Binding of Metal-Ion-Induced Tau Oligomers to Lipid Surfaces Is Enhanced by GSK-3β-Mediated Phosphorylation

While fibrillar deposits of hyperphosphorylated protein tau are a key hallmark of several neurodegenerative diseases such as Alzheimer's disease, small oligomers have been speculated to be the key toxic aggregate species. Trivalent metal ions were shown to promote tau oligomer formation in vitro. However, little is known about potential intercellular spreading mechanisms or toxic modes of action of such oligomers. We investigated interactions of tau monomers and Fe³⁺/Al³⁺-induced oligomers with small unilamellar vesicles derived from 1-palmitoyl-2-oleoyl-phosphatidylcholine (neutral, liquid-crystalline phase) and dipalmitoyl-phosphatidylcholine (neutral, gel-phase). We further evaluated the influence of glycogen synthase kinase 3β (GSK-3β)-mediated tau phosphorylation applying the single-particle fluorescence spectroscopy techniques fluorescence correlation spectroscopy, fluorescence intensity distribution analysis, and scanning for intensely fluorescent targets. In these experiments, no binding to neutral lipid surfaces was observed for tau monomers. In contrast, metal-ion-induced tau oligomers showed a gain of function in binding to neutral lipid surfaces. Of note, tau phosphorylation by GSK-3β increased both oligomer formation and membrane affinity of the resulting oligomers. In conclusion, our data imply a pathological gain of function of metal-ion-induced oligomers of hyperphosphorylated tau, enabling membrane binding irrespective of surface charge even at nanomolar protein concentrations.

Outcome prediction with serial neuron-specific enolase and machine learning in anoxic-ischaemic disorders of consciousness

BACKGROUND

The continuation of life-sustaining therapy in critical care patients with anoxic-ischemic disorders of consciousness (AI-DOC) depends on prognostic tests such as serum neuron-specific enolase (NSE) concentration levels.

OBJECTIVES

To apply predictive models using machine learning methods to examine, one year after onset, the prognostic power of serial measurements of NSE in patients with AI-DOC. To compare the discriminative accuracy of this method to both standard single-day, absolute, and difference-between-days, relative NSE levels.

METHODS

Classification algorithms were implemented and K-nearest neighbours (KNN) imputation was used to avoid complete case elimination of patients with missing NSE values. Non-imputed measurements from Day 0 to Day 6 were used for single day and difference-between-days.

RESULTS

The naive Bayes classifier on imputed serial NSE measurements returned an AUC of (0.81±0.07) for n=126 patients (100 poor outcome). This was greater than logistic regression (0.73±0.08) and all other classifiers. Naive Bayes gave a specificity and sensitivity of 96% and 49%, respectively, for an (uncalibrated) probability decision threshold of 90%. The maximum AUC for a single day was Day 3 (0.75) for a subset of n=79 (61 poor outcome) patients, and for differences between Day 1 and Day 4 (0.81) for a subset of n=46 (39 poor outcome) patients.

CONCLUSION

Imputation avoided the elimination of patients with missing data and naive Bayes outperformed all other classifiers. Machine learning algorithms could detect automatically discriminatory features and the overall predictive power increased from standard methods due to the larger data set.

CODE AVAILABILITY

Data analysis code is available under GNU at: https://github.com/emilymuller1991/outcome_prediction_nse.

Adjuvant non-bacteriolytic and anti-inflammatory combination therapy in pneumococcal meningitis: an investigation in a mouse model

OBJECTIVES

Therapy with antibiotics, dexamethasone, and supportive intensive care has improved the prognosis of pneumococcal meningitis, but mortality remains high. Here, we investigated an adjunctive combination therapy of the non-bacteriolytic antibiotic daptomycin plus several anti-inflammatory agents to identify the currently most promising adjunctive combination therapy for pneumococcal meningitis.

METHODS

C57BL/6 mice were infected by injection of pneumococci into the cisterna magna. Treatment was begun 21 h after infection, and consisted of ceftriaxone plus (a) dexamethasone, (b) dexamethasone plus daptomycin, (c) daptomycin, (d) daptomycin plus an anti-IL1 antibody, (e) daptomycin plus roscovitine, or (f) daptomycin plus an anti-C5 antibody. Animals were followed until 45 h after infection. Furthermore, adjunctive daptomycin plus anti-C5 antibodies were assessed in a long-term follow-up.

RESULTS

Adjunctive treatment with daptomycin and an anti-C5 antibody was superior to adjunctive dexamethasone and reduced disease symptoms (clinical score 1.1 ± 1.1 versus 5.0 ± 2.7, p < 0.0083), improved explorative activity (open field test 17.8 ± 8.2 versus 7.4 ± 4.3 crossed fields/2 minutes, p < 0.0083), and reduced hearing impairment (thresholds for click stimulus 96.1 ± 14.7 versus 114.8 ± 9.3 dB SPL, p < 0.0083) in the acute stage. Furthermore, explorative activity (14.4 ± 7.3 crossed fields/2 minutes versus 6.3 ± 7.2, p < 0.05) and cognitive function (t-maze test, exploration time previously unknown alley 72.4 ± 14.3 versus 48.7 ± 25.6%, p < 0.05) was improved at 2 weeks after infection. Treatment with daptomycin plus an anti-IL-1β antibody or roscovitine was not of significant benefit in comparison to adjunctive therapy with dexamethasone.

CONCLUSIONS

An adjunctive combination of the non-lytic antibiotic daptomycin plus an anti-C5 antibody was superior to standard therapy with adjunctive dexamethasone in the treatment of pneumococcal meningitis.

Intracellular formation of α-synuclein oligomers and the effect of heat shock protein 70 characterized by confocal single particle spectroscopy

Synucleinopathies such as dementia with Lewy bodies or Parkinson's disease are characterized by intracellular deposition of pathologically aggregated α-synuclein. The details of the molecular pathogenesis of PD and especially the conditions that lead to intracellular aggregation of α-synuclein and the role of these aggregates in cell death remain unknown. In cell free in vitro systems considerable knowledge about the aggregation processes has been gathered. In comparison, the knowledge about these aggregation processes in cells is far behind. In cells α-synuclein aggregates can be toxic. However, the crucial particle species responsible for decisive steps in pathogenesis such as seeding a continuing aggregation process and triggering cell death remain to be identified. In order to understand the complex nature of intracellular α-synuclein aggregate formation, we analyzed fluorescent particles formed by venus and α-synuclein-venus fusion proteins and α-synuclein-hemi-venus fusion proteins derived from gently lyzed cells. With these techniques we were able to identify and characterize α-synuclein oligomers formed in cells. Especially the use of α-synuclein-hemi-venus fusion proteins enabled us to identify very small α-synuclein oligomers with high sensitivity. Furthermore, we were able to study the molecular effect of heat shock protein 70, which is known to inhibit α-synuclein aggregation in cells. Heat shock protein 70 does not only influence the size of α-synuclein oligomers, but also their quantity. In summary, this approach based on fluorescence single particle spectroscopy, that is suited for high throughput measurements, can be used to detect and characterize intracellularly formed α-synuclein aggregates and characterize the effect of molecules that interfere with α-synuclein aggregate formation.

New-Onset Headache in Patients With Autoimmune Encephalitis Is Associated With anti-NMDA-Receptor Antibodies

OBJECTIVE

We tested the hypotheses (i) that autoimmune encephalitis is associated with new-onset headache, and (ii) that the occurrence of headache is associated with the presence of anti-N-methyl-D-aspartate (NMDA)-receptor antibodies.

BACKGROUND

Autoimmune encephalitis presents with cognitive dysfunction as well as neuro-psychiatric symptoms. Its pathophysiology might involve antibody-mediated dysfunction of the glutamatergic system as indicated by the presence of anti-NMDA-receptor antibodies in some patients.

METHODS

In this cross-sectional study, patients with autoimmune encephalitis were assessed with a standardized interview for previous headache and headache associated with autoimmune encephalitis. Headache was classified according to the International Classification of Headache Disorders, second edition. Clinical and paraclinical findings were correlated with the occurrence of headache.

RESULTS

Of 40 patients with autoimmune encephalitis, 19 did not have a history of headache. Of those, nine suffered from encephalitis-associated headache. Seven of these nine had anti-NMDA-receptor antibodies in contrast to only two among the remaining 10 patients without new-onset headache (P = .023, odds ratio: 14, 95% confidence interval: 1.5; 127). In most patients headache occurred in attacks on more than 15 days/month, was severe, and of short duration (less than 4 hours). International Headache Society criteria for migraine were met in three patients.

CONCLUSIONS

New-onset headache is a relevant symptom in patients with autoimmune encephalitis who have no history of previous headache, especially in the subgroup with anti-NMDA-receptor antibodies. This indicates a thorough investigation for secondary headaches including anti-NMDA-R antibodies for patients with new-onset headache and neuropsychiatric findings. Glutamatergic dysfunction might be important for the generation of head pain but may only occasionally be sufficient to trigger migraine-like attacks in nonmigraineurs.

Histopathology and clinical course of MOG-antibody-associated encephalomyelitis

We present histological, MRI, and clinical features of an adult patient with relapsing encephalomyelitis and antibodies against myelin oligodendrocyte glycoprotein (MOG). Furthermore, we report molecular details of the recognized epitope that is specific for human MOG. A brain biopsy revealed multiple sclerosis (MS)-type II pathology. Some features overlapped with both MS and neuromyelitis optica spectrum disorders (NMOSD), whereas others were distinct from both MS and NMOSD. Immunoadsorption and rituximab induced clinical stabilization. This case contributes a new, so far missing link in the emerging spectrum of MOG-antibody-associated encephalomyelitis.

Generation of ferric iron links oxidative stress to α-synuclein oligomer formation

BACKGROUND

Synucleinopathies such as Parkinson's disease are characterized by the deposition of aggregated α-synuclein in affected brain areas. As genes involved in mitochondrial function, mitochondrial toxins, and age-related mitochondrial impairment have been implicated in Parkinson's disease pathogenesis, an increase in reactive oxygen species resulting from mitochondrial dysfunction has been speculated to induce α-synuclein aggregation. In vitro, pore-forming, SDS-resistant α-synuclein oligomers are formed in presence of ferric iron and may represent an important toxic particle species.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the interplay of reactive oxygen species, antioxidants and iron oxidation state in regard to α-synuclein aggregation using confocal single particle fluorescence spectroscopy, Phenanthroline spectrometry and thiobarbituric acid reactive substances assay. We found that the formation of α-synuclein oligomers in presence of Fe³⁺ is due to a direct interaction. In contrast, oxidizing agents and hydroxyl radicals generated in the Fenton reaction did not directly affect α-synuclein oligomerization. However, reactive oxygen species could enhance aggregation via oxidation of ferrous to ferric iron when iron ions were present.

CONCLUSIONS/SIGNIFICANCE

Our data thus indicate that oxidative stress affects α-synuclein aggregation via oxidation of iron to the ferric state. This provides a new perspective on the role of mitochondrial toxins and mitochondrial dysfunction in the pathogenesis of Parkinson's disease.

Modelling Ser129 phosphorylation inhibits membrane binding of pore-forming alpha-synuclein oligomers

Background

In several neurodegenerative diseases, hyperphosphorylation at position Ser129 is found in fibrillar deposits of alpha-synuclein (asyn), implying a pathophysiological role of asyn phosphorylation in neurodegeneration. However, recent animal models applying asyn phosphorylation mimics demonstrated a protective effect of phosphorylation. Since metal-ion induced asyn oligomers were identified as a potential neurotoxic aggregate species with membrane pore-forming abilities, the current study was undertaken to determine effects of asyn phosphorylation on oligomer membrane binding.

Methods

We investigated the influence of S129 phosphorylation on interactions of metal-ion induced asyn oligomers with small unilamellar lipid vesicles (SUV) composed of POPC and DPPC applying the phosphorylation mimic asyn129E. Confocal single-particle fluorescence techniques were used to monitor membrane binding at the single-particle level.

Results

Binding of asyn129E monomers to gel-state membranes (DPPC-SUV) is slightly reduced compared to wild-type asyn, while no interactions with membranes in the liquid-crystalline state (POPC-SUV) are seen for both asyn and asyn129E. Conversely, metal-ion induced oligomer formation is markedly increased in asyn129E. Surprisingly, membrane binding to POPC-SUV is nearly absent in Fe³⁺ induced asyn129E oligomers and markedly reduced in Al³⁺ induced oligomers.

Conclusion

The protective effect of pseudophosphorylation seen in animal models may be due to impeded oligomer membrane binding. Phosphorylation at Ser129 may thus have a protective effect against neurotoxic asyn oligomers by preventing oligomer membrane binding and disruption of the cellular electrophysiological equilibrium. Importantly, these findings put a new complexion on experimental pharmaceutical interventions against POLO-2 kinase.

Mitochondrial membrane permeabilisation by amyloid aggregates and protection by polyphenols

Alzheimer's disease and Parkinson's disease are neurodegenerative disorders characterised by the misfolding of proteins into soluble prefibrillar aggregates. These aggregate complexes disrupt mitochondrial function, initiating a pathophysiological cascade leading to synaptic and neuronal degeneration. In order to explore the interaction of amyloid aggregates with mitochondrial membranes, we made use of two in vitro model systems, namely: (i) lipid vesicles with defined membrane compositions that mimic those of mitochondrial membranes, and (ii) respiring mitochondria isolated from neuronal SH-SY5Y cells. External application of soluble prefibrillar forms, but not monomers, of amyloid-beta (Aβ42 peptide), wild-type α-synuclein (α-syn), mutant α-syn (A30P and A53T) and tau-441 proteins induced a robust permeabilisation of mitochondrial-like vesicles, and triggered cytochrome c release (CCR) from isolated mitochondrial organelles. Importantly, the effect on mitochondria was shown to be dependent upon cardiolipin, an anionic phospholipid unique to mitochondria and a well-known key player in mitochondrial apoptosis. Pharmacological modulators of mitochondrial ion channels failed to inhibit CCR. Thus, we propose a generic mechanism of thrilling mitochondria in which soluble amyloid aggregates have the intrinsic capacity to permeabilise mitochondrial membranes, without the need of any other protein. Finally, six small-molecule compounds and black tea extract were tested for their ability to inhibit permeation of mitochondrial membranes by Aβ42, α-syn and tau aggregate complexes. We found that black tea extract and rosmarinic acid were the most potent mito-protectants, and may thus represent important drug leads to alleviate mitochondrial dysfunction in neurodegenerative diseases.

Two different binding modes of α-synuclein to lipid vesicles depending on its aggregation state

Aggregation of α-synuclein is involved in the pathogenesis of Parkinson's disease (PD). Studies of in vitro aggregation of α-synuclein are rendered complex because of the formation of a heterogeneous population of oligomers. With the use of confocal single-molecule fluorescence techniques, we demonstrate that small aggregates (oligomers) of α-synuclein formed from unbound monomeric species in the presence of organic solvent (DMSO) and iron (Fe(3+)) ions have a high affinity to bind to model membranes, regardless of the lipid-composition or membrane curvature. This binding mode contrasts with the well-established membrane binding of α-synuclein monomers, which is accompanied with α-helix formation and requires membranes with high curvature, defects in the lipid packing, and/or negatively charged lipids. Additionally, we demonstrate that membrane-bound α-synuclein monomers are protected from aggregation. Finally, we identified compounds that potently dissolved vesicle-bound α-synuclein oligomers into monomers, leaving the lipid vesicles intact. As it is commonly believed that formation of oligomers is related PD progression, such compounds may provide a promising strategy for the design of novel therapeutic drugs in Parkinson's disease.

Wildervanck's syndrome and mirror movements: a congenital disorder of axon migration?

Cell outgrowth and migration in the developing nervous system result from guidance cues, whose molecular bases and clinical correlates are only partly known. We describe a patient with brain stem malformation, paroxysmal left sided lacrimation when eating ("crocodile tears") and mirror movements in addition to Wildervanck's cervico-oculo-acusticus (COA) syndrome, which encompasses Klippel-Feil anomaly, congenital hearing loss and Duane's syndrome. The unique symptom constellation has not been reported in that combination before and can be discussed in the context of congenital disordered axonal migration based on dysfunction of signalling pathways. However, mutations in some recently discovered genes, associated with single findings also present in our patient, were not found. Therefore, we suppose that the disturbance of an as yet unknown regulatory factor may explain the congenital malformation syndrome of our patient. In general, only a few human disorders have yet been found to result from defects in axon guidance. Nevertheless, disorders of axon guidance can certainly be regarded as a new category of neurodevelopmental disorders.

AMPA-receptor-mediated excitatory synaptic transmission is enhanced by iron-induced α-synuclein oligomers

Aggregated α-synuclein (α-syn) is a characteristic pathological finding in Parkinson's disease and related disorders, such as dementia with Lewy bodies. Recent evidence suggests that α-syn oligomers represent the principal neurotoxic species; however, the pathophysiological mechanisms are still not well understood. Here, we studied the neurophysiological effects of various biophysically-characterized preparations of α-syn aggregates on excitatory synaptic transmission in autaptic neuronal cultures. Nanomolar concentrations of large α-syn oligomers, generated by incubation with organic solvent and Fe(3+) ions, were found to selectivity enhance evoked α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-receptor, but not NMDA-receptor, mediated synaptic transmission within minutes. Moreover, the analysis of spontaneous AMPA-receptor-mediated miniature synaptic currents revealed an augmented frequency. These results collectively indicate that large α-syn oligomers alter both pre- and post-synaptic mechanisms of AMPA-receptor-mediated synaptic transmission. The augmented excitatory synaptic transmission may directly contribute to nerve cell death in synucleinopathies. Indeed, already low micromolar glutamate concentrations were found to be toxic in primary cultured neurons incubated with large α-syn oligomers. In conclusion, large α-syn oligomers enhance both pre- and post-synaptic AMPA-receptor-mediated synaptic transmission, thereby aggravating intracellular calcium dyshomeostasis and contributing to excitotoxic nerve cell death in synucleinopathies.

Inhibition and disaggregation of α-synuclein oligomers by natural polyphenolic compounds

Aggregation of alpha-synuclein (αS) into oligomers is critically involved in the pathogenesis of Parkinson's disease (PD). Using confocal single-molecule fluorescence spectroscopy, we have studied the effects of 14 naturally-occurring polyphenolic compounds and black tea extract on αS oligomer formation. We found that a selected group of polyphenols exhibited potent dose-dependent inhibitory activity on αS aggregation. Moreover, they were also capable of robustly disaggregating pre-formed αS oligomers. Based upon structure-activity analysis, we propose that the key molecular scaffold most effective in inhibiting and destabilizing self-assembly by αS requires: (i) aromatic elements for binding to the αS monomer/oligomer and (ii) vicinal hydroxyl groups present on a single phenyl ring. These findings may guide the design of novel therapeutic drugs in PD.

Converse modulation of toxic alpha-synuclein oligomers in living cells by N'-benzylidene-benzohydrazide derivates and ferric iron

Intracellular alpha-synuclein (alpha-syn) aggregates are the pathological hallmark in several neurodegenerative diseases including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. Recent evidence suggests that small oligomeric aggregates rather than large amyloid fibrils represent the main toxic particle species in these diseases. We recently characterized iron-dependent toxic alpha-syn oligomer species by confocal single molecule fluorescence techniques and used this aggregation model to identify several N'-benzylidene-benzohydrazide (NBB) derivatives inhibiting oligomer formation in vitro. In our current work, we used the bioluminescent protein-fragment complementation assay (BPCA) to directly analyze the formation of toxic alpha-syn oligomers in cell culture and to investigate the effect of iron and potential drug-like compounds in living cells. Similar to our previous findings in vitro, we found a converse modulation of toxic alpha-syn oligomers by NBB derivates and ferric iron, which was characterized by an increase in aggregate formation by iron and an inhibitory effect of certain NBB compounds. Inhibition of alpha-syn oligomer formation by the NBB compound 293G02 was paralleled by a reduction in cytotoxicity indicating that toxic alpha-syn oligomers are present in the BPCA cell culture model and that pharmacological inhibition of oligomer formation can reduce toxicity. Thus, this approach provides a suitable model system for the development of new disease-modifying drugs targeting toxic oligomer species. Moreover, NBB compounds such as 293G02 may provide useful tool compounds to dissect the functional role of toxic oligomer species in cell culture models and in vivo.

Increased alpha-synuclein aggregation following limited cleavage by certain matrix metalloproteinases

Recent evidence indicates that protein aggregation and in particular the formation of toxic protein oligomers is a key mechanism in synucleinopathies such as Parkinson's disease (PD). Post mortem brain tissue studies as well as animal studies furthermore suggest that matrix metalloproteinases (MMPs) are also involved in the pathogenesis of PD. We used confocal single molecule spectroscopy to characterize the influence of MMPs and other proteases on the aggregation of alpha-synuclein. These studies were complemented by the characterization of alpha-synuclein fragment patterns generated by these proteases using gel electrophoresis and mass spectrometry. Limited digestion by MMP-1 and MMP-3, but not by MMP-9, increased the tendency of alpha-synuclein to aggregate. Proteinase K and Trypsin did not increase the level of de novo aggregation of alpha-synuclein. SDS-PAGE as well as MALDI-ToF analysis of limitedly digested alpha-synuclein demonstrate that all proteases generate different fragments of alpha-synuclein. We provide mass spectrometry data of proteolytic alpha-synuclein fragments and propose specific cleavage sites for MMP-1 and MMP-9 in alpha-synuclein. We furthermore found four additional cleavage sites of MMP-3 that had not been described previously. In order to increase aggregation of alpha-synuclein, specific cleavage between the highly charged C-terminal domain and the aggregation-prone NAC domain of alpha-synuclein seems to be crucial. Our findings obtained in vitro in a well-characterized model of pathological alpha-synuclein aggregation indicate that MMP-1 and MMP-3 may also influence pathogenesis of PD in vivo by generation of specific aggregation-enhancing alpha-synuclein fragments resulting from limited proteolysis.

Single particle characterization of iron-induced pore-forming alpha-synuclein oligomers

Aggregation of alpha-synuclein is a key event in several neurodegenerative diseases, including Parkinson disease. Recent findings suggest that oligomers represent the principal toxic aggregate species. Using confocal single-molecule fluorescence techniques, such as scanning for intensely fluorescent targets (SIFT) and atomic force microscopy, we monitored alpha-synuclein oligomer formation at the single particle level. Organic solvents were used to trigger aggregation, which resulted in small oligomers ("intermediate I"). Under these conditions, Fe(3+) at low micromolar concentrations dramatically increased aggregation and induced formation of larger oligomers ("intermediate II"). Both oligomer species were on-pathway to amyloid fibrils and could seed amyloid formation. Notably, only Fe(3+)-induced oligomers were SDS-resistant and could form ion-permeable pores in a planar lipid bilayer, which were inhibited by the oligomer-specific A11 antibody. Moreover, baicalein and N'-benzylidene-benzohydrazide derivatives inhibited oligomer formation. Baicalein also inhibited alpha-synuclein-dependent toxicity in neuronal cells. Our results may provide a potential disease mechanism regarding the role of ferric iron and of toxic oligomer species in Parkinson diseases. Moreover, scanning for intensely fluorescent targets allows high throughput screening for aggregation inhibitors and may provide new approaches for drug development and therapy.

Photo-induced crosslinking of prion protein oligomers and prions

Prion diseases are caused by a unique type of infectious agent, which is thought to consist of a misfolded beta-sheeted form of the alpha-helical cellular prion protein (PrPC). This misfolded isoform (PrPSc) tends to form insoluble amyloid-like aggregates, impeding classical structural analysis by X-ray crystallography or NMR. Intermolecular crosslinking may provide a means of stabilizing notoriously elusive oligomers for further analysis and may be used for analyzing aggregate architecture by characterising intermolecular contact sites. Using a photo-induced crosslinking method (PICUP), aggregates of recombinant PrP (rPrP) and PrPSc were linked at interacting surfaces via amino acid side chains. The degree of crosslinking within PrP aggregates was adjustable using varying light intensities and could efficiently be monitored by fluorescence correlation spectroscopy. Specific intermolecular crosslinking of PrPSc molecules was achieved even in crude brain homogenate. Functional studies showed that stabilized aggregates of rPrP did not loose their capacity to induce further protein aggregation and crosslinking of PrPSc did not alter significantly the level of infectivity, indicating that photo-induced covalent linkage of PrPSc does not destruct surfaces important for prion propagation.