Synaptic Protein Alterations in Parkinson’s Disease

The Effect of Aggregated Alpha Synuclein on Synaptic and Axonal Proteins in Parkinson’s Disease—A Systematic Review

α-synuclein is a core component of Lewy bodies, one of the pathological hallmarks of Parkinson’s disease. Aggregated α-synuclein can impair both synaptic functioning and axonal transport. However, understanding the pathological role that α-synuclein plays at a cellular level is complicated as existing findings are multifaceted and dependent on the mutation, the species, and the quantity of the protein that is involved. This systematic review aims to stratify the research findings to develop a more comprehensive understanding of the role of aggregated α-synuclein on synaptic and axonal proteins in Parkinson’s disease models. A literature search of the PubMed, Scopus, and Web of Science databases was conducted and a total of 39 studies were included for analysis. The review provides evidence for the dysregulation or redistribution of synaptic and axonal proteins due to α-synuclein toxicity. However, due to the high quantity of variables that were used in the research investigations, it was challenging to ascertain exactly what effect α-synuclein has on the expression of the proteins. A more standardized experimental approach regarding the variables that are employed in future studies is crucial so that existing literature can be consolidated. New research involving aggregated α-synuclein at the synapse and regarding axonal transport could be advantageous in guiding new treatment solutions.

Dopaminergic Axons: Key Recitalists in Parkinson's Disease

Parkinson's disease (PD) is associated with dopamine depletion in the striatum owing to the selective and progressive loss of the nigrostriatal dopaminergic neurons, which results in motor dysfunction and secondary clinical manifestations. The dopamine level in the striatum is preserved because of the innervation of the substantia nigra (SN) dopaminergic neurons into it. Therefore, protection of the SN neurons is crucial for maintaining the dopamine level in the striatum and for ensuring the desired motor coordination. Several strategies have been devised to protect the degenerating dopaminergic neurons or to restore the dopamine levels for treating PD. Most of the methods focus exclusively on preventing cell body death in the neurons. Although advances have been made in understanding the disease, the search for disease-modifying drugs is an ongoing process. The present review describes the evidence from studies involving patients with PD as well as PD models that axon terminals are highly vulnerable to exogenous and endogenous insults and degenerate at the early stage of the disease. Impairment of mitochondrial dynamics, Ca²⁺ homeostasis, axonal transport, and loss of plasticity of axon terminals appear before the neuronal degeneration in PD. Furthermore, distortion of synaptic morphology and reduction of postsynaptic dendritic spines are the neuropathological hallmarks of early-stage disease. Thus, the review proposes a shift in focus from discerning the mechanism of neuronal cell body loss and targeting it to an entirely different approach of preventing axonal degeneration. The review also suggests appropriate strategies to prevent the loss of synaptic terminals, which could induce regrowth of the axon and its auxiliary fibers and might offer relief from the symptomatic features of PD.

Increased Cerebrospinal Fluid Concentration of ZnT3 Is Associated with Cognitive Impairment in Alzheimer's Disease

BACKGROUND

Cognitive deficits arising in the course of Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and Parkinson's disease with dementia (PDD) are directly linked to synaptic loss. Postmortem studies suggest that zinc transporter protein 3 (ZnT3), AMPA glutamate receptor 3 (GluA3), and Dynamin1 are associated with cognitive decline in AD and Lewy body dementia patients.

OBJECTIVE

We aimed to evaluate the diagnostic value of ZnT3, GluA3, and Dynamin 1 in the cerebrospinal fluid (CSF) of patients with dementia due to AD, DLB, and PDD compared to cognitively normal subjective cognitive decline (SCD) patients in a retrospective study. In addition, we assessed the relationship between synaptic markers and age, sex, cognitive impairment, and depressive symptoms as well as CSF amyloid, phosphorylated tau (p-tau), and total tau (T-tau).

METHODS

Commercially available ELISA immunoassay was used to measure the levels of proteins in a total of 97 CSF samples from AD (N = 24), PDD (N = 18), DLB (N = 27), and SCD (N = 28) patients. Cognitive impairment was assessed using the Mini-Mental State Examination (MMSE).

RESULTS

We found a significant increase in the concentrations of ZnT3, GluA3, and Dynamin1 in AD (p = 0.002) and of ZnT3 and Dynamin 1 in DLB (p = 0.001, p = 0.002) when compared to SCD patients. Changes in ZnT3 concentrations correlated with MMSE scores in AD (p = 0.011), and with depressive symptoms in SCD (p = 0.041).

CONCLUSION

We found alteration of CSF levels of synaptic proteins in AD, PDD, and DLB. Our results reveal distinct changes in CSF concentrations of ZnT3 that could reflect cognitive impairment in AD with implications for future prognostic and diagnostic marker development.

Rho-kinase inhibition by fasudil modulates pre-synaptic vesicle dynamics

The Rho kinase (ROCK) signaling pathway is an attractive therapeutic target in neurodegeneration since it has been linked to the prevention of neuronal death and neurite regeneration. The isoquinoline derivative fasudil is a potent ROCK inhibitor, which is already approved for chronic clinical treatment in humans. However, the effects of chronic fasudil treatments on neuronal function are still unknown. We analyzed here chronic fasudil treatment in primary rat hippocampal cultures. Neurons were stimulated with 20 Hz field stimulation and we investigated pre-synaptic mechanisms and parameters regulating synaptic transmission after fasudil treatment by super resolution stimulated emission depletion (STED) microscopy, live-cell fluorescence imaging, and western blotting. Fasudil did not affect basic synaptic function or the amount of several synaptic proteins, but it altered the chronic dynamics of the synaptic vesicles. Fasudil reduced the proportion of the actively recycling vesicles, and shortened the vesicle lifetime, resulting overall in a reduction of the synaptic response upon stimulation. We conclude that fasudil does not alter synaptic structure, accelerates vesicle turnover, and decreases the number of released vesicles. This broadens the known spectrum of effects of this drug, and suggests new potential clinical uses.

The role of synaptic biomarkers in the spectrum of neurodegenerative diseases

INTRODUCTION

The quest for reliable fluid biomarkers tracking synaptic disruption is supported by the evidence of a tight association between synaptic density and cognitive performance in neurodegenerative diseases (NDD), especially Alzheimer's disease (AD).

AREAS COVERED

Neurogranin (Ng) is a post-synaptic protein largely expressed in neurons involved in the memory networks. Currently, Ng measured in CSF is the most promising synaptic biomarker. Several studies show Ng elevated in AD dementia with a hippocampal phenotype as well as in MCI individuals who progress to AD. Ng concentrations are also increased in Creutzfeldt Jacob Disease where widespread and massive synaptic disintegration takes place. Ng does not discriminate Parkinson's disease from atypical parkinsonisms, nor is it altered in Huntington disease. CSF synaptosomal-associated protein 25 (SNAP-25) and synaptotagmin-1 (SYT-1) are emerging candidates.

EXPERT OPINION

CSF Ng revealed a role as a diagnostic and prognostic biomarker in NDD. Ng increase seems to be very specific for typical AD phenotype, probably for a prevalent hippocampal involvement. Synaptic biomarkers may serve different context-of-use in AD and other NDD including prognosis, diagnosis, and tracking synaptic damage - a critical pathophysiological mechanism in NDD - thus representing reliable tools for a precision medicine-oriented approach to NDD.

Synaptic markers of cognitive decline in neurodegenerative diseases: a proteomic approach

See Attems and Jellinger (doi:10.1093/brain/awx360) for a scientific commentary on this article.Cognitive changes occurring throughout the pathogenesis of neurodegenerative diseases are directly linked to synaptic loss. We used in-depth proteomics to compare 32 post-mortem human brains in the prefrontal cortex of prospectively followed patients with Alzheimer's disease, Parkinson's disease with dementia, dementia with Lewy bodies and older adults without dementia. In total, we identified 10 325 proteins, 851 of which were synaptic proteins. Levels of 25 synaptic proteins were significantly altered in the various dementia groups. Significant loss of SNAP47, GAP43, SYBU (syntabulin), LRFN2, SV2C, SYT2 (synaptotagmin 2), GRIA3 and GRIA4 were further validated on a larger cohort comprised of 92 brain samples using ELISA or western blot. Cognitive impairment before death and rate of cognitive decline significantly correlated with loss of SNAP47, SYBU, LRFN2, SV2C and GRIA3 proteins. Besides differentiating Parkinson's disease dementia, dementia with Lewy bodies, and Alzheimer's disease from controls with high sensitivity and specificity, synaptic proteins also reliably discriminated Parkinson's disease dementia from Alzheimer's disease patients. Our results suggest that these particular synaptic proteins have an important predictive and discriminative molecular fingerprint in neurodegenerative diseases and could be a potential target for early disease intervention.

Inflammation alters AMPA-stimulated calcium responses in dorsal striatal D2 but not D1 spiny projection neurons

Neuroinflammation precedes neuronal loss in striatal neurodegenerative diseases and can be exacerbated by the release of proinflammatory molecules by microglia. These molecules can affect trafficking of AMPARs. The preferential trafficking of calcium-permeable versus impermeable AMPARs can result in disruptions of [Ca2+ ]i and alter cellular functions. In striatal neurodegenerative diseases, changes in [Ca2+ ]i and L-type voltage-gated calcium channels (VGCCs) have been reported. Therefore, this study sought to determine whether a proinflammatory environment alters AMPA-stimulated [Ca2+ ]i through calcium-permeable AMPARs and/or L-type VGCCs in dopamine-2- and dopamine-1-expressing striatal spiny projection neurons (D2 and D1 SPNs) in the dorsal striatum. Mice expressing the calcium indicator protein, GCaMP in D2 or D1 SPNs, were utilized for calcium imaging. Microglial activation was assessed by morphology analyses. To induce inflammation, acute mouse striatal slices were incubated with lipopolysaccharide (LPS). Here we report that LPS treatment potentiated AMPA responses only in D2 SPNs. When a nonspecific VGCC blocker was included, we observed a decrease of AMPA-stimulated calcium fluorescence in D2 but not D1 SPNs. The remaining agonist-induced [Ca2+ ]i was mediated by calcium-permeable AMPARs because the responses were completely blocked by a selective calcium-permeable AMPAR antagonist. We used isradipine, the highly selective L-type VGCC antagonist to determine the role of L-type VGCCs in SPNs treated with LPS. Isradipine decreased AMPA-stimulated responses selectively in D2 SPNs after LPS treatment. Our findings suggest that dorsal striatal D2 SPNs are specifically targeted in proinflammatory conditions and that L-type VGCCs and calcium-permeable AMPARs are important mediators of this effect.

Impaired synaptic function is linked to cognition in Parkinson's disease

Objective

Cognitive impairment is frequent in Parkinson's disease, but the underlying mechanisms are insufficiently understood. Because cortical metabolism is reduced in Parkinson's disease and closely associated with cognitive impairment, and CSF amyloid‐β species are reduced and correlate with neuropsychological performance in Parkinson's disease, and amyloid‐β release to interstitial fluid may be related to synaptic activity; we hypothesize that synapse dysfunction links cortical hypometabolism, reduced CSF amyloid‐β, and presynaptic deposits of α‐synuclein. We expect a correlation between hypometabolism, CSF amyloid‐β, and the synapse related‐markers CSF neurogranin and α‐synuclein.

Methods

Thirty patients with mild‐to‐moderate Parkinson's disease and 26 healthy controls underwent a clinical assessment, lumbar puncture, MRI, ¹⁸F‐fludeoxyglucose‐PET, and a neuropsychological test battery (repeated for the patients after 2 years).

Results

All subjects had CSF amyloid‐β 1‐42 within normal range. In Parkinson's disease, we found strong significant correlations between cortical glucose metabolism, CSF Aβ, α‐synuclein, and neurogranin. All PET CSF biomarker‐based cortical clusters correlated strongly with cognitive parameters. CSF neurogranin levels were significantly lower in mild‐to‐moderate Parkinson's disease compared to controls, correlated with amyloid‐β and α‐synuclein, and with motor stage. There was little change in cognition after 2 years, but the cognitive tests that were significantly different, were also significantly associated with cortical metabolism. No such correlations were found in the control group.

Interpretation

CSF Aβ, α‐synuclein, and neurogranin concentrations are related to cortical metabolism and cognitive decline. Synaptic dysfunction due to Aβ and α‐synuclein dysmetabolism may be central in the evolution of cognitive impairment in Parkinson's disease.

Nonmotor Symptoms and Natural History of Parkinson's Disease: Evidence From Cognitive Dysfunction and Role of Noninvasive Interventions

Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by motor and nonmotor symptoms (NMS). Several subsequent studies substantiate the great functional burden related to NMS, their progression, and negative effect on quality of life in PD. Additional evidence indicates interesting relationships between striatal dopaminergic function and NMS. The basal ganglia are implicated in the modulation and integration of sensory information and pain, bladder function is under control of both inhibitory (D1) and facilitatory (D2) dopaminergic inputs, finally reduced dopaminergic activity in the mesocortical and mesolimbic pathways is involved in the development of several NMS including mood, motivational, and cognitive alterations. Some NMS fluctuate in response to dopaminergic treatment and are relieved by dopamine replacement therapy, other are insensitive to current therapeutic strategies. The relation among the overall disease complications, perhaps the most important for PD patients and family members' well-being and functionality is dementia that affects most PD patients over the course of disease. Specific pharmacological treatment is lacking, and alternative approaches have been implemented to improve everyday functionality and quality of life. The state of the art suggests that cognitive rehabilitation in PD is possible and may either increase performance or preserve cognitive level over the time. However, it is also evident that cognitive abnormalities in PD are heterogeneous and we still do not have biomarkers to detect early patients at risk for dementia. Cognitive dysfunction is one the most prevalent NMS and is a clinically and functionally important disease milestone. Given the available clinical and imaging evidence it is possible to use cognition to model NMS progression and design nonpharmacological interventions. In this chapter we will address the use of cognitive rehabilitation and noninvasive brain stimulation techniques to modulate cognitive performance and rescue connectivity in affected brain circuitry.

Cognitive decline in Parkinson disease

Dementia is a frequent problem encountered in advanced stages of Parkinson disease (PD). In recent years, research has focused on the pre-dementia stages of cognitive impairment in PD, including mild cognitive impairment (MCI). Several longitudinal studies have shown that MCI is a harbinger of dementia in PD, although the course is variable, and stabilization of cognition - or even reversal to normal cognition - is not uncommon. In addition to limbic and cortical spread of Lewy pathology, several other mechanisms are likely to contribute to cognitive decline in PD, and a variety of biomarker studies, some using novel structural and functional imaging techniques, have documented in vivo brain changes associated with cognitive impairment. The evidence consistently suggests that low cerebrospinal fluid levels of amyloid-β₄₂, a marker of comorbid Alzheimer disease (AD), predict future cognitive decline and dementia in PD. Emerging genetic evidence indicates that in addition to the APOE*ε4 allele (an established risk factor for AD), GBA mutations and SCNA mutations and triplications are associated with cognitive decline in PD, whereas the findings are mixed for MAPT polymorphisms. Cognitive enhancing medications have some effect in PD dementia, but no convincing evidence that progression from MCI to dementia can be delayed or prevented is available, although cognitive training has shown promising results.

Cerebrospinal Fluid Biomarkers of Cognitive Decline in Parkinson's Disease

Among the nonmotor symptoms in Parkinson's disease (PD), cognitive impairment is one of the most common and devastating. Over recent years, mild cognitive impairment (MCI) has become a recognized feature of PD (PD-MCI). The underlying mechanisms which influence onset, rate of decline, and conversion to dementia (PDD) are largely unknown. Adding to this uncertainty is the heterogeneity of cognitive domains affected. Currently there are no disease-modifying treatments that can slow or reverse this process. Identification of biomarkers that can predict rate and risk of cognitive decline is therefore an unmet need. Cerebrospinal fluid (CSF) is an ideal biomarker candidate as its constituents reflect the metabolic processes underlying the functioning of brain parenchyma. The pathological hallmark of PD is the presence of aggregated α-synuclein (α-Syn) in intracellular Lewy inclusions. In addition, there is concomitant Alzheimer's disease (AD) pathology. In AD, decreased CSF β-amyloid 1-42 (Aβ42) and increased CSF tau levels are predictive of future cognitive decline, setting a precedent for such studies to be carried out in PD. CSF studies in PD have focused on the classical AD biomarkers and α-Syn. Longitudinal studies indicate that low levels of CSF Aβ42 are predictive of cognitive decline; however, results for tau and α-Syn were not consistent. This chapter summarizes recent findings of CSF biomarker studies and cognitive dysfunction in PD.

Native DIGE proteomic analysis of mitochondria from substantia nigra and striatum during neuronal degeneration and its compensation in an animal model of early Parkinson's disease

Cause of Parkinson's disease (PD) is still not understood. Motor symptoms are not observed at early stages of disease due to compensatory processes. Dysfunction of mitochondria was indicated already at preclinical PD. Selective toxin 6-OHDA was applied to kill dopaminergic neurons in substantia nigra and disturb neuronal transmission in striatum. Early phase of active degeneration and later stage, when surviving cells adapted to function normally, were analysed. 2D BN/SDS difference gel electrophoresis (DIGE) of mitochondrial proteome enabled to point out crucial processes involved at both time-points in dopaminergic structures. Marker proteins such as DPYSL2, HSP60, ATP1A3, EAAT2 indicated structural remodelling, cytoskeleton rearrangement, organelle trafficking, axon outgrowth and regeneration. Adaptations in dopaminergic and glutamatergic neurotransmission, recycling of synaptic vesicles, along with enlargement of mitochondria mass were proposed as causative for compensation. Changed expression of carbohydrates metabolism and oxidative phosphorylation proteins were described, including their protein-protein interactions and supercomplex assembly.

The 4p16.3 Parkinson Disease Risk Locus Is Associated with GAK Expression and Genes Involved with the Synaptic Vesicle Membrane

Genome-wide association studies (GWAS) have identified the GAK/DGKQ/IDUA region on 4p16.3 among the top three risk loci for Parkinson’s disease (PD), but the specific gene and risk mechanism are unclear. Here, we report transcripts containing the 3’ clathrin-binding domain of GAK identified by RNA deep-sequencing in post-mortem human brain tissue as having increased expression in PD. Furthermore, carriers of 4p16.3 PD GWAS risk SNPs show decreased expression of one of these transcripts, GAK25 (Gencode Transcript 009), which correlates with the expression of genes functioning in the synaptic vesicle membrane. Together, these findings provide strong evidence for GAK clathrin-binding- and J-domain transcripts’ influence on PD pathogenicity, and for a role for GAK in regulating synaptic function in PD.

Tetrahydroxystilbene glucoside ameliorates memory and movement functions, protects synapses and inhibits α-synuclein aggregation in hippocampus and striatum in aged mice

PURPOSE

To investigate the effects of 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (TSG) on the memory and movement functions and its mechanisms related to synapses and α-synuclein in aged mice.

METHODS

The memory ability of mice was detected by step-through passive avoidance task. The movement function was measured by the pole test and rotarod test. Transmission electron microscopy was used to observe the synaptic ultrastructure. Western blotting was applied to measure the expression of synapse-related proteins and α-synuclein.

RESULTS

Intragastrical administration of TSG for 3 months significantly improved the memory and movement functions in aged mice. TSG treatment obviously protected the synaptic ultrastructure and increased the number of synaptic connections in the hippocampal CA1 region and striatum; enhanced the expression of synaptophysin, phosphorylated synapsin I and postsynaptic density protein 95 (PSD95), elevated phosphorylated calcium/calmodulin-dependent protein kinase II (p-CaMKII) expression, and inhibited the overexpression and aggregation of α-synuclein in the hippocampus, striatum and cerebral cortex of aged mice.

CONCLUSION

TSG improved the memory and movement functions in aged mice through protecting synapses and inhibiting α-synuclein overexpression and aggregation in multiple brain regions. The results suggest that TSG may be beneficial to the treatment of ageing-related neurodegenerative diseases.

The Alzheimer disease BIN1 locus as a modifier of GBA-associated Parkinson disease

GBA mutations are among the most common genetic risk factors for Parkinson disease (PD) worldwide. We aimed to identify genetic modifiers of the age at onset (AAO) in GBA-associated PD. The study included a genome-wide discovery phase, including a cohort of 79 patients with the GBA p.N370S mutation, and candidate validation and replication analyses of 8 SNPs in patients with mild (n = 113) and severe (n = 41) GBA mutations. Genotyping was performed using the Affymetrix human SNP 6.0 array and TaqMan assays. In the genome-wide phase, none of the SNPs passed the genome-wide significance threshold. Eight SNPs were selected for further analysis from the top hits. In all GBA-associated PD patients (n = 153), the BIN1 rs13403026 minor allele was associated with an older AAO (12.4 ± 5.9 years later, p = 0.0001), compared to patients homozygous for the major allele. Furthermore, the AAO was 10.7 ± 6.8 years later in patients with mild GBA mutations, (p = 0.005, validation group), and 17.1 ± 2.5 years later in patients with severe GBA mutations (p = 0.01, replication). Our results suggest that alterations in the BIN1 locus, previously associated with Alzheimer disease, may modify the AAO of GBA-associated PD. More studies in other populations are required to examine the role of BIN1-related variants in GBA-associated PD.

Evidence for Immune Response, Axonal Dysfunction and Reduced Endocytosis in the Substantia Nigra in Early Stage Parkinson's Disease

Subjects with incidental Lewy body disease (iLBD) may represent the premotor stage of Parkinson’s disease (PD). To elucidate molecular mechanisms underlying neuronal dysfunction and alpha-synuclein pathology in the premotor phase of PD, we investigated the transcriptome of the substantia nigra (SN) of well-characterized iLBD, PD donors and age-matched controls with Braak alpha-synuclein stage ranging from 0–6. In Braak alpha-synuclein stages 1 and 2, we observed deregulation of pathways linked to axonal degeneration, immune response and endocytosis, including axonal guidance signaling, mTOR signaling, EIF2 signaling and clathrin-mediated endocytosis in the SN. In Braak stages 3 and 4, we observed deregulation of pathways involved in protein translation and cell survival, including mTOR and EIF2 signaling. In Braak stages 5 and 6, we observed deregulation of dopaminergic signaling, axonal guidance signaling and thrombin signaling. Throughout the progression of PD pathology, we observed a deregulation of mTOR, EIF2 and regulation of eIF4 and p70S6K signaling in the SN. Our results indicate that molecular mechanisms related to axonal dysfunction, endocytosis and immune response are an early event in PD pathology, whereas mTOR and EIF2 signaling are impaired throughout disease progression. These pathways may hold the key to altering the disease progression in PD.

Retrograde response in axotomized motoneurons: nitric oxide as a key player in triggering reversion toward a dedifferentiated phenotype

The adult brain retains a considerable capacity to functionally reorganize its circuits, which mainly relies on the prevalence of three basic processes that confer plastic potential: synaptic plasticity, plastic changes in intrinsic excitability and, in certain central nervous system (CNS) regions, also neurogenesis. Experimental models of peripheral nerve injury have provided a useful paradigm for studying injury-induced mechanisms of central plasticity. In particular, axotomy of somatic motoneurons triggers a robust retrograde reaction in the CNS, characterized by the expression of plastic changes affecting motoneurons, their synaptic inputs and surrounding glia. Axotomized motoneurons undergo a reprograming of their gene expression and biosynthetic machineries which produce cell components required for axonal regrowth and lead them to resume a functionally dedifferentiated phenotype characterized by the removal of afferent synaptic contacts, atrophy of dendritic arbors and an enhanced somato-dendritic excitability. Although experimental research has provided valuable clues to unravel many basic aspects of this central response, we are still lacking detailed information on the cellular/molecular mechanisms underlying its expression. It becomes clear, however, that the state-switch must be orchestrated by motoneuron-derived signals produced under the direction of the re-activated growth program. Our group has identified the highly reactive gas nitric oxide (NO) as one of these signals, by providing robust evidence for its key role to induce synapse elimination and increases in intrinsic excitability following motor axon damage. We have elucidated operational principles of the NO-triggered downstream transduction pathways mediating each of these changes. Our findings further demonstrate that de novo NO synthesis is not only "necessary" but also "sufficient" to promote the expression of at least some of the features that reflect reversion toward a dedifferentiated state in axotomized adult motoneurons.

Dynamin1 concentration in the prefrontal cortex is associated with cognitive impairment in Lewy body dementia

Dementia with Lewy Bodies (DLB) and Parkinson’s Disease Dementia (PDD) together, represent the second most common cause of dementia, after Alzheimer’s disease (AD). The synaptic dysfunctions underlying the cognitive decline and psychiatric symptoms observed throughout the development of PDD and DLB are still under investigation. In this study we examined the expression level of Dynamin1 and phospho-CaMKII, key proteins of endocytosis and synaptic plasticity respectively, as potential markers of molecular processes specifically deregulated with DLB and/or PDD. In order to measure the levels of these proteins, we isolated grey matter from post-mortem prefrontal cortex area (BA9), anterior cingulated gyrus (BA24) and parietal cortex (BA40) from DLB and PDD patients in comparison to age-matched controls and a group of AD cases. Clinical and pathological data available included the MMSE score, neuropsychiatric history, and semi-quantitative scores for AD pathology (plaques - tangles) and for α-synuclein (Lewy bodies).

Changes in the expression of the synaptic markers, and correlates with neuropathological features and cognitive decline were predominantly found in the prefrontal cortex. On one hand, levels of Dynamin1 were significantly reduced, and correlated with a higher rate of cognitive decline observed in cases from three dementia groups. On the other hand, the fraction of phospho-CaMKII was decreased, and correlated with a high score of plaques and tangles in BA9. Interestingly, the correlation between the rate of cognitive decline and the level of Dynamin1 remained when the analysis was restricted to the PDD and DLB cases, highlighting an association of Dynamin1 with cognitive decline in people with Lewy Body dementia.

Anti-amyloid compounds inhibit α-synuclein aggregation induced by protein misfolding cyclic amplification (PMCA)

Filaments made of α-synuclein form the characteristic Lewy pathology in Parkinson and other diseases. The formation of α-synuclein filaments can be reproduced in vitro by incubation of recombinant protein, but the filament growth is very slow and highly variable and so unsuitable for fast high throughput anti-aggregation drug screening. To overcome this obstacle we have investigated whether the protein misfolding cyclic amplification (PMCA) technique, used for fast amplification of prion protein aggregates, could be adapted for growing α-synuclein aggregates and thus suitable for screening of drugs to affect α-synuclein aggregation for the treatment of the yet incurable α-synucleinopathies. Circular dichroism, electron microscopy, and native and SDS-polyacrylamide gels were used to demonstrate α-synuclein aggregate formation by PMCA, and the strain imprint of the α-synuclein fibrils was studied by proteinase K digestion. We also demonstrated that α-synuclein fibrils are able to seed new α-synuclein PMCA reactions and to enter and aggregate in cells in culture. In particular, we have generated a line of “chronically infected” cells, which transmit α-synuclein aggregates even after multiple passages. To evaluate the sensitivity of the PMCA system as an α-synuclein anti-aggregating drug screening assay a panel of 10 drugs was tested. Anti-amyloid compounds proved efficient in inhibiting α-synuclein fibril formation induced by PMCA. Our results show that α-synuclein PMCA is a fast and reproducible system that could be used as a high throughput screening method for finding new α-synuclein anti-aggregating compounds.

Mitochondrial abnormality associates with type-specific neuronal loss and cell morphology changes in the pedunculopontine nucleus in Parkinson disease

Cholinergic neuronal loss in the pedunculopontine nucleus (PPN) associates with abnormal functions, including certain motor and nonmotor symptoms. This realization has led to low-frequency stimulation of the PPN for treating patients with Parkinson disease (PD) who are refractory to other treatment modalities. However, the molecular mechanisms underlying PPN neuronal loss and the therapeutic substrate for the clinical benefits following PPN stimulation remain poorly characterized, hampering progress toward designing more efficient therapies aimed at restoring the PPN's normal functions during progressive parkinsonism. Here, we investigated postmortem pathological changes in the PPN of PD cases. Our study detected a loss of neurons producing gamma-aminobutyric acid (GABA) as their output and glycinergic neurons, along with the pronounced loss of cholinergic neurons. These losses were accompanied by altered somatic cell size that affected the remaining neurons of all neuronal subtypes studied here. Because studies showed that mitochondrial dysfunction exists in sporadic PD and in PD animal models, we investigated whether altered mitochondrial composition exists in the PPN. A significant up-regulation of several mitochondrial proteins was seen in GABAergic and glycinergic neurons; however, cholinergic neurons indicated down-regulation of the same proteins. Our findings suggest an imbalance in the activity of key neuronal subgroups of the PPN in PD, potentially because of abnormal inhibitory activity and altered cholinergic outflow.

Behavioral testing regimens in genetic-based animal models of Parkinson's disease: cogencies and caveats

Although the onset and progression of Parkinson's disease (PD) is fundamentally sporadic, identification of several of the genes implicated in the disease has provided significant insight concerning patho-physiological mechanisms potentially underlying sporadic PD. Moreover, such studies have caused a revolution in the way researchers view the disease. Since single genes responsible for rare familial forms of the disease have only been identified within the past few years, animal models based on these defects have only recently been generated, thereby not leaving a lot of time for their evaluation and subsequent improvement. The current article provides an extensive review of the major motor and non-motor behavioral tests used in genetically-induced Parkinsonian animals. Moreover, we assess the insights concerning the etiopathogenesis of PD generated from use of such tests and how these have improved available treatment strategies for alleviating aspects of sporadic and non-sporadic parkinsonism.

Defective autophagy in Parkinson's disease: role of oxidative stress

Parkinson's disease (PD) is a paradigmatic example of neurodegenerative disorder with a critical role of oxidative stress in its etiopathogenesis. Genetic susceptibility factors of PD, such as mutations in Parkin, PTEN-induced kinase 1, and DJ-1 as well as the exposure to pesticides and heavy metals, both contribute to altered redox balance and degeneration of dopaminergic neurons in the substantia nigra. Dysregulation of autophagy, a lysosomal-driven process of self degradation of cellular organelles and protein aggregates, is also implicated in PD and PD-related mutations, and environmental toxins deregulate autophagy. However, experimental evidence suggests a complex and ambiguous role of autophagy in PD since either impaired or abnormally upregulated autophagic flux has been shown to cause neuronal loss. Finally, it is generally believed that oxidative stress is a strong proautophagic stimulus. However, some evidence coming from neurobiology as well as from other fields indicate an inhibitory role of reactive oxygen species and reactive nitrogen species on the autophagic machinery. This review examines the scientific evidence supporting different concepts on how autophagy is dysregulated in PD and attempts to reconcile apparently contradictory views on the role of oxidative stress in autophagy regulation. The complex relationship between autophagy and oxidative stress is also considered in the context of the ongoing search for a novel PD therapy.