Association between Parkinson's Disease and Cancer: New Findings and Possible Mediators.

Epidemiological evidence points to an inverse association between Parkinson's disease (PD) and almost all cancers except melanoma, for which this association is positive. The results of multiple studies have demonstrated that patients with PD are at reduced risk for the majority of neoplasms. Several potential biological explanations exist for the inverse relationship between cancer and PD. Recent results identified several PD-associated proteins and factors mediating cancer development and cancer-associated factors affecting PD. Accumulating data point to the role of genetic traits, members of the synuclein family, neurotrophic factors, the ubiquitin-proteasome system, circulating melatonin, and transcription factors as mediators. Here, we present recent data about shared pathogenetic factors and mediators that might be involved in the association between these two diseases. We discuss how these factors, individually or in combination, may be involved in pathology, serve as links between PD and cancer, and affect the prevalence of these disorders. Identification of these factors and investigation of their mechanisms of action would lead to the discovery of new targets for the treatment of both diseases.

The relevance of synuclein autoantibodies as a biomarker for Parkinson's disease.

Several studies have investigated if the levels of α-synuclein autoantibodies (α-syn AAb) differ in serum of Parkinson's disease (PD) patients and healthy subjects. Reproducible differences in their levels could serve as a biomarker for PD. The results of previous studies however remain inconclusive. With the largest sample size examined so far, we aimed to validate serum α-syn AAb levels as a biomarker for PD and investigated the presence of AAbs against other synucleins. We performed ELISA and immunoblots to determine synuclein AAb levels in the serum of 295 subjects comprising 157 PD patients from two independent cohorts, 46 healthy subjects, and 92 patients with other neurodegenerative disorders. Although serum α- and ß-syn AAb levels were significantly reduced in patients with PD and other neurodegenerative disorders as compared to controls, the AAb levels displayed high inter-and intra-cohort variability. Furthermore, α-syn AAb levels showed no correlation to clinical parameters like age, disease duration, disease severity, and gender, that might also be directed against beta- and gamma-syn. In conclusion, serum synuclein AAb levels do allow the separation of PD from healthy subjects but not from other neurodegenerative disorders. Thus, synuclein AAbs cannot be regarded as a reliable biomarker for PD.

The amyloid concentric ß-barrel hypothesis: Models of synuclein oligomers, annular protofibrils, lipoproteins, and transmembrane channels.

Amyloid beta (Aß of Alzheimer's disease) and α-synuclein (α-Syn of Parkinson's disease) form large fibrils. Evidence is increasing however that much smaller oligomers are more toxic and that these oligomers can form transmembrane ion channels. We have proposed previously that Aß42 oligomers, annular protofibrils, and ion channels adopt concentric ß-barrel molecular structures. Here we extend that hypothesis to the superfamily of α, ß, and γ-synucleins. Our models of numerous synuclein oligomers, annular protofibrils, tubular protofibrils, lipoproteins, and ion channels were developed to be consistent with sizes, shapes, molecular weights, and secondary structures of assemblies as determined by electron microscopy and other studies. The models have the following features: (1) all subunits have identical structures and interactions; (2) they are consistent with conventional ß-barrel theory; (3) the distance between walls of adjacent ß-barrels is between 0.6 and 1.2 nm; (4) hydrogen bonds, salt bridges, interactions among aromatic side-chains, burial and tight packing of hydrophobic side-chains, and aqueous solvent exposure of hydrophilic side-chains are relatively optimal; and (5) residues that are identical among distantly related homologous proteins cluster in the interior of most oligomers whereas residues that are hypervariable are exposed on protein surfaces. Atomic scale models of some assemblies were developed.

Triple-Knockout, Synuclein-Free Mice Display Compromised Lipid Pattern.

Recent studies have implicated synucleins in several reactions during the biosynthesis of lipids and fatty acids in addition to their recognised role in membrane lipid binding and synaptic functions. These are among aspects of decreased synuclein functions that are still poorly acknowledged especially in regard to pathogenesis in Parkinson's disease. Here, we aimed to add to existing knowledge of synuclein deficiency (i.e., the lack of all three family members), with respect to changes in fatty acids and lipids in plasma, liver, and two brain regions in triple synuclein-knockout (TKO) mice. We describe changes of long-chain polyunsaturated fatty acids (LCPUFA) and palmitic acid in liver and plasma, reduced triacylglycerol (TAG) accumulation in liver and non-esterified fatty acids in plasma of synuclein free mice. In midbrain, we observed counterbalanced changes in the relative concentrations of phosphatidylcholine (PC) and cerebrosides (CER). We also recorded a notable reduction in ethanolamine plasmalogens in the midbrain of synuclein free mice, which is an important finding since the abnormal ether lipid metabolism usually associated with neurological disorders. In summary, our data demonstrates that synuclein deficiency results in alterations of the PUFA synthesis, storage lipid accumulation in the liver, and the reduction of plasmalogens and CER, those polar lipids which are principal compounds of lipid rafts in many tissues. An ablation of all three synuclein family members causes more profound changes in lipid metabolism than changes previously shown to be associated with γ-synuclein deficiency alone. Possible mechanisms by which synuclein deficiency may govern the reported modifications of lipid metabolism in TKO mice are proposed and discussed.

Cell Responses to Extracellular α-Synuclein.

Synucleins are small naturally unfolded proteins involved in neurodegenerative diseases and cancer. The family contains three members: α-, ß-, and -synuclein. α-Synuclein is the most thoroughly investigated because of its close association with Parkinson's disease (PD), dementia with Lewy bodies and multiple system atrophy. Until recently, the synuclein's research was mainly focused on their intracellular forms. However, new studies highlighted the important role of extracellular synucleins. Extracellular forms of synucleins propagate between various types of cells, bind to cell surface receptors and transmit signals, regulating numerous intracellular processes. Here we give an update of the latest results about the mechanisms of action of extracellular synucleins, their binding to cell surface receptors, effect on biochemical pathways and the role in neurodegeneration and neuroinflammation.

The beneficial effect of a prolyl oligopeptidase inhibitor, KYP-2047, on alpha-synuclein clearance and autophagy in A30P transgenic mouse.

The misfolding and aggregation of α-synuclein (aSyn) eventually lead to an accumulation of toxic forms that disturb normal neuronal function and result in cell death. aSyn rich inclusions are seen in Parkinson's disease, dementia with Lewy bodies and other synucleinopathies. Prolyl oligopeptidase (PREP) can accelerate the aggregation process of aSyn and the inhibition of PREP leads to a decreased amount of aggregated aSyn in cell models and in aSyn transgenic mice. In this study, we investigated the effect of 5- and 28-day PREP inhibitor (KYP-2047) treatments on a mouse strain carrying a point mutation in the aSyn coding gene. Following PREP inhibition, we found a decrease in high molecular-weight oligomeric aSyn and a concomitant increase in the amount of the autophagosome marker, LC3BII, suggesting enhanced macroautophagy (autophagy) and aSyn clearance by KYP-2047. Moreover, 28-day treatment with KYP-2047 caused significant increases in striatal dopamine levels. In cell culture, overexpression of PREP reduced the autophagy. Furthermore, the inhibition of PREP normalized the changes on autophagy markers (LC3BII and p62) caused by an autophagy inhibition or aSyn overexpression, and induced the expression of beclin 1, a positive regulator of autophagy. Taken together, our results suggest that PREP inhibition accelerates the clearance of protein aggregates via increased autophagy and thus normalizes the cell functions in vivo and in vitro. Therefore, PREP inhibition may have future potential in the treatment of synucleinopathies.

Clinical presentation and differential diagnosis of dementia with Lewy bodies: a review.

BACKGROUND: Dementia with Lewy bodies is one of the most prevalent dementia diagnoses. However, differential diagnosis between dementia with Lewy bodies, Alzheimer's disease, and Parkinson's disease with dementia can still be very difficult given the overlap in neuropathology, clinical presentation, cognitive, and neuroanatomical changes. METHOD: A literature review of dementia with Lewy bodies, Alzheimer's disease, and Parkinson's disease with dementia was conducted using PubMed. RESULTS AND IMPLICATIONS: Accurate diagnosis of dementia with Lewy bodies is crucial in order to more accurately predict the progression of the disease and negative side effects from pharmacological treatment. The differences and similarities between dementia with Lewy bodies, Alzheimer's disease, and Parkinson's disease with dementia are highlighted in order to aid clinicians in differential diagnosis.

Synuclein Proteins in Cancer Development and Progression.

Synucleins are a family of small, soluble proteins mainly expressed in neural tissue and in certain tumors. Since their discovery, tens of thousands of scientific reports have been published about this family of proteins as they are associated with severe human diseases. Although the physiological function of these proteins is still elusive, their relationship with neurodegeneration and cancer has been clearly described over the years. In this review, we summarize data connecting synucleins and cancer, going from the structural description of these molecules to their involvement in tumor-related processes, and discuss the putative use of these proteins as cancer molecular biomarkers.

Different MAPT haplotypes influence expression of total MAPT in postmortem brain tissue.

The MAPT gene, encoding the microtubule-associated protein tau on chromosome 17q21.31, is result of an inversion polymorphism, leading to two allelic variants (H1 and H2). Homozygosity for the more common haplotype H1 is associated with an increased risk for several tauopathies, but also for the synucleinopathy Parkinson's disease (PD). In the present study, we aimed to clarify whether the MAPT haplotype influences expression of MAPT and SNCA, encoding the protein α-synuclein (α-syn), on mRNA and protein levels in postmortem brains of PD patients and controls. We also investigated mRNA expression of several other MAPT haplotype-encoded genes. Postmortem tissues from cortex of fusiform gyrus (ctx-fg) and of the cerebellar hemisphere (ctx-cbl) of neuropathologically confirmed PD patients (n = 95) and age- and sex-matched controls (n = 81) were MAPT haplotype genotyped to identify cases homozygous for either H1 or H2. Relative expression of genes was quantified using real-time qPCR; soluble and insoluble protein levels of tau and α-syn were determined by Western blotting. Homozygosity for H1 versus H2 was associated with increased total MAPT mRNA expression in ctx-fg regardless of disease state. Inversely, H2 homozygosity was associated with markedly increased expression of the corresponding antisense MAPT-AS1 in ctx-cbl. PD patients had higher levels of insoluble 0N3R and 1N4R tau isoforms regardless of the MAPT genotype. The increased presence of insoluble α-syn in PD patients in ctx-fg validated the selected postmortem brain tissue. Our findings in this small, but well controlled cohort of PD and controls support a putative biological relevance of tau in PD. However, we did not identify any link between the disease-predisposing H1/H1 associated overexpression of MAPT with PD status. Further studies are required to gain a deeper understanding of the potential regulatory role of MAPT-AS1 and its association to the disease-protective H2/H2 condition in the context of PD.

Loss of the Synuclein Family Members Differentially Affects Baseline- and Apomorphine-Associated EEG Determinants in Single-, Double- and Triple-Knockout Mice.

Synucleins comprise a family of small proteins highly expressed in the nervous system of vertebrates and involved in various intraneuronal processes. The malfunction of alpha-synuclein is one of the key events in pathogenesis of Parkinson disease and certain other neurodegenerative diseases, and there is a growing body of evidence that malfunction of other two synucleins might be involved in pathological processes in the nervous system. The modulation of various presynaptic mechanisms of neurotransmission is an important function of synucleins, and therefore, it is feasible that their deficiency might affect global electrical activity detected of the brain. However, the effects of the loss of synucleins on the frequency spectra of electroencephalograms (EEGs) have not been systematically studied so far. In the current study, we assessed changes in such spectra in single-, double- and triple-knockout mice lacking alpha-, beta- and gamma-synucleins in all possible combinations. EEGs were recorded from the motor cortex, the putamen, the ventral tegmental area and the substantia nigra of 78 3-month-old male mice from seven knockout groups maintained on the C57BL/6J genetic background, and 10 wild-type C57BL/6J mice for 30 min before and for 60 min after the systemic injection of a DA receptor agonist, apomorphine (APO). We found that almost any variant of synuclein deficiency causes multiple changes in both basal and APO-induced EEG oscillation profiles. Therefore, it is not the absence of any particular synuclein but rather a disbalance of synucleins that causes widespread changes in EEG spectral profiles.

Synuclein Proteins in MPTP-Induced Death of Substantia Nigra Pars Compacta Dopaminergic Neurons.

Parkinson's disease (PD) is one of the key neurodegenerative disorders caused by a dopamine deficiency in the striatum due to the death of dopaminergic (DA) neurons of the substantia nigra pars compacta. The initially discovered A53T mutation in the alpha-synuclein gene was linked to the formation of cytotoxic aggregates: Lewy bodies in the DA neurons of PD patients. Further research has contributed to the discovery of beta- and gamma-synucleins, which presumably compensate for the functional loss of either member of the synuclein family. Here, we review research from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity models and various synuclein-knockout animals. We conclude that the differences in the sensitivity of the synuclein-knockout animals compared with the MPTP neurotoxin are due to the ontogenetic selection of early neurons followed by a compensatory effect of beta-synuclein, which optimizes dopamine capture in the synapses. Triple-knockout synuclein studies have confirmed the higher sensitivity of DA neurons to the toxic effects of MPTP. Nonetheless, beta-synuclein could modulate the alpha-synuclein function, preventing its aggregation and loss of function. Overall, the use of knockout animals has helped to solve the riddle of synuclein functions, and these proteins could be promising molecular targets for the development of therapies that are aimed at optimizing the synaptic function of dopaminergic neurons.

Comparing the copper binding features of alpha and beta synucleins.

Amyloid aggregation of α-synuclein (AS) is one of the hallmarks of Parkinson's disease (PD). Copper ions specifically bind at the N-terminus of AS, accelerating protein aggregation. Its protein homolog ß-synuclein (BS) is also a copper binding protein, but it inhibits AS aggregation. Here, a comparative spectroscopic study of the Cu2+ binding properties of AS and BS has been performed, using electronic absorption, circular dichroism (CD) and electronic paramagnetic resonance (EPR). Our comparative spectroscopic study reveals striking similarities between the Cu2+ binding features of the two proteins. The Cu2+ binding site at the N-terminal group of BS protein, modeled by the BS (1-15) fragment is identical to that of AS; however, its rate of reduction is three times faster as compared to the AS site, consistent with BS having an additional Met residue in its Met1-Xn-Met5-Xn-Met10 motif. The latter is also evident in the cyclic voltammetry studies of the Cu-BS complex. On the other hand, the Cu2+ binding features of the His site in both proteins, as modeled by AS(45-55) and BS(60-70), are identical, indicating that the shift in the His position does not affect its coordination features. Finally, replacement of Glu46 by Ala does not alter Cu2+ binding to the His site, suggesting that the familial PD E46K mutation would not impact copper-induced aggregation. While further studies of the redox activity of copper bound to His50 in AS are required to understand the role of this site in metal-mediated aggregation, our study contributes to a better understanding of the bioinorganic chemistry of PD.

Sex-Related Differences in Voluntary Alcohol Intake and mRNA Coding for Synucleins in the Brain of Adult Rats Prenatally Exposed to Alcohol.

Maternal alcohol consumption is one of the strong predictive factors of alcohol use and consequent abuse; however, investigations of sex differences in response to prenatal alcohol exposure (PAE) are limited. Here we compared the effects of PAE throughout gestation on alcohol preference, state anxiety and mRNA expression of presynaptic proteins α-, ß- and γ-synucleins in the brain of adult (PND60) male and female Wistar rats. Total RNA was isolated from the hippocampus, midbrain and hypothalamus and mRNA levels were assessed with quantitative RT-PCR. Compared with naïve males, naïve female rats consumed more alcohol in "free choice" paradigm (10% ethanol vs. water). At the same time, PAE produced significant increase in alcohol consumption and preference in males but not in females compared to male and female naïve groups, correspondingly. We found significantly lower α-synuclein mRNA levels in the hippocampus and midbrain of females compared to males and significant decrease in α-synuclein mRNA in these brain areas in PAE males, but not in females compared to the same sex controls. These findings indicate that the impact of PAE on transcriptional regulation of synucleins may be sex-dependent, and in males' disruption in α-synuclein mRNA expression may contribute to increased vulnerability to alcohol-associated behavior.

Role of exosomes in the pathogenesis of inflammation in Parkinson's disease.

Inflammatory responses, including glial cell activation and peripheral immune cell infiltration, are involved in the pathogenesis of Parkinson's disease (PD). These inflammatory responses appear to be closely related to the release of extracellular vesicles, such as exosomes. However, the relationships among different forms of glial cell activation, synuclein dysregulation, mitochondrial dysfunction, and exosomes are complicated. This review discusses the multiple roles played by exosomes in PD-associated inflammation and concludes that exosomes can transport toxic α-synuclein oligomers to immature neurons and into the extracellular environment, inducing the oligomerization of α-synuclein in normal neurons. Misfolded α-synuclein causes microglia and astrocytes to activate and secrete exosomes. Glial cell-derived exosomes participate in communications between glial cells and neurons, triggering anti-stress and anti-inflammatory responses, in addition to axon growth. The production and release of mitochondrial vesicles and exosomes establish a new mechanism for linking mitochondrial dysfunction to systemic inflammation associated with PD. Given the relevance of exosomes as mediators of neuron-glia communication in neuroinflammation and neuropathogenesis, new targeted treatment strategies are currently being developed that use these types of extracellular vesicles as drug carriers. Exosome-mediated inflammation may be a promising target for intervention in PD patients.

Occurrence of Total and Proteinase K-Resistant Alpha-Synuclein in Glioblastoma Cells Depends on mTOR Activity.

Alpha-synuclein (α-syn) is a protein considered to be detrimental in a number of degenerative disorders (synucleinopathies) of which α-syn aggregates are considered a pathological hallmark. The clearance of α-syn strongly depends on autophagy, which can be stimulated by inhibiting the mechanistic target of rapamycin (mTOR). Thus, the overexpression of mTOR and severe autophagy suppression may produce α-syn accumulation, including the proteinase K-resistant protein isoform. Glioblastoma multiforme (GBM) is a lethal brain tumor that features mTOR overexpression and severe autophagy inhibition. Cell pathology in GBM is reminiscent of a fast, progressive degenerative disorder. Therefore, the present work questions whether, as is analogous to neurons during degenerative disorders, an overexpression of α-syn occurs within GBM cells. A high amount of α-syn was documented in GBM cells via real-time PCR (RT-PCR), Western blotting, immunohistochemistry, immuno-fluorescence, and ultrastructural stoichiometry, compared with the amount of ß- and γ-synucleins and compared with the amount of α-syn counted within astrocytes. The present study indicates that (i) α-syn is overexpressed in GBM cells, (ii) α-syn expression includes a proteinase-K resistant isoform, (iii) α-syn is dispersed from autophagy-like vacuoles to the cytosol, (iv) α-syn overexpression and cytosol dispersion are mitigated by rapamycin, and (v) the α-syn-related GBM-like phenotype is mitigated by silencing the SNCA gene.

Spreading of Alpha Synuclein from Glioblastoma Cells towards Astrocytes Correlates with Stem-like Properties.

Evidence has been recently provided showing that, in baseline conditions, GBM cells feature high levels of α-syn which are way in excess compared with α-syn levels measured within control astrocytes. These findings are consistent along various techniques. In fact, they are replicated by using antibody-based protein detection, such as immuno-fluorescence, immuno-peroxidase, immunoblotting and ultrastructural stoichiometry as well as by measuring α-syn transcript levels at RT-PCR. The present manuscript further questions whether such a high amount of α-syn may be induced within astrocytes, which are co-cultured with GBM cells in a trans-well system. In astrocytes co-cultured with GBM cells, α-syn overexpression is documented. Such an increase is concomitant with increased expression of the stem cell marker nestin, along with GBM-like shifting in cell morphology. This concerns general cell morphology, subcellular compartments and profuse convolutions at the plasma membrane. Transmission electron microscopy (TEM) allows us to assess the authentic amount and sub-cellular compartmentalization of α-syn and nestin within baseline GBM cells and the amount, which is induced within co-cultured astrocytes, as well as the shifting of ultrastructure, which is reminiscent of GBM cells. These phenomena are mitigated by rapamycin administration, which reverts nestin- and α-syn-related overexpression and phenotypic shifting within co-cultured astrocytes towards baseline conditions of naïve astrocytes. The present study indicates that: (i) α-syn increases in astrocyte co-cultured with GBM cells; (ii) α-syn increases in astrocytes along with the stem cell marker nestin; (iii) α-syn increases along with a GBM-like shift of cell morphology; (iv) all these changes are replicated in different GBM cell lines and are reverted by the mTOR inhibitor rapamycin. The present findings indicate that α-syn does occur in high amount within GBM cells and may transmit to neighboring astrocytes as much as a stem cell phenotype. This suggests a mode of tumor progression for GBM cells, which may transform, rather than merely substitute, surrounding tissue; such a phenomenon is sensitive to mTOR inhibition.

Synuclein in neurodegeneration.

Neurodegenerative diseases are a heterogeneous group of disorders characterized by gradual progressive neuronal loss in the central nervous system. Unfortunately, the pathogenesis of many of these diseases remains unknown. Synucleins are a family of small, highly charged proteins expressed predominantly in neurons. Following their discovery, much has been learned about their structure, function, interaction with other proteins and role in neurodegenerative disease over the last two decades. One of these proteins, α-Synuclein (α-Syn), appears to be involved in many neurodegenerative disorders. These include Parkinson's disease (PD), dementia with Lewy bodies (DLB), Rapid Eye Movement Sleep Behavior Disorder (RBD) and Pure Autonomic Failure (PAF), i.e., collectively termed α-synucleinopathies. This review focuses on α-Syn dysfunction in neurodegeneration and assesses its role in synucleinopathies from a biochemical, genetic and neuroimaging perspective.

Quantitative Profiling of Synuclein Species: Application to Transgenic Mouse Models of Parkinson's Disease.

INTRODUCTION: Improved analytical tools for detailed characterization of synucleins in pre-clinical models of Parkinson's disease (PD) and related synucleinopathies are needed. OBJECTIVE: Develop a multiple reaction monitoring (MRM) liquid chromatography tandem mass spectrometry (LC-MS/MS) assay to quantify species-specific sequences and structural heterogeneity in soluble α- and ß-synucleins in brain tissue. METHODS: Using a proteolytic digestion workflow, the MRM LC-MS/MS method assayed six proteotypic peptides from the α-synuclein sequence; three unique to mouse or human α-synuclein and three conserved in α- and ß-synuclein. For quantification, we used labeled α-synuclein as the internal standard and an external calibration curve. As proof of concept, the synuclein LC-MS/MS method was applied to brain tissue specimens from M83 transgenic PD mice, which overexpresses human α-synuclein, relative to wild-type littermate controls. RESULTS: The synuclein MRM assay was linear over a wide concentration range (at least one order of magnitude). The assay had several advantages over ligand binding analytical methods, such as western blotting and enzyme-linked immunosorbent assays. These advantages included the ability to: quantify 1) total α-synuclein, 2) combined α- and ß-synucleins, 3) species-specific contributions to total α-synuclein (e.g., in mice expressing both mouse and human α-synuclein), and 4) identify peptide-specific profile differences that may reflect post-translational modifications, all within a single analysis. CONCLUSION: With improved and expanded analytical characteristics coupled with a streamlined sample preparation workflow, the quantitative synuclein profiling LC-MS/MS assay provides a versatile and efficient platform to characterize synuclein biology in pre-clinical models and the potential for application to human tissues and fluids.

Amyloidosis and Longevity: A Lesson from Plants.

The variety of lifespans of different organisms in nature is amazing. Although it is acknowledged that the longevity is determined by a complex interaction between hereditary and environmental factors, many questions about factors defining lifespan remain open. One of them concerns a wide range of lifespans of different organisms. The reason for the longevity of certain trees, which reaches a thousand years and exceeds the lifespan of most long living vertebrates by a huge margin is also not completely understood. Here we have discussed some distinguishing characteristics of plants, which may explain their remarkable longevity. Among them are the absence (or very low abundance) of intracellular inclusions composed of amyloidogenic proteins, the lack of certain groups of proteins prone to aggregate and form amyloids in animals, and the high level of compounds which inhibit protein aggregation and possess antiaging properties.