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Concept: Alpha-synuclein

141

Recent investigations suggest that gut microbiota affects the brain activity through the microbiota-gut-brain axis under both physiological and pathological disease conditions like Parkinson’s disease. Further dopamine synthesis in the brain is induced by dopamine producing enzymes that are controlled by gut microbiota via the microbiota-gut-brain axis. Also alpha synuclein deposition and the associated neurodegeneration in the enteric nervous system that increase intestinal permeability, oxidative stress, and local inflammation, accounts for constipation in Parkinson’s disease patients. The trigger that causes blood brain barrier leakage, immune cell activation and inflammation, and ultimately neuroinflammation in the central nervous system is believed to be due to the chronic low-grade inflammation in the gut. The non-motor symptoms that appear years before motor symptoms could be reliable early biomarkers, if they could be correlated with the established and reliable neuroimaging techniques or behavioral indices. The future directions should therefore, focus on the exploration of newer investigational techniques to identify these reliable early biomarkers and define the specific gut microbes that contribute to the development of Parkinson’s disease. This ultimately should pave the way to safer and novel therapeutic approaches that avoid the complications of the drugs delivered today to the brain of Parkinson’s disease patients.

Concepts: Central nervous system, Nervous system, Brain, Neurology, Parkinson's disease, Basal ganglia, Dopamine, Alpha-synuclein

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Parkinson’s disease (PD) is one of the most epidemic neurodegenerative diseases, and is characterized by movement disorders arising from loss of midbrain dopaminergic (DA) neurons. Recently, the relationship between PD and autophagy has received considerable attention, but information about the mechanisms involved is lacking. Here, we report that autophagy-related gene 5 (ATG5) is potentially important in protecting dopaminergic neurons in a 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model in zebrafish. Using analyses of zebarfish swimming behavior, in situ hybridizatiton, immunofluorescence and expressions of genes and proteins related to PD and autophagy, we found that ATG5 expression level was decreased and autophagy flux was blocked in this model. The ATG5 down-regulation led to the upgrade of PDassociated proteins, such as β-synuclein, Parkin, and PINK1, aggravation of MPTP-induced PDmimicking pathological locomotor behavior, DA neuron loss labelled by tyrosine hydroxylase (TH) or dopamine transporter (DAT), and blocked autophagy flux in the zebrafish model. ATG5 overexpression alleviated or reversed these PD pathological features, rescued DA neuron cells as indicated by elevated TH /DAT levels, and restored autophagy flux. The role of ATG5 in protecting DA neurons was confirmed by expression of the human atg5 gene in the zebrafish model. Our findings reveal that ATG5 has a role in neuroprotection, and upregulation of ATG5 may serve as a goal in the development of drugs for PD prevention and management.

Concepts: Neuron, Gene, Gene expression, Parkinson's disease, Substantia nigra, Neurotransmitter, Dopamine, Alpha-synuclein

72

The most common allergen in fish, the highly-abundant protein β-parvalbumin, forms amyloid structures as a way to avoid gastrointestinal degradation and transit to the blood. In humans, the same amyloid structures are mostly associated with neurodegenerative disorders such as Alzheimer’s and Parkinson’s. We here assessed a putative connection between these amyloids using recombinant Atlantic cod β-parvalbumin and the key amyloidogenic protein in Parkinson’s disease, α-synuclein. Using a set of in vitro biophysical methods, we discovered that β-parvalbumin readily inhibits amyloid formation of α-synuclein. The underlying mechanism was found to involve α-synuclein binding to the surface of β-parvalbumin amyloid fibers. In addition to being a new amyloid inhibition mechanism, the data suggest that health benefits of fish may be explained in part by cross-reaction of β-parvalbumin with human amyloidogenic proteins.

Concepts: Protein, Molecular biology, Prion, Amyloid, Neurology, Neurodegenerative disorders, Alpha-synuclein, Beta sheet

69

Neurodegenerative diseases have been linked to inflammation, but whether altered immunomodulation plays a causative role in neurodegeneration is not clear. We show that lack of cytokine interferon-β (IFN-β) signaling causes spontaneous neurodegeneration in the absence of neurodegenerative disease-causing mutant proteins. Mice lacking Ifnb function exhibited motor and cognitive learning impairments with accompanying α-synuclein-containing Lewy bodies in the brain, as well as a reduction in dopaminergic neurons and defective dopamine signaling in the nigrostriatal region. Lack of IFN-β signaling caused defects in neuronal autophagy prior to α-synucleinopathy, which was associated with accumulation of senescent mitochondria. Recombinant IFN-β promoted neurite growth and branching, autophagy flux, and α-synuclein degradation in neurons. In addition, lentiviral IFN-β overexpression prevented dopaminergic neuron loss in a familial Parkinson’s disease model. These results indicate a protective role for IFN-β in neuronal homeostasis and validate Ifnb mutant mice as a model for sporadic Lewy body and Parkinson’s disease dementia.

Concepts: Alzheimer's disease, Brain, Neurology, Neurodegenerative disorders, Parkinson's disease, Dopamine, Alpha-synuclein, Dementia with Lewy bodies

39

Chronic traumatic encephalopathy is a progressive tauopathy that occurs as a consequence of repetitive mild traumatic brain injury. We analysed post-mortem brains obtained from a cohort of 85 subjects with histories of repetitive mild traumatic brain injury and found evidence of chronic traumatic encephalopathy in 68 subjects: all males, ranging in age from 17 to 98 years (mean 59.5 years), including 64 athletes, 21 military veterans (86% of whom were also athletes) and one individual who engaged in self-injurious head banging behaviour. Eighteen age- and gender-matched individuals without a history of repetitive mild traumatic brain injury served as control subjects. In chronic traumatic encephalopathy, the spectrum of hyperphosphorylated tau pathology ranged in severity from focal perivascular epicentres of neurofibrillary tangles in the frontal neocortex to severe tauopathy affecting widespread brain regions, including the medial temporal lobe, thereby allowing a progressive staging of pathology from stages I-IV. Multifocal axonal varicosities and axonal loss were found in deep cortex and subcortical white matter at all stages of chronic traumatic encephalopathy. TAR DNA-binding protein 43 immunoreactive inclusions and neurites were also found in 85% of cases, ranging from focal pathology in stages I-III to widespread inclusions and neurites in stage IV. Symptoms in stage I chronic traumatic encephalopathy included headache and loss of attention and concentration. Additional symptoms in stage II included depression, explosivity and short-term memory loss. In stage III, executive dysfunction and cognitive impairment were found, and in stage IV, dementia, word-finding difficulty and aggression were characteristic. Data on athletic exposure were available for 34 American football players; the stage of chronic traumatic encephalopathy correlated with increased duration of football play, survival after football and age at death. Chronic traumatic encephalopathy was the sole diagnosis in 43 cases (63%); eight were also diagnosed with motor neuron disease (12%), seven with Alzheimer’s disease (11%), 11 with Lewy body disease (16%) and four with frontotemporal lobar degeneration (6%). There is an ordered and predictable progression of hyperphosphorylated tau abnormalities through the nervous system in chronic traumatic encephalopathy that occurs in conjunction with widespread axonal disruption and loss. The frequent association of chronic traumatic encephalopathy with other neurodegenerative disorders suggests that repetitive brain trauma and hyperphosphorylated tau protein deposition promote the accumulation of other abnormally aggregated proteins including TAR DNA-binding protein 43, amyloid beta protein and alpha-synuclein.

Concepts: Alzheimer's disease, Neuron, Traumatic brain injury, Cerebral cortex, Cerebrum, Dementia, Alpha-synuclein, Dementia with Lewy bodies

34

To investigate the efficacy and safety of zonisamide as an adjunct to levodopa therapy for parkinsonism in patients with dementia with Lewy bodies (DLB).

Concepts: Alzheimer's disease, Randomized controlled trial, Parkinson's disease, Dementia, Progressive supranuclear palsy, Alpha-synuclein, Lewy body, Dementia with Lewy bodies

33

Parkinson’s disease is characterized by abundant α-synuclein (α-Syn) neuronal inclusions, known as Lewy bodies and Lewy neurites, and the massive loss of midbrain dopamine neurons. However, a cause-and-effect relationship between Lewy inclusion formation and neurodegeneration remains unclear. Here, we found that in wild-type nontransgenic mice, a single intrastriatal inoculation of synthetic α-Syn fibrils led to the cell-to-cell transmission of pathologic α-Syn and Parkinson’s-like Lewy pathology in anatomically interconnected regions. Lewy pathology accumulation resulted in progressive loss of dopamine neurons in the substantia nigra pars compacta, but not in the adjacent ventral tegmental area, and was accompanied by reduced dopamine levels culminating in motor deficits. This recapitulation of a neurodegenerative cascade thus establishes a mechanistic link between transmission of pathologic α-Syn and the cardinal features of Parkinson’s disease.

Concepts: Ventral tegmental area, Parkinson's disease, Basal ganglia, Substantia nigra, Striatum, Dopamine, Alpha-synuclein, Pars compacta

29

Immunotherapy is currently being intensively explored as much-needed disease-modifying treatment for neurodegenerative diseases. While Alzheimer’s disease (AD) has been the focus of numerous immunotherapeutic studies, less attention has been paid to Parkinson’s disease (PD) and other neurodegenerative disorders. The reason for this difference is that the amyloid beta (Aβ) protein in AD is a secreted molecule that circulates in blood and is readably recognized by antibodies. In contrast, α-synuclein (α-syn), tau, huntingtin and other proteins involved in neurodegenerative diseases have been considered to be exclusively of intracellular nature. However, the recent discovery that toxic oligomeric versions of α-syn and tau accumulate in the membrane and can be excreted to the extracellular environment has provided a rationale for the development of immunotherapeutic approaches for PD, dementia with Lewy bodies, frontotemporal dementia, and other neurodegenerative disorders characterized by the abnormal accumulation of these proteins. Active immunization, passive immunization, and T cell-mediated cellular immunotherapeutic approaches have been developed targeting Aβ, α-syn and tau. Most advanced studies, including results from phase III clinical trials for passive immunization in AD, have been recently reported. Results suggest that immunotherapy might be a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and propagation of toxic protein aggregates. In this manuscript we provide an overview on immunotherapeutic advances for neurodegenerative disorders, with special emphasis on α-synucleinopathies.

Concepts: Alzheimer's disease, Protein, Cell membrane, Neurology, Neurodegenerative disorders, Parkinson's disease, Dementia, Alpha-synuclein

28

This study investigated the contribution of the new G protein-coupled estrogen receptor 1 (GPER1) in neuroprotection by 17β-estradiol in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease. In intact mice, administration of GPER1 agonist G1 reproduced the effect of 17β-estradiol in increasing striatal dopamine metabolite concentrations as well as the turnover of dopamine. GPER1 antagonist G15 blocked the effect of G1 on homovanillic acid/dopamine ratio and partially for 17β-estradiol. MPTP mice treated with G15 were more susceptible to MPTP toxicity with a greater decrease in striatal dopamine concentration and dopamine transporter specific binding. In MPTP mice, dopamine concentrations as well as dopamine and vesicular monoamine transporter 2 specific binding showed that G1 treatment was as potent as 17β-estradiol in protecting striatum and substantia nigra. G15 antagonized completely the neuroprotective effects of G1 in the striatum and substantia nigra as well as protection by 17β-estradiol in the striatum but partially in the substantia nigra. This study showed an important role of GPER1 in neuroprotection and that G1 is as potent as 17β-estradiol in mediating beneficial effects.

Concepts: Parkinson's disease, Basal ganglia, Substantia nigra, Serotonin, Striatum, Dopamine, Alpha-synuclein, Dopamine transporter

28

Parkinson’s disease (PD) involves the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) that is thought to cause the classical motor symptoms of this disease. However, motivational and affective impairments are also often observed in PD patients. These are usually attributed to a psychological reaction to the general motor impairment and to a loss of some of the neurons within the ventral tegmental area (VTA). We induced selective lesions of the VTA and SNc DA neurons that did not provoke motor deficits, and showed that bilateral dopamine loss within the SNc, but not within the VTA, induces motivational deficits and affective impairments that mimicked the symptoms of PD patients. Thus, motivational and affective deficits are a core impairment of PD, as they stem from the loss of the major group of neurons that degenerates in this disease (DA SNc neurons) and are independent of motor deficits.Molecular Psychiatry advance online publication, 12 February 2013; doi:10.1038/mp.2013.3.

Concepts: Ventral tegmental area, Parkinson's disease, Basal ganglia, Substantia nigra, Striatum, Dopamine, Alpha-synuclein, Pars compacta