| 1. |
- Buck, Kerstin, et al.
(author)
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Ser129 phosphorylation of endogenous α-synuclein induced by overexpression of polo-like kinases 2 and 3 in nigral dopamine neurons is not detrimental to their survival and function.
- 2015
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In: Neurobiology of Disease. - : Elsevier BV. - 0969-9961. ; 78:Mar 25, s. 100-114
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Journal article (peer-reviewed)abstract
- Phosphorylation of the α-synuclein (α-syn) protein at Ser129 [P(S129)-α-] was found to be the most abundant form in intracellular inclusions in brains from Parkinson's disease (PD) patients. This finding suggests that P(S129)-α-syn plays a central role in the pathogenesis of PD. However, it is at present unclear whether P(S129)-α-syn is pathogenic driving the neurodegenerative process. Rodent studies using neither the phosphomimics of human α-syn nor co-expression of human wild-type α-syn and kinases phosphorylating α-syn at Ser129 gave consistent results. One major concern in interpreting these findings is that human α-syn was expressed above physiological levels inducing neurodegeneration in rat nigral neurons. In order to exclude this confounding factor, we took a different approach and increased the phosphorylation level of endogenous α-syn. For this purpose, we took advantage of recombinant adeno-associated viral (rAAV) vectors to deliver polo-like kinase 2 (PLK2) or PLK3 in the substantia nigra and investigated whether increased levels of P(S129)-α-syn compromised the function and survival of nigral dopaminergic neurons. Interestingly, we observed that hyperphosphorylated α-syn did not induce nigral dopaminergic cell death, as assessed at 1 and 4months. Furthermore, histological analysis did not show any accumulation of α-syn protein or formation of inclusions. Using in vivo microdialysis, we found that the only measurable functional alteration was the depolarisation-induced release of dopamine, while the in vivo synthesis rate of DOPA and dopamine baseline release remained unaltered. Taken together, our results suggest that phosphorylation of α-syn at Ser129 does not confer a toxic gain of function per se.
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| 2. |
- Cuellar-Baena, Sandra, et al.
(author)
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Assessment of brain metabolite correlates of AAV-mediated overexpression of human alpha-synuclein in cortical neurons by in vivo(1) H-MR spectroscopy at 9.4 T.
- 2016
-
In: Journal of Neurochemistry. - : Wiley. - 1471-4159 .- 0022-3042. ; 137:5, s. 806-819
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Journal article (peer-reviewed)abstract
- In this study, we used proton-localized spectroscopy ((1) H-MRS) for the acquisition of the neurochemical profile longitudinally in a novel rat model of human wild type alpha-synuclein (a-syn) overexpression. Our goal was to find out if the increased a-syn load in this model could be linked to changes in metabolites in the frontal cortex. Animals injected with AAV vectors encoding for human a-syn formed the experimental group, whereas green fluorescent protein (GFP) expressing animals were used as the vector-treated control group and a third group of uninjected animals were used as naïve controls. Data was acquired at 2, 4 and 8 month time-points. Nineteen metabolites were quantified in the MR spectra using LCModel software. Based on 92 spectra, we evaluated any potential gender effect and found that Lactate levels were lower in males compared to females, while the opposite was observed for Ascorbate. Next, we assessed the effect of age and found increased levels of GABA, Tau and GPC+PCho. Finally, we analyzed the effect of treatment and found that Lactate levels (p=0.005) were specifically lower in the a-syn group compared to the GFP and control groups. Additionally, Ascorbate levels (p=0.05) were increased in the vector-injected groups, while glucose levels remained unchanged. This study indicates that the metabolic switch between Glucose-Lactate could be detectable in-vivo and might be modulated by Ascorbate. No concomitant changes were found in markers of neuronal integrity (e.g. NAA) consistent with the fact that a-syn overexpression in cortical neurons did not result in neurodegeneration in this model. This article is protected by copyright. All rights reserved.
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| 3. |
- Donis, Daphne, et al.
(author)
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Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer
- 2021
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In: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:12, s. 4314-4333
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Journal article (peer-reviewed)abstract
- To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.
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| 4. |
- Landeck, Natalie, et al.
(author)
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Toxic effects of human and rodent variants of alpha-synuclein in vivo
- 2017
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In: European Journal of Neuroscience. - : Wiley. - 0953-816X .- 1460-9568. ; 45:4, s. 536-547
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Journal article (peer-reviewed)abstract
- In Parkinson's disease, abnormal alpha-synuclein (asyn) accumulation leads to the formation of soluble oligomeric species thought to be toxic to cells as well as intraneuronal inclusions. To date, the precise mechanisms leading to aggregation of asyn in the brain is not well-understood. Previous studies in yeast, drosophila, and transgenic mice suggested that a non-A beta component depleted version of human asyn [h-asyn(D70-83)] or human beta-synuclein (h-bsyn), naturally lacking this centrally located hydrophobic region, are less prone to form aggregates in vitro and are expected to be less toxic compared to h-asyn in vivo, although not all experimental studies unequivocally support the latter view. To address this outstanding issue, we directly compared the neurotoxicity of human asyn against that of h-asyn(D70-83), h-bsyn as well as rat asyn using an adeno-associated viral vector to express these proteins in a dose-response study where the vector load was varied over two orders of magnitude. By quantifying the neurodegeneration of rat substantia nigra dopamine neurons here we show that h-asyn, h-bsyn, and h-asyn(D70-83) display comparable neurotoxicity across the vector doses tested. On the other hand, rat asyn and GFP control vectors displayed a different profile, where no detectable neurodegeneration was seen except at the highest vector titer. Thus, the two main conclusions of our study are that (i) deletion of the central hydrophobic region in h-asyn is not sufficient to alter its neurotoxic properties and (ii) expression of the widely used GFP control protein can cause measurable neurodegeneration at high titers.
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| 5. |
- Landeck, Natalie, et al.
(author)
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Two C-terminal sequence variations determine differential neurotoxicity between human and mouse α-synuclein
- 2020
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In: Molecular Neurodegeneration. - : Springer Science and Business Media LLC. - 1750-1326. ; 15:1
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Journal article (peer-reviewed)abstract
- Background: α-Synuclein (aSyn) aggregation is thought to play a central role in neurodegenerative disorders termed synucleinopathies, including Parkinson's disease (PD). Mouse aSyn contains a threonine residue at position 53 that mimics the human familial PD substitution A53T, yet in contrast to A53T patients, mice show no evidence of aSyn neuropathology even after aging. Here, we studied the neurotoxicity of human A53T, mouse aSyn, and various human-mouse chimeras in cellular and in vivo models, as well as their biochemical properties relevant to aSyn pathobiology. Methods: Primary midbrain cultures transduced with aSyn-encoding adenoviruses were analyzed immunocytochemically to determine relative dopaminergic neuron viability. Brain sections prepared from rats injected intranigrally with aSyn-encoding adeno-associated viruses were analyzed immunohistochemically to determine nigral dopaminergic neuron viability and striatal dopaminergic terminal density. Recombinant aSyn variants were characterized in terms of fibrillization rates by measuring thioflavin T fluorescence, fibril morphologies via electron microscopy and atomic force microscopy, and protein-lipid interactions by monitoring membrane-induced aSyn aggregation and aSyn-mediated vesicle disruption. Statistical tests consisted of ANOVA followed by Tukey's multiple comparisons post hoc test and the Kruskal-Wallis test followed by a Dunn's multiple comparisons test or a two-tailed Mann-Whitney test. Results: Mouse aSyn was less neurotoxic than human aSyn A53T in cell culture and in rat midbrain, and data obtained for the chimeric variants indicated that the human-to-mouse substitutions D121G and N122S were at least partially responsible for this decrease in neurotoxicity. Human aSyn A53T and a chimeric variant with the human residues D and N at positions 121 and 122 (respectively) showed a greater propensity to undergo membrane-induced aggregation and to elicit vesicle disruption. Differences in neurotoxicity among the human, mouse, and chimeric aSyn variants correlated weakly with differences in fibrillization rate or fibril morphology. Conclusions: Mouse aSyn is less neurotoxic than the human A53T variant as a result of inhibitory effects of two C-terminal amino acid substitutions on membrane-induced aSyn aggregation and aSyn-mediated vesicle permeabilization. Our findings highlight the importance of membrane-induced self-assembly in aSyn neurotoxicity and suggest that inhibiting this process by targeting the C-terminal domain could slow neurodegeneration in PD and other synucleinopathy disorders.
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| 6. |
- Mantzouki, Evanthia, et al.
(author)
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Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins
- 2018
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In: Toxins. - : MDPI. - 2072-6651. ; 10:4
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Journal article (peer-reviewed)abstract
- Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
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| 7. |
- Mock, Thomas, et al.
(author)
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Multiomics in the central Arctic Ocean for benchmarking biodiversity change
- 2022
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In: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 20:10
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Journal article (peer-reviewed)abstract
- Multiomics approaches need to be applied in the central Arctic Ocean to benchmark biodiversity change and to identify novel species and their genes. As part of MOSAiC, EcoOmics will therefore be essential for conservation and sustainable bioprospecting in one of the least explored ecosystems on Earth.
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| 8. |
- Ulusoy, Ayse, et al.
(author)
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Dysregulated dopamine storage increases the vulnerability to alpha-synuclein in nigral neurons
- 2012
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In: Neurobiology of Disease. - : Elsevier BV. - 0969-9961. ; 47:3, s. 367-377
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Journal article (peer-reviewed)abstract
- Impairments in the capacity of dopaminergic neurons to handle cytoplasmic dopamine may be a critical factor underlying the selective vulnerability of midbrain dopamine neurons in Parkinson's disease. Furthermore, toxicity of alpha-synuclein in dopaminergic neurons has been suggested to be mediated by direct interaction between dopamine and alpha-synuclein through formation of abnormal alpha-synuclein species, although direct in vivo evidence to support this hypothesis is lacking. Here, we investigated the role of dopamine availability on alpha-synuclein mediated neurodegeneration in vivo. We found that overexpression of alpha-synuclein in nigral dopamine neurons in mice with deficient vesicular storage of dopamine led to a significant increase in dopaminergic neurodegeneration. Importantly, silencing the tyrosine hydroxylase enzyme - thereby reducing dopamine content in the nigral neurons - reversed the increased vulnerability back to the baseline level observed in wild-type littermates, but failed to eliminate it completely. Importantly, TH knockdown was not effective in altering the toxicity in the wild-type animals. Taken together, our data suggest that under normal circumstances, in healthy dopamine neurons, cytoplasmic dopamine is tightly controlled such that it does not contribute significantly to alpha-synuclein mediated toxicity. Dysregulation of the dopamine machinery in the substantia nigra, on the other hand, could act as a trigger for induction of increased toxicity in these neurons and could explain how these neurons become more vulnerable and die in the disease process. (C) 2012 Elsevier Inc. All rights reserved.
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