Interaction between Neuromelanin and Alpha-Synuclein in Parkinson's Disease

Catecholamines and Parkinson's disease: tyrosine hydroxylase (TH) over tetrahydrobiopterin (BH4) and GTP cyclohydrolase I (GCH1) to cytokines, neuromelanin, and gene therapy: a historical overview

The author identified the genes and proteins of human enzymes involved in the biosynthesis of catecholamines (dopamine, norepinephrine, epinephrine) and tetrahydrobiopterin (BH4): tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and GTP cyclohydrolase I (GCH1). In Parkinson's disease (PD), the activities and levels of mRNA and protein of all catecholamine-synthesizing enzymes are decreased, especially in dopamine neurons in the substantia nigra. Hereditary GCH1 deficiency results in reductions in the levels of BH4 and the activities of TH, causing decreases in dopamine levels. Severe deficiencies in GCH1 or TH cause severe decreases in dopamine levels leading to severe neurological symptoms, whereas mild decreases in TH activity in mild GCH1 deficiency or in mild TH deficiency result in only modest reductions in dopamine levels and symptoms of DOPA-responsive dystonia (DRD, Segawa disease) or juvenile Parkinsonism. DRD is a treatable disease and small doses of L-DOPA can halt progression. The death of dopamine neurons in PD in the substantia nigra may be related to (i) inflammatory effect of extra neuronal neuromelanin, (ii) inflammatory cytokines which are produced by activated microglia, (iii) decreased levels of BDNF, and/or (iv) increased levels of apoptosis-related factors. This review also discusses progress in gene therapies for the treatment of PD, and of GCH1, TH and AADC deficiencies, by transfection of TH, AADC, and GCH1 via adeno-associated virus (AAV) vectors.

Disruption of Dopamine Homeostasis Associated with Alteration of Proteins in Synaptic Vesicles: A Putative Central Mechanism of Parkinson's Disease Pathogenesis

Vestigial dopaminergic cells in PD have selectivity for a sub-class of hypersensitive neurons with the nigrostriatal dopamine (DA) tract. DA is modulated in pre-synaptic nerve terminals to remain stable. To be specific, proteins at DA release sites that have a function of synthesizing and packing DA in cytoplasm, modulating release and reingestion, and changing excitability of neurons, display regional discrepancies that uncover relevancy of the observed sensitivity to neurodegenerative changes. Although the reasons of a majority of PD cases are still indistinct, heredity and environment are known to us to make significant influences. For decades, genetic analysis of PD patients with heredity in family have promoted our comprehension of pathogenesis to a great extent, which reveals correlative mechanisms including oxidative stress, abnormal protein homeostasis and mitochondrial dysfunction. In this review, we review the constitution of presynaptic vesicle related to DA homeostasis and describe the genetic and environmental evidence of presynaptic dysfunction that increase risky possibility of PD concerning intracellular vesicle transmission and their functional outcomes. We summarize alterations in synaptic vesicular proteins with great involvement in the reasons of some DA neurons highly vulnerable to neurodegenerative changes. We generalize different potential targets and therapeutic strategies for different pathogenic mechanisms, providing a reference for further studies of PD treatment in the future. But it remains to be further researched on this recently discovered and converging mechanism of vesicular dynamics and PD, which will provide a more profound comprehension and put up with new therapeutic tactics for PD patients.

New hope for Parkinson's disease treatment: Targeting gut microbiota

There might be more than 10 million confirmed cases of Parkinson's disease (PD) worldwide by 2040. However, the pathogenesis of PD is still unclear. Host health is closely related to gut microbiota, which are affected by factors such as age, diet, and exercise. Recent studies have found that gut microbiota may play key roles in the progression of a wide range of diseases, including PD. Changes in the abundance of gut bacteria, such as Helicobacter pylori, Enterococcus faecalis, and Desulfovibrio, might be involved in PD pathogenesis or interfere with PD therapy. Gut microbiota and the distal brain achieve action on each other through a gut‐brain axis composed of the nervous system, endocrine system, and immune system. Here, this review focused on the current understanding of the connection between Parkinson's disease and gut microbiota, to provide potential therapeutic targets for PD.

Lafora Disease and Alpha-Synucleinopathy in Two Adult Free-Ranging Moose (Alces alces) Presenting with Signs of Blindness and Circling

Simple Summary

Reports of behavioral signs, such as blindness and circling in free-ranging moose from different parts of the world, have spurred comprehensive pathological investigation to find the causes of the disease that have clinical relevance. In this case study, brains collected from two adult free-ranging moose (Alces alces) cows that were seemingly blind and found walking in circles were examined by light and electron microscopy with further ancillary testing. Here, we report for the first time Lafora disease and alpha-synucleinopathy in two wild free-ranging moose cows who presented with abnormal behavior and blindness, with similar neuronal polyglucosan body (PGB) accumulations identified in humans and other animals. Microscopic analysis of the hippocampus of brain revealed inclusion bodies resembling PGBs (Lafora disease) in the neurons with ultrastructural findings of aggregates of branching filaments, consistent with polyglucosan bodies. Furthermore, α-synuclein immunopositivity was noted in the hippocampus, with accumulations of small granules ultrastructurally distinct from PGBs and morphologically compatible with alpha-synucleinopathy (Lewy body). The apparent blindness found in these moose could be related to an injury associated with secondary bacterial invasion; however, an accumulation of neurotoxicants (PGBs and α-synucleins) in retinal ganglion cells could also be the cause. Lafora disease and alpha-synucleinopathy were considered in the differential diagnosis of the young adult moose who presented with signs of blindness and behavioral signs such as circling.

Abstract

Lafora disease is an autosomal recessive glycogen-storage disorder resulting from an accumulation of toxic polyglucosan bodies (PGBs) in the central nervous system, which causes behavioral and neurologic symptoms in humans and other animals. In this case study, brains collected from two young adult free-ranging moose (Alces alces) cows that were seemingly blind and found walking in circles were examined by light and electron microscopy. Microscopic analysis of the hippocampus of the brain revealed inclusion bodies resembling PGBs in the neuronal perikaryon, neuronal processes, and neuropil. These round inclusions measuring up to 30 microns in diameter were predominantly confined to the hippocampus region of the brain in both animals. The inclusions tested α-synuclein-negative by immunohistochemistry, α-synuclein-positive with PAS, GMS, and Bielschowsky’s staining; and diastase-resistant with central basophilic cores and faintly radiating peripheral lines. Ultrastructural examination of the affected areas of the hippocampus showed non-membrane-bound aggregates of asymmetrically branching filaments that bifurcated regularly, consistent with PGBs in both animals. Additionally, α-synuclein immunopositivity was noted in the different regions of the hippocampus with accumulations of small granules ultrastructurally distinct from PGBs and morphologically compatible with alpha-synucleinopathy (Lewy body). The apparent blindness found in these moose could be related to an injury associated with secondary bacterial invasion; however, an accumulation of neurotoxicants (PGBs and α-synuclein) in retinal ganglions cells could also be the cause. This is the first report demonstrating Lafora disease with concurrent alpha-synucleinopathy (Lewy body neuropathy) in a non-domesticated animal.

α-Synuclein phase separation and amyloid aggregation are modulated by C-terminal truncations

The aggregation of α-synuclein (α-Syn) is a key pathological hallmark of Parkinson's disease (PD). α-Syn undergoes liquid-liquid phase separation (LLPS) to drive amyloid aggregation. How the LLPS of α-Syn is regulated remains largely unknown. Here, we discovered that the C-terminal region modulates α-Syn phase separation through electrostatic interactions. The wild-type (WT) and PD disease-related truncated α-Syn can co-exist in the condensates. The truncated α-Syn could dramatically promote WT α-Syn phase separation. Further studies demonstrated that the truncated α-Syn accelerated WT α-Syn turning to amyloid aggregates by modulation of phase separation. Together, our findings disclose the role of the C-terminal domain in the LLPS of α-Syn and pave the path for understanding the mechanism of truncated α-Syn in PD pathology.

α-Synuclein phosphorylation at serine 129 occurs after initial protein deposition and inhibits seeded fibril formation and toxicity

SignificanceConverging evidence points to the build-up of phosphorylated α-synuclein (α-syn) at residue serine 129 (pS129) in Lewy body disease, suggesting its central role in the regulation of α-syn aggregation and neuronal degeneration. However, a comprehensive understanding of the role of α-syn phosphorylation at pS129 in α-synuclenopathies pathogenesis is still lacking. Herein, we study the phosphorylation incidence and its effect on α-syn aggregation propensity and cellular toxicity. Collectively, our data suggest that pS129 occurred subsequent to initial α-syn aggregation, lessened aggregation propensity, and attenuated cytotoxicity through diverse assays. Our findings highlight major implications for a better understanding of the role of a molecular modification on protein aggregation.

Neuromelanin in Parkinson's Disease: Tyrosine Hydroxylase and Tyrosinase

Parkinson's disease (PD) is an aging-related disease and the second most common neurodegenerative disease after Alzheimer's disease. The main symptoms of PD are movement disorders accompanied with deficiency of neurotransmitter dopamine (DA) in the striatum due to cell death of the nigrostriatal DA neurons. Two main histopathological hallmarks exist in PD: cytosolic inclusion bodies termed Lewy bodies that mainly consist of α-synuclein protein, the oligomers of which produced by misfolding are regarded to be neurotoxic, causing DA cell death; and black pigments termed neuromelanin (NM) that are contained in DA neurons and markedly decrease in PD. The synthesis of human NM is regarded to be similar to that of melanin in melanocytes; melanin synthesis in skin is via DOPAquinone (DQ) by tyrosinase, whereas NM synthesis in DA neurons is via DAquinone (DAQ) by tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). DA in cytoplasm is highly reactive and is assumed to be oxidized spontaneously or by an unidentified tyrosinase to DAQ and then, synthesized to NM. Intracellular NM accumulation above a specific threshold has been reported to be associated with DA neuron death and PD phenotypes. This review reports recent progress in the biosynthesis and pathophysiology of NM in PD.

Examining the Toxicity of α-Synuclein in Neurodegenerative Disorders

Simple Summary

Neurodegenerative disorders are complex disorders that display a variety of clinical manifestations. The second-most common neurodegenerative disorder is Parkinson’s disease, and the leading pathological protein of the disorder is considered to be α-synuclein. Nonetheless, α-synuclein accumulation also seems to result in multiple system atrophy and dementia with Lewy bodies. In order to obtain a more proficient understanding in the pathological progression of these synucleinopathies, it is crucial to observe the post-translational modifications of α-synuclein and the conformations of α-synuclein, as well as its role in the dysfunction of cellular pathways.

Abstract

α-synuclein is considered the main pathological protein in a variety of neurodegenerative disorders, such as Parkinson’s disease, multiple system atrophy, and dementia with Lewy bodies. As of now, numerous studies have been aimed at examining the post-translational modifications of α-synuclein to determine their effects on α-synuclein aggregation, propagation, and oligomerization, as well as the potential cellular pathway dysfunctions caused by α-synuclein, to determine the role of the protein in disease progression. Furthermore, α-synuclein also appears to contribute to the fibrilization of tau and amyloid beta, which are crucial proteins in Alzheimer’s disease, advocating for α-synuclein’s preeminent role in neurodegeneration. Due to this, investigating the mechanisms of toxicity of α-synuclein in neurodegeneration may lead to a more proficient understanding of the timeline progression in neurodegenerative synucleinopathies and could thereby lead to the development of potent targeted therapies.

Changes in cytoplasmic and extracellular neuromelanin in human substantia nigra with normal aging

Neuromelanin (NM) is a dark polymer pigment produced in certain populations of catecholaminergic neurons in the brain. It is present in various areas of the human brain, most often in the substantia nigra (SN) pars compacta and the locus coeruleus, the main centers of dopaminergic and noradrenergic innervation, respectively. Interest in NM has revived in recent years due to the alleged link between NM and the particular vulnerability of NM-containing neurons to neurodegeneration. The aim of this work was to study the structural, cytochemical, and localization features of cytoplasmic and extracellular NM (eNM) in the human SN pars compacta during normal aging. Sections of human SN from young/middle-aged adults (25 to 51 years old, n=7) and older adults (60 to 78 years old, n=5), all of which had no neurological disorders, were stained histochemically for metals (Perls’ reaction, Mayer's hematoxylin) and immunohistochemically for tyrosine hydroxylase (TH), Iba- 1, and CD68. It was shown that dopaminergic neurons in SN pars compacta differ in the amount of NM and the intensity of TH-immunoreactivity. The number of NM-containing neurons with decreased TH-immunoreactivity positively correlates with age. eNM is present in SN pars compacta in both young/middle-aged and older adults. The number of eNM accumulations increases with aging. Cytoplasmic and eNM are predominantly not stained using histochemical methods for detecting metals in people of all ages. We did not detect the appearance of amoeboid microglia in human SN pars compacta with aging, but we found an age-related increase in microglial phagocytic activity. The absence of pronounced microgliosis, as well as a pronounced loss of NM-containing neurons, indicate the absence of neuroinflammation in human SN pars compacta during normal aging.

Production, purification, and characterization of Streptomyces sp. strain MPPS2 extracellular pyomelanin pigment

Melanins are natural pigments widely distributed in nature from bacteria to humans. These complex, negatively charged, amorphous, high molecular mass natural biopolymers have many different bioactive properties such as antimicrobial, antiviral, antioxidant, liver protective effects, etc. In this study, some chemical and physical properties of the purified extracellular pyomelanin pigment were investigated via XRD (X-ray diffraction), FT-IR (Fourier transform infrared), and ¹H NMR (Nuclear magnetic resonance). Additionally, the melanin pigment producer Streptomyces sp. strain MPPS2 was characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/TOF MS) and 16S rDNA sequence analysis. 16S rDNA nucleotide sequence analysis result was deposited in NCBI GenBank^® under accession number MT825616.

Levodopa partially rescues microglial numerical, morphological, and phagolysosomal alterations in a monkey model of Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative motor disorder. The mechanisms underlying the onset and progression of Levodopa (L-Dopa)-induced dyskinesia (LID) during PD treatment remain elusive. Emerging evidence implicates functional modification of microglia in the development of LID. Thus, understanding the link between microglia and the development of LID may provide the knowledge required to preserve or promote beneficial microglial functions, even during a prolonged L-Dopa treatment. To provide novel insights into microglial functional alterations in PD pathophysiology, we characterized their density, morphology, ultrastructure, and degradation activity in the sensorimotor functional territory of the putamen, using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) cynomolgus monkeys. A subset of MPTP monkeys was treated orally with L-Dopa and developed LID similar to PD patients. Using a combination of light, confocal and transmission electron microscopy, our quantitative analyses revealed alterations of microglial density, morphology and phagolysosomal activity following MPTP intoxication that were partially normalized with L-Dopa treatment. In particular, microglial density, cell body and arborization areas were increased in the MPTP monkeys, whereas L-Dopa-treated MPTP animals presented a microglial phenotype similar to the control animals. At the ultrastructural level, microglia did not differ between groups in their markers of cellular stress or aging. Nevertheless, microglia from the MPTP monkeys displayed reduced numbers of endosomes, compared with control animals, that remained lower after L-Dopa treatment. Microglia from MPTP monkeys treated with L-Dopa also had increased numbers of primary lysosomes compared with non-treated MPTP animals, while secondary and tertiary lysosomes remained unchanged. Moreover, a decrease microglial immunoreactivity for CD68, considered a marker of phagocytosis and lysosomal activity, was measured in the MPTP monkeys treated with L-Dopa, compared with non-treated MPTP animals. Taken together, these findings revealed significant changes in microglia during PD pathophysiology that were partially rescued by L-Dopa treatment. Albeit, this L-Dopa treatment conferred phagolysosomal insufficiency on microglia in the dyskinetic Parkinsonian monkeys.

Shared perturbations in the metallome and metabolome of Alzheimer's, Parkinson's, Huntington's, and dementia with Lewy bodies: A systematic review

Despite differences in presentation, age-related dementing diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases (HD), and dementia with Lewy bodies (DLB) may share pathogenic processes. This review aims to systematically assemble and compare findings in various biochemical pathways across these four dementias. PubMed and Google Scholar were screened for articles reporting on brain and biofluid measurements of metals and/or metabolites in AD, PD, HD, or DLB. Articles were assessed using specific a priori-defined inclusion and exclusion criteria. Of 284 papers identified, 198 met criteria for inclusion. Although varying coverage levels of metals and metabolites across diseases and tissues made comparison of many analytes impossible, several common findings were identified: elevated glucose in both brain tissue and biofluids of AD, PD, and HD cases; increased iron and decreased copper in AD, PD and HD brain tissue; and decreased uric acid in biofluids of AD and PD cases. Other analytes were found to differ between diseases or were otherwise not covered across all conditions. These findings indicate that disturbances in glucose and purine pathways may be common to AD, PD, and HD. However, standardisation of methodologies and better coverage in some areas - notably of DLB - are necessary to validate and extend these findings.

Association Between Parkinson's Disease and Melanoma: Putting the Pieces Together

Patients with Parkinson’s disease (PD) generally have reduced risk of developing many types of cancers, except melanoma—a malignant tumor of melanin-producing cells in the skin. For decades, a large number of epidemiological studies have reported that the occurrence of melanoma is higher than expected among subjects with PD, and the occurrence of PD is reciprocally higher than expected among patients with melanoma. More recent epidemiological studies further indicated a bidirectional association, not only in the patients themselves but also in their relatives. This association between PD and melanoma offers a unique opportunity to understand PD. Here, we summarize epidemiological, clinical, and biological evidence in regard to shared risk factors and possible underlying mechanisms for these two seemingly distinct conditions.

Rasagiline and selegiline modulate mitochondrial homeostasis, intervene apoptosis system and mitigate α-synuclein cytotoxicity in disease-modifying therapy for Parkinson's disease

Parkinson's disease has been considered as a motor neuron disease with dopamine (DA) deficit caused by neuronal loss in the substantia nigra, but now proposed as a multi-system disorder associated with α-synuclein accumulation in neuronal and non-neuronal systems. Neuroprotection in Parkinson's disease has intended to halt or reverse cell death of nigro-striatal DA neurons and prevent the disease progression, but clinical studies have not presented enough beneficial results, except the trial of rasagiline by delayed start design at low dose of 1 mg/day only. Now strategy of disease-modifying therapy should be reconsidered taking consideration of accumulation and toxicity of α-synuclein preceding the manifest of motor symptoms. Hitherto neuroprotective therapy has been aimed to mitigate non-specific risk factors; oxidative stress, mitochondrial dysfunction, apoptosis, deficits of neurotrophic factors (NTFs), inflammation and accumulation of pathogenic protein. Future disease-modify therapy should target more specified pathogenic factors, including deregulated mitochondrial homeostasis, deficit of NTFs and α-synuclein toxicity. Selegiline and rasagiline, inhibitors of type B monoamine oxidase, have been proved to exhibit potent neuroprotective function: regulation of mitochondrial apoptosis system, maintenance of mitochondrial function, increased expression of genes coding antioxidant enzymes, anti-apoptotic Bcl-2 and pro-survival NTFs, and suppression of oligomerization and aggregation of α-synuclein and the toxicity in cellular and animal experiments. However, the present available pharmacological therapy starts too late to reverse disease progression, and future disease-modifying therapy should include also non-pharmacological complementary therapy during the prodromal stage.

Selective Neuronal Death in Neurodegenerative Diseases: The Ongoing Mystery

A major unresolved problem in neurodegenerative disease is why and how a specific set of neurons in the brain are highly vulnerable to neuronal death. Multiple pathways and mechanisms have been proposed to play a role in Alzheimer disease (AD), Parkinson disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington disease (HD), yet how they contribute to neuronal vulnerability remains far from clear. In this review, various mechanisms ascribed in AD, PD, ALS, and HD will be briefly summarized. Particular focus will be placed on Rhes-mediated intercellular transport of the HD protein and its role in mitophagy, in which I will discuss some intriguing observations that I apply to model striatal vulnerability in HD. I may have unintentionally missed referring some studies in this review, and I extend my apologies to the authors in those circumstances.

α-Synuclein in Parkinson's disease: causal or bystander?

Parkinson's disease (PD) comprises a spectrum of disorders with differing subtypes, the vast majority of which share Lewy bodies (LB) as a characteristic pathological hallmark. The process(es) underlying LB generation and its causal trigger molecules are not yet fully understood. α-Synuclein (α-syn) is a major component of LB and SNCA gene missense mutations or duplications/triplications are causal for rare hereditary forms of PD. As typical sporadic PD is associated with LB pathology, a factor of major importance is the study of the α-syn protein and its pathology. α-Syn pathology is, however, also evident in multiple system atrophy (MSA) and Lewy body disease (LBD), making it non-specific for PD. In addition, there is an overlap of these α-synucleinopathies with other protein-misfolding diseases. It has been proven that α-syn, phosphorylated tau protein (pτ), amyloid beta (Aβ) and other proteins show synergistic effects in the underlying pathogenic mechanisms. Multiple cell death mechanisms can induce pathological protein-cascades, but this can also be a reverse process. This holds true for the early phases of the disease process and especially for the progression of PD. In conclusion, while rare SNCA gene mutations are causal for a minority of familial PD patients, in sporadic PD (where common SNCA polymorphisms are the most consistent genetic risk factor across populations worldwide, accounting for 95% of PD patients) α-syn pathology is an important feature. Conversely, with regard to the etiopathogenesis of α-synucleinopathies PD, MSA and LBD, α-syn is rather a bystander contributing to multiple neurodegenerative processes, which overlap in their composition and individual strength. Therapeutic developments aiming to impact on α-syn pathology should take this fact into consideration.

Melanin and Neuromelanin Fluorescence Studies Focusing on Parkinson's Disease and Its Inherent Risk for Melanoma

Parkinson’s disease is associated with an increased risk of melanoma (and vice versa). Several hypotheses underline this link, such as pathways affecting both melanin and neuromelanin. For the first time, the fluorescence of melanin and neuromelanin is selectively accessible using a new method of nonlinear spectroscopy, based on a stepwise two-photon excitation. Cutaneous pigmentation and postmortem neuromelanin of Parkinson patients were characterized by fluorescence spectra and compared with controls. Spectral differences could not be documented, implying that there is neither a Parkinson fingerprint in cutaneous melanin spectra nor a melanin-associated fingerprint indicating an increased melanoma risk. Our measurements suggest that Parkinson’s disease occurs without a configuration change of neuromelanin. However, Parkinson patients displayed the same dermatofluorescence spectroscopic fingerprint of a local malignant transformation as controls. This is the first comparative retrospective fluorescence analysis of cutaneous melanin and postmortem neuromelanin based on nonlinear spectroscopy in patients with Parkinson’s disease and controls, and this method is a very suitable diagnostic tool for melanoma screening and early detection in Parkinson patients. Our results suggest a non-pigmentary pathway as the main link between Parkinson’s disease and melanoma, and they do not rule out the melanocortin-1-receptor gene as an additional bridge between both diseases.

Immune system and new avenues in Parkinson’s disease research and treatment

Parkinson’s disease (PD) is a progressive neurological disorder characterized by degeneration of dopaminergic neurons in the substantia nigra. However, although 200 years have now passed since the primary clinical description of PD by James Parkinson, the etiology and mechanisms of neuronal loss in this disease are still not fully understood. In addition to genetic and environmental factors, activation of immunologic responses seems to have a crucial role in PD pathology. Intraneuronal accumulation of α-synuclein (α-Syn), as the main pathological hallmark of PD, potentially mediates initiation of the autoimmune and inflammatory events through, possibly, auto-reactive T cells. While current therapeutic regimens are mainly used to symptomatically suppress PD signs, application of the disease-modifying therapies including immunomodulatory strategies may slow down the progressive neurodegeneration process of PD. The aim of this review is to summarize knowledge regarding previous studies on the relationships between autoimmune reactions and PD pathology as well as to discuss current opportunities for immunomodulatory therapy.

Protective effect of roscovitine against rotenone-induced parkinsonism

BACKGROUND

Protective effect of roscovitine and deregulation of the p-RB/E2F1 have not been well studied in PD models generated by repeated oral administration of rotenone.

OBJECTIVE

These experiments evaluated the effects of repeated oral gavage of rotenone on the activation of p-RB/E2F1 and the effects of roscovitine on the regulation of dopaminergic neuronal injury and the behavior of PD in mice.

METHODS

Using 2.5% carboxymethylcellulose and 1.25% chloroform as a vehicle solution, rotenone (30 mg/kg) was administered via oral gavage once daily for 30 days in C57 mice. Behavioral profiles (pole test and traction test) were assessed in these PD models, and oxidative stress levels were evaluated in the midbrain. The immunoreactivities of TH, α-synuclein (α-syn), p-RB, E2F1 and cleaved caspase-3 in the substantia nigra were examined with a laser confocal microscope. Pharmacological inhibition of cyclin-dependent kinase with roscovitine was achieved by intraperitoneal (IP) injection at a dose of 50 mg/kg daily.

RESULTS

All rotenone-administered C57 mice showed the typical behavioral features of PD: stiffness, bradykinesia, or hypokinesia. Behavioral testing with the pole test and traction test indicated that the rotenone group, but not the vehicle group, was affected. Spectrophotometric analysis demonstrated that glutathione (GSH) and superoxide dismutase (SOD) activity was decreased, and the generation of malondialdehyde (MDA) was elevated in the midbrain of the rotenone-treated group. After oral administration of rotenone, a loss of nigral tyrosine hydroxylase (TH)-positive neurons was observed. The immune response of α-syn was enhanced in the cytoplasm of dopaminergic neurons from the rotenone-induced neurotoxicity. Rb phosphorylation at serine 780, which affected Rb binding to E2F, was induced after rotenone treatment. The activation of E2F1, which is involved in the regulation of the cell cycle, was also induced from chronic exposure to rotenone. Moreover, administration of the cell cycle inhibitor roscovitine protected against rotenone-induced nigral dopaminergic neuronal injury and inhibited cleaved caspase-3 activation. Roscovitine also markedly ameliorated the behavior of PD mice.

CONCLUSIONS

Mouse models of Parkinson's disease were established by oral rotenone administration and reproduced some of the features of dopaminergic neuronal degeneration. Roscovitine protects against rotenone-induced parkinsonism.

Role of Ionizing Radiation in Neurodegenerative Diseases

Ionizing radiation (IR) from terrestrial sources is continually an unprotected peril to human beings. However, the medical radiation and global radiation background are main contributors to human exposure and causes of radiation sickness. At high-dose exposures acute radiation sickness occurs, whereas chronic effects may persist for a number of years. Radiation can increase many circulatory, age related and neurodegenerative diseases. Neurodegenerative diseases occur a long time after exposure to radiation, as demonstrated in atomic bomb survivors, and are still controversial. This review discuss the role of IR in neurodegenerative diseases and proposes an association between neurodegenerative diseases and exposure to IR.

Drosophila melanogaster has the enzymatic machinery to make the melanic component of neuromelanin

In Drosophila, the same set of genes that are used for cuticle pigmentation and sclerotization are present in the nervous system and are responsible for neurotransmitter recycling. In this study, we carried out biochemical analysis to determine whether insects have the enzymatic machinery to make melanic component of neuromelanin. We focused our attention on two key enzymes of melanogenesis, namely phenoloxidase and dopachrome decarboxylase/tautomerase. Activity staining of the proteins isolated from the Drosophila larval brain tissue, separated by native polyacrylamide gel electrophoresis, indicated the presence of these two enzymes. Mass spectral sequence analysis of the band also supported this finding. To best of our knowledge, this is the first report on the presence of the enzymatic machinery to make melanin part of neuromelanin in any insect brain.

Neuromelanin in Parkinson's Disease: from Fenton Reaction to Calcium Signaling

Neuromelanin is supposed to play a key role in the pathogenesis of Parkinson's disease. A common theory is the formation of reactive oxygen species through the Fenton reaction catalyzed by neuromelanin-bound iron ions and subsequent death of the dopaminergic cells in the substantia nigra. From a physicochemical point of view, this pathway is rather implausible: a highly reactive radical built within a powerful radical scavenger would more promptly be inactivated before it might diffuse within the cell to reach a target to exert its deleterious potential. This review of the literature provides evidence for an interaction of neuromelanin with the calcium signaling pathway in Parkinson's disease and expands the view of the pathophysiological contribution of neuromelanin towards a cytoprotective involvement of this macromolecule in the calcium signaling system. More probably than being directly involved in the production of reactive oxygen species, neuromelanin may act as a calcium reservoir and thus protect dopaminergic cells from cell death. A loss of neuromelanin, as observed in the substantia nigra of Parkinson patients, would lead to enhanced calcium messaging through the loss of an important calcium reservoir and thus finally via the formation of reactive oxygen species to cell death within the substantia nigra.

Mutant α-Synuclein Overexpression Induces Stressless Pacemaking in Vagal Motoneurons at Risk in Parkinson's Disease

α-Synuclein overexpression (ASOX) drives the formation of toxic aggregates in neurons vulnerable in Parkinson's disease (PD), including dopaminergic neurons of the substantia nigra (SN) and cholinergic neurons of the dorsal motor nucleus of the vagus (DMV). Just as these populations differ in when they exhibit α-synucleinopathies during PD pathogenesis, they could also differ in their physiological responses to ASOX. An ASOX-mediated hyperactivity of SN dopamine neurons, which was caused by oxidative dysfunction of Kv4.3 potassium channels, was recently identified in transgenic (A53T-SNCA) mice overexpressing mutated human α-synuclein. Noting that DMV neurons display extensive α-synucleinopathies earlier than SN dopamine neurons while exhibiting milder cell loss in PD, we aimed to define the electrophysiological properties of DMV neurons in A53T-SNCA mice. We found that DMV neurons maintain normal firing rates in response to ASOX. Moreover, Kv4.3 channels in DMV neurons exhibit no oxidative dysfunction in the A53T-SNCA mice, which could only be recapitulated in wild-type mice by glutathione dialysis. Two-photon imaging of redox-sensitive GFP corroborated the finding that mitochondrial oxidative stress was diminished in DMV neurons in the A53T-SNCA mice. This reduction in oxidative stress resulted from a transcriptional downregulation of voltage-activated (Cav) calcium channels in DMV neurons, which led to a reduction in activity-dependent calcium influx via Cav channels. Thus, ASOX induces a homeostatic remodeling with improved redox signaling in DMV neurons, which could explain the differential vulnerability of SN dopamine and DMV neurons in PD and could promote neuroprotective strategies that emulate endogenous homeostatic responses to ASOX (e.g., stressless pacemaking) in DMV neurons.

SIGNIFICANCE STATEMENT

Overexpression of mutant α-synuclein causes Parkinson's disease, presumably by driving neurodegeneration in vulnerable neuronal target populations. However, the extent of α-synuclein pathology (e.g., Lewy bodies) is not directly related to the degree of neurodegeneration across various vulnerable neuronal populations. Here, we show that, in contrast to dopamine neurons in the substantia nigra, vagal motoneurons do not enhance their excitability and oxidative load in response to chronic mutant α-synuclein overexpression. Rather, by downregulating their voltage-activated calcium channels, vagal motoneurons acquire a stressless form of pacemaking that diminishes mitochondrial and cytosolic oxidative stress. Emulating this endogenous adaptive response to α-synuclein overexpression could lead to novel strategies to protect dopamine neurons and perhaps delay the onset of Parkinson's disease.

Metabolic Investigations of the Molecular Mechanisms Associated with Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by fibrillar cytoplasmic aggregates of α-synuclein (i.e., Lewy bodies) and the associated loss of dopaminergic cells in the substantia nigra. Mutations in genes such as α-synuclein (SNCA) account for only 10% of PD occurrences. Exposure to environmental toxicants including pesticides and metals (e.g., paraquat (PQ) and manganese (Mn)) is also recognized as an important PD risk factor. Thus, aging, genetic alterations, and environmental factors all contribute to the etiology of PD. In fact, both genetic and environmental factors are thought to interact in the promotion of idiopathic PD, but the mechanisms involved are still unclear. In this study, we summarize our findings to date regarding the toxic synergistic effect between α-synuclein and paraquat treatment. We identified an essential role for central carbon (glucose) metabolism in dopaminergic cell death induced by paraquat treatment that is enhanced by the overexpression of α-synuclein. PQ “hijacks” the pentose phosphate pathway (PPP) to increase NADPH reducing equivalents and stimulate paraquat redox cycling, oxidative stress, and cell death. PQ also stimulated an increase in glucose uptake, the translocation of glucose transporters to the plasma membrane, and AMP-activated protein kinase (AMPK) activation. The overexpression of α-synuclein further stimulated an increase in glucose uptake and AMPK activity, but impaired glucose metabolism, likely directing additional carbon to the PPP to supply paraquat redox cycling.

Parkinson's disease and pesticides: A meta-analysis of disease connection and genetic alterations

Parkinson's disease (PD) is a globally prevalent, multifactorial disorder that occurs due to interactions between genetic and environmental factors. Observational studies have shown a link between exposure to pesticides and the risk of PD. We performed this study to systemically review published case-control studies and estimate quantitatively the association between pesticide exposure and PD. We searched Medline (through PubMed) for eligible case-control studies. The association between pesticide exposure and PD risk or occurrence of certain genetic alterations, related to the pathogenesis of PD was presented as odds ratios (OR) and pooled under the random effects model, using the statistical add-in (MetaXL, version 5.0). The pooled result showed that exposure to pesticides is linked to PD (OR 1.46, 95% CI [1.21, 1.77]), but there was a significant heterogeneity among included studies. Exposure to pesticides increased the risk of alterations in different PD pathogenesis-related genes, such as GST (OR 1.97, 95% CI [1.41, 2.76]), PON-1 (OR 1.32, 95% CI [1.09, 1.6]), MDR1 (OR 2.06, 95% CI [1.58, 2.68]), and SNCA genes (OR 1.28, 95% CI [1.02, 1.37]). There was no statistically significant association between exposure to pesticides and alteration of CYP2D6 (OR 1.19, 95% CI [0.91, 1.54]), SLC6A3 (OR 0.74, 95% CI [0.55, 1]), MnSOD (OR 1.45, 95% CI [0.97, 2.16]), NQO1 (OR 1.35, 95% CI [0.91, 2.01]), and PON-2 genes (OR 0.88, 95% CI [0.53, 1.45]). In conclusion, this meta-analysis provides evidence that pesticide exposure is significantly associated with the risk of PD and alterations in genes involved in PD pathogenesis. However, the underlying mechanism of this association and the effect of the duration of exposure or the type of pesticides should be addressed by future research.

Review: Spreading the word: precise animal models and validated methods are vital when evaluating prion-like behaviour of alpha-synuclein

Synucleinopathies are characterized by abnormal proteinaceous aggregates, mainly composed of fibrillar α-synuclein (α-syn). It is now believed that α-syn can form small aggregates in a restricted number of cells, that propagate to neighbouring cells and seed aggregation of endogenous α-syn, in a 'prion-like manner'. This process could underlie the stereotypical progression of Lewy bodies described by Braak and colleagues across different stages of Parkinson's disease (PD). This prion-like behaviour of α-syn has been recently investigated in animal models of PD or multiple system atrophy (MSA). These models investigate the cell-to-cell transfer of α-syn seeds, or the induction and spreading of α-syn pathology in transgenic or wild-type rodent brain. In this review, we first outline the involvement of α-syn in Lewy body diseases and MSA, and discuss how 'prion-like' mechanisms can contribute to disease. Thereon, we debate the relevance of animal models used to study prion-like propagation. Finally, we review current main histological methods used to assess α-syn pathology both in animal models and in human samples and their relevance to the disease. Specifically, we discuss using α-syn phosphorylated at serine 129 as a marker of pathology, and the novel methods available that allow for more sensitive detection of early pathology, which has relevance for modelling synucleinopathies.

Cutaneous malignant melanoma and Parkinson disease: Common pathways?

The mechanisms underlying the high prevalence of cutaneous malignant melanoma (CMM) in Parkinson disease (PD) are unclear, but plausibly involve common pathways. 129Ser-phosphorylated α-synuclein, a pathological PD hallmark, is abundantly expressed in CMM, but not in normal skin. In inherited PD, PARK genes harbor germline mutations; the same genes are somatically mutated in CMM, or their encoded proteins are involved in melanomagenesis. Conversely, genes associated with CMM affect PD risk. PD/CMM-targeted cells share neural crest origin and melanogenesis capability. Pigmentation gene variants may underlie their susceptibility. We review putative genetic intersections that may be suggestive of shared pathways in neurodegeneration/melanomagenesis. Ann Neurol 2016;80:811-820.

Potential of Diffusion Tensor Imaging and Relaxometry for the Detection of Specific Pathological Alterations in Parkinson's Disease (PD)

The purpose of the present study was to evaluate the potential of multimodal MR imaging including mean diffusivity (MD), fractional anisotropy (FA), relaxation rates R2 and R2* to detect disease specific alterations in Parkinson's Disease (PD). We enrolled 82 PD patients (PD-all) with varying disease durations (≤5 years: PD≤5, n = 43; >5 years: PD>5, n = 39) and 38 matched healthy controls (HC), receiving diffusion tensor imaging as well as R2 and R2* relaxometry calculated from multi-echo T2*-weighted and dual-echo TSE imaging, respectively. ROIs were drawn to delineate caudate nucleus (CN), putamen (PU), globus pallidus (GP) and substantia nigra (SN) on the co-registered maps. The SN was divided in 3 descending levels (SL 1–3). The most significant parameters were used for a flexible discrimination analysis (FDA) in a training collective consisting of 25 randomized subjects from each group in order to predict the classification of remaining subjects. PD-all showed significant increases in MD, R2 and R2* within SN and its subregions as well as in MD and R2* within different basal ganglia regions. Compared to the HC group, the PD≤5 and the PD>5 group showed significant MD increases within the SN and its lower two subregions, while the PD≤5 group exhibited significant increases in R2 and R2* within SN and its subregions, and tended to elevation within the basal ganglia. The PD>5 group had significantly increased MD in PU and GP, whereas the PD≤5 group presented normal MD within the basal ganglia. FDA achieved right classification in 84% of study participants. Micro-structural damage affects primarily the SN of PD patients and in later disease stages the basal ganglia. Iron contents of PU, GP and SN are increased at early disease stages of PD.