Proteasomal inhibition by alpha-synuclein filaments and oligomers

Expanding role of molecular chaperones in regulating α-synuclein misfolding; implications in Parkinson's disease

Protein misfolding under stressful environmental conditions cause several cellular problems owing to the disturbed cellular protein homeostasis, which may further lead to neurological disorders like Parkinson's disease (PD), Alzheimer's disease (AD), Amyloid lateral sclerosis and Huntington disease (HD). The presence of cellular defense mechanisms like molecular chaperones and proteasomal degradation systems prevent protein misfolding and aggregation. Molecular chaperones plays primary role in preventing protein misfolding by mediating proper native folding, unfolding and refolding of the polypeptides along with vast number of cellular functions. In past few years, the understanding of molecular chaperone mechanisms has been expanded enormously although implementation to prevent protein aggregation diseases is still deficient. We in this review evaluated major classes of molecular chaperones and their mechanisms relevant for preventing protein aggregation, specific case of α-synuclein aggregation. We also evaluate the molecular chaperone function as a novel therapeutic approach and the chaperone inhibitors or activators as small molecular drug targets.

The Molecular Physiopathogenesis of Islet Amyloidosis

Human islet amyloid polypeptide or amylin (hA) is a 37-amino acid peptide hormone produced and co-secreted with insulin by pancreatic β-cells. Under physiological conditions, hA regulates a broad range of biological processes including insulin release and slowing of gastric emptying, thereby maintaining glucose homeostasis. However, under the pathological conditions associated with type 2 diabetes mellitus (T2DM), hA undergoes a conformational transition from soluble random coil monomers to alpha-helical oligomers and insoluble β-sheet amyloid fibrils or amyloid plaques. There is a positive correlation between hA oligomerization/aggregation, hA toxicity, and diabetes progression. Because the homeostatic balance between hA synthesis, release, and uptake is lost in diabetics and hA aggregation is a hallmark of T2DM, this chapter focuses on the biophysical and cell biology studies investigating molecular mechanisms of hA uptake, trafficking, and degradation in pancreatic cells and its relevance to h's toxicity. We will also discuss the regulatory role of endocytosis and proteolytic pathways in clearance of toxic hA species. Finally, we will discuss potential pharmacological approaches for specific targeting of hA trafficking pathways and toxicity in islet β-cells as potential new avenues toward treatments of T2DM patients.

Alpha-synuclein at the intracellular and the extracellular side: functional and dysfunctional implications

Alpha-synuclein (α-syn) is an abundant neuronal protein whose physiological function, even if still not completely understood, has been consistently related to synaptic function and vesicle trafficking. A group of disorders known as synucleinopathies, among which Parkinson’s disease (PD), is deeply associated with the misfolding and aggregation of α-syn, which can give rise to proteinaceous inclusion known as Lewy bodies (LB). Proteostasis stress is a relevant aspect in these diseases and, currently, the presence of oligomeric α-syn species rather than insoluble aggregated forms, appeared to be associated with cytotoxicity. Many observations suggest that α-syn is responsible for neurodegeneration by interfering with multiple signaling pathways. α-syn protein can directly form plasma membrane channels or modify with their activity, thus altering membrane permeability to ions, abnormally associate with mitochondria and cause mitochondrial dysfunction (i.e. mitochondrial depolarization, Ca2+ dys-homeostasis, cytochrome c release) and interfere with autophagy regulation. The picture is further complicated by the fact that single point mutations, duplications and triplication in α-syn gene are linked to autosomal dominant forms of PD. In this review we discuss the multi-faced aspect of α-syn biology and address the main hypothesis at the basis of its involvement in neuronal degeneration.

Aggregated Alpha-Synuclein Transfer Efficiently between Cultured Human Neuron-Like Cells and Localize to Lysosomes

Parkinson's disease and other alpha-synucleinopathies are progressive neurodegenerative diseases characterized by aggregates of misfolded alpha-synuclein spreading throughout the brain. Recent evidence suggests that the pathological progression is likely due to neuron-to-neuron transfer of these aggregates between neuroanatomically connected areas of the brain. As the impact of this pathological spreading mechanism is currently debated, we aimed to investigate the transfer and subcellular location of alpha-synuclein species in a novel 3D co-culture human cell model based on highly differentiated SH-SY5Y cells. Fluorescently-labeled monomeric, oligomeric and fibrillar species of alpha-synuclein were introduced into a donor cell population and co-cultured with an EGFP-expressing acceptor-cell population of differentiated neuron-like cells. Subsequent transfer and colocalization of the different species were determined with confocal microscopy. We could confirm cell-to-cell transfer of all three alpha-synuclein species investigated. Interestingly the level of transferred oligomers and fibrils and oligomers were significantly higher than monomers, which could affect the probability of seeding and pathology in the recipient cells. Most alpha-synuclein colocalized with the lysosomal/endosomal system, both pre- and postsynaptically, suggesting its importance in the processing and spreading of alpha-synuclein.

Pathological α-synuclein exacerbates the progression of Parkinson's disease through microglial activation

Parkinson's disease (PD) is characterized by α-synuclein accumulation, dopaminergic neuron loss and inflammation. α-Synuclein can be secreted by neurons and activate microglia to different degrees. Excessive microglial activation can increase the production of tumor necrosis factor alpha (TNF-α), interleukin-1-β (IL-1β), interleukin-6 (IL-6), interferon-γ (INF-γ), inducible nitric oxide synthase (iNOS), reactive oxygen species (ROS) and nitric oxide (NO), and can also enhance microglial phagocytosis and migration as well as lymphocyte infiltration. Pathological α-synuclein and microglial activation can potentiate each other, leading to the loss of dopaminergic neurons and accelerated PD degeneration. This review will mainly describe the profiles of α-synuclein-activated microglia, with particular emphasis on the signaling cascades involved in this process.

The fine-tuning of proteolytic pathways in Alzheimer's disease

Several integrated proteolytic systems contribute to the maintenance of cellular homeostasis through the continuous removal of misfolded, aggregated or oxidized proteins and damaged organelles. Among these systems, the proteasome and autophagy play the major role in protein quality control, which is a fundamental issue in non-proliferative cells such as neurons. Disturbances in the functionality of these two pathways are frequently observed in neurodegenerative diseases, like Alzheimer's disease, and reflect the accumulation of protease-resistant, deleterious protein aggregates. In this review, we explored the sophisticated crosstalk between the ubiquitin-proteasome system and autophagy in the removal of the harmful structures that characterize Alzheimer's disease neurons. We also dissected the role of the numerous shuttle factors and chaperones that, directly or indirectly interacting with ubiquitin and LC3, are used for cargo selection and delivery to one pathway or the other.

Tetramethylpyrazine Ameliorates Rotenone-Induced Parkinson's Disease in Rats: Involvement of Its Anti-Inflammatory and Anti-Apoptotic Actions

Parkinson's disease (PD) is a slowly progressive neurodegenerative movement disorder. Apoptosis, neuroinflammation, and oxidative stress are the current hypothesized mechanisms for PD pathogenesis. Tetramethylpyrazine (TMP), the major bioactive component of Ligusticum wallichii Franchat (ChuanXiong), Family Apiaceae, reportedly has anti-apoptotic, anti-inflammatory and antioxidant effects. This study investigated the role of 'TMP' in preventing rotenone-induced neurobiological and behavioral sequelae. A preliminary dose-response study was conducted where rats received TMP (10, 20, and 40 mg/kg, i.p.) concomitantly with rotenone (2 mg/kg, s.c.) for 4 weeks. Catalepsy, locomotor activity, striatal dopamine content, and tyrosine hydroxylase "TH" and α-synuclein immunoreactivity were evaluated. The selected TMP dose (20 mg/kg) was used for western blot analysis of Bax, Bcl2, and DJ-1, immunohistochemical detection of nuclear factor kappa B (NF-кB), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and glial fibrillary acidic protein (GFAP) expression, in addition to biochemical analysis of caspase-3 activity, nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) levels. Results showed that TMP (20 mg/kg) significantly improved midbrain and striatal TH expression and striatal dopamine content as well as the motor deficits, compared to rotenone-treated group. These results were correlated with reduction in caspase-3 activity and α-synuclein expression, along with improvement of midbrain and striatal Bax/Bcl2 ratio compared to rotenone-treated group. TMP also attenuated rotenone-induced upregulation of Nrf2/HO-1 pathway. Furthermore, TMP downregulated rotenone-induced neuroinflammation markers: NF-кB, iNOS, COX2, and GFAP expression in both the midbrain and striatum. Taken together, the current study suggests that TMP is entitled to, at least partially, preventing PD neurobiological and behavioral deficits by virtue of its anti-apoptotic, anti-inflammatory, and antioxidant actions.

Sequestration of cellular interacting partners by protein aggregates: implication in a loss-of-function pathology

Protein misfolding and aggregation are a hallmark of several neurodegenerative diseases (NDs). However, how protein aggregation leads to cytotoxicity and neurodegeneration is still controversial. Emerging evidence demonstrates that sequestration of cellular-interacting partners by protein aggregates contributes to the pathogenesis of these diseases. Here, we review current research on sequestration of cellular proteins by protein aggregates and its relation to proteinopathies. Based on different interaction modes, we classify these protein sequestrations into four types: protein coaggregation, domain/motif-mediated sequestration, RNA-assisted sequestration, and sequestration of molecular chaperones. Thus, the cellular essential proteins and/or RNA hijacked by protein aggregates may lose their biological functions, consequently resulting in cytotoxicity and neurodegeneration. We have proposed a hijacking model recapitulating the sequestration process and the loss-of-function pathology of ND.

Proteostasis impairment in ALS

In physiological conditions the maintenance of the cellular proteome is a prerequisite for optimal cell functioning and cell survival. Additionally, cells need to constantly sense and adapt to their changing environment and associated stressors. Cells achieve this via a set of molecular chaperones, protein clearance pathways as well as stress-associated signaling networks which work together to prevent protein misfolding, its aggregation and accumulation in subcellular compartments. These processes together form the proteostasis network which helps in maintaining cellular proteostasis. Imbalance or impairment in this processes is directly linked to ageing associated disorders such as diabetes, cancer, stroke, metabolic disorders, pulmonary fibrosis, inflammation and neurodegenerative diseases. In this review, we provide insights into the proteostasis process and how its failure governs neurodegenerative disorders with a special focus on Amyotrophic lateral sclerosis (ALS). This article is part of a Special Issue entitled SI:ER stress.

The utility of α-synuclein as biofluid marker in neurodegenerative diseases: a systematic review of the literature

The discovery of α-synuclein (α-syn) as a major component of Lewy bodies, neuropathological hallmark of Parkinson's disease (PD), dementia with Lewy bodies and of glial inclusions in multiple system atrophy initiated the investigation of α-syn as a biomarker in cerebrospinal fluid (CSF). Due to the involvement of the periphery in PD the quantification of α-syn in peripheral fluids such as serum, plasma and saliva has been investigated as well. We review how the development of multiple assays for the quantification of α-syn has yielded novel insights into the variety of α-syn species present in the different fluids; the optimal preanalytical conditions required for robust quantification and the potential clinical value of α-syn as biomarker. We also suggest future approaches to use of CSF α-syn in neurodegenerative diseases.

Alpha synuclein dimers and oligomers are increased in overexpressing conditions in vitro and in vivo

Parkinson's disease is characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta along with the formation of intracellular fibrillar inclusions (Lewy bodies and Lewy neuritis), which are mainly composed of aggregated α-synuclein (ASYN). This latter is a 14 kDa protein that localizes to synaptic vesicles in nerve terminals and promotes soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex assembly. We explored the monomeric and oligomeric state of ASYN in vitro in HEK293s and SH-SY5Y cell lines. In addition rats were injected in the substantia nigra with an Adeno associated virus carrying the human A53T mutation of ASYN (in vivo experiments). We show that human wild type ASYN as well as PD-linked mutations (A30P, E46K and A53T) in overexpressing conditions mostly exists in a monomeric state in equilibrium with dimeric forms. The monomer/dimer ratio is unaffected by PD-linked mutation. Furthermore, the A30P, E46K and A53T mutations overexpression strongly increased cell death compared to wild type ASYN. Taken together, our data suggest that ASYN dimers amount do not directly correlate to reduced cellular viability, suggesting a different role in protein function and induced pathology. Our data suggest that early ASYN neuro-pathogenic effects are probably mediated by other molecular processes than increased oligomerization alone.

Structure, function and toxicity of alpha-synuclein: the Bermuda triangle in synucleinopathies

Parkinson's disease belongs to a group of currently incurable neurodegenerative disorders characterized by the misfolding and accumulation of alpha-synuclein aggregates that are commonly known as synucleinopathies. Clinically, synucleinopathies are heterogeneous, reflecting the somewhat selective neuronal vulnerability characteristic of each disease. The precise molecular underpinnings of synucleinopathies remain unclear, but the process of aggregation of alpha-synuclein appears as a central event. However, there is still no consensus with respect to the toxic forms of alpha-synuclein, hampering our ability to use the protein as a target for therapeutic intervention. To decipher the molecular bases of synucleinopathies, it is essential to understand the complex triangle formed between the structure, function and toxicity of alpha-synuclein. Recently, important steps have been undertaken to elucidate the role of the protein in both physiological and pathological conditions. Here, we provide an overview of recent findings in the field of alpha-synuclein research, and put forward a new perspective over paradigms that persist in the field. Establishing whether alpha-synuclein has a causative role in all synucleinopathies will enable the identification of targets for the development of novel therapeutic strategies for this devastating group of disorders. Alpha-synuclein is the speculated cornerstone of several neurodegenerative disorders known as Synucleinopathies. Nevertheless, the mechanisms underlying the pathogenic effects of this protein remain unknown. Here, we review the recent findings in the three corners of alpha-synuclein biology - structure, function and toxicity - and discuss the enigmatic roads that have accompanied alpha-synuclein from the beginning. This article is part of a special issue on Parkinson disease.

Type 2 diabetes as a protein misfolding disease

Type 2 diabetes (T2D) is a highly prevalent and chronic metabolic disorder. Recent evidence suggests that formation of toxic aggregates of the islet amyloid polypeptide (IAPP) might contribute to β-cell dysfunction and disease. However, the mechanism of protein aggregation and associated toxicity remains unclear. Misfolding, aggregation, and accumulation of diverse proteins in various organs is the hallmark of the group of protein misfolding disorders (PMDs), including highly prevalent illnesses affecting the central nervous system (CNS) such as Alzheimer's disease (AD) and Parkinson's disease (PD). In this review we discuss the current understanding of the mechanisms implicated in the formation of protein aggregates in the endocrine pancreas and associated toxicity in the light of the long-standing knowledge from neurodegenerative disorders associated with protein misfolding.

Sirtuins and proteolytic systems: implications for pathogenesis of synucleinopathies

Insoluble and fibrillar forms of α-synuclein are the major components of Lewy bodies, a hallmark of several sporadic and inherited neurodegenerative diseases known as synucleinopathies. α-Synuclein is a natural unfolded and aggregation-prone protein that can be degraded by the ubiquitin-proteasomal system and the lysosomal degradation pathways. α-Synuclein is a target of the main cellular proteolytic systems, but it is also able to alter their function further, contributing to the progression of neurodegeneration. Aging, a major risk for synucleinopathies, is associated with a decrease activity of the proteolytic systems, further aggravating this toxic looping cycle. Here, the current literature on the basic aspects of the routes for α-synuclein clearance, as well as the consequences of the proteolytic systems collapse, will be discussed. Finally, particular focus will be given to the sirtuins’s role on proteostasis regulation, since their modulation emerged as a promising therapeutic strategy to rescue cells from α-synuclein toxicity. The controversial reports on the potential role of sirtuins in the degradation of α-synuclein will be discussed. Connection between sirtuins and proteolytic systems is definitely worth of further studies to increase the knowledge that will allow its proper exploration as new avenue to fight synucleinopathies.

Generation and characterization of novel conformation-specific monoclonal antibodies for α-synuclein pathology

α-Synuclein (α-syn), a small protein that has the intrinsic propensity to aggregate, is implicated in several neurodegenerative diseases including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), which are collectively known as synucleinopathies. Genetic, pathological, biochemical, and animal modeling studies provided compelling evidence that α-syn aggregation plays a key role in the pathogenesis of PD and related synucleinopathies. It is therefore of utmost importance to develop reliable tools that can detect the aggregated forms of α-syn. We describe here the generation and characterization of six novel conformation-specific monoclonal antibodies that recognize specifically α-syn aggregates but not the soluble, monomeric form of the protein. The antibodies described herein did not recognize monomers or fibrils generated from other amyloidogenic proteins including β-syn, γ-syn, β-amyloid, tau protein, islet amyloid polypeptide and ABri. Interestingly, the antibodies did not react to overlapping linear peptides spanning the entire sequence of α-syn, confirming further that they only detect α-syn aggregates. In immunohistochemical studies, the new conformation-specific monoclonal antibodies showed underappreciated small micro-aggregates and very thin neurites in PD and DLB cases that were not observed with generic pan antibodies that recognize linear epitope. Furthermore, employing one of our conformation-specific antibodies in a sandwich based ELISA, we observed an increase in levels of α-syn oligomers in brain lysates from DLB compared to Alzheimer's disease and control samples. Therefore, the conformation-specific antibodies portrayed herein represent useful tools for research, biomarkers development, diagnosis and even immunotherapy for PD and related pathologies.

Posttranslational Modifications and Clearing of α-Synuclein Aggregates in Yeast

The budding yeast Saccharomyces cerevisiae represents an established model system to study the molecular mechanisms associated to neurodegenerative disorders. A key-feature of Parkinson’s disease is the formation of Lewy bodies, which are cytoplasmic protein inclusions. Misfolded α-synuclein is one of their main constituents. Expression of α-synuclein protein in yeast leads to protein aggregation and cellular toxicity, which is reminiscent to Lewy body containing human cells. The molecular mechanism involved in clearance of α-synuclein aggregates is a central question for elucidating the α-synuclein-related toxicity. Cellular clearance mechanisms include ubiquitin mediated 26S proteasome function as well as lysosome/vacuole associated degradative pathways as autophagy. Various modifications change α-synuclein posttranslationally and alter its inclusion formation, cytotoxicity and the distribution to different clearance pathways. Several of these modification sites are conserved from yeast to human. In this review, we summarize recent findings on the effect of phosphorylation and sumoylation of α-synuclein to the enhanced channeling to either the autophagy or the proteasome degradation pathway in yeast model of Parkinson’s disease.

Seeking a mechanism for the toxicity of oligomeric α-synuclein

In a number of neurological diseases including Parkinson’s disease (PD), α‑synuclein is aberrantly folded, forming abnormal oligomers, and amyloid fibrils within nerve cells. Strong evidence exists for the toxicity of increased production and aggregation of α-synuclein in vivo. The toxicity of α-synuclein is popularly attributed to the formation of “toxic oligomers”: a heterogenous and poorly characterized group of conformers that may share common molecular features. This review presents the available evidence on the properties of α-synuclein oligomers and the potential molecular mechanisms of their cellular disruption. Toxic α-synuclein oligomers may impact cells in a number of ways, including the disruption of membranes, mitochondrial depolarization, cytoskeleton changes, impairment of protein clearance pathways, and enhanced oxidative stress. We also examine the relationship between α-synuclein toxic oligomers and amyloid fibrils, in the light of recent studies that paint a more complex picture of α-synuclein toxicity. Finally, methods of studying and manipulating oligomers within cells are described.

Degradation of misfolded proteins in neurodegenerative diseases: therapeutic targets and strategies

Mammalian cells remove misfolded proteins using various proteolytic systems, including the ubiquitin (Ub)-proteasome system (UPS), chaperone mediated autophagy (CMA) and macroautophagy. The majority of misfolded proteins are degraded by the UPS, in which Ub-conjugated substrates are deubiquitinated, unfolded and cleaved into small peptides when passing through the narrow chamber of the proteasome. The substrates that expose a specific degradation signal, the KFERQ sequence motif, can be delivered to and degraded in lysosomes via the CMA. Aggregation-prone substrates resistant to both the UPS and the CMA can be degraded by macroautophagy, in which cargoes are segregated into autophagosomes before degradation by lysosomal hydrolases. Although most misfolded and aggregated proteins in the human proteome can be degraded by cellular protein quality control, some native and mutant proteins prone to aggregation into β-sheet-enriched oligomers are resistant to all known proteolytic pathways and can thus grow into inclusion bodies or extracellular plaques. The accumulation of protease-resistant misfolded and aggregated proteins is a common mechanism underlying protein misfolding disorders, including neurodegenerative diseases such as Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), prion diseases and Amyotrophic Lateral Sclerosis (ALS). In this review, we provide an overview of the proteolytic pathways in neurons, with an emphasis on the UPS, CMA and macroautophagy, and discuss the role of protein quality control in the degradation of pathogenic proteins in neurodegenerative diseases. Additionally, we examine existing putative therapeutic strategies to efficiently remove cytotoxic proteins from degenerating neurons.

The degree of astrocyte activation in multiple system atrophy is inversely proportional to the distance to α-synuclein inclusions

Multiple system atrophy (MSA) exhibits widespread astrogliosis together with α-synuclein (α-syn) glial cytoplasmic inclusions (GCIs) in mature oligodendrocytes. We quantified astrocyte activation by morphometric analysis of MSA cases, and investigated the correlation to GCI proximity. Using Imaris software, we obtained "skinned" three-dimensional models of GFAP-positive astrocytes in MSA and control tissue (n=75) from confocal z-stacks and measured the astrocyte process length and thickness and radial distance to the GCI. Astrocytes proximal to GCI-containing oligodendrocytes (r<25μm) had significantly (p, 0.05) longer and thicker processes characteristic of activation than distal astrocytes (r>25μm), with a reciprocal linear correlation (m, 90μm(2)) between mean process length and radial distance to the nearest GCI (R(2), 0.7). In primary cell culture studies, α-syn addition caused ERK-dependent activation of rat astrocytes and perinuclear α-syn inclusions in mature (MOSP-positive) rat oligodendrocytes. Activated astrocytes were also observed in close proximity to α-syn deposits in a unilateral rotenone-lesion mouse model. Moreover, unilateral injection of MSA tissue-derived α-syn into the mouse medial forebrain bundle resulted in widespread neuroinflammation in the α-syn-injected, but not sham-injected hemisphere. Taken together, our data suggests that the action of localized concentrations of α-syn may underlie both astrocyte and oligodendrocyte MSA pathological features.

Noninvasive bioluminescence imaging of α-synuclein oligomerization in mouse brain using split firefly luciferase reporters

Alpha-synuclein (αSYN) aggregation plays a pivotal role in the pathogenesis of Parkinson's disease and other synucleinopathies. In this multistep process, oligomerization of αSYN monomers is the first step in the formation of fibrils and intracytoplasmic inclusions. Although αSYN oligomers are generally considered to be the culprit of these diseases, the methodology currently available to follow-up oligomerization in cells and in brain is inadequate. We developed a split firefly luciferase complementation system to visualize oligomerization of viral vector-encoded αSYN fusion proteins. αSYN oligomerization resulted in successful luciferase complementation in cell culture and in mouse brain. Oligomerization of αSYN was monitored noninvasively with bioluminescence imaging in the mouse striatum and substantia nigra up to 8 months after injection. Moreover, the visualized αSYN oligomers retained their toxic and aggregation properties in both model systems. Next, the effect of two small molecules, FK506 and (-)-epigallocatechin-3-gallate (EGCG), known to inhibit αSYN fibril formation, was investigated. FK506 inhibited the observed αSYN oligomerization both in cell culture and in mouse brain. In conclusion, the split firefly luciferase-αSYN complementation assay will increase our insight in the role of αSYN oligomers in synucleinopathies and opens new opportunities to evaluate potential αSYN-based neuroprotective therapies.

Identification of synaptosomal proteins binding to monomeric and oligomeric α-synuclein

Monomeric α-synuclein (αSN) species are abundant in nerve terminals where they are hypothesized to play a physiological role related to synaptic vesicle turn-over. In Parkinson’s disease (PD) and dementia with Lewy body (DLB), αSN accumulates as aggregated soluble oligomers in terminals, axons and the somatodendritic compartment and insoluble filaments in Lewy inclusions and Lewy neurites. The autosomal dominant heritability associated to mutations in the αSN gene suggest a gain of function associated to aggregated αSN. We have conducted a proteomic screen to identify the αSN interactome in brain synaptosomes. Porcine brain synaptosomes were fractionated, solubilized in non-denaturing detergent and subjected to co-immunoprecipitation using purified recombinant human αSN monomers or oligomers as bait. The isolated αSN binding proteins were identified with LC-LTQ-orbitrap tandem mass spectrometry and quantified by peak area using Windows client application, Skyline Targeted Proteomic Environment. Data are available via ProteomeXchange with identifier PXD001462. To quantify the preferential binding an average fold increase was calculated by comparing binding to monomer and oligomer. We identified 10 proteins preferentially binding monomer, and 76 binding preferentially to oligomer and a group of 92 proteins not displaying any preferred conformation of αSN. The proteomic data were validated by immunoprecipitation in both human and porcine brain extracts using antibodies against monomer αSN interactors: Abl interactor 1, and myelin proteolipid protein, and oligomer interactors: glutamate decarboxylase 2, synapsin 1, glial fibrillary acidic protein, and VAMP-2. We demonstrate the existence of αSN conformation selective ligands and present lists of proteins, whose identity and functions will be useful for modeling normal and pathological αSN dependent processes.

Phosphorylated α-synuclein in Parkinson's disease: correlation depends on disease severity

Introduction

α-Synuclein (α-syn) is a key protein in Parkinson’s disease (PD), and one of its phosphorylated forms, pS129, is higher in PD patients than healthy controls. However, few studies have examined its levels in longitudinally collected cerebrospinal fluid (CSF) or in preclinical cases. In this study, CSF and clinical data were contributed by >300 subjects from three cohorts (the longitudinal DATATOP cohort, a large cross-sectional cohort, and a cohort of LRRK2 mutation carriers).

Results

Consistent with our previous observation that CSF pS129 positively correlated with Unified Parkinson’s Disease Rating Scale (UPDRS) scores, CSF pS129 in the DATATOP cohort increased over approximately two years of disease progression (mean change 5.60 pg/ml, p = 0.050). Intriguingly, in the DATATOP cohort, pS129 negatively correlated with UPDRS scores at the baseline (R = −0.244, p = 0.017), but not final point, suggesting that this association may depend on disease stage. Reanalysis of our previous cohort with stratification by PD stage, and addition of a cohort of LRRK2 mutation carriers with very early/preclinical PD, supported the idea that the relationship between CSF pS129 and disease severity over a wider range of PD stages might be represented with a U-shaped curve, in which lower pS129 levels correlated with worse clinical condition at early stages, but better condition at later stages.

Conclusion

The observation of a negative-to-positive transition of correlation of pS129 to disease severity as PD progresses could have profound impact on how pS129 is used as a biomarker clinically as well as in modeling PD experimentally.

Gaucher-related synucleinopathies: the examination of sporadic neurodegeneration from a rare (disease) angle

Gaucher disease, the most common lysosomal storage disease, is caused by a recessively inherited deficiency in glucocerebrosidase and subsequent accumulation of toxic lipid substrates. Heterozygous mutations in the lysosomal glucocerebrosidase gene (GBA1) have recently been recognized as the highest genetic risk factor for the development of α-synuclein aggregation disorders ("synucleinopathies"), including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Despite the wealth of experimental, clinical and genetic evidence that supports the association between mutant genotypes and synucleinopathy risk, the precise mechanisms by which GBA1 mutations lead to PD and DLB remain unclear. Decreased glucocerebrosidase activity has been demonstrated to promote α-synuclein misprocessing. Furthermore, aberrant α-synuclein species have been reported to downregulate glucocerebrosidase activity, which further contributes to disease progression. In this review, we summarize the recent findings that highlight the complexity of this pathogenetic link and how several pathways that connect glucocerebrosidase insufficiency with α-synuclein misprocessing have emerged as potential therapeutic targets. From a translational perspective, we discuss how various therapeutic approaches to lysosomal dysfunction have been explored for the treatment of GBA1-related synucleinopathies, and potentially, for non-GBA1-associated neurodegenerative diseases. In summary, the link between GBA1 and synucleinopathies has become the paradigm of how the study of a rare lysosomal disease can transform the understanding of the etiopathology, and hopefully the treatment, of a more prevalent and multifactorial disorder.

The ubiquitin-proteasome system in neurodegeneration

SIGNIFICANCE

Impairment of the ubiquitin-proteasome system (UPS) has been implicated in the pathogenesis of a wide variety of neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases. The most significant risk factor for the development of these disorders is aging, which is associated with a progressive decline in UPS activity and the accumulation of oxidatively modified proteins. To date, no therapies have been developed that can specifically up-regulate this system.

RECENT ADVANCES

In the neurodegenerative brain, dysfunction of the UPS has been associated with the deposition of ubiquitinated protein aggregates and widespread disruption of the proteostasis network. Recent research has identified further evidence of impairment in substrate ubiquitination and proteasomal degradation, which could contribute to the loss of cellular proteostasis in neurodegenerative disease. Novel strategies for activation of the UPS by genetic manipulation and treatment with synthetic compounds have also recently been identified.

CRITICAL ISSUES

Here, we discuss the specific roles of the UPS in the healthy central nervous system and establish how dysfunctional components can contribute to neurotoxicity in the context of disease.

FUTURE DIRECTIONS

Knowledge of the UPS components that are specifically or preferentially involved in neurodegenerative disease will be critical in the development of targeted therapies which aim at limiting the accumulation of misfolded proteins without gross disturbance of this major proteolytic pathway.

Overexpression of alpha-synuclein at non-toxic levels increases dopaminergic cell death induced by copper exposure via modulation of protein degradation pathways

Gene multiplications or point mutations in alpha (α)-synuclein are associated with familial and sporadic Parkinson's disease (PD). An increase in copper (Cu) levels has been reported in the cerebrospinal fluid and blood of PD patients, while occupational exposure to Cu has been suggested to augment the risk to develop PD. We aimed to elucidate the mechanisms by which α-synuclein and Cu regulate dopaminergic cell death. Short-term overexpression of wild type (WT) or mutant A53T α-synuclein had no toxic effect in human dopaminergic cells and primary midbrain cultures, but it exerted a synergistic effect on Cu-induced cell death. Cell death induced by Cu was potentiated by overexpression of the Cu transporter protein 1 (Ctr1) and depletion of intracellular glutathione (GSH) indicating that the toxic effects of Cu are linked to alterations in its intracellular homeostasis. Using the redox sensor roGFP, we demonstrated that Cu-induced oxidative stress was primarily localized in the cytosol and not in the mitochondria. However, α-synuclein overexpression had no effect on Cu-induced oxidative stress. WT or A53T α-synuclein overexpression exacerbated Cu toxicity in dopaminergic and yeast cells in the absence of α-synuclein aggregation. Cu increased autophagic flux and protein ubiquitination. Impairment of autophagy by overexpression of a dominant negative Atg5 form or inhibition of the ubiquitin/proteasome system (UPS) with MG132 enhanced Cu-induced cell death. However, only inhibition of the UPS stimulated the synergistic toxic effects of Cu and α-synuclein overexpression. Our results demonstrate that α-synuclein stimulates Cu toxicity in dopaminergic cells independent from its aggregation via modulation of protein degradation pathways.

Failure of ubiquitin proteasome system: risk for neurodegenerative diseases

The ubiquitin proteasome system (UPS) is the primary proteolytic quality control system in cells and has an essential function in the nervous system. UPS dysfunction has been linked to neurodegenerative conditions, including Alzheimer's, Parkinson's and Huntington's diseases. The pathology of neurodegenerative diseases is characterized by the abnormal accumulation of insoluble protein aggregates or inclusion bodies within neurons. The failure or dysregulation of the UPS prevents the degradation of misfolded/aberrant proteins, leading to deficient synaptic function that eventually affects the nervous system. In this review, we discuss the UPS and its physiological roles in the nervous system, its influence on neuronal function, and how UPS dysfunction contributes to the development of neurodegenerative diseases.

Aggregation-prone c9FTD/ALS poly(GA) RAN-translated proteins cause neurotoxicity by inducing ER stress

The occurrence of repeat-associated non-ATG (RAN) translation, an atypical form of translation of expanded repeats that results in the synthesis of homopolymeric expansion proteins, is becoming more widely appreciated among microsatellite expansion disorders. Such disorders include amyotrophic lateral sclerosis and frontotemporal dementia caused by a hexanucleotide repeat expansion in the C9ORF72 gene (c9FTD/ALS). We and others have recently shown that this bidirectionally transcribed repeat is RAN translated, and the "c9RAN proteins" thusly produced form neuronal inclusions throughout the central nervous system of c9FTD/ALS patients. Nonetheless, the potential contribution of c9RAN proteins to disease pathogenesis remains poorly understood. In the present study, we demonstrate that poly(GA) c9RAN proteins are neurotoxic and may be implicated in the neurodegenerative processes of c9FTD/ALS. Specifically, we show that expression of poly(GA) proteins in cultured cells and primary neurons leads to the formation of soluble and insoluble high molecular weight species, as well as inclusions composed of filaments similar to those observed in c9FTD/ALS brain tissues. The expression of poly(GA) proteins is accompanied by caspase-3 activation, impaired neurite outgrowth, inhibition of proteasome activity, and evidence of endoplasmic reticulum (ER) stress. Of importance, ER stress inhibitors, salubrinal and TUDCA, provide protection against poly(GA)-induced toxicity. Taken together, our data provide compelling evidence towards establishing RAN translation as a pathogenic mechanism of c9FTD/ALS, and suggest that targeting the ER using small molecules may be a promising therapeutic approach for these devastating diseases.

Neurodegenerative disorders: dysregulation of a carefully maintained balance?

The aggregation of misfolded proteins has long been regarded as a pathological event in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the exact molecular mechanisms that govern protein metabolism that may lead to toxicity remain largely unclear. Originally targeted as the causative agent, it has since become evident that aggregation formation may not be necessary for disease progression and studies show that they may even serve functional and protective roles. Although the focus has since shifted to the toxicity of intermediate protein species preceding aggregation formation, many questions remain: Is the blame for the neural destruction to be put on one event alone, or rather on a state of cellular disequilibrium resulting from multiple events? If the cause is multifactorial, then what triggers the toxic cascade and how can this be targeted therapeutically? In order to understand the origin of toxicity, the exact underlying mechanism and impact of each contributing process must be assessed. Therefore, the structural properties, mechanism of formation, cytotoxic and/or protective effects, as well as the clinical impact of protein intermediates and aggregates will be reviewed here with the goal to establish a neurodegenerative disease model aimed at improving current therapeutics, which may ultimately contribute towards improved treatment modalities.

α-Synuclein Misfolding Versus Aggregation Relevance to Parkinson's Disease: Critical Assessment and Modeling

α-Synuclein, an abundant and conserved presynaptic brain protein, is implicated as a critical factor in Parkinson's disease (PD). The aggregation of α-synuclein is believed to be a critical event in the disease process. α-Synuclein is characterized by a remarkable conformational plasticity, adopting different conformations depending on the environment. Therefore, it is classified as an "intrinsically disordered protein." Recently, a debate has challenged the view on the intrinsically disordered behavior of α-synuclein in the cell. It has been proposed that α-synuclein is a stable tetramer with a low propensity for aggregation; however, its destabilization leads to protein misfolding and its aggregation kinetics. In our critical analysis, we discussed about major issues: (i) why α-synuclein conformational behavior does not fit into the normal secondary structural characteristics of proteins, (ii) potential amino acids involved in the complexity of misfolding in α-synuclein that leads to aggregation, and (iii) the role of metals in misfolding and aggregation. To evaluate the above critical issues, we developed bioinformatics models related to secondary and tertiary conformations, Ramachandran plot, free energy change, intrinsic disordered prediction, solvent accessibility, and FoldIndex pattern. To the best of our knowledge, this is a novel critical assessment to understand the misfolding biology of synuclein and its relevance to Parkinson's disease.

Ubiquitin pathways in neurodegenerative disease

Control of proper protein synthesis, function, and turnover is essential for the health of all cells. In neurons these demands take on the additional importance of supporting and regulating the highly dynamic connections between neurons that are necessary for cognitive function, learning, and memory. Regulating multiple unique synaptic protein environments within a single neuron while maintaining cell health requires the highly regulated processes of ubiquitination and degradation of ubiquitinated proteins through the proteasome. In this review, we examine the effects of dysregulated ubiquitination and protein clearance on the handling of disease-associated proteins and neuronal health in the most common neurodegenerative diseases.

In silico modeling of the effects of alpha-synuclein oligomerization on dopaminergic neuronal homeostasis

Background

Alpha-synuclein (ASYN) is central in Parkinson’s disease (PD) pathogenesis. Converging pieces of evidence suggest that the levels of ASYN expression play a critical role in both familial and sporadic Parkinson’s disease. ASYN fibrils are the main component of inclusions called Lewy Bodies (LBs) which are found mainly in the surviving neurons of the substantia nigra. Despite the accumulated knowledge regarding the involvement of ASYN in molecular mechanisms underlying the development of PD, there is much information missing which prevents understanding the causes of the disease and how to stop its progression.

Results

Using a Systems Biology approach, we develop a biomolecular reactions model that describes the intracellular ASYN dynamics in relation to overexpression, post-translational modification, oligomerization and degradation of the protein. Especially for the proteolysis of ASYN, the model takes into account the biological knowledge regarding the contribution of Chaperone Mediated Autophagy (CMA), macro-autophagic and proteasome pathways in the protein’s degradation. Importantly, inhibitory phenomena, caused by ASYN, concerning CMA (more specifically the lysosomal-associated membrane protein 2a, abbreviated as Lamp2a receptor, which is the rate limiting step of CMA) and the proteasome are carefully modeled. The model is validated by simulation studies of known experimental overexpression data from SH-SY5Y cells and the unknown model parameters are estimated either computationally or by experimental fitting. The calibrated model is then tested under three hypothetical intervention scenarios and in all cases predicts increased cell viability that agrees with experimental evidence. The biomodel has been annotated and is made available in SBML format.

Conclusions

The mathematical model presented here successfully simulates the dynamic phenomena of ASYN overexpression and oligomerization and predicts the biological system’s behavior in a number of scenarios not used for model calibration. It allows, for the first time, to qualitatively estimate the protein levels that are capable of deregulating proteolytic homeostasis. In addition, it can help form new hypotheses for intervention that could be tested experimentally.

Protein phosphorylation in neurodegeneration: friend or foe?

Protein misfolding and aggregation is a common hallmark in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and fronto-temporal dementia (FTD). In these disorders, the misfolding and aggregation of specific proteins occurs alongside neuronal degeneration in somewhat specific brain areas, depending on the disorder and the stage of the disease. However, we still do not fully understand the mechanisms governing protein aggregation, and whether this constitutes a protective or detrimental process. In PD, alpha-synuclein (aSyn) forms protein aggregates, known as Lewy bodies, and is phosphorylated at serine 129. Other residues have also been shown to be phosphorylated, but the significance of phosphorylation in the biology and pathophysiology of the protein is still controversial. In AD and in FTD, hyperphosphorylation of tau protein causes its misfolding and aggregation. Again, our understanding of the precise consequences of tau phosphorylation in the biology and pathophysiology of the protein is still limited. Through the use of a variety of model organisms and technical approaches, we are now gaining stronger insight into the effects of phosphorylation in the behavior of these proteins. In this review, we cover recent findings in the field and discuss how targeting phosphorylation events might be used for therapeutic intervention in these devastating diseases of the nervous system.

Phosphorylation modulates clearance of alpha-synuclein inclusions in a yeast model of Parkinson's disease

Alpha-synuclein (aSyn) is the main component of proteinaceous inclusions known as Lewy bodies (LBs), the typical pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. Although aSyn is phosphorylated at low levels under physiological conditions, it is estimated that ∼90% of aSyn in LBs is phosphorylated at S129 (pS129). Nevertheless, the significance of pS129 in the biology of aSyn and in PD pathogenesis is still controversial. Here, we harnessed the power of budding yeast in order to assess the implications of phosphorylation on aSyn cytotoxicity, aggregation and sub-cellular distribution. We found that aSyn is phosphorylated on S129 by endogenous kinases. Interestingly, phosphorylation reduced aSyn toxicity and the percentage of cells with cytosolic inclusions, in comparison to cells expressing mutant forms of aSyn (S129A or S129G) that mimic the unphosphorylated form of aSyn. Using high-resolution 4D imaging and fluorescence recovery after photobleaching (FRAP) in live cells, we compared the dynamics of WT and S129A mutant aSyn. While WT aSyn inclusions were very homogeneous, inclusions formed by S129A aSyn were larger and showed FRAP heterogeneity. Upon blockade of aSyn expression, cells were able to clear the inclusions formed by WT aSyn. However, this process was much slower for the inclusions formed by S129A aSyn. Interestingly, whereas the accumulation of WT aSyn led to a marked induction of autophagy, cells expressing the S129A mutant failed to activate this protein quality control pathway. The finding that the phosphorylation state of aSyn on S129 can alter the ability of cells to clear aSyn inclusions provides important insight into the role that this posttranslational modification may have in the pathogenesis of PD and other synucleinopathies, opening novel avenues for investigating the molecular basis of these disorders and for the development of therapeutic strategies.

Protein aggregation is a common hallmark in neurodegenerative disorders, but is also associated with phenotypic plasticity in a variety of organisms, including yeasts. Alpha-synuclein (aSyn) forms aggregates that are typical of synucleinopathies, and is phosphorylated at S129, but the significance of phosphorylation in the biology and pathophysiology of the protein is still controversial. Exploring the power of budding yeast, we found phosphorylation reduced aSyn toxicity and inclusion formation. While inclusions formed by WT aSyn were homogeneous, those formed by S129A aSyn were larger and heterogeneous. Interestingly, clearance of aSyn inclusions was reduced in cells expressing S129A aSyn, correlating with deficient autophagy activation. The finding that phosphorylation alters the ability of cells to clear aSyn inclusions provides novel insight into the role phosphorylation may have in synucleinopathies, and suggests posttranslational modifications might constitute switches cells use to control the aggregation and clearance of key proteins, opening novel avenues for the development of therapeutic strategies for these devastating disorders.

Integrating pathways of Parkinson's disease in a molecular interaction map

Parkinson's disease (PD) is a major neurodegenerative chronic disease, most likely caused by a complex interplay of genetic and environmental factors. Information on various aspects of PD pathogenesis is rapidly increasing and needs to be efficiently organized, so that the resulting data is available for exploration and analysis. Here we introduce a computationally tractable, comprehensive molecular interaction map of PD. This map integrates pathways implicated in PD pathogenesis such as synaptic and mitochondrial dysfunction, impaired protein degradation, alpha-synuclein pathobiology and neuroinflammation. We also present bioinformatics tools for the analysis, enrichment and annotation of the map, allowing the research community to open new avenues in PD research. The PD map is accessible at http://minerva.uni.lu/pd_map .

LRRK2 as a Potential Genetic Modifier of Synucleinopathies: Interlacing the Two Major Genetic Factors of Parkinson's Disease

Parkinson's disease (PD) and related Lewy body diseases are characterized by deposition of α-synuclein aggregates in both the central nervous system and peripheral nervous system. Synucleinopathy lesions spread to larger brain areas as the disease progresses, and prion-like cell-to-cell transmission of aggregated α-synuclein is thought to be the underlying mechanism for this pathological spreading. LRRK2 is another protein linked to the pathogenesis of PD, and its presence in Lewy bodies has attracted much attention as to whether LRRK2 and α-synuclein interplay during the pathogenesis of PD. However, the relationship between these two crucial proteins still remains unclear. In this review article, we will discuss the current state of knowledge in terms of how these proteins cause the disease and provide the hypothetical mechanisms by which LRRK2 might modify the generation and progression of synucleinopathy.

Characterizing the dynamics of α-synuclein oligomers using hydrogen/deuterium exchange monitored by mass spectrometry

Soluble oligomers formed by α-synuclein (αSN) are suspected to play a central role in neuronal cell death during Parkinson's disease. While studies have probed the surface structure of these oligomers, little is known about the backbone dynamics of αSN when they form soluble oligomers. Using hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS), we have analyzed the structural dynamics of soluble αSN oligomers. The analyzed oligomers were metastable, slowly dissociating to monomers over a period of 21 days, after excess monomer had been removed. The C-terminal region of αSN (residues 94-140) underwent isotopic exchange very rapidly, demonstrating a highly dynamic region in the oligomeric state. Three regions (residues 4-17, 39-54, and 70-89) were strongly protected against isotopic exchange in the oligomers, indicating the presence of a stable hydrogen-bonded or solvent-shielded structure. The protected regions were interspersed by two somewhat more dynamic regions (residues 18-38 and 55-70). In the oligomeric state, the isotopic exchange pattern of the region of residues 35-95 of αSN corresponded well with previous nuclear magnetic resonance and electron paramagnetic resonance analyses performed on αSN fibrils and indicated a possible zipperlike maturation mechanism for αSN aggregates. We find the protected N-terminus (residues 4-17) to be of particular interest, as this region has previously been observed to be highly dynamic for both monomeric and fibrillar αSN. This region has mainly been described in relation to membrane binding of αSN, and structuring may be important in relation to disease.

Inclusion body formation, macroautophagy, and the role of HDAC6 in neurodegeneration

The failure to clear misfolded or aggregated proteins from the cytoplasm of nerve cells and glia is a common pathogenic event in a variety of neurodegenerative disorders. This might be causally related to defects in the major proteolytic systems, i.e., the ubiquitin-proteasomal system and the autophagic pathway. Large protein aggregates and defective organelles are excluded from the proteasome. They can be degraded only by macroautophagy, which is a highly selective process. It requires p62 to act as a bridge connecting ubiquitinated protein aggregates and autophagosomes, and the tubulin deacetylase histone deacetylase 6 (HDAC6). HDAC6 has recently been identified as a constituent in Lewy bodies of Parkinson disease and glial cytoplasmic inclusions of multiple system atrophy. It is considered a sensor of proteasomal inhibition and a cellular stress surveillance factor, and plays a central role in autophagy by controlling the fusion process of autophagosomes with lysosomes. Upon proteasomal inhibition, HDAC6 is relocated and recruited to polyubiquitin-positive aggresomes. Tubulin acetylation is a major consequence of HDAC6 inhibition, and HDAC6 inhibition restores microtubule (MT)-dependent transport mechanisms in neurons. This suggests the involvement of HDAC6 in neurodegenerative diseases. Furthermore, the protein tau seems to be a substrate for HDAC6. Tau acetylation impairs MT assembly and promotes tau fibrillization in vitro. It has been suggested that acetylation and phosphorylation of tau at multiples sites may act synergistically in the pathogenesis of tau fibrillization. In this review, we will survey the process of aggresome formation, macroautophagy and the role of autophagosomal proteins and HDAC6 in inclusion body formation.

Role of protein misfolding and proteostasis deficiency in protein misfolding diseases and aging

The misfolding, aggregation, and tissue accumulation of proteins are common events in diverse chronic diseases, known as protein misfolding disorders. Many of these diseases are associated with aging, but the mechanism for this connection is unknown. Recent evidence has shown that the formation and accumulation of protein aggregates may be a process frequently occurring during normal aging, but it is unknown whether protein misfolding is a cause or a consequence of aging. To combat the formation of these misfolded aggregates cells have developed complex and complementary pathways aiming to maintain protein homeostasis. These protective pathways include the unfolded protein response, the ubiquitin proteasome system, autophagy, and the encapsulation of damaged proteins in aggresomes. In this paper we review the current knowledge on the role of protein misfolding in disease and aging as well as the implication of deficiencies in the proteostasis cellular pathways in these processes. It is likely that further understanding of the mechanisms involved in protein misfolding and the natural defense pathways may lead to novel strategies for treatment of age-dependent protein misfolding disorders and perhaps aging itself.

CSF α-synuclein improves diagnostic and prognostic performance of CSF tau and Aβ in Alzheimer's disease

Alzheimer's disease (AD) and Lewy body diseases (LBD), e.g., Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB), are common causes of geriatric cognitive impairments. In addition, AD and LBD are often found in the same patients at autopsy; therefore, biomarkers that can detect the presence of both pathologies in living subjects are needed. In this investigation, we report the assessment of α-synuclein (α-syn) in cerebrospinal fluid (CSF) and its association with CSF total tau (t-tau), phosphorylated tau181 (p-tau181), and amyloid beta1-42 (Aβ1-42) in subjects of the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 389), with longitudinal clinical assessments. A strong correlation was noted between α-syn and t-tau in controls, as well as in patients with AD and mild cognitive impairment (MCI). However, the correlation is not specific to subjects in the ADNI cohort, as it was also seen in PD patients and controls enrolled in the Parkinson's Progression Markers Initiative (PPMI; n = 102). A bimodal distribution of CSF α-syn levels was observed in the ADNI cohort, with high levels of α-syn in the subjects with abnormally increased t-tau values. Although a correlation was also noted between α-syn and p-tau181, there was a mismatch (α-syn-p-tau181-Mis), i.e., higher p-tau181 levels accompanied by lower α-syn levels in a subset of ADNI patients. We hypothesize that this α-syn-p-tau181-Mis is a CSF signature of concomitant LBD pathology in AD patients. Hence, we suggest that inclusion of measures of CSF α-syn and calculation of α-syn-p-tau181-Mis improves the diagnostic sensitivity/specificity of classic CSF AD biomarkers and better predicts longitudinal cognitive changes.

Clinical and multimodal biomarker correlates of ADNI neuropathological findings

Background

Autopsy series commonly report a high percentage of coincident pathologies in demented patients, including patients with a clinical diagnosis of dementia of the Alzheimer type (DAT). However many clinical and biomarker studies report cases with a single neurodegenerative disease. We examined multimodal biomarker correlates of the consecutive series of the first 22 Alzheimer’s Disease Neuroimaging Initiative autopsies. Clinical data, neuropsychological measures, cerebrospinal fluid Aβ, total and phosphorylated tau and α-synuclein and MRI and FDG-PET scans.

Results

Clinical diagnosis was either probable DAT or Alzheimer’s disease (AD)-type mild cognitive impairment (MCI) at last evaluation prior to death. All patients had a pathological diagnosis of AD, but only four had pure AD. A coincident pathological diagnosis of dementia with Lewy bodies (DLB), medial temporal lobe pathology (TDP-43 proteinopathy, argyrophilic grain disease and hippocampal sclerosis), referred to collectively here as MTL, and vascular pathology were present in 45.5%, 40.0% and 22.7% of these patients, respectively. Hallucinations were a strong predictor of coincident DLB (100% specificity) and a more severe dysexecutive profile was also a useful predictor of coincident DLB (80.0% sensitivity and 83.3% specificity). Occipital FDG-PET hypometabolism accurately classified coincident DLB (80% sensitivity and 100% specificity). Subjects with coincident MTL showed lower hippocampal volume.

Conclusions

Biomarkers can be used to independently predict coincident AD and DLB pathology, a common finding in amnestic MCI and DAT patients. Cohorts with comprehensive neuropathological assessments and multimodal biomarkers are needed to characterize independent predictors for the different neuropathological substrates of cognitive impairment.

α-Synuclein in Parkinson's disease: pathogenic function and translation into animal models

Parkinson's disease is a common neurodegenerative disease characterised by the loss of dopaminergic neurons in the substantia nigra pars compacta and the formation of α-synuclein aggregates found in Lewy bodies throughout the brain. Several α-synuclein transgenic mouse models have been generated, as well as viral-mediated overexpression of wild-type and mutated α-synuclein to mimic the disease and to delineate the pathogenic pathway of α-synuclein-mediated toxicity and neurodegeneration. In this review, we will recapitulate what we have learned about the function of α-synuclein and α-synuclein-mediated toxicity through studies of transgenic animal models, inducible animal models and viral-based models.

Opportunities and challenges for molecular chaperone modulation to treat protein-conformational brain diseases

A common pathological hallmark of protein-conformational brain diseases is the formation of disease-specific protein aggregates. In Alzheimer's disease, these are comprised of amyloid-β and Tau as opposed to α-synuclein in Parkinson's disease and N-terminal fragments of mutant huntingtin in Huntington's disease. Most aggregates also sequester molecular chaperones, a protein family that assists in the folding, refolding, stabilization, and processing of client proteins, including misfolded proteins in brain diseases. Molecular chaperone modulation has achieved remarkable therapeutic effects in some cellular and preclinical animal models of protein-conformational diseases. This has raised hope for chaperone-based strategies to combat these diseases. Here, we review briefly the functional diversity and medical significance of molecular chaperones, their therapeutic potential, and common and specific challenges towards clinical application.

α-Synuclein in Parkinson's disease

α-Synuclein is a presynaptic neuronal protein that is linked genetically and neuropathologically to Parkinson's disease (PD). α-Synuclein may contribute to PD pathogenesis in a number of ways, but it is generally thought that its aberrant soluble oligomeric conformations, termed protofibrils, are the toxic species that mediate disruption of cellular homeostasis and neuronal death, through effects on various intracellular targets, including synaptic function. Furthermore, secreted α-synuclein may exert deleterious effects on neighboring cells, including seeding of aggregation, thus possibly contributing to disease propagation. Although the extent to which α-synuclein is involved in all cases of PD is not clear, targeting the toxic functions conferred by this protein when it is dysregulated may lead to novel therapeutic strategies not only in PD, but also in other neurodegenerative conditions, termed synucleinopathies.