Role of alpha-synuclein in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in mice

Oxidative stress in genetic mouse models of Parkinson's disease

There is extensive evidence in Parkinson's disease of a link between oxidative stress and some of the monogenically inherited Parkinson's disease-associated genes. This paper focuses on the importance of this link and potential impact on neuronal function. Basic mechanisms of oxidative stress, the cellular antioxidant machinery, and the main sources of cellular oxidative stress are reviewed. Moreover, attention is given to the complex interaction between oxidative stress and other prominent pathogenic pathways in Parkinson's disease, such as mitochondrial dysfunction and neuroinflammation. Furthermore, an overview of the existing genetic mouse models of Parkinson's disease is given and the evidence of oxidative stress in these models highlighted. Taken into consideration the importance of ageing and environmental factors as a risk for developing Parkinson's disease, gene-environment interactions in genetically engineered mouse models of Parkinson's disease are also discussed, highlighting the role of oxidative damage in the interplay between genetic makeup, environmental stress, and ageing in Parkinson's disease.

Gene-environment interactions in Parkinson's disease: specific evidence in humans and mammalian models

Interactions between genetic factors and environmental exposures are thought to be major contributors to the etiology of Parkinson's disease. While such interactions are poorly defined and incompletely understood, recent epidemiological studies have identified specific interactions of potential importance to human PD. In this review, the most current data on gene-environment interactions in PD from human studies are critically discussed. Animal models have also highlighted the importance of genetic susceptibility to toxicant exposure and data of potential relevance to human PD are discussed. Goals and needs for the future of the field are proposed.

Mitochondrial dysfunction in Parkinson's disease: molecular mechanisms and pathophysiological consequences

Neurons are critically dependent on mitochondrial integrity based on specific morphological, biochemical, and physiological features. They are characterized by high rates of metabolic activity and need to respond promptly to activity-dependent fluctuations in bioenergetic demand. The dimensions and polarity of neurons require efficient transport of mitochondria to hot spots of energy consumption, such as presynaptic and postsynaptic sites. Moreover, the postmitotic state of neurons in combination with their exposure to intrinsic and extrinsic neuronal stress factors call for a high fidelity of mitochondrial quality control systems. Consequently, it is not surprising that mitochondrial alterations can promote neuronal dysfunction and degeneration. In particular, mitochondrial dysfunction has long been implicated in the etiopathogenesis of Parkinson's disease (PD), based on the observation that mitochondrial toxins can cause parkinsonism in humans and animal models. Substantial progress towards understanding the role of mitochondria in the disease process has been made by the identification and characterization of genes causing familial variants of PD. Studies on the function and dysfunction of these genes revealed that various aspects of mitochondrial biology appear to be affected in PD, comprising mitochondrial biogenesis, bioenergetics, dynamics, transport, and quality control.

The hypoxia imaging agent CuII(atsm) is neuroprotective and improves motor and cognitive functions in multiple animal models of Parkinson's disease

The PET imaging agent Cu^II(atsm) improves motor and cognitive function in Parkinson’s disease.

Parkinson’s disease (PD) is a progressive, chronic disease characterized by dyskinesia, rigidity, instability, and tremors. The disease is defined by the presence of Lewy bodies, which primarily consist of aggregated α-synuclein protein, and is accompanied by the loss of monoaminergic neurons. Current therapeutic strategies only give symptomatic relief of motor impairment and do not address the underlying neurodegeneration. Hence, we have identified Cu^II(atsm) as a potential therapeutic for PD. Drug administration to four different animal models of PD resulted in improved motor and cognition function, rescued nigral cell loss, and improved dopamine metabolism. In vitro, this compound is able to inhibit the effects of peroxynitrite-driven toxicity, including the formation of nitrated α-synuclein oligomers. Our results show that Cu^II(atsm) is effective in reversing parkinsonian defects in animal models and has the potential to be a successful treatment of PD.

Parkinson's disease

Parkinson's disease (PD) is the most common age-related motoric neurodegenerative disease initially described in the 1800's by James Parkinson as the 'Shaking Palsy'. Loss of the neurotransmitter dopamine was recognized as underlying the pathophysiology of the motor dysfunction; subsequently discovery of dopamine replacement therapies brought substantial symptomatic benefit to PD patients. However, these therapies do not fully treat the clinical syndrome nor do they alter the natural history of this disorder motivating clinicians and researchers to further investigate the clinical phenotype, pathophysiology/pathobiology and etiology of this devastating disease. Although the exact cause of sporadic PD remains enigmatic studies of familial and rare toxicant forms of this disorder have laid the foundation for genome wide explorations and environmental studies. The combination of methodical clinical evaluation, systematic pathological studies and detailed genetic analyses have revealed that PD is a multifaceted disorder with a wide-range of clinical symptoms and pathology that include regions outside the dopamine system. One common thread in PD is the presence of intracytoplasmic inclusions that contain the protein, α-synuclein. The presence of toxic aggregated forms of α-synuclein (e.g., amyloid structures) are purported to be a harbinger of subsequent pathology. In fact, PD is both a cerebral amyloid disease and the most common synucleinopathy, that is, diseases that display accumulations of α-synuclein. Here we present our current understanding of PD etiology, pathology, clinical symptoms and therapeutic approaches with an emphasis on misfolded α-synuclein.

Hypokinesia and reduced dopamine levels in zebrafish lacking β- and γ1-synucleins

α-Synuclein is strongly implicated in the pathogenesis of Parkinson disease. However, the normal functions of synucleins and how these relate to disease pathogenesis are uncertain. We characterized endogenous zebrafish synucleins in order to develop tractable models to elucidate the physiological roles of synucleins in neurons in vivo. Three zebrafish genes, sncb, sncg1, and sncg2 (encoding β-, γ1-, and γ2-synucleins respectively), show extensive phylogenetic conservation with respect to their human paralogues. A zebrafish α-synuclein orthologue was not found. Abundant 1.45-kb sncb and 2.7-kb sncg1 mRNAs were detected in the CNS from early development through adulthood and showed overlapping but distinct expression patterns. Both transcripts were detected in catecholaminergic neurons throughout the CNS. Zebrafish lacking β-, γ1-, or both synucleins during early development showed normal CNS and body morphology but exhibited decreased spontaneous motor activity that resolved as gene expression recovered. Zebrafish lacking both β- and γ1-synucleins were more severely hypokinetic than animals lacking one or the other synuclein and showed delayed differentiation of dopaminergic neurons and reduced dopamine levels. Phenotypic abnormalities resulting from loss of endogenous zebrafish synucleins were rescued by expression of human α-synuclein. These data demonstrate that synucleins have essential phylogenetically conserved neuronal functions that regulate dopamine homeostasis and spontaneous motor behavior. Zebrafish models will allow further elucidation of the molecular physiology and pathophysiology of synucleins in vivo.

Synuclein modulation of monoamine transporters

Although well-studied in the context of neurodegenerative disease, a clear biological function for the synuclein proteins remains elusive. Emerging data indicate a role for synucleins in monoamine neurotransmitter homeostasis. A key regulatory component of monoamine neurotransmission is re-uptake of neurotransmitter by the dopamine transporter, norepinephrine transporter, and serotonin transporter, which are common drug targets in the treatment of depression and other mood disorders. Through interactions with these transporters, the neuronal cytoskeleton, and pre-synaptic scaffolding proteins, α-synuclein, β-synuclein, and γ-synuclein modulate trafficking, expression and function of monoamine transporters at the cell surface, thus playing a central role in regulating monoamine re-uptake.

19F NMR studies of α-synuclein-membrane interactions

α-Synuclein function is thought to be related to its membrane binding ability. Solution NMR studies have identified several α-synuclein-membrane interaction modes in small unilamellar vesicles (SUVs), but how membrane properties affect binding remains unclear. Here, we use (19)F NMR to study α-synuclein-membrane interactions by using 3-fluoro-L-tyrosine (3FY) and trifluoromethyl-L-phenylalanine (tfmF) labeled proteins. Our results indicate that the affinity is affected by both the head group and the acyl chain of the SUV. Negatively charged head groups have higher affinity, but different head groups with the same charge also affect binding. We show that the saturation of the acyl chain has a dramatic effect on the α-synuclein-membrane interactions by studying lipids with the same head group but different chains. Taken together, the data show that α-synuclein's N-terminal region is the most important determinate of SUV binding, but its C-terminal region also modulates the interactions. Our data support the existence of multiple tight phospholipid-binding modes, a result incompatible with the model that α-synuclein lies solely on the membrane surface.

Biochemical and morphological consequences of human α-synuclein expression in a mouse α-synuclein null background

A consensus about the functions of human wild-type or mutated α-synuclein (αSYN) is lacking. Both forms of αSYN are implicated in Parkinson's disease, whereas the wild-type form is implicated in substance abuse. Interactions with other cellular proteins and organelles may meditate its functions. We developed a series of congenic mouse lines containing various allele doses or combinations of the human wild-type αSYN (hwαSYN) or a doubly mutated (A30P*A53T) αSYN (hm(2) αSYN) in a C57Bl/6J line spontaneously deleted in mouse αSYN (C57BL/6JOla). Both transgenes had a functional role in the nigrostriatal system, demonstrated by significant elevations in striatal catecholamines, metabolites and the enzyme tyrosine hydroxylase compared with null-mice without a transgene. Consequences occurred when the transgenes were expressed at a fraction of the endogenous level. Hemizygous congenic mice did not exhibit any change in the number or size of dopaminergic neurons in the ventral midbrain at 9 months of age. Human αSYN was predominantly located in neuronal cell bodies, neurites, synapses, and in intraneuronal/intraneuritic aggregates. The hm(2) αSYN transgene resulted in more aggregates and dystrophic neurites than did the hw5 transgene. The hwαSYN transgene resulted in higher expression of two striatal proteins, synaptogamin 7 and UCHL1, compared with the levels of the hm(2) αSYN transgene. These observations suggest that mutations in αSYN may impair specific functional domains, leaving others intact. These lines may be useful for exploring interactions between hαSYN and environmental or genetic risk factors in dopamine-related disorders using a mouse model.

Resistance to MPTP-neurotoxicity in α-synuclein knockout mice is complemented by human α-synuclein and associated with increased β-synuclein and Akt activation

Genetic and biochemical abnormalities of α-synuclein are associated with the pathogenesis of Parkinson's disease. In the present study we investigated the in vivo interaction of mouse and human α-synuclein with the potent parkinsonian neurotoxin, MPTP. We find that while lack of mouse α-synuclein in mice is associated with reduced vulnerability to MPTP, increased levels of human α-synuclein expression is not associated with obvious changes in the vulnerability of dopaminergic neurons to MPTP. However, expressing human α-synuclein variants (human wild type or A53T) in the α-synuclein null mice completely restores the vulnerability of nigral dopaminergic neurons to MPTP. These results indicate that human α-synuclein can functionally replace mouse α-synuclein in regard to vulnerability of dopaminergic neurons to MPTP-toxicity. Significantly, α-synuclein null mice and wild type mice were equally sensitive to neurodegeneration induced by 2′NH₂-MPTP, a MPTP analog that is selective for serotoninergic and noradrenergic neurons. These results suggest that effects of α-synuclein on MPTP like compounds are selective for nigral dopaminergic neurons. Immunoblot analysis of β-synuclein and Akt levels in the mice reveals selective increases in β-synuclein and phosphorylated Akt levels in ventral midbrain, but not in other brain regions, of α-synuclein null mice, implicating the α-synuclein-level dependent regulation of β-synuclein expression in modulation of MPTP-toxicity by α-synuclein. Together these findings provide new mechanistic insights on the role α-synuclein in modulating neurodegenerative phenotypes by regulation of Akt-mediated cell survival signaling in vivo.

Toxin-induced and genetic animal models of Parkinson's disease

Parkinson's disease (PD) is a common progressive neurodegenerative disorder. The major pathological hallmarks of PD are the selective loss of nigrostriatal dopaminergic neurons and the presence of intraneuronal aggregates termed Lewy bodies (LBs), but the pathophysiological mechanisms are not fully understood. Epidemiologically, environmental neurotoxins such as pesticides are promising candidates for causative factors of PD. Oxidative stress and mitochondrial dysfunction induced by these toxins could contribute to the progression of PD. While most cases of PD are sporadic, specific mutations in genes that cause familial forms of PD have led to provide new insights into its pathogenesis. This paper focuses on animal models of both toxin-induced and genetically determined PD that have provided significant insight for understanding this disease. We also discuss the validity, benefits, and limitations of representative models.

α-Synuclein and dopamine at the crossroads of Parkinson's disease

α-Synuclein is central to the Lewy body neuropathology of Parkinson's disease (PD), a devastating neurodegenerative disorder characterized by numerous motor and non-motor manifestations. The cardinal motor symptoms are linked to death of dopaminergic neurons in the nigrostriatal pathway. Here we ask why these neurons are preferentially susceptible to neurodegeneration in PD and how α-synuclein is involved. To address these questions we bring together recent findings from genome-wide association studies, which reveal the involvement of α-synuclein gene variants in sporadic PD, with recent studies highlighting important roles for α-synuclein in synaptic transmission and dopaminergic neuron physiology. These latest advances add to our understanding of PD etiology and provide a central link between the genetic findings and neurodegeneration observed in sporadic PD.

Neuromuscular pathology in mice lacking alpha-synuclein

This work was undertaken in order to study the possible role of alpha-synuclein in the function of the neuro-muscular junction in skeletal muscles. Repeated stimulation of skeletal muscle motor neurons revealed signs of neuromuscular pathology in alpha-synuclein null mutated (C57Bl/6JOlaHsd) and knockout (B6;129X1-Snca(tm1Rosl)/J) mice. This stimulation produced repetitive compound muscle action potentials in both lines of alpha-synuclein deficient mice. Muscle strength and muscle coordination during ambulation were unaffected, though motor learning was slower in alpha-synuclein deficient mice in the Rotarod test. We conclude that alpha-synuclein may play a role in acetylcholine compartmentalization at the neuromuscular junction, and in the fine control of activity of skeletal muscles.

Alpha-synuclein deficiency leads to increased glyoxalase I expression and glycation stress

The presynaptic protein alpha-synuclein has received much attention because its gain-of-function is associated with Parkinson's disease. However, its physiological function is still poorly understood. We studied brain regions of knock-out mice at different ages with regard to consistent upregulations of the transcriptome and focused on glyoxalase I (GLO1). The microarray data were confirmed in qPCR, immunoblot, enzyme activity, and behavior analyses. GLO1 induction is a known protective cellular response to glucose stress, representing efforts to decrease toxic levels of methylglyoxal (MG), glyoxal and advanced glycation endproducts (AGEs). Mass spectrometry quantification demonstrated a ubiquitous increase in MG and fructosyl-lysine as consequences of glucose toxicity, and consistent enhancement of certain AGEs. Thus, GLO1 induction in KO brain seems insufficient to prevent AGE formation. In conclusion, the data demonstrate GLO1 expression and glycation damage to be induced by alpha-synuclein ablation. We propose that wild-type alpha-synuclein modulates brain glucose metabolism.

In vivo RNAi-mediated alpha-synuclein silencing induces nigrostriatal degeneration

Two small-interfering RNAs (siRNAs) targeting alpha-synuclein (alpha-syn) and three control siRNAs were cloned in an adeno-associated virus (AAV) vector and unilaterally injected into rat substantia nigra pars compacta (SNc). Reduction of alpha-syn resulted in a rapid (4 week) reduction in the number of tyrosine hydroxylase (TH) positive cells and striatal dopamine (DA) on the injected side. The level of neurodegeneration induced by the different siRNAs correlated with their ability to downregulate alpha-syn protein and mRNA in tissue culture and in vivo. Examination of various SNc neuronal markers indicated that neurodegeneration was due to cell loss and not just downregulation of DA synthesis. Reduction of alpha-syn also resulted in a pronounced amphetamine induced behavioral asymmetry consistent with the level of neurodegeneration. In contrast, none of the three control siRNAs, which targeted genes not normally expressed in SNc, showed evidence of neurodegeneration or behavioral asymmetry, even at longer survival times. Moreover, co-expression of both rat alpha-syn and alpha-syn siRNA partially reversed the neurodegenerative and behavioral effects of alpha-syn siRNA alone. Our data show that alpha-syn plays an important role in the rat SNc and suggest that both up- and downregulation of wild-type alpha-syn expression increase the risk of nigrostriatal pathology.

Over-expression of alpha-synuclein in the nervous system enhances axonal degeneration after peripheral nerve lesion in a transgenic mouse strain

Wallerian degeneration in peripheral nerves occurs after a traumatic insult when the distal nerve part degenerates while peripheral macrophages enter the nerve stump and remove the accruing debris by phagozytosis. We used an experimental model to investigate the effect of either the absence or over-expression of alpha-synuclein (alpha-syn) after transecting the sciatic nerves of mice. alpha-Synuclein is a major component of Lewy bodies and its aggregation results in a premature destruction of nerve cells. It has also been found present in different peripheral nerves but its role in the axon remains still unclear. Following sciatic nerve transection in different mouse strains, we investigated the numbers of invading macrophages, the amounts of remaining myelin and axons 6 days after injury. All mice showed clear signs of Wallerian degeneration, but transgenic mice expressing human wild-type alpha-syn showed lower numbers of invading macrophages, less preserved myelin and significantly lower numbers of preserved axons in comparison with either knockout mice or a mouse strain with a spontaneous deletion of alpha-syn. The use of protein aggregation filtration blots and paraffin-embedded tissue blots displayed depositions of alpha-syn aggregates within sciatic nerve axons of transgenic mice. Thicker myelin sheaths and higher numbers of mitochondria were detected in old alpha-syn transgenic mice. In a human sural nerve, alpha-syn could also be identified within axons. Thus, alpha-syn and its aggregates are not only a component of Lewy bodies and synapses but also of axons and these aggregates might interfere with axonal transport. alpha-Synuclein transgenic mice represent an appropriate model for investigations on axonal transport in neurodegenerative diseases.

Vulnerability of peripheral catecholaminergic neurons to MPTP is not regulated by alpha-synuclein

Although generally considered a prototypical movement disorder, Parkinson's disease is commonly associated with a broad-spectrum of non-motor symptoms, including autonomic dysfunctions caused by significant alterations in catecholaminergic neurons of the peripheral sympathetic nervous system. Here we present evidence that alpha-synuclein is highly expressed by sympathetic ganglion neurons throughout embryonic and postnatal life and that it is found in tyrosine hydroxylase-positive sympathetic fibers innervating the heart of adult mice. However, mice deficient in alpha-synuclein do not exhibit any apparent alterations in sympathetic development. Sympathetic neurons isolated from mouse embryos and early postnatal mice are sensitive to the parkinsonian drug MPTP/MPP(+) and intoxication requires entry of the neurotoxin through the noradrenaline transporter. Furthermore, recovery of noradrenaline from cardiac sympathetic fibers is reduced in adult mice treated with MPTP systemically. However, MPP(+)-induced sympathetic neuron loss in vitro or MPTP-induced cardiac noradrenaline depletion in vivo is not modified in mice lacking alpha-synuclein. This is in clear contrast with the observation that dopaminergic neurons of the central nervous system are significantly less vulnerable to MPTP/MPP(+) in the absence of alpha-synuclein, suggesting different actions of this molecule in central and peripheral catecholaminergic neurons.

Parkinson's disease: Exit toxins, enter genetics

Parkinson's disease was long considered a non-hereditary disorder. Despite extensive research trying to find environmental risk factors for the disease, genetic variants now stand out as the major causative factor. Since a number of genes have been implicated in the pathogenesis it seems likely that several molecular pathways and downstream effectors can affect the trophic support and/or the survival of dopamine neurons, subsequently leading to Parkinson's disease. The present review describes how toxin-based animal models have been valuable tools in trying to find the underlying mechanisms of disease, and how identification of disease-linked genes in humans has led to the development of new transgenic rodent models. The review also describes the current status of the most common genetic susceptibility factors for Parkinson's disease identified up to today.

Alpha-synuclein deficiency in the C57BL/6JOlaHsd strain does not modify disease progression in the ME7-model of prion disease

We previously detailed how intrahippocampal inoculation of C57BL/6J mice with murine modified scrapie (ME7) leads to chronic neurodegeneration (Cunningham C, Deacon R, Wells H, Boche D, Waters S, Diniz CP, Scott H, Rawlins JN, Perry VH (2003) Eur J Neurosci 17:2147-2155.). Our characterization of the ME7-model is based on inoculation of this murine modified scrapie agent into C57BL/6J mice from Harlan laboratories. This agent in the C57BL/6J host generates a disease that spans a 24-week time course. The hippocampal pathology shows progressive misfolded prion (PrP(Sc)) deposition, astrogliosis and leads to behavioural dysfunction underpinned by the early synaptic loss that precedes neuronal death. The Harlan C57BL/6J, although widely used as a wild type mouse, are a sub-strain harbouring a spontaneous deletion of alpha-synuclein with the full description C57BL/6JOlaHsd. Recently alpha-synuclein has been shown to ameliorate the synaptic loss in a mouse model lacking the synaptic chaperone CSP-alpha. This opens a potential confound of the ME7-model, particularly with respect to the signature synaptic loss that underpin the physiological and behavioural dysfunction. To investigate if this strain-selective loss of a candidate disease modifier impacts on signature ME7 pathology, we compared cohorts of C57BL/6JOlaHsd (alpha-synuclein negative) with the founder strain from Charles Rivers (C57BL/6JCrl, alpha-synuclein positive). There were subtle changes in behaviour when comparing control animals from the two sub-strains indicating potentially significant consequences for studies assuming neurobiogical identity of both strains. However, there was no evidence that the absence of alpha-synuclein modifies disease. Indeed, accumulation of PrP(Sc), synaptic loss and the behavioural dysfunction associated with the ME7-agent was the same in both genetic backgrounds. Our data suggest that alpha-synuclein deficiency does not contribute to the compartment specific processes that give rise to prion disease mediated synaptotoxicity and neurodegeneration.

Mitochondrial dysfunction in Parkinson's disease

Mitochondria are highly dynamic organelles which fulfill a plethora of functions. In addition to their prominent role in energy metabolism, mitochondria are intimately involved in various key cellular processes, such as the regulation of calcium homeostasis, stress response and cell death pathways. Thus, it is not surprising that an impairment of mitochondrial function results in cellular damage and is linked to aging and neurodegeneration. Many lines of evidence suggest that mitochondrial dysfunction plays a central role in the pathogenesis of Parkinson's disease (PD), starting in the early 1980s with the observation that an inhibitor of complex I of the electron transport chain can induce parkinsonism. Remarkably, recent research indicated that several PD-associated genes interface with pathways regulating mitochondrial function, morphology, and dynamics. In fact, sporadic and familial PD seem to converge at the level of mitochondrial integrity.

Multiple tight phospholipid-binding modes of alpha-synuclein revealed by solution NMR spectroscopy

'In dopaminergic neurons, alpha-synuclein (alphaS) partitions between a disordered cytosolic state and a lipid-bound state. Binding of alphaS to membrane phospholipids is implicated in its functional role in synaptic regulation, but also impacts fibril formation associated with Parkinson's disease. We describe here a solution NMR study in which alphaS is added to small unilamellar vesicles of a composition mimicking synaptic vesicles; the results provide evidence for multiple distinct phospholipid-binding modes of alphaS. Exchange between the free state and the lipid-bound alphaS state, and between different bound states is slow on the NMR timescale, being in the range of 1-10 s(-1). Partitioning of the binding modes is dependent on lipid/alphaS stoichiometry, and tight binding with slow-exchange kinetics is observed at stoichiometries as low as 2:1. In all lipid-bound states, a segment of residues starting at the N-terminus of alphaS adopts an alpha-helical conformation, while succeeding residues retain the characteristics of a random coil. The 40 C-terminal residues remain dynamically disordered, even at high-lipid concentrations, but can also bind to lipids to an extent that appears to be determined by the fraction of cis X-Pro peptide bonds in this region. While lipid-bound alphaS exhibits dynamic properties that preclude its direct observation by NMR, its exchange with the NMR-visible free form allows for its indirect characterization. Rapid amide-amide nuclear Overhauser enhancement buildup points to a large alpha-helical conformation, and a distinct increase in fluorescence anisotropy attributed to Tyr39 indicates an ordered environment for this "dark state." Titration of alphaS with increasing amounts of lipids suggests that the binding mode under high-lipid conditions remains qualitatively similar to that in the low-lipid case. The NMR data appear incompatible with the commonly assumed model where alphaS lies in an alpha-helical conformation on the membrane surface and instead suggest that considerable remodeling of the vesicles is induced by alphaS.

Neurodegeneration in Parkinson's disease: genetics enlightens physiopathology

Parkinson's disease (PD) is a severe neurodegenerative disorder of complex etiology and enigmatic physiopathology. In the past decade, the identification of genes involved in rare familial Parkinsonian syndromes has brought hope that understanding the functions of their products will provide insight into the molecular mechanisms responsible for neurodegeneration. The knowledge accumulated thus far has delineated two putative, potentially interconnected, disease-causing pathways: alpha-synuclein accumulation may be central to Parkinsonism due to alpha-synuclein gene defects, but possibly also to sporadic PD and other genetic forms presenting with Lewy bodies; altered mitochondrial physiology may be pivotal to Parkinsonian syndromes caused by parkin, PINK1, and possibly DJ-1 gene mutations. Adding new pieces to this fragmentary picture to determine to what extent sporadic PD and Parkinsonism due to distinct genetic causes share common pathogenic mechanisms remains a major challenge toward the development of future therapeutic strategies for these disabling disorders.

Absence of alpha-synuclein affects dopamine metabolism and synaptic markers in the striatum of aging mice

Despite numerous evidences for neurotoxicity of overexpressed α-synuclein, a protective function was suggested for endogenous α-synuclein and other members of the synuclein family. This protective role is most important for and evident in presynaptic terminals, where synucleins are normally accumulated. However, mice lacking synucleins display no adverse phenotype. In particular, no significant changes in striatal dopamine metabolism and only subtle deficit of dopaminergic neurons in the substantia nigra were found in juvenile or adult mice. To assess whether aging and synuclein deficiency may have additive detrimental effect on the nigrostriatal system, we studied dopaminergic neurons of the substantia nigra and their striatal synapses in 24–26-month-old α-synuclein and γ-synuclein null mutant mice. Significant ∼36% reduction of the striatal dopamine was found in aging α-synuclein, but not γ-synuclein null mutant mice when compared to age-matching wild type mice. This was accompanied by the reduction of TH-positive fibers in the striatum and decrease of striatal levels of TH and DAT. However, no progressive loss of TH-positive neurons was revealed in the substantia nigra of synuclein-deficient aging animals. Our results are consistent with a hypothesis that α-synuclein is important for normal function and integrity of synapses, and suggest that in the aging nervous system dysfunction of this protein could become a predisposition factor for the development of nigrostriatal pathology.

The effect of alpha-synuclein knockdown on MPP+ toxicity in models of human neurons

The protein alpha-synuclein is central to the pathophysiology of Parkinson's disease (PD) but its role in the development of neurodegeneration remains unclear. alpha-Synuclein-knockout mice develop without gross abnormality and are resistant to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mitochondrial inhibitor widely used to model parkinsonism. Here we show that differentiated human dopaminergic neuron-like cells also have increased resistance to 1-methyl-4-phenylpyridine (MPP+), the active metabolite of MPTP, when alpha-synuclein is knocked down using RNA interference. In attempting to understand how this occurred we found that lowering alpha-synuclein levels caused changes to intracellular vesicles, dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2), each of which is known to be an important component of the early events leading to MPP+ toxicity. Knockdown of alpha-synuclein reduced the availability of DAT on the neuronal surface by 50%, decreased the total number of intracellular vesicles by 37% but increased the density of VMAT2 molecules per vesicle by 2.8-fold. However, these changes were not associated with any reduction in MPP+ -induced superoxide production, suggesting that alpha-synuclein knockdown may have other downstream effects which are important. We then showed that alpha-synuclein knockdown prevented MPP+ -induced activation of nitric oxide synthase (NOS). Activation of NOS is an essential step in MPTP toxicity and increasing evidence points to nitrosative stress as being important in neurodegeneration. Overall, these results show that as well as having a number of effects on cellular events upstream of mitochondrial dysfunction alpha-synuclein affects pathways downstream of superoxide production, possibly involving regulation of NOS activity.

Pathologic modifications of alpha-synuclein in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated squirrel monkeys

alpha-Synuclein expression is increased in dopaminergic neurons challenged by toxic insults. Here, we assessed whether this upregulation is accompanied by pathologic accumulation of alpha-synuclein and protein modifications (i.e. nitration, phosphorylation, and aggregation) that are typically observed in Parkinson disease and in other synucleinopathies. A single injection of the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to squirrel monkeys caused a buildup of alpha-synuclein but not of beta-synuclein or synaptophysin within nigral dopaminergic cell bodies. Immunohistochemistry and immunoelectron microscopy also revealed large numbers of dystrophic axons labeled with alpha-synuclein. Antibodies that recognize nitrated and phosphorylated (at serine 129) alpha-synuclein stained neuronal cell bodies and dystrophic axons in the midbrain of MPTP-treated animals. After toxicant exposure, alpha-synuclein deposition occurred at the level of neuronal axons in which amorphous protein aggregates were observed by immunoelectron microscopy. In a subset of these axons, immunoreactivity for alpha-synuclein was still evident after tissue digestion with proteinase K, further indicating the accumulation of insoluble protein. These data indicate that toxic injury can induce alpha-synuclein modifications that have been implicated in the pathogenesis of human synucleinopathies. The findings are also consistent with a pattern of evolution of alpha-synuclein pathology that may begin with the accumulation and aggregation of the protein within damaged axons.

Model fusion, the next phase in developing animal models for Parkinson's disease

Within the past 25 years, discoveries of environmental and monogenetic forms of parkinsonism have shaped the direction of Parkinson's disease (PD) research and development of experimental systems to study PD. In this review, we outline a remarkable array of in vivo models available, with particular emphasis on their benefits and pitfalls and the contribution each has made to enhance our understanding of pathological mechanisms involved in PD. Further, we discuss the increasingly popular approach of "model fusion" to create a new generation of animal systems in which to study gene-environment interactions, and the usefulness of such models in capturing the most common events underlying PD.

A variable poly-T sequence modulates alpha-synuclein isoform expression and is associated with aging

alpha-Synuclein, the main component of proteinaceous inclusions in synucleinopathies, is centrally involved in aggregation processes preceding Lewy body formation. Here we describe a new alpha-synuclein gene poly-T polymorphism that is situated upstream to exon 3 and consists of three different alleles. A correlation between poly-T length and expression of alpha-synuclein 126 mRNA, an isoform lacking exon 3, was detected in the human cerebral cortex. Specifically, when compared with the most frequent 7T/7T genotype, the shortest poly-T stretch (5T) was associated with the lowest alpha-synuclein 126 expression levels, whereas the longest poly-T stretch (12T) was accompanied by the highest alpha-synuclein 126 expression levels. Thus, three different expression-level-specific genotypes, with 5T+ genotypes as low alpha-synuclein 126 expression genotypes and 12T+ genotypes as high alpha-synuclein 126 expression genotypes, could be established. Poly-T genotype distributions were also analyzed in a healthy control population. Age-dependent variations in this distribution were observed and showed accumulation of low alpha-synuclein 126 expression genotypes at ages under 60 years and high alpha-synuclein 126 expression genotypes at ages over 80 years. To determine human specificity of the variable poly-T strech, the mouse alpha-synuclein gene sequence was analyzed. Although alpha-synuclein is very well conserved in vertebrates, the poly-T sequence was found to be absent in mice, and an alpha-synuclein 126 mouse homologue could not be detected. In conclusion, this newly identified poly-T polymorphism is a human-specific sequence; its length influences alpha-synuclein 126 expression levels; and, finally, it seems to exert a specific influence on normal aging.

A cell biological perspective on mitochondrial dysfunction in Parkinson disease and other neurodegenerative diseases

Dysfunction of mitochondria is frequently proposed to be involved in neurodegenerative disease. Deficiencies in energy supply, free radical generation, Ca2+ buffering or control of apoptosis, could all theoretically contribute to progressive decline of the central nervous system. Parkinson disease illustrates how mutations in very different genes finally impinge directly or indirectly on mitochondrial function, causing subtle but finally fatal dysfunction of dopaminergic neurons. Neurons in general appear more sensitive than other cells to mutations in genes encoding mitochondrial proteins. Particularly interesting are mutations in genes such as Opa1, Mfn1 and Dnm1l, whose products are involved in the dynamic morphological alterations and subcellular trafficking of mitochondria. These indicate that mitochondrial dynamics are especially important for the long-term maintenance of the nervous system. The emerging evidence clearly demonstrates the crucial role of specific mitochondrial functions in maintaining neuronal circuit integrity.

Role of mitochondrial dysfunction in Parkinson's disease: Implications for treatment

The role of mitochondrial dysfunction as a possible cause of parkinsonism became apparent in the mid-1980s with the discovery of a group of individuals with chronic parkinsonism who had been exposed to the chemical 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and the subsequent elucidation of the mode of action of this toxin as a mitochondrial complex I inhibitor. Thereafter, a defect in mitochondrial complex I was supported by biochemical studies in patients with sporadic Parkinson's disease. Recently, striking genetic findings and biological studies have further substantiated that mitochondrial dysfunction is likely an important disease mechanism in a significant percentage, if not the majority, of patients with Parkinson's disease. These findings have defined novel biochemical pathways that can directly or indirectly affect mitochondrial function and/or integrity. Although various primary insults (genetic or environmental factors) are involved in the aetiology of Parkinson's disease, emerging evidence supports the notion that attempting to prevent or compensate for mitochondrial dysfunction could have therapeutic benefits for a majority of patients with Parkinson's disease.

Whole genome expression analyses of single- and double-knock-out mice implicate partially overlapping functions of alpha- and gamma-synuclein

alpha-Synuclein has been implicated in the pathogenesis of Parkinson's disease. The function of alpha-synuclein has not been deciphered yet; however, it might play a role in vesicle function, transport, or as a chaperone. alpha-Synuclein belongs to a family of three proteins, which includes beta- and gamma-synuclein. gamma-Synuclein shares 60% similarity with alpha-synuclein. Similar to alpha-synuclein, a physiological function for gamma-synuclein has not been defined yet, but it has been implicated in tumorgenesis and neurodegeneration. Interestingly, neither alpha- (SNCA(-/-)), gamma- (SNCG(-/-)), nor alpha/gamma- (SNCA_G(-/-)) deficient mice are present with any obvious phenotype. Using microarray analysis, we thus investigated whether deficiency of alpha- and gamma-synuclein leads to similar compensatory mechanisms at the RNA level and whether similar transcriptional signatures are altered in the brain. Sixty-five genes were differentially expressed in all mice. SNCA(-/-) mice and SNCG(-/-) mice shared 84 differentially expressed genes, SNCA(-/-) and SNCA_G(-/-) expressed 79 genes, and SNCG(-/-) and SNCA_G(-/-) expressed 148 genes. For many of the physiological pathways such as dopamine receptor signaling (down-regulated), cellular development, nervous system function, and cell death (up-regulated), we found groups of genes that were similarly altered in SNCA(-/-) and SNCG(-/-) mice. In one of the pathways altered in both models, we found Mapk1 as the core transcript. Other gene groups, however, such as TGF-beta signaling and apoptosis pathways genes were significantly up-regulated in the SNCA(-/-) mice but down-regulated in SNCG(-/-) mice. beta-synuclein expression was not significantly altered in any of the models.

Alpha-synuclein induces hyperphosphorylation of Tau in the MPTP model of parkinsonism

Many neurodegenerative diseases associated with functional Tau dysregulation, including Alzheimer's disease (AD) and other tauopathies, also show alpha-synuclein (alpha-Syn) pathology, a protein associated with Parkinson's disease (PD) pathology. Here we show that treatment of primary mesencephalic neurons (48 h) or subchronic treatment of wild-type (WT) mice with the Parkinsonism-inducing neurotoxin MPP+/MPTP, results in selective dose-dependent hyperphosphorylation of Tau at Ser396/404 (PHF-1-reactive Tau, p-Tau), with no changes in pSer202 but with nonspecific increases in pSer262 levels. The presence of alpha-Syn was absolutely mandatory to observe MPP+/MPTP-induced increases in p-Tau levels, since no alterations in p-Tau were seen in transfected cells not expressing alpha-Syn or in alpha-Syn-/- mice. MPP+/MPTP also induced a significant accumulation of alpha-Syn in both mesencephalic neurons and in WT mice striatum. MPTP/MPP+ lead to differential alterations in p-Tau and alpha-Syn levels in a cytoskeleton-bound, vs. a soluble, cytoskeleton-free fraction, inducing their coimmunoprecipitation in the cytoskeleton-free fraction and neuronal soma. Subchronic MPTP exposure increased sarkosyl-insoluble p-Tau in striatum of WT but not alpha-Syn-/- mice. These studies describe a novel mechanism for MPTP neurotoxicity, namely a MPTP-inducible, strictly alpha-Syn-dependent, increased formation of PHF-1-reactive Tau, suggesting convergent overlapping pathways in the genesis of clinically divergent diseases such as AD and PD.

Highly potent and specific GSK-3beta inhibitors that block tau phosphorylation and decrease alpha-synuclein protein expression in a cellular model of Parkinson's disease

Research by Klein and co-workers suggests that the inhibition of GSK-3beta by small molecules may offer an important strategy in the treatment of a number of central nervous system (CNS) disorders including Alzheimer's disease, Parkinson's disease, and bipolar disorders. Based on results from kinase-screening assays that identified a staurosporine analogue as a modest inhibitor of GSK-3beta, a series of 3-indolyl-4-indazolylmaleimides was prepared for study in both enzymatic and cell-based assays. Most strikingly, whereas we identified ligands having poor to high potency for GSK-3beta inhibition, only ligands with a Ki value of less than 8 nM, namely maleimides 18 and 22, were found to inhibit Tau phosphorylation at a GSK-3beta-specific site (Ser 396/404). Accordingly, maleimides 18 and 22 may protect neuronal cells against cell death by decreasing the level of alpha-Syn protein expression. We conclude that the GSK-3beta inhibitors described herein offer promise in defending cells against MPP+-induced neurotoxicity and that such compounds will be valuable to explore in animal models of Parkinson's disease as well as in other Tau-related neurodegenerative disease states.

The neurotoxin, MPP+, induces hyperphosphorylation of Tau, in the presence of alpha-Synuclein, in SH-SY5Y neuroblastoma cells

Alzheimer's disease (AD) is characterized, in part, by intracellular neurofibrillary tangles composed of hyperphosphorylated filamentous aggregates of the microtubule-associated protein, Tau. Such hyperphosphorylated Tau is also found in Lewy bodies (LBs), and cytoplasmic inclusion bodies in certain forms of Parkinson's disease (PD). Further, LBs also contain aggregates of alpha-synuclein (alpha-Syn), also a microtubule-associated protein, which has been linked to the genesis of PD. To investigate a specific correlation between Tau phosphorylation and alpha-Syn, we generated a SH-SY5Y cell line that stably expresses human wild type alpha-Syn. Protein expression levels in the stably transfected cell line (SHalpha-Syn) were within the physiological range of alpha-Syn expression found in Substantia nigra. We show here, in the MPP+ (1-methyl-4-phenylpyridinium ion) cell model of parkinsonism, a time- and dose-dependent increase in the hyperphosphorylation of Tau at pSer396/404 (PHF-1-reactive Tau, p-Tau), concomitant with increased accumulation of alpha-Syn, upon treatment of cells with the neurotoxin. This increase in p-Tau was strictly dependent on the presence of alphaSyn, since in transfected cells not expressing any alpha-Syn, MPP+ failed to induce an increase in PHF-1-reactive Tau. The production of p-Tau caused increased cytotoxicity as indexed by reduced cell viability. Moreover, in the absence of alpha-Syn, the cells were more resistant to MPP+ -induced cell death. The increased levels of both p-Tau and alpha-Syn led to diminished levels of these proteins associated with the cytoskeleton, which was accompanied by enhanced presence of the proteins in the cytoskeletal-free fractions. These data indicate that alpha-Syn and p-Tau modulate the pathogenicity of one another, suggesting a novel convergent mechanism of neurodegeneration.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.

Modeling Neurodegenerative Diseases in vivo Review

Parkinson's disease (PD) is one of the major neurodegenerative disorders. The etiology of this disease is likely due to combinations of environmental and genetic factors. Symptomatic hallmarks of PD are tremor, bradykinesia, rigidity and postural instability. On the morphological and anatomical level, PD is characterized by massive degeneration of dopaminergic neurons in the substantia nigra pars compacta, leading to a severe loss of striatal dopaminergic fibers and to a massive reduction of dopamine levels in the striatum. In addition, PD is characterized by the appearance of Lewy bodies within the surviving dopaminergic neurons. Animal models of PD allow getting insight into the mechanisms of several symptoms of PD thereby providing indispensable tools for basic and applied research. The biochemical and cellular changes that occur following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rodents or monkeys are remarkably similar to those seen in idiopathic PD. In this review, the main characteristics of experimental models of PD induced by the neurotoxic compound MPTP are reviewed.

Parkinson's disease: a rethink of rodent models

Parkinson's disease (PD) is a multifactorial disease with a complex etiology that results from genetic risk factors, environmental exposures and most likely a combination of both. Rodent models of parkinsonism aim to reproduce key pathogenic features of the syndrome including movement disorder induced by the progressive loss of dopaminergic neurons in the substantia nigra, accompanied by the formation of alpha-synuclein containing Lewy body inclusions. Despite the creation of many excellent models, both chemically induced and genetically engineered, there is none that accurately demonstrates these features. Recent pathological staging studies in man have also emphasized the significant non-CNS component of PD that has yet to be tackled. Herein, we summarize rodent models of PD and what they offer to the field, and suggest future challenges and opportunities.

Secondary structure and dynamics of micelle bound beta- and gamma-synuclein

We have used solution state NMR spectroscopy to characterize the secondary structure and backbone dynamics of the proteins beta- and gamma-synuclein in their detergent micelle-bound conformations. Comparison of the results with those previously obtained for the Parkinson's disease-linked protein alpha-synuclein shows that structural differences between the three homologous synuclein family members are directly related to variations in their primary amino acid sequences. An 11-residue deletion in the lipid-binding domain of beta-synuclein leads to the destabilization of an entire segment of the micelle-bound helical structure containing the deletion site. The acidic C-terminal tail region of gamma-synuclein, which displays extensive sequence divergence, is more highly disordered than the corresponding regions in the other two family members. The observed structural differences are likely to mediate functional variations between the three proteins, with differences between alpha- and beta-synuclein expected to revolve around their lipid interactions, while differences in gamma-synuclein function are expected to result from different protein-protein interactions mediated by its unique C-terminal tail.

Down-regulation of α-synuclein expression can rescue dopaminergic cells from cell death in the substantia nigra of Parkinson’s disease rat model

Fibrillization and aggregation of alpha-synuclein may play a critical role in neurodegenerative diseases like Parkinson's diseases. Adeno-associated virus (AAV) vector delivery of an alpha-synuclein ribozyme was tested for its silencing effect on degenerating nigrostriatal neurons in the MPP(+) model of Parkinson's disease. We designed alpha-synuclein ribozyme against human alpha-synuclein gene expression and constructed alpha-synuclein ribozymes-carrying rAAV vector (designated rAAV-SynRz). Co-transfection of rAAV-SynRz and rAAV-alpha-synuclein into HEK293 cells resulted in down-regulation of alpha-synuclein protein expression in vitro. Then, rAAV-SynRz was injected into the substantia nigra (SN) of MPP(+)-treated rats. Cell counts of TH-positive neurons in the SN revealed that rAAV-SynRz significantly protected TH-positive cells against apoptotic death, compared with those of rAAV-EGFP or no rAAV injected rats. Our results indicate that the use of rAAV-SynRz allowed the survival of higher number of TH-positive neurons in SN in the MPP(+) model. Down-regulation of alpha-synuclein expression could be potentially a suitable target for gene therapy of Parkinson's disease.

Genetic mouse models of parkinsonism: strengths and limitations

Parkinson's disease (PD) is a progressive neurodegenerative disorder. Patients with PD display a combination of motor symptoms including resting tremor, rigidity, bradykinesia, and postural instability that worsen over time. These motor symptoms are related to the progressive loss of dopamine neurons in the substantia nigra pars compacta. PD patients also suffer from nonmotor symptoms that may precede the cardinal motor symptoms and that are likely related to pathology in other brain regions. Traditional toxin models of PD have focused on the nigrostriatal pathway and the loss of dopamine neurons in this region, and these models have been important in our understanding of PD and in the development of symptomatic treatments for the disease. However, they are limited in that they do not reproduce the full pathology and progression seen in PD, thus creating a need for better models. The recent discovery of specific genes causing familial forms of PD has contributed to the development of novel genetic mouse models of PD. This review discusses the validity, benefits, and limitations of these new models.

Increased sensitivity to MPTP in human alpha-synuclein A30P transgenic mice

In addition to genetic factors, environmental factors have long been suspected to contribute to the pathogenesis of Parkinson's disease (PD). We investigated the possible interaction between genetic factors and neurotoxins by testing whether alpha-synuclein A30P Tg5093 transgenic mice show increased sensitivity to secondary toxic insults like 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or rotenone. While sensitivity to chronic treatment with rotenone was not enhanced in the Tg5093 line, chronic treatment with 80 or 150 mg/kg MPTP resulted in increased deterioration of the nigrostriatal dopaminergic system as assessed by quantitation of nigral tyrosine hydroxylase (TH) positive neurons and striatal dopamine (DA) levels in Tg5093 mice when compared to non-transgenic littermate controls. Thus, the results of this study demonstrate a role for the overexpression of mutant human alpha-synuclein A30P in increased vulnerability of DA neurons to MPTP.

Subcellular localisation of recombinant alpha- and gamma-synuclein

alpha-Synuclein, a protein implicated in neurodegenerative diseases and of elusive physiological function owes its name to an observed presence in presynaptic and nuclear compartments. However, its nuclear localisation has remained controversial. We expressed synuclein-eGFP fusion proteins in organotypic rat hippocampal slice cultures and murine hippocampal primary neurons using a Sindbis virus expression system. Recombinant full-length alpha-synuclein accumulated in presynaptic locations, mimicking its native distribution. Expression of deletion mutant alpha-synuclein revealed that presynaptic targeting depended on the presence of its N-terminal and core region. This domain also causes nuclear exclusion of the alpha-synuclein fusion protein. In contrast, the C-terminal domain of alpha-synuclein directs fusion proteins into the nuclear compartment. The related protein gamma-synuclein contains a similar N-terminal and core domain as alpha-synuclein. However, gamma-synuclein lacks a C-terminal domain that causes nuclear localisation of the fusion protein, suggesting that the two synucleins might have different roles relating to the cell nucleus.

Occurrence of neuronal inclusions combined with increased nigral expression of α-synuclein within dopaminergic neurons following treatment with amphetamine derivatives in mice

In recent years several clinical and research findings have demonstrated the involvement of the presynaptic protein alpha-synuclein in a variety of neurodegenerative disorders which are known as synucleinopathies. Although the function of this protein in the physiology of the cell remains unknown, it is evident that both genetic alterations or a mere overexpression of the native molecule produces a degeneration of nigral dopamine-containing neurons leading to movement disorders, as demonstrated in inherited Parkinson's disease. In the present study, we investigated whether widely abused drugs such as methamphetamine and methylenedioxymethamphetamine (ecstasy), which are known to damage the nigrostriatal dopamine pathway of mice, increase the expression of alpha-synuclein within dopamine neurons of the substantia nigra pars compacta. The results of this study demonstrate that nigrostriatal dopamine denervation and occurrence of intracellular inclusions in nigral neurons produced by amphetamine derivatives are related to increased expression of alpha-synuclein within dopamine neurons of the substantia nigra. This lends substance to the hypothesis that increased amounts of native alpha-synuclein may be per se a detrimental factor for the dopamine neurons.

A complete genetic analysis of neuronal Rab3 function

Rab3A, Rab3B, Rab3C, and Rab3D are closely related GTP-binding proteins of synaptic vesicles that may function in neurotransmitter release. We have produced knock-out (KO) mice for Rab3B and Rab3C and crossed them with previously generated Rab3A and 3D knock-out mice to generate double, triple, and quadruple Rab3 knock-out mice. We have found that all single and double Rab3 knock-out mice are viable and fertile. Most triple Rab3 knock-out mice perish whenever Rab3A is one of the three deleted proteins, whereas all triple knock-out mice that express Rab3A are viable and fertile. Finally, all quadruple knock-out mice die shortly after birth. Quadruple Rab3 KO mice initially develop normally and are born alive but succumb to respiratory failure. Rab3-deficient mice display no apparent changes in synapse structure or brain composition except for a loss of rabphilin, a Rab3-binding protein. Analysis of cultured hippocampal neurons from quadruple knock-out mice uncovered no significant change in spontaneous or sucrose-evoked release but an approximately 30% decrease in evoked responses. This decrease was caused by a decline in the synaptic and the vesicular release probabilities, suggesting that Rab3 proteins are essential for the normal regulation of Ca2+-triggered synaptic vesicle exocytosis but not for synaptic vesicle exocytosis as such. Our data show that Rab3 is required for survival in mice and that the four Rab3 proteins are functionally redundant in this role. Furthermore, our data demonstrate that Rab3 is not in itself essential for synaptic membrane traffic but functions to modulate the basic release machinery.

The MPTP model of Parkinson's disease

The biochemical and cellular changes that occur following administration of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) are remarkably similar to that seen in idiopathic Parkinson's disease (PD). In this review, we detail the molecular activities of this compound from peripheral intoxication through its various biotransformations. In addition, we detail the interplay that occurs between the different cellular compartments (neurons and glia) that eventually consort to kill substantia nigra pars compacta (SNpc) neurons.

Helix periodicity, topology, and dynamics of membrane-associated alpha-synuclein

The protein alpha-Synuclein (aS) is a synaptic vesicle-associated regulator of synaptic strength and dopamine homeostasis with a pathological role in Parkinson's disease. The normal function of aS depends on a membrane-associated conformation that is adopted upon binding to negatively charged lipid surfaces. Previously we found that the membrane-binding domain of aS is helical and suggested that it may exhibit an unusual structural periodicity. Here we present a study of the periodicity, topology, and dynamics of detergent micelle-bound aS using paramagnetic spin labels embedded in the micelle or attached to the protein. We show that the helical region of aS completes three full turns every 11 residues, demonstrating the proposed 11/3 periodicity. We also find that the membrane-binding domain is partially buried in the micelle surface and bends toward the hydrophobic interior, but does not traverse the micelle. Deeper submersion of certain regions within the micelle, including the unique lysine-free sixth 11-residue repeat, is observed and may be functionally important. There are no long-range tertiary contacts within this domain, indicating a highly extended configuration. The backbone dynamics of the micelle-bound region are relatively uniform with a slight decrease in flexibility observed toward the C-terminal end. These results clarify the topological features of aS bound to membrane-mimicking detergent micelles, with implications for aS function and pathology.