^NAcα-Syn) accumulate in various regions of the brain. In PD, these ^NAcα-Syn aggregates have been found to contain covalent dityrosine crosslinks, which can occur either intermolecularly or intramolecularly. Cerebral metal imbalance is also a hallmark of PD, warranting investigations into the effects of brain biometals on ^NAcα-Syn. ^NAcα-Syn is an intrinsically disordered protein, and metal-mediated conformational modifications of this structurally dynamic protein have been demonstrated to influence its propensity for dityrosine formation. In this study, a library of tyrosine-to-phenylalanine (Y-to-F) ^NAcα-Syn constructs were designed in order to elucidate the nature and the precise residues involved in dityrosine crosslinking of Fe-bound ^NAcα-Syn. The structural capacity of each mutant to form dityrosine crosslinks was assessed using Photo-Induced Cross-Linking of Unmodified Proteins (PICUP), demonstrating that coordination of either Fe^III or Fe^II to ^NAcα-Syn inhibits dityrosine crosslinking among the C-terminal residues. We further demonstrate that Y39 is the main contributor to dityrosine formation of Fe-bound ^NAcα-Syn, while Y125 is the main residue involved in dityrosine crosslinks in unmetalated ^NAcα-Syn. Our results confirm that iron coordination has a global effect on ^NAcα-Syn structure and reactivity.

Copper and iron ions accelerate the prion-like propagation of α-synuclein: A vicious cycle in Parkinson's disease

Protein fibrils drive the onset and progression of many diseases in a prion-like manner, i.e. they transcellular propagate through the extracellular space to health cells to initiate toxic aggregation as seeds. The conversion of native α-synuclein into filamentous aggregates in Lewy bodies is a hallmark of Parkinson's disease (PD). Copper and iron ions accumulate in PD brains, however, whether they influence the prion-like propagation of α-synuclein remain unclear. Here, we reported that copper/iron ions accelerate prion-like propagation of α-synuclein fibrils by promoting cellular internalization of α-synuclein fibrils, intracellular α-synuclein aggregation and the subsequent release of mature fibrils to the extracellular space to induce further propagation. Mechanistically, copper/iron ions enhanced α-synuclein fibrils internalization was mediated by negatively charged membrane heparan sulfate proteoglycans (HSPGs). α-Synuclein fibrils formed in the presence of copper/iron ions were more cytotoxic, causing increased ROS production, cell apoptosis, and shortened the lifespan of a C. elegans PD model overexpressing human α-synuclein. Notably, these deleterious effects were ameliorated by two clinically used chelators, triethylenetetramine and deferiprone. Together, our results suggest a new role for heavy metal ions, e.g. copper and iron, in the pathogenesis of PD through accelerating prion-like propagation of α-synuclein fibrils.

Neuroprotection or Neurotoxicity of Illicit Drugs on Parkinson's Disease

Parkinson's Disease (PD) is currently the most rapid growing neurodegenerative disease and over the past generation, its global burden has more than doubled. The onset of PD can arise due to environmental, sporadic or genetic factors. Nevertheless, most PD cases have an unknown etiology. Chemicals, such as the anthropogenic pollutant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amphetamine-type stimulants, have been associated with the onset of PD. Conversely, cannabinoids have been associated with the treatment of the symptoms'. PD and medical cannabis is currently under the spotlight, and research to find its benefits on PD is on-going worldwide. However, the described clinical applications and safety of pharmacotherapy with cannabis products are yet to be fully supported by scientific evidence. Furthermore, the novel psychoactive substances are currently a popular alternative to classical drugs of abuse, representing an unknown health hazard for young adults who may develop PD later in their lifetime. This review addresses the neurotoxic and neuroprotective impact of illicit substance consumption in PD, presenting clinical evidence and molecular and cellular mechanisms of this association. This research area is utterly important for contemporary society since illicit drugs' legalization is under discussion which may have consequences both for the onset of PD and for the treatment of its symptoms.

Interaction of α-synuclein and Parkin in iron toxicity on SH-SY5Y cells: implications in the pathogenesis of Parkinson's disease

The toxicity of accumulated α-synuclein plays a key role in the neurodegeneration of Parkinson's disease (PD). This study has demonstrated that iron in varying concentrations (up to 400 µM) causes an increase in α-synuclein content in SH-SY5Y cells associated with mitochondrial depolarization, decreased cellular ATP content and loss of cell viability during incubation up to 96 h. Knocking-down α-synuclein expression prevents cytotoxic actions of iron, which can also be prevented by cyclosporine A (a blocker of mitochondrial permeability transition pore). These results indicate that iron cytotoxicity is mediated by α-synuclein acting on mitochondria. Likewise siRNA mediated knock-down of Parkin causes an accumulation of α-synuclein accompanied by mitochondrial dysfunction and cell death during 48 h incubation under basal conditions, but these changes are not further aggravated by co-incubation with iron (400 µM). We have also analyzed mitochondrial dysfunction and cell viability in SH-SY5Y cells under double knock-down (α-synuclein and Parkin concurrently) conditions during incubation for 48 h with or without iron. Our results tend to suggest that iron inactivates Parkin in SH-SY5Y cells and thereby inhibits the proteasomal degradation of α-synuclein, and the accumulated α-synuclein causes mitochondrial dysfunction and cell death. These results have implications in the pathogenesis of sporadic PD and also familial type with Parkin mutations.

Computer simulations of protein-membrane systems

The interactions between proteins and membranes play critical roles in signal transduction, cell motility, and transport, and they are involved in many types of diseases. Molecular dynamics (MD) simulations have greatly contributed to our understanding of protein-membrane interactions, promoted by a dramatic development of MD-related software, increasingly accurate force fields, and available computer power. In this chapter, we present available methods for studying protein-membrane systems with MD simulations, including an overview about the various all-atom and coarse-grained force fields for lipids, and useful software for membrane simulation setup and analysis. A large set of case studies is discussed.

Protein Misfolding during Pregnancy: New Approaches to Preeclampsia Diagnostics

Preeclampsia (PE) is a multisystem heterogeneous complication of pregnancy remaining a leading cause of maternal and perinatal morbidity and mortality over the world. PE has a large spectrum of clinical features and symptoms, which make diagnosis challenging. Despite a long period of studying, PE etiology is still unclear and there are no reliable rapid tests for early diagnosis of this disease. During the last decade, it was shown that proteins misfolding and aggregation are associated with PE. Several proteins, including amyloid beta peptide, transthyretin, alpha-1 antitrypsin, albumin, IgG k-free light chains, and ceruloplasmin are dysregulated in PE, resulting in toxic deposition of amyloid-like aggregates in the placenta and body fluids. It is also possible that aggregated proteins induce defective trophoblast invasion, placental ischemia, ER stress, and promote PE manifestation. The fact that protein aggregation is an emerging biomarker of PE provides an opportunity to develop new diagnostic approaches based on amyloids special features, such as Congo red (CR) staining and thioflavin T (ThT) enhanced fluorescence.

High-Affinity Detection of Alpha-Synuclein by Aptamer-Gold Conjugates on an Amine-Modified Dielectric Surface

Parkinson's disease (PD) is a progressive health issue and influences an increasingly larger number of people, especially at older ages, affecting the central nervous system (CNS). Alpha-synuclein is a biomarker closely correlated with the CNS and PD. The loss of neuronal cells in the substantia nigra leads to the aggregation of alpha-synuclein in the form of Lewy bodies, and Lewy neuritis is a neuropathological hallmark. The therapeutic approach of PD focuses on alpha-synuclein as an important substrate of PD pathology. So far, research has focused on antialpha-synuclein to minimize the burden of extracellular alpha-synuclein in the brain, and as a consequence, it ameliorates inflammation. Interdigitated electrode (IDE) biosensors are efficient tools for detecting various analytes and were chosen in this study to detect alpha-synuclein on amine-modified surfaces by using antiaptamer-alpha-synuclein as the probe. In addition, a gold nanoparticle-conjugated aptamer was used to enhance the detection limit. The limit of detection for the binding between alpha-synuclein and aptamer was found to be 10 pM. Control experiments were performed with two closely related proteins, amyloid-beta and tau, to reveal the specificity; the results show that the aptamer only recognized alpha-synuclein. The proposed strategy helps to identify the binding of aptamer and alpha-synuclein and provides a possible method to lower alpha-synuclein levels and inflammation in PD patients.

A Review of the Molecular Mechanisms of Traumatic Brain Injury

Traumatic brain injury (TBI) refers to any insult to the brain resulting in primary (direct) and secondary (indirect) damage to the brain parenchyma. Secondary damage is often linked to the molecular mechanisms that occur post TBI and result in excitotoxicity, neuroinflammation and cytokine damage, oxidative damage, and eventual cell death as prominent mechanisms of cell damage. We present a review highlighting the relation of each of these mechanisms with TBI, their mode of damaging brain tissue, and therapeutic correlation. We also mention the long-term sequelae and their pathophysiology in relation to TBI focusing on Parkinson disease, Alzheimer disease, epilepsy, and chronic traumatic encephalopathy. Understanding of the molecular mechanisms is important in order to realize the secondary and long-term sequelae that follow primary TBI and to devise targeted therapy for quick recovery accordingly.

Effects of vagus nerve stimulation are mediated in part by TrkB in a parkinson's disease model

Vagus nerve stimulation (VNS) is being explored as a potential therapeutic for Parkinson's disease (PD). VNS is less invasive than other surgical treatments and has beneficial effects on behavior and brain pathology. It has been suggested that VNS exerts these effects by increasing brain-derived neurotrophic factor (BDNF) to enhance pro-survival mechanisms of its receptor, tropomyosin receptor kinase-B (TrkB). We have previously shown that striatal BDNF is increased after VNS in a lesion model of PD. By chronically administering ANA-12, a TrkB-specific antagonist, we aimed to determine TrkB's role in beneficial VNS effects for a PD model. In this study, we administered a noradrenergic neurotoxin, DSP-4, intraperitoneally and one week later administered a bilateral intrastriatal dopaminergic neurotoxin, 6-OHDA. At this time, the left vagus nerve was cuffed for stimulation. Eleven days later, rats received VNS twice per day for ten days, with daily locomotor assessment. Daily ANA-12 injections were given one hour prior to the afternoon stimulation and concurrent locomotor session. Following the final VNS session, rats were euthanized, and left striatum, bilateral substantia nigra and locus coeruleus were sectioned for immunohistochemical detection of neurons, α-synuclein, astrocytes, and microglia. While ANA-12 did not avert behavioral improvements of VNS, and only partially prevented VNS-induced attenuation of neuronal loss in the locus coeruleus, it did stop neuronal and anti-inflammatory effects of VNS in the nigrostriatal system, indicating a role for TrkB in mediating VNS efficacy. However, our data also suggest that BDNF-TrkB is not the sole mechanism of action for VNS in PD.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

A secret that underlies Parkinson's disease: The damaging cycle

Parkinson's disease (PD) is a movement disorder, and its common characteristics include the loss of dopaminergic neurons and the accumulation of a special type of cytoplasmic inclusions called Lewy bodies in the substantia nigra pars compacta, which are more prevalent in the elderly. However, the pathophysiology of PD is still elusive. In this review, we summarized five common factors involved in PD, namely, (i) oxidative stress, (ii) mitochondrial dysfunction, (iii) inflammation, (iv) abnormal α-synuclein, and (v) endogenous neurotoxins, and proposed a hypothesis involving a damaging cycle. Oxidative stress-triggered aldehydes react with biogenic amines to produce endogenous neurotoxins. They cause mitochondrial dysfunction and the formation of inflammasomes, which induce the activation of neuroglial cells and the infiltration of T lymphocytes. The synergistic effect of these processes fosters chronic inflammation and α-synuclein aggregation and further exacerbates the impact of oxidative stress to establish a damaging cycle that eventually results in the degeneration of dopaminergic neurons. This damaging cycle provides an explanation of progressive neuronal death during the pathogenesis of PD and provides new potential targets beneficial for developing new drugs and approaches for clinical neuroprotection.

The primary neuronal cells are more resistant than PC12 cells to α-synuclein toxic aggregates

BACKGROUND

Alpha-synuclein (αSN) is an abundant presynaptic brain protein that its aggregated species believed to play pivotal roles in the development of neurodegenerative diseases, especially Parkinson's disease (PD). In this study, we compared the response of primary neuronal cells with a well-known cell line model, PC12, against the toxic aggregates of αSN.

METHODS

Primary hippocampal neurons (PHNs) were isolated from 17 to 18 days old rat embryos. Fibrillization was induced in recombinant αSN and monitored by standard methods. The toxicity of different aggregates of αSN on the treated cells was then studied. Furthermore, changes in the intracellular reactive oxygen species (ROS) and Ca²⁺ levels were also compared in two kinds of treated cells. We also studied the gene expression profile of certain Ca²⁺ channels and carriers using the GEO2 database.

RESULTS

The viability rate was significantly lower in PC12 versus PHNs, in response to αSN. This is while the intracellular ROS and Ca²⁺ levels were significantly increased in both cell types. Analysis of microarray data indicated that some factors involved in Ca²⁺ hemostasis may face significant changes in the PD condition.

CONCLUSION

By putting these data together, it is clear that PHN is more resistant than PC12 toward αSN cytotoxicity even in the presence of rising cytoplasmic ROS and Ca²⁺ levels. Exploring the supporting mechanisms which PHN uses to be more resistant to αSN cytotoxicity can help to open a roadmap toward therapeutic plans in PD and other synucleinopathy disorders.

Translational inhibition of α-synuclein by Posiphen normalizes distal colon motility in transgenic Parkinson mice

Parkinson disease (PD) is a neurodegenerative disease with motor as well as non-motor symptoms, including gastrointestinal dysfunction. In humans, these precede the motor symptoms by decades. Previously developed and characterized transgenic mice expressing the mutant human α-synuclein gene (SNCA) (either A53T or A30P), but not the endogenous mouse Snca, serve as models for familial PD. These animals demonstrate both robust abnormalities in enteric nervous system (ENS) function as well as synuclein-immunoreactive aggregates in ENS ganglia by 3 months of age, recapitulating early gastrointestinal abnormalities seen before the gait impairment characteristics of human and murine PD. Posiphen is a translational inhibitor of α-synuclein that targets the 5' untranslated region (UTR) of SNCA mRNA and could be a potential drug for the treatment of PD. However, its efficacy in ameliorating symptoms of PD has not yet been evaluated. Here, we used these transgenic mouse models to investigate the efficacy of Posiphen in reversing the gastrointestinal dysfunction. We show that Posiphen normalizes the colonic motility of both transgenic mouse models, although it did not affect the Whole Gut Transit Time (WGTT). Pharmacokinetics studies revealed that Posiphen is more abundant in the brain than in blood, in agreement with its lipophilicity, and the main metabolite is N⁸-NorPosiphen, a molecule with similar properties as Posiphen. The brain Posiphen levels necessary to effect optimal function were calculated and compared with efficacious brain levels from previous studies, showing that a 2-3 mM concentration of Posiphen and metabolites is sufficient for functional efficacy. Finally, 10 mg/kg Posiphen reduced α-synuclein levels in the gut of hSNCA^A53T mice treated for twenty-one weeks, while 50 and 65 mg/kg Posiphen reduced α-synuclein levels in the brain of hSNCA^A53T mice treated for twenty-one days. In conclusion, this is the first study showing the preclinical efficacy of Posiphen in normalizing the colonic motility in mouse models of gastrointestinal dysfunction in early PD. This result is in agreement with the ability of Posiphen to reach the nervous system, and its mechanism of action, the translational inhibition of α-synuclein expression. These significant findings support further development of Posiphen as a drug for the treatment of PD.

Current and future functional imaging techniques for post-traumatic stress disorder

Posttraumatic stress disorder (PTSD) is a trauma and stressor related psychiatric disorder associated with structural, metabolic, and molecular alternations in several brain regions including diverse cortical areas, neuroendocrine regions, the striatum, dopaminergic, adrenergic and serotonergic pathways, and the limbic system. We are in critical need of novel therapeutics and biomarkers for PTSD and a deep understanding of cutting edge imaging and spectroscopy methods is necessary for the development of promising new approaches to better diagnose and treat the disorder. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) criterion, all forms of traumatic stress-induced disorder are considered acute stress disorder for the first month following the stressor. Only after symptoms do not remit for one month can the disorder be deemed PTSD. It would be particularly useful to differentiate between acute stress disorder and PTSD during the one month waiting period so that more intensive treatments can be applied early on to patients with a high likelihood of developing PTSD. This would potentially enhance treatment outcomes and/or prevent the development of PTSD. Comprehension of the qualities and limitations of currently applied methods as well as the novel emerging techniques provide invaluable knowledge for fast paced development. Conventional methods of studying PTSD have proven to be insufficient for diagnosis, measurement of treatment efficacy, and monitoring disease progression. As the field currently stands, there is no diagnostic biomarker available for any psychiatric disease, PTSD included. Currently, emerging and available technologies are not utilized to their full capacity and in appropriate experimental designs for the most fruitful possible studies in this area. Therefore, there is an apparent need for improved methods in PTSD research. This review demonstrates the current state of the literature in PTSD, including molecular, cellular, and behavioral indicators, possible biomarkers and clinical and pre-clinical imaging techniques relevant to PTSD, and through this, elucidate the void of current practical imaging and spectroscopy methods that provide true biomarkers for the disorder and the significance of devising new techniques for future investigations. We are unlikely to develop a single biomarker for any psychiatric disorder however. As psychiatric disorders are incomparably complex compared to other medical diagnoses, its most likely that transcriptomic, metabolomic and structural and connectomic imaging data will have to be analyzed in concert in order to produce a dependable non-behavioral marker of PTSD. This can explain the necessity of bridging conventional approaches to novel technologies in order to create a framework for further discoveries in the treatment of PTSD.

Conventional methods of studying posttraumatic stress disorder (PTSD) have proven to be insufficient for diagnosis. We have reviewed clinical and preclinical imaging techniques as well as molecular, cellular, and behavioral indicators for PTSD.

SNAP25 Gene Polymorphisms Protect Against Parkinson's Disease and Modulate Disease Severity in Patients

Parkinson's disease (PD) is a α-synucleinopathy in which intracellular aggregates of α-synuclein (α-syn) result in neurodegeneration and in the impairment of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex-mediated release of neurotransmitters. SNAP25 is a SNARE complex component: its concentration is increased in the cerebrospinal fluid of PD patients and this is related to the severity of cognitive and motor symptoms. Five SNAP25 single-nucleotide polymorphisms (SNPs) that modulate gene expression and were described to play a role in neurologic conditions (rs363050, rs363039, rs363043, rs3746544, and rs1051312) were analyzed in a cohort of 412 sporadic Italian PD patients and 1103 healthy controls (HC) in order to identify possible correlation with the disease. The SNAP25 rs1051312 C allele and CC genotype confer protection against PD onset, in particular in males (p = 0.003, OR(95%CI) = 0.67(0.51-0.88)) (p_c = 0.008, OR(95%CI) = 0.28(0.10-0.70)). Co-segregation analyses revealed that the rs1051312 effect was reinforced when present within the rs363043 C-rs3746544 T-rs1051312 C haplotype (p = 3.3 × 10^-4, OR = 0.47, 95%CI = 0.31-0.72), once again in males. Finally, rs363039 influenced age at onset (p = 0.02) and MMSE (Mini-Mental State Examination) scores (p = 0.01). The SNAP25 SNPs analyzed herein modulate gene expression at different levels as they are involved in binding miRNA and transcription factors; this suggests a possible synergistic effect of SNAP25 SNPs in the pathogenesis of PD. A replication in a larger and independent sample will help to further explore this hypothesis.

Neuronal Cell Death Mechanisms in Major Neurodegenerative Diseases

Neuronal cell death in the central nervous system has always been a challenging process to decipher. In normal physiological conditions, neuronal cell death is restricted in the adult brain, even in aged individuals. However, in the pathological conditions of various neurodegenerative diseases, cell death and shrinkage in a specific region of the brain represent a fundamental pathological feature across different neurodegenerative diseases. In this review, we will briefly go through the general pathways of cell death and describe evidence for cell death in the context of individual common neurodegenerative diseases, discussing our current understanding of cell death by connecting with renowned pathogenic proteins, including Tau, amyloid-beta, alpha-synuclein, huntingtin and TDP-43.

Structural discordance in HIV-1 Vpu from brain isolate alarms amyloid fibril forming behavior- a computational perspective

HIV-1 being the most widespread type worldwide, its accounts for almost 95% of all infections including HIV associated dementia (HAD) that triggers neurological dysfunction and neurodegeneration in patients. The common features associated with HAD and other neurodegenerative diseases are accumulation of amyloid plaques, neuronal loss and deterioration of cognitive abilities, amongst which amyloid fibrillation is considered to be a hallmark. The success of effective therapeutics lies in the understanding of mechanisms leading to neurotoxicity. Few viral proteins like gp-120 are known to be involved in aggregation and enhancement of viral infectivity while comprehending the neurotoxic role of some other proteins is still underway. In the current study, amyloidogenic potential of HIV-1 Vpu protein from brain isolate is investigated through computational approaches. The aggregation propensity of brain derived HIV-1 Vpu was assessed by several amyloid prediction servers that projected the region 4-35 to be amyloidogenic. The protein structure was modeled and subjected to 70 ns molecular dynamics (MD) simulation to investigate the transformation of α-helical conformation of the predicted aggregate region into β-sheet, proposing the protein's ability to initiate fibril formation that is central to amyloidogenic proteins. The structural features of brain derived HIV-1 Vpu were consistent with the in silico amyloid prediction results that depicts the conformational change in the region 8-28 of which residues Ala8, Ile9, Val10, Ala19, Ile20 and Val21 constitutes β-sheet formation. The α-helix/β-sheet discordance of the predicted region was reflected in the simulation study highlighting the possible structural transition associated with HIV-1 Vpu protein of brain isolate.

Early events in copper-ion catalyzed oxidation of α-synuclein

Previous studies on metal-ion catalyzed oxidation of α-synuclein oxidation have mostly used conditions that result in extensive modification precluding an understanding of the early events in this process. In this study, we have examined time-dependent oxidative events related to α-synuclein modification using six different molar ratios of Cu²⁺/H₂O₂/protein and Cu²⁺/H₂O₂/ascorbate/protein resulting in mild to moderate extents of oxidation. For a Cu²⁺/H₂O₂/protein molar ratio of 2.3:7.8:1 only low levels of carbonyls were detected (0.078 carbonyls per protein), whereas a molar ratio of 4.7:15.6:1 gave 0.22 carbonyls per α-synuclein within 15 min. With the latter conditions, rapid conversion of 3 out of 4 methionines (Met) to methionine sulfoxide, and 2 out of 4 tyrosines (Tyr) were converted to products including inter- and intra-molecular dityrosine cross-links and protein oligomers, as determined by SDS-PAGE and Western blot analysis. Limited histidine (His) modification was observed. The rapid formation of dityrosine cross-links was confirmed by fluorescence and mass-spectrometry. These data indicate that Met and Tyr oxidation are early events in Cu²⁺/H₂O₂-mediated damage, with carbonyl formation being a minor process. With the Cu²⁺/H₂O₂/ascorbate system, rapid protein carbonyl formation was detected with the first 5 min, but after this time point, little additional carbonyl formation was detected. With this system, lower levels of Met and Tyr oxidation were detected (2 Met and 1 Tyr modified with a Cu²⁺/H₂O₂/ascorbate/protein ratio of 2.3:7.8:7.8:1), but greater His oxidation. Only low levels of intra- dityrosine cross-links and no inter- dityrosine oligomers were detected under these conditions, suggesting that ascorbate limits Cu²⁺/H₂O₂-induced α-synuclein modification.

Mitochondrial Dysfunction in Parkinson's Disease: New Mechanistic Insights and Therapeutic Perspectives

Purpose of Review

Parkinson’s disease (PD) is a complex neurodegenerative disorder, the aetiology of which is still largely unknown. Overwhelming evidence indicates that mitochondrial dysfunction is a central factor in PD pathophysiology. Here we review recent developments around mitochondrial dysfunction in familial and sporadic PD, with a brief overview of emerging therapies targeting mitochondrial dysfunction.

Recent Findings

Increasing evidence supports the critical role for mitochondrial dysfunction in the development of sporadic PD, while the involvement of familial PD-related genes in the regulation of mitochondrial biology has been expanded by the discovery of new mitochondria-associated disease loci and the identification of their novel functions.

Summary

Recent research has expanded knowledge on the mechanistic details underlying mitochondrial dysfunction in PD, with the discovery of new therapeutic targets providing invaluable insights into the essential role of mitochondria in PD pathogenesis and unique opportunities for drug development.

MicroRNA expressing profiles in A53T mutant alpha-synuclein transgenic mice and Parkinsonian

α-synuclein gene mutations can cause α-synuclein protein aggregation in the midbrain of Parkinson's disease (PD) patients. MicroRNAs (miRNAs) play a key role in the metabolism of α-synuclein but the mechanism involved in synucleinopathy remains unclear. In this study, we investigated the miRNA profiles in A53T-α-synuclein transgenic mice and analyzed the candidate miRNAs in the cerebrospinal fluid (CSF) of PD patients. The 12-month A53T-transgenic mouse displayed hyperactive movement and anxiolytic-like behaviors with α-synuclein aggregation in midbrain. A total of 317,759 total and 289,207 unique small RNA sequences in the midbrain of mice were identified by high-throughput deep sequencing. We found 644 miRNAs were significantly changed in the transgenic mice. Based on the conserved characteristic of miRNAs, we selected 11 candidates from the 40 remarkably expressed miRNAs and explored their expression in 44 CSF samples collected from PD patients. The results revealed that 11 microRNAs were differently expressed in CSF, emphatically as miR-144-5p, miR-200a-3p and miR-542-3p, which were dramatically up-regulated in both A53T-transgenic mice and PD patients, and had a helpful accuracy for the PD prediction. The ordered logistic regression analysis showed that the severity of PD has strong correlation with an up-expression of miR-144-5p, miR-200a-3p and miR-542-3p in CSF. Taken together, our data suggested that miRNAs in CSF, such as miR-144-5p, miR-200a-3p and miR-542-3p, may be useful to the PD diagnosis as potential biomarkers.

Pleiotropic neuropathological and biochemical alterations associated with Myo5a mutation in a rat Model

In this study, we analyze the neuropathological and biochemical alterations involved in the pathogenesis of a neurodegenerative/movement disorder during different developmental stages in juvenile rats with a mutant Myosin5a (Myo5a). In mutant rats, a spontaneous autosomal recessive mutation characterized by the absence of Myo5a protein expression in the brain is associated with a syndrome of locomotor dysfunction, altered coat color, and neuroendocrine abnormalities. Myo5a encodes a myosin motor protein required for transport and proper distribution of subcellular organelles in somatodendritic processes in neurons. Here we report marked hyperphosphorylation of alpha-synuclein and tau, as well as region-specific buildup of the autotoxic dopamine metabolite, 3,4-dihydroxyphenyl-acetaldehyde (DOPAL), related to decreased aldehyde dehydrogenases activity and neurodegeneration in mutant rats. Alpha-synuclein accumulation in mitochondria of dopaminergic neurons is associated with impaired enzymatic respiratory complex I and IV activity. The behavioral and biochemical lesions progress after 15 days postnatal, and by 30-40 days the animals must be euthanized because of neurological impairment. Based on the obtained results, we propose a pleiotropic pathogenesis that links the Myo5a gene mutation to deficient neuronal development and progressive neurodegeneration. This potential model of a neurodevelopmental disorder with neurodegeneration and motor deficits may provide further insight into molecular motors and their associated proteins responsible for altered neurogenesis and neuronal disease pathogenesis.

TrkB neurotrophic activities are blocked by α-synuclein, triggering dopaminergic cell death in Parkinson's disease

BDNF/TrkB neurotrophic signaling is essential for dopaminergic neuronal survival, and the activities are reduced in the substantial nigra (SN) of Parkinson's disease (PD). However, whether α-Syn (alpha-synuclein) aggregation, a hallmark in the remaining SN neurons in PD, accounts for the neurotrophic inhibition remains elusive. Here we show that α-Syn selectively interacts with TrkB receptors and inhibits BDNF/TrkB signaling, leading to dopaminergic neuronal death. α-Syn binds to the kinase domain on TrkB, which is negatively regulated by BDNF or Fyn tyrosine kinase. Interestingly, α-Syn represses TrkB lipid raft distribution, decreases its internalization, and reduces its axonal trafficking. Moreover, α-Syn also reduces TrkB protein levels via up-regulation of TrkB ubiquitination. Remarkably, dopamine's metabolite 3,4-Dihydroxyphenylacetaldehyde (DOPAL) stimulates the interaction between α-Syn and TrkB. Accordingly, MAO-B inhibitor rasagiline disrupts α-Syn/TrkB complex and rescues TrkB neurotrophic signaling, preventing α-Syn-induced dopaminergic neuronal death and restoring motor functions. Hence, our findings demonstrate a noble pathological role of α-Syn in antagonizing neurotrophic signaling, providing a molecular mechanism that accounts for its neurotoxicity in PD.