The regulatory role of α-synuclein and parkin in neuronal cell apoptosis; possible implications for the pathogenesis of Parkinson’s disease

Distinct molecular mechanisms contribute to the reduction of melanoma growth and tumor pain after systemic and local depletion of alpha-Synuclein in mice

Epidemiological studies show a coincidence between Parkinson's disease (PD) and malignant melanoma. It has been suggested that this relationship is due, at least in part, to modulation of alpha-Synuclein (αSyn/Snca). αSyn oligomers accumulate in PD, which triggers typical PD symptoms, and in malignant melanoma, which increases the proliferation of tumor cells. In addition, αSyn contributes to non-motor symptoms of PD, including pain. In this study, we investigated the role of αSyn in melanoma growth and melanoma-induced pain in a mouse model using systemic and local depletion of αSyn. B16BL6 wild-type as well as αSyn knock-down melanoma cells were inoculated into the paws of αSyn knock-out mice and wild-type mice, respectively. Tumor growth and tumor-induced pain hypersensitivity were assessed over a period of 21 days. Molecular mechanisms were analyzed by RT-PCR and Western Blot in tumors, spinal cord, and sciatic nerve. Our results indicate that both global and local ablation of Snca contribute to reduced tumor growth and to a reduction of tumor-induced mechanical allodynia, though mechanisms contributing to these effects differ. While injection of wild-type cells in Snca knock-out mice strongly increased the immune response in the tumor, local Snca knock-down decreased autophagy mechanisms and the inflammatory reaction in the tumor. In conclusion, a knockdown of αSyn might constitute a promising approach to inhibiting the progression of melanoma and reducing tumor-induced pain.

Neurexin 2 p.G849D variant, implicated in Parkinson's disease, increases reactive oxygen species, and reduces cell viability and mitochondrial membrane potential in SH-SY5Y cells

Parkinson's disease (PD) is a neurodegenerative movement disorder, affecting 1-2% of the human population over 65. A previous study by our group identified a p.G849D variant in neurexin 2α (NRXN2) co-segregating with PD, prompting validation of its role using experimental methods. This novel variant had been found in a South African family with autosomal dominant PD. NRXN2α is an essential synaptic maintenance protein with multiple functional roles at the synaptic cleft. The aim of the present study was to investigate the potential role of the translated protein NRXN2α and the observed mutant in PD by performing functional studies in an in vitro model. Wild-type and mutant NRXN2α plasmids were transfected into SH-SY5Y cells to assess the effect of the mutant on cell viability and apoptosis [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) Assay; ApoTox-Glo™ Triplex Assay)], mitochondrial membrane potential (MMP; MitoProbe™ JC-1 Assay), mitochondrial network analysis (MitoTracker^®) and reactive oxygen species (ROS; ROS-Glo™ H₂O₂ Assay). Cells transfected with the mutant NRXN2α plasmid showed decreased cell viability and MMP. They also exhibited increased ROS production. However, these cells showed no changes in mitochondrial fragmentation. Our findings led us to speculate that the p.G849D variant may be involved in a toxic feedback loop leading to neuronal death in PD. Mitochondrial dysfunction and synaptic dysfunction have been linked to PD. Therefore, findings from this exploratory study are in line with previous studies connecting these two processes and warrants further investigation into the role of this variant in other cellular and animal models.

Vascular smooth muscle cell dysfunction in neurodegeneration

Vascular smooth muscle cells (VSMCs) are the key moderators of cerebrovascular dynamics in response to the brain's oxygen and nutrient demands. Crucially, VSMCs may provide a sensitive biomarker for neurodegenerative pathologies where vasculature is compromised. An increasing body of research suggests that VSMCs have remarkable plasticity and their pathophysiology may play a key role in the complex process of neurodegeneration. Furthermore, extrinsic risk factors, including environmental conditions and traumatic events can impact vascular function through changes in VSMC morphology. VSMC dysfunction can be characterised at the molecular level both preclinically, and clinically ex vivo. However the identification of VSMC dysfunction in living individuals is important to understand changes in vascular function at the onset and progression of neurological disorders such as dementia, Alzheimer's disease, and Parkinson's disease. A promising technique to identify changes in the state of cerebral smooth muscle is cerebrovascular reactivity (CVR) which reflects the intrinsic dynamic response of blood vessels in the brain to vasoactive stimuli in order to modulate regional cerebral blood flow (CBF). In this work, we review the role of VSMCs in the most common neurodegenerative disorders and identify physiological systems that may contribute to VSMC dysfunction. The evidence collected here identifies VSMC dysfunction as a strong candidate for novel therapeutics to combat the development and progression of neurodegeneration, and highlights the need for more research on the role of VSMCs and cerebrovascular dynamics in healthy and diseased states.

Involvement of heat shock proteins and parkin/α-synuclein axis in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurological diseases, next only to Alzheimer's disease (AD) in terms of prevalence. It afflicts about 2-3% of individuals over 65 years old. The etiology of PD is unknown and several environmental and genetic factors are involved. From a pathological point of view, PD is characterized by the loss of dopaminergic neurons in the substantia nigra, which causes the abnormal accumulation of α-synuclein (α-syn) (a component of Lewy bodies), which subsequently interact with heat shock proteins (HSPs), leading to apoptosis. Apoptosis is a vital pathway for establishing homeostasis in body tissues, which is regulated by pro-apoptotic and anti-apoptotic factors. Recent findings have shown that HSPs, especially HSP27 and HSP70, play a pivotal role in regulating apoptosis by influencing the factors involved in the apoptosis pathway. Moreover, it has been reported that the expression of these HSPs in the nervous system is high. Apart from this finding, investigations have suggested that HSP27 and HSP70 (related to parkin) show a potent protective and anti-apoptotic impact against the damaging outcomes of mutant α-syn toxicity to nerve cells. Therefore, in this study, we aimed to investigate the relationship between these HSPs and apoptosis in patients with PD.

Activation of α7-nAChRs Promotes the Clearance of α-Synuclein and Protects Against Apoptotic Cell Death Induced by Exogenous α-Synuclein Fibrils

Misfolding and abnormal aggregation of α-synuclein (αSyn) have been shown to increase the risk of developing Parkinson's disease (PD). Finding some way to reduce the aggregation of αSyn is particularly important for the treatment of PD. The main route in prion-like αSyn spreading is the cholinergic innervated vagus nervous system and central cholinergic neurons. Since the degenerative changes and death of cholinergic neurons also run through the pathological process of PD, we hypothesize an involvement of the cholinergic system in αSyn aggregation. The α7 nicotinic acetylcholine receptors (α7-nAChRs) are one of the most abundant nAChRs in the mammalian brain. Using nicotine and a selective α7-nAChRs agonist PNU-282987, we found a protective effect of α7-nAChRs on the cell damage induced by αSyn-PFF (preformed fibrils) through inhibiting apoptotic cell death. We further discovered an additive effect of α7-nAChRs on the clearance of αSyn in normal and αSyn stably transduced SH-SY5Y cells. Moreover, using α7-nAChRs knockout mice, we noticed that α7-nAChRs deficiency increased the deposition of αSyn and aggravated the loss of dopaminergic neurons in a chronic MPTP mouse model of PD. Our findings for the first time indicated that α7-nAChRs activation exhibited a neuroprotective effect on αSyn pathology and aggregation by promoting the clearance of αSyn.

Downregulation of microRNA-15b-5p Targeting the Akt3-Mediated GSK-3β/β-Catenin Signaling Pathway Inhibits Cell Apoptosis in Parkinson's Disease

Parkinson's disease (PD) is an incurable progressive disorder resulting from neurodegeneration, and apoptosis is considered a dominant mechanism underlying the process of neurodegeneration. MicroRNAs (miRNAs), which are small and noncoding RNAs involved in many a biological process like apoptosis and regulation of gene expressions, have been found in postmortem brain samples of patients with PD, as well as in vitro and in vivo models of PD. To explore the impact of miR-15b-5p and Akt3 on apoptosis in the progression of PD, the method of quantitative reverse transcription polymerase chain reaction (qRT-PCR) was employed, and the analysis result showed upregulated expression of miR-15b-5p and downregulated expression of Akt3 in the serum of PD patients, MPP+-induced SH-SY5Y cells, and the brain tissues of MPTP-induced mice. Meanwhile, the dual-luciferase reporter assay was used to demonstrate the regulator-target interaction between miR-15b-5p and Akt3; flow cytometry and spectrophotometry revealed that transfection of miR-15b-5p mimic and si-Akt3 increased the rate of apoptosis and caspase-3 activity, whereas transfecting the miR-15b-5p inhibitor and Akt3-overexpression plasmid repressed the rate of apoptosis and caspase-3 activity in the MPP+-induced SH-SY5Y cell model and the MPTP-induced mouse model. Additionally, analysis of western blotting (WB) assays in vivo and in vitro revealed that proapoptosis proteins (Bax, caspase-3, GSK-3β, and β-catenin) showed markedly upregulated expression in the miR-15b-5p inhibitor and si-Akt3-overexpression groups, while the expression of an antiapoptosis gene (i.e., Bcl2) was downregulated. These analysis results indicate that downregulation of miR-15b-5p by targeting the Akt3-mediated GSK-3β/β-catenin signaling pathway would repress cell apoptosis in PD in vivo and in vitro. It is expected that the research findings would help find new therapeutic targets for treatment of PD.

The Role of Natural Compounds and their Nanocarriers in the Treatment of CNS Inflammation

Neuroinflammation, which is involved in various inflammatory cascades in nervous tissues, can result in persistent and chronic apoptotic neuronal cell death and programmed cell death, triggering various degenerative disorders of the central nervous system (CNS). The neuroprotective effects of natural compounds against neuroinflammation are mainly mediated by their antioxidant, anti-inflammatory, and antiapoptotic properties that specifically promote or inhibit various molecular signal transduction pathways. However, natural compounds have several limitations, such as their pharmacokinetic properties and stability, which hinder their clinical development and use as medicines. This review discusses the molecular mechanisms of neuroinflammation and degenerative diseases of CNS. In addition, it emphasizes potential natural compounds and their promising nanocarriers for overcoming their limitations in the treatment of neuroinflammation. Moreover, recent promising CNS inflammation-targeted nanocarrier systems implementing lesion site-specific active targeting strategies for CNS inflammation are also discussed.

The potential roles of deubiquitinating enzymes in brain diseases

Most proteins undergo posttranslational modification such as acetylation, methylation, phosphorylation, biotinylation, and ubiquitination to regulate various cellular processes. Ubiquitin-targeted proteins from the ubiquitin-proteasome system (UPS) are degraded by 26S proteasome, along with this, deubiquitinating enzymes (DUBs) have specific activity against the UPS through detaching of ubiquitin on ubiquitin-targeted proteins. Balancing between protein expression and degradation through interplay between the UPS and DUBs is important to maintain cell homeostasis, and abnormal expression and elongation of proteins lead to diverse diseases such as cancer, diabetes, and autoimmune response. Therefore, development of DUB inhibitors as therapeutic targets has been challenging. In addition, understanding of the roles of DUBs in neurodegeneration, specifically brain diseases, has emerged gradually. This review highlights recent studies on the molecular mechanisms for DUBs, and discusses potential therapeutic targets for DUBs in cases of brain diseases.

Nanoformulations of Herbal Extracts in Treatment of Neurodegenerative Disorders

Nanotechnology is one of the methods that influenced human life in different ways and is a substantial approach that assists to overcome the multiple limitations of various diseases, particularly neurodegenerative disorders (NDs). Diverse nanostructures such as polymer nanoparticles, lipid nanoparticles, nanoliposomes, nano-micelles, and carbon nanotubes (CNTs); as well as different vehicle systems including poly lactic-co-glycolic acid, lactoferrin, and polybutylcyanoacrylate could significantly increase the effectiveness, reduce the side effects, enhance the stability, and improve the pharmacokinetics of many drugs. NDs belong to a group of annoying and debilitating diseases that involve millions of people worldwide. Previous studies revealed that several nanoformulations from a number of natural products such as curcumin (Cur), quercetin (QC), resveratrol (RSV), piperine (PIP), Ginkgo biloba, and Nigella sativa significantly improved the condition of patients diagnosed with NDs. Drug delivery to the central nervous system (CNS) has several limitations, in which the blood brain barrier (BBB) is the main drawback for treatment of NDs. This review discusses the effects of herbal-based nanoformulations, their advantages and disadvantages, to manage NDs. In summary, we conclude that herbal-based nano systems have promising proficiency in treatment of NDs, either alone or in combination with other drugs.

In silico drug screening by using genome-wide association study data repurposed dabrafenib, an anti-melanoma drug, for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by dopaminergic neuron loss. At present, there are no drugs that stop the progression of PD. As with other multifactorial genetic disorders, genome-wide association studies (GWASs) found multiple risk loci for PD, although their clinical significance remains uncertain. Here, we report the identification of candidate drugs for PD by a method using GWAS data and in silico databases. We identified 57 Food and Drug Administration-approved drug families as candidate neuroprotective drugs for PD. Among them, dabrafenib, which is known as a B-Raf kinase inhibitor and is approved for the treatment of malignant melanoma, showed remarkable cytoprotective effects in neurotoxin-treated SH-SY5Y cells and mice. Dabrafenib was found to inhibit apoptosis, and to enhance the phosphorylation of extracellular signal-regulated kinase (ERK), and inhibit the phosphorylation of c-Jun NH2-terminal kinase. Dabrafenib targets B-Raf, and we confirmed a protein-protein interaction between B-Raf and Rit2, which is coded by RIT2, a PD risk gene in Asians and Caucasians. In RIT2-knockout cells, the phosphorylation of ERK was reduced, and dabrafenib treatment improved the ERK phosphorylation. These data indicated that dabrafenib exerts protective effects against neurotoxicity associated with PD. By using animal model, we confirmed the effectiveness of this in silico screening method. Furthermore, our results suggest that this in silico drug screening system is useful in not only neurodegenerative diseases but also other common diseases such as diabetes mellitus and hypertension.

Nucleic Acid-Based Therapeutics for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is diagnosed largely on clinical grounds due to characteristic motor manifestations that result from the loss of nigrostriatal dopaminergic neurons. While traditional pharmacological approaches to enhance dopamine levels, such as with L-dopa, can be very effective initially, the chronic use of this dopamine precursor is commonly plagued with motor response complications. Additionally, with advancing disease, non-motor manifestations emerge, including psychosis and dementia that compound patient disability. The pathology includes hallmark intraneuronal inclusions known as Lewy bodies and Lewy neurites that contain fibrillar α-synuclein aggregates. Evidence has also accumulated that these aggregates can propagate across synaptically connected brain regions, a phenomenon that can explain the progressive nature of the disease and the emergence of additional symptoms over time. The level of α-synuclein is believed to play a critical role in its fibrillization and aggregation. Accordingly, nucleic acid-based therapeutics for PD include strategies to deliver dopamine biosynthetic enzymes to boost dopamine production or modulate the basal ganglia circuitry in order to improve motor symptoms. Delivery of trophic factors that might enhance the survival of dopamine neurons is another strategy that has been attempted. These gene therapy approaches utilize viral vectors and are delivered stereotaxically in the brain. Alternative disease-modifying strategies focus on downregulating the expression of the α-synuclein gene using various techniques, including modified antisense oligonucleotides, short hairpin RNA, short interfering RNA, and microRNA. The latter approaches also have implications for dementia with Lewy bodies. Other PD genes can also be targeted using nucleic acids. In this review, we detail these various strategies that are still experimental, and discuss the challenges and opportunities of nucleic acid-based therapeutics for PD.

Integration of risk factors for Parkinson disease in 2 large longitudinal cohorts

OBJECTIVE

To prospectively examine how selected lifestyle factors and family history of Parkinson disease (PD) combine to determine overall PD risk.

METHODS

We derived risk scores among 69,968 women in the Nurses' Health Study (NHS) (1984-2012) and 45,830 men in the Health Professionals Follow-up Study (HPFS) (1986-2012). Risk scores were computed for each individual based on the following factors previously associated with PD risk: total caffeine intake, smoking, physical activity, and family history of PD for the NHS, and additionally total flavonoid intake and dietary urate index for the HPFS. Hazard ratios were estimated using Cox proportional hazards models. In addition, we performed tests of interactions on both the multiplicative and additive scale between pairs of risk factors.

RESULTS

We documented 1,117 incident PD cases during follow-up. The adjusted hazard ratios comparing individuals in the highest category of the reduced risk score to those in the lowest category were 0.33 (95% confidence interval: 0.21, 0.49; p_trend < 0.0001) in the NHS and 0.18 (95% confidence interval: 0.10, 0.32; p_trend < 0.0001) in the HPFS. Results were similar when applying the risk scores computed by summing the predictors weighted by the log of their individual effect sizes on PD risk in these cohorts. Additive interaction was present between no family history of PD and caffeine in men and between caffeine and physical activity in women.

CONCLUSIONS

Our results suggest that known protective factors for PD tend to have additive or superadditive effects, so that PD risk is very low in individuals with multiple protective risk factors.

Propagated but Topologically Distributed Forebrain Neurons Expressing Alpha-Synuclein in Aged Macaques

In neurodegenerative disorders, such as Parkinson's disease (PD), alpha-synuclein (α-syn) accumulates to induce cell death and/or form a cytoplasmic inclusion called Lewy body (LB). This α-syn-related pathology is termed synucleinopathy. It remains unclear how α-syn accumulation expands during the progress of synucleinopathy in the human brain. In our study, we investigated the patterns of distribution and propagation of forebrain neurons expressing α-syn in aged macaques. It was found that the occurrence of α-syn-positive neurons proceeded topologically based on the midbrain dopamine pathways arising from the substantia nigra and the ventral tegmental area where they were primarily observed. In the nigrostriatal or mesolimbic dopamine pathway, the age-dependent increase in α-syn-positive neurons was evident in the striatum or the nucleus accumbens, respectively. Concerning the nigrostriatal pathway, a mediolateral or rostrocaudal gradient was seen in the substantia nigra or the striatum, respectively, and a compensatory increase in dopamine transporter occurred in the striatum regardless of the decreased dopamine level. In the mesocortical dopamine pathway, α-syn-positive neurons appeared in the prefrontal and then motor areas of the frontal lobe. Given that neither LB formation nor clinical phenotype manifestation was detected in any of the monkeys examined in the present study, aged macaques may be useful as a potential presymptomatic model for PD and LB-related neuropsychiatric disorders.

Oral biomarkers in exercise-induced neuroplasticity in Parkinson's disease

In this article, we review candidate biomarkers for Parkinson's disease (PD) in oral cavity, potential of oral biomarkers as markers of neuroplasticity, and literature on the effects of exercise on oral cavity biomarkers in PD. We first describe how pathophysiological pathways of PD may be transduced from brain stem and ganglia to oral cavity through the autonomic nervous system or transduced by a reverse path. Next we describe the effects of exercise in PD and potential impact on oral cavity. We propose that biomarkers in oral cavity may be useful targets for describing exercise-induced brain neuroplasticity in PD. Nevertheless, much research remains to be carried out before applying these biomarkers for the determination of disease state and therapeutic response to develop strategies to mitigate motor or non-motor symptoms in PD.

Mitochondrial dysfunctions in neurodegenerative diseases: relevance to Alzheimer's disease

Mitochondrial dysfunctions are supposed to be responsible for many neurodegenerative diseases dominating in Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). A growing body of evidence suggests that defects in mitochondrial metabolism and particularly of electron transport chain may play a role in pathogenesis of AD. Structurally and functionally damaged mitochondria do not produce sufficient ATP and are more prominent in producing proapoptotic factors and reactive oxygen species (ROS), and this can be an early stage of several mitochondrial disorders, including neurodegenerative diseases. Mitochondrial dysfunctions may be caused by both mutations in mitochondrial or nuclear DNA that code mitochondrial components and by environmental causes. In the following review, common aspects of mitochondrial impairment concerned about neurodegenerative diseases are summarized including ROS production, impaired mitochondrial dynamics, and apoptosis. Also, damaged function of electron transport chain complexes and interactions between pathological proteins and mitochondria are described for AD particularly and marginally for PD and HD.

Acetyltransferases (HATs) as targets for neurological therapeutics

The acetylation of histone and non-histone proteins controls a great deal of cellular functions, thereby affecting the entire organism, including the brain. Acetylation modifications are mediated through histone acetyltransferases (HAT) and deacetylases (HDAC), and the balance of these enzymes regulates neuronal homeostasis, maintaining the pre-existing acetyl marks responsible for the global chromatin structure, as well as regulating specific dynamic acetyl marks that respond to changes and facilitate neurons to encode and strengthen long-term events in the brain circuitry (e.g., memory formation). Unfortunately, the dysfunction of these finely-tuned regulations might lead to pathological conditions, and the deregulation of the HAT/HDAC balance has been implicated in neurological disorders. During the last decade, research has focused on HDAC inhibitors that induce a histone hyperacetylated state to compensate acetylation deficits. The use of these inhibitors as a therapeutic option was efficient in several animal models of neurological disorders. The elaboration of new cell-permeant HAT activators opens a new era of research on acetylation regulation. Although pathological animal models have not been tested yet, HAT activator molecules have already proven to be beneficial in ameliorating brain functions associated with learning and memory, and adult neurogenesis in wild-type animals. Thus, HAT activator molecules contribute to an exciting area of research.

Prenatal activation of maternal TLR3 receptors by viral-mimetic poly(I:C) modifies GluN2B expression in embryos and sonic hedgehog in offspring in the absence of kynurenine pathway activation

Activation of the immune system during pregnancy is believed to lead to psychiatric and neurological disorders in the offspring, but the molecular changes responsible are unknown. Polyinosinic:polycytidylic acid (poly(I:C)) is a viral-mimetic double-stranded RNA complex which activates Toll-Like-Receptor-3 and can activate the metabolism of tryptophan through the oxidative kynurenine pathway to compounds that modulate activity of glutamate receptors. The aim was to determine whether prenatal administration of poly(I:C) affects the expression of neurodevelopmental proteins in the offspring and whether such effects were mediated via the kynurenine pathway. Pregnant rats were treated with poly(I:C) during late gestation and the offspring were allowed to develop to postnatal day 21 (P21). Immunoblotting of the brains at P21 showed decreased expression of sonic hedgehog, a key protein in dopaminergic neuronal maturation. Expression of α-synuclein was decreased, while tyrosine hydroxylase was increased. Disrupted in Schizophrenia-1 (DISC-1) and 5-HT2C receptor levels were unaffected, as were the dependence receptors Unc5H1, Unc5H3 and Deleted in Colorectal Cancer (DCC), the inflammation-related transcription factor NFkB and the inducible oxidative enzyme cyclo-oxygenase-2 (COX-2). An examination of embryo brains 5 h after maternal poly(I:C) showed increased expression of GluN2B, with reduced doublecortin and DCC but no change in NFkB. Despite altered protein expression, there were no changes in the kynurenine pathway. The results show that maternal exposure to poly(I:C) alters the expression of proteins in the embryos and offspring which may affect the development of dopaminergic function. The oxidation of tryptophan along the kynurenine pathway is not involved in these effects.

α-Synuclein and mitochondrial dysfunction in Parkinson's disease

α-Synuclein (SNCA) is a substantive component of Lewy bodies, the pathological hallmark of Parkinson's disease (PD). The discovery and subsequent derivation of its role in PD has led to a suprising but fruitful convergence of the fields of biochemistry and molecular genetics. In particular, the manipulation of the cell lines of a number of forms of familial PD has implicated SNCA in distinct and diverse biochemical pathways related to its pathogenesis. This current and rapidly evolving concept indicates PD is a disease in which interacting pathways of oxidative stress, mitochondrial dysfunction and impaired regulation of protein turnover interact to cause dopaminergic cell dysfunction and death. SNCA has a central role in these processes and manipulation of its expression, degradation and aggregation appear to be promising neuroprotective therapeutic targets.

G proteins, p60TRP, and neurodegenerative diseases

Alzheimer's disease (AD) is a complex brain disorder of the limbic system and association cortices. The disease is characterized by the production and deposition of the amyloid β-peptide (Aβ) in the brain, and the neuropathological mechanisms involved must be deciphered to gain further insights into the fundamental aspects of the protein biology responsible for the development and progression of this disease. Aβ is generated by the intramembranous cleavage of the β-amyloid precursor protein, which is mediated by the proteases β- and γ-secretase. Accumulating evidence suggests the importance of the coupling of this cleavage mechanism to G protein signaling. Heterotrimeric G proteins play pivotal roles as molecular switches in signal transduction pathways mediated by G protein-coupled receptors (GPCRs). Extracellular stimuli activate these receptors, which in turn catalyze guanosine triphosphate-guanosine diphosphate exchange on the G protein α-subunit. The activation-deactivation cycles of G proteins underlie their crucial functions as molecular switches for a vast array of biological responses. The novel transcription regulator protein p60 transcription regulator protein and its related GPCR signaling pathways have recently been described as potential targets for the development of alternative strategies for inhibiting the early signaling mechanisms involved in neurodegenerative diseases such as AD.

An involvement of oxidative stress in endoplasmic reticulum stress and its associated diseases

The endoplasmic reticulum (ER) is the major site of calcium storage and protein folding. It has a unique oxidizing-folding environment due to the predominant disulfide bond formation during the process of protein folding. Alterations in the oxidative environment of the ER and also intra-ER Ca²⁺ cause the production of ER stress-induced reactive oxygen species (ROS). Protein disulfide isomerases, endoplasmic reticulum oxidoreductin-1, reduced glutathione and mitochondrial electron transport chain proteins also play crucial roles in ER stress-induced production of ROS. In this article, we discuss ER stress-associated ROS and related diseases, and the current understanding of the signaling transduction involved in ER stress.

Impact of intravenous immunoglobulin on the dopaminergic system and immune response in the acute MPTP mouse model of Parkinson's disease

Intravenous immunoglobulin (IVIg) is a blood-derived product, used for the treatment of immunodeficiency and autoimmune diseases. Since a range of immunotherapies have recently been proposed as a therapeutic strategy for Parkinson’s disease (PD), we investigated the effects of an IVIg treatment in a neurotoxin-induced animal model of PD. Mice received four injections of MPTP (15 mg/kg) at 2-hour intervals followed by a 14-day IVIg treatment, which induced key immune-related changes such as increased regulatory T-cell population and decreased CD4⁺/CD8⁺ ratio. The MPTP treatment induced significant 80% and 84% decreases of striatal dopamine concentrations (P < 0.01), as well as 33% and 40% reductions in the number of nigral dopaminergic neurons (P < 0.001) in controls and IVIg-treated mice, respectively. Two-way analyses of variance further revealed lower striatal tyrosine hydroxylase protein levels, striatal homovanillic acid concentrations and nigral dopaminergic neurons (P < 0.05) in IVIg-treated animals. Collectively, our results fail to support a neurorestorative effect of IVIg on the nigrostriatal system in the MPTP-treated mice and even suggest a trend toward a detrimental effect of IVIg on the dopaminergic system. These preclinical data underscore the need to proceed with caution before initiating clinical trials of IVIg in PD patients.

α-Synuclein and neuronal cell death

Parkinson’s disease (PD) is a progressive neurodegenerative disorder affecting ∼1 % of people over the age of 65. Neuropathological hallmarks of PD are prominent loss of dopaminergic (DA) neurons in the substantia nigra and formation of intraneuronal protein inclusions termed Lewy bodies, composed mainly of α-synuclein (αSyn). Missense mutations in αSyn gene giving rise to production of degradation-resistant mutant proteins or multiplication of wild-type αSyn gene allele can cause rare inherited forms of PD. Therefore, the existence of abnormally high amount of αSyn protein is considered responsible for the DA neuronal death in PD. Normally, αSyn protein localizes to presynaptic terminals of neuronal cells, regulating the neurotransmitter release through the modulation of assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex. On the other hand, of note, pathological examinations on the recipient patients of fetal nigral transplants provided a prion-like cell-to-cell transmission hypothesis for abnormal αSyn. The extracellular αSyn fibrils can internalize to the cells and enhance intracellular formation of protein inclusions, thereby reducing cell viability. These findings suggest that effective removal of abnormal species of αSyn in the extracellular space as well as intracellular compartments can be of therapeutic relevance. In this review, we will focus on αSyn-triggered neuronal cell death and provide possible disease-modifying therapies targeting abnormally accumulating αSyn.

Synuclein accumulation is associated with cell-specific neuronal death after spinal cord injury

Spinal cord injury axotomizes neurons and induces many of them to die, whereas others survive. Therefore, it is important to identify factors that lead to neuronal death after injury as a first step toward developing better strategies for increasing neuronal survival and functional recovery. However, the intrinsic molecular pathways that govern whether an injured neuron lives or dies remain surprisingly unclear. To address this question, we took advantage of the large size of giant reticulospinal (RS) neurons in the brain of the lamprey, Petromyzon marinus. We report that axotomy of giant RS neurons induces a select subset of them to accumulate high levels of synuclein, a synaptic vesicle-associated protein whose abnormal accumulation is linked to Parkinson's disease. Injury-induced synuclein accumulation occurred only in neurons that were classified as "poor survivors" by both histological and Fluoro-Jade C staining. In contrast, post-injury synuclein immunofluorescence remained at control levels in neurons that were identified as "good survivors." Synuclein accumulation appeared in the form of aggregated intracellular inclusions. Cells that accumulated synuclein also exhibited more ubiquitin-containing inclusions, similar to what occurs during disease states. When synuclein levels and cell vitality were measured in the same neurons, it became clear that synuclein accumulation preceded and strongly correlated with subsequent neuronal death. Thus, synuclein accumulation is identified as a marker and potential risk factor for forthcoming neuronal death after axotomy, expanding its implications beyond the neurodegenerative diseases.

The potential prognostic role of cardiovascular autonomic failure in α-synucleinopathies

Cardiovascular autonomic failure is the second most common dysautonomic feature of α-synucleinopathies and has significant impact on daily activities and quality of life. Here we provide a systematic review of cardiovascular autonomic failure in α-synucleinopathies, emphasizing its impact on cognitive functions and disease outcomes. Articles spanning the period between January 1985 and April 2012 were identified from the PubMed database using a keyword-based search. Epidemiological studies highlight the negative prognostic effect of cardiovascular autonomic failure on cardiovascular and cerebrovascular outcomes and overall mortality in all α-synucleinopathies. Altered cerebral perfusion, vascular pressure stress, and related disruption of the blood-brain barrier may also contribute to the white matter hyperintensities and cognitive dysfunction frequently found in patients affected by neurocardiovascular instability. These findings support the hypothesis that cardiovascular autonomic failure may play a negative prognostic role in α-synucleinopathies and suggest that precocious screening and therapeutic management of cardiovascular autonomic failure may positively impact disease course.

The role of α-synuclein in neurodegeneration — An update

Genetic, neuropathological and biochemical evidence implicates α-synuclein, a 140 amino acid presynaptic neuronal protein, in the pathogenesis of Parkinson’s disease and other neurodegenerative disorders. The aggregated protein inclusions mainly containing aberrant α-synuclein are widely accepted as morphological hallmarks of α-synucleinopathies, but their composition and location vary between disorders along with neuronal networks affected. α-Synuclein exists physiologically in both soluble and membran-bound states, in unstructured and α-helical conformations, respectively, while posttranslational modifications due to proteostatic deficits are involved in β-pleated aggregation resulting in formation of typical inclusions. The physiological function of α-synuclein and its role linked to neurodegeneration, however, are incompletely understood. Soluble oligomeric, not fully fibrillar α-synuclein is thought to be neurotoxic, main targets might be the synapse, axons and glia. The effects of aberrant α-synuclein include alterations of calcium homeostasis, mitochondrial dysfunction, oxidative and nitric injuries, cytoskeletal effects, and neuroinflammation. Proteasomal dysfunction might be a common mechanism in the pathogenesis of neuronal degeneration in α-synucleinopathies. However, how α-synuclein induces neurodegeneration remains elusive as its physiological function. Genome wide association studies demonstrated the important role for genetic variants of the SNCA gene encoding α-synuclein in the etiology of Parkinson’s disease, possibly through effects on oxidation, mitochondria, autophagy, and lysosomal function. The neuropathology of synucleinopathies and the role of α-synuclein as a potential biomarker are briefly summarized. Although animal models provided new insights into the pathogenesis of Parkinson disease and multiple system atrophy, most of them do not adequately reproduce the cardinal features of these disorders. Emerging evidence, in addition to synergistic interactions of α-synuclein with various pathogenic proteins, suggests that prionlike induction and seeding of α-synuclein could lead to the spread of the pathology and disease progression. Intervention in the early aggregation pathway, aberrant cellular effects, or secretion of α-synuclein might be targets for neuroprotection and disease-modifying therapy.

The biochemical and cellular basis for nutraceutical strategies to attenuate neurodegeneration in Parkinson's disease

Future therapeutic intervention that could effectively decelerate the rate of degeneration within the substantia nigra pars compacta (SNc) could add years of mobility and reduce morbidity associated with Parkinson’s disease (PD). Neurodegenerative decline associated with PD is distinguished by extensive damage to SNc dopaminergic (DAergic) neurons and decay of the striatal tract. While genetic mutations or environmental toxins can precipitate pathology, progressive degenerative succession involves a gradual decline in DA neurotransmission/synaptic uptake, impaired oxidative glucose consumption, a rise in striatal lactate and chronic inflammation. Nutraceuticals play a fundamental role in energy metabolism and signaling transduction pathways that control neurotransmission and inflammation. However, the use of nutritional supplements to slow the progression of PD has met with considerable challenge and has thus far proven unsuccessful. This review re-examines precipitating factors and insults involved in PD and how nutraceuticals can affect each of these biological targets. Discussed are disease dynamics (Sections 1 and 2) and natural substances, vitamins and minerals that could impact disease processes (Section 3). Topics include nutritional influences on α-synuclein aggregation, ubiquitin proteasome function, mTOR signaling/lysosomal-autophagy, energy failure, faulty catecholamine trafficking, DA oxidation, synthesis of toxic DA-quinones, o-semiquinones, benzothiazolines, hyperhomocyseinemia, methylation, inflammation and irreversible oxidation of neuromelanin. In summary, it is clear that future research will be required to consider the multi-faceted nature of this disease and re-examine how and why the use of nutritional multi-vitamin-mineral and plant-based combinations could be used to slow the progression of PD, if possible.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Neuroimaging for Lewy body disease: is the in vivo molecular imaging of α-synuclein neuropathology required and feasible?

Alpha-synuclein aggregation is a neuropathological hallmark of many neurodegenerative diseases including Parkinson's disease (PD), Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB), collectively termed the α-synucleinopathies. Substantial advances in clinical criteria and neuroimaging technology over the last 20 years have allowed great strides in the detection and differential diagnosis of these disorders. Nevertheless, it is clear that whilst the array of different imaging modalities in clinical use allow for a robust diagnosis of α-synucleinopathy in comparison to healthy subjects, there is no clear diagnostic imaging marker that affords a reliable differential diagnosis between the different forms of Lewy body disease (LBD) or that could facilitate tracking of disease progression. This has led to a call for a biomarker based on the pathological hallmarks of these diseases, namely α-synuclein-positive Lewy bodies (LBs). This potentially may be advantageous in terms of early disease detection, but may also be leveraged into a potential marker of disease progression. We here aim to firstly review the current status of neuroimaging biomarkers in PD and related synucleinopathies. Secondly, we outline the rationale behind α-synuclein imaging as a potential novel biomarker as well as the potential benefits and limitations of this approach. Thirdly, we attempt to illustrate the likely technical hurdles to be overcome to permit successful in vivo imaging of α-synuclein pathology in the diseased brain. Our overriding aim is to provide a framework for discussion of how to address this major unmet clinical need.