Parkinson's Α-synuclein Research Articles

Protein transmission in neurodegenerative disease.

Most neurodegenerative diseases are characterized by the intracellular or extracellular aggregation of misfolded proteins such as amyloid-β and tau in Alzheimer disease, α-synuclein in Parkinson disease, and TAR DNA-binding protein 43 in amyotrophic lateral sclerosis. Accumulating evidence from both human studies and disease models indicates that intercellular transmission and the subsequent templated amplification of these misfolded proteins are involved in the onset and progression of various neurodegenerative diseases. The misfolded proteins that are transferred between cells are referred to as 'pathological seeds'. Recent studies have made exciting progress in identifying the characteristics of different pathological seeds, particularly those isolated from diseased brains. Advances have also been made in our understanding of the molecular mechanisms that regulate the transmission process, and the influence of the host cell on the conformation and properties of pathological seeds. The aim of this Review is to summarize our current knowledge of the cell-to-cell transmission of pathological proteins and to identify key questions for future investigation.

In Vitro Conversion Assays Diagnostic for Neurodegenerative Proteinopathies.

In vitro conversion assays, including real-time quaking-induced conversion (RT-QuIC) and protein misfolding cyclic amplification (PMCA) techniques, were first developed to study the conversion process of the prion protein to its misfolded, disease-associated conformation. The intrinsic property of prion proteins to propagate their misfolded structure was later exploited to detect subfemtogram quantities of the misfolded protein present in tissues and fluids from humans and animals with transmissible spongiform encephalopathies. Currently, conversion assays are used clinically as sensitive and specific diagnostic tools for antemortem diagnosis of prion disease. In vitro conversion assays are now being applied to the development of diagnostics for related neurodegenerative diseases, including detection of misfolded α-synuclein in Parkinson disease, misfolded amyloid-β in Alzheimer disease, and misfolded tau in Pick disease. Like the predicate prion protein in vitro conversion diagnostics, these assays exploit the ability of endogenously misfolded proteins to induce misfolding and aggregation of their natively folded counterpart in vitro. This property enables biomarker detection of the underlying protein pathology. Herein, we review RT-QuIC and PMCA for (a) prion-, (b) α-synuclein-, (c) amyloid-β-, and (d) tau-opathies. Although already in routine clinical use for the detection of transmissible spongiform encephalopathies, in vitro conversion assays for other neurodegenerative disorders require further development and evaluation of diagnostic performance before consideration for clinical implementation.

Stress-Induced Cellular Clearance Is Mediated by the SNARE Protein ykt6 and Disrupted by α-Synuclein

Age-related neurodegenerative disorders are characterized by a slow, persistent accumulation of aggregated proteins. Although cells can elicit physiological responses to enhance cellular clearance and counteract accumulation, it is unclear how pathogenic proteins evade this process in disease. We find that Parkinson's disease α-synuclein perturbs the physiological response to lysosomal stress by impeding the SNARE protein ykt6. Cytosolic ykt6 is normally autoinhibited by a unique farnesyl-mediated regulatory mechanism; however, during lysosomal stress, it activates and redistributes into membranesto preferentially promote hydrolase trafficking and enhance cellular clearance. α-Synuclein aberrantly binds and deactivates ykt6 in patient-derived neurons, thereby disabling the lysosomal stress response and facilitating protein accumulation. Activating ykt6 by small-molecule farnesyltransferase inhibitors restores lysosomal activity and reduces α-synuclein in patient-derived neurons and mice. Our findings indicate that α-synuclein creates a permissive environment for aggregate persistence by inhibiting regulated cellular clearance and provide a therapeutic strategy to restore protein homeostasis by harnessing SNARE activity.

Extracellular RNAs as Biomarkers of Sporadic Amyotrophic Lateral Sclerosis and Other Neurodegenerative Diseases.

Recent progress in the research for underlying mechanisms in neurodegenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS) has led to the development of potentially effective treatment, and hence increased the need for useful biomarkers that may enable early diagnosis and therapeutic monitoring. The deposition of abnormal proteins is a pathological hallmark of neurodegenerative diseases, including β-amyloid in AD, α-synuclein in PD, and the transactive response DNA/RNA binding protein of 43kDa (TDP-43) in ALS. Furthermore, progression of the disease process accompanies the spreading of abnormal proteins. Extracellular proteins and RNAs, including mRNA, micro RNA, and circular RNA, which are present as a composite of exosomes or other forms, play a role in cell–cell communication, and the role of extracellular molecules in the cell-to-cell spreading of pathological processes in neurodegenerative diseases is now in the spotlight. Therefore, extracellular proteins and RNAs are considered potential biomarkers of neurodegenerative diseases, in particular ALS, in which RNA dysregulation has been shown to be involved in the pathogenesis. Here, we review extracellular proteins and RNAs that have been scrutinized as potential biomarkers of neurodegenerative diseases, and discuss the possibility of extracellular RNAs as diagnostic and therapeutic monitoring biomarkers of sporadic ALS.

123I-FP-CIT SPECT [(123) I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane single photon emission computed tomography] Imaging in a p.A53T α-synuclein Parkinson's disease cohort versus Parkinson's disease.

The p.A53T point mutation in the α-synuclein gene (SNCA) is a rare but highly relevant cause of autosomal dominant Parkinson's disease (PD). The objective of this study was to assess striatal dopaminergic denervation in a cohort of symptomatic carriers of the p.A53T SNCA mutation as compared to PD patients. Data from the Parkinson's Progression Markers Initiative database of 11 symptomatic p.A53T SNCA mutation carriers who underwent 123I-FP-CIT SPECT [(123) I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane single photon emission computed tomography] imaging at our site were compared with those of 33 age-, sex-, and disease duration-matched PD patients. The p.A53T mutation carriers had significantly lower caudate nucleus binding ratio both contralaterally and ipsilaterally to the most affected side (P = .002 and P = .006) and a decreased contralateral caudate/putamen signal ratio (P = .007) as compared to PD. A similar degree of striatal asymmetry was observed in both subgroups. No correlation between scores in neuropsychological tests and caudate nucleus dopaminergic denervation could be demonstrated. PD patients harboring the p.A53T SNCA mutation show evidence of a more severe nigrostriatal denervation, especially evident in the caudate nucleus. The lack of significant differences in the putaminal binding ratios may reflect a floor effect or a true preferential targeting of the caudate terminals in p.A53T SNCA-associated PD. © 2018 International Parkinson and Movement Disorder Society.

Amyloid oligomers prevent protein folding

BackgroundProtein Misfolding Disorders (PMDs) are a group of diseases where at least one protein or peptide misfold, aggregates into amyloid‐like structures and accumulates in tissues where the disease‐specific damage occurs. There are at least 30 different diseases in the PMDs group, including several neurodegenerative disorders such as Alzheimer disease (AD), Parkinson disease (PD), as well as diverse systemic disorders, such as Type 2 Diabetes (T2D). A general collapse of protein homeostasis in cells harboring amyloids has been extensively reported. However, the mechanism is not completely understood. Nascent polypeptide chains and non‐native proteins, such as proteins undergoing translocation across membranes or unfolding before degradation, typically expose hydrophobic regions, which are prone to aggregate by non‐native interactions. Molecular chaperones transiently bind these exposed hydrophobic motifs, in an organized manner to prevent aggregation, followed by the release of the client when folding progresses and the hydrophobic segments become buried inside the protein. Interestingly, disease associated amyloids including, amyloid β (Aβ) and tau in AD, α‐synuclein in PD or islet amyloid polypeptide (IAPP) in T2D also expose hydrophobic surfaces in the cellular environment and have a high propensity to bind hydrophobic sequences.HypothesisWe propose that amyloid oligomers disrupt protein folding inside cells by irreversibly binding nascent polypeptide chains or non‐native proteins displaying exposed hydrophobic surfaces, sequestering them, preventing their interaction with molecular chaperones and ultimately arresting their proper folding.MethodsWe prepared amyloid aggregates of Aβ, tau and α‐synuclein and characterized them by CD, FTIR and electron microscopy. Next, we tested refolding of chemically denatured luciferase protein in presence of these amyloids. As controls, we used globular proteins such as bovine serum albumin (BSA) and non‐disease polymeric proteins, such as actin polymers. We also compared the binding affinity of the amyloids for unfolded and natively folded luciferase.ResultsOur results indicate that aggregates of Aβ, tau and α‐synuclein significantly reduced spontaneous refolding efficiency of denatured luciferase in a dose dependent manner. Importantly, neither BSA nor actin polymer produced any significant reduction in refolding efficiency. We also demonstrated that oligomeric species are more potent inhibitors of protein refolding compared to fibrillar aggregates.ConclusionFailure of the proteostasis system in the presence of disease associated amyloids leads to further protein misfolding. Hijacking of chaperone system and the protein degradation machinery by protein aggregates has been postulated as the underlining cause. Our data suggest that disease associated amyloids may directly interact with nascent polypeptide chains or non‐native proteins, preventing protein folding in general, which may lead to a collapse of protein homeostasis.Support or Funding InformationMitchell Foundation Center Grant to CS.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Lysosomal response in relation to α-synuclein pathology differs between Parkinson's disease and multiple system atrophy

Intracellular deposition of pathologically altered α-synuclein mostly in neurons characterises Parkinson's disease (PD), while its accumulation predominantly in oligodendrocytes is a feature of multiple system atrophy (MSA). Recently a prion-like spreading of pathologic α-synuclein has been suggested to play a role in the pathogenesis of PD and MSA. This implicates a role of protein processing systems, including lysosomes, supported also by genetic studies in PD. However, particularly for MSA, the mechanism of cell-to-cell propagation of α-synuclein is yet not fully understood. To evaluate the significance of lysosomal response, we systematically compared differently affected neuronal populations in PD, MSA, and non-diseased brains using morphometric immunohistochemistry (cathepsin D), double immunolabelling (cathepsin D/α-synuclein) laser confocal microscopy, and immunogold electron microscopy for the disease associated α-synuclein. We found that i) irrespective of the presence of neuronal inclusions, the volume density of cathepsin D immunoreactivity significantly increases in affected neurons of the pontine base in MSA brains; ii) volume density of cathepsin D immunoreactivity increases in nigral neurons in PD without inclusions and with non-ubiquitinated pre-aggregates of α-synuclein, but not in neurons with Lewy bodies; iii) cathepsin D immunoreactivity frequently colocalises with α-synuclein pre-aggregates in nigral neurons in PD; iv) ultrastructural observations confirm disease-associated α-synuclein in neuronal and astrocytic lysosomes in PD; v) lysosome-associated α-synuclein is observed in astroglia and rarely in oligodendroglia and in neurons in MSA. Our observations support a crucial role for the neuronal endosomal-lysosomal system in the processing of α-synuclein in PD. We suggest a distinct contribution of lysosomes to the pathogenesis of MSA, including the possibility of oligodendroglial and eventually neuronal uptake of exogenous α-synuclein in MSA.

Dysfunction of the orexin system in Parkinson's disease

Traditionally, Parkinson's disease (PD) is associated with the lesion of the substantia nigra and dopamine system dysfunction. However, current studies show the involvement of other CNS regions, which extend far beyond the substantia nigra, in the pathogenesis of PD. The prevalence of altered α-synuclein in PD leads to the dysfunction of several neurotransmitter systems including the orexin system located in the hypothalamus. The involvement of this system in the neurodegenerative process explains some symptoms of PD including daily drowsiness and eating disorders. The authors consider the pathophysiology of the orexin system and its role in the pathogenesis of PD.

Activating Autophagy as a Therapeutic Strategy for Parkinson's Disease.

Parkinson's disease is a progressive neurodegenerative disease characterized by Lewy body pathology of which the primary constituent is aggregated misfolded alpha-synuclein protein. Currently, there are no clinical therapies for treatment of the underlying alpha-synuclein dysfunction and accumulation, and the standard of care for patients with Parkinson's disease focuses only on symptom management, creating an immense therapeutic gap that needs to be filled. Defects in autophagy have been strongly implicated in Parkinson's disease. Here, we review evidence from human, mouse, and cell culture studies to briefly explain these defects in autophagy in Parkinson's disease and the necessity for autophagy to be carefully and precisely tuned to maintain neuron survival. We summarize recent experimental agents for treating alpha-synuclein accumulation in α-synuclein Parkinson's disease and related synucleinopathies. Most of the efforts for developing experimental agents have focused on immunotherapeutic strategies, but we discuss why those efforts are misplaced. Finally, we emphasize why increasing autophagy flux for alpha-synuclein clearance is the most promising therapeutic strategy. Activating autophagy has been successful in preclinical models of Parkinson's disease and yields promising results in clinical trials.

Protein folding, misfolding and aggregation: The importance of two-electron stabilizing interactions.

Proteins associated with neurodegenerative diseases are highly pleiomorphic and may adopt an all-α-helical fold in one environment, assemble into all-β-sheet or collapse into a coil in another, and rapidly polymerize in yet another one via divergent aggregation pathways that yield broad diversity of aggregates’ morphology. A thorough understanding of this behaviour may be necessary to develop a treatment for Alzheimer’s and related disorders. Unfortunately, our present comprehension of folding and misfolding is limited for want of a physicochemical theory of protein secondary and tertiary structure. Here we demonstrate that electronic configuration and hyperconjugation of the peptide amide bonds ought to be taken into account to advance such a theory. To capture the effect of polarization of peptide linkages on conformational and H-bonding propensity of the polypeptide backbone, we introduce a function of shielding tensors of the Cα atoms. Carrying no information about side chain-side chain interactions, this function nonetheless identifies basic features of the secondary and tertiary structure, establishes sequence correlates of the metamorphic and pH-driven equilibria, relates binding affinities and folding rate constants to secondary structure preferences, and manifests common patterns of backbone density distribution in amyloidogenic regions of Alzheimer’s amyloid β and tau, Parkinson’s α-synuclein and prions. Based on those findings, a split-intein like mechanism of molecular recognition is proposed to underlie dimerization of Aβ, tau, αS and PrPC, and divergent pathways for subsequent association of dimers are outlined; a related mechanism is proposed to underlie formation of PrPSc fibrils. The model does account for: (i) structural features of paranuclei, off-pathway oligomers, non-fibrillar aggregates and fibrils; (ii) effects of incubation conditions, point mutations, isoform lengths, small-molecule assembly modulators and chirality of solid-liquid interface on the rate and morphology of aggregation; (iii) fibril-surface catalysis of secondary nucleation; and (iv) self-propagation of infectious strains of mammalian prions.

Toll-like receptor 2 is increased in neurons in Parkinson\u2019s disease brain and may contribute to alpha-synuclein pathology

Inflammation is likely a key contributor to the pathogenesis of Parkinson’s disease (PD), a progressively debilitating neurodegenerative disease that is accompanied by a pathological accumulation of the α-synuclein protein in a staged manner through the brain. What leads to the accumulation of α-synuclein in PD and how this relates to inflammatory pathways, however, is not entirely clear. Toll-like receptor (TLR) signaling is a major pathway mediating inflammation and, in particular, TLR2 is increasingly being implicated in PD. We have, therefore, examined the expression of TLR2 in postmortem brain tissue from PD patients and matched controls. We confirm that TLR2 is increased in PD brain, and find that levels of TLR2 correlate with the accumulation of pathological α-synuclein. TLR2 was expressed on neurons as well as microglia; however, the neuronal rather than glial expression of TLR2 was significantly increased in PD brain in accordance with disease staging, and TLR2 was strongly localized to α-synuclein positive Lewy bodies. In cell culture, activation of neuronal TLR2 induced an inflammatory response, including the secretion of inflammatory cytokines and microglial-activating chemokines, as well as the production of reactive oxygen species. Moreover, activation of neuronal TLR2 increased levels of endogenous α-synuclein protein, which was in turn associated with increased levels of the autophagy/lysosomal pathway marker p62. Finally, promoting autophagy with rapamycin or pharmacological inhibition of the TLR2 signaling pathway prevented the TLR2-mediated increase in α-synuclein in neuronal cell cultures. These results implicate neuronal TLR2 expression in human PD pathogenesis. In particular, the increased expression of TLR2 on neurons may provide new insight into disease pathogenesis and/or options for therapeutic intervention.

Parkinson Disease

This cross-section of midbrain from an older man with a neurodegenerative disease exhibits marked pallor of the substantia nigra (arrow) compared with a normal brain. What is the most likely diagnosis and protein abnormality?a.Parkinson disease, α-synucleinb.Alzheimer disease, β-amyloidc.Frontotemporal dementia, taud.Amyotrophic lateral sclerosis, TDP-43 (TAR DNA-binding protein 43) Answer: a. Parkinson disease, α-synuclein Parkinson disease is characterized by bradykinesia, rigidity, stooped shuffling gate, and often resting tremor as well as nonmotor features such as anxiety, depression, and sleep disorders, among others.1Ahlskog J.E. Parkinson disease treatment in hospitals and nursing facilities: avoiding pitfalls.Mayo Clin Proc. 2014; 89: 997-1003Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar The midbrain may exhibit pallor of the substantia nigra. Microscopic neuronal inclusions called Lewy bodies, a complex accumulation of proteins including α-synuclein, play a key role in the pathogenesis.2Dehay B. Bourdenx M. Gorry P. et al.Targeting α-synuclein for treatment of Parkinson's disease: mechanistic and therapeutic considerations.Lancet Neurol. 2015; 14: 855-866Abstract Full Text Full Text PDF PubMed Scopus (325) Google Scholar On hematoxylin and eosin stain (A), Lewy bodies appear as neuronal intracytoplasmic inclusions that are roughly spherical, eosinophilic, and surrounded by a pale “halo” (arrow). Lewy bodies are highlighted by the immunohistochemical stain for α-synuclein (B).

Triptolide Promotes the Clearance of α-Synuclein by Enhancing Autophagy in Neuronal Cells.

Parkinson's disease (PD) is an aging-associated neurodegenerative disease with a characteristic feature of α-synuclein accumulation. Point mutations (A53T, A30P) that increase the aggregation propensity of α-synuclein result in familial early onset PD. The abnormal metabolism of α-synuclein results in aberrant level changes of α-synuclein in PD. In pathological conditions, α-synuclein is degraded mainly by the autophagy-lysosome pathway. Triptolide (T10) is a monomeric compound isolated from a traditional Chinese herb. Our group demonstrated for the first time that T10 possesses potent neuroprotective properties both in vitro and in vivo PD models. In the present study, we reported T10 as a potent autophagy inducer in neuronal cells, which helped to promote the clearance of various forms of α-synuclein in neuronal cells. We transfected neuronal cells with A53T mutant (A53T) or wild-type (WT) α-synuclein plasmids and found T10 attenuated the cytotoxicity induced by pathogenic A53T α-synuclein overexpression. We observed that T10 significantly reduced both A53T and WT α-synuclein level in neuronal cell line, as well as in primary cultured cortical neurons. Excluding the changes of syntheses, secretion, and aggregation of α-synuclein, we further added autophagy inhibitor or proteasome inhibitor with T10, and we noticed that T10 promoted the clearance of α-synuclein mainly by the autophagic pathway. Lastly, we observed increased autophagy marker LC3-II expression and autophagosomes by GFP-LC3-II accumulation and ultrastructural characterization. However, the lysosome activity and cell viability were not modulated by T10. Our study revealed that T10 could induce autophagy and promote the clearance of both WT and A53T α-synuclein in neurons. These results provide evidence of T10 as a promising mean to treat PD and other neurodegenerative diseases by reducing pathogenic proteins in neurons.

Direct α-synuclein promoter transactivation by the tumor suppressor p53.

BackgroundParkinson’s disease (PD) is a motor disease associated with the degeneration of dopaminergic neurons of the substantia nigra pars compacta. p53 is a major neuronal pro-apoptotic factor that is at the center of gravity of multiple physiological and pathological cascades, some of which implying several key PD-linked proteins. Since p53 is up-regulated in PD-affected brain, we have examined its ability to regulate the transcription of α-synuclein, a key protein that accumulates in PD-related Lewy bodies.ResultsWe show that pharmacological and genetic up-regulation of p53 expression lead to a strong increase of α-synuclein protein, promoter activity and mRNA levels. Several lines of evidence indicate that this transcriptional control is due to the DNA-binding properties of p53. Firstly, p53 DNA-binding dead mutations abolish p53 regulation of α-synuclein. Secondly, the deletion of p53 responsive element from α-synuclein promoter abrogates p53-mediated α-synuclein regulation. Thirdly, gel shift and chromatin immunoprecipitation studies indicate that p53 interacts physically with α-synuclein promoter both in vitro and in a physiological context. Furthermore, we show that the depletion of endogenous p53 in cells as well as in knockout mice down-regulates α-synuclein transcription.ConclusionsOverall, we have identified α-synuclein as a new transcriptional target of p53 and delineated a cellular mechanism feeding the accumulation of toxic aggregated α-synuclein in PD. This original α-syn regulatory mechanism may be central to PD-related cell death and may lead to novel opportunities to design alternative neuroprotective strategies in PD.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-016-0079-2) contains supplementary material, which is available to authorized users.

MODERN VIEW ON ETIOLOGY OF PARKINSON’S DISEASE

«Research Center of Neurology» of Russian Academy of Medical Sciences, Moscow, Russian Federation Etiology of Parkinson’s disease (PD) is still undetermined despite long-term investigations. Monogenic forms occur predominantly in young persons and amount to about 5–10% of PD cases, while most cases of the disease are sporadic and have multifactorial nature. The key molecular mechanism of neurodegeneration in PD is the conformational change of vesicular protein α-synuclein, its self-fibrilization with formation of neurotoxic cytoplasmic aggregates and Lewy bodies/ Lewy neurites. Misfolding of α-synuclein in PD is caused by specific interaction of environmental factors, genomic factors and systemic metabolism, that all together influence on such processes as cell detoxication, mitochondrial functioning, synaptic transmission and endosomal transport. The review presents possible exogenous and endogenous triggers of pathological process in PD. Among the etiologic factors, the role of different neurotoxins, mitophagy disorders, prion-like mechanism of PD development and genetics of familial and sporadic cases of PD are discussed in detail.

Sustained Systemic Glucocerebrosidase Inhibition Induces Brain α-Synuclein Aggregation, Microglia and Complement C1q Activation in Mice

Aims: Loss-of-function mutations in GBA1, which cause the autosomal recessive lysosomal storage disease, Gaucher disease (GD), are also a key genetic risk factor for the α-synucleinopathies, including Parkinson's disease (PD) and dementia with Lewy bodies. GBA1 encodes for the lysosomal hydrolase glucocerebrosidase and reductions in this enzyme result in the accumulation of the glycolipid substrates glucosylceramide and glucosylsphingosine. Deficits in autophagy and lysosomal degradation pathways likely contribute to the pathological accumulation of α-synuclein in PD. In this report we used conduritol-β-epoxide (CBE), a potent selective irreversible competitive inhibitor of glucocerebrosidase, to model reduced glucocerebrosidase activity in vivo, and tested whether sustained glucocerebrosidase inhibition in mice could induce neuropathological abnormalities including α-synucleinopathy, and neurodegeneration. Results: Our data demonstrate that daily systemic CBE treatment over 28 days caused accumulation of insoluble α-synuclein aggregates in the substantia nigra, and altered levels of proteins involved in the autophagy lysosomal system. These neuropathological changes were paralleled by widespread neuroinflammation, upregulation of complement C1q, abnormalities in synaptic, axonal transport and cytoskeletal proteins, and neurodegeneration. Innovation: A reduction in brain GCase activity has been linked to sporadic PD and normal aging, and may contribute to the susceptibility of vulnerable neurons to degeneration. This report demonstrates that systemic reduction of GCase activity using chemical inhibition, leads to neuropathological changes in the brain reminiscent of α-synucleinopathy. Conclusions: These data reveal a link between reduced glucocerebrosidase and the development of α-synucleinopathy and pathophysiological abnormalities in mice, and support the development of GCase therapeutics to reduce α-synucleinopathy in PD and related disorders. Antioxid. Redox Signal. 23, 550–564.

Low levels of astroglial markers in Parkinson’s disease: relationship to α-synuclein accumulation

Although gliosis is a normal response to brain injury, reports on the extent of astrogliosis in the degenerating substantia nigra in Parkinson’s disease (PD) are conflicting. It has also been recently suggested that accumulation of nigral α-synuclein in this disorder might suppress astrocyte activation which in turn could exacerbate the degenerative process. This study examined brain protein levels (intact protein, fragments, and aggregates, if any) of astroglial markers and their relationship to α-synuclein in PD and in the positive control parkinson-plus conditions multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). Autopsied brain homogenates of patients with PD (n=10), MSA (n=11), PSP (n=11) and matched controls (n=10) were examined for the astroglial markers glial fibrillary acidic protein (GFAP), vimentin, and heat shock protein-27 (Hsp27) by quantitative immunoblotting. As expected, both MSA (putamen>substantia nigra>caudate>frontal cortex) and PSP (substantia nigra>caudate>putamen, frontal cortex) showed widespread but regionally specific pattern of increased immunoreactivity of the markers, in particular for the partially proteolyzed fragments (all three) and aggregates (GFAP). In contrast, immunoreactivity of the three markers was largely normal in PD in brain regions examined with the exception of trends for variably increased levels of cleaved vimentin in substantia nigra and frontal cortex. In patients with PD, GFAP levels in the substantia nigra correlated inversely with α-synuclein accumulation whereas the opposite was true for MSA. Our biochemical findings of generally normal protein levels of astroglial markers in substantia nigra of PD, and negative correlation with α-synuclein concentration, are consistent with some recent neuropathology reports of mild astroglial response and with the speculation that astrogliosis might be suppressed in this disorder by excessive α-synuclein accumulation. Should astrogliosis protect, to some extent, the degenerating substantia nigra from damage, therapeutics aimed at normalization of astrocyte reaction in PD could be helpful.

Miro1 overexpression protects against α-synuclein-induced mitochondrial loss in neuronal culture

Mitophagy is a selective degradation of mitochondria that promotes the turnover of mitochondria and prevents the accumulation of damaged organelles. Pink1 and Parkin proteins are crucial in the removal of damaged mitochondria. Mutations in the corresponding PINK1 and PARK2 genes are associated with Parkinson’s disease (PD), and mitochondrial impairments are central to PD pathogenesis. Pink1 has been shown to interact with the atypical Rho GTPases Miro, the outer mitochondrial membrane proteins involved in mitochondrial trafficking. Miro1 is degraded shortly after mitochondrial damage in a Parkin-dependent manner. α-synuclein is a major component of Lewy bodies, the characteristic cellular inclusions in PD. Mutations of α-synuclein, including A53T, are linked to familial PD. α-synuclein has been shown to bind to the mitochondrial membrane, and increased membrane-bound α-synuclein in PD contributes to the functional disturbance of mitochondria. Overexpression of A53T-mutated α-synuclein has been shown to induce mitophagy in vitro and in vivo. We hypothesized that Miro1 function is disturbed in an α-synuclein (A53T)-overexpressing model, and the aim of this study was to elucidate the involvement of Miro1 in α-synuclein-induced mitophagy. We have found that α-synuclein is one component of the Miro1 interactome. Moreover, co-expression of Miro1 restored mitochondrial length and density in primary neuronal culture overexpressing A53T-mutated α-synuclein. Miro1 overexpression did not change the basal mitophagy, but decreased significantly α-synuclein-induced mitochondrial removal. Together, our results suggest that Miro and α-synuclein may interact in the mitophagic pathway.

Animal models for prion-like diseases

Prion diseases or Transmissible Spongiform Encephalopathies (TSEs) are a group of fatal neurodegenerative disorders affecting several mammalian species being Creutzfeldt-Jacob Disease (CJD) the most representative in human beings, scrapie in ovine, Bovine Spongiform Encephalopathy (BSE) in bovine and Chronic Wasting Disease (CWD) in cervids. As stated by the “protein-only hypothesis”, the causal agent of TSEs is a self-propagating aberrant form of the prion protein (PrP) that through a misfolding event acquires a β-sheet rich conformation known as PrPSc (from scrapie). This isoform is neurotoxic, aggregation prone and induces misfolding of native cellular PrP. Compelling evidence indicates that disease-specific protein misfolding in amyloid deposits could be shared by other disorders showing aberrant protein aggregates such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic lateral sclerosis (ALS) and systemic Amyloid A amyloidosis (AA amyloidosis). Evidences of shared mechanisms of the proteins related to each disease with prions will be reviewed through the available in vivo models. Taking prion research as reference, typical prion-like features such as seeding and propagation ability, neurotoxic species causing disease, infectivity, transmission barrier and strain evidences will be analyzed for other protein-related diseases. Thus, prion-like features of amyloid β peptide and tau present in AD, α-synuclein in PD, SOD-1, TDP-43 and others in ALS and serum α-amyloid (SAA) in systemic AA amyloidosis will be reviewed through models available for each disease.

Nitration of α-synuclein in Parkinson disease: recent progress

Nitration of α-synuclein in Parkinson disease: recent progress