Mitochondria-Targeted Oligomeric α-Synuclein Induces TOM40 Degradation and Mitochondrial Dysfunction in Parkinson's Disease and Parkinsonism-Dementia of Guam

Mitochondrial dysfunction is a central aspect of Parkinson's disease (PD) pathology, yet the underlying mechanisms are not fully understood. This study investigates the link between α-Synuclein (α-Syn) pathology and the loss of translocase of the outer mitochondrial membrane 40 (TOM40), unraveling its implications for mitochondrial dysfunctions in neurons. We discovered that TOM40 protein depletion occurs in the brains of patients with Guam Parkinsonism Dementia (Guam PD) and cultured neurons expressing α-Syn proteinopathy, notably, without corresponding changes in TOM40 mRNA levels. Cultured neurons expressing α-Syn mutants, with or without a mitochondria-targeting signal (MTS) underscore the role of α-Syn's mitochondrial localization in inducing TOM40 degradation. Parkinson's Disease related etiological factors, such as 6-hydroxy dopamine or ROS/metal ions stress, which promote α-Syn oligomerization, exacerbate TOM40 depletion in PD patient-derived cells with SNCA gene triplication. Although α-Syn interacts with both TOM40 and TOM20 in the outer mitochondrial membrane, degradation is selective for TOM40, which occurs via the ubiquitin-proteasome system (UPS) pathway. Our comprehensive analyses using Seahorse technology, mitochondrial DNA sequencing, and damage assessments, demonstrate that mutant α-Syn-induced TOM40 loss results in mitochondrial dysfunction, characterized by reduced membrane potential, accumulation of mtDNA damage, deletion/insertion mutations, and altered oxygen consumption rates. Notably, ectopic supplementation of TOM40 or reducing pathological forms of α-Syn using ADP-ribosylation inhibitors ameliorate these mitochondrial defects, suggesting potential therapeutic avenues. In conclusion, our findings provide crucial mechanistic insights into how α-Syn accumulation leads to TOM40 degradation and mitochondrial dysfunction, offering insights for targeted interventions to alleviate mitochondrial defects in PD.

Peptide-based approaches to directly target alpha-synuclein in Parkinson's disease

Peptides and their mimetics are increasingly recognised as drug-like molecules, particularly for intracellular protein-protein interactions too large for inhibition by small molecules, and inaccessible to larger biologics. In the past two decades, evidence associating the misfolding and aggregation of alpha-synuclein strongly implicates this protein in disease onset and progression of Parkinson's disease and related synucleinopathies. The subsequent formation of toxic, intracellular, Lewy body deposits, in which alpha-synuclein is a major component, is a key diagnostic hallmark of the disease. To reach their therapeutic site of action, peptides must both cross the blood-brain barrier and enter dopaminergic neurons to prevent the formation of these intracellular inclusions. In this review, we describe and summarise the current efforts made in the development of peptides and their mimetics to directly engage with alpha-synuclein with the intention of modulating aggregation, and importantly, toxicity. This is a rapidly expanding field with great socioeconomic impact; these molecules harbour significant promise as therapeutics, or as early biomarkers during prodromal disease stages, or both. As these are age-dependent conditions, an increasing global life expectancy means disease prevalence is rising. No current treatments exist to either prevent or slow disease progression. It is therefore crucial that drugs are developed for these conditions before health care and social care capacities become overrun.

SPEADI: Accelerated Analysis of IDP-Ion Interactions from MD-Trajectories

The disordered nature of Intrinsically Disordered Proteins (IDPs) makes their structural ensembles particularly susceptible to changes in chemical environmental conditions, often leading to an alteration of their normal functions. A Radial Distribution Function (RDF) is considered a standard method for characterizing the chemical environment surrounding particles during atomistic simulations, commonly averaged over an entire or part of a trajectory. Given their high structural variability, such averaged information might not be reliable for IDPs. We introduce the Time-Resolved Radial Distribution Function (TRRDF), implemented in our open-source Python package SPEADI, which is able to characterize dynamic environments around IDPs. We use SPEADI to characterize the dynamic distribution of ions around the IDPs Alpha-Synuclein (AS) and Humanin (HN) from Molecular Dynamics (MD) simulations, and some of their selected mutants, showing that local ion-residue interactions play an important role in the structures and behaviors of IDPs.

α-Synuclein induces Th17 differentiation and impairs the function and stability of Tregs by promoting RORC transcription in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons (DA) and the accumulation of Lewy body deposits composed of alpha-Synuclein (α-Syn), which act as antigenic epitopes to drive cytotoxic T-cell responses in PD. Increased T helper 17 (Th17) cells and dysfunctional regulatory T cells (Tregs) have been reported to be associated with the loss of DA in PD. However, the mechanism underlying the Th17/Treg imbalance remains unknown.

METHODS

Here, we examined the percentage of Th17 cells, the percentage of Tregs and the α-Syn level and analysed their correlations in the peripheral blood of PD patients and in the substantia nigra pars compacta (SNpc) and spleen of MPTP-treated mice and A53 transgenic mice. We assessed the effect of α-Syn on the stability and function of Tregs and the differentiation of Th17 cells and evaluated the role of retinoid-related orphan nuclear receptor (RORγt) upregulation in α-Syn stimulation in vivo and in vitro.

RESULTS

We found that the α-Syn level and severity of motor symptoms were positively correlated with the increase in Th17 cells and decrease in Tregs in PD patients. Moreover, α-Syn stimulation led to the loss of Forkhead box protein P3 (FOXP3) expression in Tregs, accompanied by the acquisition of IL-17A expression. Increased Th17 differentiation was detected upon α-Syn stimulation when naïve CD4⁺ T cells were cultured under Th17-polarizing conditions. Mechanistically, α-Syn promotes the transcription of RORC, encoding RORγt, in Tregs and Th17 cells, leading to increased Th17 differentiation and loss of Treg function. Intriguingly, the increase in Th17 cells, decrease in Tregs and apoptosis of DA were suppressed by a RORγt inhibitor (GSK805) in MPTP-treated mice.

CONCLUSION

Together, our data suggest that α-Syn promotes the transcription of RORC in circulating CD4⁺ T cells, including Tregs and Th17 cells, to impair the stability of Tregs and promote the differentiation of Th17 cells in PD. Inhibition of RORγt attenuated the apoptosis of DA and alleviated the increase in Th17 cells and decrease in Tregs in PD.

Distribution of Lewy-related pathology in the brain, spinal cord, and periphery: the population-based Vantaa 85 + study

Evolving evidence has supported the existence of two anatomically distinct Lewy-related pathology (LRP) types. Investigation of spinal cord and peripheral LRP can elucidate mechanisms of Lewy body disorders and origins of synuclein accumulation. Still, very few unselected studies have focused on LRP in these regions. Here we analysed LRP in spinal cord, dorsal root ganglion, and adrenal gland in the population-based Vantaa 85 + study, including every ≥ 85 years old citizen living in the city of Vantaa in 1991 (n = 601). Samples from spinal cord (C6-7, TH3-4, L3-4, S1-2) were available from 303, lumbar dorsal root ganglion from 219, and adrenal gland from 164 subjects. Semiquantitative scores of LRP were determined from immunohistochemically stained sections (anti-alpha-synuclein antibody 5G4). LRP in the ventral and dorsal horns of spinal cord, thoracic intermediolateral column, dorsal root ganglion and adrenal gland were compared with brain LRP, previously determined according to DLB Consortium criteria and by caudo-rostral versus amygdala-based LRP classification. Spinal LRP was found in 28% of the total population and in 61% of those who had LRP in the brain. Spinal cord LRP was found only in those subjects with LRP in the brain, and the quantity of spinal cord LRP was associated with the severity of brain LRP (p < 0.001). Unsupervised K-means analysis identified two cluster types of spinal and brain LRP corresponding to caudo-rostral and amygdala-based LRP types. The caudo-rostral LRP type exhibited more frequent and severe pathology in spinal cord, dorsal root ganglion and adrenal gland than the amygdala-based LRP type. Analysis of specific spinal cord regions showed that thoracic intermediolateral column and sacral dorsal horn were the most frequently affected regions in both LRP types. This population-based study on brain, spinal and peripheral LRP provides support to the concept of at least two distinct LRP types.

Direct Observation of "Elongated" Conformational States in α-Synuclein upon Liquid-Liquid Phase Separation

α-Synuclein (α-syn) is an intrinsically disordered protein (IDP) that undergoes liquid-liquid phase separation (LLPS), fibrillation, and forms insoluble intracellular Lewy bodies in neurons, which are the hallmark of Parkinson's Disease (PD). Neurotoxicity precedes the formation of aggregates and might be related to α-syn LLPS. The molecular mechanisms underlying the early stages of LLPS are still elusive. To obtain structural insights into α-syn upon LLPS, we take advantage of cross-linking/mass spectrometry (XL-MS) and introduce an innovative approach, termed COMPASS (COMPetitive PAiring StatisticS). In this work, we show that the conformational ensemble of α-syn shifts from a "hairpin-like" structure towards more "elongated" conformational states upon LLPS. We obtain insights into the critical initial stages of LLPS and establish a novel mass spectrometry-based approach that will aid to solve open questions in LLPS structural biology.

Intracranial administration of alpha-synuclein fibrils in A30P-synuclein transgenic mice causes robust synucleinopathy and microglial induction

Synucleinopathies are neurodegenerative disorders involving pathological alpha-synuclein (αSyn) protein, including dementia with Lewy bodies, multiple system atrophy and Parkinson's disease (PD). Current in vivo models of synucleinopathy include transgenic mice overexpressing αSyn variants and methods based on administration of aggregated, exogenous αSyn. Combining these techniques offers the ability to study consequences of introducing pathological αSyn into primed neuronal environments likely to develop synucleinopathy. Herein, we characterize the impacts pre-formed fibrils (PFFs) of recombinant, human αSyn have in mice overexpressing human A30P αSyn, a mutation associated with autosomal dominant PD. A30P mouse brain contains detergent insoluble αSyn biochemically similar to PD brain, and these mice develop Lewy-like synucleinopathy with age. Administration of PFFs in A30P mice resulted in regionally-specific accumulations of phosphorylated synuclein, microglial induction and a motor phenotype that differed from PFF-induced effects in wildtype mice. Surprisingly, PFF-induced losses of tyrosine hydroxylase were similar in A30P and wildtype mice. Thus, the PFF-A30P model recapitulates key aspects of synucleinopathy with induction of microglia, creating an appropriate system for evaluating neurodegenerative therapeutics.

Protective effect of plastrum testudinis extract on dopaminergic neurons in a Parkinson's disease model through DNMT1 nuclear translocation and SNCA's methylation

The pathological characteristics of Parkinson's disease (PD) include dopaminergic neuron damage, specifically disorders caused by dopamine synthesis, in vivo. Plastrum testudinis extract (PTE) and its bioactive ingredient ethyl stearate (PubChem CID: 8122) were reported to be correlated with tyrosine hydroxylase (TH), which is a biomarker of dopaminergic neurons. This suggests that PTE and its small-molecule active ingredient ethyl stearate have potential for development as a therapeutic drug for PD. In this study, we treated 6-hydroxydopamine (6-OHDA)-induced model rats and PC12 cells with PTE. The mechanism of action of PTE and ethyl stearate was investigated by western blotting, bisulfite sequencing PCR (BSP), real-time PCR, immunofluorescence and siRNA transfection. PTE effectively upregulated the TH expression and downregulated the alpha-synuclein expression in both the substantia nigra and the striatum of the midbrain in a PD model rat. The PC12 cell model showed that both PTE and its active monomer ethyl stearate significantly promoted TH expression and blocked alpha-synuclein, agreeing with the in vivo results. BSP showed that PTE and ethyl stearate increased the methylation level of the Snca intron 1 region. These findings suggest that some of the protective effects of PTE on dopaminergic neurons are mediated by ethyl stearate. The mechanism of ethyl stearate may involve disrupting the abnormal aggregation of DNA (cytosine-5)-methyltransferase 1 (DNMT1) with alpha-synuclein by releasing DNMT1, upregulating Snca intron 1 CpG island methylation, and ultimately, reducing the expression of alpha-synuclein.

Immunotherapies for Parkinson's disease: Progression of Clinical Development

Parkinson's disease is a common neurodegenerative disease affecting the movement and wellbeing of most elderlies. The manifestations of Parkinson's disease often include resting tremor, stiffness, bradykinesia and muscular rigidity. The typical hallmark of Parkinson's disease is the destruction of neurons in the substantia nigra and the presence of Lewy bodies in different compartments of the central nervous system. Due to various limitations to the currently available treatments, immunotherapies have emerged to be the new approach to Parkinson's disease treatment. This approach shows some positive outcomes on the efficacy in removing the aggregated species of alpha-synuclein, which is believed to be one of the causes of Parkinson's disease. In this review, an overview of how alpha-synuclein contributes to Parkinson's disease and the effects of a few new immunotherapeutic treatments, including BIIB054 (cinpanemab), MEDI1341, AFFITOPE and PRX002 (prasinezumab) that are currently under clinical development, will be discussed.

Alpha-Synuclein and Mitochondrial Dysfunction in Parkinson's Disease: The Emerging Role of VDAC

Alpha-Synuclein (αSyn) is a protein whose function is still debated, as well as its role in modulation of mitochondrial function in both physiological and pathological conditions. Mitochondrial porins or Voltage-Dependent Anion Channel (VDAC) proteins are the main gates for ADP/ATP and various substrates towards the organelle. Furthermore, they act as a mitochondrial hub for many cytosolic proteins, including αSyn. This review analyzes the main aspects of αSyn-mitochondria interaction, focusing on the role of VDAC and its emerging involvement in the pathological processes.

Changes in the mesocorticolimbic pathway after low dose reserpine-treatment in Wistar and Spontaneously Hypertensive Rats (SHR): Implications for cognitive deficits in a progressive animal model for Parkinson's disease

Reserpine (RES) is an irreversible inhibitor of VMAT2 used to study Parkinson's disease (PD) and screening for antiparkinsonian treatments in rodents. Recently, the repeated treatment with a low dose of reserpine was proposed as a model capable of emulating progressive neurochemical, motor and non-motor impairments in PD. Conversely, compared to Wistar rats, Spontaneously Hypertensive Rats (SHR) are resistant to motor changes induced by repeated treatment with a low dose of RES. However, such resistance has not yet been investigated for RES-induced non-motor impairments. We aimed to assess whether SHR would have differential susceptibility to the object recognition deficit induced by repeated low-dose reserpine treatment. We submitted male Wistar and SHR rats to repeated RES treatment (15 s.c. injections of 0.1 mg/kg, every other day) and assessed object memory acquisition and retrieval 48 h after the 6^th RES injection (immediately before the appearance of motor impairments). Only RES Wistar rats displayed memory impairment after reserpine treatment. On the other hand, untreated SHR rats displayed object recognition memory deficit, but RES treatment restored such deficits. We also performed immunohistochemistry for tyrosine hydroxylase (TH) and α-synuclein (α-syn) 48 h after the last RES injection. In a different set of animals submitted to the same treatment, we quantified DA, 5-HT and products of lipid peroxidation in the prefrontal cortex (PFC) and hippocampus (HPC). SHR presented increased constitutive levels of DA in the PFC and reduced immunoreactivity to TH in the medial PFC and dorsal HPC. Corroborating the behavioral findings, RES treatment restored those constitutive alterations in SHR. These findings indicate that the neurochemical, molecular and genetic differences in the SHR strain are potentially relevant targets to the study of susceptibility to diseases related to dopaminergic alterations.

Glial activation precedes alpha-synuclein pathology in a mouse model of Parkinson's disease

Neuroinflammation is increasingly recognized as an important feature in the pathogenesis of Parkinson's disease (PD). However, it remains unclear whether neuroinflammation contributes to nigral degeneration in PD or is merely a secondary marker of neurodegeneration. We aimed to investigate the temporal relationship between synucleopathy, neuroinflammation and nigrostriatal degeneration in a mouse model of PD. Mice received unilateral intrastriatal injection of alpha-synuclein pre-formed fibrils, alpha-synuclein monomer or vehicle and were sacrificed at 15, 30 and 90 days post-injection. Intrastriatal inoculation of alpha-synuclein fibrils led to significant alpha-synuclein aggregation in the substantia nigra peaking at 30 days after injection while the significant increase in Iba-1 cells, GFAP cells and IL-1β expression peaked earlier at 15 days. At 90 days, the striatal dopaminergic denervation was associated with astroglial activation. Alpha-synuclein monomer did not result in long-term glia activation or increase in inflammatory markers. The spread of alpha-synuclein aggregates into the cortex was not associated with any changes to neuroinflammatory markers. Our results demonstrate that in the substantia nigra glial activation is an early event that precedes alpha-synuclein inclusion formation, suggesting neuroinflammation could play an important early role in the pathogenesis of PD.

L-DOPA-Induced Dyskinesia in a Genetic Drosophila Model of Parkinson's Disease

Motor symptoms in Parkinson’s disease (PD) are directly related to the reduction of a neurotransmitter dopamine. Therefore, its precursor L-DOPA became the gold standard for PD treatment. However, chronic use of L-DOPA causes uncontrollable, involuntary movements, called L-DOPA-induced dyskinesia (LID) in the majority of PD patients. LID is complicated and very difficult to manage. Current rodent and non-human primate models have been developed to study LID mainly using neurotoxins. Therefore, it is necessary to develop a LID animal model with defects in genetic factors causing PD in order to study the relation between LID and PD genes such as α-synuclein. In this study, we first showed that a low concentration of L-DOPA (100 µM) rescues locomotion defects (i.e., speed, angular velocity, pause time) in Drosophila larvae expressing human mutant α-synuclein (A53T). This A53T larval model of PD was used to further examine dyskinetic behaviors. High concentrations of L-DOPA (5 or 10 mM) causes hyperactivity such as body bending behavior (BBB) in A53T larva, which resembles axial dyskinesia in rodents. Using ImageJ plugins and other third party software, dyskinetic BBB has been accurately and efficiently quantified. Further, we showed that a dopamine agonist pramipexole (PRX) partially rescues BBB caused by high L-DOPA. Our Drosophila genetic LID model will provide an important experimental platform to examine molecular and cellular mechanisms underlying LID, to study the role of PD causing genes in the development of LID, and to identify potential targets to slow/reverse LID pathology.

The status of the terminal regions of α-synuclein in different forms of aggregates during fibrillization

The α-synuclein (αSN) amyloid fibrillization process is known to be a crucial phenomenon associated with neuronal loss in various neurodegenerative diseases, most famously Parkinson's disease. The process involves different aggregated species and ultimately leads to formation of β-sheet rich fibrillar structures. Despite the essential role of αSN aggregation in the pathoetiology of various neurological disorders, the characteristics of various assemblies are not fully understood. Here, we established a fluorescence-based model for studying the end-parts of αSN to decipher the structural aspects of aggregates during the fibrillization. Our model proved highly sensitive to the events at the early stage of the fibrillization process, which are hardly detectable with routine techniques. Combining fluorescent and PAGE analysis, we found different oligomeric aggregates in the nucleation phase of fibrillization with different sensitivity to SDS and different structures based on αSN termini. Moreover, we found that these oligomers are highly dynamic: after reaching peak levels during fibrillization, they decline and eventually disappear, suggesting their transformation into other αSN aggregated species. These findings shed light on the structural features of various αSN aggregates and their dynamics in synucleinopathies.

Loss of fragile X mental retardation protein precedes Lewy pathology in Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) and the gradual appearance of α-synuclein (α-syn)-containing neuronal protein aggregates. Although the exact mechanism of α-syn-mediated cell death remains elusive, recent research suggests that α-syn-induced alterations in neuronal excitability contribute to cell death in PD. Because the fragile X mental retardation protein (FMRP) controls the expression and function of numerous neuronal genes related to neuronal excitability and synaptic function, we here investigated the role of FMRP in α-syn-associated pathological changes in cell culture and mouse models of PD as well as in post-mortem human brain tissue from PD patients. We found FMRP to be decreased in cultured DA neurons and in the mouse brain in response to α-syn overexpression. FMRP was, furthermore, lost in the SNc of PD patients and in patients with early stages of incidental Lewy body disease (iLBD). Unlike fragile X syndrome (FXS), FMR1 expression in response to α-syn was regulated by a mechanism involving Protein Kinase C (PKC) and cAMP response element-binding protein (CREB). Reminiscent of FXS neurons, α-syn-overexpressing cells exhibited an increase in membrane N-type calcium channels, increased phosphorylation of ERK1/2, eIF4E and S6, increased overall protein synthesis, and increased expression of Matrix Metalloproteinase 9 (MMP9). FMRP affected neuronal function in a PD animal model, because FMRP-KO mice were resistant to the effect of α-syn on striatal dopamine release. In summary, our results thus reveal a new role of FMRP in PD and support the examination of FMRP-regulated genes in PD disease progression.

Aβ, Tau, and α-Synuclein aggregation and integrated role of PARK2 in the regulation and clearance of toxic peptides

Alzheimer's and Parkinson's diseases are one of the world's leading causes of death. >50 million people throughout the world are suffering with these diseases. They are two distinct progressive neurodegenerative disorders affecting different regions of the brain with diverse symptoms, including memory and motor loss respectively, but with the advancement of diseases, both affect the whole brain and exhibit some common biological symptoms. For instance, >50% PD patients develop dementia in their later stages, though it is a hallmark of Alzheimer's disease. In fact, latest research has suggested the involvement of some common pathophysiological and genetic links between these diseases, including the deposition of pathological Aβ, Tau, and α-synuclein in both the cases. Therefore, it is pertinent to diagnose the shared biomarkers, their aggregation mechanism, their intricate relationships in the pathophysiology of disease and therapeutic markers to target them. This would enable us to identify novel markers for the early detection of disease and targets for the future therapies. Herein, we investigated molecular aspects of Aβ, Tau, and α-Synuclein aggregation, and characterized their functional partners involved in the pathology of AD and PD. Moreover, we identified the molecular-crosstalk between AD and PD associated with their pathogenic proteins- Aβ, Tau, and α-Synuclein. Furthermore, we characterized their ubiquitinational enzymes and associated interaction network regulating the proteasomal clearance of these pathological proteins.

Time course and magnitude of alpha-synuclein inclusion formation and nigrostriatal degeneration in the rat model of synucleinopathy triggered by intrastriatal α-synuclein preformed fibrils

Animal models that accurately recapitulate the accumulation of alpha-synuclein (α-syn) inclusions, progressive neurodegeneration of the nigrostriatal system and motor deficits can be useful tools for Parkinson's disease (PD) research. The preformed fibril (PFF) synucleinopathy model in rodents generally displays these PD-relevant features, however, the magnitude and predictability of these events is far from established. We therefore sought to optimize the magnitude of α-syn accumulation and nigrostriatal degeneration, and to understand the time course of both. Rats were injected unilaterally with different quantities of α-syn PFFs (8 or 16 μg of total protein) into striatal sites selected to concentrate α-syn inclusion formation in the substantia nigra pars compacta (SNpc). Rats displayed an α-syn PFF quantity-dependent increase in the magnitude of ipsilateral SNpc inclusion formation at 2 months and bilateral loss of nigral dopamine neurons at 6 months. Unilateral 16 μg PFF injection also resulted in modest sensorimotor deficits in forelimb adjusting steps associated with degeneration at 6 months. Bilateral injection of 16 μg α-syn PFFs resulted in symmetric bilateral degeneration equivalent to the ipsilateral nigral degeneration observed following unilateral 16 μg PFF injection (~50% loss). Bilateral PFF injections additionally resulted in alterations in several gait analysis parameters. These α-syn PFF parameters can be applied to generate a reproducible synucleinopathy model in rats with which to study pathogenic mechanisms and vet potential disease-modifying therapies.

MicroRNA-7 facilitates the degradation of alpha-synuclein and its aggregates by promoting autophagy

Alpha-Synuclein (α-Syn) is an important protein in the pathogenesis of Parkinson disease (PD) as it accumulates as fibrillar inclusions in affected brain regions including dopaminergic neurons in the substantia nigra. Elevated levels of α-Syn seem to be crucial in mediating its toxicity. Thus, detailed information regarding the regulatory mechanism of α-Syn expression in several layers such as transcription, post-transcription and post-translation is needed in order to devise therapeutic interventions for PD. Previously, we reported that expression of α-Syn is repressed by microRNA-7 (miR-7) through its effect on the 3'-untranslated region (UTR) of α-Syn mRNA. Here, we show that miR-7 also accelerates the clearance of α-Syn and its aggregates by promoting autophagy in differentiated ReNcell VM cells. Further, miR-7 facilitates the degradation of pre-formed fibrils of α-Syn transported from outside the cells. This additional mechanism for reducing α-Syn levels show miR-7 to be an important molecular target for PD and other alpha-synucleinopathies.

Inflammation kinase PKR phosphorylates α-synuclein and causes α-synuclein-dependent cell death

Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy comprise a group of neurodegenerative diseases termed synucleinopathies. Synucleinopathie are, characterized by presence of inclusion bodies in degenerating brain cells which contain aggregated α-synuclein phosphorylated on Ser129. Although the inflammation-associated serine-threonine kinase, PKR (EIF2AK2), promotes cellular protection against infection, we demonstrate a pro-degenerative role of activated PKR in an α-synuclein-dependent cell model of multiple system atrophy, where inhibition and silencing of PKR decrease cellular degeneration. In vitro phosphorylation demonstrates that PKR can directly bind and phosphorylate monomeric and filamenteous α-synuclein on Ser129. Inhibition and knockdown of PKR reduce Ser129 phosphorylation in different models (SH-SY5Y ASYN cells, OLN-AS7 cells, primary mouse hippocampal neurons, and acute brain slices), while overexpression of constitutively active PKR increases Ser129 α-syn phosphorylation. Treatment with pre-formed α-synuclein fibrils, proteostatic stress-promoting MG-132 and known PKR activators, herpes simplex virus-1-∆ICP34.5 and LPS, as well as PKR inducer, IFN-β-1b, lead to increased levels of phosphorylated Ser129 α-synuclein that is completely blocked by simultaneous PKR inhibition. These results reveal a direct link between PKR and the phosphorylation and toxicity of α-synuclein, and they support that neuroinflammatory processes play a role in modulating the pathogenicity of α-synuclein.

α-Synuclein's Uniquely Long Amphipathic Helix Enhances its Membrane Binding and Remodeling Capacity

α-Synuclein is the primary protein found in Lewy bodies, the protein and lipid aggregates associated with Parkinson's disease and Lewy body dementia. The protein folds into a uniquely long amphipathic α-helix (AH) when bound to a membrane, and at high enough concentrations, it induces large-scale remodeling of membranes (tubulation and vesiculation). By engineering a less hydrophobic variant of α-Synuclein, we previously showed that the energy associated with binding of α-Synuclein's AH correlates with the extent of membrane remodeling (Braun et al. in J Am Chem Soc 136:9962-9972, 2014). In this study, we combine fluorescence correlation spectroscopy, electron microscopy, and vesicle clearance assays with coarse-grained molecular dynamics simulations to test the impact of decreasing the length of the amphipathic helix on membrane binding energy and tubulation. We show that truncation of α-Synuclein's AH length by approximately 15% reduces both its membrane binding affinity (by fivefold) and membrane remodeling capacity (by nearly 50% on per mole of bound protein basis). Results from simulations correlate well with the experiments and lend support to the idea that at high protein density there is a stabilization of individual, protein-induced membrane curvature fields. The extent to which these curvature fields are stabilized, a function of binding energy, dictates the extent of tubulation. Somewhat surprisingly, we find that this stabilization does not correlate directly with the geometric distribution of the proteins on the membrane surface.

Glycogen synthase kinase-3 beta (GSK-3β) signaling: Implications for Parkinson's disease

Glycogen synthase kinase 3 (GSK-3) dysregulation plays an important role in the pathogenesis of numerous disorders, affecting the central nervous system (CNS) encompassing both neuroinflammation and neurodegenerative diseases. Several lines of evidence have illustrated a key role of the GSK-3 and its cellular and molecular signaling cascades in the control of neuroinflammation. Glycogen synthase kinase 3 beta (GSK-3β), one of the GSK-3 isomers, plays a major role in neuronal apoptosis and its inhibition decreases expression of alpha-Synuclein (α-Synuclein), which make this kinase an attractive therapeutic target for neurodegenerative disorders. Parkinson's disease (PD) is a chronic neurodegenerative movement disorder characterized by the progressive and massive loss of dopaminergic neurons by neuronal apoptosis in the substantia nigra pars compacta and depletion of dopamine in the striatum, which lead to pathological and clinical abnormalities. Thus, understanding the role of GSK-3β in PD will enhance our knowledge of the basic mechanisms underlying the pathogenesis of this disorder and facilitate the identification of new therapeutic avenues. In recent years, GSK-3β has been shown to play essential roles in modulating a variety of cellular functions, which have prompted efforts to develop GSK-3β inhibitors as therapeutics. In this review, we summarize GSK-3 signaling pathways and its association with neuroinflammation. Moreover, we highlight the interaction between GSK-3β and several cellular processes involved in the pathogenesis of PD, including the accumulation of α-Synuclein aggregates, oxidative stress and mitochondrial dysfunction. Finally, we discuss about GSK-3β inhibitors as a potential therapeutic strategy in PD.

Prolongation of Chemically-Induced Methemoglobinemia in Mice Lacking α-synuclein: A Novel Pharmacologic and Toxicologic Phenotype

The protein α-synuclein is considered central to the pathogenesis of Parkinson disease (PD) on genetic and histopathological grounds. It is widely expressed in fetal life and continues to be highly expressed in adult neural tissues, red blood cells and platelets, while the remainder of adult tissues are reported to have little or no expression. Despite cellular and molecular evidence for a role in neuronal function including synaptic vesicle trafficking, neurotransmitter release, mitochondrial function, lipid metabolism, neurogenesis, neuroprotection, and neuromelanin biosynthesis, mice ablated for the gene encoding α-synuclein (Snca) have little or no neurological phenotype. Thus, nearly 20 years of intensive study have yet to reveal conclusively what the normal function of this highly abundant protein is in the nervous system. Interestingly, α-synuclein has also been shown to have enzymatic activity as a ferrireductase capable of reducing Fe⁺³ to Fe⁺². Given its abundant expression in red blood cells, we set out to explore the role of α-synuclein in converting chemically-induced Fe⁺³ methemoglobin to normal Fe⁺² hemoglobin. Initial in vivo experiments with the potent methemoglobin inducer, para-aminopropiophenone and its active metabolite, 4-hydroxy para-aminopropiophenone, demonstrated significantly greater and more prolonged methemoglobinemia in Snca−/− mice compared to Snca+/+ mice. In vitro experiments with red blood cells, however, and in vivo experiments in genetically engineered mouse strains that differ in their α-synuclein expression in various tissues, including the nervous system, red blood cells and liver, revealed that contrary to the initial hypothesis, a lack of expression of α-synuclein in red blood cells did not correlate with higher levels or more prolonged duration of methemoglobinemia. Instead, the greater sensitivity to chemically induced methemoglobinemia correlated with the absence of hepatic α-synuclein expression. We have uncovered a new and robust whole-animal phenotype in mice lacking α-synuclein that reflects its hitherto unrecognized role in xenobiotic detoxification.

Evidence of native α-synuclein conformers in the human brain

α-Synuclein aggregation is central to the pathogenesis of several brain disorders. However, the native conformations and functions of this protein in the human brain are not precisely known. The native state of α-synuclein was probed by gel filtration coupled with native gradient gel separation, an array of antibodies with non-overlapping epitopes, and mass spectrometry. The existence of metastable conformers and stable monomer was revealed in the human brain.

Mitochondrial acetylation and genetic models of Parkinson's disease

Parkinson's disease (PD) is frequent at old age, leading to atrophy of specific neurons and to early death. Lifespan and healthy aging of organisms depend on growth factor/nutrient signaling and on bioenergetics via mitochondria, all of which regulate downstream nuclear functions through FOXO and SIR proteins. Mammalian SIRtuins include the mitochondrial deacetylase SIRT3, and recently mitochondrial lysine acetylation (AcLys) was found to initiate mitochondrial degradation by autophagy. This mitophagy process is closely regulated by PINK1 and Parkin, two interacting proteins which relocalize to mitochondria with deficient proton gradients, and whose mutations cause autosomal recessive variants of PD. Strong generalized deacetylation of mitochondrial proteins and altered SIRT3 levels occur in rodent models of PD before the onset of toxic aggregate formation. We propose that the development of site-specific AcLys-antibodies and their characterization in patients will have medical value.

A blood-brain barrier (BBB) disrupter is also a potent α-synuclein (α-syn) aggregation inhibitor: a novel dual mechanism of mannitol for the treatment of Parkinson disease (PD)

The development of disease-modifying therapy for Parkinson disease has been a main drug development challenge, including the need to deliver the therapeutic agents to the brain. Here, we examined the ability of mannitol to interfere with the aggregation process of α-synuclein in vitro and in vivo in addition to its blood-brain barrier-disrupting properties. Using in vitro studies, we demonstrated the effect of mannitol on α-synuclein aggregation. Although low concentration of mannitol inhibited the formation of fibrils, high concentration significantly decreased the formation of tetramers and high molecular weight oligomers and shifted the secondary structure of α-synuclein from α-helical to a different structure, suggesting alternative potential pathways for aggregation. When administered to a Parkinson Drosophila model, mannitol dramatically corrected its behavioral defects and reduced the amount of α-synuclein aggregates in the brains of treated flies. In the mThy1-human α-synuclein transgenic mouse model, a decrease in α-synuclein accumulation was detected in several brain regions following treatment, suggesting that mannitol promotes α-synuclein clearance in the cell bodies. It appears that mannitol has a general neuroprotective effect in the transgenic treated mice, which includes the dopaminergic system. We therefore suggest mannitol as a basis for a dual mechanism therapeutic agent for the treatment of Parkinson disease.