Stabilization of alpha-synuclein protein with aging and familial parkinson's disease-linked A53T mutation

Proteasome Activation by Small Molecules

Drugs that increase 26S proteasome activity have potential therapeutic applications in the treatment of neurodegenerative diseases. A chemical genetics screen of over 2,750 compounds using a proteasome activity probe as a readout in a high-throughput live-cell fluorescence-activated cell sorting-based assay revealed more than ten compounds that increase proteasome activity, with the p38 MAPK inhibitor PD169316 being one of the most potent ones. Genetic and chemical inhibition of either p38 MAPK, its upstream regulators, ASK1 and MKK6, and downstream target, MK2, enhance proteasome activity. Chemical activation of the 26S proteasome increases PROTAC-mediated and ubiquitin-dependent protein degradation and decreases the levels of both overexpressed and endogenous α-synuclein, without affecting the overall protein turnover. In addition, survival of cells overexpressing toxic α-synuclein assemblies is increased in the presence of p38 MAPK inhibitors. These findings highlight the potential of activation of 26S proteasome activity and that this can be achieved through multiple mechanisms by distinct molecules.

HIV-1 Vpr disrupts mitochondria axonal transport and accelerates neuronal aging

Disruption of mitochondria axonal transport, essential for the maintenance of synaptic and neuronal integrity and function, has been identified in neurodegenerative diseases. Whether HIV-1 viral proteins affect mitochondria axonal transport is unknown, albeit HIV-associated neurocognitive disorders occur in around half of the patients living with HIV. Therefore, we sought to examine the effect of HIV-1 viral protein R (Vpr) on mitochondria axonal transport. Using mice primary neuronal cultures, we demonstrated that 4-day Vpr treatment reduced the ratio of moving mitochondria associated with (i) less energy (ATP) supply, (ii) reduction in Miro-1 and (iii) increase of α-synuclein which led to loss of microtubule stability as demonstrated by inconsecutive distribution of acetylated α-tubulin along the axons. Interestingly, the effect of Vpr on mitochondria axonal transport was partially restored in the presence of bongkrekic acid, a compound that negatively affected the Vpr-adenine nucleotide translocator (ANT) interaction and totally restored the ATP level in neurons. This indicated Vpr impaired mitochondria axonal transport partially related to its interaction with ANT. The above effect of Vpr was similar to the data obtained from hippocampal tissues isolated from 18-month-old aging mice compared to 5-month-old mice. In accord with previous clinical findings that HIV infection prematurely ages the brain and increases the susceptibility to HAND, we found that Vpr induced aging markers in neurons. Thus, we concluded that instead of causing cell death, low concentration of HIV-1 Vpr altered neuronal function related with inhibition of mitochondria axonal transport which might contribute to the accelerated neuronal aging.

α-synuclein toxicity in neurodegeneration: mechanism and therapeutic strategies

Alterations in α-synuclein dosage lead to familial Parkinson's disease (PD), and its accumulation results in synucleinopathies that include PD, dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Furthermore, α-synuclein contributes to the fibrilization of amyloid-b and tau, two key proteins in Alzheimer's disease, which suggests a central role for α-synuclein toxicity in neurodegeneration. Recent studies of factors contributing to α-synuclein toxicity and its disruption of downstream cellular pathways have expanded our understanding of disease pathogenesis in synucleinopathies. In this Review, we discuss these emerging themes, including the contributions of aging, selective vulnerability and non-cell-autonomous factors such as α-synuclein cell-to-cell propagation and neuroinflammation. Finally, we summarize recent efforts toward the development of targeted therapies for PD and related synucleinopathies.

Toxic effects of human and rodent variants of alpha-synuclein in vivo

In Parkinson's disease, abnormal alpha-synuclein (asyn) accumulation leads to the formation of soluble oligomeric species thought to be toxic to cells as well as intraneuronal inclusions. To date, the precise mechanisms leading to aggregation of asyn in the brain is not well-understood. Previous studies in yeast, drosophila, and transgenic mice suggested that a non-A beta component depleted version of human asyn [h-asyn(D70-83)] or human beta-synuclein (h-bsyn), naturally lacking this centrally located hydrophobic region, are less prone to form aggregates in vitro and are expected to be less toxic compared to h-asyn in vivo, although not all experimental studies unequivocally support the latter view. To address this outstanding issue, we directly compared the neurotoxicity of human asyn against that of h-asyn(D70-83), h-bsyn as well as rat asyn using an adeno-associated viral vector to express these proteins in a dose-response study where the vector load was varied over two orders of magnitude. By quantifying the neurodegeneration of rat substantia nigra dopamine neurons here we show that h-asyn, h-bsyn, and h-asyn(D70-83) display comparable neurotoxicity across the vector doses tested. On the other hand, rat asyn and GFP control vectors displayed a different profile, where no detectable neurodegeneration was seen except at the highest vector titer. Thus, the two main conclusions of our study are that (i) deletion of the central hydrophobic region in h-asyn is not sufficient to alter its neurotoxic properties and (ii) expression of the widely used GFP control protein can cause measurable neurodegeneration at high titers.

LRRK2 at the interface of autophagosomes, endosomes and lysosomes

Over the past 20 years, substantial progress has been made in identifying the underlying genetics of Parkinson's disease (PD). Of the known genes, LRRK2 is a major genetic contributor to PD. However, the exact function of LRRK2 remains to be elucidated. In this review, we discuss how familial forms of PD have led us to hypothesize that alterations in endomembrane trafficking play a role in the pathobiology of PD. We will discuss the major observations that have been made to elucidate the role of LRRK2 in particular, including LRRK2 animal models and high-throughput proteomics approaches. Taken together, these studies strongly support a role of LRRK2 in vesicular dynamics. We also propose that targeting these pathways may not only be beneficial for developing therapeutics for LRRK2-driven PD, but also for other familial and sporadic cases.

TRIM28 regulates the nuclear accumulation and toxicity of both alpha-synuclein and tau

Several neurodegenerative diseases are driven by the toxic gain-of-function of specific proteins within the brain. Elevated levels of alpha-synuclein (α-Syn) appear to drive neurotoxicity in Parkinson's disease (PD); neuronal accumulation of tau is a hallmark of Alzheimer's disease (AD); and their increased levels cause neurodegeneration in humans and model organisms. Despite the clinical differences between AD and PD, several lines of evidence suggest that α-Syn and tau overlap pathologically. The connections between α-Syn and tau led us to ask whether these proteins might be regulated through a shared pathway. We therefore screened for genes that affect post-translational levels of α-Syn and tau. We found that TRIM28 regulates α-Syn and tau levels and that its reduction rescues toxicity in animal models of tau- and α-Syn-mediated degeneration. TRIM28 stabilizes and promotes the nuclear accumulation and toxicity of both proteins. Intersecting screens across comorbid proteinopathies thus reveal shared mechanisms and therapeutic entry points.

DOI:http://dx.doi.org/10.7554/eLife.19809.001

Behind many neurodegenerative diseases are specific proteins that abnormally accumulate inside neurons and damage the cells. In Parkinson’s disease, the protein alpha-synuclein accumulates; in Alzheimer’s disease, the protein tau is one of the toxic culprits; and in other neurodegenerative diseases, alpha-synuclein and tau both accumulate. Genetic studies suggest that accumulation of the two proteins may be linked, but little is known about the factors that regulate the levels of these proteins inside neurons.

Rousseaux et al. set out to identify how these proteins are regulated in the hope of finding new ways of targeting them and reducing their toxicity. Screening a subset of human genes led to one that encodes a protein called TRIM28, which regulates the levels of both alpha-synuclein and tau. When the TRIM28 protein was depleted in human and mouse cells, the levels of alpha-synuclein and tau also went down. This effect was specific because the levels of other proteins with the potential to cause neurodegeneration remained unaffected.

Models of neurodegenerative disease in fruit flies and mice were then used to explore how TRIM28 affects the levels of tau and alpha-synuclein in animals. In each case, the proteins’ levels dropped when TRIM28 was suppressed and this in turn protected the neurons from damage. Rousseaux et al. went on to show that TRIM28 affected how alpha-synuclein and tau were cleared in cells. Overexpressing TRIM28 revealed that it could encourage both alpha-synuclein and tau to accumulate in the nucleus of cells over time.

Finally, Rousseaux et al. compared post-mortem brain tissue from people who had neurodegenerative conditions that are driven by or associated with tau and alpha-synuclein with tissue from those who did not. The cell nuclei in the diseased tissue had much more TRIM28 associated with alpha-synuclein and tau than those in the healthy tissues.

Overall, the findings show that TRIM28 promotes the accumulation and damaging effects of both alpha-synuclein and tau. The next steps will be to understand how TRIM28 does this. It will also be important to determine if this effect can be targeted, whilst leaving others roles of TRIM28 intact, in order to explore it as a potential target to treat or prevent neurodegenerative diseases.

DOI:http://dx.doi.org/10.7554/eLife.19809.002

Untangling the Manganese-α-Synuclein Web

Neurodegenerative diseases affect a significant portion of the aging population. Several lines of evidence suggest a positive association between environmental exposures, which are common and cumulative in a lifetime, and development of neurodegenerative diseases. Environmental or occupational exposure to manganese (Mn) has been implicated in neurodegeneration due to its ability to induce mitochondrial dysfunction, oxidative stress, and α-synuclein (α-Syn) aggregation. The role of the α-Syn protein vis-a-vis Mn is controversial, as it seemingly plays a duplicitous role in neuroprotection and neurodegeneration. α-Syn has low affinity for Mn, however an indirect interaction cannot be ruled out. In this review we will examine the current knowledge surrounding the interaction of α-Syn and Mn in neurodegenerative process.

Alpha-synuclein-induced oxidative stress correlates with altered superoxide dismutase and glutathione synthesis in human neuroblastoma SH-SY5Y cells

Alpha-synuclein (α-syn) is a major component of Lewy bodies found in sporadic and inherited forms of Parkinson's disease (PD). Mutations in the gene encoding α-syn and duplications and triplications of wild-type (WT) α-syn have been associated with PD. Several mechanisms have been implicated in the degeneration of dopaminergic neurons in PD, including oxidative stress and mitochondrial dysfunction. Here we defined the occurrence of oxidative stress in SH-SY5Y cells overexpressing WT α-syn in a doxycycline (Dox) regulated manner, before and after exposure to iron (500 µM), and determined the changes in proteins involved in the intracellular antioxidant defense system. Data evidenced an increase in caspase-3 activation and diminished reducing capacity of -Dox cells, associated with decreased activity of mitochondria complex I and reduced mitochondrial transcription factor A (TFAM) levels in these cells. Furthermore, total and mitochondrial reactive oxygen species levels were higher under basal conditions in cells overexpressing α-syn (-Dox) and this increase was apparently correlated with diminished levels and activities of SOD1 and SOD2 in -Dox cells. Moreover, both reduced and oxidized glutathione levels were diminished in -Dox cells under basal conditions, concomitantly with decreased activity of GCL and reduced protein levels of GCLc. The effects caused by iron (500 µM) were mostly independent of α-syn expression and triggered different antioxidant responses to possibly counterbalance higher levels of free radicals. Overall, data suggest that overexpression of α-syn modifies the antioxidant capacity of SH-SY5Y cells due to altered activity and protein levels of SOD1 and SOD2, and decreased glutathione pool.

Proaggregant nuclear factor(s) trigger rapid formation of α-synuclein aggregates in apoptotic neurons

Cell-to-cell transmission of α-synuclein (αS) aggregates has been proposed to be responsible for progressive αS pathology in Parkinson disease (PD) and related disorders, including dementia with Lewy bodies. In support of this concept, a growing body of in vitro and in vivo experimental evidence shows that exogenously introduced αS aggregates can spread into surrounding cells and trigger PD-like pathology. It remains to be determined what factor(s) lead to initiation of αS aggregation that is capable of seeding subsequent propagation. In this study we demonstrate that filamentous αS aggregates form in neurons in response to apoptosis induced by staurosporine or other toxins-6-hydroxy-dopamine and 1-methyl-4-phenylpyridinium (MPP+). Interaction between αS and proaggregant nuclear factor(s) is associated with disruption of nuclear envelope integrity. Knocking down a key nuclear envelop constituent protein, lamin B1, enhances αS aggregation. Moreover, in vitro and in vivo experimental models demonstrate that aggregates released upon cell breakdown can be taken up by surrounding cells. Accordingly, we suggest that at least some αS aggregation might be related to neuronal apoptosis or loss of nuclear membrane integrity, exposing cytosolic α-synuclein to proaggregant nuclear factors. These findings provide new clues to the pathogenesis of PD and related disorders that can lead to novel treatments of these disorders. Specifically, finding ways to limit the effects of apoptosis on αS aggregation, deposition, local uptake and subsequent propagation might significantly impact progression of disease.

Amyloid proteotoxicity initiates an inflammatory response blocked by cannabinoids

The beta amyloid (Aβ) and other aggregating proteins in the brain increase with age and are frequently found within neurons. The mechanistic relationship between intracellular amyloid, aging and neurodegeneration is not, however, well understood. We use a proteotoxicity model based upon the inducible expression of Aβ in a human central nervous system nerve cell line to characterize a distinct form of nerve cell death caused by intracellular Aβ. It is shown that intracellular Aβ initiates a toxic inflammatory response leading to the cell's demise. Aβ induces the expression of multiple proinflammatory genes and an increase in both arachidonic acid and eicosanoids, including prostaglandins that are neuroprotective and leukotrienes that potentiate death. Cannabinoids such as tetrahydrocannabinol stimulate the removal of intraneuronal Aβ, block the inflammatory response, and are protective. Altogether these data show that there is a complex and likely autocatalytic inflammatory response within nerve cells caused by the accumulation of intracellular Aβ, and that this early form of proteotoxicity can be blocked by the activation of cannabinoid receptors.

α-Synuclein aggregation in the olfactory bulb of middle-aged common marmoset

The synaptic protein α-synuclein has been identified as a major component of Lewy bodies, a pathological hallmark of Parkinson's disease (PD). Prior to the formation of Lewy bodies, mislocalization and aggregation of the α-synuclein in brain tissue is frequently observed in various neurodegenerative diseases. Aberrant accumulation and localization of α-synuclein are also observed in the aging human brain, for which reason aging is regarded as a risk factor for neurodegenerative disease. To investigate changes in α-synuclein properties in the aging brain, we compared α-synuclein immunoreactivity in brain tissue of young (2-years-old) and middle-aged (6-years-old) common marmoset (Callithrix jacchus). Our analyses revealed marked changes in α-synuclein immunoreactivity in the olfactory bulb of common marmosets of these age cohorts. Perikaryal α-synuclein aggregations were formed in the olfactory bulb in middle-aged animals. We also observed signals of α-synuclein accumulation in hippocampus in this cohort; however, unlike in the olfactory bulb, hippocampal α-synuclein signals were localized in the synaptic terminals. We did not observe either of these features in younger marmosets, which suggest that aging may play a role in these phenomena. Our results using common marmoset brain corresponded with the observation that the α-synuclein aggregations were first occurred from olfactory bulb in human normal aged and PD brain. Therefore, common marmoset is expected as useful model for α-synuclein pathology.

Delaying aging is neuroprotective in Parkinson's disease: a genetic analysis in C. elegans models

Aging is the greatest risk factor for the development of Parkinson’s disease (PD). However, the role of aging in the pathogenesis of PD is not known and it is currently uncertain why the symptoms take many decades to develop when inherited mutations that cause the disease can be present from birth. We hypothesize that there are specific changes that take place during the aging process that make cells susceptible to disease-causing mutations that are well-tolerated at younger ages. If so, then interventions that increase lifespan should be beneficial in the treatment of PD. To test this hypothesis, we used the powerful genetics of C. elegans, as this worm has been used extensively in aging research. We crossed transgenic worm models of PD expressing either human mutant α-synuclein (A53T) or LRRK2 (G2019S) with the long-lived insulin-IGF1 receptor mutant, daf-2. The daf-2 mutation increased the lifespan of both PD mutants. The increase in lifespan resulting from the daf-2 mutation rescued the degeneration of dopamine neurons in both worm models of PD and importantly rescued deficits in dopamine-dependent behaviors including basal slowing, ethanol avoidance, and area-restricted searching. Increasing lifespan through daf-2 mutation also delayed the formation of small aggregates in a worm model of PD expressing α-synuclein in the body wall muscle and rescued deficits in resistance to different stresses that were present in the PD mutant worms. Overall, this work suggests that slowing down the aging process may provide an effective treatment for PD.

Analysis of in vivo turnover of tau in a mouse model of tauopathy

BACKGROUND

Intracellular accumulation of tau as neurofibrillary tangles (NFTs) is the hallmark of Alzheimer's disease (AD) as well as in other tauopathies. Tau is present not only in the cytoplasm but also in the extracellular space such as cerebrospinal fluid (CSF) and brain interstitial fluid (ISF). Although clearance is one critical parameter leading to such intracellular/extracellular tau accumulation, in vivo turnover of tau has not been well characterized. The current study has attempted to precisely determine in vivo turnover rates of tau utilizing tet-off regulatable mice. In particular, we assessed intracellular tau and extracellular tau, soluble tau, insoluble tau and phosphorylated tau at certain sites utilizing a combination of in vivo microdialysis, biochemical analysis and specific ELISAs recognizing each species. To examine the effect of a tauopathy-associated mutation on tau clearance, half-lives of various tau species were compared between the mice with a FTDP-17 mutation that induces β-sheet formation, ΔK280 mutation (pro-aggregant mice) and control mice with additional β-sheet breaking mutations (anti-aggregant mice).

RESULTS

Here we report that tau is metabolized at much slower turnover rates in vivo than in cell culture. We found that insoluble tau in pro-aggregant mice had a significantly slower half-life (t1/2 = ~34.2 days) than soluble tau (t1/2 = ~9.7 days). In contrast, soluble tau phosphorylated in the proline rich region was cleared faster than total soluble tau. When comparing pro-aggregant mice to anti-agregant mice, turnover rates of soluble tau species were not significantly different.

CONCLUSIONS

The current study provides a comprehensive description of in vivo turnover of various tau species present in mice that express human tau. The turnover rate of soluble tau was not significantly altered between pro-aggregant mice and anti-aggregant mice. This suggests that altered conformation by ΔK280 does not have a major impact on clearance pathways for soluble tau. In contrast, different tau species displayed different half-lives. Turnover was significantly delayed for insoluble tau whereas it was accelerated for soluble tau phosphorylated in the proline rich region. These differences in susceptibilities to clearance suggest that aggregation and phosphorylation influences tau clearance which may be important in tau pathogenesis.

Αlpha-Synuclein as a Mediator in the Interplay between Aging and Parkinson's Disease

Accumulation and misfolding of the alpha-synuclein protein are core mechanisms in the pathogenesis of Parkinson's disease. While the normal function of alpha-synuclein is mainly related to the control of vesicular neurotransmission, its pathogenic effects are linked to various cellular functions, which include mitochondrial activity, as well as proteasome and autophagic degradation of proteins. Remarkably, these functions are also affected when the renewal of macromolecules and organelles becomes impaired during the normal aging process. As aging is considered a major risk factor for Parkinson's disease, it is critical to explore its molecular and cellular implications in the context of the alpha-synuclein pathology. Here, we discuss similarities and differences between normal brain aging and Parkinson's disease, with a particular emphasis on the nigral dopaminergic neurons, which appear to be selectively vulnerable to the combined effects of alpha-synuclein and aging.

Parkinson's disease as a result of aging

It is generally considered that Parkinson's disease is induced by specific agents that degenerate a clearly defined population of dopaminergic neurons. Data commented in this review suggest that this assumption is not as clear as is often thought and that aging may be critical for Parkinson's disease. Neurons degenerating in Parkinson's disease also degenerate in normal aging, and the different agents involved in the etiology of this illness are also involved in aging. Senescence is a wider phenomenon affecting cells all over the body, whereas Parkinson's disease seems to be restricted to certain brain centers and cell populations. However, reviewed data suggest that Parkinson's disease may be a local expression of aging on cell populations which, by their characteristics (high number of synaptic terminals and mitochondria, unmyelinated axons, etc.), are highly vulnerable to the agents promoting aging. The development of new knowledge about Parkinson's disease could be accelerated if the research on aging and Parkinson's disease were planned together, and the perspective provided by gerontology gains relevance in this field.

Sirtuins and proteolytic systems: implications for pathogenesis of synucleinopathies

Insoluble and fibrillar forms of α-synuclein are the major components of Lewy bodies, a hallmark of several sporadic and inherited neurodegenerative diseases known as synucleinopathies. α-Synuclein is a natural unfolded and aggregation-prone protein that can be degraded by the ubiquitin-proteasomal system and the lysosomal degradation pathways. α-Synuclein is a target of the main cellular proteolytic systems, but it is also able to alter their function further, contributing to the progression of neurodegeneration. Aging, a major risk for synucleinopathies, is associated with a decrease activity of the proteolytic systems, further aggravating this toxic looping cycle. Here, the current literature on the basic aspects of the routes for α-synuclein clearance, as well as the consequences of the proteolytic systems collapse, will be discussed. Finally, particular focus will be given to the sirtuins’s role on proteostasis regulation, since their modulation emerged as a promising therapeutic strategy to rescue cells from α-synuclein toxicity. The controversial reports on the potential role of sirtuins in the degradation of α-synuclein will be discussed. Connection between sirtuins and proteolytic systems is definitely worth of further studies to increase the knowledge that will allow its proper exploration as new avenue to fight synucleinopathies.

The Role of α-Synuclein and LRRK2 in Tau Phosphorylation

There is now a considerable body of experimental evidence that Parkinson's disease arises through physiological interaction of causative molecules, leading to tau pathology. In this review, we discuss the physiological role of α-synuclein and LRRK2 in the abnormal phosphorylation of tau. In addition, as recent reports have indicated that heat shock proteins- (HSPs-) inducing drugs can help to ameliorate neurodegenerative diseases associated with tau pathology, we also discuss therapeutic strategies for PD focusing on inhibition of α-synuclein- and LRRK2-associated tau phosphorylation by HSPs.

Differential expression of genes related to mitochondrial biogenesis and bioenergetics in fatigued prostate cancer men receiving external beam radiation therapy

OBJECTIVES

This prospective study explored relationships between expression changes of genes related to mitochondrial biogenesis/bioenergetics and fatigue in men with prostate cancer receiving external beam radiation therapy (EBRT).

METHODS

Fatigue and gene expression were measured before (Day 0), at midpoint (Days 19-21), and at completion (Days 38-42) of EBRT using the seven-item Patient-Reported Outcomes Measurement Information System-Fatigue short form and from whole blood cell RNA, respectively. The human mitochondria RT2 Profiler PCR Array System was used to identify differential expression of mitochondrial biogenesis/bioenergetics-related genes. Mixed linear modeling estimated the changes in fatigue and gene expression over time and determined significant associations between gene expression and fatigue.

RESULTS

Subjects were 50 men with prostate cancer (scheduled for EBRT = 25, active surveillance as matched controls = 25). The mean Patient-Reported Outcomes Measurement Information System-Fatigue T-score (mean = 50 ± 10 in a general population) for study subjects was 44.87 ± 5.89 and for controls was 43.5 ± 2.8 at baseline. Differential expression of two genes inside the mitochondria involved in critical mitochondrial complexes: BCS1L (β = 1.30), SLC25A37 (β = -2.44), and two genes on the outer mitochondrial membrane vital for mitochondrial integrity: BCL2L1 (β = -1.68) and FIS1 (β = -2.35) were significantly associated with changes in fatigue scores of study subjects during EBRT.

CONCLUSION

Genes related to oxidative phosphorylation, energy production, and mitochondrial membrane integrity are associated with worsening fatigue during EBRT. Further investigation of the pathways involved with this association may explain mechanisms behind the development of fatigue in this population.

Augmentation of phenotype in a transgenic Parkinson mouse heterozygous for a Gaucher mutation

The involvement of the protein α-synuclein (SNCA) in the pathogenesis of Parkinson's disease is strongly supported by the facts that (i) missense and copy number mutations in the SNCA gene can cause inherited Parkinson's disease; and (ii) Lewy bodies in sporadic Parkinson's disease are largely composed of aggregated SNCA. Unaffected heterozygous carriers of Gaucher disease mutations have an increased risk for Parkinson's disease. As mutations in the GBA gene encoding glucocerebrosidase (GBA) are known to interfere with lysosomal protein degradation, GBA heterozygotes may demonstrate reduced lysosomal SNCA degradation, leading to increased steady-state SNCA levels and promoting its aggregation. We have created mouse models to investigate the interaction between GBA mutations and synucleinopathies. We investigated the rate of SNCA degradation in cultured primary cortical neurons from mice expressing wild-type mouse SNCA, wild-type human SNCA, or mutant A53T SNCA, in a background of either wild-type Gba or heterozygosity for the L444P GBA mutation associated with Gaucher disease. We also tested the effect of this Gaucher mutation on motor and enteric nervous system function in these transgenic animals. We found that human SNCA is stable, with a half-life of 61 h, and that the A53T mutation did not significantly affect its half-life. Heterozygosity for a naturally occurring Gaucher mutation, L444P, reduced GBA activity by 40%, reduced SNCA degradation and triggered accumulation of the protein in culture. This mutation also resulted in the exacerbation of motor and gastrointestinal deficits found in the A53T mouse model of Parkinson's disease. This study demonstrates that heterozygosity for a Gaucher disease-associated mutation in Gba interferes with SNCA degradation and contributes to its accumulation, and exacerbates the phenotype in a mouse model of Parkinson's disease.

Nutrient deprivation induces α-synuclein aggregation through endoplasmic reticulum stress response and SREBP2 pathway

Abnormal accumulation of filamentous α-synuclein (α-syn) in neurons, regarded as Lewy bodies (LBs), are a hallmark of Parkinson disease (PD). Although the exact mechanism(s) underlying LBs formation remains unknown, autophagy and ER stress response have emerged as two important pathways affecting α-syn aggregation. In present study we tested whether cells with the tetracycline-off inducible overexpression of α-syn and accumulating α-syn aggregates can benefit from autophagy activation elicited by nutrient deprivation (ND), since this approach was reported to effectively clear cellular polyglutamine aggregates. We found that nutrient deprivation of non-induced cells did not affect cell viability, but significantly activated autophagy reflected by increasing the level of autophagy marker LC3-II and autophagic flux and decrease of endogenous α-syn. Cells with induced α-syn expression alone displayed autophagy activation in an α-syn dose-dependent manner to reach a level comparable to that found in non-induced, nutrient deprived counterparts. Nutrient deprivation also activated autophagy further in α-syn induced cells, but the extent was decreased with increase of α-syn dose, indicating α-syn overexpression reduces the responsiveness of cells to nutrient deprivation. Moreover, the nutrient deprivation enhanced α-syn aggregations concomitant with significant increase of apoptosis as well as ER stress response, SREBP2 activation and cholesterolgenesis. Importantly, α-syn aggregate accumulation and other effects caused by nutrient deprivation were counteracted by knockdown of SREBP2, treatment with cholesterol lowering agent-lovastatin, or by GRP78 overexpression, which also caused decrease of SREBP2 activity. Similar results were obtained from studies of primary neurons with α-syn overexpression under nutrient deprivation. Together our findings suggested that down-regulation of SREBP2 activity might be a means to prevent α-syn aggregation in PD via reducing cholesterol levels.

α-Synuclein as a ferrireductase

Many proteins associated with neurodegenerative diseases have poorly defined or unknown functions. α-Synuclein is one such protein which is associated with a range of diseases including Parkinson's disease. Now accepted as a metal-binding protein, α-synuclein's function could possibly be defined in relation to the binding of cofactors. It has been suggested recently that α-synuclein is able to reduce iron using copper as its catalytic centre. The consequence of this is that possibly the function of α-synuclein can now be defined. The evidence for this and the consequences for Parkinson's disease are discussed in the present review.

The degeneration and replacement of dopamine cells in Parkinson's disease: the role of aging

Available data show marked similarities for the degeneration of dopamine cells in Parkinson’s disease (PD) and aging. The etio-pathogenic agents involved are very similar in both cases, and include free radicals, different mitochondrial disturbances, alterations of the mitophagy and the ubiquitin-proteasome system. Proteins involved in PD such as α-synuclein, UCH-L1, PINK1 or DJ-1, are also involved in aging. The anomalous behavior of astrocytes, microglia and stem cells of the subventricular zone (SVZ) also changes similarly in aging brains and PD. Present data suggest that PD could be the expression of aging on a cell population with high vulnerability to aging. The future knowledge of mechanisms involved in aging could be critical for both understanding the etiology of PD and developing etiologic treatments to prevent the onset of this neurodegenerative illness and to control its progression.

Phenotypic screens for compounds that target the cellular pathologies underlying Parkinson's disease

Parkinson's disease (PD) is a devastating neurodegenerative disease that affects over one million patients in the US. Yet, no disease modifying drugs exist, only those that temporarily alleviate symptoms. Because of its poorly defined and highly complex disease etiology, it is essential to embrace unbiased and innovative approaches for identifying new chemical entities that target the underlying toxicities associated with PD. Traditional target-based drug discovery paradigm can suffer from a bias toward a small number of potential targets. Phenotypic screening of both genetic and pharmacological PD models offers an alternative approach to discover compounds that target the initiating causes and effectors of cellular toxicity. The relative paucity of reported phenotypic screens illustrates the intrinsic difficulty in establishing model systems that are both biologically meaningful and adaptable to high-throughput screening. Parallel advances in PD models and in vivo screening technologies will help create opportunities for identifying new therapeutic leads with unanticipated, breakthrough mechanisms of action.

Isogenic human iPSC Parkinson's model shows nitrosative stress-induced dysfunction in MEF2-PGC1α transcription

Parkinson's disease (PD) is characterized by loss of A9 dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). An association has been reported between PD and exposure to mitochondrial toxins, including environmental pesticides paraquat, maneb, and rotenone. Here, using a robust, patient-derived stem cell model of PD allowing comparison of A53T α-synuclein (α-syn) mutant cells and isogenic mutation-corrected controls, we identify mitochondrial toxin-induced perturbations in A53T α-syn A9 DA neurons (hNs). We report a pathway whereby basal and toxin-induced nitrosative/oxidative stress results in S-nitrosylation of transcription factor MEF2C in A53T hNs compared to corrected controls. This redox reaction inhibits the MEF2C-PGC1α transcriptional network, contributing to mitochondrial dysfunction and apoptotic cell death. Our data provide mechanistic insight into gene-environmental interaction (GxE) in the pathogenesis of PD. Furthermore, using small-molecule high-throughput screening, we identify the MEF2C-PGC1α pathway as a therapeutic target to combat PD.

Non-motor parkinsonian pathology in aging A53T α-synuclein mice is associated with progressive synucleinopathy and altered enzymatic function

Aging, the main risk factor for Parkinson's disease (PD), is associated with increased α–synuclein levels in substantia nigra pars compacta (SNc). Excess α-synuclein spurs Lewy-like pathology and dysregulates the activity of protein phosphatase 2A (PP2A). PP2A dephosphorylates many neuroproteins, including the catecholamine rate-limiting enzyme, tyrosine hydroxylase (TH). A loss of nigral dopaminergic neurons induces PD movement problems, but before those abnormalities occur, behaviors such as olfactory loss, anxiety, and constipation often manifest. Identifying mouse models with early PD behavioral changes could provide a model in which to test emerging therapeutic compounds. To this end, we evaluated mice expressing A53T mutant human (A53T) α–synuclein for behavior and α–synuclein pathology in olfactory bulb, adrenal gland, and gut. Aging A53T mice exhibited olfactory loss and anxiety that paralleled olfactory and adrenal α-synuclein aggregation. PP2A activity was also diminished in olfactory and adrenal tissues harboring insoluble α-synuclein. Low adrenal PP2A activity co-occurred with TH hyperactivity, making this the first study to link adrenal synucleinopathy to anxiety and catecholamine dysregulation. Aggregated A53T α–synuclein recombinant protein also had impaired stimulatory effects on soluble recombinant PP2A. Collectively, the data identify an excellent model in which to screen compounds for their ability to block the spread of α-synuclein pathology associated with pre-motor stages of PD.

The function of α-synuclein

Human genetics has indicated a causal role for the protein α-synuclein in the pathogenesis of familial Parkinson's disease (PD), and the aggregation of synuclein in essentially all patients with PD suggests a central role for this protein in the sporadic disorder. Indeed, the accumulation of misfolded α-synuclein now defines multiple forms of neural degeneration. Like many of the proteins that accumulate in other neurodegenerative disorders, however, the normal function of synuclein remains poorly understood. In this article, we review the role of synuclein at the nerve terminal and in membrane remodeling. We also consider the prion-like propagation of misfolded synuclein as a mechanism for the spread of degeneration through the neuraxis.

Attenuation of age-related increase of protein carbonylation in the liver of mice by melatonin and curcumin

Protein carbonyls are formed as a consequence of the oxidative modification of proteins by reactive oxygen species and are commonly used as a marker of protein oxidation in cells and tissues. Melatonin has free radical scavenging ability besides its classical role as a hormonal signaling agent. Curcumin, a phytochemical, has a wide variety of biological actions including anti-inflammatory and antioxidative. In the present study, the effects of melatonin and curcumin on age-related carbonyl content of liver in mice were investigated. Young (1 month) and aged (18 month) were administered with melatonin (10 mg/kg body weight) and curcumin (90 mg/kg body weight) in dimethyl sulfoxide intraperitoneally. Livers were excised from each experimental group and processed. The level of protein carbonylation was assessed spectrophotometrically and further confirmed by Western blotting analysis. Protein carbonyls of liver have been found to be significantly higher in 18-month-old mice as compared to 1-month-old mice. The carbonyl content in 1- and 18-month-old mice decreases significantly upon administrations of melatonin and curcumin. This study thus suggests that the formation of protein carbonyls in the liver of the aging mice can be prevented by the antioxidative effects of melatonin and curcumin, which may provide health benefits in aging animals.

Oxidative and nitrative alpha-synuclein modifications and proteostatic stress: implications for disease mechanisms and interventions in synucleinopathies

Alpha-synuclein (ASYN) is a major constituent of the typical protein aggregates observed in several neurodegenerative diseases that are collectively referred to as synucleinopathies. A causal involvement of ASYN in the initiation and progression of neurological diseases is suggested by observations indicating that single-point (e.g., A30P, A53T) or multiplication mutations of the gene encoding for ASYN cause early onset forms of Parkinson's disease (PD). The relative regional specificity of ASYN pathology is still a riddle that cannot be simply explained by its expression pattern. Also, transgenic over-expression of ASYN in mice does not recapitulate the typical dopaminergic neuronal death observed in PD. Thus, additional factors must contribute to ASYN-related toxicity. For instance, synucleinopathies are usually associated with inflammation and elevated levels of oxidative stress in affected brain areas. In turn, these conditions favor oxidative modifications of ASYN. Among these modifications, nitration of tyrosine residues, formation of covalent ASYN dimers, as well as methionine sulfoxidations are prominent examples that are observed in post-mortem PD brain sections. Oxidative modifications can affect ASYN aggregation, as well as its binding to biological membranes. This would affect neurotransmitter recycling, mitochondrial function and dynamics (fission/fusion), ASYN's degradation within a cell and, possibly, the transfer of modified ASYN to adjacent cells. Here, we propose a model on how covalent modifications of ASYN link energy stress, altered proteostasis, and oxidative stress, three major pathogenic processes involved in PD progression. Moreover, we hypothesize that ASYN may act physiologically as a catalytically regenerated scavenger of oxidants in healthy cells, thus performing an important protective role prior to the onset of disease or during aging.

Upregulation of α-synuclein during localized radiation therapy signals the association of cancer-related fatigue with the activation of inflammatory and neuroprotective pathways

PURPOSE

Neuroinflammatory mechanisms are associated with fatigue in neurodegenerative conditions such as Parkinson's. The symptoms in Parkinson's including fatigue are thought to be related to α-synuclein overexpression. This study investigated genomic correlates of fatigue experienced by men with prostate cancer receiving external beam radiation therapy (EBRT).

PATIENTS AND METHODS

Sixteen men with non-metastatic prostate cancer who were scheduled to receive EBRT were enrolled. Fatigue scores and blood were obtained at baseline (prior to EBRT, D0); one hour following initiation of EBRT (D1), day 7 (D7), day 14 (D14), midpoint (days 19-21, D21), completion (days 38-42, D42), and four weeks post-EBRT (days 68-72, D72). Gene expression profiling using microarray analysis was performed from peripheral blood and confirmatory qPCR and protein (ELISA) analyses verified the microarray results. Correlations between fatigue and gene/protein expressions were determined using a mixed model approach.

RESULTS

Microarray data showed significant, differential expression of 463 probesets following EBRT. SNCA had a 2.95-fold change at D21 from baseline. SNCA expression was confirmed by qPCR (p<0.001) and ELISA (p<0.001) over time during EBRT. Fatigue scores were significantly correlated with SNCA gene expression on D14 (r=0.55, p<0.05) and plasma α-synuclein concentrations on D42 of EBRT (r=0.54, p=0.04).

CONCLUSION

Fatigue experienced during EBRT may be mediated by α-synuclein overexpression. Alpha-synuclein may serve as a useful biomarker to understand the mechanisms and pathways related to the development of fatigue in this population.

An in vivo ultrahigh field 14.1 T (1) H-MRS study on 6-OHDA and α-synuclein-based rat models of Parkinson's disease: GABA as an early disease marker

The detection of Parkinson's disease (PD) in its preclinical stages prior to outright neurodegeneration is essential to the development of neuroprotective therapies and could reduce the number of misdiagnosed patients. However, early diagnosis is currently hampered by lack of reliable biomarkers. (1) H magnetic resonance spectroscopy (MRS) offers a noninvasive measure of brain metabolite levels that allows the identification of such potential biomarkers. This study aimed at using MRS on an ultrahigh field 14.1 T magnet to explore the striatal metabolic changes occurring in two different rat models of the disease. Rats lesioned by the injection of 6-hydroxydopamine (6-OHDA) in the medial-forebrain bundle were used to model a complete nigrostriatal lesion while a genetic model based on the nigral injection of an adeno-associated viral (AAV) vector coding for the human α-synuclein was used to model a progressive neurodegeneration and dopaminergic neuron dysfunction, thereby replicating conditions closer to early pathological stages of PD. MRS measurements in the striatum of the 6-OHDA rats revealed significant decreases in glutamate and N-acetyl-aspartate levels and a significant increase in GABA level in the ipsilateral hemisphere compared with the contralateral one, while the αSyn overexpressing rats showed a significant increase in the GABA striatal level only. Therefore, we conclude that MRS measurements of striatal GABA levels could allow for the detection of early nigrostriatal defects prior to outright neurodegeneration and, as such, offers great potential as a sensitive biomarker of presymptomatic PD.

What's to like about the prion-like hypothesis for the spreading of aggregated α-synuclein in Parkinson disease?

α-Synuclein is a key protein in Parkinson disease. Not only is it the major protein component of Lewy bodies, but it is implicated in several cellular processes that are disrupted in Parkinson disease. Misfolded α-synuclein has also been shown to spread from cell-to-cell and, in a prion-like fashion, trigger aggregation of α-synuclein in the recipient cell. In this mini-review we explore the evidence that misfolded α-synuclein underlies the spread of pathology in Parkinson disease and discuss why it should be considered a prion-like protein.

Adenosine monophosphate-activated protein kinase overactivation leads to accumulation of α-synuclein oligomers and decrease of neurites

Neuronal inclusions of α-synuclein (α-syn), termed Lewy bodies, are a hallmark of Parkinson disease (PD). Increased α-syn levels can occur in brains of aging human and neurotoxin-treated mice. Because previous studies have shown increased brain lactate levels in aging brains, in PD affected subjects when compared with age-matched controls, and in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP), we tested the effects of lactate exposure on α-syn in a cell-based study. We demonstrated that (1) lactate treatment led to α-syn accumulation and oligomerization in a time- and concentration-dependent manner; (2) such alterations were mediated via adenosine monophosphate-activated protein kinase (AMPK) and associated with increasing cytoplasmic phosphorylated AMPK levels; (3) AMPK activation facilitated α-syn accumulation and phosphorylation; (4) lactate treatment or overexpression of the active form of AMPK decreased α-syn turnover and neurite outgrowth; and (5) Lewy body-bearing neurons displayed abnormal cytoplasmic distribution of phosphorylated AMPK, which normally is located in nuclei. Together, our results suggest that chronic neuronal accumulation of α-syn induced by lactate-triggered AMPK activation in aging brains might be a novel mechanism underlying α-synucleinopathies in PD and related disorders.

The role of free radicals in the aging brain and Parkinson's Disease: convergence and parallelism

Free radical production and their targeted action on biomolecules have roles in aging and age-related disorders such as Parkinson's disease (PD). There is an age-associated increase in oxidative damage to the brain, and aging is considered a risk factor for PD. Dopaminergic neurons show linear fallout of 5-10% per decade with aging; however, the rate and intensity of neuronal loss in patients with PD is more marked than that of aging. Here, we enumerate the common link between aging and PD at the cellular level with special reference to oxidative damage caused by free radicals. Oxidative damage includes mitochondrial dysfunction, dopamine auto-oxidation, α-synuclein aggregation, glial cell activation, alterations in calcium signaling, and excess free iron. Moreover, neurons encounter more oxidative stress as a counteracting mechanism with advancing age does not function properly. Alterations in transcriptional activity of various pathways, including nuclear factor erythroid 2-related factor 2, glycogen synthase kinase 3β, mitogen activated protein kinase, nuclear factor kappa B, and reduced activity of superoxide dismutase, catalase and glutathione with aging might be correlated with the increased incidence of PD.

Increased α-synuclein phosphorylation and nitration in the aging primate substantia nigra

Post-translational modifications of α-synuclein occur in the brain of patients affected by Parkinson's disease and other α-synucleinopathies, as indicated by the accumulation of Lewy inclusions containing phosphorylated (at serine 129) and nitrated α-synuclein. Here we found that phospho-Ser 129 and nitrated α-synuclein are also formed within dopaminergic neurons of the monkey substantia nigra as a result of normal aging. Dopaminergic cell bodies immunoreactive for phospho-Ser 129 and nitrated α-synuclein were rarely seen in adult mature animals but became significantly more frequent in the substantia nigra of old primates. Dual labeling with antibodies against phospho-Ser 129 and nitrated α-synuclein revealed only limited colocalization and mostly stained distinct sub-populations of dopaminergic neurons. Age-related elevations of modified protein paralleled an increase in the number of neurons immunoreactive for unmodified α-synuclein, supporting a relationship between higher levels of normal protein and enhanced phosphorylation/nitration. Other mechanisms were also identified that likely contribute to α-synuclein modifications. In particular, increased expression of Polo-like kinase 2 within neurons of older animals could contribute to phospho-Ser 129 α-synuclein production. Data also indicate that a pro-oxidant environment characterizes older neurons and favors α-synuclein nitration. Aging is an unequivocal risk factor for human α-synucleinopathies. These findings are consistent with a mechanistic link between aging, α-synuclein abnormalities and enhanced vulnerability to neurodegenerative processes.

Accumulation of toxic α-synuclein oligomer within endoplasmic reticulum occurs in α-synucleinopathy in vivo

In Parkinson's disease (PD) and other α-synucleinopathies, prefibrillar α-synuclein (αS) oligomer is implicated in the pathogenesis. However, toxic αS oligomers observed using in vitro systems are not generally seen to be associated with α-synucleinopathy in vivo. Thus, the pathologic significance of αS oligomers to αS neurotoxicity is unknown. Herein, we show that, αS that accumulate within endoplasmic reticulum (ER)/microsome forms toxic oligomers in mouse and human brain with the α-synucleinopathy. In the mouse model of α-synucleinopathy, αS oligomers initially form before the onset of disease and continue to accumulate with the disease progression. Significantly, treatment of αS transgenic mice with Salubrinal, an anti-ER stress compound that delays the onset of disease, reduces ER accumulation of αS oligomers. These results indicate that αS oligomers with toxic conformation accumulate in ER, and αS oligomer-dependent ER stress is pathologically relevant for PD.

Endoplasmic reticulum stress is important for the manifestations of α-synucleinopathy in vivo

Accumulation of misfolded α-synuclein (αS) is mechanistically linked to neurodegeneration in Parkinson's disease (PD) and other α-synucleinopathies. However, how αS causes neurodegeneration is unresolved. Because cellular accumulation of misfolded proteins can lead to endoplasmic reticulum stress/unfolded protein response (ERS/UPR), chronic ERS could contribute to neurodegeneration in α-synucleinopathy. Using the A53T mutant human αS transgenic (A53TαS Tg) mouse model of α-synucleinopathy, we show that disease onset in the αS Tg model is coincident with induction of ER chaperones in neurons exhibiting αS pathology. However, the neuronal ER chaperone induction was not accompanied by the activation of phospho-eIF2α, indicating that α-synucleinopathy is associated with abnormal UPR that could promote cell death. Induction of ERS/UPR was associated with increased levels of ER/microsomal (ER/M) associated αS monomers and aggregates. Significantly, human PD cases also exhibit higher relative levels of ER/M αS than the control cases. Moreover, αS interacts with ER chaperones and overexpression of αS sensitizes neuronal cells to ERS-induced toxicity, suggesting that αS may have direct impact on ER function. This view is supported by the presence of ERS-activated caspase-12 and the accumulation of ER-associated polyubiquitin. More important, treatment with Salubrinal, an anti-ERS compound, significantly attenuates disease manifestations in both the A53TαS Tg mouse model and the adeno-associated virus-transduced rat model of A53TαS-dependent dopaminergic neurodegeneration. Our data indicate that the accumulation αS within ER leads to chronic ER stress conditions that contribute to neurodegeneration in α-synucleinopathies. Attenuating chronic ERS could be an effective therapy for PD and other α-synucleinopathies.

α-Synuclein mRNA and soluble α-synuclein protein levels in post-mortem brain from patients with Parkinson's disease, dementia with Lewy bodies, and Alzheimer's disease

α-Synuclein is a neuronal protein implicated in the etiology of Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Whilst increased α-synuclein expression due to gene duplication or triplication can cause familial PD, previous studies of α-synuclein levels in idiopathic disease have produced conflicting data. We quantified α-synuclein mRNA and soluble protein in five human post-mortem brain regions from four groups of individuals with PD, DLB, Alzheimer's disease (AD) and matched controls. α-Synuclein mRNA levels, measured using quantitative real-time PCR, did not differ significantly between groups in any brain regions examined. In contrast, levels of soluble α-synuclein protein, measured by ELISA, were significantly lower in 4 of the 5 regions for patients with DLB, and in 2 of the 5 regions for patients with PD, compared to controls. Soluble α-synuclein protein levels were not significantly different in the AD patients, compared to controls, in 4 of the 5 regions. This study indicates that although levels of soluble α-synuclein protein are lower in DLB and PD, there is no evidence for a corresponding decrease in α-synuclein mRNA levels. This might result from altered translation, or removal of α-synuclein protein from a soluble detectable state, either by turnover or conversion to an insoluble form.

What genetics tells us about the causes and mechanisms of Parkinson's disease

Parkinson's disease (PD) is a common motor disorder of mysterious etiology. It is due to the progressive degeneration of the dopaminergic neurons of the substantia nigra and is accompanied by the appearance of intraneuronal inclusions enriched in α-synuclein, the Lewy bodies. It is becoming increasingly clear that genetic factors contribute to its complex pathogenesis. Over the past decade, the genetic basis of rare PD forms with Mendelian inheritance, representing no more than 10% of the cases, has been investigated. More than 16 loci and 11 associated genes have been identified so far; genome-wide association studies have provided convincing evidence that polymorphic variants in these genes contribute to sporadic PD. The knowledge acquired of the functions of their protein products has revealed pathways of neurodegeneration that may be shared between inherited and sporadic PD. An impressive set of data in different model systems strongly suggest that mitochondrial dysfunction plays a central role in clinically similar, early-onset autosomal recessive PD forms caused by parkin and PINK1, and possibly DJ-1 gene mutations. In contrast, α-synuclein accumulation in Lewy bodies defines a spectrum of disorders ranging from typical late-onset PD to PD dementia and including sporadic and autosomal dominant PD forms due to mutations in SCNA and LRRK2. However, the pathological role of Lewy bodies remains uncertain, as they may or may not be present in PD forms with one and the same LRRK2 mutation. Impairment of autophagy-based protein/organelle degradation pathways is emerging as a possible unifying but still fragile pathogenic scenario in PD. Strengthening these discoveries and finding other convergence points by identifying new genes responsible for Mendelian forms of PD and exploring their functions and relationships are the main challenges of the next decade. It is also the way to follow to open new promising avenues of neuroprotective treatment for this devastating disorder.

Α-synuclein neuropathology is controlled by nuclear hormone receptors and enhanced by docosahexaenoic acid in a mouse model for Parkinson's disease

α-Synuclein (α-Syn) is a neuronal protein that accumulates progressively in Parkinson's disease (PD) and related synucleinopathies. Attempting to identify cellular factors that affect α-Syn neuropathology, we previously reported that polyunsaturated fatty acids (PUFAs) promote α-Syn oligomerization and aggregation in cultured cells. We now report that docosahexaenoic acid (DHA), a 22:6 PUFA, affects α-Syn oligomerization by activating retinoic X receptor (RXR) and peroxisome proliferator-activated receptor γ2 (PPARγ2). In addition, we show that dietary changes in brain DHA levels affect α-Syn cytopathology in mice transgenic for the PD-causing A53T mutation in human α-Syn. A diet enriched in DHA, an activating ligand of RXR, increased the accumulation of soluble and insoluble neuronal α-Syn, neuritic injury and astrocytosis. Conversely, abnormal accumulations of α-Syn and its deleterious effects were significantly attenuated by low dietary DHA levels. Our results suggest a role for activated RXR/PPARγ 2, obtained by elevated brain PUFA levels, in α-Syn neuropathology.

A feedforward loop links Gaucher and Parkinson's diseases?

Mutations in the GBA gene that encodes glucocerebrosidase cause the lysosomal storage disorder Gaucher disease but also increase the risk for Parkinson's disease. Mazzulli et al. (2011) uncover a possible mechanism to explain this connection: loss of glucocerebrosidase creates a positive feedback loop of reduced lysosomal function and α-synuclein accumulation, ultimately leading to neurodegeneration.

Trichloroethylene and Parkinson disease

Multiple genetic and environmental etiologies have been implicated in the pathogenesis of idiopathic Parkinson disease. Recent observations have suggested an association between chronic exposure to trichloroethylene (TCE) and development of clinical parkinsonism. Animal models of TCE exposure have shown nigrostriatal degeneration and the development of parkinsonian features. Animal and cell culture models indicate mitochondrial dysfunction as the probable mechanism, most likely mediated by TaClo, a potential TCE metabolite. These observations endorse the hypothesis that a variety of environmental risk factors may cause nigrostriatal degeneration and clinical parkinsonism in genetically predisposed individuals.

Ageing as a primary risk factor for Parkinson's disease: evidence from studies of non-human primates

Ageing is the greatest risk factor for the development of Parkinson's disease. However, the current dogma holds that cellular mechanisms that are associated with ageing of midbrain dopamine neurons and those that are related to dopamine neuron degeneration in Parkinson's disease are unrelated. We propose, based on evidence from studies of non-human primates, that normal ageing and the degeneration of dopamine neurons in Parkinson's disease are linked by the same cellular mechanisms and, therefore, that markers of cellular risk factors accumulate with age in a pattern that mimics the pattern of degeneration observed in Parkinson's disease. We contend that ageing induces a pre-parkinsonian state, and that the cellular mechanisms of dopamine neuron demise during normal ageing are accelerated or exaggerated in Parkinson's disease through a combination of genetic and environmental factors.

Transcriptional regulation of the beta-synuclein 5'-promoter metal response element by metal transcription factor-1

The progression of many human neurodegenerative disorders is associated with an accumulation of alpha-synuclein. Alpha-synuclein belongs to the homologous synuclein family, which includes beta-synuclein. It has been proposed that beta-synuclein may be a natural regulator of alpha-synuclein. Therefore controlling beta-synuclein expression may control the accumulation of alpha-synuclein and ultimately prevent disease progression. The regulation of synucleins is poorly understood. We investigated the transcriptional regulation of beta-synuclein, with the aim of identifying molecules that differentially control beta-synuclein expression levels. To investigate transcriptional regulation of beta-synuclein, we used reporter gene assays and bioinformatics. We identified a region -1.1/-0.6 kb upstream of the beta-synuclein translational start site to be a key regulatory region of beta-synuclein 5'-promoter activity in human dopaminergic cells (SH-SY5Y). Within this key promoter region we identified a metal response element pertaining to a putative Metal Transcription Factor-1 (MTF-1) binding site. We demonstrated that MTF-1 binds to this 5'-promoter region using EMSA analysis. Moreover, we showed that MTF-1 differentially regulates beta-synuclein promoter binding site, as well as beta-synuclein mRNA and protein expression. This effect of MTF-1 on expression was found to be specific to beta-synuclein when compared to alpha-synuclein. Understanding the regulation of synucleins and how they interact may point to molecular targets that could be manipulated for therapeutic benefit. In this study we showed that MTF-1 differentially controls the expression of beta-synuclein when compared to its homolog alpha-synuclein. This could potentially provide a novel targets or pathways for therapeutic intervention and/or treatment of synucleinopathies.